25071 September 2002 UTHE WORMBANK Ground water >1 Quality Protection a guide for water utilities, municipal authorities, and environment agencies Lw,~~~~~~L * . - s / .* L~~~~~~~~~~~~~~L * ,. ~~~~~~~~~~~~~~~M nic D'li * M -t Paris aC:~ ~ ~ cotibto to main groundwte mor visbl - an thu moemngal ;i Z :- ;, ; . ... ; .. ~ ~ L, LL F . . | ~a contribution to making groundwater more visible ,j ~~~~~~and thus more manageableJ Groundwater L Quality Protection a guide for water utilities, municipal authorities, and environment agencies Stephen Foster Ricardo Hirata Daniel Gomes Monica D'Elia Marta Paris Groundwater Management Advisory Team (GW.MATE) in association with the Global Water Partnership co-sponsored by WHO-PAHO-CEPIS & UNESCO-ROSTLAC-PHI THE WORLD BANK Washington, D.C. Copyright © 2002 The World Bank/The Initernational Bank for Reconstruction and Development 1818 H Street, N.W. Washington, D.C. 20433, USA Telephone: 202 477-1234 Facsimile: 202 477-6391 " Internet: wvw.worldbank.org E-mail: feedback@worldbank.org All rights reserved Designed and produced by Words and Publications, Oxford, United Kingdom Printed in the United States of America * First printing September 2002 The findings, interpretations, and conclusions expressed here are those of the author(s) and do not necessarily reflect the views of the Board of Executive Directors of the World Bank or the governments they represent. The World Bank cannot guarantee the accuracy of the data included in this work. The boundaries, colors, denominations, and other information shown on any map in this work do not imply on the part of the World Bank any Judgment of the legal status of any territory or the endorsement or acceptance of such boundaries. Rights and Permissions The material in this work is copyrighted. 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Stephen Foster is Leader of the World Bank-Global Water Partnership Groundwater Management Advisory Team (GW-MATE), Visiting Professor of Contaminant Hydrogeology in the University of London, Vice-President of the International Association of Hydrogeologists and was formerly the World Health Organization's Groundwater Advisor for the Latin American-Caribbean Region and Divisional Director of the British Geological Survey. Ricardo Hirata is Professor of Hydrogeology at the Universidade de Sio Paulo-Brazil, having previously been a Post-Doctoral Research Fellow at the University of Waterloo- Canada and a Young Professional of the WHO/Pan-American Health Organization. Daniel Gomes is a Senior Consultant of Waterloo Hydrogeologic Inc-Canada, having previously been a Hydrogeologist with CETESB-Brazil and a Young Professional of the WHO/Pan-American Health Organization. Monica D'Elia and Marta Paris are both Researchers and Lecturers in Geohydrology at the Universidad Nacional del Litoral-Facultad de Ingenieria y Ciencias Hidricas, * Argentina. Cover photo courtesy of Ron Giling/Still Pictures. * ISBN 0-8213-4951-1 The Library of Congress Cataloging-in-Publication data has been applied for. 1 2 3 4 5 05 04 03 02 Contents Forewords vi Acknowledgments, Dedication vii Rationale for Groundwater Protection 1 1. Why has this Guide been written? 2 2. Why do groundwater supplies merit protection? 2 3. What are the common causes of groundwater quality deterioration? 3 4. How do aquifers become polluted? 4 5. How can groundwater pollution hazard be assessed? 6 6. What does groundwater pollution protection involve? 7 7. Why distinguish between groundwater resource and supply protection? 9 8. Who should promote groundwater pollution protection? 1 0 9. What are the human and financial resource implications? 11 Methodological Approaches to Groundwater Protection 1 3 Bi Mapping Aquifer Pollution Vulnerability 15 W Principles Underlying the Vulnerability Approach 15 C Development of the Vulnerability Concept 16 Q Need for an Absolute Integrated Vulnerability Index 1 7 * Application of GOD Vulnerability Index 19 Q Comparison with Other Methodologies 25 Q Limitations of Vulnerability Mapping 27 D Procedural Issues in Vulnerability Mapping 29 B2 Delineation of Groundwater Supply Protection Areas 31 J Basis for Definition of Perimeters of Areas 31 (A) Total Source Capture Area 33 (B) Microbiological Plrotection Area 34 (C) Wellhead Operational Zone 36 (D) Further Subdivision 36 ,ii Groundwater Quality Protection: a gutide for ivater utilities, ntunicipal atuthorities, and environinent agencies JD Factors Controlling Shape of Zones 36 W, 4D~~~~~ Limitations to Supply Protection Area Concept 40 (A) Common Problems with Suggested Solutions 40 I4fr~~~~~~I ~~(B) Case of Karstic Limestone Aquifers 42 (C) Case of Spring and Gallery Sources 44 (D) Implementation in Urbani Settings 45 K' ,~~~~II 0 ~~~Methods for Definition of Protection Zone Perimeters 45 (A) Analytical Versus Numerical Aquifer Models 46 (B) 2-D Versus 3-D Aquifer Representation 48 (C) Practical Considerations 49 JD Dealing with Scientific Uncertainty 49 0D Perimeter Adjustment and Map Production Si B3 Inventory of Subsurface Contaminant Load 53 Q Common Causes of Groundwater Pollution 53 O Basic Data Collection Procedures 56 (A) Designing a Contaminant Load Inventory 56 (B) Characteristics of Subsurface Conitaminant Load 58 (C) Practical Survey Considerationis 58 0 Classification and Estimation of Subsurface Contaminant Load 60 (A) Spatial and Temporal Occurrence 60 (B) The l'OSH Method of Load Characterization 62 O Estimation of Subsurface Contaminant Load 63 (A) Diffuse Sources of Pollution 63 (B) Poinlt Sources of Pollution 69 Presentation of Results 77 B4 Assessment and Control of Groundwater Pollution Hazards 79 0 Evaluation of Aquifer Pollution Hazard 79 (A) Recommended Approach 79 (B) Distinction Betweeni Hazard and Risk 80 0 Evaluation of Groundwater Supply Pollution Hazard 80 ~~~~~~~~~~~~~~~~~~~~~~~~~~IV > ~ ~ ~ ~~~~~~A Approiachon to Inoprto fSupply Crtcin Aptur Zncest 80 ; ~~~~~~(B) Complementaryo Weiha SraniStaryg Suvys8 * zY ~~1 eD Methods for Definition of Protect~~~~ivnZn eiees4 Groundwater Quality Protection a gui(de for wvater uitilities, nmunicipal auithorities, anid environment agencies C Strategies for Control of Groundwater Pollution 81 (A) Preventing Future Pollution 81 (B) Dealing with Existing Pollution Sources 86 (C) Approach to Historic Land Contamination 89 (D) Selecting New Groundwater Supply Areas 89 C Role and Approach to Groundwater Quality Monitoring 92 (A) Limitations of Production Well Sampling 92 (B) Systematic Monitoring for Groundwater Pollution Control 93 (C) Selection of Analytical Parameters 93 @ Mounting Groundwater Quality Protection Programs 95 (A) Institutional Requirements and Responsibilities 95 (B) Addressing Key Uncertainties and Challenges 96 (C) Creating a Consensus for Action 98 References 100 v I. Forewords T his is a much welcomed publication that provides clear This Guide has been produced in the belief that guidance to water-sector decision makers, planners, and T groundwater pollution hazard assessment must become practioners on how to deal with the quality dimension of an essential part of environmental best practice for water groundwater resources management in the World Bank's client supply utilities. Such assessments should lead to a clearer countries. It is very timely, since there is growing evidence of appreciation of priority actions required of municipal increasing pollution threats to groundwater and some well- authorities and environmental regulators to protect documented cases of irreversible damage to important aquifers, groundwater, both in terms of avoiding future pollution and following many years of widespread public policy neglect. mitigating threats posed by existing activities. In the majority v, vof cases the cost of these actions will be modest compared to The idea to undertake such a review came from Carl Bartone that of developing new water supply sources and linking them and Abel Mejia of the World Bank, following an initial attempt into existing water distribution networks. to draw attention to the need for groundwater protection in the Latin American-Caribbean Region by the WHO-PAHO Centre The situation in some Latin American countries has become for Sanitary Engineering & Environmental Science (CEPIS), critical, in part because many of the aquifers providing many who together with the UNESCO-IHP Regional Office for Latin municipal water supplies are experiencing serious overdraft American-Caribbean Region have provided support for this and/or increasing pollution. Among the cities of the region that new initiative. are highly dependent upon groundwater resources, are Recife in Brazil, Lima in Peru, numerous Mexican cities, and most of The publication has been prepared for a global target audience the Central American capitals. under the initiative of the World Bank's Groundwater Management Advisory Team (GW-MATE), which works in The Guide is thus particularly relevant for the World Bank's association with the Global Water Partnership, under the Latin American and Caribbean Region, where many countries } coordination of the GW-MATE leader, Dr. Stephen Foster. It is have initiated major changes to modernize their institutional practically based in a review of the last decade's experience of and legal framework for water resources management, but may groundwater protection in Latin America and of concomitant not yet have considered groundwater at the same level as advances in the European Union and North America. surface water, because of lack of awareness and knowledge of Following the approaches advocated will help make groundwater issues and policy options. A process of specialist groundwater more visible at the policy level and in civil society. consultation informed the present work, and came out with the I9. recommendation that the Guiide should focus on one technique John Briscoe for each component of groundwater pollution hazard World Bank Senior Water Adviser assessment in the interest of clarity and consistency for the t ~~~~~~~~~~~~~~~~~~~average user. Abel Mejia-Betancourt Sector Manager, Water Cluster; Finance, Private Sector, and Infrastructure, Latin America and Caribbean Region 9 vi Acknowledgments Four meetings in Latin America represented key steps in * San Jose, Costa Rica: Novenmber 2001 undertaking the systematic assessment of relevant experience in Maureen Ballesteros and Yamileth Astorga (GWP- that region and in reviewing the substantive content of this CATAC), Arcadio Choza (MARENA - Nicaragua), Jenny Gutide. The following are acknowledged for their support and Reynolds (UNA-Costa Rica) and Jose-Roberto Duarte input to the respective meetings: (PRISMA-EI Salvador). * Santa Fe, Argentina: October 1999 K- the late Mario Fili (Universidad Nacional del Litoral); The production of the Guide was managed by Karin Kemper, K 7Z Mario Hernandez (Universidad Nacional de La Plata); Coordinator of the Bank-Netherlands Water Partnership Program Monica Blasarin (Universidad Nacional de Rio Cuarto); (BNWPP), with the assistance of Carla Vale. and Claudio Lexouw (Universidad Nacional del Sur), all from Argentina The authors would also like to acknowledge valuable * Montevideo, Unrguay: October 2000 discussions with the following of their respective colleagues: Carlos Fernandez-Jauregui and Angelica Obes de Lussich Hector Gardufio (GW-MATE), Brian Morris (British (UNESCO); Alejandro Delleperre and Maria-Theresa Geological Survey), Paul Martin (Waterloo Hydrogeologic 1Cmc) Roma (OSE-Uruguay) and Ofelia Tujchneider (Universidad Nacional del Litoral- * Lima, Peni: March 2001 Argentina). Henry Salas and Plilar Ponce (WHO-PAHO-CEPIS), Maria- ConsueloVargas (INGEOMINAS-Colombia), Hugo Rodriguez The design and production of the publicationl was carried out, (ICAyA-Costa Rica), Julia Pacheco (CNA-Yucatan-Mexico) on behalf of the World Bank Group, by Words and Publications and Juan-Carlos Ruiz (SEDAPAL-Pcru) of Oxford, UK, with the support of Gill Tyson Graphics. U Dedication 4. j-y ; .4s g The authors wish to dedicate this Guide to the menmory of Professor Mario Fili of the F -} Universidad Nacional del Litoral-Facultad de Ingenieria y Ciencias Hidricas, Santa Fe- Argentina, who died prematurely during the project. Mario tvas one of the leading i -- i. X groundwater specialists of Argenztina and Latiu Amzerica, author of some 70 published w *4J(- j technical papers and articles, a life-long professional friend of the first author and much-loved professor and colleague of two other authors of this Gutide. MP= vii PART A: EXECUTIVE OVERVIEW Rationale for Groundwater Protection An Executive Overview for senior personnel of water service companies, municipal authorities, and environment agencies, answering anticipated questions about groundwater pollution threats and protection needs, and providing essential background and standardized approaches to adopt in compliance with their duty to safeguard the quality of water destined for public supply. 1. Why has this Guide been written? 2 2. Why do groundwater supplies merit protection? 2 3. What are the common causes of groundwater quality deterioration? 3 4. How do aquifers become polluted? 4 5. How can groundwater pollution hazard be assessed? 6 6. What does groundwater pollution protection involve? 7 7. Why distinguish between groundwater resource and supply protection? 9 8. Who should promote groundwater pollution protection? 10 9. What are the human and financial resource implications? 11 1 PART A: EXECUTIVE OVERVIEW Rationale for Groundwater Protection 1. Why has this Guide been written? * At the broad scale, groundwater protection strategies (and their prerequisite pollution hazard assessment) have to be promoted by the water or environmental regulator (or that agency, department, or office of national, regional, or local government charged with performing this function). It is important, however, that attention is focused at the scale and level of detail of the assessment and protection of specific water supply sources. * All too widely in the past, groundwater resources have, in effect, been abandoned to chance. Often those who depend on such resources for the provision of potable water supplies have taken no significant action to assure raw-water quality, nor have they made adequate efforts to assess potential pollution hazard. * Groundwater pollution hazard assessments are needed to provide a clearer appreciation of the actions needed to protect groundwater quality against deterioration. If undertaken by water supply utility companies, it is hoped that, in turn, both preventive actions to avoid future pollution, and corrective actions to control the pollution threat posed by existing and past activities, will be realistically prioritized and efficiently implemented by the corresponding municipal authorities and environmental regulators. 2. Why do groundwater supplies merit protection? * Groundwater is a vital natural resource for the economic and secure provision of potable water supply in both urban and rural environments, and plays a fundamental (but often little appreciated) role in human well-being, as well as that of many aquatic ecosystems. * Worldwide, aquifers (geological formations containing useable groundwater resources) are experiencing an increasing threat of pollution from urbanization, industrial development, agricultural activities, and mining enterprises. * Thus proactive campaigns and practical actions to protect the (generally excellent) natural quality of groundwater are widely required, and can be justified on both broad environmental sustainability and narrower economic-benefit criteria. * In the economic context, it is also important that water companies make assessments of the strategic value of their groundwater sources. This should be based on a realistic evaluation of their replacement value, including both the cost of developing the new supply source and 2 Part A: Executive Overview * Rationale for Gronundw,atcr Protection also (most significantly) the cost of connecting and operating increasingly distant sources into existing distribution networks. * Special protection measures are (in fact) needed for all boreholes, wells, and springs (both public and private) whose function is to provide water to potable or equivalent standards. This would thus include those used as bottled mineral waters and for foocl and drink processing. * For potable mains water supply, a high and stable raw water quality is a prerequisite, and one that is best niet by protected groundwater sources. Recourse to treatment processes (beyond precautionary disinfection) to achieve this end should be regarded as a last- resort, in view of their technical complexity and financial cost, and the operational burden they impose. 3. What are the common causes of groundwater quality deterioration? * There are various potential causes of quality deterioration in an aquifer and/or in a groundwater supply. These are classified by genesis and further explained in Table A.l. In this Guide we are primarily concerned with protection against aquifer pollution and wellhead contamination, but it is necessary to be aware that other processes can also be operative. Table A.1 Classification of groundwater quality problems TYPE OF PROBLEM UNDERLYING CAUSE CONTAMINANTS OF CONCERN AQUIFER inadequate protection of vulnerable aquifers pathogens, nitrate or ammonium, chloride, POLLUTION against manmade discharges and leachates sulphate, boron, arsenic, heavy metals, from urban/industrial activitres and dissolved organic carbon, aromatic and intensification of agricultural cultivation halogenated hydrocarbons, certain pesticides WELLHEAD inadequate well design/construction allowing mainly pathogens CONTAMINATION direct ingress of polluted surface water or shallow groundwater Saline Intrusion saline (and sometimes polluted) groundwater mainly sodium chloride, but can also induced to flow into freshwater aquifer as include persistent manmade contaminants result of excessive abstraction Naturally Occurring related to chemical evolution of mainly soluble iron and fluoride, sometimes Contamination groundwater and solution of minerals (can magnesium sulphate, arsenic, manganese, be aggravated by manmade pollItion and/or selenium, and other inorganic species excessive abstraction) 3 Groundwater Quality Protection: a guide for water zitilities, mtiizicipal auithorities, and environmzent agencies Figure A.1 Common processes of groundwater pollution solid waste tip- p :Ig industrial leaking In-situ farmryard leaking wastewater agricultural or landfill 'losing' river Mie drainage storage tanks sanitation drainage sewers lagoons intensification 4. H-ow do aquifers become pofluted? 0 Most groundwater originates as excess rainfall infiltrating (directly or indirectly) at the land surface. In consequence, activities at the land surface can threaten groundwater quality. The pollution of aquifers occurs where the subsurface contaminant load generated by manmade discharges and leachates (from urban, industrial, agricultural, and mining activities) is inadequately controlled, and in certain components exceeds the natural attenuation capacity of the overlying soils and strata (Figure A.1). o Natural subsoil profiles actively attenuate many water pollutants, and have long been considered potentially effective for the safe disposal of human excreta and domestic wastewater. The auto-elimination of contaminants during subsurface transport in the vadose (unsaturated) zone is the result of biochemical degradation and chemical reaction, but processes of contaminant retardation due to sorption phenomena are also of importance, since they increase the time available for processes resulting in contaminant elimination. o However, not all subsoil profiles and underlying strata are equally effective in contaminant attenuation, and aquifers will be particularly vulnerable to pollution where, for example, consolidated highly fissured rocks are present. The degree of attenuation will also vary widely with types of pollutant and polluting process in any given environment. o Concern about groundwater pollution relates primarily to the so-called unconfined or phreatic aquifers, especially where their vadose zone is thin and water-table shallow, but significant pollution hazard may also be present even where aquifers are semi-confined, if the confining aquitards are relatively thin and permeable. o An idea of the more common types of activity capable of causing significant groundwater pollution and the most frequently encountered contaminant compounds can be gained from Table A.2. It is important to recognize that these depart widely from the activities and compounds most commonly polluting surface water bodies, given the completely different controls governing the mobility and persistence of contaminants in the respective water systems. 4 Part A: Executive Overview * Rationiale for Grounzdwater Protection Table A.2 Common groundwater contaminants and associated pollution sources POLLUTION SOURCE TYPE OF CONTAMINANT - Agricultural Activity nitrates; ammonium; pesticides; fecal organisms In-situ Sanitation nitrates; halogenated hydrocarbons; microorganilsms Gas Stations and Garages aromatic hydrocarbon; benzene; phenols; halogenated hydrocarbons Solid Waste Disposal ammonium; salinity; halogenated hydrocarbons; heavy metals Metal Industries trichloroethylene; tetrachloroethylene; halogenated hydrocarbons; phenols; heavy metals; cyanide Painting and Enamel Works alkylbenzene; halogenated hydrocarbons; metals; aromatic hydrocarbons; tetrachloroethylene Timber Industry pentachlorophenol; aromatic hydrocarbons; halogenated hydrocarbons Dry Cleaning trichloroethylene; tetrachloroethylene Pesticide Manufacture halogeneted hydrocarbons; phenols; arsenic Sewage Sludge Disposal nitrates; halogenated hydrocarbons; lead; zinc Leather Tanneries chromium; halogeneted hydrocarbons; phenols Oil and Gas Exploration/Extraction salinity (sodium chloride); aromatic hydrocarbons Metalliferous and Coal Mining acidity; various heavy metals; iron; sulphates a * It is also important to stress that certain activities (and specific processes or incremental practices within such activities) often present disproportionately large threats to groundwater quality. Thus sharply focused and well-tuned pollution control measures can produce major benefits for relatively modest cost. * Human activity at the land surface modifies aquifer recharge mechanisms and introduces new ones, changing the rate, frequency, and quality of groundwater recharge. This is especially the case in arid climates, but also pertains in more humid regions. Understanding of these mechanisms and diagnosis of such changes are critical in the assessment of groundwater pollution hazard. * Water movement and contaminant transport from the land surface to aquifers can in many cases be a slow process. It may take years or decades before the impact of a pollution episode by a persistent contaminant becomes fully apparent in groundwater supplies, especially those abstracted from deeper wells. This factor can simultaneously be a valuable benefit and a serious concern because: 5 I4- Groundwater Quality Protection: a giuide for water uitilities, ininzcipal authorities, and environment agencies * it allows time for the breakdown of degradable contaminants * it may lead to complacency about the likelihood of penetration of persistent contaminants. The implication is also that once groundwater quality has become obviously polluted, large volumes of the aquifer are usually involved. Clean-up measures, therefore, nearly always have a high economic cost and are often technically problematic. 5. How can groundwater pollution hazard be assessed? 0 The most logical approach to groundwater pollution hazard is to regard it as the interaction between: * the aquifer pollution vulnerability, consequent upon the natural characteristics of the strata separating it from the land surface * the contaminant load that is, will be, or might be, applied on the subsurface environment as a result of human activity. Adopting such a scheme, we can have high vulnerability but no pollution hazard, because of the absence of significant subsurface contaminant load and vice versa. Both are perfectly consistent in practice. Moreover, contaminant load can be controlled or modified, but aquifer vulnerability is essentially fixed by the natural hydrogeological setting. 0 The term aquifer pollution vulnerability is intended to represent sensitivity of an aquifer to being adversely affected by an imposed contaminant load (Figure A.2). In effect, it is the inverse of "the pollutant assimilation capacity of a receiving water body" in the jargon of river quality management. Figure A.2 Significance of contrasting aquifer pollution vulnerability high aquifer vulnerability low aquifer vulnerability time scale of water f low W J L L W 7 0 ~~~~~~~~~~~~~~wyeeakss yers shallow unconfined aquifer , 3 heavy metals nitrate (? salinity (3 organic carbon (!) faecal pathogens l pesticides 6 Part A: Executive Overview . Rationale for Grouinzdwvater Protection * Aquifer pollution vulnerability can be readily mapped. On such maps the results of surveys of potential subsurface contaminant load can be superimposed, to facilitate the assessment of groundwater pollution hazard. The term groundwater resource pollution hazard relates to the probability that groundwater in an aquifer will become contaminated to concentrations above the corresponding WHO guideline value for drinking-water quality. * Whether this hazard will result in a threat to groundwater quality at a given public-supply I source depends primarily on its location with respect to the groundwater capture area of the source, and secondarily on the mobility and dispersion of the contaminant(s) concerned within the local groundwater flow regime. The assessment of groundwater supply pollution hazard can be undertaken by superimposing the supply protection perimeters on the aquifer vulnerability (Figure A.3), and subsequently relating the zones thus defined to summary maps derived from a the inventory of potential subsurface contaminant load. It should be noted, however, that assessing the risk that such a hazard represents in terms of the resultant contaminant exposure for water users or in terms of increased water treatment costs are outside the scope of this Gtiide. L * The scales at which survey and mapping of the various components that are needed to assess groundwater pollution hazard are undertaken varies significantly with the main focus of the work-water supply protection or aquifer resource protection (Figure A.4), g and this is discussed further below. Figure A.3 Components of groundwater pollution hazard assessment used for groundwater protection land surface zoning \ | AX,\;4@, increasedolevel of land-use restriction 9 Groundwater Quality Protection: a guide for wvater utilities, municipal authorities, and environment agencies 0 This approach is best suited to the more uniform, unconsolidated aquifers exploited only by a relatively small and fixed number of high-yielding municipal water supply boreholes with stable pumping regimes. It is most appropriate in the less densely populated regions where their delineation can be conservative without producing conflict with other interests. They cannot be so readily applied where there are very large and rapidly growing numbers of individual abstractions, which render consideration of individual sources and the establishment of fixed zones impracticable, and a broader approach needs to be taken. * Aquifer-oriented strategies are more universally applicable, since they endeavour to achieve a degree of protection for the entire groundwater resource and for all groundwater users. They would commence with aquifer pollution vulnerability mapping of more extensive areas (including one or more important aquifers) working at a scale of 1:100,000 or more if the interest was limited to general information and planning purposes. Such mapping would normally be followed by an inventory of subsurface contaminant load at a more detailed scale, at least in the more vulnerable areas. 8. Who should promote groundwater pollution protection? * The possible institutional options for the promotion of groundwater protection are summarized in Figure A.6. Given the responsibility of water-service companies to conform to codes and norms of sound engineering practice, there is an obligation on them to be proactive in undertaking or promoting pollution hazard assessments for all their groundwater sources. This will provide a sound basis for representations to be made to the local environment and water resource regulator for action on protection measures where Figure A.6 Institutional arrangements for groundwater pollution evaluation and control COMPONENT SCALE OF OPERATION ACTIVITY 25,000 50,000 100,000 250,000 Aquifer Vulnerability Mapping NATIONAL GOVERNMENT Contaminant Load Inventory level) Source Protection Area Delineation Groundwater Pollution Hazard Assessment NATIONAL GOVERNMENT (policy and Groundwater Pollution legal framework) Control Measures preferred institutional possible alternative institutional responsibility for key actions FT] arrangement and initiatives 10 Part A: Executive Overview * Rationale for Grouindwvater Protection needed. Even where no adequate pollution control legislation or agency exists, it will normally be possible for the local government or municipal authority to take protective action under decree in the greater interest of the local population. * The procedures for groundwater pollution hazard assessment presented also constitute an effective vehicle for initiating the involvement of relevant stakeholders (including water user interests and potential groundwater polluters). 9. What are the human and financial resource implications? * The proposed assessment procedure will require the participation of at least two qualified professionals-a groundwater specialist/hydrogeologist (as team leader) and an environment engineer/scientist-normally supported by some auxiliary staff with a local office base and field transport. * Although the methodology presented is relatively simple, it will be necessary for the professional staff involved to have a reasonable understanding of groundwater pollution. Moreover, skills will need to be developed (both on job and through consultation) in ranking some of the more subjective components of aquifer pollution vulnerability and subsurface contaminant load assessment. Figure A.7 Scope of Guide in context of overall scheme of groundwater resource management |REGIONAL RECONNAISANCE GEOLOGICAL MAPPING |HYDROGEOLOGICAL MAPPING l AQUIFER PROPERTIE FLOW REGIMES OF CONTAMINANT RECHARGE ~ ~ ~ ~ ~ ~ ~ ~~OLUNTION VINERBIIT ~ LAGENERATION Dlneon f , tSIpPly Preliminary Groundwater Resources Assessment wae n _ mlal Groundwater Resources Evaluation ". _ iYI t,ff f (based on operational monitoring program) lt_en 'A-vi ites_ l ~~~~~Groundwater Management Policy ter Potct2le l r - * ~~(control on well drilling and pumping rates) Nnfieiramn?ltlrP n controls) _- A ROUTINE GROUNDWATER LEVEL _ _ _ _ _ __ _ _ _ _ _& QUALITY MONITORING___________ ____________. Groundwater Quality Protection: a guide for water utilities, municipal authorities, and environment agencies 0 The boundaries of an assessment area (while recognizing the focus of particular interest) must be defined on a physical basis to include an entire aquifer or groundwater sub- catchment within an aquifer, so as always to include the probable recharge area of the system under consideration. * The assessment procedure is highly complementary to other groundwater investigation, evaluation, and management actions (Figure A.7). It is designed to be undertaken relatively rapidly, and to utilize data that has already been collected for other purposes, or that can readily be collected at field level. Following the methodology presented, it should be possible for an appropriate team to complete a groundwater resource and supply pollution hazard assessment within 2-12 months, depending on the size and complexity of the area under consideration. 12 L -PART B: TECHNICAL GUIDE Methodological Approaches to Groundwater Protection A Technical Guide for professional groundwater specialists, environment engineers, and scientists, who are called upon to develop groundwater quality protection strategies for water service companies and water resource agencies, or are concerned with land-use planning, effluent discharge, and waste disposal control in environment agencies and municipal authorities. BI Mapping Aquifer Pollution Vulnerability 15 B2 Delineation of Groundwater Supply Protection Areas 31 B3 Inventory of Subsurface Contaminant Load 53 B4 Assessment and Control of Groundwater Pollution Hazards 79 13 PART B: TECHNICAL GUIDE Methodological Approaches to Groundwater Protection BI Mapping Aquifer Pollution Vulnerability The mapping of aquifer polltition vulnerability will nornally be the first step in groundwater pollution hazard assessment and quality protection, when the interest is at municipal or provincial scale. This chapter discusses the evolution of the aquifer pollution vulnerability concept before recommending a nmethodological basis for vulnerability evaluation that can be used for nmapping at that scale. The concept is also valid for vulnerability appraisal at more local levels within individital grountdwater supply catchient areas. D Groundwater recharge mechanisms and the natural contaminant attenuationi capacity of subsoil profiles vary widely with near-surface geological conditions. Thus, instead of applying universal controls over potentially polluting land uses and effluent discharges, it is more cost effective (and less prejudicial to economic development) to vary the type and level of control according to this attenuation capacity. This is the basic premise underlying the concept of aquifer pollution vulnerability and the need for vulnerability mapping. In view of the complexity of factors governing pollutant transport into aqulfers in any given situation, it might at first sight appear that: * hydrogeological conditions are too complex to be encapsulated by mapped vulnerability zones * it would be more logical to treat each polluting activity on individual inerit and undertake an independent assessment of the pollution hazard it generates. 15 Groundwater Quality Protection: a guiide for water utilities, municipal authorities, and environment agencies However this type of approach: i is unlikely to achieve universal coverage and avoid inconsistent decisions * requires large human resources and major financial investment for field investigations * can present administrative problems where institutional responsibility is split. In hydrogeology the term "vulnerability" began to be used intuitively from the 1970s in France (Albinet and Margat, 1970) and more widely in the 1980s (Haertle, 1983; Aller and others, 1987; Foster and Hirata, 1988). While the implication was of relative susceptibility of aquifers to anthropogenic pollution, initially the term was used without co any attempt at formal definition. Z The expression began to mean different things to different people. A useful and > consistent definition would be to regard aquifer pollution vulnerability as those intrinsic Z characteristics of the strata separating the saturated aquifer from the land surface, which 0 1- determine its sensitivity to being adversely affected by a surface-applied contaminant load (Foster, 1987). It would then be a function of: 0 0 the accessibility of the saturated aquifer, in a hydraulic.sense, to the penetration of rU pollutants 0 the attenuation capacity of strata overlying the saturated zone resulting from the physiochemical retention or reaction of pollutants. z In the same way, groundwater pollution hazard would then be defined as the probability that groundwater in the uppermost part of an aquifer will become contaminated to an > unacceptable level by activities on the immediately overlying land surface (Foster and r. . Hirata, 1988; Adams and Foster, 1992). co Subsequently two major professional working groups reviewed and pronounced upon the applicability of the vulnerability concept and come out strongly in favor of its usefulness (NRC, 1993; IAHNrba and Zaporozec, 1994). It would have been desirable for them to have made a clearer statement on the use of the term, for example associating it specifically with the intrinsic characteristics of the strata (unsaturated zone or confining beds) separating the saturated aquifer from the land surface (Foster and Skinner, 1995). This would (most importantly) have related it directly with the potential impact of land-use decisions at the location concerned on the immediately underlying groundwater. Some, however, considered that a factor representing the natural mobility and persistence of pollutants in the saturated zone be included in vulnerability. This, however, does not appear to view vulnerability mapping from the most useful perspective, namely that of providing a framework for planning and controlling activities at the land surface. 16 Part B: Technical Guide * Methodological Approaches to Grotindwvater Protection ... S i *e * * * -. - .5 Two fundamental questions that arise in relation to aquifer pollution vulnerability are whether it is possible: * to present a single integrated vulnerability index, or be obliged to work with specific vulnerability to individual contaminants and to pollution scenarios * to provide an absolute indicator of integrated pollution vulnerability, or be restricted to much less useful relative vulnerability indices. Subsurface water flow and contaminant transport are intricate processes. In reality, the interaction between components of aquifer pollution vulnerability and subsurface contaminant load, which determine the groundwater pollution hazard, can be complex (Figure 1.1). In particular, the degree of contaminant attenuation can vary significantly with the type of pollutant and polluting process in any given situation. Thus a "general > (integrated) vulnerability to a universal contaminant in a typical pollution scenario" has v z no strict validity in rigorous terms (Foster and Hirata, 1988). C) ,0 Scientifically, it is more consistent to evaluate vulnerability to pollution by each c 5M pollutant, or failing this by each class of pollutant (nutrients, pathogens, microorganics, heavy metals, etc.) individually, or by each group of polluting activities (unsewered 0 sanitation, agricultural cultivation, industrial effluent disposal, etc.) separately. For this w reason (Andersen and Gosk, 1987) suggested that vulnerability mapping would be 0 better carried out for individual contaminant groups in specific pollution scenarios. Z However, the implication would be an atlas of maps for any given area, which would be C difficult to use in most applications, except perhaps the evaluation and control of diffuse Z agricultural pollution (Carter and others, 1987; Sokol and others, 1993; Loague, 1994). > Moreover, there will not normally be adequate technical data and/or sufficient human resources to achieve this ideal. In consequence, a less refined and more generalized system of aquifer vulnerability mapping is required. The way forward for most practical purposes is to produce an integrated vulnerability map, provided the terms being used are clearly defined and the limitations clearly spelled out (Foster and Hirata, 1988). Such health warnings have been elegantly expressed in the recent U.S. review (NRC, 1993) in the form of three laws of groundwater vulnerability: * all groundwater is to some degree vulnerable to pollution * uncertainty is inherent in all pollution vulnerability assessments * in the more complex systems of vulnerability assessment, there is risk that the obvious may be obscured and the subtle indistinguishable. An absolute index of aquifer pollution vulnerability is far more useful (than relative indications) for all practical applications in land-use planning and effluent discharge control. An absolute integrated index can be developed provided each class of vulnerability is clearly and consistently defined (Table 1.1). In this way it is possible to 17 Groundwater Quality Protection: a guiide for water utilities, municipal auithorities, and environment agencies Figure 1.1 Interactions between components of subsurface contaminant load and aquifer pollution vulnerability determining aquifer pollution hazard SUBSURFACE AQUIFER _ CONTAMINAJNT POLLUT.ION LOAD VULNERA4iTY see Figure 3.3 see Figure 1.2 B A B I CONTAMINANT I CLASS transformation -W I LU Ie z~~~~~~~~~~~~~~~~~~~~~~~~~~~ > _ AB t z o MODE OF | GROUNDI,WATER 1- |DISPOSITION | CONFINEMENT _j - m hydraulic load | 0 B LU U- u A B' sediments z PollutionPotential A r Polun ense rocks . . AB' 18B" +AB'c X |~~~~~~~~~~~~~~~CONTAMINANT| EPHT |INTENSITY| |GONWTR DURATIO OF Aqui-fer A I ~~~~~~~LOAD Vulnerability |probability | Index Pollution Potenta Aquifer Poilution Ranking ) azard ) 18 Part B: Technical Guide * Methodological Approaches to Groundwvater Protection VULNERABILITY CLASS CORRESPONDING DEFINITION Extreme vulnerable to most water pollutants with rapid impact in many pollution scenarios High vulnerable to many pollutants (except those strongly absorbed or readily transformed) in many pollution scenarios Moderate vulnerable to some pollutants but only when continuously discharged or leached Low only vulnerable to conservative pollutants in the long term when continuously and widely discharged or leached Negligible confining beds present with no significant C) vertical groundwater flow (leakage) > :-v m overcome most (if not all) the common objections to the use of an absolute integrated O vulnerability index as a framework for groundwater pollution hazard assessment and E protection policy formulation. 0 z C 4D ~~~~~z The GOD method of aquifer pollution vulnerability assessment has had wide trials in > Latin America and the Caribbean during the 1990s (Table 1.2), and because of its simlplicity of concept and application, it is the preferred method described in this Guide. Two basic factors are considered to determine aquifer pollution vulnerability: * the level of hydraulIc inaccessibility of the saturated zone of the aquifer * the contaminant attenuation capacity of the strata overlying the saturated aquifer; however they are not directly measurable and depend in turn on combinations of other parameters (Table 1.3). Since data relating to many of these parameters are not generally available, simplification of the list is unavoidable if a practical schellmc of aquifer pollution vulnerability mapping is to be developed. Based on such considerations, the GOD vulnerability index (Foster, 1987; Foster and Hirata, 1988) characterizes aquifer pollution vulnerability on the basis of the following (generally available or readily determined) parameters: * Groundwater hydraulic confinement, in the aquifer under consideration. * Overlying strata (vadose zone or confining beds), in terms of lithological character and degree of consolidation that determine their contaminant attenuation capacity * Depth to groundwater table, or to groundwater strike in confined aquifers. 19 Bi: MAPPING AQUIFER POLLUTION VULNERABILITY s 0 0. 0 Area of Authors Date Working Vulnerability Contaminant Source Capture GISm of Study Map Scale Method Adopted Inventory Zones Defined Used 0 Barbados Chilton and others 1990 1:100,000 GOD vv S5o Paulo, Brazil Hirata and others 1990 1:500,000 GOD v V Rio Cuarto, Argentina Blarasin and others 1993, 1999 1:50,000 GOD V Managua, Nicaragua Scharp and others 1994, 1997 1:100,000 DRASTIC/GOD V v v Leon, Mexico Stuart and Milne 1997 1:50,000 GOD v v N Cacapava, Brazil Martin and others 1998 1:100,000 GOD v V V Esperanza, Argentina Paris and others 1998, 1999 1:50,000 GOD v v a Cauca Valley, Colombia Paez and others 1999 1:200,000 GOD(S) V 'These are the sources of information for all the text boxes. Part B: Technical Guide * Methodological Approaches to Groundwvater Protection Box 1.1 Vulnerability of semi-confined aquifers-field data from Le6n, Mexico It is important to ntote that a semi-confined aquifer of low pollution vulnerability can be seriouisly impacted in the long run by persistent contaminants (such as chloride, nitrate, and certain synthetic organic compounds), if they are continuously discharged on the overlying groun1d surface. This possibility muist always be taken into accounzt when assessing the pollution hazard to waterwells abstracting fromiz suich aquifers. * Le6n (Guanajuato) is one of the fastest-growing cities in Mexico and one of the most important leather- (A) Attenuation of chromium in soils of manufacturing and shoe-making centers in Latin America. wastewater irrigation area The city is located in an arid upland tectonic valley filled total Cr in soil (mg/kg) by a mixture of alluvial, volcanic, and lacustrine deposits, 0 100 200 0 100 200 which form a thick complex multi-aquifer system. 0 * A substantial proportion of the municipal water supply is 0.2 z derived from downstream wellfields, which tap a semi- n confined aquifer from below a 100-meter depth. One of D 0.4 the wellfields is situated where municipal wastewater has E been used over various decades for agricultural irrigation. 5 The inefficient irrigation characteristic of wastewater reuse n 0.6 0 results in a substantial (and continuous) recharge of the r local groundwater system. Thus groundwater levels have 0 8 0 here remained within 10 meters of the land surface, despite Z the fact that in neighboring areas they have been in steady < c long-term decline at rates of 1-3 meters per year (ni/a). 1 .0 Z long-term wastewater floor of former * The wastewater historically included an important irrigation field wastewater lagoon component of industrial effluent with very high dissolved chromium, organic carbon and overall salinity. Detailed field investigations in the mid-1990s by the Comision Nacional del Agua-Gerencia de Aguas Subterraneas and (B) Variation of groundwater quality with depth the Servicio de Agua Potable de Leon have shown that benearh _wastewater_irrigation most elements of the contaminant load (including SOURCE OF TYPICAL PUBLIC SUPPLY pathogenic microbes and heavy metals) are rapidly SAMPLE SHALLOW WELL BOREHOLES attenuated in the subsoil profile (Figure A). Very little intake depth .30 m 200-300 in reaches the semi-confined aquifer (Stuart and Milne, 1997), whose pollution vulnerability under the GOD EC (pS/cm) 3400 1000 system would classify in the low range. CI (Mg/I) 599 203 * However, persistent contaminants-notably salinity as HCO3 (mg/') 751 239 indicated by Cl concentrations (Figure B)-do penetrate into the semi-confined aquifer and are threatening the NO3 (mg/I) 13.5 6.0 quality and security of municipal water supplies in this Na (mg/I) 227 44 area (Stuart and Milne, 1997). 21 Groundwater Quality Protection: a guide for water uitilities, municipal auithorities, and environmaent agencies COMPONENT OF HYDROGEOLOGICAL DATA VULNERABILITY ideally required normally available Hydraulic Inaccessibility degree of aquifer confinement type of groundwater confinement depth to groundwater table or depth to groundwater table or top groundwater strike of confined aquifer unsaturated zone moisture content . vertical hydraulic conductivity of strata in vadose zone or confining beds Attenuation Capacity grain and fissure size distribution of grade of consolidation/fissuring strata in vadose zone or confining beds these strata «j mineralogy of strata in vadose zone or lithological character of these strata Z confining beds z 0 I- Further considerarion reveals rhat these paramerers embrace, if only in a qualitative _ sense, the majority of those in the original list (Table 1.3). 0 rw The empirical methodology proposed for the estimation of aquifer pollution Li- vulnerability (Foster and Hirata, 1988) involved a number of discrete stages: <: * first, identification of the type of groundwater confinement, with consequent z indexing of this parameter on scale 0-1 * second, specification of the strata overlying the aquifer saturated zone in terms of (a) grade of consolidation (and thus likely presence or absence of fissure permeability) and (b) type of lithology (and thus indirectly dynamic-effective- co porosity, matrix permeability, and unsaturated zone moisture content or specific retention); this leads to a second score on a scale 0.4-1.0 * third, estimation of the depth to groundwater table (of unconfined aquifers) or depth of first major groundwater strike (for confined aquifers), with consequent ranking on the scale 0.6-1.0. The final integrated aquifer vulnerability index is the product of component indices for these parameters (Figure 1.2). It should be noted that this figure has been modified slightly from the original version (Foster and Hirata, 1988) in light of experiences in its application during the 1990s. The modifications include: * somewhat reduced weighting to the "depth to groundwater" factor * some simplification of the geological descriptors as regards "potentially fractured rocks of intermediate intrinsic vulnerability" * clarification of the "groundwater confinement" factor as regards semi-confined aquifers. 22 Part B: Technical Guide - Methodological Approaches to Groundwater Protection Figure 1.2 GOD system for evaluation of aquifer pollution vulnerability *0 r_ Q- GROUNDWATER || CONFINEMENT _ | O | a, 0 u c~~~~~~~~ 0 0.2 0.4 0-6 1.0 I I I I I lacustrine! resi(dual alluvial silts, aoin alluvial and alui-fn UC NOIAE estuarine soils loesst ao, sands fl uvo-glaci al a lfan UNCONSOLIDATED n) OVERLYING STRATA (lithological character mudstones siltstones sandstones chalky | CONSOLIDATED _ __ consolidation of vadose shales volcanic tuffs calcarenites (porous rocks) zone or confining beds) | > igneous/metamorphic recent calcretes + O formations and older volcanic karst l e Nroc volcanics ~~lavas karst limestones (dense rocks) z (x) 0.4 05 0.6 07 0.8 09 1 0 ,0 I I-I I I | _______q________ ' in DEPTH TO GROUNDWATER E 0 TABLE (unconfined) _ A rE OR STRIKE (confined) 6 A V 0 T TTT T z (x) 0.6 07 0.8 0.9 1 0 < z ; ~~~~~~~~~~~~~~~~~~~~~~rn 0 0.1 02 03 0.4 05 06 0.7 0.8 0.9 1 0 AQUIFER POLLUTION NEGLIGIBLE LOW MODERATE HIGH EXTREME VULNERABILITY It should also be noted that, where a variable sequence of deposits is present, the predominant or limiting lithology should be selected for the purpose of specification of the overlying strata. In the GOD scheme, a descriptive subdivision of geological deposits (involving grain-size and mineral characteristics) could have been used and might appear easier to apply. However, a genetic classification better reflects factors important in the pollution vulnerability context (such as depositional structure), and thus a hybrid system (compatible with those used for many geological maps) is adopted. Almost all of the sediments in the classification (Figure 1.2) are transported geological deposits. However, two other types of deposits are retained because of their widespread distribution-deep residual soils (such as the laterites of the tropical belt) and desert calcretes (an in-situ deposit). 23 Groundwater Quality Protection: a guitde for water utilities, municipal authorities, and environment agencies In the context of the classification of overlying strata, there was concern that too much consideration might inadvertently be placed on dynamic porosity (and thus merely on recharge time lag rather than contaminant attenuation). Vulnerability would then * (incorrectly) become more a measure of when (as opposed to if and which) pollutants reach the aquifer. Thus greatest emphasis was put upon the likelihood of well-developed fracturing being present, since this may promote preferential flow even in porous strata such as some sandstones and limestones (Figure 1.3). The possibility of such flow is considered the most critical factor increasing vulnerability and reducing contaminant lf attenuation, given that hydraulic (fluid) surcharging is associated with many pollution scenarios. The original GOD vulnerability scheme did not include explicit consideration of soils in an agricultural sense. However, most of the processes causing pollutant attenuation and/or elimination in the subsurface occur at much higher rates in the biologically active Z soil zone, as a result of its higher organic matter, larger clay mineral content and very > much larger bacterial populations. A possible modification to the method (GODS) Z incorporates a soil leaching susceptibility index (based on a soil classification according 0 to soil texture and organic content), as a fourth step capable of reducing overall ranking Oj in some areas of high hydrogeological vulnerability. Within urban areas the soil is often 0 removed during construction or the subsurface pollutant load is applied below its base ui in excavations (such as pits, trenches, or lagoons), thus the soil zone should be assumed absent and the uncorrected hydrogeological vulnerability used. U Figure 1.3 Development and consequences of preferential flow in the Q_ vadose zone CONTAMINANT SOLUBLE DENSE IMMISCIBLE WATERBORNE LOAD ON MOBILE IONS COMPOUNDS COLLOIDAL PARTICLES co LAND (chloride, nitrate) (DNAPLs, creosote) (bacteria, virus) VADOSE ZONE 24 Part B: Technical Guide - Methodological Approaches to Groinidivater Protection erg . _ *.*ml- m A number of other schemes of aquifer pollution vulnerability assessment have been presented in the literature, and these can be classified into three main groups according to the approach adopted (Vrba and Zaporozec, 1995): * Hydrogeological Settings: these base vulnerability assessment in qualitative terms on the general characteristics of the setting using thematic maps (eg. Albinet and Margat, 1970) * Analogue Models: these utilize mathematical expressions for key parameters (such as average vadose zone transit time) as an indicator of vulnerability index (EC/Fried approach in Monkhouse, 1983) * Parametric Systems: these use selected parameters as indicative of vulnerability and assign their range of values and interactions to generate some form of relative or absolute vulnerability index (examples of this approach include Haertle, 1983 and > -v DRASTIC of Aller and others, 1987, in addition to the GOD methology described _ z in this Guide). A further method of note in this category is EPIK, which is Z specifically designed for karst limestone aquifers only and usefully discussed by > Doerfliger and Zwahlen, 1998; Gogu and Dassargues, 2000; Daly and others, 2001. c m M- Among these the best known is the DRASTIC methodology. It attempts to quantify O I- relative vulnerability by the summation of weighted indices for seven hydrogeological m variables (Table 1A). The weighting for each variable is given in parentheses, but O 0 changes (especially for parameters S and T) if vulnerability to diffuse agricultural Z pollution alone is under consideration. z The method has been the subject of various evaluations (Holden and others, 1992; Bates and § others, 1993; Kalinski and others, 1994; Rosen, 1994). All of these evaluations revealed both - various benefits and numerous shortcomings of this methodology. On balance, it is considered that the method tends to generate a vulnerability index whose significance is rather obscure. This is a consequence of the interaction of too many weighted parameters, some of which are not independent but quite strongly correlated. The fact that similar indices can be obtained by a very different combination of circumstances may lead to dangers in decision making. Table 1.4 Factors and weightings in the DRASTIC pollution vulnerability index * Soil media (X2) 25 Groundwater Quality Protection: a guide for water utilities, muinicipal authorities, and environment agencies X Box 1.2 Aquifer pollution vulnerability mapping incorporating a soil-cover factor in the Cauca Valley, Colombia Some Latin American workers have proposed a modification to the GOD method of aquifer pollution vulnerability estimation, which adds a factor in respect of the attenuation capacity of the soil cover, based on texture alone. In general terms it is considered valid to include a "soil factor," although not in areas where there is risk that the soil profile has been removed or disturbed and not in cases where the contaminant load is applied below the base of the soil. Moreover, if a soil factor is to be included it is preferable to base it upon soil thickness, together with those properties which most directly influence in-situ denitrification and pesticide attenuation (namely the soil texture and organic content). * The Cauca Valley has the largest groundwater storage characteristics of the soil, which range from very fine resources of Colombia, and its aquifers currently support (predominantly clayey) to very coarse (gravelly), in areas o 3an abstraction of around 1000 Mm3/a, which is of where this is more than 0.5m thick. u. fundamental importance to the valley's economic z _) development and provides the municipal water supply for * A map of the values of this soil-cover factor was > various towns including Palmira, Buga, and parts of Cali. produced, which was then overlaid on the GOD aquifer O The valley is a major tectonic feature with a large vulnerability index map. In areas where the soil cover thickness of mixed valley-fill deposits in which alluvial was well preserved and of substantial thickness, the value _J fan and lacustrine deposits predominate. of the GOD index was correspondingly reduced (Paez, 0 0C 1999). 0 With the aim of providing a tool for land-use planning to D protect these resources, the pollution vulnerability of the * The Environment Agency of England & Wales also zC' aquifers was mapped by the local water resource agency include a soil factor in their aquifer vulnerability u (the Corporaci6n del Valle de Cauca) using the GOD mapping. This is based on a set of soil properties s- method. A modification was introduced (as first proposed determining leaching susceptibility, but its effect is limited < by the Pontificia Universidad de Chile-Dpto de Ingenieria to potentially reducing the mapped vulnerability level in -7 Hidraulica y Ambiental) incorporating an S factor in rural areas, and it is not considered operative in urban X. . respect of the contaminant attenuation capacity of the areas-where soil profile disturbance due to engineering soil cover. The modified methodology (known as GODS) construction is widespread (Foster, 1997). involves assigning values of S according to the textural GOD Index Value (0-1.0) S OIL I I IIIII COVER * nonshrinking silty silt silty shrinking coarse sand thin/ TYPE clay clay sand clay & gravel absent 0.5 0.6 0.8 0.9 1.0 II I l l AQUIFER 0 0.1 0.2 0 3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 POLLUTION I NONE NEGLIGIBLE LOW MODERATE HIGH EXTREME VULNERABILITY (GODS Index Value) 26 Part B: Technical Guide * Methodological Approaches to Groundwater Protection More specifically it should also be noted that: * the method underestimates the vulnerability of fractured (compared to unconsolidated) aquifers * including a parameter reflecting contaminant mobility in the saturated zone is an unnecessary complication (for reasons stated earlier). A number of hydrogeological conditions present problems for aquifer pollution vulnerability assessment and mapping: * the occurrence of (permanent or intermittent) losing streams, because of uncertainties in evaluating the hydrological condition, in defining the quality of the watercourse and in appraising streambed attenuation capacity (it is, however, essential to indicate potentially influent sections of streams crossing unconfined > aquifers) z * excessive aquifer exploitation for water supply purposes, which can vary the depth C) to groundwater table and even the degree of aquifer confinement, but given the > scheme of indexation proposed, such effects will only occasionally be significant C m * over-consolidated (and therefore potentially fractured) clays, for which there are usually significant uncertainties about the magnitude of any preferential flow O I- component. c O 0 Aquifer vulnerability maps are only suitable for assessing the groundwater pollution Z hazard associated with those contaminant discharges that occur at the land surface and < in the aqueous phase. Strictly speaking they should not be used for assessing the hazard Z m from: > * contaminants discharged deeper in the subsurface (as may be the case in leakage of large underground storage tanks, solid-waste landfill leachate, effluent discharges to quarries, and mine shafts, etc.) * spillages of heavy immiscible synthetic organic pollutants (DNAPLs). Both are likely to result in high groundwater pollution hazard regardless of aquifer vulnerability. The only consideration in such circumstances will be the intensity and probable duration of the load. The technical validity of the aquifer pollution vulnerability index and map can be maintained, if it is made clear that these types of contaminant load are excluded from consideration by the proposed methodology and that such practices need to be specifically controlled irrespective of field conditions. Another condition that needs a special procedure is the existence of naturally poor- quality (normally saline) groundwater at shallow depth. This requires specific mapping since such aquifers will not generally merit special protection, even in cases of high anthropogenic pollution vulnerability. 27 Groundwater Quality Protection: a gtide for water utilities, municipal authorities, and environnient agencies Figure 1.4 Interpretation of the pollution vulnerability of semi-confined aquifers Problem: using the GOD method, the 0 factor vadosezone- represents the lithology of confining beds or - water i unsaturated zones, but for semi-confined aquifers table this is difficult to determine s ~~~~~~~~~~~~~~~~~~ ~~~~sh-allow arguifer-- ihallow aquIfr -C -Solution: consider the thinnest part of the aquitard aquitard and calculate the 0 factor as a weighted value of different materials (vadose zone, shallow aquifer, and aquitard) co U-J 6J L >~----------------------------- Problem: using the GOD method, the D factor is z ~~~~~~~~~~~~~ ~ ~~water A. *<' ' the distance between the land surface and the O table water table or water strike, but for a semi-confined D sh,alloDw aquifer - - ' > * ---'aquifer what is the correct value? __J I - . -f . ^ ^ Solution: use the depth to the aquifer (A+B) 0, Zu. z 0- O Problem: poor quality shallow aquifer covering water 'vaz the semi-confined aquifer that requires protection table co .. -_fi___ - Solution: consider the shallow aqulifer as a potential contaminant source and thus use the characteristics of the aquitard only for the 0 and D factors aquitard Problem: hydraulic inversion caused by vd ®zpiezometric groundwater extraction from deep aquifer vadose zone surface.v Solution: use G factor appropriate to new table hydraulic condition and treat deep aquifers as now cshallowi semi-confined or even covered aquitard 28 28 Part B: Technical Guide * Metbodologtcal Approaches to Groindwater Protection * * _ *** * m The generation of the map of GOD aquifer vulnerability indices follows the procedures indicated in Figure 1.5. Such a process can be carried out manually for a series of points on a grid basis and contoured, but is increasingly generated by GIS (geographical information system) technology. In the majority of instances, hydrogeological maps and/or groundwater resource reports will be available, and generally these will contain adequate basic data to undertake the evaluation procedure proposed. However, it will often be necessary to supplement this information by the direct study of geological maps and waterwell drilling records, and sometimes by limited field inspection. (A) Approach to Layered Aquifers > One of the most frequent difficulties encountered in aquifer pollution vulnerability Z z mapping is the presence of layering of strata of widely different water-transmitting C) properties. Stratification is a fundamental characteristic of both sedimentary and > .0 volcanic geological formations, and such formations include almost all ma jor, and many c minor, aquifers. Problems may result when the layering occurs both: rn * above the regional groundwater table, giving rise to perched aquifers or covered 0 I- unconfined aquifers (where weighted average or limiting values of the relevant c- properties need to be considered), and O 0 z Figure 1.5 Generation of aquifer pollution vulnerability map using the c GOD system Z unconfined aquifer semi-confined aquifer 5< - 1 0 -- GROUNDWATER HYDRAULIC / 0.4 / CONFINEMENT fluvio-glacial 04 colluvial gravel sands ard ii t __ OVERLYING STRATA 0 6 (lithology and consolidation) DEPTH TO GROUNDWATER TABLE (unconfined) OR STRIKE (confined) AQUIFER POLLUTION VULNERABILITY < ! X 7 r ex~~~~~treme low moderate high 29 Groundwater Quality Protection: a guiide for water utilities, municipal authorities, and environment agencies * below the regional groundwater table, causing semi-confinement of aquifers at X depth (for which a consistent decision needs to be clearly made and stated on U which aquifer is represented by vulnerability mapping, and the attenuation *1 capacity of the overlying strata assessed accordingly). The approach to classification detailed in Figure 1.4 should then be followed for vulnerability estimation, and a record made (by suitable ornament) where an overlying (more vulnerable) local aquifer is also present. (B) Necessary Level of Simplification It must be stressed that aquifer pollution vulnerability maps are designed to provide a general framework within which to base groundwater protection policy. The two, however, are distinct in both concept and function. The former should represent a simplified (but factual) representation of the best available scientific data on the ffi hydrogeological environment, no more or no less. This general framework is not Z intended to eliminate the necessity to consider in detail the design of actual potentially > polluting activities before reaching policy decisions. z 0 Aquifer vulnerability maps are aimed only at giving a first general indication of the -J _J potential groundwater pollution hazard to allow regulators, planners, and developers to 0 O. make better informed judgements on proposed new developments and on priorities in groundwater pollution control and quality monitoring. They are based on the best U- available information at the time of production and will require periodic updating. Z In concept and in practice they involve much simplification of naturally complex geological variations and hydrogeological processes. Site-specific questions need to be answered by site-specific investigations, but the same philosophical and methodological approach to the assessment of groundwater pollution hazard is normally possible. The data required for the assessment of aquifer pollution vulnerability-and for that matter inventories of subsurface contaminant loads-should (wherever possible) be developed on a suitable GIS platform, to facilitate interaction, update, and presentation. Separate colors can be used for major lithological divisions of the strata overlying the saturated zone, with different densities of color for each subdivision of depth to groundwater. 30 PART B: TECHNICAL GUIDE Methodological Approaches to Groundwater Protection B2 Delineation of Groundwater Supply Protection Areas Groundwater supply protection areas (called wellhead protection zones in the United States) should be delmeated'to provide special vigilance against pollution for water sources destined for public (mains) water supply. Consideration must also be given to sources developed for other potentially sensitive uses, and especially of bottled natural mineral waters, which do not receive any form of disinfection. 4D a WON - - I * The concept of groundwater supply protection is long established, being part of legal codes in some European countries for many decades. However, increasing hydrogeological knowledge and changes in the nature of threats to groundwater quality mean that the concept has had to evolve significantly and requires consolidation (US-EPA, 1994; NRA, 1995; EA, 1998). A key factor influencing the hazard posed by a land-use activity to a groundwater supply (well, borehole, or spring) is its proximity. More specifically, the pollution threat depends on: * whether the activity is located within the (subsurface) capture area of that supply (Figure 2.1) * the horizontal groundwater flow time in the saturated aquifer from the location of the activity to the point of abstraction of the supply. 31 Groundwater Quality Protection: a guide for water utilities, municipal auithorities, and environment agencies Figure 2.1 Distinction between area of capture and zone of influence a1 of a production waterwell S a) vertical profile __________CAPTURE AREA _ I ZONE OF _ groundwater _ S g INFLUENCE : 0 divide 5 | Ippumping _ land I ~~~~~~~~~~~~~~well 9 IA z 3~~~~~~~~~~~~~~~~~~~~~~~~~~~~ae tal ru- 1-- 0 b) plan view ____ ____ ___ CAPTURE _ _ _ _ _ _ AREA Dz ZONE OF ( VA INFLUENCE I water-table~ contours z 0 z:c ~~~~~~~~~A i/A LL g r o u n d w t e r V_It' divXide-J. I t z 0 z D ~~~~~~~~~~~~~~flow direction Supply protection areas (SPAs)-also known as source protection zones (SPZs)-have to defend against: * contaminants that decay with time, where subsurface residence time is the best measure of protection * nondegradable contaminants, where flowpath-dependent dilution must be provided. Both are necessary for comprehensive protection. Contaminant dilution resulting from the advection and dispersion mechanisms associated with groundwater flow is usually the dominant attenuation process, but degradation (breakdown) is also likely to occur 32 Part B: Technical Guide - Methodological Approacbes to Groindwater Protectioni for some contaminants (and various other processes such as adsorption and precipitation for others). In order to eliminate completely the risk of unacceptable pollution of a supply source, all potentially polluting activities would have to be prohibited (or fully controlled) within its entire recharge capture area. This will often be untenable or uneconomic, however, due to socio-economic pressure for development. Thus, some division of the recharge capture zone is required, so that the most stringent land-use restrictions will only be applied in areas closer to the source. This subdivision could be based on a variety of criteria (including: horizontal distance, horizontal flow time, proportion of recharge area, saturated zone dilution, and/or attenuation capacity), but for general application it is considered that a combination of (horizontal) flow tine and flow distance criteria are the most appropriate. Special m protection of a proportion of the recharge capture area might (under certain D circumstances) be considered the preferred solution to alleviate diffuse agricultural 0 pollution, but even here the question arises of which part it is best to protect. z 0 A series of generally concentric land-surface zones around the groundwater source can C) be defined, through knowledge of (and assumptions about) local hydrogeological 0 conditions and the characteristics of the groundwater supply source itself. The three Z most important of these zones (Figure 2.2) are described below (Adams and Foster, 1992; Foster and Skinner, 1995). In the interests of supply protection, the zones will need to be subjected to increasing levels of control over land-use activities, which will m tend to vary with local conditions and needs. (A) Total Source Capture Area 0 The outermost protection zone that can be defined for an individual source is its i recharge captire (or catchment) area. This is the perimeter within which all aqulfer i recharge (whether derived from precipitation or surface watercourses) will be captured 0 z in the water supply under consideration. This area should not be confused with the area > of hydraulic interference caused by a pumping borehole, which is larger on the down- gradient side (Figure 2.1). Recharge capture areas are significant not only for quality protection but also in resource management terms, and in situations of intensive groundwater exploitation they might also be used as areas of resource conservation (or reserve) for potable supply. The total capture zone is determined in area by water balance considerations and in geometry by groundwater flowpaths. It is the zone providing the protected long-term yield. Thus, if the groundwater flow system is assumed (as is normally the case) to be in steady-state, its area will be determined by reference to the long-term average groundwater recharge rate. However, it should be recognized that in extended drought (when groundwater recharge is lower than average), the actual capture area will be 33 Groundwater Quality Protection: a guide for water utilities, municipal authorities, and environment agencies larger than that protected. Moreover, in areas where the aquifer is confined beneath * impermeable strata, the capture area will be located distant from the actual site of groundwater abstraction (Figure 2.2b). The protected yield is usually taken as the authorized (licensed) annual abstraction, but may be less than this where the licensed quantity is in practice: - * unobtainable, since it exceeds the hydraulic capacity of the borehole installation * unsustainable, since it exceeds the available groundwater resource * unreasonable, because it greatly exceeds actual abstraction. In such situations the protected yield is better based on recent abstraction rates, together (A with any reasonably forecast increase. z (B) Microbiological Protection Area 0 Preventing ingestion of groundwater contaminated with pathogenic bacteria, viruses, U and parasites is of paramount importance. These pathogens enter shallow aquifers from r°0 some septic tanks soakaways, latrines, contaminated drainage or surface watercourses, and various other routes. Inadequately constructed wells are particularly prone to this type of contamination. However, in all but the most vulnerable formations, V) contamination via the aquifer roufte is prevented by the natural attenuation capacity of W the vadose zone or the semi-confining beds. I- D An inner protection zone based on the distance equivalent to a specified average z O) horizontal flow time in the saturated aquifer has been widely adopted to protect against 0 activities potentially discharging pathogenic viruses, bacteria, and parasites (Foster and Skinner, 1995), such as (for example) the spreading of wastewater and slurries on O farmland. The actual flow time selected in different countries and at various times in the 0 past, however, has varied significantly (from 10 to 400 days). =i Published data (Lewis and others, 1982) suggests that the horizontal travel distance of pathogens in the saturated zone is governed principally by groundwater flow velocity. In ..i all reported contamination incidents resulting in waterborne-disease outbreaks, the horizontal separation between the groundwater supply and the proven source of pathogenic pollution was (at maximum) the distance travelled by groundwater in 20 days in the corresponding aquifer flow regime. This was despite the fact that hardy pathogens are known to be capable of surviving in the subsurface for 400 days or more. Thus the 50-day isochron was confirmed a reasonable basis with which to define the zone (Figure 2.2), and this conforms with existing practice in many countries. This protection perimeter is perhaps the most important of all in terms of public health significance, and since it is usually small in size, implementation and enforcement are more readily achieved. Experience has shown that in fissure-flow aquifers (which are often very heterogeneous in hydraulic properties), it is prudent to establish a limiting criterion of 50 m radius. 34 Part B: Technical Guide - Methodological Approaches to Groundwater Protection Figure 2.2 Idealized scheme of groundwater capture areas and transit- time perimeters around a waterwell and springhead r a) unconfined aquifer waterwell -- -… 200m 50 days SQO days 10 years m WELLHIEAD I SANITARY MICROBIOLOGICAL TOTAL SOURCE OPERATIONAL ZONE | INSPECTION ZONE PROTECTION AREA CAPTURE AREA Z 0 z b) locally confined aquifer C) SOm precautionary \ - O waterwell (no 50-day zone) - lirit of - - confining-| / /; beds / 20m- _ (____~~ _ -- / C 20m -~- 200m 500 days 10 years co 0 c) unconfined spring source 0 z springhead . . 200m 50 days 500 days 10 years oo 35 Groundwater Quality Protection: a guide for water utilities, uniincipal auithorities, and environment agencies Moreover, even if aquifers are covered or confined beneath thick low permeability * strata, a 50-meter-radius zone is also recommended as a precautionary measure (Figure 2.2b), in recognition of the uncertainties of vertical flow and to protect against subsurface engineering construction, which could compromise source protection. (C) Wellhead Operational Zone The innermost protection perimeter is that of the wellhead operational zone, which comprises a small area of land around the supply source itself. It is highly preferable for this area to be under ownership and control of the groundwater abstractor. In this zone no activities should be permitted that are not related to water abstraction itself, and even these activities need to be carefully assessed and controlled (Figure 2.3) to avoid the ;:5 possibility of pollutants reaching the source either directly or via adjacent disturbed < ground. All parts of the zone used for well maintenance activities should have a concrete z floor to prevent infiltration of oils and chemicals used in pump maintenance. Fencing is 0 also standard practice to prevent invasion by animals and vandalism. u UJ O Specification of the dimension of this area is necessarily rather arbitrary and dependent to some degree on the nature of local geological formations, but a radius of at least 20 meters is highly desirable (Figure 2.2a). Detailed inspections of sanitary integrity, V) however, should be conducted over a larger area of 200 meters or more radius. < (D) Further Subdivision Q It may be found useful to subdivide the total source capture area further, to allow z D gradational land-use controls beyond the microbiological protection zone. This can be 0 CC done on the basis of a horizontal flow isochron of 500 days, for example (Figure 2.2a), LA. to provide attenuation of slowly degrading contaminants. The selection of the time-of- Z travel is somewhat arbitrary. In reality such a perimeter is most significant in terms of O providing time for remedial action to control the spread of persistent pollutants (at least in cases where a polluting incident is immediately recognized and notified) and is thus z _J sometimes called the source inner-defensive zone. . . Furthermore, a horizontal flow isochron of 10 years or more (Figure 2.2a) is sometimes substitiLted for the perimeter of the total capture area in high-storage aquifer systems with complex boundary conditions and/or abstraction regimes, where the former will be of less complex shape and subject to less scientific uncertainty. Most protection zone delineation has to assume that steady-state groundwater flow conditions effectively exist. On this basis the factors controlling the actual shape of the various zones to be delineated are summarized in Table 2.1. 36 Part B: Technical Guide - Metbodological Approacbes to Groundivater Protectionl Figure 2.3 Actual examples of welihead completion for major public water supply boreholes A~~~~~~~~~~~~~~~~~~~~~~~~~~~ V A.~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~e .. b.1U...F rr, _.;_ ]! - 1 E s~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~r 0 z 0 C) ;O a) well-designed, drained, and maintained welihead operational zone in rural wooded area 0 C z m ; - X - T1 - -v ~~~~~~ 0 R - a _S~~~ '- Z 1. 1 f Z .-~ - _g- _ - > ,˘-~j;/i 0 z r~~ ~ ~ . a , > P ! N - X ji&W!_ ! Ym a~~~~~~~~ b) inadequately sized and protected welihead operational zone threatened by agricultural irrigation with urban wastewater 37 Groundwater Quality Protection: a guide for water utilities, municipal authorities, and environment agencies Box 2.1 Operation of a long-standing groundwater source protection zone policy in Barbados This case study reveals the benefits of early introduction of grouindwater supply protection areas, even in situations where the nature of the aquifer flow regime and the pollution hazards are not yet completely understood. Supplementary actions can always be taken to subsequently reinforce existing provisions. * The Caribbean island of Barbados is very heavily urbanization with in-situ sanitation around the capital, dependent upon groundwater for its public water supply, Bridgetown, and leakage from commercial and domestic abstracting some 115 Ml/d from 17 production wells in a oil storage installations. highly permeable karstic limestone aquifer of extreme pollution vulnerability. * However, additional threats have subsequently emerged (Chilton and others, 1990) such as: * The potential impact of urban development and the great - the replacement of traditional extensive sugar-cane O strategic importance of groundwater supplies led the cultivation with much more intensive horticultural Barbados government to establish special protection areas cropping involving much higher fertilizer and pesticide u- 1-- around all of its public-supply wells about 30 years ago. applications 0 The perimeters of these protection areas are defined on - illegal disposal of industrial solid waste disposal by the basis of average groundwater travel times to the fly tipping in abandoned small limestone quarries and wells, and the range of restrictions imposed is effluent disposal down disused wells. V) summarized in the table below. These for the most part Measures have now been introduced to control and to w have been successful in conserving water supply quality. monitor such activities. * At the time of introducing the policy, the main hazards to Z groundwater was perceived to be the spread of D 0 Principal features of development control zones Z Zone Definition of Maximum Depth of Domestic Industrial 0 Outer Boundary Wastewater Soakaway Pits Controls Controls 1 300-day none no new housing; no new DU travel time allowed no changes to existing industrial .~ .wastewater disposal development 2 600-day 6.5 m septic tank with separate soakaway travel time - - pits, for toilet effluent and other all liquid domestic wastewater, no storm industrial waste runoff to sewage soakaway pits, no to disposal new fuel tanks specified by Water Authority 3 5-6 year 13 m as above for domestic wastewater, fuel with maximum travel time tanks subject to approved leakproof design soakaway pit depths as for 4 other areas no limit no restrictions on domestic wastewater domestic waste disposal, fuel tanks approved subject to leakproof design 38 Part B: Technical Guide - Methodological Approaches to Groundwater Protection Table 2.1 Factors determining the shape and extension of groundwater supply protection areas* PROTECTION AREA CONTROLLING FACTORS _ Overall Location and Shape aquifer recharge and flow regime (recharge area/boundaries, natural discharge areas, hydraulic condition of streams', aquifer boundaries, aquifer confinement, aquifer hydraulic gradients) w presence of other pumping wells/boreholes't Area of Supply Capture Zone protected/licensed annual abstraction rate annual groundwater recharge rate(s)*m Perimeter of Inner Flow-Time- aquifer transmissivity distribution Z Based Zones (50-day and aquifer dynamic flow thickness* o 500-day isochron) Z aquifer (effective) dynamic porosity** O excludes manmade changes in groundwater regime due to urban construction and C) mining activities 0 these factors are generally time variant in nature and will provoke transient changes in z the form of capture zones and isochrons, but average (or in some instances worst case) values are taken in steady-state formulations > termed dynamic in view of the fact that in heterogeneous (and especially fissured) aquifers, only a part of the total thickness and/or porosity (and in some cases only a minor 21 part) may be involved in the flow regime to the groundwater supply source concerned C 0 rn Microbiological protection zones are generally of fairly simple geometry, tending to be 0 z ellipsoidal or circular in form reflecting the cone of pumping depression around an > abstraction borehole. For fissured aquifers the areal extent of these zones is very sensitive to the values taken for effective aquifer thickness and dynamic porosity (Figure 2.4), while their shape is sensitive to aquifer hydraulic conductivity. The key factors determining the geometry of overall source capture zones are the aquifer recharge regime and boundary conditions (Adams and Foster, 1992); their shape can vary from very simple to highly complex. More complex shapes may be the result of variable groundwater/river interactions, the interference effects from other groundwater abstractions and/or lateral variations in hydraulic properties. Long narrow protection zones will be delineated where the supply source is located at large distance from aquifer boundaries and/or where the abstraction rate is small, the hydraulic gradient is steep and the aquifer transmissivity is high. 39 Groundwater Quality Protection: a guide for wvater utilities, municipal authorities, and environment agencies Figure 2.4 Sensitivity of 50-day transit-time perimeter to * interpretation of fissured aquifer properties _~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~5-a |iS-dacischrnn regional ~ axallngh 27m groundwater flow z o 0 total groundwater _i chlege a b oe b hsewodeadethrgeae roetosource capture area CASE A B effective 1 0 thickness (in) S0 200 _i effective 0.02 0.40 I-) CommonProbl0 km 1 porosity < z 0 0~~~~~~~~~~~~~~~4 z ~~~~~~~~~~~~~The supply protection area (SPA) concept is a simple and powerful one, which is readily o understood by land-use planners and others who need to make the often difficult public decisions generated by groundwater protection policies. However, many technical z _J ~~~~~~~~~~~~~challenges can be posed by those who demand either greater protection or less restriction, and the test of any concept is whether it deals fairly with these competing criticisms, in (N ~~~~~~~~~~~~~the context of the circumstances it has to address (Foster and Skinner, 1995). SPAs are most easily defined and implemented for major municipal wells and wellfields in relatively uniform aquifers that are nor excessively exploited, but it is a valuable and instructive exercise to attempt to define them regardless of local conditions and constraints. (A) Common Problems with Suggested Solutions There are a number of hydrogeological situations where the concept encounters significant complications: S the most serious limitation arises when aquifers are subject to heavy seasonally variable pumping for agricultural irrigation or industrial cooling, since interference 40 Part B: Technical Guide * Methodological Approaches to Grounedwater Protection Figure 2.5 Effect of various types of hydraulic interference and boundaries on the shape and stability of groundwater supply capture areas (a) effect of intermittent abstraction - g/j/g/,/X ,J/ ' //,7gog total groundwater supply capture area FT+ > F when irrigation ,0,/ /- ---/S§X// wells NOT pumping when irrigation i wells pumping public water-supply irrigation wells borehole (seasonal pumping) (continuous pumping) (b) effect of effluent river (c) effect of influent river K) area of potential influence via river rm public water-supply boreholeD- 0 7 4- ~~~~~~~~~~~~~~~~0 effluent /) (gaining) ri'ver / public water-supply borehole public water-supply borehole m total groundwater supply capture area C between pumping wells produces excessively complex and unstable protection O zones (Figure 2.Sa); recourse to overall resource protection via aquifer 0 vulierability criteria may then be the only feasible approach l * for aquifers wbose long-term abstraction considerably exceeds their long-term 0 recharge, a condition of continuously falling groundwater levels and inherently > unstable SPAs arises * the presence of surface watercourses gaining intermittently or irregularly from natural aquifer discharge can produce similar complications (Figure 2.5b) * where losing surface watercourses are present within the capture zone to a supply source, any potentially polluting activity in the surface water catchment upstream of the recharge capture area could affect groundwater quality (Figure 2.5c), although it will usually be impractical to include this catchment in the source protection area * special problems arise, especially with the definition of recharge capture areas, in situations where the groundwater divide is at a great distance and/or the regional hydraulic gradient is very low, and it will often be necessary to adopt a cut-off isochron (of 10 years) 41 Groundwater Quality Protection: a guide for water utilities, municipal authorities, and environment agencies * the presence of multi-layered aquifers, where vertical hydraulic gradients may *1 develop inducing vertical leakage between aquifer units; each multi-layered aquifer situation will need to be examined on a site-by-site basis and some simplifying assumptions on hydraulic behavior made * where the annual variation of the source capture area is very large (as in low- storage aquifers), the maximum (rather than average) area might be more appropriate, and local modifications may thus be required * small groundwater supplies (with yields of less than 0.5 MI/d ) because in some situations their capture areas will be very narrow and of unstable locus. Some may regard the 50-day travel-time criterion as excessively conservative because it ;:5 takes no account of the large time-lag during percolation down the vadose zone, but in reality this needs to be balanced against the following factors: z * the possibility of rapid preferential flow through fissures, which can significantly 0 reduce the retardation normally associated with vadose zone transport u 0* the isochron is calculated using mean saturated flow velocities, derived from 0 average local aquifer properties and hydraulic gradients, and in fissure-flow aquifers a proportion of the water will travel much more rapidly than the average L some contaminants may enter the ground with significant hydraulic loading (via drainage soakaways) and others (such as dense immiscible organic solvents) may have physical properties that favor more rapid penetration into the ground than 1-_ < water D 0 there is significant scientific evidence that some more environmentally hardy z z pathogens (such as Cryptosporidium oocysts) can survive much longer than 50 0 days in the subsurface (Morris and Foster, 2000). O (B) Case of Karstic Limestone Aquifers O Flow patterns in karstic limestone aquifers are extremely irregular due to the presence of dissolution features (such as caves, channels, and sinks), which short-circuit the more z DJ diffuse flowpaths through the fractured media as a whole. Contaminants moving Lii C through such a system can travel at much higher velocities than those calculated by .. average values of the aquifer hydraulic properties on an "equivalent porous media" approach. This simplification can be valid if the scale of analysis (and modelling) is regional, and if known major dissolution cavities associated with faults, or other structural features, are included, but in other cases the assumption can be misleading. Where karstic features are present, they should be systematically mapped through field reconnaissance, aerial photograph interpretation, and (possibly) geophysical survey, at least in the vicinity of the springs or wells to be protected. Knowledge gained through local hydrogeological investigation (especially using artificial tracer tests and/or environmental isotopes) and speleological inspection should be also used on a site-by-site basis for protection area delineation, rather than using average aquifer properties and hydraulic gradients for the calculation. It must be accepted that major departures from 42 Part B: Technical Guide . Methodological Approaches to Groundivater Protection Box 2.2 Delineation of groundwater supply protection zones for land-use planning in Esperanza, Argentina The delineation of groundwater capture and flow-time zones, together with the mapping of aquifer pollution vulnerability, is an essential component of water source protection and land-use planning at the mumlcipal level. * The town of Esperanza (Sante Fe Province) meets its WHPA semi-analytical method using groundwater travel water demand entirely from groundwater. Locally, the times up to 5 years, as a basis for recommending graduated semi-confined aquifer is intensively exploited not only to measures of aquifer pollution control and land-use restriction meet these demands, but also for agricultural irrigation (Paris and others, 1999). and for a neighboring industrial center. The implementation of groundwater source protection areas, * The town's groundwater sources comprise: however, is not a straightforward task, and it may be - a wellfield in a rural setting, where no land-use strongly resisted by those industries for which severe D regulations or restrictions exist constraints or total relocation are proposed (as a result of - a number of individual wells within the urban area, their character). Such actions can prove difficult to achieve in 5 which has incomplete sanitary infrastructure and view of their socioeconomic repercussions. Because of these O various industrial premises and services. considerations and with the object of facilitating improved Z levels of groundwater source protection, the alternative 0 This situation, coupled with an aquifer pollution strategy of relocating groundwater abstraction to a new vulnerability rated as moderate by the GOD methodology, wellfield outside the area of urban influence has been O suggested the existence of a significant groundwater proposed. The perimeters of protection for the proposed C pollution hazard and the need for the introduction of wellfield would then be delineated, with legal provision and protection measures including land-use planning. technical regulations being introduced to guarantee their > effectiveness. A groundwater monitoring network would r For this purpose a range of possible protection perimeters also be established for the early detection and remediation of c were delineated for the 20 municipal wells, employing the any potential problems. 0 U ~~~~~~~~~~~~~~~~~~~~~n urban area - -'1 z m location of 5-year / travel protection perimeters for Esperanza wellfields industrial premises 1 km 43 Groundwater Quality Protection: a guide for water uitilities, municipal authorities, and environment agencies Figure 2.6 Adaptation of microbiological protection perimeters for the a case of karstic limestone aquifers _ clay-covered $ ~~~~~~~~~~~~~~~swallow t0>< 21 ~~~~~~~~~~~ ~ ~ ~ ~ ~~doline X Z groundwater 0 LU 1-O 50-day isochron using > spring*gK r ' average aquifer hydraulic C_I El additional 15-m buffer zones LI l-i < normal zone geometry should be expected (Daly and Warren, 1998) and that known surface solution features at large distances from the supply source, and the surface water z O) catchment draining to them, will also warrant special protection (Figure 2.6). 0 LL (C) Case of Spring and Gallery Sources 0 In some places groundwater abstraction takes place from springs, that is from points of z o natural discharge at the surface. Springs present special problems for protection area delineation in that the abstraction is governed by natural groundwater flow driven by Z; gravity. The size of the capture area is thus dependent on the total flow to the spring, rather D) than the proportion of the flow actually abstracted. Springflow may be intermittent, .i .reducing drastically or even drying-up in the dry season as the water table falls. Springs often occur at the junction of geological discontinuities, such as lithology changes, faults or barriers, the nature and extent of which may be at best only partially understood. Moreover, there may also be considerable uncertainty on the actual location of springs, given the presence of infiltration galleries and pipe systems. Inevitably for all these cases, rather approximate, essentially empirical, and somewhat conservative assumptions have to be made in the delineation of protection perimeters (Figure 2.2). The delineation of protection zones around well sources can also be complicated by the presence of galleries (or adits), which distort the flow-field by providing preferential pathways for water movement; empirical adjustment is normally the method used to 44 Part B: Technical Guide * Methodological Approaches to Groundwvater Protection deal with this problem, although numerical modelling may also be an aid where sufficient data are available. (D) Implementation in Urban Settings The concept of groundwater supply capture areas and flow zones is equally valid in all environments, but substantial problems often occur in both their delineation through hydrogeological analysis and their implementation as protection perimeters in the urbani environment. This results from the complexity of aquifer recharge processes in urban areas, the frequently large number of abstraction wells for widely differing water uses and the fact that most of the SPAs defined will already be occupied by industrial and/or residential development. Nevertheless, the zones delineated will serve to prioritize groundwater quality monitoring, inspection of industrial premises and groundwater pollution mitigation m measures (such as changes in industrial effluent handling or chemical storage and Z introduction of mains sewer coverage in areas of high aquifer pollution vulnerability). l 0 z 0 r_ * C)* 6~ 0 0 - w ~14 The delineation of perimeters of source protection zones can be undertaken using a wide 0 variety of methods (Table 2.2), ranging from the oversimplistic to extremely elaborate. Z Historically, arbitrary fixed-radius circular zones and highly simplified, elliptical shapes have been used. However, due to the obvious lack of a sound scientific foundation, it was often difficult to implement them on the ground, because of their questionable X reliability and general lack of defensibility. 0 Table 2.2 Assessment of methods of delineation of groundwater m supply protection areas - 0 METHOD OF DELINEATION COST RELIABILITY z lowest least Arbitrary Fixed/Calculated Radius Simplified Variable Shapes Analytical Hydrogeological Models Hydrogeological Mapping Numerical Groundwater Flow Models (with particle tracking routines for flowpath definition) highest most 45 Groundwater Quality Protection: a guide for water utilities, municipal authorities, and environment agencies Emphasis will thus be put here on two methodological options: . * simple, but scientifically based, analytical formula, tools, and models * more systematic aquifer numerical modelling * but the choice between them will depend more on hydrogeological data availability than any other consideration. M In both cases it is essential to reconcile the zones defined with local hydrogeological conditions, as depicted by hydrogeological maps. The delineation process is highly 3 dependent upon the reliability of the conceptual model adopted to describe the aquifer system and on the amount and accuracy of data available. However, the geometry of the protection zone defined will also be influenced by the method used for its delineation. <