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Home My WebLink AboutHDR - CAP Part 1 TOCCorrective Action Plan Part 1 01 Allen Steam Station Ash Basin Contents ExecutiveSummary...................................................................................................................................... 1 ES -1 Introduction.......................................................................................................................................... 1 ES -1.1 Regulatory Background...................................................................................................... 1 ES -1.2 Summary of CSA................................................................................................................ 2 ES -2 Background Concentrations and COI Screening Level Summary ...................................................... 2 ES -2.1 Proposed Provisional Background Concentrations............................................................ 3 ES -2.2 Updated COI Screening Evaluation Summary................................................................... 4 ES -3 Site Conceptual Model........................................................................................................................ 5 ES -3.1 Geological/Hydrogeological Properties...............................................................................5 ES -3.2 Site Geochemical Conditions..............................................................................................5 ES -3.3 Correlation of Hydrogeologic and Geochemical Conditions of COI Distribution ................ 6 ES -4 Modeling.............................................................................................................................................. 7 ES -4.1 Model Scenarios................................................................................................................. 7 ES -4.2 Groundwater Modeling Conclusions................................................................................... 7 ES -4.2.1 Flow Model.............................................................................................................. 7 ES -4.2.2 Fate and Transport Model....................................................................................... 8 ES -4.3 Groundwater -Surface Water Interaction Modeling.......................................................9 ES -5 Recommendations.............................................................................................................................. 9 1 Introduction........................................................................................................................................ 11 1.1 Site History and Overview.......................................................................................................12 1.1.1 Site Location, Acreage, and Ownership..................................................................... 12 1.1.2 Site Description.......................................................................................................... 12 1.2 Permitted Activities and Permitted Waste............................................................................... 14 1.3 History of Site Groundwater Monitoring.................................................................................. 14 1.4 Summary of Comprehensive Site Assessment....................................................................... 15 1.5 Receptor Survey...................................................................................................................... 15 1.5.1 Surrounding Land Use............................................................................................... 16 1.5.2 Findings of Drinking Water Supply Well Survey Conducted per the Coal Ash Management Act of 2014, N.C. Gen. Stat. SS 1 30A-309-200 et seq......................... 16 1.6 Summary of the Screening Level Risk Assessment............................................................... 16 1.7 Geological/Hydrogeological Conditions.................................................................................. 17 1.8 Results of the CSA Investigations........................................................................................... 17 1.9 Regulatory Requirements........................................................................................................ 18 1.9.1 CAMA Requirements.................................................................................................. 18 1.9.2 Standards for Site Media............................................................................................19 2 Background Concentrations and Regulatory Exceedances.............................................................. 21 2.1 Introduction.............................................................................................................................. 21 2.2 Groundwater............................................................................................................................23 2.2.1 Background Wells and Concentrations......................................................................23 2.2.2 Groundwater Exceedances of 2L Standards or IMACs............................................. 26 2.2.3 Radionuclides in Groundwater...................................................................................29 Corrective Action Plan Part 1 �� Allen Steam Station Ash Basin 2.3 Seeps...................................................................................................................................... 30 2.4 Surface Water......................................................................................................................... 33 2.5 Sediments............................................................................................................................... 35 2.6 Soils.........................................................................................................................................36 2.6.1 Background Soil and Concentrations......................................................................... 36 2.6.2 Soil Exceedances of NC PSRGs for POGs............................................................... 38 2.7 Ash.......................................................................................................................................... 40 2.8 Porewater................................................................................................................................ 41 2.9 PWR and Bedrock...................................................................................................................43 2.10 COI Screening Evaluation Summary...................................................................................... 44 2.11 Interim Response Actions....................................................................................................... 45 2.11.1 Source Control...........................................................................................................45 3 Site Conceptual Model......................................................................................................................46 3.1 Site Hydrogeologic Conditions................................................................................................ 46 3.1.1 Hydrostratigraphic Units.............................................................................................46 3.1.2 Hydrostratigraphic Unit Properties............................................................................. 47 3.1.3 Potentiometric Surface — Shallow Flow Layers.......................................................... 47 3.1.4 Potentiometric Surface — Deep Flow Layer............................................................... 48 3.1.5 Potentiometric Surface — Bedrock Flow Layer...........................................................48 3.1.6 Horizontal and Vertical Hydraulic Gradients..............................................................48 3.2 Site Geochemical Conditions.................................................................................................. 51 3.2.1 COI Sources and Mobility in Groundwater................................................................. 51 3.2.2 Geochemical Characteristics..................................................................................... 58 3.2.3 Source Area Geochemical Conditions....................................................................... 64 3.2.4 Mineralogical Characteristics..................................................................................... 65 3.3 Correlation of Hydrogeologic and Geochemical Conditions to COI Distribution .....................65 4 Modeling............................................................................................................................................ 68 4.1 Groundwater Modeling............................................................................................................ 68 4.1.1 Model Scenarios.........................................................................................................68 4.1.2 Calibration of Models.................................................................................................. 69 4.1.3 Kd Terms..................................................................................................................... 70 4.1.4 Flow Model................................................................................................................. 70 4.1.5 Fate and Transport Model.......................................................................................... 71 4.2 Groundwater - Surface Water Interaction Modeling................................................................ 80 4.2.1 Mixing Model Approach..............................................................................................80 4.2.2 Surface Water Model Results.................................................................................... 81 4.3 Refinement of SCM................................................................................................................. 82 5 Summary and Recommendations..................................................................................................... 83 6 References........................................................................................................................................ 87 Corrective Action Plan Par'' �� Allen Steam Station Ash Basin Tables 2-1 Initial COI Screening Evaluation 2-2 Background Groundwater Concentrations for the Allen Site: Ranges of Analytical Results with Sample Turbidity <10 NTU 2-3 Groundwater Exceedance Results for COls Compared to PPBCs, 2L Standards, IMACs, or DHHS HSLs, and Frequency of Exceedances 2-4 Radionuclide Concentrations 2-5.1 Seep Exceedance Results for COls Compared to 2L Standards, IMACs or DHHS HSLs and Frequency of Exceedances 2-5.2 Seep Exceedance Results for COls Compared to 2B Standards or USEPA Criteria and Frequency of Exceedances 2-6.1 Surface Water Exceedance Results for COls Compared 2B or USEPA Standards, and Frequency of Exceedances 2-6.2 Surface Water Exceedance Results for Cols Compared 2L or IMAC, and Frequency of Exceedances 2-7 Sediment COls Exceedances Compared to Upstream Sediment Concentrations, NC PSRGs for POG and Frequency of Exceedances 2-8 Proposed Provisional Background Soil Concentrations 2-9 Soil Exceedance Results for COls Compared to NC PSRGs for POG, PPBCs, and Frequency of Exceedances 2-10 Ash Exceedance Results for COls Compared to NC PSRGs for POG, PPBCs, and Frequency of Exceedances 2-11 Porewater Exceedance Results for COls Compared to 2L Standards, IMACs, or DHHS HSLs, and Frequency of Exceedances 2-12 Updated COI Screening Evaluation Summary 3-1 Vertical Gradient Calculations for Shallow/Deep Well Pairs 3-2 Vertical Gradient Calculations for Deep/Bedrock Well Pairs 3-3 Categories and Threshold Concentrations to Identify Redox Processes in Groundwater 3-4 Field Parameters from CSA 4-1 Mixing Zone Sizes and Percentages of Upstream River Flows 4-2 Catawba River (Lake Wylie) Calculated Surface Water Concentrations Corrective Action Plan Part 1 �� Allen Steam Station Ash Basin Figures 1-1 Site Location Map 1-2 Site Layout Map 1-3 Compliance and Voluntary Monitoring Wells 1-4 Monitoring Well and Sample Locations 1-5 Seep and Surface Water Sample Locations 1-6 Receptor Map 1-7 Site Vicinity Map 2-1 Groundwater Analytical Results Map 2-2 Surface Water and Seep Analytical Results 2-3 Soil Analytical Results 3-1 Site Conceptual Model — 3-D View 3-2.1 Site Conceptual Model — Cross Sectional 3-2.2 Site Conceptual Model — Cross Sectional 3-3 Water Table Surface Map — Shallow Wells 3-4 Potentiometric Surface Map — Deep Wells 3-5 Potentiometric Surface Map — Bedrock Wells 3-6 Vertical Gradient — Shallow to Deep Wells 3-7 Vertical Gradient — Deep to Bedrock Appendices A Regulatory Correspondence B Background Well Analysis C UNCC Groundwater Flow and Transport Model D UNCC Soil Sorption Evaluation E Surface Water Modeling Methods iv