Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases 9811528446, 9789811528446

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Beidou Xi · Juan Li · Yang Wang · Chenning Deng · Xiang Li · Yan Ma · Yanna Xiong

Investigation and Assessment Technology for Typical Groundwatercontaminated Sites and Application Cases

Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases

Beidou Xi Juan Li Yang Wang Chenning Deng Xiang Li Yan Ma Yanna Xiong •

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Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases

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Beidou Xi Chinese Research Academy of Environmental Sciences Beijing, China Yang Wang Chinese Research Academy of Environmental Sciences Beijing, China Xiang Li Chinese Research Academy of Environmental Sciences Beijing, China Yanna Xiong China Soild Waste and Chemicals Management Center Beijing, China

Juan Li Technical Centre for Soil, Agriculture and Rural Ecology and Environment Ministry of Ecology and Environment Beijing, China Chenning Deng Chinese Research Academy of Environmental Sciences Beijing, China Yan Ma School of Chemical and Environmental Engineering China University of Mining and Technology Beijing, China

ISBN 978-981-15-2844-6 ISBN 978-981-15-2845-3 https://doi.org/10.1007/978-981-15-2845-3

(eBook)

© Springer Nature Singapore Pte Ltd. 2021 This work is subject to copyright. All rights are reserved 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 Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Foreword

The environmental impacts of contaminated sites on soil and groundwater have attracted increasing attention worldwide and emerged as an important bottleneck for the sustainable development of human society. In China, a large number of groundwater pollution sites have been formed due to the disorderly stacking of garbage, the leakage of landfills, the leakage of petrochemical enterprises’ transmission pipelines, and the relocation of backward enterprises. The number of groundwater-contaminated sites is increasing, and it has shown a trend of spreading from cities to rural areas, from east to west, and from local to regional expansion. Especially in economically developed areas such as Beijing-Tianjin-Hebei, Yangtze River Delta, and Pearl River Delta, the problem of groundwater pollution is more serious. According to the nationwide investigations of groundwater contamination conducted by the Ministry of Ecology and Environment and the China Geological Survey in recent years, municipal domestic waste landfills (MSWLFs), hazardous waste landfills (HWLFs), and oil-contaminated sites (OCS) have become typical sources of groundwater contamination that pose a serious threat to the surrounding ecological environment. Recognizing the increasing importance of groundwater pollution prevention and control, the Chinese government has issued a series of plans and documents in recent years, such as the National Groundwater Pollution Prevention and Control Plan (2011–2020), Action Plan for Water Pollution Prevention and Control, and Action Plan for Soil Pollution Prevention and Control, all of which place emphasis on municipal solid waste landfills, hazardous waste landfills, and oil-contaminated sites in environmental protection. It is challenging to identify and treat groundwater pollution as such pollution is concealed, persistent, and complex. In China, the proactive investigation and evaluation of typical contaminated sites will help grasp the status and trends of groundwater pollution and provide preconditions and precise guidance for subsequent pollution prevention and control. On the basis of systematic study of typical groundwater contamination sites in China, Chinese Research Academy of Environmental Sciences has organized multiple domestic and international scientific research institutions to compile the v

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“Technologies for Investigation and Evaluation of Typical Groundwater Contamination Sites and Cases of Application.” This book discusses the methods for investigation and assessment of such typical contaminated sites while taking into account their characteristics, which covers site investigation, source intensity evaluation, risk assessment, and cases of application in selected sites in central, northern, southwestern, southeastern, and northwestern parts of China. It is of significance to guide the environmental management and zoned remediation of typical contaminated sites and also contributes to the management and control of groundwater contamination sites at home and abroad. Beijing, China April 2020

Hongliang Liu

Acknowledgements

This study was supported by the National Water Pollution Control and Management Technology Major Project of China (2018ZX07109-001) and the National Groundwater Pollution Prevention and Control Plan (2011–2020).

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Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Overview of Groundwater Contamination Sites . . . . . . 1.2 Research Progress at Home and Abroad . . . . . . . . . . . . 1.2.1 Evolution and Current Situation of Investigation and Assessment in Developed Countries . . . . . . 1.2.2 Evolution and Current Situation of Investigation and Assessment in China . . . . . . . . . . . . . . . . . 1.3 Problems and Trends . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2 Environmental Background Investigation of Groundwater Contamination Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Process of Investigation . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2 Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Content of Investigation . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Field Investigation . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Hydrogeological Survey . . . . . . . . . . . . . . . . . . . 2.2.4 Monitoring Well Deployment . . . . . . . . . . . . . . . 2.2.5 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.6 Analytical Testing . . . . . . . . . . . . . . . . . . . . . . . 2.2.7 Status Quo Evaluation . . . . . . . . . . . . . . . . . . . . 2.3 Brief Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 Rating and Evaluation of Pollution Source Intensity for Typical Groundwater Contamination Sites . . . . . . . . . . . . . . 3.1 Indicators of Pollution Source Intensity Evaluation . . . . . . . . . 3.1.1 Characteristic Factors of MSWLFs Hazards . . . . . . . . 3.1.2 Characteristic Factors of HWLFs Hazards . . . . . . . . . . 3.1.3 Characteristic Factors of OCS Hazards . . . . . . . . . . . . 3.1.4 Characteristic Factors for Mitigation Performance of Vadose Zone in Contaminated Sites . . . . . . . . . . . . 3.1.5 Indicator Library for Groundwater Pollution Source Intensity Rating and Evaluation . . . . . . . . . . . . . . . . . 3.2 Method of Groundwater Pollution Source Intensity Rating and Evaluation for Typical Groundwater Pollution Studies . . . 3.2.1 Indicator System for Rating and Evaluation of Groundwater Pollution Source Intensity . . . . . . . . . . . 3.2.2 Method for Hazard Rating and Evaluation of Pollution Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Method for Rating and Evaluation of Mitigation Performance of Vadose Zone . . . . . . . . . . . . . . . . . . . 3.2.4 Rating and Evaluation of Groundwater Pollution Source Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Strategies for Groundwater Pollution Prevention and Control . 3.3.1 Potential Sources of Pollution . . . . . . . . . . . . . . . . . . . 3.3.2 Existing Sources of Pollution . . . . . . . . . . . . . . . . . . . 3.4 Brief Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4 Risk Assessment of Groundwater Contamination Sites . . . . . . . . . 4.1 Health Risk Assessment of Typical Groundwater Contamination Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Process of Health Risk Assessment . . . . . . . . . . . . . . . . 4.1.2 Prevailing Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Groundwater Pollution Risk Assessment of Typical Groundwater Contamination Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Assessment of Intrinsic Vulnerability . . . . . . . . . . . . . . 4.2.2 Assessment of Specific Vulnerability . . . . . . . . . . . . . . 4.2.3 Identification of External Pollutant Types and Hazard Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.4 Groundwater Value/Function Evaluation . . . . . . . . . . . . 4.2.5 Methods for Groundwater Pollution Risk Assessment . . 4.3 Brief Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5 Application Cases . . . 5.1 Central China . . . 5.2 Northwest China . 5.3 Southwest China . 5.4 Southeast China . 5.5 North China . . . . 5.6 East China . . . . .

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Chapter 1

Introduction

Abstract The environmental impacts of contaminated sites on soil and groundwater have attracted increasing attention worldwide and emerged as an important bottleneck for the sustainable development of human society. According to the nationwide investigations of groundwater contamination conducted by the Ministry of Ecology and Environment and the China Geological Survey in recent years, municipal domestic waste landfills, hazardous waste landfills, and oil-contaminated sites have become typical sources of groundwater contamination that pose a serious threat to the surrounding ecological environment. This chapter first introduces the concept of groundwater contaminated sites, then introduces the history of groundwater contaminated site surveys and assessments in China and the world, and finally points out the problems and development trends of groundwater contaminated site surveys and assessments in China.







Keywords Municipal solid waste landfill Hazardous waste landfill Oil-contaminated site Groundwater Pollution source Risk assessment




1.1







Overview of Groundwater Contamination Sites

Referring to China’s Codes for Environmental Pollution Source Categories (GB/T 16706–1996), groundwater contamination sites mean areas where the groundwater environment suffers from or is exposed to direct discharge of physically, chemically and biologically hazardous substances or energy. Along with economic and social development, both national productivity and pollution emissions exhibit an increasing trend. A considerable number of groundwater sites are polluted due to disorderly trash mound, landfill leakage, leakage of petrochemical transmission lines, and relocation of backward enterprises. As a result, the unrelieved soil and groundwater pollution aggravates the already grave water shortage. In the Beijing-Tianjin-Hebei region, for example, groundwater supports more than 75% of urban drinking water supply, but the current situation of groundwater quality is not optimistic at all. About 72% of shallow groundwater has been contaminated to © Springer Nature Singapore Pte Ltd. 2021 B. Xi et al., Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases, https://doi.org/10.1007/978-981-15-2845-3_1

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Introduction

different degrees, and the overall groundwater quality deteriorates year by year. According to rough statistics, there are 12,600 groundwater contamination sites in the region, including petrochemical sites, municipal solid waste landfills (MSWLFs), seepage pits, and hazardous waste landfills (HWLFs), which seriously undermines the safety of groundwater environment (National Bureau of Statistics 2010). Groundwater contamination, characterized by latency, hysteresis and persistence, poses a huge threat to the surrounding ecological environment and human health (Luo 2018; Lv 2009; Liu et al. 2015). The research on groundwater pollution, compared with surface water pollution, started late in China. Given a string of groundwater contamination incidents, the relevant state departments have gradually attached importance to addressing groundwater pollution and taken the research on groundwater pollution as one of the priorities in recent years. In 2011, China published the National Groundwater Pollution Prevention and Control Plan (2011–2020) (hereinafter referred to as the Groundwater Plan), which analyzed the current situation and existing problems of groundwater pollution in China and set down the objectives and main tasks of groundwater pollution prevention and control in the next stage. Issued in 2013, the Work Plan for Groundwater Pollution Prevention and Control in North China Plain defined the overall objective of future groundwater environmental protection in the North China Plain. In line with the tasks specified in the Groundwater Plan, China launched the National Survey and Evaluation of Groundwater Environmental Status in 2011, which classified typical groundwater contamination sites into seven categories: MSWLFs, HWLFs, oil-contaminated sites (OCS), industrial parks, mining areas, agricultural land using reclaimed water, and golf courses. This book reviews the methods of investigating and assessing three most typical and representative groundwater contamination sites, i.e. MSWLFs, HWLFs and OCS.

1.2

Research Progress at Home and Abroad

In the process of accelerated urbanization and adjustment of urban economic structure and functions, a large number of difficult-to-treat pollutants with complex and rich components are left behind after the relocation or shutdown of many MSWLFs, HWLFs and oil refining sites. These pollutants migrate to deeper soil layers by ways of gravity or atmospheric precipitation and eventually contaminate the groundwater (Wang and Qian 2000). Due to weak self-purification capacity, groundwater as an important part of water resources can hardly be restored once contaminated. At present, the investigation and assessment of groundwater environment has become a worldwide concern.

1.2 Research Progress at Home and Abroad

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Evolution and Current Situation of Investigation and Assessment in Developed Countries

In the 1970s, HWLFs in the United States seriously threatened public health and the environment due to improper disposal. In view of this, the United States Environmental Protection Agency (USEPA) developed risk assessment guidelines, technical specifications and related laws, and began the risk assessment of typical contaminated sites (U.S.EPA. 1992, 1999, 2000, 2007, 2012, 2015). Following this, other countries turned attention to the investigation and assessment of contaminated sites, and the philosophy of environmental protection shifted focus from post-contamination treatment to pre-contamination prediction and management, giving rise to environmental risk assessment. In 1980, the World Health Organization (WHO) worked with the Organization for Economic Cooperation and Development (OECD) and the US EPA to build a framework for assessing human health risks and ecological risks. In 1992, the United Kingdom set off the research on exposure assessment methodology for contaminated sites adapted to the national context, which was refined in 2009. In 1996, the European Union published the guidelines for risk assessment for contaminated sites based on concerted action. Soon afterwards, Canada, Australia and Finland established respective risk assessment systems in national contexts based on the U.S. risk assessment standards. More and more international environmental organizations and national environmental agencies have also drawn attention to environmental risk assessment (Zhou et al. 2007). To date, many foreign countries have developed assessment models specifically for groundwater contaminated sites, which simplifies the process of risk assessment, such as EUSES (EU), CalTOX (US), RBCA (US), CLEA (UK), CETOX (Denmark), CSOIL (Netherlands) and UMS (Germany). In terms of investigation and risk assessment of contaminated sites, both technical standards and assessment systems have been standardized in developed countries. 1. United States Groundwater resources are invaluable because they contribute to about half of drinking water resources in the United States. In view of this particularity, the United States early established a relatively complete legal system for groundwater protection, and set up a special agency for groundwater environmental management which regularly investigates the groundwater environment on a regular basis (Zheng and Qi 2012). In 1980, the U.S. Congress enacted the Comprehensive Environmental Response, Compensation and Obligation Act (CERCLA), commonly known as Superfund, in response to the dump at the Love Canal. Pursuant to this Act, the US EPA designed and implemented the Superfund Program, in which fines and punitive damages paid by offenders, site repair costs and fund interests shall be used for the management, restoration and remediation of contaminated sites. In order to support with the CERCLA enforcement, the American Society for Testing and Materials (ASTM), a well-known standard-setting organization, has developed, from 1993 onwards, a

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Introduction

series of operational guidelines for site pollution investigation and evaluation, including ASTME 1527 Standard Practice for Site Environmental Assessments: Phase I Site Environment Assessment Process, ASTME 1528 Standard Practice for Site Environmental Assessments: Transaction Screen Process, ASTME 1903 Standard Practice for Site Environmental Assessments: Phase II Site Environment Assessment Process, ASTMD 1452 Standard Practice for Soil Exploration and Sampling, and ASTMD 5092 Standard Practice for Design and Installation of Groundwater Monitoring Wells. All these standards provide a reference for groundwater environmental investigation and assessment. With the formulation of investigation and pre-assessment policies and guidelines, targeted code for risk assessment of contaminated sites have also been established. In 1995, the U.S. standards and material measurement institutes proposed the Risk Assessment and Corrective Action Process for Petroleum Release Sites which was revised in 2002. The technical process typically consists of five steps: initial site assessment, site characterization and interim actions, tier-1 risk assessment, tier-2 risk assessment, and tier-3 risk assessment. The initial site assessment gathers information on soil and groundwater pollution by means of site investigation and soil sampling to determine the main contaminants, contaminated environmental media, affected environmental receptors, and pathways of pollution. Site characterization is necessary to ascertain the extent of groundwater pollution based on initial site assessment, and determine the need for actions according to the degree of threat to humans and environmental receptors. Tier-1 risk assessment calculates the risk-based screening levels (SLs) for groundwater, and compares them with pollutant concentration levels identified in the site investigation to determine whether a site is exposed to pollution. Tier-2 risk assessment is specific to sites and exposure points, and tier-3 risk assessment is more complicated and may involve software-based simulation of pollutant migration and transformation. This corrective action process has been recognized by the International Organization for Standardization (ISO) and other countries. 2. United Kingdom In 2000, the UK Environment Agency set out a framework for site investigations based on risk assessment, which consists of three steps: preliminary investigation, exploratory investigation, and focus investigation. The preliminary investigation includes desktop study and site walkover survey to identify potential site risks and develop site-specific conceptual model based on obtained information. By way of investigation and sampling, the exploratory investigation is intended to clarify the source-pathway-receptor route and revise the conceptual model. The focus investigation refers to full investigation, sampling and analysis (including invasive and non-intrusive investigations) to further refine the established conceptual model. 3. Japan In 1999, the Japanese Ministry of the Environment developed the Survey and Countermeasures Guidelines for Soil and Groundwater Pollution based on the

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U.S. management model for contaminated sites. Under the Guidelines, the survey of soil and groundwater pollution is divided into three categories: vicinity wells contamination-type, site assessment-type, and site contamination-type. The technical process focuses on the survey of site contamination and consists of data site survey, general site condition survey and detailed site survey. The data site survey includes site walkover survey, interview, and data collection, but excludes the analysis of samples, and the general site condition survey collects and tests ground soil and topsoil samples. The detailed site survey makes clear the spatial distribution of pollutants by such technical means as exploration drilling, which paves the foundation for soil and groundwater remediation in the next step. 4. Canada Canada promulgated the Contaminated Sites Regulations in 1997 and 2005 respectively. Based on sampling and testing, the condition of pollution is described and the risk of contamination scoped to identify the potential migration and exposure pathways for pollutants, the location of sensitive receptors, the direct or potential exposure pathways for population and to develop a conceptual site model. The National Classification System for Contaminated Sites (NCSCS) is a comprehensive risk assessment system that takes into account pollutant characteristics, pollutant migration capabilities and exposure pathways. It evaluates the risk of groundwater contamination at sites based on calculated risk values. 5. Netherlands In the Netherlands, groundwater is deemed seriously contaminated where the average pollutant concentration exceeds the intervention value by more than 100 m3. In this case, the hazards to human and ecosystem health will be evaluated using appropriate models, so as to determine the urgency of contaminated sites under the step-by-step risk assessment system. 6. Germany At present, Germany has put in place a relatively complete management system for contaminated sites, covering the identification, risk assessment, remediation and test of contaminated sites.

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Evolution and Current Situation of Investigation and Assessment in China

Relative to developed countries, China started the investigation and risk assessment late for contaminated sites and has not yet established a perfect legal system for groundwater pollution prevention and control. It is not until early twenty-first century that China began to conduct investigation and risk assessment for typical

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Introduction

groundwater contaminated sites and gradually explored the investigation and assessment system for groundwater contaminated sites (Yin et al. 2011). In 1997, Cai Shuying et al. used the refined second-order matrix method and Monte Carlo method to predict and measure the risk probability of groundwater pollution, and estimated the sensitivity and impact of various parameters (Cai and Yang 1997). In 2006, Chen Honghan et al. building on domestic and foreign health risk assessment methods for contaminated sites, proposed the concepts and measurement methods of “superimposed risks” and “cumulative health risks from exposures to the same pollutant via multiple pathways” to make up for the deficiencies of prevailing methods (Chen et al. 2006). In 2007, Li Shaofei et al. explored the risk assessment index system for groundwater environment, and combined it with fuzzy mathematics to assess several typical areas of the Haihe River Basin (Li et al. 2007). In 2011, Cai Wutian et al. carried out site identification, site walkover survey and pollution source tracking to examine the way of pollutant transport in an OCS site in the Yizhong Plain, and further determined the scope and depth of pollution through a combination of geophysical exploration, trial pits and exploration drilling (Cai et al. 2011). This approach provided a basis for oil field investigation. Zhang Jiashuang et al. investigated an OCS site in Northeast China, used the risk assessment model for quantitative health risk assessment for groundwater in the study area in accordance with relevant theory, and obtained the carcinogenic and non-carcinogenic risk values at potential points of human exposure (Zhang et al. 2010). In 2011, with Beijing Beitiantang Landfill as an example, Hong Mei et al. proposed a methodology for groundwater pollution risk assessment that took into account aquifer vulnerability and MSWLF nature (Hong et al. 2011). Li Yan et al. calibrated the parameters of the RAIS model according to the demographic characteristics of China and the pollutant types specific to water source areas, and used the RAIS exposure dose calculation method to evaluate the health risk of exposure through drinking water and skin contact (Li et al. 2011). In 2012, Li Guanghe et al. constructed a parameter system for assessing pollution source hazards that reflects pollution source characteristics and pollutant properties, and built a model that couples the evaluation of pollution source characteristic and pollutant properties (Jin et al. 2012, 2012). In 2016, Ren Jianfei et al. simulated the vertical transformation of pollutants based on Hydrus-1d models and evaluated the risk of groundwater pollution (Ren 2015). Regarding technical standards, the Water Law of the People's Republic of China and the Law of the People's Republic of China on Prevention and Control of Water Pollution serve as the basic law on water environmental protection, and the Environmental Protection Law of the People's Republic of China targets environmental protection. Provisions on groundwater protection included in these laws are limited to the basic principles and do not define specific work and responsibilities. In practice, it is difficult to take effective measures to protect groundwater as relevant departments shirk their responsibilities. In order to solve the problem of increasingly prominent groundwater contamination, the former State Environmental Protection Administration (SEPA) issued the Circular on Effective Prevention and Control of Environmental Pollution for Industrial Enterprise Relocation (SEPA,

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No. 47) in 2004, stipulating the relocated production and operation entities are responsible for remedying and restoring use functions of soils subject to residual pollutants during the relocation process. This document represents a milestone in promoting the management of contaminated sites in China. Issued in 2014, the Technical Guidelines for Site Environmental Investigation (HJ 25.1–2014), Technical Guidelines for Site Environmental Monitoring (HJ 25.2–2014), Technical Guidelines for Risk Assessment of Contaminated Sites (HJ 25.3–2014), and Guidelines on Health Risk Assessment for Groundwater Pollution (Trial) also provide technical guidance and support for groundwater environmental investigations and risk assessments. Generally speaking, China's risk assessment system for contaminated sites remains immature and needs further improvement according to national circumstances.

1.3

Problems and Trends

Currently, the investigation and assessment of groundwater contamination sites meets with the following problems in China: (1) Large number, wide range and diversity of groundwater contaminations sites, making investigation and assessment difficult In recent years, urban sewage discharge without proper treatment has sharply increased amid rapid urban expansion. Due to investment shortage and inappropriate pipe network construction and maintenance, sewage seeps through pipes and some penetrates into groundwater bodies. Without complete separation from rainwater, sewage overflows with rainwater during the flood season, causing groundwater pollution. Surface sewage leads directly to aquifer contamination and cross-contamination as groundwater facilities and activities do not integrate sound waterstop measures. Some industrial enterprises also threaten the safety of groundwater environment. Groundwater contamination incidents often take place as a result of leakage in chromium slag and manganese slag heaps where industrial solid waste has not been effectively utilized or treated. In the petrochemical industry, exploration, mining and production activities significantly affect groundwater quality, while groundwater contamination associated with gas station leakage becomes increasingly prominent. Groundwater is also prone to pollution from industrial wastewater discharge and dump of industrial enterprises through seepage wells, seepage pits and crevices. Fertilizers, pesticides and sewage irrigation also pose a threat to groundwater safety in the relevant areas because some soil pollutants are easily leached. In China, fertilizers and pesticides applied per unit of farmland are 2.8 times and 3 times of the world average, and a large number of fertilizers and pesticides contaminate groundwater through soil infiltration. In some areas, long-term

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Introduction

sewage irrigation has undermined farmland and groundwater environment by increasing ammonia nitrogen, nitrate nitrogen and nitrite nitrogen far beyond the limits and exacerbating organic pollution. In addition, surface water pollution exerts a growing impact on groundwater. Since surface water and groundwater are connected, groundwater pollution is grave especially in areas with serious surface water pollution, such as the Yellow River, Liaohe River, Haihe River and Taihu Lake. In some coastal areas, seawater intrusion in groundwater occurs because groundwater over-exploitation has destroyed the balance between freshwater and salt water in the coastal aquifers. (2) Limited scope of investigation and unclear base number of contaminated sites China carried out a nationwide investigation of soil pollution in 2006 and a national survey and evaluation of groundwater environmental status in 2011. However, the scope of these investigations is constrained by many factors, which hinders the full grasp of groundwater contamination in typical sites. About the limited number of contaminated sites that have been investigated, many basic data and materials are seriously missing, which adds great difficulty in the investigation, assessment and remediation of contaminated sites. (3) Late start of investigation and assessment and imperfect relevant policies and regulations Compared with developed countries such as Europe and the United States, China started the investigation and assessment late of groundwater contamination sites and have not yet established a robust legal system for groundwater pollution prevention and control. Gradually paying attention to the management of contaminated sites, the state and local environmental authorities published a series of environmental standards in 2014, such as the Technical Guidelines for Site Environmental Investigation (HJ 25.1–2014) and Technical Guidelines for Risk Assessment of Contaminated Sites (HJ 25.3–2014). Nevertheless, the laws and guidelines dedicated to the investigation and remediation of contaminated sites remain absent. As a result, more often than not, there are no statutes to apply in the supervision of contaminated sites for environmental authorities at all levels. (4) Backward technical methods for investigation, assessment and remediation Technical problems restrict the development of contaminated site remediation industry. At this stage, the remediation of contaminated sites focuses on soil remediation and often ignores the investigation, assessment and remediation of contaminated groundwater. From the view of concept, remediation technologies for contaminated sites are mainly integrated into projects through imitation that draws on foreign advanced technologies. Given complex situation in groundwater contamination sites, in the absence of appropriate background investigation, pollution source intensity assessment and risk assessment, it is impossible to adopt appropriate remediation technologies and methods according to pollution types and pathways, pollution source intensity and

1.3 Problems and Trends

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human damage model. As a result, the expected remediation targets are rarely achieved despite high remediation costs paid. At the same time, the prevailing remediation techniques are relatively extensive and the remediation equipment are relatively backward. China remains in the early stage in terms of the production and development of remediation equipment, the development of remediation chemicals, and the application of remediation technologies. At present, for the investigation, assessment and remediation of contaminated sites in China, it is most imperative to establish and improve the risk assessment system and to develop and apply assessment and remediation technologies. While drawing on the advanced experiences of developed countries, China should formulate, as soon as possible, technical specifications for investigation and assessment that considers both China's national conditions and contaminated sites. With the development of pollution remediation industry, China's contaminated site remediation industry will adopt a risk assessment based on approach for remediation and gradually foster a technical system for whole process management of contaminated sites, including environmental investigation, source intensity assessment, risk assessment, and remediation.

References CAI Shuying, YANG Jinzhong. A Study on the Risk Analysis of Groundwater Pollution [J]. Journal of Wuhan University of Hydraulic and Electric Engineering, 1997(01): 8-12. CAI Wutian, ZHANG Min, LIU Xuesong, et al. On Procedure and Contents of Investigation and Risk Assessment with Regard to Site Soil and Groundwater Contamination[J]. Hydrogeology & Engineering Geology, 2011, 38(6): 125–134. CHEN Honghan, CHEN Hongwei, HE Jiangtao, et al. Health-based Risk Assessment of Contaminated Sites: Principles and Methods[J]. Earth Science Frontiers, 2006(01): 216-223. HONG Mei, ZHANG Bo, LI Hui, WANG Dong. Risk Assessment of Groundwater Pollution by Domestic Waste Landfill Site: A Case Study of Beijing Beitiantang Landfill[J]. Environmental Pollution & Control, 2011, 33(03): 88–91+95. JIN Aifang, LI Guanghe, ZHANG Xu. Groundwater pollution risk source identification and classification method[J]. Earth Science (Journal of China University of Geosciences), 2012, 37 (02): 247–252. JIN Aifang, ZHANG Xu, LI Guanghe. Study on the Hazard Assessment Method of Pollution Sources in Groundwater Source Fields[J]. Chine Environmental Science, 2012, 32(6): 1075– 1079. LI Shaofei, FENG Ping, LIN Chao. Investigation on the Index System of Groundwater Environment Risk and Its Application[J]. Journal of Arid Land Resources and Environment, 2007(01): 38-43. LI Yan, SUN Yajun, LIU Yong, WANG Hesheng, YANG Zhibin. Health risk assessment of groundwater sources based on RAIS[J]. Yellow River, 2011, 33(05): 48-50. LIU Weijiang, WANG Dong, WEN Yi, et al. Countermeasures of Groundwater Remediation in China-An Interpretation of Water Pollution Control Action Plan[J]. Environmental Protection Science, 2015(3): 12-15. LUO Lan. Research on Groundwater Pollution and Its Prevention-Control Policy in China[J]. Journal of China University of Geosciences (Social Sciences Edition), 2018, 8(2): 72-75.

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Introduction

LV Shujun. Analysis on Groundwater Contamination in Our Country[J]. Ground Water, 2009, 31 (1): 1-5. National Bureau of Statistics. Bulletin of the First National Pollution Source Census[R]. 2010. REN Jianfei. Groundwater pollution risk assessment and numerical simulation research[J]. Inner Mongolia Water Resources, 2015(03):11-12. U.S.EPA Strengthens Underground Storage Tank Requirements[J]. 2015. U.S.EPA. EPA Looking for Pollution Source in Underground Water [R]. 2012. U.S.EPA. Hazard ranking system guidance manual [M].1992. U.S.EPA. Leaking Underground Storage Tanks Corrective Action Resources [R].1999.https:// www.epa.gov/ust/leaking-underground-storage-tanks-corrective-action-resources U.S.EPA. Musts for USTs – A summary of federal regulations for underground storage tank systems [R]. 2007. U.S.EPA. Oil pollution prevention and response: Non-transportation-related facilities [R]. 2000. WANG Yuqiu, QIAN Qian. Discussion on Hazards of Groundwater Pollution Sources and Countermeasures[J]. Shandong Environment, 2000(S1): 204-205. YIN Yafang, LIU Deshen, LI Jing, et al. Research Progress of Groundwater Pollution Prevention in China[J]. Environmental Science and Management, 2011, 36(6): 27-30. ZHANG Jiashuang, YANG Yuesuo, DU Xinqiang, FAN Wei. Health risk assessment of groundwater pollution in the petroleum contaminated sites[J]. Journal of Anhui Agricultural Sciences, 2010, 38(36): 20887–20890. ZHENG Chunmiao, QI Yongqiang. International Experience on Groundwater Pollution Prevention and Control– A Case Study of the United States[J]. Environmental Protection, 2012(4): 30–32. ZHOU Youya, YAN Zengguang, GUO Guanlin, et al. National Classified Management Model and Method for Contaminated Sites[J]. Environmental Protection, 2007(10).

Chapter 2

Environmental Background Investigation of Groundwater Contamination Sites

Abstract It is necessary to identify target sites before carrying out the environmental background investigation of contaminated sites. Which it comes to specific groundwater contamination site, the environmental background investigation covers the hydrogeological environment of the site and its surrounding areas and the characterization of groundwater contaminants in the site, laying the foundation for comprehensive investigation and assessment. This chapter expounds the process and content of investigation into three kinds of typical groundwater contamination sites: MSWLFs, HWLFs and OCS.







Keywords Municipal solid waste landfill Hazardous waste landfill Oil-contaminated site Groundwater Pollution source Pollution investigation




2.1 2.1.1







Process of Investigation Scope

(1) MSWLFs Landfills can be divided into two categories: standard landfills and non-standard landfills. Standard landfills refer to landfills that are constructed and operated in accordance with relevant state standards and regulations to achieve environmentally sound treatment by applying sanitary landfill technologies. Standard MSWLFs are all included in the scope of investigation. Non-standard MSWLFs are screened according to the following four principles: (a) located in the vicinity of drinking water sources or in groundwater recharge and runoff areas; (b) located in areas with high groundwater vulnerability; (c) operated for more than five years; and (d) having a landfill capacity of more than 400 * 103 m3. (2) HWLFs Hazardous waste landfills are all included as key investigation objects.

© Springer Nature Singapore Pte Ltd. 2021 B. Xi et al., Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases, https://doi.org/10.1007/978-981-15-2845-3_2

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2 Environmental Background Investigation of Groundwater …

12

(3) Gas station (oil depot) contaminated sites Based on the established list, gas stations (oil depots) will be screened for key groundwater investigation and assessment according to the following principles: (a) all oil depots; (b) gas stations that have witnessed oil spill incidents; and (c) where oil spills are not confirmed: (i) gas stations located in the areas where the groundwater is protected as drinking water source and replenished and areas with groundwater runoff, and (ii) gas stations beyond these areas, with priority given to those established for more than 20 years or conditionally those established a shorter period of time.

2.1.2

Process

2.1.2.1

MSWLFs and HWLFs

Given the current construction and operation models of MSWLFs and HWLFs in China, the background investigation of groundwater environment is conducted through steps as shown in Fig. 2.1.

2.1.2.2

OCS

Based on the current construction and operation models of China’s oil production and sales industry, the background investigation of groundwater environment follows steps as shown in Fig. 2.2.

2.2 2.2.1

Content of Investigation Data Collection

The data collection covers the reports on feasibility study (FS), environmental impact assessment (EIA) and engineering geological survey related to contaminated sites, site photos, site lists, basic information questionnaires, hydrogeological and meteorological information questionnaires, onsite sampling information tables, information tables and distribution map of monitoring wells, and historical monitoring data (Cai et al. 2011; Zhang et al. 2011; Xu et al. 2017). The data sources, uses and requirements are described in Table 2.1. As it is difficult to obtain the basic data of non-standard MSWLFs and non-standard OCS, the large-scale basic data can be drawn from the relevant local departments of land resources, water resources and environmental protection, and

2.2 Content of Investigation

13

Fig. 2.1 Steps of background investigation and assessment of groundwater environment for MSWLFs and HWLFs

relevant information further determined and supplemented through field investigation and hydrogeological survey.

2.2.2

Field Investigation

The field investigation encompasses the following tasks: (1) Provide additional basic information that is unavailable during data collection Such additional information covers environmentally sensitive sites in the surrounding area, including their quantity, type, distribution, impact, protective measures, geographical location, scale, relative position to landfills, environmental

14

2 Environmental Background Investigation of Groundwater …

Fig. 2.2 Steps of groundwater environmental background investigation for OCS

functional area, and surrounding land use. It can be obtained through interviews with field management personnel, nearby residents, and etc. (2) Verify the accuracy of data collected The focus is to verify whether the hydrogeological conditions, existing monitoring wells (distribution, location, well depth, and etc.), regular monitoring and environmental management are consistent with described in the data collected.

2.2 Content of Investigation

15

Table 2.1 Data inventory, sources, uses and requirements No.

Title

Sources

Requirements and description

Uses

1

 Feasibility study report (standard*)

Landfill operators

Printed copy

2

 Environmental impact assessment report (standard*)  Engineering geological survey report (standard*)

Landfill operators

Printed copy

Landfill operators or third-party geological surveyors Engineering geological survey reports Engineering geological survey reports

Printed copy

Information collection and review Information collection and review Information collection and review

3

4

5

6

 Plane distribution map of prospecting sites (standard*)  Hydrogeological map and engineering geological cross-sections (standard*)  Site photos

7

 Basic information questionnaires

8

 Hydrogeological survey questionnaires  Information table of monitoring wells

9

10

 Historical monitoring data (standard*)

11

 Distribution map of monitoring wells

Field investigation Field survey

Field survey On-site interviews or feasibility study reports Landfill operators

Printed copy or electronic version (preferred) Printed copy or electronic version (preferred), (scale 1:1000– 1:500) Electronic version (JPG format) Printed copy or electronic version Printed copy or electronic version Printed copy or electronic version

Printed copy or electronic version for recent three to five years Printed copy or electronic version (preferred)

Data collection

Model building

Database establishment Basic information survey Hydrogeological survey Monitoring well information collection Data analysis

On-site Data collection interviews or feasibility study reports Note Standard * indicates data collection is limited only to standard MSWLFs, standard HWLFs and standard gas station (oil depot) contaminated sites

16

2 Environmental Background Investigation of Groundwater …

(3) Get real-time site photos The site photos are physical pictures of landfills, sewage treatment facilities, monitoring wells, and etc. (4) Determine the need for hydrogeological survey Hydrogeological survey is required where the hydrogeological data is insufficient to characterize groundwater flow field. By observing the terrain and surrounding environment, field investigation determines the suitability of conditions for geological measurements and use of different geophysical techniques. (5) Examine the effectiveness of existing groundwater monitoring wells The feasibility of using existing groundwater monitoring wells is examined based on the actual site conditions, including the layout, location and depth of monitoring wells. Additional groundwater monitoring wells need to be deployed if the existing ones are unable to meet the investigation requirements.

2.2.3

Hydrogeological Survey

Based on existing hydrogeological data, hydrogeological survey or where the conditions for hydrogeological survey are not met, hydrogeological exploration is carried out to obtain hydrogeological information that provides a basis for deploying monitoring wells. It should basically make clear the hydrogeological structure, groundwater recharge, runoff and discharge conditions, and groundwater flow field characteristics. (1) Hydrogeological structure The hydrogeological survey investigates the lithology, thickness and its variation of aquifers, aquitard and aquiclude of landfills and surrounding areas within a certain range. It produces a cross-sectional view or where the data is abundant, a perspective view of the hydrogeological structure. (2) Groundwater recharge, runoff and discharge conditions Groundwater recharge conditions should include precipitation, artificial recharge, surface water replenishment and etc. Focusing on data collection, the hydrogeological survey collects the changes of precipitation and (monthly/yearly) water chemistry in landfills and the surrounding areas; collects or observes changes in surface water level, flow and quality, and analyzes the relationship between surface water and groundwater. Groundwater runoff conditions mainly include aquifer hydraulic conductivity, hydraulic gradient, and thickness. Generally, hydrogeological structure maps and water chemistry data are used to analyze runoff conditions in a certain site.

2.2 Content of Investigation

17

Groundwater discharge conditions include evaporation, exploitation, runoff, springs and etc. (3) Groundwater flow field characteristics The groundwater depth of wells (holes) in landfills and surrounding areas within a certain range is clarified, and a groundwater contour map is drawn to analyze the groundwater flow direction and hydraulic gradient. (4) Hydrogeological parameters Where existing hydrogeological parameters lag behind requirements, hydrogeological tests (pumping tests, dispersion tests, and etc.) can be carried out based on existing wells and hydrogeological monitoring wells (boreholes), which are combined with integrated ground geophysical methods and hydrogeological exploration wells to identify the hydrogeological parameters of the study area. When the hydrogeological data are unavailable, borehole drilling is needed to analyze the stratigraphic feature of sites, especially of non-standard MSWLFs and non-standard oil depot contaminated sites. Boreholes drilled for hydrogeological survey should serve multiple purposes: contributing to exploration in prospective sites of monitoring wells and later functioning as pollution monitoring wells. The large-scale groundwater flow direction in an area can be found through consultation with local relevant units, such as departments responsible for water resources and environmental protection or geological survey agencies. Further, the groundwater flow direction specific to investigation objects can be clarified through geological exploration. Appropriate and effective techniques should be selected for hydrogeological survey according to actual site conditions and existing working conditions.

2.2.4

Monitoring Well Deployment

(1) Principles For groundwater contamination sites, groundwater monitoring wells are deployed according to the following principles: • Deploying at least six wells for MSWLFs, including one for groundwater background monitoring and five for the spread of contamination monitoring; deploying at least five wells for HWLFs, and at least five for comprehensive waste disposal sites which should meet the requirements of the Pollution Control Standards for Hazardous Waste Landfills (GB18598–2001); for gas station (oil depot) contaminated sites, deploying two to three wells for pore water monitoring, at least two wells for karst water monitoring and five to six wells for fissure water monitoring, with focus on the upper bed of light non-aqueous phase liquid (LNAPL)-contaminated aquifer and on the lower bed of dense non-aqueous phase liquid (DNAPL)-contaminated aquifer.

18

2 Environmental Background Investigation of Groundwater …

• Giving full consideration to representative monitoring wells and scientific well deployment, and making full use of existing monitoring wells. If the quantity and quality requirements cannot be met, additional monitoring wells need to be deployed; • Making prospecting sites denser in areas prone to leakage and pollution diffusion as the liners of landfills are met or folded; • Extending or reducing the distance between monitoring sites and landfills according to factors such as the natural environment, topographical features and hydrogeological characteristics of the site; • Where there are springs near the sites, using upstream springs for monitoring site background and downstream springs for monitoring pollution diffusion; • Deploying monitoring wells based on existing monitoring network and historical monitoring of groundwater quality (or based on groundwater vulnerability assessment) in the sites; • Setting groundwater monitoring sites in the karst area along the groundwater channel that is closely related to landfills. (2) Deployment method (a) Standard MSWLFs • Pore water in plains and gentle plateaus – One of landfill boundaries is perpendicular to or forms a minimum angle of less than 10° with the direction of groundwater flow. A site background monitoring well is laid in the upstream, 30–50 m from the landfill; Among the five pollution diffusion monitoring wells, one is installed 30–50 m from landfill boundary on each of the two sides, in the direction perpendicular to groundwater flow. In the downstream, two are installed 30 m from the lower landfill boundary and 30–50 m from each other, and one 50 m from the lower landfill boundary, as shown in Fig. 2.3. – One of landfill boundaries forms a minimum angle of greater than 10° but less than or equal to 45° with the direction of groundwater flow. A site background monitoring well is laid in the upstream, 30–50 m from the upper vertex boundary of the landfill. Five to six pollution diffusion monitoring wells are installed with an equidistant spacing of 30–50 m in the downstream, 30–50 m away from and perpendicular to landfill boundaries, and one set in the downstream, 80 m from the lower vertex boundary of the landfill, as shown in Fig. 2.4. • Karst water and fissure water in mountainous and hilly areas A site background monitoring well is set in the upstream, 30–50 m from the landfill boundary. Upstream springs with close hydraulic relation to the site, if any, can be used for monitoring site background;

2.2 Content of Investigation

Fig. 2.3 Schematic diagram of monitoring well layout in a standard MSWLF site

Fig. 2.4 Schematic diagram of monitoring well layout in a standard MSWLF site

19

20

2 Environmental Background Investigation of Groundwater …

Five to six pollution diffusion monitoring wells are deployed in the T shape (Fig. 2.5) or in the + shape (Fig. 2.6). Linear-shaped monitoring wells are equally spaced (50–80 m) in the mountainous areas in the direction of groundwater flow. Downstream springs, if any, can be used for monitoring pollution diffusion. (b) Non-standard MSWLFs • Pore water in plains and gentle plateaus A site background monitoring well is set in the upstream, 30–50 m from the landfill; Among the six pollution diffusion monitoring wells, one is installed 30–50 m from landfill boundary on each of the two sides, in the direction perpendicular to groundwater flow. Four are installed in the downstream, in a diamond shape with a diagonal length of 50–100 m in the direction perpendicular to groundwater flow, including one 5–10 m away, one 30–50 m away for landfills with an age of less than 10a, and one 50–80 m away for landfills with an age of more than 10a, as shown in Fig. 2.7.

Fig. 2.5 Schematic diagram of the T-shaped layout in a standard MSWLF site

2.2 Content of Investigation

Fig. 2.6 Schematic diagram of the +-shaped layout in a standard MSWLF site

Fig. 2.7 Schematic diagram of monitoring well layout in a non-standard MSWLF site

21

2 Environmental Background Investigation of Groundwater …

22

• Karst water and fissure water in mountainous and hilly areas The method for such deployment in a standard MSWLF site can be referred to. (c) HWLFs • General landfill sites – Pore water in plains and gentle plateaus Where one of landfill boundaries is perpendicular to or forms a minimum angle of less than 10° with the direction of groundwater flow, a site background monitoring well is laid in the upstream, 30–50 m from the landfill. As to pollution diffusion monitoring wells, one is installed 30–50 m from the landfill in the direction perpendicular to groundwater flow, two installed in the downstream, 30–50 m from the landfill and 80–120 m from each other, and one installed in the downstream, 80– 120 m from the landfill, as shown in Fig. 2.8. Where one of landfill boundaries forms a minimum angle of greater than 10° but less than or equal to 45° with the direction of groundwater flow, a site background monitoring well is laid in the upstream, 30–50 m from the upper vertex boundary of the landfill. As to pollution diffusion monitoring wells, three are installed 30–50 m from and parallel to landfill boundaries, and one installed in the downstream, 80–120 m from the lower vertex boundary of the landfill, as shown in Fig. 2.9.

Fig. 2.8 Schematic diagram of monitoring well layout in a non-standard HWLF site

2.2 Content of Investigation

23

Fig. 2.9 Schematic diagram of monitoring well layout in a non-standard HWLF site

– Karst water and fissure water in mountainous and hilly areas A site background monitoring well is set in the upstream, 30–50 m from the landfill boundary. Upstream springs with close hydraulic relation to the site, if any, can be used for monitoring site background; Four to five pollution diffusion monitoring wells are deployed in linear, T, triangle or quadrilateral shapes. Linear-shaped monitoring wells are equally spaced (less than 30 m) in the mountainous areas in the direction of groundwater flow. Triangle or quadrilateral shaped monitoring wells are symmetrically distributed along the direction of groundwater flow. Downstream springs, if any, can be used for monitoring pollution diffusion. The commonly used methods for such deployment are as illustrated in Figs. 2.10 and 2.11. • Comprehensive disposal sites A site background monitoring well is installed in the upstream of the site according to the direction of groundwater flow. A pollution diffusion monitoring well is installed in the downstream of each disposal unit. A pollution diffusion monitoring well is laid in the downstream of the site, and where the landfill is located downstream of the site, the well can serve for both the landfill and the disposal site.

24

Fig. 2.10 Scenario 1

Fig. 2.11 Scenario 2

2 Environmental Background Investigation of Groundwater …

2.2 Content of Investigation

25

(d) OCS • Pore water Where the direction of groundwater flow is known, a site background monitoring well is laid 30–50 m away in the upstream; and pollution diffusion monitoring well (s) are installed 5–30 m away from the buried oil tank in the downstream; Where the direction of groundwater flow is not unknown, a site background monitoring wells is laid 30–50 m away in the upstream; at least two pollution diffusion monitoring wells are installed 5–30 m away from the buried oil tank in the downstream. The three monitoring wells present triangular distribution with the largest possible spacing. • Karst water In principle, at least two monitoring wells are installed on the main channel in the karst water investigation area. According to the distribution and flow direction of the underground river, two monitoring wells are laid on the upper and lower reaches, which are used for monitoring site background and pollution respectively. Where there is well-developed karst and complex underground rivers, one or two monitoring wells can be added, depending on the site circumstances. Two are added if the primary tributary is more than 2 km long, and one added if the primary tributary is less than 2 km long. The deployment method for fissure water investigation can be referred to. • Fissure water Two monitoring wells are placed in the fissure water background area, and three to four monitoring wells in the pollution diffusion area. (3) Quality control of monitoring well construction (a) Depth of monitoring wells Where municipal solid waste (MSW) and hazardous waste are landfilled above the water level of the shallow aquifer, monitoring wells should be installed in the shallow aquifer. Where municipal solid waste and hazardous waste are landfilled below water level of the shallow aquifer, the bottom of monitoring wells should be 3–5 m lower than the waste. As the characteristic pollutants in a gas station site are largely light non-aqueous phase liquids (LNAPLs), groundwater samples should be taken as close as possible to the upper aquifer, and preferably within 1 m from groundwater table. The depth of monitoring wells should be determined according to monitoring purpose and aquifer type, depth and thickness. Preferably, monitoring wells are located 2 m below the known maximum groundwater depth. (b) Waterstop selection Waterstops are especially important to the construction of monitoring wells, so that monitoring wells can take water from the target aquifer section while avoiding

2 Environmental Background Investigation of Groundwater …

26

cross-contamination between aquifers. Waterstops are generally made of high-quality ball clay, such as bentonite. The single aquiclude should be no less than 5 m thick, with the filled ball clay 2–3 m vertically higher than the top plate of aquiclude. Pressurized water monitoring wells shall be layered to stop water, and phreatic water monitoring wells shall not penetrate the bottom plate of aquiclude under the unconfined aquifer. (c) Post-construction cleaning Monitoring wells should be cleaned one week after constructed. The methods can be determined according to wellbore structure, well pipe materials and aquifer types, and it is advisable to apply a combination of methods to the same well. Well cleaning should follow the Technical Specifications for Water Supply Pipelines and Wells (GB50296–1999). For areas with low background value of sand content, well cleaning can be ended if groundwater effluent is visually clear. For areas with high background value of sand content, well cleaning is deemed completed if the error is less than 10% for three consecutive measurement of water parameters, such as potential of hydrogen (pH), temperature, dissolved oxygen, conductivity and turbidity. (d) Information records Detailed records specific to monitoring wells should be kept, including the location, structure, orientation relationship with the site, and especially waterstops.

2.2.5

Sampling

(1) Frequency Monitoring wells take groundwater samples once every quarter or four times a year; Original landfill leachate is sampled once every quarter or four times a year, in order to synchronize the monitoring of landfill leachate and groundwater. (2) Quality control (a) Preparation before sampling The containers used for sampling should be carefully cleaned before use. For specific requirements and methods, please refer to the Technical Guidelines for Environmental Monitoring in Groundwater Investigation. Generally, the water pumped for cleaning wells is no less than 3 to 5 times the well volume or 30 min. The specific pumping volume or duration depends on the actual circumstances, such as cleaning equipment, well specifications, test items and samples. The well cleaning does not complete until water-related parameters (pH, conductivity, water temperature, dissolved oxygen, oxidation reduction potential (ORP), and etc.) are stabilized.

2.2 Content of Investigation

27

(b) Sample collection Typically, transient water samples are collected for groundwater investigation. For monitoring wells in the same site, sampling should be conducted in a relatively concentrated and small period of time which should be limited to three days. Negative pressure pumps should not be used during groundwater sampling, in order to avoid degassing of dissolved gases and loss of volatile organic compounds (VOCs) to be tested. Samples should be taken as close as possible to wellbores, with no or little contact with the atmosphere to avoid sample contamination, volatile loss and morphological transformation. The specific place that water samples are taken is determined by test items. For example, water samples for DNAPL measurement should be taken from the lower bed of aquifer or the upper bed of aquiclude, and those for LNAPL measurement taken from the upper bed of aquifer. Water samples for the measurement of VOCs and semi-volatile organic compounds (SVOCs) must fill the sample containers with no gap in the upper part. Water samples for the determination of sulfides, oil, heavy metals, bacteria, radioactivity and etc. should be collected separately. Quality control of samples is required for each batch of water samples, including but not limited to field duplicates and field blanks. Field duplicates should be no less than 10% of the total samples and generally divided into at least two groups in each batch. They should be randomly inserted into the entire batch rather than continuously aligned. There are at least three field blanks in each batch of water samples. (3) On-site measurement All items are measured on site if possible, including water level, temperature, pH, conductivity, turbidity, chromaticity, flavor level, macroscopic objects, dissolved oxygen, ORP and etc. Instrument must be calibrated before used for on-site measurement, and the measurement results truthfully reflected in the relevant forms. (4) Sample storage Sample containers should meet different material requirements, depending on test items. For example, sodium ion samples should be stored in tetrafluoroethylene (C2F4) containers, and organic samples should be stored in glass containers. Containers need to be cleaned before use. After collected, samples should be transported in refrigerated storage tanks and delivered to the testing laboratory as soon as possible. Samples for different purposes are stored according to the corresponding conditions, and especially, organic samples must be stored exactly as required. Normally, VOC water samples should be stored in bottles upside down and away from light, at 4 °C within 7 days, and SVOC water samples stored away from light, at 4 °C within 15 days.

2 Environmental Background Investigation of Groundwater …

28

2.2.6

Analytical Testing

Table 2.2 shows groundwater monitoring indicator system for MSWLFs. For natural background ions and conventional indicators, all samples taken from groundwater monitoring wells should be analyzed. For characteristic indicators, analysis should be conducted to all site background monitoring wells and the pollution diffusion monitoring well nearest to the landfill. Based on test reports, the detected indicators are classified as the characteristic pollution indicators of such landfills, and then samples of other groundwater monitoring wells are tested and analyzed. For indicator-specific analysis methods, please refer to groundwater sampling, analysis, and quality control groups. The mandatory indicators for groundwater environmental investigation into HWLFs are as shown in Table 2.3. The optional indicators which can be found in the List of National Hazardous Waste are screened according to the characteristic pollutants of each waste disposal unit. The monitoring indicator system for groundwater environmental investigation into OCS is as shown in Table 2.4. The optional indicators can be found in the Guidelines for Groundwater Environmental Assessment (Trial).

Table 2.2 Groundwater monitoring indicator system for typical MSWLFs Type

Name

Natural background ions Conventional indicators

Potassium, calcium, sodium, magnesium, sulfate, chloride, carbonate, bicarbonate

Characteristic indicators

pH, dissolved oxygen, ORP, conductivity, chromaticity, flavor level, turbidity, macroscopic objects, total hardness, total dissolved solids (TDS), iron, manganese, copper, zinc, volatile phenol, total phosphorus, total organic carbon (TOC), anionic synthetic detergents, permanganate index, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, fluoride, cyanide, mercury, arsenic, selenium, cadmium, hexavalent chromium, lead, total coliforms Nickel, bismuth, molybdenum, bromide, iodide, sulfide, dichloroethylene, benzene, toluene, ethylbenzene, trichloroethylene, tetrachloroethylene, chloroform, trichloroethane, xylene, styrene, (total) chlorobiphenyl, dimethyl phthalate (DMP), hexachlorocyclohexane (HCH), dichloro-diphenyl-trichloroethane (DDT), methyl parathion, benzo(a)pyrene (BaP), naphthalene, chlorobenzene, tribromomethane, dichloropropane, dichloromethane, vinyl chloride, carbon tetrachloride, fluoranthene, fluorene, benzo(b) fluoranthene (BbF), dinitrotoluene, chlorophenol, gross alpha radioactivity, gross beta radioactivity

Quantity 8

31

36

2.2 Content of Investigation

29

Table 2.3 Mandatory indicators for groundwater investigation into typical HWLFs Type

Name

Natural background ions (mandatory) Conventional indicators (mandatory)

Potassium, calcium, sodium, magnesium, sulfate, chloride, carbonate, bicarbonate pH, dissolved oxygen, ORP, conductivity, chromaticity, favor level, turbidity, macroscopic objects, total hardness, TDS, iron, manganese, volatile phenols, anionic synthetic detergents, permanganate index, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, fluoride, selenium, total coliforms Hexavalent chromium, zinc, copper, nickel, cadmium, lead, mercury, arsenic, cyanide

Quantity 8 21

Mandatory 9 characteristic indicators Note For indicator-specific analysis methods, please refer to groundwater sampling, analysis, and quality control groups

Table 2.4 Groundwater monitoring indicator system for typical OCS Type

Name

Quantity

Basic indicators (mandatory)

Potassium, calcium, sodium, magnesium, sulfate, chloride, carbonate, bicarbonate pH, dissolved oxygen, ORP, conductivity, chromaticity, flavor level, turbidity, macroscopic objects, total hardness, TDS, iron, manganese, copper, zinc, volatile phenols, anionic synthetic detergents, permanganate index, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, fluoride, cyanide, mercury, arsenic, selenium, cadmium, chromium (hexavalent), lead, total coliforms, HCH, DDT, molybdenum, cobalt, rhodium, ruthenium, nickel, gross alpha radioactivity, gross beta radioactivity, total bacteria Total nitrogen, total phosphorus, oil, sulfide, total lead, total chromium, total arsenic, total vanadium, total nickel, cyanide Naphthalene, volatile phenols, polycyclic aromatic hydrocarbons (PAHs), BaP, phenol, halogenated hydrocarbons Benzene, toluene, ethylbenzene, o-xylene, m-(p-xylene), 5-alkylbenzene Methyl tert-butyl ether (MTBE) TPH, C5-C9, C10-C4 Ethylene dibromide (EDB), 1,2-dichloroethane (DCA)

8

Mandatory characteristic indicators

Optional characteristic indicators

VOCs

Oil Leaded gasoline additives for shock absorber

49

6

6 1 3 2

2 Environmental Background Investigation of Groundwater …

30

2.2.7

Status Quo Evaluation

(1) Groundwater quality Based on collected data and survey results, groundwater quality is evaluated using the single factor standard index method and the comprehensive evaluation method proposed in the Quality Standards for Groundwater (GB/T14848–93). Groundwater quality assessment adopts the standard index method for individual factor evaluation. The standard index greater than 1 means that the water quality factor has exceeded the prescribed limit, and the larger the index value, the more the excess. For water quality factors whose evaluation criteria are fixed values, the equation for standard index calculation is written as follows: Pi ¼

Ci Csi

ð2:1Þ

Wherein Pi is the standard index of water quality factor i, dimensionless; Ci and Csi denote the monitored mass concentration and standard mass concentration of water quality factor i respectively, expressed as mg/L. For water quality factors (e.g. pH) whose evaluation criteria are value ranges, the equations for standard index calculation are written as follows: PpH ¼

7:0  pH 7:0  pHsd

pH  7:0

ð2:2Þ

PpH ¼

pH  7:0 pHsu  7:0

pH [ 7:0

ð2:3Þ

Wherein PpH is the standard index of pH, dimensionless; pH denotes the monitored pH value, and pHsu and pHsd represent the standard upper and lower limits respectively. (2) Groundwater contamination status Groundwater pollution is assessed using the single factor index method. According to the definition of groundwater contamination, groundwater is contaminated when a chemical component exceeds its natural background value. A higher excess indicates more serious contamination. Using the single factor index method proposed by China Geological Survey (2008), the degree of contamination of groundwater samples by specific component is evaluated, with the equation written as follows: I¼

Ci C0

ð2:4Þ

2.2 Content of Investigation

31

Wherein I is the pollution index of component i; Ci denotes the measured content of component i and C0 denotes the background value (control value) of component i or detection limit of the standard detection method. Where the background value (control value) is expressed by a content range, the equation is re-written as follows: I¼

jC  C m j Cmax  Cm

ð2:5Þ

Wherein Cm is the median of the background value (control value) range and Cmax is the maximum value; other symbols represent the same as above. I  1 means uncontaminated. I > 1 means contaminated, and the larger the I value, the heavier the contamination.

2.3

Brief Summary

This chapter describes in detail the methodology of basic environmental investigation into MSWLFs, HWLFs and OCS which are typical groundwater contamination sites. The investigation covers all HWLFs and key MSWLFs and OCS which are screened according to their types. The process and content of investigation vary widely among the three typical sites. The process of investigation into MSWLFs and HWLFs highlights monitoring well deployment and groundwater sampling and monitoring, while for OCS, the process is more complicated and encompasses the sampling and monitoring of groundwater, surface water and soil. The indicator system for analytical testing is also different, with more indicators for OCS and less for HWLFs. After a detailed investigation that makes clear the environmental status, pollution source intensity evaluation can be conducted for groundwater contaminations sites.

References CAI Wutian, ZHANG Min, LIU Xuesong, et al. On Procedure and Contents of Investigation and Risk Assessment with Regard to Site Soil and Groundwater Contamination[J]. Hydrogeology & Engineering Geology, 2011, 38(6): 125–134. XU Shihao, CHEN Jing. Study on Environmental Investigation & Assessment of an Organic Contaminated Sites and Remediation Design[J]. China Resources Comprehensive Utilization. 2017, 35(11): 13–17. Zhang Min, Cai Wutian. Introduction to the key ideas and methods of soil and groundwater surveys on contaminated sites—taking demonstration project surveys as an example [J]. Environmental Science and Management, 2011, 36(06): 31–35.

Chapter 3

Rating and Evaluation of Pollution Source Intensity for Typical Groundwater Contamination Sites

Abstract Pollution source intensity evaluation for typical groundwater contamination sites clarifies groundwater pollution load and lays the foundation for groundwater risk assessment. The variety of pollution sources leads to differences in the process of pollution and in the types, migration pathways and enrichment areas of pollutants. Therefore, it is necessary to systematically examine the whole process of groundwater contamination specific to source, pathway and receptor, and to develop a methodology for rating and evaluating pollution source intensity of major groundwater contamination sites, which takes into account pollution sources, vadose zone and aquifer characteristics.







Keywords Municipal solid waste landfill Hazardous waste landfill Oil-contaminated site Groundwater Pollution source Pollution source intensity




3.1







Indicators of Pollution Source Intensity Evaluation

Typical groundwater contamination sites include HWLFs, MSWLFs and OCS. They affect groundwater in different ways due to a variety of factors, such as pollutant types, leakage models, pollution pathways, emission outlets and periods, and emission source intensity (Ju et al. 2009). In order to evaluate pollution source intensity, appropriate indicators should be selected for different groundwater contamination sites based on systematic analysis of the characteristics of groundwater environmental pollution (Li et al. 2014; Xi 2016).

3.1.1

Characteristic Factors of MSWLFs Hazards

With consideration to population density, economic status and natural environment, data collection, field investigation, and on-site sampling and analysis are carried out to collect the basic information of landfills, covering characteristic pollutants, site © Springer Nature Singapore Pte Ltd. 2021 B. Xi et al., Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases, https://doi.org/10.1007/978-981-15-2845-3_3

33

34

3 Rating and Evaluation of Pollution Source Intensity …

evolution, hydrogeological conditions, existing monitoring wells (distribution, depth and etc.), regular monitoring and environmental management, as well as surrounding environment. For example, environmentally sensitive sites in the surrounding area are investigated to make clear their quantity, category, distribution, impact, protective measures, geographical location, scale, position relative to landfills, environmental functional area and surrounding land use (Hong et al. 2011; Wang and Ji 2010; Yang et al. 2010). The risk factors of uncontrolled landfills are preliminarily identified, including waste hazard, potential groundwater contamination and the impact on the surrounding environment. Each risk factor is carefully divided into multiple indicators that together form an environmental risk assessment indicator system for uncontrolled landfills (Liu 2013; Wang 2013). Risk assessment indicators for waste hazard are listed below: • Landfill volume: Total amount of waste landfilled (m3); • Landfill period: A longer period of landfill means that the stock waste is more stable and likely less harmful to the environment; • Landfill type: Toxic waste, MSW, MSW mixed with construction waste, rural solid waste, construction waste (in descending order of risk); • Organic content: 20% (in ascending order of risk); • Seepage control: Two composite anti-seepage layers, single composite anti-seepage layer, impervious clay, or natural-soil bottom layer (in ascending order of risk); • Leachate collection: Collection and treatment system, collection system only, or no collection system (in ascending order of risk).

3.1.2

Characteristic Factors of HWLFs Hazards

Through data collection, on-site interview and field investigation, it is found that typical HWLFs waste in various regions of China mainly come from the industrial sector and are dominated by hazardous wastes containing heavy metals. Typical hazardous wastes include fly ash, slag, and sludge containing heavy metals. Since heavy metals are highly stable and do not decompose under the action of microorganisms, hazardous waste containing typical heavy metals will pose persistent toxicity hazard. Moreover, the leachate generated under the external conditions such as rain or acid rain is also harmful by producing long-term environmental hazards. Leakage sources formed due to lack of landfill security techniques will cause new environmental pollution and human health risks. The leakage source intensity is closely related to factors such as the types and characteristics of hazardous wastes (Liu 2014; Xi 2012).

3.1 Indicators of Pollution Source Intensity Evaluation

35

(1) Types of pollutants Pollutants common in HWLFs include slag, fly ash, sludge, solidified fly ash, electroplating sludge, inorganic cyanide waste, non-ferrous metal waste, chromium-containing waste, zinc-containing waste, copper-containing waste, arsenic-containing waste, lead-containing waste, mercury-containing waste, strontium-containing waste, nickel-containing waste, cadmium-containing waste, fluoride, cyanide, paint waste, surface treatment waste, incineration residue, incineration fly ash, sewage treatment sludge, industrial water treatment sludge, solid waste from automotive industry, and cured dye block. They vary in characteristics and hazards, as well as in migration and transformation in groundwater. The results of investigation and analysis showed that the main pollutant types are slag and typically, fly ash (solidified fly ash) and sludge, and the dominant hazardous components are heavy metals. Before final safe landfill, hazardous waste must be pretreated and the products evaluated and proved to reach the acceptance criteria for typical hazardous wastes (Zhang 2014). (2) Components and contents The hazardous components of typical HWLFs leachate fail to meet the acceptance criteria. Regardless of the level of development in different regions, hazardous wastes have similar components of heavy metals. Among them, the hazardous components beyond the acceptance limits mainly include mercury, lead, zinc and chromium. In addition, the hazardous components of typical HWLFs leachate generally exceed the Grade III limits of groundwater quality standards (Liu 2017). (3) Landfill security techniques Techniques for the disposal of hazardous wastes are divided into pretreatment and final disposal. Pretreatment is to treat hazardous wastes by physical, chemical or biological methods before final disposal, so that their physical, chemical, biological and other characteristics are changed to achieve minimum toxicity, volume and landfill occupation (Geng 2017). In specific, the physical methods of pretreatment mainly include curing/ stabilization and phase separation, while oxidation reduction and acid-base neutralization are commonly used chemical methods. Chemical pretreatment changes the harmful components of waste through chemical reactions towards safety or transforms waste into a form suitable for further disposal. It is mainly applied to inorganic waste, such as acid, alkali, heavy metal waste liquid, cyanide waste liquid, cyanide and emulsified oil. Biological pretreatment means biodegradation-based decomposition of organic matter in hazardous waste, and mainly applies to organic waste or wastewater. The prevailing methods include anaerobic treatment, aerobic treatment and facultative anaerobic treatment, which can be achieved through activated sludge process, aeration pond, anaerobic digestion, composting treatment, biological filter, and stabilization pond. Safe landfills provide the final disposal of hazardous waste. During landfill operation, waste may physico-chemically react with rainwater or other substances

3 Rating and Evaluation of Pollution Source Intensity …

36

to produce leachate that discharges contaminants in the hazardous waste beyond landfills. If not well collected and treated, such leachate will contaminate groundwater sources (Sun 2012). Due to factors such as improper pretreatment measures, the leachate produced in China’s typical HWLFs, which contains hazardous components, undermines more seriously the groundwater safety and human health in the surrounding areas. (4) Leakage source intensity Field investigation, testing and sampling found a common risk of leakage in the impervious layer in China’s typical HWLFs. The leakage source intensity associated with leachate leakage seriously threatens the health of humans that rely on soil and groundwater resources. The consequent persistent environmental risks have attracted increasing attention of the state. The leakage source intensity involves the volume of leachate produced and the concentration of contaminants contained therein (Tang 2014). • Volume of leachate The amount of leachate produced is related to local hydrogeological conditions such as precipitation and water content of landfilled waste. Given such great uncertainties, it can be quantitatively described using the Monte Carlo method. • Concentration of contaminants contained The concentration of contaminants in the leachate refers to the concentration at which the leachate begins to form after the landfill is closed. It is related to the types and characteristics of landfilled hazardous waste, as well as precipitation, and can be calculated using the equation recommended in the EPACMTP model.

3.1.3

Characteristic Factors of OCS Hazards

Pollution in OCS sites is mainly caused by crude oil, residual oil, solvent oil, gasoline and diesel and dominated by benzene-related groundwater contamination (Zhu 2015; Yao et al. 2012). There are two ways of groundwater contamination in oilfield development: infiltration and penetration, of which the former is more common and dominant (Liu et al. 2010). The mud pit, oily sewage, oil sludge and casing oily sewage can all infiltrate into the unconfined aquifer through the vadose zone and lead to groundwater contamination (Tao et al. 2017). A thinner vadose zone has better water permeability and weaker pollution-proof capacity and more facilitates pollution in the unconfined aquifer, and vice versa. Penetration mainly occurs to the reinjection water returned outside casing during the oil recovery process and to the mud pit during the drilling process (Li et al. 2016). In the process of oil recovery, if there is an accident of water return, the oily sewage can directly enter the aquifer in the path of return under the effect of water head pressure difference, and then diffuse

3.1 Indicators of Pollution Source Intensity Evaluation

37

and migrate in the aquifer to contaminate groundwater. In the drilling process, the mud pit may cut the unconfined aquifer, typically in areas with shallow aquifers. In this case, without seepage control measures, leakage will be inevitable, and lead to groundwater contamination with the direct entry of pollutants into the aquifers (Xu and Chen 2017). Groundwater pollution sources include drilling wastewater, waste mud, oil sludge, oily sewage, and injection water (Zhang et al. 2010). Under normal circumstances, these sources do not have significant influence on groundwater as long as they are timely collected, prevented from seepage and landfilled. However, groundwater quality may be undermined in the event of overflow in the rainy season, collection failure and leakage. (1) Types of pollutants Pollutants mainly fall into two categories: VOCs and SVOCs. Among them, VOCs are mainly composed of olefins, alkanes and benzene, and SVOCs composed of PAHs. (2) Direction of groundwater flow fields Soil pollution in OCS sites is obviously characterized by blocks. It is prominent near oil tanks, oil reservoirs and oil drains, with high detection rate of organic pollutants. Groundwater contamination is not limited to blocks as flowing shallow groundwater in the whole oil processing and production area is subject to contiguous contamination. Therefore, the direction of groundwater flow fields is of great significance to the spread of contamination. (3) Soil lithology In the depth range of pollution, pollutants are more concentrated in cohesive soil than in non-cohesive soil; pollutant concentration is relatively high in groundwater fluctuation zone; and pollutants in dry sand layer mainly exist in the gas phase with high concentration. During the infiltration process, pollutants are redistributed under the influence of lithology and its characteristics (water content, organic matter content, and etc.). The organic matter content of clay stratum is higher than that of silt stratum because cohesive soil adsorbs greater organic pollutants than silt according to the theory of similar polarity. (4) Depth to water table According to the results of investigation and analysis, in most areas of contaminated sites, as the depth to water table increases, the concentrations of halogenated hydrocarbons, monocyclic aromatic hydrocarbons and chlorinated benzenes decrease while the dissolved oxygen concentration (DOC), ORP and pH show an upward trend. In other words, shallow groundwater has low DOC, ORP and pH, implying a high degree of contamination, and deep groundwater has high DOC, ORP and pH, implying a low level of contamination.

38

3.1.4

3 Rating and Evaluation of Pollution Source Intensity …

Characteristic Factors for Mitigation Performance of Vadose Zone in Contaminated Sites

Ground and shallow surface pollutants must first pass through the vadose zone to reach the groundwater. The vadose zone is an environmentally sensitive zone with complex lithology and structure, rich material composition, and three-phase (gas, liquid, solid) coexistence. It is closely related to the atmosphere, biosphere lithosphere and human sphere, and serves as an important natural shield against groundwater contamination through pollutant convection, dispersion, adsorption and degradation. Therefore, the mitigation performance of vadose zone is of high significance for the prevention and control of groundwater contamination (Xi 2016).

3.1.4.1

Screening Main Factors Based on Inherent Vulnerability

The DRASTIC method offers a classic model for evaluating groundwater vulnerability and has been widely used in groundwater vulnerability assessments around the world. Seven parameters are used in the DRASTIC model, including depth to water table (D), net recharge (R), aquifer media (A), soil media (S), topography (T), impact of vadose zone media (I), and hydraulic conductivity (C). They have different effects on the mitigation performance of vadose zone. Net recharge represents the total quantity of water that infiltrates and returns from irrigation into the aquifer, which is difficult to accurately quantify in practice. It may bring more pollutants into the ground, and meanwhile dilutes and reduces pollutant concentrations to a certain extent by increasing the amount of groundwater. The dual effects make the final R value controversial. Aquifer media refers to the media in which groundwater is stored in the aquifer, and can be ignored when screening the mitigation factor of vadose zone. Topography affects the possibility of pollutants entering the groundwater by affecting the infiltration of land surface precipitation, and it is negligible for site-scale pollution sources. Soil media denotes the uppermost portion of the vadose zone characterized by significant biological activity, and vadose zone denotes the zone from the water table to the bottom of soil biological activity layer. They are collectively referred to as impact of vadose zone media when the DRASTIC model is generalized. Hydraulic conductivity affects the velocity of pollutant migration after entering the aquifer, rather than the process of pollutant entry into the groundwater from land surface. Therefore, its influence can also be embodied in the impact of vadose zone media. In short, only D and I in the DRASTIC model are considered as the main factors of mitigation performance of vadose zone.

3.1 Indicators of Pollution Source Intensity Evaluation

3.1.4.2

39

Screening Main Control Factors Based on Specific Vulnerability

In view of the specific vulnerability of vadose zone, “maximum pollution thickness (M)” (Fig. 3.1) is introduced, which refers to the vertical distance from the location of discharge by pollution sources to the groundwater table. A larger M value means longer time that pollutants come into contact with soil media before entering the groundwater. It allows for more complete reactions (adsorption, degradation, and etc.), more significant attenuation, and better mitigation performance of vadose zone, and vice versa. The impact of vadose zone media on mitigation performance of vadose zone is mainly manifested in the thickness of media particles and the degree of fissure development. Finer media particles or less developed fissures denotes greater adsorption and slower pollutant transport, which allows for more complete various reactions of contaminants and better mitigation performance of vadose zone, and vice versa. In addition, the impact of vadose zone media is also closely related to the thickness of media. Thicker media implies better mitigation performance of vadose zone. Therefore, vadose zone media are divided by the diameter of particles into cohesive soil media and non-cohesive soil media. The thickness of cohesive soil layer (M1) and the thickness of non-cohesive soil layer (M2) are taken as the main factors of mitigation performance of vadose zone.

Fig. 3.1 Schematic diagram of maximum contamination thickness (M)

40

3 Rating and Evaluation of Pollution Source Intensity …

Hydraulic conductivity determines the velocity of water migration in the vadose zone. It is affected by the quantity and connectivity of pores generated by intergranular pores and fissures and interlaminar fractures of vadose zone media. The greater hydraulic conductivity, the worse mitigation performance of vadose zone. According to the type of vadose zone media, hydraulic conductivity can be divided into the permeability of cohesive soil layer (K1) and the permeability of non-cohesive soil layer (K2). Both K1 and K2 are used as the main factors of mitigation performance of vadose zone. In view of the different adsorption and degradability of vadose zone media for different pollutants, with reference to the consideration to chemical reactions of pollutants in the HYDRUS-1D model, the adsorption (Kd) and degradability (l) of rocks and soils are taken the main factors of mitigation performance of vadose zone. In short, the main factors of mitigation performance of vadose zone include maximum pollution thickness (M), thickness of cohesive soil layer (M1), thickness of non-cohesive soil layer (M2), permeability of cohesive soil layer (K1), permeability of non-cohesive soil layer (K2), adsorption of rocks and soils (Kd) and degradability of rocks and soils (l).

3.1.5

Indicator Library for Groundwater Pollution Source Intensity Rating and Evaluation

Based on the above analysis, the characteristic factors of groundwater pollution sources can be summarized as the forms of pollution sources, types of pollution sources, characteristic pollutant properties, location of discharge, pollution source intensity, pollution pathway, affected area, seepage control measures, and time of discharge. Depending on whether the groundwater has been contaminated, groundwater pollution sources are divided into potential sources and existing sources in the indicator system for groundwater pollution source intensity evaluation. The characteristic factors of the vadose zone include depth to water table, topography, impact of vadose zone media, thickness of rock-soil layer, permeability of rocks and soils, adsorption of rocks and soils, and degradability of rocks and soils. On this basis, an indicator library is constructed for the evaluation of groundwater pollution source intensity, as shown in Table 3.1.

3.2 Method of Groundwater Pollution Source Intensity Rating …

41

Table 3.1 Indicator library for groundwater pollution source intensity evaluation Indicators

Primary indicators

Secondary indicators

Characteristic indicators of pollution sources

Form of pollution sources Type of pollution sources Characteristic pollutant properties Location of discharge Pollution source intensity Pollution pathway

Point sources, line sources, area sources

Characteristic indicators of vadose zone

3.2

3.2.1

Affected area Seepage control measures Time of discharge Depth to water table Topography Impact of vadose zone media Thickness of rock-soil layer Permeability of rocks and soils Adsorption of rocks and soils Degradability of rocks and soils

Potential sources, existing sources Toxicity, migration, degradability, solubility Land surface, vadose zone, aquifer Amount of discharge, concentration of discharge Intermittent infiltration, continuous infiltration, overflow and runoff Pollution source area, evaluation area Seepage control, no seepage control Year Maximum pollution thickness Terrain slope Cohesive soils, non-cohesive soils Thickness of cohesive soil layer, thickness of non-cohesive soil layer Permeability coefficient of saturated soils, soil bulk density, water content Adsorption coefficient Reaction rate of pollutants

Method of Groundwater Pollution Source Intensity Rating and Evaluation for Typical Groundwater Pollution Studies Indicator System for Rating and Evaluation of Groundwater Pollution Source Intensity

The indicator system for rating and evaluation of groundwater pollution source intensity mainly considers the characteristics of pollution sources and the characteristics of vadose zone (Xi 2016). Based on preceding analysis, the characteristics of pollution sources are mainly reflected in the amount of discharge and mode of

3 Rating and Evaluation of Pollution Source Intensity …

42

Fig. 3.2 Indicator system for rating and evaluation of groundwater pollution source intensity

discharge, and the characteristics of vadose zone reflected in the mitigation performance and vulnerability (Li et al. 2014, 2015, 2015). The specific indicator system is as shown in Fig. 3.2. According to seepage control in potential and existing sources of pollution, the actual contaminated sites are classified into four categories: potential pollution sources with seepage control, potential pollution sources without seepage control, existing pollution sources with seepage control, and existing pollution sources without seepage control. On this basis, a hierarchical rating and evaluation system is constructed, and the specific evaluation process is as illustrated in Fig. 3.3.

3.2.2

Method for Hazard Rating and Evaluation of Pollution Sources

3.2.2.1

MSWLFs

(1) Indicator system A hazard rating and evaluation indicator system that considers the pollution source characteristics of MSWLFs is constructed, including landfill volume, landfill period, landfill type, leachate production, seepage control and leachate treatment, as shown in Fig. 3.4.

3.2 Method of Groundwater Pollution Source Intensity Rating …

Fig. 3.3 Flow chart for rating and evaluation of groundwater pollution source intensity

Fig. 3.4 Hazard rating and evaluation indicator system for MSWLFs

43

3 Rating and Evaluation of Pollution Source Intensity …

44

Table 3.2 Weights of MSWLFs hazard indicators Indicator

Y1

Y2

Y3

Y4

Y5

Y6

Weight

0.3130

0.2049

0.1707

0.1262

0.0993

0.0861

(2) Method The indicator weights and scores for hazard evaluation or environmental risk assessment of MSWLFs are determined using the analytic hierarchy process (AHP), literature reference and expert scoring method. (a) Indicator weights and scores The AHP method is applied to determine the weights of MSWLFs hazard indicators, which involves threes steps: to establish the hierarchical structure; to construct pairwise comparison matrixes; and to calculate the relative weight. The weights of MSWLFs hazard indicators are calculated, as shown in Table 3.2, and their scores are as shown in Table 3.3. (b) Rating and evaluation The hazard scoring equation for MSWLFs is established based on indicator weights and scores: S ¼ b1 Y1 þ b2 Y2 þ b3 Y3 þ b4 Y4 þ b5 Y5 þ b6 Y6

ð3:1Þ

Table 3.3 Scores of MSWLFs hazard indicators Landfill volume

Landfill period

Leachate production

Landfill type

Seepage control

Leachate treatment

Y1 (104 m3)

Y2 (a)

Y3 (104 m3/ a)

Y4

Y5

Y6

 50

10

10

10

Toxic substance

10

Natural soils

10

No collection system

10

40– 50

8

5–10

8

5–10

8

MSW

8

Clay seepage control

5

Only collection system

4

30– 40

6

10– 15

5

1–5

6

MSW and construction waste

6

Single-layer composite seepage control

3

Collection and processing system

1

20– 30

4

 15

1

0.5–l

4

Rural solid waste

4

Double-layer composite seepage control

1

 20

2

 0.5

2

Construction waste

2

3.2 Method of Groundwater Pollution Source Intensity Rating …

45

Wherein S stands for the landfill hazard score; bi and and Yi represent indicator-specific weight and score respectively. Based on the calculation results of Eq. (3.1), three grades are divided using the approach of non-equidistant value range (0-10). Hazard reaches Grade I when S < 4.0, Grade II when 4.0  S < 7.0 and Grade III when S  7.0. The greater the S value, the higher the hazard of groundwater pollution sources.

3.2.2.2

HWLFs

(1) Indicator system A hazard rating and evaluation indicator system that considers the pollution source characteristics of HWLFs is constructed, as shown in Fig. 3.5. It includes landfill volume, landfill period, leachate production, impervious materials and impervious layer thickness. (2) Method The indicator weights and scores for hazard evaluation or environmental risk assessment of HWLFs are determined using the AHP method, literature reference and expert scoring method. (a) Indicator weights and scores The AHP method is applied to determine the weights of MSWLF hazard indicators, which involves three steps: to establish the hierarchical structure; to construct pairwise comparison matrixes; and to calculate the relative weight. The weights of HWLF hazard indicators are calculated, as shown in Table 3.4, and their scores are as shown in Table 3.5. (b) Rating and evaluation The hazard scoring equation for HWLFs is established based on indicator weights and scores: W ¼ a1 X1 þ a2 X2 þ a3 X3 þ a4 X4 þ a5 X5

Fig. 3.5 Hazard rating and evaluation indicator system for HWLFs

ð3:2Þ

3 Rating and Evaluation of Pollution Source Intensity …

46

Table 3.4 Weights of HWLF hazard indicators Indicator

X1

X2

X3

X4

X5

X1

Weight

0.2549

0.2133

0.2049

0.1707

0.1562

0.2549

Table 3.5 Scores of HWLF hazard indicators Landfill volume

Landfill period

Leachate production

Impervious materials

Impervious layer thickness

X1 (104 m3)

X2 (a)

X3 (104 m3/ a)

X4

X5

 50

10

10

10

Natural material lining

8

HDPE film < 1.5 mm Natural material < 1 m

10

40– 50

8

5–10

8

5–10

8

Natural material lining and underlayer

6

1.5 mm < HDPE film < 2.0 mm 1 m < natural material < 5 m

5

30– 40

6

10– 15

5

1–5

6

Natural material lining + synthetic material lining

4

HDPE film > 2.0 mm Natural material > 5 m

1

20– 30

4

 15

1

0.5–l

4

 20

2

 0.5

2

Wherein W represents the HWLF hazard score; ai and and Xi represent indicator-specific weight and score respectively. Based on the calculation results of Eq. (3.2), three grades are divided using the approach of non-equidistant value range (0–10). Hazard reaches Grade I when W < 4.0, Grade II when 4.0  W < 7.0 and Grade III when W  7.0. The greater the W value, the higher the hazard of groundwater pollution sources.

OCS (1) Indicator system A hazard rating and evaluation indicator system that considers OCS pollution source characteristics is constructed, as shown in Fig. 3.6. It includes pollutant characteristics, discharge source intensity, location of discharge, mode of discharge, affected area, seepage control measures, and duration of existence. (2) Method The indicator weights and scores for hazard evaluation or environmental risk assessment of OCS are determined using the AHP method, literature reference and expert scoring method.

3.2 Method of Groundwater Pollution Source Intensity Rating …

47

Fig. 3.6 Hazard rating and evaluation indicator system for OCS

(a) Indicator weights and scores The AHP method is applied to determine the weights of OCS hazard indicators, which involves four steps: to establish the hierarchical structure; to construct pairwise comparison matrixes; and to calculate the relative weight. The weights of OCS hazard indicators are calculated, as shown in Table 3.6, and their scores are as shown in Table 3.7. (b) Rating and evaluation The OCS hazard scoring equation is established based on indicator weights and scores: P ¼ c1  Z1 þ c2  Z2 þ c3  Z3 þ c4  Z4 þ c5  Z5 þ c6  Z6 þ c7  Z7

ð3:3Þ

Wherein P represents the OCS hazard score; Ci and and Zi represent indicator-specific weight and score respectively. Based on the calculation results of Eq. (3.3), three grades are divided using the approach of non-equidistant value range (0–10). Hazard reaches Grade I when P < 4.0, Grade II when 4.0  P < 7.0 and Grade III when P  7.0. The greater the P value, the higher the hazard of groundwater pollution sources. (c) Comprehensive evaluation of pollution factors (Z1) In order to comprehensively evaluate the potential hazards of pollutants to the groundwater environment, the refined Nemerow’s pollution index is introduced to

Table 3.6 Weights of OCS hazard indicators Indicator

Z1

Z2

Z3

Z4

Z5

Z6

Z7

Weight

0.22

0.17

0.16

0.1

0.09

0.12

0.14

Aquifer

Land surface Vadose zone

 50 50–l00 100–500 500–1000 >1000

7.20

1 3 5 7 10

Z3 /

Z2 104 m3/a

2 4 6 8 10

Location of discharge

Discharge source intensity

Comprehensive evaluation of pollution factors Z1 /

Table 3.7 Scores of OCS hazard indicators

10

6 8

6 8 10

Intermittent infiltration Continuous infiltration Overflow and runoff

Z4 /

Mode of discharge

0.1–1% 1–10% 10–100%

 0.1%

Z5 / 2.5 5 7.5 10

Affected area

Exposed

Sealed Partially sealed

Z6 /

Seepage control measures

10

1 5

1 1–5 5–10 10–20 >20

Z7 a

1 3 5 7 10

/

Duration of existence

48 3 Rating and Evaluation of Pollution Source Intensity …

3.2 Method of Groundwater Pollution Source Intensity Rating …

49

carry out related research. The Nemerow’s pollution index is an environmental quality index used to calculate the hazard of various pollutants, which can better highlight the role of extreme values. • Traditional Nemerow’s integrated pollution index The equations for calculation are written as follows: Pi ¼

Ci C0ij

ð3:4Þ

Pn

Pi n rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P2iave þ P2imax ¼ 2

Piave ¼

Pint

ð3:5Þ

i¼1

ð3:6Þ

Wherein Pi is the Nemerow’s pollution index of pollutant i; Ci is the measured concentration of pollutant i, expressed by mg/L; C0ij is the limit of water quality standard j for pollutant i, expressed by mg/L; Piave is the average Nemerow’s pollution index of n kinds of pollutants; Pimax is the maximum Nemerow’s pollution index of n kinds of pollutants; Pcom is the Nemerow’s integrated pollution index under water quality standard j; n is the number of pollutants; j is the selected water quality standard (I–V). • Refined Nemerow’s integrated pollution index The Nemerow’s integrated pollution index is revised to differentiate pollution factors at the same level of quality by increasing the weighting factors in the calculation process. The refined method highlights the extreme values and reflects more scientifically the contribution of different pollutants to the groundwater environment. The specific steps are described as follows: First, the concentration and standard for pollutant i are compared based on the Quality Standards for Groundwater (GB/T14848–93), and then the score of pollutant i is determined according to Table 3.8. The characteristic properties of pollutants include concentration, toxicity, migration, degradation and etc. Based on identified priority groundwater pollutants, the refined Nemerow’s integrated pollution index introduces the weighted sequence of pollutants (li) in the calculation and replaces Liave (average score of n kinds of pollutants) with Lwei ave (weighted average score of n kinds of pollutants). Lwei ave is calculated using Eq. (3.7):

Table 3.8 Groundwater quality score

Level

I

II

III

IV

V

Li

0

1

3

6

10

3 Rating and Evaluation of Pollution Source Intensity …

50

Pn Lweiave ¼

i¼1 ðLi

 ai Þ

n

ð3:7Þ

Wherein Lwei ave is the weighted average score of n kinds of pollutants; ai is the weight of pollutant i; and li is the pollutant sequence by hazard to groundwater. The equation for ai calculation is written as follows: n=li ai ¼ Pn i¼1 n=li

i 2 ð1; 2; . . .; nÞ

ð3:8Þ

Wherein li is the order of priority pollutant i. The revised Nemerow’s integrated pollution index is calculated as shown in Eq. (3.9): Lint

rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi L2weiave þ L2imax ¼ Z1 ¼ 2

ð3:9Þ

Wherein Lint is the refined Nemerow’s integrated pollution index, i.e. the comprehensive evaluation index for priority pollutants Z1.

3.2.3

Method for Rating and Evaluation of Mitigation Performance of Vadose Zone

3.2.3.1

Lithology of Vadose Zone

Based on the observation of lithologic changes of the vadose zone in typical areas and the comprehensive analysis of hydrogeological profile data in different regions, the vadose zones of pore water, fissure water and karst water can be divided into eight specific types (monolithologic pore, bi-lithologic pore, multi-lithologic pore, weathering fissure, tectonic fissure, bare karst, covered karst, and karst-hole) and four broad types (monolithologic type, bi-lithologic type, multi-lithological type, and preferential migration passage). The classification is detailed below: (1) Pore water regions Based on the comprehensive analysis of hydrogeological profile data of different regions in China, the vadose zone in pore water regions is classified into three categories according to the permeability of rocks and soils: monolithologic, bi-lithologic and multi-lithological. (a) Monolithologic vadose zone The monolithologic vadose zone is composed of specific monolithologic porous medium where groundwater is stored, such as clay, silty clay, silt, silty sand, fine

3.2 Method of Groundwater Pollution Source Intensity Rating …

51

Fig. 3.7 Structure of monolithologic vadose zone

sand, medium sand, coarse sand, gravel (Fig. 3.7). The maximum and minimum hydraulic conductivity of such media can differ by eight orders of magnitude, and the change of hydraulic conductivity can reflect the lithologic change of monolithologic vadose zone. (b) Bi-lithologic vadose zone The bi-lithologic vadose zone consists of two layers of porous media with large permeability difference. The upper part is a low-permeability clay layer composed of clay, silty clay, silt and the like, or combinations thereof, while the lower part is a high-permeability sand layer (Fig. 3.8) composed of silt, fine sand, medium sand, coarse sand, pebbles, gravel and the like, and combinations thereof. Groundwater is stored in the aqueous medium at the bottom. The difference in the permeability of bi-lithologic vadose zone exceed two orders of magnitude.

Fig. 3.8 Structure of bi-lithologic vadose zone

52

3 Rating and Evaluation of Pollution Source Intensity …

Fig. 3.9 Structure of multi-lithologic vadose zone

(c) Multi-lithologic vadose zone The multi-lithologic vadose zone consists of at least two porous media with wide permeability differences that form three layers (e.g., silty clay layer, medium and fine sand layer, silty clay layer) or more (Fig. 3.9). Above the groundwater are complex layers of low-permeability clay and high-permeability sand. The permeability of multi-lithologic vadose zone differs by at least an order of magnitude. Transformation among the above-mentioned three types may take place along with the change of depth to water table. For example, when the groundwater table decreases or the aquifer is dried up, the monolithologic or bi-lithologic vadose zone may become multi-lithologic. (3) Fissure water regions (a) Weathering fissure type The vadose zone of weathering fissure type contains aqueous media and includes the upper strongly weathered zone and the lower weakly weathered zone where groundwater exists. In view of similar structure, the weathering fissure type can be generalized into bi-lithologic vadose zone, but the permeability ratio of strongly and weakly weathered zones is smaller than that of the upper and lower porous media in bi-lithologic vadose zone (Fig. 3.10). Fig. 3.10 Vadose zone structure—weathering fissure type

3.2 Method of Groundwater Pollution Source Intensity Rating …

53

Fig. 3.11 Vadose zone structure—tectonic fissure type

(b) Tectonic fissure type The tectonic fissure type is characterized by perpendicular tectonic fissures below land surface, which differ little in scale and maturity degree and have flat sections. Groundwater generally exists in the tectonic fissures connected the groundwater. In view of similar structure, the tectonic fissure type can be generalized into monolithologic vadose zone, but with stronger permeability, the value should be greater and the value range should be narrowed (Fig. 3.11). (4) Karst water regions (a) Bare karst type Under the dissolution effect, erosional fissures form below land surface in the vadose zone, but they vary in form and scale of sections. In the vadose zone of bare karst type, groundwater generally exists in erosional fissures connected to groundwater. In view of similar structure, the bare karst type can be generalized into monolithologic vadose zone, but with stronger permeability, the value should be greater and the value range should be narrowed (Fig. 3.12). (b) Covered karst type The covered karst type consists of low-permeablity clay layer at the top and high-permeability erosional fissure media at the bottom. Groundwater is stored in the erosional fissures. In view of similar structure, the covered karst type can be

Fig. 3.12 Vadose zone structure—bare karst type

54

3 Rating and Evaluation of Pollution Source Intensity …

Fig. 3.13 Vadose zone structure—covered karst type

generalized into monolithologic vadose zone, but the media in the lower erosional fissures has greater permeability, at least relative to sand and gravel (Fig. 3.13). (c) Karst-hole type The karst-hole type is characterized by large-scale erosional fissures which are perpendicular to vertical wells and formed by dissolution, erosion and collapse. Groundwater is freely recharged by surface water and stored in an underground river system. Therefore, the karst hole is a preferential migration passage (Fig. 3.14). Based on the above analysis, groundwater vadose zones can be divided into eight specific types (monolithologic pore, bi-lithologic pore, multi-lithologic pore, weathering fissure, tectonic fissure, bare karst, covered karst, and karst-hole) or broadly into four types (monolithologic type, bi-lithologic type, multi-lithological type, and preferential migration passage). For the evaluation of groundwater pollution source intensity, the proper understanding of vadose zone lithology and the reasonable generalization of vadose zone media is fundamental to identify the main factors of pollution mitigation of vadose zone.

Fig. 3.14 Vadose zone structure—karst-hole type

3.2 Method of Groundwater Pollution Source Intensity Rating …

3.2.3.2

55

Selection of Main Factors of Pollution Mitigation of Vadose Zone

(1) Selection basis The main processes that affect the migration and transformation of pollutants in the vadose zone include convection, dispersion, adsorption and degradation. The combined effects of these processes will ultimately affect the time taken for pollutants to reach groundwater and the concentration of pollutants in groundwater. Therefore, when selecting the main factors of pollution mitigation of vadose zone, priority is given to factors affecting the migration rate and concentration attenuation of pollutants. In addition, the main factors should be easy to obtain and quantifiable. Based on the above principles, the main factors are identified for four categories of vadose zone. (2) Main factors by vadose zone categories (a) Monolithologic type Four factors are selected, of which maximum pollution thickness, permeability of rocks and soils, and adsorption of rocks and soils measure the impact on the duration of pollutant migration, and degradability of rocks and soils measures the impact on pollutant concentrations. Maximum pollution thickness (M) defines the maximum distance that pollutants may migrate in the vadose zone (Fig. 3.15), which denotes the vertical distance from the location of discharge by pollution sources to the groundwater table. Where Fig. 3.15 Schematic diagram of maximum pollution thickness

56

3 Rating and Evaluation of Pollution Source Intensity …

the pollution sources sit on the ground, the maximum pollution thickness refers to the depth to water table. Where the pollution sources are located in the vadose zone below the ground, the maximum pollution thickness equals the thickness of vadose zone minus the buried depth of pollution sources. The permeability and adsorption of rocks and soils reflect the migration rate of pollutants in the vadose zone, which is closely related to the duration of pollutant existence in the groundwater. The permeability is described by the permeability coefficient (K) of rocks and soils, and the adsorption described by the distribution coefficient or adsorption coefficient (Kd) of pollutants in the media. The degradability of rocks and soils mainly reflects the ability of microorganisms to degrade pollutants in the vadose zone, so it is closely related to the composition of microorganisms in the vadose zone. The degradability is described by the rate of degradation (l). (b) Bi-lithologic type A total of six factors are considered, of which maximum pollution thickness, clay layer thickness, clay layer permeability, sand layer permeability and clay adsorption examine the impact on the duration of pollutant migration, and clay degradability examines the impact on pollutant concentrations. The maximum pollution thickness means the same as that for monolithologic vadose zone. The thickness, permeability and adsorption of clay layer reflect the dominant role of the clay layer in the vadose zone in blocking pollutant migration. The clay layer refers to a layer of such soils as clay, mucky clay, silty clay and silt, and the adsorption is described by the distribution coefficient (Kd) of pollutants in the media. The sand layer consists of silt, fine sand, medium sand, coarse sand, pebble and gravel. The sand layer thickness is not deemed a main factor for two reasons: the sand layer thickness can be calculated based on the maximum pollution thickness and clay layer thickness; and with high permeability, the sand layer hardly blocks pollutant migration. The sand layer permeability is described by the permeability coefficient (K). The degradability of rocks and soils is defined and described the same as that for monolithologic vadose zone. For the sake of conservatism, the degradation parameters of least-degradability layer should be adopted for the bi-lithologic vadose zone. (c) Multi-lithologic type Totally six factors are selected, of which maximum pollution thickness, clay layer thickness, equivalent permeability of clay layer, equivalent permeability of sand layer, and clay adsorption examine the impact on the duration of pollutant migration, and the degradability of rocks and soils examines the impact on pollutant concentrations. The clay layer in the multi-lithological vadose zone contains such soils as clay, mucky clay, silty clay and silt.

3.2 Method of Groundwater Pollution Source Intensity Rating …

57

The equivalent permeability of clay layer or sand layer in the multi-lithological vadose zone is calculated using the following equation: K¼

K1 M1 þ K2 M2 þ . . . þ Kn Mn M1 þ M2 þ . . . þ Mn

ð3:10Þ

Wherein K is the equivalent permeability coefficient of layer layer or sand layer (m/ d); K1, K2, …, Kn is the permeability coefficient of each clay layer or sand layer (m/d); M1, M2, …, Mn is the thickness of each clay layer or sand layer (m). The clay adsorption and the degradability of rocks and soils in the multi-lithologic vadose zone mean the same as that in the bi-lithologic vadose zone. (d) Preferential migration passage When the mitigation effect of the vadose zone is not considered, there are no mitigation factors for preferential migration passages. The intensity of groundwater pollution source is equal to the intensity of soil pollution sources. The main factors of pollution prevention for different types of vadose zone are summarized, as shown in Table 3.9.

3.2.3.3

Indicators and Scores for Mitigation Performance Evaluation of Vadose Zone

(1) Indicators and scores for pollution prevention of vadose zone For existing projects without seepage control measures, the pollution prevention of vadose zone is graded as “strong, moderate or weak” according to the single-layer thickness and permeability coefficient of vadose zone rocks (soils), as shown in Table 3.10. (2) Indicators and scores for vadose zone vulnerability Based on the main factors identified in Sect. 3.2.3.2, weights are assigned to the indicators for vadose zone vulnerability assessment, using the method of DRASTIC model 1–5 while reflecting differences in main factors between different types of vadose zone, as shown in Tables 3.11 and 3.12.

3.2.3.4

Rating and Evaluation of Mitigation Performance of Vadose Zone

The rating and evaluation of mitigation performance of vadose zone takes into account pollution prevention and vulnerability of vadose zone. The score for

3 Rating and Evaluation of Pollution Source Intensity …

58

Table 3.9 Main factors of pollution prevention by vadose zone types Groundwater types

Characteristics of overlying vadose zone

Types of vadose zone

Main factors of pollution prevention

Number of factors

Pore water

Monolithologic

Monolithologic

4

Bi-lithologic

Bi-lithologic

Multi-lithologic

Multi-lithologic

Weathering fissure Tectonic fissure

Bi-lithologic

Bare karst

Monolithologic

Covered karst

Bi-lithologic

Karst-hole

Preferential migration passage

Maximum pollution thickness, permeability of rocks and soils, adsorption of rocks and soils, degradability of rocks and soils Maximum pollution thickness, clay layer thickness, equivalent permeability of clay layer, permeability of sand layer, clay adsorption, degradability of rocks and soils Maximum pollution thickness, cumulative thickness of clay layer, equivalent permeability of clay layer, equivalent permeability of sand layer, clay adsorption, degradability of rocks and soils Maximum pollution thickness, permeability Maximum pollution thickness, permeability Maximum pollution thickness, permeability Maximum pollution thickness, permeability No, pollutants can directly enter the groundwater

Fissure water

Karst water

Monolithologic

6

6

2 2 2 2 0

pollution prevention (V) is integrated as a factor in the calculation, which is determined according to Table 3.10. In the case of weak pollution prevention, the comprehensive rating and evaluation of vadose zone will not be conducted. The mitigation index (DI′) of vadose zone is calculated using Eq. (3.10), and the DI′ value range depends on the number of main factors. When there are two main factors, the DI′ value ranges from 9 to 90. When there are four main factors, the DI′ value ranges from 14 to 140. When there are six main factors, the DI′ value ranges

3.2 Method of Groundwater Pollution Source Intensity Rating …

59

Table 3.10 Grades for pollution prevention performance of vadose zone Grade

Permeability of vadose zone rocks (soils)

Score

Strong

Thickness of single rock (soil) layer (Mb)  1.0 m, permeability coefficient (K)  10−7 cm/s, and continuous and stable distribution Thickness of single rock (soil) layer 0.5 m  Mb < 1.0 m, permeability coefficient (K)  10−7 cm/s, and continuous and stable distribution. Thickness of single rock (soil) layer (Mb)  1.0 m, permeability coefficient of 10−7 cm/s < K  10−4 cm/s, and continuous and stable distribution The rock (soil) layer does not satisfy the above-mentioned conditions for grades “strong” and ”moderate”

1

Moderate

Weak

0

Table 3.11 Weights for vadose zone vulnerability assessment indicators Groundwater types

Characteristics of overlying vadose zone

Types of vadose zone

Main factors and their weights

Pore water

Monolithologic

Monolithologic

Bi-lithologic

Bi-lithologic

Multi-lithologic

Multi-lithologic

Weathering fissure Tectonic fissure

Bi-lithologic Monolithologic

Bare karst

Monolithologic

Covered karst

Bi-lithologic

Karst-hole

Preferential migration passage

Maximum pollution thickness(5), permeability of rocks and soils(4), adsorption of rocks and soils(3), degradability of rocks and soils(2) Maximum pollution thickness(5), clay layer thickness(5), equivalent permeability of clay layer(4), permeability of sand layer(2), clay adsorption(3), degradability of rocks and soils(1) Maximum pollution thickness(5), cumulative thickness of clay layer (5), equivalent permeability of clay layer(4), equivalent permeability of sand layer(2), clay adsorption(3), degradability of rocks and soils(1) Maximum pollution thickness(5), permeability(4) Maximum pollution thickness(5), permeability(4) Maximum pollution thickness(5), permeability(4) Maximum pollution thickness(5), permeability(4) Pollution prevention of the vadose zone not considered

Fissure water

Karst water

M1 (m)

 54 1.6–3.3 3.3–5.0 5.0–7.8 7.8–13.5 10.7–13.5 13.5–14.5 14.5–15.5 15.5–16.5 >16.5

M (m)

0 1.5–4.6 4.6–6.8 6.8–9.1 9.1–12.1 12.1–15.2 15.2–22.9 22.9–26.7 26.7–30.5 >30.5

Indicator

10 9 8 7 6 5 4 3 2 1

>2.2  10−1 2.0  10−1 to 1.8  10−1 to 6.0  10−2 to 2.4  10−2 to 6.0  10−3 to 1.2  10−3 to 6.0  10−4 to 6.0  10−5 to 1.2  10−6 to

10−7 10−7 10−7 10−7 10−7 10−7 10−7 10−7 10−7

9  10−7 to 12 8  10−7 to 9 7  10−7 to 8 6  10−7 to 7 5  10−7 to 6 4  10−7 to 5 3  10−7 to 4 2  10−7 to 3 1  10−7 to 2 9

Kd (g/cm3)

 0.001 0.001–0.002 0.002–0.003 0.003–0.004 0.004–0.005 0.005–0.006 0.006–0.007 0.007–0.008 0.008–0.009 >0.009

l (1/d)

60 3 Rating and Evaluation of Pollution Source Intensity …

3.2 Method of Groundwater Pollution Source Intensity Rating …

61

from 20 to 200. The deterrent performance of vadose zone can be divided into three grades. The deterrent performance reaches Grade I When DI′ is less than 30% of the maximum value, Grade II when DI′ is greater than or equal to 30% of the maximum value and less than 70% of the maximum value, Grade III when DI′ is greater than or equal to 70% of the maximum value. DI 0 ¼ V  ðx1  M þ x2  M1 þ x3  K1 þ x4  K2 þ x5  Kd þ x6  lÞ ð3:11Þ Wherein V, M, M1, K1, K2, Kd and l are the scores of each factor. A greater DI′ value means worse pollution prevention, higher vulnerability and higher grade of the vadose zone.

3.2.4

Rating and Evaluation of Groundwater Pollution Source Intensity

The evaluation of groundwater pollution source intensity needs to comprehensively consider the characteristics of both pollution sources and vadose zones. Matrixes are built to reflect, in a concise and intuitive way, the coupling effects of these characteristics on groundwater pollution source intensity, with results as shown in Table 3.13. Higher grade denotes higher groundwater pollution source intensity. Higher grade implies greater impact of pollution sources on groundwater. Therefore, Grade III contaminated sites are classified for priority pollution control (hereinafter referred to as “priority sites”), Grade II contaminated sites for regular pollution control (hereinafter referred to as “regular sites”), and Grade I contaminated sites for general pollution control (hereinafter referred to as “general sites”).

Table 3.13 Groundwater pollution source intensity rating Grade of groundwater pollution source intensity

Grade of mitigation performance of vadose zone

I II III

Grade of pollution source hazard I II I I I II II III

III II III III

62

3.3

3 Rating and Evaluation of Pollution Source Intensity …

Strategies for Groundwater Pollution Prevention and Control

Groundwater pollution, concealed and complex as it is, can cause environmental and ecological damages that are hardly reversible. Groundwater pollution prevention and control should place more emphasis on prevention than control, and pay attention to protecting from pollution sources and blocking pollution processes (Lu et al. 2012). Using the dual interface method, groundwater pollution processes are identified and analyzed, and based on the results of groundwater pollution source intensity evaluation, targeted strategies are developed to prevent and control pollution from potential and existing sources respectively (Fig. 3.16). The strategies will identify the level of seepage control in potential sources of pollution, and provide programs for classification and combination of prevention and control techniques applicable to existing sources of pollution (Li et al. 2016).

3.3.1

Potential Sources of Pollution

The prevention and control of pollution from potential sources should place emphasis on source prevention, which mainly involves the protection from pollution sources and the determination of site seepage prevention levels (Yang et al.

Fig. 3.16 Schematic diagram of classified strategies for groundwater pollution prevention and control based on pollution source intensity evaluation

3.3 Strategies for Groundwater Pollution Prevention and Control

63

Table 3.14 Seepage prevention levels of potential pollution sources Type of contaminated sites

Requirements for seepage prevention

General sites

The permeability coefficient of the anti-seepage layer should not exceed 1.0 * 10−7 cm/s The performance in seepage prevention should be equivalent to that of 1.5 m thick clay layer (permeability coefficient 1.0 * 10−7 cm/s) The performance in seepage prevention should be equivalent to that of 6.0 m thick clay layer (permeability coefficient 1.0 * 10−7 cm/s)

Regular sites Priority sites

2014). Where groundwater pollution sources cannot be removed, based on the results of pollution source intensity evaluation, prevention and control grades are determined according to the relevant requirements for seepage prevention (Table 3.14).

3.3.2

Existing Sources of Pollution

The prevention and control of pollution from existing sources should take into account source reduction and process control, including the removal of pollution sources, the reduction of pollution source intensity and the blockage of pollution processes. Based on the results of pollution source intensity evaluation, appropriate prevention and control strategies are developed according to the grades of pollution sources. (1) For priority sites, priority is given to the removal of pollution sources. It is necessary to make clear the way, scope and direction that the removable sources of pollution are removed. Where the sources of pollution are not removable, the pollution source intensity should be reduced and stricter requirements set for seepage control and duration of such sources. Measures should also be taken to remedy contaminated soil and groundwater, so that the absolute concentrations of priority pollutants in the environment can be quickly and efficiently reduced to levels below the limits. The options include removing priority pollutants from the contaminated soil, removing excess pollutants for off-site disposal, and combining pollution source control techniques with remediation techniques. (2) For regular sites, priority is given to the protection from pollution sources and the reduction of pollution source intensity. While strengthening the protection from pollution sources, it is necessary to reduce pollution source intensity by imposing stricter requirements for seepage control and duration of such sources. Measures should also be taken to remedy contaminated soil and groundwater, so as to quickly and efficiently reduce the absolute concentrations of priority

3 Rating and Evaluation of Pollution Source Intensity …

64

pollutants in the environment levels below the limits. For example, the contaminated soil can be solidified and stabilized to block the migration pathway of heavy metals and limit the leaching concentration below the environmental quality standards for groundwater. Bioremediation of contaminated soil or groundwater can be applied to control and reduce the concentration of organic matters in the environment, and natural attenuation can be used to monitor the removal of organic matter. (3) For general sites, priority is given to the monitoring of pollution sources. The pollution source monitoring system and groundwater quality monitoring and early warning system should be put in place to accurately grasp the groundwater quality trends. The risk level is adjusted according to the situation, and measures are taken in a timely manner to eliminate or reduce the risk of pollution.

3.4

Brief Summary

This chapter describes the methods for rating and evaluating the pollution source intensity of three typical groundwater contamination sites: HWLFs, MSWLFs, and OCS. According to the evaluation results, the contaminated sites are classified into three categories: priority sites, regular sites and general sites for pollution prevention and control. Further, a process-wide management strategy is proposed, including source prevention/reduction, process control, and comprehensive management. As there are differences in the processes of pollution and in the types, migration pathways and enrichment areas of pollutants from different sources, the indicator system and indicator weights for pollution source intensity evaluation vary to some extent. Based on pollution source intensity evaluation, human health risks and groundwater pollution risks associated with these sources can be assessed.

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Li J, Yang Y, Huan H, et al. Method for screening prevention and control measures and technologies based on groundwater pollution intensity assessment[J]. Science of the Total Environment, 2016, 551–552:143–154. LI Juan, YANG Yang, YANG Yu, et al. Application of Grey Relational Analysis Method to the Quantitative Assessment of the Intensity of the Polluted Groundwater Resource[J]. Journal of Safety and Environment, 2015(4): 342–348. LI Menglong, DONG Weihong, BAO Lixin, et al. Health Risk Assessment of Typical Petroleum Contaminated Groundwater and Soil in Northeast China[J]. China Rural Water and Hydropower, 2016(7): 67–71. LIU Zengchao. Research for Groundwater Contamination Risk Assessment Methodology of Uncontrolled Landfill Site[D]. Jilin University, 2013. LIU Fang. Treatment of Leachate from Landfills for Hazardous Waste[J]. Guangdong Chemical Industry, 2017, 44(19): 124–124. LIU Xiaomin. Effect of Hazardous Waste Landfill Site Leachate on Groundwater Environment[J]. Environmental Engineering, 2014, 32(12): 5–9. LIU Xuesong, CAI Wutian, LI Shengtao. Survey of Soil and Groundwater Contamination in Oil Pollution Site[J]. Hydrogeology & Engineering Geology, 2010, 37(4): 121–125. LU Yan, HE Jiangtao, WANG Junjie, et al. Groundwater Pollution Sources Identification and Grading in Beijing Plain[J]. Chinese Journal of Environmental Science, 2012, 33(5): 1526– 1531. SUN Jiao. Study on Stability of Hazardous Waste Landfill[D]. Chongqing Jiaotong University, 2012. TANG Wei. Study on the Leakage Source Strength of Typical Hazardous Waste Landfill and Its Assessment on the Environmental Risk[D]. Hefei University of Technology, 2014. TAO Xinhai, RUAN Wei, ZHANG Yanhua. Study on Monitoring System of Groundwater Contamination in an Oil Refinery[J]. China Chemical Trade, 2017, 9(16). WANG Shuyang. Study on Health Risk Assessment Method of Groundwater Pollution in Landfill Site[D]. Liaoning Technical University, 2013. WANG Jianfei, JI Hua. Study on Risk Assessment and Ranking Method of Groundwater Pollution in Informal Landfills[J]. Geotechnical Investigation & Surveying, 2010(S1): 791–796. XI Beidou. Risk Assessment and Risk Ranking Management Technology of Groundwater Contamination in Hazardous Waste Landfill[M]. China Environmental Science Press, 2012. XI Beidou. Study on Groundwater Pollution Source Intensity Evaluation, Classification and Prevention and Control Technology[M]. China Environmental Science Press, 2016. XU Shihao, CHEN Jing. Study on Environmental Investigation & Assessment of an Organic Contaminated Sites and Remediation Design[J]. China Resources Comprehensive Utilization. 2017, 35(11): 13–17. YANG Yang, LI Juan, LI Mingxiao, et al. Application of HYDRUS-1D Model in Quantitative Assessment of Groundwater Pollution Resource Intensity[J]. Chinese Journal of Environmental Engineering. 2014, 8(12): 5293–5298. YANG Yu, JIANG Yonghai, XI Beidou, HE Xiaosong, AN Da, ZHANG Jinbao. Study on the Risk Classification Methodology of Groundwater Pollution near Landfill Sites[J]. Ecology and Environment, 2010, 19(07): 1704–1709. YAO Honghua, ZHENG Libo, ZHANG Dazheng. Pollution Characteristics of Groundwater from Petrochemical Enterprise in Coastal Area of Zhejiang Province[J]. Environmental Science and Management, 2012, 37(3): 39–45. ZHANG Jiashuang, YANG Yuesuo, DU Xinqiang, et al. Health Risk Assessment of Groundwater Pollution in the Petroleum Contaminated Sites[J]. Journal of Anhui Agricultural Sciences, 2010, 38(36): 391–394. ZHANG Xuguang. Analysis of Hazardous Solid Waste Treatment and Disposal Status in China[J]. Journal of Green Science and Technology, 2014(12): 190–193. ZHU Zhenhui. Study on Organic Pollution Characteristics of Soil and Groundwater in Crude Oil Exploitation Site[D]. Shandong University of Science and Technology, 2015.

Chapter 4

Risk Assessment of Groundwater Contamination Sites

Abstract The risk assessment of groundwater contamination sites addresses key issues such as the necessity and the target value of remediation. Based on basic site environmental investigation and pollution source intensity evaluation, human health risks and eco-environmental risks should be assessed to identify the risk of groundwater contamination sites, paving the foundation for site risk management. The risk assessment of groundwater contamination sites encompasses health risk assessment and groundwater pollution risk assessment, which targets human health and groundwater quality respectively.







Keywords Municipal solid waste landfill Hazardous waste landfill Oil-contaminated site Groundwater Pollution source Pollution risk assessment Health risk assessment




4.1










Health Risk Assessment of Typical Groundwater Contamination Sites

The health risk assessment of groundwater contamination sites describes the feature that adverse health effects result from human exposure to environmental hazards (Chen et al. 2006). It studies the damage to human health through three pathways of exposure to pollutants in groundwater: ingestion, inhalation, and skin contact. The study includes several elements: determining the nature of potential adverse health effects based on toxicology, epidemiology, environmental monitoring and clinical data; estimating and extrapolating the types and severity of adverse health effects under defined exposure conditions; giving judgments on the scale and characteristics of affected populations under different conditions of exposure intensity and time; and providing a comprehensive analysis of public health problems that exist (Chen 2006; Hua 2012; Zhang 2013). In 1983, the National Academy of Sciences of the United States (NRC) set forth the concept of health risk assessment and identified the basic steps to assess health risk: hazard identification, dose–response assessment, exposure assessment, and risk characterization. The NRC paradigm has © Springer Nature Singapore Pte Ltd. 2021 B. Xi et al., Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases, https://doi.org/10.1007/978-981-15-2845-3_4

67

68

4 Risk Assessment of Groundwater Contamination Sites

been recognized by most countries and widely used in the assessment of human health risk associated with accidents and pollution of environmental media such as air, water and soil (Wu et al. 2011; Zhang et al. 2014; Wang 2013; Song 2017) (Fig. 4.1).

Fig. 4.1 Process of health risk assessment for typical groundwater contamination sites (HJ 25.3– 2014)

4.1 Health Risk Assessment of Typical Groundwater Contamination Sites

4.1.1

Process of Health Risk Assessment

4.1.1.1

Hazard Identification

69

Hazard identification is a process of qualitatively determining whether exposure to a chemical substance causes or increases the incidence of specific diseases (e.g. cancers and birth defects), which is essential to human health risk assessment. In the case of chemical substances, the process examines whether such substances are harmful to human health by collecting and evaluating the toxicological and epidemiological data. Internationally, there are two methods for classifying chemical substances: the International Agency for Research on Cancer (IARC) system and the Integrated Risk Information System (IRIS) prepared by the US EPA. In China, the Technical Guidelines for Environmental Impact Assessment: Human Health (Draft for Comment), jointly released by the Chinese Research Academy of Environmental Sciences (CRAES) and the School of Public Health of Peking University (PKU-SPH) in 2008, incorporated the IRIS database as the main reference. The Technical Guidelines for Risk Assessment of Contaminated Sites (Draft for Approval), issued by the Ministry of Environmental Protection of China (MEP), published the toxicity parameters for exposure to some pollutants through different pathways. Apart from these, China has not yet established a relatively complete database of pollutant toxicity. Based on preliminary and detailed investigations, sampling and analysis, hazard identification encompasses the following tasks: collecting EIA data and project acceptance data of enterprises through communication with technical personnel; based on planned land use, identifying the main pollutants in contaminated sites and their potential scope; determining site use, focus pollutants and their spatial distribution; identifying the types of sensitive receptors and the parameters for site characteristics; establishing the system for data quality management and control target; and further refining the conceptual model of contaminated sites to guide risk assessment. The sources of data for hazard identification include environmental monitoring data, epidemiological studies and biotoxicological studies. As to specific content, hazard identification involves identifying the types of pollutants that may threaten human health; measuring the concentrations of pollutants in the environment; assessing the toxicity of pollutants under different conditions; and determining the structure of pollutants. The hazard identification of groundwater contamination sites examines carcinogenic and non-carcinogenic virulence factors of focus pollutants based on the following sequence of materials: • Technical Specifications of Risk Assessment of Contaminated Sites issued by MEP (HJ 25.3–2014); • Guidelines for Health Risk Assessment of Groundwater Pollution (Trial) (October 2014); • IRIS;

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• Technical Evaluation of the Intervention Values for Soil/Sediment and Groundwater issued by the Netherlands National Institute for Public Health and the Environment (RIVM); • IARC; • Toxicity Factors and Chemical/Physical Parameters of the Texas Risk Reduction Program.

4.1.1.2

Dose–Response Assessment

Dose–response assessment analyzes the adverse human health effects of focus pollutants based on hazard identification, including carcinogenic and non-carcinogenic effects, and further determines parameters related to focus pollutants, including reference dose, reference concentration, cancer slope factor, and inhalation unit risk. In the case of chemical substances, the dose–response relationship is estimated on the basis of investigations and experimental data. Therefore, the epidemiological data of humans is preferred, while the long-term carcinogenicity data of sensitive animals are of extreme importance. For threshold compounds, the no observed adverse effect level (NOAEL) is often used as the reference level for risk assessment of genotoxic-free substances, and expressed by acceptable daily intake (ADI) which refers to the maximum amount of chemical substances ingested daily by humans without causing any visible damage. Since the experiment parameters in toxicology database are not designed for ADI identification, it is difficult to find results with appropriate observation endpoints and appropriate exposure time in existing database for dose–response assessment. In this case, new experiments are needed to quantify ADI values, or the actual intake and the temporarily established ADI values are considered to determine whether new experiments are needed. For non-threshold compounds, the traditional extrapolation model in toxicology is adopted to extrapolate human dose–response relationship from animal experimental data, usually by weight, body surface area or safety factor. Where the extrapolation is beyond the range of experimental dose, the predicted value and the response value can differ by several orders of magnitude. Therefore, the model should be carefully selected according to the characteristics of non-threshold compounds and the relevant data collected. However, regardless of thresholds or methods, the dose–response relationship is estimated by models based on epidemiological investigations and experimental data. The IRIS toxicity database contains toxicology data about carcinogenic and non-carcinogenic effects of more than 540 chemical substances. The toxicity criteria database built by California Office of Environmental Health Hazard Assessment (OEHHA) contains information on the toxicity of more than 400 chemical substances. China still lags behind in such basic data collection and toxicology database establishment.

4.1 Health Risk Assessment of Typical Groundwater Contamination Sites

4.1.1.3

71

Exposure Assessment

Exposure assessment aims to examine the likelihood that focus pollutants in the contaminated sites migrate and threaten sensitive receptors on the basis of hazard identification. This involves defining the main exposure pathways and exposure assessment models for soil and groundwater pollutants, determining the values of model parameters, and calculating the exposure of sensitive populations to soil and groundwater pollutants. Exposure assessment focuses on the measurement, estimate or prediction of the magnitude, frequency, duration and pathway of human body (or other organisms) exposure to a chemical substance or physical factor, which serves as a quantitative basis for risk assessment. It also includes discussion of the size, distribution, activity status, and contact method of exposed populations (or organisms), as well as discussion of the uncertainties in the above information. Exposure can be measured directly, but more commonly is estimated using mathematical models that integrate parameters for pollutant emissions, concentrations, transport and transformation trends. However, the methods vary for assessing past, current and future exposures. Using appropriate models, the total exposure of different populations at different times can be estimated based on pollutant concentrations and distribution in the environmental media, population activity parameters and biometric data. In cancer risk assessment, typically the lifetime exposure is calculated. The Guidelines for Exposure Assessment published by the US EPA in 1992 expounded on the general concepts, quantification approaches, data collection and development, exposure estimation, uncertainty assessment, and exposure characterization involved in exposure assessment. Both exposure scenarios and exposure pathways are highlighted in exposure assessment. Exposure scenarios mean the scenarios that pollutants in the contaminated sites migrate and contact populations via different routes under defined land use patterns. In theory, exposure assessment describes pollution sources, exposure pathways and receptors, as well as uncertainties in the assessment process. Regardless of hazards, chemical pollutants will not cause health risks if there are no exposure routes for them to contact receptors. Since risk is always associated with exposure, risk assessment must first examine the exposure scenarios and exposure pathways of hazardous chemicals. In view of this, exposure assessment consists of three basic components: exposure scenario characterization, exposure pathway identification and exposure quantification, specified as follows: (1) Exposure scenario characterization: The characteristics of exposure scenarios and exposed populations are assessed. The basic characteristics of exposure scenarios include local climate (e.g. temperature and precipitation), meteorology (e.g. wind speed, wind direction), agricultural production (e.g. farmland, woodland and grassland), hydrogeological conditions (e.g. soil types and aquifer characteristics), and surface water. The characteristics of exposed populations include locations subject to pollutants, population activities, and potential sensitive receptors.

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(2) Exposure pathway identification: Potential exposed populations may come into contact with pollutants through multiple pathways. The mechanism of interaction between pollutants and exposed populations varies under different exposure pathways. Exposure pathway identification should consider a variety of factors, including pollution sources, discharge pathways, pollutant types, and potential migration and fate characteristics of pollutants (including persistence, distribution, migration and transformation), as well as activity patterns of potential exposed receptors, point and way of contact between exposed receptors and pollutants (e.g. ingestion and inhalation). (3) Exposure quantification: The concentration, frequency and duration of exposure needs to be quantified. Exposure concentration refers to the concentration of pollutants that may come into contact with receptors throughout the exposure period. Where the exposure occurs over a period of time, the total exposure divided by the exposure duration is the average exposure per unit of time. As the average exposure may also be a function of body weight, the exposure standardized by weight and time is defined as average daily exposure (ADE), i.e. the dose of exposure to pollutants per unit of time and per unit of weight [mg/(kg
d)]. The ADE calculation depends on exposure concentration, exposure rate, exposure frequency, exposure period, body weight, and mean duration of action. Equations for quantifying exposure through different pathways are listed in Tables 4.1 and 4.2.

4.1.1.4

Risk Characterization

Risk characterization aims to summarize and integrate information from the proceeding steps of health risk assessment to synthesize a quantitative and qualitative conclusion about risk. It is a bridge between risk assessment and risk management and the most critical step for the final decision-making. Since carcinogens and non-carcinogens vary in chemical toxicity, carcinogenic and non-carcinogenic effects should be considered separately in the assessment. To characterize a potential non-carcinogenic effect, a comparison should be made between intake and toxicity. To characterize a potential carcinogenic effect, the probability of cancer resulting from individual lifelong exposure should be assessed based on intake and specific stoichiometric response data. The approach to extrapolation of exposure and dose characterizes risk by the maximum excess risk or by the number of excess cases. The maximum excess risk refers to the maximum excess risk of an individual continuously exposed to a hazardous factor at a certain exposure level during a certain period of time. This model is the most widely used for risk calculation in recent years. The number of excess cases refers to the number of excess cases in a given population exposed to a hazardous factor at a certain exposure level. Acceptable risk is a criterion for judging whether human health risks associated with environmental pollution can be tolerated, which takes into account social,

Exposure pathway

Groundwater intake

Inhalation of gaseous groundwater pollutants in outdoor air

Inhalation of gaseous groundwater pollutants in indoor air

No

1

2

3

Non-carcinogenic exposure

Non-carcinogenic exposure Carcinogenic exposure

Carcinogenic exposure Non-carcinogenic exposure Carcinogenic exposure

Category GWCRa EFa EDa BWa ATca

c EFIc EDc IIVERnc2 ¼ VFgwia  DAIRBW c ATnc

IIVERca2 ¼ VFgwia   DAIRc  EFIc  EDc DAIRa  EFIa  EDa  þ BWc  ATca BWa  ATca

c EFOc EDc IOVERnc3 ¼ VFgwoa  DAIRBW c ATnc

IOVERca3 ¼ VFgwoa   DAIRc  EFOc  EDc DAIRa  EFOa  EDa  þ BWc  ATca BWa  ATca

c EFc EDc CGWERnc ¼ GWCR BWc ATnc

c EFc EDc CGWERca ¼ GWCR þ BWc ATca

Calculation equation

Table 4.1 Equations for quantifying exposure to groundwater pollutants through different pathways (sensitive land)

4.1 Health Risk Assessment of Typical Groundwater Contamination Sites 73

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Table 4.2 Equations for quantifying exposure to groundwater pollutants through different pathways (sensitive land) No

Exposure pathway

Category

1

Groundwater intake

Carcinogenic exposure Non-carcinogenic exposure Carcinogenic exposure Non-carcinogenic exposure Carcinogenic exposure Non-carcinogenic exposure

2

3

Inhalation of gaseous groundwater pollutants in outdoor air Inhalation of gaseous groundwater pollutants in indoor air

Calculation equation a EFa EDa CGWERca ¼ DWCR BWa ATca a EFa EDa CGWERnc ¼ DWCR BWa ATnc a EFOa EDa IOVERca3 ¼ VFgwoa  DAIRBW a ATca a EFOa EDa IOVERnc3 ¼ VFgwoa  DAIRBW a ATnc a EFIa EDa IIVERca2 ¼ VFgwia  DAIRBW a ATca a EFIa EDa IIVERnc2 ¼ VFgwia  DAIRBW a ATnc

economic and technological factors. A group of countries, regions and agencies in the world have specified the maximum acceptable risk in health risk assessment, but provided different acceptable exposure limits. As China has not yet developed such limits, foreign standards are common applied, including the acceptable health risk of 1*10−6/yr recommended by the Swedish Environmental Protection Agency, the Netherlands Ministry of Infrastructure and Water Management and the Royal Society, the human health risk of 1*10−4/yr recommended by the US EPA, and the maximum acceptable risk of 5*10−5/yr recommended by the International Commission on Radiological Protection (ICRP). In environmental risk assessment, the results are often uncertain due to incomplete understanding of the current and future state of studied systems, hazard severity and characterization. In exposure assessment, uncertainties arise from measurement, sampling and systematic errors in the investigation process of exposure parameters. They can be divided into parameter uncertainty, model uncertainty and scenario uncertainty. (1) Parameter uncertainty may be related to all parameters in the assessment, involving sampling, analysis and systematic errors. For example, soil pollutant concentrations or wind speed in the sites may produce uncertainties. (2) Model uncertainty is related to the extent to which the models used can simulate the real world. In essence, models help us understand and predict the real system by simplifying the real situation. (3) Scenario uncertainty is related to the constraints of the conceptual model in the exposure assessment. For example, simple assumptions are made to assess relatively complex real-life scenarios, while numerous social and economic conditions are considered. The variability in the structure of actual exposed populations can also lead to uncertainties in risk assessment. Unlike the uncertainties described above, such

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75

variability cannot be reduced through in-depth research, but rather better described and understood. For example, by scaling up population samples, it is possible to more accurately grasp the changes in body weight with gender and age.

4.1.2

Prevailing Models

The health risk assessment of contaminated sites is a complex task that requires some site parameters, exposure parameters and ecotoxicological parameters. In order to simplify the process, some models have been developed abroad, such as CLEA (UK), CETOX (Denmark), CSOIL (Netherlands), CalTOX (US), UMS (Germany), EUSES (EU), and RBCA (US). Although all these models consider the hazard of pollutants in the environment to human health through the food chain, only the RBCA model is commonly used for the health risk assessment of groundwater contamination sites (Cui 2012; Liu et al. 2013; Li et al. 2008). In recent years, with the increasing emphasis on the environmental quality of soil and groundwater, some Chinese scholars have conducted studies on the health risk assessment of contaminated soil and groundwater. Among them, the Chen Mengyu-led research team of the Site remediation Center, Nanjing Institute of Soil Science, Chinese Academy of Sciences, has independently developed the Health and Environmental Risk Assessment Software for Contaminated Sites (HERA) model, the first of its kind in China, which meets the urgent needs of China's environmental remediation industry for contaminated sites. The RBCA and HERA models adopt the same technical framework for the health risk assessment of groundwater contamination sites: hazard identification (e.g. site investigation, data acquisition and integration, assessment), exposure assessment, toxicity assessment, and risk characterization.

4.1.2.1

RBCA Model

The RBCA model is developed by Groundwater Services Inc. (GSI) according to the ASTM Standard Guide for Risk-Based Corrective Actions. It can be used to set risk-based SLs and target levels (TLs) for soils, in addition to risk analysis of contaminated sites. Given this, the model has seen wide application in various US states, European countries, Chinese Taiwan, as well as Canada, Australia and Finland. In China, Chen Honghan et al. and Yu Hongwei et al. conducted relatively complete health risk assessment for contaminated sites respectively. The RBCA model adopts a three-tier approach to assessment. Tier-I assesses the point of exposure exactly above the point of pollution sources, assuming the receptor exposed to pollutants is in situ at the point of contamination. It involves large-scale use of empirically conservative values for parameters required for the assessment, such as soil, groundwater, air and pollutant characteristics. Tier II assesses the actual point of exposure in the zone affected by pollution. Where the point of

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exposure differs from the point of pollution source, it needs to consider the change in pollutant concentrations in the lateral distance, i.e. the attenuation of pollutant concentrations caused by horizontal movement. In contrast, Tier I only considers the vertical migration of pollutants since only the point of in-situ exposure is analyzed. Generally, simple analytical modelling is conducted in Tier I and Tier II to measure the migration and attenuation of pollutants in the environment, and the predicted concentrations at the point of exposure are higher than the actual concentrations, so TLs determined thereof will also be safe. In Tier III, a more complex numerical simulation model is used to simulate the migration and attenuation of pollutants in the environment. Therefore, more thorough site investigation is needed to obtain a large amount of required hydrogeological and natural degradation parameters for contaminated sites. In this book, the RBCA model is simplified to assess health risks in the following steps: (1) Establish a conceptual model for health risk assessment that takes into account the excess pollutants from sources, the receptors in the pollution-affected zone, and the exposure pathways identified through preliminary assessment; (2) Determine the concentrations of pollutants in the soil based on observational and experimental data; (3) Estimate exposure; (4) Estimate health risks. Based on health assessment results, the urgency of hazard posed by pollutants to human health are estimated, so that where necessary, emergency measures are taken at the point of pollution to reduce such hazard. Exposure can be measured by chronic daily intake (CDI) (mg/kg/day). Since exposure can occur through ingestion, skin contact and inhalation, CDI is calculated as follows: C  IR  EF  ED ð4:1Þ BW  AT where in C denotes the concentration of pollutants (mg/kg); IR stands for the intake rate (kg), EF exposure frequency (1/days), ED exposure duration (years), BW body weight (kg), and AT average time (years). In the case of chemical substances, pollutants are classified into carcinogens and non-carcinogens according to the US EPA classification system. It is generally believed that under low-dose exposure conditions, there is a linear relationship between CDI and cancer risk (CR) for human body, expressed as CR = CDISF, wherein SF stands for slop factor. Therefore, the CR value of carcinogens is calculated as follows: CDI ¼

CR ¼

C  IRoral  EForal  SForal C  IRdermal  EFdermal  SFdermal þ BW  AT BW  AT C  IRinh  EFinh  SFinh þ BW  AT

ð4:2Þ

4.1 Health Risk Assessment of Typical Groundwater Contamination Sites

77

The hazard quotient (HQ) of non-carcinogens is generally measured by reference dose (RfD), expressed as HQ = CDI/RfD. Hence, the HQ value for non-carcinogens is calculated as follows: HQfood ¼

C  IRoral  EForal  EDoral C  IRdermal  EFdermal  EDdermal þ BW  AT  RfDoral BW  AT  RfDdermal C  IRinh  EFinh  EDinh þ BW  AT  RfDinh ð4:3Þ

where in the subscripts oral, dermal and inh represent ingestion, skin contact, and inhalation pathways respectively. For carcinogens, the CR value is calculated with 10−6 as the lower limit of acceptable risk and 10−4 the upper limit. For non-carcinogens, the HQ criterion is set to 1.

4.1.2.2

HERA Model

The HERA model is designed for soil and groundwater risk assessment based on the RBCA and CLEA models and China’s Technical Guidelines for Risk Assessment of Contaminated Sites (Draft for Comment). Compared with RBCA and CLEA, HERA is superior in interface, function, stability and operation. It contains more than 20 multi-media migration models and includes 610 physical and toxicity parameters (which are subject to update), and can quickly produce a conceptual model of contaminated sites that considers in-situ and off-site health and water environment. The HERA model is applicable to the investigation, assessment and restoration of contaminated sites, and pursuant to Technical Guidelines for Risk Assessment of Contaminated Sites (Draft for Comment), completely localized to provide reasonable interface, strong functionality, high stability and user-friendly operation. The main features are described below: (1) Multi-tier soil and groundwater risk assessment of contaminated sites. The HERA models adopts a two-tier risk assessment system. Tier-I assessment applies only to in-situ receptors and generally, uses default models and parameters for SL and CR/HQ calculation. Tier-II assessment is applicable to in-situ and off-site receptors and selects models and parameters according to the actual sites for TL and CR/HQ calculation (Fig. 4.2). (2) Risk assessment for protection of human health and water environment. The HERA model supports risk assessment with the objective of protecting human health and water environment in situ and off site. For protection of human health, the assessment considers exposure through ingestion, skin contact and inhalation. For protection of water environment, the exposure pathways considered are soil leaching and groundwater migration (Fig. 4.3).

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Fig. 4.2 Conceptual model for site assessment

Fig. 4.3 Interface for exposure pathway selection

(3) Calculation of SLs/TLs and CR/HQs for pollutants. The HERA model can be used to calculate SLs/TLs and CR/HQs for exposure to soil and groundwater pollutants in a single pathway, as well as SLs/TLs based on protecting human health and water environment, and CR/HQs based on human health protection. In addition, the contribution rate of a single exposure pathway in forward and reverse modes can be calculated separately. In the forward mode, the concentrations of pollutants in environmental media such as crops, indoor and outdoor air, groundwater, soil particles, soil gas, and soil solution can be predicted.

4.1 Health Risk Assessment of Typical Groundwater Contamination Sites

79

Fig. 4.4 Parameter management interface

(4) Multi-tier database management system. The HERA model consists of three tiers of databases: The first tier is the default database, which contains characteristic parameters of pollutants such as basic physical and chemical properties and toxicological information, and exposure parameters of the model, such as receptor exposure, air characteristics, soil and groundwater characteristics, building characteristics, crop absorption and off-site migration. Default as they are, the parameter values cannot be modified by users. The second tier is the basic database that provides physical and chemical parameters of pollutants. The basic database is located in the parameter management module of the user interface, and subject to adjustment by users, such as parameter values and pollutant information. The third tier is a shared database where pollutant characteristic parameters and exposure parameters are derived from the basic database and the default database respectively and their values can be modified by users. During model calculations, the parameter values in the shared database are called (Fig. 4.4). (5) Statistical analysis of pollutant data. The HERA model can perform statistical analysis of pollutant data according to the CL: AIRE and CIEH Statistical Guidance, including eliminating outliers and calculating sample mean, standard deviation, and lower and upper confidence limits for pollutant means (Fig. 4.5).

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Fig. 4.5 Result output interface

4.2

Groundwater Pollution Risk Assessment of Typical Groundwater Contamination Sites

Groundwater pollution risk refers to the likelihood that the groundwater in the aquifer is contaminated to an unacceptable level due to human activities. It is an objective, uncertain, and developing result of the interaction between the aquifer vulnerability to pollution and the pollution load caused by human activities (Aller et al. 1987; Zhang 2014). Given this, groundwater pollution risk is characterized by the following attributes: (1) Natural attributes: The groundwater system itself has certain resistance and resilience to external pollution stress. When the concentration of pollutants stays in the acceptable range, the groundwater system can be restored to equilibrium by self-regulation. The recovery and regulating ability depends on the natural conditions of the aquifer. (2) Social attributes: Groundwater pollution risk is widely affected by human activities. The unreasonable ways of production and life of humans have not only produced massive pollutants, but also undermined the groundwater environment by changing the groundwater circulation process such as infiltration, recharge and runoff. (3) Uncertainties: Groundwater pollution risk involves multiple factors and variables. The uncertainties therein manifest the objective stochastic characteristics of the groundwater system, including the heterogeneity of system variables and the uncertainty of risk in time and space. (4) Dynamics: The groundwater system is a huge dynamic open system that exists in a changing environment. External stress factors and system developments make groundwater pollution risk dynamic (Li et al. 2013; Liu et al. 2013; Shen and Li 2010; Teng et al. 2012). Groundwater pollution risk assessment should encompass the incidence of pollution accidents and the consequences of pollution damages. In other words, the

4.2 Groundwater Pollution Risk Assessment of Typical Groundwater …

81

assessment needs to consider (a) the capacity of aquifer systems against pollution and the impact of external pollution load associated with human activities, as well as (b) the change in groundwater value/functions and the migration and attenuation of external pollutants in the soil-groundwater system (Guo et al. 2012; Hong et al. 2011; Javadi et al. 2011; Wang and Ji 2010). At present, the assessment and study of groundwater pollution risks include the assessments of intrinsic vulnerability and specific vulnerability, identification of external pollutant types and hazard levels, and groundwater value/function evaluation (Wang 2013; Kou et al. 2013; Jin et al. 2012; Li et al. 2008; Shi 2013; Wang et al. 2012; Yang et al. 2010).

4.2.1

Assessment of Intrinsic Vulnerability

Intrinsic vulnerability, also known as inherent vulnerability, is a manifestation of the groundwater system's capacity to adapt to changes in the external environment (Huan et al. 2012; Focazio et al. 2003; Debernardi et al. 2008; Chen 2013). It is highly stable as it emphasizes the natural attributes of regional aquifers. The magnitude of intrinsic vulnerability is determined by many factors such as the depth to water table, media in the seepage zone, and hydraulic conductivity of the aquifer (Chen et al. 2002; China Geological Survey 2006; Hathhorn and Wubbena 1996). It reflects the speed at which external pollutants reach the aquifer and the capacity of the groundwater environment to absorb pollutants. The models for groundwater vulnerability assessment currently used at home and abroad mainly include DRASTIC, GOD, AVI, SEEPAGE, SINTACS and EPIK. They integrate basically the same factors and highlights, but each has its own advantages (Chen et al. 2010; Fan et al. 2007; Fu et al. 2000) (Table 4.3). Among them, the DRASTIC model developed by the US EPA in 1985 is most widely used to assess intrinsic vulnerability at home and abroad. It contains seven indicators, and the calculation equation is written as follows: Vi ¼ Dw Dr þ Rw Rr þ Aw Ar þ Sw Sr þ Tw Tr þ Iw Ir þ Cw Cr

ð4:4Þ

wherein Vi represents the intrinsic vulnerability index; D denotes the depth to water table, R net recharge of the aquifer; A aquifer media, S soil media, T topography, I impact of vadose zone media, and C hydraulic conductivity; subscript r and w indicate the rating and weight of the indicator respectively. The intrinsic vulnerability index is obtained by model weighting, and further the vulnerability index is rated. The research on the intrinsic vulnerability of groundwater serves as an embryonic form of groundwater pollution contamination assessment. It in essence simply superimposed the natural attributes of groundwater environment on regional conditions such as hydrogeology, land use and climate. Assessment at this stage mainly rested on the linear assessment model based on the exponential superposition

Groundwater type (G), overburden layer (O), depth to water table (D)

Depth to water table (D), vadose zone media (S), hydraulic conductivity (C), hydraulic gradient (G), horizontal distance of solid waste discharge site (H) Epikarst (E), protective cover (P), infiltration conditions (I), karst network development (K)

Overburden layer (O), current (C), precipitation (P), karst water network development (K)

Overburden factor (O), current (C)

Depth to water table (D), net recharge of the aquifer (R), aquifer media (A),soil media (S), topography (T), impact of vadose zone media (I), hydraulic conductivity of the aquifer (C)

GOD

Legrand

OCP

LEA

DRASTIC

EPIK

Parameters

Model

Karst water

Di = aE + bP + cI + dK, wherein a, b, c, d are parameter weights. A higher Di value implies better mitigation performance and less vulnerability of the aquifer to contamination The results are obtained by coupling various parameters. The coupling method is determined according to the hydrogeological characteristics of assessed area, which can make the sum or product. O, C, and P are selected when assessing the mitigation performance of resources, and O, C, P and K when assessing the performance in protection of water sources It follows the concept of the PI method, but it is simplified with no numerical indicators. It produces qualitative and relative classification results, and more applies to resource vulnerability assessment Vi = DwDr + RwRr + AwAr + SwSr + TwTr + IwIr + CwCr. A larger Vi values indicates more vulnerability to contamination

(continued)

Unconfined water and confined water in porous media

Areas with small data volumes

Karst water

Unconfined water and confined water in porous media (empirical method) Lots that may be affected by solid waste discharge sites

Application

The mitigation index Di = G*O* D, but in the case of confined aquifer, O is ignored, that is, Di = G*D. The parameter value ranges from 0 to 1 Di = D + S + C + G + H. A higher Di value implies better mitigation performance, and vice versa

Description

Table 4.3 Model for assessment of inherent groundwater vulnerability

82 4 Risk Assessment of Groundwater Contamination Sites

Parameters

Protective cover (P), infiltration conditions (I)

Vertical hydraulic conductivity, thickness of layers above the water surface

Soil media (S), vadose zone media (I), ground surface slope (G), aquifer media (A)

Depth to water table (S), net recharge (I), vadose zone dilution capacity (N), soil media (T), aquifer media (A), hydraulic conductivity (C), slope (S)

Model

PI

AVI

SIGA

SINTACS

Table 4.3 (continued) Description

Same as DRASTIC model

Di = PTS*I. A lower Di value indicates worse mitigation performance and more vulnerability of the aquifer to contamination. The model is more applicable to vulnerability assessment of resource protection The model measures the aquifer sensitivity by the hydraulic resistance of layers in the direction perpendicular to water flow and quantifies the average time of transport from land surface to groundwater for pollutants A higher score indicates worse mitigation performance, and vice versa

It is complex with difficulty in obtaining parameter values, but the score is relatively accurate Medium and large-scale assessment

Simple and fast

Karst water

Application

4.2 Groundwater Pollution Risk Assessment of Typical Groundwater … 83

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method, which masks many pollution details and problems, so it cannot be called the groundwater pollution risk assessment in the true sense.

4.2.2

Assessment of Specific Vulnerability

The specific vulnerability of groundwater characterizes the impact on the natural groundwater flow field brought by pollution sources associated with human activities and the development of land resources. It is a dynamic and controllable manifestation of the sensitivity of groundwater to external disturbance. The magnitude of specific vulnerability is jointly determined by the types and scale of pollution sources and the rules of migration and transformation of pollutants in the groundwater environment. The assessment of specific vulnerability gives quantitative scores to such indicators as external pollution sources and land use types, and the weighted results are superimposed with the final assessment results for intrinsic vulnerability. The assessment of specific vulnerability stems from the study of intrinsic vulnerability and serves as an important part of groundwater pollution risk assessment in the transition phase. Table 4.4 describes several methods for risk assessment of pollution load sources.

4.2.3

Identification of External Pollutant Types and Hazard Levels

External pollutant types and hazard levels can be identified in qualitative and quantitative manner based on the research on type, distribution, load and migration of pollution sources. Risk sources can be evaluated and graded by establishing a quantitative system of characteristic pollutants and their emissions or a multi-factor coupled risk source identification model.

4.2.4

Groundwater Value/Function Evaluation

The damage associated with risk of contamination to the groundwater system can be characterized by changes in groundwater value/functions. There are many methods for groundwater value/function evaluation, but the majority quantify groundwater value/function, broadly in the following two ways: (1) Evaluation based on groundwater quality and groundwater storage. The equation for calculation is written as follows:

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85

Table 4.4 Methods for risk assessment of pollution load sources Method

Description

Results

Advantages

Disadvantages

Simple judgment

Classifies pollution sources into seven categories: nature, agriculture, forestry, household, solid waste, sewage treatment, working conditions, and water mismanagement, and divides them into high, medium and low levels based on experience Classifies pollution sources into four categories: industry, agriculture, animal husbandry and others, and divides them into nine levels according to their type and size. A higher level indicates greater risk Divides the pollution source risk into high, medium and low levels by constructing the pollutant migration matrix and pollution source intensity matrix Rates according to pollution sources and pollution load generated by them Considers the possibility and severity of pollution

Qualitative

Easy to use and less data demanding

Influence of human factors and lack of regional comparability

Qualitative

Easy to use and more refined than simple judgment

Lack of regional comparability

Quantitative

Human subjectivity avoided, which is conducive to pollution source control and groundwater protection

In-depth field investigations required to obtain detailed information on a large number of pollution sources

Qualitative and quantitative

Less data demanding and highly operable

Quantitative

Clear rating system that facilitates comparison

Lack of comparison between different types of pollution sources Failure to cover all types of pollution sources, and detailed investigation of pollution sources required

DCI

Detailed rating

POSH

Priority setting

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V ¼ GQ  GS

ð4:4Þ

wherein V indicates groundwater value, GQ groundwater quality and GS groundwater storage. (2) Evaluation based on exploitation value and in-situ value. The exploitation value highlights the usability and economic significance of groundwater, including groundwater required for various human activities. The in-situ value covers the ecological and regulating value of groundwater and the value of maintaining groundwater system stability and immunity. By applying the disaster risk theory, the measurement and evaluation of groundwater value/function makes the system of groundwater pollution risk assessment more systemic and comprehensive. However, such evaluation remains difficult because groundwater value/function, as an embodiment of groundwater importance, requires great data support for description and quantification. In addition, the in-situ value of groundwater, which largely rests on ecological significance, is very ambiguous and difficult to quantify.

4.2.5

Methods for Groundwater Pollution Risk Assessment

The selection of risk assessment methods needs to fully consider the exhaustiveness of regional data and information, the adoption of assessment models, and the reliability of assessment results (Przemysław et al.2016; Huang et al. 2008; RUPERT 2001; Zhong 2005). It is a core content of risk research that directly determines result credibility. At present, there are many methods for assessing groundwater pollution risks, including index superposition, simulation of complex physical, chemical and biological processes, uncertainty analysis, and mathematical statistics, of which the first three are most commonly used (Zhang et al. 2012; Jiang 2002; Schlosser et al. 2002).

4.2.5.1

Index Superposition Method

The index superposition method calculates and rates the risk index according to the established index and rating system. More specifically, the intrinsic vulnerability index characterizing the mitigation performance of groundwater is superposed, in a weighted manner, with the external stress index that characterize groundwater pressure from external pollution sources, in order to identify the possibility of groundwater contamination. Then, the result is superimposed with the groundwater value index that characterizes groundwater importance to obtain the groundwater pollution risk index of the study area. The ArcGIS software and the alike that supports spatial analysis and visualization are used for calculation and representation.

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The index superposition method has the advantages of simple operation, easy acquisition of indicator data, and low cost. However, the dominant use of linear models increases subjectivity in indicator selection, rating, and final risk determination. The results are too general to reflect the specific migration and attenuation process of external pollutants, so the method is not suitable for risk assessment of single-point source pollution. In the process of indicator selection, the causal connection between indicators should be considered to avoid the repeatability of indicators (Table 4.5).

4.2.5.2

Process Simulation Method

The process simulation method can make up for the deficiency of index superposition method in the risk assessment of contaminated sites and individual pollution sources. It presupposes risk characterization and then infers the level of risk by inversion. Based on simulating the status of groundwater flow and the whole process of pollutant migration and attenuation during entry to the aquifer, the method can predict the impacts of external potential pollutants on groundwater over time under different external conditions, and finally determine the level of risk according to pollutant concentration distribution and scope of influence. By quantitatively describing the level of groundwater contamination, the method can Table 4.5 Techniques for index superposition in groundwater pollution risk assessment Technique

Steps

Advantages and disadvantages

Overlay

The intrinsic vulnerability, specific vulnerability and value of groundwater are superimposed using the spatial analysis tool Overlay, and each given weight according to respective importance, to produce a map of groundwater pollution risk The indicator layer is rasterized, and the pixel value of each raster layer is calculated using the Map Algebra method, so as to determine the groundwater pollution risk The intrinsic vulnerability and value maps are superimposed to generate the groundwater protection urgency map. Using the matrix method, the groundwater protection urgency map and groundwater pollution grade map are superimposed to obtain the groundwater pollution risk map. Based on the results, the pollution risk is rated

Easy management of indicator data, but lack of process associations between layers

Map Algebra

Matrix method

Basically the same as the Overlay method, but the accuracy highly influenced by pixel size

Clear and explicit, but deficient in the assignment of weights to each indicator

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be integrated into risk assessment of contaminated sites, optimal selection of new sites, and determination of design parameters. The application in groundwater pollution risk assessment requires the support of mathematical models and simulation models. Using established mathematical formula, parameters are quantified to obtain the comprehensive index of regional groundwater pollution risk. In essence, process simulation is a part of the numerical simulation of groundwater. MODFLOW is an early groundwater simulation software developed by the US Geological Survey (USGS), which is mainly applied to the numerical simulation of three-dimensional finite-difference groundwater flow in porous media. Afterwards, many software and models for groundwater numerical simulation emerged, such as FEFLOW, HYDRUS, GMS, Groundwater Vistas, Visual Modflow, and Geostudio. Among them, FEFLOW and MT3DMS (groundwater solute transport model) have been recognized as standard models for groundwater flow and pollutant migration. The application of mathematical models and simulation models facilitates quantitative and systematic assessment and more real results about groundwater pollution risk. However, great uncertainties lie in the internal and external characteristics and the formation mechanism of complex, dynamic and open groundwater system. It is also difficult to obtain hydrogeological data and physical parameters on which the simulation relies. Due to the limitations of human cognition and the temporal and spatial constraints of monitoring activities, the simulation is too ambiguous to reflect, in many cases, the true level of risk. In addition, the process simulation method is not combined with the disaster theory, but rather focuses on the temporal and spatial distribution characteristics of pollutants, which hinders the representation of the true connotation of risk.

4.2.5.3

Uncertainty Analysis Method

The essence of risk assessment is uncertainty analysis because without uncertainty, there is no risk. The results will be more scientific if the level of risk is reflected based on qualitative and quantitative research of uncertain factors in the whole process. The groundwater system, huge, dynamic and open as it is, has complex internal and external structures and strong uncertainties. With the establishment and development of uncertainty theory, the related theories have been gradually introduced into groundwater pollution risk assessment. The main approaches for uncertainty analysis in this field can be classified into three categories: stochastic model based on probability theory, fuzzy mathematics based on fuzzy set theory, and coupled stochastic-fuzzy analysis. The existing relevant studies mainly focus on groundwater health risk assessment because of simple models and fewer parameters. In contrast, groundwater pollution risk assessment needs to consider complex problems and various parameters, so under uncertain conditions, emphasis is put on intrinsic

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vulnerability. This also provides a good opportunity for the further application of uncertainty theory. Since stochastic mathematics theory and fuzzy mathematics theory are highly complementary, coupled stochastic-fuzzy analysis will become the prevailing method for groundwater pollution risk assessment in the future.

4.3

Brief Summary

This chapter discusses the methods for assessing the health risk and groundwater pollution risk respectively in three typical sites of groundwater contamination: HWLFs, MSWLFs, and OCS. Health risk assessment consists of hazard identification, dose–response assessment, exposure assessment and risk characterization to calculate the risk control value for soil and groundwater contamination. The RBCA model (USA) and the HERA model (China) are commonly used for this purpose. Groundwater pollution risk assessment encompasses the assessment of intrinsic vulnerability, assessment of specific vulnerability, identification of external pollutant types and hazard levels, and groundwater value/function evaluation. The prevailing methods include index superposition, process simulation and uncertainty analysis. The findings about human health risk control values and groundwater pollution risks are helpful for the rational selection of pollution prevention and control measures and remediation measures towards better management of contaminated sites.

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Debernardi L, De Luca D A, Lasagna M. Correlation between nitrate concentration in groundwater and parameters affecting aquifer intrinsic vulnerability[J]. Journal of the American Pharmaceutical Association, 2008, 55(3):539-558. FAN Qi, WANG Guiling. LIN Wenjing, et al. New Method for Evaluating the Vulnerability of Groundwater[J]. Journal of Hydraulic Engineering, 2007, 38(5): 601–605. Focazio M J, Reilly T E, Rupert M G, et al. Assessing Ground-Water Vulnerability to Contamination: Providing Scientifically Defensible Information for Decision Makers[J]. Journal of Chromatography A, 2003, 1136(2):210–220. FU Surong, WANG Yanxin, CAI Hesheng, et al. Vulnerability to Contamination of Groundwater in Urban Regions[J]. Earth Science-Journal of China University of Geosciences, 2000, 25(5): 482-486. GUO Yongli, TENG Yanguo, WANG Wei. Risk Assessment of Groundwater Pollution in Uncertainty Process Simulation[J]. Advances in Earth Science, 2012, 27(S1): 343-345. Hathhorn W E, Wubbena T. Site Vulnerability Assessment for Wellhead Protection Planning[J]. Journal of Hydrologic Engineering, 1996, 1(4):152-160. HONG Mei, ZHANG Bo, LI Hui, WANG Dong. Risk Assessment of Groundwater Pollution by Domestic Waste Landfill Site: A Case Study of Beijing Beitiantang Landfill[J]. Environmental Pollution & Control, 2011, 33(03): 88–91+95. HUA Yongpeng. Study on Health Risk Assessment of Contaminated Site and Method to Determine the Remediation Goals[D]. China University of Geosciences, 2012. Huan H, Wang J, Teng Y. Assessment and validation of groundwater vulnerability to nitrate based on a modified DRASTIC model: a case study in Jilin City of northeast China. Sci Total Environ 2012;440:14–23. HUANG Guanxing, SUN Jichao, JING Jihong, et al. Discussion on Assessment of Shallow Groundwater Intrinsic Vulnerability in the Pearl River Delta Region[J]. Geotechnical Investigation & Surveying, 2008 (11): 44–49. Javadi S, Kavehkar N, Mousavizadeh MH, Mohammadi K. Modification of DRASTIC model to map groundwater vulnerability to pollution using nitrate measurements in agricultural areas. J Agric Sci Technol 2011;13:239–49. JIANG Guihua. The Development of Study on Groundwater Vulnerability[J]. World Geology, 2002, 21(1): 33–38. JIN Aifang, ZHANG Xu, LI Guanghe. Study on the Hazard Assessment Method of Pollution Sources in Groundwater Source Fields[J]. Chine Environmental Science, 2012, 32(6): 1075– 1079. KOU Wenjie, CHEN Zhongrong, LIN Jian. Pollution Risk Assessment of Groundwater Below Different Types of Garbage Site[J]. Yellow River, 2013, 35(1): 42-44. LI Jun, PEI Zhaojun, HAN Guorui, YANG Xian. Groundwater Pollution Risk Assessment of Hazardous Waste Landfill[J]. Environmental Science Survey, 2013, 32(06): 74-77. LI Zhenghong, BI Erping, ZHANG Sheng, YIN Miying, MA Linna, WANG Wenzhong, ZHANG Yilong. Method for Health Risk Assessment of Groundwater Pollution[J]. South-to-North Water Transfers and Water Science & Technology, 2008, 6(06): 47–51. LIANG Huanhuan, AN Da, YANG Yu, WANG Yue, XI Beidou, WU Minghong, ZHANG Boqiang. Risk Ranking for Groundwater Pollution from Hazardous Waste Landfills by MCDA Model[J]. Research of Environmental Sciences, 2016, 39(01): 131–137. LIU Liu, ZHANG Lan, LI Lin, ZHANG Xiangming, ZHU Yunjie. Research Progress on Health Risk Assessment[J]. Capital Journal of Public Health, 2013, 7(06): 264–268. LIU Zengchao, DONG Jun, HE Liansheng, XI Beidou, MENG Rui, LI Yiwei, YAN Ganggang. The Method Study on Groundwater Pollution Risk Assessment Based on Process Simulation [J]. China Environmental Science, 2013, 33(06): 1120-1126. Przemysław Wachniew, Anna J. Zurek, Christine Stumpp, et al. Towards Operational Methods for the Assessment of Intrinsic Groundwater Vulnerability: a Review[J]. Critical Reviews in Environmental Science\s&\stechnology, 2016:00–00. RUPERT M G. Calibration of the DRASTIC ground water vulnerability mapping method[J]. Ground Water,2001,39 (4):625–630.

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Chapter 5

Application Cases

Abstract We selected 13 typical sites in Central China, North China, South China, East China, Southwest China, and Northwest China to conduct groundwater environmental surveys and risk assessments. These sites include hazardous waste landfills, municipal solid waste landfills, and oil-contaminated sites. Due to the different hydrogeological conditions in different regions, the methods used in the evaluation are also different.







Keywords Municipal solid waste landfill Hazardous waste landfill Oil-contaminated site Groundwater Pollution source Pollution risk assessment Health risk assessment Application case




5.1











Central China

Case 1 Groundwater pollution investigation, source intensity evaluation and risk assessment of a given landfill in Hubei Province (1) Overview of the study area (a) Geographical features The area where the given landfill sits generally slopes down from southwest to northeast with an elevation of 50–130 m, and embraces nearly a hundred of rolling mountain peaks. The low-lying landfill has an elevation of about 50 m, while mountains surrounding the landfill in the east, west and north are 80–120 m above sea level and higher than the terrain in the south. (b) Climate and hydrological characteristics • Climate characteristics The area is subject to subtropical monsoon climate. Despite mild climate, it is cold in winter and hot in summer with distinct four seasons. The water and heat conditions are superior given abundant sunshine, heat and precipitation. The © Springer Nature Singapore Pte Ltd. 2021 B. Xi et al., Investigation and Assessment Technology for Typical Groundwater-contaminated Sites and Application Cases, https://doi.org/10.1007/978-981-15-2845-3_5

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temperature averages 17 °C in the year and 29 °C in the hottest month (July). Due to the dense water network with numerous rivers and lakes, it is relatively humid with large evaporation under long duration of sunshine, but it is extremely stuffy when the temperature climbs to 40 °C. The coldest month (January) sees an average temperature of around 4.5 °C and an average minimum temperature of 2 °C. The annual frost-free period averages 237–261 days, while rainfall occurs in 130– 150 days per year, reaching about 1406.6 mm. The southeast wind dominates the area, with an annual average wind speed of 2.17 m/s. • Hydrological characteristics On a city scale, lakes account for 27% of the city’s total area, mainly distributed in riverside plain and low hilly farmland along the Yangtze River. In the administrative area, waters cover about 3.5 km2. There are three small reservoirs with a total storage capacity of 1.5768 million m3: Jiangyang Reservoir, Yuanmen Reservoir and Fenglei Reservoir; and 135 ponds with a total storage capacity of 624,000 m3. The distribution and direction of surface water systems are as shown in Fig. 5.1. (c) Soil and vegetation Soils in the area are mainly made up of limestone, quartz diorite porphyry, yellow-sand shale, purple-sand shale and Quaternary red clay parent rock. Plant resources are abundant. Among them, arbors include cedar, masson pine, oak and maple; shrubs include Loropetalum chinense var. rubrum, Buxus sempervirens L, hybrida vicary privet, and French holly; grass includes Cymbopogon citratus, Brassica campestris, Ipomoea pescaprae, Polygonum lapathifolium, Artemisia argyi; aquatic plants include lotus root, water chestnut, duckweed, calamus, algae (black algae), and water lotus. (d) Mineral resources Mineral resources are rich in the area. There are 11 kinds of proven mineral resources, including gold, iron ore, coal, lead-zinc, pyrite, dolomite, granite, gypsum, clay and celestite. (e) Groundwater utilization Groundwater resources in the city amount to 125 million m3/year, of which 78% is karst water. However,the groundwater resources are unevenly distributed,as more than 70% of the groundwater resources exist in central and southern areas which industries are underdeveloped. According to the investigation, before the tap water is accessible, wells have been drilled without reaching the bedrock in each household to extract the Quaternary pore water for domestic use. In mountainous areas with large water depths, artificial groundwater extraction is difficult and residents use springs as a source of water. Well water is used for cleaning after residents have access to tap water for drinking.

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Distribution of surface water systems in Huangshi City

Image map of Xialu District

Distribution and direction of surface water systems in Xialu District

Fig. 5.1 Distribution of surface water systems

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(2) Environmental background investigation of the landfill (a) Landfill overview Built in September 1999, the given landfill is 9 km from the city center and covers an area of 8 ha. It has a storage capacity of 1.5 million m3 and a daily garbage disposal capacity of 350 tons. While about 1.2 million tons of waste has been landfilled, the garbage almost fill the entire mountain. Due to the simple landfill treatment, a large amount of biogas has been generated during the degradation process of organic matter and discharged directly into the atmosphere. In 2007, the municipal government invested 10 million yuan to introduce the 3R comprehensive treatment technology for landfill. Biogas has therefore been produced by intercepting, recirculating and leading landfill leachate into the closed circulation system. In October 2009, the landfill was fully closed for reforestation by planting trees and grass. According to the recent field investigation, a driving training base has been built in the east of the landfill. The installed biogas pipeline has been broken, making the previous biogas collection and utilization project failed to proceed. Newly filled waste is also particularly conspicuous. Rainwater converges in ditches on the east and west sides, and then flows to the south side where the terrain is relatively low. It is then collected by pipelines and discharged to the leachate tank at the southern end along with the leachate produced by the simple landfill treatment. The specific site topography is as shown in Fig. 5.2. (b) Water quality survey • Layout of sampling sites According to collected data and interviews, there is no monitoring well in the given landfill but agricultural wells in peripheral villages. In order to analyze the

Fig. 5.2 Peripheral topography

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groundwater quality of landfill and the surrounding environment, a total of five sampling sites were set up, called L1, B1, G1, G2 and S1 respectively. Among them, L1 is located in the leachate monitoring outlet at the southern end of the landfill, B1 in the groundwater monitoring well in Shilingtou Village in the upper reaches, G1 and G2 in the groundwater monitoring wells in Xiamen of Chengjiawan, about 260 m downstream, and S1 in the surface water monitoring pond, about 70 m downstream (Fig. 5.3). • Characteristics of peripheral flow field The elevations of surface water and groundwater in the vicinity of the given landfill was measured using Nikon NPL-322 Total Station on October 27, 2015, as shown in Fig. 5.4. Based on the layout of measuring sites, as shown in Fig. 5.5, groundwater table contours ware drawn using surfer, as shown Fig. 5.6. Groundwater flows from well G1 to well G2 and from well G4 to well G3 where the measured water surface elevations are 32.621 m, 31.674 m, 26 m and 24.681 m respectively. As to surface water, the elevation reaches 35.655 m at the nearest pond P1, 33.336 m at the farther pond P2, and 32.334 m at the farthest pond P3. Overall, the groundwater surface is 6–7 m higher in G1 and G2 than G3 and G4, which is consistent with the terrain trend. • Sample collection and monitoring According to the Technical Specifications for Groundwater Environmental Monitoring (HJ/T164–2004), sampling was conducted twice, covering 49 indicators. Ll and G1 sample groups were taken on October 9, 2015, and Sl, L1′, B1 and G2 sample groups on November 10, 2015.

Fig. 5.3 Deployment of sampling sites

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Fig. 5.4 Elevation measurement site

Fig. 5.5 Layout of elevation measuring points

A total of 23 conventional indicators were tested. Among them, physiochemical indicators tested on-site include temperature, pH, dissolved oxygen, conductivity, and macroscopic objects; wet chemistry indicators include permanganate index, total hardness, TDS, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, sulfate,

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Fig. 5.6 Change in groundwater flow field

volatile phenol, total cyanide, fluoride, chloride, and hexavalent chromium; heavy metal indicators include arsenic, mercury, cadmium, iron, manganese, and lead. In addition, 26 organic indicators were selected, including monocyclic aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylene, and styrene), fumigant (1,2-dichloropropane), halogenated aliphatic hydrocarbons (chlorine ethylene, 1,1-dichloroethylene, dichloromethane, trans-1,2-dichloroethylene, cis-1,2-dichloro ethylene, 1,1,1-trichloroethane, carbon tetrachloride, 1,2-dichloroethane, trichloro ethylene, 1,1,2-trichloroethane, and tetrachloroethylene), halogenated aromatic hydrocarbons (chlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2-dichloro benzene, and 1,2,4-trichlorobenzene), trihalomethanes (chloroform, bromodichloro methane, dibromochloromethane chloride and bromoform), and PAHs (BaP). The specific test and analysis methods are as shown in Table 5.1.

Table 5.1 Methods for water quality monitoring and analysis Indicators

Method

Detection limit

Ammonia nitrogen Nitrite nitrogen Total cyanide Fluoride Nitrate nitrogen Chloride Sulfate Total soluble solids Total hardness Permanganate index Volatile phenol Hexavalent chromium Arsenic Cadmium Lead

GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T

0.025 0.01 0.004 0.05 0.1 10 0.1 5 5 0.5 0.002 0.004 0.005 0.0001 0.001

5750.5-2006 5750.5-2006 5750.5-2006 5750.5-2006 5750.5-2006 5750.5-2006 5750.5-2006 5750.4-2006 5750.4-2006 5750.7-2006 5750.4-2006 5750.6-2006 5750.6-2006 5750.6-2006 5750.6-2006

Unit mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L (continued)

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Table 5.1 (continued) Indicators

Method

Detection limit

Unit

Mercury Iron Manganese Benzene Toluene Ethylbenzene M-xylene and p-xylene Styrene O-xylene 1,2-dichloropropane Vinyl chloride Trans-1,2-dichloroethylene Cis-1,2-dichloroethylene 1,1,1-trichloroethane Carbon tetrachloride 1,2-dichloroethane Trichloroethylene 1,1,2-trichloroethane Tetrachloroethylene Chlorobenzene 1,3-dichlorobenzene 1,4-dichlorobenzene 1,2-dichlorobenzene 1,2,4-trichlorobenzene Chloroform Bromomethylene chloride Dibromochloromethane Tribromomethane BaP

GB/T 5750.6-2006 GB/T 5750.6-2006 GB/T 5750.6-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006 USEPA 8260C-2006

0.0005 0.01 0.005 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.05

mg/L mg/L mg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L lg/L

The test items specific to sample group are described in Table 5.2. The sampling preparation and process are as shown in Fig. 5.7. (3) Groundwater environmental assessment (a) Test results of groundwater components (Tables 5.3 and 5.4) (b) Groundwater quality assessment  Standards and methods Grade III standards specified in the Quality Standards for Groundwater (GB/ T14848–2017) were applied to the study area. The standard index method described

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Table 5.2 Test items specific to sample group Sample group

Test items

G1 G2 B1

All 49 indicators All 49 indicators 23 conventional indicators and 5 types of monocyclic aromatic hydrocarbons All 49 indicators Ammonia, permanganate index, arsenic, iron, manganese, and 5 types of monocyclic aromatic hydrocarbons 23 conventional indicators and 5 types of monocyclic aromatic hydrocarbons

L1 L1’ (selective retest) S1

Fig. 5.7 Sampling preparation

in Sect. 2.2.7 is used for indicator-specific evaluation and comprehensive evaluation (Table 5.5). • Results As a number of items were tested for the three sample groups in the lab, the indicators set in the Quality Standards for Groundwater (GB/T14848–2017), including ammonia, iron, manganese and 30 indicators, are used for groundwater quality assessment. Where the limits are the same for indicators of different water quality categories, the lower limits shall prevail (Grade I limits for undetected indicators). The results of groundwater quality evaluation are as shown in Table 5.6. As shown in Table 5.4, groundwater in G1, G2 and B1 is not contaminated and reaches the Grade I standard for majority indicators. Groundwater in G1 and G2 overall reaches Grade II standard, in terms of ammonia nitrogen, nitrate nitrogen and TDS in G1 and in terms of sulfate, TDS and total hardness in G2. The overall

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Table 5.3 Results of conventional groundwater quality indicators Indicators pH Macroscopic objects Flavor level Dissolved oxygen Conductivity Ammonia nitrogen Nitrite nitrogen Total cyanide Fluoride Nitrate nitrogen Chloride Sulfate Total soluble solids Total hardness Permanganate index Volatile phenol Hexavalent Chromium Arsenic Cadmium Lead Mercury Iron Manganese Note The air pressure in

Detection limit

Unit

G1

G2

B1

– – – – – 0.025 0.01 0.004 0.05 0.1 10 0.1 5 5 0.5 0.002 0.004

Dimensionless – – mg/L S/cm mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L

6.63 None None 3.55 642 0.043