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OCR for page R1
GROUND WATER MODEM
Scientific and Regulatory Applications
Water Science and Technology Board
Committee on Ground Water Modeling Assessment
Commission on Physical Sciences, Mathematics, and Resources
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C. 1990
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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 competences 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.
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.
Frank Press 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. Samuel O. Thier 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. Frank Press and Dr. Robert M. White are chairman and vice
chairman, respectively, of the National Research Council.
Support for this project was provided by the Electric Power Research Institute under
Contract No. RP2485-10, the U.S. Nuclear Regulatory Commission under Contract No.
NRC-04-87-096, the U.S. Environmental Protection Agency under Contract No. CR-814067
the National Science Foundation under Grant No. CES/8708081, and the U.S. Army under
Purchase Order No. DAAD05-88-M-M061.
Library of Congress Cataloging-in-Publication Data
Ground water models: scientific and regulatory applications /
Committee on Ground Water Modeling Assessment. Water Science and
Technology Board, Commission on Physical Sciences, Mathematics, and
Resources, National Research Council.
p. cm.
Includes bibliographical references.
ISBN 0-309-03993-2
1. Groundwater Bow. 2. Liability for water pollution damages. I. National Research
Council (U.S.). Committee on Ground Water Modeling Assessment.
TC176.G76 1989
363.73'94-dc2089-14033
CIP
Copyright (~)1990 by the National Academy of Sciences
No part of this book may be reproduced by any mechanical, photographic, or electronic
process, or in the form of a phonographic recording, nor may it be stored in a retrieval
system, transmitted, or otherwise copied for public or private use, without written permission
from the publisher, except for the purposes of official use by the U.S. government.
Printed in the United States of America
First Printing, January 1990
Second Printing, September 1990
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COMMITTEE ON GROUND WATER
MODELING ASSESSMENT
FRANK W. SCHWARTZ, Ohio State University, Columbus,
Chairman
CHARLES B. ANDREWS, S. S. Papadopulos & Associates, Inc.,
Rockville, Maryland
DAVID L. FREYBERG, Stanford University, Stanford, California
CHARLES T. KINCAID, Battelle, Pacific Northwest Laboratory,
RichIand, Washington
LEONARD F. KONIKOW, U.S. Geological Survey, Reston,
Virginia
CHESTER R. McKEE, In Situ, Inc., I,aramie, Wyoming
DENNIS B. McLAUGHLIN, Massachusetts Institute of Technology,
Cambridge
JAMES W. MERGER, GeoTrans, Inc., Herndon, Virginia
ELLEN J. QUINN, Northeast Utilities, Hartford, Connecticut
P. SURESH CHANDRA RAO, University of Florida, Gainesville
BRUCE E. RITTMANN, University of Illinois, Urbana-Champaign
DONALD D. RUNNELLS, University of Colorado, Boulder
PAUL K. M. van der HEl]DE, HoIcomb Research Institute,
Indianapolis, Indiana
WlI.I`lAM J. WALSH, Pepper, Hamilton & Scheetz, Washington,
D.C.
Staff
WENDY L. MELGIN, Project Manager
JEANNE AQUlLINO, Project Secretary
Agency Liaisons to Committee
EDWARD H. BRYAN, National Science Foundation
DONALD L. CHERY, JR., U.S. Nuclear Regulatory Commission
STEPHEN R. CORDLE, U.S. Environmental Protection Agency
IRA MAY, U.S. Army Toxic and Hazardous Materials Agency
ISHWAR P. MURARKA, Electric Power Research Institute
·~e
111
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WATER SCIENCE AND TECHNOLOGY BOARD
MICHAEL C. KAVANAUGH, James M. Montgomery Consulting
Engineers, Oakland, California, Chairman
NORMAN H. BROOKS, California Institute of Technology,
Pasadena
STEPHEN J. BURGES, University of Washington, Seattle
(through 6/30/89)
RICHARD A. CONWAY, Union Carbide Corporation, South
Charleston, West Virginia
JAMES P. HEANEY, University of Florida, Gainesville
R. KEITH HIGGINSON, Idaho Department of Water Resources,
Boise (through 6/30/89)
HOWARD C. KUNREUTHER, University of Pennsylvania,
Philadelphia
LUNA B. LEOPOLD, University of California, Berkeley (through
6/30/89)
G. RICHARD MARZOLF, Murray State University, Murray,
Kentucky
ROBERT R. MEGLEN, University of Colorado at Denver
.lAMFS W MFIRC]F~R GeoTrans Herndon. Virginia (through
6/30/89)
DONALD J. O'CONNOR, Manhattan College, Bronx, New York
BETTY H. OLSON, University of California, Irvine
P. SURESH C. RAO, University of Florida, Gainesville
GORDON G. ROBECK, Consultant, Laguna Hills, California
(through 6/30/89)
PATRICIA L. ROSENFIELD, The Carnegie Corporation of New
York
DONALD D. RUNNELLS, University of Colorado, Boulder
A. DAN TARLOCK, Chicago Kent College of Law
HUGO F. THOMAS, Department of Environmental Protection,
Hartford, Connecticut
JAMES R. WALLIS, IBM T.~. Watson Research Center, Yorktown
Heights, New York
M. GORDON WOLMAN, The Johns Hopkins University,
Baltimore, Maryland
1V
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Staff
STEPHEN D. PARKER, Director
SHEILA D. DAVID, Staff Officer
CHRIS ELFRING, Staff Officer
WENDY L. MELGIN, Staff Officer
JEANNE AQUlLINO, Administrative Assistant
ANITA A. HALL, Senior Secretary
RENEE A. HAWKINS, Adrffinistrative Secretary
v
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COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS,
AND RESOURCES
NORMAN HACKERMAN, Robert A. Welch Foundation,
Chairman
ROBERT C. BEARDSLEY, Woods Hole Oceanographic Institution
B. CLARK BURCHFIEL, Massachusetts Institute of Technology
GEORGE F. CARRIER, Harvard University
RALPH J. CICERONE, University of California, Irvine
HERBERT D. DOAN, The Dow Chemical Company (retired)
PETER S. EAGLESON, Massachusetts Institute of Technology
DEAN E. EASTMAN, IBM T.~. Watson Research Center
MARYE ANNE FOX, University of Texas, Austin
GERHART FRIEDLANDER, Brookhaven National Laboratory
LAWRENCE W. FUNKHOUSER, Chevron Corporation (retired)
PHILLIP A. GRIFFITHS, Duke University
NEAL F. LANE, Rice University
CHRISTOPHER F. McKEE, University of California, Berkeley
RICHARD S. NICHOLSON, American Association for the
Advancement of Science
JACK E. OLIVER, Cornell University
JEREMIAH P. OSTRIKER, Princeton University Observatory
PHILIP A. PALMER, E.~. du Pont de Nemours & Company
FRANK L. PARKER, Vanderbilt University
DENIS J. PRAGER, MacArthur Foundation
DAVID M. RAUP, University of Chicago
ROY F. SCHWITTERS, Superconducting Super Collider
Laboratory
LARRY L. SMARR, University of Illinois, Urbana-Champaign
KARL K. TUREKIAN, Yale University
MYRON F. UMAN, Acting Executive Director
V1
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Preface
The issue of how ground water models should be used to address
legal and regulatory concerns was brought to the attention of the
Water Science and Technology Board in 1986. The U.S. Army re-
quested assistance in assessing the efficacy of a specific modeling
effort focused on an evaluation of contamination at a specific Army
facility. The Army wanted to know to what extent that particu-
lar mode! could be used to apportion liability among several pos-
sible sources. The board concluded that investigation of such a
site-specific problem was not appropriate for the NRC and decided
instead to initiate a broader study dealing with the scientific basis
and applicability of ground water models.
This initiative probably could not have come at a better time.
Hydrogeologists are being caught in the middle between some major
advances in science and increasing pressure from legal and regulatory
bodies to use models to provide answers to specific questions. On the
scientific side, there has been an explosion in knowledge in the past
10 years concerning the processes that control flow and mass trans-
port in all kinds of hydrogeologic settings. This new understanding
of how ground water systems behave has been incorporated in a va-
riety of models. On the practical side, there is a community of users,
employed by engineering consulting firms, government agencies, and
national laboratories, who are being asked to solve increasingly com-
plicated legal and regulatory problems. It is not at all clear whether
·.
V11
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·~.
V111
PREFACE
existing models axe appropriate for the tasks being set for them,
nor is it clear to what extent new knowledge has changed modeling
practice.
These issues provided the backdrop for an 18-month study sup-
ported by the Electric Power Research Institute, the U.S. Nuclear
Regulatory Commission, the Environmental Protection Agency, the
U.S. Army, and the National Science Foundation. The goal of this
study was to address two questions: "To what extent can the cur-
rent generation of ground water models accurately predict complex
hydrogeologic and chemical phenomena?" and "Given the accuracy
of these models, is it reasonable to assign liability for specific ground
water contamination incidents to individual parties or make regula-
tory decisions based on long-term prediction?"
The members of the committee formed to address these topics
came from universities, government, and private industry with broad
experience related to the scientific and legal aspects of modeling. We
benefited from the guidance and expert assistance provided by the
staff of the Water Science and Technology Board. Our sponsors, to
be sure, supplied money for the study, but, far more than that, they
provided yet other points of view for us to consider and assistance in
gathering information.
Our intention in writing this report was to produce a document
that was stimulating, readable, and comprehensive. All of us came
away from this task with some different views about models and
modeling issues as the result of some very stimulating and provocative
meetings. This report represents our best attempt at addressing some
of the most controversial issues in ground water science today.
FRANK W. SCHWARTZ, Chairman
Committee on Ground Water
Modeling Assessment
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Contents
OVERVIEW, CONCLUSIONS, AND RECOMMENDATIONS....1
Overview, 1
Conclusions and Recommendations, 7
1 INTRODUCTION c c
The Growth in the Use of Models, 23
References, 27
2 MODELING OF PROCESSES..
Introduction, 28
What is a Model?, 52
References, 73
FLOW PROCESSES c
Introduction, 79
Saturated Continuum Flow, 80
Flow in the Unsaturated Zone, 88
Concepts of Water Flow in the Unsaturated Zone, 91
Fracture Flow, 97
Issues in Modeling, 104
References, 109
LX
22
. 28
79
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x
CONTENTS
4 TRANSPORT e . e e e e e e e e e e 113
Introduction, 113
Transport of Conservative Solutes, 115
Nonconservative Solutes, 123
Transport in the Unsaturated Zone, 138
Multiphase Transport, 148
References, 156
EXPERIENCE WITH CONTAMINANT FLOW MODELS
IN THE REGULATORY SYSTEM.ee...ee..eeeeeeeeeeeeeeee 160
Introduction, 160
UeSe Nuclear Regulatory Commission Regulations
and Guidance, 161
Environmental Protection Agency Regulations and
Guidance, 164
Selected Case Studies, 172
Notes, 207
Bibliography, 208
6 ISSUES IN THE DEVELOPMENT AND USE OF
MODELS e e e e e e e e e e e e e e e e e e e e e e · · · e e e e e . e e e e e e e e e e e e e e e . e . e e · e
Introduction, 211
The People Problem, 213
Uncertainty and Reliability, 216
Assuring the Quality of Models, 233
Quality Assurance Procedures for Code Development, 235
Mode! Application, 239
Bibliography, 243
RESEARCH NEEDSee eeeeeeeeeeeeee e
Introduction, 249
Use of Models, 252
Scientific mends and Research, 255
Policy Mends and Support for Research, 276
References, 281
APPENDIX: BIOGRAPHICAL SKETCHES OF
COMMITTEE MEMBERS .......................................
INDEX.
211
249
285
....291
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Tables and Figures
TABLES
1.1 Estimated Numbers of Contarn~nation Problems That
Need to Be Addressed Under Various Statutes ...
2.1 A Summary of the Processes Important in Dissolved
Contaminant Transport and Their Impact on
Contaminant Spreadin g .. .. ..... .. .. ... .. .. .... ... .. .. .
2.2 Classes of Xenobiotic Organic Compounds Known to
Be Biodegraded by Aerobic Bacteria..................
Classes of Xenobiotic Organic Compounds Known to
Be Biodegraded Under Strictly Anaerobic Conditions 51
Summary of the Steps Involved in Developing the
Unsaturated Flow Equation.................................
Summary of the Steps Involved in Developing
Two-Component Flow Equations......
2.6 Typical Boundary Conditions for Ground Water Flow and
Transport Problems e · ~ - 65
A Summary of the Common Solution Techniques for
Problems of Fluid Flow and Dissolved Mass Transport 69
Some O(h) Relationships Reported in the Literature..
Some K (~) or K (h) Relationships Reported in the
Literature ....................................................
2.3
2.4
2.5
-.. 24
- 38
.51
58
. .59
X1
.93
94
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·.
X11
3.3
4.3
5.1
5.2
5.3
5.4
FIGURES
TABLES AND FIGURES
Some Expressions Developed to Describe the Time
Dependence of Infiltration Rate (i) Following Ponding
of Water e e e
3.4 Major Differences Between Saturated and Transient
Unsaturated Water Flow in Porous Media e 98
..... 94
Summary and Evaluation of Thermodynarn~cs of Abiotic
Transformation Mechanisms for Aqueous Species eeeeeeeee
Summary and Evaluation of Kinetics of Abiotic
Transformation Mechanisms e e e e e e e . e 127
Summary and Evaluation of the Thermodynamics of
Phase Transfers.............................................
126
Synopsis of Case Studies e
RCRA Delisting Data for Gould, Inc. Facility,
McConnelsville, Ohio..............................
Calculated Estimates of Trichloroethene Releases from
Source Areas ~ ~
Calculated Relative Contributions from Individual
Source Areas e
Capillary Pressure and Relative Permeability Data for
ADL Simulation 1
131
.174
.179
197
199
. 204
Data Used in ADL Simulation 1 . e e 204
2.1 An example of a regional ground water flow system 30
2.2 Dependence of the pattern of ground water flow on
the recharge rate, as reflected by the configuration
of the water table 31
2.3 Dependence of the pattern of ground water flow on
the hydraulic conductivity distribution
2.4 Example of the relationships between pressure head
and hydraulic conductivity for an unsaturated soil
2.5 The distribution of water in the unsaturated zone can
be described in terms of pressure head and moisture
content ~
The flow of a nonaqueous-phase liquid that is
(a) less dense than water (oil) and (b) more dense
than water (chlorohydrocarbon) in the unsaturated and
saturated zones..
...... 31
...... 34
.34
..36
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TABLES AND FIGURES
· e.
X111
2.7 Plume produced (a) by advection alone and (b) by
advection and dispersion 40
2.8 Idealized pattern of plume spreading in three
dimensions is characterized by a longitudinal and two
transverse dispersion components 41
2.9 (a) Microscale and (b) macroscale variability
contributing to the development of dispersion 42
2.10 Many of the geochemical processes like radioactive
decay and sorption attenuate the spread of
2.11
contaminants 44
The components of a model: input data, a governing
equation solved in the code, and the predicted distribu
tion, which for this example is hydraulic head 53
2.12 An example of how (a) a "real" system is represented
by (b) a mode} system, which is defined by a region
shape, boundary conditions, and hydraulic parameters 54
2.13 Mode! system from the previous figure subdivided by
a rectangular grid system
3.1 Relationship between pore size (r) on capillary rise
3.2
.68
and pressure head (h)89
Examples of soil-water characteristic curves O(h), for
several soils
3.3 Examples of K(h) relationships for several soils
3.4 Examples of the changes in infiltration rate (i) with
time for different water application scenarios
3.5 Variations in soil water content as a result of several
episodes of water inputs at the surface ,, 97
Conceptualization of discontinuities in a fractured
medium. . . e · ~
3.7 Idealization of a natural fracture as parallel plates
with an aperture of 2b -. 100
Experimental data that illustrate how flux in the
fracture and aperture change as a function of effective
stress for a sandblasted, sawcut fracture surface 101
Three different conceptualizations of fracture networks:
(a) a two-dimensional system of line segments;
(b) a three-dimensional system of rectangular fractures;
and (c) a three-dimensional system of "penny-shaped"
.90
........ 92
3.6
. .95
3.8
3.9
... t 99
cracks...................................
3.10 Variation in hydraulic conductivity as a function of
the averaging volume. .
.103
.. 105
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XIV
3.11 Examples of percolating and noncercolatinz
networks in two dimensions..
TABLES AND FIGURES
Variation of dispersivity with distance (or scale of
..106
measurement) 117
Flow through fractures and diffusion of contaminants
from fractures into the rock matrix of a dual-porosity
medium.....................................................
.118
Effect of sampling scale on estimation of dispersivity 119
Overview of the role of simulation models in
evaluating ground water contamination problems 123
4.5 Sequential leaching of two sorbed contaminants (1,2)
and one nonsorbed contaminant (3) through the
root zone as a result of rainfall shown in (a) 142
4.6 Attenuation of three contaminants during their
transit through the unsaturated zone 143
4.7 (a) Episodes of pesticide loadings to shallow water
table located beneath a citrus grove. (b) Daily
pesticide loadings predicted by PROM and used in
saturated zones simulations 144
4~8 Measured and simulated movement of aldicarb
residues. ~ eats e
145
.149
4~9 Seawater intrusion in an unconfined aquifer.......
4~10 Organic liquid contamination of unsaturated and
saturated porous media 151
5~1 Location of case studies
5~2
5~3
.174
Schematic of vertical-horizontal spread model 177
Predicted dilution factor as a function of waste
amount
~ 179
5~4 Time-drawdown curves for mode! node near hypo
thetical pumping wells in the Madison limestone183
5~5 Calculated probability distribution of drawdowns
at the Niobrara well field
~ 184
5~6 Observed distribution of waste chloride in ground
water in the Snake River plain aquifer, Idaho,
ICPP-TRA vicinity in 1972 ~188
5~7 Model-projected distribution of waste chloride in the
Snake River plain aquifer for 1980 (ICPP-TRA
vicinity), assuming disposal continues at 1973 rates and
the Big Lost River recharges the aquifer in ocId
numbered years 189
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TABLES AND FIGURES
5.8
xv
Distribution of waste chloride in the Snake River
plain aquifer (ICPP-TRA vicinity), October 1980 190
5.9 Location of Tucson Airport 192
5.10 Example calculation of relative contribution to
aquifer contamination 196
5.11a Simulated individual trichIoroethene plumes 198
5.1Ib Simulated combined trichloroethene plumes 198
5.12 A conceptual cross section of the hydraulic contain
ment system to be implemented at the S-Area
landfill 202
5.13 NAPL saturation profiles at one time for the two-layer
simulation.....................................
Conceptual framework for ground water model
accuracy analysis..........................................
7.1 The relationship of reasonable assurance to bounding
analysis, regulatory limit, and realistic estimates.
.205
.217
278
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