Contents Preface Introduction Model Concepts

Transcription

1 Preface xi 1 Introduction Environmental Problems and Geochemical Modeling High-Level Radioactive Waste Disposal Mining Related Environmental Issues Landfills Deep Well Injection of Hazardous Wastes Artificial Recharge to Aquifers The Regulatory Framework CERCLA or Superfund RCRA NEPA Clean Water Act Safe Drinking Water Act The Role of Geochemical Modeling Contamination Issues Water Resource Issues Current Practice Model Usage The State of the Art Overview 16 2 Model Concepts Model Definitions A Holistic View of Geochemical Models Types of Geochemical Models Speciation solubility Models Reaction Path Models Inverse Mass Balance Models Coupled Mass Transport Models Model Verification and Validation Model Usefulness and Limitations 31 v

2 vi Contents 3 Thermodynamic Background Systems and Equilibrium Real and Model Systems Equilibrium The Role of Kinetics Chemical Reactions Gibbs Energy Enthalpy and Entropy Activity, Fugacity, and Chemical Potential Activity and Fugacity Activity Coefficients Chemical Potential The Equilibrium Constant Direct and Indirect Determination of K values Solubility Product and Saturation Index Dependence of K on Temperature Components and Species Components and the Basis Species An Alternative Basis The Phase Rule The Extensive Phase Rule Redox Oxygen Fugacity, log f O Redox Potential, Eh Electron Potential, pe Alkalinity The Carbonate Component Carbonate Speciation Titration Alkalinity The Alkalinity to Carbonate Component Correction Acidity Titration Acidity The Acidity to Carbonate Component Correction Alkalinity and Acidity: A Summary The Local Equilibrium Assumption (LEA) Scales of Interest Calculation of t eq and l eq Summary 74 4 Computer Programs for Geochemical Modeling Codes, Databases, and Models The Code The Database Review of Popular Computer Programs Databases 82

3 vii A Typical Database Data Quality Chemical Concentration Units Examples of Input/Output Program Input Program Output 93 5 Preparation and Construction of a Geochemical Model Introduction Establish the Goals Learn the Groundwater Flow System Collection of Field and Laboratory Data Decide Which Parameters to Measure for Groundwater Characterize the Solids Evaluate Quality of Water Analyses. Charge Balance I Decide What Types of Model to Construct Gather Chemical Properties Select a Computer Code Set Up a Model Basis Swapping Charge Balance II Interpretation of Modeling Results Accuracy and Completeness of the Database Input Constraints Who produced the model? Reporting and Presentation of Modeling Results Speciation and Solubility Modeling Introduction A Uranium Mill Tailings Impoundment The Site The Purpose of Geochemical Modeling Site Geology and Data Selection of Modeling Code and Model Input Geochemical Modeling Modeling Results Analysis of Mineral Saturation Indices Activity Activity Diagrams Geochemical Evolution Along A Flow Path Comments on the Bear Creek Site Applications to Bioavailability and Risk Assessment Studies Interpretations of Column Experiments 131

4 viii Contents 7 Modeling Surface Adsorption Introduction The Solid Water Interface Ion Exchange Cation Exchange Capacity Exchange Reactions Isotherms Ion Exchange vs. Surface Complexation Surface Complexation The Electrical Double layer Other Surface Models Sorption Implementation in Computer Programs Examples Why Surface Modeling is Not Perfect Retardation of Radionuclides at Oak Ridge Mobility of Radionuclides at a Uranium Mill Tailings Impoundment Why Geochemical Modeling? Modeling Approach Modeling Results Comparison with Field Data Discussion of Modeling Results Adsorption of Arsenic in Smelter Flue Dust Reaction Path Modeling Introduction Alkalinity Titration Acidity of Acid Mine Water ph Buffering Deep Well Injection of Hazardous Wastes Background A Case Study Pit Lake Chemistry Artificial Recharge Applications to Natural Background Studies Inverse Mass Balance Modeling Introduction Model Assumptions Groundwater Genesis, Black Mesa, Arizona Acid Mine Drainage, Pinal Creek, Arizona C dating, Black Mesa, Arizona Estimate of Microbial Metabolism Rates in Deep Aquifers Chapelle and Lovley (1990) Murphy and Schramke (1998) 202

5 ix 10 Coupled Reactive Transport Models Introduction Multi-component Reactive Transport Models Isotherm-based Reactive Transport Models Linear Isotherm, K d Freundlich isotherm Langmuir isotherm Applicability of the Isotherm-Retardation- Factor Based Reactive Transport Models A Simple Example Buffering in Reactive Transport The Buffer Concept Application of the Buffer Concept Migration of an Acid Plume at a Uranium Mill Tailings Site Model Description Modeling Results Remedial Design of a Uranium Tailings Repository Summary and Comments Kinetics Modeling Introduction Some Basic Theory The Progress Variable The Reaction Rate Rate Laws Temperature Dependence of Rate Constants Kinetics of Precipitation and Dissolution Reactions Kinetics of Acetate Decomposition Coupled Aqueous Speciation and Biological Processes Application to Landfill Leachate into Aquifers Conclusions 258 Appendix 260 A Modifying a Database 261 A.1 Why Modify a Database? 261 A.1.1 Adding Arsenic Data to phreeqc 262 References 268