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Draft Technical Report CONSIDERATIONS RELATED TO POST CLOSURE MONITORING OF URANIUM IN-SITU LEACH/IN-SITU RECOVERY (ISL/ISR) SITES Background Information Document for the Revision of 40 CFR Part 192 Radiation Protection Division Office of Air and Radiation U.S. Environmental Protection Agency Revision 8 September 2014 EPA-402-D-14-001 TABLE OF CONTENTS Acronyms and Abbreviations ........................................................................................................ ix Overview ..........................................................................................................................................1 Background ..........................................................................................................................1 Overview of Report Contents ..............................................................................................2 1.0 Introduction ..........................................................................................................................4 1.1 Background versus Baseline Wells ..........................................................................7 1.2 ISR Facilities in the United States ...........................................................................9 2.0 Resource Conservation and Recovery Act ........................................................................14 2.1 Summary ................................................................................................................14 2.2 Ground Water Monitoring Requirements for Treatment, Storage, and Disposal Facilities ..................................................................................................15 2.2.1 Overview ....................................................................................................15 2.2.2 Permitted Facilities ....................................................................................15 2.2.3 Detection Monitoring .................................................................................16 2.2.4 Compliance Monitoring .............................................................................17 2.2.5 Corrective Action .......................................................................................17 2.3 Application to ISR Facilities ..................................................................................18 3.0 Ground Water Monitoring at ISR Facilities .......................................................................20 3.1 Overview ................................................................................................................20 3.2 Pre-operational Monitoring (Phase 1) ....................................................................21 3.3 The ISR Leaching Process (Phase 2) .....................................................................22 3.3.1 Excursions during Operations ....................................................................24 3.4 Post-operational Monitoring (Phases 3 through 5) ................................................30 3.5 Selection of Parameters to Be Used in Ground Water Sampling Programs ..........31 3.5.1 Regulated Constituents ..............................................................................31 3.5.2 Summary of Species Potentially Required for Compliance Monitoring – Tiered Approach ..................................................................39 3.5.3 Well Construction and Low-Flow Sampling Methodologies ....................42 3.5.4 Species Required for Geochemical Modeling ...........................................45 3.5.5 Species Required for Excursion Monitoring..............................................48 3.5.6 Case History – Evolution of Constituent Monitoring List .........................49 3.5.7 Formal Approach to Acceptable Restoration .............................................50 4.0 Technical Considerations for ISR Ground Water Monitoring ...........................................54 4.1 Uranium Geology...................................................................................................54 4.1.1 Formation of Uranium Containing Ore Deposits.......................................55 4.2 Aquifer Exemption Requirement ...........................................................................59 4.3 Establishing Baseline Conditions ..........................................................................59 4.3.1 Variability in Baseline Measurements .......................................................64 4.4 Extraction Operations Phase ..................................................................................68 4.5 Post-extraction Phase .............................................................................................70 4.6 Factors Affecting Post-mining Time Frames and Wellfield Stability ...................70 4.7 Modeling ................................................................................................................73 Draft Technical Report ii Revised Draft – September 2014 4.7.1 Objectives and Conceptual Model Development ......................................73 4.7.2 Ground Water Flow and Contaminant Transport Modeling ......................75 4.7.3 Geochemical Modeling ..............................................................................77 4.7.4 Demonstrating Long-term Stability of Restored ISR Wellfields – Long-Term Monitoring and Geochemical Modeling ................................91 5.0 Active/Existing ISR Facilities: Monitoring Issues ............................................................94 5.1 Ground Water Baseline: Case Studies ...................................................................94 5.2 Wellfield Restoration .............................................................................................96 5.3 Wellfield Restoration: Case Study .........................................................................97 6.0 Issues Associated with Establishment of Post-restoration Steady State ............................99 6.1 Post-restoration Stability Monitoring ....................................................................99 6.2 Factors That Affect Time Frames for Post-mining Monitoring...........................100 6.2.1 Fate and Transport Processes ...................................................................100 6.2.2 Natural Attenuation Processes .................................................................103 6.3 Geochemically Based Restoration Techniques ....................................................109 6.4 Monitored Natural Attenuation ............................................................................110 6.4.1 Tiered Approach to Assessing Suitability of Monitored Natural Attenuation ...............................................................................................112 6.4.2 First-Order Attenuation Rate Determination ...........................................112 7.0 Statistical Analyses to Compare Pre- and Post-ISR Conditions ......................................115 7.1 Determine Baseline Characteristics .....................................................................119 7.1.1 Design for Baseline Sampling .................................................................122 7.1.2 Selection of Baseline Monitoring Wells ..................................................123 7.1.3 Determining the Number of Baseline Samples ........................................126 7.1.4 Summary ..................................................................................................130 7.2 Determining the Number of Monitoring Wells Required to Detect Noncompliance ....................................................................................................136 7.2.1 Determining the Number of Monitoring Wells based on Hypergeometric Sampling .......................................................................136 7.2.2 An Alternative Graduated Approach to Hypergeometric Sampling ........146 7.2.3 Determining Connectivity of the Wellfield .............................................160 7.3 Hypothesis Testing and Data Quality Objectives ................................................162 7.3.1 Decision Errors and Confidence Levels ..................................................164 7.3.2 Hypothesis Tests for Comparisons with Baseline ...................................165 7.3.3 Selecting a Test Form ..............................................................................168 7.3.4 Hypothesis Tests for Detecting Trends ....................................................170 7.4 Selecting the Statistical Approach – Parametric Versus Nonparametric Methods................................................................................................................172 7.4.1 Determining If Data Have a Normal Distribution ...................................173 7.4.2 The Shapiro-Wilk W Test ........................................................................173 7.4.3 The Studentized Range Test ....................................................................173 7.5 Outlier Detection ..................................................................................................174 7.5.1 Parametric Tolerance Limits for Outliers ................................................175 7.5.2 Calculating an Upper Tolerance Limit ....................................................176 7.6 Determining the Number of Samples per Well ....................................................178