GROUND WATER MODELS -- Copyright -- Preface -- Contents -- Overview, Conclusions, and Recommendations -- OVERVIEW -- CONCLUSIONS AND RECOMMENDATIONS -- Models and Subsurface Processes -- Conclusions -- Models and Decisionmaking -- Conclusions -- Recommendations -- Maintaining Scientific Integrity -- Conclusions -- Recommendations -- Recommendations for the Future -- 1 Introduction -- THE GROWTH IN THE USE OF MODELS -- REFERENCES -- 2 Modeling of Processes -- INTRODUCTION -- Ground Water Flow -- Multiphase Flow -- Dissolved Contaminant Transport -- Advection -- Diffusion -- Dispersion -- Radioactive Decay -- Sorption -- Precipitation and Dissolution -- Acid/Base Reactions -- Complexation -- Hydrolysis/Substitution -- Redox Reactions -- Biological Transformations -- WHAT IS A MODEL? -- Governing Equations -- Boundary and Initial Conditions and Parameter Values -- Solving Flow and Transport Equations -- REFERENCES -- 3 Flow Processes -- INTRODUCTION -- SATURATED CONTINUUM FLOW -- State of the Art -- Implications for the Use of Saturated Continuum Flow Models in Decisionmaking -- Spatial Dimensionality -- Boundary Conditions -- Transient Versus Steady State -- Discretization -- Velocity Computation -- Parameter Values -- FLOW IN THE UNSATURATED ZONE -- Characterization of the Unsaturated Zone -- CONCEPTS OF WATER FLOW IN THE UNSATURATED ZONE -- FRACTURE FLOW -- Theory of Flow in Fractures -- Strategies for Modeling -- ISSUES IN MODELING -- A Fractured Medium as a Continuum -- Computational Constraints on Discrete Network Models -- Uncertainty in Establishing the Network Geometry -- Adequacy of Modeling Technology -- REFERENCES -- 4 Transport -- INTRODUCTION -- TRANSPORT OF CONSERVATIVE SOLUTES -- NONCONSERVATIVE SOLUTES -- Equilibrium and Kinetic Models of Reactions -- Abiotic Reactions -- Geochemical Models.

Incorporation of Abiotic Transformations into Solute Transport Models -- Phase Transfers -- Assessment of Kinetics -- Incorporation of Phase Transfers into Solute Transport Models -- Biological Reactions -- Microbiological Kinetics -- Incorporation of Biological Processes into Solute Transport Models -- TRANSPORT IN THE UNSATURATED ZONE -- Unsaturated Flow and Transport in Structured Soils -- MULTIPHASE TRANSPORT -- Seawater Intrusion -- Organic Fluid Contamination -- Governing Equations for Multiphase Flow -- Parameters and Initial and Boundary Conditions for Multiphase Flow -- Problems Associated with Multiphase Flow -- REFERENCES -- 5 Experience With Contaminant Flow Models in the Regulatory System -- INTRODUCTION -- U.S. NUCLEAR REGULATORY COMMISSION REGULATIONS AND GUIDANCE -- U.S. ENVIRONMENTAL PROTECTION AGENCY REGULATIONS AND GUIDANCE -- Superfund -- Law and Regulations -- Guidance -- Resource Conservation and Recovery Act -- Law and Regulations -- Guidance -- Underground Injection Control (UIC) Program -- Law and Regulations -- Guidance -- Conclusion -- SELECTED CASE STUDIES -- Vertical-Horizontal Spread (VHS) Model Background -- Model -- Application at a Particular Site -- Regulatory Context -- Discussion -- Madison Aquifer-Well Withdrawals from a Deep Regional Aquifer -- Background -- Initial Modeling Studies -- Initial Results -- Other Model Studies -- Regulatory Context -- Discussion -- Snake River Plain-Point Source of Contamination -- Background -- Hydrogeologic Setting -- Model Formulation -- Results and Conclusion -- Discussion -- Tucson Airport -- Background -- Hydrogeologic Setting -- Approach -- Model to Assess Relative Contributions -- Model of Source Contributions -- Results and Conclusions -- Regulatory Context -- Discussion -- S-Area, Niagara Falls, New York -- Background -- Site Conditions -- Model Formulation.

Results and Conclusions -- Regulatory Context -- Discussion -- NOTES -- BIBLIOGRAPHY -- 6 Issues in the Development and Use of Models -- INTRODUCTION -- THE PEOPLE PROBLEM -- UNCERTAINTY AND RELIABILITY -- The Sampling Process -- Process and Parameter Identification -- Input Estimation -- Model Validation and Accuracy Assessment -- ASSURING THE QUALITY OF MODELS -- QUALITY ASSURANCE PROCEDURES FOR CODE DEVELOPMENT -- Verification of Program Structure and Code -- Model Validation -- Recordkeeping -- Software Documentation -- Scientific and Technical Reviews -- MODEL APPLICATION -- BIBLIOGRAPHY -- 7 Research Needs -- INTRODUCTION -- USE OF MODELS -- SCIENTIFIC TRENDS AND RESEARCH -- Basic Understanding and Process Models -- Process Models -- Multiphase Fluid Flow and Transport Models -- Linking Geochemical and Physical Transport Models -- Probabilistic Methods -- Translation of State of the Art to State of the Practice -- Field-Scale Code Developments -- Validation or Accuracy Estimation Methods -- Advances in Computer Hardware and Numerical Methods -- Artificial Intelligence and Expert Systems -- Some Existing Applications -- Expert Systems in the Future -- Interdisciplinary Efforts -- POLICY TRENDS AND SUPPORT FOR RESEARCH -- REFERENCES -- Appendix: Biographical Sketches of Committee Members -- Index.