Delivery and Mixing in the Subsurface: Processes and Design Principles for In Situ Remediation (SERDP ESTCP Environmental Remediation Technology Book 4)

This volume is meant to provide the practitioner with information on the natural mixing processes occurring in aquifers as well as to describe basic strategies that can be implemented to enhance mixing in particular cases. For example, when it comes to mixing miscible liquids, one can speed up mixing in the formation by manipulating the flow such as through the use of recirculation wells. Furthermore, much of the mixing can be achieved partially within recirculation wells themselves, where contaminated water is admixed with additives, volatile products may be removed through a vapor mass exchanger, etc. Thus, adding mixing wells can significantly increase the performance of the delivery and mixing system and speed up the process of remediation. Delivery and Mixing in the Subsurface: Processes and Design Principles for In Situ Remediation 3 Preface 7 About the Editors 11 About the Authors 13 External Reviewers 17 Contents 19 List of Figures 25 List of Tables 30 CHAPTER 1: Introduction 31 BACKGROUND 31 OVERVIEW OF THE CONTENTS OF THIS VOLUME 34 ONGOING RESEARCH AND OUTSTANDING CHALLENGES 34 REFERENCES 3 CHAPTER 2: CHEMICAL AND BIOLOGICAL PROCESSES: THE NEED FOR MIXING 37 INTRODUCTION 37 GROUNDWATER CONTAMINANTS 37 REACTION AND MASS TRANSFER PROCESSES 42 Overview 42 Stoichiometry 42 Reaction and Mass-Transfer Processes 43 Reaction Kinetics 47 Summary 50 BIOLOGICAL PROCESSES 51 Biological Processes 51 Chlorinated Solvents 54 Biological Reaction Kinetics 57 Mass Transfer Limitations 59 Bioaugmentation 61 Organic Bioremediation Example: Edwards AFB, California 64 CHEMICAL PROCESSES 66 Oxidative Chemical Processes 67 Reductive Chemical Processes 67 Precipitation 68 pH Control 71 Example 72 Chemicals for pH Control 73 COSOLVENT AND SURFACTANT FLUSHING 75 Cosolvent Flushing 75 Surfactant Flushing 75 INORGANIC BIOREMEDIATION EXAMPLE: OAK RIDGE FIELD RESEARCH CENTER 76 SUMMARY 78 REFERENCES 3 CHAPTER 3: TRANSPORT AND MIXING 83 INTRODUCTION 83 MIXING 84 Mass Transfer from Separate Phases 86 Transverse Mixing 86 Longitudinal Mixing and Chromatographic Mixing 86 SCALE DEPENDENCY 87 PORE SCALE 89 Flow 90 Advection 92 Molecular Diffusion 92 LABORATORY-SCALE PROCESSES 94 Darcy ́s Law 96 Diffusion 97 Advection-Dispersion Equation 98 Dual-Porosity Models 99 Sorption 100 FIELD-SCALE PROCESSES 101 CONCLUDING REMARKS 102 REFERENCES 3 CHAPTER 4: HYDROGEOCHEMICAL MODELS 106 INTRODUCTION 106 MIXING AND REACTION PROCESSES 107 Overview 107 Example Remediation Technologies 109 HYDROGEOCHEMICAL MODEL GOVERNING EQUATIONS 113 Solution of Governing Equations 115 SURVEY OF AVAILABLE HYDROCHEMICAL MODELS 118 Analytical Models 119 Numerical Models 120 CALIBRATION AND VALIDATION 124 CASE STUDIES OF MODEL APPLICATIONS 128 Natural Attenuation of Organic Pollutants 128 Enhanced In Situ Cometabolic Degradation of TCE 131 In Situ Chemical Oxidation of TCE by Potassium Permanganate 133 SUMMARY AND CONCLUSIONS 136 REFERENCES 3 CHAPTER 5: TRAVEL-TIME BASED REACTIVE TRANSPORT MODELING FOR IN SITU SUBSURFACE REACTOR 146 INTRODUCTION 146 RESIDENCE-TIME THEORY 148 TRAVEL-TIME BASED REACTIVE TRANSPORT 151 ESTIMATION OF TRAVEL-TIME DISTRIBUTION 152 AN ILLUSTRATIVE EXAMPLE 153 DISCUSSION AND EXTENSIONS 157 Spatial Mapping 157 Multiple-Reactor System 158 Mixing Within Reactor 161 Chemical Heterogeneities 162 Reaction Rate Estimation 163 SUMMARY 164 REFERENCES 3 CHAPTER 6: RECIRCULATION SYSTEMS 168 INTRODUCTION 168 TYPES OF RECIRCULATION SYSTEMS 168 Injection-Extraction 169 Groundwater Circulation Wells (GCWs) 170 Tandem Recirculating Wells (TRWs) 171 System Cost Comparisons 173 DESIGN PRINCIPLES 173 Effect of Remediation Goal 173 Environmental Factors to Consider in Design 174 Physical 174 Hydrogeology 174 Hydraulic Conductivity 174 Regional Hydraulic Head and Flow Field 175 Dispersion 175 Chemical/Biological 175 Groundwater Chemistry 175 Sorption 175 Reaction Kinetics 176 Engineering Factors to Consider in Design 176 Construction 176 System Type 176 Well Screen Locations 177 Mixing Mechanism 177 Operation 178 Water Flow Rates in Wells 178 Chemical Amendment 178 Chemical Addition Schedule 179 Biofouling Control 179 Regulatory Considerations 180 Modeling Applications 181 Screening Models 181 System Design Models 181 Example Designs 183 Effect of Physical Factors 183 Effect of Chemical/Biological Factors 188 SYSTEM OPERATION AND MAINTENANCE (O&M) 189 Process and Performance Monitoring 189 System Optimization 191 CASE STUDIES 191 Injection-Extraction Application: Schoolcraft, Michigan Site 191 Groundwater Circulation Well Application: Port Hueneme Naval Exchange Site, California 192 Tandem Recirculating Well Application (Trichloroethene Bioremediation at Edwards AFB, California) 192 CONCLUSIONS 193 REFERENCES 3 CHAPTER 7: PERMEABLE BARRIER WALLS 198 INTRODUCTION 198 REACTIVE MATERIALS 199 Granular Metallic Iron 200 Organic Carbon Amendments 203 Oxygen Addition 204 Sorptive Materials 204 Other Materials 205 DESIGN CONSIDERATIONS 206 Reaction Rates 206 Hydrogeologic Considerations 207 LONG-TERM PERFORMANCE 208 Granular Iron 209 METHODS OF INSTALLATION 211 PRB Configuration 211 Construction Methods 212 SUMMARY COMMENTS 214 REFERENCES 3 CHAPTER 8: IN SITU SPARGING FOR DELIVERY OF GASES IN THE SUBSURFACE 221 INTRODUCTION 221 BRIEF OVERVIEW OF THE PHYSICS OF IN SITU SPARGING 222 APPLICATIONS OF GAS DELIVERY SYSTEMS 223 Air Biosparging 223 Oxygen Biosparging 223 Cometabolic Biosparging 223 Gas Injection of Chemical Oxidants 223 DESIGN PRINCIPLES 225 Conceptual Design 225 Physical Characteristics 225 Biological Characteristics 226 Pilot Testing 226 System Design 230 System Operation and Maintenance 230 Performance Monitoring 231 CASE STUDIES 231 Air Biosparging: Environmental Security Technology Certification Program (ESTCP) Multi-Site In Situ Air Sparging Project 231 Pressure Response Test Data 232 Sparge Gas Recovery Test Data 232 Gas Distribution Test Data 235 Oxygen Biosparging: Methyl Tertiary-Butyl Ether (MTBE) Biodegradation at Port Hueneme NAS, California 235 System Configuration 235 Oxygen Concentration Data 237 Contaminant Removal Data 237 Cometabolic Biosparging: McClellan AFB, California 237 System Configuration 238 Tracer Tests to Assess Cometabolic Performance 239 Contaminant Removal Data 241 Unsaturated Zone ``Bioreactor ́ ́ 241 SUMMARY 241 REFERENCES 3 CHAPTER 9: INTRINSIC REMEDIATION IN NATURAL-GRADIENT SYSTEMS 245 INTRODUCTION 245 ANALYTICAL SOLUTIONS FOR ZERO- AND FIRST-ORDER DECAY IN STEADY STATE 247 IMPLICIT ASSUMPTIONS OF ZERO- AND FIRST-ORDER DECAY 248 GENERAL OUTLINE OF COMPUTING MIXING-CONTROLLED REACTIVE TRANSPORT 250 Direct Simulation of Coupled Systems 250 Simulation Via Mixing Ratios 250 DETERMINING CONCENTRATIONS OF INDIVIDUAL REACTIVE SPECIES FROM TOTAL CONCENTRATIONS 252 Chemical Equilibrium of Dissolved Compounds 252 Chemical Equilibrium in the Presence of a Mineral Phase 255 Instantaneous, Complete, Irreversible Reaction 257 Biokinetic Irreversible Reaction in Steady State 260 SUMMARY AND CONCLUSIONS 264 REFERENCES 3 CHAPTER 10: SOURCE REMEDIATION CHALLENGES 267 INTRODUCTION AND BACKGROUND 267 DNAPL SOURCE ZONE ARCHITECTURE: EVOLUTION AND CHARACTERIZATION 272 Influence of DNAPL and Subsurface Properties on Source Zone Architecture 272 Characterization Tools 274 Surface-Based Geophysics 275 Inverse Methods 275 Tracer Tests 276 Source Zone Architecture Metrics 277 MASS FLUX FROM DNAPL SOURCE ZONES 279 Influence of Architecture on Mass Discharge and Plume Response 279 Tools for Mass Flux Quantification 282 Integral Pump Tests 285 Multilevel Sampling Arrays 287 Passive Flux Meter 288 PARTIAL MASS REMOVAL AND COMBINED REMEDIES 290 Benefits of Partial Source Removal 290 Combined Remedies 290 Surfactant Flushing and Bioremediation 291 Chemical Oxidation and Bioremediation 291 Thermal Treatment and Bioremediation 292 Thermal Treatment and Chemical Oxidation 292 CONCLUSION 292 REFERENCES 3 Outline placeholder 0 APPENDIX AList of Acronyms and Abbreviations 305 APPENDIX BUnit Conversion Table 308 Index 336 This volume describes the principles of chemical delivery and mixing systems and their design and implementation for effective in situ remediation. The intended audiences include the decision makers, practicing engineers and hydrogeologists who will select, design and operate remedial systems, as well as the researchers seeking to improve the current state of the science and technology. Our hope is that this volume will serve as a useful resource to assist remediation professionals in designing, applying and developing remedial technologies as effectively as possible. Topics addressed in this volume include: ·¡¡¡¡¡¡¡¡ An overview of the current state of understanding related to in situ chemical delivery and mixing, including a brief review of some of the remaining challenges and ongoing research. ·¡¡¡¡¡¡¡¡ A tutorial on the reactions and processes of importance in groundwater remediation. Chapter 2 focuses on chemical and biological processes, while Chapter 3 focuses on transport and mixing. ·¡¡¡¡¡¡¡¡ A discussion of available hydrogeochmicalmodeling approaches, including a detailed discussion of the travel-time approach to modeling. Protocols for practical implementation for design and monitoring of processes are included. ·¡¡¡¡¡¡¡¡ Design issues and principles for introducing and mixing chemicals with groundwater contaminants are discussed, including: §¡ Recirculation systems, where mixing is controlled through and takes place mostly in wells is presented. The challenges of operating and maintaining injection-extraction wells, the non-uniform distribution of biomass, plugging issues, and strategies such as pulsing are discussed. Case studies are provided. §¡ The use and design of reactive barriers--where contaminants are brought through normal groundwater advection to the reacting chemicals contained within permeable barrier walls through which the groundwater passes--are discussed. §¡ Technologies such as air sparging used for introducing and mixing gaseous reactants as well as for removing volatile contaminants are discussed. Ageneral background on processes for mixing of gases is provided along with design issues forair sparging. Case studies are included. §¡ Intrinsic remediation in natural-gradient systems, where the kinetics are controlled through mixing of contaminant plumes with ambient species, such as dissolved oxygen, over long periods of times is covered. Issues including monitoring and estimation of long-term reaction rates, lengths of plumes, and other important parameters are illustrated with case studies. §¡ The special case of source remediation and its challenges are discussed. Each chapter in this volume has been thoroughly reviewed for technical content by one or more experts in each of the subject areas covered. The editors and chapter authors have produced a well-written and up-to-date treatise that we hope will be a useful reference for those making decisions on remediation of contaminated groundwater and for those involved in research and development of advanced technology for the in situ remediation of groundwater Front Matter....Pages i-xxx Introduction....Pages 1-6 Chemical and Biological Processes: The Need for Mixing....Pages 7-52 Transport and Mixing....Pages 53-75 Hydrogeochemical Models....Pages 77-116 Travel-Time Based Reactive Transport Modeling for In Situ Subsurface Reactor....Pages 117-138 Recirculation Systems....Pages 139-168 Permeable Barrier Walls....Pages 169-191 In Situ Sparging for Delivery of Gases in the Subsurface....Pages 193-216 Intrinsic Remediation in Natural-Gradient Systems....Pages 217-238 Source Remediation Challenges....Pages 239-276 Back Matter....Pages 277-325