Water Engineering [1 ed.] 9781622571338, 9781612099149

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Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved. Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved. Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

WATER RESOURCE PLANNING, DEVELOPMENT AND MANAGEMENT

Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

WATER ENGINEERING

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Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

WATER RESOURCE PLANNING, DEVELOPMENT AND MANAGEMENT

WATER ENGINEERING

DOMINIC P. TORRES

Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

EDITOR

Nova Science Publishers, Inc. New York

Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

Copyright © 2011 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS.

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Additional color graphics may be available in the e-book version of this book. Library of Congress Cataloging-in-Publication Data Water engineering / editor, Dominic P. Torres. p. cm. Includes bibliographical references and index. ISBN:  (eBook) 1. Water-supply. 2. Water--Purification. 3. Waterworks. I. Torres, Dominic P. II. Title. TD345.W262155 2011 628.1--dc22

2011004975

Published by Nova Science Publishers, Inc.© New York

Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

CONTENTS Preface Chapter 1

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Chapter 2

vii  Methods and Approaches of Groundwater Investigation, Development and Management M. H. Ali and I. Abustan  Industrial Wastewater Treatment Using a Combination of Cavitational Reactors and Fenton Processes: A Review Parag R. Gogate  

1 

123 

Chapter 3

The Slug Tests as a Technical Tool in Aquifers Characterization A. Alfonso Aragón and M. P. Verma 

149 

Chapter 4

Water Cluster Ion Beam Processing Gikan H. Takaoka 

189 

Chapter 5

Water Engineering: A Challenge for Sustainable Development for Vulnerable Communities-Case Colombia Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo, Miguel Angel Gonzalez, Luis Camilo Caicedo, David Gereda and Felipe Muñoz 

Chapter 6

Guar Gum Based Materials for Water Remediation Vandana Singh 

Index

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275  299 

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PREFACE Engineers and scientists work to secure water supplies for potable and agricultural use. They evaluate the water balance within a watershed and determine the available water supply, the water needed for various needs in that watershed, the seasonal cycles of water movement through the watershed and they develop systems to store, treat and convey water for various uses. This new book presents current research in the study of water engineering including the methods and approaches of groundwater investigation, development and management; industrial wastewater treatment using cavitational reactors and the Fenton process; acquifer characterization using slug tests; water cluster ion beam processing and sustainable water engineering for vulnerable communities in Colombia. (Imprint: Nova Press) Chapter 1 - Water is one of the Earth's natural resources. It is a finite resource, especially in terms of quality and quantity (in temporal and spatial scale). Most of the world's water supply is saltwater stored in the oceans. Converting saltwater to freshwater is generally too expensive to be used for industrial, agricultural or household purposes. Groundwater makes up about 70% of the entire world’s freshwater. It plays a very important role in our environment and economies. Groundwater is the main source of water supply to both urban and rural populations as well as to industry and agriculture. Many reasons make groundwater a good choice for a water supply. For proper planning, design, and management purposes, we should know the nature of groundwater, including its source, movement, and behavior. A well dug or drilled into saturated rocks (called aquifers) will fill with water approximately to the level of the water table. Performance of the well depends on proper identification of waterbearing strata, and proper design and installation of pumping well. If the withdrawal rate by pumping is higher than the natural recharge or replenishment, water-table depletion occurs. The groundwater (i.e. aquifer) can be contaminated if any contaminants are present in the water pathway. It is troublesome and sometimes impossible to rectify the aquifer if it is contaminated. So proper measures should be taken to prevent contamination of groundwater, and managed it in a sustainable manner. Chapter 2 - Cavitational reactors offer considerable promise for wastewater treatment applications due to the significant effects such as generation of free radicals, hot spots, conditions of intense turbulence etc, which are extremely suitable for oxidation of toxic pollutants present in the wastewater. However, these cannot find actual application for large scale wastewater treatment due to higher processing costs and some limitations as regards lower degradation rates for highly loaded effluent streams. An innovative approach has been to combine cavitational reactors with other synergistic oxidation processes such as Fenton chemistry. The present work provides an overview of the combined treatment strategy based

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Dominic P. Torres

on cavitation and Fenton processes. Both the types of cavitational reactors, i.e. sonochemical reactors based on the use of ultrasound for generation of cavities and hydrodynamic cavitation reactors where cavitation is generated due to alterations in the flow field, will be discussed in the work for possible synergism with Fenton processes. The Fenton process can be based on the conventional approach which uses the combination of ferrous sulphate and hydrogen peroxide whereas the advanced Fenton process can be based on the use of other constituents such as iron metal or cupric oxide in combination with hydrogen peroxide, with an objective of possible reduction in the treatment cost. The work highlights the mechanistic details pointing towards synergism, different reactor configurations, an overview about different pollutants being degraded using combinatorial approach and guidelines for selection of the important operating parameters such as ratio of the oxidants, pH, temperature, configuration of cavitational reactors etc. based on a detailed analysis of the existing literature in this area. Overall it appears that combined treatment strategies are more suitable as compared to individual operation of either cavitational reactors or the Fenton based processes. Chapter 3 - Aquifer test methods available for characterizing hazardous waste sites are sometimes restricted because of problems with disposal of contaminated groundwater. These problems, in part, have made slug tests a more desirable method of determining hydraulic properties at such sites. The slug test method is a popular and inexpensive mean of estimating the hydraulic properties of aquifers (primarily hydraulic conductivity). There is a clearly need to develop test methods that can be used to characterize higher permeability aquifers without removing large amounts of contaminated groundwater. Similarly the corroboration of test results indicates that slug testing is a viable hydraulic characterization method and may represent one of the few test methods that can be used in sensitive areas where groundwater is contaminated. Besides, of particular interest are test methods that can be performed rapidly, and that minimize the removal of large quantities of water (i.e., tests that minimize purgewater disposal problems). The slug tests can be carried out using a single well or two, in this last case it is used the interference test concept. The general test procedure requires initiating an instantaneous head increase or decrease at the well used as the tester, and monitoring the associated formation response at the neighboring observation well. The pressure response is analyzed at the monitored well and the results provide estimates of the formation transmissivity and its storativity. The methods developed for the analysis of slug tests were done, assuming single characteristics of the system, due that the increases in the water level are too very small compared with those of an output tests. So, in this work is shown the applicability of four of the existing methods for analyzing slug tests. In this work are analyzed and discussed, the behavior of the results obtained from the analysis methods of Hvorslev; Cooper, Bredehoeft and Papadopulos; Bower and Rice; and Gilg and Gavard. The obtained results from the use of such methods are useful in the aquifers characterization in order to design properly their exploitation. In order to show the application the four discussed methods were used data of measurements during slug tests carried out in ten wells in order to characterize the aquifer where they are located. Through determined values it was done a correlation of formation properties for characterizing the aquifer and to define the zone whose hydraulic conductivity is the best. Chapter 4 – The author has developed a polyatomic cluster ion source and investigated the impact process of cluster ions on solid surfaces. High-energy-density deposition and collective motions of the cluster ions during impact play important roles in the surface process. Cluster ion irradiation forms the reaction field at nano-level on the impact area, and

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Preface

ix

represents distinctive irradiation effects, which are not obtained by the conventional ion beam process. In this chapter, water cluster ion beam processing is described from the viewpoints of water cluster formation and ion beam engineering. The size analysis of water cluster ions is described, and the water cluster formation is discussed based on thermodynamics and gas dynamics. Furthermore, interactions of water cluster ion beams with solid surfaces are investigated, and surface processing such as high-rate sputtering, atomically flat surface formation and nano-level chemical modification by water cluster ion beams is described from the viewpoints of advanced water engineering. Chapter 5 – According to estimates of IDEAM1, Colombia has 742,705 drainage basin units, indicating the total water supply will surpass 2,000 km3/year, which corresponds to 57,000 m3/year*Hab. Despite this abundant water supply, in this country, a considerable amount of the population has no access to drinking water because of problems associated with availability (quantity, quality or accessibility), the rural population being the most affected. Currently in the country, 13.6 million people live in rural areas, of which 39.7% have no water supply system, 60% have no sanitary or sewer units and only 11% have access to treated water. The situation in 2009 was reflected by the 189,480 cases of disease and 7,900 people who died because of perinatal mortality, acute diarrheal disease, malaria, dengue, and cholera, all of which are diseases associated with water quality. Problems with the availability of water resources are associated with causes such as population growth, spatial distribution, pollution, and mismanagement of the resource associated with poor governing and implementation of policies. These problems make a water-rich country such as ours a failure in ensuring resource availability as a right for all the people. Although the legal structure in Colombia is one of the most important in Latin America, complementary mechanisms of action and control tend to be insufficient. For this reason, the Government, through the Decree 421/00, regulated by Resolution 151/01, has empowered organized communities constituted as non-profit legal entities, to provide public services in smaller municipalities and rural areas. This scenario requires linking different members with the objective to design innovative solutions to increase coverage of safe water. In this context, the organizational system, Ingenieros sin Fronteras - Colombia (ISFC), is established. Constituted by engineering schools (teachers and students) to work with communities and local government entities in formulating a social model which designs and implements technological solutions that are accessible and culturally appropriate. ISFC develops projects based on the CDIO approach (Conceive, Design, Implement and Operate), engineering solutions that improve the quality of life of vulnerable communities in Colombia, working together with them through collective participation. The chapter will address each of the problems mentioned by a critical analysis in light of the Millennium Development Goals and other United Nations regulations that require states to provide quality water. Additionally, it will also present a case study in a Colombian town in which ISFC, through collective participation and the CDIO methodology, improved the water quality of the population. The framework developed during this process is shown as a workable model to be replicated in other parts of Colombia, in order to propose innovative alternatives that generate sustainable development for the most vulnerable in Colombia. Chapter 6 - Guar gum (GG) is an edible carbohydrate polymer consisting of a straight chain of β (1→4) linked mannose units where every second mannose unit has a side branch of 1

Institute of Hydrology, Meteorology and Environmental Studies. Colombia

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glycosidically linked α(1→6) galactose unit. It is cold water swelling biopolymer and is known to be highly efficient water thickener. The gum is routinely used as a dispersion agent, as a viscosity builder and water binder in many industries such as, pharmaceutical, cosmetics, mining, textiles, explosives, paper and petroleum. However due to quick biodegradation, the viscosity of the gum solution can not be controlled and therefore the gum is rarely used in its natural form. There are several reports on the chemical modification of guar gum where a range of conventional and nonconventional methods have been used till date. Structurally guar gum is galactomannan and its mannan backbone has numerous hydroxyl groups in cisarrangement. Potentially these hydroxyl groups are capable of chelating with the pollutants in waste water. Several guar gum based materials are known to be efficient adsorbents/ flocculants and have been used in water remediation. Stability, solubility and functionality of the gum have been modified in several ways for extending its use for several such applications. Present chapter focuses on the guar gum based materials which are used in water purification and remediation. Synthesis and applications of these materials are discussed herein with an insight for the wider utilization of guar gum in water remediation.

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In: Water Engineering Editor: Dominic P. Torres

ISBN: 978-1-61209-914-9 © 2011 Nova Science Publishers, Inc.

Chapter 1

METHODS AND APPROACHES OF GROUNDWATER INVESTIGATION, DEVELOPMENT AND MANAGEMENT M. H. Ali and I. Abustan School of Civil Engineering, University Sains Malaysia

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1

Basics of groundwater 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

2

Occurrence of groundwater Presence of groundwater Relevant terminologies Groundwater storage and movement Groundwater abstraction Groundwater recharge Groundwater flow Groundwater - sea-water interface

Investigation of Groundwater and determining its potential 2.1 Planning an investigation 2.1.1 Steps involved in a site investigation 2.2 Approaches of investigation 2.2.1 Mechanical approach • Features • Limitations • Sampling interval and representation • General guidelines and steps • Relevant activities 2.2.2 Geo-physical approaches 2.2.2.1 Electrical method • Principle of the method • Theoretical aspects • Different configurations of resistivity survey

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M. H. Ali and I. Abustan • • • • 2.2.2.2 • • • • 2.2.2.3 2.2.2.4 2.2.2.5 2.2.2.6 2.2.2.7 2.2.2.8

Electrode geometry Field survey procedure Discussion Interpretation of resistivity data Electromagnetic method Principle of the method Applicability Description of the methods General guidelines and field procedure for EM method Seismic method Magnetic geophysical method Ground penetrating radar method Borehole geophysical method Gravity method Very low frequency electromagnetic method

2.3 Estimation of GW potential 2.3.1 Qualitative identification 2.3.2 Quantitative estimation

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3

Groundwater quality aspects 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8

Significance of quality study Sampling of groundwater Elements to be analyzed Laboratory analysis and ionic balances Issues on the factors affecting quality Isotope and age indicator analysis Discussion on quality issues Guidelines on water quality for different uses

4

Groundwater development and well design 4.1 Assessing groundwater availability 4.1.1 Water budget approach • Basics of water budget • Expression of water budget 4.2 Groundwater yield 4.2.1 General perspectives 4.2.2 Relevant terminologies 4.2.3 Well yield in unconfined aquifer 4.2.4 Well yield in confined aquifer

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Methods and Approaches of Groundwater Investigation … 4.3 Construction and design of water supply wells 4.3.1 Importance of proper well construction and design 4.3.2 Types of well 4.3.3 Well construction • Principal activities • Drilling methods 4.3.4 Well design 4.3.4.1 Design elements and considerations 4.3.4.2 Design criteria and procedure 4.3.5 4.3.6 4.3.7 4.3.8

Well completion Well development Disinfection of well Economic considerations

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4.4 Pumping test & Determination of aquifer parameters 4.4.1 Assumptions in pumping test 4.4.2 Constant rate test 4.4.3 Stepwise test 4.4.4 Analysis of pump test data • Theis method • Cooper-Jacob method - Time-drawdown - Distance –drawdown - Theis recovery

5

Groundwater withdrawal and water-table trends – Case studies 5.1 Over-withdrawal of groundwater: Effects and areal extents around the globe 5.2 Groundwater withdrawal and trend in Bangladesh 5.3 Groundwater withdrawal and trend in India 5.4 Groundwater withdrawal and trend in China

6

Management of Groundwater 6.1 Major obstacles to groundwater management 6.2 Amelioration/Remedial measures for obstacles 6.2.1 Groundwater policies 6.2.2 Establishing a GW data and retrieval system 6.3 Management measures 6.3.1 Resource inventory 6.3.2 Monitoring groundwater dynamics and its trend 6.3.3 Management measures for reducing contamination 6.3.4 Enhancing groundwater reserve

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4

M. H. Ali and I. Abustan • Enhancing natural recharge • Initiating artificial recharge 6.3.5 Other supply management 6.3.6 Maintaining sustainability in groundwater withdrawal 6.3.7 Modelling and use of model for impact study

7

Groundwater threats and pollution potentials 7.1 7.2 7.3 7.4 7.5 7.6 7.7

8

Pollution potentials and threats for groundwater contamination Sources of GW contamination/ pollution Pathways for contaminant transport Arsenic in groundwater - A major threat for groundwater Over-exploitation Impact of climate change on groundwater Impact of land-use change on groundwater

Groundwater protection

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8.1 Delineating protection zones 8.2 Measures for controlling quality degradation • Source-water protection • Groundwater monitoring • Laws and regulations • Some general guidelines/ solution options for specific problems 8.3 Opportunities to improve groundwater 8.4 Challenges in groundwater protection and management References

ABSTRACT Water is one of the Earth's natural resources. It is a finite resource, especially in terms of quality and quantity (in temporal and spatial scale). Most of the world's water supply is saltwater stored in the oceans. Converting saltwater to freshwater is generally too expensive to be used for industrial, agricultural or household purposes. Groundwater makes up about 70% of the entire world’s freshwater. It plays a very important role in our environment and economies. Groundwater is the main source of water supply to both urban and rural populations as well as to industry and agriculture. Many reasons make groundwater a good choice for a water supply. For proper planning, design, and management purposes, we should know the nature of groundwater, including its source, movement, and behavior. A well dug or drilled into saturated rocks (called aquifers) will fill with water approximately to the level of the water table. Performance of the well depends on proper identification of water-bearing strata, and proper design and installation of pumping well. If the withdrawal rate by pumping is higher than the natural recharge or replenishment, water-table depletion

Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

Methods and Approaches of Groundwater Investigation …

5

occurs. The groundwater (i.e. aquifer) can be contaminated if any contaminants are present in the water pathway. It is troublesome and sometimes impossible to rectify the aquifer if it is contaminated. So proper measures should be taken to prevent contamination of groundwater, and managed it in a sustainable manner.

1. BASICS OF GROUNDWATER Only 3% of the world's water supply is freshwater and two-thirds of that is frozen, forming the polar ice caps, glaciers, and icebergs. The remaining 1% of the total world water supply is freshwater available as either surface water or ground water; ground water accounts for two-thirds of this amount. Surface water is water that is visible above the ground surface, such as creeks, rivers, ponds and lakes. Ground water is water that either fills the spaces between soil particles or penetrates the cracks and spaces within rocks. The resource groundwater compared to surface waters is so valuable because it is available throughout the year and (normally) cleaner. Many countries of the world are dependent upon groundwater, with an estimated 2 billion people worldwide relying on aquifers for their drinking water supply. At a regional level, groundwater is of vital importance in Africa, Asia, Central and South America. Numerous countries rely on groundwater for their drinking water, both from shallow hand-dug wells and from deeper public water boreholes. In a rural context, groundwater provides the mainstay for agricultural irrigation and will be the key to provide additional resources for food security. In urban centers, groundwater supplies are important as a source of relatively low cost and generally high quality municipal and private domestic water supply.

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1.1 Occurrence of groundwater Groundwater is an integral part of continuous cycle of water (called water cycle or hydrologic cycle). Groundwater can be found almost everywhere (e.g. beneath hills, plains, mountain and deserts). When rain falls to the ground, some of it flows along the surface to streams or lakes, some of it is used by plants, some evaporates and returns to the atmosphere, and some infiltrates or sinks into the ground (Fig.1.1). The infiltrated water moves into the spaces between the particles of sand or rock. Groundwater is water that is found underground in the spaces in soil, sand and rock, and cracks. Literally, groundwater means ‘water under the ground or earth’, including both in saturated and unsaturated zone. But in utility sense, water in unsaturated zone is referred to as ‘soil moisture’ and water in the saturated zone (aquifer) is referred to as ‘groundwater’. The word aquifer comes from two Latin words, “aqua” (meaning water), and ferre (meaning bear or carry). Aquifers literally means ‘strata or layer bearing water’. An aquifer may be a layer of gravel or sand, a layer of sandstone or cavernous limestone, a rubbly top or base of lava flows, or even a large body of massive rock, such as fractured granite, that has sizable openings. Typically, aquifers consist of gravel, sand, sandstone, or fractured rock, like limestone. Groundwater is stored in- and moves slowly through aquifers. Aquifers can thus be defined as a permeable rock or porous soil that stores groundwater and allows it to flow readily into a well or borehole.

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Fig.1.1. Schematic of hydrologic cycle and position of groundwater.

Thus, it is evident that groundwater is a component of a regions water budget. The water budget of USA are explained below. The U.S. receives enough annual precipitation to cover the entire country to a depth of 30 inches. This 30 inches is known as the U.S. water budget. The eastern half of the country receives more rainfall than the western half. Most of this precipitation returns to the water cycle through evapotranspiration. Of the 30 inches of rainfall, 21 inches returns to the atmosphere in this manner. Water loss by plants, the transpiration portion of evapotranspiration, is most significant. One tree transpires approximately 50 gallons of water a day. Approximately 8.9 inches of annual precipitation flows over the land in rivers and returns to the ocean. Only 0.1 of an inch of precipitation infiltrates into the ground water zone by gravity percolation. The actual amount of water that enters the groundwater zone for any specific area depends upon the annual rainfall in that area and its temporal distribution, and soil surface and geological condition.

1.2 Presence of groundwater There are two major types of aquifers in the substrata: shallow, and deep. Near the stream, the aquifers have special characteristics, which may be considered as another type.

Shallow Aquifers Shallow aquifers may be of two types: those that are perched in the near surface or those that are adjacent to stream. The perched aquifers may occur within the extensive exposures of alluvium, recessional outwash, and glacial. Groundwater recharge to the perched aquifers is local, recharging via short travel paths between a recharge area and an aquifer discharge

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point, typically a stream or a well. Although groundwater recharge is local, it occurs over virtually the entire exposed extent of the shallow aquifers. The stream-adjacent aquifers are directly connected to streams, so groundwater flows towards the river during periods of high water tables and towards the aquifer during periods of high stream-flow. The volume of recharge and discharge from the stream-adjacent aquifers is dominated by surface water to groundwater interaction; however, precipitation-driven groundwater recharge is still important. In addition to discharging water to the underlying aquifers, perched aquifers feed numerous lakes, streams, and wetlands.

Deep aquifers A group of deep aquifers and aquitards may present beneath the surface. The deep unconsolidated aquifers are recharged by water originating in the overlying aquifers and percolating downward through the aquitards. These aquifers are generally a minor source of water to streams and lakes.

1.3 Characteristics of different types of aquifers

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Physical properties of the aquifer The physical properties of aquifer materials and of the aquifers themselves (i.e., thickness, depth) are important in determining how quickly ground water will move and what routes it will take as it moves through an aquifer. The physical properties include porosity, isotropy, homogeneity, compressibility. This knowledge helps decide how best to get water out of the ground for drinking water, irrigation, and other uses. These same properties are important in defining how contaminants originating on the surface will flow in the aquifer and in determining an appropriate cleanup remedy if the aquifer becomes contaminated.

Bedrock aquifer The bedrock aquifer generally consists of hard fractured rocks, which possess minimal primary (inter-granular) porosity or permeability. Groundwater flow and storage occur almost entirely within the fractures, and borehole yields are dependent on the number, size and degree of lateral and vertical interconnection between the fractures. Under such conditions, failure to penetrate an adequate number of productive fractures will result in a low yielding or sometimes effectively dry borehole. Fractures are generally most common, larger and better interconnected at relatively shallow depths; and generally become fewer, less dilated and less well interconnected with increasing depth. Total yields commonly increase cumulatively with depth, as a borehole penetrates an increasing number of productive fractures.

1.4 Relevant terminologies Water-table The top water surface of an unconfined aquifer at atmospheric pressure. The water-table rises and falls according to the season of the year and the amount of rain and snow melt that

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occur. It is typically higher in early spring and lower in late summer. Heavy rainfall or drought conditions may cause changes in the typical pattern, however. The water-table is actually the boundary between the unsaturated and saturated zones. It represents the upper surface of the groundwater. Technically speaking, it is the level at which the hydraulic pressure is equal to atmospheric pressure.

Spring Area where there is a concentrated discharge of groundwater that flows at the ground surface.

The Unsaturated Zone A zone is usually present between the water-table and the land surface where the openings, or pores, in the soil are only partially filled with water. This is the unsaturated zone. Water seeps downward through it to the water-table below. Plant roots can capture the moisture passing through this zone, but it cannot provide water for wells.

Saline water

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Water that is considered generally unsuitable for human consumption or for irrigation because of its high content of dissolved solids; generally expressed as milligrams per liter (mg/L) of dissolved solids; seawater is generally considered to contain more than 35,000 mg/L of dissolved solids. A general salinity scale is as follows: Scale

Concentration of dissolved solids, in milligrams per liter

Slightly Saline

1,000 - 3,000

Moderately Saline

3,000 - 10,000

Very Saline

10,000 - 35,000

Brine

More than 35,000

Aquitard A confining bed and/or formation composed of rock or sediment that retards but does not prevent the flow of water to or from an adjacent aquifer. It does not readily yield water to wells or springs, but stores ground water. Base-flow The portion of stream flow that is maintained by the groundwater discharge is known as base-flow.

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Contaminant Any substance or property preventing the use or reducing the usability of the water for ordinary purposes such as drinking, preparing food, bathing washing, recreation, and cooling. Any solute or cause of change in physical properties that renders water unfit for a given use (Generally considered synonymous with pollutant).

Groundwater Basin An alluvial aquifer or a stacked series of alluvial aquifers with reasonably well-defined boundaries in a lateral direction and having a definable bottom.

Permeability The capability of soil (or other geologic formations) to transmit water, normally expressed as qualitative term.

Hydraulic Conductivity A measure of the capacity for a rock or soil to transmit water; generally has the units of m3/m2/sec or ft3/ft2/day.

Overdraft

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The condition of a groundwater basin in which the amount of water withdrawn by pumping exceeds the amount of water that recharges the basin over a period of years during which water supply conditions approximate average conditions.

Safe Yield The maximum quantity of water that can be continuously withdrawn from a groundwater basin without adverse effect.

Specific Yield The ratio of the volume of water a rock or soil will yield by gravity drainage to the total volume of the rock or soil.

Transmissivity Transmissivity is a measure of the subsurface's ability to transmit groundwater horizontally through its entire saturated thickness and affects the potential yield of wells. It is the product of hydraulic conductivity and aquifer thickness; a measure of a volume of water to move through an aquifer (generally expressed as per unit width). Transmissivity has the units of m3/m/day (wrongly expressed as m2/day) or gallons per day/foot.

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1.5 Groundwater storage and movement

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In terms of storage at any instant in time, ground water is the largest single supply of fresh water available for use by humans. Groundwater begins as precipitation and soaks into the ground where it is stored in underground geological water systems called aquifers. Sometimes groundwater feeds springs, lakes, and other surface waters, or is drawn out of the ground by humans through wells. The quantity of water a given type of formation will hold depends on the rock's/formation material’s porosity - a measure of pore space between the grains of the rock or of cracks in the rock that can fill with water. The speed at which groundwater flows, depends on the size of the spaces in the soil or rock and interconnection of the spaces (Fig.1.2). For example, if the grains of a sand or gravel aquifer are all about the same size, or "well sorted," the waterfilled spaces between the grains account for a large proportion of the volume of the aquifer. If the grains, however, are poorly sorted, the spaces between larger grains may be filled with smaller grains instead of water. Sand and gravel aquifers having well-sorted grains, therefore, hold and transmit larger quantities of water than such aquifers with poorly sorted grains.

Fig.1.2. Schematic of an aquifer-aquitard system.

If water is to move through rock, the pores must be connected to one another. If the pore spaces are connected and large enough that water can move freely through them, the rock is said to be permeable. A rock that will yield large volumes of water to wells or springs must have many interconnected pore spaces or cracks. A compact rock almost without pore spaces, such as granite, may be permeable if it contains enough sizable and interconnected cracks or fractures. After entering an aquifer, water moves slowly toward lower lying places and eventually is discharged from the aquifer from springs, seeps into streams, or is

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intercepted by wells. Groundwater that becomes trapped under impermeable soil or rock may be under pressure. Confined or Artesian Aquifer

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Ground water in aquifers between layers of poorly permeable rock, such as clay or shale, may be confined under pressure. If such a confined aquifer is tapped by a well, water will rise above the top of the aquifer and may even flow from the well onto the land surface. Water confined in this way is said to be under artesian pressure, and the aquifer is called an artesian aquifer or confined aquifer (Fig.1.3). The word artesian comes from the town of Artois in France, the old Roman city of Artesium, where the best known flowing artesian wells were drilled in the Middle Ages. The level to which water will rise in tightly cased wells in artesian aquifers is called the potentiometric or piezometric surface or potential water level. A well that pierces a confined aquifer is known as an artesian well. Water pressure in the confined aquifer will cause water in the well to rise above the aquifer level.

Fig.1.3. Schematic of artesian aquifer and flowing well.

Unconfined or Water-table Aquifer Aquifers that are not confined under pressure are called unconfined or water-table aquifers. The water level in a well is the same as the water-table outside the well. Where ground water is not confined under pressure, it is described as being under water-table conditions. Water-table aquifers generally are recharged locally, and water tables in shallow aquifers may fluctuate up and down directly in unison with precipitation or stream-flow. A spring is the result of an aquifer being filled to the point that the water overflows onto the land surface. There are different kinds of springs and they may be classified

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according to the geologic formation from which they obtain their water, such as limestone springs or lava-rock springs; or according to the amount of water they discharge-large or small; or according to the temperature of the water-hot, warm, or cold; or by the forces causing the spring-gravity or artesian flow.

1.6 Groundwater abstraction

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Water in aquifers is brought to the surface naturally through a spring or can be discharged into lakes and streams. Groundwater can also be extracted through a well drilled into the aquifer (Fig.1.4). A well is a pipe in the ground that fills with groundwater. This water can be brought to the surface by a pump. Shallow wells may go dry if the water-table falls below the bottom of the well. Some wells, called artesian wells, do not need a pump because of natural pressures that force the water up and out of the well.

Fig.1.4. Schematic of groundwater abstraction and groundwater depletion over time.

Wells: Cone of Depression Pumping from wells lowers the water table near a well (Fig.1.5). This known as the cone of depression. The land surface overlying the cone of depression is also referred to as the area of influence. Groundwater flow is diverted towards the well as it flows into the depression cone.

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Fig.1.5. Cone of depression near the pumping well.

Well Contribution Zone A groundwater recharge area that is the source of water for a well is known as the contribution zone or catchment area. This may include only a portion of a larger aquifer recharge area. The area of influence due to well pumping, that overlies the cone of depression, may extend beyond the contribution zone. Induced recharge from well pumping causes groundwater to flow towards the well that would not normally contribute water to a well.

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Induced Recharge The cone of depression from a pumping well may extend to a nearby stream or lake. This lowers the adjacent water table below the steam or lake level. As a result, the stream or lake begins to lose water to the adjacent groundwater aquifer in the vicinity of the well. This is known as induced recharge. Streams and wetlands have been completely dried up by induced recharge from well pumping.

1.7 Groundwater recharge Recharge is the process by which aquifers are replenished with water from the surface. Groundwater supplies are replenished, or recharged, by rain and snow melt. In some areas of the world, people face serious water shortages because groundwater is used faster than it is naturally replenished. Water seeping into an aquifer is known as recharge. This takes place intermittently during and immediately following periods of rain and snow-melt. This process occurs naturally as part of the hydrologic cycle as infiltration when rainfall infiltrates the land surface and as percolation of water into underlying aquifers. A number of factors influence the rate of recharge including physical characteristics of the soil, surface cover, slope, water content of surface materials, rainfall intensity and duration, and the presence and depth of confining layers and aquifers. Surface water bodies may also recharge groundwater. This occurs most often in arid areas. Lakes and dry creek beds may fill up with water during heavy rains. If the water table

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iss low in undeerlying aquifeers, water maay seep from the sides of these water bodies b and peercolate into th he ground watter. Recharge occurs o where permeable soil or rock allows a water to t readily seeep into the grround. These areas are knoown as recharrge areas. Perm meable soil orr rock formations where reecharge occurss may occupy only a very small area or extend e over maany square miiles. Valley aqquifers may also a receive recharge r from m hillside runoff or stream ms that flow down d from hiillsides in add dition to the raain and snow thhat falls directly onto the laand surface ovverlying the aqquifer. In some pllaces, artificiaal recharge iss used to repllenish aquiferrs. This is acccomplished thhrough the pum mping or injecction of waterr into wells whhere it replenishes the aquiffer directly, orr through the spreading off water over thhe land surfacce where it can seep into the t ground (F Fig.1.6). Artifficial rechargee is done to replenish r the ground waterr supply whenn rains are heeavy in order to preserve water w for laterr use or, in thhe case of injeection wells, to t dilute or coontrol the flow w of contaminaated ground water w (e.g. salinne water).

Fiig.1.6. Schemattic of groundwaater recharge.

Aquifers may m be artificiially rechargeed in two maiin ways: One way is to sppread water ovver the land in n pits, furrows, or ditches, or to erect sm mall dams in sttream channells to detain annd deflect surface runoff, thhereby allowinng it to infiltrrate to the aquuifer; the otheer way is to coonstruct rechaarge wells annd inject wateer directly innto an aquiferr. The latter is a more exxpensive meth hod but may be justified where the spreadding method iss not feasible. Although some s artificiaal-recharge projects have been b reported successful, others o have beeen disappoin ntments; therre is still muuch to be leearned about different groound-water ennvironments and a their recepptivity to artifiicial-recharge practices.

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1.8 Groundwater flow

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Factors governing flow in groundwater systems are the head gradient, or slope of the water-table, the hydraulic conductivity of the aquifer, and the area through which flow can occur. Gravity is the dominant driving force in groundwater movement (which generally means it moves downward) in unconfined aquifers. As such, under natural conditions, groundwater moves "downhill" until it reaches the land surface at a spring or through a seep in the side or bottom of a river bed, lake, wetland, or other surface water body. However, groundwater can also move upwards if the pressure in a deeper aquifer is higher than that of the aquifer above it. This often occurs where pressurized confined aquifers occur beneath unconfined aquifers. Ground water can also leave the aquifer via the pumping of a well. Groundwater moves very slowly from recharge areas to discharge points. After entering an aquifer, water moves slowly toward lower lying places and eventually is discharged from the aquifer from springs, seeps into streams, or is intercepted by wells (Fig.1.7). In the case of groundwater in confined aquifers, it is pressure rather than gravity that makes water move. In this case, water flows from areas of high pressure to areas of low pressure. The steeper the gradient or slope, the faster the ground water will flow. It is important to note that the rate of ground water flow, especially in confined systems, is very slow compared to the flow of water on the surface. It is typically in the range of fraction of a meter (m) per year to several meters per year. Groundwater can move through pores or fractures. For water to move freely through a rock, the pores and/or fractures must be large enough and connected enough so that the friction from the water moving past the rock particle does not impede the flow. The degree of an aquifer’s porosity and permeability is key to the movement of ground water through an aquifer.

Fig.1.7. Schematic of groundwater flow.

Flow rates in aquifers are typically measured in meter per day. Flow rates are much faster where large rock openings or crevices exist (often in limestone) and in loose soil, such as coarse gravel. It may take years, decades or even centuries for groundwater to move long distances through some aquifers. However, groundwater may take only a few days or weeks to move for a short distance through loose soil. Groundwater typically moves in parallel paths (i.e., layers) with little mixing, due to the slow movement of groundwater, which does not

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create sufficient turbulence to cause mixing to occur. This becomes an important factor in the location and movement of contaminants that enter the groundwater. A groundwater divide, like a surface water divide, indicates distinct groundwater flow regions within an aquifer. A divide is defined by a line on the either side of which groundwater moves in opposite directions. Groundwater divides often occur in highland areas, and in some geologic environments coincide with surface water divides. This is common where aquifers are shallow and strongly influenced by surface water flow. Where there are deep aquifers, surface and ground water flows may have little or no relationship. As groundwater flows downwards in an aquifer, its upper surface slopes in the direction of flow. This slope is known as the hydraulic gradient and is determined by measuring the water elevation in wells tapping the aquifer. For confined aquifers, the hydraulic gradient is the slope of the potentiometric surface. For unconfined aquifers, it is the slope of the watertable. The velocity at which groundwater moves is a function of three main variables: hydraulic conductivity, porosity, and the hydraulic gradient. The hydraulic conductivity is a measure of the water transmitting capability of an aquifer. High hydraulic conductivity values indicate an aquifer can readily transmit water; low values indicate poor transmitting ability. Because geologic materials vary in their ability to transmit water, hydraulic conductivity values range through 12 orders of magnitude. Some clays, for example, have hydraulic conductivities of 0.00000001 centimeters per second (cm/sec), whereas gravel hydraulic conductivities can range up to 10,000 cm/sec. Hydraulic conductivity values should not be confused with velocity even though they appear to have similar units. cm/sec, for example, is not a velocity but is actually a contraction of cubic centimeters per square centimeter per second (cm3/cm2sec). In general, course-grained sands and gravels readily transmit water and have high hydraulic conductivities (in the range of 50-1000 m/day). Fine grained silts and clays transmit water poorly and have low hydraulic conductivities (in the range of 0.001-0.1 m/day). The porosity of an aquifer also has a bearing on its ability to transmit water. Porosity is a measure of the amount of open space in an aquifer. Both clays and gravels typically have high porosities, while silts, sands, and mixtures of different grain sizes tend to have low porosities. The velocity at which water travels through an aquifer is proportional to the hydraulic conductivity and hydraulic gradient, and inversely proportional to the porosity. Of these three factors, hydraulic conductivity generally has the most effect on velocity. Thus, aquifers with high hydraulic conductivities, such as sand and gravel deposits, will generally transmit water faster than aquifers with lower hydraulic conductivities, such as silt or clay beds. The volume of groundwater flow is controlled by the hydraulic conductivity and gradient, and in addition is controlled by the volume of the aquifer. A large aquifer will have a greater volume of ground water flow than a smaller aquifer with similar hydraulic properties. But if the cross-sectional area - that is, the height and width - are the same for both aquifers, the aquifer with a greater hydraulic conductivity and hydraulic gradient will produce a greater volume of water.

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1.9 Groundwater – Sea-water interface In some coastal areas, intensive pumping of fresh groundwater causes salt-water to intrude into fresh-water aquifers (Fig.1.8).

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Fig. 1.8. Schematic presentation of salt-water intrusion in coastal aquifers.

2. INVESTIGATION OF GROUNDWATER In many countries (developed and developing), there is not only a heavy reliance on groundwater as a primary drinking supply but also as a supply of water for both agricultural and industrial use. A rapidly growing population has increased the demand for water in both urban and rural areas. Groundwater is an important source of domestic, municipal, and industrial water and its use is projected to grow. The reliance on groundwater is such that it is necessary to ensure that there are significant quantities of water and that the water is of a high quality. This calls for a systematic investigation of the groundwater resource. Groundwater may occur in three modes: •

Near-surface groundwater (in alluvium)

•

Intermediate perched groundwater (in the vadose zone), and

•

Groundwater in the regional aquifer beneath the water-table.

In a particular location, it may exist in all of the three forms or any combination of the above.

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Previous synoptic studies of groundwater quality and quantity around the world were found healthy groundwater systems. However, the increasing population of the region and the accompanying increasing demand for groundwater means that the availability and health of the groundwater resources could change. These increased pressures on the groundwater resource increase the need to establish a comprehensive groundwater monitoring system in a region. In addition, area-specific studies can and should inform decisions regarding land use and water resource management. Well yield, water quality, and monitoring well locations can be optimized by detailed fracture studies (mapping the fracture patterns and depositional environments that will affect well yield, water quality, and off-site impact) using various methods (aerial photographs, geophysical methods or borehole logging) to identify "sweet spots". Proper Well location can be critical in preventing a negative impact on environment and providing long-term life of a well. Groundwater investigation may need to carry out with the following objectives (a single or in combination): •

To describe the hydrogeologic units (aquifers and aquitards)

•

Characterization of the aquifer

•

To assess groundwater availability as both a source of potable water and as source of discharge to lakes, streams, and wetlands

•

To assess the magnitude, sustainability and origin of ‘deep’ groundwater resources

•

To examine both current and future groundwater availability

•

To develop a picture of the current groundwater quality

•

To assess future groundwater quality as urban and rural development continues

•

To quantify a water budget

•

To relate existing groundwater quality conditions to land uses and development densities; and

•

To project how future land uses could impact groundwater availability and quality.

2.1 Planning an investigation The plan generally consists of a detailed outline of the objectives, scope, level of detail procedures, available equipment, existing and potential problems, necessary data, wellthought-out schedule of tasks, and the resources available. Hydrogeologic investigation is generally complex and interdisciplinary, and requires expertise from a number of different fields. In order to properly plan a hydrogeologic site investigation, the purpose of the investigation, the general geologic and hydrologic characteristics of the site, and the management constraints under which the investigation is to take place (financial and time restraints, availability of necessary equipment, availability of expertise) should be well understood by the personnel involved in the project.

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2.1.1 Steps involved in a site investigation The general steps in groundwater and hydrogeologic investigations include: •

Field reconnaissance

•

Literature search

•

Assessment of additional data requirement

•

Planning field study/conceptual model development

•

Materialization of field study

•

Synthesize/evaluation of field data

•

Data analysis and reporting

Field reconnaissance

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Site investigation should be done involving all the personnel in the project. This will provide a more complete understanding of site hydrogeology, and will help in determining appropriate method of study. The points which should be recorded include: •

Topographic features

•

General character of the local geology

•

Nature and location of any significant impermeable areas

•

Location of any potential surface and subsurface contamination (including volume and nature)

•

Location of surface water (including nature, volume and flow)

•

Flow rates of existing wells (if any)

Literature search Existing data should be availed first to any hydrogeologic site investigation. Much of the data necessary for developing a conceptual model may already have been collected during different previous investigations. Data can be obtained from research papers, reports (from Geologic and Natural Resources Departments, Public Works Departments, Water Resources Departments), local/federal agencies, and private organizations (specially pump drilling/boring agencies and agricultural consultancy agencies). Data that should be reviewed include: -

Previous boring log data of tubewells (if any)

-

Previous investigations of aquifer and surface water

-

Regional hydrogeologic report

-

Geophysical data

-

Production well data

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Topographic, geologic, and hydrogeologic map

-

Soil map

-

Land-use map

-

Long-term climatic data (specially rainfall)

Topographic maps aid in delineating drainage areas, locating desired cross-sections, and locating boundaries for other maps (including geologic, depth to water, flow gradients, recharge and discharge areas, and other related features). Aerial photos are often used as substitutes for topographic maps. Multiple photographs may be used with a stereoscope to obtain a three-dimensional view of the area. Geologic maps and sections are helpful when complex geologic structures and variances occurs. When accompanied by analysis reports, they aid in locating aquifers, water level conditions, structural and stratigraphic control of water movement, and other related factors. Water-table contour maps are similar to topographic maps, the difference being that they show water-table elevations as opposed to ground elevations. Cross-sectional maps are developed using borehole data. The vertical stratigraphy of the subsurface is mapped out using multiple boreholes spaced in a horizontally planar manner. The hydrographs may be for individual well (changes in water level over time), river/canal flow, and depth to water-table. Fence diagrams are maps similar to cross-sectional maps, except they illustrate the surface and subsurface in three dimensions.

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Determination of data requirement and selection of method Based on the specific object of the investigation (and general objectives, if any), data requirement from the detailed investigation should be assessed. The investigator should choose the investigation method based on the data requirement, taking into consideration that which method will provide the most valuable data within time and cost constraints.

Conceptual model establishment A conceptual model is a simplified description of the groundwater system to be studied. It is most important if it is intended to develop a computer model. Natural area boundaries, hydro-stratigraphy, water budget, aquifer properties, potentiometric surfaces and other features are described in a level of details that the data represent the system adequately. Each type of data may be consists of as follows: Aquifer materials properties-Porosity, storativiity/specific yield, isotropy, etc.

hydraulic

conductivity,

transmissibility,

Boundary conditions - Depth to bedrock, impermeable layer boundaries, fluxes, heads, natural water bodies, withdrawal wells, infiltration trenches, etc. Water budget – Inflows and outflows such as surface infiltration, lateral boundary flux, leakage through confining units, withdrawals and injections.

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Graphic descriptions of the conceptual model can include simplified hydrogeologic crosssections, potentiometric surface maps, structure maps of hydrogeologic units, threedimensional graphics, and schematic water balance diagram. Graphics may complement a written description. Once a complete conceptual model has been developed, a numerical model can be generated. Parameters determined during conceptual model development are integrated into a computer model. The computer model is then calibrated to reproduce measured field conditions. If model calibration is judged acceptable, it can be used to predict other hydrogeologic changes due to new stresses (e.g. the introduction of a new pumping well for groundwater cleanup within the site).

2.2 Approaches of investigation

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Different approaches and methods have been used to investigate the groundwater resource throughout the world. The approaches include: •

Mechanical approach (Drilling bore-hole)

•

Geo-physical approach

•

-

Electrical

-

Electro-magnetic

-

Seismic

-

Gravity

-

Magnetic

-

Ground penetrating radar

-

Borehole

-

Other approaches (magnetic resonance, Induced potential, etc.)

Aerial photograph

The choice of a method depends on the availability of the respective instruments, technical expertise, cost, practical implementation difficulties, required precision of the results, capabilities or limitations of the method, and physiographic, socio-economic and socio-environmental factors. Subsurface investigations are dynamic and inexact science. The ability of the data acquired to provide an increasingly accurate representation of the hydrogeologic system increases with time, money, and the expertise of the specialists involved.

2.2.1 Mechanical approach 2.2.1.1 Features This is the direct method of groundwater investigation. Mechanical approach involves drilling, constructing boreholes, sampling and logging of boreholes to depths ranging from

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surface to target depth. Drilling method for investigations often aimed at resolving the origin and resource potential of ‘deep’ groundwater. In addition, it is also useful for chemical, isotopic and age dating of groundwaters obtained from the boreholes to better define the age, extent and origin of the deep water. A visual appraisal and mapping of the site conditions and features should be done before the starting of drilling. For near surface information, the uppermost 1.5 metre section of the borehole may be drilled with hand-auger (at higher number) or using a hammer and bit assembly. The dipper boreholes can be constructed with a variety of instruments, including truck mounted drill rig with hollow flight augers, a track mounted rotary down-hole hammer (DHH) with air flush drilling rig, etc. A typical borehole is indicated diagrammatically on Figure 2.1.

Fig.2.1. Schematic of a borehole.

Drilling of Exploratory Bore Wells As a part of investigation program, exploratory bore holes are periodically drilled with the following objectives: (i)

To explore the sub-surface lithological characteristics

(ii)

To arrive at the sub-surface hydrogeological parameters

(iii)

To find out the quality of groundwater at different aquifers.

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Water samples are obtained from constructed boreholes to be drilled at locations chosen as being the most likely to yield water. In essence, boreholes are drilled to whatever depth the experts and drillers believe is necessary (normally up to a maximum depth of 750 feet). After test drilling, the boreholes are fully lined and grouted throughout the depth to avoid crosscontamination with locally sourced water.

Avoiding cross contamination during drilling It is necessary to specify a design for investigation boreholes that would permit water samples to be obtained from the shallow productive horizons whilst drilling, and then seal out those horizons before drilling deeper to obtain uncontaminated water samples from the greater depths. This involved drilling to a depth a few metres above that which the ‘underground stream’ is predicted by the water experts and well drillers, installing casing and filling the borehole with impermeable grout to provide a seal that would prevent any groundwater originating from the shallow productive fractures from entering the borehole. Once the grout had set, the borehole would be redrilled back through the casing and into the underlying rock to the required depth. Thus it would be possible to obtain groundwater samples at selected depths throughout the drilling process whilst preventing cross contamination between shallow and deep productive horizons.

2.2.1.2 Limitations For irregular land surface and uneven/discontinuous lithological condition, it requires a greater number of boreholes for complete information; which is very costly to perform and time consuming.

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2.2.2.3 Sampling interval and representation Sampling interval depends on the specific objective and the pattern of lithological condition. If no abrupt change is occurred, sampling at 10 ft interval is sufficient. At transition, frequent sampling may be needed. The soil samples are analyzed in the laboratory for particle size distribution. For aquifer materials, it is analyzed for specific yield, well screen design, and envelop material design. Water sample should be collected during drilling and development for quality analysis. The bore logs are represented in log diagram (e.g. Fig.2.2).

2.2.1.4 General guidelines and steps in borehole drilling and construction The sequence of activities to be undertaken at the borehole site may be as follows: •

Move rig and equipment to site and set up at the precise location previously selected. Erect temporary fencing around the drilling site and install drainage ditches (if required).

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Depth (m) 0

24 Clay 27 Sandy Clay 36 Sandy Clay Loam 39 Sandy Clay 42 Clay 48 Loamy Sand 51 Clay

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Fig.2.2. Sample bore log diagram.

•

Drill @ 254 mm (10 inch) diameter to below the base of unconsolidated/ weathered materials and install 254 mm OD plain steel drill casing.

•

Drill @ 200 mm (8 inch) diameter to the required depth.

•

Insert permanent 152 mm (6 inch) ID casing to the full depth of the borehole.

•

Insert cement grout into the borehole from total depth to ground surface using a tremmie pipe (withdrawing the tremmie pipe as the inside of the casing and annulus fills).

•

Grout should be left to harden for a minimum of 24 hours.

•

Drill (at a diameter of c.152 mm (6 inch)) back through the casing to the total grouted depth.

•

Drill open hole at a diameter of 152 mm to final total depth.

•

Clean hole of rock chips (cuttings) and develop by flushing until water produced is clean.

•

Install surface completion.

•

Make good, dismantle and move to next site.

2.2.1.5 Relevant activities During the drilling of the boreholes, other relevant activities that should be carried out include: •

Maintain a site diary recording items such as drilling progress, geological logs, water strikes etc.

•

Maintain a photographic record of events during borehole drilling and construction.

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•

Record drilling cuttings, including the photographing of samples of cuttings laid in sequence along lengths of half pipe as pseudo-cores.

•

Record drilling penetration rates.

•

Recording depths of water strikes.

•

Measure and record of water flush yields following water strikes and at regular depth intervals.

•

Sampling air flush water for inorganic and isotopic analysis (if needed).

•

Measurement of rest (static) water levels below ground level after cessation of drilling (e.g. before start of drilling each morning, after lunch or other breaks longer than 1 hour).

•

Plumbing the borehole depth after the drilling tools were removed from the borehole.

•

Monitoring of the grouting procedure, in particular ensuring that the volume of grout pumped into the borehole was sufficient to fill the annulus and inside of the casing from total depth to ground level.

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2.2.2 Geo-physical approach The main use of geophysics in the geosciences is for hydrocarbon exploration typically at depths greater than 1000m. Near-surface geophysics for groundwater investigations is usually restricted to depths less than 250m below the surface. Groundwater applications of nearsurface geophysics include mapping the depth and thickness of aquifers, mapping aquitards or confining units, locating preferential fluid migration paths such as fractures and fault zones and mapping contamination to the groundwater such as that from saltwater intrusion. The use of geophysics for groundwater studies has been stimulated in part by a desire to reduce the risk of drilling dry holes and also a desire to offset the costs associate with poor groundwater production. It also provides useful parameters for hydrogeological modelling of both new groundwater supplies and for the evaluation of existing groundwater contamination. Geophysical methods can be used in groundwater related investigations to: • • • • • • • • • •

Locate geological structures such as faults and formation contacts Identify gravel channels within finer grained materials Define watertable in unconsolidated sediments Identify subsurface voids Map higher permeable areas within aquifers Define the extent of weathering, fracturing and faulting Define the extent of protective clay layers Map soil conductivity Identify freshwater-seawater interface /sea-water intrusion Provide complimentary data for correlating borehole and monitoring well data

In saline-water interface, the increase in conductivity is due to a large increase in specific conductance of groundwater within the soil/rock pores. Groundwater resource development Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

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can be optimized by the use of geophysical methods. Large areas can be investigated to focus drilling in high-grade potential locations reducing development cost by reducing dry holes and increased yield in completed wells. Geophysical techniques are also suited to detect subsurface acid mine drainage (AMD) pollution; the best methods include DC resistivity and electromagnetic methods.

Principle of geophysical approach

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For soils and rocks, the properties can be divided into a framework or matrix component and the pore content component. All geophysical techniques measure variations in a material’s physical properties. Different materials exhibit different parameter signatures such as their resistivity or its inverse, conductivity, acoustic velocity, magnetic permeability and density. These parameters are influenced by the mineral type, grain packing arrangement, porosity, permeability, and pore content (i.e. gas or fluid type). In general, no one property is unique to any materials; rather a material is described by ranges of each property. In most geophysical surveys therefore it is important that the changes or contrasts in geophysical parameters are measured and that the target shows large property differences with surrounding material.

Implications Geophysics is typically used in one of two ways: either it is used to project an interpretation of the geology and hydrogeology from boreholes and surface exposure into a formation, or the geophysics is used in an area of unknown geology and hydrogeology in order to better focus the direct sampling program. For both of these types of use, if the geophysics is discussed early in the proceedings then the most appropriate techniques can be found and used in the most cost effective manner. A parallel for groundwater development can be found in the hydrocarbon world where the successful use of an integrated geophysical program is seen at all stages of developing a hydrocarbon reservoir. First a geophysical regional recognisance study is conducted with potential field methods (gravity and magnetics). This is followed by regional seismic programs and exploration wells. Based on these results, more detailed local 3D geophysical surveys are made and the surface geophysics is tied to the subsurface geology by borehole geophysics. Ultimately high frequency borehole geophysics is conducted for reservoir modelling purposes. This integrated use of geophysics is recommended in developing a groundwater resource however, due to cost limitations it is not always possible. It is therefore vital that the geophysics is used in the most appropriate manner at the most appropriate time in a project if it is to be successful in helping to develop a groundwater resource. Many geophysical techniques have been applied to groundwater investigations with some showing more success than others. In the past, geophysics has either been used as a tool for groundwater resource mapping or as tool for groundwater character discrimination. For groundwater resource mapping it is not the groundwater itself that is the target of the geophysics rather it is the geological situation in which the water exists. Potential field methods, gravity and magnetics, have been used to map regional aquifers and large scale basin features. Seismic methods have been used to delineate bedrock aquifers and fractured rock systems. Electrical and electromagnetic methods have proved particularly applicable to groundwater studies as many of the geological formation properties that are critical to

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hydrogeology such as the porosity and permeability of rocks can be correlated with electrical conductivity (or resistivity) signatures. General methods of practice have been produced for geophysical techniques in groundwater exploration but situations with complex geology and hydrogeology do not lend themselves to the generic approach and require specific targeting of methods for particular problems. Most geophysical techniques have been used for groundwater characterization but once again it is with the electrical and electromagnetic methods that the greatest success has been shown in directly mapping and monitoring contaminated and clean groundwater.

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Considerations in geophysical approach Success of a geophysical survey largely depends on the definition of a clear set of objectives and the choice of appropriate methods. The objectives must be based on reasonable, geophysically achievable criteria. For this it is important that the geophysical target has physical properties that can be distinguished from background signatures (geological and hydrogeological features) and background noise (ambient cultural noise together with system induced noise). The next stage in defining a project is to be able to provide an adequate site description along with any previous data that has been collected, site maps or other data that would pertain to the project. This includes logistical features such as access to the site, noise sources and working restrictions. Other factors that influence the success of the investigation include depth of burial target and size of the target area. The depth of burial of the feature of interest is important as different techniques have different investigation ranges. The depth range is technique dependant; however there is always a tradeoff between penetration depth and resolution of the technique with respect to the feature of interest. A technique that will look deep into the earth generally has lower resolution than a technique that is only looking to shallow depths. Choosing the appropriate geophysical method and applying the method in an appropriate manner is also critical to a successful survey. The incorrect choice of technique and insufficiently experienced personnel conducting the investigation may cause failure of the geophysical survey. Quality control throughout all stages of the work is important for a successful outcome. Field quality control should include basic equipment calibration procedures, accurate field reporting including field printouts of digital data, checks for digital data recording and uploading to computers, and repeat measurements at base or calibration sites. During processing this quality control will include manual calculations of computer-processed data, documentation of processing steps and separate data reviews by an independent person not directly involved in the project.

2.2.2.1 Electrical method Electrical techniques have been extensively used in groundwater geophysical investigations because of the correlation that often exist between electrical properties, geologic formations and their fluid content. This method is also termed as electrical conductivity or resistivity method, and resistivity imaging method.

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Principle of the method Most electrical techniques induce an electrical current in the ground by directly coupling with the ground. Electrical conductivity, or its inverse resistivity, is the proportionality factor relating the electrical current that flows in a medium to the applied electric field. The resulting electrical potential is then used to measure the variation in ground conductivity, or its inverse, resistivity. Different materials, and the fluids within them, will show different abilities to conduct an electric current (Table 2.1). This method has also been applied to assess water flow in the non-saturated zone of the soil. The resistivity decreases as moisture content or the dissolved solids in the interstitial water increases. Table 2.1. Resistivity of different materials (after Custis, 1994) Materials

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Unconsolidated clays

Resistivity range (ohmm) 1.0×100 - 1.0×102

Unconsolidated alluvium and sands

1.0×101 - 8.0×102

Shale

2.0×101 - 2×103

Quartizite

1.0×101 - 2×108

Sandstone

1.0×102 - 6.4×108

Limestone

5.0×101 - 1×107

Basalt

1.0×101 – 1.3×107 (dry)

Pyrite, FeS2

6.0×10-5 – 1.2×108

Cuprite, Cu2O

1.0×101 - 5×101

Arsenopyrite, FeAsS

2.0×10-5 – 1.5×101

Theoretical aspects Electrical resistivity is the specific resistance of a body to let electric current pass through it. This property is based on Ohm's law, which states that if the injected current (I, apmeres), the voltage (difference in voltage potential, ΔV, volts) and the position of current injection and potential points (current and voltage electrodes respectively) are known; resistivity is calculated with the equation (Orellana, 1972): ∆

.

(2.1)

where, K is a geometric factor dependent on the spatial arrangement of current (AB) and voltage (MN) electrodes. 2 . (2.2) where, x is the spacing adopted for AB and MN dipoles; and n is a depth factor of the survey, and

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(2.3) In Equation 2.1, it is assumed that the electric currents are applied to homogeneous and isotropic terrains; in other words, whatever the electrode array, the electrodes are considered to be located in points of equal resistivity. However, this is not observed in nature. Electrical resistivity methods involve the measurement of apparent resistivity of soils and rock as a function of depth and position. For groundwater investigations, the most significant parameters that have been used for describing an aquifer system are ones that relate to the porosity and permeability of the aquifer and surrounding aquitard. A relationship often exists between electrical conductivity and the clay content or fluid type. In general, sequences with high clay content show higher conductivity as do saturated sequences and especially sequences where saline (or sometimes other contamination) fluids are present.

Different configurations of resistivity survey

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Electrical resistivity survey can be performed in 3 general configurations: •

Vertical electrical sounding (resistivity sounding)

•

Horizontal profiling, and

•

A combination of the above two

Vertical sounding (VS) is a process by which the separation between the current and potential electrodes is progressively increased over a fixed central point. This causes the array to measure the apparent resistivity at progressively deeper depths. Vertical sounding is used to investigate vertical changes in subsurface layering and produces a geo-electrical cross section. Horizontal profiling (HP) is a method for measuring the lateral variations in resistivity by progressing the survey along a linear traverse using a constant electrode spacing. A constant spacing implies a constant depth of investigation. Horizontal profiling is used to locate geologic structures such as buried channels, faults, dikes, and anomalous 2-D and 3-D bodies. The combined method repeats horizontal profiling method at wider electrode spacings to obtain a series of profiles that can be presented as a geo-electric pseudo- cross-section.

Electrode geometry Different arrays which can be followed for different problems include Wenner, Wenner– Schlumberger, Dipole–Dipole, Pole–Pole and Pole–Dipole arrays. In direct current (DC) resistivity studies, commonly used electrode configurations are: •

Wenner

•

Wenner–Schlumberger

•

Dipole–Dipole

•

Lee-partioning.

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The Winner array uses 4 electrodes placed in a straight line and spaced at equal intervals. The apparent resistivity is a function of the distance between electrodes. The Schlumberger array uses four electrodes along a straight line but with an irregular spacing where the distance (AB) between the current electrodes is equal to greater than 5 times the distance (MN) between the potential electrodes (Fig.2.3). The apparent resistivity is a function of the distance AB/2. In practice, MN is kept constant and AB/2 is expanded to obtain deeper soundings. As the distance AB/2 widens, the voltage drop across MN is reduced. At some point, it is necessary to increase the MN distance to obtain deeper soundings.

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Fig.2.3. Schematic of Wenner and Schlumberger Electrode Configurations.

The Lee-partitioning array is similar to the Wenner array except that an additional electrode (O) is placed midway between M and N potential electrodes. Potential differences are measured between the MO and NO. The dipole-dipole array differs from the others in that the current electrodes are separated from the voltage electrodes. The separation between each electrode within a pair is often kept the same and is significantly smaller than the distance between the current and potential electrodes. This method has an advantage over Schlumberger, Wenner and Lee-partioning because shorter AB and MN spacings are needed for deep penetration. The dipole-dipole resistivity method is inherently better for resolving resistive basement beneath the conductive anomaly, and DC resistivity interpretation techniques are presently better to handle the complex two-dimensional geology. The Wenner and Schlumberger resistivity methods are best suited for delineating horizontal layers and vertical contacts, and are less useful for bodies of irregular shape. The actual depth of investigation of each type of array is governed by a number of factors including signal-to-noise ratio, sensitivity to surficial inhomogeneity, sensitivity to bedrock topography, sensitivity to dip of layers, etc.

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Field survey procedure

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Common field practice for electrical surveying relies on directly placing an electrical current into the ground (direct current electrical resistivity surveying) and measuring the response (the electrical potential drop) to that current over a set distance. The resistivity of soils is a function of porosity, permeability, ionic content of the pore fluids, and clay mineralization. Apparent resistivity is the bulk average resistivity of all soils and rock influencing the flow of current. It is calculated by dividing the measured potential difference with the input current, and multiplying by a geometric factor related to the array being used and electrode spacing. In resistivity soundings, the distance between the current electrodes or the distance between the current and potential dipoles is expanded in a regular manner between readings, thus yielding information of the electrical properties of soils from deeper and deeper depths. With resistivity profiling the electrode spacing is fixed and measurements are taken at successive intervals along a profile. Data are generally presented as profiles or contour maps and interpreted qualitatively (Fig.2.4). Low resistivity layers indicate the presence of sand and gravel layers/lenses full with water (aquifer), in contrast the high resistivity represents the unsaturated layer. The geophysical results are used for optimum placement of monitoring wells, soil gas probes and future remediation planning. The general guidelines and steps for field survey are outlined below: •

Several sites should be selected to develop an understanding of the range of resistivity and thickness. Site selection should be based on locations where information would be of maximum benefit.

•

The small electrode spacing should be at least one-half the minimum depth at which a change in material is expected.

•

Surveys should be 1 or 2 electrode spacing away from sharp changes in topography.

•

Electrodes should be seated in soils, and not driven into gravels or rock.

•

Plot and evaluate VS survey data in the field to make adjustments in survey direction and spacing (or method), and to detect errors in equipment and survey procedures.

•

There is a tendency for the value of resistance to decrease with the widening of the spacing of survey. If the increase in resistance occurs, it may be due to the reason that the electrode is placed in or above materials of much higher resistivity, or the dip of the underlying layer is changing rapidly. In such case, a new survey should be run at right angles to evaluate the cause of such change.

•

To develop correlation between VS data and aquifer properties or groundwater quality, surveys should be run adjacent to the production or monitoring wells.

•

As horizontal profiles are conducted to find lateral changes in the subsurface, surveys should be run over targets.

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Fig.2.4. Schematic of subsurface lithology.

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Discussion The direct-current (DC) electrical resistivity method for conducting a vertical electrical sounding (VES) has proved very popular with groundwater studies due to the simplicity of the technique and the ruggedness of the instrumentation. It has been used in mapping boundary conditions in an aquifer system (Van Overmeeren, 1989), for siting wells and boreholes in crystalline basement aquifers (Barker et al., 1992), to assess the directional variation in hydraulic conductivity of glacial sediments (Sauck and Zabik, 1992), and so on. An excellent example of the use of the technique was shown by Reynolds (1997) in a survey for a rural water supply in northern Nigeria. The typical results of electrical surveys are electrical profiles or geo-electric images and geo-electric depth soundings. The profile or transect method for mapping lateral resistivity changes is now largely replaced by electromagnetic techniques as the electrical technique is slow (when probes have to be placed directly into the ground) and thus is not cost effective relative to the electromagnetic techniques. Electrical methods are still widely used however for conducting soundings and electrical cross-sections. Electrical resistivity is one of the most effective geophysical methods for investigating the presence of groundwater. In hard-rock areas, especially granitic terrain, even within small areas the nature and extent of weathering may vary considerably, depending mostly on the presence of fractures at depth and geomorphological features at the surface. Hence with groundwater studies, identification and analysis of underground fractures and concealed lineaments are crucial in hard-rock terrains. Conventionally, apparent resistivity values are used to detect such underground structures. The two-dimensional Electrical Resistivity Imaging (ERI) method provides a more realistic model of the subsurface in geologically complex areas. A good example of this for groundwater exploration is shown by Dahlin and Owen (1998) using 2D resistivity surveys with an ABEM Lund Imaging System together with a ground penetrating radar in shallow alluvial aquifers in Zimbabwe. The results were used to build conceptual geological/ hydrogeological models of the aquifers as a basis for guiding the drilling programme. Olayinka and Barker (1990) used similar micro-processor controlled resistivity traversing techniques for siting boreholes in Nigeria. Most recent surveys tend not to rely on the electrical method alone for data but rather to integrate it with other geophysical techniques. Examples of the multi-technique approach include using electrical and electromagnetic techniques.

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Interpretation of resistivity data/ Modeling of underground structure The vertical sounding (VS) is generally interpreted by using a numerical model to find a best-fit match of the data to an ideal geologic VS curve. Now-a-days, it is performed by means of suitable software (e.g. RES2DINV), which will transform in quantitative data the qualitative positioning supplied by the pseudo-depth sections. Such transformation corresponds to mathematical inversions resultant from the application of the minimum-square smoothing method. Inversion takes place in three stages: firstly, the field data constitute a pseudo-section; secondly, the data are calculated, and thirdly, adjustments are made between the measures and calculated data in order to reduce the differences between them, yielding a result closer to real. Horizontal profiling is interpreted qualitatively by plotting the field apparent resistivity values as either a linear trend plotted on an X-Y graph, or by contouring a map of apparent resistivity at a specific electrode spacing. The contour map presents a two-dimensional picture of the apparent resistivity at a constant but at an apparent depth. The combined method of horizontal profiling at different electrode spacings usually presents the data as a contoured geoelectric cross-section or pseudo-section. The resistivity contours are pseudo-contours since the field apparent resistivity data are arbitrarily assigned to a point below the centre of the array (at a depth often set equal to one-half the current electrode spacing). The shape of the apparent resistivity curve is influenced by the electrode spacing, the width of the discontinuity, the resistivity of the rock units, etc. There can be abrupt changes in the slope of the apparent resistivity curve where the electrodes of a horizontal profile survey cross a buried structure, or a fault zone. A fault zone can increase or decrease conductivity depending on the nature of the surrounding rock and the material that fills the fault zone.

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2.2.2.2 Electromagnetic method While the final output of electromagnetic method is similar to that of electrical techniques, several advantages with the electromagnetic techniques result in an increased resolution and more cost-effective application. Two types of electromagnetic survey are currently practiced: i)

Time domain electromagnetic (TDEM) surveys which are mainly used for depth soundings and recently in some metal-detector type instruments, and

ii) Frequency domain electromagnetic (FDEM) surveys that are used predominantly for mapping lateral changes in conductivity. In both electromagnetic survey techniques no direct contact is made by electrodes with the ground and thus the rate of surveying can be far greater than for electrical techniques where electrode probes must be placed in the ground for every measurement.

Principle of the method Both techniques measure the conductivity of the ground by inducing an electric field through the use of time varying electrical currents in transmitter coils located above the surface of the ground. These time-varying currents create magnetic fields that propagate in the earth and cause secondary electrical current to flow in the subsurface (the process is

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known as electromagnetic induction). The secondary current can be measured either while the primary field is transmitting (during frequency domain surveys) or after the primary field has been switched off (for time domain surveys). The receiving coil responds to an electromotive force generated by the resultant of the primary and secondary fields. Buried metal objects (e.g. drums, pipelines, etc.) and water bearing strata produce characteristic anomalies which result from the geometrical relation between the object and the instrument coils along with the very high conductivity of the metal. Instrumentation exists to survey to a range of depths.

Applicability

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Electromagnetic induction (EM) methods are used in many different types of geological and environmental applications. As the equipment generally is lightweight and portable, large areas can be mapped rapidly and accurately. EM methods have proven to be quite reliable for the detection and mapping of buried structures such as building foundations, as well as for the detection of highly conductive metallic objects like steel drums, tanks, metallic utilities and other nondescript buried ferrous metallic objects. EM methods can provide high quality information about soil types and variations as well as the presence of sinkholes, or bedrock formations when interpreted correctly. EM induction surveys can be conducted to:

•

Map geologic structure /characterize subsurface hydrogeology

•

Soils mapping

•

Locate conductive fault and fracture zones

•

Conduct groundwater exploration

•

Map conductive soil and groundwater contamination

•

Delineate landfill boundaries

•

Map buried channel deposits

•

Locate pits and trenches

•

Locate buried tanks and pipes

Description of the methods Frequency-domain Electromagnetics (FDEM) This technique is usually used to measure lateral conductivity variations along line profiles either as single lines or grids of data. Further recent improvements in FDEM has seen the integration of GPS technology with the FDEM instruments which has led to a dramatic increase in the rate at which electromagnetic surveys can be accomplished. A number of manufacturers offer FDEM equipment that vary in physical size, ease of operation and survey depth. Typically survey results for FDEM surveys are presented as contour maps of conductivity and 2D geo-electric sections showing differences in con-

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ductivity along a line profile. Changes in conductivity are often associated with differences between lithological sequences and over disturbed ground such as faulted or mineralised zones. A comparison of electromagnetic techniques for reconnaissance groundwater mapping has been given by Richards et al. (1995). A useful example of FDEM for groundwater studies has been given by Godio et al. (1998) in a mountainous area in north-eastern Italy. Here a frequency domain survey using 20m and 40m coil separations gave information on the electrical resistivity for locating a number of water wells. The FDEM resistivity values were calibrated using the results of vertical electrical soundings and significant features noted along the FDEM traverses collaborated with VLF profiles. Van Lissa et al. (1987) demonstrated the use of FDEM for mapping lateral geological changes and water bearing faults and fractures in the Nyanza Province, western Kenya. A methodology was developed that first located potential fault and fracture zones from aerial photographs and satellite images. These were then targeted with the FDEM together with resistivity profiling and vertical DC-resistivity electrical soundings. The combined use of the three geophysical techniques resulted in a success rate of over 80% for borehole locations with the depths for the boreholes determined by the geophysics at only about half that for traditional boreholes and with yields of 140% of the traditional holes. Moreover, it was estimated that the relatively low survey costs for the geophysical methods approximated 3% of the construction costs of a borehole, and thus were more than justified by the increase in yield and success rates. Taylor et al. (1997) also used electromagnetics to locate shallow water wells in highly fractured aquifers. Beeson and Jones (1988) and Hazell et al. (1988 and 1992) have also demonstrated a combination of FDEM and vertical electrical soundings to locate zones of enhanced groundwater yield from fractures in arid areas.

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Time-domain Electromagnetics (TDEM) TDEM techniques produce one-dimensional and two-dimensional geo-electric crosssections in a similar manner to electric cross-sections. Survey depths for TDEM are from 5m to in excess of 100s of metres with high vertical and lateral resolution. The techniques do not however give high resolution from 5m to the surface. It is also possible to conduct electromagnetic surveying using logging tools in non-metal cased boreholes. This procedure has been shown to be extremely sensitive to lithological changes and is important for the calibration of the surface geophysics with sub-surface geology. Additional correlation between electrical/electromagnetic measurements and physical samples can be obtained by measuring resistivity in the laboratory on borehole samples. Many regional case histories are now available to demonstrate the utility of TDEM for groundwater exploration with background work on salt water intrusion given by Wolfe et al. (1999), and Jensen et al. (2000). Hild et al. (1996) used this approach to map the fresh water lens floating on the saltwater beneath the island of Guam in the Northern Mariana Islands, western Pacific. This approach has seen much success in these types of groundwater exploration projects (Hild et al., 1996). In these types of study, use is made of the GhybenHerzberg principle where a basal lens of fresh water floating on denser salt water has a thickness which forces the freshwater-saline water contact to a depth below sea level that is 40 times the elevation of the top of fresh water above sea level. The fresh water/saline water boundary shows a high electrical contrast that is easily mapped with TDEM techniques

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especially in resistive bedrock. This freshwater resource is a significant one for many of these islands where water storage is poor and water demand is on the increase. The integrated use of TDEM methods has very successfully been demonstrated with the regional mapping programmes undertaken by the Danish Survey and reported by Christensen and Sorensen (1998), Sorensen et al. (2000). Traditionally, frequency and time domain electromagnetic systems have been used for mineral prospecting but there has been an increased hydrogeological interest in these techniques particularly in urban areas over the last decade (Paine et al., 2000). The advantage of airborne systems is the rapid data acquisition over large areas and thus the techniques are ideally suited to regional studies. However, the disadvantages are the poor horizontal resolution, a narrow bandwidth giving reduced vertical resolution and the susceptibility of the systems to environmental noise. The techniques are always applied together with ground surveying for calibration such as ground based TDEM, borehole logging and the integration with other geological information. Future work will determine if the technique is one that will find widespread use within groundwater evaluations. Another application of EM airborne techniques has been to map the depth to basement beneath aquifers. Wynn et al (2000) demonstrated the increase in resolution obtained from this type of survey over the more traditional gravity data in the San Pedro Valley, southern Arizona. In this study, a number of difficulties were encountered with human cultural interference (power lines, pipelines etc) and also static geologic noise from Tertiary volcanic flows that would require further processing in the future.

General guidelines and field procedure for EM method

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The pre-requisites of field survey are: •

Identification of target area

•

Definition of objectives of the survey

•

Selection of proper EM method based on sensitivity and applicability, and

•

Layout of survey points and grids

For specific instrument calibration and operation, the operating manual should be consulted. The general guidelines for field survey are as follows: •

Select target area

•

Determine orientation of feature of interest, if possible

•

Optimize sample point and line spacing, intercoil separation based on results of test lines, knowledge of target dimensions and depth

•

Estimate whether ground conductivity contrast is sufficient to identify the plume or buried object of interest. Target should have an apparent ground conductivity of 150 % above or below background

•

Lay out grid and identify sample points with non-conductive stakes or markers

•

If required (by manufacturer), calibrate instrument at the site

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•

Orient traverses perpendicular to strike of target, if possible

•

Avoid areas of irregular topography

•

Record the extend of interference from power lines, pipes, and fences by making a traverse perpendicular any such features until EM readings stabilize

•

In addition to data loggers, written note of data is necessary

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2.2.2.3 Seismic method Seismic velocity is related to the elastic moduli and the density of a material with compressional wave velocity, and also correlated to porosity and fluid content. In seismic methods, measurements are made of acoustic energy propagation within a medium. The velocity of acoustic energy in the form of compressional and shear waves is related to the dynamic elastic moduli and density of a material. Seismic geophysical methods for subsurface investigations are divided into two categories: refraction and reflection. These methods differ in the progression of seismic energy through the earth’s layers, and data collection and interpretation. The use of seismic surveys in groundwater exploration have traditionally relied on seismic refraction techniques using compressional waves which show increasing velocity with density. This contrasts with the use of seismic in the hydrocarbon industry where the reflection technique dominates exploration. This is mainly due to the high costs associated with acquisition and processing reflection data. The major use of refraction seismics are to map the depth and geometry of bedrock surface underlying unconsolidated (drift) sediment, mapping the water-table (as there is significant velocity increase across the water-table from unsaturated to saturated material), finding depth of bedrock and depth of water-table, and to infer aquifer properties such as porosity. Recent studies for groundwater evaluation include those of Holman et al (1999) at the Pleistocene Crag aquifer in northeast Norfolk, England. The seismic survey provided information on the internal structure of the aquifer which shows layers of clay and silt strata that limit the overall vertical permeability of the aquifer. Young et al. (1998) used high resolution seismic reflection for defining the structural control and the base of alluvium aquifers on the Batinah Plain, Gulf of Oman. Shtivelman and Goldman (1998) used an integrated study of high-resolution reflection and TDEM at several sites along the Mediterranean coast of Israel to define the coastal aquifer of Quaternary marine and continental deposits. The interpretation of the combined geophysical data sets allowed the discrimination of the higher porosity sand sequences from the lower porosity/permeability clay sequences. This discrimination was important in order to manage the salt water intrusion.

2.2.2.4 Magnetic geophysical method Land based magnetic surveys measure the variations in the earth’s magnetic field caused by near-surface ferrous materials to locate buried targets. It has been used for regional surveys since the early 1900’s in the hydrocarbon industry and for longer in mineral prospecting however little use has been made directly for groundwater studies. This is mainly because groundwater does not have a magnetic signature.

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The main use for regional groundwater investigations has been as part of combined surveys with gravity for defining large-scale basin structures. It is used for mapping bedrock topography, and in particular possible groundwater reservoirs in hard-rock (igneous and metamorphic) terrains (Babu et al., 1991). Other use of the magnetic technique together with resistivity surveys in volcanic terrain has been described by Aubert et al. (1984). Magnetic surveys are also often used to locate the cause of contaminated groundwater by surveying for buried metallic objects such as hydrocarbon storage tanks, and chemical containers. Magnetic surveys have also been used to identify basement faulting and other locations of crustal weakness that may represent preferential fluid flow paths. The magnetometer survey is generally carried out along a linear traverse or a grid. Modern magnetometer instruments measure the total magnetic field intensity. An alternate method is the vertical gradient magnetometer survey. This method measures the magnetic field at two points vertically separated by about 1 meter with the gradient being the change in magnetism between sensors. While there are several types of instruments used for measuring the earth’s magnetic field, the proton-precession magnetometer is the most common in environmental and engineering studies. The proton-precession magnetometer can read the total magnetic field to a sensitivity of 0.1 gamma.

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2.2.2.5 Ground penetrating radar method Ground penetrating radar method is an electromagnetic technique for measuring the displacement currents in the ground. Displacement currents are defined by the movement of charge within the ground by polarization and can be related to the applied electrical field by the electric permitivity of the ground or the dielectric constant. Ground penetrating radar (GPR) - a ground based, high frequency, electromagnetic geophysical instrument; employs a short duration, electromagnetic pulse using a broad-bandwidth antenna placed directly on the ground. The depth of penetration and resolution are controlled by the antenna frequency, which normally ranges from 80 Hz to 1000 Hz. GPR detects differences in the dielectric properties of buried materials. Voids and buried objects such as sewer lines have sufficiently different dielectric properties to be detected. Ground penetrating radar has seen a significant increase in use through the 1990's in near surface investigations with a number of case histories now recorded for groundwater surveys. The increase in use has in part been stimulated by an increase in computing power and the decrease in cost of computing. Although the technique often results in spectacular, high resolution sections of the earth, some degree of caution is recommended with the GPR as the technique can be limited to penetrations of less than 50cm when the surface ground electrical conductivity is above 30 mSm-1. Unfortunately such values are often reached in clay and clayey-silt soils or 100% saline saturated soils and therefore a measure of the near surface conductivity is recommended before embarking on a GPR survey. The water table is often also a strong GPR reflector, as shown by the work of Trenholm and Bentley (1998), which can limit the penetration depth of the signals. Arcone et al. (1998) have demonstrated the use of the GPR in permafrost areas for mapping the bedrock and groundwater in zones where the permafrost shows a discontinuous nature and thus may act as a barrier to fluid migration. Harari (1996) demonstrated the high resolution possible with the technique in imaging a sand dune aquifer complex in the Eastern Province of Saudi Arabia.

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2.2.2.6 Borehole geophysical method Borehole geophysical includes all methods for lowering a sensing device down a borehole (cased or uncased) to record physical, chemical, electrical, electromagnetic, or radioactive parameters along the well bore. Borehole logging is used extensively by the mineral and petroleum industries, and to a limited extent by the water resources and geotechnical industries. In recent years, it is becoming a popular tool to assist the geologist and hydro-geologist in interpreting subsurface geology and hydrology. There are numerous borehole geophysical methods, and many variations on each method developed for special circumstances. The types of borehole geophysical logging devices are numerous, but can be grouped as follows: •

Electrical resistivity and conductivity

•

Nuclear

•

Acoustic

•

Borehole fluid

•

Well construction logs

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Acoustic logging uses sound waves generated by the logging probe to measure formation properties (primarily porosity), fracture density and orientation, and the quality of annular space cementation. This method includes: sonic, tube wave amplitude, variable density, borehole acoustic televiewer, and acoustic cement bond logs. Well-construction logs include: downhole video camera, casing-collar indicator, directional survey, and caliper. These can be run after completion of the well construction, or as part of the engineering design of the well. Interpretation of the borehole logs can be done qualitatively or quantitatively.

2.2.2.7 Gravity method Gravity or micro-gravity surveys are commonly used to record the changes in density of materials. While gravity methods have not been widely used for groundwater applications, there are some notable examples of its use for mapping the location of low density rocks (typically sedimentary sequences) within more dense basement rocks. Yuhr et al. (1993) used a combination of electromagnetics and microgravity to design a strategic approach to mapping karstic features. Other common applications are the detection of voids within the subsurface where the small changes in the Earth’s gravitational attraction caused by such contrasts in density can be recorded with modern instrumentation. Interpretation of gravity data however is difficult as the causes of the changes in gravitational field can be many and varied. In addition, the collection of gravity data is typically a slow process and thus expensive. The results of gravity surveys are presented as gravity maps and 3D models in a similar manner to those of magnetic data. Van Overmeeren (1975) used a combined approach of micro-gravity and seismic refraction for groundwater evaluation near Taltal province, Chile with a similar study including the use of electrical resistivity to study groundwater in Sudan (van Overmeeren, 1981). Allis and Hunt (1986) used measurements of micro-gravity changes to monitor the draw-down in the steam zone in the Wairakei geothermal field.

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2.2.2.8 Very Low Frequency Electromagnetic (VLF-EM) method Very low frequency (VLF) survey methods rely on eleven major stations (military transmitters) that transmit continuous VLF electromagnetic waves distributed throughout the world. These transmitters are used to provide communication with submarines deep under water. Due to the nature of these radio transmitters (frequency range 15 – 25 KHz), they are very powerful and induce electric currents in conductive bodies thousands of miles away. The signals from these transmitters cause secondary effects in the subsurface (secondary magnetic field in local conductors). Localized conductors, such as water-filled fractures, cause angular disturbances in this signal which can be measured. The depth of investigation is dependent on the subsurface conductivity but, survey depths of several hundred feet are common. This method has been found useful application in groundwater investigation in basement terrain, most especially as a reconnaissance tool. The basement aquifers are often limited in extent both laterally and vertically. This discontinuous nature of the basement aquifer makes details knowledge of the subsurface geology, its weathering depth and structural disposition through geological and geophysical investigations inevitable. The interaction of the electromagnetic plane waves emitted from these transmitters can be measured as the waves impinge on different material conductors in the earth. Vertical sheet conductors are particularly sensitive the waves. Examples of vertical sheet conductors include faults, dykes and fracture or joint zones. These features are often associated with enhanced fluid (groundwater) flow. Survey profile lines conducted perpendicular to the conductors show a strong response to the conductor. The method is generally inexpensive with final data output from the instrument providing a direct indication of linear conductor anomalies. The method is often conducted as a recognisance survey as large areas of ground can be rapidly covered. The VLF method is typically used in conjunction with other follow-up techniques such as DC resistivity (e.g. Adiat et al., 2009). The instruments employ for this survey (e.g. ABEM WADI) measure the in-phase (real) and quadrature (imaginary) components of the induced vertical magnetic field as a percentage of the horizontal primary field. The VLF measurements are made along traverses. The raw real VLF data are converted with the aid of appropriate software (either supplied with instrument or suggested) into filtered real data in which anomaly inflections appear as peak positive anomalies and false VLF anomaly infections as negative anomalies of the profiles (Fig.2.5). The specific operational procedures of each instrument are provided in respective instrument’s manual. A full review of VLF methods has been given by McNeill and Labson (1991) and a good example of locating bedrock wells in water bearing fracture zones for contaminant migration prevention has been given by Covel et al. (1996). Michaud and Covel (1998) have demonstrated the technique together with that of downhole logging during a hydrogeologic study of an island in Narragansett Bay, Rhode Island.

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Fig.2.5. Schematic Pseudo Section of the Inverted VLF- EM Real component of the Profile (adapted from Adiat et al., 2009).

2.2.2.9 Other electrical and electromagnetic methods

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Three other methods have had limited use for groundwater studies, namely: •

Induced potential,

•

Spontaneous potential,

•

Telluric methods

•

Nuclear Magnetic Resonance method

Induced potential The measurement of induced potential (IP) is made using conventional electrical resistivity electrode configuration where the voltage between electrodes is measured as a decay function with time after the current has been switched off or as the current is switched on. The technique has found most use in the search for mineral deposits but has had some limited success in groundwater applications. Two case histories have been provided by Vacquier et al. (1957) where measured rations of IP values 5sec and 10sec after current shutoff. The higher rations were associated with finder grained material in a buried channel aquifer. Further studies are given by Draskovits et al. (1990), Ruhlow et al. (1999) and for contamination studies by Sanberg et al. (1998). Spontaneous potential The method of natural electrical potential – also known as spontaneous potential or self potential geophysics uses naturally occurring ground potentials from mineral bodies, geochemical reactions, and groundwater movement. The techniques have most often been used in exploration for mineral deposits and successful applications have been seen for groundwater surveying in association with geothermal systems (Corwin and Hoover, 1979),

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and groundwater flow (Wanfang et al., 1999). The methods have also been used recently to investigate the leakage of systems such as landfill sites and natural dams.

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Telluric methods Telluric methods that utilise natural fluctuations in the Earth’s magnetoshpere causing low frequency currents within the ground have been developed for regional (deep) geologic studies over the last 30years. In the early 1970’s controlled sources were introduced to the method (CSAMT) for increasing the reliability of the source signatures (Zonge and Hughes, 1991). Examples of the use for deep groundwater surveys have been given by Giroux et al. (1997), Miele et al. (2000) for deep aquifers of Senegal where it not only was used as a method to find the base of the local Maestrichtian aquifer but also to estimate porosity values. Ritz et al. (1997) showed that this method could be used to measure the water content and quality in Reunion Island. Meju et al. (1993) demonstrated the use of CSAMT methods in conjunction with time domain electromagnetic surveying.

Proton Nuclear Magnetic Resonance Method The Proton Nuclear Magnetic Resonance method, also called the Magnetic Resonance Sounding method (MRS), has been emerged as groundwater investigation tool for various geological environments for complementing the traditional geophysical methods. Its capacity to give quantitative information for characterising the water layers (depth and thickness, porosity, permeability after calibration) give it a special place in the range of geophysical tool for hydrogeologists. Due to the low levels of the signals which are measured in Magnetic Resonance field surveys, to make the method efficient, one must take special care of the accuracy of the Larmor frequency used in relation with the local Earth Magnetic field and of the filtering of the natural and industrial electromagnetic noises. The shape of the wire loop used to energise the ground and to receive the relaxation signals (square loop, eight-square loop, compensated square loop) from which the initial amplitudes and the time constants are determined is also a matter of importance as it shares the control of the depth of penetration together with the transmitter power, and it directly acts on the way the local noise is primarily filtered.

2.3 Estimation of groundwater potential Groundwater investigations are carried out with a view to evaluate its groundwater potential and ultimately recommend the appropriate way of providing adequate and good quality water for the intended use.

2.3.1 Qualitative identification The VLF – EM and Electrical probing data over an area need to be inverted and interpreted in terms of the distribution of the geoelectrical parameters in the area. Interpretation of both the EM profiles and equivalent current density map may identify some areas of hydrogeologic importance in form of fractures and permeable zones (Fig.2.6).

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Fig.2.6. Schematic showing of groundwater potential map (after Adiat et al., 2009).

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2.3.2 Quantitative estimation of groundwater Assessment of extractable groundwater quantity is the main objective of groundwater investigation. From the areal and depth information, quantification of groundwater is possible knowing the specific yield of the formation. Specific yield of the aquifer is the volume of water per unit volume of aquifer that can be extracted by pumping (or gravity drainage). Specific yield and porosity are related as follows: Porosity = specific yield + specific retention

Specific yield (Sy) is clearly an important factor in water availability, and is the factor that is used to convert saturated thickness (Ts) to the actual volume of groundwater available. Extractable water can be calculated as follows: V = A× Ts × Sy (2.4) Where, V = total volume of extractable water (m3) A = saturated area of the formation (arial extent) (m2) Ts = saturated thickness of the formation/aquifer (m) Sy = Specific yield of the formation (m3/m3)

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For a stratified formation, or total yield from a well field, the total amount can be computed as:

V=

∑

n i =1

( Ai × TSi × S yi )

( 2.5)

Where, i is the number of strata or aquifer. Specific yield is generally expressed as the percentage of the total volume (volume of saturated formation) (%), or volume per unit volume (m3/m3). For alluvial deposits (medium to coarse sand, sandstone, sand and gravel), the specific yield varies from 20 to 35%. Specific yield for a particular formation material can be estimated by saturating a specific volume of formation materials, and then collecting the gravity drainage from the materials. At any given location, the porosity of the formation remains essentially constant, but the volume of water in storage, the average local porosity, and the specific yield all vary with changes in saturated thickness (water table elevation). Some of this variation can be explained (and quantitatively predicted) on the basis of straight forward physical principles, but some of it is due to local variations in the aquifer structure. This hydrogeologic variability is difficult to predict or measure with detailed accuracy.

3. GROUND WATER QUALITY ASPECTS

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3.1 Significance of quality study The quality of water of the explored aquifer should be analyzed /tested for the suitability of domestic, agriculture and industrial purposes. The quality of water for various uses is determined by its physical characteristics, chemical composition, biological parameters and the conditions of use. Variations in natural and human activities reflect spatial variations in the hydro-chemical parameters of the groundwater. The difference of dissolved ions concentration in groundwater are generally governed by lithology (type of rocks), age of groundwater, velocity and quantity of groundwater flow, nature of geochemical reactions, solubility of salts and human activities. Now-a-days, the groundwater quality has been regarded as dynamic system. Previously the aquifer which was regarded as safe, may not safe now. Increased health concerns, introduction of new pollutants in groundwater, and increased emphasis on governmental policies in the environmental protection of natural resources have led to many rigorous investigations of the pollutant levels in soil and groundwater.

3.2 Sampling of groundwater For preliminary investigation purpose, groundwater should be collected from the target depth. To perform this, PVC pipe (~50 mm diameter) may be installed to the target depth with a reasonable screened section (approx. 1.5 m). For metals analyses, the sample should be filtered before storage.

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For regular monitoring of groundwater from selected wells and observation wells, sampling scheduling should be done taking into account the yearly variations of rainfall/recharge and withdrawal pattern. It should cover corresponding to maximum and minimum depth to water-table, to observe the seasonal variations of quality parameters. At first, the pump should be run about 10 to 15 minutes to avoid filtering effect, and then the sample should be collected in non-contaminated/purified container or bottle. If the sample is to be analyzed at later time, it should be preserved in refrigerator.

3.3 Elements to be analyzed Groundwater laboratory analysis should be performed for pH, EC, major anions, major cations and metals (As, Cd, Pb, Ni, Cu, Cr, Zn). Groundwater legislation (and other regulatory instruments, if any) that are relevant to the Project Site should be considered in water quality analysis. The analytical results should be compared and interpreted with reference to local/state groundwater quality standard/guidelines applicable for drinking water and agricultural use.

3.4 Laboratory analysis and ionic balances It is not intended to describe here the detail analytical methods. Readers are referred to relevant analytical text books, such as “Water and Waste-water Analysis”, by APHA (American Public Health Association). A general guideline of the analytical method for different quality parameters (including cations and anions) are cited in Table 3.1.

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Table 3.1. Water quality parameters and their analytical methods

Parameter

Method

pH

pH meter /glass electrode (portable or lab-top type)

EC (electrical conductivity) TDS (Total dissolved solids) Anions, Cations, Heavy metals

Conductivity meter (portable or lab-top type), Salinity bridge Glass electrode, Conductivity meter Flame photometer, Spectro-photometer, Gas chromatography, Titration

Calculation of ionic balances and alkalinity Ionic balances should be calculated for each of the samples to be collected. Detail checking procedure for ionic balances can be found in Ali (2010). Samples with no alkalinity measurement may show unsurprisingly a deficit of negative ions (anions). Where alkalinity is measured, the ionic balances should be within ±10% (which indicates the major ion data are

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of good quality). Where alkalinity is not measured, concentrations may be calculated from the deficit of anions.

3.5 Issues on the factors affecting quality Effect of air flush on water quality during drilling / construction The samples collected during drilling /construction of the boreholes are brought to the surface using airlift flushing. This technique is likely to mix air in with the water and in so doing can increase dissolved oxygen concentrations and reduce dissolved carbon dioxide concentrations. An increase in dissolved oxygen can lead to the oxidation of dissolved trace metals in a reduced form, especially iron. A reduction in dissolved carbon dioxide will increase the pH of the water, which if previously saturated with respect to the common carbonate mineral calcite could reduce both calcium and alkalinity (dissolved carbonate) as calcite precipitates out of the water.

Issues on validity of samples as measures of water quality changes with depth It is important to note that as water could enter the borehole over the whole uncased section(s), water samples collected at increasing depths (except the first sample) reflect the average quality of water over that uncased depth range. This average quality reflects the main inflows over that uncased section to that depth i.e. the data are unlikely to reflect the water quality at that specific depth.

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3.6 Isotopic and Age Indicator Analyses Background Modern groundwater investigations rely on combining the results of physical observations (rest or static water levels, drawdown during pumping, etc) with chemical measurements. While inorganic chemistry is still one of the most useful components of the latter, in complex investigations any additional evidence may be useful. The two techniques considered in this section – stable isotopes and trace gases – can be bracketed together as examples of environmental tracers – that is, characteristics that are automatically imparted to groundwaters, either naturally (stable isotopes) or anthropogenically (trace gases). Stable isotopes are basically used as indicators of groundwater provenance, while trace gases are mainly used as residence time indicators, but both can also be used to shed more light on processes like groundwater mixing.

Sampling Samples during investigation process for stable isotope analysis are generally obtained as drilling proceeds (e.g. from the air flush water). Several replicates should be taken. The samples should be taken at depths where water strikes are recorded to have occurred or where a significant change in air flush yield is observed. The borehole depths at which the samples

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are obtained should be recorded. All samples are to be stored in glass bottles. During the test pumping of the boreholes, the samples should also be taken.

Analytical methods All measurements should be conducted in designated laboratory. Stable isotopes are analyzed by mass spectrometry following standard preparation methods, i.e. CO2 equilibration for δ18O and reduction with zinc shot for δ2H.

Data interpretation Stable isotope data are conventionally expressed in ‰ (permil) with respect to Vienna Standard Mean Ocean Water (VSMOW) on the delta scale: δ = [(Rsample/Rstandard)-1] x 103 where Rsample is the 18O/16O or 2H/1H ratio of the samples, and Rstandard the corresponding ratio in VSMOW. In temperate climates, the stable isotope values of rainfall and resulting groundwater normally plot on or near the World Meteoric Line (WML) of Craig (1961). The gradient of this line, defined using the equation δ2H = 8 δ18O + 10, is actually an approximation of the average of observations from many rainfall stations, but serves as a convenient baseline to judge whether or not waters have been significantly affected by processes such as evaporation or saline intrusion.

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3.7 Discussion on quality issues The groundwater quality may be influenced by many factors: seasonal variation (recharge and discharge), subsurface mineral content, soil permeability, waste disposal site, agricultural chemical use, etc. The quality of groundwater in many regions of a country, particularly shallow ground water, is changing as a result of human activities. Groundwater is less susceptible to bacterial pollution than surface water because the soil and rocks through which ground water flows screen out most of the bacteria. Bacteria, however, occasionally find their way into groundwater, sometimes in dangerously high concentrations. But freedom from bacterial pollution alone does not mean that the water is fit to drink. Many unseen dissolved mineral and organic constituents are present in groundwater in various concentrations. Most are harmless or even beneficial; though occurring infrequently, others are harmful, and a few may be highly toxic. Water is a solvent and dissolves minerals from the rocks with which it comes in contact. Groundwater may contain dissolved minerals and gases that give it the tangy taste enjoyed by many people. Without these minerals and gases, the water would taste flat. The most common dissolved mineral substances are sodium, calcium, magnesium, potassium, chloride, bicarbonate, and sulfate. In water chemistry, these substances are called common constituents. Water typically is not considered desirable for drinking if the quantity of dissolved minerals exceeds 1,000 mg/L (milligrams per liter). Water with a few thousand mg/L of dissolved minerals is classed as slightly saline, but it is sometimes used in areas where less-

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mineralized water is not available. Water from some wells and springs contains very large concentrations of dissolved minerals and cannot be tolerated by humans and other animals or plants. Many regions may underlain at depth by highly saline ground water that has only very limited uses. Dissolved mineral constituents can be hazardous to animals or plants in large concentrations; for example, too much sodium in the water may be harmful to people who have heart trouble. Boron is a mineral that is good for plants in small amounts, but is toxic to some plants in only slightly larger concentrations. Water that contains a lot of calcium and magnesium is said to be hard. The hardness of water is expressed in terms of the amount of calcium carbonate - the principal constituent of limestone - or equivalent minerals that would be formed if the water were evaporated. Water is considered soft if it contains 0 to 60 mg/L of hardness, moderately hard from 61 to 120 mg/L, hard between 121 and 180 mg/L, and very hard if more than 180 mg/L. Very hard water is not desirable for many domestic uses; it will leave a scaly deposit on the inside of pipes, boilers, and tanks. Hard water can be softened at a fairly reasonable cost, but it is not always desirable to remove all the minerals that make water hard. Extremely soft water is likely to corrode metals, although it is preferred for laundering, dishwashing, and bathing. Ground water, especially if the water is acidic, in many places contains excessive amounts of iron. Iron causes reddish stains on plumbing fixtures and clothing. Like hardness, excessive iron content can be reduced by treatment. A test of the acidity of water is pH, which is a measure of the hydrogen-ion concentration. The pH scale ranges from 0 to 14. A pH of 7 indicates neutral water; greater than 7, the water is basic; less than 7, it is acidic. A one unit change in pH represents a 10-fold difference in hydrogen-ion concentration. For example, water with a pH of 4 has 10 times more hydrogen-ions than water with a pH of 5. Water that is basic can form scale; acidic water can corrode.

3.8 Guidelines on water quality for different uses In recent years, the growth of industry, technology, population, and water use has increased the stress upon both our land and water resources. Locally, the quality of groundwater has been degraded. Municipal and industrial wastes and chemical fertilizers, herbicides, and pesticides (that not properly managed/used) have entered the soil, infiltrated some aquifers, and degraded the groundwater quality. All these factors have made groundwater at risk. The water quality guidelines for agricultural use is suggested by FAO (Ayers and Westcot, 1985). It is based on salinity, infiltration influence by salinity, and specific ion toxicity effect on the degree of restriction on use. Based on this guideline, different countries/provinces have set their own guideline/criteria. A water quality class suggested by USDA [Richards (1954)] is given in Fig.3.1. In quality class, C1, C2, C3, C4 means low, medium, high, and very high sodium water, respectively. Similarly, S1, S2, S3, S4 means low, medium, high, and very high salinity water, respectively.

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Fig.3.1. Diagram for classification of irrigation water (after USDA, 1954).

A water quality guideline for drinking purpose has been suggested by World Health Organization (WHO). The suggested upper limits for Arsenic, Aluminium, Boron, Cadmium, Chloride, Chromium, Copper, Cyanide, Fluoride, Lead, Manganese, Mercury, Molybdenum, Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

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Nickel, Nitrate and nitrite (total nitrogen), Selenium, Sodium, Sulfate, Uranium, and Zinc are 0.01, 0.2, 0.3, 0.003, 250, 0.05, 2.0, 0.07, 1.5, 0.01, 0.5, 0.001, 0.07, 0.02, 50, 0.01, 200, 500, 1.4, and 3 mg/l, respectively (WHO, 1993).

4. GROUNDWATER DEVELOPMENT AND WELL DESIGN 4.1 Assessing GW availability 4.1.1 Water Budget approach Basics of water budget

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A water budget quantifies the major components of the hydrologic cycle in an attempt to assess the volume of water available for consumptive use. Large groundwater systems, usually achieve equilibrium between water input, changes in water storage, and water outflow when viewed over a period of decades or centuries. A large withdrawal in one year typically has no measurable impact on the resource (e.g. no change in storage) so long as it is balanced by an increase in input or decrease in output the following year; however, the timing and source of water consumptively used is an important consideration. Water levels in wells tapping a shallow water-table aquifer may decline during a single year of reduced precipitation, whereas water levels in wells tapping a deeper confined aquifer may not decline even after several years or even decades of reduced precipitation. The water available for sustainable use must be balanced against the volume of water input to the system. Therefore, the water available for sustainable use is independent of the recharge volume, but is dependent on the response of the aquifer system to the volume of water withdrawn.

Expression of water budget The components of the water budget (input, output and changes in storage) can be expressed mathematically. If the system is in equilibrium, the water budget can be expressed in its simplest form by the mass balance equation: (4.1) O = I ± ΔS where O = water output or discharge; I = the water input or precipitation; and S = water storage, ΔS = change in storage

I—Input Rainfall makes up 100% of the water input in some aquifer system, where no major river systems traverse or otherwise deliver water to the catchment. Input may be formed from canal or river system, where available. Groundwater recharge from the adjacent aquifers can be

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considered negligible, where the groundwater systems beneath the area are elevated above the surrounding systems; otherwise may be significant. Estimation of potential recharge In order to know the potential recharge in a region, inter-relationship between rainfall, run-off and infiltration, percolation, ET, and groundwater level response to rainfall should be studied. Potential recharge is not only dependent on surface water balance component and recharge opportunity, but also dependent on the withdrawal from the aquifer. Potential recharge can be mathematically expressed as: (4.2) Rp = ƒ(Ss, Sb, P, R, ET, D, …) Where, Rp = potential recharge ƒ = function Ss = soil surface condition Sb = subsurface soil condition P = rainfall characteristics (intensity, duration) R = surface runoff ET =evapotranspiration D = discharge or withdrawal from the aquifer Investigations should be carried out at micro level and basic data like infiltration through rainfall, seepage from applied water for crops, from tanks, from canals etc. These parameters will help in the assessment of groundwater potential, and the block-wise groundwater assessment can be made at macro level for the entire catchment.

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O—Output The output may be comprised of direct surface runoff or stormflow, groundwater discharge, evapotranspiration, and groundwater consumption. Surface Runoff Surface runoff is the volume of water that runs directly off the land surface into streams without infiltrating into the groundwater system. The surface runoff leaving a catchment can be estimated by subtracting stream baseflow from the mean annual streamflow. Groundwater Discharge Groundwater discharge can be assumed to be equal to the groundwater recharge (if there is no puming), which is assumed to be equal to the stream baseflow. Evapotranspiration Evapotranspiration (ET) is the combined effect of evaporation from wet surfaces and transpiration from plants. The ET can be estimated using various available methods and tools.

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S - Storage Changes in aquifer storage are reflected in water-table elevation changes for unconfined aquifers and the piezometric surface elevation for confined aquifers. Changes in aquifer storage are also reflected in changes in spring production and stream flow. Changes in spring production and stream flow are very difficult to measure. Changes in water-table elevation, on the other hand, can be determined if there are sufficient data available. Water level measurements can be made on wells on the catchment. Therefore, while changes in groundwater storage cannot be estimated in absolute terms, it is possible to determine if there are any declines that would indicate a loss of storage, or increases that would indicate an increase in storage, by examining changes in water-table elevation. Statistical significance test of water-table elevation change (for long-term trend) can be performed. Estimation of absolute change (amount) Change in absolute volume in an aquifer system can be estimated as: ∆Sv = ∆Sh × Sy × A Where,

(4.3)

∆Sv = change in water volume (m3) ∆Sh = change in water level in observation well (m) Sy = specific yield of the aquifer (%) A = area of the aquifer (m2)

4.2 Groundwater yield

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4.2.1 General perspectives Depending on the permeability of the rocks containing the groundwater, and the pressure under which groundwater is held, the ease of groundwater extraction can vary significantly. Both water quality and aquifer yield determine whether groundwater is appropriate for human consumption, stock water supplies, irrigation, or mining uses. The salinity and yield characteristics of groundwater resources vary considerably across the continent. Groundwater is particularly important as a water resource in semi-arid to arid parts of the world, and also in humid region, where rainfall is too infrequent or inadequate, or unevenly distributed throughout the year, to reliably meet water needs. Often such groundwater resources have accumulated over long periods and are replenished only when rainfall is sufficient to infiltrate soil and rock. This means groundwater can be a finite, or slowly replenished resource. In more temperate areas where rainfall rates are higher, groundwater may be replenished on a regular basis and extraction can be managed on a renewable basis. However, in many instances groundwater use exceeds the rate at which groundwater is replenished. How aquifers respond when water is withdrawn from a well is an important topic in groundwater hydrology. It explains how a well gets its water, how it can deplete adjacent wells, or how it can induce contamination.

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When water is withdrawn from a well, its water level drops. When the water level falls below the water level of the surrounding aquifer, ground water flows into the well. The movement of water from an aquifer into a well alters the surface of the aquifer around the well. It forms what is called a cone of depression. A cone of depression is a funnel-shaped drop in the aquifer's surface (Fig.4.1). The well itself penetrates the bottom of the cone. Within a cone of depression, all groundwater flows to the well. The outer limits of the cone is termed as the well's area of influence.

Fig.4.1. Schematic of cone of depression during pumping.

4.2.2 Relevant terminologies Drawdown: The drawdown in a well is the difference between the pumping water level and the static (non-pumping) water level. Drawdown begins when the pump is turned on, and increases until the well reaches "steady state" sometime later. Therefore, drawdown measurements are usually reported along with the amount of time that has elapsed since pumping began. For example, "The drawdown was 2 m, half-hour after pumping began." Drawdown cone: The depression in the water table near the well that is caused by pumping is called the "drawdown cone" or sometimes the "cone of depression". When

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the well is pumping, water levels are drawn down most near the well and the amount of drawdown decreases as the distance from the well increases. At some distance from the well at any given time there is a point at which the pumping does not change the water table and the drawdown is zero. Measuring point: Water levels in wells are usually reported as depths below land surface, although the measuring point can be any convenient fixed place near the top of the well. In this drawing the measuring point is the top of the casing. The altitude of the measuring point is commonly recorded so that static water levels can also be reported as altitudes. Pumping water level: The pumping water level is the distance from the land surface (or measuring point) to the water in the well while it is pumping. The time that the pumping water level is measured is usually recorded also. For example, "The pumping water level was 28 meter below land surface, 1 hour after pumping began." Static water level: The static water level is the distance from the land surface (or the measuring point) to the water in the well under non-pumping (static) conditions. Static water levels can be influenced by climatic conditions (by evapotranspiration) and pumping of nearby wells and are often measured repeatedly to gain information about how aquifers react to climatic change and development. Water table: The top of the saturated part of an unconfined (also known as water-table) aquifer. Below the water-table, pore spaces (or fractures) in the geologic media are filled with water. Above the water-table, the pore spaces are filled with air.

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Specific Capacity The yield of the well per unit of drawdown, usually expressed as gallons per minute (gpm) per foot of drawdown, is called specific capacity. It is obtained by dividing the pumping rate by the drawdown for a specific pumping period. For example, if the pumping rate is 1500 gpm and the drawdown is 20 feet, the specific capacity of the well is 75 gpm per foot of drawdown. Well Capacity or Yield The volume of water per unit of time discharged from a well is its capacity. Well capacity is usually measured as the pumping rate in gallons per minute (gpm) or cubic feet per second (cfs). Well Efficiency The ratio of the actual specific capacity of a well at the design yield to the maximum specific capacity possible calculated from formation hydraulic characteristics and well geometry is the well efficiency. This is the same as the ratio of the theoretical drawdown to obtain design yield from a 100% efficient well to the actual drawdown measured in the well when producing at the design yield. Efficiency is usually expressed as a percent. The difference (drawdown increase) between the theoretical drawdown and actual drawdown

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represents the head loss required to force water through the well screen. This head loss should be a minimum. Well efficiency should not be confused with pump efficiency. Pump efficiency is a characteristic of the pump only and is completely independent of well efficiency. For example, the pump efficiency may be 75% while the well efficiency of a poorly designed and constructed well may be only 45%. Test Hole Assessment – Drilling a test hole provides an opportunity to collect and assess certain design-critical information, such as formation samples for sieve analysis (screen and filter pack design) and lithologic and geophysical data for screen and seal placement. Well Development Assessment – Properly developing a new water well is one of the most important steps in bringing it online. Development is both a scientific and intuitive process of increasing the specific capacity of the well, while reducing the residual plugging from drilling fluids and sediment in the filter pack. Zone Testing for Water Quality – In certain locations, mostly because of water quality concerns (e.g. arsenic, uranium), depth-specific water samples should be collected from an open borehole, through a procedure known as “zone testing”. Zone testing involves constructing a temporary well inside the open borehole, and then collecting a water sample for analysis. This data is useful for selecting or avoiding zones with low or high, concentrations of constituents of concern, respectively.

4.2.3

Well yield in aquifer

4.2.3.1 Flow of water to well in unconfined Aquifer

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Well discharge equations for equilibrium conditions in unconfined aquifer have been derived by several investigators over the years. These equations relating well discharge to drawdown ignored vertical component of flow.

Fig.4.2. Schematic of WT during puming in unconfined aquifer.

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Theim equation Let us consider flow of water to well in unconfined aquifer as shown in Fig.4.2. According to Darcy’s law: Q = KiA Considering elementary horizontal contributing extent of ‘x’ and vertical extent of ‘y’, the area contributing to flow is ‘xy’. Thus, . 2

. .

Or,

2

.

. .

Integrating over the area of screen diameter to ‘area of influence’ along the x-axis, and from the top of well screen to the free watertable, we obtain:

2

.

Which reduces to: 2.3

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Considering the horizontal extent between well screen or face of the well (where drawdown is maximum) and at the upper most influential area (radius of influence), vertical extent from top of the well screen (hw) to saturated thickness of the aquifer (H) we can write:

.

(4.4)

Where, Q = well discharge (m3/d) K = hydraulic conductivity of the aquifer (m3/m2/d) H = saturated thickness of the aquifer [i.e. height of water-table from the bottom of the screen at steady-state (non-pumping) condition] (m) hw = height of water-table at the well-face from the bottom of the screen at pumping condition (m) R = radius of influence due to pumping (m) rw = radius of the screen pipe (m) This is the well-known Theim equation (Theim, 1906; originally proposed by Dupuit (1863)) for well discharge from unconfined aquifer.

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4.2.3.2 Flow of water to well in confined Aquifer

Fig.4.3. Schematic of cone of depression and radius of influence in confined aquifer.

Theis equation

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Theis (1935) derived equation for discharge from confined aquifer under customary assumptions. Assumptions of Theis equation are as follows: •

Aquifer is confined top and bottom

•

There is no source of recharge to aquifer

•

The Aquifer is compressible and water is released instantaneously from the aquifer as the head is lowered

•

The well is pumping at a constant rate.

The well discharge in a confined aquifer (Fig.4.3) is expressed as: .

(4.5)

Where, Q = well discharge (m3/d) T = transmissivity of the aquifer (T = Kb) (m3/m/d) h = height of peizometric watertable from the bottom of the screen at steady-state (nonpumping) condition (m)

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hw= height of watertable at the well from the bottom of the screen during stabilized drawdown (m) R = radius of influence due to pumping (m) rw = radius of the screen pipe (m)

Derivation of the equation Using Darcy’s law: . Or,

.

2

. 2

.

.

Integrating over the area of screen diameter to ‘area of influence’ along the x-axis, and from the top of well screen to the piezometric water-table, we obtain: 2 Which reduces to: .

(4.6)

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4.3 Construction and design of water supply wells Wells are used to extract water from aquifers. Basically, a well is a hole drilled into an aquifer. A well consists of a bottom sump, well screen, and well casing (pipe) surrounded by a gravel pack and appropriate surface and borehole seals (Fig.4.4). Water enters the well through perforations or openings in the well screen. A pipe and a pump are used to pull water out of the ground, and a screen filters out unwanted particles that could clog the pipe. Well design and construction details are determined after a test hole has been completed and the geological zones have been logged.

4.3.1 Importance of proper design and construction of well Well design and construction choices affect how efficiently the water in the aquifer enters into the well. The less efficiently water enters into the well, the greater the pumping lift and yearly energy bill, regardless of the pumping plant design and level of pumping plant efficiency. Efficient wells result in less total pumping lift and higher specific well capacity (gpm/ft drawdown). This translates to reduced horsepower needed to lift the water and to decreased hours of pump operation to irrigate a given acreage of crops. The actual cost of a well depends on the depth to groundwater, the desired well capacity, and choices among a variety of well drilling, well design, well construction, and well development considerations. Choosing the most appropriate approach when investing in a well is site specific and largely dependent upon how extensively the well will be used.

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Sometimes a simple, less expensive well will suffice and other times added investment in drilling, design, construction, and development will pay back substantially.

4.3.2 Types of Well Wells come in different shapes and sizes, depending on the type of material the well is drilled into and how much water is being pumped out. There are two main types of wells, each distinguished by the diameter of the bore hole. The two types are bored wells and drilled wells. Bored or shallow wells are usually bored into an unconfined water source, generally found at depths of 30 meter or less. Drilled wells may be of two categories, based on the underlying formation: Consolidated or rock wells: drilled into a formation consisting entirely of a natural rock formation that contains no soil and does not collapse. Their average depth is about 80 m. Unconsolidated or sand wells: drilled into a formation consisting of soil, sand, gravel or clay material that collapses upon itself.

Bored wells

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A bored well is constructed when low yielding groundwater sources are found relatively close to the surface, usually under 30 m. Bored wells are constructed using a rotary bucket auger. They are usually completed by perforating the casing or using a sand screen with continuous slot openings (Fig.4.4).

Fig.4.4. Schematic of a bored well.

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One advantage of bored wells is the large diameter of the casing, from 45-90 cm (18-36 in.). It provides a water storage reservoir for use during peak demand periods. A disadvantage of utilizing a shallow groundwater aquifer is that it relies on annual precipitation for recharge. Water shortages may occur following long dry periods in summer and extended freeze up during winter months.

Drilled wells Drilled wells are smaller in diameter, usually ranging from 15-30 cm, and completed to much greater depths than bored wells, up to several hundred metres. The producing aquifer is generally less susceptible to pollution from surface sources because of the depth. Also, the water supply tends to be more reliable since it is less affected by seasonal weather patterns.

4.3.3 Well Construction Proper design, construction, development, and completion of the well will result in a long life for the well (as long as half a century or more) and efficient well operation. For many large production wells, a test hole is drilled before well drilling to obtain more detailed information about the depth of water-producing zones, confining beds, well production capabilities, water levels, and groundwater quality.

4.3.3.1 Principal activities in well construction

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Well construction involves appropriate site selection, drilling, aquifer identification and yield-test, screen and envelop (gravel pack) design, case and screen setting, sealing ( to prevent water from leaking between uncontaminated and contaminated aquifers or from the land surface into the well), well development, installation of pump and power source, and sanitary seal of the well head. Implementation of an aquifer test is normally done for production (large capacity) well. Site selection In constructing a new well, we have to think carefully about the best location, that is, a high point of land with good access and separation from potential contaminants. Wells must be located a safe distance from potential sources of contamination such as fuel storage tanks, stockpiles of chemicals like pesticides or road salt, septic systems, gardens, manure piles, livestock, and roads and driveways. Drilling The drilling process itself may last from a few hours (for a shallow, small-diameter well) to several weeks (for a deep, large-diameter well). Sometimes, particularly for large production wells and where water quality is particularly important, the driller will drill a small-diameter pilot hole before drilling the well bore. From information obtained from the pilot hole, a driller or consultant can determine aquifer formations and groundwater quality at various depths and then optimize the final well design for the specific hydrogeological conditions at the site. Appropriate materials (screen, casing, gravel) can then be ordered in a timely fashion prior to the final drilling.

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4.3.3.2 Drilling methods The most common drilling techniques are auger drilling, rotary, reverse rotary, air rotary, and cable tool. So, there are two primary methods of drilling: •

Rotary

•

Cable tool.

In unconsolidated and semi-consolidated materials, (reverse) rotary and cable tool methods are most commonly employed. Hardrock wells generally are drilled with air rotary drilling equipment. Auger drilling is often employed for shallow wells that are not used as supply well. Rotary drilled wells are constructed using a drill bit on the end of a rotating drill-stem. Drilling fluid or air is circulated down through the drillstem in the hole and back to the surface to remove cuttings. Rotary drilling rigs operate quickly and can reach depths of over 300 m, with casing diameters of 10 - 45 cm.

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Cable tool drilled wells are constructed by lifting and dropping a heavy drill bit in the bore hole. The resulting loose material, mixed with water, is removed using a bailer or sand pump. This method, also called percussion drilling, reaches depths up to 300 m. Well diameters can range from 10 to 45 cm. The drilling rate is typically much slower than for a rotary rig, but when aquifers are low yielding, they may be more easily identified using this method. During drilling, drillers must keep a detailed log of the drill cuttings obtained from the advancing borehole. In addition, after the drilling has been completed but before the well is installed, it is often desirable to obtain more detailed data on the subsurface geology by taking geophysical measurements in the borehole.

4.3.3.3 Definition of relevant terminologies Casing: Steel or plastic pipe placed in the borehole to keep it from collapsing. The casing is sealed to the borehole wall near the land surface with the annular seal. Screen or perforations: All wells are open to the aquifer so that water can enter the well. Well completions vary from "open hole" in consolidated rock that does not need a casing, to "open bottom" where the only way for the water to enter the well is through the end of the casing. However, many wells have some sort of well screen installed or perforations cut into the casing through which water can enter. The openings must be correctly sized so that water will enter, but sand and other aquifer materials do not. Total depth: The total depth of the well is the distance from land surface to the bottom. Tailpipe and end cap: Wells that are completed with well screens may have a tailpipe installed below the screen. The tailpipe provides a place where sand that may enter the well through the screen can settle away from the pump. The end cap forces all water to

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enter the well through the well screen. Most wells that are completed with perforations may not have a tailpipe. 4.3.4 Well design Designing a water well involves selecting the proper dimensional factors and the proper materials to insure the optimum combination of performance, long service life, and reasonable cost. The overall objective of the design is to create a structurally stable, longlasting, efficient well that has enough space to house pumps or other extraction devices, allows groundwater to move effortlessly and sediment-free from the aquifer into the well at the desired volume and quality, and prevents bacterial growth and material decay in the well.

4.3.4.1 Design elements and design considerations

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There are many components to well design which must be taken into account. Decisions should be made about: •

Well depth

•

Type of well

•

Casing material, size and wall thickness

•

Intake (screen) design

•

Filter material design

•

Formation seal

•

Monitoring and preventive maintenance provisions.

Well depth During the test hole drilling, the drilling contractor will complete a formation log. Soil and rock samples are taken at various depths and the type of geologic material is recorded. This allows to identify aquifers with the best potential for water supply. Sometimes it is also run an electric or gamma-ray log in the test hole to further define the geology. This gives more accurate information about aquifer location. Generally a well is completed to the bottom of the aquifer. This allows more of the aquifer to be utilized and ensures the highest possible production from the well. There are two reasons for this. First, more of the aquifer thickness can be used as the intake portion of the well resulting in higher specific capacity. Second, more drawdown can be made available, permitting a greater yield. One departure from casing to the bottom of the aquifer is when the bottom of the aquifer contains fine sand, or is known to contain poor quality water. In this case the well should be completed above the fine materials, or to a depth which will avoid poor quality water.

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Casing size and material type

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Choosing the right diameter for the well casing and screen is important because it has an effect on both the cost of the well and its efficiency. Decisions about the diameter and type of well casing are made after considering the following: •

Aquifer characteristics

•

Hydraulic factors that influence well performance

•

Drilling method

•

Well depth

•

Cost (in discussion with the well owner)

•

Pump diameter (The casing must be large enough to house the pump and allow sufficient clearance for installation and efficient operation).

For deep wells and wells larger than 4 inches, the diameter is usually chosen to accommodate the size of pump required. The diameter should be 2 nominal sizes larger than the pump to allow sufficient clearance for ease of installation and operation. If the screened interval is to be at much lower depths than the pump, the casing below the pump may be of a smaller diameter. For wells smaller than 4 inches it is satisfactory to select casing which is only 1 size larger than the pump. In shallow wells where the pump is directly connected to the top of the well casing or connected to a suction pipe inside the well, the casing diameter should be selected in relation to the diameter of the suction inlet of the pump. If a submersible pump is going to be used, the casing must have an inside diameter of at least 10.16 cm (4 in.), by law. It is recommended that the casing be at least one nominal size larger than the outside diameter of the pump. The more space there is between the pump and the casing, the easier it will be to service and repair the pump in the future. There are two common materials used for casing: steel and plastic (PVC). Steel casing is the strongest but is susceptible to corrosion. Plastic casing is becoming more popular because of its resistance to corrosion. For PVC, maximum depths are usually less than 200 feet and, for strength, the diameters are not larger than 6 inches. All casing must be new and uncontaminated. Plastic casing must be made of virgin resin, not recycled material.

Well screen The greatest influence on the efficient performance of a well is the design and construction of the well screen. The well screen serves as the intake section of the well allowing water and is considered adequate only when it allows sand-free water to flow into the well with a minimum loss of head. A properly designed well screen combines the highest percentage of open area with adequate strength. Water moves from the aquifer into the well through either a manufactured screen or mechanically slotted or perforated casing. Screens are manufactured with regularly shaped and sized openings. They are engineered to allow the maximum amount of water in with minimal entry of formation sediments. Stainless steel screens are the most widely used because they are strong and relatively able to

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withstand corrosive water. Screens are manufactured with various slot sizes and shapes to match the characteristics of the aquifer. Slotted or perforated casing or liner is made by creating openings using a cutting tool or drill. Pre-slotted plastic pipe is also available. Slot openings and perforations are spaced further apart than screen openings. This reduces the amount of open area to allow water into the well. The openings tend to vary in size and may have rough edges depending on how they were made. This impedes the flow of water into the well and may not hold back the formation sediments. After examining the cuttings from the borehole, a judgement should be made whether to use a screen, or slotted or perforated casing/liner. While a screen is the more expensive alternative, it is necessary if the aquifer is composed of loose material such as fine sand, gravel or soft sandstone. A slotted or perforated casing/liner can be used when the aquifer formation is more consolidated, such as hard sandstone or fractured shale. After a choice is made between a screen, or slotted or perforated casing/liner other decisions will be made regarding: •

Size of slot opening

•

Total area of screen or perforation that is exposed to the aquifer

•

Placement of the screen or perforations within the aquifer.

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Slot size openings The slot openings must be small enough to permit easy entry of water into the well while keeping out sediment. The slot size chosen will depend on the particle size of the earth materials in the producing aquifer (also termed as formation materials). Typically, select a slot size that allows 60 percent of the aquifer material to pass through during the well development phase of drilling. The remaining 40 percent, comprising the coarsest materials, will form a natural filter pack around the perforations or screen. Screen length, pattern, total open area, and placement A well screen is an engineered device that is used in wells to help maximize inflow from the aquiferand allow for long-term satisfactory operation of the well. Well screens are typically installed in wells where the aquifer is comprised of loose or unstable material. The screen prevents rock fragments from entering the well, helps support the wall of the well and allows water to enter slowly. Turbulent flow can more easily transport unwanted rock particles and agitated water may release minerals and clog up the well. The purpose of the screen is to keep sand and gravel from the gravel pack out of the well while providing ample water flow to enter the casing. The screen should also be designed to allow the well to be properly developed. Slotted, louvered, and bridge-slotted screens and continuous wire wrap screens are the most common types. Slotted screens provide poor open area. They are not well suited for proper well development and maintenance, and are therefore not recommended. Wire wrap screens or pipe-based wire wrap screens give the best performance. The additional cost of wire wrap screens can be offset if only screen sections are installed in the most productive formations along the borehole.

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Irrigation wells must be capable of producing adequate water during peak seasonal use and under drought conditions. Without a reliable, efficient, and economical supply of water, the entire irrigation system, regardless of the most sophisticated well head equipment design, becomes nearly useless. Wells can be screened continuously along the bore or at specific depth intervals depending on the water bearing strata. The latter is necessary when a well taps multiple aquifer zones, to ensure that screened zones match the aquifer zones from which water will be drawn. In alluvial aquifers, which commonly contain alternating sequences of coarse material (sand and gravel) and fine material, the latter construction method is much more likely to provide clean, sediment-free water and is more energy efficient than the installation of a continuous screen. On the other hand, hardrock wells are constructed very differently. Often, the borehole of a hardrock well will stand open and will not need to be screened or cased unless the hard rock crumbles easily. The purposes of the blank well casing between and above the well screens are to prevent fine and very fine formation particles from entering the well, to provide an open pathway from the aquifer to the surface, to provide a proper housing for the pump, and to protect the pumped ground water from interaction with shallower ground water that may be of lower quality. In some cases it may be necessary to place additional casing to seal off parts of the drilled hole where, for example, the water may have high iron content, or some other unwanted chemical attribute. For naturally developed wells, the size(s) of well screen slot openings will depend on the gradation of the sand, and slot openings are selected using the results of sieve analyses of water-bearing formation samples. A sieve analysis curve should be plotted for each sand sample. The size of the screen opening is selected so that the screen will retain 40-50% of the sand. The total area of the slot openings is dependent on the length and diameter of the screen. While the length of the screen is variable, the diameter of the screen is determined by the diameter of the well casing. The yield from a well increases with an increase in screen diameter but not proportionately so. While high specific capacity is obtained by using as long a screen as possible, short screens provide more available drawdown. These two conflicting aims are satisfied, in part, by using an efficient well screen. The amount of open area of the screen or slotted or perforated casing/liner must be calculated to ensure the water from the aquifer does not enter the well too quickly. A larger amount of open area allows the water to enter the well at a slower rate, causing a lower drop in pressure in the water as it moves into the well. If the water flows too quickly, there will be problems with incrustation. Incrustation is a buildup that occurs when dissolved minerals in the groundwater come out of solution and deposit on the screen or casing. As a result, the perforations get plugged and water cannot enter the well at the same rate, and the yield from the well will be reduced. The pore spaces in the aquifer immediately adjacent to the perforations may also get plugged with fine material which could result in yield reduction. The screen or perforations on the casing/liner must be placed adjacent to the aquifer. If improperly placed, the well may produce fine sediment which will plug plumbing fixtures and cause excessive wear on the pump. If geophysical logging equipment is used to accurately identify the boundaries of the aquifer, the exact placement will be easier.

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Screen Material Depending on the results of preliminary investigation, the well screen should be fabricated of materials that are as corrosion resistant as necessary. If the screen corrodes, sand and/or gravel will enter the well, which may eventually require either replacement of screen or drilling a new well. Corrosion of screens can occur from bimetallic corrosion if two different metals have been used in the fabrication; therefore, bimetallic screen should always be avoided. Water with high total dissolved solids accelerates this type of corrosion because the water is a more effective electrolyte. Corrosion can also occur from dissolved gases in the water such as oxygen, carbon dioxide, and hydrogen sulfide. The choice of the well screen material is sometimes based on strength requirements regarding column load and collapse pressure. When a long screen supports a considerable weight of pipe, it functions as a slender column. The pressure of the formation and materials caving into the well pipe can squeeze the screen. Therefore, the well material should be able to withstand the pressure. It is impossible to accurately determine or calculate earth pressures with depth but generally greater strength is needed at greater depths.

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Filter material It is important to match the grain size of the filter material with the size of the slot openings of the screen to attain maximum yield from the well. Gravel packing makes the zone immediately surrounding the well screen more permeable by removing the formation materials and replacing them with artificially graded coarser materials. The size of this artificially graded gravel (filter material) should be chosen so that it retains essentially all of the formation particles. The well screen slot opening size is then selected to retain the gravel pack. Gravel pack design includes specification of gradation, thickness, and quality of the gravel pack material. Part of the aquifer thickness to be screened should be evaluated by examining the samples collected during the test hole drilling. A sieve analysis should be prepared for the strata comprising the portion of the aquifer where the screen will be set. Results of sieve analysis for the finest stratum should be used to design the gravel pack grading. It is best to design as uniform a pack as possible. A uniform gravel pack has significantly greater permeability and is easier to install without segregation. The gravel pack material should consist of clean and well-rounded grains that are smooth. These characteristics increase the permeability and porosity of the gravel pack. The gravel placement should be completed in one continuous operation.

Casing materials The casing (or well pipe) is a very critical element in well construction. Casing may be metallic (black iron or galvanized steel) or nonmetallic (polyvinyl chloride (PVC) or ABS plastic). It must be adequately seated in a consolidated formation (limestone, sandstone, etc.) or attached to a screen suitably designed and situated in unconsolidated materials (shell, sand, gravel, etc.). The purpose of casing is to seal off materials that may enter the pumping system from strata other than the aquifer selected and prevent mixing between aquifers. To prevent contamination from surface flow into the well, the casing must be extended above surface

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flood water levels, and the top portion must be grouted with cement or an approved alternative material.

4.3.4.2 Design criteria and procedure Water wells need to be designed to suit the geologic conditions, the purpose for needing the water and to comply with local regulations. The final design is subject to site-specific observations made in the test hole or during the well drilling. Diameter of slot/ screen opening For naturally developed well (no artificial gravel pack): Ds < D0.50p Where, Ds is the slot size, D0.50p is the diameter that retain 50% of the formation materials (sands). Artificial gravel pack: Typically the slot size of the screen (Ds) is selected so that greater than 85 percent of the artificial pack material remains outside of the screen. i.e. Ds < D0.85p Where, D0.85p = diameter that retain 85% pack/filter materials Screen open area Screen open area (A) should be calculated as:

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A = Q/V Where, Q is the well discharge, and V is the maximum flow velocity of water to screen (0.03 m/s). Then, the total screen area, AT = A/(Ea×Ps) Where, Ps is the percent open area in the screen, Ea is the effective open area considered for design (50%) [as some of the openings may be clogged after operation of some period]. Length of screen Length of screen is selected based on other two factors - screen diameter (d) and open area (A), as: L = AT/(πd) Available drawdown is also considered in selecting length. Drawdown during pumping ( specially in dry period) must be above the screen. Position of screen Artesian aquifer: Lower 70% – 80% of the water bearing strata.

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Watertable aquifer: Bottom 30% - 60% of the aquifer. Screen material Factors to be considered are corrosivity of water, strength requirement (length of pipe and hence load on it), and economy. For non-corrosive water: plastic (PVC), galvanized steel, stainless steel, For corrosive water: stainless steel Hydraulic criteria/velocity of water Vw = Q/AT Where, Vw is the velocity of water entering the screen, Q is the desired well yield/discharge, and AT is the effective total open area in the screen. Vw < 0.03 m/s Diameter of screen pipe, Vertical velocity The screen diameter should be such that the velocity of vertical water flow to the pump does not exceeds 1.5 meter per second. That is, Vv < 1.5 m/s Where, Vv is the vertical velocity of water within the screen pipe towards the pump. Gravel pack / Filter material

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Grading of filter material: Based on screen opening and aquifer materials. Df(85%) = 4 to 6 times of aquifer materials (Daqf) Uniformity coefficient (D40/D90): < 2.5 Thickness of filter: 0.08 to 0.2 m.

4.3.5 Well Completion A properly constructed well forms an effective barrier against surface run-off that may enter and contaminate the well (Fig.4.5). Water must infiltrate and pass downward through the soil and/or rock before it can reach the aquifer. Over the years, well design has improved to reflect advances in technology and our understanding of potential pathways of contamination.

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Well casing and sealing New wells should be lined with a watertight casing designed to prevent the walls of the well from collapsing. Well casings must be of sufficient length to keep contaminants out of the well water. Steel casings are typically used, but casings can also be made from plastic. The Well Drilling regulations in a region (or State), under the Water Resources Act, outline minimum construction requirements for drilled wells. The annular seal When a well is drilled the hole in the ground is bigger than the well casing. The resulting gap – the annular space – must be filled with a watertight sealant such as bentonite that does not shrink or crack under the ground. For maximum protection, the sealant should extend the full length of the casing. The annular seal serves as a barrier to run-off, surface water, and near-surface waters that could otherwise travel down the outside of the casing and contaminate the aquifer.

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Annulus seal Sealing the well protects the well’s producing zone from contamination. The diameter of the bore hole is usually slightly larger than the casing being installed. The space between the bore hole and the casing is called the annulus of the well. It must be sealed to prevent any surface contamination from migrating downward and contaminating the water supply. It also prevents any mixing of poor quality aquifers with the producing aquifer of the well (Fig.4.5). It is filled with gravel or coarse sand and fine sand particles. The uppermost section of the annulus is normally sealed with a bentonite clay and cement grout to ensure that no water or contamination can enter the annulus from the surface. To isolate the producing zone of the well, the annulus is filled from immediately above the perforated zone to the ground surface. Well cap The drilled well must be capped with a commercially manufactured vermin-proof well cap. Vermin-proof caps have rubber gaskets and screened vents inside to prevent entry of “foreign material” such as vermin, insects, and decaying plant material. Loose fitting caps found on older wells make these wells a comfortable home for insects and vermin. Filter material If the aquifer formation does not naturally have any relatively coarse particles to form a filter, it may be necessary to install an artificial filter pack. The pack is placed around the screen or perforations so the well can be developed. For example, this procedure is necessary when the aquifer is composed of fine sand and the individual grains are uniform in size. Once the well has been drilled and the equipment is in place, there are several procedures the drilling contractor must complete before the well is ready to use. The drilling contractor is responsible for: •

Well development

•

Disinfecting the well

•

Conducting a yield test.

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Fiig.4.5. Sketch of o well seal.

4.3.6

Welll developmen nt

After the well w screen, well casing, and gravel pack have beeen installed, the t well is deeveloped to cllean the borehhole and casinng of drilling fluid and to properly p settlee the gravel paack around th he well screenn. A properly developed d graavel pack keepps fine sedim ments out of thhe well and prrovides a cleann and unrestriccted flow pathh for ground water. w Proper well w design annd good well development d w result in lower will l pumpinng costs, a longger pump life,, and fewer biiological problems such as iron-bacteria and slim me build-up. Poorly dessigned and unnderdeveloped d wells are subbject to more frequent pumpp failures becaause sand and fines enter thhe well and cau use significanntly more wearr and tear on pump p turbines. Well devellopment is thee process of removing r finee sediment andd drilling fluiid from the arrea immediateely surroundinng the perforaations. This inncreases the well’s w ability to produce w water and maaximize produuction from the aquifer. Jetting, surgging, backwasshing, and ovverpumping (h higher than thhe design pum mping rate) arre methods ussed to developp a well. A tyypical method d for well development is too surge or jett water or air in- and out- of o the well sccreen opening gs. This proceddure may takee several dayss or perhaps loonger, dependding on the siize and depth of o the well. Water W or air is surged s back annd forth throuugh the perforaations. Any fine materials that t are in the formation become dislodgeed and are puumped or baileed from the w well. This procedure is continnued until no fine particles remain and thhe water is cleear. Coarser

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particles are left behind to form a natural filter pack around the screen, slot openings or perforations.

Testing for Sand. The sand content should be tested after development and performance (pump) testing. Sand production should be measured by a centrifugal sand sampler or other acceptable means. Following development (i.e., stabilization of the formation and/or gravel pack) and pump testing, the sand content should not exceed a concentration of 5 ppm (parts per million) by weight 15 minutes after the start of pumping. Sand production exceeding this limit indicates that the well may not be completely developed or may not have been properly designed. In that event, redevelopment may be appropriate or as an alternative, a sand separator installed. In existing wells should this value be exceeded significantly, rehabilitation (redevelopment) or repair is probably needed. Again, as an alternative, a sand separator may need to be installed. 4.3.7 Disinfection of well Some Provincial regulations require the drilling contractor to disinfect new wells with chlorine. The concentration is calculated on the volume of water that is in the well. The concentration must be at least 200 milligrams of chlorine per litre of water present throughout the water in the well and must be left in the well for at least 12 hours to ensure any bacteria present are destroyed. Chlorination is done after the pumping equipment is installed and before the well is put into production. The yield test provides a benchmark of the well's performance. Repeating this test at a later date can be used to assess any changing conditions of the well and determine when maintenance is required.

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4.3.8 Economic considerations

Some of the most important things that should be considered in well construction and design are: i.

Desired life expectancy of the well

ii. Appraisal value of the land iii. Power cost (power/fuel cost)

iv. Water quality In designing a well, considerations should be given concerning the use of top/bottom water. The water below the depth of the well has a much less value when it is not tapped by the original well; whereas, if that same water is tapped by the original well (although possibly not immediately being pumped), has much value in the future. The decision on how much of the available producing aquifer to incorporate into any given well design should be based on expected well life and that affect on land appraisal value. The shallow well can be looked at as a band-aid solution, the deeper wells would be a valuable investment in that particular property.

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4.4 Pumping test /well yield test and determination of aquifer parameters The main objective of aquifer test is to determine the ability of the aquifer to transmit and store water (which could be used to design capacity of the pump in new well) and to determine adverse effects on existing wells created by new withdrawals.

4.4.1 Relevant terminologies Residual drawdown After pumping is stopped, the water level rises and approaches the original static water level. During water-level recovery, the distance between the recovery water level (RWL) and the initial static water level (SWL) is called residual drawdown.

Residual Drawdown = RWL – SWL Specific capacity Specific capacity is the pumping rate divided by the drawdown (L/min/m or GPM/foot). It is a measure of the drawdown caused by the pumping rate and is used as a basis for determining the well’s performance. The specific capacity usually changes with both pumping rate and time. Specific Capacity of a well = Pumping Rate/Drawdown

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Well Efficiency Well efficiency is defined as the ratio of the theoretical drawdown in the formation to the actual drawdown in the well. The difference between the two is caused by frictional energy losses of the water as it moves from within the formation to the pump intake. Thus, well efficiency describes the effectiveness of a well in yielding water. Well efficiency should not be confused with pumping-plant (motor and pump) or "wire-to-water" efficiency used to measure pumping-plant performance.

4.4.2 Perspectives of pumping test Once the well is completed and developed, it is a good practice to conduct an aquifer test (or pump test). Aquifer tests are used to determine the efficiency and capacity of the well and to provide information about the permeability of the aquifer. The information about the pumping rate and resulting pumping water levels are also critical in determining pump size and optimize well-field production, providing maximum groundwater withdrawal while limiting stress on the aquifer system. Once the yield test is complete, it can be decided at what rate the aquifer can be pumped without lowering the water level below the top boundary of the aquifer, the top of the perforations or below the pump intake. The pump that is installed in the well should have a capacity equal to, or less than, the rate at which the well can supply water for an extended period of time without lowering the level below the pump intake. That rate is considered the safe pumping rate for the well.

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The information gathered during the test assists to determine the: •

Rate at which to pump the well

•

Depth at which to place the pump.

The pump test must be performed at or above the pumping rate for which it is intended to operate. The test pump should be capable of pumping 125 percent of the desired yield of the well. Pumping should be continued at a uniform rate until the "cone of depression" reflects any boundary condition that could affect the performance of the well. This could be as short as six hours and as long as several days, depending on aquifer characteristics. The discharge rate and drawdown established should be maintained for specified time period. No pumping should be conducted at or near the test site for at least 24 hours prior to the test. There are several accepted methods for determining aquifer properties. Which method should be used is dependent on the characteristics of the aquifer being tested (confined, unconfined, leaky confining layer) and the solution approach to be used. For an aquifer test, the well is pumped at a constant rate or with stepwise increased rates.

4.4.3 General assumptions in pumping test

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The underlying assumptions involved in the tests are: •

The aquifer is homogeneous, isotropic, and of uniform thickness over the area influenced by the test.

•

The flow is Darcian

•

Prior to pumping, the piezometric surface is horizontal, or nearly so, over the area to be influenced by the test.

•

The well is fully penetrating, thereby the flow is horizontal to the well

•

Well diameter is very small compared to radius of influence in aquifer

•

The water removed from storage in the aquifer is discharged instantaneously with decline of head.

•

Non-linear well losses are negligible.

The following assumptions/conditions apply to leaky confined aquifers: •

The aquitard is infinite in areal extent

•

The aquitard is homogeneous, isotropic and of uniform thickness

•

The water supplied by leakage from the aquitard is discharged instantaneously with decline in head

4.4.4 Constant rate test In this method, the well is pumped at a constant rate typically for 12 hours to 7 days, while the water levels in the well are checked and recorded frequently as they decline from their standing water level to their pumping water level. Static water levels must be measured

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in advance of the test and after the test during recovery. Typically, pump tests shall be conducted for a minimum of 72 hours at a constant pumping rate. Time-drawdown or distance-drawdown approach can be used. The volume of water pumped and the water level in the well are monitored simultaneously. Once the pumping has stopped, the recovery of the well (i.e. rising water level) is also monitored. Recovery measurements must be taken at specific time intervals ( 5 minutes for first 30 min. and 30 min. interval for the remainders) for several hours or until the water level returns to 90 percent of its original level. Using this data and applying certain calculations (described in a later section) we can determine the exact capacity of the well.

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Observation wells For distance-drawdown approach, at least three observation wells (in the same line) should be monitored during the pump test. The horizontal distance between each observation well and the pumping well should be measured. The vertical elevation of a fixed reference point on each observation well and on the pumping well (e.g., "top of casing") should be established. One observation well should be located outside of the expected influence of the pumping well; this observation well should serve to monitor background conditions during the pump test. The remaining observation wells should be placed so as to best define the hydrogeologic characteristics of the aquifer with respect to the pumping well. For unconfined aquifers, at least two observation wells should generally be placed no farther than 100m from the pumping well and at least one additional observation well should be placed beyond the 100m radius. For thick confined aquifers that are considerably stratified, at least two observation wells should be placed within 250 m of the pumping well and at least one observation well be located further than 250 m from the pumping well. Observation wells should be screened in, or open to, the same formation as the pumping well. Additional observation wells beyond the specified minimum number may be screened in, or open to, formations above or below the formation tapped by the pumping well to determine if there is any hydraulic connection between formations.

4.4.5 Stepwise test After the well development, the step test should be performed by pumping at a minimum of 3, and preferably 4 rates, with the pumping time being three hours minimum at each rate. The highest rate should usually be at the highest rate at which the well was developed, with drawdown and flow rates recorded at minimum 5-minute intervals during the first 30 minutes of each pumping rate, and at least 30- minute intervals for the remainder of each rate. Recovery readings should be taken at minimum 5-minute intervals for the first 30 minutes after pump shutdown, and at least 30- minute intervals for four (4) to eight (8) hours. After the step test is completed, a 24- hour pump test should be run at the rate calculated for the well based on the results of the step test. A schematic of time vs drawdown plot for step test is shown in Fig.4.6.

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Fig.4.6. Schematic of Time drawdown plot for step-test.

4.4.6 Analysis of pump test data

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The pump test and recovery data can be analyzed to determine the hydrogeological characteristics of the aquifer (such as hydraulic conductivity, transmissivity, and specific capacity) as well as to ascertain the eventual long-term production capability of the well. Commonly used methods are: •

Theis drawdown

•

Cooper-Jacob drawdown

•

Theis recovery

Theis method Theis (1935) derived the following discharge-drawdown relationship, called Theis equation: (4.5) Where, 0.577216

ln

1

and,

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4 Where, T is the transmissivity of the aquifer, t is the time since pumping started, and Q is the pumping rate. The steps in Theis curve analysis are as follows: -

Plot log drawdown (s) versus log time (t) on the same scale of matching (master) curve

-

Overlay plotted and master curve (keeping axes parallel)

-

Identify a match point and record values of s, t, u, and W(u)

-

Solve for T as: 4

-

Solve for S as:

-

Derive K as:

4

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Where, b is the thickness of the aquifer

Fig.4.7(a). Well function vs 1/u (inverse of well parameter) curve (Thies master curve).

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Fig.4.7(b). Theis analysis of time vs drawdown data.

Cooper-Jacob method Cooper and Jacob (1946) observed that as the variables decreases with time ( / . ! 0 , and thus the term W(u) can be approximated by: 0.577216

ln

The Theis equation then becomes: 4

0.5772

4 4

4

0.5772

In terms of log10 (As the term lnX = 2.303 log10X), the above eqn. can be expressed as: .

.

There are 3 types of solution approaches using Cooper-Jacob simplification: •

Time-drawdown

•

Distance-drawdown, and

•

Recovery

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Time-drawdown approach If the drawdown at time t1 and t2 are s1 and s2, the above eqn. can be written as:

2.3 4 If the data is plotted on semi-log paper, and the time t1 and t2 are chosen as one log-cycle apart, the above eqn. is reduces to:

∆

2.3 4

Where, ∆s is the drawdown per log-cycle of time. Or, .

(4.7)

∆

Again, from observation of eqn. (4.6), it is revealed that, when the term

is zero, the s value will be zero. That is, 2.25 That is, when

.

0,

.

0

1, .

(4.8)

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The time for zero drawdown (t0) can be obtained by extrapolating the graph to intersect the drawdown axis.

Fig.4.8. Schematic of Time-drawdown plot.

Distance-drawdown approach If several observation wells are installed, then from the semi-log plot of distancedrawdown data, eqn. (4.6) can be written as:

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2.3 4 Or,

∆

.

Taking drawdown per log-cycle of distance in the graph (Fig.4.9), the T can be obtained as: . ∆

,

where ∆s is the drawdown per log-cycle of distance (r).

Following the same principle of time-drawdown, the S value can be obtained as: 2.25 Where, r0 is the intersection of the straight-line portion of the graph with the abscissa at s = 0.

Fig.4.9. Schematic of distance-drawdown analysis.

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Theis recovery approach Recovery test (also termed as residual drawdown test) involves measuring water level rise after the pump is shut down. In this approach, a well is pumped at a constant rate (Q) for a certain period of time (t). The residual drawdowns (s ΄) in pumped well or in an observation well are measured at different time intervals (t΄) from the stop of pumping. The s΄ and t/t΄ are plotted in semi-log paper (s΄ in log-scale) (Fig.4.10). The transmissivity T is obtained as that of Jacob’s method as: 2.3 4 ∆ ΄ The S can be determined from the data when pumping stopped, or from the timedrawdown data as: 2.25 Limitations In presence of hydraulic boundaries, the above method is not accurate.

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Fig.4.10. Graphical display of recovery data.

5. GROUNDWATER WITHDRAWAL AND WATER-TABLE TRENDS – CASE STUDIES 5.1 Over-withdrawal of groundwater: Effects and areal extents around the globe Groundwater level data provide a direct means of measuring the impacts of both natural and anthropogenic changes to groundwater resources. When the withdrawal of ground water in an aquifer exceeds the recharge rate over a period of time, the aquifer is over withdrawal. There are two possible effects from the over-withdrawal of water from an aquifer. First, when the amount of fresh water being pumped out of an aquifer in a coastal area can not be replaced as fast as it is being withdrawn, salt water migrates towards the point of withdrawal. This movement of salt water into zones previously occupied by fresh water is called salt water intrusion. Salt water intrusion can also occur in inland areas where saline/briney water underlies fresh water (Fig.5.1). Secondly, in some areas over-withdrawal can make the ground sink because ground water pressure helps to support the weight of the land. This is called land subsidence. Sinkholes are an example of this effect.

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Fig.5.1. Schematic of fresh-saline water and saline water intrusion.

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For example, the Australian Water Resources 2005 concluded that 30 per cent of Australia's groundwater management units were at a high level of development and approaching or beyond sustainable extraction limits. Groundwater has been over-exploited in many parts of the world – United States (Dennehy et al., 2002), Europe Union (RIVM & RIZA, 1991), Caribbean Islands (Boak et al, 2003), India (World Bank, 2010; Shah, 2009), Bangladesh (Sarkar and Ali, 2007; Ali and Rahman, 2009), China (Yueqing et al., 2005; Ma et al., 2005) and many other arid and semiarid regions worldwide.

5.2 Groundwater withdrawal and watertable trend in Bangladesh In Bangladesh (formerly East Pakistan, a part of greater India), tubewell irrigation extracting groundwater started in the late 1960’s. National economic plan for more food-grain production led to a massive expansion in the tubewell programs, and by 1985, 17000 DTW (Deep tubewells) and 156,000 STW (Shallow tubewells) were in operation. The number was increased to 24059 DTWs and 348875 STWs by the end of 1992-93, and 32,174 DTWs and 13,74,548 STWs in 2008 (BADC, 2008). This massive as well as rapid expansion of the tubewell program has led to overdraft of ground water in many parts of the country. Fig.5.2 Shows the long-term groundwater table trend (yearly maximum values) of north-eastern part of Bangladesh (Mymensingh region, latitude: 24˚22 ,́ longitude: 88˚39 )́ . The water extracted by tubewells are used for irrigation in dry-season cropping. The figure shows a steady depletion of watertable (increase in depth to watertable) in almost all the observation wells. Among the wells shown, the highest depletion was 7.86 m in 19 years, on average 0.39 m per year.

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0

Relative year (1985 to 2004) 5 10 15

0

20

Bhaluka

Well-84

Depth to WT (m)

Depth to WT (m)

Bhaluka

4

8 y = 0.1218x + 5.2104 R² = 0.2774

20 Well-85

4

8 y = 0.0658x + 6.8181 R² = 0.5295

12

12 0

5

10

15

0

20

5

10

15

20

25

0

0

Nandail

Well-60

Bhaluka

Well-48

4

4

8

y = 0.1652x + 4.2963 R² = 0.4255

y = 0.2239x + 4.0635 R² = 0.6989

12

12 0 0

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Relative year 10 15

0

0

8

5

5

10

15

20

25

Nandail Well-44

4 8 12

y = 0.3652x + 5.6367 R² = 0.7843

16

Fig.5.2. Trend of groudwater table at north-eastern part (Mymensing) of Bangladesh.

Fig.5.3 illustrates the long-term groundwater table trend (yearly maximum values) of north-western part of Bangladesh (Rajshahi region, latitude: 24˚45 ́ , longitude: 90˚24 )́ . Here also, the water extracted by tubewells are used for irrigation in dry-season cropping. The figure shows a steady depletion of watertable in all the observation wells. Among the wells, the highest depletion was 8.65 m in 20 years, on average 0.43 m per year.

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5

Relative year (1985-2005) 10 15

83

20

25

Watertable depth (m)

0 5

Well-42 Well-91

Godagari-1

10

WT(91) = 0.5274x + 9.4415 R2 = 0.7748

15 20 25

0

WT(42) = 0.251x + 14.343 R2 = 0.7202

5

10

Relative year 15

20

25

0

Watertable (m)

2

Godagari-2 Well-93

4

Well-104

6

WT(104) = 0.1434x + 6.4497 R2 = 0.5708

8

10

WT(93) = 0.0207x + 8.7015 R2 = 0.0357

0

5

Relative year 10 15

20

25

0 2 4

Watertable (m)

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12

Well-80

Well-124

Godagari-3

Well-123

6

WT (80) = 0.0735x + 8.0229 R2 = 0.5717

8

10 12 14

WT(123) = 0.0115x + 11.691 R2 = 0.015

WT (124)= 0.0205x + 10.866 R2 = 0.0339

.

Fig.5.3. Trend of groudwater table at north-western part (Rajshahi region) of Bangladesh.

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Fig.5.4. demonstrates the trend of groudwater table at different wells of Dhaka city of Bangladesh, from 1988 to 2004. Here, the groundwater is used for municipal water supply, mainly household use. The graph shows a sharp decline in watertable in most wells. The highest depletion occurs at Mirpur location followed by Motizheel. The situation is alarming and may lead to catastrophic situation at future if the present trend is continued, and no measures are taken to reduce the abstraction or increase the recharge by artificial means. 0

Relative Year (1988-2004) 0 y = 0.5875x + 11.167 R² = 0.9146

Sutrapur Well No. DH-013

10

40

15

y = 2.7842x + 3.9419 R² = 0.8918

60

20

80

25 1

3

5

7

9

11

13

15

1

17

3

5

7

9

11

13

15

17

0

0

Motizheel Well No. DH-103

9

WT

18

Motizheel Well No. 124

10 20

WT

30

27

y = 1.795x + 6.8999 R² = 0.9054

36

40

y = 2.2854x + 13.622 R² = 0.9113

50

45

60

1

3

5

7

9

11

13

15

17

1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17

0

0 y = 1.848x + 11.692 R² = 0.9066

10

Lalbagh Well No. 110

20

5

y = 0.7254x + 16.067 R² = 0.7282

10

Mohammedpur Well No. DH-108

WT

WT

15

30

20 25

40

30

50 1

3

5

7

9

11

13

15

17

35 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17

0

0 5

y = 0.961x + 12.898 R² = 0.9537

10

Mohammedpur Well No. 111/A

15

y = 1.4592x + 18.443 R² = 0.9895

10

Ramna Well No.DH-112

20

WT

WT

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Mirpur Well No. DH-15

20

WT

WT

5

20

30

25

40

30

50

35 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17

1

2

3

4

5

Fig.5.4. Trend of groudwater table at Dhaka city of Bangladesh.

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7

8

9

10 11 12 13 14 15 16 17

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5.3 Groundwater withdrawal and trend in India

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India uses an estimated 230 cubic km of groundwater every year, making it the largest user in the world. Groundwater supports approximately 60 percent of irrigated agriculture and more than 80 percent of rural and urban water supplies. About 60 percent of the aquifers will be in critical condition within the next 20 years (World Bank, 2010). This also amounts to more than a quarter of the global total groundwater usage. In fact, groundwater use has been steadily increasing in India over the last 4-5 decades. However, groundwater resources are being depleted at an alarming rate. The report of World Bank pointed out that of a total of 5,723 groundwater blocks in the country, 1,615 are classified as semi-critical, critical or over-exploited, and the situation is deteriorating rapidly. Regulatory directives have been issued by the Central Ground Water Authority for 108 blocks. Climate change will further strain on the nation’s groundwater resources. Amongst its several suggestions to prevent overexploitation and making use of groundwater more sustainable, the report has called for community management of ground water wherein the user community is the primary custodian of groundwater and is charged with implementing management measures, indicating that the now age old traditions should be practiced again. The report also indicates that there is growing awareness that the continued pace of groundwater use is unsustainable, as aquifers are getting increasingly depleted and showcases the community groundwater management model adopted in Andhra Pradesh. About urban water supply planning, the report says that: “There is a need to move from opportunistic exploitation of groundwater resources to more systematic evaluation of the status of urban groundwater use and the contribution it can make to meeting future demand.”

5.4 Groundwater withdrawal and trend in China In China, agriculture is the major consumer of groundwater, with about 85% of the total groundwater withdrawals. Large-scale water resources development associated with dramatic population growth in the last 50 years, has led to tremendous changes in the groundwater regime. Depletion of groundwater is caused mainly by agricultural water use (Yueqing et al., 2005). Increased water use in several irrigated areas (such as Hebei Plain, north China plain, arid northwest China) has caused serious groundwater level decline and many geological problems which have become the biggest threat to social-economic sustainability. Ma et al. (2005) postulated that recharge has been reduced by 50% and groundwater abstraction exceeds by 0.41 ×109 m3/yr. Consequently, the groundwater level has fallen widely by between 3 and 5 m, with a maximum fall of 35 m. in several towns. Wang et al. (2007) analyzed the trends in the expansion of agricultural groundwater use, resource management challenges, and institutional and policy responses in the particular context of northern china. They noted that groundwater problems and their agricultural consequences in northern China are heterogeneous across space and changing rapidly over time.

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6. GROUNDWATER MANAGEMENT

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Groundwater resource management aims to secure longevity of the region’s groundwater systems by using the understanding of how these systems operate and establishing the sustainable groundwater yield for each system. Groundwater management includes the exploitation, evaluation and the protection of the resource in an effective and efficient way so as to ensure its sustainability for the present and future generations. The groundwater resource in almost all parts of the world is currently being over exploited considering the increase in groundwater facilities and the increase in demand (due to consequences of fast population growth). Groundwater facilities have been developed for metropolitan cities as well as for rural water supply, utilizing mechanized piped schemes and boreholes fitted with hand pumps. The exploitation of the groundwater resource shall continue into the future to meet the increasing demand of the population in order to accomplish the accelerated development in industrial, cities, and agricultural sectors. There is however growing concern about the sustainability of the groundwater resource as it is being exploited. In many regions, there have been reported cases of depleting groundwater pattern, in some cases very sharp declining trend (Ali and Rahman, 2009, Sarker and Ali, 2009). These cases seem to heighten the fear of groundwater depletion in the long term. There is therefore the need for an efficient and equitable use and an integrated management of the resource. This will be done with the background of understanding the societal need for groundwater, process involved in influencing the demand for and supply of water as well as the allocation of groundwater. Most communities where groundwater facilities have been provided for rural water supply under the community ownership policy have obligations which include; •

Community having legal ownership and control of the groundwater facility. These include formal agreements between project and donor agencies.

•

Community involvement in the location of the facility. This becomes very important in cases where hand pump installation boreholes are the facilities to be provided since people usually have to go to the borehole source to fetch water.

•

Selecting a committee responsible for managing the facility with additional responsibilities for operating and maintenance of the facilities. This committee is responsible for the maintenance and repair of the groundwater facility during breakdown.

6.1 Major obstacles to groundwater management In many regions, groundwater remains a neglected and misunderstood resource because funding for management and protection has not achieved the required attention and is always considered at the bottom of the environmental table. In most cases emphasis is placed on groundwater exploitation with no official policy framework for the protection of these facilities for the sustainability of the resource.

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Major obstacles for sound groundwater management in many areas which have to be addressed include: (i)

Absence of an effective legal and regulatory framework governing groundwater abstraction and protection

There must be a legal framework regarding abstraction of groundwater which must be enforced. The main governmental agency responsible for managing groundwater must set some thresholds regarding abstraction of groundwater and issuing of groundwater permits to make sure that the resource is exploited by qualified personnel and in a sustainable way. (ii)

Groundwater monitoring

A low priority has been attached to groundwater monitoring in many regions and as a results boreholes have been drilled without any monitoring wells in the catchments to monitor the quality over the years. Monitoring wells have to be installed in groundwater catchments to monitor the quality so as to prevent the breakdown of the system in case of pollution and contamination. The lack of monitoring wells is a serious problem and so it must be enforced with legal backing to integrate groundwater monitoring wells into the various groundwater programs.

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(iii)

Knowledge gaps

The impacts of climate variability and change will vary across regions, not only due to differences in climate from region to region, but also due to the nature of the groundwater system being affected. Regional case studies involving detailed characterization of aquifers are required to gain a better understanding of the potential impacts on groundwater resources. The impacts of climate variability and change on groundwater recharge are not well understood and are a major deficiency in current groundwater models. The dynamics of the interaction between shallow aquifers and surface water are poorly understood and not well studied in most areas. To address these knowledge gaps, historic and future climatic and hydrologic data will be of critical importance for describing changes to the overall water balance and flow regime within an aquifer system, and managing the resource into the future.

6.2 Amelioration/Remedial measures for obstacles 6.2.1 Groundwater policies Where the use of groundwater is concentrated or strategic, the resources should be protected by Prescription under the Water Resources Act. Where the acts/legislations are not available, should be established. These plans should be developed with the local community and irrigators to ensure that valuable groundwater resources are protected and used sustainably. Appropriate government agencies (like the district assemblies – Local Government Engineering Department, Water and Sanitary Authority) must be efficiently equipped to mobilize all stakeholders in the groundwater business in the management process. A formulation of a national policy must be carried out including:

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Formulating a natural groundwater policy with respect to the legal, administrative and regulatory measures with regards to the best available technologies and economic instruments. This will reduce indiscriminate drilling by obsolete equipment and machinery so as to avoid groundwater contamination.

•

Outlining procedures to implement abstraction and recharge permits so that the abstraction and recharge of aquifers will be controlled taking into accounts the reserve and its replenishment. The license will include the purpose, amount, location and the technical characteristics of abstraction and the legal status of the user as is practiced in some developed nations.

•

Formulation of laws governing groundwater pollution by ensuring that the drilling of boreholes is carried out by qualified and properly skilled and with appropriate personnel. The law will also make room for constant groundwater monitoring to avoid total groundwater pollution and contamination.

6.2.2 Establishing a groundwater data and retrieval system It needs to establish a groundwater data and retrieval system to collect, store, continuously update information to enable planning and management of the resource so as to ensure its sustainability. Records of boreholes which have to be included in the database include: depth of borehole, construction details of the boreholes, water level, yield and geological descriptions of the material penetrated by the drilling and aquifer depths.

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6.3 Management measures The engineers have to identify practical and politically feasible, socially acceptable, environmentally sustainable and economically viable strategies for managing groundwater use.

6.3.1 Resource Inventory There will be an increasing need for aquifer resource inventories and aquifer characterizations, particularly in water demanding areas. There is an increased need for protection of both surface and ground water resources by means of establishing land-use guidelines.

6.3.2 Monitoring of groundwater dynamics and its trend Since groundwater is a dynamic resource, continuous monitoring of water level is essential which helps to assess the gravity of the situation during adverse seasonal condition like drought. Groundwater level data provide a direct means of measuring the impacts of both natural and anthropogenic changes to groundwater resources. The stresses caused by these changes affect recharge to, storage in, and discharge from aquifers. Groundwater level measurements from observation wells are the principal source of information on the effects of hydrologic

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stresses on groundwater systems. These data in combination with precipitation records, stream-flow and withdrawal data are essential for monitoring the effectiveness of groundwater management and protection schemes. Similar to stream-flow and climatic data, groundwater level data become progressively more valuable with increased record length and continuity. Data on groundwater withdrawal are similarly critical in assessments of the behavior of water levels in aquifers. Without withdrawal data, it is impossible to separate the impact of pumping from that caused by climatic variability and change. In most cases, reliable withdrawal data are often absent. Insufficient and of very short duration data can not support any evidence of impacts of climate variability and change on groundwater resources are. Therefore, the collection of the following long-term data is critical. Water level data: A nation-wide network of observation wells for long-term groundwater level monitoring should be established. The network should include wells completed in both stressed and natural environments. It also should be tied into the climate and stream-flow networks. Groundwater withdrawal data: Information about groundwater withdrawals (pumping) is critical to the proper interpretation of water-level data and a basic input parameter into groundwater models.

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6.3.3 Management measures for reducing contamination There is a need to utilize groundwater resources to foster economic development throughout the country/region. Management of these resources is crucial to ensure that these systems will continue to provide quality water into the future. Example of improper use of groundwater systems have occurred where industrial wastes have been discharged into the aquifers through bores as a means of waste disposal. Examples are - septic effluent is discharged into the shallow aquifers and wastes from diary product factories are disposed of into drainage bores. Such practices should be prohibited. Groundwater is a significant part of the environment and needs to be managed and cared for. In recognition of the potential for pollution, biological and chemical analyses should be made routinely on municipal and industrial water supplies. Federal, State, and local agencies should take steps to increase water-quality monitoring. Analytical techniques to be refined so that early warning can be given, and plans can be implemented to mitigate or prevent waterquality hazards.

6.3.4 Enhancing groundwater reserve Using the County’s aquifers to store surface runoff from the wetter months for use during the drier months should be explored as well. The process involves augmenting natural recharge, or collecting surface water or rainwater and facilitating/injecting it directly into the aquifer.

6.3.4.1 Augmenting natural recharge In the recharging process, exposure of the soil to the water is a must. Water bodies (lowland, canal, rivers) have an important role in recharge. Water from the water bodies continuously seeps into the ground. Water may be prolonged by making dikes, dam, etc.

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6.3.4.2 Artificial recharge

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Recharge can be increased through artificial arrangements. Recharge through structures may be the most effective means for increasing groundwater potential in the rapidly declining groundwater areas. Artificial recharge process includes: •

from crop lands by making ridge

•

by making large reservoir

•

through canal water supply during off-irrigation season

•

through land-overflow/infiltration basin

•

by making dam/sluice gates

•

through recharge well

Large amount of water can be recharged through recharge well. In many areas of the world, high intensity rainfall in certain part of the year creates flash flood that goes to sea as waste. Such flash floods need to be arrested at various locations for recharge at accelerated rate. In such areas, recharge structures with tubewell (recharge well) are often better choice than surface storage. In areas having alluvial aquifers with good transmissibility, hydraulic conductivity and specific yield; recharge tubewells improve water availability more quickly than gradual percolation from percolation tank or check dams. Recharge wells are similar in construction to wells for pumping. A sketch of recharge well is given in Fig.6.1. A filter pit is excavated and filled with filter material. Filter materials should be designed properly, so that suspended solids and contaminants can not enter to the aquifer. The filter materials would be in the order - pebbles at the bottom, then gravels, and then coarse sand at the top. For wells in alluvial materials, specific capacities for recharge often are only 25 to 75 % of those for pumping. The cost of groundwater recharge with injection wells usually is about an order or magnitude higher than with infiltration basins.

6.3.5 Other supply management 6.3.5.1 Searching for alternate water source To minimize pressure on groundwater, possible alternate source of water should be searched. The possible sources include: •

Rubber dam for surface water storage

•

Utilizing marginal quality water

•

Purification of slightly contaminated surface water

•

Duel quality water supply for feasible uses

•

Diversion of river/stream water from one zone to another

•

Rain-water harvesting

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Filter materials

Fig.6.1 Sketch of a recharge well.

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6.3.5.2 Conjunctive use of surface and groundwater The available surface water should be preserved and utilized efficiently. The groundwater should be used only when it is essential. For example, at the peak demand period when the canal supply cannot meet the demand of irrigation, and at very long dry-spill of weather (natural rainfall).

6.3.6 Maintaining sustainability in groundwater withdrawal Sustainable use of groundwater depends on the current and future pattern of use by the residents, change of land-use pattern, level of contamination, virtual water market, etc. In most regions of the world, especially in arid and semi-arid regions (and also in humid subtropic areas), current groundwater consumption (both in urban and agricultural areas) is not sustainable, and already exceeds their estimated sustainable yield. Groundwater systems have generally established, over times past, a balance between the rates of inflow (or recharge), outflow (or discharge) and the volume of water stored within the aquifer. This is called the water balance (or budget) of a groundwater system. Any new use (or extraction) of groundwater from a system will cause a change in this balance. There is a need to utilize these groundwater resources to foster economic development throughout the world. Management of these resources is crucial to ensure that these systems will continue to provide quality water into the future.

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6.3.7 Modelling and use of model for impact study Well-calibrated groundwater models could be used to simulate and anticipate the possible impacts of climate change on the sustainability of groundwater resources. Models should be built to simulate and predict: •

groundwater changes due to human actions (pumping),

•

interactions with surface water bodies (rivers, streams, lakes and wetlands),

•

climate variability (hydrological cycle scale), and

•

climate change (long-term scale).

In addition to the above, models could be excellent tools for water management, when used for assessing the natural sustainable yield of aquifers and their vulnerability to contamination.

6.3.8 Institutional initiatives The following institutional considerations are suggested: •

encouraging watershed approaches to water management and protection

•

increasing cooperation between federal and provincial agencies regarding implementation and operation of monitoring networks

•

fostering linkages between water scientists and water managers

•

promoting integrated water resource management

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7. GROUNDWATER THREATS AND POLLUTION POTENTIALS 7.1 Groundwater threats In areas where material above the aquifer is permeable, pollutants can readily sink into groundwater supplies. Groundwater can be polluted by landfills, septic tanks, leaky underground gas tanks, and from overuse of fertilizers and pesticides. If groundwater becomes polluted, it will no longer be safe to drink. More than half of the world’s residents depend on groundwater as their primary source of fresh drinking water - either through public water supply systems or private drinking water wells. For many communities, groundwater is the only possible source of fresh water for drinking. Thus, a contamination of the resource will pose a threat to human health directly by drinking, and indirectly through food grain and other agricultural products. The crop plants are also sensitive to some major pollutants. Once contaminated, cleanup of groundwater contamination sites is expensive and slow, and often creates hardships for the persons affected. Groundwater therefore needs to be regulated and protected. It is important for all of us to learn to protect our groundwater because of its importance as a source of water for drinking and irrigation. In order to do

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this effectively, the threats to groundwater first need to be identified and defined, so that regulatory instruments can be designed to deal with the threats. The principal threats to groundwater resource are: •

Pollution/contamination sources

•

Over-exploitation

•

Climate change

•

Population growth and urbanization (through excessive or over-exploitation, and reducing recharge surface)

Groundwater contamination may be localized or spread over a large area, depending on the nature and source of the pollutant and on the nature of the groundwater system. Identification of threats provides a sound scientific basis for future remedial actions and longterm monitoring.

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7.2 Sources of groundwater contamination/pollution Any substance that is placed or injected in the ground has the potential to affect groundwater quality. Businesses such as dry cleaners, photographers and hair salons serve as examples of potentially hazardous land uses due to the types of chemicals they routinely use. If these businesses operate on individual well and septic service, the chance of groundwater contamination, through an accidental spill or mishandling, is especially high. Other businesses normally considered environmentally sound, such as golf courses, can actually threaten groundwater. These businesses often use relatively large amounts of lawn chemicals. Directly applying these chemicals to the ground presents an uninterrupted opportunity for groundwater contamination. Substances that can contaminate groundwater can be divided into two basic categories: (1) substances that occur naturally, and (2) substances produced or introduced by man’s activities. Substances that occur naturally include minerals such as iron, calcium, selenium, arsenic, etc. Substances resulting from man’s activities include synthetic organic chemicals and hydrocarbons (e.g., solvents, pesticides, petroleum products), landfill leachates (liquids that have dripped through the landfill and carry dissolved substances from the waste materials), containing such substances as heavy metals and organic decomposition products, salt, bacteria, and viruses. Based on the sources of groundwater contamination, contaminants can be broadly classified as: •

Point source, and

•

Non-point source (or diffuse source)

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Point source In this case, the pollutants/contaminates originates from one single point. Examples are septic tank, industrial outlet, dairy farm, landfill/ waste disposal site, etc. Some sources of potential groundwater contamination are somewhat easier to identify. They include industrial operations which may use hazardous chemicals, landfills, gasoline filling stations, and other direct sources of contaminates (Table 7.1). In most cases, these sources are heavily regulated by the state or federal government. These include regulations affecting landfill, hazardous wastes, and underground storage tanks (removal and construction). In general, the point sources are easier to identify and manage.

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Table 7.1. Groundwater contaminants and pollution sources Pollution source

Type of contaminant

Agricultural fields

nitrates; ammonium; pesticides

Pesticide Manufacture

Arsenic, phenols, and various halogenated hydrocarbons

Solid Waste Disposal

Heavy metals, ammonium

Sewage Sludge Disposal

Nitrates, various halogenated hydrocarbons, lead, zinc

Gasoline Filling Stations & Garages Metal Industries

Benzene, phenols, and other aromatic hydrocarbons

Timber Industry

Heavy metals, phenols, cyanide, trichloroethylene, tetrachloroethylene, and other halogenated hydrocarbons Metals, some aromatic hydrocarbons, alkylbenzene, tetrachloroethylene, other halogenated hydrocarbons Pentachlorophenol, some aromatic hydrocarbons

Dry Cleaning

Trichloroethylene, tetrachloroethylene

Painting and Enamel Works

Non-point source/ diffuse source Those that lack a well defined single point of origin, such as those created by intensive use of fertilizers, herbicides, and pesticides in agricultural fields. In addition, small point sources, such as numerous domestic septic tanks or small accidental spills from both agricultural and industrial sources, threaten the quality of regional aquifers. A problem of growing concern is the cumulative impact of contamination of a regional aquifer from nonpoint sources. Pollution from diffuse sources has been a problem for groundwater for some time. Anything soluble which is put on the land has the potential to get into an underlying aquifer, so everybody needs to be careful about what they put on gardens, roads and fields.

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Nitrate Nitrate is one of the most common groundwater pollutants. It can come from widespread sources, like concentrated livestock excretion, the use of nitrogenous fertilisers on farmland and nitrogen-fixing plants, or leaking sewers. More than two thirds of the nitrate in groundwater comes from past and present agriculture, mostly from chemical fertilisers and organic materials. Organic materials, such as manure or treated sewage sludge, can be a valuable source of nutrients and organic matter to soils. If too much is applied, or is applied in the wrong place or at the wrong time, it can get into and harm groundwater. It is estimated that over 10 million tonnes per year of organic material is spread on the land in the UK. More than 90 per cent of this is animal manure, the rest is treated sewage sludge, green waste compost, paper sludge and organic industrial wastes. High nitrate levels with inappropriate land use management activity is often a significant cause of diffuse-source pollution. Other major sources of nitrate are leaking sewers, septic tanks, water mains and atmospheric deposition. Atmospheric deposition of nitrogen makes a significant contribution to nitrate inputs to groundwater. Sources of atmospheric deposition of nitrate include transport, power generation and farm animals.

Pesticides and herbicides Pesticides are used to control weeds and pests, and can cause diffuse pollution. They can get into groundwater if they are able to leach through the soil. Some pesticides break down slowly, so will stay in groundwater for a long time. Others break down quickly, but some produce more toxic chemicals in the process. Some pesticides have been banned from use but we need to make sure that the replacements are better for the environment. Herbicides can pollute shallow groundwater systems if not managed correctly.

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Solvents, hydrocarbons, and fuel additives Fuel, fuel additives and solvents can contaminate groundwater under cities and industrial areas. Some of these chemicals are quite new, so we do not know how much of a problem they will be. Chlorinated solvents are widely used as degreasers in the metal engineering, electronics and leather industries. They are denser than water, they degrade slowly and are toxic at very low levels so small amounts can pollute large volumes of groundwater. There is widespread contamination possibility in the aquifers below our industrial cities. Groundwater can be contaminated by hydrocarbons (such as oils and fuels) from installations such as petrol stations that are not properly installed or maintained. Hydrocarbons can disperse in water and be transported over long distances.

Naturally occurring substances Contamination also results from an overabundance of naturally occurring iron, sulphides, manganese, and substances such as arsenic. Excess iron and manganese are the most common natural contaminants. As water flows through the ground, the chemistry changes as elements are released from the rocks. In many aquifers around the world, iron, manganese, arsenic, fluoride and radon are found at relatively high concentrations. Another form of contamination results from radioactive decay of uranium in bedrock, which creates the radioactive gas radon. Methane and other gases sometimes cause problems. Dissolved radon can be released

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as a gas and accumulate in confined spaces. Seawater can also seep into groundwater and is a common problem in coastal areas. It is referred to as "saltwater intrusion". The high risk of contamination by these compounds is because they are very mobile (as leachate) in groundwater environments. The improper management of hazardous substances has contributed directly to localized and regional ground water contamination throughout the world. It only takes a small amount of contamination to impact an aquifer and raise health concerns.

Salinity There is a natural boundary where fresh and saline groundwater meet in coastal aquifers. When fresh water is pumped out, this boundary moves and seawater is sucked into the aquifer. This can also happen inland, with groundwater abstraction causing saltwater to be drawn up from deep water aquifers. If too much water is taken from a coastal aquifer, it can eventually become too salty to drink.

Microbes Potential sources of microbiological contaminants are sewage and effluent.

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Mining Metal and coal mines can have a huge impact on groundwater systems. While mining is happening groundwater is usually pumped out in large quantities. When mining and pumping stops the rising groundwater can become contaminated. The mine structures can also change groundwater flow permanently. The main pollutants from mining are iron, zinc, lead, cadmium and acidic water. These substances can leach down into groundwater from spoil heaps, or can contaminate the upper part of the aquifer as groundwater levels (previously artificially lowered by pumping) begin to rise. The impacts can remain for hundreds of years. Metal mining has caused high concentrations of heavy metal pollutants in groundwater across Wales, the south west and northern England.

Landfills Landfills are another major source of contamination. Landfills are the places that our garbage is taken to be buried. Landfills are supposed to have a protective bottom layer to prevent contaminants from getting into the water. However, if there is no layer or it is cracked, contaminants from the landfill (car battery acid, paint, household cleaners, etc.) can make their way down into the groundwater. Many different types of waste go to landfill, so there are lots of potential pollutants. They are only a problem if the landfill has not been lined properly, or is badly maintained.

Road-salts The widespread use of road salts and chemicals is another source of potential groundwater contamination. Road salts are used in the winter-time to melt ice on roads to

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keep cars from sliding around. When the ice melts, the salt gets washed off the roads and eventually ends up in the water.

Contaminated land Industry can leave behind land contaminated by chemicals or radiological material that can leach through soils and rock and pollute groundwater.

Well Contamination A well can easily be contaminated if it is not properly constructed or if toxic materials are released into the well. Toxic material spilled or dumped near a well can leach into the aquifer and contaminate the groundwater drawn from that well. Contaminated wells used for drinking water are especially dangerous. Wells can be tested to see what chemicals, pathogens and other contaminants may be in the well. A well connects the land surface to an aquifer. This connection can be exploited by contaminants released near the well. The contaminants can travel directly from the surface into the aquifer via the same bore hole used to draw water from the aquifer. Wells can also connect aquifers across aquitards, allowing contaminants from one aquifer to reach another. Seals on unused, orphaned, and improperly abandoned wells can deteriorate over time, creating a connection from the surface to the aquifer. Unused wells can become an important contaminant pathway.

Contaminants from other parts of hydrologic cycle

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We have to remember that since groundwater is part of the hydrologic cycle, contaminants in other parts of the cycle, such as the atmosphere or bodies of surface water, can eventually be transferred into our groundwater supplies.

Pollution potential in Fractured Limestone In most basic groundwater textbooks, you’ll find hydrogeology discussed in terms of porous media, with aquifers composed of well-sorted sand, and groundwater moving through pores between sand grains. In the dolomite terrain (e.g. of northeastern Wisconsin) or cracking clay soil (e.g. in Australia), however, the story is much different. In such zone, the fracture or crack is exposed at or near the land surface. The vertical and horizontal fractures in the underlying soils are typical features. Rain or snow falling on this landscape enters the groundwater system through an interconnected network of vertical and horizontal bedrock fractures. In such systems, rapid groundwater movement and minimal contaminant attenuation are common, and so the land-use practices in the areas where the water originates (often called the capture zones or contributing areas) highly influence the quality of groundwater produced by local wells. Determining these capture zones and understanding how groundwater moves from recharge to local wells are critical to protect groundwater in fractured-rock terrains. Undertaking wellhead-protection studies in fractured-rock settings is a challenging endeavor.

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7.3 Pathways for contaminant transport

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As water percolates downward into the ground, pollutants, present at or below the ground surface may become dissolved. Once dissolved, the contamination may easily seep into the aquifer. Ground water moves from areas where the water table is high to where the water table is low. When water is being pumped from a well, the water table in the immediate vicinity of the well is lowered, thereby increasing ground water flow in the direction of the well. The resulting ‘Zone of Contribution’ represents the area within the aquifer, which contributes recharge to the well. As such, contamination which enters the Zone of Contribution will eventually move towards and pumping well. There are hundreds of chemicals that could get into groundwater. We look for substances that are not a problem now, but that we think might be in the future. Pharmaceuticals have been found in groundwater in many countries, usually near landfills that have been used to dispose of hospital or pharmaceutical industry waste. In a sand and gravel aquifer, contaminants move by diffuse flow. The gasoline from the underground storage tank spreads very slowly and contaminates the lake. Contaminants in a fractured rock aquifer move quickly through the fissures in the rock by conduit flow. This type of flow is less predictable than diffuse flow. When pumping occurred, the contaminant plume moved from one well to another and to the stream. Understanding pathways for aqueous transport of contaminants is necessary for determining the location and mass of contaminants at a given time, predicting their migration throughout the site’s hydrogeologic system, and estimating if and when there might be impacts on regional groundwater. To better characterize potential pathways for contaminant transport, monitoring wells must intercept the contaminant pathways. Toward developing a monitoring program, understanding of pathways is essential for: •

Planning the locations of wells to sample the alluvial groundwater, perchedintermediate groundwater, and the regional aquifer so that the wells are most likely to intercept a contaminant plume;

•

Determining the well-sampling frequency and types of analyses needed; and

•

Providing a rationale or model for interpreting the sample results.

Geochemistry is central to understand the extent to which contaminants move with groundwater; it is a tool for better understanding hydrogeologic pathways; and it is essential for determining the degree to which monitoring data are representative of actual groundwater. The specific need is to understand how contaminant migration caused by groundwater is affected by geologic or anthropogenic media that are encountered along the groundwater’s flow-path.

7.4 Arsenic contamination – A major threat for groundwater The occurrence of metallic and non-metallic elements (e.g. iron, manganese, arsenic, barium, etc.) in the groundwater is considered to be natural. Arsenic in groundwater above the maximum allowable concentration level (MCL) has been found more widespread and prevalent throughout the world than previously thought.

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Arsenic occurs naturally in the environment and is found in groundwater. Arsenic can occur as a free element, but it most commonly found as arsenopyrite (FeSAs). The concentrations of naturally occurring arsenic in groundwater can vary widely. Arsenic concentrations average 580 micrograms per liter (μg/l) in the earth’s crust, 0.01 μg/l in streams. Complex chemical reactions and biological activity can alter immobile forms of arsenic and cause them to dissolve into groundwater. Arsenic is principally used as a poison and in semiconductors. The current MCL for arsenic is 10 μg/l as suggested by WHO and in many countries. Acute exposure to arsenic above the MCL can produce disease in the respiratory, gastrointestinal, cardiovascular, nervous, and hematopoietic (blood cell production) systems. Arsenic occurs naturally in groundwater as a result of geothermal activity and dissolution of iron oxides and sulfide minerals. The adsorption of arsenic to iron oxydroxides is strongly influenced by pH, oxidation/reduction (redox) potential, and the presence of competing ions (Stollenwerk, 2003). Chemical reactions involving iron oxides and sulfide minerals appear to influence the mobility of arsenic. An increase in pH can cause arsenic to dissolve into groundwater. Changes in redox potential can change the number of available adsorption sites, reducing or increasing the amount of arsenic in groundwater. Microbial action can promote the release of arsenic into groundwater (Cummings et al., 1999; Roller et al., 2003). Conversion of sulfides to sulfates by introducing oxygen into an aquifer system can release of arsenic into groundwater.

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7.5 Over-exploitation The amount of water taken from an aquifer (abstracted by pumps and the amount of water that plants uptake) needs to be in balance with the rate of recharge. Despite a general abundance of groundwater in many areas, there is growing concern about the availability of good quality groundwater for municipal, industrial, agricultural and domestic use, and for adequate base-flow to our lakes, streams and wetlands. Natural shortages of groundwater may have occurred due to weather conditions and geologic setting (e.g., prolonged drought and crystalline bedrock aquifers with low yields). Human activities also cause quantity problems. Due to excessive withdrawals, groundwater levels have dropped dramatically in many parts of India, Bangladesh, China, USA, England, and also in other countries, because high-capacity wells are pumping too much water and the aquifers aren't being given enough time to recharge naturally. In urban areas, recharge is difficult because much of the land surface is covered with pavement and roofs, causing rainwater and snowmelt to flow away rather than seep into the ground. In many countries, regulation of groundwater quantity is extremely weak and has resulted in major concerns. Where abstraction of groundwater and potentially polluting activities are not regulated, social and economic pressures usually lead to over-abstraction and contamination of fragile aquifers.

Altered Groundwater Levels Water quantity problems can stem from reduced groundwater levels as well as artificially increased levels. Reduced recharge occurs when water that would otherwise filter into the aquifer is diverted to surface water bodies or taken out of the groundwater recharge basin, or

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there is very low rainfall amount. One of the most significant causes of recharge problems is the increase in impermeable surfaces, such as buildings, other structures, and pavement in recharge areas. Withdrawals from the aquifer that are not returned also lower the groundwater table. This has been a problem in big cities and urban areas. Problems of artificially increased groundwater levels can stem from an increased rate of groundwater recharge (from surface water irrigation), or a disruption in groundwater discharge. Common effects of elevated groundwater levels include mineralized soils (saline soil) in irrigated areas and property damage from basement flooding.

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7.6 Impact of Climate Change on Groundwater It is necessary to investigate the possible influences of global climate changes on this precious natural good. This can be done by observing the other sections of the water cycle, since it responds very sensitively to climate changes. This is due to the fact that higher temperatures in the atmosphere and of the ocean surfaces lead to an increased energy exchange between surface and atmosphere. Warm air can induce a higher water vapour concentration than cold air. Global climate models show that when the atmospheric CO2-content doubles (which is expected by about 2070) the average global precipitation per year will rise by 3 to 15 percent, and the global evapotranspiration (the total water evaporated from plants and open water surfaces) by 5 to 10 percent. Ten to twenty percent more rainfall is expected in the midlatitudes in winter, but there will be less rain in summer. In arid and semi-arid regions precipitation amounts are expected to decrease even further. The increased temperature will cause increased crop-water demand (Ali and Adham, 2007). The forecast for tropical and subtropical regions is more uncertain, but changes are expected to be less pronounced than in the temperate zones. Generally a shift can be expected towards higher precipitation amounts, higher variability of rainfalls and more extreme occurrences. Groundwater resources are generally influenced by the following factors: •

Changes in annual precipitation amounts, intensity and seasonal distribution

•

Changes in the evapotranspiration due to temperature changes, but also in the vegetation

•

Occasionally increased abstraction of groundwater (in some places the only water resource throughout the year) in drier periods.

The predicted increase in mean global temperature due to climate change is thus expected to affect water availability. Recent research by Herrera-Pantoja and Hiscock (2008) using a stochastic weather generator to drive calculations of actual evapotranspiration and potential groundwater recharge time series for the historic baseline 1961-90 and for a future High greenhouse gas emissions scenario showed that south-east England is likely to experience a reduction of 40% in recharge by the end of this century, with the persistence of dry periods shown to increase during the 2050s and 2080s. It has long been known that natural climate variability and climate change both affect water levels in aquifers. One can predict that as an important part of the hydrologic cycle,

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groundwater resources will be affected by climate change in relation to the nature of recharge, the kinds of interactions between the groundwater and surface water systems, and changes in water use (e.g., irrigation). We expect that changes in temperature and precipitation will alter recharge to groundwater aquifers, causing shifts in water table levels in unconfined aquifers as a first response (Changnon et al., 1988; Zektser and Loaiciga, 1993). Decreases in groundwater recharge will not only affect water supply, but may also lead to reduced water quality. There may also be detrimental environmental effects on fisheries and other wildlife as a result of changes to the baseflow dynamics in streams (e.g., Gleick, 1986). Other potential impacts include altering the equilibrium in coastal aquifers (e.g., Custodio, 1987; Lambrakis, 1997; Vengosh and Rosenthal, 1994), and reducing the volume of water stored in aquifers. As the various inputs to (recharge) and outputs from (discharge) aquifers are affected, so too will be the overall storage of groundwater in an aquifer.

7.7 Impacts of land-use change on groundwater

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Now-a-days, land-use is changing rapidly – from unused to cultivated, cultivated to town/cities and industrial areas, barren to land-fill, etc. For each type of use, there is specific type of pollution possibilities/potentials. But different types of soil exhibit different mode of pollution transport capabilities. As a result, there is a possibility of increasing pollution hazard with the changing pattern. For example, sandy and stony strata transport water quickly than that of clayey strata. Similarly, the cracking clay provides a preferential pathway of water at the starting of rainfall event, and quickly and directly add the flowing water to the shallow aquifer. Thus, if these factors are not considered, there is a chance of pollution hazard and adverse impact on the regional aquifer and groundwater.

8. GROUNDWATER PROTECTION In most part of the world, groundwater supplies up to 90% of the drinking water that we get through our taps. It is crucial that we look after this source and ensure that our water is completely safe to drink. Groundwater protection is vital to states/provinces where majority of the people draw their drinking water from underground aquifers. Identification and control of contamination sources are essential for groundwater protection. Most of the problems affecting groundwater are associated with human development. The most common problem posing a threat to groundwater supply is degradation of the water quality due to surface-level pollution or saline intrusion. Groundwater pollution or degradation is the main threat to the achievement of sustainable water resources management. Worldwide, aquifers (geological formations containing usable groundwater resources) are experiencing an increasing threat of pollution from urbanization, industrial development, agricultural activities and mining enterprises. In some cases it may take many years or decades before the impact of a pollution episode by a persistent contaminant becomes fully apparent in groundwater supplies abstracted from deeper wells. This can lead to complacency over the pollution threat. But the real implication is that once groundwater quality has become obviously polluted, large volumes of aquifer are usually involved. Thus clean-up measures

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nearly always have a high economic cost and are often technically problematic. Thus proactive campaigns and practical actions to protect the natural (generally excellent) quality of groundwater are widely required, and can be justified on both broad environmentalsustainability and narrower economic-benefit criteria. Controlling a source of aqueous waste could involve treating that waste to remove contaminants or reducing or stopping the discharges. Controlling solid waste could involve ensuring that it is emplaced in such a way that it cannot release contaminants or, if necessary, recovering the disposed waste, repackaging it, and possibly shipping it offsite. We should regulate onsite wastewater disposal in a manner that is protective of the groundwater and in such a way as to minimize the possibility of endangering the health and welfare of the public. The overall aim of the groundwater protection scheme is to preserve the quality of groundwater, particularly for drinking and irrigation water purposes, and maintaining/ sustaining the groundwater reserve for the benefit of present and future generations. Once the groundwater protection zone is defined for an area, the hazards posed by selected human activities can be evaluated to assess the appropriate risk management measures, or Groundwater Protection Responses, for those activities. Datasets of vulnerability, aquifer potential, and source protection areas can be generated by the GSI using field mapping in combination with readily available existing information and a limited amount of targeted drilling and testing. The vulnerability and aquifer datasets cover the entire land surface of a given area, while the source protection area datasets are specific to the catchments of selected groundwater supply sources. We should work towards a groundwater protection strategy suitable to Nation’s physical and socio-economic environment. Groundwater protection program should be made up of the following elements: -

Identification

-

Prevention/control

-

Monitoring

-

Restoration, and

-

Communication

8.1 Delineating protection zones Before a plan or program can be developed to protect ground water, it is important to identify existing or potential threats to the ground water. This will generally mean conducting an inventory to learn the location of facilities using, manufacturing, or storing materials that have the potential to pollute ground water. Groundwater protection zones should be developed based on local conditions and different concept and principles. Criteria commonly used for zoning includes the following (Chave et al., 2006): Distance: The measurement of the distance from the abstraction point to the point of concern such as a discharge of effluent or the establishment of a development site.

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Drawdown: The extent to which pumping lowers the water table of an unconfined aquifer. This is effectively the zone of influence or cone of depression. Time of travel: The maximum time it takes for a contaminant to reach the abstraction point. Assimilative capacity: The degree to which attenuation may occur in the subsurface to reduce the concentration of contaminants. Flow boundaries: Demarcation of recharge areas or other hydrological features which control groundwater flow. Approaches using such criteria range from relatively simple methods based on fixed distances, through more complex methods based on travel times and aquifer vulnerability, to sophisticated modelling approaches using log reduction models and contaminant kinetics. Uncertainty of the underlying assessment of contamination probability is reduced with increasing complexity. Use of tracer test in determining travel time and flow direction of the contaminant is highly recommended. Commonly used tracers are described in Table 8.1. Table 8.1. Tracers for groundwater study

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Tracer type Natural environmental isotopes (stable/unstable)

Examples C, 14C, 2H, 3H,18O, 3He, 36 Cl, 34S, 4He, 39Ar, 85Kr, 15 N, 234U 13

Radioactive tracers

60

Co,3H, 24Na, 51Cr, Br, 131J,

Fluorescent dyes

Rhodamine B, Amidrhodamin G, Uranine

82

The program consists of four interconnecting elements: (1) preventing pollution of the groundwater, (2) monitoring the effectiveness of engineered and administrative controls at operating facilities and groundwater treatment systems, (3) restoring the environment by cleaning up contaminated soil and groundwater, and (4) communicating with stakeholders on groundwater protection issues.

8.2 Measures for controlling quality degradation A strategy for developing a protection plan for the aquifer should be based on the assessment of risk for contamination of the aquifer and the relative value of the water to the society. The strategy may include: •

Source-water protection

•

Mitigation measures

•

Laws and regulations

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Community involvement

•

Practical method

Source-water protection

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Contaminated groundwater is very difficult and expensive to clean up. Solutions can be found after groundwater has been contaminated but this isn't always easy. The best thing is to adopt pollution prevention and conservation practices in order to protect important groundwater supplies from being contaminated or depleted in the first place. ‘Source Water Protection’ is a process that enables citizens to protect local groundwater supplies which serve as a source for drinking water. For source-water protection, we have to define Source Protection Zones (SPZs) for groundwater sources such as wells, boreholes and springs used for public drinking water supply. These zones show the risk of contamination from any activities that might cause pollution in the area. The closer the activity, the greater the risk. The maps of SPZ show three main zones (inner, outer and total catchment) and a fourth zone of special interest, which we occasionally apply, to a groundwater source. We can use the zones in conjunction with our Groundwater Protection Policy to set up pollution prevention measures in areas which are at a higher risk, and to monitor the activities of potential polluters nearby. Use of regulations, land acquisition, and education programs can play a key role in protecting groundwater. Examples of land use control activities include the following: -

Land use plans which take into account groundwater vulnerability;

-

Zoning ordinance and site plan review standards related to aboveground secondary containment, interior floor drains, and other topics;

-

Purchase of land and/or conservation easements to provide a wellhead protection buffer around municipal wellfields; and

-

Public education through public meetings, school-based classroom programs, library displays, cable television videos, public information flyers, and municipal newsletters.

Protection of groundwater resources requires efforts on several fronts, including the need for regional planning, land planning for individual sites, and technological advances that may offer alternative solutions. Regional planning must be based on the entire Watershed; it will do little good for one community to implement solutions to its problems only to find that neighboring communities do not. Groundwater has no respect for community boundaries. From a land planning perspective, simply requiring larger lots does little or nothing to enhance groundwater quality. One of the few readily available solutions to polluted wells or failed septic systems is to obtain public water and sewer. With the larger lots sizes and frontages prevalent in many of the communities within the watershed, the costs to provide water and sewer services to homes are likely to be exorbitant. On the other hand, where lot frontages are lower, so too will be the cost to provide public utilities. Several regulations are in place by the counties within the watershed which target the protection of water resources. Septic system regulation, for example, is the responsibility of

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the various Health Departments in relation to permitting, placement, and enforcement. The county health departments are also responsible for the inspection of septic systems prior to the sale of a parcel of land. If the system fails the counties' tests, the system must be upgraded or maintenance must be completed before a permit will be issued to the new property owner.

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Septic System Maintenance It is generally recommended that septic tanks be pumped out or the sludge and scum layers be measured at least every three years so that solids don't wash out into the soil treatment system. Solids can clog the soil and limit its ability to properly treat the septic-tank effluent. A local government may choose to impose septic system maintenance requirements on individual developments. However, implementing this recommendation is sometimes difficult without adequate cooperation between the community and county health departments. One solution may be to adopt a local ordinance that establishes "septic system maintenance districts," where higher concentrations of septic systems are present. Within these districts, property owners could be required to submit evidence of inspection or maintenance of septic systems at periodic intervals. This may be particularly effective for any approved Open Space Developments which have homeowner associations. Secondary Containment A common groundwater protection method for identified potential sources of groundwater contamination (such as above ground fuel storage tanks and facilities) is a requirement for secondary containment. A variety of containment methods are possible, but the most common is the construction of "traps" for runoff and spillage areas where possible contaminants are contained within walls or other structures and any runoff captured and contained within the structure. Local units of government through the site plan review process should be made aware of the locations for possible contamination and the measures planned by the operator to reduce the risks associated with those materials. This can be done as part of the site plan review process for potential point sources of contamination, such as industrial uses involving chemicals or hazardous materials. Each site plan should contain a storm-water management plan that details the impact of proposed land use on water quantity and quality, both on-site and within the watershed. This may be implemented by adding a requirement for site plans for submission of information regarding potential hazardous materials, and measures to be taken to protect drainage ways, water bodies, or other areas from accidental spills. Another provision which can be made part of the site plan review process, as well as for discretionary zoning approvals, such as planned unit developments and special land uses, is a requirement for monitoring wells for specific land uses with potential to affect groundwater resources. Monitoring wells have long been required for certain uses, such as landfills. Increasingly, communities are requiring them for other uses, such as golf courses, sand and gravel mining operations, higher density residential developments in identified groundwater vulnerability areas, and others. On-Site Community Treatment Systems In cases where soil conditions are inadequate to support a conventional onsite wastewater disposal system, we have to consider the site for an approved alternative system. The expense Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

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involved in resolving groundwater issues for a single site makes some solutions financially difficult. One area-wide solution intended for limited use is a package treatment system which serves smaller areas. Although a single, small development project may not be able to afford the installation and operation of a compact treatment system, several combined projects may join forces to implement an effective waste treatment system. A number of management and financial issues would obviously need to be resolved before such a system is implemented. Administering the system will likely be the responsibility of individual property owners formed into an association or authority. Questions of who will pay for the initial acquisition and installation of the system as well as maintenance responsibilities will need to be addressed. Issues of liabilities and other legal problems must also be examined. Generally, engineering expertise will be needed to conduct routine repairs and inspections, and replace system components when needed.

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Wellhead Protection The purpose of wellhead protection programs is to protect public water supplies taken from groundwater from potential sources of contamination. Protection is provided by identifying the area supplying groundwater to the community's wells, identifying potential sources of contamination within that area, and developing methods to cooperatively manage the area and minimize the potential threat to groundwater. Wellhead protection programs must address the following elements: -

Establishment of roles and duties for communities and property owners within the wellhead protection area.

-

A description of the wellhead protection area.

-

Identification of potential sources of contamination within the wellhead protection area.

-

Procedures to manage the protection area and minimize threats to the water supplies.

-

Plans for water supply emergencies.

-

Procedures for the development of new well sites.

-

Public participation methods.

A wellhead protection area is defined as the surface and subsurface area surrounding a water-well or well-field, supplying a public water system, through which contaminants are reasonably likely to move toward and reach such water-well or well-field. Zoning and land use measures to protect wellhead areas are generally similar to those that protect open spaces, including purchase of lands, conservation easements, and other similar measures. In many States or Provins, grants are available from the ‘Department of Environmental Quality’ to assist communities in developing wellhead protection programs and legislation.

Groundwater Monitoring Elements of the groundwater monitoring program include installing monitoring wells; planning and scheduling; developing and following quality assurance procedures; collecting and analyzing samples; verifying, validating, and interpreting data; and reporting. Monitoring

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wells are used to evaluate progress in restoring groundwater quality, to comply with regulatory permit requirements, to monitor active research, and to assess the quality of groundwater that enters and exits the site.

Laws and regulations

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To provide for the sustainable use of groundwater, governments should protect and manage both fresh and brackish groundwater resources. The development and implementation of policy on groundwater protection may be based on an analysis of threats to groundwater and the development of instruments to address the threats. In the absence of regulation of groundwater (both abstractions and discharges), with increasing development, the consequences sooner or later will be: (i)

Degradation of the fresh groundwater resources, with more fresh water having to be imported or manufactured, at much higher cost, as natural reserves decline.

(ii)

Health risks to consumers, from, for example, unregulated discharges from septic tanks.

(iii)

Increased costs for treatment of drinking water to potable standard, if the groundwater is contaminated with hydrocarbons, industrial solvents, or pesticides, for example.

(iv)

Increasing dependence on imported fossil fuels to support energy-hungry processes like reverse osmosis.

(v)

Loss of tourist revenue if water supply becomes unsafe or unreliable, or if the environment deteriorates.

We also have to adopt regulations and do outreach to carry out those mitigation measures. The measures should be designed to prevent continued movement to groundwater in contaminated areas and to prevent problems before they occur in other areas. Laws and Regulations are a better way to protect groundwater. Groundwater regulations are restrictions to protect groundwater from contamination resulting from use of pesticides in sensitive areas. Background on the development of the new legislation should be directive on protection of groundwater against pollution and deterioration. Different countries have formulated legislative framework for groundwater protection (e.g. European Commission (EC), USA) and gave directive guidelines to the member states. Sample legislative guidelines of European Commission Groundwater Environment are (EC, 2006): •

Groundwater bodies within River Basin Districts to be designated and reported to the European Commission by Member States.

•

Establish registers of protected areas within each river basin districts for those groundwater areas or habitats and species directly dependent on water.

•

Establish groundwater monitoring networks based on the results of the classification analysis .

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Set up a river basin management plan (RBMP) for each river basin district which must include a summary of pressures and impacts of human activity on groundwater status, a presentation in map form of monitoring results, a summary of the economic analysis of water use, a summary of protection programmes, control or remediation measures, etc.

•

Take into account by 2010 the principle of recovery of costs for water services, including environmental and resource costs in accordance with the polluter pays principle.

•

Establish by the end of 2009 a programme of measures for achieving WFD environmental objectives (e.g. abstraction control, prevent or control pollution measures) that would be operational by the end of 2012. Basic measures include, in particular, controls of groundwater extraction, controls (with prior authorisation) of artificial recharge or augmentation of groundwater bodies (providing that it does not compromise the achievement of environmental objectives). Point source discharges and diffuse sources liable to cause pollution are also to be regulated under the basic measures.

Regulatory instruments

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Regulatory instruments can take the form of primary legislation (such as an Act of Parliament), secondary legislation (such as regulations published by a Government minister with the backing of enabling legislation), less formal codes of good practice (often aimed at a particular industry sector), and sometimes just public information campaigns. Regulatory instruments may be as follows: 1) Licensing of abstractions Licensing of groundwater abstraction allows the quantities, locations and timing of abstraction from an aquifer unit to be controlled and limited to sustainable levels, to avoid long-term degradation of the resource. Exemptions can be built into the licensing regime, so that for example, abstraction for domestic use below a certain threshold daily quantity does not require a license. This helps regulatory bodies with limited resources to concentrate on the larger abstractions, and makes abstraction licensing more politically acceptable. Desirable features of an abstraction licensing regime include: time-limiting licenses, so that they are not irreversible; some form of license trading, to enable unused licenses to be reallocated and to encourage higher value uses of water; and the ability to add conditions to a license. 2) Charging for abstraction Abstraction charging (in conjunction with abstraction licensing) is an economic instrument commonly employed to tackle the threat of over-abstraction, as it provides an economic incentive to reduce abstraction, especially if payments are imposed on each unit volume of groundwater abstracted. Often the charge is levied only on abstractions above a defined minimum volume, and then there are bands of charges for increasing volumes. The charge may also vary with the season, and the quality of water abstracted. For example, abstraction from brackish sources can be expected to be at a lower price. Similarly, the use to

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which abstracted water is put can affect the charge, so that low consumptive uses are charged at a lower rate. Flexibility can also be retained to exempt certain categories of abstractor. 3) Licensing of well drillers This is a relatively straightforward administrative regime to put in place, and consists of licensing professionals to carry on activities of groundwater exploration, drilling and well construction. Anyone wishing to drill and equip a well must use a licensed well driller. This ensures that wells are drilled and equipped to the required standards, by people who have been properly trained and are aware of the risks of groundwater contamination. The aim is to avoid contamination of aquifers via poorly-constructed wells. The system also enables information and data on groundwater to be collected, as well drillers are usually required to submit records of all wells drilled, whether or not they go on to be used for abstraction or disposal.

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4) Effluent discharge consents Discharge consents are an instrument to control the disposal of liquid effluents to land, surface water and groundwater. They regulate the volume and toxicity of wastewater or effluent which it is permissible to discharge in a certain location, and usually control the method of discharge as well. Without them, uncontrolled discharges to groundwater can easily lead to widespread pollution. Once groundwater has been polluted, it is very difficult to clean up. Discharge consents are sometimes made tradable, but this is not always desirable. It can lead to ongoing pollution, for example if a powerful industry buys up unused consents to enable it to carry on with unabated discharges. 5) Effluent discharge fees These are applied in conjunction with discharge consents, and are designed to increase the cost payable by a polluter for using the natural or man-made environment as a discharge outlet for wastes. The fees usually vary depending on the pollution potential of the effluent, and the location of the discharge (in other words, the sensitivity of the environment receiving the effluent). This is an economic instrument, encouraging a reduction in the use of toxic substances in production processes, or stimulating the pre-treatment of wastewater. The level of fees can be raised until the volume and toxicity of effluents are reduced to an environmentally acceptable level, if that exists. 6) Groundwater protection zones Groundwater Protection Zones (GPZs) are designed to protect sources of groundwater from contamination, particularly sources of fresh groundwater for public water supply. The regulatory body is given statutory authority to demarcate various zones around a groundwater source to control activities within the zones which could contaminate the source. The zones are usually based on criteria such as the total catchment area of the source, and/or the time of travel for pollutants (Foster et al 2002). The zone immediately around the source receives the greatest protection, with progressively less strict controls on activities in concentric zones moving out from the source. GPZs are an important part of the land use planning process. 7) Land use planning The objective of land use planning is to secure a spatial pattern of land use development that best serves the cultural, social, environmental and economic interests of the nation, while taking into account the views of the people who live and work in the defined area.

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Groundwater often suffers from being out of sight and therefore out of mind, and there is a great need to elevate groundwater to the status of a strategic national resource. The land use planning system in general, in conjunction with GPZs, has a very important role in preempting threats to groundwater by not allowing certain activities to take place in certain locations, or at least to control the way in which the activities take place. This does not mean that reasonable development proposals should not be allowed to happen, but only that groundwater should be taken into account when the planning decision is made. 8) Building regulations Building Regulations enable Building Control Officers to monitor the standards of building works with reference to detailed obligatory specifications and minimum standards published in Building Codes, usually controlled through permits. From the point o f view of groundwater, the idea is to ensure minimum standards of materials and construction for items such as septic tanks, disposal wells, drainage wells, grease traps and oil interceptors, so that the contamination threat to groundwater is minimized. This is a powerful instrument (if properly enforced), and can make a significant contribution to groundwater protection.

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9) Solid waste disposal controls Leachates from solid waste transfer, disposal and landfill sites can be a serious threat to groundwater quality. Solid waste disposal controls lay down where solid waste and sludge may be disposed of, and what type of waste is permitted to go to landfills and rubbish tips. Techniques include the separation of types of sludge and solid waste so that the appropriate types of waste go for the appropriate type of disposal, whether incineration, landfill, landspreading or recycling. It is important to give strong backing to the implementation of solid waste management plans, with a cradle-to-grave approach to the management and disposal of solid waste. 10) Controls on the use of biocides and fertilizers The diffuse application of chemical and microbiological substances to land in agriculture, horticulture, and public amenity for controlling pests or providing nutrients can have a significant long -term impact on groundwater quality. This instrument involves setting up product controls, so that the use of certain substances is banned or at least strictly controlled, especially in areas of groundwater vulnerability. The controls can range from banning the importation to the country (or manufacture within the country) of certain substances, to the publication of good practice guidelines for the responsible use of the substances. 11) Prosecution of pollution offences Under the environmental law of most jurisdictions it is an offence to cause pollutants or contaminants to enter the environment (including groundwater). This is intended to retard people from polluting the environment, and to ensure that the polluter pays if an offence is committed. Unfortunately, these laws are not always adequately enforced, and major pollution incidents sometimes go unprosecuted. This is often due to difficulties with the level of proof required to achieve a conviction. Consideration may also need to be given to increasing the penalties applicable to pollution offences to increase the deterrence. 12) Contamination clean-up orders Where contaminated land is identified as being an on-going source of pollution for groundwater, it may be technically feasible and cost-effective to remediate the land, to reduce

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the detrimental effect on groundwater resources. Many jurisdictions have established procedures for identifying areas of contaminated land, and a process for attributing responsibility for the contamination. It is important to realize that prosecution of polluters is not always possible, sometimes because the contamination is historic, and was not caused by the current site owner. Even if successful, prosecution of polluters does not always lead to the site being cleaned up. Clean-up orders are therefore a useful instrument, especially for historic contamination.

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13) Environmental impact assessments Environmental impact assessment (EIA) is a key instrument, feeding into the planning process, for the control of larger projects which could potentially have a detrimental impact on groundwater. They consist of a statutory iterative process by which planning decisionmakers can assess the environmental effects of certain categories of developments. They also subject the environmental effects of development projects to expert and public scrutiny in a methodical and transparent manner. A key component of any EIA is the Environmental Statement, which is usually prepared by the developers- consultants, setting out the environmental impact of the project and proposed methods of mitigation, as well as information provided by statutory consultees. 14) Statutory consultation The principal focus of this instrument is on ensuring that there are strong statutory links between the various bodies whose activities might have an impact on groundwater. Whereas an environmental regulator might have control of several key instruments (such as abstraction licensing/charging, discharge consents/fees, licensing of well drillers, etc), some instruments which are vital to groundwater protection may lie outside the formal powers of the environmental regulator (such as building regulations and product controls). These are controlled by other bodies, such as a Ministry of Works. It is important to ensure that the right bodies are statutory consultees in the processes which impact on groundwater protection (for example, through the land use planning process and the EIA regime). 15) Environmental education This instrument, which is a social process aimed at strengthening a new culture of water, can significantly reduce quantitative and qualitative stress on groundwater. Public education can encourage: leakage reduction and the sensible pricing of water by water utilities; the better treatment and recycling of wastewater; water-efficient techniques of irrigation; the provision of secure supplies of fresh water and decent sanitation in housing areas; and the prudent use of water in all sectors of society. This instrument takes a very wide variety of forms, such as: teaching materials for schools; posters, leaflets, books, audio-visual materials; coverage in the press, radio and television; and the dissemination of user-friendly Codes of Practice designed for specific industrial and commercial sectors (which can be an effective preventative means of achieving groundwater protection objectives without recourse to the enforcement of regulations through court prosecution).

Community involvement Community involvement can make a program sustainable. How your community conducts the inventory of contamination source will depend largely on the resources available, particularly the number of people available to do the work and funds. The inventory

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of existing or potential threats to the community’s groundwater may be quite long, and it is unlikely that your community will have the resources to address all of these threats. How do community officials decide which threats are the most serious or set priorities? One way is to assess these threats on the basis of their relative risks to the community’s ground water. This requires determining which of the specific pollutants are most likely to be released and reach the groundwater in concentrations high enough to pose health risks. In addition to having an incentive to protect its ground water, your community has a number of powers that can be used for that purpose. These include implementing zoning decisions; developing land-use plans; overseeing building and fire codes; implementing health requirements; supplying water, sewer, and waste disposal services; and using their police powers to enforce regulations and ordinances. A few communities have begun developing their own groundwater protection programs using a variety of management tools based on these powers. Groundwater Monitoring: This should be done to assess the quality of local aquifers by sampling public and private wells for selected contaminants. Household Hazardous Waste Collection: To alleviate the threat to groundwater from the disposal in regular trash pick-ups, sewers, or septic systems of household products that contain hazardous substances or other materials that can be harmful to groundwater, such as paints, solvents, or pesticides. Water Conservation: To reduce the total quantity of water withdrawn from groundwater aquifers and to protect against contamination by reducing the rate at which contaminants can spread in the aquifer (e.g., excessive withdrawals from an aquifer located near the ocean can draw salt-water into the aquifer and contaminate wells).

Lining and sealing method of groundwater protection Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

Lining and sealing A German based Company, Naue Fasertechnik Gmbh & Co.( Anthony et al., 1991) claimed that Carbofol ® (a registered brand product of them) offers complete lining systems for groundwater protection. They noted that Naue Fasertechnik is the single source for complete groundwater protection. Single component sealing systems featuring Carbofol geomembranes, are used in industrial facilities for storage, filling and transferring and for production, treatment and utilization - where there is a danger of groundwater contamination by hazardous materials. When used in the construction of collection basins, Carbofol® high-density polyethylene (HDPE) geomembranes effectively protect groundwater and soil resources from pollution by potentially harmful contaminants. With a minimum thickness of 1.5 mm, Carbofol HDPE geomembranes fulfil a wide range of chemical resistance as well as physical durability requirements. In addition to their long-term chemical resistance, Carbofol® HDPE geomembranes have long-term UV resistance and are resistant to rodents as well as root growth when manufactured with a minimum thickness of 1.0 mm. By virtue of Carbofol's® high flexibility, more complicated connections are feasible without sacrificing quality or performance. Due to their advantageous melt index properties, Carbofol® geomembranes can be welded under a wider range of conditions, producing gas and watertight overlaps. Quality

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control tests are to be conducted continuously on every project in addition to the standard manufacturing quality control practices. Protection To ensure the performance and quality of a single component sealing system, mechanically bonded Secutex® or Depotex® protection nonwovens should be used above and below the Carbofol® geomembrane, the selection of which should be based upon project specific conditions. With a low gravel content sandy subsoil (< 30 % gravel portion), a 400 g/m² mechanically bonded polypropylene (PP) Secutex® protection nonwoven is sufficient. However, with coarser grained soils, mechanically bonded Secutex® protection nonwovens with a mass per unit area of up to 1,200 g/m² should be considered. Alternatively, if the sealing system must perform in an aggressive chemical environment, Depotex® HDPE nonwovens should be used for the protection components to ensure long-term protection.

Some general guidelines/solution options for specific problems

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1) Over-abstraction: Pumping fresh groundwater at too high a rate, or from too concentrated an area, usually from individual wells or sections of well-fields, causing localized salinity increases. The practical solution consists of careful management of well-fields and monitoring of the output and salinity of individual wells or trenches. Given enough time, the effects of over-abstraction can be reversed. 2) Physical disturbance: Salt water invades areas which were previously fresh through the construction of marinas, canals, and waterways which are connected to the sea. The damage to the fresh groundwater is usually permanent. Also included in this category is any excavation below the water table, such as borrow pits for road construction, which expose open water and lead to salinization through evaporation. The practical solution includes impact assessment of plans for new marina or waterfront developments, approving designs, and inspecting construction. Also, avoiding excavation below the water table, if possible. 3) Point-source pollution: Specific incidents or local sources of pollution such as oil spills, leaks from underground storage tanks at gas stations, engineering workshops, chemical spills etc. The practical solution is good working practices, approving designs for fuel and chemical storage and handling facilities, then inspecting construction and monitoring operation. 4) Solid waste disposal: Pollution from leachates from landfills, sludge disposal, and illegal dumping. This is really another form of point-source pollution, but has been separated out because it is usually regulated by different legislation. The practical solution is good working practices, ensuring landfills are correctly designed and constructed, and public education on illegal dumping. 5) Disposal wells: Pollution from disposal or drainage wells which have been badly constructed, wrongly sited, or drilled to the wrong depth. Also inadequate treatment of waste before disposal down wells. The problem here is not with the concept of using disposal wells, which can be a safe, effective and low-impact method of disposal for liquid waste. The threat is from bad design,

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bad construction, or bad operation. The practical solution is therefore approving designs, inspecting construction, and monitoring operation. 6) Septic tanks: Pollution from septic tanks, cesspits and latrines which have been badly constructed, built in the wrong place (such as below the water table), not emptied often enough, or not equipped with an accompanying disposal well. The practical solution is approving designs, inspecting construction, and public education. 7) Abstraction wells: Abstraction wells (mostly private wells) which have been badly constructed, wrongly sited, or drilled to the wrong depth. Again, the practical solution is approving designs, inspecting construction, and public education. 8) Diffuse pollution: Pollution over wide areas from poor use of fertilizers, chemicals and manures in agriculture, on golf courses, sports fields and public parks, poor use of treated effluent for irrigation. The practical solution is good working practices, control of products and public education.

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The following guidelines can help to protect groundwater and water-well: •

Maintain your well and test the water quality annually.

•

Keep household chemicals, paint and motor oil away from your well and dispose of them properly by taking them to a recycling center or household hazardous waste collection site.

•

Limit your use of pesticides and fertilizers.

•

Install a well cap and keep it clear of leaves, mulch, dirt, snow and other materials.

•

Use caution when mowing around your well so you don't damage the well casing.

•

Practice water conservation measures in your home and install low water use appliances.

8.3 Opportunities to improve groundwater There are technological advances on the horizon that may offer opportunities to improve groundwater. These include: -

man-made wetlands

-

terraced, overland flow systems

-

package plants

-

sand-filter systems, and

-

greenhouse, peat, and bio-filter systems.

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8.4 Challenges in groundwater protection and management Groundwater protection program faces substantial technical challenges. There is considerable uncertainty about the contamination sources themselves. The pathways for transport of contaminants from their sources may include four different hydrologic regimes: (1) surface streams and runoff, (2) near-surface groundwater, (3) intermediate-perched groundwater in the unsaturated (vadose) zone, and (4) a deep, regional aquifer. Each of these regimes adds considerable uncertainty to the understanding of the overall system. Even with best efforts to understand contaminant sources and pathways, the uncertainty will always be great. Groundwater protection will become increasingly important as population densities continue to increase. In a watershed, contaminated groundwater has a potentially devastating effect. As a result, maintaining appropriate densities of development and proper disposal of sanitary sewer wastes are critical factors in ensuring the adequacy and quality of domestic water sources. Lowering of water-table can have a range of geo-chemical changes (e.g. arsenic contamination by oxidation process), which may pose a threat to groundwater.

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Hazell, J. R. T., Cratchley, C. R. and Jones, C. R. C. (1992). The hydrogeology of Crystalline Aquifers in Northern Nigeria and Geophysical Techniques used in their Exploration. In: E. P. Wight and W. G. Burgess, (eds), The Hydrogeology of Crystalline Basement Aquifers in Africa. Geological Society Special Publication, No. 66, pp. 155-182 Hazell, J. R. T., Cratchley, C. R. and Preston, A. M. (1988). The Location of Aquifers in Crystalline Rocks and Alluvium in Northern Nigeria using Combined Electromagnetic and Resistivity Techniques. Quarerly Journal of Engineering Geology, vol. 21, pp. 159175 Herrera-Pantoja, M. and Hiscock ,K. M. (2008). The effects of climate change on potential groundwater recharge in Great Britain. Hydrological Processes, 22(1): 73-86 Holman, I.P., Hiscock, K. M. and Chroston, P. N. (1999). Crag Aquifer Characteristics and Water Balance for the Thurne Catchment, notheast Norfolk. Quarterly Journal of Engineering Geology, vol. 32, pp. 365-380 Jansen, J. Jurcek, P. and Voigt, J. (2000). TEM Survey to Map Saline Ground Water in the Cambrian-Ordovician Aquifer of Eastern Wisconsin. Symposium on the Application of Geophysics to Engineering and Environmental Problems, pp. 719-728 Lambrakis, N. (1997). The impact of urbanisation of Malia coastal area (Crete) on groundwater quality. Environ. Geol. 36: 87-92

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Zonge, K. L. and Hughes, L. H. (1991). Controlled-source Audio-frequency magnetotellurics. In: Nabighian, M. C. (ed.), Electromagnetic Methods in Applied Goephysics, vol. 2: Applications, part B. Tulsa: Society of Exporation Geophsicists, pp. 713-809.

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Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved. Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

In: Water Engineering Editor: Dominic P. Torres

ISBN: 978-1-61209-914-9 © 2011 Nova Science Publishers, Inc.

Chapter 2

INDUSTRIAL WASTEWATER TREATMENT USING A COMBINATION OF CAVITATIONAL REACTORS AND FENTON PROCESSES: A REVIEW Parag R. Gogate1 Chemical Engineering Department, Institute of Chemical Technology, Matunga, Mumbai- 400019, India

ABSTRACT

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Cavitational reactors offer considerable promise for wastewater treatment applications due to the significant effects such as generation of free radicals, hot spots, conditions of intense turbulence etc, which are extremely suitable for oxidation of toxic pollutants present in the wastewater. However, these cannot find actual application for large scale wastewater treatment due to higher processing costs and some limitations as regards lower degradation rates for highly loaded effluent streams. An innovative approach has been to combine cavitational reactors with other synergistic oxidation processes such as Fenton chemistry. The present work provides an overview of the combined treatment strategy based on cavitation and Fenton processes. Both the types of cavitational reactors, i.e. sonochemical reactors based on the use of ultrasound for generation of cavities and hydrodynamic cavitation reactors where cavitation is generated due to alterations in the flow field, will be discussed in the work for possible synergism with Fenton processes. The Fenton process can be based on the conventional approach which uses the combination of ferrous sulphate and hydrogen peroxide whereas the advanced Fenton process can be based on the use of other constituents such as iron metal or cupric oxide in combination with hydrogen peroxide, with an objective of possible reduction in the treatment cost. The work highlights the mechanistic details pointing towards synergism, different reactor configurations, an overview about different pollutants being degraded using combinatorial approach and guidelines for selection of the important operating parameters such as ratio of the oxidants, pH, temperature, configuration of cavitational reactors etc. based on a detailed analysis of the existing literature in this area. Overall it appears that combined treatment strategies are more

1

E-mail: [email protected]

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Parag R. Gogate suitable as compared to individual operation of either cavitational reactors or the Fenton based processes.

Keywords:Cavitational Reactors, Fenton chemistry, Advanced Fenton processes, Wastewater treatment, Process Intensification, Hydrodynamic Cavitation.

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INTRODUCTION Due to the increasing presence of molecules, refractory to the micro-organisms in the wastewater treatment streams, the conventional biological methods can not be used for complete treatment of the effluent and hence research into alternate treatment schemes including advanced oxidation processes have been of broader interest over the recent years [1]. Advanced Oxidation Processes are defined as the processes that generate hydroxyl radicals in sufficient quantities to be able to oxidize majority of the complex chemicals present in the effluent water. Hydroxyl radicals are powerful oxidizing reagents with an oxidation potential of 2.33 V, which is a lot higher than other oxidants such as hydrogen peroxide, permanganate ion etc. Some of the AOPs which have been used for wastewater treatment include cavitation, Fenton chemistry, and photocatalytic oxidation [2-6]. However, it has been observed that none of the methods can be used individually in wastewater treatment applications considering their energy efficiency and economics [7]. Hence combinations of different AOPs have been used for wastewater treatment in recent times, which have been notably efficient at laboratory scale as compared to the individual treatment scheme [8-10]. Cavitational reactors have shown certain limitations for large scale applications though these have been immensely successful for degradation of pollutants at laboratory scale operations [3,11-12]. An innovative approach, for cost effective application and to increase the applicability of cavitational reactors for wastewater treatment, has been to combine cavitation with other advanced oxidation processes such as photocatalytic oxidation or Fenton based processes. Recently, Joseph et al. [13] have given an excellent review on the use of combination of ultrasound and ultraviolet irradiations for wastewater treatment. Taking a lead from the work, it was thought worthwhile to present an analysis of another important combinatorial technique based on the use of cavitation and Fenton chemistry, which has been of great interest in the recent years. The current work highlights the combination of cavitation (acoustic as well as hydrodynamic) and Fenton chemistry (conventional as well as advanced) with a special emphasis on wastewater treatment applications. Conventionally, Fenton chemistry is based on the use of Fe2+ ions in combination with hydrogen peroxide (optimized ratio of about 1:5 to 1:10) for generation of hydroxyl radicals and its subsequent attack on the pollutants [6]. In recent years there have been studies reporting the use of iron metal with H2O2 to give Fenton like mechanism but at much lower costs of operation [14-15] and has been referred to as Advanced Fenton processes.

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Combination of Acoustic Cavitation and Fenton Chemistry

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Acoustic cavitation is generated by using high frequency sound waves, usually ultrasound with frequencies in the range of 16 kHz – 100 MHz. Alternate compression and rarefaction cycles of the sound waves results in various phases of cavitation, such as generation of the bubbles/cavity, growth phase and finally collapse phase releasing large amount of energy locally. The violent collapse of the cavitation bubbles results in a specific environment, with extremely high temperature (up to 50000 C) and high pressure (about 100 to 5000 atm), which is suitable for destruction of pollutants by two simultaneously acting mechanisms. First, the pollutants present at the cavitating conditions can be thermally decomposed by pyrolytic mechanism and secondly there is a generation of large amount of the reactive radicals including OH· due to thermal dissociation of water, which can initiate a series of radical reactions to decompose pollutants. The controlling mechanism depends mainly on the type of the pollutant and the liquid physicochemical properties of the liquid along with the operating pH. In conditions where free radical mechanism is dominant, use of Fenton chemistry in combination with acoustic cavitation leads to beneficial effects. For systems based on combination of ultrasound with Fe+2/H2O2, hydrogen peroxide reacts with ferrous ions to generate active hydroxyl radicals, which results in the degradation of the pollutant via the usual Fenton chemistry. The resulting Fe+3 can react with H2O2 to generate an intermediate complex (Fe – O2H2+) which can be effectively dissociated into Fe+2 and HO2· under ultrasonic irradiation. The regenerated Fe+2 further reacts with H2O2 and generates a higher concentration of hydroxyl radicals compared to that in the absence of ultrasonic irradiation. Thus, in the presence of ultrasonic irradiations, a chain of radical reactions occur ensuring the continuous regeneration of Fe2+ ions and consequently the enhanced generation of the hydroxyl radicals in the system. The typical radical reactions occurring can be represented as follows:

Fe+2 + H2O2 Æ Fe+3 + OH- + HO· Fe+3 + H2O2 Æ Fe – O2H2+ + H+ Fe – O2H2+ ))) Æ Fe+2 + HO2· Use of iron powder (in the presence of hydrogen peroxide) instead of Fe2+ has also been seen to yield beneficial results and give a Fenton like mechanism for degradation of pollutants. Elemental iron (Fe0) is a mild reductant with an EH0 = -0.44 V. Acoustic cavitation induced due to ultrasonic irradiations can increase the surface area of the reactive solids by causing particles to rupture and sonication in the presence of elemental iron can be a useful combination for degradation of effluents. The combination of ultrasound and Fe0 is a heterogeneous reaction system involving solid/liquid, gas/solid and gas/liquid interfaces. In the presence of ultrasonic irradiation, the Fe0 surface area is increased, the reactive surface is cleaned continuously and the mass transfer rate is enhanced. It is hypothesized that initially iron metal is corroded in the presence of H2O2 under acidic conditions oxidizing Fe° to Fe2+, which then further reacts with H2O2 in a Fenton-like process to generate hydroxyl radicals and Fe3+ [16]. The Fe° then reduces the Fe3+ back to Fe2+ and the cycle continues. The possible

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free radical reactions occurring in the presence of iron species bound to the surface of the catalysts (Fe2+/Fe3+) and H2O2 are given below:

Use of iron powder also results in enhanced cavitational activity by virtue of surface cavitation. Presence of solid phase tends to provide additional nucleation sites due to deformities favoring the process of cavitation inception.

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Reactors designs for combination of Acoustic cavitation and Fenton chemistry Generally speaking, the studies related to combination of acoustic cavitation and Fenton based processes have been mainly carried out at laboratory scale operation using conventional ultrasonic horn or ultrasonic bath type of reactors. Typically low frequencies of irradiation have been used successfully though some studies refer to the use of high frequency irradiation [17-19]. It should be noted here that the scale up prospects of horn type systems, especially at lower frequency operation, are very poor as it cannot effectively transmit the acoustic energy into large process volume. Also, they suffer from erosion and particle shedding at the delivery tip surface, they may also be subject to cavitational blocking (acoustic decoupling), and the large transducer displacement increases stress on the material of construction, resulting in the possibility of failure. Thus, ultrasonic horn type systems are generally recommended for laboratory scale investigations. Very recently Dion [20] have described a new continuous reactor design based on the high power converging acoustic waves in a tube to produce a relatively large volume confined acoustic cavitation zone in flowing liquid reagents under pressure. It has been reported that the new cylindrical sonoreactor design does not contaminate the processed liquids with erosion products since the cavitation zone is maintained away from the wall of the tube. The processing capacity of the largest models may be up to several tons per hour, depending on the required cavitation energy per unit volume to produce the desired process enhancement, using an electric power input of about 50 kW. The

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application of this design however needs to be tested for wastewater treatment applications especially for combination with advanced Fenton process where solid particles will be used. The designs based on multiple transducers irradiating either same or different frequency are most feasible designs for large scale operation. To increase the active zones existing in the reactor, one can easily modify the position of the transducers so that the wave patterns generated by the individual transducers overlap, also resulting into uniform and increased cavitational activity. More recent developments have employed direct bonding of the transducer to the surface of the vessel. Improvements in the bonding method, and a move to transducers with lower individual outputs, have enabled the move to systems with large numbers of transducers to give an acoustic pattern that is uniform and noncoherent above the cavitational threshold throughout the working volume. Arrangements such as tubular reactors with two ends either irradiated with transducers or one end with transducer and other with a reflector [21], parallel plate reactors with each plate irradiated with either same or different frequencies [22] and transducers each on sides of hexagon [23] can be constructed. A schematic representation of some of these reactor configurations, which have a great possibility of application at large scale operation, has been shown in Figure 1. The use of multiple low-output transducers gives the additional advantage of avoiding the phenomenon of cavitational blocking (acoustic decoupling), which arises where power densities close to the delivery point are very high. In addition these multi-transducer units very effectively concentrate ultrasonic intensity towards the central axis of the cylinder and away from the vessel walls, thus reducing problems of erosion and particle shedding.

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Overview of literature and guidelines for optimum operating parameters: We now overview some representative recent applications related to the use of combined sonochemistry and Fenton oxidation for treatment of pollutants present in wastewater with an objective of providing guidelines for optimum operating parameters in terms of sonic intensity, frequency of irradiation, oxidant dosage, ratio of Fe2+ to hydrogen peroxide, operating pH etc. which can maximize the extent of degradation at possibly lower energy consumptions and operating costs. Neppolian et al. [24] reported the application of combination technique for the degradation of methyl tert-butyl ether (MTBE). The reactor used was made up of borosilicate glass with a capacity of 150 ml equipped with ultrasonicator. The reactor was double walled type and cooling water was circulated between the walls of the reactor to maintain the temperature at 200C. Sonication was employed at 20 kHz operating at 40% power amplitude. It has been reported that the reaction followed pseudo first order rate kinetics. The reaction rate constant decreased with an increase in the initial concentration of MTBE whereas higher operating power density for ultrasonic irradiations favored the degradation of MTBE. The results also showed that addition of Fe+2 ions has no influence on the degradation of MBTE by ultrasound without H2O2. This is due to the fact the concentration of both Fe+2 ion (added) and H2O2 produced during ultrasound was very less and hence there was no Fenton’s reaction in absence of externally added H2O2. It has been reported that complete degradation of MTBE was observed within 3 h in US/Fenton process, whereas 49% and 48% degradation occurred in the case of only Fenton process and only ultrasound respectively.

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Parag R. Gogate Cooling water-in

Thermocouple

Cooling water-out

Transducers Cooling pipe

25 kHz

40 kHz

Rectangular Flow Cell

Reaction mixture

Transducers

Ultrasonic Bath

T1

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T6

T2

Quartz tube Reactants

T5

T3 T4

Ultrasound Transducers Quartz tube Hexagonal Flow Cell Figure 1: Schematic representation of multiple transducer based sonochemical reactors.

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Papadaki et al. [25] investigated the application of a horn type sonifier capable of operating either continuously or in a pulse mode at a fixed frequency of 20 kHz and a maximum electric output power of 250 W for treatment of phenolic compounds. FeSO4.7H2O was used as Fenton’s reagent and the operating temperature was maintained constant at 350C. It has been observed that only 10, 15 and 20% removals are obtained for phenol, dichlorophenol and chlorophenol respectively using only ultrasonic irradiations. The degradation efficiency was highest for the Fenton process among US, Fenton and US/Fenton processes. It might be due to that, iron ions and the ultrasound compete for H2O2 decomposition through different routes which could involve, catalytic decomposition to hydroxyl radicals or thermal decomposition to water and oxygen rather than to reactive radical species. Guo et al. [26] investigated the degradation of 2,4 dinitrophenol (DNP) using an ultrasonic horn and the reactions were carried out in a cylindrical water jacketed glass vessel (75 ml). The temperature was maintained around 150C using cooling water. Ultrasonic pulses (20 kHz, on/off = 1s/1s) were used to initiate the degradation reaction. The degradation of DNP was studied under varied concentration of Fe2+ (100 mg/l, 300 mg/l and 500 mg/l). The total reaction time for the comparison purpose was 60 minutes. It has been reported that increasing the output sonication intensity as well as the H2O2 loading favored the degradation of DNP. To give a quantitative idea, the observed extents of degradation of DNP in US, Fe+2/H2O2 and US/Fe+2/H2O2 was found to be 4%, 82% & 98% respectively after 60 minutes. Ioan et al. [27] investigated the effect of sonochemical treatment at low frequency (45–47 kHz) on the Fenton degradation of low concentration aqueous solution of bisphenol A (BPA). The sonochemical reactor used in the investigation was a typical ultrasonic bath reactor with rated power dissipation of 500 W. It has been observed that the degradation efficiency of BPA is the highest at operating pH of 4. Further the degradation rate of BPA increased with increasing initial Fe2+ concentration and was faster with sono-Fenton as compared to Fenton oxidation alone. Sun et al. [28] investigated the combination of sonochemical oxidation and Fenton chemistry for the degradation of Azo dye acid black 1 (AB1) using an ultrasonic cleaner with a frequency of 40 kHz. A 100 ml conical flask with a plane bottom of thin glass was used as a reactor and was located in the maximum energy area. Low concentration iron (< 3 mg/l) of Fenton process has been used to treat wastewater. 0.5 mg/ml of various inorganic anions were added to conical flask before Fenton ion. It has been reported that the degradation of AB1 increased with an increase in the Fe+2 dosages. Further, the decoloration efficiency increased with an increase in H2O2 dosage but too high H2O2 resulted in lower degradation rates due to the scavenging effects of H2O2 and the recombination of OH·. The degradation of AB1 was inversely proportional to initial AB1 concentration. The rate of redox reaction could be accelerated by increasing the temperature, so higher temperature increased the reaction rate between H2O2 and Fe+2 ions, thereby increasing the rate of generation of OH· as well as degradation rate of AB1. Cravotto et al. [29] investigated degradation of nonylphenol using a cylindrical cup-horn type reactor operating at 300 kHz with 120 W as the power dissipation. It has been reported that use of ultrasound or Fenton chemistry alone did not result in any degradation of nonylphenol but the combination approach resulted in almost 95% degradation for 100 ppn initial loading of the pollutant. Also the extent of removal was strongly dependent on the initial concentration of nonylphenol with extent of degradation reducing to 66% for 1000 ppm initial concentration. The treated stream showed improved biodegradability as compared to

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the nonylphenol. The combined treatment strategy resulted in about 90% removal for the 1000 ppm initial concentration stream. Song et al. [30] investigated the degradation of CI acid red 88 dye in an aqueous solution using a combination of ultrasonic irradiations and Fenton’s process. The sonochemical reactor used in the investigation was a cleaning tank type reactor operating at 40 kHz and maximum power rating of 250 W. The effluent solution was taken in a 100 ml capacity glass reactor immersed in water (indirect irradiations). It has been reported that the combination of ultrasonic irradiation and low concentration iron of Fenton’s reagent can be more useful in the degradation of Acid Red 88 in aqueous solution, giving an enhancement in degradation ratio in comparison with the individual methods. The optimum conditions for the degradation of Acid Red 88 in aqueous solution was: 1.96 mmol/L of H2O2, 0.108 mmol/L of Fe2+, pH 3.0 and the maximum degradation efficiency of 98.6% was achieved within 135 min under these optimum conditions. It has been also observed that the degradation of the dye increased with increasing H2O2 concentration at constant loading of the Fe2+. Also at a constant loading of the oxidant, increasing the concentrations of Fe2+ beyond an optimum value did not result in any increase in the extent of degradation possibly attributed to the fact that the initial formation rate of hydroxyl radicals originating mainly from the decomposition of H2O2 was so high that much of the hydroxyl radicals were consumed by side reactions before they could be utilized effectively for removal of the dye. Pradhan and Gogate [31] investigated the application of combination of sonochemical reactors and Fenton chemistry for degradation of p-nitrophenol. The sonochemical reactor used in the work is basically an ultrasonic bath equipped with single large transducer having longitudinal vibrations. The ultrasonic bath has an operating frequency of 25 kHz and rated power output of 1 kW. Three ratios of FeSO4:H2O2 viz. 1:5, 1:7.5 and 1:10 were incorporated to study the effects of FeSO4 loading as well as H2O2 concentration. It has been reported that the extent of degradation of p-nitrophenol using the combination of ultrasound and conventional Fenton process is much higher as compared to the combination of ultrasound and H2O2 or the individual operation of ultrasound/Fenton chemistry. Investigations with varying oxidant loadings in terms of different loadings of FeSO4 and hydrogen peroxide indicated that the extent of degradation is marginally higher at higher loading of FeSO4 at a constant loading of hydrogen peroxide whereas an optimum concentration of hydrogen peroxide exists for constant loading of FeSO4. These observations are consistent with earlier reported results for pollutants like Acid black 1 [28] and Acid Red 88 [30]. It has also been observed that H2O2 concentration was more controlling in deciding the extent of degradation of p-nitrophenol. Maximum extent of degradation of 57.6% was observed for 0.5% pnitrophenol solution at 1 g/l FeSO4 loading and 5 g/l of H2O2 concentration. Beyond 5 g/l concentration of H2O2, extent of degradation was lowered due to scavenging effect of the excess concentration of H2O2. The optimum loading of hydrogen peroxide was found to be also dependent on the initial loading of the pollutant. For 1% p-nitrophenol solution, the optimum H2O2 concentration was 7.5 g/l where maximum degradation of 52.2% has been observed. Zhang et al. [32] have also reported similar existence of optimum loading of hydrogen peroxide for the degradation of CI reactive black 8 using a sonicator operating at 20 kHz frequency and 250 W as the rated power dissipation. It has been shown that the decolorisation efficiency and COD removal efficiency increased almost linearly with the increase in H2O2 concentration till the optimum level and further increase in H2O2 concentration produced less removal efficiency. It has been also established in the work that

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the combination of ultrasound and Fenton chemistry did not affect the decolorisation efficiency significantly but overall COD removal efficiency was intensified substantially. It would be now worthwhile to overview some of the recent applications depicting the use of advanced Fenton process based on the use of iron metal and hydrogen peroxide in combination with sonochemistry. The important advantage in terms of using iron metal is lower costs of operation attributed to the fact that waste iron particles or mixture of ores/sludge etc can also be used as a source of oxidant. Also the presence of solid phase in the system is likely to increase the cavitational activity in the reactor which can lead to overall beneficial results for the combination approach. Hung and Hoffmann [33] have studied the sonochemical destruction of carbon tetrachloride in the presence of elemental iron. The reactor configuration consisted of a 300 ml cell irradiated with Branson 200 sonifier operating at 20 kHz and power dissipation of 62 W. The degradation was reported to be complete within 90 minutes irradiation time for an initial concentration of 10-4 M at operating pH of 7; it was almost 40 times faster as compared to oxidation by iron alone. It has been also observed that the enhancement observed due to the presence of iron in the powder form was 8 times more as compared to iron turnings even though the total catalyst mass was same. This can be attributed to the increased surface area available in the case of iron powder. The degradation was also reported to increase with an increase in the mass of iron but only till an optimum value. The optimum value again is dependent on the type of pollutant. Hung et al. [34] have reported that the destruction of nitrobenzene continuously increased with an increase in the iron loading in the range 0 to 88 g/lit. Hung et al. [33] also studied the dependence of reaction rate on the power density (power dissipation per unit volume) and reported that the rate increased by almost 100% with an increase in the power density from 39 to 73 W/ml but further increase to 139 W/ml, increased the rate by only 50%. The observed effect of the power density for the combined process is quite similar to that observed for the individual sonication operation. The observed optimum power density levels can be attributed to the fact that at higher intensities of irradiation, there exist a large number of gas/vapor bubbles in the solution, which scatters the sound waves to the walls of the vessel or back to the transducer. This scattering is also enhanced by the presence of solid particles in fully suspended form (higher projected surface area as well) at higher levels of power dissipation. This point is quite important due to the fact that one might expect that an increase in the power dissipation might lead to enhanced turbulence leading to good surface cleaning and elimination of mass transfer effects. Optimum power density may be dependent on the concentration of iron mass and the pollutant as well as the reactor configuration and more studies are required in this direction to establish some generalized trends in terms of optimum concentration of iron as well as magnitude of power density. Neppolian et al. [35] investigated the degradation of para-chlorobenzoic acid (p-CBA) using sonolysis, Fenton-like oxidation (FeOOH–H2O2), and a combination of the two processes. For Fenton like process FeOOH (Goethite) has been used. It has been observed that with an increase in the operating pH, the degradation efficiency of p-CBA decreased and the optimum value was at pH 3. An increase in the FeOOH concentration increased the H2O2 decomposition which in turn resulted in a faster degradation of p-CBA whereas the rate of degradation of p-CBA increased slightly with increase in H2O2 concentration at fixed loading of FeOOH. The first-order rate constant, k, for p-CBA degradation by ultrasound was 4.5 × 10−3 min−1 and Fenton-like process alone, it was observed to be 7.3 × 10−3 min−1. The

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combination technique resulted in much higher values of degradation rate constant (1.54 × 10−2 min−1). For the combination technique, the extent of degradation was found to be dependent on the ultrasonic power density, which controls the extent of mixing and turbulence generated in the system due to acoustic streaming. The observed rate enhancements for the degradation of p-CBA can be attributed primarily to the continuous cleaning and chemical activation of the FeOOH surfaces by acoustic cavitation and the accelerated mass transport rates of reactants and products between the solution phase and the FeOOH surface. Zhang et al. [36] investigated the effectiveness of combination of ultrasound and iron powder (US/Fe0) for the decolorization of azo dye using C.I. Acid Orange 7 as a model compound. Sonication was performed with an KS-250 ultrasonic generator (250 W, 20 kHz) equipped with a titanium probe transducer. The tip of the probe was 1 cm in diameter and was placed 2 cm into the liquid layer. The sonication was administered in pulses with a 50% duty cycle. The reactor was immersed into a water bath to keep the temperature around 200C. It has been reported that the extent of decolorisation is 91% in the coupled US/Fe0 system, 63% in Fe0 system, while ultrasound alone had a negligible effect on the decolorisation. The observed enhancement in the extent of decolorisation due to the use of ultrasound has been attributed to the indirect chemical effects associated with the continuous ultrasonic cleaning and activation of the Fe0 surface and the enhancement of mass transfer resulting from the turbulent effects of cavitation. The decolorisation was also reported to strongly dependent on the operating pH. To give a quantitative idea, at an operating initial pH of 3, the extent of decolorisation was 91%, but at neutral pH, the extent of decolorisation was significantly reduced to only 15%. Also, the decolorisation of C.I. Acid Orange 7 by US/Fe0 was found to be directly proportional to the iron loading in the reactor. It has been also reported that the decolorisation of C.I. Acid Orange 7 fits the first order kinetic model. Dai et al. [37] investigated the degradation of pentachlorophenol (PCP) using an ultrasound generator (600 W power dissipation and operating frequency of 40 kHz) equipped with two glass vessels. Iron powder was added in one glass vessel for the combined process of ultrasound and iron and the other glass vessel was used for US system in the absence of Fe0. A stirrer was equipped in the two vessels to achieve uniform suspension of iron powder and cooling water was used to keep the temperature of the reactor at 20 ± 20C. Kinetic studies revealed that the degradation of PCP followed first order kinetic model. The degradation rate constant of PCP by US/Fe0 was greater than the sum of the individual rate constants in the US and Fe0 system. Quantitatively, the rate constant in the US/Fe0 system was a factor of 4.2 greater than that in the US system, and a factor of 14.8 greater than that in the Fe0 system. Experiments with addition of a radical scavenger, t-Butyl alcohol, indicated that the degradation efficiency of PCP decreased with the increase of concentration of t-BuOH in solution, and the degradation was nearly quenched in the presence of 50 mM t-BuOH. The results conclusively establish that most of the degradation in the combined system (US/Fe0) proceeds via hydroxyl radical formation and the subsequent attack on the pollutant. Zhang et al. [38] investigated the degradation of CI reactive black 8 dye using a combination of ultrasonic irradiations and zero valent iron metal. A magnetic stirrer was provided for complete mixing of the solution in the reactor as often the acoustic streaming generated by ultrasound is not sufficient to ensure complete suspension of the solids. It has been conclusively established that the presence of ultrasonic irradiation enhanced the decolorisation of CI Reactive Black 8. Further, the decolorisation efficiency decreased with

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increasing pH, but increased with increasing iron addition and temperature. Decolorisation occurs at the Fe0/H2O interface and increasing iron addition would provide more surface active sites. In the Fe0 system, initial dye concentration had little effect on the decay constant, however the decay constant decreased in coupled US/Fe0 system. Liang et al. [39] studied the effects of three kinds of solid Fe-containing catalysts, namely iron powder, basic oxygen furnace (BOF) slag and mill scale on the degradation rate of 4chlorophenol (4-CP) in aqueous solutions containing hydrogen peroxide. The combination of ultrasonic irradiation with the addition of iron powder or mill scale resulted in a significant enhancement to the 4-CP degradation rate depending on the amount of H2O2 addition to the solution and the initial operating pH. The maximum intensification was obtained when 1 g/l of iron or mill scale powder was added to the 4-CP solution containing 100 mg/l of H2O2 at pH of 3. Under these conditions, 4-CP was completely decomposed within 2 min of ultrasonic irradiation when its initial concentration in the solution was 100 mg/l. BOF slag had little catalytic effect on the degradation of 4-CP because it contains calcium oxide with a certain ratio, which reduces the acidity of solution on dissolving. Measurements revealed that the solution pH increases up to 11 when 1 g/l of slag was added. Under such a high pH, iron ions cannot be produced, and hence the Fenton-like system conditions are not fulfilled. Thus, it is important to maintain acidic conditions for obtaining the synergistic effects. Namkung et al. [40] investigated the combination of a bath type sonicator with advanced Fenton process for degradation of phenol. The power measured using the calorimetric method was 3.2 W and the frequency of sonication was 20 kHz. Additional studies were also undertaken with a cuphorn reactor (diameter: 11.5 cm) operating at 20 kHz frequency and a variable power dissipation over the range of 0 to 600 W. The operating temperature was maintained at 25 ± 10C and the time of treatment was fixed at 90 min. It has been reported that the initial concentration of phenol and H2O2 loading significantly affected the TOC removal rate for the individual operation of advanced Fenton process though the changes in operating temperature over the range 140C to 420C had negligible influence on the extent of TOC removal. Under ultrasound irradiation, a marked increase of iron concentration in the solution was observed indicating that the ultrasound has a significant effect on the corrosion process of the iron surface. The main reason for enhanced corrosion by sonication is ascribed to removal or destruction of passivation films on the metal surface by cavitation effects. In such a case, active corrosion increases at the pristine metal surface. The extent of iron released into the solution was also found to be dependent on the ultrasonic power dissipation and it increased with an increase in the power dissipation. Surprisingly, though the extent of iron released into the solution and hence available for Fenton chemistry increased due to the use of ultrasound, the TOC removal trend was similar to that observed for operation without the use of ultrasound. This may be ascribed to recalcitrance of the fragmented small molecules formed as the result of phenol oxidation. It should be also noted here that the obtained result for similar extents of TOC removal is very specific to the system investigated in the present work and cannot be generalized. Zhou et al. [41] investigated the degradation of 2,4 dichlorophenol (DCP) using a combination of ultrasound and Fe/EDTA system. Comparison of experiments related to degradation efficacy of different approaches showed that the degradation of the DCP was the maximum in the combination technique US/Fe/EDTA as compared to US/Fe approach and least for the use of ultrasound alone. Low DCP removal rates via Fe and US/Fe system were attributed to the stable structure of CPs, which makes it difficult to substitute chloride in the

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aromatic ring by hydrogen atom generated in Fe system. Quantitatively speaking, the kinetic rate constant for the combination approach was 32 times higher as compared to US alone. Fe/EDTA and the hydrogen peroxide generated insitu in the system results in Fenton like reactions, efficacy of which is further enhanced due to the presence of ultrasound attributed to improvement of mass transfer and solid surface cleaning. EDTA combines with ferrous to form a series of organic ligands, which then break down O-O bond of oxygen & eventually produce H2O2. Complete degradation of DCP was achieved in US/Fe/EDTA system after 1 h reaction. The extent of degradation was also found to be strongly dependent on the concentration of Fe and EDTA whereas no significant dependency was obtained on the DCP concentration over the concentration range of 50 to 150 mg/l. Liang et al. [42] have investigated the removal of nitrite by ultrasound-dispersed nanoscale zerovalent iron (NZVI) particles. NZVI particles used were nearly spherical with a size range of 20 – 80 nm. It has been reported that ultrasonication itself could not cause any reduction of nitrite even after 60 minutes when NZVI was not present. The combination of ultrasound and NZVI yielded much better results as compared to reduction due to NZVI alone possibly attributed to the improvement in the mixing and dispersion of NZVI due to the turbulence and acoustic streaming caused by ultrasound. An important finding of the work is that initial solution pH did not have a strong effect on the nitrite reduction rate. Thus it was concluded that the application of this technique does not require a harsh low pH environment and allows a wider range of pH. Also the removal efficiency of nitrites decreased with increase in initial nitrite concentration, which is typically observed for sonochemically induced degradation of pollutants. Oturan et al. [43] have reported a novel hybrid treatment scheme, described as sonoelectroFenton (sono-EF) process, based on the use of ultrasonic irradiations coupled with in situ generation of Fenton’s reagent using electrochemical technique. Use of ultrasound can result in enhanced mass transfer into the solution due to enhanced turbulence and acoustic streaming leading to improved micro-mixing. An undivided electrolytic cell with a Pt anode and a three-dimensional carbon-felt cathode has been used to carry out the very effective electro-Fenton (EF) process at constant current, which allows the production of great amounts of hydroxyl radicals. The model pollutants investigated in the work is a commonly used herbicide, 4,6-dinitro-o-cresol (DNOC), 2,4-dichlorophenoxyacetic acid (2,4-D) and dye azobenzene (AB). It has been observed that synergistic effects are obtained for the degradation of 2,4-D and DNOC whereas for AB, which is easily degradation, use of ultrasound did not result in much improvement in the efficacy of electroFenton processes. The synergistic effects were observed to independent of the frequency of irradiation suggesting that the main contribution to the oxidation process arises from Fenton’s reaction and not from the effects of sonication on organics. In contrast, the output power has been found to be greatly influencing the sono-EF process performance and 20W was reported to be the optimum power as higher values hamper the dissolved O2 concentration and, consequently, affects the cathodic H2O2 electrogeneration required for Fenton’s reaction. Zhang et al. [44] have investigated the degradation of CI acid orange 7 using a combination of ultrasound and the advanced Fenton process (AFP, zero-valent iron and hydrogen peroxide). The work deals with study of the effect of hydrogen peroxide concentration, initial pH, ultrasonic power density, dissolved gas, and iron powder addition on the extent of decolorization. The results showed that the decolorization rate increased with the increase of hydrogen peroxide concentration and power density, but decreased with the

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increase of initial pH value. An optimal iron powder loading exists at which maximum decolorization efficiency is observed. The presence of dissolved gas enhanced the extent of color removal, and the enhancement was more significant when dissolved oxygen was present. Bremner et al. [45] have investigated the influence of different ultrasonic frequencies ranging from 20 to 1142 kHz on the efficiency of the US/Fe2O3/SBA-15/H2O2 (sono-Fenton) system. It has been established that the optimum frequency of ultrasonic irradiation is 584 kHz for the degradation of aqueous phenol solutions by the sono-Fenton system. Use of this optimum frequency of irradiation resulted in complete removal of phenol after 30 min and typical aromatic by-products of oxidation, such as catechol, hydroquinone or benzoquinones are also not detected after this time. The effect of different variables, such as hydrogen peroxide concentration or catalyst loadings in the reaction was studied by factorial design of experiments at this optimum operating frequency. Catalyst loadings of 0.6 g/L and hydrogen peroxide concentration, close to the stoichiometric amount, show high organic mineralization, accompanied by excellent catalyst stability in a wide range of concentrations of aqueous phenol solutions (0.625–10 mM). Additionally, the catalyst can be easily recovered by filtration for reuse in subsequent reactions without appreciable loss of activity. The coupling of US (584 kHz)/Fe–SBA-15/H2O2 at room temperature have been thus established as a promising technique for wastewater treatment. The work also reports a new approach of latent remediation where ultrasonic irradiation has been used only as pretreatment for 15 min in an attempt at reducing the cost of the degradation process. It has been observed that latent remediation provides TOC degradation of around 21% after 15 min sonication followed by 6 h silent reaction while the typical sono-Fenton reaction affords 29% TOC reduction after 6 h sonication. Segura et al. [46] reported a novel approach based on the ultrasound and Fenton like processes by introducing additional photocatalytic oxidation into the hybrid treatment scheme. The efficacy of the different combination schemes using Fenton-like processes (H2O2/Fe2O3–SBA-15) for degradation of phenol has been assessed. The sequential system evidences an enhancement in terms of phenol and TOC conversions compared to the ultrasound or UV–light irradiation processes. A total phenol degradation and 90% TOC reduction were achieved by sequentially using ultrasound followed by UV–visible light irradiation. These effects are ascribed to cavitation effect of ultrasound producing a reduction of particle size that provides a higher amount of available active sites due to an increased surface area for the subsequent photo-Fenton system. Also the simplified energy cost assessment of all processes reported in the work indicated that the sequential US-UV process also shows the best cost-effective ratio for mineralization of phenol. Another important aspect of the work is that the solid Fe2O3–SBA-15 catalyst used for this study evidenced a high stability under the operation conditions of ultrasound and UV–light irradiations during both oxidation processes and the amount of iron leached out into the resultant aqueous solution after reaction is reported to be always lower than 4 mg/L, which is within the limits stated in the EU water legislation. Thus, the approach of using proper design of the supported catalyst shows a direction to limit the TDS related problems in the conventional Fenton processes. In another very recent study, Pradhan and Gogate [31] have investigated the use of advanced Fenton process, on similar lines as the conventional Fenton chemistry, for quantifying the extent of degradation of p-nitrophenol under different operating conditions. In this case, iron powder of 100 mesh size was used in place of FeSO4, 7H2O as the oxidant.

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Unlike FeSO4, iron powder is insoluble in water and hence stirring was provided so that iron powder is well suspended in the reactor and it gets evenly distributed in the reactor. It has been observed that maximum degradation of 66.4% was obtained at 1 g/l of Fe dosage and 5 g/l H2O2. Beyond 5 g/l of H2O2 concentration the degradation was lowered as in the case of conventional Fenton process. For 1% p-nitrophenol solution, maximum degradation of 59.2% was observed at 1 g/l Fe dosage and 7.5 g/l of H2O2 concentration. Beyond that there was no increase in the degradation even with higher concentration of H2O2 due to scavenging effect on the OH· radicals. The extent of degradation was higher in the case of advanced Fenton process as compared to the conventional Fenton process at equivalent loadings. Ultrasound in combination with AFP yielded about 10% more degradation than ultrasound combined with conventional Fenton process. Based on the discussion of different investigations related to the use of the combination approach of ultrasound and Fenton based processes, we now give firm recommendations for optimization of the different operating parameters for maximizing the extent of degradation using the combination approach: 1.

It is recommended to use optimum ratio of ferrous irons/iron metal and hydrogen peroxide as too much hydrogen peroxide can result in scavenging action. Also usually by increasing the concentration of iron, a higher formation of hydroxyl radicals is generated, but after a certain iron concentration, no further enhancement in the extent of degradation is observed. Higher concentrations of iron result in a greater operating cost and a faster disappearance rate of ferrous ion as well as hydroxyl radicals by side reactions thereby decreasing the overall efficacy.

2.

It is also important to consider the residual amount of the added ferrous/ferric salts or iron metal along with the total concentration of the dissolved solids. An infinite increase in the TDS content of the effluent is not permitted as it leads to low gas solubility, ionization of the salts and also leads to lower biodegradation rates. The problem of TDS content in the treated effluent can be effectively handled by designing the matrix of the supported catalysts or using a specific form of Fenton catalyst which will be easily separable after the treatment of the target effluent stream.

3.

The change of pH also has significant effects on the performance of combined ultrasound/Fenton process. At pH greater than 4, the system efficiency is decreased since iron ions are in the hydroxide form. Typically acidic conditions are recommended through some recent studies using nanoscale iron have revealed that effect of pH is not important when nanoscale iron is used. However, this needs to be verified for a wider range of pollutants, before firm recommendations can be established.

4.

Ultrasonic power density is another important factor which will decide the efficacy of the combined process. Typically increase in the ultrasonic power density has been observed to be favoring the combination technique though an optimum value needs to be maintained as a drastic increase in the power dissipation is likely to result in acoustic decoupling phenomena limiting the passage of ultrasonic energy into the system.

5.

Optimum frequency of irradiation has been reported to exist at which maximum degradation of the pollutants is observed. Typically the optimum value is in the range of 200 to 600 kHz, though it is always better to use low frequencies of irradiations due to

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the erosion problems associated with high frequency sonochemical reactors at industrial scale operations. 6.

Recent studies have also indicated that a new approach of latent remediation can be used for efficiently reduce the cost of the degradation process as the approach requires that ultrasonic irradiation, which is the most cost intensive operation, is used only as pretreatment (typically for 15 – 30 min time). The validity of this approach, however, needs to be tested for different pollutants, most importantly for actual industrial systems.

7.

The efficacy of combined operation can be further enhanced by using additives either to increase the cavitational activity in the reactor (by using dissolved gases) or to increase the oxidation capacity of the system (by using chemicals such as EDTA or CCl4 which decompose under the ultrasonic action thereby generating additional free radicals to give a series of reactions).

8.

Use of hybrid treatment strategies such as photocatalytic oxidation or electrochemical oxidation in combination with ultrasound/Fenton based processes have also been reported to be beneficial though it is recommended to evaluate the total economics of the process as synergistic effects may not be always observed by combining many oxidation techniques.

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COMBINATION OF HYDRODYNAMIC CAVITATION AND FENTON PROCESSES: Hydrodynamic cavitation, which generates similar effects as the well established acoustic cavitation, has long being known for its detrimental effects and tackled accordingly. However, over recent years, it has been realized that hydrodynamic cavitation can indeed be applied to improve the energy efficiencies of chemical and physical processing applications [47] and same holds good for the application to wastewater treatment either alone or in combination with advanced oxidation processes such as Fenton chemistry based processes. In line with the focus of the paper, we will overview different applications reporting the beneficial effects of combination techniques. The expected mechanism for the intensification of efficacy for wastewater treatment as compared to individual operation remains exactly identical to that discussed earlier for the combination of ultrasound and Fenton based processes as the controlling action is based on the cavitational effects which are same in both the cases. It would be worthwhile to understand in depth the mechanism of generation of hydrodynamic cavitation and the available reactor designs for better understanding of the subject. Hydrodynamic cavitation can simply be generated by using a constriction such as an orifice plate, venturi or throttling valve in a liquid flow. If the throttling is sufficient to cause the pressure around the point of vena contracta to fall below the threshold pressure for cavitation (usually vapor pressure of the medium at the operating temperature), cavities are generated. Subsequently, as the liquid jet expands reducing the average velocity, the pressure increases, resulting in the collapse of the cavities. Very high intensity fluid turbulence is also generated downstream of the constriction; its intensity depends on the magnitude of the pressure drop and the rate of pressure recovery, which, in turn, depend on the geometry of the

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constriction and the flow conditions of the liquid, i.e., the scale of turbulence [48-49]. The intensity of turbulence has a profound effect on cavitation intensity. Thus, by controlling the geometric and operating conditions of the reactor, the required intensity of the cavitation for the desired physical or chemical change can be generated with maximum energy efficiency.

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Reactor designs for hydrodynamic cavitation and Fenton chemistry: It should be noted here that not many reports can be found based on the use hydrodynamic cavitation and Fenton chemistry as this is relatively a new field of application. Thus we will discuss all the available hydrodynamic cavitation reactor configurations as addition of Fenton’s reagent can be achieved in all these configurations and then the combination approach can be investigated for the specific wastewater treatment problem. For the case of advanced Fenton process, however, all the designs may not be feasible because of the use of solid particles such as iron metal or furnace slag etc. In such cases specific modifications are required in the reactor configuration which has been also highlighted later. A commonly used device based on hydrodynamic cavitation phenomena is the high pressure homogenizer, which is, in essence, a high pressure positive displacement pump with a throttling device that operates according to the principle of high-pressure relief. Typically, a high pressure homogenizer reactor consists of a feed tank and two throttling valves, designated as first stage and second stage, to control the operating pressure in the hydrodynamic cavitation reactor. There is a critical discharge pressure at which cavitation inception occurs, and significant cavitational yields are obtained beyond this discharge pressure. However, there is not enough control over the cavitationally active volume and the magnitude of the pressure pulses that will be generated at the end of the cavitation events (cavitational intensity), thereby limiting the scope of application. Cavitation can also be generated in rotating equipment. When the tip speed of the rotating device (impeller) reaches a critical speed, the local pressure near the periphery of the impeller drops and approaches the vapor pressure of the liquid. This results in the generation of vaporous cavities. Subsequently, as the liquid moves away from the impeller to the boundary of the tank, the liquid pressure recovers at the expense of the velocity head. This causes the cavities that have traveled with the liquid bulk to collapse. Again, similar to the high pressure homogenizer, there exists a critical speed for the inception of cavitation. It should be noted that the energy consumption in these types of reactors is much higher, and flexibility over the design parameters is hardware-dependent as compared to reactors based on the use of multiple-hole orifice plates. In reactors based on the use of orifice plates, the flow through the main line passes through a constriction where the local velocities suddenly rise due to the reduction in the flow area, resulting in lower pressures that may even decrease to below the vapor pressure of liquid medium. A schematic representation of the setup has been given in Figure 2. Choosing a correct flow arrangement in the hydrodynamic cavitation reactor system is of paramount importance to maximize the effects of cavitation in desired and cost effective manner. The constriction can be a venturi, a single hole or multiple holes in an orifice plate. Use of multiple-hole orifice plates helps achieve different intensities of cavitation. Additionally, the number of cavitational events generated in the reactor varies. Thus, the orifice plate set-up offers tremendous flexibility in terms of the operating (control of the inlet pressure, inlet flow rate, temperature) and geometric conditions (different arrangements of holes on the orifice

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plates, such as circular, triangular pitch, etc., and also the geometry of the hole itself, which alters the resultant fluid shear, leading to different cavitational intensities). The cavitation chamber can be modified so that the cavitation bubbles or nuclei are introduced in the flow externally, upstream of the nozzle using a sparger. Different gases can be used for the introduction of the bubbles. Also, the size of the gas distributor (usually a glass frit), flow rate of gas and the pressure of gas in the reservoir (or source) from which it is withdrawn can be suitably controlled in order to achieve the desired initial size of the cavitational nuclei, which significantly affects the resultant cavitational intensity. For the case of advanced Fenton processes, as solids are involved, a configuration represented in Figure 2 may not be feasible as it is likely that the solid particles will have a great impact on the cavitation chamber resulting in either erosion or blockage of the cavitation chamber. In such cases the solid particles need to be packed separately and introduced in the circulation loop of the wastewater. Figure 3 shows a schematic representation of such setup used for industrial wastewater treatment [50]. The configuration is based on the use of liquid whistle reactor but can be equally applied to other types of cavitation chambers namely orifice, venturi or throttling valves. The location of the iron bed also plays an important role in deciding the efficacy of the treatment scheme. The acceleration in the process performance with the respect to the catalyst bed location is due to the continuous cleaning of the active catalyst surface by the impingement of the liquid jet stream with high force at the iron metal surface and also by the collapsing micro bubbles at the reactive sites on the surface generated by the hydrodynamic cavitation. Due to these issues, the iron bed always needs to be downstream of the cavitation chamber and within optimum distance such the generated cavities travel that distance and impact the iron bed.

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Blade Orifice

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Figure 3: Schematic representation of the experimental setup for combination of hydrodynamic cavitation and advanced Fenton process.

Apart from the reactor configurations, the selection of the operating and geometric parameters also plays a crucial role in deciding the efficacy of hydrodynamic cavitation reactors. The magnitudes of collapse pressures and temperatures as well as the number of free radicals generated at the end of cavitation events are strongly dependent on the operating parameters and the configuration of hydrodynamic cavitation reactors. Bubble dynamics investigations can aid in obtaining some recommendations regarding the selection of optimum set of parameters. The detailed discussion into the bubble dynamics approaches in cavitational reactors is beyond the scope of present work; however the readers may refer to earlier work [49,51] for better understanding. In the present work only important considerations regarding the selection of operating parameters have been presented in Table 1. Liquid phase physicochemical properties also affect the cavitating conditions significantly. Aim should be to use liquids or conditions favouring the process of cavitation inception and also should result in cavities with lower initial size which would grow to a larger extent and give violent collapse and hence greater cavitational activity. Some recommendations for selection of liquid phase physicochemical properties have been made in table 2.

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Table 1. Optimum operating conditions for the Hydrodynamic Cavitation reactors No. 1

2

3

Property Inlet pressure into the system/Rotor speed depending on the type of equipment Diameter of the constriction used for generation of cavities e.g. hole on the orifice plate

Favorable conditions Use increased pressures or rotor speed but avoid super-cavitation by operating beyond a certain optimum value Optimisation needs to be carried out depending on the application. Higher diameters are recommended for applications which require intense cavitation whereas lower diameters with large number of holes should be selected for applications with reduced intensity Percentage free area offered for the Lower free areas must be used for producing flow (Ratio of the free area available high intensities of cavitation and hence the for the flow i.e. cross-sectional area desired beneficial effects of holes on the orifice plate to the total cross-sectional area of the pipe)

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Table 2. Guidelines for selection of liquid physicochemical properties No. 1.

Property Liquid Vapor pressure (Range: 40 to 100 mm of Hg at 30°C)

2.

Viscosity (Range: 1 to 6 cP) Surface tension (Range: 0.03 to 0.072 N/m) Bulk liquid temperature (Range: 30 to 70°C)

3. 4.

5.

Dissolved gas A. Solubility B. Polytropic constant and thermal conductivity

Affects Cavitation threshold, Intensity of cavitation, rate of chemical reaction. Transient threshold

Favourable Conditions Liquids with low vapor pressures

Size of the nuclei (Cavitation threshold) Intensity of collapse, rate of the reaction, threshold/ nucleation, almost all physical properties.

Low surface tension

Gas content, nucleation, collapse phase Intensity of cavitation events.

Low viscosity

Optimum value exits, generally lower temperatures are preferable

Low solubility Gases with higher polytropic constant and lower thermal conductivity (monoatomic gases)

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Overview of work in the area of wastewater treatment using combination of hydrodynamic cavitation and Fenton chemistry based processes: To get an insight into the optimum operating parameters, we will now overview different literature illustrations related to the combination of hydrodynamic cavitation and Fenton based processes for degradation of variety of pollutants. Chakinala et al. [52] were the first to report the combination of hydrodynamic cavitation generated using a liquid whistle reactor (LWR) and advanced Fenton processes (based on the use of iron metal particles) for treatment of phenolic wastewaters. The degradation was studied in semi-batch mode of operation and the effect of different operating parameters such as pressure, operating pH, H2O2 concentration and the concentration of industrial wastewater samples on the extent of mineralization of wastewater quantified in terms of the total organic carbon (TOC). It has been reported that typically higher pressures are more favorable for a rapid TOC mineralization. In continuation of the same work, Chakinala et al. [50] investigated the efficacy of combination approach in more details for treatment of industrial wastewater comprising mainly of phenolic compounds and another dyestuff industry wastewater. The treatment system consists of feed vessel tank with 5 L capacity, plunger pump with power consumption of 3.6 kW and an orifice (orifice area = 7.74 x 10-7 m2). Two types of effluents were treated with 80 gm of zero valent iron pieces and H2O2 (1900 ppm) for reaction time of 3-5 hrs. The temperature was maintained around 35 ± 30 C. Optimization, in terms of the extent of dilution, operating pressure and oxidant loading for maximizing the extent of degradation was achieved. It has been observed that higher pressure, sequential addition of H2O2 and lower concentration of the effluents are more favorable for rapid TOC mineralization. The acceleration in degradation of organic contaminants with increasing pressure can be attributed to enhancement of the hydroxyl radical production as a result of intensification of cavitation activity. A dilution ratio of 50, operating pressure of 1500 psi (10340 kPa) and two cycles of addition of hydrogen peroxide (each of 1900 ppm loading) was found to be optimum and the maximum TOC removal obtained under these conditions was about 336 mg/l (under diluted conditions) within a treatment time of 150 min. It has been also reported that step wise addition of the oxidant is more beneficial as it maintains low concentrations of hydrogen peroxide in the system at a given time. Chakinala et al. [53] reported the use of a multivariate design of experiments has been used to ascertain the influence of hydrogen peroxide dosage and iron catalyst loadings on the oxidation performance of the modified AFP. It has been reported that the influence of the catalyst loadings is negligible and the results seem to be only dependent on hydrogen peroxide concentration in the modified AFP. However, the presence of iron metal catalyst is necessary for mineralization of phenol as preliminary experiments indicated that the combination of hydrodynamic cavitation and hydrogen peroxide (without iron metal catalyst) does not result in any TOC removal. Thus, even if catalyst loading does not play a significant role in deciding the extent of degradation, its presence in the system is equally important. Another important investigation reported in the work included the effect of position of the catalyst bed. It is expected that the catalyst bed should be subjected to the influence of cavities generated downstream of the orifice to get maximum benefits. The acceleration/ enhancement in the process performance with respect to the catalyst bed location is due to the continuous cleaning of the active catalyst surface by the impingement of the liquid jet stream with high force at the iron metal surface and also by the collapsing microbubbles at the

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reactive sites on the surface generated by the hydrodynamic cavitation. It has been reported that the extent of TOC mineralisation was marginally higher (however not within the limits of the experimental errors for these experimental runs) when the catalyst bed was located near the orifice (57%) as compared to that observed at a location away from the orifice (53%). Similar results were obtained with measurements of the total dissolved iron content (concentration was 252 mg/L for near location and 243 mg/L for location away from the orifice). The results indicate that the intensity of hydrodynamic cavitation generated in the system is crucial in determining the dependency of the extent of degradation on the catalyst bed location. In the work of Chakinala et al. [53] due to very high inlet pressures into the cavitation chamber, it is expected that the cavitational intensity will be high to maintain the active cavitation zone over a distance of 50 cm away from the point of generation (orifice) and only a marginal decay in the intensity of cavitation is observed as indicated by a decrease in the TOC removal rates. It should be noted here that the location of the catalyst bed in the system is an important design parameter especially in the case of large scale industrial wastewater treatment plants where higher distances are expected and where low operating pressures are to be used based on a optimum design of the cavitation chamber. Bremner et al. [54] have reported the application of hydrodynamic cavitation reactor in combination with the advanced Fenton process for the degradation of 2,4 dichloro phenoxyacetic acid. Hydrodynamic cavitation was generated using a specially constructed unit, termed a Hydrocavitator. The system consists of a reservoir with a 25 L capacity, a triplex plunger pump (Speck NP25) with a maximum discharge pressure of 4500 psi, an orifice unit (orifice area about 7 × 10−7 m2) and a catalyst bed. The catalyst bed was filled with iron pieces (150 g) made from bending sheet iron (2 cm by 1 cm) in the middle. The heat exchanger used in the configuration ensures that the temperature does not rise above 30 °C. The temperature was kept at 18 ± 2 °C by the heat exchanger; the working pressure of 1500 psi was selected as being optimum for cavitation and the flow rate was 5.2 L/min. It has been reported that there is a rapid decrease in organic content within 20 min and thereafter the value remains the same at about 30% residual TOC content. The effectiveness of the degradation augmented by hydrodynamic cavitation is probably due to the combined effect of the advanced Fenton process in producing more hydroxyl radicals and super-efficient mixing provided by the Hydrocavitator. The work also provides some direct comparison between the efficacies of ultrasound and hydrodynamic cavitation assisted advanced Fenton processes. It has been reported that in 20 min of treatment time (beyond this time, the increase in the TOC removal is only marginal), the combination of acoustic cavitation and the advanced Fenton process gives around 60% TOC removal whereas 70% TOC removal is observed with hydrodynamic cavitation combined with the advanced Fenton process. The extent of energy supplied for generation of cavitation in the reactor system is approximately similar in both the cases (450 W/L) though the volume treated using hydrodynamic cavitation reactors is much higher as compared to acoustic cavitation reactor (8 L as compared to only 200 mL). Thus, it appears that hydrodynamic cavitation is more suitable for treating effluent at a much larger scale of operation as compared to acoustic cavitation generated using a horn type system. Pradhan and Gogate [55] have also recently established the utility of combination of hydrodynamic cavitation and Fenton process. Amongst the different cavitating devices investigated in the work, it has been reported that venturi results in more intense cavitation as compared to single hole orifice and higher inlet pressures are recommended for maximizing the extent of removal. Step wise addition of oxidant was found to be more beneficial for

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intensification of the removal of p-nitrophenol for a combination of hydrodynamic cavitation and hydrogen peroxide at higher loadings. For the combined use of hydrodynamic cavitation and Fenton chemistry, an optimum loading of FeSO4 as 1 g/l and H2O2 concentration as 5 g/l was observed for an initial p-nitrophenol concentration of 5 g/l and the maximum extent of removal under these conditions was 3.16 g/l. For 10 g/l initial p-nitrophenol solution, the maximum extent of removal was 5.62 g/l under optimized conditions. Efficacy of removal using the combined approach was found to be strongly dependent on the operating pH and pH of 3.75 was found to be optimum. Mishra and Gogate [56] have investigated the efficacy of combination of hydrodynamic cavitation and Fenton chemistry for the degradation of Rhodamine B using FeSO4:H2O2 in the ratio of 1:5 for 10 ppm initial concentration of the Rhodamine B at pH of 2.5 using venturi as the cavitating device. It has been reported that 99.9% degradation of Rhodamine B was obtained using the combination with TOC degradation of 57%. The obtained results for the enhanced efficacy of combination of hydrodynamic cavitation and Fenton chemistry can be attributed to the generation of higher quantum of free radicals due to the presence of Fe2+ ions. Pradhan and Gogate [55] have reported similar results for the combination of hydrodynamic cavitation with FeSO4:H2O2 in the ratio 1:5. It has been reported that the combination approach gave 63.2% degradation of p-nitrophenol as against 53.4% using only hydrodynamic cavitation. Comparing the extent of intensification obtained due to the use of combination approach, it can be said that the type of the pollutant also plays an important role in deciding the efficacy of the combination approach and those pollutants that have stronger affinity towards hydroxyl radicals are likely to be affected to a larger extent. In the work, the effect of operating temperature on the extent of degradation has also been reported. Degradation of rhodamine B is faster at higher operating temperatures. Quantitatively at the end of 5 minutes treatment, the extent of degradation is 93.5% at 30°C whereas at 40°C, the observed extent of degradation is 97.7%. For complete degradation of rhodamine B, the required time for operation at 40°C is around 15 minutes whereas at 30°C the complete degradation of the pollutant dye is achieved in 30 minutes of treatment. The obtained results as regards the effect of temperature can be attributed to the fact that the efficacy of Fenton process in terms of generation of hydroxyl radicals is significantly enhanced at higher operating temperatures. It should be also noted here that due to the fact that cavitational intensity decreases with an increase in the temperature due to formation of vaporous cavities which collapse less violently, it is not recommended to increase the operating temperature beyond 40 °C. This also depends on the availability of the dye wastewater at a particular temperature as it may not be always feasible to increase the temperature of the wastewater in actual practice due to the costs associated with heating a large quantum of wastewaters. Based on the discussion of different investigations related to the use of the combination approach of hydrodynamic cavitation and Fenton based processes, we now give firm recommendations for optimization of the different operating parameters for maximizing the extent of degradation using the combination approach: 1.

It is better to operate under acidic conditions in general and exact operating pH can be decided based on the specific pollutant under question

2.

Slightly higher temperatures (optimum would exist) are suitable for the combined operation and to avoid cost considerations, it might be recommended to use the

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temperatures at which the effluent is generally available (recommended range would be between 20 and 40 °C. 3.

For hydrodynamic cavitation reactor operation, optimum inlet pressures for the orifice/venturi type setup or optimum operating speed for reactors based on high speed rotation are recommended to maximize the effects

4.

For combination of hydrodynamic cavitation reactors and advanced Fenton process where a catalyst bed has been used, it is recommended to maintain an optimum distance of the catalyst bed and the cavitation chamber.

5.

For parameters related to Fenton chemistry, the recommendations made earlier in terms of oxidant loading and ratio of iron and hydrogen peroxide holds good in this case as well.

6.

The obtained intensification and hence the decision of using combination technique would be dependent on the type of the pollutant and combination approach is generally recommended when free radical attack is the controlling mechanism of degradation.

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CONCLUSION The detailed discussion presented in the chapter has allowed us to understand the mechanistic details behind the successful usage of cavitational reactors and Fenton based processes for the wastewater treatment application. Amongst the cavitational reactors, it might be more beneficial to use hydrodynamic cavitation reactors as compared to ultrasound based reactors. For the sonochemical reactors, configurations based on the multiple frequency multiple transducers are recommended for efficient large scale operation. The efficacy of the combination approach is strongly dependent on the type of the pollutant and optimization of the operating parameters as per the guidelines presented in the work should result in maximizing the extents of degradation with favorable economics.

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In: Water Engineering Editor: Dominic P. Torres

ISBN: 978-1-61209-914-9 © 2011 Nova Science Publishers, Inc.

Chapter 3

THE SLUG TESTS AS A TECHNICAL TOOL IN AQUIFERS CHARACTERIZATION A. Alfonso Aragón1 and M. P. Verma Instituto de Investigaciones Eléctricas, Calle Reforma 113, Col. Palmira, Cuernavaca, Morelos, México. CP 62490

ABSTRACT

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Aquifer test methods available for characterizing hazardous waste sites are sometimes restricted because of problems with disposal of contaminated groundwater. These problems, in part, have made slug tests a more desirable method of determining hydraulic properties at such sites. The slug test method is a popular and inexpensive mean of estimating the hydraulic properties of aquifers (primarily hydraulic conductivity). There is a clearly need to develop test methods that can be used to characterize higher permeability aquifers without removing large amounts of contaminated groundwater. Similarly the corroboration of test results indicates that slug testing is a viable hydraulic characterization method and may represent one of the few test methods that can be used in sensitive areas where groundwater is contaminated. Besides, of particular interest are test methods that can be performed rapidly, and that minimize the removal of large quantities of water (i.e., tests that minimize purgewater disposal problems). The slug tests can be carried out using a single well or two, in this last case it is used the interference test concept. The general test procedure requires initiating an instantaneous head increase or decrease at the well used as the tester, and monitoring the associated formation response at the neighboring observation well. The pressure response is analyzed at the monitored well and the results provide estimates of the formation transmissivity and its storativity. The methods developed for the analysis of slug tests were done, assuming single characteristics of the system, due that the increases in the water level are too very small compared with those of an output tests. So, in this work is shown the applicability of four of the existing methods for analyzing slug tests. In this work are analyzed and discussed, the behavior of the results obtained from the analysis methods of Hvorslev; Cooper, 1

E-mail: [email protected]

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A. Alfonso Aragón and M. P. Verma Bredehoeft and Papadopulos; Bower and Rice; and Gilg and Gavard. The obtained results from the use of such methods are useful in the aquifers characterization in order to design properly their exploitation. In order to show the application the four discussed methods were used data of measurements during slug tests carried out in ten wells in order to characterize the aquifer where they are located. Through determined values it was done a correlation of formation properties for characterizing the aquifer and to define the zone whose hydraulic conductivity is the best.

Keywords: Slug test, Aquifer, Hydraulic characterization, Hvorslev method, Cooper et al. Method, Bouwer and Rice Method, Gilg and Gavard method, Water level, Drawdown pressure, output test.

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1. BACKGROUND The theory of well testing in general terms was developed in order to characterize the reservoir formation. The results obtained from its analysis among others are the determination of the physical characteristics. Generally any type of well test is carried out by introducing a stimulus into the well and observe the reservoir response through the behavior of its water level. During the transient pressure tests, the stimulus applied in a well is a change in the flow conditions. The flow rate in the well could be of production or injection. In cases of well production, if the change in the flow rate is increasing, the water level will decrease and by this reason, this is called a drawdown test. By other side, if the change in the flow rate production is decreasing, the level water will rise, so is called build-up test (or pressure increment). For flow injection cases, increment test occurs when the flow rate increases and a drawdown test occurs with the diminution of flow rate. The components of observed drawdown in a pumping well, were first described by Jacob (1947), and the test was refined independently by Hantush (1961) as consisting of two related components:

s = BQ + CQ2

(1)

where s is the water level drawdown, Q is the production flow rate, B is the aquifer loss coefficient (which increases with time, as predicted by the Theis solution) and C is the well loss coefficient (which is constant for a given flow rate). A variation of the well tests is through the use of a small variation in the water level produced by an instantaneous production or injection, which is called a pulse or slug test. An alternative way is to sink a solid heavy rod into the groundwater. So, the objective here is to displace water to produce a rise in its level into the well (Schwartz and Zhang, 2003). The main hydrogeologic parameters which are evaluated by most aquifer tests are: hydraulic conductivity or permeability (K) transmissivity (T) and storage coefficient (S) The Hydraulic conductivity or permeability, symbolically represented as K, is the water flow rate crossing a unitary section of the aquifer, by the influence of a unitary gradient, at mean temperature of the field, its expression is:

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2 where c = dimensionless constant. d2 = Parameter dependent of the intergranular surface. γ = Specific weight of the fluid. µ = liquid viscosity at temperature to. The product cd2 = k, is known as the specific or intrinsic permeability and is a dependent variable of the formation characteristics. Transmissivity is measured by the water volume crossing an unitary section of the aquifer during one unit time with a load of one meter. It represents the aquifer capacity for water production. So, from the last definition, the Transmissivity´s dimensions are:

T = [L3/T]/L = L2 T-1 (3) Where T is time dimension and L is length dimension The ordinary units of Transmissivity are (m2/d), (m2/h) or (m2/s), however the units of 2 (m /d) give values that can be processed in the calculations. The characteristic values of Transmissivity are shown in Table 1. Table 1. Relation between Transmissivity values and formation capacity (Taken from Custodio and Llamas, 1983)

T

Qualitative estimation

Observations

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(m2/d) Less than 10 Very low

Production less than 1 l/s with drawdown of 10 m in the level. Between 10 Low Production between 1 and 10 l/s with drawdown of 10 m. in the level and 100 Between 100 Mean value Production between 10 and 50 l/s and 500 with drawdown of 10 m. in the level Between 500 High Production between 50 and 100 l/s and 1000 with drawdown of 10 m. in the level Upper than Very high Production upper than 100 l/s with 1000 drawdown of 10 m. in the level Permeability is calculated as a result of the ratio between the Transmissivity (T) and the aquifer thickness (b).

4 So, writing the Transmissivity in dimensions as L2T-1, dimensions of permeability will be, as follows:

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5 According to the consistency of the units used in the Transmisivity, the units for the permeability will be (m/d). Permeability is a characteristic of the aquifer´s formation and does not represent its production capacity. So, an aquifer highly permeable but with a short thickness could be of low Transmisivity and its wells could produce low flow rates. The storage coefficient (S) is defined as the volume of water that produces a section of an aquifer with unitary area in its base and with a unit drawdown. The storage coefficient does not have dimensions. Table 2 shows representative values of storage coefficient for different permeable materials. Table 2. Representative values of storage coefficient for different formation types (after Custodio and Llamas, 1983) Material type

Karst Jurassic limestones and dolomites

Tertiary limestones and dolomites

Performance the aquifer Free

2x10-2

Semiconfined

5x10-4

Confined

5x10-5

Free

from 2x10-2 to 6x10-2

Semiconfined

from 10-3 to 5 x 10 -4

Confined

from 10-4 to 5x10-5

Free

from 5x10-2 to 15x10-2

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Porous intergranular Gravel and sand Semiconfined Karst and porous Tertiary marine calcarenites

of Mean value of storage coefficient (S)

10-3

Confined

10-4

Free

from 15x10-2 to 18x10-2

The research focused to determine the hydraulic behavior of an aquifer is based in the determination of the behavior of the water levels in the wells in relation with the time. There is a need clear for developing new test methods and/or modifying currently used techniques in order to improve the hydraulic characterization techniques ongoing and futures. The test methods that can be performed rapidly, and that minimize the removal of large quantities of water are useful because of the environmental problems. As an alternative to aquifer pump tests, slug tests can be performed to determine the hydraulic conductivity of the formation in the immediate vicinity of a monitoring well. If the water level is shallow, the slug of water can be removed with a bailer or a bucket. During a slug test a small volume of water is suddenly removed or added to the well, and the rise and/or fall of the water level is measured. Also, a solid body can also be submerged into the well to displace the water. No matter which method you use enough water needs to be removed or displaced to raise or lower the water level by about 0.10 to 0.50 m.

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No pumping, or piezometers are needed, and the slug test can be completed within a few minutes, or at the most a few hours. Because slug tests are less expensive and less time consuming, they are more popular than pumping tests (Mace, 1999; Boonstra and Kselik, 2002). However they should be regarded as a substitute for conventional pumping tests. Slug tests only determine the characteristics of a small volume of aquifer material surrounding the well (Batu, 1999) and this volume may have been disturbed during well drilling and construction. A slug test is a variation on the typical aquifer test where an instantaneous change (increase or decrease) is made, and the effects are observed in the same well. This is often used in geotechnical or engineering settings to get a quick estimate (minutes instead of days) of the aquifer properties immediately around the well. The schematic behavior of the level water in the well during a slug test is shown in Figure 1. From the graph of the figure it can be seen two disturbances along the test: a) The first, corresponds to the introduction of a solid body, used as stimulus to produce variations in the water level of the well, after it, occurs the recovery period to initial conditions; b) The second disturbance refers to extraction of the solid body from the well and its corresponding recovery period to achieve the steady state (initial conditions). 18.0

h (m)

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17.5

Immersion of a solid body

17.0

16.5

Extraction of a solid body

16.0 0

500

1000

1500

2000

2500

Time (s)

Figure 1. Ordinary behavior of variations water levels in a slug test during the immersion and extraction of a solid body in the well.

The time required to recovery the steady state conditions in the well is function of the reservoir characteristics. A slug test is in contrast to standard aquifer tests, which typically involve pumping a well at a constant flow rate. The size of the slug required is determined by

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the aquifer properties, the size of the well and the amount of time which is available for the test. For very permeable aquifers, the pulse produced by the slug test will dissipate very quickly. If the well has a large diameter, a large volume of water must be added to increase the level in the well a measurable amount. A description of development of immersion operation of a solid body in the well to produce variations in its level water is shown in Figure 2.

Ho

Hi

Variation of the water level in the well as a function time

Initial water level

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Used tool to produce changes in the water in the well level during test

Figure 2. Example of the prevailing conditions before and after immersing of the solid body in the level water of the well during a slug test.

A scheme of the physical behavior of the level water in the well caused by the introduction of a solid body during a slug test is shown in Figure 3. Because the flow rate into or out of the well is not constant, as is the case in a typical aquifer test, the standard Theis solution does not work. Mathematically, the Theis equation is the solution of the groundwater flow equation for a step increase in discharge rate at the pumping well; a slug test is instead an instantaneous pulse at the pumping well. The aquifer parameters obtained from a slug test are typically less representative of the aquifer surrounding the well than an aquifer test which involves pumping in one well.

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Initial conditions

t =0

t = t1

t=t2

155

t = t3

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Figure 3. Scheme of behavior of the variations of water level in the well, during a slug tests, using the immersion of a solid body.

From a slug test, for instance, it is only possible to determine the characteristics of a small volume of aquifer material surrounding the well. But nevertheless, some authors (Ramey et al. 1975; Shinohara, and Ramey, 1979; Yeh and Chen, 2007) state that fairly accurate transmissivity values can be obtained from slug tests. The homogeneity and constant thickness of the aquifer are hypotheses that are adopted, which is quite true, because the radius of influence in most slug tests is fairly small. All of the methods outlined in this work are based on theories that neglect the forces of inertia in both the aquifer and the well: the water level in the well is assumed to return to the equilibrium level exponentially. These inertia effects can not be ignored in highly permeable aquifers or in deep wells, and other methods would need to be used. The applicability of the slug test is extended to petroleum systems, so, solutions for this type of tests (decreasing flow rate) drill stem test (DST), including wellbore storage and skin effect, were presented by Ramey et al. (1975). The slug test type-curves can be applied to both the flow period and the pressure buildup after a short initial shut-in Spane and Swason (1993) carried out slug tests in shallow aquifer systems and they found that the transmissivity values estimated from these tests were comparable (within a factor of 2 to 3) to values calculated using traditional testing methods. Current hydrologic characterization studies have, in some cases, been restricted by existing site conditions such as contaminated groundwater, purge-water disposal problems, high formation permeabilities, etc. The presence of contaminated ground water and, in some locations, areas of extremely high transmissivity greatly diminishes the use of standard hydraulic test methods in the hydrologically characterization of the aquifers. The presence of delayed-yield behavior can be discerned by converting the recorded slug test data to an equivalent head response that would be observed for a constant-rate pumping test.

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2. FACTORS AFFECTING SLUG RESPONSE The transmissivity, storativity, anisotropy of the aquifer, radial distance, partial penetration, wellbore storage and the characteristics of the stress and observation well, are among others, factors which influencing the transmission and the amplitude of the response of slug tests (Novakowski, 1990; Spane, 1993). Although analyzable lug test responses at the stress well are limited to test formations with Transmissivities of 86.4 m2/d or less (Spane, 1993), Spane and Swanson (1993) found that Transmissivity has no affect on the magnitude of test response, but does exert a strong influence on the predicted response time of the slug test. High aquifer transmissivities are associated with fast test responses, while lower transmissivities are associated with lagged (delayed) responses. The shape (amplitude) of the slug response at the well is strongly influenced by the storativity of the aquifer. Spane and Swanson (1993) showed that for an aquifer with Transmissivity of 86.4 m2/d, and storativity of 10-1 presents a more clear response, than those with storativity values of 10-4. So, the time response of the aquifers is an inverse function of the increase of its storativity. The capacity to detect a response during the test is enhanced, the closer an observation well is located to the tested well and the lower the storativity value of the geologic material. For the storativity range considered to be representative of the most shallow alluvial-aquifer conditions (elastic storage components of 10-2 to 10-4), slug test responses should be observable to maximum distances between 8 and 30 m from the testing well (Custodio, 1993). When the tested wells show great wellbore storages, tend to have responses to be lagged and attenuated from those expected. The effects of a well with partial penetration cause distortion of the radial equipotential pattern that would normally develop during testing within a homogeneous, isotropic aquifer surrounding a fully penetrating well. Partial penetration effects cause additional drawdown in the water level to occur within the section of the aquifer intersected by the well-screen depth interval. In cases of partial penetration does not occur completely radial flows and also results in the presence of vertical flow components. By this reason the use of traditional equations (Theis, Jacob, etc) could produce some errors. Deviations induced by partial penetration are more significant near the tested well and diminish with distance. The effects of the vertical anysotropy also tend to accentuate test response deviations caused by partial penetration. The vertical anisotropy occurs when (Kv ≠ KH), where the vertical hydraulic conductivity is expressed with Kv and KH is the horizontal hydraulic conductivity. Because of the stratification evident to some degree in most sediments, so, vertical anisotropy would be expected to influence test results obtained within sedimentary alluvial aquifers. Within unconfined aquifers, where the vertical anisotropy ratio is less than 1 (Kv/KH < 1) the effects of elastic storage and delayed yield are accentuated during the aquifer test response (Neuman, 1972). However Hantush (1984) found that for a given distance, r, from a partially penetrating well, the response within an anisotropic aquifer would be the same as that the value of [r (Kv/KH)1/2] within an equivalent isotropic aquifer.

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3. TEST THEORY Initially we must make mention to the meaning of a slug. So we found that a slug is a mass unity in the unity system FPS (foot, pound second). The slug is defined as the mass that moves to an acceleration of 1 m/s2 under the influence of a force of 1 lbf. So a slug test is referred to a mass that moves in this case the water level. The general expression of a slug is done as follows:

1

1

6

A slug test involves inducing a rapid change in water level in a test well. By measuring and recording the rate of return to static conditions, one is able to estimate the local horizontal hydraulic conductivity of the formation surrounding the well (Randal, et al., 2009). The data of a slug test are generally analyzed using relatively standard analytical solutions to the equations which govern ground water flow. There are methods that rely on the assumption that water and soil are incompressible, that is, aquifer storativity is zero. This assumption allows use of a modified Thiem equation in the analysis to predict well response. However there are methods of analysis that assume a non zero storativity. The steady-state radial flow to a production well, is commonly called the Thiem solution. It comes about from application of Darcy's law to cylindrical shell control volumes (i.e., a cylinder with a larger radius which has a smaller radius cylinder cut out of it) about the production well; which is commonly written as:

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2

ln

7

where (h-h0) is the drawdown at the production well, whose radius is r, Q is the discharge rate of the production well (at the origin), T is the transmissivity, and R is the radius of influence, or the distance at which the water level is still h0. These conditions (steady-state flow to a production well with no nearby boundaries) never truly occur in nature, but it can often be used as an approximation to actual conditions; the solution is derived by assuming there is a circular constant head boundary (e.g., a lake or river in full contact with the aquifer) surrounding the production well at a distance R. Equation 7 was designed for determining the Transmissivity value (T), from the knowledge of the drawdown (h-h0), the flow rate (Q) and the ratio value, between radius of the well (r) and the influence radius (R). In this work we apply the methodologies for analyzing slug tests, according to their chronologically proposed by: Hvorslev (1951), Cooper et al., (1967), Bower and Rice (1976) and Gilg and Gavard (Custodio and Llamas 1983; González et al. 2002).

3.1 Methodology of analysis from Hvorslev The analytical solution for a slug test response for a stress well with a finite radius within an aquifer containing a semicompressible fluid was first presented by Hvorslev (1951). The method was designed for using in partially or totally penetrating wells. For the analysis of a

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sllug test the Hvorslev H methhod is a comm mon engineeriing solution, which approxximates the m more rigorous solution s to trannsient aquifer flow with a simple decayinng exponentiall function. The Hvorsllev (1951) meethod of slug test t analysis addresses a a vaariety of well and a aquifer geeometries, is easy e to apply, and is widelyy used. Its undderlying mathhematical moddel assumes neegligible com mpressive storaage (aquifer water w and matrrix are incom mpressible, flow w is quasistteady). The co onsequences of o this assumpption are expllored here forr the particulaar case of a w well fully pen netrating a coonfined, radially infinite, homogeneous, h , isotropic aqquifer. The C Cooper et al. (1967) model of this settingg includes thee effect of com mpressive storrage and is ottherwise identtical to Hvorsslev. Thereforre, for this settting the perfoormance of the Hvorslev m method is gaug ged against thaat of the Coopeer et al. modell. In order to o facilitate thhe comparisoon with coopeer et al. (19667) model, thhe original H Hvorslev modeel can be appproached intoo conventionall equations governing g the flow. The H Hvorslev metho od makes estim mations of hyydraulic conduuctivity for this setting, and is accurate onnly to within n an order of magnitude, assuming noo knowledge of the aquiffer storage cooefficient. Acccuracy of thee Hvorslev esstimate dependds on the norrmalized aquifer storage cooefficient , on o the matchinng procedure used to fit thee Hvorslev moodel, and on thhe analyst's chhoice for the Hvorslev H effecctive radius re. The Hvorsllev model proovides no physsical basis for selecting re. Some S insight iss gained by viiewing the con nstant head coondition at raddius re as an “infinite “ storagge” at re. Flow w from this diiscrete “storaage” approxim mates the disstributed storrage of a coompressible aquifer. a By reeference to Cooper C et al. (1967) one can select a value v of re, which w leads too a correct H Hvorslev estim mate of hydrauulic conductivvity, given prrior knowledgge of the aquiifer storage cooefficient. matical solution by Hvorsleev (1951) is useful u for deetermining thee hydraulic A mathem coonductivity off confined aquuifers. Analysiis involves maatching a straiight-line soluttion to slug teest data. The main m assumptions of the phyysical model applied a by Hvorslev in his analysis a are shhown in Figurre 4. This metho od shows a good g resolutioon for values of L/R greatter than 8. Thhe analysis asssumes a hom mogeneous, isootropic mediuum in which soil and water are incompreessible. For deetermining thee hydraulic conductivity thee Hvorslev meethod uses the expression:

w where K = hydrau ulic conductiviity (L/T) (m/dd) r = radius of o well casing (m) R = radius of well screenn (m) Le = length h of well screeen (m) To = time itt takes for watter level to rise/fall 37% of initial change (dimensionleess value)

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The Slug Tests as a Technical Tool in Aquifers Characterization r

level water

pipe

slotted pipe

L

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gravel pack

hole R

Figure 4. Parameters used in the Hvorslev method for the analysis of a slug test.

Analysis procedure The steps followed in the technique of analysis of Hvorslev method are: 1) Plot (h/ho) vs Time on semi log plot (see Figure 5). 2) Draw straight line through data. 3) Determine To at (h/ho) = 0.37 4) Calculate K using To, r, L, R If (Le/R) > 8 then use equation (8) mentioned before

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A. Alfonso Aragón and M. P. Verma 1 0.9 0.8 0.7 0.6

[H0-H(t)]/(Hmax-Ho)

0.5 0.4

0.3

0.2

0.1 0

2

4

t

6

8

10

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Figure 5. Example for determining the TL value from the graph of [H0-H(t)]/(Hmax-H0) versus time, according with Hvorslev (1951).

3.2 Cooper, Bredehoeft and Papadopulos method The main assumptions taken in account in the analysis of a slug test by model of Cooper et al. (1967) are shown in Figure 6. There it can be seen the geometrical array of the well in the aquifer, its steady state conditions and the change of the water level caused by the immersion of a solid body. The method considers an initial rise in the water level generated by the immersion of the solid body and the corresponding measurements of the changes in the level water as function of time to achieve the initial state of the water level in the well. The behavior in the water level is monitored after a stimulus in the well is applied. As mentioned before, in the slug test the stimulus could be a short discharge or the immersion of a solid body, in order to produce a change in the water level. The methodology (Hsieh, et al., 1988) uses the initial condition in the water level (Ho), and its behavior (H) after the stimulus is retired from the well.

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Figure 6. Main assumptions related with the well and the aquifer, taken in account in the numerical model of Cooper et al. (1967).

The changes in the levels can be expressed as following: Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

,

9

where the function (F) implies the parameters α and β, whose expressions are:

S and

Tt

10

11

where the nomenclature used is: T = Transmissivity of test interval t = Test time rc = Radius of well casing in the interval over which head change takes place R = Effective radius of well within test interval S = Storage coefficient of the test interval. The storage coefficient (S) can be determined by:

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A. Alfonso Aragón and M. P. Verma

2

exp

2 2

12

∆

where

2

∆

2

13

The definitions of the used variables are as follows: Jo and J1 are the Bessel functions of zero and first order for the first class. Yo y Y1 are the Bessel functions of zero and first order for the second class. The solution of the Equation (12) results in a curves family, where it can be obtained a graph of β versus H/Ho for different values of α. The set of curves are known as Type-curves of the method of Cooper et al. (1967) and is shown in Figure 7. In relation with the numerical solution of the method of Cooper et al. (1967), a program TYPCURV (Novakowski, 1990) was developed to generate slug test type curves based on the analytical solutions and boundary conditions presented by the authors. This program was applied for developing predictive test response. 1.0 0.9 0.8

-4

-2

10

10

0.5

-5

-3

0.6

10

10

-1

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0.7 10

h ho

0.4 0.3 0.2 0.1

using data from Cooper et al, 1967

0.0 0.001

0.01

0.1

1

T t/r

10

30

2

Figure 7. Type curve of Cooper et al. (1967) for determining the hydraulic conductivity in aquifers, from the measurements of the water level behavior in a well during a slug test.

The methodology to analyze data of a slug test using this type-curve, is based in to graph the data of the well test, taking in account two conditions: 1) The time (t) elapsed of the test must be graphed in logarithmic scale, at the abscissa axis, against the value of H/Ho in

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millimetric scale; and 2) The graph developed with the data of the well must have the same dimensions that of the type-curve of Cooper et al. The graph with data of the well is overlapped on the type-curve of Cooper et al. and sliding it horizontally, must be found the curve that best fits to the graph of the measured values. After obtaining the best match between both curves, it must to fix a value of the time in the graph of the well and its corresponding value of Tt/(rc)2 on the type-curve. The value obtained in the last step corresponds to the β value (Eq. 11). In order to obtain the Transmissivity value, it must to substitute the β value, and solve the equation (11) for T. By other hand, as can be seen in type-curve of Cooper et al. (Fig. 7) each curve corresponds to any value which represents to the α value. So α varies from 10-5 to 10-1 and this value can be taken in Equation (10) to obtain the storativity (S). Only it is necessary substitute the value of α in equation (10) and solve it for S. Similarly, to analyze slug tests, Ramey et al. (1975) introduced type curves based on a function F, which has the form of an inversion integral and is expressed in terms of three independent dimensionless parameters: KDt/(rw)2S, (rc)2/2(rw)2S, and the skin factor. To reduce these three parameters to two, Ramey et al. (1975) showed that the concept of effective well radius (rew= rwe-skin) also works for slug tests. If rew is used in the function F, the two remaining independent parameters relate to Cooper's dimensionless parameters α and β. The set of type curves given by Ramey et al. (Earlougher, 1977) are identical in appearance to Cooper's, and either set will produce approximately the same results for the aquifer transmissivity. The variables used by Ramey et al. (1975) are: K, the formation permeability; D, the total thickness of the aquifer; t, the time needed to that the aquifer recovers its initial condition; rw, is the wellbore radius; rc, is the casing radius and S, is the skin factor.

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3.3 Bouwer-Rice method The Bouwer and Rice (1976) method can be applied to determine the hydraulic conductivity of an unconfined aquifer if the following assumptions and conditions are satisfied: •

The aquifer is homogeneous, isotropic, and of uniform thickness over the area.

•

Prior to the test, the water table is (nearly) horizontal over the area that will be evaluated.

•

The head in the well is lowered instantaneously at to = 0.

•

The inertia of the water column in the well and the linear and non-linear well losses are function of the formation capacity.

•

The well either partially or fully penetrates the saturated thickness of the aquifer.

•

The well diameter is finite; hence storage in the well cannot be neglected.

•

The flow to the well is in a steady state.

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A. Alfonso Aragón and M. P. Verma The aquifer is unconfined and has an apparently infinite areal extent; •

Influenced by the slug test;

•

Influenced by the test;

•

Water table around the well is negligible; there is no flow above the water table; are negligible.

To determine the hydraulic conductivity of an unconfined aquifer from a slug test, Bouwer and Rice (1976) presented a method that is based on Thiem’s equation, For flow into a well after the sudden removal of a slug of water, this equation is written as the head’s subsequent rate of rise, dh/dt, can be expressed as:

2 KD

h R ln r

14

The expression of the subsequent rate of the rise head, dh/dt, is:

15 Due that the filter gravel around the well, and along the total length of the gravel pack Le (Bouwer, 1989), could influence on the geometry of the well, it can be used an expression, for determining rc modified that involves porosity factor (φ ), whose equation is:

1

16

Combining Equations (15) and (16), integrating the result, and solving for K, yields:

1 Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

2

17

Where ho = Head in the well at time to = 0. ht = Head in the well at time t > to. Le = Length of the well screen or open section of the well. Lw = Height between level water and depth of the well. rc = Radius of the unscreened part of the well, where the head is rising. rw = Horizontal distance from well centre to the gravel pack. Re = Radial distance over which the difference in head, ho, is dissipated in the aquifer. A diagram of the model of the system well-aquifer assumed by Bouwer-Rice (1976) is shown in Figure 8. The Re value cannot be identified easily in the aquifer, so Bouwer and Rice determined the values of Re experimentally, using a resistance network analog for different values of rw, Le, rc, and rw. They derived the following empirical equations, which relate Re to the geometry and boundary conditions of the system.

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L

165

H L

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Figure 8. Main assumptions taken into account by Bouwer-Rice in their model.

So, for partially penetrating wells, the value of ln (Re/rw) can be obtained from Equation (18), whose expression is:

1.1

18

where A and B are dimensionless parameters, which are functions of Le/rw. For fully penetrating wells the determination of the value of ln (Re/rw) is done trough applying the next Equation (19):

1.1

19

where C is a dimensionless parameter, which is a function of d/rw. For determining the values of parameters A, B and C, it can be used the graph proposed by Bouwer and Rice that is shown in Figure 9.

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C

12 10

A

A 8 and C 6

4 3

B

4

2

2

1

0

1

5

10

50 100

L e / rw

5001000

5000

B

0

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Figure 9. Determination of dimensionless parameters A, B and C, through the use of the ratio (Le/rw), according with Bouwer and Rice (1976).

The A and B parameters are used for the case of partially penetrating wells, while C parameter is applied for fully penetrating wells. Equations (18) and (19) are used for determining the ln (Re/R) value Zlotnik (1994), through the application of the values of A and B, or C, respectively. The shape factor related with grade of the penetration (full or partial) of the well, into the aquifer´s formations is analyzed by Zlotnik et al. (2010). Since K, rc, rw, Re, and Le in equation (17) are constants, so (l/t) ln(ho/ht) is also a constant. Hence, when the values of ht are plotted against t on semi-log paper (ht, on the logarithmic scale), the plotted points will fall on a straight line. Applying this procedure, this straight-line plot is used to evaluate (l/t) ln(ho/h). The recommended procedure in the analysis during application of the Bouwer-Rice method is: •

On semi-log paper, plot the observed head h, against the corresponding time t.

•

Fit a straight line through the plotted points.

•

Using this straight-line plot, calculate (l/t)ln(ho/ht) for an arbitrarily selected value of t and its corresponding h.

•

Knowing Le/rw, determine A and B from Figure 9 if the well is partially penetrating, or determine C from the same Figure 9 if the well is fully penetrating;

•

If the well is partially penetrating, substitute the values of A, B, rc, Le, Lw and rw into Equation (18) and calculate ln(Re/rw).

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•

If the well is fully penetrating, substitute the values of C, rc, Le, Lw and rw into Equation (19) and calculate ln(Re/rw) on the logarithmic scale.

•

Knowing ln(Re/rw), (l/t)ln(ho/ht), rc, and Le, calculate K from Equation (17).

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It is necessary to do some remarks about the application of this method, between the main are the next: •

Bouwer and Rice showed that if H >> Lw, an increase in H has little effect on the flow system and, hence, no effect on Re. The effective upper limit of ln[(H-Lw)/rw] in Equation (18) was found to be 6. Thus, if H is considered infinite, or H – Lw is so large that ln[(H-Lw)/rw] > 6, a value of 6 should still be used for this term in same Equation (18).

•

If the water level is rising in the screened part of the well instead of in its unscreened part, allowance should be made for the fact that the hydraulic conductivity of the zone around the well (gravel pack) may be much higher than that of the aquifer.

•

It should not be forgotten that a slug test only permits the estimation of K of a small part of the aquifer a cylinder of small radius, Re, and a height somewhat larger than L e.

•

The values of ln(Re/rw) calculated by Equations (18) and (19) are accurate to within 10 to 25 per cent, depending on the ratio Le/Lw.

•

In a highly permeable aquifer, the level water in the well will rise rapidly during a slug.

Bouwer (1989) pointed out a double straight line effect in certain slug test analyses, when the well screen is partially penetrating in the aquifer. In other cases, data from a slug test may show a concave upward appearance. According to Butler (2002), this effect becomes more pronounced as the storage (α) increases. Due that the Bouwer and Rice method is routinely used in the analysis of slug tests, several programs (Kemblowski and Klein, 1988) were developed in which values of Le/rw are stored for direct calculation of ln(Re/rw).

3.4 Analysis method proposed by Gilg-Gavard The Gilg-Gavard method allows determining the formation permeability in wells of small diameter, quickly and using a little volume. The volume could be referred as water produced/injected or a solid body whose immersion into the well produces a change in its level water. There are two ways for application this analysis method: a) Assuming constant water level; and b) For variable water level.

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3.4.a Gilg-Gavard´s method of constant water level This method consists in to inject water into the well and maintain stabilized the water level (hm) to a fixed value. The hydraulic conductivity (k) is a function of the maximum variation of level water, of the pipe geometry and the necessary flow rate to maintain constant that water level (Custodio and Llamas, 1996), and through the use of this method is obtained from the expression:

20 where k is the permeability or the hydraulic conductivity, α is a shape factor whose value is 1 if the well is punctual, Q is the necessary injected7produced flow rate to maintain constant the water level, d is the diameter of the well with gravel pack and hm is the maximum variation of the level. In the practice, using the flow rate in l/min and the permeability in cm/s, the general equation is:

21

600

where A is a shape factor (Custodio, 1993) as a function of the length of the filter zone (L) and of the diameter of the gravel pack (d). Two expressions allow for calculating the shape factor, that were proposed by Custodio (1983), depending of the value of L. For L value greater than 6 m. A = (1.032 L + 30 d)

(22)

For L value less than or equal to 6 m. Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

A = (1.032 L + 30 d) (-0.014 L2 + 0.178 L + 0.481) (23)

3.4.b Gilg-Gavard´s method with variable water level This method implies the alternative for using in flow regimen variable, which is too easy for applying and only needs a little water volume. This method is suitable in formations with low permeability and values medium. The practical methodology of this test includes the injection of water, until the level reaches a height known in the pipe. The drawdown in the levels is measured as a function of time, after that injection was stopped. Under these conditions, next equation can be used:

1.308

∆ ∆

24

where k is the hydraulic conductivity of the formation, A is the shape factor (Custodio and Llamas, 1983; González et al., 2002) as mentioned before, hm in this expression is the mean level during the interval time Δt, d is the diameter of the well with gravel pack and Δh is the drawdown in the level according with Δt. The two above alternatives of methods shown before, can be applied for wells under injection or production conditions. But for the case of the immersion of a solid body into the

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water level, the analysis method of variable flow rate must be applied, because it does not need the value of Q, only the value Δh/Δt. After reviewing the main representative methods for analyzing slug test, now the concepts are applied to examples of slug tests carried out in wells of the studied valley. By this reason in the next section will mention the appropriate tasks be applied in field tests.

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4. METHODOLOGY APPLIED IN FIELD TESTS As mentioned earlier the slug tests are carried out by the applying a small stimulus in the well tested. Because the stimulus is small, so the responses of the well also are too little. By this reason the changes in the level water of the well must be measured using continuous logging tools. In the industry there are several logging equipments with capabilities for doing measurements at intervals time too short. These, are too useful in wells, whose behavior allows a quickly recovery of its initial conditions. First, it is recommended to measure the depth of the water level in the well in order to define the appropriate depth to introduce the logging tool, taking care that the conditions are stabilized. If the slug test is performed with injection in the well, the logging tool could be located five meters down the water level, because the injection raises the water level. But if the slug test is carried out using the well´s production, it must take care in locate the logging tool to an enough depth for that always the logging tool can be down of the water level and record the changes produced by the water extraction. For this last case it is recommended to locate the logging tool, 20 m down of the water level. In both cases mentioned before, it must take care in to know exactly the volume of water produced/injected, because this value is useful in all analysis methods. Another mean for causing a stimulus in the slug test is by immersion of a solid body into the well. So, after the perturbation caused its water level tends to recovery its original position, so quickly as be possible. The rise of the water level by the immersion of the solid body is instantaneous and any electronic logging tool can identify it, but its behavior does not allow any interpretative analysis. As mentioned earlier, the period time to recover its original state and the shape of the graphic curve is a function of the characteristics of formation´s reservoir. So, a complete procedure of a slug test involves the immersion and extraction of a solid body. These are the instruments that cause the perturbation in the well. But after the conditions alteration in the well, in each case follows a recovery period time for reaching its original water level. As mentioned before all methods designed for analyzing well tests, use the graphic curve´s behavior as a time function for determining the aquifer´s characteristics. Figure 1 shows graphically (repeated here for quick reference) the behavior of the water level response through the immersion and extraction a body solid in a well tested with a slug test. For a quickly reference, the Figure 1 is shown again, and the stages mentioned before, appear in it with its corresponding numbers of identification.

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h (m)

17.5

17.0

2

1

16.5

4

3

16.0 0

500

1000

1500

2000

2500

Time (s)

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Figure 1. Profile of a complete slug test, involving the time periods of immersion and extraction with its corresponding recovery times.

From the last figure it can be identified next steps: 1. The immersion of the solid body in the well and the quickly rise of its water level as a response of the well. 2. The time´s period of recovery of its water level to reach the original state. 3. The extraction of the solid body from the well, and the instantaneous drawdown of the water level, again as a response of the well. 4. The behavior of the level water in the well to reach its initial state, through the period recovery time. The behavior of Δh against t of the recovery periods are used for determining the aquifer´s parameters. So, there is a direct relation between a high value of the parameters and the short time to reach the pseudo steady state in the well. The equipment used is an electronic level logger programmed for obtaining data (time, water level variation, temperature) each five seconds, the appropriate software and a portable computer for reading data logged.

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Procedure test Different steps are used in the development of a field test all of these are focused to obtain the most information useful for determining parameters of the aquifer that support his performance in a manner certainly.

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Each step considers a particular condition in the well, by this reason the procedure applied in the field tests carried out in all the wells studied that are shown in this work is demonstrated as follows: •

Determine the initial static water level in the well in order to take decision about the best depth for locate the level logger and the solid body for causing the perturbation during the test.

•

After knowing the static level water in the well, we must introduce the level logger into the well 10 meters depth down static water level and to leave it for logging data by a period of 10 minutes in order to obtain stabilized data. The periodicity for taking measurements is according with the characteristics of the system (aquifer-well).

•

Introduce the solid body into the well 9 meters down the determined water level, that is, the solid body will be located just only one meter above of the level logger. The immersion of the solid body causes the disturbance in the water level of the well, so it must recommended to leave it in the same depth by a period of 30 minutes in order to logging the recovery of the water level at the conditions before the disturbance.

•

Extract the solid body from the well leaving the level logger in the well located at the same depth during a period time of 30 minutes. The extraction of the solid body causes an instantaneous drawdown of the water level, which will tend to recovery its initial state. As mentioned before the recovery time is a function of the aquifer characteristics.

•

Extract the level logger from the well and connect it to the computer for to download the measurements. Make a preliminary revision of the test´s behavior in order to take decision about if the water level in the well reached the pseudo steady state condition, that is, the water level in the well recovered its initial conditions, so it can be said that the test was successful. Under these circumstances the equipment can be retired from the well, but if the pseudo steady state has not been reached, will be necessary to repeat the test with more long times.

5. APPLICATION TO FIELD CASES In order to characterize the aquifer´s performance, slug tests in 10 wells located in a valley of Mexico were carried out. The analysis of the data is used to characterize the aquifer and its use in this work serves to show the applicability of the methods described previously. The main identification´s characteristics of the studied wells are shown in the Table 3. As can be seen from the data of the Table 3, the valley where the majority of the wells are located has a slope too small. Last thing is supported also by the Figure 10 which shows a map of the topographic level of the studied area. The majority of the wells included in this work are located in a topographic plane of only two meters of slope in a cross section of about 10 km.

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From table 3 it can be seen the depths of the wells involved in this study, so the depths vary from 80 to 507 meters and the water levels are between 287.6 and 308.8 m. It is appropriate to make mention that for each well, not necessarily exist correspondence between the static water level and its topographic level. Through the application of the procedure mentioned before, all tests carried out in the studied wells showed a different behavior, each one of these according with the characteristics of the well. So, while in one well, the variation of the water level was of two meters as maximum in another it found a maximum variation in the water level of only few centimeters. Table 3. Data locations and mechanic characteristics of the wells studied through the slug tests

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Well

x Y Geographic ubication

z

Static Depth water level

Diameter

Slotted thickness

(masl)*

(m)

(masl)

(m)

(m)

N-1

65993

86595

309.28

507

293.58

0.0508

from 426 to 507

N-2

67970

86812

310.46

154

295.54

0.0508

from 123 to 147

N-3

67837

89971

311.4

159

288.08

0.0508

from 105 to 147

N-5

66347

78752

312.34

147

287.68

0.0508

from 88 to 133

N-6

72178

89863

311.87

165

301.46

0.0508

from 111 to 165

N-7

71804

87117

313.49

171

298.34

0.0508

from 134 to 158

N-9

64478

89133

311.47

159

295.77

0.0508

from 80 to 143

N-10

57920

83483

322.21

153

308.80

0.0508

from 94 to 144

N-11

59476

79689

309.78

151

296.83

0.0508

from 82 to 133

N-12

65995

86589

309.2

80

297.37

0.0508

from 60 to 79

*masl.- meters above sea level

By other side, it was found a main characteristic related with the required time to reach the pseudo steady state conditions in the well after each disturbance. The behavior of these parameters (time, and water level) for each well is related with the formation´s characteristics prevailing in its surrounding. The appendix A shows the graphic behavior of water level against elapsed time for each slug tests carried out in the wells. From the preliminary analysis of each graph it can be seen qualitatively the performance of each studied well.

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Figure 10. Distribution of the studied wells along the valley selected to characterize its behavior.

5.1 Using methodology of Hvorslev The application of the analysis methodology proposed by Hvorslev (1951) is shown through the Figure 11, which is an example of the use of this methodology for determining the TL value. In the figure above mentioned, is shown the graph of time versus Hvorslev´s parameter in order to obtain the value of TL that is used in equation (8). As mentioned before the TL value is determined from the graph to the condition of {[Hmax – H(t)] / (Hmax – Ho)} = 0.37 in the logarithmic scale. From the Figure 11 it can be seen that in the logarithmic scale it is feasible to distinguish the variation of the water level in the well during the test. In this single case the TL value is determined in 255, which is the used in the equation (8) and with the required data of the well is determined its hydraulic conductivity. The characteristic values influencing in the determination of the well´s properties using the slug tests are shown in Table 4. In this table are included the variables of all wells analyzed in this work. As can be seen in the table, the different columns correspond to values of the open thickness to the formation in each well, its maximum variation of the water level along the test, the time to reach the pseudo steady state and the value of TL as defined above.

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It is important the observation of time required to reach the pseudo steady state in each well. So it could be found some relation with the obtained results. 10.00 9 8 7 6 5 4 3

[H o -H (t)]/(H m ax -H o )

2

1.00 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03

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0.02

0.01

0

500

Time (s)

1000

1500

Figure 11. Demonstrative graph of application of the method proposed by Hvorslev for determining TL at the value of 0.37 of the parameter of water level variation [H0-H(t)]/(Hmax-H0).

5.2 Analysis by applying the Cooper, Bredehoeft and Papadopulos method. For the application of the measured data using the method of Cooper et al., (1967) in this work it was used the comparison of the type-curve with the graph in semi-logarithmic scale of t versus Ht/Ho, with Ht as the value of the variation of the water level measured along the test as a function time. The measured data during the slug test of the well N1 are graphed for apply the method of Cooper et al. using their type curve, whose result is shown in Figure 12.

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Table 4. Summary of parameters used in the analysis of slug tests carried out in the wells of the studied valley for its characterization. The elapsed time for to reach the pseudo steady state in each well, also is shown as a variable influences in the obtained results

Well N1 N2 N3 N5 N6 N7 N9 N10 N11 N12

L (m) (Thickness open to formation) 81 24 42 45 54 24 63 50 51 19

TL (s) 255 75 144 32 675 950 13 27 34 28

Δh (m) (variation of water level) 0.79 0.114 0.42 0.22 0.69 0.55 0.12 0.28 0.31 0.13

Elapsed time to reach pseudo steady state (s) 800 450 200 80 920 1500 120 100 310 190

1

0.6

h/ho

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0.8

0.4

0.2

0 0.1

1

10

Time (s)

100

1000

Figure 12. Graph of behavior of the ratio h/h0 against t during the recovery time of the level water in the well N1, after the immersion of a solid body in the process of the slug test.

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The condition to use the type curve of Cooper et al. (1967), is that in both graphs it must use the lengths of the axis of the same magnitude. So, the graph of the figure 12 was prepared with the same dimensions of the type curve (shown in Figure 7). The comparison between both graphs, it is, the type curve of Cooper et al.(1967) and that which was done using measured data during the slug test, carried out in well N1, is shown in Figure 13. According with the methodology proposed by Cooper et al. (1967), it must find the best match between the curve of measured data of the well, with any of the curves of the type curve. After the best match was found between both graphs, it must to fix a point in the graph of the measured data [t, (h/h0)] with its corresponding point in the type curve [(Tt/r2), (h/h0)]. As can be seen from equation (11), the value of Tt/r2 corresponds to β value, so, as we selected a point in which is involved this total value, then only it is necessary to solve for T (Hydraulic Transmissivity) from this equation. The value of t involved in same equation corresponds to that selected in the match point during the comparison of the graphs. In the particular case of the analysis of the slug test of the well N1, it was found that for Tt/r2 = 1.0 in the type curve, t = 59 (s) in the curve of measured data. 1.0 0.9

1

0.8 0.7

-5

-4

-2

10

10

0.5

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10

-3

-1

0.6 0.6

h/ ho

0.4

10

0.8

10

h ho

0.3

0.4

using data from Cooper et al, 1967

0.2 0.1

0.2

0.0 0.001

0.01

0 0.1

0.1 1

10

T t/r

2

1

Time (s)

10 100

30 1000

Figure 13. Example of the comparison between the graph of the measured data of the slug test carried out in well N1 and the type curve of Cooper et al. (1967).

For determining the storage coefficient (S) it is used equation (10), where α is determined from the curve selected in the best match during the comparison of graphs. After knowing the α value, we substitute it in equation 10 and solve for S, because are known the values of the radii´s wellbore and casing. In the particular case of the analysis of the well N1, in general terms there is not a clear tendency for selecting a curve, however it can be chosen the curve for α = 10-4, because it, is that best fits to the measured data.

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It is appropriate to make emphasis that sometimes the comparisons between two graphs do not produce a satisfactory match, by these reasons the results must be taken with caution. Last thing due to that the type curves were developed assuming idealistic conditions of the parameters that govern the flow in the reservoir. However in this work we make a revision of this method because gives an estimation of Hydraulic Transmissivity values and Storage Coefficient, which is useful in the formulation of criteria for the characterization of the aquifer. Also is highly important to make mention that one alone analysis method does not can support the veracity of the results obtained, because each method is focused to certain characteristics of the reservoir, that another does not assumes.

5.3 Analysis using methodology proposed by Bouwer and Rice

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As mentioned before, the method proposes to plot on semi-log paper, the observed of the water level variation (h), against the corresponding time t. Having the graph done, fit a straight line through the plotted points. Using this straight-line plot, calculate (l/t)ln(ho/ht) for an arbitrarily selected value of t and its corresponding h. Using the data of the well N1 as example, Figure 14 shows the graph resulting from the application of this method. This well in particular is assumed as partially penetrating, so, we determined A and B from the figure 9 from the value of Le/rw. For this reason were substituted the values of A, B, rc, Le, Lw and rw into Equation (18) and calculated the value ln(Re/rw). Having known the value of ln(Re/rw), (l/t)ln(ho/ht), rc, and Le, it is feasible calculate K from Equation (17). The same process was applied in the data of the tests of wells involved in this study for characterizing the aquifer and the obtained results are shown in Table 5.

5.4 Methodology of analysis of Gilg and Gavard The use of the method is too single, due that this methodology is focused in determination of the calculation of hydraulic conductivity through the use of two main parameters: The shape factor and the variation in the water level in the well during the test. The shape factor can be determined from the use of equations (22) or (23) and is a variable dependent of the value of the length of the filter zone (L) and of the diameter of the gravel pack (d). As mentioned before equation (22) is used if L > 6 m and equation (23) is used for values of L≤ 6 m. Having determined the shape factor value is feasible to apply equation (24) for determining the hydraulic conductivity (K).

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Ht (m)

0.1

0.01 B

0.001 0

500

Time (s)

1000

1500

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Figure 14. Illustrative graph of the use of methodology of Bouwer and Rice using the measured data of well N1.

6. TESTS RESULTS The measured data during the tests of wells involved in this study were applied with this methodology and the results obtained are shown in Table 5 The obtained results using the measured data during the slug tests in all the wells involved in this study show the feasibility of to apply different methods for analyzing the data and determining the well´s properties for its characterization. By the use of the methodologies of Hvorslev; Bouwer and Rice; and Gilg and Gavard can be determined the Hydraulic Conductivity, and by using the methodology of Cooper, Bredehoeft and Papadopulos the Hydraulic Transmissivity can be obtained. It is common to observe that the calculated values using the different methods are different from one to another method. Because as be mentioned before, each method was designed according with certain single characteristics in the well. However the global result of to applied methods helps to know the reservoir properties in order to define its characterization and establish the best design of its exploitation. As can be seen from the table

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5 there is some variation in the calculated values of the parameters, but it was found that the values are into a moderate rank for considering a value in the reservoir. Table 5. Summary of the slug tests results obtained through the use of four of the analysis methods

T (m2/d)

K (m/d) Well

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N1 N2 N3 N5 N6 N7 N9 N10 N11 N12

Hvorslev

BouwerRice

GilgGavard

CooperBredehoeftPapadopulos

0.0165 0.0525 0.0325 0.1339 0.0055 0.0019 0.2712 1.0007 0.1117 0.0358

0.0162 0.0739 0.0297 0.6298 0.0012 0.0034 0.3527 1.7071 0.2965 0.0636

0.0123 0.0623 0.0193 0.3926 0.0054 0.0029 0.2963 1.5081 0.1092 0.0493

9.15 7.68 33.75 17.53 2.51 2.45 7.34 30.02 12.37 8.06

Besides, the obtained results for each well are a representative example of the formation properties and these values helps to understand the behavior of the system during its continuous exploitation.

7. DISCUSSION RESULTS According with the variation of the calculated values, from one method to another, of the reservoir properties it is appropriate to make emphasis in that those determined values must be taken as an indicator and do not as a fixed value. Last thing, because there is not an unique analysis model that involves all characteristics of the reservoir, that could be considered as totally global. It is important to make emphasis that the values obtained using each analysis method, are influenced by the particular assumptions of each method. The variables that can be considered, during the tests, be of the maximum influence in the obtained results are the behavior of the water level and the period of elapsed time for reaching the pseudo steady state. However the basic concept to take into account from obtained results and the use of different analysis method is the mean range of the values, useful in the reservoir characterization.

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The main idea is that the characterization of the aquifer involves its properties, and the mechanical conditions of the wells, in order to have technical support for defining the appropriate exploitation design. Figure 15 shows the results obtained from the analysis done by applying the different methods treated in this work. From this figure it can be observed the distribution of the aquifer´s properties in the studied valley, and it is feasible to adopt an idea about the most attractive zones for exploitation and for extending the development of the field. As can be seen through the comparison between the map shown in figure 10 and the map of the figure 15, the topographic level does not influences in the characteristics reservoir. As practical application of the obtained results it is feasible to assume that the best area for exploitation is located at the west side of the valley (see map of Figure 15).

Figure 15. Characterization of the studied valley, through the distribution of the Hydraulic Conductivity determined from the slug tests carried out in analyzed wells.

So, the behavior of the water levels during the slug tests in the wells in general terms can be considered that it is influenced by the formation´s characteristics where each well is Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

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located. Although each method has its particular assumptions it can to say that the measured data were applied satisfactorily in the use of the four analysis methods discussed in this work. The analytical methods for solving the slug tests (Hvorslev, Bouwer-Rice, Gilg-Gavard) do not show greater difficulty in the data measured application, but the method of CooperBredehoeft-Papadopulos showed more difficulties in adjusting of the measured data during the tests, with the type curve. In wells N1, N6 and N7 can be appreciated a wide curvature in the graphs after each disturbance caused by the immersion and extraction of the solid body, which results in long times for reaching the pseudo steady state. The graphic of the water level behavior of the well N9 during the periods of immersion and extraction of the solid body of the test, shows some difficulty for identifying the real time of the recovery of water level. The analysis methods of the slug tests consider similar variables that those that are taken into account in the transient pressure tests, which basically are the variation of water level (pressure) as a time function. From this view point, it is important the proposed of Gilg and Gavard for incorporating the shape factors into the analysis. A sensibility analysis of the behavior of equation (22) assuming that the well has a length of thickness open to formation (L) greater than 6 m was carried out and the results are shown in Figure 16. 45 L = 40 m

40

35

A= 1.032 L + 30 d

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L = 30 m

30

25 L = 20 m

20

15 rw = 0.0635 m

L = 10 m

rw = 0.0508 m 10 0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

K (m/d) Figure 16. Sensibility analysis using equation of shape factor, with respect to hydraulic conductivity, for thickness open to formation with length greater than 6 m.

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The main conclusions of this analysis are that the hydraulic conductivity increases as direct function of the hole diameter, and decreases as inverse function of the thickness opened in the formation. Through the last graph it can be seen that the greater variation in the determination of the hydraulic conductivity values occurs for the cases of small values of L. Another important observation is related with the variation of the L value during the operative life of the well, because the thickness open to formation, varies due to sediments transported near of wellbore by the turbulence of the flow. By this reason it is appropriate to carry out periodically tests in wells to update the characterization of the system and to restate the global management of the field.

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CONCLUSION Results of the slug tests evaluation which are shown as examples indicate that those can be taken as hydrologic method for characterizing shallow alluvial aquifers. Also may successfully be employed for characterizing sites for which standard hydrologic test methods are not applicable. The slug test are recommended be used in sites of difficult access to use great water volumes or with problems to dispose of contaminated water. By these reason, such tests can be used in place of the transient pressure tests, which use as disturbance tool in the well, injection or water discharge. The obtained results of the analysis of measured data taken during slug tests indicates small changes in the water level because of the weight of the solid body used for cause the disturbance in the water level. But this aspect can be solved with the resolution of the tool used for measuring the variations of the water level. Through this work it was shown the feasibility for using the four discussed methods taking in account that the results obtained with each one must be taken with caution, because of the assumptions done in those. The global characterization of the studied system allows for identifying the zones of highest and lowest values of the reservoir properties and helps to establish technical criteria about the best exploitation design in the field. Although each method provides different results, all these are within a range to estimate a representative value for each well, and through the correlation of all wells in the studied valley, characterize the aquifer in order to design properly its exploitation and enhance the development of the field with new wells.

REFERENCES Batu, V., 1999. “Aquifer Hydraulics: A Comprehensive Guide to Hydrogeologic Data Analysis”, John Wiley & Sons, New York, 727 p. Boonstra, J., Kselik, R.A.L., 2002. “SATEM 2002: Software for aquifer test evaluation. Wageningen”, The Netherlands: International Institute for Land Reclamation and Improvement. ISBN 9070754541.

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Bouwer, H., 1989. “The Bouwer and Rice slug test--an update”, Ground Water, vol. 27, No. 3, pp. 304-309. Bouwer, H., R.C. Rice, 1976. “A slug test method for determining hydraulic conductivity of unconfined aquifers with completely or partially penetrating wells”, Water Resources Research, vol. 12, no. 3, pp. 423-428. Butler, J.J., Jr., 2002. “A simple correction for slug tests in small-diameter wells”, Ground Water, vol. 40, no. 3, pp. 303-307. Cooper, H.H., Bredehoeft, J.D., Papadopulos, S.S., 1967. “Response of a finite-diameter well to an instantaneous charge of water”, Water Resources Research, vol. 3, no. 1, pp. 263269. Custodio, E., 1993. “Aquifer intensive exploitation and over-exploitation with respect to sustainable development”, European Centre for Pollution Research, vol. 2, pp. 509-516. Custodio, E., Llamas, M. R., 1983. “Hidrología subterránea”, Editorial Omega, 2 volumes, Barcelona España, pp. 1-2350. Custodio, E., Llamas, M. R., 1996. “Hidrología subterránea”, Vol. II, Editorial Omega, second edition, Barcelona España, 1224 p.. Earlougher, R. C. Jr., 1977. “Advances in well test analysis”, Monograph, vol. 5, Society of Petroleum Engineers of AIME, Dallas TX, U.S.A. 175 p. González, L. I., Ferrer, M., Ortuño, L., Oteo, C., 2002. “Ingeniería Geológica”, Prentice Hall, 715 p.

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Hantush, M. S., 1961."Aquifer Tests on Partially Penetrating Wells”, Journal of the Hydraulics Division, Proceedings of the American Society of Civil Engineers, HY5, pp. 171-195. Hantush, M.S., 1984. "Hydraulics of wells”, In advances in Hydroscience, Editor V. T. Chow, Vol. I, Academic Press, New York, U.S.A. pp. 282-433. Hsieh, P. A., Bredehoeft, J. D., Rojstaczer, S. A., 1988. “Response of well aquifer systems to earth tides: problem revisited”, Water Resour. Res., 24(3), pp. 468-472. Hvorslev, M.J., 1951., “Time Lag and Soil Permeability in Ground-Water Observations”, Bull. No. 36, Waterways Exper. Sta. Corps of Engrs, U.S. Army, Vicksburg, Mississippi, pp. 1-50. Jacob, C. E., 1947. “ Drawdown test to determine effective radius of artesian well”, Trans. Amer. Soc. Of Civil Engrs., vol. 112, paper 2321, pp. 1047-1064. Kemblowski, M. W., Klein, C. L., 1988. “An automated numerical evaluation of slug test data”, Ground Water, Vol. 26, pp. 435-438. Mace, R. E., 1999. “Estimation of hydraulic conductivity in large diameter, had dug wells using slug lest methods”, Journal of Hydrology, vol. 219, pp. 34- 45. Neuman, S. P., 1972. “Theory of flow in unconfined aquifers considering delayed response of the water table”, Water Resources Research, Vol. 8, No. 4, pp. 1031-1045.

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Novakowski, K.S., 1990. "Analysis of Aquifer Tests Conducted in Fractured Rock: A Review of the Physical Background and the Design of a Computer Program for Generating Type Curves", Groundwater, vol. 28, No. 1, pp. 99-105. Ramey, H.J., Jr., Agarwal, R.G., and Martin, I., 1975. "Analysis of 'Slug Test' or DST Flow Period Data," J. Can. Pet. Tech. (July-Sept. 1975), pp. 1-11. Randal, L., Wu, J. Q., Wang, L., Hanrahan, T. P., Barber, M. E., Qiu, H., 2009. “Heterogeneus characteristics of streambed saturated hydraulic conductivity of the Touchet river, South eastern Washington, USA”, Hydrological Proccesses, vol 23, No. 8, pp. 1236–1246. Schwartz, F.W. and Zhang, H., 2003. “Fundamentals of Groundwater”, Published by John Wiley & Sons, Inc. New York, NY. Shinohara, K., and Ramey, H.J., Jr., 1979. "Analysis of 'Slug Test' DST Flow Period Data with Critical Flow," Paper SPE 7981, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, California, Apr. 18-20. Spane, F.A. Jr., 1993. "Selected Hydraulic Test Analysis Techniques for Constant-Rate Discharge Tests", PNL-8539, Pacific Northwest Laboratory, Richland, Washington. Spane, F. A., Swanson, L. C., 1993. “Applicability of slug interference testing of hydraulic characterization of contaminated aquifer sites”, PNL-SA-22393, Pacific Northwest Laboratory, Richland, Washington. Yeh, H. D., Chen, Y. J., 2007. “Determination of skin and aquifer parameters for a slug test with wellbore skin effect”, Journal of Hydrology, vol. 342, No. 3, pp. 1283 – 294.

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Zlotnik, V., 1994. “Interpretation of slug and packer tests in anisotropic aquifers”, Ground Water, vol. 32, no. 5, pp. 761-766 Zlotnik, V., Vitaly A., David Goss, and Glenn M. Duffield, 2010. “General Steady-State Shape Factor for a Partially Penetrating Well”, Ground Water, vol. 48 No.1, pp.111 123.

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Appendix A Behavior of water level in wells during slug tests carried out to characterize the aquifer. 8.0

13.0

Well N5

Well N3 12.5

7.5

12.0 7.0 11.5 6.5

h (m)

h (m)

11.0 10.5 10.0

6.0

5.5

9.5 5.0 9.0 4.5

8.5

4.0

8.0 0

500

1000

Time (s)

1500

2000

0

500

1000

1500

Time (s)

2000

2500

14.0

16.0

Well N6

Well N7

15.5

13.5

15.0

13.0

14.5

12.5

14.0

12.0

h (m)

13.5

h (m)

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3000

13.0

11.5 11.0

12.5 10.5

12.0

10.0

11.5

9.5

11.0

9.0

10.5 10.0

8.5 0

500

1000

Time (s)

1500

2000

0

500

1000

1500

2000

2500

Time (s)

3000

3500

4000

4500

Figure A1. Behavior of water level in wells N3, N5, N6 and N7 caused by the immersion and extraction of a solid body during its slug tests.

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A. Alfonso Aragón and M. P. Verma 10.5

Well N9

10.0

h (m)

9.5

9.0

8.5

8.0 0

500

1000

1500

Time (s)

2000

13.0

Well N10

h (m)

12.5

12.0

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11.5 0

500

1000

1500

Time (s)

2000

2500

3000

Figure A1. (Continued).

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10.0

h (m)

Well N11

9.5

9.0 0

500

1000

1500

Time (s)

2000

2500

15.0

3000

Well N12

14.5

h (m)

14.0

13.5

13.0

12.5

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12.0 0

500

1000

Time (s)

1500

2000

Figure A2. Behavior of water level in wells N9, N10, N11 and N12 caused by the immersion and extraction of a solid body during its slug tests.

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In: Water Engineering Editor: Dominic P. Torres

ISBN: 978-1-61209-914-9 © 2011 Nova Science Publishers, Inc.

Chapter 4

WATER CLUSTER ION BEAM PROCESSING Gikan H. Takaoka Photonics and Electronics Science and Engineering Center Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan

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ABSTRACT We have developed a polyatomic cluster ion source and investigated the impact process of cluster ions on solid surfaces. High-energy-density deposition and collective motions of the cluster ions during impact play important roles in the surface process. Cluster ion irradiation forms the reaction field at nano-level on the impact area, and represents distinctive irradiation effects, which are not obtained by the conventional ion beam process. In this chapter, water cluster ion beam processing is described from the viewpoints of water cluster formation and ion beam engineering. The size analysis of water cluster ions is described, and the water cluster formation is discussed based on thermodynamics and gas dynamics. Furthermore, interactions of water cluster ion beams with solid surfaces are investigated, and surface processing such as high-rate sputtering, atomically flat surface formation and nano-level chemical modification by water cluster ion beams is described from the viewpoints of advanced water engineering.

1. INTRODUCTION Water is a well-known liquid material which exists on earth and in the human body, and it has an important role in maintaining a clean environment and safe life. Liquid water exhibits different properties depending on the assembly of water molecules. In recent years, experimental and theoretical studies have been carried out to investigate the microscopic structure of liquid water in terms of clusters of water molecules [1-6]. With regards to the structure of liquid water, two types of states are proposed, one of which is the molecular state.

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Gikan H. Takaoka

Another is the cluster state, and it has a three dimensional structure of hydrogen bridge networks between the single molecules. The properties of liquid water are influenced by the cluster size as well as the structure [7-9], and the chemical reactivity between solvent and solution reduces for large cluster-sized waters [10-13]. In order to understand these aspects, it is necessary to carry out the size analysis of water clusters. Furthermore, liquid water has been applied to the surface treatment for various kinds of materials and devices. For example, surface processing such as impinging of water droplets on material surfaces has been studied and applied to surface cleaning, polishing, etching and cutting. In this process, the speed of water jets is a key factor for changing the surface properties, although it is limited within a few hundred meters per second [14,15]. In order to fabricate advanced materials and devices, the demand for material processing technologies employed has recently been increasing, and the development of new surface treatment including dry and wet processes has attracted much attention. For example, the development of a new phase of water such as functional water, supercritical state water, etc. has received special interest from the fundamental and applicable viewpoints [16, 17]. On the other hand, the ion beam process is one of the basic technologies in nanostructure fabrications [18,19]. It represents several features in material processing, one of which is that it can transfer charge, energy and mass employed for material surface treatment. It can also be applied to the surface processing such as deposition, sputtering and implantation by adjusting the accelerating energy. Another feature is that various kinds of species such as atomic, molecular and cluster ions are available [20]. In particular, polyatomic molecular ions such as water and alcohol ions contain several kinds of radicals such as hydroxyl and alkyl radicals, and these radicals have an important role in surface modification and chemical erosion of material surfaces. Furthermore, in cluster ion beam process, impact process of an energetic cluster ion on target surface represents unique properties [21,22]. A cluster is an aggregation of atoms (or molecules), and it is an isolated particle with a few nm in diameter. Since thousands of atoms impact the target at almost the same time, the many-body interactions between clusters and target atoms are induced by the dense energy deposition. This is different from linear cascade of two-body collisions, which is applied to the impact of monomer ions on a target surface. Furthermore, the high-energy-density deposition and the collective motions of the clusters during impact play important roles in the surface process. It has the ability of achieving an extremely high temperature and pressure state on the impact area by accelerating the cluster ion beams [23,24]. Based on these features, distinctive irradiation effects with water cluster ion beams, which are not obtained by conventional ion beam process and/or wet process, are expected. We have developed several kinds of polyatomic cluster ion sources and investigated the impact process of polyatomic cluster ions on solid surfaces [25,26]. In a previous study, using alcohol cluster ions, solid surfaces such as silicon, metal and polymer surfaces were etched with high sputtering yield, and they exhibited a lower damage and an atomically flat surface [27-29]. These features have not been obtained by the conventional wet process using liquid alcohol. In this chapter, water cluster ion beam processing is described from the viewpoints of water cluster formation and ion beam engineering. Water clusters are produced by an adiabatic expansion phenomenon in the vacuum and ionized by an electron bombardment method. The size analysis of the water cluster ions is performed, and the water cluster formation is discussed from the viewpoints of thermodynamics and gas dynamics.

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Furthermore, the interactions of water cluster ions with solid surfaces are investigated, and the chemical reactivity of water cluster ions is discussed based on the role of hydroxyl radicals and hydrogen atoms produced. In addition, water cluster ion beam processing is discussed based on functional properties of the water cluster ion itself. In addition, several kinds of surface processing such as sputtering, surface smoothing and surface modification by water cluster ion beams are described.

2. WATER CLUSTER FORMATION Water clusters are produced by an adiabatic expansion phenomenon [30,31]. When water vapors are ejected through a nozzle into a vacuum they are cooled down by an adiabatic expansion and purified by a distillation process. During the expansion, a large number of water molecules collide with each other, and nucleation and growth occur spontaneously due to the perturbation through the collisions of vapors, resulting in the water cluster formation. In general, clusters with a smaller radius than the critical radius are not stable, and they are dissociated to evaporation. In contrast, larger aggregates (clusters) grow to become stable due to the condensation. The critical radius r * of the cluster is given by [32]

r* = where

2σVc kT ln S

(1)

σ is the surface energy, V c is the molecular volume in a cluster, T is the vapor

temperature, k is Boltzmann constant, and S is the saturation ratio ( P / P∞ ) of the vapor

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pressure (P ) to the equilibrium vapor pressure ( P∞ ). In addition, with regard to the cluster

growth, the nucleation rate is proportional to the concentration N which is described as follows [33]:

*

(

N * = N 0 exp − ΔG * / kT where N 0 is the concentration of vaporized molecules, and the Gibbs free energy [32]:

of the critical nuclei,

)

(2)

ΔG * is the maximum value of

ΔG at the critical radius r * . The value ΔG * is described as follows ΔG * =

16πσ 3 ⎞ ⎛ kT 3⎜⎜ ln S ⎟⎟ ⎠ ⎝ Vc

(3)

2

Based on these equations (1) to (3), the critical radius r * and the barrier height ΔG of water clusters can be estimated. They become larger compared with ethanol clusters, because the surface energy of the water such as 72.8 dyne/cm is larger than that of the ethanol such as 22.8 dyne/cm [34]. As a result, the average size of water cluster ions was larger than that of ethanol cluster ions at the same vapor pressure [35].

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3. CLUSTER SIZE ANALYSIS 3.1 TOF Method

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The cluster size was measured by a time-of-flight (TOF) method. The principle of this method is based on the fact that the time of flight is proportional to a square root of mass [36,37]. In the TOF measurement, it was assumed that the cluster ion had a single charge, and multiply charged cluster ions might be dissociated due to the Coulomb repulsion force [38,39]. As shown in Fig. 1, the accelerated cluster ions enter a flight tube and are deflected by a pulsed negative-voltage. When the pulsed voltage is applied the cluster ions drift toward a Faraday cup mounted on the end of the flight tube. The flight ions are detected by the Faraday cup. In the TOF measurement, the acceleration voltage (Va) for water cluster ions was set at 6 kV and the pulse voltage was 2 kV. The duration time and the repetition rate of the pulse voltage were 10 μsec and 100 Hz, respectively. The drift distance was 0.51 m. The cluster size was calculated based on the drift time ranging from μsec to msec, which was different depending on the mass.

Figure 1: Schematic of the TOF instrument for cluster ions.

3.2 Size Distribution Figure 2 shows a size distribution for water cluster ions as a parameter of vapor pressure. The water clusters are formed at vapor pressures larger than 1 atm, and the intensity of the water cluster increases with increase of the vapor pressure. The cluster size is distributed between a few hundreds and a few tens of thousands. The peak size changes depending on the vapor pressure, and it is between 1000 and 2500 molecules per cluster for vapor pressure greater than 1 atm. According to the thermodynamics and the gas dynamics, the cluster beam intensity ( I ) depends on vapor pressure P0, nozzle diameter D and temperature of the source materials T0. It is described as follows [40,41]: γ

⎛ T ⎞ γ −1 I ∝ P0 D⎜⎜ b ⎟⎟ , ⎝ T0 ⎠

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where γ and Tb are the specific heat ratio and the boiling temperature of the source materials, respectively. The values of Tb and γ for water are 373 K and 1.33, respectively. With regards to the value of (Tb/To)γ/(γ-1) for water, it decreases with an increase of the source temperature, when the source temperature is larger than the boiling temperature. Therefore, the cluster beam intensity seems to decrease with an increase of the source temperature. However, the vapor pressure increases remarkably with an increase of the source temperature. For example, the vapor pressure such as 1 atm, 2 atm, 3 atm, and 4 atm corresponds to the source temperature such as 373 K, 394 K, 407 K and 418 K, respectively. When the vapor pressure is high, the water cluster is produced effectively by an adiabatic expansion phenomenon. As a result, the cluster beam intensity increases with an increase of the source temperature, and it is proportional to the value of P0(Tb/To)γ/(γ-1).

Figure 2: Size distribution of water cluster ions as a parameter of vapor pressure.

The size distribution of water cluster ions depends on the electron voltage (Ve) and the electron current (Ie) for ionization. The peak size of water cluster ions decreased with an increase of the electron voltage and the electron current for ionization [42]. When clusters are ionized by electron bombardment, multiply charged cluster ions as well as singly charged cluster ions are produced. On the other hand, the fragmentation of the multiply charged cluster ions also occurs due to the Coulomb repulsion force, because the molecules in the cluster are weakly bound by van der Waals forces. While the multiply charged cluster ions

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such as doubly charged cluster ions increase with an increase of the electron voltage for ionization, the fragmentation of the doubly charged cluster ions is also enhanced. In addition, the production probability of doubly charged cluster ions might be larger at higher electron voltages for ionization, and the increase of electron current for ionization by keeping the electron voltage at a higher voltage such as a few hundred volts could enhance the production of doubly charged cluster ions. As a result, the fragmentation of the doubly charged cluster ions is also enhanced with increasing the electron current for ionization. Therefore, the peak size decreased with increase of the electron voltage and the electron current for ionization. In another case of producing the water clusters, helium (He) gas was used to mix with vapors of water. Figure 3 shows a size distribution of water clusters as a parameter of He gas pressure. The temperature of water was room temperature, and the vapor pressure was 0.02 atm. As shown in the figure, the water clusters are not produced without He gas. When the He gas pressure is larger than 0.5 atm the water clusters are produced. The intensity of the water cluster ions increases with an increase of the He gas pressure, and it is saturated at higher pressures than 3 atm. The peak size of water cluster ions is between 500 and 1250 molecules per cluster. When water vapors are ejected through the nozzle into the vacuum region together with the He gas, they are cooled down by the collision with the He gas, which results in the effective formation of water clusters even at room temperature.

Figure 3: Size distribution of water cluster ions as a parameter of He gas pressure. Vapor pressure of water was 0.02 atm.

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4. SURFACE PROCESSING WITH WATER CLUSTER ION BEAMS A water cluster is an aggregation of water molecules a few nm in diameter, which is in a position to link between the molecular state and the bulk state. The physical and chemical properties of the water cluster are different from those of the bulk liquid state. As well as the properties of the cluster itself, the impact process of an energetic cluster ion on a solid surface represents unique features. For example, the reaction field at nano-level in space and time is formed on the impact surface [43]. Another feature is that the local heating effect as well as the high-density irradiation effect can be controlled by adjusting the incident energy of the cluster ions. Using these features, water cluster ion beams can be applied to the surface treatment for various kinds of materials such as metal, semiconductor, insulator and polymer. In this section, to begin with, the experimental procedure is described, and surface processing such as sputtering, smoothing and chemical modification with water cluster ion beams is described from the viewpoints of advanced water engineering.

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4.1 Experimental Apparatus Figure 4 shows the schematic illustration of the cluster source. Liquid materials such as water are introduced into the cluster source, and heated up to 150℃ by a wire heater attached around the source. When vapors of water without He gas are ejected through a nozzle into a vacuum region, water clusters are produced by an adiabatic expansion phenomenon. The nozzle is made of glass, and it is a converging-diverging supersonic nozzle with a throat diameter of 0.1 mm. Figure 5 shows the schematic illustration of the water cluster ion beam system [43]. The system consists of four chambers such as source chamber, differentially pumped chamber, ionizer chamber and target chamber. The water clusters produced in the cluster source pass through a skimmer and a collimator, and enter an ionizer. In the ionizer, the neutral clusters are ionized by an electron bombardment method. The electron voltage for ionization (Ve) is adjusted between 0 V and 300 V, and the electron current for ionization (Ie) is adjusted between 0 mA and 250 mA. The cluster ions are accelerated by applying an extraction voltage to the extraction electrode. The extraction voltage (Vext) is adjusted between 0 kV and 2 kV. The extracted cluster ions are size-separated by a retarding potential method, and the cluster size used is larger than 100 molecules per cluster. The size-separated cluster ion beams are accelerated toward a substrate, which is set on a substrate holder. The acceleration voltage (Va) is adjusted between 0 kV and 10 kV. The substrates used are Si(100) and polymethyl-methacrylate (PMMA), and the substrate temperature is at room temperature. To compare with the cluster ion irradiation on the Si(100) surface, SiO2 and metal films, which are grown on the Si(100) substrates are also irradiated by the water cluster ion beams. The film thickness is 500 nm. The background pressure around the substrate is 2 x 10 –7 Torr, which is attained using a turbo molecular pump. While water cluster ion beams are irradiated on substrate surfaces, the pressure is in the range of 1 x 10 –5 Torr.

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Figure 4: Schematic illustration of the water cluster source.

Figure 5: Schematic of the water cluster ion beam system.

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4.2 Evaluation of Surface Characteristics Irradiation effects of water cluster ions on solid surfaces were investigated. The sputtered depth of Si(100) substrates as well as SiO2 and metal films were measured using a step profiler. The sputtered surfaces were also investigated by using an atomic force microscope (AFM), and the surface roughness was measured. The surface roughness was defined as the average roughness, and the absolute value of difference in the height of a surface plane and a standard plane was averaged. In addition, the irradiation damage was investigated by using the Rutherford backscattering spectrometry (RBS) method. In order to derive the number of displacement atoms, the RBS channeling spectra were measured for the Si(100) surfaces irradiated by the water cluster ions. From the area of the Si(100) surface peaks, the number of displacement atoms was estimated by using the values such as the density of bulk Si, the ratio of aligned and random spectra for surface peak, and the energy per channel measured. Furthermore, the oxidation of Si(100) and Ti surfaces by the water cluster ion irradiation was investigated using X-ray photoelectron spectroscopy (XPS), and O1s spectra as well as Si2p and Ti2p spectra were measured. In addition, the depth profile of the XPS peaks was investigated by etching the irradiated surfaces in the XPS measurement.

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4.3 Irradiation Damage Figure 6 shows the number of displacement atoms for the Si(100) surfaces irradiated at (a) different ion doses and (b) different acceleration voltages by water cluster ions and by Ar monomer ions. The water vapor pressure was 3 atm, and the peak size of water clusters was approximately 2500 molecules per cluster. The cluster size used was larger than 100 molecules per cluster. As shown in Fig. 6(a), the number of displacement atoms for the water cluster ion irradiation increases with an increase of ion dose and it is saturated at ion doses larger than 1.0 x 1014 ions/cm2. The saturation is ascribed to the equivalently high-dose implantation of water molecules within the shallow depth. For example, when the cluster size is 1000 molecules per cluster, the ion doses of 1.0 x 1014 ions/cm2 corresponds to the molecular dose of 1.0 x 1017 molecules/cm2. In addition, the incident energy of a water molecule in a cluster ion is estimated to be the accelerating energy divided by the cluster size, and it is small such as 6 eV. As a result, the impact depth is extremely low. Therefore, the number of displacement atoms is saturated at ion doses larger than 1.0 x 1014 ions/cm2. On the other hand, the number of displacement atoms for the Ar monomer ion irradiation increases with an increase of ion dose. High energetic Ar monomer ions with 6 keV are irradiated on the Si(100) surface, and the implanted depth of Ar ions is larger than that of water cluster ions. Therefore, the irradiation damage by Ar monomer ion beams is not saturated, and it is much larger than that for the water cluster ion irradiation at an ion dose of 1.0 x 1016 ions/cm2. With regards to the acceleration voltage dependence, the number of displacement atoms increases with an increase of the acceleration voltage, as shown in Fig. 6(b). The irradiation damage by the water cluster ion beams is less than that by the Ar monomer ion beams at the same acceleration voltage. For the water cluster ion irradiation, the incident energy of a water molecule is the accelerating energy divided by the cluster size, and it is equivalently small.

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Therefore, the irradiation damage by water cluster ion beams is less than that by Ar monomer ion beams.

Figure 6: Number of displacement atoms for the Si surfaces irradiated at (a) different ion doses and (b) different acceleration voltages by water cluster ions and by Ar monomer ions.

4.4 Surface Sputtering (a) Physical/Chemical Sputtering Water is a polyatomic molecule, in which a radical, such as a hydroxyl radical is included. After impact of the water cluster ions on the solid surface, various kinds of species

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such as hydrogen atoms and a hydroxyl radical are produced. Figure 7 shows the mass spectra for the vacuum chamber (a) after impact of water cluster ions beams on Si surface and (b) at water vapor atmosphere. The acceleration voltage was 9 kV. The peaks appeared at mass numbers 1, 2, 17 and 18 corresponding to H, H2, OH and H2O. Compared with the mass spectra at evaporated water atmosphere, the H2 peak is stronger for the water cluster ion irradiation. Some of the H atoms produced react with another H atom, which result in the formation of the H2 molecule. The particles such as hydrogen atoms and a hydroxyl radical have an important role in sputtering Si surfaces by water cluster ion beams.

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Figure 7: Q-mass spectra for water molecules dissociated (a) after impact of water cluster ions and (b) at the atmosphere of water vapors.

The sputtered depth of Si(100) surfaces was investigated by changing the ion dose and the acceleration voltage. Figure 8 shows the dependence of sputtered depth for Si(100)and SiO2 surfaces on the ion dose. The acceleration voltage was 6 kV, and the cluster size used was larger than 100 molecules per cluster. As shown in the figure, the sputtered depth increases with the increase of ion dose. At a lower ion dose of 1.0 x 1014 ions/cm2, the ratio of the sputtered depth of Si(100) surface to SiO2 surface becomes approximately ten, which indicates that the chemical erosion such as silicon hydride occurs, resulting in enhancement of chemical sputtering of Si(100) surface. At a higher ion dose of 1.0 x 1016 ions/cm2, the sputtered depth of Si(100) surface is similar to that of SiO2, which indicates that oxide reaction occurs on the Si(100) surface. The possible mechanism for oxide and hydride reactions of Si surfaces by water cluster ion irradiation is as follows; H2O → H + OH

(5)

Si + OH → SiOH

(6)

Si + nH → SiHn

(7)

Here, the water molecule after impact is dissociated to a hydrogen atom and a hydroxyl radical, and they are adsorbed on the Si surface. After staying on the surface for a while, the SiOH reacts with another OH, resulting in SiO2 formation. On the other hand, hydride reaction on the Si surface occurs at the initial stage of irradiation, because Si atoms exposed

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after the irradiation are very reactive. Therefore, the volatile materials such as silicon hydride are produced, and the chemical sputtering is enhanced. However, the oxide reaction rather than the hydride reaction increases with the increase of the ion dose, and the Si surface is oxidized, which results in decrease of the chemical sputtering by hydride reaction.

Figure 8: Dependence of sputtered depth for Si(100) and SiO2 on the ion dose.

In more details, the rate of chemical reaction (ν ) with various kinds of reaction channels is described as follows [44]:

v∝N

kT h

n

∑ i =1

⎛ Qi ⎞ ⎟ , (8) ⎝ kT ⎠

exp ⎜ −

where N is the number density of water molecule, h is Planck constant, k is Boltzmann constant, T is the temperature of water molecules after impact, and Q i (i = 1, 2, , , , , n ) is the activation energy for a reaction channel (i) . The equation indicates that the rate of chemical

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reaction increases with the increase of temperature. When water cluster ions impact on solid surfaces, the cluster ions are broken up, and the multiple collisions between water molecules and surface atoms occur. As a result, many surface atoms are displaced and vibrated, and the incident energy of the cluster ions is used for heating an impact region of the surfaces. The molecular dynamic (MD) simulations showed that the surface temperature of the Ar cluster impact region was a few tens of thousands degrees, although the Si substrate temperature was at room temperature [23,24]. Therefore, the thermal vibration of the water molecules, which is expressed by kT / h , becomes extremely high, and the barrier height for the chemical reaction, which is expressed by Q i / kT , becomes comparably low. As a result, the high

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temperature at the impact region enhances chemical reactions such as oxide and hydride reactions, although the reaction rate is different depending on the activation energy for the oxide and hydride reactions.

Figure 9: Dependence of sputtered depth for Si(100) substrates and SiO2 films on acceleration voltage for water cluster ions.

Figure 9 shows the dependence of sputtered depth for Si(100) substrates and SiO2 films on acceleration voltage for water cluster ions. The cluster size used was larger than 100 molecules per cluster. The ion dose was 1.0 x 1016 ions/cm2. As shown in the figure, sputtering starts to be observed at an acceleration voltage of a few kV, and the sputtered depth increases with an increase of the acceleration voltage. Furthermore, the sputtered depth of SiO2 is larger than that of Si(100). Taking account of the sputtered depth and the ion dose, the sputtering yield was calculated by estimating the density of Si and SiO2 such as 2.42 g/cm3

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and 2.63 g/cm3, respectively. The sputtering yield at an acceleration voltage of 9 kV was 17.8 atoms per ion for Si and 17.1 molecules per ion for SiO2, which was approximately ten times larger than that for Ar monomer ion irradiation. It should be noted that the Si surface is oxidized at an ion dose of 1.0 x 1016 ions/cm2, and the physical sputtering occurs thereafter. Therefore, the sputtering yield for Si and SiO2 surfaces is almost the same. With regard to the incident angle dependence, the sputtered depth of the Si(100) surfaces was investigated. The acceleration voltage was changed from 3 kV to 9 kV. The ion dose was 1.0 x 1015 ions/cm2, and both the physical and chemical sputtering occurred on the surface at this condition. In general, for the case of physical sputtering by cluster ion irradiation, the sputtering yield decreases with an increase of the incident angle, and it changes according to cosθ [43]. This is in contrast to the change by the monomer ion irradiation, i.e., 1/cosθ, where θ is the angle from the surface normal [45,46]. As shown in Fig. 10, the sputtering yield has a maximum value at an incident angle between 10 deg and 60 deg. The angle corresponding to the maximum peak increases with an increase of the acceleration voltage. When the incident angle changes from normal to oblique, the number of reactive Si atoms exposed without oxidation increases. In addition, hydride reaction frequency in the near surface region becomes high, and the number of particles ejected as volatile material increases, resulting in high sputtering yield. Furthermore, the optimum energy for the hydride reaction is related to the normal component of the incident energy for the water cluster ions, and the incident energy corresponding to the highest sputtering yield changes depending on the acceleration voltage.

Figure 10: Dependence of sputtering yield for Si(100) substrates on incident angle for water cluster ions. The ion dose was 1.0 x 1015 ions/cm2. Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

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The sputtering yield was investigated for several kinds of metal films. Figure 11 shows sputtering yields for Ti, Ni, Cu, Ag and Au films together with Si substrate. The acceleration voltage was 9 kV and the cluster size was larger than 100 molecules per cluster. The ion dose was 1.0 x 1016 ions/cm2. In the figure, the sputtering yield by irradiation of Ar ion beams is shown at an acceleration voltage of 9 kV. As shown in the figure, the sputtering yield is larger than that by Ar monomer ion irradiation, even if the incident energy per molecule in a water cluster is less than 90 eV per molecule. This is due to the high-density irradiation effect by water cluster ion beams.

Figure 11: Sputtering yield for Ti, Ni, Cu, Ag and Au films as well as Si substrate irradiated by water cluster ions and Ar monomer ions. The ion dose was 1.0 x 1016 ions/cm2.

(b) Patterning with High-Rate Sputtering PMMA is a transparent polymer and it is used in various kinds of engineering fields as an organic glass. It is also applied to a micro reactor, in which micro patterning is performed. The sputtered depth of PMMA surfaces by the water cluster ion beams was investigated. As shown in Fig. 12, the sputtered depth increases with an increase of the acceleration voltage and it is 2.9 μm at an acceleration voltage of 9 kV. Taking account of the ion dose of 1.0 x 1016 ions/cm2, the sputtering yield is calculated to be 206 molecules per ion by assuming the density of 1.19 g/cm3. According to the XPS measurement for the PMMA substrates, the chemical erosion of the substrate surfaces occurred through the exchange of the CH3 radical in COOCH3 with H atom of the water molecule or the exchange of OCH3 radical with OH

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radical of the water molecule. As a result, the PMMA surface changes to a poly-methacrylic acid surface, which represents the low melting point less than room temperature and is dissolved by water. The impact of water cluster ions following-up enhances the ejection of the methacrylic acid molecule at the monomer state from the surface. Therefore, the high rate sputtering of PMMA surfaces is achieved by the chemical erosion of the surface as well as the momentum transfer of the incident energy with water cluster ion beams.

Figure 12: Dependence of sputtered depth for PMMA substrates on acceleration voltage for water cluster ions.

Figure 13 shows (a) mask pattern and (b) micro-patterning of PMMA substrate demonstrated with water cluster ion beams. The acceleration voltage was 9 kV and the ion dose was 3.0 x 1016 ions/cm2. The mask-pattern representing the letters “KYOTO” is prepared on the PMMA substrate and the sputtered depth of the substrate is approximately 10 μm. Also, the width of a letter prepared is larger than that of the mask, which is 50 μm. This is ascribed to the lateral sputtering of PMMA surface under the cover mask by the water cluster ion irradiation. In order to perform a sharp-edged pattern, the contact of the mask on the substrate should be improved.

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Figure 13: (a) mask pattern such as KYOTO and (b) micro-patterning of PMMA substrate demonstrated with water cluster ion beams.

4.5 Surface Flatness Si(100) surfaces sputtered by water cluster ion beams were investigated using AFM and the surface roughness as well as the surface morphology was measured. Figure 14 shows the dependence of the Si(100) surface roughness on (a) ion dose and (b) acceleration voltage. As shown in a dotted line in the figure, the surface roughness for the unirradiated Si(100)

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surface is 0.18 nm, which is smaller than that for the irradiated Si(100) surfaces. The diameter of a water cluster ion is a few nm, and the influence of the cluster ion impact such as shock wave generation occurs, which results in crater formation [47]. For an atomically flat surface like an unirradiated Si surface, e.g. with a roughness less than sub-nm, the surface sputtered by the cluster ion beams is considered to form a crater-like hole, and the surface roughness increases.

Figure 14: Dependence of the surface roughness of Si(100) substrates sputtered by water cluster ion beams on (a) the ion dose and (b) the acceleration voltage. Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

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Therefore, as shown in Fig.14(a), the surface roughness increases slightly with an increase of the ion dose. Furthermore, the surface roughness increases with an increase of the acceleration voltage, and it is 0.78 nm at an acceleration voltage of 9 kV. However, the lateral sputtering effect increases with an increase of the acceleration voltage, which assists the surface roughness to be depressed. As a result, the smooth surface with a roughness less than 1 nm is obtained even after sputtering at higher acceleration voltages. Also, for PMMA surfaces, the smooth surface with a roughness less than 2 nm was obtained even after sputtering at a sputtered depth of 2.9 μm. Thus, the water cluster ion beams have unique characteristics such as high-rate sputtering and smooth surface formation at an atomic level, which are not performed by the monomer ion beam process. The water cluster ion beam processing exhibits new functional properties of liquid water, and it can be applied to the surface treatment for various kinds of materials as a new phase of water engineering.

4.6 Surface Modification

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(a) Oxidation The chemical modification such as surface oxidation is useful for functional surface formation. The hydroxyl radical of water molecule has an important role in the oxidation of material surfaces. The irradiated Si(100) and Ti surfaces were investigated using XPS. Figure 15 shows the dependence of the XPS peak intensities for (a) Si2p spectra and (b) O1s spectra on the etched depth. The acceleration voltage was 6 kV, and the ion dose was 1.0 x 1016 ions/cm2. The Si2p peak for the Si(100) surface irradiated by the water cluster ion beams is shifted to the higher value of binding energy, which corresponds to the peak for SiO2. The peak decreases with an increase of the depth, and another peak corresponding to the peak for Si appears. At a depth of 10.5 nm, the SiO2 peak disappears, and only the Si peak is observed. On the other hand, O1s peaks move to the lower value of binding energy at larger depths. The peak intensity decreases with an increase of the depth, and it is very weak at a depth of 10.5 nm. This indicates that the silicon oxide layer is formed by the water cluster ion irradiation, and the oxide layer thickness is approximately 10 nm. In addition, SiOx layers with a different composition ratio (x) is formed near the surface. Figure 16 shows the dependence of the XPS peak intensities for (a) Ti2p spectra and (b) O1s spectra on the etched depth. The acceleration voltage was 6 kV, and the ion dose was 1.0 x 1016 ions/cm2. As shown in the figure, the Ti2p peak is split, and two peaks such as Ti2p1/2 and Ti2p3/2 appear. These peaks are shifted to the higher values of binding energy on the irradiated surface, and they move to the lower energy values with an increase of the depth. In addition, the Ois peak decreases with an increase of the depth, and it is very weak at a depth of 8.8 nm. This indicates that the titanium oxide layer is formed by the water cluster ion irradiation, and the oxide layer thickness is approximately 9 nm.

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Figure 15: Dependence of the XPS peak intensities for (a) Si2p spectra and (b) O1s spectra on the etched depth of the Si(100) surface.

(b) Wettability Material surfaces exhibit a hydrophilic property or a hydrophobic property depending on the difference of surface energy, and the control of wettability is useful for the application of surface modification. Furthermore, the surface decoration by polyatomic molecules and/or radicals has attracted much interest, and a self assembled monolayer formation on the surface has become important. The wettability of the Si(100) and Ti surfaces irradiated by water cluster ion beams were investigated by measuring the contact angles for a water droplet, which was put on the Si(100) and Ti surfaces immediately after their removal from the vacuum chamber. Figure 17 shows the dependence of the contact angle on the ion dose for the water cluster ion irradiation. The acceleration voltage (Va) was 6 kV. The cluster size was

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larger than 100 molecules-per-cluster. The contact angles for the unirradiated surfaces are about 45 degrees for the Si(100) surface and about 30 degrees for the Ti surface, respectively. As shown in the figure, the contact angle for the Si(100) surface decreases with an increase of the ion dose, and it is less than 5 degrees at ion doses larger than 1.0 x 1015 ions/cm2. The wettability of the Si(100) surface is remarkably enhanced by the irradiation of the water cluster ions.

Figure 16: Dependence of the XPS peak intensities for (a) Ti2p spectra and (b) O1s spectra on the etched depth of the Ti surface.

On the other hand, the contact angle for the Ti surface increases with an increase of the ion dose, and it is about 80 degrees at ion doses larger than 1.0 x 1015 ions/cm2. The Ti

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surface becomes hydrophobic by the irradiation of the water cluster ions. This is ascribed to the difference in the chemical modification of Si and Ti surfaces by the hydroxyl radicals, which are produced after impact of the water cluster ions on the surfaces. The dangling bonds produced on the Si surfaces as well as the Ti surfaces have a bond with the hydroxyl radicals, which result in the oxide layer formation on the surfaces. To be compared with water cluster ion irradiation, ethanol cluster ion irradiation was performed on Si(100) and Ti surfaces. The change of contact angles for Si(100) and Ti surfaces was completely opposite to the water cluster ion irradiation. The Si(100) surface became hydrophobic, and the Ti surface became hydrophilic. This is ascribed to the different way of attachment on the irradiated surface by hydroxyl and alkyl radicals. Thus, the surface modification such as the hydrophilic and hydrophobic properties can be controlled by selecting the radicals such as hydroxyl and alkyl radicals.

Figure 17: Dependence of the contact angles of the Si and Ti surfaces by the water cluster ion irradiation on the ion dose.

5. SUMMARY Water is a well-known liquid material, which is used as a solvent in the wet process. As liquid water itself is in a neutral state, it does not represent any chemical reactivity. However,

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it has been reported that the microscopic structure of liquid water influences its property including chemical reactivity. In order to clarify the influence, it is necessary to carry out the size analysis of water clusters. On the other hand, a cluster is an aggregation of atoms (or molecules) a few nm in diameter, which is in a position to link between the atomic state and the bulk state. The physical and chemical properties of the cluster are different from those of the bulk state, and the cluster represents a new phase of matter. As well as the properties of the cluster itself, the impact process of an energetic cluster ion on a solid surface has attracted much interest. Based on these backgrounds, the water cluster ion source was developed. Water clusters were produced at vapor pressures larger than 1 atm by an adiabatic expansion phenomenon. The cluster size was measured by the TOF method. It was distributed between a few hundred and a few tens of thousands, and the peak size was approximately 2500 molecules per cluster. The intensity of the water clusters increased with an increase of the vapor pressure. In future work, the size separation of water clusters could be of much more importance in order to clarify the microscopic structure and the chemical reactivity of water cluster ions. Furthermore, the interactions of water cluster ion beams with various kinds of solid surfaces were investigated. High-rate sputtering and low damage formation with water cluster ion beams were achieved, and the atomically flat surface formation was performed. These characteristics could not be obtained by the conventional ion beam process. Furthermore, the chemical reactivity of the water cluster ions, which was very related to the radicals such as hydroxyl radical and excited hydrogen atoms, was enhanced by accelerating the water cluster ions. These resulted in the enhancement of oxide and hydride reactions on silicon surfaces with water cluster ion beams. As well as the chemical erosion, the surface modification such as hydrophilic and hydrophobic properties was preformed on Si(100) and Ti surfaces. In more detail, the irradiation effects of water cluster ions on solid surfaces such as Si(100) and SiO2 surfaces were investigated. The irradiation damage of the Si(100) surfaces was investigated by utilizing the RBS measurement. The number of displacement atoms for the water cluster ion irradiation at ion doses larger than 1x1015 ions/cm2 was less than that for the Ar monomer ion irradiation at the same acceleration voltage. The sputtered depth of the Si(100) and SiO2 surfaces increased with an increase of the acceleration voltage, and the SiO2 surfaces were sputtered more than the Si(100) surfaces. The sputtering yield at an acceleration voltage of 9 kV was 17.8 atoms per ion for Si and 17.1 molecules per ion for SiO2, which was approximately ten times larger than that for Ar monomer ion irradiation. The XPS measurement showed that Si(100) surfaces sputtered at an ion dose of 1.0 x 1016 ions/cm2 and had an oxide layer such as SiOx. This was due to the oxidation of Si(100) surfaces by hydroxyl radicals. Furthermore, it was noted that the hydride reaction of the Si(100) surface occurred at a lower dose of 1.0 x 1014 ions/cm2, and it resulted in the enhancement of chemical sputtering of the Si(100) surface. As well as the ion dose dependence, the incident angle dependence of sputtered depth indicated that the chemical sputtering of Si(100) surfaces occurred at an oblique incidence. The hydrogen atom in a water molecule, which was dissociated during impact of the water cluster ions on the Si surface, had an important role in the chemical sputtering. With regard to the high-rate sputtering of PMMA surfaces, the XPS analysis indicated that the chemical erosion of the PMMA surfaces occurred through the exchange between CH3 and H radicals, and the chemical sputtering by the ejection of the methacrylic acid molecule was enhanced. The AFM analysis showed that the surface roughness of PMMA substrates

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Gikan H. Takaoka

irradiated was less than 2 nm, and the smooth surface at the nano-level was obtained. Based on these results, the micro-patterning of PMMA substrate surfaces was demonstrated with water cluster ion beams and the mask patterns were performed on the substrate.

ACKNOWLEDGMENTS The author was grateful to the Quantum Science and Engineering Center of Kyoto University for the RBS measurement. Furthermore, a part of the work such as SEM observation was supported by “Nanotechnology Support Project” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

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In: Water Engineering Editor: Dominic P. Torres

ISBN: 978-1-61209-914-9 © 2011 Nova Science Publishers, Inc.

Chapter 5

WATER ENGINEERING: A CHALLENGE FOR SUSTAINABLE DEVELOPMENT FOR VULNERABLE COMMUNITIES-CASE COLOMBIA Maria Catalina Ramirez1, Andrea Maldonado2, Diana Calvo2, Miguel Angel Gonzalez1, Luis Camilo Caicedo1, David Gereda1 and Felipe Muñoz3 1

Industrial Engineering Department, Universidad de los Andes, Bogota, Columbia 2 Environmental Engineering Department 3 Chemical Engineering Department

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ABSTRACT

According to estimates of IDEAM1, Colombia has 742,705 drainage basin units, indicating the total water supply will surpass 2,000 km3/year, which corresponds to 57,000 m3/year*Hab. Despite this abundant water supply, in this country, a considerable amount of the population has no access to drinking water because of problems associated with availability (quantity, quality or accessibility), the rural population being the most affected. Currently in the country, 13.6 million people live in rural areas, of which 39.7% have no water supply system, 60% have no sanitary or sewer units and only 11% have access to treated water. The situation in 2009 was reflected by the 189,480 cases of disease and 7,900 people who died because of perinatal mortality, acute diarrheal disease, malaria, dengue, and cholera, all of which are diseases associated with water quality.Problems with the availability of water resources are associated with causes such as population growth, spatial distribution, pollution, and mismanagement of the resource associated with poor governing and implementation of policies.

1

Institute of Hydrology, Meteorology and Environmental Studies. Colombia

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Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al. These problems make a water-rich country such as ours a failure in ensuring resource availability as a right for all the people. Although the legal structure in Colombia is one of the most important in Latin America, complementary mechanisms of action and control tend to be insufficient. For this reason, the Government, through the Decree 421/00, regulated by Resolution 151/01, has empowered organized communities constituted as non-profit legal entities, to provide public services in smaller municipalities and rural areas. This scenario requires linking different members with the objective to design innovative solutions to increase coverage of safe water. In this context, the organizational system, Ingenieros sin Fronteras - Colombia (ISFC), is established. Constituted by engineering schools (teachers and students) to work with communities and local government entities in formulating a social model which designs and implements technological solutions that are accessible and culturally appropriate. ISFC develops projects based on the CDIO approach (Conceive, Design, Implement and Operate), engineering solutions that improve the quality of life of vulnerable communities in Colombia, working together with them through collective participation.The chapter will address each of the problems mentioned by a critical analysis in light of the Millennium Development Goals and other United Nations regulations that require states to provide quality water. Additionally, it will also present a case study in a Colombian town in which ISFC, through collective participation and the CDIO methodology, improved the water quality of the population. The framework developed during this process is shown as a workable model to be replicated in other parts of Colombia, in order to propose innovative alternatives that generate sustainable development for the most vulnerable in Colombia.

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1. INTRODUCTION: SHORTAGE DESPITE ABUNDANCE The perception of most of the inhabitants of the planet regarding water is that this is an infinite resource. Even though almost the 70% of the surface of our planet is covered by water (CIA, 2010), only 3% is fresh water (FAO, 2007). This percentage is divided in a 70% in glaciers water and the remaining 30% as groundwater and superficial water associated to rivers and lakes. However, despite the small amount of water that is available (42.000 km3/year), this amount is enough to cover the demand of the 6,500 million people on the planet, that demands around 3,000 km3/year of this resource. In Colombia, the situation is even more significant. The amount of available fresh water per person is much higher than the world average, being in the 24th place among 182 countries studied (IDEAM, 2005). This abundant amount of water is noticeable in departments like Chocó or Amazonas. In this scenario, the logical conclusion would be that the amount of fresh water is more than enough to supply the global demand, as well as the Colombian demand. However, this amount cannot be seen so broadly. It is important to take into account three basic aspects that determine the quantity of water a specific community can have: availability1, accessibility2 and quality3 (Defensoría del Pueblo, 2009). Sadly, these three components are on a decline due to the mismanagement. The misperception of the water as an infinite resource generates a lack of concern regarding the need to preserve the resource and the ecosystems that generate it. The degree of 1

Sustainable supply capacity based in the water quality of the basins, as well as in the regularity of the public services. 2 Capacity to supply drinkable water for all the people without compromising their physical integrity. 3 Physical-chemical state of the water whose concentration of polluters do not exceed the limits to avoid compromising the health of the population.

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irresponsibility has reached to the extremes of endangering ecosystems like the páramo, which supplies a vast amount of water in excellent condition to numerous villages in the country. An additional aggravating factor relatedto the lack of water conservation is the consequence in morbidity and mortality, especially in children. A bad quality of the resource on top of the lack of the resource results in millions of deaths each year because of diseases related to water, like cholera, dengue fever, diarrhea, among others. This condition is so critical in Colombia that the leading cause of death in children under 5 years old is the acute diarrheal disease. That is why it is necessary to raise awareness of the problem in Colombia and the world, and it is vital to take improvement measures related to the resource, its conservation, and the conservation of the systems that produce it.

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Variability of the water resources in Colombia As noted above, Colombia has a large quantity of water sources that makes it known as a water-rich territory. Plentiful rivers like the Caquetá, Magdalena, Orinoco and Amazonas, as well as lakes, ponds and creeks support this reputation. For example, the Caquetá River’s streamflow can reach up to to 15000 m3/s, while the Magdalena River, the most important in Colombia due to it uses and history, reaches 7000 m3/s (IDEAM, 2001). Moreover, the volume of rainfall in the Colombian territory is higher than in most zones of the world. The multi-annual average is 3000 mm, a figure that represents a very important affluence to the surface runoff (IDEAM, 2009). These two factors make possible that, when comparing regional numbers with global ones, the Andean region has a water availability per capita three times the average that in the rest of America and 6 times the world average; (IDEAM, 2005; FAO, 2010) (see table 1-1) and that Colombia has the capacity to procure 53000 m3/year per inhabitant. However, the variability in space and in time of the water sources and of the rainfall makes the availability of the resource limited in some zones of the country. In terms of water bodies, while in zones like the Orinoquía and the Amazonia are rich in the resource, other zones like the inter--Andean valleys and planes, the Caribbean Zone, the upper Magdalena, among others, suffer from a deficit of the resource (Marin, 2003; Defensoría del Pueblo, 2009). To illustrate this problem with the distribution of the resource, almost 20 million Colombians (close to 45% of the population) have only 2.67% of the available water, while the 85% of the water can be used by 37% of the population (Defensoría del Pueblo, 2009). This shows Colombia as a country inhabited in the dry areas, surrounded by humid zones sparsely populated (Marín, 2003). Regarding the climate variability, the country faces strong dry seasons with high humidity. In the floods seasons, several municipalities in Colombia are badly affected by the adverse weather, leaving numerous people homeless (v.g. 1,200,000 because of the winter of 2010) and prone to several diseases caused by the humidity and the contact with bad quality water; the water bodies and the sewer systems overflow, and the infrastructure of the country is not adequate to store the resource. Conversely, in the drought season, the people do not

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have available water for consumption, several municipalities have to ration the resource and the offer is not enough to satisfy the demand of the population. Table 1-1. Fresh water availability in several regions Region

World Africa Asia Europe Oceania America Andes1

Precipitations

IRWR

Percentage of fresh water in the world

Available per inhabitant

km3/year

km3/year

%

m3/year

112100 20359 26798 16391 4733 43820 8777

43002 3931 12393 6548 892 19238 5186

100% 9% 29% 15% 2% 45% 12%

6380 4008 3037 8941 32366 20928 41439

Because of this, it is important to take into account the natural regulation depending on the ecosystems and the way we take care of them.

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The hydrological cycle and preserving the ecosystems First of all, the lack of understanding of the citizens about the hydrological cycle that regulates the planet’s climate and the regeneration of fresh water (ACSE, 1996) has as a consequence, among others, which is the human intervention in unique ecosystems, generating devastating impacts. The Colombian hydrological cycle shows once again the vast amounts of water “produced” in the country. Taking into account the surface runoff, groundwater and superficial water, still and flowing water bodies, the amount of water is overwhelming. First, if we add all of the contribution of surface runoff that arrives and creates creeks, rivers, lakes, among others, the approximate total streamflow is 67000 m3/s. Another important amount is in rivers and creeks that arrive to the sea that do not have any use. Additionally, the groundwater obtained by infiltration may be equal to 70 times the amount of Colombian surface water. Finally, cienagas, lakes and still water bodies, shelters 38 million m3 (IDEAM, 2001), which is enough to sustain the whole Colombian population. The big amount of sheltered water will not be possible without the different ecosystem types of the country. Big cienagas able to regulate the weather, unique paramos worldwide that are known as “water factories”, and very special types of soils for the retention of the resource, increase its availability for the population. Unfortunately, the privilege of having so many and so particular ecosystems that produces a big water offer, is wrongly translated as an “excess”, resulting in a lack of care by the population towards this kind of natural system. Countries like Finland, Denmark, among 1

Andes includes Bolivia, Ecuador, Venezuela and Colombia

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others, value in an implicit way the ecosystems and the water, because they have such a short offer of it. Colombia does the opposite: the care and the protection of the ecosystems and water sources is minimal, despite of all the efforts of the Government; the lack of awareness of the average Colombian is so deep, that the idea of the resource being infinite is a common place in the society. Sad examples of this situation are the paramos. Only six countries in the world have them (Colombia, Venezuela, Ecuador, Peru, Panama and Costa Rica), all of them –except Costa Rica- located over the Andes. This neo-tropical zone is affected daily by the demographic and agro-industrial growth, with a severe consequence: less available fresh water.

Scarcity index

Scarcity index High Medium High Medium Minimum Not Significant

Municipalities 21 51 38 257 694

% 2% 5% 4% 24% 65%

Population 980.616 13.250.271 2.624.747 11.713.232 13.669.325

% 2% 31% 6% 28% 32%

Natural Regulation

Natural Regulation Unregulated Very Low Low Moderate High Very High Vulnerability Very High High Medium Low Very Low Minimum

Municipalities 31 107 554 221 159 41 Municipalities 6 175 568 285 33 1

% 3% 10% 50% 20% 14% 4% % 1% 16% 53% 27% 3% 0%

Population 634.966 3.580.490 27.646.078 5.199.126 4.867.791 1.135.712 Population 301.586 20.036.370 14.705.174 6.508.034 700.107 25.220

% 1% 8% 64% 12% 11% 3% % 1% 47% 35% 15% 2% 0%

Vulnerability

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Table 1-2. Indicators that show the availability of the resource

In order to determine the amount of water available for the population, one must take into account the natural regulation, responsible for the capacity of an ecosystem to self-sustain the population; the scarce index, which indicates the amount of water needed by the population of a place over the amount of the water “produced” in its jurisdiction; and lastly, the vulnerability index, that combines the former two. Table 1-2 shows the level of the three indexes in the Colombian municipalities, showing a situation that, although manageable, should put us in alert regarding the care of the resource.

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Accessibility of the water in Colombia Taking into account the amount of water available for the Colombians, it is vital to take into consideration how accessible the resource is for the population. This means that the available water should be physically easy to obtain. This takes us directly to the capacity of the water works and sewer in the country, since the infrastructure associated to these two services is the fundamental determinant to make the access to the water easy and realistic. Based on data given by the DANE’s 2005 Census, 65.1% of the countries housing are connected to a water system, while 41.2% have sewerage. Pitifully, of the 1099 municipalities of the country and 20 departmental corregimientos (departmental divisions), 665 have a water works coverage under 75% and 964 have less than 75% of coverage in their sewer system (Defensoría del Pueblo, 2009). An even worst situation is seen in 110 municipalities of the country, which have coverage of less than 30% in their water works, while 440 municipalities have a covering of less than that in sewage (see Table 1-3) (DANE, 2005). This means that the population that lives in these municipalities is under a severe lack of water, and also confirms the fact that is not enough to have a large amount of water sources, but is necessary to secure its availability and accessibility to the whole population. Table 1-3. Coverage by ranges

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Total Coverage Rages 0 to 15% 15 to 30% 30 to 45% 45 to 60% 60 to 75% 75 to 90% 90 to 100% Total

AQUEDUCT Average total Municipalities coverage 49 60 102 182 272 327 127 1.119

3,8% 24,2% 37,8% 53,7% 67,4% 82,3% 94,3% 65,1%

SEWERAGE Average total Municipalities coverage 204 236 216 169 139 103 52 1119

5,80% 22,30% 37,20% 52,30% 67,20% 82,00% 94,20% 41,20%

An aggravating factor to these figures is the access to drinking water of the child population. Nearly 3 million children have no access to the services (Defensoría del Pueblo, 2009), which leads to a very delicate public health problem that should be addressed as a priority in the country.

Quality of the water in Colombia In parallel with the problems of distribution, the problems associated with the quality of the resource should also be contemplated; these can drastically limit the availability and accessibility of a given population to drinking water. The quality of the groundwater and

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suuperficial watter is deeply at a risk becausse of the leakking of wastewater. Since the colony anndthe people have used thee water bodies to transport and dump liqquid and solidd wastes, a prractice that affects a the quuality of the water for thee people locaated downstreeam of the diisposal, it hass, as a conseequence, a severe deterioraation of the quality q of waater by the afffected populaation. According to the resoluution 2115 of 2007 (that will be menttioned in thee following seection), the waater should haave acceptablee minimum off quality to be drinkable, whhich are not m in most of met o the occasioons. As we can c see in Figure 1-1, onnly 16% of the t studied m municipalities have h water SU UITABLE, ann alarming 800% have wateer NOT SUITABLE and thhe remaining 4% 4 have wateer NON-VIAB BLE (accordinng to the Qualiity Water Riskk Index). Ii iss important to o clarify that the t lack of innformation is another comm mon denominnator in the coountry (Figuree 1-1 has inforrmation from only o 541 munnicipalities), which w makes it even more diifficult to plan n possible soluutions.

20 0; 4% 87; 16%

434; 80%

Municipalities with SAFE  water Municipalities with  UNSAFE water

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Municipalities with  ABLE  water NON‐VIA

Fiigure 1-1. Qualiity of the waterr in the differentt municipalitiess of the country. Source: SIVIC CAP.

r the loow quality of the water souurces in Colom mbia, with ann additional This data reflects agggravating point: most of thhe populationn is crowded inn very small areas, a which generates g a poollution pressure to the waater bodies. Rivers R like thee Bogotá, Meedellín, Orinoco and the M Magdalena Riv ver have beenn used for ceenturies as recceptor bodiess of wastewatters, which prroduces a serious chain effeect, where poppulations dow wn the river haave to consume the water frrom population ns up the riverr, as we mentiioned before. Therefore, it is essential to have a holiistic approach to the water service: s water works that diistribute wateer of good quuality, adequaately treated, and sewer systems s that collect the w wastewater of the t municipaliities, which shhould be treatted before beinng poured intoo receiving w water bodies. o the treatmeent of drinkabble water, the actions perfoormed generaally are the In terms of saanitation of water, w which is an essentiial step to avvoid several diseases. d Reggarding the w wastewater, thee situation beccomes worse. Only O 12% of the t urban pouuring effluents are treated

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(SUI, 2005), and the future does not look encouraging, because there are more than 97425 pouring points identified1, of which 43% do not have a sanitary plan. These figures can also be compared with the levels of contamination of the most important basins of the country, which are alarming: of the 88 studied, 84 have alarming indexes of organic matter (measured as COD2); most of them have a pH completely unacceptable; only 7 have a good level of oxygen; and in terms of solids and conductivity, even thought the situation looks more promising, there is a lack of information (IDEAM, 2005). Additional to the data presented, lack of treatment of wastewater and lack of control of effluents, according to the health statistics (WHO, 2010) in 2008, more than 5 million people of the countries with low income needs sewage treatment (ST), due to the use of the receptor bodies. The lowers numbers of coverage corresponded to the Oriental Mediterranean region (where only one in ten people needing ST receive it) and is higher in the American Region (where one in two people needing ST receive it).This outlook is apparently encouraging for our region, and in fact, the figures of covering of sanitation have improved and the access to improved drinking water sources is optimal. In contrast, the rural population has very low figures of covering in improved sources of sanitation and access to drinking water. Table 1-4 shows the covering percentages and the position occupied by Colombia among the 154 countries that WHO has information for. Table 1-4. Covering of the sanitation and improved water sources in Colombia

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Covering

Urban

Rural

% of covering

% of covering

Place among 154 countries

Improved sanitation

99%

81%

55

Improved sources

73%

55%

73

water

As has been exposed, it is essential to take into account the quality when we want to determine the available water for a population, because a bad quality of the water causes multiple problems of morbidity and mortality, especially in children.

Morbidity and mortality associated with the water in Colombia The water is the larger vector of diseases of the planet, because of its unequalled characteristics and how necessary is it to the existence of life. Diseases related with the consumation or presence of polluted water, like the infections caused by the E. coli, Salmonella, rotavirus, poliomyelitis, enteroviruses, hepatitis A, typhoid fever, cholera and malaria among others, have taken the lives of millions of people around the world.

1 2

By the Procuraduría General de la Nación and the Superintendencia de Servicios Públicos Domiciliarios Chemical Oxygen Demand.

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In Colombia, the situation is not different: in 2007, 173712 cases of diseases related with the water were reported, with malaria being the most common, with 62.9% of the reported cases (see Table 1-5) (INS, 2009). Table 1-5. Cases of diseases possibly related to the water 2006

MORBIDITY

2007

Num. Cases Weight Num. Cases Weight Cholera

0

0%

3

0%

33.614

23%

38.551

22%

8.562

6%

5.563

3%

615

0%

581

0%

Hepatitis A

4.212

3%

5.917

3%

Drug intoxication

1.306

1%

2.641

2%

Heavy metal poisoning

34

0%

61

0%

Methanol intoxication

47

0%

138

0%

Intoxication by other chemicals

2.107

1%

3.796

2%

Pesticide intoxication

5.219

3%

6.247

4%

Solvents intoxication

64

0%

247

0%

835

1%

630

0%

Clasic dengue Intoxication transmitted by Food or Water Typhoid and Paratyphoid fever

Leptospirosis Complicated malaria Falciparum malaria Malariae malaria

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Mix Malaria Vivax malaria Total

10

0%

60

0%

30.793

21%

29.997

17%

10

0%

18

0%

1.003

1%

1.275

1%

60.745

41%

77.987

45%

149.176

173.712

In terms of mortality, the cases reported in the Colombian territory for 2007 according to the National Health Institute reached 7465, being the case with the highest incidence of perinatal mortality (see Table 1-6). It is important to highlight the relation of this kind of death with a proper coverage of a water and sewerage system, because the sanitary conditions at birth are essential for the life of the newborn. In this manner, we can asseverate that about 80% of the diseases related with the water are due to inadequate sanitary conditions, and is quite likely that about 90% of the deaths are due to this cause. As we can see, the availability, the accessibility and the quality of the water are essential to guarantee the health of a country. Currently, Colombia is surrounded by paradoxes: is a country rich in water, yet several zones still suffer from a lack of the resource, are prone to changing weather, face a lack of good quality water, and finally does not have a proper care of the resources and ecosystems1. 1

It is important to recognize that the governmental entities are working to improve the water conditions in the country.

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These figures reflect the hard work that is required in order to preserve the resource and improve the quality of life of the populations, based in technically feasible, economical, financial, environmental, and social engineering solutions. The approach to these solutions should be based on the knowledge of the availability of the resource and its quality. Table 1-6. Death cases because of diseases possibly related with the water Morbidity Maternal mortality Perinatal mortality Mortality by ADD 0-4 years Dengue mortality Mortality by ARD 0-4 years Malaria mortality Total

2006 Num. Cases Weight 420 6% 6.257 84% 206 3% 44 1% 489 7% 30 0% 7.446

2007 Num. Cases Weight 415 5,56% 6.387 85,56% 20 0,27% 205 2,75% 418 5,60% 20 0,27% 7.465

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2. RESPONSE OF THE COLOMBIAN GOVERNMENT TO WATER-ACCESS SITUATION The concern about environmental topics associated to the use of forests, the water and the land, became relevant in the country through the creation of the first Corporación Autónoma de Colombia (Colombian Autonomous Corporation), the 22 of October of 1954, during the government of Gustavo Rojas Pinilla. This first corporation aimed to promote the development of the Upper Cauca valley (Cauca, Valle, Caldas), due to the need to generate actions to protect the population of water-related threats in the region associated with overflows, avalanches and floods of the Cauca River and its tributaries. This first corporation, which was supported by the World Bank, the president of the Tennessee Valley Corporation and local leaders, performed environmental, civil and socioeconomical studies. With the purpose of adopting strategic measures that would guide the government investments in plans to improve the quality of life of the population both during seasons of drought and winter, following an agricultural {refer for missing text} and of management of the natural resources scope. One of the greatest impacts that the corporation had in the country was the preparation of the Plan for Economic Development of the Water Basin of the Upper Cauca, which became a reference for the Territory Development Plans. In these plans, several topics were taken into account including those associated to water. In parallel, the General Assembly of the United Nations in 1966 created and approved diverse covenants about socioeconomical and cultural rights, as well as civil and political rights. These covenants were included in the legislation by the Colombian Congress through the Law 74 of 1968, which recognizes, among others, that “everyone has the right to enjoy the highest possible level of physical and mental health”. This obligates the Government to take measures to ensure:

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a) The reduction of the mortality, in particular, the child mortality, as well as the healthy development of the child. b) The improvement in all aspects of the hygiene of the workplace and the environment. c) The prevention and treatment of the epidemic, endemic, professional and other kinds of diseases and the fight against them. d) The creation of conditions to ensure to all of the citizens receive medical attention and has access to medical services in case of emergency. In this fashion, the door was open in Colombia for the setting of a clear regulation and management of the environmental topics, considering the impacts that these may have in the public health of a region. Among these topics above, one of the most relevant is the topic of the water that in the developing countries is one of the topics with the largest impact in the morbidity of the population, especially for the children. In 1968, the Instituto Nacional de Recursos Naturales (INDERENA, National Institute of Natural Resources)was created, an entity that was alive until 1994. It had a relevant role in the administrative strengthening of the management, development and protection of the natural resources and the environment. This institution was the base for the creation of the Ministry of Environment in 1993. The Inderena had the following functions:

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• • •

Coordinate environmental corporations. Create awareness about the environmental problem at the communitarian level. Create a vision of the control and surveillance of the resources.

Sadly, the Institute had a low control capacity, it did not properly coordinate the corporations and its function was limited to surveillance, rather than management, which prevented it from accomplishing its functions. This finally caused its closure. In 1972, and in the framework of the environmental Conference of Stockholm, the need to determine common criteria and principles that would provide the nations with patterns on how to preserve and improve the environment became relevant. There was a general call to the nations about the importance of their intervention in environmental aspects. This conference allowed them to trace global guidelines of investment for attending the environmental problems, which are condensed into the following principles: 1. The concern for the preservation of the environment. 2. The importance of preserving the natural resources for the next generations. 3. The development of policies aiming to control the growth of the population of the developing countries. 4. The free flow of information. As a respond to the global guidelines established in Stockholm, Colombia, through the Decree Law 2811 of 1974, the Code of Renewable Natural Resources and Environmental Protection was created. This code was a global example of a remarkable environmental legislation for almost 15 years.

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However, the fines imposed in the code were not updated and, after its implementation, it was evident that the ineffectiveness of the institutions responsible for its execution, as well as the lack of management and coercion capacity of the institutions. Because of this, before the promulgation of the Constitution of 1991, there was not a single organism able to control the state of the natural and environmental resources in the country; the management and environmental control were divided among several organizations, generating duplication of functions and affecting the government actions. The Constitution of 1991 incorporates the environmental dimension as a necessary condition for the economical development in the medium and long terms, and a set of instruments were created which made possible to monitor the compliance of those rules. Furthermore, the latter rules and regulations have made it possible to specify the conceptual and legal frameworks, which allowed our country to move forward in the framework of the sustainable growth. In the Constitution, the protection of the environment is raised to the category of collective rights and gave to the people mechanisms for overseeing its fulfillment such as popular or group actions, tutela actions and fulfillment actions. In the framework of the new Constitution and of the United Nations Conference on Environment and Development of Rio de Janeiro in 1992, emerges the Law 99 of 1993, in which the current fundamental principles of the Colombian environmental policy are embodied. Additionally, the Sistema Nacional Ambiental is created (SINA, National Environmental System), which aims to integrate and coordinate the actions and institutions related to the environment and the natural resources. The objective is to give to the environmental management in Colombia a systemic dimension; decentralized, participative, multi-ethnic and multi-cultural. The SINA is the set or guides, norms, activities, resources, programs and institutions that makes it possible to start up the general environmental principles in the Law 99 of 1993. Is integrated by the following components1: ƒ ƒ ƒ ƒ ƒ ƒ

The general principles and guidelines contained in the National Constitution, in the Law 99 and in the environmental regulations that develops it. The current specific regulations that are not revoked by this law and the law that develops under this law. The State entities responsible of the environmental policy and action, pointed down in the law. The communitarian organizations and non-governmental related with the environmental problems. The sources and economical resources for the management and recuperation of the environment. The public, private or mixed entities that performs activities of information production, scientific research and technological development in the environmental field.

The principal public entities that conforms the SINA and that are directly in charge of the environmental management, may be seen in Figure 2-1. 1

Law 99 of 1993, article 4.

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227

SINA

Set of guidelines, sstandards,  activities, reso ources,  programs and insstitutions  allowing the start of the Law  99 of 1993.

Regional  Enviromental  Authorities  ( (Corporations) Urb ban Enviromental  A Authorities E.g.  Disttrict Environment  Secretariat

M Ministry of  En nviroment

Regulatory  Commission of  Drinking Water and  Basic Sanitatio

National Planning  Deparrtment

Research Institutes

Direction of Urban  Developm ment and  Environ nmental  Policies

IDEAM Von Humbold dt SINCHI

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Fiigure 2-1: Entities that conform ms the SINA.

e deffines the objeectives and fuunctions of each of the The Law 99 of 1993 explicitly mentioned enttities, howeveer in this chhapter, we will m w focus onn two: the Ministry M of Environment an nd the Comisiión de Regulación de Agua Potable y Sanneamiento Bássico (CRA, R Regulatory Com mmission of Drinking D Wateer and Basic Sanitation). The Ministtry of Environment becom mes the governning body of the managem ment of the ennvironment and of the rennewable natuural resourcess. In this fashhion it is in charge of prromoting a relation r of respect and haarmony betweeen man and nature, and to define, acccording to the law, thee policies annd regulationss that will guide g the reccuperation, coonservation, protection, p orddering, manageement, use andd exploitation of the renewaable natural reesources and the environnment of thee Nation, aiming to guaarantee the sustainable deevelopment, according a to thhe Article 2 off the Law 99 of o 1993. The main objectives off the Ministryy, according to the Decreee 216 of 20003, are to coontribute and promote sustaainable develoopment througgh the formulaation and adopption of the poolicies, plans, programs, projects p and regulation reelated with thhe environmeent, natural reenewable reso ources, soil use, u territoriaal development plans, driinking water and basic saanitation and environmentaal sanitation, territorial andd urban devellopment, as well w as the suubject of integ gral housing. Attached to o the Ministryy of Environm ment, the CRA A is created, a special adm ministrative unnit, with adm ministrative, teechnical and patrimony autonomy; a its purpose is to t regulate m monopolies and to promotee the competeence in the seector, preventting abuses off dominant poositions and driving d the susstainability off the sector annd the renderinng of quality services at

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reasonable prices and wide covering. This purpose is achieved through the regulatory development that includes the participations of the users and the providers1. Inside of this legislative framework, we will proceed to enunciate a short list of laws, decrees and resolutions in force in the sector of drinking water and sanitation.

Laws a) Law 9 de 1979. National Sanitary Code. b) Law 99 de 1993. National Environmental System “Sistema Nacional Ambiental” – SINA-. c) Law 100 of 1993. Social security, pension liabilities and pension bonus in public entities. d) Law 142 of 1994. Regimen of Public Utilities. e) Law 226 of 1996. Alienation of the State Property. f)

Law 286 of 96. About the factors of benefits and contributions, modifies the Law 142 de 1994.

g) Law 373 of 1997. Efficient and rational use of the water. h) Law 388 of 1998. Land Use Plans. i)

Law 430 of 1998. By which the environmental prohibitive norms are dictated, referring the solid waste.

j)

Law 505 of 1999. Determines competences and dates for the adoption and application of the stratification.

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k) Law 549 of 1999. Coverage of pension liabilities in territorial entities. l)

Law 550 of 1999. Liabilities restructuration.

m) Law 617 of 2000. Categorization of territorial entities. Modifies the Law 136 of 1994. n) Law 632 of 2000. Extend periods to eliminate the rate lag and announces dispositions for the ordinary cleaning. o) Law 689 of 2001. Partially modifies the Law 142 of 1994, regarding the competences of the SPU, the AEGR and the socioeconomical stratification, among other topics. p) Law 715 of 2001. Partially modifies the Law 142 of 1994, regarding health, education, and drinking water. Abolishes Law 60 of 1993. q) Law 732 of 2002. Establishes new periods and terms to adopt and apply urban and rural stratifications and redefines some competences regarding the control.

1

http://www.cra.gov.co/estructura.shtml#, retrieved on 10 November 2010.

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Decrees a) Decree 2811 of 1974. Natural Resources Code. b) Decree 1594 of 1984of the Ministry of Health. Regarding the Dumping of Liquid Waste. c) Decree 1753 of 1991. The environmental licenses theme is regulated. d) Decree 2200 of 1993. Competences socioeconomical stratification.

framework

and

methodologies

in

e) Decree 2649 of 1993. Accounting principles. f)

Decree 2785 of 1994. Transformation and characterization of the statutory for the service providers.

g) Decree 1324 of 1995. Partial regulation of the Law 56 of 1981, in harmony with the Law 142 of 1994. h) Decree 1429 of 1995. Citizen participation mechanisms (control speakers), in the SPD. i)

Decree 1748 of 1995. Pension bonus.

j)

Decree 565 of 1996. Regulates the solidarity funds and redistribution of the income for drinking water and basic sanitation sector.

k) Regulates the cleaning service. Mostly abolished by the Decree 1723 of 2002. l)

Decree 1538 of 1996. Concepts, grounds or refusals and recognition because of the inadequate application of stratification by providers of PU.

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m) Decree 2034 of 1996. Last term for the adoption of urban stratification. n) Decree 901 of 1997. Retributive rate for pouring to the sewer. o) Decree 1474 of 1997. About pension bonuses. p) Decree 3102 of 1997. The article 15 of the Law 373 of 1997, related to the installation of equipment, systems and implements of low consumption of drinking water. q) Decree 810 of 1998. Constitution of autonomous patrimonies in decentralized entities for the payment of pension bonuses and quotas. r)

Decree 1311 of 1998. Regulates the literal g of the Article 11 of the Law 373 of 1997, regarding the information of the consume –each 4 months- to the Ministry of Economical Development.

s) Decree 302 of 2000. Regulation for the services of water and sewage (Partially modified with the Decree 229 of 2002). t)

Decree 421 of 2000. Rendering of PU by authorized in minor municipalities.

u) Decree 1905 of 2000. Modifies the statutes and the functioning regulation of the Regulation Commission of Drinking Water and Basic Sanitation. Water Engineering, edited by Dominic P. Torres, Nova Science Publishers, Incorporated, 2011. ProQuest Ebook Central,

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Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al. v) Decree 1987 of 2000. Regulation of the article 11 of the Law 142 of 1994, among other topics. w) Decree 2676 of 2000. Regarding the management of hospital waste. x) Decree 229 of 2002. Partially modifies the Decree 302 of 2000, regarding concepts of water and sewage, among other topics. y) Decree 398 of 2002. Regulates the incise 3 of the numeral 6.4 of the Law 142 of 1994 (selections of providers). z) Decree 849 of 2002. Regulates Law 715 regarding the certification of se SPU for the change of the reassignment of the transfers of the Nation for drinking water and basic sanitation sector. aa) Decree 891 of 2002. Regulation of the Law 632 of 2000, regarding the exclusive service areas and the concession contracts between territorial entities and people provider of the cleaning service. bb) Decree 941 of 2002. Regulates the constitution of the accounting and financial management of the autonomous patrimonies or of guarantee to the companies that are in charge of jubilation pensions. cc) Decree 990 of 2002. Restructuration of the Superintendents of Public Utilities. dd) Decree 991 of 2002. Defines the staff of the Superintendents of Public Utilities. ee) Decree 1713 of 2002. Regulates the ordinary cleaning service, in its technical components, especially, with the exception of chapter I of the title IV, abolished the other parts of the Decree 605 of 1996.

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ff) Decree 1575 of 2007 of the Ministry of Social Protection. System for the Protection and Quality Control of the Drinking Water.

Resolutions Issued by the CRA a) Resolution 151 of 2001. Central resolution regarding the rate regime, abolished and compiled relevant topics. b) Resolution 9 of 1994. Update rate for 1995. c) Resolution 12 of 1995. Criteria, characteristics indicators and model to evaluate the management and the results of the companies of water and sewerage and cleaning. d) Resolution 8 of 1995 of the CRA (Art 3 and 24 still valid). The criteria are created and the methodology is adopted fixing that the water public utilities should determine the rates for the services. e) Resolution 19 of 1995. Update rate for 1996. f)

Resolution 5 of 1996. Establish the methodology for the evaluation of the business viability.

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g) Resolution 18 of 1996. Criteria for the approval of the PGR of the ESPD of the water system. h)

Resolution 29 of 1996. Update rate for 1997.

i)

Resolution 11 of 1997. Establish rules to promote balance in the control mechanisms of the management and the results.

j)

Resolution 16 of 1997. The criteria for the evaluation of the fulfillment of the first plan of management and results –PMR-, are established.

k) Resolution 17 of 1997. The conditions for the first presentation of the update PMR are established. l)

Resolution 32 of 1997. Update rate for 1998.

m) Resolution 36 of 1998. The minimum values of the rates are established for the services of water and sewerage. n) Resolution 37 of 1998. Addition to the Resolution 16 of 1997, to determine the evaluation criteria of the fulfillment of the first PMR. o) Resolution 54 of 1998. By which the unique paragraph of article 7 of Resolution 12 of 1995 is added and the articles second and third of the Resolution 17 of 1997 regarding the update of the PMR. p) Resolution 60 of 1998. The conditions for the presentation and update of the PMR of 1998 are established.

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q) Resolution 62 of 1998. The pointing is requested to the Direction of Public Utilities of the Ministry of Economical Development, through administrative acts, of the technical requirements that should be met by the works, equipments and processes used by the drinking water and basic sanitation public utility companies. r)

Resolution 66 of 1998. Update rate for 1999.

s) Resolution 74 of 1999. Conditions to present the PMR by the PSPD with less than 24000 users. t)

Resolution 84 of 1999. The assignment of subsidies is regulated in the payment of services of water and seweage and cleaning to the users affected by the earthquake of the 25th of January of 1999.

u) Resolution 114 of 1999. Update rate for 2000. v) Resolution 117 of 1999. Only in paragraphs 1 and 2 of article 4 and article 16. w) Resolution 148 of 2000. Update rate for 2001. x) Resolution 150 of 2001. Basic consumption and maximum consumption are established according to the Law 373 of 1997. y) Resolution 151 of 2001. Of the CRA, Integral Regulation of the Services of Water, Sewerage and Cleaning.

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Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al. z) Resolution 200 of 2001. About the increases in the rate because the update will be made according to the caused inflation, when, as a minimum, there are at least 3 points certified by the Dane. aa) Resolution 201 of 2001. The conditions for the preparation, update and evaluation of the plans and management are established.

Issued by the Ministry of Health Resolution 541 of 1994. Regulates the load, transportation, storage and final disposal of the rubble.

Issued by the Ministry of Environment Housing and Territorial Development a) Resolution 273 of 1997. Values and parameters to estimate the retribution rate. b) Resolution 372 of 1998. Values and parameters to estimate the retribution rate. c) Resolution 1096 of 2000. Technical Regulation for the Water and Basic Sanitation Sector, RAS. Modified by the Resolution 2320 of 2009. d) Resolution 2115 of 2007 of the Ministries of Social Protection and of Environment Housing and Territorial Development. Points the characteristics, basic instruments and frequencies of the control and surveillance for drinking water quality.

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Issued by the Superintendence of Public Utilities a) Resolution 1416 of 1997. Accounting plan for providers of the sector of drinking water and basic sanitation –APSB-. b) Resolution 1417 of 1997. Unified cost and expenses system for providers of the sector of APSB. c) Resolution 4640 of 2000. Accounting plan for providers of public services. d) Resolution 010541 of 2002. Formats for certification are adopted, that allows the change of destination of transferences for the sector of APSB, according to the Law 715 of 2001 and the Decree 849 of 2002. e) Resolution 16965 of 2005 of the SPU. Establishes the regimen of inscription, updating and cancelation of the providers of public utilities in the Unique Regime of Public Providers – RUPS.

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3. THE CONTEXT As a member of the United Nations, Colombia must accept and implement the decisions that the organism makes on every subject. One of the most important subjects is water; regarding this, the General Comment No. 15 of the Committee on Economic, Social, and Cultural Rights describes the fundamental factors of the human right to water1: 1. Availability of drinking water 2. Accessibility to the drinking water

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3. Quality of water In this way, the universal right of every human being to access the water resource without any reservations and everything this implies is established (Defensoría del Pueblo, 2006). Even though the Covenant is signed by the United Nations, including the National Government, it would not have much significance if the magna carta of our country, the 1991 Political Constitution, didn’t demand also that all levels of government in the national territory guarantee the compliance of these global postulates, and forbids at all costs that they go unfulfilled. For the issue of quality of water, several dispositions and rules have been established worldwide in order to adjust all the procedures concerning this subject and set the tone for every country that wishes to improve its levels of water quality, given the huge importance of this subject and the significative influence and impact it has on the world population, especially for children under five. For this reason, the Colombian Government, through the Ministry of Social Protection and the Ministry of Environment, Housing, and Territorial Development, issued the resolution 2115 of June 22nd, 2007, which establishes “characteristics, basic instruments and frequencies of the supervision and control system for the quality of water for human consumption” (Ministerio de la Protección Social, 2007). These characteristics were divided in the following components: •

Physical Characteristics

•

Chemical Characteristics

•

Microbiological Characteristics

These three characteristics blend in a grand index named the Index of Risk of Quality of the Water for Human Consumption (Spanish acronym, I.R.C.A.), which shows the level of hazard to which a human being is exposed each time he/she drinks water.

1

(Defensoría del Pueblo, 2009)

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This index must be reported by every municipality of the country, identifying each risk point of the water, and uniting all of these analysis in a measure of the risk of water. Table 3-1. Risk scores assigned to each characteristic analyzed for IRCA measuring Characteristic

Risk score

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Apparent Color

6

Turbidity

15

pH

1,5

Free residual chlorine

15

Total alkalinity

1

Calcium

1

Phosphates

1

Manganese

1

Molybdenum

1

Magnesium

1

Zinc

1

Total hardness

1

Sulfates

1

Total iron

1,5

Chlorides

1

Nitrates

1

Nitrites

3

Aluminum (Al)

3

Fluorides

1

COT

3

Total coliforms

15

Escherichia Coli

25

Total sum of assigned scores

100

Source: (Defensoría del Pueblo, 2006) Hence, it is important to assign the risk scores to every sample analyzed, in order to determine the IRCA percentage of the respective analysis, as it is shown in the following formula:

%

∑ ∑

100

Formula 3-1. IRCA percentage of each sample (Ministerio de la Protección Social, 2007)

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Using the IRCA scores obtained from each sample, the monthly index is analyzed using the following formula: ∑

%

100

∑ Formula 3-2. Monthly IRCA Percentage (social M. d., 2010)

Through the analysis of the samples reported throughout the country, and the enforcement of the Decree 1575 of 2007, the following reports were generated:

Table 3-2. Risk Index of the Quality of the Water for Human Consumption (I.R.C.A.) by department and/or district IRCA Average

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Department

2007

2008

2009

AMAZONAS

25,5%

25,4%

23,9%

ANTIOQUIA

7,8%

4,4%

4,8%

ARAUCA

17,0%

13,3%

1,7%

ARCHIPIÉLAGO DE SAN ANDRES Y PROVIDENCIA Y SANTA CATALINA

11,4%

5,6%

6,4%

ATLÁNTICO

6,7%

5,1%

5,5%

BOGOTÁ

0,1%

8,6%

16,4%

BOLÍVAR

28,4%

44,4%

34,7%

BOYACÁ

21,5%

30,1%

30,4%

CALDAS

11,3%

47,9%

58,5%

CAQUETÁ

28,6%

27,2%

23,7%

CASANARE

37,2%

22,7%

33,1%

CAUCA

30,7%

28,5%

24,4%

CESAR

31,9%

32,0%

22,0%

CÓRDOBA

41,1%

14,7%

18,5%

CUNDINAMARCA

11,1%

7,7%

8,5%

GUAINÍA

52,2%

44,8%

53,7%

100,0%

68,9%

51,6%

HUILA

12,5%

28,0%

24,8%

LA GUAJIRA

21,5%

31,8%

15,6%

MAGDALENA

46,5%

24,5%

35,3%

META

38,0%

40,4%

43,5%

NARIÑO

36,6%

35,6%

37,2%

GUAVIARE

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Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al. Table 3-2. (Continued) NORTE DE SANTANDER

14,4%

17,1%

11,9%

PUTUMAYO

47,6%

41,7%

49,8%

QUINDIO

14,1%

0,3%

0,2%

RISARALDA

29,4%

25,7%

26,8%

SANTANDER

20,7%

19,4%

18,0%

SUCRE

23,6%

22,0%

20,4%

TOLIMA

33,9%

32,9%

33,1%

VALLE DEL CAUCA

17,7%

17,9%

20,6%

100,0%

92,2%

33,5%

30,5%

VAUPÉS VICHADA

34,1%

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Source: National Health Institute, (Instituto Nacional de Salud, 2009) Despite the evident difficulties of the country, the National Government has invested around 1,360 billion pesos in 2009 in different projects related to improving the coverage and quality of water. Most of these resources are assigned to the Departmental Plans for Water (PDA), which are instruments used by the ministries for assigning resources to the departments, without taking into consideration the needs of each department and without making an equitable distribution according to the requirements of each region. (Ministerio Ambiente, Vivienda y Desarrollo Territorial, 2010). This becomes very relevant when analyzing the impact of these plans in departments such as Cundinamarca, whose urban area shows remarkable satisfactory numbers, with a coverage of the aqueduct, sewer and sanitation systems of around 95%, a figure that differs considerably from the one of the rural area, where the coverage of water works is 58.7%, sewer is 19.6% and there is no coverage in sanitation. The severity of this situation increases since the rural sector is the worst poverty and violence-ridden area of Colombia. The shocking figures evidence a conjuncture that establishes a significant priority in the accomplishment of projects in these areas destined to fulfill the need of these areas for basic elements, which are essential for the development of any human being. The Ministry of Environment generates the regulation required for developing the departmental plans for water, which are the instrument used by the territorial entities to manage the resources for complying with the needs and requirements exposed in the PDA, making the resources destination much more effective. That regulation was entitled Decree 3200, of August 29th 2008, and it intends to provide a legal tool that contemplates all of the elements that a PDA should have, and, thus, execute the projects referred to. Initially, this seems to be a very useful tool, but the civilians, including the citizens of the populations directly interested, are not taken into account in the Decree, and therefore, their voice hasn’t been heard.

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This is evidenced in the regulation when it establishes that the stakeholders required for the development of the PDAs are:

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1. The Department. 2. The Municipalities and/or Districts. 3. The Ministry of Environment, Housing and Territorial Development- MAVDT. 4. The National Planning Department - DNP. 5. The environmental authorities with jurisdiction in the municipalities located in the territory of the department. (Ministerio Ambiente, Vivienda y Desarrollo Territorial, 2010)

Figure 3-1. Risk Map; Inviable Sanitariamente = Not Viable; Alto = High; Medio = Medium; Bajo = Low; Sin riesgo = No risk.

Source: National Health Institute (Instituto Nacional de Salud, 2009).

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4. PARTICIPATORY METHODOLOGY FOR WATER ENGINEERING Given the situation explained above, it is possible to assert that the organizational mechanisms ordinarily used have not managed to design water management solutions for a considerable amount of vulnerable communities. Next, we will present some alternative models that have helped in the past and may help in the future to find appropriate local solutions. This section introduces the proposal for an organizational model based in the OCDIO (Observe, Conceive, Design, Implement, and Operate) intervention methodology and the PAR (Participatory Action Research) participation methodology. This model contains a proposal of joint work of the universities, the communities, and the local governmental stakeholders, which has been conceived and headed by the organization Ingenieros sin Fronteras Colombia (ISF Colombia). The Ingenieros sin Fronteras group proposes to analyze the management and innovation associated to the water subject as an engineering project. Consequently, there are several challenges to be faced from the engineering perspective, such as: −

−

How should the problem situations associated to a particular subject be defined? How should a technological solution be defined so as to tend to the real needs of the water users? How could the balance between a solution that is technologically innovative and the appropriation of that technology by the community be guaranteed?

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In order to approach these challenges, the first step is to define the problem situation. Engineers are used to solving “structured” problems, that is, problems with single solutions, algorithmic methodologies and precise results. In this order of ideas, the water matter is related to questions such as: − − −

How to design an appropriate technology in order to improve the quality of water, within a specific context? What are the restrictions that have to be considered in the design? What are the technical variables that have to be considered?

We could define the questions that will let us propose a technically structured engineering solution that applies a simple or complex algorithm. However, considering that the context facing the engineer presents difficulties related to the social order, poverty, inequity, among others, the question should be more complex: − − − −

How to guarantee that the solution takes into account the real needs of the community? How to guarantee that the proposed solution will help in improving the quality of life in the poverty and inequity context in which it takes place? How to generate an engineering solution that promotes autonomy in the community? How to guarantee that the solution does not bring along other types of problems?

For these questions, there are not pre-defined algorithms. Therefore, it is necessary to consider solutions based on effective organizations design. For understanding the problem situation, there are four characteristics to be taken into consideration (Aldana y Reyes, 2004):

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−

The problem situations are transdisciplinary; this means that the source of the problem goes beyond the methodologies of a discipline or a single group of disciplines. Of course, the quality of water issue can be approached through simulation models, lab tests, etc., but also is valuable to find out which systems, and in which way, have contributed or not to the improvement of the quality of water; why no solutions have been reached yet; which variables guarantee the cultural appropriateness of a technical solution; among other aspects. The main point is that the solution can come from different disciplines and with different terms. For example, an environmentalist may define the problem in terms of the lack of conscience of the inhabitants regarding water sources contamination; an administrator may refer to the lack of leadership or communication between the community and the local entities, and so on. There are not more or less valid answers, rather they are all pertinent.

−

The formulation and description of the problem situation depends both on who originates it and who observes it; this means that the solution must be a construction in which several actors participate or are represented. In the quality of water, matter is pertinent to identify the view points of the different stakeholders (researchers, managers, students, community), clients (community, researchers), potential suppliers (of information, of technology, of resources), intervenors (other members of the community, local and national law makers). Once again, all of their view points are pertinent, and should be taken into account.

−

The problem situations are derived from the relations between the different stakeholders; this means that it is through the analysis of these relations that the situation will become clearer. In the context of quality of water for vulnerable communities, the relevant relations include those of the community/community leaders/local government, health, and education entities/researchers. Therefore, it is fundamental to identify and understand all of the relevant stakeholders (that is, all those who affect or are affected by the problem situation) and their relationships, in order to properly approach specific subjects such as negotiation processes with local entities, current and future diseases, lack of education and awareness, among others.

−

The comprehension of a problem situation should be understood as a system; this means that the solution should be designed from an integral and inclusive perspective. The quality of water situation should be looked at from a systemic point of view, rather than an analytical one. That is to say that the solution shouldn’t be approached or conceived in an independent way, from a single perspective.

What would happen then, if we reduce the proposals and solutions to just the spheres of technical design? Or what would happen if we reduce the proposals and solutions to just the spheres of organizational design? The first case is a technically viable engineering proposal, assuming that the technical design fulfills the necessary requirements. The zone in which Ingenieros sin Fronteras has undertaken water related projects, there are aqueducts built with correct technical specifications, but are abandoned due to a poor management or improper use. The second case is a viable management proposal, assuming that all those involved in the solution are interested and willing. But a strategic alliance between the local entities and the

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community for solving technical problems is not enough to guarantee technically viable longterm solutions. This usually does not go further than the group of people solving a specific immediate problem, or even worse, the solution solves one specific problem, but generates a different one. These challenges are related to proposals of the “Organizational Diagnosis and Design” research line. In this framework, we present below the proposal that seeks to guide engineering projects related to water management (and, of course, for similar fields).

The OCDIO- PAR Model

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The proposed integrated model is based on Figure 4-1 and is described below:

Figure 4-1: OCDIO – PAR Model; Based on Lucena et al. (2010).

Taking into account the aforementioned premises, it is intended that the proposal for managing water-related problem situations takes into account not only experts of different engineering fields (industrial, chemical, environmental, etc.), but also different interested parties of the community (users, local government entities, local health entities, local education entities, etc.). Even though the work focus is the community itself (as can be seen in the pyramid on Figure 3), in the process of developing the project there is constant feedback between the community and the engineers (looking for a permanent and systemic learning model). For this, the synergy between the community’s lore regarding water and the new engineering techniques proposed is essential. In this way, two key factors would be guaranteed: development and sustainability.

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It is intended, then, that both the engineers and the community play a main role, based on the steps proposed by the PAR methodology (Bodorkós et al., 2009):

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1. Generate communication and information capacity between the community and the engineers. 2. Generate decision-making processes where the points of view of both the community and the engineers are taken into account. 3. Promote the active participation of individuals in the process: the community provides labor, resources, local knowledge and feedback, and the team of engineers provides technical knowledge and research facilities. 4. Increase interactive participation so that local communities are involved at all phases of project design. 5. Promote self-development. 6. Develop knowledge through the interaction and feedback between the community and the engineers. Taking into account the previously presented systemic framework, it is necessary to define a teamwork methodology. For this, the CDIO framework is presented. In traditional engineering education, it was not explicitly necessary to strengthen the competences that enable the future professional to face, in an innovative and flexible manner, the complex problems of society. Taking into account what was said by Deutsch (1968) and Shaw (1976), and being aware that engineering know-how must be translated into real life situations, students and teachers have begun working on direct application cases called CDIO (Conceive, Design, Implement and Operate) engineering projects. The students and teachers approach the problem by interviewing the people involved, exchanging ideas with experts and researchers and exploring knowledge on the subject at hand. Once the observation process is finished, the group conceives the formulation, contextualization and a possible solution to the observed reality together with the community. This conception requires a great deal of creativity and innovation to offer technology that meets the community’s needs. After an evaluation stage, the process moves on to the preliminary design phase of the prototype and a proposal for implementing the technology in order to improve water conditions in the community. Subsequently, assistance from teachers is intensified and the development of the project is deepened. Thus, the design is carried out with greater precision regarding the prototype, the implementation is clearer and the project is finally put into operation. During the process, the efficiency of the filtering prototype is monitored and adjusted periodically through lab tests and community visits. The group and the community regularly evaluates the experience and learning generated during the project’s design and evaluation, in order to improve the cooperation model and the methodology hoping to replicate the project in other areas of the country which also present drinking water problems and unsatisfied basic needs. In that sense, the group used a combination between the traditional engineering projects development context and a participation methodology which guarantees that the different inputs of everyone interested in the situation will be considered.

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5. CASE STUDY : GUAYABAL DE SIQUIMA, COLUMBIA Problem situation Technical diagnosis of the water consumed in the Torres district The water supply system of the Torres district is fed by a 30000 L (30 cubic meters) tank made of reinforced concrete, which is supplied by a little spring located approximately 5 meters above the tank. Figures 5-1 and 5-2 show the spring and the tank.

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Figure 5-1. Spring (Up)

Figure 5-2. 30.000 L. Concrete Tank (Down)

A volumetric analysis was made in order to establish the average flow rate of the spring (0.291 L/s). Likewise, measurements of turbidity and conductivity were conducted; the results are shown below: Table 5-1. Turbidity #MEASUREMENT

*TURBIDITY (NTU)

1 2 3 4 5

12.3 10.2 10.8 10.5 10.1

6

9.85

13.9 10.2 9.2 9.94 11.1

14.1 10.6 9.14 9.15

Source: Authors’ calculations *Approximately, three measurements per each sample were taken.

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Table 5-2. Conductivity #MEASUREMENT 1 2 AVERAGE

CONDUCTIVITY (us/cm): 353 355

O.D.(mg/l)

T(°C)

6.69 6.7

20.4 20.2

354

6.695

20.3

PH:

7

Source: Authors’ calculations In order to establish the microbiological conditions of the water in the Torres district, different microbiological tests were conducted. The samples were taken on May 6th, 2008, at the spring, the tank and Mr. Adán’s house. The results are shown below: Table 5-3. Microbiological analysis results–“Las Torres” district Spring Reference Test Lot 06/05/2008 Coliforms 220 E. Coli Source: Authors’ calculations.

Tank

House

Good Countless 40

1580 -

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Social and economical diagnosis of the district The following is the profile of the social and economical conditions of the community of Torres district. The profile was based on the group observations and a survey conducted with 11 families of the community of San Felipe, a sector near the Torres district. Both sectors share the same socioeconomic profile. In their initial observations of the group, they found a settlement of families who are dedicated to being day laborers in the large crops of the area, or to making panela (unrefined whole cane sugar). This last job is done in a sugar mill built archaically in the community; and the panela sale is done in the nearby towns. The sale of this panel was held in nearby towns. However, it should be noted that neither the day’s wages nor the sale of panela are an economical source that provides sufficient and adequate income for the families. The following are the conclusions of the survey: − The families in these districts belong to the strata 1 and 2 and have a low economic capacity according to the Department of National Planning. − The community is composed mostly of the women (55% of the population). The main age range of the population is between 30 and 60 years old. − 63% of the population live in nuclear families (both parents and their children). − Regarding the necessities perceived by the community, 38% of the population said that the most urgent necessity is related to the water resources in the community, since due to the bad quality of the water, there have been diseases outbreaks among the population. On the

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other hand, 18% feel that the most pressing necessities are related to work and transportation, and in lower percentages, to health and housing. − 72.73% of the families live in houses; the rest of them live in houses with a plot of land, which they use for agricultural activities. The main construction materials are blocks, bricks, tiles and, in lesser proportions, wood. In the majority of cases, the floors are made of mud. 90% of the families said they felt comfortable in their current house.

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Regarding the economic conditions, the study identified that in relation to family income, 63.64% of the population subsists on a monthly income of less than 120 thousand pesos. The main source of income is the agricultural work, followed by the daily wages, which do not exceed 15 thousand pesos, this situation evidences the community’s high degree of vulnerability. Regarding public services, the families consider that the most expensive one is the electricity (45.45%), followed by gas (27.7%), which is supplied through cylinders because there is no pipeline system; the water service is perceived as the less expensive (9.09%), also this service is regarded as the most relevant and the one that requires an urgent improvement on supply and quality. Since the analysis showed the community’s concern regarding the drinkable water, and 82% of the water resource comes from water works which may not comply with the necessary water treatment conditions, some questions were asked to the families regarding the condition of the water. The results show that 54.55% consider that the water is crystal clear, and 45.45% perceive it cloudy, which makes for a good overall perception of water quality by the population.

Figures 5-3: Torres community.

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Students and teachers involved: From the University Corporation Minuto de Dios participated the teachers Camilo Torres (Civil Engineering) and Juan Fernando Pacheco (vice chancellor), and the students Diego Grisales and Julián Castañeda (Civil Engineering). From Los Andes University, teachers Catalina Ramírez (Industrial Engineering), Jaime Plazas, Andrea Maldonado, Diana Calvo (Environmental Engineering) y Felipe Muñoz (Chemical Engineering); and the students Miguel González, Paula González, María Paula Valderrama, Juan Camilo Silva (Industrial Engineering), María Fernanda Díaz, David Zuñiga, Oscar Vaca (Industrial Engineering), Nathalia Torres (Chemical Engineering) participated.

Planning of the project OCDIO methodology:

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In order to plan the Project, the Observe, Conceive and Design phases of the OCDIO methodology were carried out. Here is a summary of the work developed: Observe: During the observation and initial conceive phase of the project, first-hand information about the main characteristics (economic, political, socio-cultural and geographical) of the community was collected, through visits and cooperation with an employee of the UMATA1. With this information, and its discussion and validation with the members of the community (see PAR methodology), the team of engineers was able to begin the design of sustainable solutions based on the population’s needs, characteristics and input. For example, later in the design phase, the filter was designed taking into account the general characteristics of the homes and the habits of its inhabitants, so that it could meet their water-related needs and be placed in an appropriate location which would facilitate its use. (Ramirez et al., 2010) Conceive: In order to conceive a project that could be supported by the actors involved, the interests of the main stakeholders were taken into account: EWB-Colombia, community members and their community and political leaders, the UMATA employee and the district’s aqueduct. During the development of the project, active participation of the stakeholders was promoted, particularly of the district’s inhabitants, by conducting surveys and interviews to understand their problems and needs, training workshops to help them appropriate the technology and encouraging their collaboration in the adaptation of land for the installation of the filters in order to help develop a sense of ownership. This learning process between EWB-Col and the community has allowed the group to adjust the initial proposal based on the community’s feedback, resulting in a more appropriate and productive solution. (Ramirez et al., 2010) The analysis begins with the identification of the problem. EWB-Colombia and the population identified the problem associated with the quality of water used for human 1

UMATA: Unidad Municipal de Asistencia Técnica Agropecuaria - Municipal Unit for Agricultural Technical Assistance.

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consumption. Then, the stakeholders were identified: the inhabitants of the community, EWB-Colombia, Universidad de los Andes, Universidad Minuto de Dios, the directors and employees of the district’s water worksand the mayor of Guayabal de Síquima. After this, EWB Colombia aimed to the involvement of stakeholders through various activities organized by the group, which included questionnaires about basic sanitation and hygiene practices among other subjects, training workshops on the use and operation of the filter and education on basic hygiene practices. All of this work was achieved with the support of data collection, which was carried out during visits and interviews with people with previous experience working within the community, allowing the group to revise initial assumptions and adjust the proposals based on the interaction with the community. The visits were scheduled according to the daily activities of the inhabitants and taking into account special dates (market days, political activities, holidays, etc.) to avoid any inconvenience. The debate and discussion within the community revealed different positions among stakeholders regarding the management of water resources and their availability and generated an opportunity to build consensus within the population, as well as between it and EWB-Col regarding the scope of the project, its aims and technical details. (Ramirez et al., 2010) Design Two strategies were identified for the management of water resources in the project; basic education on hygiene practices for disease prevention and community training in the management of slow sand filters and their installation in family homes. The group sought to establish close links with key local authorities in an effort to enlist their support and collaboration, obtaining good results from the collaboration with the Mayor and the UMATA. This strategy has been important in developing the project. (Ramirez et al., 2010) The group evaluated different types of filtration technologies in a search for those which are best-suited to the characteristics and conditions of the community. The evaluation was made taking into consideration the cost, ease of construction and procurement of materials and ease of maintenance. The aim throughout the project was to ensure that the technology chosen would be sustainable in the long-term and that the community might appropriate it and eventually no longer need help from the engineering group. After the evaluation process, the group decided to use slow sand filters due to their low cost, ease of use and installation, and good results in the removal of micro-organisms. (Ramirez et al., 2010) PAR Methodology: Concerned by the bad quality of life in Colombian rural communities, EWB-Col looked for a suitable community to develop a participative project to improve the quality of water. In this process, the communities were selected preliminarily, and afterwards, the Torres district was chosen. After some initial visits, intended to confirm the socioeconomic vulnerability and the existence of water related problems, ISF proposed to the community to work together, and received a positive response by the community. Since the beginning, the community had an active participation in the project’s development. As a matter of fact, the community leader who had been running the water works helped the engineers team to understand the main

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problems related to water in the community, and personally introduced the ISF team to each family. (Ramirez et al., 2010) The selection of the technology and design of methodologies were the result of a dialogue with the community, based on an understanding of their needs and concerns. Likewise, the work with the community was structured and developed based on its major socioeconomic and cultural characteristics, seeking to ensure compatibility between the lifestyle of the local population and the project to promote long-term sustainability and appropriation of the technology by its inhabitants. This is how the PAR methodology was implemented. (Ramirez et al., 2010) The financing of the project is an interesting example of the application of the participative methodology. In this case, the group of engineers funds the research required to develop the technologies and implement them, usually with support from their corresponding educational institutions, interested in the academic results and learning opportunities for students. The other stakeholders make a financial contribution of some sort to the development of the project. The local population, for example, commits to building the necessary infrastructure for the installation of the technical solutions; and the local authorities provide the resources required to guarantee the sustainability of the project (allocation of municipal resources, for instance). It is very important that the community help finance the project by providing their work and skills in order to promote a sense of ownership and empowerment. (Ramirez et al., 2010)

Implementation of the project

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Technical proposal for intervention As mentioned above, during the design phase of the project, the group evaluated different technological alternatives for implementing a system that improved the quality of water in the Torres district. This evaluation concluded in the selection of the sand filter as the most suitable alternative for implementation. Below, this technology is explained, as well as the design process for adapting this technology to the specific conditions of the district, the filter construction process with its associated costs, and the results of the lab tests for the technology. 1. Slow sand filters Sand filtering has proven to be an effective method for improving the quality of raw water, mainly due to its simplicity and low cost. Nevertheless, experience has shown that a proper design and a diligent maintenance program are indispensable requirements for its operation. In a slow sand filter, the water percolates slowly through its pores. During this process the biological and physical quality of the water improves considerably due to a group of biological, chemical and physical processes. The functioning mechanism of these filters emulates the purifying process that takes place in nature, in which the rain water penetrates through the soil and, little by little, forms underground deposits of water known as aquifers. Sand filters are commonly used due to its efficiency in reducing water turbidity. Moreover, with a proper design and operation, it can be considered an effective disinfection system. The

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formation of a biological layer on the sand surface, works as a barrier that prevents pathogens from getting through, because the biological film composed by microorganisms consumes, absorbs and filters the pathogens of raw water. 2. Slow sand filter design for the Torres district Since the filter design is the first main stage for the success in water treatment, it was important to come up with several possible designs, and afterwards selecting the most suitable for this case. In that order of ideas, two filters with different configurations in their filtering bed were proposed. Both designs would be contained in 40 gallons plastic barrels. Figures 5-3 and 5-4 sketch each filter’s configuration.

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Figures 5-4 and 5-5. Left: Fine sand, coarse sand and gravel filter. Right: Fine sand and gravel filter.

Table 5-4 displays the characteristics each stratum should have for functioning properly. Table 5-4. Granulometric properties of the strata

Material Fine sand Coarse sand Gravel

E (mm) 0,3 – 0,45 0,7 – 1,2 20

U ≤2 ≤2 -

Source: Author’s calculations. Each filter should keep a constant hydraulic head of 5cm, as shown on Figures 5-4 and 55. In order to achieve this, a floating valve that regulated water entrance was designed. A 5cm free zone at the top of the filter was kept in order to ensure the survival of the microorganisms present on the top of the bed.

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Additionally, the filtered water collecting was located on the bottom of the container, and had a fish spine configuration, made with PVC pipes and accessories of ½”, bored with 5 mm openings. Finally, the water would be taken from a pipe to a garden faucet, which the user would use whenever he wants treated water. The optimal height of the garden faucet would be established in the lab, so as to maximize the flow and provide comfort for the user. Figure 5-6 shows the filtered water draining system.

Figure 5-6. Filter’s draining system.

3. Materials acquisition The materials were purchased in stores specialized in PVC articles and stores of materials for construction. The cost of each material is presented in Tables 5-5 and 5-6.

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Table 5-5. Costs for filter of fine sand and gravel FILTER FINE SAND - GRAVEL Unitary Value Quantity Total Value Tube 1/2" $ 1.333,33 2 $ 2.666,66 Tee $ 400,00 6 $ 2.400,00 Cap $ 300,00 8 $ 2.400,00 Elbow $ 400,00 2 $ 800,00 Floater $ 16.000,00 1 $ 16.000,00 Flanche $ 5.500,00 2 $ 11.000,00 Welding $ 7.000,00 1 $ 7.000,00 Cleaner $ 3.000,00 1 $ 3.000,00 Female coupling $ 300,00 2 $ 600,00 Male coupling $ 300,00 2 $ 600,00 Tap $ 5.000,00 1 $ 5.000,00 Teflon $ 600,00 1 $ 600,00 Tank $ 35.000,00 1 $ 35.000,00 Fine Sand $ 12.500,00 2 $ 25.000,00 Coarse Sand $ 12.500,00 1 $ 12.500,00 Gravel $ 12.500,00 1 $ 12.500,00 Total $ 137.066,66

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Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al. Table 5-6. Costs for filter of fine sand, coarse sand and gravel FILTER COARSE SAND - COARSE SAND - GRAVEL Unitary Value Quantity Total Value Tube 1/2" $ 1.333,33 2 $ 2.666,66 Tee $ 400,00 6 $ 2.400,00 Cap $ 300,00 8 $ 2.400,00 Elbow $ 400,00 2 $ 800,00 Floater $ 16.000,00 1 $ 16.000,00 Flanche $ 5.500,00 2 $ 11.000,00 Welding $ 7.000,00 1 $ 7.000,00 Cleaner $ 3.000,00 1 $ 3.000,00 Female coupling $ 300,00 2 $ 600,00 Male coupling $ 300,00 2 $ 600,00 Tap $ 5.000,00 1 $ 5.000,00 Teflon $ 600,00 1 $ 600,00 Tank $ 35.000,00 1 $ 35.000,00 Fine Sand $ 12.500,00 3 $ 37.500,00 Gravel $ 12.500,00 1 $ 12.500,00 Total $ 137.066,66 The fine sand, the coarse sand and the gravel were bought in 50 Kg sacks each.

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4. Construction of sand filters The first step in the construction of the filters was the drilling of the entrance and exit openings for each barrel, with a ½” hole saw. The figures 5-7 and 5-8 illustrate the procedure.

Figure 5-7. Entrance opening drilling Figure 5-8. Exit opening drilling.

Afterwards, the draining system was built. Initially the fish spine design only had parallel pipes; however, due to the low flow obtained in the faucet, more pipes were included and the number of orifices was considerably increased. The new and definitive design is shown on Figure 5-9.

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Figure 5-9. Draining system.

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Later, the pipe that takes the water to faucet was installed and the heights of each stratum were marked, before pouring the sand. This procedure can be seen on Figures 5-10 and 5-11.

Figure 5-10. Garden faucet installation Figure 5-11. Demarcation of each stratum height.

Next, the materials of the filtering bed were washed. This is very important because it can condition the success or failure of the treatment. Washing the sand and gravel is fundamental because these materials are mixed with many impurities that may produce odor, flavor, and color problems in the flow. For washing the finest materials, it is necessary to use buckets with capacities above 10 liters. The sand is poured in the bucket until it is half full, afterwards water is added –not necessarily drinking water- and the whole content is manually stirred for approximately two minutes, making sure that the bottom sand gets washed as well. Then the content is left to rest for 2 to 3 minutes, so the sand sediments and the impurities remain in the water. After that, the water is emptied slowly, making sure that the sand doesn’t get out. This procedure must be repeated several times until the water doesn’t present so much

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turbidity after being stirred. A good indicator of the cleanliness is the foam present. If after the sand has been washed there is still foam present in the water, it is necessary to repeat the process until it disappears. Finally, the floating valve is graduated so it closes when the water is 5 cm over the filtering bed. The procedure is shown in Figure 5-12.

Figure 5-12. Floating valve installation.

Table 5-7. Physical analysis results Before Date / Hour

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1

15/04/2008

Turbidity (NTU) 12,8

pH (.) 9,37

After

Conduct. (µs/cm³)

True Color (UPC)

59

10

10:50 a.m. 2

16/04/2008

9,42

7,81

76,7

7

11:00 a.m. 3

21/04/2008

16,3

8,11

56,1

10

11:00 a.m. 4

24/04/2008

12,7

6,8

75,4

10

10:50 a.m. 5

25/04/2008

17,9

8,23

94,7

10

11:00 a.m. 6

28/04/2008

12,4

8,96

92,6

10

11:30 a.m. 7

07/05/2008

16,8

8,75

75,8

10

10:00 a.m. 8

30/04/2008 01:00 p.m.

17,5

8,56

85,8

10

Filters Turbdity (NTU)

pH (.)

Conduct. (µs/cm³)

True Color (UPC)

1

7,99

4,61

135,5

7

2

7,86

6,14

84,1

7

1

4,47

7,35

89,5

10

2

11,8

7,41

90,2

7

1

7,33

7,99

100,3

7

2

5,96

7,03

109,3

5

1

4,03

6,35

99,4

5

2

3,49

6,37

110,6

7

1

6,25

8,26

94,8

10

2

8,23

8,72

112,9

10

1

3,22

8,71

98,9

7

2

4,58

8,64

105,1

7

1

2,06

8,22

107,3

7

2

3,47

8,21

103,8

7

1

4,08

8,32

101,5

7

2

0,66

8,35

99,7

7

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5. Start up and technical tests For the start up of the two filters, drinkable water was added regularly throughout one day, in order to “purge” the filters. This is done with the purpose of eliminating the finer particles of the bed until a stabilization point is reached, in which the turbidity of the flow is below 10 NTU. For the fine sand, coarse sand, and gravel filter, 162 L of water were required to obtain the aforementioned turbidity reduction. Every technical test pilot was done using water of the San Francisco River, collected in Bogota’s 1st street. Thus, measurements of pH, turbidity, true color and conductivity for raw water –from the San Francisco River- were taken, as well as for the flows of both filters, three times a week for 3 weeks. The results are presented on Table 5-7. The filter of fine sand and gravel was named filter 1, and the fine sand, coarse sand, and gravel filter was named filter 2. Additionally, Table 5-8 presents the reduction percentages of physical parameters for both filters.

Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

Table 5-8. Reduction percentages

Filters 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2

Turbidity % 37,578 38,594 52,548 -25,265 55,031 63,436 68,268 72,520 65,084 54,022 74,032 63,065 87,738 79,345 76,686 84,800 87,738 79,345

% Remotion pH % Conductivity % 50,800 -56,458 34,472 -29,845 5,890 -14,302 5,122 -14,967 1,480 -44,068 13,317 -48,673 6,618 -24,145 6,324 -31,826 -0,365 -0,105 -5,954 -16,120 2,790 -6,370 3,571 -11,893 6,057 -29,357 6,171 -29,975 2,804 -15,468 2,453 -13,942 6,057 -29,357 6,171 -26,975

True Color % 30 30 -30 0 30 50 50 30 0 0 30 30 30 30 30 30 30 30

Similarly, several flow measures were taken on the output of both filters. For this, a 500ml test tube and a stopwatch were used to measure the flow rate. Likewise, the hydraulic losses were registered using a piezometer installed previously. Table 5-9 shows the flow rate and hydraulic losses results for both filters.

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Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al.

Turbidity (NTU)

20.0 15.0 10.0

Agua no tratada

5.0

Agua tratada

0.0

Limite  0

10

20

Days Figure 5-13. Hydraulic analysis results – Fine sand and gravel filter: Turbidity.

10.00

pH

9.00 8.00

Agua no tratada

7.00

Agua tratada

6.00

limite inferior

5.00

Limite superior

Upper limit

4.00 10 Days

20

Figure 5-14. Hydraulic analysis results – Fine sand and gravel filter: pH.

30 True Color (UPC)

Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

0

25 20 15

Agua no tratada

10

Agua tratada

5

Limite 

0 0

10

20

Days Figure 5-15. Hydraulic analysis results – Fine sand and gravel filter: True Color.

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Table 5-9. Hydraulic analysis results – Fine sand, coarse sand, and gravel filter Filter 1

Monday Tuesday Wednesday Thursday Friday

Monday Tuesday Wednesday Thursday Friday

Monday Tuesday Wednesday

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Holiday

Date 14/04/ 2008 15/04/ 2008 16/04/ 2008 17/04/ 2008 18/04/ 2008 21/04/ 2008 22/04/ 2008 23/04/ 2008 24/04/ 2008 25/04/ 2008

Tuesday Wednes day Thursday Friday

Monday Tuesday Wednesday

21/04/20 08 22/04/20 08 23/04/20 08

Q

(s)

(l/s)

27,84

0,0179611

25,89

0,0193125

24,77

0,0201884

23,7

0,0210948

t2

t3

t4

29,53

27,72

28,99

27,81

26,11

25,3

24,45

27,7

25,65

24,29

24,36

24,31

23,71

23,55

23,22

24,99

25,123

24,44

0,0204546

(l/h) 64,6598 18 69,5249 13 72,6783 31 75,9413 56 73,6366 98

22,75

23,1

22,86

22,90

0,0218309

78,591 180

25,22

24,32

26,12

25,22

0,0198255

23,48

22,91

23,1

23,2

0,0215858

24,76

25,4

24,53

24,9

0,0200830

11,12

11,05

0,0452489

22,3

22,5

0,0222222

24,34

24,11

0,0207383

t5 25,1 4

23,24

Filter 2

Monday

Q obtained

t1

28/04/ 2008 10,98 11,12 29/04/ 2008 23,11 21,88 30/04/ 2008 23,45 24,54 01/05/ 2008 *Data taken with 250 ml test tube

Date 14/04/20 08 15/04/20 08 16/04/20 08 17/04/20 08 18/04/20 08

T average

T average

Q obtained

(s)

(l/s)

13,42

0,0372578

71,3719 27 77,7090 23 72,2988 35 162,895 928 80,0000 00 74,6578 18

Q

Looses hf-open (cm) 18 23 29 32

22

31 27

25 27 22

Looses hf-open (cm)

14,14

0,0353669

13,25

13,857

0,0360837

(l/h) 134,12816 7 27 135,91744 3 21 127,20848 1 25 127,32095 5 32 129,90137 1 30

14,82

14,8

14,78

0,0338295

121,78619 8

23

13,83

13,3

14,040

0,0356125

128,20512 8

25

t1

t2

t3

t4

12

14

13,8

13,7

13,12

14,42

12,19

13,243

0,0377548

14,16

13,81

14,52

14,15

0,0353357

13,36

13,99

14,54

14,93

13,39

14,74

14,99

14,66

t5 13, 6

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256

Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al. Table 5-9. (Continued)

Thursday Friday

Monday Tuesday Wednes day Holiday

24/04/20 08 25/04/20 08

13,22

13,58

13,3

13,4

0,0374065

14,73

15,19

15,36

15,09

0,0331272

7,1

7,17

0,0697837

14,5

14,53

0,0344116

14,57

14,307

0,0349487

28/04/20 08 7,24 7,09 29/04/20 08 14,14 14,91 30/04/20 08 14,49 13,86 01/05/20 08 *Data taken with 250 ml test tube

134,66334 2 119,25795 1 251,22121 4 123,88162 4 125,81547 1

23 29

21 23 19

Finally, Table 5-10 presents the results of the microbiologic tests performed once a week per three weeks. These analyses were made to the raw water of the San Francisco River, as well as to the water treated by each filter. Table 5-10. Microbiological analysis results Date / hour

1

15/04/2008 10:00 a.m.

2

24/04/2008

Copyright © 2011. Nova Science Publishers, Incorporated. All rights reserved.

11:30 a.m.

3

09/05/2008 10:44 a.m.

Ex

Filter 1

Reference Test Lot

Filter 2

Good

Coliforms

220

E. Coli Reference Test Lot

1200

Coliforms

25600

Countless

4400

E. Coli Reference Test Lot

23500

23000

200

Good

Good

Coliforms

600

2100

0

E. Coli

300

0

0

Development of the organizational intervention proposal After the first visits, a meeting with the community was arranged, looking to identify who was interested in working in the design and surveillance of the systems for improving the quality of water. Thus, groups with engineers and people from the community were formed in order to establish the characteristics of the filters that were going to be used. The group began a pilot project in which four families cooperated. Approximately every fifteen days, the EWB team visited the community and met with the people. Through these meetings, the team was able to determine that the filter was useful for all the homes which were to take part in the pilot project. For each home, a committee was established, formed by the owner of the house who provided the details of the installation and a couple of students who provided technical support, and its task was to determine the specific characteristics of the filter and the installation. The knowledge gained by the students through this process was shared each week with the rest of the team during meetings. It is

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Water Engineering

257

worth pointing out that the characteristics of the filter were the same for all of the homes but each committee determined the optimal conditions for installation based on the preferences of the homeowner, the characteristics of the landscape and the house. The experience with this group of people was used to verify the acceptability of the technology, identify problems in its use (technical and cultural), measure improvements in water quality and make adjustments to the participatory methodology to improve cooperation and make better use of the community’s local knowledge. Later, 10 additional families got involved in the project after having verified the effectiveness of the filters and their cultural suitability. Parallel to this process, other activities like training workshops were developed, in order to look for a high degree of sense of ownership in the community and an independent and autonomous management of technology which is vital to ensuring sustainability and the potential for replication in the future. Systemic intervention proposal:

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The systemic focus used in the project entailed a coordinated work between the technical and the organizational aspects of the project, as mentioned above. Additionally, the systemic focus facilitated the approach to other social and cultural aspects that affect the development of the project, but are not always taken into consideration. One of these aspects is the involvement of other stakeholders. Work with stakeholders: Aside from working with the community, EWB Colombia also worked together with the mayor and an employee from the UMATA to try and establish a relationship of trust with the community’s inhabitants from the beginning. Working together with the mayor has improved the probability of effective outcomes of the participatory methodology used. Thanks to the mayor, the EWB group and the local population who have been working together have had the chance to show their findings to the political leaders representing each of the districts attached to the municipality. This has created a positive "tension" which has increased the number of people interested in making a contribution with their local knowledge and participating in creating better living conditions for their communities. Testimonials such as that of the mayor are presented: "I was able to go and look at the functioning of the filters and we are definitely very happy because we found that. thanks to the collective work, water was improved and is fit for human consumption. What we liked best is that this is a professional job, well done (1), which benefits us and also enables us to keep the filters working”. Moreover Leonel Riaño, community leader says that "... All the work of implementing the filters was very good, the community was actively involved and we learned several things about the composition of the filters and their maintenance. The learning process has been fundamental for students in order to actively participate in the design of other proposals”. (Ramirez et al., 2010) In this process, the help from other stakeholders such as the community leaders, the mayor and the UMATA employee has been crucial for the success in organizing the community. The group has had to be careful in dealing with politicians, as they might try to claim some of the results of the project as their own in order to obtain support from the community and portray a more positive and proactive image. Communication with the community and the politicians has been crucial in this process, the group has been very

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Maria Catalina Ramirez, Andrea Maldonado, Diana Calvo et al.

careful not to promise more than it can deliver and not to make commitments it can’t keep. (Ramirez et al., 2010)

Results of the project Results of the filters in the field In order to make a pilot test of the filters, four families were chosen and the filters were constructed along with them, with the objective studying the impact of these filters on the microbiological quality of the water consumed by these families. The following tables sum up the results of the microbiological tests performed before and after installing the filters. Table 5-11. Monitoring of the first four installed filters July 18th, 2008 Units

Problem water

Carlos

Dionel

Don Jorge

E. Coli

Parameter

UFC/100m/L

7

0

2

2

Total Coliforms

UFC/100m/L

Uncountable

Uncountable

Uncountable

Uncountable

U. PT/CO