Ground Water Abstraction Structures (SpringerBriefs in Water Science and Technology) 303134880X, 9783031348808

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SpringerBriefs in Water Science and Technology Divya A. S. · Joji V. S.

Ground Water Abstraction Structures

SpringerBriefs in Water Science and Technology

SpringerBriefs in Water Science and Technology present concise summaries of cutting-edge research and practical applications. The series focuses on interdisciplinary research bridging between science, engineering applications and management aspects of water. Featuring compact volumes of 50 to 125 pages (approx. 20,000–70,000 words), the series covers a wide range of content from professional to academic such as: • • • •

Literature reviews In-depth case studies Bridges between new research results Snapshots of hot and/or emerging topics

Topics covered are for example the movement, distribution and quality of freshwater; water resources; the quality and pollution of water and its influence on health; and the water industry including drinking water, wastewater, and desalination services and technologies. Both solicited and unsolicited manuscripts are considered for publication in this series.

Divya A. S. · Joji V. S.

Ground Water Abstraction Structures

Divya A. S. Department of Marine Geology and Geophysics Cochin University of Science and Technology Kochi, India

Joji V. S. Department of Marine Geology and Geophysics Cochin University of Science and Technology Kochi, India

ISSN 2194-7244 ISSN 2194-7252 (electronic) SpringerBriefs in Water Science and Technology ISBN 978-3-031-34880-8 ISBN 978-3-031-34881-5 (eBook) https://doi.org/10.1007/978-3-031-34881-5 © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

This book is dedicated to our family, friends and students

Preface

The book entitled Ground Water Abstraction Structures is useful to faculty and students of Geology, Geography and Civil Engineering, research scholars, hydrogeologists, planners and professionals in the field of groundwater. The arrangement of chapters in the book is as follows. Chapter 1 is Ground Water Abstraction Structures on an introduction to various structures used for ground water extraction. Natural and artificial abstraction structures and its various classifications are detailing in the first chapter. Chapter 2 is Site Selection on various methods used for selecting suitable sites for well construction. Surface, subsurface, geological, hydrogeological, geophysical and remote sensing and GIS methodology for site selection discussed in the chapter. The initial step in site selection is to use RS and GIS to reduce the targeted region and then use hydrogeological, geological and geophysical survey to pin point the site. Chapter 3 is Drilling Methods on the different drilling methods adopted for construction of wells. Manual drilling methods and power used mechanical drilling methods are explained in this chapter. Chapter 4 Development of Well on the development of a well after it has been drilled is explained. Well rehabilitation, its necessity and various ways for it are discussed in the chapter. Chapter 5 is Pumping Test Data Analysis on measuring the hydraulic parameters of aquifers, including transmissivity (T), hydraulic conductivity (K), storage coefficient (S), specific yield (Sy ) and leakage factor (B) using various curves. The pumping test examines the aquifer’s response to water extraction under controlled settings. Kochi, India

Divya A. S. Dr. Joji V. S.

Acknowledgments The authors wish to express wholehearted thanks to Vice Chancellor and Registrar, Cochin University of Science and Technology, for the support and encouragement. Our special thanks to colleagues, teachers, research scholars and students of the Department of Marine

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Geology and Geophysics, Cochin University of Science and Technology, Kochi, for their cooperation and suggestions. We also express our sincere gratitude to our friends, family members and all well-wishers for their sincere support, useful suggestions and kind cooperation.

Contents

1 Ground Water Abstraction Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Natural Ground Water Abstraction Structures . . . . . . . . . . . . . . . . . . . 1.2.1 Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Artificial Groundwater Abstraction Structures . . . . . . . . . . . . . . . . . . 1.3.1 Water Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Functions of Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Classification of Water Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.1 Tube Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.2 Bore Wells in Hard Rock Terrain . . . . . . . . . . . . . . . . . . . . . . 1.4.3 Skimming Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.4 Open Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.5 Open Wells in Hard Rock Formations . . . . . . . . . . . . . . . . . . 1.4.6 Open Wells in Hard Rock Formation . . . . . . . . . . . . . . . . . . . 1.4.7 Horizontal Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.8 Bored Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 2 2 7 7 7 8 8 12 13 14 16 17 18 21 22

2 Site Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Groundwater Flow Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Environmental Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Methodologies for Well Site Selection . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Hydrogeological Field Reconnaissance . . . . . . . . . . . . . . . . 2.3.2 Aerial Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Airborne Electromagnetic [AEM] Survey . . . . . . . . . . . . . . 2.3.4 Surface Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.5 Sub-surface Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.6 Esoteric Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.7 Remote Sensing and GIS Studies . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

25 25 27 27 28 29 30 30 31 38 38 39 42

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3 Drilling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Manual Methods Used to Dig Water Well . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Hand-Digging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Sludging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3 Hand Auger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.4 Drive Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.5 Manual Percussion Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Powered Methods Used to Drill Water Well . . . . . . . . . . . . . . . . . . . . 3.2.1 Jetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Hand-Auger Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Cable Tool Drilling/Churn Drilling/Percussion Drilling/Standard Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 Mud Rotary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 Air Rotary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6 Rotary-Percussion Drilling Method . . . . . . . . . . . . . . . . . . . . 3.2.7 Diamond Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.8 Calyx Drilling/Chilled Shot Drilling . . . . . . . . . . . . . . . . . . . 3.2.9 DTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

45 45 45 47 47 47 48 51 51 51

4 Development of Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Well Development Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Basic Principles—Well Development . . . . . . . . . . . . . . . . . . 4.3 Typical Causes for Reduced Well Yield . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Well Rehabilitation Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Limitations of Chlorination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Testing Well Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Well Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

63 63 64 64 67 67 70 71 71 72 73

5 Pumping Test Data Analysis (PTDA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Pumping Test Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Pumping Test Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Determination of Hydraulic Parameters of Water Bearing Formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Steady and Unsteady Time-Drawdown Tests . . . . . . . . . . . . 5.4.2 Recovery Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 Injection Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Test for Determining Well Hydraulic Attributes . . . . . . . . . . . . . . . . . 5.5.1 Step-dd Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6 Design of Pumping Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Measurement of Pumping Rate and Groundwater Level . . . . . . . . . . 5.8 Schedule of Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

75 75 77 77

52 55 57 58 59 59 60 61

78 78 79 80 80 80 81 82 82

Contents

5.9 Image Well Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10 Determination of Confined Aquifer Parameters . . . . . . . . . . . . . . . . . 5.10.1 Theis Type-Curve Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10.2 Jacob–Cooper Straight-Line Method for Time-dd . . . . . . . . 5.10.3 Cooper–Jacob Straight-Line Method for Distance-dd Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10.4 Residual Drawdown (RDD)-Time Ratio Method for Recovery Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.11 Determination of Unconfined Aquifer Parameters . . . . . . . . . . . . . . . 5.11.1 Unconfined Aquifer Without Delayed Yield . . . . . . . . . . . . 5.11.2 Aquifer with Delayed Yield in an Unconfined Aquifer . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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82 83 83 84 85 86 88 88 88 88

About the Authors

Divya A. S. born and brought up at Kottarakkara, Kollam district, Kerala State, India, completed M.Sc. Marine Geology from Cochin University of Science and Technology (CUSAT), Kochi, Kerala, India. She secured the University first rank in M.Sc. Marine Geology. She qualified UGC-NET-2018 and 2022 December. Currently, she is doing Ph.D. in Hydrochemistry at the Department of Marine Geology and Geophysics under the guidance of Dr. Joji, V. S. with the Kerala State Council for Science, Technology and Environment (KSCSTE) Fellowship.

Dr. Joji V. S. born and brought up at Chirayinkil, Thiruvananthapuram district, Kerala State, India, completed Higher Secondary, Graduation and Post-graduation from University of Kerala, Thiruvananthapuram. The Ph.D. work is carried out at the University of Kerala availing financial assistance from University Grants Commission, Government of India (GoI), in the form of UGC-Junior Research Fellowship (UGC-JRF). Dr. Joji V. S. Former Faculty at Rajiv Gandhi National Ground Water Training and Research Institute, Central Ground Water Board (CGWB), Ministry of Jal Shakti, GoI, Raipur, Chhattisgarh State, and Scientist in CGWB is at present working as Associate Professor and Head, Department of Marine Geology and Geophysics, CUSAT. He could be able to qualify many national level competitive examinations in the field of geology and a few among them are NET, CSIR-JRF, GATE, Geologist in ONGC, GSI and College Lecturer. He is University xiii

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About the Authors

Rank Holder, won gold medal, many merit scholarships and more than 100 cash prizes, trophies, certificates and books at local, school, district, college and university levels in quiz and elocution contests. He has successfully completed many TOT courses of DoPT, GoI like SAT, NTP, TNA, MOP, mentoring skills, EOT, DTS and DOT designed by Thames Valley University, UK. He is also working as GoI TNA Consultant and Recognized Trainer (National Resource Person) in DTS. The author has more than 85 published international, national research, technical papers and reports to his credit.

List of Figures

Fig. 1.1 Fig. 1.2

Fig. 1.3 Fig. 1.4

Fig. 1.5 Fig. 1.6 Fig. 1.7 Fig. 1.8 Fig. 1.9 Fig. 1.10 Fig. 1.11 Fig. 2.1 Fig. 2.2 Fig. 2.3 Fig. 2.4 Fig. 2.5 Fig. 2.6 Fig. 3.1 Fig. 3.2 Fig. 3.3 Fig. 3.4

Karst spring (https://www.pahasapagrotto.org/karst.html& psig=AOvVaw133bbN525l) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . a Depression spring, b contact spring, c perched spring, d fracture spring, e fault spring, f artesian spring (https://doi. org/10.1007/978-1-4020-4409-0_162) . . . . . . . . . . . . . . . . . . . . . . Schematic diagram of a cavity well (Raghunath 2007) . . . . . . . . . Driven well (https://www.ontario.ca/document/test-holesand-dewatering-wells-requirements-and-best-managementpractices) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jetted well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification of aquifers based on aquifer characteristics (https://www.in.gov/dnr/water/7258) . . . . . . . . . . . . . . . . . . . . . . . . Vertical cross section along a qanat (Beaumont 2009) . . . . . . . . . . Infiltration gallery (https://www.theconstructor.org/enviro nmental-engg/infiltration-galleries-features-construction) . . . . . . . Collector wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surangam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bored wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Various tools used for locating well sites . . . . . . . . . . . . . . . . . . . . Preliminary study, correlate maps, pictures and photos of the area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wenner configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Schlumberger configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resistivity imaging showing the general setup and resulting image processing by 2D inversion . . . . . . . . . . . . . . . . . . . . . . . . . . Flow chart showing identification procedures of GW potential site using RS and GIS. Modified after Ajaya Kumar (2020) . . . . . Hand-digging (Elson and Shaw 1995) . . . . . . . . . . . . . . . . . . . . . . . Sludging (Elson and Shaw 1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . Hand auger (Elson and Shaw 1995) . . . . . . . . . . . . . . . . . . . . . . . . . Drive point (Elson and Shaw 1995) . . . . . . . . . . . . . . . . . . . . . . . . .

4

6 10

11 11 13 18 19 20 21 22 28 29 35 36 36 41 46 48 49 49 xv

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Fig. 3.5 Fig. 3.6 Fig. 3.7 Fig. 3.8 Fig. 3.9 Fig. 3.10 Fig. 3.11 Fig. 3.12 Fig. 4.1 Fig. 4.2 Fig. 4.3 Fig. 5.1 Fig. 5.2 Fig. 5.3 Fig. 5.4 Fig. 5.5

Fig. 5.6

List of Figures

Manual percussion drilling (Elson and Shaw 1995) . . . . . . . . . . . . Jetting (Unhcr 1992) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Auger drilling (Life water International 2015) . . . . . . . . . . . . . . . . Cable tool drilling (Life water International 2015) . . . . . . . . . . . . . a Mud rotary, b LSS200 portable mud rotary drill rig (Life water International 2015) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air rotary (Life water International 2015) . . . . . . . . . . . . . . . . . . . . a Rotary percussion drilling, b rotary percussion drilling (with flush) (Life water International 2015) . . . . . . . . . . . . . . . . . . DTH (https://www.gilldrilling.com/dth-hammers.html) . . . . . . . . . Drilled well: well depth and diameter (AAFC n.y.) . . . . . . . . . . . . Brushing of a drilled well (AGR n.y.) . . . . . . . . . . . . . . . . . . . . . . . Schematic diagram showing concept of well efficiency . . . . . . . . . Drawdown pattern in a Confined aquifer; b unconfined aquifer (Roscoe Moss Company 1990) . . . . . . . . . . . . . . . . . . . . . . Plot of time-dd and recovery tests (Schwartz and Zhang 2003) . . . Illustration of step dd test (Romeo-Eftimi 2006) . . . . . . . . . . . . . . Pumping test for aquifers (https://doi.org/10.1007/978-3319-75115-3_11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Straight-line curve to the distance-dd data (https://www.goo gle.com/url?sa=i&url=http%3A%2F%2Fecoursesonline. iasri.res.in) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Schematic diagram of the aquifer recuperation after pumping stopped (https://www.google.com/url?sa=i&url=https%3A% 2F%2Fwww.waterloohydrogeologic.com) . . . . . . . . . . . . . . . . . . .

50 52 53 55 56 57 59 60 68 69 73 76 80 81 83

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List of Tables

Table 1.1 Table 2.1 Table 2.2 Table 2.3

Classification of springs (Meinzer 1923) . . . . . . . . . . . . . . . . . . . . Methods and technique of groundwater exploration . . . . . . . . . . . Different types of VES curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saaty’s scale of preference between two factors in AHP . . . . . . . .

6 30 38 42

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Chapter 1

Ground Water Abstraction Structures

Abstract Groundwater abstraction structures deals with various natural and artificial structures can be used to extract groundwater. Natural structures are springs and artesian aquifer. Artificial structures include Open dug well, Tube well, Filter point well, Bore well, Surangam/Tunnel well, Dug-cum-bore well (Kokarani), Auto flow well/Artesian well/Free Flow Well etc.

1.1 Introduction Groundwater, which is water held beneath the Earth’s surface in soil and porous rock aquifers, which accounts for up to 33% of total water withdrawals globally. Over two billion people rely on groundwater as their primary source of water (Alley et al. 2002), and underground sources provide 50% or more of the agricultural production required to cultivate the world’s food (Siebert et al. 2010). Ground water is the best suited freshwater resource in India which is available with minimum investment for variety of uses such as drinking, agriculture and commercial or manufacturing purpose (Tiwari 2021). Rainfall, climate, geology, irrigation techniques, anthropogenic sources of contamination, and a variety of other factors all have an impact on groundwater quality. Groundwater’s hydro-chemical parameters are important in determining its quality for various reasons. It also allows for a better knowledge of potential groundwater quality changes (Chen 2013). There is always some vacant space in geologic materials (such as rock, soil, and sediment). The pore space is the empty space, and the porosity is the percentage of pore space by volume in a rock or sediment. Moisture is always present in the pore space of all naturally existing rock units. The amount of moisture below the surface is minimal, and the amount of moisture gradually gets increases with depth. The amount of moisture in the soil or sediment eventually reaches a point where the pore space is totally filled with water and the soil or sediment is saturated. As a result, we can differentiate two main zones in the subsurface: the unsaturated and the saturated zones and the water table separates these two zones.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 D. A. S. and J. V. S., Ground Water Abstraction Structures, SpringerBriefs in Water Science and Technology, https://doi.org/10.1007/978-3-031-34881-5_1

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1 Ground Water Abstraction Structures

Natural and artificial abstraction structures can be used to extract groundwater. Aquifers are layers of rock and/or sediment that store groundwater. The term “groundwater” refers to precipitation that has entered the soil below the surface and accumulated in voids of underground. Ground water extraction structures include open dug wells (small diameter open wells and large diameter irrigation wells), tube wells, filter point wells, bore wells, surangams, and dug-cum-bore wells. The shallow unconfined aquifer is tapped in the context of an open dug well, and the ground water is under phreatic condition. The Tube wells are used to draw ground water from deeper aquifers in sedimentary formations, while bore wells are used to retrieve ground water from fractured crystalline formations. Water occurs in restricted to semi-confined conditions in tube wells and bore wells. The filter point wells with a depth of 5–11 m bgl and PVC pipes pushed into riverine natural levees/embankments are known as tiny tube wells. In locations where the weathered rock thickness is less, dug wells frequently get dry, prompting people to construct bore wells in addition to dug wells, which are referred to as dug-cum-bore wells. Surangam/tunnel well, kokarani (extracting water from the weathered portion like a dug well and hard rock portion, where dimension of crystalline portion is also having the dimension of dug well), and auto flow well/artesian well/free flow well are all common in northern Kerala. Groundwater is an important and necessary source of water for people all around the world. Groundwater accounts for 0.94% of total water balance and 30% of the world’s fresh water supply. Groundwater is a vital source of drinking water among freshwater resources, and its demand for various purposes is increasing day by day as a result of rapid population growth, rapid urbanization with changing lifestyles, growing industrialization, and agricultural activities. Groundwater can be extracted naturally or artificially through a variety of abstraction structures such as natural and artificial structures. Unscientific groundwater abstraction, directly or indirectly changes the quality of groundwater. The types and numbers of abstraction structures of artificial (man-made) groundwater have diversified as technology has advanced. Natural groundwater abstraction structures include springs and artesian aquifer; whereas artificial structures include dug well, tube well, open well etc.

1.2 Natural Ground Water Abstraction Structures Natural ground water abstraction structures include spring and artesian aquifer.

1.2.1 Springs Natural discharge of groundwater at the surface of the ground or directly into the bed of a stream, lake or sea is called springs. On the basis of their mode of occurrence, quantity of water and rate of flow springs show great variation. Conditions favorable

1.2 Natural Ground Water Abstraction Structures

3

for the occurrence of springs include favorable slope of the valley, presence of fault across the water bearing formation, presence of localized impervious obstructions, fissured zone etc. Elevated areas mostly satisfying this condition, hence most of the springs found in this area. Highly mineralized water (including dissolved minerals and certain dissolved gases) characterizes springs, with water quality ranging from crystal clear pure water to turbid and hot to cool. The water yield of springs varies according to the season. They might be either permanent or ephemeral. The water temperature may be similar to the mean yearly air temperature. Bryan classified springs in to two types -gravity springs (resulting from gravitational forces) and non-gravity springs (resulting from non-gravitational forces). Gravity springs flow to the surface along a natural subsurface slope. Water emerges from the ground in a more or less horizontal flow. Contact spring, Fault spring, Depression spring, Joint/Fracture spring etc., are examples of gravitational spring whereas fumaroles, geysers, thermal springs belongs to non-gravitational spring. According to the origin, the springs are classified into different types and these include

1.2.1.1

Depression Spring

Depression springs arise when the surface of a hill’s slope meets or touches the water table, causing ground water to flow out as a spring or seepage.

1.2.1.2

Contact Spring

When a permeable formation overlies a less permeable formation, contact springs form. A line of springs, which may be in the main water table or perched water table, generally marks a lithological contact. It is not necessary for the underlying layer to be impermeable; only have a large enough difference in hydraulic conductivity. If the permeable strata are cut by the dyke, as shown in the diagram, contact springs can form. In this area, the dyke could act as a natural dam.

1.2.1.3

Sinkhole Springs/Karst Springs/Tubular Springs

Sink hole springs developed in limestone bed rock. Diffuse flow in pores and fissures in the rock or channelized flow in caves are both possibilities. Where a cavern is connected to a shaft (vertical entrance) that rises to the surface, spring may be found (Fig. 1.1).

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1 Ground Water Abstraction Structures

Fig. 1.1 Karst spring (https://www.pahasapagrotto.org/karst.html&psig=AOvVaw133bbN525l)

1.2.1.4

Fracture/Joint Spring

Joint spring can be explained by the formation of jointed or permeable fractured zones in low permeability rocks. At low elevations, springs can emerge where these fractures join the land surface, and water circulation is predominantly through fractures.

1.2.1.5

Fault Spring

Faulting may create a geologic control that favours the creation of springs. An impermeable faulted rock unit could be positioned next to an aquifer. This can act as a regional border for ground water movement, forcing water in the aquifer to flow as a fault spring.

1.2.1.6

Artesian Spring

Artesian springs/fissure springs are springs that release water under artesian pressure (pressure in water-bearing soil or rock), usually through a fissure or other opening in the confining bed that overlies the aquifer.

1.2 Natural Ground Water Abstraction Structures

1.2.1.7

5

Tubular or Fracture Spring

Issuing from rounded channels such as lava tubes, solution channels or fractures in impermeable rock connecting with ground water.

1.2.1.8

Impervious Rock Spring

Occurs in tubular channels or fractures of impervious rocks.

1.2.1.9

Thermal Spring

Thermal spring discharge water has a temperature approximately 6.5° higher than the usual local ground water temperature. Thermal spring water is frequently mineralized and comprises primarily of meteoric water that has had its quality altered by its passage underground.

1.2.1.10

Geyser

The tremendous force of superheated steam within limited subsurface pathways causes a periodic thermal (hot) spring, which is known as geyser. Water from a shallow aquifer drains into a deep vertical opening, where it is heated to temperatures above boiling point. Steam pulls upward as pressure rises, releasing some water at the surface, lowering hydrostatic pressure and causing the deeper superheated water to accelerate upward and flash into steam. The geyser then surges (rises suddenly) into full eruption for a brief period before the pressure dissipates.

1.2.1.11

Mudpot

A kind of Hot spring results when only a limited supply of water is available. Here water mixes with clay and undissolved particles brought to the surface, forming a muddy suspension. Meinzer (1923) classified the springs on the basis of their magnitude (discharge) and high magnitude springs occur in volcanic and limestone terrains (Table 1.1 and Fig. 1.2).

6 Table 1.1 Classification of springs (Meinzer 1923)

1 Ground Water Abstraction Structures

Magnitude

Mean discharge

First order

> 10 m3 /s

Second order

1–10 m3 /s

Third order

0.1–1 m3 /s

Fourth order

10–100 l/s

Fifth order

1–10 l/s

Sixth order

0.1–1 l/s

Seventh order

10–100 ml/s

Eighth order

< 10 ml/s

Fig. 1.2 a Depression spring, b contact spring, c perched spring, d fracture spring, e fault spring, f artesian spring (https://doi.org/10.1007/978-1-4020-4409-0_162)

1.3 Artificial Groundwater Abstraction Structures

7

1.3 Artificial Groundwater Abstraction Structures 1.3.1 Water Wells Water wells are major artificial groundwater abstraction structures; they are hole or shaft, usually vertically, dug into the earth for bringing groundwater to the surface (Todd 1980). Since the earliest civilizations in Africa and Asia, water wells have been a source of water for people, animals, and crops. The abstraction of relatively pure water sources from wells and springs facilitated the growth of numerous towns and cities in Europe during the middle Ages and into the Industrial Period. Water well is a hole or shaft drilled deep into the ground to bring ground water up to the surface. Wells are also used for underground study and analysis, artificial recharge, and waste water disposal. For monitoring groundwater quality and water level wells are extensively used. Water wells are usually vertical, but they can also be horizontal (infiltration gallery), vertical and horizontal (radial collector well), or even inclined. Long lived and efficient wells can be ensured through proper design of the well. Ground water for irrigation and water supply requires various types of wells which is suited for diverse geological formation. Different types of wells are Open dug well, Tube well, Filter point well, Bore well, Surangam/Tunnel well, Dug-cum-bore well (Kokarani), Auto flow well/Artesian well/Free Flow Well etc.

1.3.2 Functions of Wells Wells are utilized for a variety of reasons, including the following: • To provide water to suit the needs of home, municipal, industrial, and agricultural users. • To keep seawater out of the house. • To drain untreated water from an aquifer that has been contaminated. • To facilitate construction operations by lowering the water table. • To alleviate pressure on dams. • Drainage of agricultural or urban land. • To replenish groundwater resources by injecting surface water or previously used groundwater into the subsurface. To put it another way, artificially recharge aquifers at higher rates than natural recharge. • To dump effluent or hazardous material into isolated aquifers. Because of the negative consequences on the environment, this role of wells is now severely limited.

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1 Ground Water Abstraction Structures

1.4 Classification of Water Wells The water wells are divided into four categories based on their purposes: (a) water supply wells, (b) recharge wells, (c) drainage wells, and (d) monitoring wells. Open wells and tube wells are two types of water supply, recharge, and drainage wells, depending on their design and construction method. Based on availability of aquifer layers and the quantity of necessary water supply, tubewells are categorized as shallow tube wells or deep tube wells. Borewells and cavity wells are two different forms of tube wells. A dug-cum-bore well is a form of open well that is similar to a dug-cum-bore well. Monitoring wells or observation wells, on the other hand, are small-diameter (typically 1'' to 2'' ) tube wells used to monitor groundwater levels and collect groundwater samples for testing water quality.

1.4.1 Tube Well The tube wells are type of water well which is constructed for the extraction of ground water. It is characterized by 100–200 mm wide stainless-steel tube or pipe bored into an underground aquifer. Broadly tube wells are divided into four types based on how water enters the well, the construction process, the depth, and the type of aquifer tapped.

1.4.1.1

Based on Water Inflow

Based on the entry of water from the aquifer to the well, tube wells are classed as screen wells or cavity wells. (a) Screen Well Screen wells are wells characterized by small slots or openings. Different types of well screens are used to suit the specific requirements of the aquifer. Strainer, slotted well type, Louver-TypeScreen, Coir-Rope strainer; bamboo strainer, agricultural strainers etc. are examples for different types of screen wells. (i) Strainer Tube Well Strainer tube wells are essentially consisting of a perforated or slotted pipe wrapped in a wire mesh with a smaller annular space between the two. In this type well screens are placed against the water bearing stratum. Sand particles larger than the mesh size are kept out of the well pipe by the wire screen, which prevents sand particles from entering the pipe through the fine mesh (screen). As a result, the risk of sand removal is reduced, and higher flow velocities can be achieved. Drilling continues through several layers in a strainer type tube well, and after determining the water bearing

1.4 Classification of Water Wells

9

strata, strainers are placed opposite these strata to allow water to enter the tube well. Plain pipes should be installed against the non-water-bearing strata. (ii) Slotted Type Tube Well A slotted type tube well is made out of a pipe that is slotted for part of its length at one end and is blank the rest of the way. The pipe’s slotted section is normally around 5 m long and penetrates the constrained aquifer. The slots are typically 25 mm × 3 mm in size, with 10–12 mm spacing. (b) Cavity Well The shallow tube well drilled in an alluvial formation is known as a cavity well. A cavity tube well is made out of a pipe which is dug into the earth and rests on top of a thick clay layer. Water is drawn from the bottom of a hollow tube well rather than the sidewalls. The flow pattern of a screenwell and a cavity well differs in a way that the flow in a strainer well is radial, whereas the flow in a cavity well is not radial. During the earliest phases of pumping, fine sand is discharged with water, resulting in the formation of a hollow at the bottom. Through this cavity, water from the aquifer enters the well pipe. As the pumping continues, the cavity’s spherical area expands outwards, lowering the velocity of flow and, as a result, preventing sand particles from entering the well pipe. As a result, sandy water is produced from a cavity type tube well at first, but clear water is obtained after the passage of time. As the water is extracted from the bottom, the cavity type tube well can only tap into one aquifer. In theory, a cavity type tube well is identical to a deep open well, with the exception that a cavity type tube well may tap any lower strata, but a deep open well taps just the first aquifer immediately below the layer (Fig. 1.3).

1.4.1.2

Based on Construction Process

Based on the method of construction wells are categorized as drilled wells, driven wells and jetted wells. (a) Drilled Tube Wells Drilled wells are those wells which having a smaller diameter range from 10 to 20 cm. It is constructed as deeper wells and characterized by less pollution susceptibility due to its greater depth from surface source. Drilled wells are less affected by seasonal weather pattern, so its water supply tends to be more reliable. These wells are constructed by drilling. There are two primary methods of drilling: Rotary and Cable tool. (b) Driven Wells A driven well is also known as instantaneous well or sand-point well. It consists of a series of connected lengths of pipes driven by repeated impacts into the ground below the water table and characterized by perforated pipe with a pointed end. These wells

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1 Ground Water Abstraction Structures

Fig. 1.3 Schematic diagram of a cavity well (Raghunath 2007)

are suitable for sandy formations. Yield from driven wells is usually very small, it’s about 100–250 m3 /day. It’s suited for domestic supplies, temporary water supplies, exploration and observation purposes. Loose formations with no large gravel or boulders are suitable for driven wells. The driven wells can build in a short period of time, at a low cost, and even by one person is an important advantage (Fig. 1.4). (c) Jetted Wells Jetted wells are made by the cutting effect of a downstream of water. The ground is washed away by a high-velocity stream, while the casing, which is lowered into the deepening hole, transports the water and cuts up and out of the well. Generally, it has a diameter of 3–10 cm and maximum up to 30 cm or more and its depth is about 15 m. Jetted wells have only small yields. These wells act as useful for exploratory test holes, observation wells and well-point systems (Fig. 1.5).

1.4.1.3

Based on Depth

On the basis of their depth tube wells are classified as shallow or deep tube wells. (a) Shallow Tube Well Low-capacity wells with depth less than 35 m are known as shallow tube wells. Cavity tube wells and strainer tube wells with coir strainers are examples of this

1.4 Classification of Water Wells

11

Fig. 1.4 Driven well (https://www.ontario.ca/document/test-holes-and-dewatering-wells-requir ements-and-best-management-practices)

Fig. 1.5 Jetted well

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1 Ground Water Abstraction Structures

category. Most dug wells are shallow and excavated in poorly permeable material. Drought and seasonal decline in the water table readily affects the well water level. (b) Deep Wells Deep tube wells are large-capacity wells that access multi aquifers. Their depth normally ranges between 60 and 300 m bgl. Depending on the characteristics of the aquifer formation, deep tube wells might be strainer wells or gravel-pack wells. (c) Filter Point Wells Filter point wells are shallow (15 m deep) and consist of a well screen and a short casing pipe in deltaic locations, where the aquifer deposits are largely coarse sand and gravel. These tube wells are called Filter point well. They are tube wells with a tiny diameter (7.5 cm) from which water is primarily extracted manually (Sarma 2009).

1.4.1.4

Based Aquifer Characteristics

Water table wells, semi-artesian wells, artesian wells, and hard rock bore wells are different types of tube well based on the aquifer characteristics. (a) Water Table Wells Water Table wells are constructed in unconfined aquifer under water table condition. In this type aquifer water is not under pressure. Groundwater is in direct contact with the atmosphere through the open pore spaces of the overlying rock. The depth of water table varies with geology, topography, season and tidal effect. (b) Artesian Aquifers/Artesian Well Artesian wells penetrate the aquifer’s confining layers below and above the aquifer’s surface. At high elevations, rainfall enters the aquifer through porous layers, putting ground water under pressure at lower elevations. The water level in the well is higher than the aquifer due to this pressure. A “flowing well” is a well that produces water through artesian pressure at the earth surface. (c) Semi-artesian Wells In aquifers having a semi-artesian condition, semi-artesian wells are constructed. Water is under pressure, but not to the point that it can’t flow out of the well (Fig. 1.6).

1.4.2 Bore Wells in Hard Rock Terrain Bore wells are wells in hard rock settings because the bore hole can hold on its own for the most of its depth and the tube (casing) is only placed against the upper weathered

1.4 Classification of Water Wells

13

Fig. 1.6 Classification of aquifers based on aquifer characteristics (https://www.in.gov/dnr/water/ 7258)

soil zone. Borewells have proven to be effective as drinking water wells in situations where discharge is restricted. Bore wells for irrigation are becoming increasingly popular, particularly with drip irrigation systems. The excessive drawdown, which results in a high head and high suction heads, is one of the fundamental problems of such wells. As a result, submersible and jet pumps must be employed in most cases.

1.4.3 Skimming Wells The Indo-Gangetic plain is primarily underlain by a massive water-bearing aquifer produced by alluvial deposits, some of which contain native seawater. The brackishness of the deep subsurface water is extreme (Zuberi and Whorter 1973). Fresh water has accumulated in the upper portion due to seepage and deep percolation from rains, rivers, canals, and cultivated fields. This layer of water is of sufficient quality to be used for irrigation. Advantages and Disadvantages of Tube Wells Advantages Major advantages include • They do not require a lot of area. • Can be built rapidly, not time consuming. • Even in drought years, a rather consistent yield of water can be achieved.

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1 Ground Water Abstraction Structures

• When encountering deep entrenched aquifers, it is cost effective. • Occasionally, flowing artesian wells are struck. • Water of generally high quality is tapped. Disadvantages Major disadvantages of tube wells include • It necessitates the use of expensive and difficult drilling equipment and technology. • Drilling and completing the tube well requires professional employees and considerable care. • It is necessary to install pricey turbine or submersible pumps. • Missing fractures, fissures, and joints in hard rock locations may result in a large number of dry holes.

1.4.4 Open Wells Throughout the documented history of mankind, open wells have been the primary source of domestic water. Open wells have relatively large diameters but modest yields (or discharges) and are shallow. The diameters of open wells typically range from 1 to 10 m. In most situations, the yield of such wells is less than 20 m3 /h. A correctly designed open well penetrating a permeable aquifer, on the other hand, can produce 100–300 m3 per hour. Open wells can be anywhere between 2 and 20 m deep. These wells are sometimes referred to as dug wells because they are frequently excavated. An open well’s walls can be made of brick or stone masonry, as well as precast concrete rings. Depending on the depth of the well, the thickness ranges from 0.5 to 0.75 m. They’re also commonly utilised for small-scale irrigation. Open wells are shallower than tube wells and are typically used to tap water table aquifers. There are three main uses for open wells. • To draw ground water from fine-grained shallow-depth aquifers where the risk of ingesting microscopic particles necessitates a large area of contact with the aquifer, • To tap ground water in hard rock locations, and • To function as reservoirs for ground water progressively replenishing the well. The storage of water in an open well allows for more frequent extraction than the rate of ground water recovery into it. Open wells are best suited to aquifers that are shallow and low-yielding. Construction does not necessitate sophisticated equipment or expert staff. They can be powered by man- or animal-powered indigenous water lifts or low-cost mechanical centrifugal pumps. Deepening or adding bores to the bottom or sides of open wells can revive them.

1.4 Classification of Water Wells

15

Limitations of Open Wells • The well building, as well as the dumping of excavated material, necessitates a large amount of room, • Well construction is time-consuming and difficult, • Open dug wells are inappropriate for reaching deep aquifers since the cost of construction rises exponentially as the well’s depth rises (Deeper aquifers could, however, be tapped by resorting to dug-cum-bore wells), • Unless appropriately protected, they are vulnerable to contamination or pollution from surface sources and • There are substantial water level changes and the possibility of well drying up due to the shallower depth water table, especially during drought years. Open wells are classed based on the characteristics of the groundwater bearing formation to be tapped. • Open wells in unconsolidated formation • Open wells in hard rock formation. The cross section of open wells can be round or rectangular. Because of its increased structural strength and ease of well sinking, the circular design is used in alluvial and other porous formations. Advantages of Open Well • • • •

Water storage capacity is available in the well itself, Construction does not necessitate sophisticated equipment or experienced labour, Installing an a centrifugal pump makes it simple to run, and Deepening by blasting or digging vertical or side bores can revive it.

Disadvantages Disadvantages of open well include • • • • • • • •

A large amount of area is necessary for the well and the excavated materials. Deep aquifers cannot be profitably exploited. Uncertainty about obtaining high-quality water. Contamination risk if not protected against surface water infiltration. High cost of construction as the depth increases in hard rock areas. Construction is time-consuming and laborious. The water table fluctuates dramatically throughout the year. Prone to drying out during drought years.

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1 Ground Water Abstraction Structures

1.4.5 Open Wells in Hard Rock Formations Open wells in hard rock formations, on the other hand, are commonly rectangular in shape. The perimeter of a rectangle well is more than that of a circular well for the same cross-sectional area, and thus the area exposed to seepage of water into it through fractures and fissures is significantly greater in a rectangular well than in a circular one. Open wells in unconsolidated formation are classified as unlined wells, wells with pervious lining, wells with impervious lining, and Dug-cum-bore well.

1.4.5.1

Unlined Wells

Lining is not frequently used to cover wells excavated for strictly temporary purposes because it raises the expense of construction, which is not always justified in a given case. Because the sides of well are not covered, it is critical that the subsoil be compact enough to stand upright in natural conditions. The water table should be no lower than 4 m bgl. The depths of unlined wells are limited to roughly 6.5 m bgl to ensure stability.

1.4.5.2

Wells with Pervious Lining

Dry bricks or stone masonry are commonly used to line these wells. Water seeps into the wells from the surrounding aquifer via the well’s sides. When the water-bearing structure consists of gravel or coarse sand deposits, pervious lining is appropriate. When the formation is made up of layers of fine sand, the sand particles, together with the water, escape through the pervious lining and into the well. As a result, a hollow area or void forms beneath the well lining, endangering the well’s structural integrity. In loose formations, the annular hollow region around the well lining will self-seal, but in cohesive materials, it must be filled with brick or stone ballast. Ballast is approximately 2 cm in diameter and is packed behind the liner. It should go up to the static water table at the very least.

1.4.5.3

Wells with Impervious Lining

In alluvial deposits, open wells with a permanent masonry lining built in cement mortar are prevalent. As long as ground water conditions remain appropriate, they create a permanent structure for tapping water. Though wells with impervious lining are typically deeper than the lined wells and wells with pervious lining, their depths rarely exceed 30 m bgl. Beyond that, the expense becomes prohibitive, and the well becomes uneconomical. Weep holes are included in these linings to allow water to enter from the side.

1.4 Classification of Water Wells

1.4.5.4

17

Dug-cum-Bore Wells

Vertical bores are occasionally installed at the bottom of dug wells to increase yields. Such wells are known as dug-cum-bore wells. Boring entails drilling small-diameter holes ranging in diameter from 7.5 to 15 cm through the bottom of the well and extending them up to or into the water-bearing formation lying beneath the bottom of the excavated well. In unconsolidated rocks, only one hole is normally drilled at or near the bottom of the well. However, in hard-rock areas, the number of holes might range from one to six, depending on the type of the rock and the size of the well. Ordinary dug wells are hydraulically inferior to dug-cum-bore wells. Their effectiveness, however, will be contingent on the existence of restricted aquifers at suitable depths below the well’s excavated section. When a pump set is used to operate a dugcum-bore well, the pump’s suction pipe is put on the bored section itself; the well effectively becomes a tube well. The flow of ground water from the upper unconfined aquifer into such wells, however, is restricted. The well staining is then used solely as a pump house. In this case, a standard tube well will be less expensive to construct than an excavated cum-bore well. The only benefit is that it allows for a phased development of the well structure.

1.4.6 Open Wells in Hard Rock Formation Open wells in hard rock areas, also known as hard rock wells; the aquifer’s recharging is directly dependent on precipitation. As a result, the water table is subject to significant variations in response to the frequency of rainfall. The worn mantle overlying the unchanged rock, as well as the fracture porosity of the unaltered rock itself, forms the shallow ground water reservoir. They are distinguished by their low permeability. As a result, they can only produce a limited amount of ground water. Tube wells are typically unsuitable in such rocks due to their low permeability. Open wells can store quite large amounts of water throughout a given recovery period. As a result, available water supplies can be obtained at low drawdown in relatively short times, allowing for adequate recuperation between subsequent bouts of pumping. Open wells also expose a larger surface area of the aquifer to seepage. The weathered zone is the most crucial zone in which ground water typically appears in hard rock terrains where ground water occurrence is illusory. The thickness of weathered zones varies according to terrain, climatic circumstances, and rock type. As a result, a study of the weathered zone profile, manner of weathering, structural features, and connection of all of these variables with lithology are all beneficial. A good yield in basement rock can be expected only if it is located in a shear, fracture, or fault zone. Dykes, which operate as obstacles to ground water circulation, are frequently encountered in granitic terrain on an irregular basis. A dyke is an excellent negative sign of ground water. Dykes function as subsurface dams, effectively stopping and/or changing ground water lateral movement. On the

18

1 Ground Water Abstraction Structures

upstream side of a dike, one may find high-yielding wells, whereas on the downstream side, ground water supply may be limited. In hard rock locations, open wells may be dug wells or dug-cum-bore wells.

1.4.6.1

Dug Wells

Regardless of the rocky sub-stratum, well construction is carried out in hard rock areas since it is the only convenient local source of irrigation and water supply. These wells are often open, excavated pits into the rock, with only a few metres of liner. Typically, pneumatic rock blasting equipment with jack-hammers and explosives is used to excavate a well through hard rocks. Pumping water from open wells is frequently done with standard horizontal centrifugal pumps.

1.4.7 Horizontal Wells The development of ground water can be traced back to ancient times. ‘Qanats’ were horizontal wells that provided ground water in ancient times. These are still alive today and can be found in a band throughout the arid regions of Southern Asia and Northern Africa stretches from Afghanistan to Morocco. Qanats are made up of a succession of vertical shafts that resemble wells and are joined by a gently sloping tunnel that carries a water channel. Without the need for pumping, qanats efficiently bring vast amounts of subterranean water to the surface. The water is gravity-fed, usually from an upland aquifer, and the destination is lower than the source. Water may be carried over long distances in hot, dry climates using qanats, with little water loss due to evaporation (Fig. 1.7). Infiltration Galleries, Horizontal pipes and collector wells are different types of horizontal wells. Fig. 1.7 Vertical cross section along a qanat (Beaumont 2009)

1.4 Classification of Water Wells

19

Fig. 1.8 Infiltration gallery (https://www.theconstructor.org/environmental-engg/infiltration-gal leries-features-construction)

1.4.7.1

Infiltration Galleries

Infiltration Gallaries are horizontal conduits for intercepting and collecting ground water by gravity flow eg: Qanats, Surangams. Galleries constructed at the water table elevation, discharge into a sump where a pump lifts the water to the ground surface for use. Many cases infiltration galleries are laid parallel to river beds. Infiltration galleries work best when it is surrounded by sufficiently permeable soil so that the gallery can easily collect the water. Gravel is one such permeable soil material that facilitates the flow of water to the infiltration gallery with ease. Gravel also helps to trap the large particles that can result in blocking the perforations. A Gallery alone cannot meet the demand of a big population. One or more galleries are constructed that together connect to a central point like a spring box or a hand-dug well. Hence these center point water collection structures are called collector wells. It is to be constructed in a way that it is prevented from getting contaminated and safe distance of generally 30 m from septic tanks. Infiltration galleries are constructed such that the entry of unfiltered surface water is prevented (Fig. 1.8).

1.4.7.2

Horizontal Pipes

On sloping ground surfaces small diameter horizontal holes can be drilled by rotary method. Perforated pipes placed in these holes tap ground water that would otherwise be discharged by seepage or from small springs.

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1 Ground Water Abstraction Structures

Fig. 1.9 Collector wells

1.4.7.3

Collector Wells

Collector well is used for tapping permeable alluvial aquifers to get high quality, low temperature water at reasonable cost. If located adjacent to the surface water source, a collector well lowers the water table and induces infiltration of surface water through the bed of the water body to the well. A central cylinder, a concrete caisson about 5 m diameter is sunk into the aquifer by excavating the inside earth material. At requisite depth, a thick concrete plug is poured to seal the bottom. Perforated pipes, 15–20 cm dia are jacked hydraulically into the water bearing formation through the precast portholes in the caisson to form a radial pattern of horizontal pipes. During construction fine grained materials are washed into the caisson so that natural gravel pack can form around the perforations, number, length and radial pattern of the collector pipes can be varied to obtain maximum capacity, and its average yield is about 15,000 m3 /day (Fig. 1.9).

1.4.7.4

Surangams

The surangams means tunnel in Malayalam language and other vernacular names are thurangam and thorappu. They are horizontal or slightly inclined tunnels dug in

1.4 Classification of Water Wells

21

Fig. 1.10 Surangam

sloping laterite terrains, which act as water collectors from the walls and the roofs and act as a conduit to discharge water out. Surangam are common in the Western Ghats regions of south Karnataka and Goa and used for irrigating coconut, areca nut, plantains and vegetables. The surangams are fast disappearing traditional ground water extraction structures from its place of origin and are rapidly replaced by bore wells (Fig. 1.10).

1.4.8 Bored Wells Hand-operated or power-driven earth augers are used to bore wells. Hand augers come in a variety of forms and sizes, but they all include cutting blades at the bottom that rotate to bore into the ground. The auger is withdrawn from the hole and emptied when the blades are full of loose earth; the process continues until the required hole depth is attained. Bored wells are those that are dug with an auger until it reaches the water table or runs into a material that prevents or stops the auger, such as

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1 Ground Water Abstraction Structures

Fig. 1.11 Bored wells

rock. Unlike drilled wells, bore wells are shallow and receive water from layers of the soil above the bedrock. The amount of water obtained is proportional to the amount of water in the water table as well as the rate at which the well can recharge. A 24-in.-diameter concrete pipe covers bore wells and is inserted when it reaches the water table. Pea gravel is put around the casing as a filter or screen to keep silt out of the well and strengthen the side walls of the bored hole. Twenty feet below the surface, bore wells are also grouted on the outside of the casing (Fig. 1.11).

References American Water Works Association (1997) ANSI/AWWA A100-97 standard for water wells. American Water Works Association, Denver, CO Andreas NA (2016) In: Chiotis E, Eslamian S, Weingartner H (eds) Underground aqueducts handbook. CRC Press, Boca Raton, p 244 Environmental Protection Agency (1975) Manual of water well construction practices EPA 570/ 9-75-001. U.S Environmental Protection Agency, Water Supply Division, Washington, DC Meinzer OE (1923) Outline of groundwater hydrology with definitions. US geological survey water supply paper 494, 71 p Michael AM, Khepar SD, Sondhi SK (2008) Water well and pump engineering, 2nd edn. Tata McGraw Hill Education Pvt. Ltd., New Delhi Raghunath HM (2007) Ground water. New Age International (P) Limited, New Delhi

References

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Sarma PBS (2009) Groundwater development and management. Allied Publishers Pvt. Ltd., New Delhi Todd DK (2005) Groundwater hydrology. Wiley, New York Well owner.org (2021) Water well resources and water well directory

Chapter 2

Site Selection

Abstract Various methods used for selecting suitable sites for well construction include Surface, subsurface, geological, hydrogeological, geophysical and remote sensing and GIS methodology. The initial step in site selection is to use RS and GIS to reduce the targeted region, then use hydrogeological, geological and geophysical survey to pin point the site. Surface and subsurface method give detailed picture of the selected site which helps for the investigation, water level and quality monitoring, and artificial groundwater recharge.

2.1 Introduction Groundwater is a renewable resource that can be replenished in the natural world. Due to inadequate surface water resources and frequent monsoon interruption, it is an essential source for a variety of functions, including drinking, irrigation, and industrial uses. Many factors, such as seasonal rainfall, run-off, soil grain size, geographic features, type of natural landscape, drainage conditions, lithological properties, landuse practises, depth to groundwater level, and natural factors, all of which are not homogeneous in any area, contribute to the characterization of groundwater zones. A water well is a carefully designed hole in the earth that leads down to a potential aquifer and is used to bring ground water to the surface (production well). Wells are occasionally used for various reasons, such as subsurface investigation, water level and quality monitoring, and artificial groundwater recharge. Selections of sites for construction of water wells are important. Guide lines for selection of sites for well construction is discussing below (Subba Rao 2011) • As groundwater flows in the direction of the lowering slope, low-lying locations are better for sinking wells than slopy areas and highlands. • Vegetation thrives were groundwater available at smaller depths. As a result, the presence of dense vegetation suggests a considerable amount of groundwater storage at a shallow depth. However, the presence of flora such as desert plants, which take water from the subsurface and store it in their thick fleshy leaves and stems, suggests a paucity of groundwater at shallow depths. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 D. A. S. and J. V. S., Ground Water Abstraction Structures, SpringerBriefs in Water Science and Technology, https://doi.org/10.1007/978-3-031-34881-5_2

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• Groundwater storage is indicated by areas with extensive soil or alluvium cover, as well as worn, cracked, jointed, and faulted rocks, which facilitate infiltration of groundwater recharge. Fine-grained soils, such as clay, cannot support groundwater infiltration. Furthermore, these formations are unable to transport water from one location to another and, as a result of stagnation, contain saline groundwater. Because coarse-grained soils carry water, the water is safe to drink. Bald rocky places lack such favorable conditions because water cannot infiltrate. As a result, these rocks point to a lack of groundwater. • Tanks, ponds, lakes, streams, reservoirs, and rivers are examples of surface water bodies that act as recharge sources for the surroundings. As a result, if we drill wells in and around surface water bodies, the wells will be able to provide enough water. • Existing wells in the neighborhood of proposed well sites should be investigated for soil cover, rock types (hard rock or soft rock), structural problems (fractures, joints, faults, etc.), depth to water table, and well yield to provide a comprehensive picture of the area’s hydrogeological conditions. • The ground surface must be scanned for sub-surface hydrogeological characteristics such as depth of soil zone, weathered zone, fractured/jointed zone, and unfractured zone. These surveys can be used to determine the depth of the saturated zone and the water quality (saline or non-saline). These surveys should be carried out in the summer to determine the true depth of the saturated zone. This zone is usually deep in the summer and shallow monsoon periods. If the surveys are conducted in seasons other than summer, there may be a drop or drying up of water conditions in summer, since the shallow depth of saturated zone observed in the other seasons may decrease. • When two wells are close to each other in a more or less flat area, the supply of water can be severely impacted by well-interference when both wells are pumped at the same time, especially during the summer. This is due to the fact that shallow well water depletes or dries up more quickly than deep well water. Between two wells, keep a gap of 150–300 m in alluvial areas and 75–150 m in rocky areas. • In the summer, due to a lack of groundwater replenishment, any area’s water level can drop or dry up. However, due to excessive pumping of wells in low-lying lands, which can sometimes lead to well drying, the depletion of water level in the uplands can be faster than in low-lying sections of the same place, regardless of the distance between wells. These situations can reach frightening proportions, with over-exploitation causing the apartments to be overcrowded. • Integration of satellite data with hydrogeological data can aid in quick surveying of a region for large-scale well-sinking projects. Major points consider while selecting site for well construction include it must be the point at which aquifer is potential enough to provide sufficient quantity of water to well, water well that’s an appropriate distance away from contamination sites, choose an area that is not prone to flooding, and water well that is an appropriate distance from another production wells.

2.2 Groundwater Flow Direction

27

The location of a well should be based on hydrogeology initially, but there are numerous additional aspects to consider. In our efforts to generate a dependable source of clean, safe water, a handful of other well location issues become very critical. First and foremost, the drill rig must be capable of penetrating the rocks in the area and reaching groundwater within the rig’s depth limit. Second, wells must be far enough away from latrines and other areas where human and animal waste is accumulated to avoid disease-causing bacteria being introduced into the well water. When one well is that far apart from a latrine, the soil can filter hazardous organisms out before they enter the well. We have to understand three factors to establish the minimum safe separation distance between latrine and well: • The direction in which the groundwater is flowing. • The distance between the bottom of latrine and the water table, and • Soil type between the latrine’s bottom and the water table.

2.2 Groundwater Flow Direction If the direction of groundwater flow is understood, it is advisable to locate a well up-gradient from a latrine so that contamination is directed away from the well. Knowing which way, the flow is going can be tricky. Groundwater in an unconfined aquifer, on the other hand, flows from a recharge location to a discharge point in the same direction as the earth slopes. Knowing this, finding a well uphill from a toilet is usually preferable to finding one downwards. The minimum safe separation distance between the latrine and the well is determined by the distance between the latrine and the water table, as well as the type of soil that lies between the latrine and the groundwater level.

2.2.1 Environmental Factors The considerations that go into locating water well include • As previously stated, the direction in which groundwater flows is a critical environmental component to understand. Pollution from any point should be detached from the well rather than toward it, • It’s also vital to consider the type of soil near the surface. Clay, silt, and fine sand, as previously indicated, can prevent toxins from reaching groundwater, • Wells should be at least 15 m away from surface waters such as streams, rivers, and ponds since they may contain biological, agricultural, or industrial contaminants, • Avoid flooded locations because people will be unable to access the well during times of high water, and the well may be contaminated as a result of floodwaters overflowing and seeping into the well,

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• Surface runoff should be directed away from the well site, which should be elevated, • Because saltwater intrusion can impact shallow groundwater near the coast, wells should be sunk into a deep aquifer or situated away from the coastline, and • Quality of groundwater can be impacted by naturally occurring pollutants such as arsenic, boron, and selenium, thus water should be analyzed in locations where this is a concern.

2.3 Methodologies for Well Site Selection The following considerations must be made while choosing a location for the construction of water wells • The point at which an aquifer has adequate potential to supply enough water to a well, • A water well that is located at a safe distance from contamination sources, • Select a location that is not prone to flooding, and • A water well that is a safe distance away from other production wells. Hydro-geological tools, Geophysical tools, and Remote Sensing and GIS tools are all important methodologies for locating well sites (Fig. 2.1). The initial step in the site selection is to use RS and GIS to reduce the targeted region, then use hydrogeological and geophysical surveys to pin point the site. Target

Fig. 2.1 Various tools used for locating well sites

2.3 Methodologies for Well Site Selection

29

is the area having millions of point and object is finalizing one point out of million points which is suitable for construction of well.

2.3.1 Hydrogeological Field Reconnaissance Hydrogeological Field Reconnaissance allows for the quick and cost-effective assessment of huge areas on a preliminary basis in order to determine their potential for ground water development. This covers the gathering, analysis, and hydrogeologic interpretation of all topographic maps, aerial images, geology maps, logs, and other relevant records. It includes the study of stratigraphy and geologic history of the area: i.e., • • • •

Stratigraphic sequence of the area, Depth and type of aquifer, Horizontal and vertical continuity, and Connection with the over lying strata (Fig. 2.2).

Different methods can be used to investigate groundwater. The aerial method, surface method, subsurface method, and esoteric approach are the four basic groundwater prospecting methods (Table 2.1). The esoteric method is the least scientific of the group, relying largely on conventional signs. Each of the above-mentioned groundwater exploration methods has its

Fig. 2.2 Preliminary study, correlate maps, pictures and photos of the area

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Table 2.1 Methods and technique of groundwater exploration Methods and techniques of ground water exploration Aerial

Surface

Sub-surface

Esoteric

Photo geologic methods

Geological methods

Geological

Water divining

Landsat/IRS

Geomorphological methods

Hydrogeological

Astrological

Infrared imagery

Hydrogeological methods

Tracer techniques

Biophysical

Electromagnetic techniques

Geophysical methods (a) Electrical (b) Seismic (c) Magnetic (d) Gravity

Geophysical logging techniques

own set of sub-methods. As a result, under the surface way of groundwater exploration, geophysical survey is one of the sub-methods. This method is critical for both mapping groundwater resources and assessing water quality. Because of the significant advancements in computer packages and accompanying numerical modeling solutions, its use for groundwater research has increased in recent years.

2.3.2 Aerial Method Aerial survey is the convenient reconnaissance tools for learning about basin watershed characteristics and discovering potential regions.

2.3.3 Airborne Electromagnetic [AEM] Survey Airborne Electromagnetic (AEM) data is used in the investigation of minerals, energy, and groundwater resources. The AEM method covers the determination of inherent changes in electrical conductivity under the surfaces that are caused by differences in rock and pore fluid characteristics. Electrically conductive minerals, clays, and sulphide minerals, as well as electrically conductive fluids, such as saline groundwater, result in higher conductivity than non-conductive mineral complexes or nonconductive fluids (typically fresh ground water). The AEM datasets are typically analyzed in combination with down-well information relevant to conductivity, as well as other spatial and aerial data sets such as surface geology, magnetics, and gravity, due to the influence of both rock and pore water characteristics on the AEM response. AEM data is acquired by sending an electromagnetic signal from a plane or helicopter to a receiver. In AEM, the transmitter coil generates the primary magnetic

2.3 Methodologies for Well Site Selection

31

field, while the receiver coil picks up the secondary magnetic field. Eddy currents in the ground are induced by the signal, which are collected by receiver coils trailed below and behind the aircraft. Depending on the acquisition method, geology and hydrogeological strata, the AEM techniques can detect differences in the conductivity of the ground to a depth of several hundred meters. Because AEM surveys necessitate significant processing in order to be interpreted, they are typically designed to detect specific subsurface targets based on a perceived conductivity contrast. The technique is well suited to regional investigations since it allows for rapid data collection over wide areas. It allows for a quick measurement of the bulk resistivity of a vast area’s subsurface and the survey is carried out at a height of 60–120 m agl in the air.

2.3.4 Surface Methods Surface variations of several techniques from geology, geomorphology, hydrogeology, geophysics, and other disciplines are the most frequent and time-tested procedures. These methods are used when a detailed examination of the distribution of prospective water bearing zones in lateral and vertical directions is required.

2.3.4.1

Geological Methods

The collection, analysis, and hydrogeologic interpretation of existing topographic maps, aerial images, geologic maps and logs, and other applicable materials is the first step in a geologic inquiry. When possible, geology field reconnaissance and appraisal of available hydrologic data on stream flow and springs, well yield, groundwater recharge, discharge, level, and quality should be augmented. The existence of minor and significant features such as joints, faults, and lineaments can completely govern drainages in some regions. Such zones are favourable and potentially productive for groundwater exploration. These are the channels via which groundwater flows.

2.3.4.2

Geomorphologic Methods

After the analysis of satellite data and geomorphology maps, a field check is necessary to determine the geomorphological elements needed to assess ground water potential. Geomorphic units such as pediments, flood plains, drainage patterns, soil types, and lineaments must be explored since they essentially affect the occurrence, movement, and potential of ground water.

32

2.3.4.3

2 Site Selection

Hydrogeological Methods

The hydrogeologic unit, saturated regolith thickness, and bedrock cracks are the three hydrogeologic parameters employed in the selection of well sites (Daniel and Sharpless 1983).

2.3.4.4

Geophysical Method

Ground water geophysics is the study of ground water using geophysical methods. On the surface of the earth, geophysical studies are carried out to investigate ground water resources by observing physical characteristics such as density, velocity, conductivity, resistivity, magnetic, electromagnetic, and radioactive phenomena. Signals from natural or induced phenomena of physical qualities of subsurface formation are measured by using geophysical methods. Geophysical technologies discover changes in physical qualities, or anomalies, within the earth’s crust. The most typically measured qualities are density, magnetism, elasticity, and electrical resistivity. The goal of exploration is to find possible exploitation zones by detecting indirect clues. The Electrical, seismic, magnetic and gravity methods are the main geophysical methods that are beneficial in solving some of the difficulties of hydrogeology. Groundwater geophysical methods are technological methods for determining conditions beneath the subsurface without drilling a hole. These methods are most typically employed to search for and locate underground water in areas of hard crystalline rock, although they can also be helpful in areas of alluvial deposits. All of these geophysical surveys measure a different physical attribute of the rock or sediment, such as electrical resistance, electrical conductance, density, and magnetic properties. Changes in these attributes can be linked to variations in sediment or rock type, aquifer potential, and, in some cases, groundwater quality. Each of these geophysical methods, however, has its own set of drawbacks. These methods can’t tell you if an aquifer exists or where it is. Groundwater exploration is the study of subsurface formations in order to better understand the hydrologic cycle, determine the quality of groundwater, and determine the nature, number, and type of aquifers. Groundwater exploration can be done in a variety of ways. One of the groundwater exploration approaches is the surface geophysical method. The vertical electrical sounding method is thus one of the surface geophysical approaches. Vertical electrical sounding (VES) is a technique for obtaining detailed information on the vertical thicknesses and resistivity values of subsurface geo-materials. It is a quick and effective method for determining aquifer thickness in a given area, as well as a cost-effective strategy for groundwater research. The purpose of this study was to determine two well site locations for water supply demands using surface geophysical methods. However, in addition to the geophysical surveying efforts, hydrogeological and geological researches were also included for the project’s benefit. Finally, the integrated techniques were used

2.3 Methodologies for Well Site Selection

33

to identify the proposed well site locations, as well as their thickness and resistivity values. (a) Gravity Method In sedimentary terrain, the gravity method is a widely used geophysical approach for locating mineral resources and groundwater. This method use gravimeters to measure density changes on the earth’s surface that may reveal underlying geologic features. The gravity method has little utility in groundwater prospecting because it is expensive and because changes in water content in subterranean strata rarely result in noticeable differences in specific gravity at the surface. The overall configuration of an aquifer can be detected via gravity fluctuations under particular geologic conditions, such as a vast buried valley. (b) Magnetic Method The magnetic approach allows for the detection of the earth’s magnetic fields, which may then be measured and plotted. Magnetometers are devices that measure magnetic fields and their variations. Because magnetic contrasts are rarely connected with groundwater occurrence, the approach has limited utility in groundwater exploration. This method could be used to collect indirect information relevant to groundwater studies, such as the presence of dikes that define aquifer boundaries or the limits of a basaltic flow. (c) Seismic Method Seismic methods are classified into two types: seismic refraction methods and seismic reflection methods. The seismic refraction method is creating a minor shock near the earth’s surface, either through the impact of a heavy instrument or through the use of a small explosive charge, and then measuring the time taken for the ensuing sound, or shock, wave to travel defined distances. Seismic waves follow the same propagation rules as light rays and can be reflected or refracted at any interface where there is a velocity change. Seismic reflection methods provide information on geologic structure thousands of metres below the surface, whereas seismic refraction methods, which are useful in groundwater research, only penetrate around 100 m down. The travel period of a seismic wave is determined by the medium through which it passes. The travel period of a seismic wave is determined by the medium through which it passes. Velocity is greatest in solid igneous rocks and lowest in unconsolidated materials. It is feasible to outline the subsurface zones of fractures, fissures, faults, and lineaments based on these signals. (d) Electrical Resistivity Method For groundwater investigation, the geoelectric resistivity approach is thought to be the most suited and efficient. It is based on the idea of subsurface determination, which can provide useful information on soil structure, composition, and water content. The aquifer depth, stratigraphy, and water quality may all be determined by using geoelectric (Mohamaden et al. 2016). It determines the type of electrical current in

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the earth and the change in resistance of sub surface rock strata by injecting a highvoltage DC current (direct current) into the ground. This approach is more efficient for shallow investigation, such as determining bedrock depth, searching for water reservoirs, and geothermal exploration. One of the physical qualities of rock is its ability to convey an electric current, which is also known as resistance (Robinson 1998). Humans utilize this capacity to identify the geological features such as rocks etc. without having to make physical contact or dig, which takes time and money, but the accuracy level of data is dependable since the pumping test can provide vital information on groundwater aquifer transmissivity and storativity (Mahmoud and Ghoubachi 2017). For groundwater exploration, there are numerous geoelectric measurement methods. There are numerous types of resistivity method based on the design of potential electrodes and current electrodes, such as the Schlumberger method, Wenner method, and dipole sounding method. The Schlumberger method is the most commonly utilized approach for ground water investigation in alluvial and hard rock areas. Geo-electric exploration can be used to determine not just the kind of rock layers, but also prospective groundwater information such as the depth of the aquifer and its dispersion under the surface. Furthermore, the type of rock layers revealed by geoelectric studies can be used to analyze groundwater circulation. Geoelectric is a technique for detecting and measuring the electrical resistance of rocks beneath the surface from above ground level. This technique can also be used to investigate the freshwater lens in the aquifer along the coast. Lengthy distances and long periods can be used to investigate the type of resistance, from unsaturated layers to saturated seawater and freshwater zones. Extreme resistivity levels in freshwater saturation zones, which are barely identified by pressure, are examples of large resistivity values that often lead to highly difficult interpretations. The true resistivity of the subsoil can be determined using these data. Ground resistivity is affected by geological characteristics such as mineral and fluid content, porosity, and the degree of water saturation in the rock. Electrical resistivity studies have been utilized in hydrogeological, mining, and geotechnical investigations for many decades. It has recently been utilized for environmental surveys. Geoelectric technique works by placing electrical current into the earth. The electrode is comprised of two current electrodes (C1 and C2) to deliver the electric current and two potential electrodes (P1 and P2) that measure the potential difference after the current has passed through the rocks. At a particular distance, the four electrodes are inserted into the ground surface. The longer the distance between the current electrodes and the rock layer, the deeper the flow of electric current can enter. Electrical voltage in the ground is caused by the flow of electric current. A multi-meter is used to measure the electrical voltage at the ground surface via two voltage electrodes, P1 and P2, which are connected by a shorter distance than the C1-C2 electrodes. When the current electrode distance is altered to be greater than the electric voltage, the potential electrode changes as well, depending on the type of rock that present at deeper level. The apparent resistivity (ρa ) value is computed from the current (I) and voltage (V) values using ρa = kΔV/I, where k is the geometric factor that depends on the configuration of the four electrodes. Arrays are the electrode arrangements used

2.3 Methodologies for Well Site Selection

35

in these studies. Wenner, Schlumberger, Half-Schlumberger, pole-pole, pole-dipole, and dipole-dipole arrays are some of the most common electrode arrays. Hoel (1954) proposed a pole-dipole electrode arrangement that is similar to the Schlumberger array but only has one current electrode. Eve and Keys (1956) and Coggon (1973) both used a three-electrode setup, but exclusively for profiling. Smith (1986) presented on the use of pole-dipole resistivity identifying cavity solutions beneath the highway. For resistivity, a similar setup has been suggested, in which the potential electrode’s location is constant and just one current electrode is employed as the electrode moves along the line (Yadav 1997). (i) Wenner Array Wenner Array has four collinear equi-potential point electrodes, A, M, N and B are placed at the surface of the ground along a straight line symmetrically. AM = MN = NB = a, where ‘a’ is called the inter-electrode separation. Through current electrodes A and B, current (I) is transmitted into the ground, and potential (V) is detected through M and N. Configuration factor for this array is 2πa, apparent resistivity (Fig. 2.3), ρa = 2πa(ΔV/I) (ii) Schlumberger Array Four electrodes are placed along a straight line symmetrically over centre point ‘O’. Current (I) is sent through the outer current electrodes A, B and the potential is measured across inner potential electrodes M and N. The separation between the potential electrodes is kept small with compared to the current electrodes separation (MN < 1/5 AB) (Figs. 2.4 and 2.5). The configuration or geometric factor for the Schlumberger array is given by Apparent resistivity, ρa = K(ΔV/I), where

a

a

a

A

M

N

B

C1

P1

P2

C2

Fig. 2.3 Wenner configuration

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2 Site Selection I

V

2l A C1

M

N

B

P1

P2

C2

2L

Fig. 2.4 Schlumberger configuration

Fig. 2.5 Resistivity imaging showing the general setup and resulting image processing by 2D inversion

K =

(AB/2)2 (M N /2)2 π (M N /2) 2

Resistivity Formula for Dipole-Dipole Configuration is R = n(n + 1)(n + 2)aΔV /I Applications of Electrical Resistivity Method • To determine the thickness of overburden, soil, and weathered zones, • To find fractures (hard rocks), • To determine the thickness of layers (ex. sand or clay) (Soft Rocks),

2.3 Methodologies for Well Site Selection

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• Identify an appropriate drilling site, and • To define the freshwater-saltwater interface. Applications of Resistivity Method in Hard Rock Areas The Resistivity method is mostly used in hard rock areas to determine • The thickness of the overburden (Depth to massive formation), • The weathered zone’s thickness (Eastern part hilly area of Kozhikode), and • It is beneficial for determining possible groundwater drilling zones (For example, Fractures and Lineaments). Applications of Resistivity Method in Coastal Areas The resistivity approach is mostly used to define: The Saline/Fresh water boundary, the layer/beds thickness and resistance. Vertical Electrical Sounding Vertical electrical sounding, or VES, is used to determine the variation in resistivity with depth. Since sounding curves can only be understood using a horizontally layered earth (1D) model, single VES should be used only in places where the ground is considered to be horizontally layered with very little lateral variation. A resistivity meter is used to measure the apparent resistivity values. As resistivity meters generally provide a resistance value, R = V/I, the apparent resistivity value is determined by ρa = kR. The anticipated resistivity value is not the true subsoil resistivity, but the resistivity of a homogeneous ground that produces the same electrical resistance for the same electrode configuration. The relationship between “apparent” and “actual” resistivity is complex. To determine the true subsurface resistivity, an inversion of the measured apparent resistivity values must be performed using a computer programme. Normally, the measured apparent resistivity values are plotted on loglog graph paper. In order to analyse the data from such a survey, it is usually believed that the subsurface is made up of horizontal layers. Types of VES Curve See Table 2.2. Electrical Profiling The profiling method is another traditional survey methodology. The spacing between the electrodes remains constant in this example, but the complete array is moved in a straight line. This provides some information on lateral changes in subsurface resistivity, but it cannot detect vertical changes. Data from profiling surveys are mostly interpreted qualitatively. The most serious restriction of the resistivity

38 Table 2.2 Different types of VES curve

2 Site Selection

Type

Curve

H-type (ρ1 > ρ2 < ρ3 ) K-type (ρ1 < ρ2 > ρ3 )

A-type (ρ1 < ρ2 < ρ3 )

Q-type (ρ1 > ρ2 > ρ3 )

sounding approach is that horizontal (or lateral) fluctuations in subsurface resistivity are frequently discovered. Subsurface geology is particularly complex in many engineering and environmental research, where resistivity can change rapidly over short distances. In such cases, the resistivity sounding approach may be insufficiently accurate. Resistivity surveys provide information on the subsurface resistivity distribution. It is necessary to have some understanding about typical resistivity values for different types of subsurface material, as well as the geology of the area examined, in order to turn the resistivity picture into a geological picture.

2.3.5 Sub-surface Methods Both Test Drilling and Borehole Geophysical Logging techniques are used in subsurface groundwater exploration. Subsurface procedures are highly expensive when compared to surface approaches. These are carried out for government initiatives involving large-scale studies to determine the outcomes of surface surveys. Subsurface approaches are extremely precise since they allow for direct observation of features in the form of bore-hole lithologs as core samples, as well as geophysical measurements of formation parameters.

2.3.6 Esoteric Method The esoteric approaches are those that have been around for a long time. These are the oldest water divining methods, which have been used by ancient people for hundreds of years. The esoteric approaches are those that have been around for a long time. These are the oldest water divining methods, which have been used by ancient people for hundreds of years. Water-dowsing is another name for it. People believed that

2.3 Methodologies for Well Site Selection

39

groundwater flow may cause important currents to form above the surface. When a moist plant twig is moved above such zones, the twig tries to rotate. Dowsing materials have included wet tree twigs, coconuts with the husk removed, watches, and other things. Because the person manipulating the twig has a role in induction, it is not appropriate for everyone wanting to divine water. All of these techniques have been used since the seventeenth century. With regard to these approaches, there is no scientific explanation provided. It is just a coin tossing experiment when it comes to success probability. Water divining is the name given to these techniques.

2.3.7 Remote Sensing and GIS Studies Remote sensing is the process of gathering geographic information about items without actually touching them. In other words, it is the technique of detecting and monitoring an area’s physical features by measuring the reflected and emitted radiation from a distance. Images of locations on the Earth are collected using special cameras installed in planes and satellites. Geologists assess items in the area with the use of this data (images). This method is best suited for large-scale groundwater investigation. Remote sensing allows for a faster hydrological mapping of large and inaccessible areas. The collected data will be processed into precise mapping using the GIS approach. Identifying prospective water harvesting locations is a critical step in increasing water availability and land productivity in arid and semi-arid settings. The GIS is essential for data management and analysis of best placements. The GIS is a tool that saves the time and cost of site selection while also providing a digital data bank for future site monitoring. Drilling tests and hydrogeological studies have typically been employed extensively. These techniques are useful for detecting subsurface water properties, but they are exceedingly expensive and time-consuming when used to estimate the distribution of groundwater resources across a vast area. Furthermore, utilizing RS techniques, groundwater can be monitored indirectly. The RS approaches provide recurrent coverage of a region using a variety of electromagnetic spectrum ranges, and they are excellent for gathering spatio-temporal data over large areas in a short period of time. RS describes aspects on the Earth’s surface, such as geomorphology and drainage patterns, in addition to providing high-precision spatial-temporal observations. As a result, RS has lately gained popularity in the field of groundwater evaluation due to its versatility. The GIS are computer software that is used to collect, store, analyse, model, archive, and share geographic data (Goodchild 2012). The GIS is a useful tool for managing large amounts of geographical data and may be utilized in the decision-making stage to extract appropriate variables from which hydrologists can assess groundwater potential. Because it is a cost-effective and efficient way,

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exploration using the combination of RS and GIS has gotten a lot of attention recently (Elfadaly et al. 2017). However, researchers have used frequency ratios (Lee et al. 2019; Al-Abadi 2017), random forest, logistic regression, neural network, and fuzzy logic to determine the impact of various elements in GIS-based groundwater evaluations (Das and Mukhopadhyay 2018; Anbarasu et al. 2019). Frequency ratios and neural networks are high-accuracy methods, but they need a lot of groundwater data in the research area and are difficult to use when there isn’t enough. When remote sensing and GIS are used together, the full potential of both can be realised. In groundwater investigations, combining the two technologies has proven to be a useful tool (Krishnamurthy et al. 1996; Sander 1996). Remote sensing data provides accurate spatial information and can be used more cost-effectively than traditional hydrogeological survey methods. The extraction of maximal information and better interpretability are the effects of digital augmentation of satellite data. GIS technology makes it easier to integrate and analyse enormous amounts of data. Field investigations, on the other hand, aid in the further validation of data. A deeper knowledge of groundwater regulating characteristics in hard rock aquifers can be gained by combining all of these methods. The basic methodology included data preparation (primarily digitizing), data pre-processing (georeferencing and resampling), data processing [edge detection and principal components analysis (PCA)], data analysis and integration (lineament extraction and statistics, geostatistical analysis, and IDW) (Hung et al. 2005; Prasad et al. 2013). Thematic layers of the extracted features were created and categorized in terms of hydrogeological relevance, including lithology, geomorphology, drainage density, slope, lineaments, and land use/land cover. According to the groundwater potential, weighting factors were assigned to themes and their related groups. To create a composite groundwater potential map of the research area, the classed layers were combined in a GIS context. Field checks and existing groundwater yield data were used to validate the calculated groundwater potential zones (Fig. 2.6). Following criteria were considered in this diverse location based on traditional geological, RS, and hydrological data: rock, fault density, spring index, slope, drainage density, EVI, convergence index, rainfall, and distance from rivers. After a multi collinear check, the weights of each factor were computed using the AHP approach. Overlay analysis was used to create a groundwater potential map, which was then confirmed with drill data.

2.3.7.1

Weighting Method and Overlay Analysis

For a reasonable assessment, AHP, a good multicriteria decision-making procedure, was utilised to assign weights to each established element (Saaty 1987). Prior knowledge is required to categorise and investigate the occurrence and transport of groundwater using the AHP technique. Using the AHP approach, the following stages were modified to assign weights to the factors: (1) Establishing a pairwise comparison metric based on the relative scale weights of selected factors; (2) determining the

2.3 Methodologies for Well Site Selection

41

Fig. 2.6 Flow chart showing identification procedures of GW potential site using RS and GIS. Modified after Ajaya Kumar (2020)

factors about the occurrence and movement of groundwater and defining scaled weights for each factor according to Saaty’s scale from 1 to 9; (3) establishment of pairwise comparison metric based on the relative scale weights of selected factors; (4) calculating the geometric mean of pairwise comparison matrix; (5) calculating the inconsistency index; (6) Obtaining the factors’ total generated weights The weight ratings on the comparison scale are on a scale of 1–9. The consistency ratio was calculated using the normalized weights of all factors (CR) (Table 2.3).

2.3.7.2

GIS Used in GW Exploration

• Well data, including location, depth to water, aquifer, water quality, and aquifer features, can be managed and modified in a GIS to present geographical attributes for analysis and water resource planning, • The impact of a new well on existing groundwater and surface water can be investigated using GIS, • Decision makers can utilise the findings of such a research to determine whether or not to proceed with drilling, • Application of GIS concerns water quality in groundwater -construction/situating of industrial plants, landfills, agricultural activities, groundwater contamination sources,

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Table 2.3 Saaty’s scale of preference between two factors in AHP Scale

Degree of preference

Description

1

Equally

When two parameters contribute equally to the objective

2

Intermediate

Preference between 1 and 3

3

Moderately

The judgment slightly to-moderately favor one parameter

4

Intermediate

Preference between 3 and 5

5

Strongly

The judgment strongly or essentially favors one parameter

6

Intermediate

Preference between 5 and 7

7

Very strongly

Very strong preference or importance

8

Intermediate

Preference between 7 and 9

9

Extremely

Quite preferred or quite important

• GIS could be used as the front end of a groundwater modelling simulation that captures the contamination completely, • In coastal areas, GIS handles groundwater over pumping and land subsidence or intrusion, and • Over pumping can raise the salt water interface, contaminating an aquifer and these issues can be avoided or alleviated by carefully studying and managing groundwater within GIS or with modeled GIS data. Geophysical groundwater research methods are used once a preliminary assessment of well sites has been completed and there are no financial or time limitations, with the electrical resistivity approach proving to be particularly effective in well site selection. Test drilling and logging procedures can also be used to explore different rock formations at different depths, as well as their water-bearing capacity. Subsurface research, on the other hand, is only required and economically justified for large-scale water delivery projects. The type of well suitable for the purpose can be chosen after establishing the purpose and the amount of water necessary. Aside from these two major factors, the following information is useful in determining a suitable type of well: availability, stratigraphy and hydrogeologic characteristics of subsurface formations, seasonal fluctuations in groundwater levels, well construction and water-lifting device costs, groundwater pumping economics, which can be overlooked if there is no other reliable source of potable water in an area.

References Al-Abadi AM (2017) Modeling of groundwater productivity in northeastern Wasit Governorate, Iraq using frequency ratio and Shannon’s entropy models. Appl Water Sci 7:699–716 Anbarasu S, Brindha K, Elango L (2019) Multi-influencing factor method for delineation of groundwater potential zones using remote sensing and GIS techniques in the western part of Perambalur district, southern India. Earth Sci Inform 13:317–332

References

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Brodie R, Sambridge M (2009) Holistic inversion of frequency-domain airborne electromagnetic data with minimal prior information. Explor Geophys 40:765–778 Daniel CC III. Evaluation of site-selection criteria, well design, monitoring techniques, and cost analysis for a ground-water supply in piedmont crystalline rocks, North Carolina Das N, Mukhopadhyay S (2018) Application of multi-criteria decision making technique for the assessment of groundwater potential zones: a study on Birbhum district, West Bengal, India. Environ Dev Sustain 22:931–955 Elfadaly A, Attia W, Lasaponara R (2017) Monitoring the environmental risks around MedinetHabu and Ramesseum Temple at West Luxor, Egypt, using remote sensing and GIS techniques. J Archaeol Method Theor 25:587–610 Elmahdy SI, Mohamed MM (2014) Automatic detection of near surface geological and hydrological features and investigating their influence on groundwater accumulation and salinity in southwest Egypt using remote sensing and GIS. Geocarto Int 30:1–13 Golkarian A, Naghibi SA, Kalantar B, Pradhan B (2018) Groundwater potential mapping using C5.0, random forest, and multivariate adaptive regression spline models in GIS. Environ Monit Assess 190:149 Goodchild MF (2012) Geographic information systems. In: Encyclopedia of theoretical ecology. University of California Press, Oakland, CA, USA, pp 341–345 Kim JC, Jung HS, Lee S (2019) Spatial mapping of the groundwater potential of the Geum river basin using ensemble models based on remote sensing images. Remote Sens 11(19):2285 Kord M, Moghaddam AA (2014) Spatial analysis of Ardabil plain aquifer potable groundwater using fuzzy logic. J King Saud Univ Sci 26:129–140 Lee S, Hyun Y, Lee MJ (2019) Groundwater potential mapping using data mining models of big data analysis in Goyang-si, South Korea. Sustainability 11:1678 Life water International. Annual report-Abaida (2019) Mahmoud H, Ghoubachi SY (2017) Geophysical and hydrogeological investigation to study groundwater occurrences in the Taref Formation, south Mut area–Dakhla Oasis-Egypt. J Afr Earth Sci 129:610–622 Mohamaden MII, Hamouda AZ, Mansour S (2016) Application of electrical resistivity method for groundwater exploration at the Moghra area, Western Desert, Egypt. Egypt J Aquat Res 261–268 Panahi M, Sadhasivam N, Pourghasemi HR, Rezaie F, Lee S (2020) Spatial prediction of groundwater potential mapping based on convolutional neural network (CNN) and support vector regression (SVR). J Hydrol 588:125033 Park S, Hamm S-Y, Jeon H-T, Kim J (2017) Evaluation of logistic regression and multivariate adaptive regression spline models for groundwater potential mapping using R and GIS. Sustainability 9:1157 Pradhan AMS, Kim Y-T, Shrestha S, Huynh T-C, Nguyen B-P (2021) Application of deep neural network to capture groundwater potential zone in mountainous terrain, Nepal Himalaya. Environ Sci Pollut Res 28:18501–18517 Rahmati O, Pourghasemi HR, Melesse AM (2016) Application of GIS-based data driven random forest and maximum entropy models for groundwater potential mapping: a case study at Mehran Region, Iran. CATENA 137:360–372 Robinson DG (1998) A survey of probabilistic methods used in reliability, risk and uncertainty analysis: analytical techniques. Sandia National Lab, Report SAND981189 Saaty R (1987) The analytic hierarchy process—what it is and how it is used. Math Model 9:161–176 Yadav G et al (1997) Fast method of resistivity sounding for shallow groundwater investigations. J Appl Geophys 45–52

Chapter 3

Drilling Methods

Abstract Water is obtained by hand pumps constructed above shallow (less than 60 m deep) boreholes in many developing countries. However, if typical machine drilling rigs are employed, drilling the borehole might be costly. This technical briefly explains how to employ simple, low-cost drilling methods in a variety of scenario. Each one is simple to use and maintain. Making holes in rock is referred to as drilling. Drilling is used to create deep, high-capacity wells. Brown drilling is for a production well, whereas green drilling is for an exploratory well. When going for drilling, there are a few things to keep in mind • The type of rock determines the amount of energy required to drill. Unconsolidated formations, such as sand, silt, or clay, are weak and much easier to drill than consolidated rocks, which are hard, strong, and dense, such as granite, basalt, or slate, • Cutting tools for hard rock will require cooling and lubrication, • Debris and rock cuts must be removed, and • To keep the crater from collapsing, unconsolidated formations will require support. For thousands of years, hand dug wells and other laborious techniques of digging a well have existed. Despite the fact that mechanical methods are more efficient and accurate, people and communities in need of water frequently have no other options.

3.1 Manual Methods Used to Dig Water Well 3.1.1 Hand-Digging The earliest and perhaps most commonly used technique of acquiring access to subsurface water is digging a well by hand with simple instruments like a pick and shovel and a bucket on a rope to remove cuttings.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 D. A. S. and J. V. S., Ground Water Abstraction Structures, SpringerBriefs in Water Science and Technology, https://doi.org/10.1007/978-3-031-34881-5_3

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3 Drilling Methods

Advantages • Hand dug wells simply require ordinary tools and skills, anyone can accomplish it. Men have specialized in this trade as a business in various regions, and • This is usually the least expensive form of well construction where labour expenses are low. A large diameter hand dug well in a low permeability aquifer may generate more water than a borehole in the same aquifer. Disadvantages • Hand digging a well is extremely difficult due to the significant risk of cave-ins and a lack of air. For one person, digging a well is quite difficult. Hand-dug wells deeper than 30 m are unusual due to the difficulty of digging too deep, • It is impossible to dig more than a meter below the water table unless the groundwater seeps in slowly. Digging through rock takes a long time, • It is very hard to prevent pollution in a hand-dug well. Surface water can leak into the groundwater in a variety of ways, including the traditional bucket on a rope used to retrieve water, which easily transports bacteria to the groundwater, and • Sealing the walls, pouring a concrete apron, placing a lid over the top, and adding a hand pump can all help to safeguard a hand dug well. However, these procedures raise the well’s construction cost (Fig. 3.1). Fig. 3.1 Hand-digging (Elson and Shaw 1995)

3.1 Manual Methods Used to Dig Water Well

47

3.1.2 Sludging Sludging in which an open pipe is raised and lowered in a water-filled hole. The worker puts his hand over the top of the pipe during the up stroke. The worker raises the pipe just before it reaches the peak of the stroke and begins to descend. Water and cuttings are forced out the top when the pipe is pressed down quickly. The pipe can be made of anything from hollowed-out bamboo to PVC pipe joints with a pointed bit at the end. A borehole can be deepened to at least 70 m with the right drilling pipe. Beyond roughly 10 m, the pipe must be raised with a rope and a tripod. Advantage • Making a hand dug well is far more difficult and dangerous than sludging. The materials needed are extremely basic and can be changed from what is available locally. Disadvantage • Sludging is exhausting and needs a team of individuals to work in shifts. Only soft substances like silt and sand can be drilled with it. Rock cannot be drilled, but hard clay can be progressively penetrated. The borehole cannot be emptied of large pebbles. Because the borehole diameter is often only slightly larger than the well casing diameter, installing a sufficient sanitary seal to avoid cross-contamination from surface water is difficult (Fig. 3.2).

3.1.3 Hand Auger A small-diameter open-bottom bucket with slanted teeth at the end is used to cut through the earth in this manual drilling method. A series of steel rods connect the bucket to a T-shaped handle at the top, which rotates the bucket. The bucket is hauled out and emptied as it fills. As the hole goes deeper, more rods are inserted. Auguring is often used to collect soil samples, although it has recently been promoted for use in the building of shallow wells (Fig. 3.3).

3.1.4 Drive Point Drive point sometimes known as a “sand point,” uses a pointed hard steel point at the end of a short (1 m) segment of perforated pipe. A massive sledge hammer is used to push the assembly into the ground after a robust steel pipe is screwed onto the driving point (Fig. 3.4).

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Fig. 3.2 Sludging (Elson and Shaw 1995)

Advantage • This is a one-man operation that can install a shallow well in a short span of time. Disadvantage • A drive point is only effective on loose sand near a river or lake, where the water table is high. Driving more than roughly 5 m is really tough. Because a suitable sanitary seal cannot be installed, a well-constructed using this approach is easily contaminated.

3.1.5 Manual Percussion Drilling The Chinese are claimed to have utilized this method of drilling over 4000 years ago. It is still widely performed nowadays all throughout the world. It entails repeatedly dropping a heavy drill bit attached to a rope or cable into a water-filled pit. The bit loosens the soil or removes rock fragments. Once the hole has accumulated enough cuttings, the bit is removed and to gather the cuttings, the bailer is lowered. A bailer is a pipe with a bottom-mounted one-way valve or flap that permits cuttings

3.1 Manual Methods Used to Dig Water Well Fig. 3.3 Hand auger (Elson and Shaw 1995)

Fig. 3.4 Drive point (Elson and Shaw 1995)

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3 Drilling Methods

to enter but not exit. When the bailer is hauled to the surface, it is tipped up to empty the cuttings. The drill bit and bailer can be raised and lowered in a variety of ways, including by tugging on a rope or by utilizing a flexible pole known as a “spring pole”. Manual percussion and sledging methods can be combined with a sharpened bit and a oneway valve at the bottom of the drill pipe to obtain better penetration than sludging and more effective cuttings removal than percussion drilling, while being safer than digging a hand dug well (Fig. 3.5). Advantages • While manual percussion drilling necessitates more specialized equipment and ability than digging a hand dug well, it is a method that everyone can master. • It is significantly faster and safer than digging a hand dug well, and it may reach depths of 70 m or more. Percussion drilling may also penetrate boulders or solid rock with the right bit design (very slowly). • Another advantage over a hand dug well is that the borehole may be capped to prevent surface water from entering the well, and with a hand pump installed, it can give a good supply of safe water. Disadvantages • Boreholes are frequently started by excavating a small-diameter beginning hole that is more than a meter deep. Although lifting the drill bit and bailer is difficult, a group of individuals can work together to divide and conquer the task. To drill water well, powered equipment is required. This increases the speed and depth that can be reached.

Fig. 3.5 Manual percussion drilling (Elson and Shaw 1995)

3.2 Powered Methods Used to Drill Water Well

51

3.2 Powered Methods Used to Drill Water Well The majority of manual well drilling techniques have been modified to employ machine power rather than human power. Furthermore, mechanized drilling systems have been created that can drill larger diameter boreholes much deeper and faster than manual drilling methods. A “drill rig” or simply a “rig” is a machine that is used to dig water well. • • • • • • •

Jetting Hand-Auger drilling Cable Tool drilling/Churn drilling/Percussion drilling Mud Rotary Rotary drilling (Direct rotary, Reverse rotary, Diamond drilling and calyx drilling) DTH (Down Tool Hammer drilling or Down the Hole Hammer drilling) Combination drilling.

3.2.1 Jetting A pump is used to drive water down a drill pipe and out a narrow nozzle, creating a “jet” of water that loosens the silt. Cuttings are carried to the surface and deposited in a settling pit by the back flow of water outside the drill pipe. The water is subsequently returned to the pipe by the pump. To keep the borehole vertical, the drill pipe is positioned from a tripod and turned by hand. Advantages • This approach just requires a few lengths of pipe and a water pump capable of producing enough pressure. The pipe is frequently left in the ground as a well casing, and • A 5 cm wide PVC pipe can be advanced to more than 60 m in fine sand. To jet a well, only two people are required. Disadvantages • Particularly soft, fine-grained sediments are suited for jetting. Gravel is too heavy to be carried to the surface by the return water, and • The borehole diameter is only slightly greater than the drill pipe/casing diameter. As a result, installing a sufficient sanitary liner to isolate the well from surface water contamination is challenging (Fig. 3.6).

3.2.2 Hand-Auger Drilling The auger head (cutting tool) rotates to cut into the earth, then retracts to extract the materials. The process continues until you reach the required depth. This method

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Fig. 3.6 Jetting (Unhcr 1992)

applies solely to unconsolidated material. It can be used for the detection of thickness of alluvium or unconsolidated materials and not for hydro geological purposes. Advantages of Hand-Auger Drilling • Inexpensive, and • Simple to operate and maintain. Disadvantages of Hand-Auger Drilling • • • •

Slow, in comparison with other drilling methods, Equipment can be hefty, Problems with weak geological formations, and Water is needed for dry holes (Fig. 3.7).

3.2.3 Cable Tool Drilling/Churn Drilling/Percussion Drilling/Standard Drilling Cable tool drilling machines, also known as percussion or spudder rigs, work by raising and lowering a heavy string of drilling tools into the borehole repeatedly. When drilling unconsolidated formations, the drill bit breaks or smashes consolidated rock into minute fragments, whereas when drilling cemented formations, the bit mostly loosens the material. The reciprocating movement of the tools in both cases

3.2 Powered Methods Used to Drill Water Well

53

Fig. 3.7 Auger drilling (Life water International 2015)

combines the crushed or loosened particles with water to generate a slurry or sludge at the borehole’s bottom. If the formation contains little or no water, water is added to create a slurry. As the drilling progresses, slurry accumulation builds, reducing the impact of the instruments. Slurry is evacuated from the borehole at intervals by a sand pump or bailer when the penetration rate becomes undesirable. Drill bit, drill stem, drilling jaws, swivel socket, and cable comprise up a complete string of cable tool drilling equipment. Each component has an important function drilling process. To crush and combine all types of material, the cable tool bit is usually massive and heavy. When drilling through hard rock, the drill stem adds weight to the bit and its length aids in maintaining a straight hole. Drilling jars are made up of two heat-treated steel bars that are connected together. When the bit becomes stuck, most of the time it may be dislodged by blows upwards from the free-sliding jars. Drilling jars are primarily used for this reason; they are not used in the drilling process unless there are exceptional circumstances. The swivel socket connects the string of tools to the cable, and the weight of the socket provides some of the upward energy to the jars when they are used. The socket sends the

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3 Drilling Methods

cable’s rotation to the tool string and bit, guaranteeing that the rock is cut on each downstroke and a circular, straight hole is created. Right hand threaded tool joints of standard API design and dimension are used to connect the tool string’s components. The drill line is the wire cable that transports and turns the drilling tool. It’s a lefthand lay cable that twists the tool joint on every upstroke to keep it from unscrewing. The drill line is run from the top of the mast to the spudding sheave on the walking beam, the heel sheave, and finally to the working line side of the bull reel. Bull reels usually have a separator on the drum that separates the working line from the storage line. Bailers are made out of a pipe with a check valve at the bottom that is used to drain mud or rock slurry. The valve might be a flat pattern or a dart valve, which is a ball and tongue pattern. The top of this instrument has a bail handle that connects to a sand line cable. The sand line is threaded down to the sand line reel through a separate sheave at the top of the mast. The sand line’s diameter can vary depending on the predicted loads. Because it is reliable in a range of geological environments, the cable tool method has persisted for thousands of years. In coarse glacial till, boulder deposits, or rock layers that are severely disturbed, shattered, fissured, or cavernous, it may be the best, and in some cases the only, method to utilise. When thin aquifers with poor yield, the cable tool operation allows for the identification of zones that would otherwise be missed by other drilling methods. The following are some of the advantages of using a cable tool method • • • • • • • • • • • • • •

Rigs are relatively low-cost, Rigs are simple in design, but they do require some advanced maintenance, Machines use very little energy, Throughout the drilling process, the borehole is stabilized, Unless heaving circumstances occur, valid samples can be recovered from any depth, Wells can be drilled in regions where there is a little amount of makeup water, Wells can be dug with very minimal risk of contamination, By keeping a hand on the drilling cable, the driller keeps close contact with the drilling process and materials encountered, A drilling rig normally only requires one person to operate, though a helper is frequently available to assist, Machines can operate in more difficult, inhospitable terrain or in other regions where room is limited due to their size, Operation is possible above and below the water table, Rigs can work in a wide range of temperatures, Wells can be bored in rocks when there is a concern with lost circulation, and Wells can be drilled at any moment to estimate the yield at a given depth. The following are some of the downsides of using a cable tool

• The rate of penetration is relatively slow, • Casing prices are frequently higher because larger diameter or heavier wall casing is sometimes required,

3.2 Powered Methods Used to Drill Water Well

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Fig. 3.8 Cable tool drilling (Life water International 2015)

• In some geological circumstances, pulling back large strings of casing may be difficult unless specific equipment is provided, • Equipment can be hefty, • Problems can with weak formations, and • To extract cuttings from dry holes, water is required (Fig. 3.8).

3.2.4 Mud Rotary The basic notion of well jetting, as mentioned above, is used to start this process of drilling water well. A mud rotary drill rig consists of a bigger cutting bit, lengths of steel drill pipe with threaded joints, a motor to turn and raise the drill pipe, and a solid mast to hold the pipe. Adding bentonite clay or other ingredients in the water improves the fluid’s power to lift cuttings out of the hole; this fluid is known as “drilling mud” or simply “mud.”

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Drilling water well can be done with a variety of mud rotary drill rigs. Table drive, in which the drill pipe is moved by a rotating mechanism near the rig’s base and top-head drive, in which the drill pipe is turned by a motor attached to the pipe’s higher end, are the two fundamental types. The drill pipe’s upper end is coupled to a lifting mechanism that raises and lowers it along the mast in both versions. A swivel is linked to the upper end of the drill pipe on both types of mud rotary rig, allowing drilling mud to be pushed down the drill pipe as it is rotating. The faster and deeper a rig can drill, larger the rig is. The LS100 and LS200 drill rigs are mud rotary rigs that are on the smaller side of the drill rig range. Advantages • It is not essential to employ a drive casing since the borehole is held open by the pressure of the drilling mud, as it is with cable tool drilling, and • Mud rotary drilling is also far more efficient than cable drilling. A big mud rotary rig can drill boreholes up to 1000 m in diameter. A small rig like the LS200, for example, can drill a 20 cm porthole to a depth of 60 m. Disadvantages • Because drilling through rock necessitates a lot of weight on the drill bit, only the largest mud rotary rigs are capable of drilling in rock, • A motor rotates and lifts the drill pipe, while a motor operates the mud pump on most mud rotary rigs, and • As a result, mud rotary rigs consume more gasoline per hour than a cable tool rig of equivalent size. Most large mud rotary rig drilling operations also require support vehicles to transport water and drill pipe (Fig. 3.9).

Fig. 3.9 a Mud rotary, b LSS200 portable mud rotary drill rig (Life water International 2015)

3.2 Powered Methods Used to Drill Water Well

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3.2.5 Air Rotary The mechanical features of an air rotary drill rig are identical to those of a mud rotary drill rig; the two fundamental options for spinning the drill pipe are table drive and top-head drive. The main distinction is that an air rotary rig removes cuttings using compressed air instead of drilling mud. To improve cuttings removal and borehole stability, a form of “foam” can be injected to the air stream. The same drill bits as a mud rig can be used in an air rotary rig, but it can also drill with a down-the-hole hammer. This bit breaks up rock with compressed air and can drill quite quickly. A big air rotary rig can drill boreholes with diameter between 60 cm and 500 m. Advantage • An air rotary rig may be put up rapidly because there is no drilling mud to mix or settling pits to dig. In addition, an air rotary rig drills quicker than any other rig of same size. Disadvantages • A big air compressor is required for an air rotary drill rig, especially if a down-hole hammer is employed. This increases the rig’s cost, maintenance requirements, and fuel consumption dramatically, and • A large air rotary rig consumes 40–60 L of fuel per hour, making it one of the most costly drill rigs to run. Support trucks are also required for large air rotary rigs (Fig. 3.10).

Fig. 3.10 Air rotary (Life water International 2015)

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3.2.6 Rotary-Percussion Drilling Method The only method to drill a hole in exceptionally hard rocks like granite is to pulverize the rock with a rapid-action pneumatic hammer, commonly known as a ‘down-thehole hammer’ (DTH). This instrument requires compressed air to operate. The air helps clears the borehole of cuttings and dust. The borehole is vertical and round in cross-section when rotated at 10–30 rpm. • Drilling in unconsolidated strata in a short span of time, • Deeper wells of up to 45 cm in diameter, and even greater with the use of a reamer, can be dug, • It works continually by forcing a mixture of clay and water (drilling mud) through a hollow spinning bit. The rising mud carries the loosed material upward in the hole, • No casing is required during drilling because the mud develops a clay liner or mud cake on the well walls owing to filtering, and • This seals the walls, preventing caving, groundwater intrusion, and drilling mud loss. 3.2.6.1

Rotary Drilling Using Flush Method

To cut the rock, a drill-pipe and bit are rotated. To flush out the debris, air, water, or drilling mud is pumped down the drill-pipe. The flush velocity in the drill annulus must be high enough to raise the cuttings (Fig. 3.11). Advantages of Rotary Drilling (with Flush) • • • • • •

Most rock formations can be drilled, Water and mud support unstable formations, Fast, Operation can be done above and below the water-table, It can drill to depths of over 40 m, and Possible to use compressed air flush.

Disadvantages of Rotary Drilling (with Flush) • • • •

Requires capital expenditure in equipment, Water is required for pumping, There can be problems with boulders, and Rig requires careful operation and maintenance.

3.2 Powered Methods Used to Drill Water Well

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Fig. 3.11 a Rotary percussion drilling, b rotary percussion drilling (with flush) (Life water International 2015)

3.2.7 Diamond Drilling Diamond drilling is a type of core drilling that employs the use of a rotary drill and a diamond drill bit to generate precisely measured holes. Core splitter, litho logging (foot by foot description of the sample—texture, mineralogy, grain size, laminations, igneous, sedimentary or metamorphic mineral veins, etc.). Drill bit is attached to a powerful drill rod. Solid core is recovered from depth for inspection on the surface. • Advantage—Core extraction and litho logging. • Disadvantage—Time consuming and costly.

3.2.8 Calyx Drilling/Chilled Shot Drilling Drilling of the calyx Core drilling method that involves rotating a steel cylinder and cutting a formation core with chilled shot of about 2.4 m diameter. Cuttings are carried up to a basket-like chamber at the top of the core barrel by circulating water. One barrel length at a time, the core is pushed into the barrel and dragged up. Shafts with a diameter of up to 2 m and holes with a depth of more than 300 m can be bored. Slow technique that is used to create ventilation shafts or ventilations in mines.

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3.2.9 DTH A jackhammer screwed on the bottom of a drill string is known as DTH. The rapid hammering process shreds hard rock into small fragments and dust, which are then blown away by a fluid (air, water or drilling mud). It is the most efficient method of drilling in hard crystallines. The drill bit is right above the hammer. Drill pipes carry the required feed force and rotation to the hammer and bit, as well as the fluid (air, water, or drilling mud) to actuate the hammer and flush the cuttings. As the hole goes deeper, the drill pipes are added to the drill string one by one behind the hammer. Drill pipes transmit the required feed force and rotation to the hammer and bit, as well as the fluid (air, water, or drilling mud) to actuate the hammer and flush the cuttings. As the hole goes deeper, the drill pipes are added to the drill string one by one behind the hammer. A drilling hammer is used at the bottom of a drill string in down-the-hole drilling (DTH). For drilling holes, it relies on three elements: bit loading (weight), rotation, and air. These active ingredients work together to crumble rock effectively. The drilling hammer is repeatedly driven into the rock while the drill string slowly rotates. Compressed air drives a piston inside the hammer, which provides striking power. For larger, deeper holes in medium-hard rocks, DTH drilling has significant advantages over top-hammer drilling. As the hole widens, power loss is low because the hammer is at the bottom. That means no energy is lost in the drill string, and penetration rates do not drop dramatically as depth increases—as long as back pressure in the borehole does not rise excessively. With a few exceptions, DTH drilling is best for holes with a diameter of 4–10 in. (https://www.gilldrilling.com/dth-hammers.html) (Fig. 3.12).

Fig. 3.12 DTH (https://www.gilldrilling.com/dth-hammers.html)

References

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References Daniel CC III. Evaluation of site-selection criteria, well design, monitoring techniques, and cost analysis for a ground-water supply in piedmont crystalline rocks, North Carolina Elson B, Shaw R (1995) WEDC Loughborough University Leicestershire LE11 3TU UK (www. lboro.ac.uk/departments/cv/wedc/[email protected]) https://www.gilldrilling.com/dth-hammers.html Proby F (2015) Life water International World Bank (2012) Rural water supply design manual, vol I. The World Bank Office Manila, Manila

Chapter 4

Development of Well

Abstract Well development is a process of washing out the clay and silt encountered during the drilling procedure, and also the smaller area of the aquifer immediately encircling the well screen, before the well is re-commissioned. Various developmental methods include over pumping, surging, air surging and pumping, Jetting, Jetting and simultaneous pumping, Hydro-fracturing, Supplementary development method. The efficiency with which water from the aquifer enters the well is influenced by the well design and production decisions. Cleaning and disinfecting the well, as well as the execution of well (re-)development processes in some circumstances is important after the development of well.

4.1 Introduction After the installation of the well and before the last cleaning, well development (or borehole development) of production wells is a standard practice. Following well completion, it is vital to maximize the well’s yield and optimize the gravel pack’s screening efficiency (Wal 2010). Well rehabilitation (or well cleaning) of dug and drilled wells is required when functioning wells fail to deliver acceptable water quality and availability owing to environmental factors or events that cause the well to remain polluted or obstructed (e.g. flooding of the well, sea water intrusion, etc.). It entails cleaning and disinfecting the well, as well as the execution of well (re-) development processes in some circumstances (e.g., badly clogged wells). In the oil sector, the term “well remediation” is employed. It refers to the cleaning of oil wells in order to become more efficient, and it necessitates completely different approaches than water well rehabilitation. Increased efficiency and safe drinking water reliability are two advantages of well development and rehabilitation. Basic procedures are simple to implement and inexpensive. Even for completely destroyed wells, rehabilitation is frequently more cost-effective than drilling new ones. Reduced pumping expenses, extended pump performance, and less biological issues like iron-bacteria and slime build-up can all be attributed to appropriate well development and design. Pump malfunctions are more common in badly built and © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 D. A. S. and J. V. S., Ground Water Abstraction Structures, SpringerBriefs in Water Science and Technology, https://doi.org/10.1007/978-3-031-34881-5_4

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underdeveloped wells because sand and particles enter the well and create much more stress and strain on pump rotors.

4.2 Well Development Basics Well development is a process of washing out the clay and silt encountered during the drilling procedure, and also the smaller area of the aquifer immediately encircling the well screen, before the well is re-commissioned. A potent well development increases the rate at which water moves from the aquifer into the well, maintains the aquifer to reduce sand pumping, result in enhanced water quality and extends the pump cylinder and well service life, and removes organic and inorganic substances that may obstruct effective well disinfection (Schreurs 1988). Well development to be continued till the drainage water is clear and all fine particle from the well and neighboring aquifer has been eliminated. The amount of material removed from the well prior to installing the filter pack, as well as the sort of technology and level of development desired, all have an impact on the time required to develop. The removal of drilling fluid having clay particles necessitates a substantial fraction of development energy (Driscoll 1986); well development can take as little as one hour but as much as ten hours (Brush 1972).

4.2.1 Basic Principles—Well Development The development of a well after it has been drilled is a standard element of the drilling process. Fines and drilling fluid additive from the drilling operation persist in the borehole and obstruct the pores of the neighboring aquifer, altering the flow behavior of formation materials in the region of the borehole. By eliminating particles and additives and allowing the gravel layer to settle and compact, advancement methods are aimed to recover or enhance these properties in order to increase the well’s efficiency. After the borehole is completed, further types of development, known as aquifer stimulation, may be used to increase the formation’s transmission qualities in semi-consolidated and consolidated strata. The well completion configuration (screen slot size, open area, gravel pack thickness, and whether a graded or natural pack is present), the type of drilling fluid used (air or water-based fluids using clays or polymers), and the nature of the formation itself all depend on the type and best outcome of such development. There have been many various different methodologies established. However, the majority of them are exclusively used in huge, high-tech drilled wells. Over-pumping and surging can be highly important for small, low-cost drilled wells (Wurzel 2001).

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Various developmental methods include over pumping, surging, air surging and pumping, Jetting, Jetting and simultaneous pumping, Hydro-fracturing, Supplementary development method. • Over-pumping: This technique comprises pumping the well at a faster rate than typical. This is the simplest way in terms of materials and work, but it is also the least accurate. It usually only develops the aquifer’s more permeable portions, and because water only flows internally toward the borehole, it can draw too much material against the screen openings, causing bridging, in which the formation is only partially stabilized. If the formation is stirred and the connections fall, formation substance may reach the hole. Pumping a well at 2–3 times the intended flow rate for an extended period is the easiest but least successful development approach. This does not adequately churn the earth material to create a true filter around the screen, and only a tiny portion of the screen’s length develops (Anderson 1993). It is, however, helpful because if a well can be pumped sandfree to a large extent, it can also be pumped sand-free at a lower rate (Driscoll 1986). If the level of water in the well is within 3.05–4.57 m (10–15 ft) of the ground level, the mud pump can be used as a suction pump to pump water for 2–3 h. If this is not possible, install the bush pump and use a different cylinder for the development process, as particle matter removed during development can cause the pump to degrade at an unusually high rate, leading to premature failure. The well development will be more effective if a larger pump cylinder is used than was planned for the final installation. Attaching a rubber gasket to the head of the pump cylinder and lowering it into the well until it reaches near the top of the well screen should boost the effectiveness of over pumping even more. Begin developing the well at the head of the screen to admit fine material around the screen to loosen and be pumped out of the well without obstructs the pump. Pump until the water clears, then lower the pump more into the screening phase until the water is clear. • Backwashing: This is another relatively simple method of development that requires water lifting equipment and a container in which water may be stored and returned to the well quickly. Water is pumped to the surface until the container is full, then swiftly returned to the well. Repeating this motion multiple times can assist in the development of the surrounding water-carrying structure. It’s vital that the water pumped to the surface sit for a while to settle the suspended material. After being decanted into a second container, the pure water should be tossed back into the well. This will prevent fine particulates from being returned into the well by unintentionally. It may be feasible to combine over pumping and backwashing if a gasket has not been applied to the top of the pump cylinder by collecting water from the overpumping operation, allowing it to settle, and then swiftly dumping the decanted water back into the well. • Bailer: A bailer is a pipe with a bottom-mounted one-way valve. When the bailer has filled up with water and silt, it is lifted to the surface and emptied. Water from aquifer will then flow towards the well, bringing more drilling fluid in. A bailer’s to-and-fro motion creates a surging action that widens the space around

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the screen. Because it has higher pressure to force water through the screen, the stronger the bailer performs, the heavier and wider it is (Brush 1972). Surging: This usual approach involves flushing water back and forth through the screen to prevent particles from bridging behind the screen and entering the hole. The surge effect can be created mechanically using a close-fitting plunger/bailer (surge block) operated vertically and horizontally on the hole by the drilling rig, or by periodic pumping and periodically allowing the water column to fall back into the hole. In the screen, the bailer operates as a piston, pulling loose material into the well for disposal (Wurzel 2001). Surge Block: Surge blocks are flat gaskets that fit into the casing and function as a plunger underneath the water level. Because it seals securely to the casing, it has a direct positive influence on well movement (Brush 1972). Because some water moves upwards through tube when a surge block is placed just on termination of Water touching with a one-way valve. This is beneficial because it prevents particles from being forced deeper into the formation and aids in the removal of silt that has been loosened by the surging motion. This keeps the screen from becoming completely obscured by fines accumulated over time. Use an up-anddown motion to successfully surge a well, elevating and lowering the plunger 2– 3 ft each time. The plunger should quickly descend on the down-stroke, allowing turbid water to be pushed out of the connecting tubing. While the plunger can be forced down on each stroke, placing weight right above the surge block allows you to operate for longer periods of time. To avoid the surge block being “sandlocked,” surges should start above the screen (Anderson 1993). The hole should be cleared after surging above the screen, and then surging should resume from the bottom end of the screen, eventually progressing upward until the entire screen has been developed (Anderson 1993). Air surging and pumping: This approach combines an airlift pumping action with the above-mentioned surging effect. The hole is injected with air to elevate the water column, which is then stopped off, allowing the column to descend down into the hole. Jetting: To remove particles and drilling fluids, high-pressure air or water is injected through the screens in this method. It works by directing lateral jets onto the screens to break up any filter cake and agitate and cleanse the nearby gravel pack or formation. Rotary rigs are the ideal options for this technology. Jetting and simultaneous pumping: This technique incorporates high-pressure water jetting with pumping (typically via an airlift system) and is especially useful in poorly consolidated sands and gravel. The jetting process loosens the fine material, which is then drawn through the screen and to the surface by the pumping motion. Hydro-fracturing: Groundwater is trapped in fissures in bedrock aquifers, and borehole yields are frequently limited. In such circumstances, an aquifer stimulation approach like as hydro-fracturing may be used to increase yield. This is the second stage of aquifer development, when high-pressure jets are used to inject fluid into the borehole to withstand the overlying rock pressure and open

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up existing and new fractures, allowing water to flow into the borehole. It’s going to need a lot of pumping pressure. • Supplementary development methods: Acid insertion in carbonate aquifers to expand fissures by dissolving aquifer material, and “shooting” in hard-rock terrain using explosive charges inserted in the borehole to raise the number of fracturing around the hole are two further development or stimulation methods. These are highly specialised procedures that are rarely used in the bulk of water borehole drilling projects.

4.3 Typical Causes for Reduced Well Yield • Mechanical Blockage (e.g. fine-grained soil materials, corrosion by-products): Fine-grained soil particles or corrosion by-products coming from metallic well parts can enter the well through the screen, reducing the flow of water from the aquifer into the well. • Chemical Encrustation (e.g. iron/manganese oxides, calcium/magnesium carbonates, sulphates): It is the deposition of minerals on the well screen or gravel pack, which restricts the flow of water into the well. Changes in flow and/or pressure conditions at the well create chemical encrustation, which is caused by the precipitation of minerals dissolved in the groundwater. • Bacteriological Plugging (e.g., iron bacteria): Bacteria and other microorganisms can block wells, pipelines, and treatment facilities. This comprises bacteria that use dissolved iron as a source of energy (Anon 2012).

4.4 Well Rehabilitation Procedures It’s important to remember that the specific work procedures necessary for well rehabilitation are highly dependent on the real causes of low well flow or poor water quality. Step 1: Notify all well users not to drink the water during the rehabilitation procedures and to save enough water for the course of the rehabilitation. Step 2: Determine the well characteristics such as depth and diameter. Enquire of the consumers as well: What was the original depth of the well? What was the well’s previous yield compared to the present one? Determine the pH value of drilled wells. The pH level would ideally be 7 or below. If it is higher than 7, pour one litre of vinegar or citric acid into the well and retest before continuing.

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Fig. 4.1 Drilled well: well depth and diameter (AAFC n.y.)

Step 3: Using chlorine solution clean the removed pumping mechanism/lifting device as well as the headwalls, drainage curtain, sanitary seal, cover, and lifting device and repairs (Fig. 4.1). Step 4: Clean the well of all unclean water, silt, and debris. Buckets or pumps can be used to remove debris from dug wells. There are various ways to do this with drilled wells, the simplest of which is jetting. After the polluted water, sediments, and debris have been removed, run the pump for about an hour to clear any suspended fines left over from the disaster or the jetting procedure. When utilizing a pump to extract water from polluted wells, more caution is required (Vilholth 2011). Step 5: Fix the problems to the well’s interior. Increase depth of the well, make localized well lining repairs, or propose re-lining to minimize subsurface pollution in excavated wells in sedimentary formations.

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Fig. 4.2 Brushing of a drilled well (AGR n.y.)

Step 6: Physically clean the well. Cleanse the well lining physically with a brush and chlorinated water in excavated wells. Clean the well casing and screen with a brush or by adopting the same jetting or surging techniques used for well development on drilled wells (Fig. 4.2). Step 7: Chemically clean the well (only if necessary). The chemicals are chosen based on the current pollution of water. For 24–72 h, the specified chemicals are positioned in the well and stirred repeatedly. The chemicals are subsequently removed by dewatering the well. A liquid bacterium acid is effective against iron bacteria and slime. If the bacteria problem persists, stronger chemicals such as muriatic acid and hydroxyacetic acid are utilized. Sulphamic acids, along with inhibitors and modifiers, are utilised to clear clogs caused by carbonate scale. Step 8: Disinfect the well—Chlorination is the most prevalent method of decontamination. High strength calcium hypochlorite (HSCH) in powder or granular form, which contains 60–80% chlorine, is the most often used chlorine chemical. Sodium hypochlorite in the form of liquid bleach or bleaching powder can also be employed. Depending on how long the product has been preserved or exposed to the atmosphere, each chlorine compound contains a varying amount of useable chlorine (Godfrey and Reed 2011). The amount of chlorine solution (i.e. chlorine-infused water) that must be injected into the excavated or drilled well is the same as the amount of water that is now there.

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Then, depending on the degree of microbial contamination, dissolve 50–100 mg/l of HSCH in a bucket of water. The disinfection process will be rendered ineffective if you use too much or too little chlorine. Fill the well with the chlorine liquid and let it there for 12–24 h. Before letting it sit in drilled wells, run the pump till the chlorine can be detected in the outflow (Godfrey and Reed 2011). Open all outflows (e.g. tabs) until the chlorine scent is observed at each one if disinfecting the distribution network is also a goal. Step 9: Dewater the well—Use the manual or, preferable, motorized pump to remove all of the chlorinated water. Users can check the residual chlorine content in water if you have a chlorine test kit. It should be kept to a minimum of 0.5 mg/l. alternatively, pumps the water until it has lost its chlorine odour. Make sure that during dewatering in coastal areas, no water with a high chlorine concentration runs into small streams or wetlands; saltwater intrusion is avoided (Vilholth 2011). No water is allowed to enter your septic system because the chemicals and amount of water required to flush it could overburden or damage it. Step 10: Seal the top of the well—Using a sanitary cap, close the top of the well (e.g. made of layers of clay). To keep surface water, insects, and rodents out of the well, build a drainage apron and a head wall around it. Wrap the well with a cover. Additional steps (e.g. well deepening or broadening) can be used if well rehabilitation is insufficient to improve the yield in terms of quantity (Wurzel 2001). Some rehabilitation chemicals (e.g. acids, chlorine, etc.) can harm materials (e.g. casing, screen, etc.) as well as human health. Use careful when it comes to the goods you use, and handle them with care.

4.5 Limitations of Chlorination Chlorination mainly kills microorganisms that are present in the well, pumping apparatus, and distribution network. It won’t destroy germs in the aquifer outside the well’s immediate vicinity. If there is some exterior contaminant, the problem will only be solved momentarily. A well’s contamination must be avoided through adequate design, installation, and maintenance. The following issues will not be resolved by well disinfection. • When contamination comes from a recurring source like a septic system or an animal feedlot, • When a well or plumbing system is built, located, or broken and needs to be repaired (disinfection should follow repair work), and • If there is nitrate, arsenic, fuel, pesticides, or other chemicals in the pollutant.

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4.6 Applicability • Well development ought to be used to enhance the productivity of practically all drilled wells after drilling processes or during well rehabilitation. The operations that are eligible range from the most basic to the most complex. As a result, applicability is granted in the vast majority of cases, particularly those involving regions with limited financial or technical resources or skilled contractors, • If the well’s yield is diminishing and/or the quality fails to satisfy drinking water guidelines, and a prior investigation has shown that building a new well would not be more cost-effective, well rehabilitation (including disinfection) should be used. In terms of well-being, simple and basic rehabilitation techniques, which do not necessitate expensive technology or highly skilled labour, can be extremely beneficial, and • Because of the wide range of well types and constructions, each well requires its own set of well development and rehabilitation processes. Many of these steps are simple and straightforward, but they must be followed with caution because disobeying basic guidelines might jeopardise the well’s quality of the water and long-term functionality.

4.7 Testing Well Yield • The volume of water that can be pumped in a certain amount of time is referred to as well yield (It is expressed as litres or gallons/minute). Existing well yields are sometimes examined to see if drilling in the same location is worthwhile. If a submersible pump is installed, a comprehensive pump test can be done. If you are using a hand pump, try to keep an eye on the water level both before and after you pump. Pump at a consistent rate for as long as possible (1–4 h if new wells will be heavily used). This pumping rate appears feasible if the water level restores to pre-pumping levels within 6–12 h. The better the aquifer, the less time it takes. • If you’re unsure about the productivity of a newly drilled well, you should test it to see if it’s worth laying a concrete pad and installing a bush pump. A well capable of supporting a heavily used bush pump should produce at least 0.2 L/s (3 gpm) and have a specific capacity of approximately 0.01 L/s per meter of decline. • To make rough estimations of the yield of new Lifewater wells, use an air compressor, Waterra tubing with a foot valve, or a bailer. • If you have access to an air compressor, use it to pump enormous amounts of air into the well. As a result, water will spill over the top of the well casing. To avoid ponding, a trench should be built ahead of time to transport the water away from the well. After 30 min, the amount of water still pouring over the top of the well casing will give you an estimate of how much water the well can produce. Turn off the pump and time how long it takes for the well water to return to its pre-pump level. Check the water level every minute for the first ten minutes, then

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every five minutes for the next half hour, every fifteen minutes for an hour, and every half hour until the recovery is complete. These measurements can be used by hydrogeologists to investigate the aquifer. • Lastly, an inertia-lift device (Waterra) or a bailer can be used to evaluate the yield of a newly constructed well. • Remove as much casing as required and fill the well with clay or silty sand, then cover the top 2 m with concrete if the well yield is too low to justify a manual pump. If this is not maintained, future well supplies may be jeopardized, as the well may allow contaminants to infiltrate the groundwater.

4.8 Well Efficiency The ratio of aquifer loss (theoretical drawdown) to total (actual) drawdown in a pumping well is known as its efficiency (Kruseman and de Ridder 1990). The efficiency with which water from the aquifer enters the well is influenced by the well design and production decisions. Regardless of the pumping plant structure and efficiency level, the less efficiently water enters the well, the higher the pumping lift and yearly energy bill. Well, which are more efficient have a lower total pumping lift and a higher specific well capacity (gpm/ft drawdown). This means fewer horsepower is required to raise the water and fewer hours of pump operation are required to irrigate a given acreage of crops. Pump bowl life is extended as a result of improved well design, which prevents sand and other abrasives from entering the well. By preventing encrustation of the well screens, improved well design can extend the well’s life. By focusing on specific aquifers and avoiding others, improved well designs can reduce the impact on other groundwater consumers (Fig. 4.3). A well efficiency of 70% or above is normally regarded acceptable, with a minimum efficiency of 65% permitted (Kresic 1997). The well efficiency V is calculated as follows: ( ) V = BQ/ BQ + CQ2 , where B Formation loss coefficient, Q Discharge, C Well loss coefficient. Aquifer test is frequently used to assess well efficiency, which is a percentage reflecting the portion of total observed drawdown in a pumping well that is related to aquifer losses (as opposed to being due to flow through the well screen and inside the borehole). The efficiency of a perfectly efficient well with a perfect well screen and frictionless water movement inside the well would be 100%. Unfortunately, well efficiency is difficult to evaluate between wells because it is also dependent on the

References

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Fig. 4.3 Schematic diagram showing concept of well efficiency

aquifer’s properties (the same amount of well losses compared to a more transmissive aquifer would give a lower efficiency). Factors affecting well efficiency include well location. Drilling rigs should be able to quickly access the well site, and if rotary drilling methods are to be utilised, the well site may need to be large enough to construct a huge pit to manage drilling fluid and well drilling methods.

References AAFC (n.y) Water well disinfection—using the simple chlorination method. Water stewardship information series. Agriculture and Agri-Food Canada (AAFC), Ottawa Anderson K (1993) Ground water handbook. National Groundwater Assoc, Dublin, Ohio Brush R (1972) Wells construction: hand dug and hand drilled. US Peace Corps, Washington DC Driscoll F (1986) Groundwater and wells. Johnson Division, St. Paul Godfrey S, Reed B (2011) Cleaning and disinfecting boreholes. Technical notes on drinking-water, sanitation and hygiene in emergencies, 2. World Health Organization (WHO), Geneva Harter T. Water well design and construction MDH (2012) Well and water system disinfection for private wells. Minnesota Department of Health (MDH), St. Paul, MN Moffat B (1988) Efficient water wells, developing world water. Grosvenor Press Int’l, Hong Kong, pp 36–37 Proby F (2015) Life water International Schreurs R (1988) Well development is critical, developing world water. Grosvenor Press Int’l, Hong Kong Smet, Wijk (2002), Wal (2010) Factsheet block body Vilholth (2011) Cleaning wells after seawater flooding. Technical notes on WASH in emergencies #15. Water, Engineering and Development Centre (WEDC), Leicestershire

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World Bank (2012) Rural water supply design manual, vol I. The World Bank Office Manila, Manila Wurzel P (2001) Drilling boreholes for hand pumps. Working papers on water supply and environmental sanitation, 2. Swiss Centre for Development Cooperation in Technology and Management (SKAT), St. Gallen

Chapter 5

Pumping Test Data Analysis (PTDA)

Abstract Pumping Test Data Analysis on measuring the aquifer’s hydraulic parameters includes co-efficient of transmissivity (T), specific yield (Sy ), co-efficient of Permeability (K), leakage factor (B) and storage coefficient (S) using various curves. The Pumping Test examines the aquifer’s response to water extraction under controlled settings. The processes involving water underground are difficult to observe and intricate, and it is essential to create models for effective planning, designing, and managing of groundwater systems.

5.1 Introduction Ground water has significant role in the world’s water supply. Its slow steady destruction and contamination, there is an immediate need to evaluate how aquifers react to different human activities in accordance with the quality and quantity of groundwater, in order to minimize serious and often irreversible harm to humanity and the environment. To attain this wide goal, practically all groundwater-related investigations require prior understanding of the hydraulic parameters of various aquifer basins. Furthermore, subsurface water processes are hidden and extremely complicated, modeling is critical in the preparation, designing, and governance of groundwater resources. A thorough understanding of water bearing formation parameters is required for fruitful and time-tested modeling as well as better handling. Because of the variation in hydraulic heads at the water bearing formation and in the well induced by draft, water flows into the well from the adjacent aquifers. Before pumping, the water level inside the well should be theoretically corresponding to the static water pressure in the saturated thickness enclosing the well, and the depth to the water table (DTW) is commonly called as the static water level (SWL). When the draft in progress, water is extracted from the water bearing formation encompassing the well, which eventually causes a decrease in the DTW inside the well, called the piezometric level in confined aquifers or DTW in phreatic water bearing formations. The term ‘pumping water level’ denotes the DTW at the time of lifting of water (Fig. 5.1). © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 D. A. S. and J. V. S., Ground Water Abstraction Structures, SpringerBriefs in Water Science and Technology, https://doi.org/10.1007/978-3-031-34881-5_5

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Fig. 5.1 Drawdown pattern in a Confined aquifer; b unconfined aquifer (Roscoe Moss Company 1990)

The drawdown (dd) is the variance between the static water level (SWL) and pumped water level (PWL) and is influenced by several factors, including the rate and duration of pumping as well as the spacing between the pumping well (PW) and the point of measurement. The greatest dd is always near the PW, and it reduces as the distance from the PW increases. Pumping test data analysis (Aquifer Performance Test/APT) involves the interpretation of data collected during a pumping test, which is a common technique used to measure the hydraulic attributes of an aquifer. The APT involves lifting of water from a well at a constant rate and determining the PWL and in nearby observation wells (OBWs) over time. The data collected during the test is used to determine co-efficient of permeability, T, S, and other properties of the aquifer. Here are the general steps involved in pumping test data analysis (PTDA): 1. Pre-test analysis: Before running the pumping test, it is important to gather information about the aquifer, such as its geologic characteristics and the location of near by wells. This information can be used to select the appropriate test parameters, such as pumping rate and duration. 2. Data collection: During the pumping test, DTWs are recorded in the PW and in nearby OBWs at regular intervals. The data is typically recorded using a data logger or manually recorded. 3. Data analysis: The collected data is analyzed using various methods, such as graphical analysis, type curve analysis, and analytical solutions. The goal of the analysis is to estimate the hydraulic attributes of the water bearing formations. 4. Model development: Once the hydraulic properties are estimated, a mathematical model of the aquifer can be developed. This model can be used to simulate different scenarios and predict the behavior of the aquifer under different conditions.

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5. Interpretation and reporting: The results of the PTDA should be interpreted and reported. The report should include a summary of the test parameters, estimated hydraulic properties, and any limitations or uncertainties in the analysis. It is to be noted that PTDA can be complex and requires a thorough understanding of hydrogeology and groundwater modeling. It is recommended that the analysis be conducted by a trained hydro geologist or groundwater modeler. The hydraulic characteristics of piezometric aquifer, water table aquifer, and semi permeable aquifers are determined using the time-drawdown data received at a specific location. The hydraulic properties of leaky confining layers (aquitards) can also be determined using a well-planned pumping test. Pumping experiments can thus be used to acquire an integrated K value across a large aquifer segment. Pumping tests produce aquifer parameters that are averaged over a large portion of the aquifer, making them more dependable than techniques that produce fundamentally point estimates (such as slug/bail testing and laboratory methods). A number of methods of evaluating pumping-test data in order to derive parameters of water bearing formations are present, rely on type of data and the nature of aquifer. Several methods of evaluating pumping-test data to derive aquifer characteristics are present, relaying on what sort of data and the nature of the water bearing formation in which the analysis is performed. The Pumping Test examines the aquifer’s response to water extraction under controlled settings. A well test (to measure well yield and efficiency) or an aquifer test is examples of pumping tests. Hydro geologists aim to find the most accurate figures for water bearing characteristics of lithological formations. Major aim of APT includes determination of well yield, estimation of well efficiency, aquifer parameters and examines water chemistry (Harvey 2005).

5.2 Pumping Test Principles A pumping test involves extracting water from an underground well, which creates pressure on the aquifer. The response of the aquifer to this pressure is then measured by tracking the dd over time.

5.3 Pumping Test Types The main categories of pumping tests and aquifer tests are four. Here are some of them: • • • •

Time-Drawdown Test, Recovery Test, Step-Drawdown Test, and Injection Tests.

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APT is used to find out different hydraulic attributes of distinct Water bearing formations (viz., pressure aquifer, semi permeable, and water table aquifers). The step-drawdown test, on the other hand, is used to examine the condition of existing wells and determine the hydraulic characteristics of producing wells. An injection test is when a pumping analysis is performing using an injection well rather than a production well. A “time-depth to water table rise” in the injection well or OBWs can be detected using the injection test.

5.4 Determination of Hydraulic Parameters of Water Bearing Formations 5.4.1 Steady and Unsteady Time-Drawdown Tests Aquifer parameters can be determined by time-drawdown pumping studies. Timedrawdown pumping tests are classified into two groups based on the type of data they produce: (i) steady-state or equilibrium tests, and (ii) unsteady-state or transient tests. Throughout the test, two groups rate of pumping are maintained constant. Unsteady-state testing measures groundwater level fluctuations over time in relation to a constant pumping rate. Transient test data is able to be used to establish practically all of the attributes of water bearing formations. Pumping continues until near-equilibrium conditions are reached in steady-state measurements. In most aquifer systems, steady-state test barely address quasi-steadystate condition. True equilibrium may never be established under field settings due to the ongoing aquifer recharge and discharge in a groundwater system. Only aquifer transmissivity or hydraulic conductivity may be computed using data from steadystate testing, and in rare situations, leakage factor; the storativity of an aquifer cannot be estimated using these information.

5.4.1.1

Interference Test

An interference test is the measuring of groundwater level fluctuations (drawdown) following pumping in one or more observation wells. Because interference measurements do not include turbulent flow components like PW data, the dd found in monitoring wells is similar to that found in aquifers. As a result, interference-test results are favored when evaluating aquifer properties. In order to perform interference tests, the monitoring wells must construct in the similar water bearing formation as the PW. For determining co-efficient of transmissivity (T) or co-efficient of permeability (K) from steady-state, dd data from 2 monitoring wells or dd information from at least one OBW in addition to the PW are usually required; the dd calculated in a PW must be rectified for well losses. Same dd data from one monitoring well/PW

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can also be used to derive hydraulic conductivity or transmissivity if the extent of impact is known. However, evaluating aquifer characteristics like storage coefficient just needs information on temporary dd from a single monitoring well.

5.4.1.2

Distance-Drawdown Test

In distance-dd investigations, dd is observed in 3 or more OBWs positioned at varied radial extent from a PW, resulting in a collection of distance-dd data. A data set can be produced utilizing time-dd measurements gathered at numerous areas throughout a time-dd test, rather than performing the test individually in the field. Distance-dd data be either distance-steady dd data/distance-unsteady dd records rely on the nature of the time-dd tests; first database can only yield aquifer co-efficient of transmissivity (T) or co-efficient of permeability (K), whereas the latter database can provide transmissivity and storativity (S). The distance-dd data can be used to double-check the aquifer parameters acquired from time-dd data. The ‘well loss’ and ‘radius of influence’ (R0 ) and can also be calculated using the distance-dd data.

5.4.1.3

Single Well Test

During a time-dd test, the dd is typically measured only in the well being pumped or used for production. This approach is often used when there are no OBWs available in a particular basin, or when constructing OBW is not practical due to budget or time limitations. As a result, single well testing is generally a more cost-effective option than interference testing. Total dd in a PW or well dd (Sw ) is Sw is the aquifer Loss + Well Loss. Sw = B Q + C Q n , where, B—aquifer/formation loss coefficient, Q—yield, and C—well loss coefficient.

5.4.2 Recovery Test A pumping/production well or monitoring well are used to measure the rise in groundwater over time during an unsteady-state aquifer test. An aquifer time-dd test is followed by a recovery test (Fig. 5.2).

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Fig. 5.2 Plot of time-dd and recovery tests (Schwartz and Zhang 2003)

5.4.3 Injection Test In regions where well injection projects for artificial recharge are in use, injection tests can be conducted. With the exception of the injection pressure heads (i.e., the variation between the stationary and injection water levels), which are substituted for dd and the injection rate, respectively, for pumping rate, the injection well test procedures and equations are similar to those used for dd tests (Roscoe 1990).

5.5 Test for Determining Well Hydraulic Attributes 5.5.1 Step-dd Test To measure variations in the dd of a pumping or production well depending on variation in pumping rate (that is, well discharge), a step-dd test is utilized. This test typically entails pumping a producing well for 5–8 stages (pumping rates) at gradually higher pumping rates (i.e., Q1, Q2, Q3, Q4, Q5). The entire test can be finished in one day (Fig. 5.3). A steady-state condition is often achieved by measuring the dd for a specified step (pumping rate). You can also run this test by pumping a producing well for 1–2 h at each consecutively higher pumping rate and looking for an unstable decline at the end of every phase. On the other hand, studying discharge-unsteady dd data becomes more challenging. Step-dd test produces a set of “discharge-dd” for a specific PW.

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Fig. 5.3 Illustration of step dd test (Romeo-Eftimi 2006)

Step-dd tests are essential for pumping plant design and monitoring, as well as calculating basin or sub-basin-wide safe aquifer yields.

5.6 Design of Pumping Test Pumping test planning and design are critical for obtaining high-quality pumping-test data. In addition to proper perceptive of the local geology and kinds of water bearing formation, a suitable choice of production wells to be PW and OBWs for dd measure is essential. The second task mentioned involves gathering field data, including data on the depth, designing, and status of PWs, as well as the existence of a facility for disposing of water and design, the number, depth, and position of observation wells. Furthermore, before to the execution of pumping tests, certain extra judgments must be made. Number of Tests and Monitoring Wells—According to Roscoe Moss Company’s guidelines from 1990, it is advisable to install OBWs in four quadrants of the PW, at radial distances varying from 3 to 300 m. The spacing between the OBWs should be closer to the PW in areas where the maximum dd is observed. Because the form of the cone of depression is determined by these two key criteria, observation wells should be located taking into account together the period of a APT and aquifer properties. In contrast to the wide and planar cone of depression in high T water bearing formations, the cone of depression in low T aquifers is sharp and constrained. Similar to a shortduration pumping test, a longer-duration pumping test will likely cause the cone

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of depression to spread further out from the PW. For locating monitoring wells, it is also necessary to have a thorough understanding of the aquifer type. In order to prevent complication in the PTDA, both the PW and OBW should be fully penetrated. The number of aquifer tests and monitoring wells required is determined by the amount of data needed, the expected level of precision, the aquifer’s heterogeneity/ anisotropy, and the funds and time available for investigation. In general, as many as is technologically and economically viable should be used to gain a greater knowledge of the geographic variance in aquifer characteristics across a basin.

5.7 Measurement of Pumping Rate and Groundwater Level In an aquifer test, the most essential measurements recorded include time, yield, and depth to water table (i.e., dd). All start, halt, and pumping interval times must be precisely timed (~ 0.1 min). Ideally, it is recommended to maintain a constant pumping rate or well discharge when conducting an aquifer test. This involves regularly measuring the well discharge during the test and making adjustments to ensure it remains consistent. The volumetric technique can be utilized to appropriately quantify a small well discharge. A water meter mounted in the pump’s delivery pipe can be used if the well discharge is substantial. A manual water-level indicator or an automatic water-level recorder can provide DTW.

5.8 Schedule of Data Collection Within the first one or two hours after commencing an aquifer test, underground water levels in monitoring well decrease (after starting pumping)/rebound (after stopping pumping) quite quickly. As a result, the groundwater level is initially recorded at short intervals before gradually increasing as the pumping advances.

5.9 Image Well Theory A recharging border or impermeable boundaries are the two types of boundaries. A recharge border is an area where the water bearing formation is replenished. A location on the aquifer’s perimeter where it thins out, abuts a low-permeability formation is known as an impermeable boundary (barrier boundary) (Fetter 1994). If a PW is located in close proximity to an impermeable boundary or a recharge area, the pattern of radial flow will change significantly. This makes it challenging to solve the flow towards wells in these situations, and conventional radial-flow equations such as Theim or Theis equations are not suitable for application. The image well theory (Ferris 1959) was created to attempt flow problems in constrained aquifers

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using analytical methodologies. To imitate the operation of a PW, a “discharging image well” is used.

5.10 Determination of Confined Aquifer Parameters Time-dd, distance-dd, and recuperation data can all be utilised to compute the hydraulic characteristics of confined (Fig. 5.4).

5.10.1 Theis Type-Curve Method Theis type curve method has been graphically modified to permit for non-numerical understanding of pumping analysis data. It can be used to find the hydraulic attributes of piezometric aquifers, such as Transmissivity and Storativity. Theis’s equation is the established framework for analysing pumping tests in confined aquifers in the case of non-steady-state condition. It specifies the dd (s) at a definite radius (r) from a well in terms of pumping rate (Q) and duration (t). T=

Q W (u) 4π S

Fig. 5.4 Pumping test for aquifers (https://doi.org/10.1007/978-3-319-75115-3_11)

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r S Also, u = 4T can be also written as S = 4Tr 2tu . t Theis’s type-curve approach for identifying restricted aquifer characteristics from time-dd data is as follows:

• Plot u and W(u) on the log–log sheet to create Theis Type Curve. • Plot a field-data curve on log–log sheet with the identical scale as the Type Curve 2 using observed values of dd(s) versus rt . • Overlay the data curve onto the Type Curve sheet, aligning the coordinate axes of the two graphs. Adjust data curve until the data points match the Type Curve as closely as possible • Select a matching point on the Type Curve and record the corresponding field-data 2 curve coordinates (dd and time(s and rt ), as well as the values of W(u) and u from the Type Curve. Q • Finally, use Equation T = 4πS W (u) to determine T by substituting the values of coordinates and the value of Q. Then, in equation S = 4Tr 2tu substitute the values of the known variables to get S. 5.10.1.1

Assumptions

The following assumptions are made when using the Theis equation for groundwater flow analysis: • The potentiometric surface is initially horizontal (no slope) before pumping begins, • The aquifer is confined and appears to extend infinitely, • The aquifer is homogeneous, isotropic and infinite in areal extent, • The well is pumped at a constant rate, • The well is fully penetrated, • Water is discharged from storage instantaneously as the head declines, and • The diameter of the well is so small enough that water stored in the well can be neglected.

5.10.2 Jacob–Cooper Straight-Line Method for Time-dd In 1946, H. H. Cooper and C. E. Jacob proposed a simple method for calculating the Theis well function, (W(u)) by substituting W(u) with an infinite series, which is as follows: W (u) = −0.577216 − ln(u) + u −

u3 u4 u2 + − + ··· 2 × 2! 3 × 3! 4 × 4!

According to Jacob and Cooper’s (1946) findings, as the PW operates for an extended period, the value of u decreases, and the higher-order terms of the Equation

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(which include u2 , u3 , u4 , and so on) become negligible and can be ignored. If the limiting condition (u 0.01) is met, the Jacob-Cooper equation represents dd(s) as a straight line function of ln(t) or log(t). This can be true for both large and small value of t and r. After enough time has passed since the start of pumping, a linear plot of dd(s) against time (t) on semi-logarithmic paper can be made. When there are numerous monitoring wells, the near ones will meet the conditions first, followed by the farther ones. [ ] 2.25T t 2.3Q log sw = 4πT r2S where sw is drawdown, S—Storativity, T—Transmissivity and t—time. The Cooper-Jacob straight-line approach for estimating constrained aquifer parameters from time-dd data is as follows • Plot a data curve of dd (Y-axis) against time (X-axis) on semi-log sheet, with time on the logarithmic and dd on the arithmetic. • Create a linear line that best fits the field data. • Extend the fitted linear line backwards until it intersects the zero-dd line, then set time to, • Calculate the variation in dd per log cycle (Δs) using the slope of the linear line, and • At last, using following equation, calculate the values of Transmissivity and Storativity. T =

2.25T t0 2.3Q and S = 4πΔs r2

5.10.3 Cooper–Jacob Straight-Line Method for Distance-dd Data Observing the dd simultaneously in multiple observation wells reveals that the distance from the PW varies as per the Theis equation. With a slight adjustment, the Jacob–Cooper straight-line approach for distance-dd data can be utilised for time-dd data, provided that the dd is calculated simultaneously in three or more OBWs at a specific time. The Jacob-Cooper straight-line approach is used to find the parameters of a restricted aquifer from distance-dd data (Fig. 5.5). • Plot the field-data for dd against distance on semi-logarithmic graph paper to create a curve. Distance is depicted on the X-axis using a logarithmic scale, whereas dd is represented using a linear scale, • Connect field-data points with a straight line,

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Fig. 5.5 Straight-line curve to the distance-dd data (https://www.google.com/ url?sa=i&url=http%3A% 2F%2Fecoursesonline.iasri. res.in)

• Extend the line of best fit until it intersects with the zero-dd line and mark the distance as r0 , • Subtract slope of the linear line from the variation in the value of the dd per log cycle, and • Finally, use the following equations to compute the values of T and S: T =

2.25T t 2.3Q and S = 2πΔs r02

5.10.4 Residual Drawdown (RDD)-Time Ratio Method for Recovery Data To study the aquifer’s response during the recovery period when pumping stops, an artificial recharging well is placed on top of the PW with a constant flow rate. This allows for the PW to maintain its constant production rate, but the two opposing flow rates result in the well becoming inactive. As considerable well losses in PWs, examination of recuperation from PWs can merely produce T or K, not S. The examination of recovery data from OBWs, on the other hand, can produce both T (and K) and S. Based on Theis (1935), the RDD, after pumping has stopped, s' = where,

( ) Q W (u) − W u ' 4πT

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Fig. 5.6 Schematic diagram of the aquifer recuperation after pumping stopped (https://www.goo gle.com/url?sa=i&url=https%3A%2F%2Fwww.waterloohydrogeologic.com)

u=

r 2s r 2s' and u ' = 4T t 4T t '

s' is RDD, is the spacing from well to OBW, T is the transmissivity, S and S' are storativity during pumping and revival respectively, t' are elapsed times from the beginning and ending of draft respectively (Fig. 5.6). Using the estimate for the well function, W(u), as in the Cooper-Jacob method, this equation becomes: s' =

) ( 4T t 4T t ' Q ln 2 − ln 2 ' 4π T r S r S

When S, S' and T are constant and S' and S equal, this equation become: s' =

) ( t 2.3Q log ' 4π T t

The following is a gradual technique to calculate coefficient of transmissivity and storativity using recuperation data • On semi-logarithmic graph paper, plot a RDD versus time ratio (t/t) curve with RDD on Y-axis (arithmetic scale) the time ratio on X-axis (logarithmic scale), • Connect the field-data points with a linear line, • Using the inclination of linear line,

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• determine RDD value per log cycle (s' ), and • Determination of Transmissivity (T) as follows: T =

2.3Q 4π Δs '

5.11 Determination of Unconfined Aquifer Parameters 5.11.1 Unconfined Aquifer Without Delayed Yield For aquifer exhibiting no delayed yield the methods for confined aquifers are applicable.

5.11.2 Aquifer with Delayed Yield in an Unconfined Aquifer The aquifer parameters cannot be determined using the afore mentioned methods if the time- dd data from free-flowing water bearing formations show a considerable delayed yield. In this scenario, two strategies for obtaining accurate results have been proposed: (i) the Type-Curve Method, and (ii) the Neuman Straight-Line Method. These tactics are well described by Fetter (1994), Schwartz and Zhang (2003), and Batu (2003), among others.

References Batu V (1998) Aquifer hydraulics: a comprehensive guide to hydrogeologic data analysis. Wiley, New York Duffield GM. Pumping tests. Hydrosolve, Inc Ferris JG (1959) Groundwater. In: Wisler CO, Brater EF (eds) Hydrology. Wiley, New York Fetter CW (1994) Applied hydrogeology, 3rd edn. Prentice Hall, NJ Harvey C (2005) Groundwater hydrology lecture packet 8 Kasenow M (2001) Applied groundwater hydrology and well hydraulics, 2nd edn. Water Resources Publications, Highlands Ranch, Colorado Kruseman GP, de Ridder NA (1994) Analysis and evaluation of pumping test data, 2nd edn. ILRI Publication 47, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands Raghunath HM (2007) Ground water. New Age International (P) Limited, New Delhi Roscoe Moss Company (1990) Handbook of ground water development. Wiley, New York Schwartz FW, Zhang H (2003) Fundamentals of ground water. Wiley, New York Todd DK (1980) Groundwater hydrology. Wiley, New York