GROUND WATER VULNERABILITY ASSESSMENT

Contamination Potential Under Conditions of Uncertainty

Committee on Techniques for Assessing Ground Water Vulnerability

Water Science and Technology Board

Commission on Geosciences, Environment, and Resources

National Research Council

NATIONAL ACADEMY PRESS
WASHINGTON, D.C.
1993



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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty GROUND WATER VULNERABILITY ASSESSMENT Contamination Potential Under Conditions of Uncertainty Committee on Techniques for Assessing Ground Water Vulnerability Water Science and Technology Board Commission on Geosciences, Environment, and Resources National Research Council NATIONAL ACADEMY PRESS WASHINGTON, D.C. 1993

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty National Academy Press 2101 Constitution Avenue, N.W. Washington, D.C. 20418 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. Support for this project was provided by the U.S. Department of Agriculture Contract No. 59-0700-1-145, U.S. Environmental Protection Agency Grant No. CR-817614-01-1, and the U.S. Geological Survey Contract No. 14-08-001-AO834. Library of Congress Cataloging-in-Publication Data Ground water vulnerability assessment: predicting relative contamination potential under conditions of uncertainty / Committee on Techniques for Assessing Ground Water Vulnerability, Water Science and Technology Board, Commission on Geosciences, Environment, and Resources, National Research Council. p. cm. Includes bibliographical references and index. ISBN 0-309-04799-4 1. Groundwater—Pollution. 2. Water—Pollution potential. I. National Research Council (U.S.). Committee on Techniques for Assessing Ground Water Vulnerability. TD426.G725 1993 628.1'68—dc20 93-32944 CIP Copyright 1993 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty COMMITTEE ON TECHNIQUES FOR ASSESSING GROUND WATER VULNERABILITY ARMANDO J. CARBONELL, Chair, Cape Cod Commission, Barnstable, Massachusetts; and Harvard University, Cambridge, Massachusetts WILLIAM M. ALLEY, U.S. Geological Survey, Reston, Virginia LAWRENCE G. BATTEN, Environmental Systems Research Institute, Boulder, Colorado CHERYL K. CONTANT, The University of Iowa, Iowa City PAMELA G. DOCTOR, Battelle Pacific Northwest Laboratories, Richland, Washington ANTHONY S. DONIGIAN, JR., AQUA TERRA Consultants, Mountain View, California ROBERT H. DOWDY, University of Minnesota/USDA-Agricultural Research Service, St. Paul P. SURESH C. RAO, University of Florida, Gainesville DONALD I. SIEGEL, Syracuse University, Syracuse, New York GALE W. TeSELLE, U.S. Department of Agriculture, Soil Conservation Service, Washington, D.C. ROBERTO R. TESO, California Department of Pesticide Regulation, Riverside SCOTT R. YATES, University of California, Riverside/USDA-Agricultural Research Service Former Committee Members HUGO F. THOMAS, Chair, Connecticut Department of Environmental Protection, Hartford (through 3/22/91) KEITH LOAGUE, University of California, Berkeley (through 4/29/92) JAMES R. WALLIS, IBM Watson Research Center, Yorktown Heights, New York (through 10/18/91) Staff SARAH CONNICK, Study Director PATRICIA L. CICERO, Senior Project Assistant

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty WATER SCIENCE AND TECHNOLOGY BOARD DANIEL A. OKUN, Chair, University of North Carolina, Chapel Hill A. DAN TARLOCK, Vice Chair, Illinois Institute of Technology, Chicago-Kent College of Law J. DAN ALLEN, Chevron USA, Inc., New Orleans, Louisiana KENNETH D. FREDERICK, Resources for the Future, Washington, D.C. DAVID L. FREYBERG, Stanford University, Stanford, California WILFORD R. GARDNER, University of California, Berkeley DUANE L. GEORGESON, Metropolitan Water District of Southern California, Los Angeles LYNN R. GOLDMAN, California Department of Health Services, Emeryville WILLIAM GRAF, Arizona State University, Tempe THOMAS M. HELLMAN, Bristol-Myers Squibb Company, New York, New York ROBERT J. HUGGETT, Virginia Institute of Marine Science, Gloucester Point CHARLES C. JOHNSON, Consultant, Bethesda, Maryland JUDY L. MEYER, University of Georgia, Athens STAVROS S. PAPADOPULOS, S. S. Papadopulos & Associates, Inc., Rockville, Maryland KENNETH W. POTTER, University of Wisconsin, Madison BRUCE E. RITTMANN, Northwestern University, Evanston, Illinois PHILIP C. SINGER, University of North Carolina, Chapel Hill JOY B. ZEDLER, San Diego State University, San Diego Staff STEPHEN D. PARKER, Director SARAH CONNICK, Senior Staff Officer SHEILA D. DAVID, Senior Staff Officer CHRIS ELFRING, Senior Staff Officer GARY KRAUSS, Staff Officer JACQUELINE MACDONALD, Staff Officer JEANNE AQUILINO, Administrative Associate ANITA A. HALL, Administrative Assistant PATRICIA L. CICERO, Senior Project Assistant MARY BETH MORRIS, Senior Project Assistant GREGORY K. NYCE, Senior Project Assistant

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES M. GORDON WOLMAN, Chair, The Johns Hopkins University, Baltimore, Maryland PATRICK R. ATKINS, Aluminum Company of America, Pittsburgh, Pennsylvania PETER S. EAGLESON, Massachusetts Institute of Technology, Cambridge EDWARD A. FRIEMAN, Scripps Institution of Oceanography, La Jolla, California HELEN M. INGRAM, University of Arizona, Tucson W. BARCLAY KAMB, California Institute of Technology, Pasadena GENE E. LIKENS, The New York Botanical Garden, Millbrook SYUKURO MANABE, NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey JACK E. OLIVER, Cornell University, Ithaca, New York FRANK L. PARKER, Vanderbilt/Clemson University, Nashville, Tennessee DUNCAN T. PATTEN, Arizona State University, Tempe RAYMOND A. PRICE, Queen's University at Kingston, Ontario, Canada MAXINE L. SAVITZ, Garrett Ceramic Components, Torrance, California LARRY L. SMARR, University of Illinois, Urbana-Champaign STEVEN M. STANLEY, The Johns Hopkins University, Baltimore, Maryland WARREN WASHINGTON, National Center for Atmospheric Research, Boulder, Colorado EDITH BROWN WEISS, Georgetown University Law Center, Washington, D.C. IRVIN L. WHITE, Battelle Pacific Northwest Laboratories, Washington, D.C. Staff STEPHEN RATTIEN, Executive Director STEPHEN D. PARKER, Associate Executive Director LORRAINE W. WOLF, Assistant Executive Director JEANETTE SPOON, Administrative Officer BARBARA SINGLETARY, Administrative Associate ROBIN ALLEN, Senior Project Assistant

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council.

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty Preface The topic of assessing ground water vulnerability first came to the attention of the Water Science and Technology Board (WSTB) in December 1988. Concerned about the scientific basis for vulnerability assessments and the potential for their inappropriate application, the board organized and hosted a planning session in February 1990 to become better informed on the issues. The session was attended by experts from industry, academe, and federal, state, and local agencies interested in ground water protection issues; they concluded that the WSTB should undertake a study of techniques for assessing ground water vulnerability. The board then drew on the deliberations of the planning session to develop the terms of reference for this study. With financial support from the U.S. Environmental Protection Agency, U.S. Geological Survey, and U.S. Department of Agriculture, the WSTB appointed the Committee on Techniques for Assessing Ground Water Vulnerability. The committee's study expands on two National Research Council reports: Ground Water Models: Scientific and Regulatory Applications (1990), and Spatial Data Needs: The Future of the National Mapping Program (1990). These reports served as points of departure for committee deliberations on broader, generic issues pertaining to regional assessments of ground water contamination. Specifically, the committee's charge was to: Identify the existing and proposed uses of vulnerability assessment

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty   methods, identify extant methods, and review their scientific bases and effectiveness. Review, in cooperation with other efforts, available spatially referenced databases to determine their applicability to regional assessments of ground water contamination potentials, and recommend parameters for inclusion in data collection and protocols for database development. Develop generic guidelines and criteria for evaluating assessment methods in terms of (a) interpretation of their outputs and (b) their use in decision making. Develop a research agenda for: (a) acquiring minimum databases required for making valid vulnerability assessments, and (b) developing more reliable assessment techniques. Following an initial meeting in Washington, D.C., the committee met on four other occasions, in Barnstable, Massachusetts; Fresno, California; Orlando, Florida; and Oahu, Hawaii. At each site, the committee heard presentations from technical experts engaged in the development of vulnerability assessment methods and from managers actively involved in policy formulation and the application of these techniques in county, state, and national ground water protection programs. Firsthand discussions with leading practitioners of both the scientific and management aspects of ground water vulnerability assessment were extremely helpful to the committee's deliberations, which often took the form of lively debate, both during and following formal sessions. Each of these locations or states, along with Iowa, which was not visited, is the subject of a case study in Chapter 5 of this report. The committee did not attempt to issue the last word on the problem it was given. Despite considerable progress over the last 20 years in research and understanding of contamination transport and fate processes, adequate understanding of these processes is still lacking in many areas. This gap in understanding precludes our ability to predict, with high certainty, the effects on ground water vulnerability of a change in management practices in a region. The members of this committee believe this report should be useful to managers who will rely on vulnerability assessments. The report includes guidance for making informed judgments on whether an assessment provides the necessary information to be useful in the decision making process and how the assessment might be lacking. For example, a key piece of information, which is rarely included in assessment results, is the uncertainty of the ground water vulnerability assessment. The committee addressed fundamental questions regarding the definition of ground water vulnerability, a concept that is in turn subtle and obvious, and has stated its most general findings as the three Laws of Ground Water Vulnerability. The committee was not bound by preconceptions

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty of validity or invalidity of existing vulnerability assessment techniques in its evaluation of the potential scope of the field and looked beyond the limitations of current techniques and databases. Our recommendations for further development of techniques and databases, and for directions of scientific research appear in Chapter 6. Some readers may feel that this report provides an overly pessimistic view on the use of vulnerability assessments. It is true that the committee, in struggling with the manifold technical and practical difficulties affecting the performance of vulnerability assessments today, nearly concluded that their limitations are so great as to be no use in management decision making. Recognizing that managers will make decisions about ground water with or without vulnerability assessments, the committee instead asked whether it is better to have the information provided by a vulnerability assessment or not. With due regard to the danger of misapplication of vulnerability assessments by managers unfamiliar with the limitations of assessment methods, the committee felt that assessments provide an increment of useful information, albeit not enough to provide the sole support for any decision. Early in its work, the committee decided to treat ground water vulnerability assessment foremost as a tool for management. Accordingly, this report is designed to be of direct use to managers as well as to those who develop techniques for assessing vulnerability and the science that supports these techniques. The report is consumer oriented in that it reflects current and future management needs and the ability or inability of existing or foreseeable assessment techniques to meet these needs. On the immediate horizon, the most significant and potentially controversial use of vulnerability assessments is in differential management of ground water resources, as contemplated by federal programs that would have states perform assessments in support of management plans for areas based on their vulnerability to contamination. Differential management has as its goal efficient resource management and relies on an ability to discriminate between areas of higher and lower ground water vulnerability. Regulatory regimes developed under differential management could, for example, include differences in allowable uses and management practices for potential ground water contaminants, such as agricultural pesticides. Policy makers and regulators engaged in differential management should be cautioned by the sections of this report that describe the limits of existing assessment techniques in making discriminating predictions of the likelihood of ground water contamination. Reworded, the Third Law of Ground Water Vulnerability says extreme differences in vulnerability can be differentiated, but subtle ones cannot. An important issue, which was not considered by this committee in an attempt to keep the scope of the report manageable, is the economics of vulnerability assessment. Risk-cost-benefit analyses are likely to play an

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty integral role in determining whether vulnerability assessments are used in the future. Economics will be especially important in determining when it is cost-effective to collect additional data for newer or more complex approaches or whether existing data will suffice. This issue requires further consideration. The committee comprised, by design, individuals representing diverse disciplines, expertise, interests, and geographies, and our report reflects this diversity. A problem with investigations of large-scale, multidisciplinary problems such as ground water vulnerability or contamination is that difficulties can arise in communicating ideas among scientific disciplines rooted in different philosophies and approaches to problems. In such cases, differences in concepts and terminology can become a problem. However, one of the strengths of the National Research Council study process is that it challenges members of the committee to reevaluate their own ideas in the context of the problem at hand. Members are required to convey what they see personally as truth and to communicate their ideas in terms that can be understood by people outside their individual disciplines. It should also be mentioned that, although this report reflects the consensus of the committee, it does not necessarily reflect each member's beliefs in their entirety. It was a privilege for me to spend many hours struggling with these diverse and talented individuals over difficult and sometimes contentious questions, at times equipped only with metaphors to see us through to consensus. Many individuals from all parts of the country, acknowledged by name in Appendix C, gave generously of their time to share expertise and advise the committee on ground water science and management aspects of vulnerability assessment. The willingness of local hosts to provide access to both informed people and instructive field experiences was critically important to the project. The National Research Council and its Water Science and Technology Board unstintingly supported the committee's efforts during the course of this study. Senior Project Assistant Patricia Cicero proved indispensable as both logician and logistician. It is a pleasure to convey the entire committee's respect for Project Director Sarah Connick, without whose rare combination of insight, persistence, patience, and good humor this report truly would not have been possible. Last, on a personal note, I would like to acknowledge the support of Barnstable County and the Cape Cod Commission during this effort. Armando J. Carbonell, Chair Committee on Techniques for Assessing Ground Water Vulnerability

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty Contents       EXECUTIVE SUMMARY   1     Introduction   1     Management   4     Approaches to Vulnerability Assessment   5     Data and Databases   9     Case Studies   9     Research Recommendations   10     Reference   11 1   INTRODUCTION   13     Protecting Ground Water from Future Contamination   14     Assessing Ground Water Vulnerability   19     The Vulnerability Assessment Process   26     References   29     BOXES     President's Water Quality Initiative   15     EPA's Pesticides and Ground Water Strategy   16     The Many Ways of Defining Ground Water Vulnerability   17     Scale, Size, and Maps   23 2   CONSIDERATIONS IN THE SELECTION AND USE OF VULNERABILITY ASSESSMENTS   30     Introduction   30

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty     Existing and Potential Uses for Vulnerability Assessments   31     Factors Affecting Selection and Use of Vulnerability Assessments   35     Summary   40 3   APPROACHES TO VULNERABILITY ASSESSMENTS   42     Introduction   42     Review of Current Approaches   44     Uncertainty in Vulnerability Assessment Methods   63     Testing and Evaluation of Vulnerability Assessments   77     Computing Environments for Vulnerability Assessments   86     Summary   94     References   97     BOXES         First-Order Uncertainty Analysis   69     Uncertainty in Pesticide Leaching Assessments   70     Field-Scale Model Testing and Validation   78     Evaluation of Regional Vulnerability Assessment   82     Geographic Information Systems   88 4   DATA AND DATABASES   104     Introduction   104     Topography   109     Soils   112     Hydrogeology   121     Weather and Climate   123     Land Use and Land Cover   126     Management Factors   129     Conclusion   131     References   132     BOXES         The Spatial Data Transfer Standard   107     Soil Mapping   113 5   CASE STUDIES   135     Introduction   135     Iowa   135     Cape Cod   139     Florida   144     The San Joaquin Valley   151     Hawaii   155     Application of a Vulnerability Index for Decision-Making at the National Level   162

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty     Summary   165     References   167 6   CONCLUSIONS AND RECOMMENDATIONS   170     Management Implications   171     Approaches   173     Data and Databases   174     Research Agenda   175     APPENDIXES         A SOURCES FOR DIGITAL RESOURCE DATABASES   181     B BIOGRAPHICAL SKETCHES OF COMMITTEE MEMBERS   185     C CONTRIBUTORS TO THE COMMITTEE'S EFFORT   189     INDEX   193

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Ground Water Vulnerability Assessment: Contamination Potential Under Conditions of Uncertainty GROUND WATER VULNERABILITY ASSESSMENT

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