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Home My WebLink AboutNC0003425_Roxboro CSA October 2017 Report_201710312017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2 of 2 Explanation of altered or items not initialed: Item 1. The CSA was specifically designed to assess the coal ash management areas of the facility. Sufficient information is available to prepare the groundwater corrective action plan for the ash management areas of the facility. Data limitations are discussed in Section 11 of the CSA report. Continued groundwater monitoring at the Site is planned. Item 2. Imminent hazards to human health and the environment have been evaluated. The NCDEQ data associated with nearby water supply wells is provided herein and is being evaluated. Item 5. The groundwater assessment plan for the CSA as approved by NCDEQ was specifically developed to assess the coal ash management areas of the facility for the purposes of developing a corrective action plan for groundwater. Other areas of possible contamination on the property, if noted, are anticipated to be evaluated separately. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx EXECUTIVE SUMMARY ES.1 Source Information Duke Energy Progress, LLC (Duke Energy) owns and operates the Roxboro Steam Electric Plant (the Roxboro Plant, Plant or Site), located in Person County, near Semora, North Carolina. The Comprehensive Site Assessment (CSA) update was conducted to refine and expand the understanding of subsurface conditions and evaluate the extent of impacts from historical management of coal ash. This CSA update contains an assessment of site conditions based on a comprehensive interpretation of geologic and sampling results from the initial site assessment and geologic and sampling results obtained subsequent to the initial assessment. The Roxboro Plant began operations in 1966 and continues to operate. Coal combustion residuals (CCRs) have historically been managed at the Plant’s two on-site ash basins (surface impoundments): the East Ash Pond/Basin (EAB), which was constructed in 1964, and the West Ash Basin (WAB), which was constructed in 1973. Both ash basins are located within natural drainage basins impounded by earthen dams. CCRs were deposited in the EAB by hydraulic sluicing operations until the Plant was modified for dry fly ash (DFA) handling in the 1980s. An industrial landfill, permitted by the North Carolina Department of Environment Quality (NCDEQ)1 Division of Waste Management (DWM) Permit 7302, was constructed partially in the waste boundary of the EAB for the placement of the DFA. The construction of the landfill isolated a section of the EAB, now called the EAB extension impoundment, where minor amounts of CCR material remain. The initial industrial landfill unit was unlined with lined phases constructed over portions of the unlined area in the EAB beginning in 2002. The WAB was modified in 1986 for additional storage capacity, including the installation of a filter dike that separated the southern end of the basin, now called the WAB extension impoundment, where minor amounts of CCR material are present. The WAB still receives bottom ash by hydraulic sluicing methods. CCR at the facility is managed: as DFA within the lined portion of the landfill constructed on the EAB, by hydraulically sluicing bottom ash to the WAB, or by transporting offsite for beneficial reuse. A discharge canal constructed during the WAB modification receives waste streams from various on-site sources including: WAB effluent from bottom ash sluicing; EAB 1 Prior to September 18, 2015, the NCDEQ was referred to as the North Carolina Department of Environment and Natural Resources (NCDENR). Both naming conventions are used in this report, as appropriate. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx landfill leachate and drainage; storm water runoff from the two ash basins; discharge from the Flue Gas Desulfurization (FGD) Pond treatment process; cooling tower blowdown; domestic sewage treatment plant discharge; and surface water flow from the extension impoundment. Effluent from the WAB discharge canal passes through National Pollution Discharge Elimination System (NPDES) Internal Outfall 002 into the heated water discharge pond, which ultimately flows into Hyco Lake through NPDES Outfall 003 under Permit NC0003425. The EAB discharge canal is isolated from the EAB by the landfill and receives only surface water flow from the EAB extension impoundment, which discharges to the cooling water intake canal. NCDEQ is considering the applicable mechanism to provide coverage for this area in the renewed NPDES permit. Assessment results indicate the thickness of CCR in the EAB is approximately 55 to 80 feet and in the WAB is approximately 80 feet with residual CCR present in the basin extension impoundments and the basin effluent discharge canals. Assessment findings determined that the CCRs that have accumulated in the ash basins are the primary source of impact to groundwater. The inferred general extent of constituent migration from the ash basins based on evaluation of constituent concentrations greater than both groundwater quality standards and background is shown on Figure ES-1. A detailed evaluation of constituent migration is included in the CSA update report. ES.2 Initial Abatement and Emergency Response Duke Energy Progress has not conducted emergency responses because groundwater impacts from the ash basins do not present an imminent hazard to public health or the environment that would require emergency action. No abatement or source removal activities have been conducted at the Roxboro Plant related to the ash basins other than converting from a wet to dry fly ash handling system in 1986. In preparation for closure of the ash basins, new retention basins and wastewater treatment systems are being designed and constructed. ES.3 Receptor Information In accordance with NCDEQ direction, CSA receptor survey activities include listing and depicting all water supply wells (both public and private, including irrigation wells and unused wells) within a 0.5-mile radius of the ash basin compliance boundary. ES.3.1 Public Water Supply Wells Three public supply wells are located within 0.5-mile radius of the ash basin compliance boundary – one is located at a building materials manufacturing facility (northeast of the plant cooling water intake canal) and the other two are located at Woodland Elementary School on Semora Road (southwest of the plant 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx property). The building materials facility well is located approximately 2,500 feet northeast of the EAB beyond the cooling water intake canal. The Woodland Elementary School wells are located approximately 2,000 feet southwest of the WAB discharge canal, topographically and hydraulically upgradient of the WAB compliance boundary. Analytical data provided for the public water supply wells indicate constituent concentrations consistent with statistically determined background concentrations. Geochemistry data for the public water supply wells (cation/anion distribution) support no CCR impact. ES.3.2 Private Water Supply Wells No private supply wells are located within 0.5 mile downgradient of the ash basin compliance boundary. Approximately 102 reported or observed private water supply wells are located within a 0.5-mile radius of the compliance boundary upgradient of the ash basins, mostly along McGhees Mill Road, The Johnson Lane, Dunnaway Road, Archie Clayton Road, Daisy Thompson Road, and Semora Road. Particle track modeling indicates that well capture zones are limited to the immediate vicinity of the well head and do not extend toward the ash basins. None of the particle tracks originating in the ash basins have moved into the well capture zones. Available analytical data for the private water supply wells show detected concentrations below statistically derived background concentrations and geochemistry (cation/anion distribution) are not attributable to CCR impacts. ES.3.3 Surface Water Bodies Groundwater influenced by the ash basins flows toward various internal plant water features (the heated water discharge pond, the cooling tower pond, cooling tower intake pond, the water intake basin and the cooling water intake canal). Hyco Lake is beyond the plant water features. The surface water classification for Hyco Lake is Class B and WS-V waters (protected as a water supply that is upstream and draining to WS-IV or water used for drinking water supply purposes). ES.3.4 Human and Ecological Receptors A baseline human health and ecological risk assessment was performed in 2016 as a component of CAP Part 2 (SynTerra, 2016a) concluding no unacceptable risks to humans resulting from hypothetical exposure to constituents detected in the ash basins. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Based on review and analysis of groundwater and surface water data collected since completing the human health and ecological risk assessment in 2016, there is no evidence of potential risks to humans and wildlife at the Roxboro Site. This update to the human health and ecological risk assessment supports a risk classification of “Low” for both basins. ES.3.5 Land Use The Site is bordered by industrial (a building materials manufacturing facility), agricultural (pasture), rural residential (R), wooded land and Hyco Lake. No change in surrounding land use is currently anticipated. ES.4 Sampling/Investigation Results The comprehensive site assessment included evaluations of the hydrogeological and geochemical properties of soil and groundwater at multiple depths and distances from the ash basins. ES.4.1 Background Concentration Determinations Naturally occurring background concentrations were determined using statistical analysis for both soil and groundwater. Statistical determinations of proposed provisional background threshold values (PBTVs) were performed in strict accordance with the revised Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities (statistical methods document) (HDR and SynTerra, 2017). The background monitoring well (MW) network consists of wells installed within two hydrostratigraphic flow zones – transition zone and fractured bedrock. Background datasets used to statistically determine naturally occurring concentrations of inorganic constituents in soil and groundwater are provided herein. As of September 1, 2017, DEQ approved a number of the statistically derived background values, however others are still under evaluation and thus considered preliminary at this time. Background results may be greater than the PBTVs due to the limited valid dataset currently available. The statistically derived background threshold values will continue to be adjusted as additional data becomes available. ES.4.2 Nature and Extent of Contamination Site-specific groundwater constituents of interest (COIs) were developed by evaluating groundwater sampling results with respect to NCDEQ Title 15A Subchapter 02L.0200 Groundwater Classification and Standards (2L), Interim Maximum Allowable Concentrations (IMACs), PBTVs, and additional regulatory input/requirements. The distribution of constituents in relation to the ash 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx management areas, co-occurrence with CCR indicator constituents such as boron and sulfate, and migration directions based on groundwater flow direction are considered in determination of groundwater COIs. The following list of groundwater COIs has been developed for Roxboro: Antimony pH Boron Selenium Chromium (Hexavalent) Strontium Chromium (Total) Sulfate Cobalt Total Dissolved Solids (TDS) Iron Uranium Manganese Vanadium Molybdenum At Roxboro, boron, sulfate and TDS are key indicators of CCR impacts in groundwater and are detected at concentrations greater than the 2L values downgradient of the ash basins. The CCR distribution in groundwater at concentrations greater than 2L is depicted in Figure ES-1. West Ash Basin – Boron, sulfate and TDS are detected greater than the 2L values in bedrock monitoring wells underlying the WAB and in downgradient transition zone wells. Boron was not detected above background levels in the downgradient bedrock wells; however, sulfate and TDS were detected above 2L values in one downgradient bedrock well. The heated water discharge pond lies immediately adjacent to the WAB downgradient monitoring wells. CCR constituents are generally not detected in groundwater upgradient of the WAB, effluent discharge canal and the extension impoundment with the exception of two wells screened in deep bedrock fractures southwest of the ash basin. Assessment of the area further to the southwest and upgradient of this area in similar deep fracture zones indicates background conditions. East Ash Basin – CCR constituents including boron, sulfate and TDS are detected above 2L in the bedrock monitoring wells underlying the EAB and in several downgradient saprolite/transition zone and bedrock monitoring wells, including wells downgradient and proximal to the gypsum storage area adjacent to the cooling water intake canal. No CCR constituents are detected upgradient of the EAB, effluent discharge canal and the extension impoundment. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx ES.4.3 Maximum Contaminant Concentrations (Source Information) The source areas at Roxboro include CCR material and pore water accumulated in the West Ash Basin and the East Ash Basin. Ash pore water samples collected from wells installed within the ash basins and screened in the ash layers have been monitored since 2015. The concentrations of detected constituents have been relatively stable with minor fluctuations. The ash basins are permitted wastewater systems; therefore comparison of pore water within the wastewater treatment residuals (ash) to 2B or 2L/IMAC is not required. Soil samples collected below the ash/soil interface from seven locations within the ash basins indicate chromium, cobalt, iron, manganese and vanadium were detected greater than their respective PBTV and Preliminary Soil Remediation Goals (PSRG) Protection of Groundwater (POG) values. ES.4.4 Site Geology and Hydrogeology The subsurface at the Site is composed of regolith/saprolite, a transition zone and bedrock. The regolith/saprolite includes residual soils, fill and reworked soils, and alluvium. The transition zone is comprised of partially weathered rock that is gradational between saprolite and competent bedrock. The crystalline bedrock consists of gneiss or granitic gneiss/granite. Shallow bedrock is fractured; however, only mildly productive fractures (providing water to wells) were observed within the top 50 feet of competent rock. Groundwater exists under unconfined or water table conditions throughout the Site. For the most part, saturated conditions are limited to secondary fractures within the underlying bedrock. Saturated conditions in residual soil (saprolite) and partially weathered rock are limited across the site and present in close lateral proximity to surface water features including the ash basins, Hyco Lake and, to a lesser degree, streams. The regolith/saprolite/transition zone, where it is saturated, acts as a reservoir for supplying groundwater to the secondary fractures in the bedrock. Localized groundwater high elevations are centered around the ash basins, with radial flow in these areas. Recharge areas at the Site are located to the east and south. Each stream valley in which the ash basins were constructed is a distinct slope-aquifer system in which flow of groundwater into and out of the ash basins is restricted to the local flow regime. Groundwater and surface water from the ash basins flow north and west toward the Plant water features (heated water discharge pond, cooling tower intake pond and the cooling water intake canal). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx ES.5 Conclusions and Recommendations The investigation described in the CSA presents the results of the assessments required by the Coal Ash Management Act (CAMA) and 2L. Based on the data, a limited area of groundwater contamination is attributed to the CCR within the two ash basins. In the ash basin locations where soil samples were collected, analytical results indicate a few, limited detections of COIs greater than background and the PSRG POG values. The management of gypsum may be an additional, non-CAMA related source of risk to groundwater and surface water. The assessment investigated the Site hydrogeology, determined the direction of groundwater flow from the ash basins, and determined the horizontal and vertical extent of impacts to groundwater and soil sufficient to proceed with preparation of a CAP. Assessment results indicate groundwater impacts from ash basin CCR material pore water seepage is limited to beneath the ash basins, downgradient in areas between the ash basins and internal plant water features (the heated water discharge pond, the cooling tower pond, cooling tower intake pond and the cooling water intake canal) and a limited area southwest of the WAB. The comprehensive evaluation of groundwater flow characteristics demonstrates that groundwater flow is to the north and west toward the internal plant water features away from the topographically higher areas, south and east, where the water supply wells are located. Roxboro Plant’s ash basins are currently designated as “Intermediate” risk under CAMA, meaning that closure of the ash basins is required by 2024. The updated evaluation of risks has determined no changes from the previous risk assessment conclusion of no imminent risk to human health or the environment due to groundwater, surface water, or sediment impacts attributable to groundwater migration from the ash basins. Water supply wells located within a 0.5-mile radius of the Roxboro ash basins compliance boundary are not impacted by the ash basins. This conclusion is supported by the detailed characterization of groundwater chemistry including evaluation of CCR indicators and correlation evaluations. The results of the chemical correlation analyses indicate that, based on the different constituent clustering patterns from the ash basin pore water wells and the water supply wells, the source water for the water supply wells is not CCR-impacted groundwater. A pore water evaluation of the private and public water supply well data and the detailed statistical analysis of regional background groundwater data indicate that constituent concentrations in the water supply wells are generally consistent with background conditions. A “Low” risk classification and closure via a cap-in-place scenario is considered viable. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ES-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx A preliminary evaluation of groundwater corrective action alternatives is included in this CSA to provide insight into the Corrective Action Plan (CAP) preparation process. For Roxboro, the primary source control (closure) methods anticipated to be evaluated in the CAP are: Dewater the ash within the basins and cap the residuals with a low permeability engineered cover system to minimize infiltration; Excavate the ash to remove the source of the COIs from the groundwater flow system; and Potentially some combination of the above. The source control (closure) options will be evaluated in the CAP to determine the most technically and economically feasible means of removing or controlling the ash and ash pore water as a source to the groundwater flow system. The evaluation will include predictive groundwater modeling to evaluate the cost-benefit associated with various options. For basin closure, ash dewatering and reduction of the amount of water migrating from the basins to groundwater will have the greatest positive impact on groundwater and surface water quality downgradient of the ash basins based on preliminary fate and transport and geochemical modeling results. A well-designed capping system can be expected to minimize ongoing migration to groundwater after dewatering. In addition to source control measures, the CAP will evaluate measures to address groundwater conditions associated with the ash basins. Groundwater corrective action by monitored natural attenuation (MNA) is anticipated to be a remedy further evaluated in the CAP. As warranted, a number of other viable groundwater remediation technologies such as phytoremediation, groundwater extraction, or hydraulic barriers may be evaluated based upon short-term and long-term effectiveness, implementability, and cost. Results of the evaluation, including groundwater fate and transport modeling, and geochemical modeling, will be used for remedy selection in the CAP. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page i P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx TABLE OF CONTENTS SECTION PAGE ES.1 SOURCE INFORMATION ....................................................................................... ES-1 ES.2 INITIAL ABATEMENT AND EMERGENCY RESPONSE ................................ ES-2 ES.3 RECEPTOR INFORMATION .................................................................................. ES-2 ES.3.1 Public Water Supply Wells ................................................................................... ES-2 ES.3.2 Private Water Supply Wells ................................................................................. ES-3 ES.3.3 Surface Water Bodies ............................................................................................. ES-3 ES.3.4 Human and Ecological Receptors ........................................................................ ES-3 ES.3.5 Land Use .................................................................................................................. ES-4 ES.4 SAMPLING/INVESTIGATION RESULTS .......................................................... ES-4 ES.4.1 Background Concentration Determinations ...................................................... ES-4 ES.4.2 Nature and Extent of Contamination .................................................................. ES-4 ES.4.3 Maximum Contaminant Concentrations (Source Information) ...................... ES-6 ES.4.4 Site Geology and Hydrogeology ......................................................................... ES-6 ES.5 CONCLUSIONS AND RECOMMENDATIONS ................................................ ES-7 1.0 INTRODUCTION ......................................................................................................... 1-1 1.1 Purpose of Comprehensive Site Assessment ........................................................ 1-1 1.2 Regulatory Background ........................................................................................... 1-2 Notice of Regulatory Requirements ............................................................... 1-2 1.2.1 Coal Ash Management Act Requirements .................................................... 1-3 1.2.2 1.3 Approach to Comprehensive Site Assessment ..................................................... 1-4 NORR Guidance ................................................................................................ 1-4 1.3.1 USEPA Monitored Natural Attenuation Tiered Approach ........................ 1-5 1.3.2 ASTM Conceptual Site Model Guidance ....................................................... 1-5 1.3.3 1.4 Technical Objectives ................................................................................................. 1-6 1.5 Previous Submittals .................................................................................................. 1-6 2.0 SITE HISTORY AND DESCRIPTION ..................................................................... 2-1 2.1 Site Description, Ownership and Use History...................................................... 2-1 East Ash Pond/Basin History .......................................................................... 2-1 2.1.1 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx TABLE OF CONTENTS SECTION PAGE West Ash Basin History ................................................................................... 2-2 2.1.2 2.2 Geographic Setting, Surrounding Land Use, Surface Water Classification ..... 2-3 2.3 CAMA-related Source Areas ................................................................................... 2-5 2.4 Other Primary and Secondary Sources .................................................................. 2-5 2.5 Summary of Permitted Activities ........................................................................... 2-6 2.6 History of Site Groundwater Monitoring .............................................................. 2-7 Ash Basin Voluntary Groundwater Monitoring .......................................... 2-8 2.6.1 Ash Basin NPDES Groundwater Monitoring ............................................... 2-8 2.6.2 Ash Basin CAMA Groundwater Monitoring................................................ 2-9 2.6.3 Landfill Groundwater Monitoring ............................................................... 2-10 2.6.4 2.7 Summary of Assessment Activities ...................................................................... 2-11 2.8 Summary of Initial Abatement, Source Removal or other Corrective Action .................................................................................................... 2-11 3.0 SOURCE CHARACTERISTICS ................................................................................. 3-1 3.1 Coal Combustion and Ash Handling System ....................................................... 3-1 3.2 General Physical and Chemical Properties of Ash............................................... 3-1 3.3 Site-Specific Coal Ash Data ..................................................................................... 3-3 4.0 RECEPTOR INFORMATION ..................................................................................... 4-1 4.1 Summary of Receptor Survey Activities................................................................ 4-2 4.2 Summary of Receptor Survey Findings ................................................................. 4-3 Public Water Supply Wells .............................................................................. 4-4 4.2.1 Private Water Supply Wells ............................................................................ 4-4 4.2.2 4.3 Private and Public Well Water Sampling .............................................................. 4-5 4.4 Numerical Capture Zone Analysis ......................................................................... 4-7 4.5 Surface Water Receptors .......................................................................................... 4-7 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY ............................................... 5-1 5.1 Regional Geology ...................................................................................................... 5-1 5.2 Regional Hydrogeology ........................................................................................... 5-2 6.0 SITE GEOLOGY AND HYDROGEOLOGY ............................................................ 6-1 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page iii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx TABLE OF CONTENTS SECTION PAGE 6.1 Site Geology ............................................................................................................... 6-2 Soil Classification .............................................................................................. 6-2 6.1.1 Rock Lithology .................................................................................................. 6-4 6.1.2 Structural Geology ............................................................................................ 6-6 6.1.3 6.2 Site Hydrogeology .................................................................................................... 6-6 Hydrostratigraphic Layer Development ....................................................... 6-6 6.2.1 Hydrostratigraphic Layer Properties ............................................................. 6-7 6.2.2 6.3 Groundwater Flow Direction .................................................................................. 6-9 6.4 Hydraulic Gradients ............................................................................................... 6-10 6.5 Hydraulic Conductivity ......................................................................................... 6-11 6.6 Groundwater Velocity ............................................................................................ 6-12 6.7 Contaminant Velocity ............................................................................................. 6-13 6.8 Slug Test and Aquifer Test Results ...................................................................... 6-14 6.9 Fracture Trace Study Results ................................................................................. 6-15 7.0 SOIL SAMPLING RESULTS ...................................................................................... 7-1 7.1 Background Soil Data ............................................................................................... 7-1 7.2 Facility Soil Data ....................................................................................................... 7-2 8.0 SEDIMENT RESULTS ................................................................................................. 8-1 8.1 Sediment/Surface Soil Associated with Areas of Wetness (AOWs) .................. 8-1 8.2 Sediment in Major Water Bodies ............................................................................ 8-2 8.3 Sediment Associated with Extension Impoundments/Effluent Discharge Canals ...................................................................................................... 8-2 9.0 SURFACE WATER RESULTS .................................................................................... 9-1 9.1 Comparison of Exceedances to 2B Standards ....................................................... 9-2 9.2 Discussion of Results for Constituents Without Established 2B ........................ 9-3 9.3 Discussion of Surface Water Results ...................................................................... 9-4 10.0 GROUNDWATER SAMPLING RESULTS ............................................................ 10-1 10.1 Background Groundwater Concentrations ......................................................... 10-2 Background Dataset Statistical Analysis ..................................................... 10-3 10.1.1 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page iv P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx TABLE OF CONTENTS SECTION PAGE Piper Diagrams (Comparison to Background) ........................................... 10-5 10.1.2 10.2 Downgradient Groundwater Concentrations..................................................... 10-6 Monitoring Wells Beneath WAB................................................................... 10-6 10.2.1 Monitoring Wells Beneath EAB .................................................................... 10-7 10.2.2 Saprolite/Transition Zone Downgradient Monitoring Wells (WAB) ...... 10-7 10.2.3 Saprolite/Transition Zone Downgradient Monitoring Wells (EAB) ....... 10-8 10.2.4 Bedrock Downgradient Monitoring Wells (WAB) ..................................... 10-9 10.2.5 Bedrock Downgradient Wells (EAB) ......................................................... 10-10 10.2.6 Piper Diagrams (Comparison to Downgradient/ Separate 10.2.7 Flow Regime) ................................................................................................. 10-12 10.3 Site Specific Exceedances (Groundwater COIs) ............................................... 10-13 Provisional Background Threshold Values (PBTVs) ............................... 10-13 10.3.1 Applicable Standards ................................................................................... 10-13 10.3.2 Additional Requirements ............................................................................. 10-14 10.3.3 Roxboro Plant COIs ...................................................................................... 10-15 10.3.4 11.0 HYDROGEOLOGICAL INVESTIGATION .......................................................... 11-1 11.1 Plume Physical and Chemical Characterization ................................................ 11-1 Plume Physical Characterization .................................................................. 11-1 11.1.1 Plume Chemical Characterization ................................................................ 11-3 11.1.2 11.2 Pending Investigation(s) ...................................................................................... 11-16 12.0 RISK ASSESSMENT .................................................................................................. 12-1 12.1 Human Health Screening Summary .................................................................... 12-2 12.2 Ecological Screening Summary ............................................................................. 12-3 12.3 Private Well Receptor Assessment Update ......................................................... 12-3 12.4 Risk Assessment Update Summary ..................................................................... 12-4 13.0 GROUNDWATER MODELING RESULTS........................................................... 13-1 13.1 Summary of Fate and Transport Model Results................................................. 13-2 Flow Model Construction .............................................................................. 13-3 13.1.1 Transport Model Construction ..................................................................... 13-8 13.1.2 Summary of Flow and Transport Modeling Results To Date ................ 13-11 13.1.3 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page v P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx TABLE OF CONTENTS SECTION PAGE 13.2 Summary of Geochemical Model Results ......................................................... 13-13 Model Construction ...................................................................................... 13-13 13.2.1 Summary of Geochemical Model Results To Date................................... 13-16 13.2.2 13.3 Groundwater to Surface Water Pathway Evaluation ...................................... 13-17 14.0 SITE ASSESSMENT RESULTS ................................................................................ 14-1 14.1 Nature and Extent of Contamination ................................................................... 14-1 14.2 Maximum COC Concentrations ........................................................................... 14-3 14.3 Contaminant Migration and Potentially Affected Receptors ........................... 14-6 15.0 CONCLUSIONS AND RECOMMENDATIONS ................................................. 15-1 15.1 Overview of Site Conditions at Specific Source Areas ...................................... 15-1 15.2 Revised Site Conceptual Model ............................................................................ 15-1 15.3 Interim Monitoring Program ................................................................................. 15-3 IMP Implementation ....................................................................................... 15-4 15.3.1 IMP Reporting ................................................................................................. 15-4 15.3.2 15.4 Preliminary Evaluation of Corrective Action Alternatives............................... 15-4 CAP Preparation Process ............................................................................... 15-5 15.4.1 Summary .......................................................................................................... 15-7 15.4.2 16.0 REFERENCES ............................................................................................................... 16-1 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page vi P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES Executive Summary Figure ES-1 Approximate Extent of Impacts 1.0 Introduction Figure 1-1 Site Location Map 2.0 Site History and Description Figure 2-1 Roxboro Plant Vicinity Map Figure 2-2 1951 Aerial Photograph Figure 2-3 1964 Aerial Photograph Figure 2-4 1977 Aerial Photograph Figure 2-5 1993 Aerial Photograph Figure 2-6 2008 Aerial Photograph Figure 2-7 2016 Aerial Photograph Figure 2-8 General Area Map Figure 2-9 1968 USGS Topographic Map Figure 2-10 Process Flow Diagram Figure 2-11 Site Layout Map - West Ash Basin Figure 2-12 Site Layout Map - East Ash Basin 3.0 Source Characteristics Figure 3-1 Known Sample of Ash for Comparison Figure 3-2 Elemental Composition for Bottom Ash, Fly Ash, Shale, and Volcanic Ash Figure 3-3 Coal Ash TCLP Leachate Concentration Ranges Compared to Regulatory Limits Figure 3-4 Piper Diagram – Pore Water 4.0 Receptor Information Figure 4-1 USGS Map with Water Supply Wells Figure 4-2 Water Supply Well Location Map Figure 4-3 Piper Diagram - Water Supply Wells Figure 4-4 Water Supply Well Capture Zone 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page vii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES (CONTINUED) 5.0 Regional Geology and Hydrogeology Figure 5-1 Regional Geologic Map Figure 5-2 Generalized Site Geologic Map Figure 5-3 Piedmont Slope-Aquifer System 6.0 Site Geology Figure 6-1 Geologic Cross Section - Section A-A' Figure 6-2 Geologic Cross Section - Section B-B' Figure 6-3 Geologic Cross Section - Section C-C' Figure 6-4 Geologic Cross Section - Section D-D' Figure 6-5 Generalized Water Level Map - October 31, 2016 Figure 6-6 Generalized Water Level Map - April 10, 2017 Figure 6-7 Potential Vertical Gradient Between Shallow and Deep Flow Zones Figure 6-8 Potential Fracture Trace Analysis 7.0 Soil Sampling Results Figure 7-1 Potential Secondary Source Soil Analytical Results 9.0 Surface Water Results Figure 9-1 Piper Diagram - Surface Water and AOWs 10.0 Groundwater Sampling Results Figure 10-1 Piper Diagram - Saprolite and Transition Zone Figure 10-2 Piper Diagram – Bedrock 11.0 Hydrogeological Investigation Figure 11-1 Isoconcentration Map - Antimony in Transition Zone Groundwater Figure 11-2 Isoconcentration Map - Antimony in Bedrock Groundwater Figure 11-3 Isoconcentration Map - Boron in Transition Zone Groundwater Figure 11-4 Isoconcentration Map - Boron in Bedrock Groundwater Figure 11-5 Isoconcentration Map - Chromium and Chromium (VI) in Transition Zone Groundwater Figure 11-6 Isoconcentration Map - Chromium and Chromium (VI) in Bedrock Groundwater Figure 11-7 Isoconcentration Map - Cobalt in Transition Zone Groundwater Figure 11-8 Isoconcentration Map - Cobalt in Bedrock Groundwater Figure 11-9 Isoconcentration Map - Iron in Transition Zone Groundwater Figure 11-10 Isoconcentration Map - Iron in Bedrock Groundwater 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page viii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES (CONTINUED) Figure 11-11 Isoconcentration Map - Manganese in Transition Zone Groundwater Figure 11-12 Isoconcentration Map - Manganese in Bedrock Groundwater Figure 11-13 Isoconcentration Map - Molybdenum in Transition Zone Groundwater Figure 11-14 Isoconcentration Map - Molybdenum in Bedrock Groundwater Figure 11-15 Isoconcentration Map - pH in Transition Zone Groundwater Figure 11-16 Isoconcentration Map - pH in Bedrock Groundwater Figure 11-17 Isoconcentration Map - Selenium in Transition Zone Groundwater Figure 11-18 Isoconcentration Map - Selenium in Bedrock Groundwater Figure 11-19 Isoconcentration Map - Strontium in Transition Zone Groundwater Figure 11-20 Isoconcentration Map - Strontium in Bedrock Groundwater Figure 11-21 Isoconcentration Map - Sulfate in Transition Zone Groundwater Figure 11-22 Isoconcentration Map - Sulfate in Bedrock Groundwater Figure 11-23 Isoconcentration Map - Total Dissolved Solids in Transition Zone Groundwater Figure 11-24 Isoconcentration Map - Total Dissolved Solids in Bedrock Groundwater Figure 11-25 Isoconcentration Map - Uranium in Transition Zone Groundwater Figure 11-26 Isoconcentration Map - Uranium in Bedrock Groundwater Figure 11-27 Isoconcentration Map - Vanadium in Transition Zone Groundwater Figure 11-28 Isoconcentration Map - Vanadium in Bedrock Groundwater Figure 11-29 Concentration Versus Distance - East Ash Basin - Antimony, Boron, Chromium (Total), Chromium (VI), Cobalt, Iron, Manganese, and Molybdenum Figure 11-30 Concentration Versus Distance - East Ash Basin - pH, Selenium, Strontium, Sulfate, Total Dissolved Solids, Uranium, and Vanadium Figure 11-31 Concentration Versus Distance - West Ash Basin - Antimony, Boron, Chromium (Total), Chromium (VI), Cobalt, Iron, Manganese, and Molybdenum Figure 11-32 Concentration Versus Distance - West Ash Basin - pH, Selenium, Strontium, Sulfate, Total Dissolved Solids, Uranium, and Vanadium Figure 11-33 Antimony Analytical Results Cross Section A-A’ Figure 11-34 Antimony Analytical Results Cross Section B-B’ Figure 11-35 Antimony Analytical Results Cross Section C-C’ Figure 11-36 Antimony Analytical Results Cross Section D-D’ Figure 11-37 Boron Analytical Results Cross Section A-A’ Figure 11-38 Boron Analytical Results Cross Section B-B’ Figure 11-39 Boron Analytical Results Cross Section C-C’ Figure 11-40 Boron Analytical Results Cross Section D-D’ 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ix P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES (CONTINUED) Figure 11-41 Hexavalent and Total Chromium Analytical Results Cross Section A-A’ Figure 11-42 Hexavalent and Total Chromium Analytical Results Cross Section B-B’ Figure 11-43 Hexavalent and Total Chromium Analytical Results Cross Section C-C’ Figure 11-44 Hexavalent and Total Chromium Analytical Results Cross Section D-D’ Figure 11-45 Cobalt Analytical Results Cross Section A-A’ Figure 11-46 Cobalt Analytical Results Cross Section B-B’ Figure 11-47 Cobalt Analytical Results Cross Section C-C’ Figure 11-48 Cobalt Analytical Results Cross Section D-D’ Figure 11-49 Iron Analytical Results Cross Section A-A’ Figure 11-50 Iron Analytical Results Cross Section B-B’ Figure 11-51 Iron Analytical Results Cross Section C-C’ Figure 11-52 Iron Analytical Results Cross Section D-D’ Figure 11-53 Manganese Analytical Results Cross Section A-A’ Figure 11-54 Manganese Analytical Results Cross Section B-B’ Figure 11-55 Manganese Analytical Results Cross Section C-C’ Figure 11-56 Manganese Analytical Results Cross Section D-D’ Figure 11-57 Molybdenum Analytical Results Cross Section A-A’ Figure 11-58 Molybdenum Analytical Results Cross Section B-B’ Figure 11-59 Molybdenum Analytical Results Cross Section C-C’ Figure 11-60 Molybdenum Analytical Results Cross Section D-D’ Figure 11-61 pH Analytical Results Cross Section A-A’ Figure 11-62 pH Analytical Results Cross Section B-B’ Figure 11-63 pH Analytical Results Cross Section C-C’ Figure 11-64 pH Analytical Results Cross Section D-D’ Figure 11-65 Selenium Analytical Results Cross Section A-A’ Figure 11-66 Selenium Analytical Results Cross Section B-B’ Figure 11-67 Selenium Analytical Results Cross Section C-C’ Figure 11-68 Selenium Analytical Results Cross Section D-D’ Figure 11-69 Strontium Analytical Results Cross Section A-A’ Figure 11-70 Strontium Analytical Results Cross Section B-B’ Figure 11-71 Strontium Analytical Results Cross Section C-C’ Figure 11-72 Strontium Analytical Results Cross Section D-D’ Figure 11-73 Sulfate Analytical Results Cross Section A-A’ Figure 11-74 Sulfate Analytical Results Cross Section B-B’ Figure 11-75 Sulfate Analytical Results Cross Section C-C’ 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page x P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES (CONTINUED) Figure 11-76 Sulfate Analytical Results Cross Section D-D’ Figure 11-77 Total Dissolved Solids (TDS) Analytical Results Cross Section A-A’ Figure 11-78 Total Dissolved Solids (TDS) Analytical Results Cross Section B-B’ Figure 11-79 Total Dissolved Solids (TDS) Analytical Results Cross Section C-C’ Figure 11-80 Total Dissolved Solids (TDS) Analytical Results Cross Section D-D’ Figure 11-81 Total Uranium Analytical Results Cross Section A-A’ Figure 11-82 Total Uranium Analytical Results Cross Section B-B’ Figure 11-83 Total Uranium Analytical Results Cross Section C-C’ Figure 11-84 Total Uranium Analytical Results Cross Section D-D’ Figure 11-85 Vanadium Analytical Results Cross Section A-A’ Figure 11-86 Vanadium Analytical Results Cross Section B-B’ Figure 11-87 Vanadium Analytical Results Cross Section C-C’ Figure 11-88 Vanadium Analytical Results Cross Section D-D’ 12.0 Screening-Level Risk Assessment Figure 12-1 Exposure Areas Human Health Risk Assessment Figure 12-2 Exposure Areas Ecological Risk Assessment 14.0 Site Assessment Results Figure 14-1 Time versus Concentration - Antimony in Ash Pore Water Figure 14-2 Time versus Concentration - Antimony in Transition Zone Figure 14-3 Time versus Concentration - Antimony in Bedrock Figure 14-4 Time versus Concentration - Boron in Ash Pore Water Figure 14-5 Time versus Concentration - Boron in Transition Zone Figure 14-6 Time versus Concentration - Boron in Bedrock Figure 14-7 Time versus Concentration – Total and Hexavalent Chromium in Ash Pore Water Figure 14-8 Time versus Concentration – Total and Hexavalent Chromium in Transition Zone Figure 14-9 Time versus Concentration – Total and Hexavalent Chromium in Bedrock Figure 14-10 Time versus Concentration - Cobalt in Ash Pore Water Figure 14-11 Time versus Concentration - Cobalt in Transition Zone Figure 14-12 Time versus Concentration - Cobalt in Bedrock Figure 14-13 Time versus Concentration - Iron in Ash Pore Water Figure 14-14 Time versus Concentration - Iron in Transition Zone Figure 14-15 Time versus Concentration - Iron in Bedrock 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page xi P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES (CONTINUED) Figure 14-16 Time versus Concentration - Manganese in Ash Pore Water Figure 14-17 Time versus Concentration - Manganese in Transition Zone Figure 14-18 Time versus Concentration - Manganese in Bedrock Figure 14-19 Time versus Concentration - Molybdenum in Ash Pore Water Figure 14-20 Time versus Concentration - Molybdenum in Transition Zone Figure 14-21 Time versus Concentration - Molybdenum in Bedrock Figure 14-22 Time versus Concentration - pH in Ash Pore Water Figure 14-23 Time versus Concentration - pH in Transition Zone Figure 14-24 Time versus Concentration - pH in Bedrock Figure 14-25 Time versus Concentration - Selenium in Ash Pore Water Figure 14-26 Time versus Concentration - Selenium in Transition Zone Figure 14-27 Time versus Concentration - Selenium in Bedrock Figure 14-28 Time versus Concentration - Strontium in Ash Pore Water Figure 14-29 Time versus Concentration - Strontium in Transition Zone Figure 14-30 Time versus Concentration - Strontium in Bedrock Figure 14-31 Time versus Concentration - Sulfate in Ash Pore Water Figure 14-32 Time versus Concentration - Sulfate in Transition Zone Figure 14-33 Time versus Concentration - Sulfate in Bedrock Figure 14-34 Time versus Concentration - TDS in Ash Pore Water Figure 14-35 Time versus Concentration - TDS in Transition Zone Figure 14-36 Time versus Concentration - TDS in Bedrock Figure 14-37 Time versus Concentration – Total Uranium in Ash Pore Water Figure 14-38 Time versus Concentration – Total Uranium in Transition Zone Figure 14-39 Time versus Concentration – Total Uranium in Bedrock Figure 14-40 Time versus Concentration - Vanadium in Ash Pore Water Figure 14-41 Time versus Concentration - Vanadium in Transition Zone Figure 14-42 Time versus Concentration - Vanadium in Bedrock Figure 14-43 Groundwater Concentration Trend Analysis Antimony In All Flow Layers Figure 14-44 Groundwater Concentration Trend Analysis Antimony In Surface Water Figure 14-45 Groundwater Concentration Trend Analysis Boron In All Flow Layers Figure 14-46 Groundwater Concentration Trend Analysis Boron In Surface Water Figure 14-47 Groundwater Concentration Trend Analysis Chromium (VI &Total) In All Flow Layers Figure 14-48 Groundwater Concentration Trend Analysis Total Chromium In Surface Water 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page xii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES (CONTINUED) Figure 14-49 Groundwater Concentration Trend Analysis Cobalt In All Flow Layers Figure 14-50 Groundwater Concentration Trend Analysis Cobalt In Surface Water Figure 14-51 Groundwater Concentration Trend Analysis Iron In All Flow Layers Figure 14-52 Groundwater Concentration Trend Analysis Iron In Surface Water Figure 14-53 Groundwater Concentration Trend Analysis Manganese In All Flow Layers Figure 14-54 Groundwater Concentration Trend Analysis Manganese In Surface Water Figure 14-55 Groundwater Concentration Trend Analysis Molybdendum In All Flow Layers Figure 14-56 Groundwater Concentration Trend Analysis Molybdendum In Surface Water Figure 14-57 Groundwater Concentration Trend Analysis pH In All Flow Layers Figure 14-58 Groundwater Concentration Trend Analysis pH In Surface Water Figure 14-59 Groundwater Concentration Trend Analysis Selenium In All Flow Figure 14-60 Groundwater Concentration Trend Analysis Selenium In Surface Water Layers Figure 14-61 Groundwater Concentration Trend Analysis Strontium In All Flow Layers Figure 14-62 Groundwater Concentration Trend Analysis Strontium In Surface Water Figure 14-63 Groundwater Concentration Trend Analysis Sulfate In All Flow Layers Figure 14-64 Groundwater Concentration Trend Analysis Sulfate In Surface Water Figure 14-65 Groundwater Concentration Trend Analysis Total Dissolved Solids In All Flow Layers Figure 14-66 Groundwater Concentration Trend Analysis Total Dissolved Solids In Surface Water Figure 14-67 Groundwater Concentration Trend Analysis Total Uranium In All Flow Layers Figure 14-68 Groundwater Concentration Trend Analysis Vanadium In All Flow Layers Figure 14-69 Groundwater Concentration Trend Analysis Vanadium In Surface Water Figure 14-70 Comprehensive Soil and Sediment Data – East Ash Basin Figure 14-71 Comprehensive Surface Water and AOW Data – East Ash Basin Figure 14-72 Comprehensive Groundwater Data – East Ash Basin Figure 14-73 Comprehensive Soil and Sediment Data – West Ash Basin 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page xiii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF FIGURES (CONTINUED) Figure 14-74 Comprehensive Surface Water and AOW Data – West Ash Basin Figure 14-75 Comprehensive Groundwater Data – West Ash Basin 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page i P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF TABLES 2.0 Site History and Description Table 2-1 Well Construction Data Table 2-2 NPDES Groundwater Monitoring Requirements 3.0 Source Characteristics Table 3-1 Ash, Rock, and Soil Composition Table 3-2 Physical Properties of Ash Table 3-3 Mineralogy of Ash Table 3-4 Whole Rock Metal Oxide Analysis of Ash Table 3-5 Whole Rock Elemental Analysis of Ash 6.0 Site Geology Table 6-1 Physical Properties of Soil Table 6-2 Chemical Properties of Soil Table 6-3 Soil, Sediment, and Ash Analytical Methods Table 6-4 Ash Pore Water, Groundwater, Surface Water, and AOW Analytical Methods Table 6-5 Historical Water Level Data Table 6-6 Horizontal Groundwater Gradients Table 6-7 Vertical Hydraulic Gradients Table 6-8 In-situ Hydraulic Conductivity Results Table 6-9 Vertical Hydraulic Conductivity of Undisturbed Soil Sample 7.0 Soil Sampling Results Table 7-1 Background Threshold Values for Soil Table 7-2 Secondary Source Assessment – Soil Analytical Results 10.0 Groundwater Sampling Results Table 10-1 Groundwater Background Threshold Values Table 10-2 Groundwater Constituents of Interest 13.0 Groundwater Modeling Results Table 13-1 Summary of Kd Values From Batch and Column Studies 15.0 Interim Groundwater Monitoring Plan Table 15-1 Groundwater Interim Monitoring Program Analytical Methods Table 15-2 Interim Groundwater Monitoring Plan Sample Locations 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF APPENDICES Appendix A Regulatory Correspondence NCDEQ Expectations Document (July 18. 2017) Completed NCDEQ CSA Update Expectations Check List – Roxboro Steam Electric Plant Zimmerman to Draovitch (September 1, 2017) NCDEQ Background Dataset Review (July 7, 2017) Revised Interim Monitoring Plans for 14 Duke Energy Facilities (May 1, 2017) NCDENR NORR Letter (August 13, 2014) Appendix B Comprehensive Data Table Comprehensive Data Table Notes Table 1 Groundwater Analytical Results Table 2 Surface Water Results Table 3 AOW Results Table 4 Soil and Ash Results Table 5 Sediment Results Table 6 SPLP Results Appendix C Site Assessment Data CSA Data Reports (Physical) UNCC Soil Sorption Evaluation UNCC Soil Sorption Report Addendum Slug Test Results BG-1BRLR Data Logger Results Appendix D Receptor Surveys Drinking Water Well and Receptor Survey – Roxboro Steam Electric Plant (SynTerra, September 2014) Supplement to Drinking Water Well and Receptor Survey – Roxboro Steam Electric Plant (SynTerra, November 2014) Update to Drinking Water Well and Receptor Survey – Roxboro Steam Electric Plant (SynTerra, September 2016) Dewberry Potable Water Evaluation 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page iii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF APPENDICES CONTINUED Appendix E Supporting Documents STANTEC Draft Report WSP Drawings Appendix F Boring Logs and Construction Diagrams Appendix G Methodology Duke Energy Low Flow Sampling Plan (June 10, 2015) Assessment Methodology Appendix H Background Statistical Evaluation Report Appendix I Lab Reports 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page i P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx LIST OF ACRONYMS 2B NCDENR Title 15A, Subchapter 2B. Surface Water and Wetland Standards 2L NCDENR Title 15A, Subchapter 2L. Groundwater Classification and Standards ADD Average Daily Dose AOW Areas of Wetness ASTM American Society for Testing and Materials BGS Below Existing Ground Surface CAMA Coal Ash Management Act CAP Corrective Action Plan CCB Coal Combustion By-Products CCR Coal Combustion Residuals CFR Code of Federal Register COI Constituent of Interest CP&L Carolina Power & Light CSA Comprehensive Site Assessment DEP Duke Energy Progress, LLC DFA Dry Fly Ash DO Dissolved Oxygen DWR Division of Water Resources EAB East Ash Pond/Basin EDR Environmental Data Resources, Inc. EMP Effectiveness Monitoring Plan FGD Flue Gas Desulfurization GAP Groundwater Assessment Work Plan HAO Hydroxide Phases of Aluminum HFO Hydroxide Phases of Iron HMO Hydroxide Phases of Manganese IHSB Inactive Hazardous Sites Branch IMAC Interim Maximum Allowable Concentrations IMP Interim Monitoring Plan MCL Maximum Contaminant Level 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page ii P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx MNA Monitored Natural Attenuation MW Monitoring Well NCAC North Carolina Administrative Code NCDENR North Carolina Department of Environment and Natural Resources NCDEQ North Carolina Department of Environmental Quality NCDEQ-DWM North Carolina Department of Environmental Quality – Division of Waste Management NCDEQ-DWR North Carolina Department of Environmental Quality – Division of Water Resources NORR Notice of Regulatory Requirements NPDES National Pollution Discharge Elimination System NTU Nephelometric Turbidity Unit NURE National Uranium Resource Evaluation PBTV Provisional Background Threshold Value Plant/Site Roxboro Steam Electric Plant POG Protection of Groundwater PSRG Preliminary Soil Remediation Goal PWR Partially Weathered Rock R Residential RBC Risk-Based Concentration RCP Reinforced Concrete Pipe SCM Site Conceptual Model SMCL Secondary Maximum Contaminant Level SPLP Synthetic Precipitation Leaching Procedure SW Surface Water TCLP Toxicity Characteristic Leaching Procedure TDS Total Dissolved Solids TOC Total Organic Carbon TRV Toxicity Reference Values UNCC University of North Carolina - Charlotte USEPA United States Environmental Protection Agency USGS United States Geological Survey UTL Upper Tolerance Limit WAB West Ash Basin 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 1-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 1.0 INTRODUCTION Duke Energy Progress, LLC (Duke Energy, DEP) owns and operates the Roxboro Steam Electric Plant (the Roxboro Plant, Plant, or Site) located at 1700 Dunnaway Road in Semora, Person County, North Carolina (Figure 1-1). The Plant began operations in 1966 as a coal-fired electrical generating station with additional generating units added in 1968, 1973, and 1980, which are currently maintained with a combined electric generating capacity of 2,422 megawatts. Coal combustion residuals (CCRs) have historically been managed at the Plant’s two on-site ash basins (surface impoundments): the East Ash Pond/Basin (EAB), which was constructed in 1964, and the West Ash Basin (WAB), which was constructed in 1973. CCRs were initially deposited in the EAB by hydraulic sluicing operations until the Plant was modified for dry fly ash (DFA) handling in the 1980s. An industrial landfill, permitted by the North Carolina Department of Environment Quality (NCDEQ)2 Division of Waste Management (DWM) Permit 7302, was constructed partially in the waste boundary of the EAB for the placement of the DFA. The construction of the industrial landfill isolated a section of the EAB, now called the EAB extension impoundment, where minor amounts of CCR material remain. The initial industrial landfill unit was unlined with lined phases subsequently constructed over portions of the unlined area and EAB beginning in 2002. The WAB was modified in 1986 for additional storage capacity, including the installation of a filter dike that separated the southern end of the basin, now called the WAB extension impoundment, where minor amounts of CCR material are present. CCR at the facility is managed within the lined portion of the industrial landfill or transported offsite for beneficial reuse. The WAB still receives bottom ash by hydraulic sluicing methods. Discharge from the WAB passes through National Pollution Discharge Elimination System (NPDES) internal outfall 002 into the heated water discharge pond, which ultimately flows into Hyco Lake through NPDES Outfall 003 under Permit NC003425. 1.1 Purpose of Comprehensive Site Assessment This Comprehensive Site Assessment (CSA) update was conducted to refine and expand the understanding of subsurface geologic/hydrogeologic conditions and evaluate the extent of impacts from historical management of coal ash in the ash basins. This CSA update contains an assessment of Site conditions based on a comprehensive interpretation of geologic and sampling results from the initial Site assessment and geologic and sampling results obtained subsequent to the initial assessment and has 2 Prior to September 18, 2015, the NCDEQ was referred to as the North Carolina Department of Environment and Natural Resources (NCDENR). Both naming conventions are used in this report, as appropriate. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 1-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx been prepared in coordination with Duke Energy and NCDEQ in response to requests for additional information, including additional sampling and assessment of specified areas. This CSA update was prepared in conformance to the most recently updated CSA table of contents provided by NCDEQ to Duke Energy on September 29, 2017. In response to a request from NCDEQ for an updated CSA report, this submittal includes the following information: Review of baseline assessment data collected and reported as part of CSA activities; A summary of NPDES and Coal Ash Management Act (CAMA) groundwater monitoring information; A summary of potential receptors including results from water supply wells; A description and findings of additional assessment activities conducted since submittal of the CSA Supplement report(s); An update on background concentrations for groundwater and soil; and, Definition of horizontal and vertical extent of CCR constituents in soil and groundwater based upon NCDEQ approved background concentrations. An update to human health and ecological risk assessment to evaluate the existence of imminent hazards to public health, safety and the environment. The NCDEQ Expectations Document (July 18, 2017) and the completed NCDEQ CSA Update Expectations Check List are included in Appendix A. 1.2 Regulatory Background The CAMA of 2014 directs owners of CCR surface impoundments in North Carolina to conduct groundwater monitoring, assessment, and remedial activities, if necessary. The CSA was performed to collect information necessary to evaluate the horizontal and vertical extent of impacts to soil and groundwater attributable to CCR source area(s), identify potential receptors, and screen for potential risks to those receptors. Notice of Regulatory Requirements 1.2.1 On August 13, 2014, North Carolina Department of Environment and Natural Resources (NCDENR) issued a Notice of Regulatory Requirements (NORR) letter notifying Duke Energy that exceedances of groundwater quality standards were reported at 14 coal ash facilities owned and operated by Duke Energy. Those groundwater quality standards are part of 15A North Carolina Administrative 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 1-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Code (NCAC) 02L (2L) .0200 Classifications and Water Quality Standards Applicable to the Groundwaters of North Carolina. The NORR stipulated that for each coal ash facility, Duke Energy was to conduct a CSA. The NORR also stipulated that before conducting each CSA, Duke was to submit a Groundwater Assessment Work Plan (GAP or Work Plan) and a receptor survey. In accordance with the NORR requirements, a receptor survey was performed to identify all receptors within a 0.5-mile radius (2,640 feet) of the ash basin compliance boundary, and a CSA was conducted for each facility. The NORR letter is included in Appendix A. Coal Ash Management Act Requirements 1.2.2 The Coal Ash Management Act (CAMA) of 2014 — General Assembly of North Carolina Senate Bill 729 Ratified Bill (Session 2013) (SB 729) requires that ash from Duke Energy coal plant sites located in North Carolina either (1) be excavated and relocated to fully lined storage facilities or (2) go through a classification process to determine closure options and schedule. Closure options can include a combination of excavating and relocating ash to a fully lined structural fill, excavating and relocating the ash to a lined landfill (on-site or off- site), and/or capping the ash with an engineered synthetic barrier system, either in place or after being consolidated to a smaller area on-site. As a component of implementing this objective, CAMA provides instructions for owners of coal combustion residuals surface impoundments to perform various groundwater monitoring and assessment activities. Section §130A-309.209 of the CAMA ruling specifies groundwater assessment and corrective actions, drinking water supply well surveys and provisions of alternate water supply, and reporting requirements as follows: (a) Groundwater Assessment of Coal Combustion Residuals Surface Impoundments. – The owner of a coal combustion residuals surface impoundment shall conduct groundwater monitoring and assessment as provided in this subsection. The requirements for groundwater monitoring and assessment set out in this subsection are in addition to any other groundwater monitoring and assessment requirements applicable to the owners of coal combustion residuals surface impoundments. (1) No later than December 31, 2014, the owner of a coal combustion residuals surface impoundment shall submit a proposed Groundwater Assessment Plan for the impoundment to the Department for its review 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 1-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx and approval. The Groundwater Assessment Plan shall, at a minimum, provide for all of the following: a. A description of all receptors and significant exposure pathways. b. An assessment of the horizontal and vertical extent of soil and groundwater contamination for all contaminants confirmed to be present in groundwater in exceedance of groundwater quality standards. c. A description of all significant factors affecting movement and transport of contaminants. d. A description of the geological and hydrogeological features influencing the chemical and physical character of the contaminants. 2) The Department shall approve the Groundwater Assessment Plan if it determines that the Plan complies with the requirements of this subsection and will be sufficient to protect public health, safety, and welfare; the environment; and natural resources. (3) No later than 10 days from approval of the Groundwater Assessment Plan, the owner shall begin implementation of the Plan. (4) No later than 180 days from approval of the Groundwater Assessment Plan, the owner shall submit a Groundwater Assessment Report to the Department. The Report shall describe all exceedances of groundwater quality standards associated with the impoundment. 1.3 Approach to Comprehensive Site Assessment The CSA has been performed to meet NCDEQ requirements associated with potential site remedy selection. The following components were utilized to develop the assessment. NORR Guidance 1.3.1 The NORR requires that site assessment provide information to meet the requirements of 2L .0106 (g). This regulation lists the items to be included in site assessments conducted pursuant to Paragraph (c) of the rule. These requirements are listed below and referenced to the applicable sections of this CSA. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 1-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 15A NCAC 02L .0106(g) Requirement CSA Section(s) (1) The source and cause of contamination; Section 3.0 (2) Any imminent hazards to public health and safety, as defined in G.S. 130A-2, and any actions taken to mitigate them in accordance with Paragraph (f) of this Rule; Section ES.2 and 2.8 (3) All receptors and significant exposure pathways; Sections 4.0 and 12.0 (4) The horizontal and vertical extent of soil and groundwater contamination and all significant factors affecting contaminant transport; and Sections 7.0, 8.0, and 14.0 (5) Geological and hydrogeological features influencing the movement, chemical, and physical character of the contaminants. Sections 6.0, 11.0, and 15.0 USEPA Monitored Natural Attenuation Tiered Approach 1.3.2 The assessment data is compiled in a manner to be consistent with “Monitored Natural Attenuation of Inorganic Contaminants in Groundwater” (EPA/600/R- 07/139) (USEPA, 2007). The tiered analysis approach discussed in this guidance document is designed to align site characterization tasks to reduce uncertainty in remedy selection. The tiered assessment data collection includes information to evaluate: Active contaminant removal from groundwater and dissolved plume stability, The mechanisms and rates of attenuation, The long-term capacity for attenuation and stability of immobilized contaminants, and Anticipated performance monitoring needs to support the selected remedy. ASTM Conceptual Site Model Guidance 1.3.3 The American Society for Testing and Materials (ASTM) E1689-95 generally describes the major components of conceptual site models, including an outline for developing models. To the extent possible, this guidance was incorporated into preparation of the Site Conceptual Model (SCM). The SCM is used to integrate site information, identify data gaps, and determine whether additional 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 1-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx information is needed at the site. The model is also used to facilitate selection of remedial alternatives and effectiveness of remedial actions in reducing the exposure of environmental receptors to contaminants (ASTM, 2014). 1.4 Technical Objectives The rationale for CSA activities fall into one of the following categories: Determine the range of background soil and groundwater quality from pertinent geologic settings (horizontal and vertical) across a broad area of the Site. Evaluate groundwater quality from pertinent geologic settings (horizontal and vertical extent of CCR leachate constituents). Establish perimeter (horizontal and vertical) boundary conditions for groundwater modeling. Provide source area information including ash pore water chemistry, physical and hydraulic properties, CCR thickness, and residual saturation within the ash basins. Address soil chemistry in the vicinity of the ash basins (horizontal and vertical extent of CCR leachate constituents in soil) compared to background concentrations. Determine potential routes of exposure and receptors. Compile information necessary to develop a groundwater Corrective Action Plan (CAP) protective of human health and the environment in accordance with 2L. 1.5 Previous Submittals Detailed descriptions of the Site operational history, the Site conceptual model, physical setting and features, geology/hydrogeology, and results of the findings of the CSA and other CAMA-related works are documented in full in the following: Comprehensive Site Assessment Report - Roxboro Steam Electric Plant (SynTerra, 2015a). Corrective Action Plan Part 1 - Roxboro Steam Electric Plant (SynTerra, 2015b). Corrective Action Plan Part 2 – Roxboro Steam Electric Plant (SynTerra, 2016a). Comprehensive Site Assessment Supplement 1 – Roxboro Steam Electric Plant (SynTerra, 2016c). Ash Basin Extension Impoundments and Discharge Canals Assessment Report – Roxboro Steam Electric Plant (SynTerra, 2016b). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 2.0 SITE HISTORY AND DESCRIPTION An overview of the Roxboro Steam Electric Plant setting and operations is presented in the following sections. 2.1 Site Description, Ownership and Use History The Roxboro Plant is a coal-fired electricity-generating facility located in north-central North Carolina in the northwestern corner of Person County, North Carolina, northwest of the City of Roxboro. The Roxboro Plant address is 1700 Dunnaway Road, Semora, North Carolina. A plant vicinity map is provided in Figure 2-1. The Site was originally owned by the Carolina Power & Light (CP&L) Company which constructed Hyco Lake and developed the Roxboro plant. CP&L merged with Florida Progress Corporation in 2000 to become Progress Energy Inc. Progress Energy merged with Duke Energy in July 2012 to become Duke Energy Progress, LLC, the current owner of the Site. Based on a review of available historical aerial photography, the Site consisted of a combination of agricultural land, rural residential (R), and woodlands prior to the impoundment of the Hyco River and its three main tributaries: North Hyco Creek, South Hyco Creek and Cobbs Creek, to form Hyco Lake (Figure 2-2). By 1964, the construction of Hyco Lake and clearing operations for the Plant had begun (Figure 2-3). The Plant began operations in 1966 as a coal-fired electrical generating station with additional steam generating units added in 1968, 1973, and 1980 (Figure 2-4). CCRs have historically been managed at the Plant’s two on-site ash basins (surface impoundments): the EAB and WAB. East Ash Pond/Basin History 2.1.1 The EAB was originally developed in 1964 with the construction of an earthen dam, approximately 50 feet in height with a crest width of 15 feet, in a former stream channel. CCRs were deposited in the EAB by hydraulic sluicing operations in 1966. Waste water from the ash basin began discharging in 1966 via a discharge canal to the cooling tower intake canal of Hyco Lake. In 1973, the East Ash Basin dam was raised 20 feet to its present configuration and the discharge canal relocated to increase treatment capacity. A NPDES permit application was submitted to the USEPA in the early 1970s; however, the first NPDES permit (Permit #0003425) was not issued until 1981. By 1983, hydraulic sluicing to the EAB was discontinued. The spillway remained opened so water continued to flow out of the pond to the plant’s cooling water intake canal via Outfall 001. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx In 1986, Duke Energy and the NC Department of Environmental Quality (NCDEQ, Department) entered into a Special Order by Consent that required the Roxboro facility to convert to dry fly ash (DFA) handling resulting in construction of the industrial landfill permitted by NCDEQ DWM (Permit 7302), which was constructed partially in the waste boundary of the EAB in 1988. The landfill was created with the construction of an earthen separator dike on the eastern portion of the EAB which formed a barrier separating the EAB from the discharge canal and a portion of the former basin (Figure 2-5). As part of the landfill project, bottom ash from Steam Units 1 and 2 was routed to a section of the EAB flowing to the WAB rather than to the EAB. The NCDEQ required continued monitoring of Outfall 001 from the EAB until 1991. NCDEQ is considering the applicable mechanism to provide coverage for this area in the renewed NPDES permit. The initial industrial landfill unit was unlined with lined phases constructed over portions of the unlined area in the EAB beginning in 2002 (Figures 2-6 and 2-7). CCR at the facility is managed in lined portion of the landfill or transported offsite for beneficial reuse. West Ash Basin History 2.1.2 The West Ash Basin (WAB) was created in 1973 with the construction of an earthen dam (main dam) in a former stream channel (Sargents Creek) to the southwest of the main plant and was included the facilities 1981 NPDES permit (Figure 2-4). The main dam is an earth fill embankment with a central earth core constructed between two cofferdams over a prepared rock foundation with a central core keyway excavated 10 feet into rock. A row of engineered toe drains are located at the base of the main dam which discharges to the heated water discharge pond. In 1986, the main dam was raised 13 feet and a series of dikes (Dikes #1 through 4) and a discharge canal were constructed to increase the storage capacity of the WAB and modify the circulation pattern to increase ash settling time. The rock filter dike (Dike #1), constructed of rock fill with a sand filter blanket, was installed near the southern end of the WAB to create a secondary settling basin and to isolate the major portion of the WAB (Figure 2-5). The modifications to the WAB were authorized by NCDEQ in a Permit to Construct issued March 26, 1986. Flue gas desulfurization (FGD) technology was installed in 2008 to reduce SO2 emissions for all the steam units. Three FGD Ponds were constructed within the 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx WAB footprint to support treatment of the scrubber wastewater (Figure 2-6). The three FGD Ponds are located on the western side of the WAB and are formed by dams that share abutment features. The three ponds are the West FGD Settling Pond, East FGD Settling Pond, and FGD Forward Flush Pond. The FGD settling ponds receive FGD blowdown. The FGD Forward Flush Pond receives inflow from the back-flush of the facility bioreactor. The ponds are lined impoundments constructed with an 18-inch compacted clay sub-base, 60 milliliter LLDPE liner, and a heavy nonwoven geotextile membrane. The treated wastewater enters the WAB effluent discharge canal. In 2016, alterations were made to the discharge structures on the filter dike with the original 48-inch diameter riser structures abandoned in place. An alternate spillway, consisting of a 36-inch diameter pipe and two 200-foot emergency spillways, was constructed (Figure 2-7). At the date of this report, the WAB still receives bottom ash by hydraulic sluicing methods. The WAB discharge canal receives waste streams from various on-site sources including: WAB effluent from bottom ash sluicing; EAB landfill leachate drainage; storm water runoff from the two ash basins; discharge from the FGD Pond treatment process; cooling tower blowdown; domestic sewage treatment plant discharge; and surface water runoff. Effluent from the discharge canal passes through NPDES Internal Outfall 002 with discharge into the heated water discharge pond, which ultimately flows into Hyco Lake through NPDES Outfall 003. 2.2 Geographic Setting, Surrounding Land Use, Surface Water Classification The Roxboro Plant is situated in a rural area in the northwest corner of Person County, approximately 10 miles northwest of Roxboro, North Carolina (Figure 2-8). A description of the physical setting for the Roxboro Plant is provided in the following sections. Geographic Setting The Plant is located on approximately 6,095 acres situated between McGhees Mill Road to the east; Concord-Ceffo Road to the south; Semora Road to the west and Hyco Lake to the north. The Site is developed with the power plant structures located primarily on the north side of the Site near the Hyco Lake and ash management areas located generally south of the power plant buildings. The ash management areas, including the EAB and WAB with associated extension impoundments and effluent channels, the industrial landfill, the FGD ponds and the Land Clearing and Inert Debris (LCID) 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx landfill, are the dominant features in the central portion of the property. Land beyond the ash management areas to the east, south, and west are wooded and transected by transmission lines. Hyco Lake borders the Site to the west and north (Figure 2-9). Surrounding Land Use Properties located within a 0.5-mile radius of the Roxboro ash basin compliance boundary include industrial (a building materials manufacturing facility), agricultural (pasture), rural residential, wooded land, a school (Woodland Elementary School) and Hyco Lake. According to the Person County Geographic Information System Department, the Duke property, incorporating the Plant and the WAB, and the building materials manufacturing facility property are zoned General Industrial (GI). The remaining portions of the Duke property, including the EAB, and all surrounding properties are zoned Residential (R). No future change in use of the surrounding land is currently anticipated. Meteorological Setting The Site lies within the Piedmont region of the southeastern United States and exhibits a humid, subtropical climate type (NOAA, 2013). More specifically, the Site lies in the northern Piedmont of North Carolina where the mean annual temperature is about 58 degrees Fahrenheit (F) and average annual precipitation is approximately 44 inches (State Climate Office, 2017). A weather data stationed maintained by the state is located just east of the city of Roxboro. The mean annual temperature recorded in Roxboro is about 56.9 degrees F with a minimum annual temperature average of 25.7 degrees F in January and a maximum annual temperature average of 87.8 degrees F in July. Precipitation in Roxboro averages 46.6 inches annually, slightly higher than the average for the northern Piedmont (State Climate Office, 2017). Surface Water Classification The Site is located in the Roanoke River Basin. The ash basins are located in proximity to Hyco Lake, which is a part of the Site. Hyco Lake was constructed in the early 1960s by Carolina Power and Light Company (now DEP) as a cooling reservoir for the steam electric generating plant. The lake covers approximately 3,750 acres and has 3 main tributaries, North Hyco Creek, South Hyco Creek, and Cobbs Creek. The lake has approximately 120 miles of shoreline. The lake is impounded by an earthen dam with a concrete spillway overflow at an elevation of 410.5 feet 3. An afterbay is located immediately downstream of the reservoir dam and is used to maintain downstream river flow for the Hyco River. Downstream of the spillway, the Hyco River flows northeastward. 3 The datum for all elevation information presented in this report is NAVD88. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Surface water classifications in North Carolina are defined in 15A NCAC 02B (2B). 0101 (c). The surface water classification for Hyco Lake is Class B and WS-V waters, protected as water supplies that are upstream and draining to WS-IV or water previously used for drinking water supply purposes. Class B waters are protected for all Class C uses in addition to primary recreation (swimming). Class C are waters protected for uses such as secondary recreation, fishing, wildlife, fish consumption, aquatic life including propagation, survival and maintenance of biological integrity, and agriculture. 2.3 CAMA-related Source Areas CAMA provides for groundwater assessment of CCR surface impoundments defined as topographic depressions, excavations, or diked areas formed primarily of earthen materials, without a base liner, and that meet other criteria related to design, usage, and ownership (Section §130A-309.201). At Roxboro, groundwater assessment was conducted for the CCR surface impoundments: the EAB and the WAB with related extension impoundments and effluent discharge canals. The approximate size of the combined ash basins is 220 acres with a total estimated ash inventory in both ash basins of 19,500,000 tons. The ash inventory in the industrial landfill is estimated to be 7,320,000 tons. Structural fill areas contain an estimated 7,800,000 tons. The total estimated CCR at the Roxboro facility is approximately 34,620,000 tons (Duke Energy, 2017). 15A NCAC 02L .0106 (f)(4) requires secondary sources that could be potential continuing sources of possible impact to groundwater be addressed in the Corrective Action Plan (CAP). At the Roxboro Site, the soil located below the EAB and WAB could be considered a potential CAMA-related secondary source. Information to date indicates that the thickness of soil impacted by ash would generally be limited to the depth interval near the ash/soil interface. 2.4 Other Primary and Secondary Sources CSA activities included an assessment of the horizontal and vertical extent of constituents related to the CCR impoundments and observed at concentrations greater than 2L/Interim Maximum Allowable Concentrations (IMAC) or background concentrations. If the CSA indicates constituent exceedances related to sources other than the EAB and WAB, those sources will be addressed as part of a separate process in compliance with the requirements of 2L. Other sources identified at the time of this report are noted below. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Gypsum Storage Area A by-product of the FGD process is the production of gypsum. At Roxboro most of the gypsum produced is used by the adjacent building materials manufacturing business for the fabrication of wallboard. Gypsum is staged in an area referred to as the Gypsum Storage Area, which is located adjacent to and on the north side of the EAB prior to transport for beneficial re-use. The gypsum storage area was constructed in 2007 and incorporated approximately 131,319 cubic yards of DFA as structural fill approved in 2005 by the NCDEQ DWM (Facility ID CCB003) in accordance with Section .1700 of the Solid Waste Management 15A NCAC 13B Rules. A groundwater assessment of the gypsum storage area structural fill was conducted in the spring of 2017 with the installation of groundwater monitoring wells (MWs)within each hydrogeologic unit, as applicable, at strategic locations in the vicinity of the gypsum storage area (GPMW-1S/1D/1BR; GPMW-2D/2BR, and GPMW-3D/BR). The wells were installed to augment CSA information for the area. The structural fill was determined to be situated above the water table with no apparent impacts to the shallow groundwater. However, groundwater exceedances of coal ash and gypsum related constituents in the bedrock layer, were determined to be influenced from several potential sources: the upgradient EAB; the unlined portion of the industrial landfill, infiltration from the wastewater system north of the gypsum storage area; and preferential groundwater flow along western side of the adjacent EAB effluent discharge canal. No impacts were found in groundwater further east and upgradient of the gypsum storage area and the EAB effluent discharge canal. Groundwater flows horizontally across the gypsum storage area to the north-northwest from the EAB towards the cooling water intake canal. Groundwater flow is also downward in the surficial and bedrock hydrostratigraphic units. The assessment findings, as documented in the Gypsum Storage Area Structural Fill (CCB003) Assessment Report, were provided to the NCDEQ DWM Solid Waste Section and the Division of Water Resources on June 28, 2017 and are provided and evaluated in this CSA. 2.5 Summary of Permitted Activities The Site is permitted to discharge wastewater under NPDES Permit NC0003425, which authorizes discharge from the facility to Hyco Lake in accordance with effluent limitations, monitoring requirements, and other conditions set forth in the permit. Surface water monitoring has been conducted since the NPDES permit has been issued. The permit authorizes discharges from the ash basin treatment system at Outfall 003 and the coal pile runoff treatment system at Outfall 006. These outfalls discharge to the Hyco Lake. Several internal outfall discharges are also authorized via Outfall 003 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx including: the ash basin treatment system (Internal Outfall 002), the cooling tower blowdown system (Internal Outfall 005); the domestic wastewater treatment system (Internal Outfall 008), the chemical metal cleaning treatment system (Internal Outfall 009), and the flue gas desulfurization treatment system (Internal Outfall 010). A process flow diagram including NPDES outfalls is presented in Figure 2-10. A permit renewal request has been submitted to NCDENR and is pending. In addition to surface water monitoring, the NPDES permit requires groundwater monitoring. Permit Condition A (6) Attachment X, Version 1.0, dated March 17, 2011, lists the groundwater monitoring wells to be sampled, the parameters and constituents to be measured and analyzed, and the requirements for sampling frequency and results reporting. Details are provided in Section 2.6. The Roxboro Industrial Waste Landfill is permitted to receive coal combustion by- products (CCBs) and incidental amounts of other wastes generated at the Plant and other Duke Energy facilities in accordance with NCDEQ DWM Solid Waste Section Permit No. 7302-INDUS. Over 90 percent of the CCBs managed at the landfill consist of fly ash, bottom ash, and off-spec flue gas desulfurization (FGD) residue (gypsum). Phases 1-6 of the Roxboro landfill were constructed with an engineered liner system and are contained within an area of approximately 93.4 acres. Phase 1 initial waste placement began in 2004. Waste placement is currently occurring in Phase 6. The LCID landfill is located to the west of the EAB abutting the Dunnaway Road entrance to the Plant and encompasses approximately 4.5 acres. The landfill was permitted to operate in 2002 (NCDEQ DWM Permit No. 73-D) and was used to dispose general construction debris and asbestos containing material. The landfill still maintains an open permit to operate. The landfill is currently covered with soil and vegetation. 2.6 History of Site Groundwater Monitoring The following sections discuss groundwater monitoring activities associated with CCR conducted prior to CSA activities. The location of the ash basin voluntary and compliance monitoring wells, the CSA wells, the approximate ash basin waste boundary, and the compliance boundary are shown in Figures 2-11 and 2-12. Construction details for site monitoring wells are provided in Table 2-1. At Roxboro, CAMA monitoring wells are designated with an S, D, BR, or BRL identifier. These designations correspond to the flow unit in which the well is screened. “S” refers to the surficial flow layer (alluvium and saprolite); “D” refers to the poorly weathered rock within a transition zone between the surficial flow zone and bedrock; and “BR” and 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx “BRL” refer to the bedrock flow zone for upper bedrock (BR) and lower bedrock (BRL). The following sections discuss groundwater monitoring activities prior to CSA activities through current CAMA-related monitoring activities. Groundwater monitoring results are presented in Section 10.0. Ash Basin Voluntary Groundwater Monitoring 2.6.1 In the mid-1980s, the Plant was modified for dry fly ash handling and an industrial landfill was constructed partially in the waste boundary of the EAB for the placement of the DFA. To assess and monitor downgradient and background groundwater conditions for the landfill, a total of 17 groundwater monitoring and observation (piezometers) wells were installed in December 1986 with one replacement well installed in October 1987. No information is available regarding historical monitoring including frequency or analytical parameters. Several of the circa 1986 monitoring wells remain on the site including: MW-1, MW-2, GMW-1/1A, and GMW-2/2A, and are used for CAMA related site wide water level measurements (Figure 2-12). None of these wells are included in the NPDES-related monitoring. Ash Basin NPDES Groundwater Monitoring 2.6.2 The NPDES permit requires groundwater monitoring. Permit Condition A (6) Attachment X, Version 1.0, dated March 17, 2011, lists the groundwater monitoring wells to be sampled, the parameters and constituents to be measured and analyzed, and the requirements for sampling frequency and results reporting. Permit Condition A (6) Attachment X also provides requirements for well location and well construction. Groundwater monitoring events related to the NPDES permit for the Site are conducted three times per year. The current groundwater compliance monitoring plan under the NPDES Permit includes the sampling of eight monitoring wells which includes one background well (BG-1) and seven downgradient wells (CW-1, CW-2/2D, CW-3/3D, CW-4, and CW-5) (Figure 2-11 and Figure 2-12). Duke Energy initiated routine compliance boundary monitoring for the ash basin in December 2010. Currently, Duke Energy conducts routine NPDES compliance boundary groundwater monitoring during April, July, and November of each year for the parameters listed in Table 2-2. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-9 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Ash Basin CAMA Groundwater Monitoring 2.6.3 A total of thirty three (33) groundwater monitor wells or piezometers were installed at the Site between February and June 2015 as part of the CSA groundwater assessment (Figure 2-11 and Figure 2-12). Groundwater monitoring wells (BG-1D, BG-1BR, MW-14S/14D/14BR, MW-15D/15BR, MW- 17BR, and MW-18D/18BR) were installed and are considered background wells. Sixteen groundwater monitoring wells (MW-1BR, MW-2BR, MW-3BR, MW-4BR, MW-5D/5BR, MW-6D/6BR, MW-7BR, MW-8BR, MW-9BR, MW-10BR, MW-11BR, MW-12BR, MW-13BR, and MW-16BR were installed at locations outside of the perimeter of the ash basins. Fourteen (14) groundwater monitoring wells were installed in the ash basins including the West Ash Basin (ABMW-1/1BR, ABMW- 2/2BR, ABMW-3/3BR) and the East Ash Basin (ABMW-4/BR, ABMW-5/5D/5BR, ABMW-6/6BR, and ABMW-7/7BR). NPDES compliance monitoring wells BG-1, CW-1, CW-2, CW-2D, CW-3, CW-3D, CW-4, and CW-5, as well as Solid Waste Landfill monitoring wells GMW-6 through GMW-11 (Section 2.6.4) were used for this assessment. During the first part of 2016, additional assessment activities (i.e., “data gap” activities) were conducted at the Site which included: (1) well installation and sampling in bedrock based on a fracture trace analysis, (2) well installation and sampling to assess the vertical extent of impacts in bedrock, and (3) an investigation of the Ash Basin extension impoundments. The additional assessment activities involved the installation of fourteen monitoring wells in the various hydrogeologic flow zones including the lower bedrock (ABMW-3BRL, ABMW-7BRL, BG-1BRL, MW-4BRL, MW-19BRL, MW-20BRL, MW-21BRL, MW- 22D/22BR/22BRL, MW-23BR, MW-24BR, MW-25BR, and MW-26BR) (Figure 2-11 and Figure 2-12). In February 2017, further assessment activities were conducted to evaluate groundwater quality associated with the ash basin effluent discharge canals. The assessment included the installation of four bedrock wells related to the EAB effluent discharge canal (MW-27BR, MW-28BR, MW-29BR, and MW- 30BR) and three bedrock wells associated to the WAB effluent discharge canal (MW-31BR, MW-32BR, and MW-33BR). In addition, MW-11D was installed as a companion well to MW-11BR. During the February 2017 assessment activities, several previously installed wells (MW-23BR and BG-1BRL) were replaced due to elevated pH related to grout contamination with wells MW-23BRR and BG-1BRLR. For MW-23BRR, the well was installed approximately 80 feet deeper than MW-23BR owing to the heterogeneity of the bedrock fractures and the presence of a water bearing 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-10 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx fracture zone with a yield greater than 1.0 gpm. Upon completion, the hydrostatic head in MW-23BRR was significantly greater than the adjacent MW- 23BR and consistent with artesian conditions demonstrated at nearby MW- 20BRL. For BG-1BRL, the well was initially drilled to a depth of 300 feet below existing ground service (bgs) with its location based on the 2015 CSA fracture trace analysis and its proximity to the Woodland Elementary School wells. Although no water bearing fractures were determined from 200 to 300 feet bgs, the well was completed to a depth of 275 feet bgs to be consistent with the Woodland Elementary School well with a reported total depth of 280 feet bgs. However, low yields and elevated pH (> 11) rendered the well unusable for assessment and was approved by NCDEQ for replacement. The replacement well, BG-1BRLR, was initially drilled to a depth of 400 feet bgs; however, no significant water bearing fractures (>1.0 gpm) were encountered during borehole installation with the exception of a zone determined at 154 feet bgs. Therefore, the replacement well was installed with a screen set to a depth of 150-160 feet bgs. Groundwater sampling for BG-1BRLR conducted in March and April 2017 revealed the presence of boron at 97 µg/L and 101 µg/L, respectively. To address the presence of boron in BG-1BRLR, a second bedrock well (BG-2BR) was installed in the BG-1/BG-1D/BG-1BR location (Figure 2-10) which is upgradient of BG-1BRLR and nearer to the school wells. The location of BG-2BR was approved by NCDEQ in June 2017. BG-2BR was installed in August 2017 utilizing rock coring techniques. The boring was cored to a depth of 241 feet bgs where a significant water bearing fracture zone, related to an intrusive quartz sill/dike, was encountered from a depth of 229 to 231 feet bgs. Confirmed with packer testing for groundwater flow, BG-2 was installed with a screen set from 225-235 feet bgs. The boring log with lithologic descriptions and well information for BG-2BR is included in Appendix F. Landfill Groundwater Monitoring 2.6.4 Groundwater monitoring at the landfill consists of six groundwater monitoring wells (GMW-6 through GMW-11) which were installed around the landfill footprint in March and October 2002. Exceptions include Piezometer-14 (P-14), which was installed in December 2009, and GMW-7 and GMW-11, which were installed in 2010 and 2011, respectively, as replacement wells. Monitoring well GMW-9 is identified as the upgradient background well. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 2-11 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Duke Energy conducts routine solid waste landfill compliance monitoring during April and November each year in accordance with NCDEQ DWM Solid Waste Section Permit No. 7302-INDUS associated with the lined landfill. The monitoring includes the six monitoring wells and six landfill leachate locations (LP-1 through LP-6) (Figure 2-12). Due to the vicinity of the landfill compliance wells to the ash basin, these wells are included as a part of this CSA. 2.7 Summary of Assessment Activities With the exception of the voluntary and compliance well installation/groundwater monitoring described above, no other known CCR-related groundwater investigations or environmental site assessments have been conducted at the Roxboro Plant prior to implementation of the CAMA GAP (SynTerra, 2014c). 2.8 Summary of Initial Abatement, Source Removal or other Corrective Action No abatement or source removal activities have been conducted at the Roxboro Plant related to the ash basins other than converting from a wet to dry fly ash handling system in 1986. In preparation for closure of the ash basins, new retention basins and wastewater treatment systems are being designed and constructed. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 3-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 3.0 SOURCE CHARACTERISTICS For purposes of this assessment, the source area is defined by the ash waste boundary as depicted on Figures 2-10 and 2-11. For the Roxboro Site, source areas include the ash management areas comprised of the WAB, EAB, industrial landfill, and the gypsum storage area. 3.1 Coal Combustion and Ash Handling System Coal ash is produced from the combustion of coal. The coal is dried, pulverized, and conveyed to the burner area of a boiler. The smaller particles produced by coal combustion, referred to as fly ash, are carried upward in the flue gas and are captured by an air pollution control device, such as an electrostatic precipitator. The larger particles of ash that fall to the bottom of the boiler are referred to as bottom ash or boiler slag. CCR was initially deposited in the EAB by hydraulic sluicing operations until the Plant was modified for dry fly ash handling in the 1980s. An industrial landfill was constructed on top of the EAB for the placement of the DFA. DFA produced at the facility is managed at the on-site industrial landfill or transported offsite for beneficial reuse. The WAB still receives bottom ash by hydraulic sluicing methods. 3.2 General Physical and Chemical Properties of Ash Coal ash consists of fly ash and bottom ash produced from the combustion of coal. The physical and chemical properties of coal ash are determined by reactions that occur during the combustion of the coal and subsequent cooling of the flue gas. Physical Properties Approximately 70 to 80 percent of the ash produced during coal combustion is fly ash (EPRI, 1993). Typically 65 to 90 percent of fly ash has particle sizes that are less than 0.010 millimeter (mm). In general, fly ash has a grain size distribution similar to that of silt. The remaining 20 to 30 percent of ash produced is considered to be bottom ash. Bottom ash consists of angular particles with a porous surface and is normally gray to black in color. Bottom ash particle diameters can vary from approximately 38 to 0.05 mm. In general, bottom ash has a grain size distribution similar to that of fine gravel to medium sand (EPRI, 1995). Physical properties of ash are provided on Table 3-1. Based on published literature not specific to Roxboro, specific gravities of fly ash range from 2.1 to 2.9. The specific gravities of bottom ash typically range from 2.3 to 3.0. The permeability of fly ash and bottom ash vary based on material density, but would be within the range of a soil with a similar gradation and density (EPRI, 1995). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 3-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Chemical Properties The specific mineralogy of coal ash varies based on many factors including the chemical composition of the coal, which is directly related to the geographic region where the coal was mined, the type of boiler where the combustion occurs (i.e., thermodynamics of the boiler), and air pollution control technologies employed. The overall chemical composition of coal ash resembles that of siliceous rocks from which it was derived, particularly shale. Oxides of silicon, aluminum, iron, and calcium make up more than 90 percent of most siliceous rocks, soils, fly ash, and bottom ash. Other major and minor elements (sulfur, sodium, potassium, magnesium, and titanium) make up an additional 8 percent, while trace constituents account for less than 1 percent. The following constituents are considered to be trace elements: arsenic, barium, cadmium, chromium, lead, mercury, selenium, copper, manganese, nickel, lead, vanadium, and zinc (EPRI, 2010). The majority of fly ash particles are glassy spheres mainly composed of amorphous or glassy aluminosilicates, crystalline matter, and carbon. Figure 3-1 presents a photograph of ash collected from the ash basin at Duke Energy's Cliffside Steam Station (considered representative of the ash at the Site) showing a mix of fly ash and bottom ash at 10 µm and 20 µm magnifications. The glassy spheres can be observed in the photograph. The glassy spheres are generally immune to dissolution. During the later stages of the combustion process and as the combustion gases are cooling after exiting the boiler, molecules from the combustion process condense on the surface of the glassy spheres. These surface condensates consist of soluble salts [e.g., calcium (Ca+2) and sulfate (SO-2)], metals [e.g., copper (Cu) and zinc (Zn)], and other minor elements [e.g., boron (B), selenium (Se), and arsenic (As)] (EPRI, 1994). The major elemental composition of fly ash (approximately 95 percent by weight) is composed of mineral oxides of silicon, aluminum, iron, and calcium. Oxides of magnesium, potassium, titanium and sulfur comprise approximately 4 percent by weight (EPRI, 1995). Trace elemental composition typically is approximately 1 percent by weight and may include arsenic, antimony, barium, boron, cadmium, chromium, copper, manganese, mercury, nickel, lead, selenium, silver, thallium, zinc, and other elements. For comparison, Figure 3-2 shows the elemental composition of fly ash and bottom ash compared with typical values for shale and volcanic ash. Table 3-1 shows the bulk composition of fly ash and bottom ash compared with typical values for soil and rock. In addition to these constituents, fly ash may contain unburned carbon. Bituminous coal ash typically yields slightly acidic to alkaline solutions (pH 5 to 10) on contact with water. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 3-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The geochemical factors controlling the reactions associated with leaching of ash are complex. Factors such as the chemical speciation of the constituent, solution pH, solution-to-solid ratio, and other factors control the chemical concentration of the resultant solution. Constituents that are held on the glassy surfaces of fly ash such as boron, arsenic, and selenium may initially leach more readily than other constituents. As noted in Table 3-1, aluminum, silicon, calcium, and iron represent the larger fractions of fly ash by weight. Calcium and iron may limit the release of arsenic by forming calcium-arsenic precipitates. Formation of iron hydroxide compounds may also sequester arsenic and retard or prevent release of arsenic to the environment. Similar processes and reactions may affect other constituents of concern; however, certain constituents such as boron and sulfate will likely remain highly mobile. In addition to the variability that might be seen in the mineralogical composition of the ash, based on different coal types, different age of ash in the basin, etc., it is anticipated that the chemical environment of the ash basin varies over time, distance, and depth. EPRI (2010) reports that 64 samples of coal combustion products (including fly ash, bottom ash, and flue gas desulfurization residue) from 50 different power plants were subjected to United States Environmental Protection Agency (USEPA) Method 1311 Toxicity Characteristic Leaching Procedure (TCLP) leaching and no TCLP result exceeded the TCLP hazardous waste limit (EPRI, 2010). Figure 3-3 provides the results of that testing. 3.3 Site-Specific Coal Ash Data Source characterization was performed to identify the physical and chemical properties of the ash in the ash basins. The source characterization involved developing selected physical properties of ash, identifying the constituents found in ash, measuring concentrations of constituents present in the ash pore water, and performing laboratory analyses to estimate constituent concentrations resulting from the leaching process. The physical and chemical properties evaluated as part of this characterization will be used to better understand impacts to soil and groundwater from the source area and will also be utilized as part of groundwater model development in the CAP. Source characterization was performed through the completion of soil borings, installation of monitoring wells, and associated solid matrix and aqueous sample collection and analysis. Characterization of the ash basins was accomplished by completing seven borings and installing sixteen monitoring wells in three phases. The first phase included borings that were installed using direct push technology (DPT) and continuous sample recovery. Each boring (ex. AB-1) was advanced to the bottom of each basin. A second phase was conducted to collect samples of soil, saprolite, and 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra bedrock beneath the ash, and install groundwater monitoring wells in various water- bearing horizons beneath and within each ash basin (ABMW wells). A third phase of work was completed to verify the lack of impact to deeper groundwater directly beneath the ash basins. This “data gap” effort resulted in the installation of deep monitoring wells ABMW-3BRL and ABMW-7BRL. The initial assessment effort employing the DPT methods was undertaken to collect samples of ash and to determine the bottom of the deposited ash. A smaller, lighter DPT drilling rig was used so that conditions could be observed during transport and drilling activities and to determine if it was safe to move larger, heavier drilling equipment onto the ash basins. It was determined that the larger rotary sonic rigs could be employed if restricted in the WAB and exterior to the EAB industrial landfill. Ash and soil samples were collected from each boring for physical and chemical testing in accordance with GAP Section 7.1.1 (SynTerra, 2014c) and as Site conditions allowed. Laboratory results of ash samples are presented in Appendix B, Table 4. GeoProbe core from AB-2 showing one inch diameter sample in acetate tube. Soil (left) contact with saturated ash (right) is distinct with little vertical migration of ash. The thickness of the ash encountered in borings in the EAB was approximately 55 to 80 feet thick (in locations of the original basin that are accessible and not covered by landfill HDPE membranes) and in borings in the WAB the ash was approximately 80 feet thick. Ash pore water levels in the EAB were approximately 10 feet bgs. In the WAB, ash pore water levels were three to six feet bgs. The unsaturated zone in the WAB is comprised almost wholly of ash; in the EAB one to five feet of fill material cover the ash. Page 3-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 3-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Physical Properties of Ash Physical properties (grain size, specific gravity, and moisture content) and mineralogy determinations were performed on samples from the EAB. Physical properties were measured using ASTM methods and mineralogy was determined by X-ray diffraction (Appendix G). Bottom ash is generally characterized as a loose, poorly graded (fine- to coarse-grained) sand. Fly ash is generally characterized as a moderately dense silty fine sand or silt. Compared to soil, fly ash exhibits a lower specific gravity. The moisture content of the fly ash samples ranges from 13.4 percent to 65.2 percent. The specific gravity varied from 2.154 to 2.685 (Table 3-2). Mineralogy analyses was determined for ash samples collected from a direct push boring, AB-4, at a depth interval of 50 feet to 55 feet below ground surface (bgs). The ash sample was predominately quartz (46.3 percent), feldspar (29.4 percent) and chlorite (22.4 percent). A minor amount of amphibole was detected (1.5 percent) (Table 3-3). One ash sample (AB-04) was tested by Energy Dispersive X-Ray Fluorescence for metal oxides (Table 3-4) and a suite of elements (Table 3-5). The ash sample from AB-04 (50 feet to 55 feet) was comprised primarily of silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3). Chemical Properties of Ash A total of 18 samples of ash, seven from the WAB borings and 11 from the EAB borings, were analyzed for total metals and total organic carbon (TOC). Concentrations of arsenic, boron, chromium, cobalt, iron, manganese, selenium, and vanadium were reported above the North Carolina Preliminary Soil Remediation Goal (PSRG) for Industrial Health and/or Protection of Groundwater for ash samples collected within the EAB and WAB waste boundaries (Appendix B, Table 4). In addition to total organic testing, ash samples from each ash basin were submitted for metals susceptible to leaching by the USEPA Synthetic Precipitation Leaching Procedure (SPLP). The SPLP is designed to more closely approximate leaching from a material by rainwater and to evaluate the leaching potential of constituents that may result in impacts to groundwater. SPLP leachate analytical results are compared to 2L and/or IMAC for reference purposes only. Those results do not represent groundwater samples therefore; comparison to 2L and/or IMAC is not required. The SPLP analyses indicated leachate concentrations greater than 2L or IMAC in one or more samples for antimony, arsenic, manganese, nitrate, selenium, and vanadium in samples from both ash basins. WAB sample leachate also contained boron, cadmium, nickel, and thallium greater than 2L and EAB sample leachate also contained barium, chromium, iron, lead and nickel greater than 2L in one or more samples (Appendix B, Table 6). The SPLP is not intended to mimic complete leaching processes and results are not necessarily 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 3-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx indicative of resultant concentrations in groundwater. Further, of the detected constituents in SPLP leachate data from the ash, cobalt, iron, manganese, and vanadium are prevalent in samples from background locations Chemistry of Ash Pore Water Pore water refers to water samples collected from wells installed within the ash basins and screened in the ash layer. Three pore water monitoring wells were completed in the WAB (ABMW-1 through ABMW-3) and four pore water monitoring wells in the EAB (ABMW-4 through ABMW-7). Since installation of the wells in early 2015, the wells have been sampled eight times including the second quarter of 2017 as part of the CAMA monitoring program. Pore water analytical results are compared to 2L and/or IMAC for reference purposes only. The ash basins are a permitted wastewater system; therefore, comparison of pore water within the wastewater treatment residuals (ash) to 2B or 2L/IMAC is not required. Fourteen analytes (antimony, arsenic, barium, beryllium, boron, cobalt, iron, manganese, nickel, sulfate, pH, total dissolved solids (TDS), thallium, and vanadium) were detected above the corresponding 2L or IMAC in one or more pore water samples (Appendix B, Table 1). In February 2017, hexavalent chromium was detected at 10.5 µg/L above its 2L of 10 µg/L; however, during all other sampling events concentrations of Cr (VI) were detected less than 3 µg/L. Species of radium and uranium were detected in pore water from each well; however, only groundwater from ABMW-4 showed a concentration of total uranium which exceeded a comparison criterion. Concentrations of detected constituents in ash pore water have been relatively stable. Relative redox conditions were determined using an Excel® workbook for identifying redox processes in groundwater (Jurgens, McMahon, Chapelle, & Eberts, 2009). This workbook allows a standardized method to identify and describe the redox state of groundwater. Ash pore water from the WAB is oxic (ABMW-1, O2 ), and mixed (oxic/anoxic; ABMW-2 and ABMW-3, O2-Fe(III)-SO4 process). In comparison, ash pore water in the EAB is anoxic (ABMW-4, ABMW-5, ABMW-6, Fe(III) process), and suboxic (ABMW-7, suboxic). Ash pore water at the Roxboro Plant is generally representative of calcium-magnesium- sulfate type water with the exception of ABMW-02 and ABMW-06 which have shifted toward calcium bicarbonate type. Constituent concentrations at ABMW-02 have been steadily declining since monitoring began in 2015 (Figure 3-4). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 4-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 4.0 RECEPTOR INFORMATION Section §130A-309.201(13) of the CAMA defines receptor as “any human, plant, animal, or structure which is, or has the potential to be, affected by the release or migration of contaminants. Any well constructed for the purpose of monitoring groundwater and contaminant concentrations shall not be considered a receptor.” In accordance with the NORR CSA guidance, receptors cited in this section refer to public and private water supply wells (including irrigation wells and unused wells) and surface water features used for drinking water supply. Additional receptors (described in Section 12.0) were evaluated as part of risk assessment related to the CSA effort. The NORR CSA receptor survey guidance requirements include listing and depicting water supply wells, public or private, including irrigation wells and unused wells (other than those that have been properly abandoned in accordance with 15A NCAC 2C .0100) within a minimum of 1,500 feet of the known extent of contamination. In NCDEQ’s June 2015 response to Duke Energy’s proposed adjustments to the CSA guidelines, North Carolina Division of Environmental Quality (NCDEQ) Division of Water Resources (DWR) acknowledged the difficulty with determining the known extent of contamination at this time and stated that it expected all drinking water wells located 2,640 feet (0.5-miles) downgradient from the established compliance boundary to be documented in the CSA reports as specified in the CAMA requirements. The approach to the receptor survey in this CSA includes listing and depicting all water supply wells (public or private, including irrigation wells and unused wells) within a 0.5-mile radius of the ash basin compliance boundary (Appendix D). Properties with water supply wells located within a 0.5 mile radius of the ash basin compliance boundary for the EAB and WAB include residential properties on Dunnaway Road, The Johnson Lane and Archie Clayton Road and to the south on Daisy Thompson Road and Semora Road. Additional properties include public school property (Woodland Elementary School, located on Semora Road southwest of the West Ash Basin) and commercial property (Building Materials Manufacturing Company, located on Shore Drive, north of the East Ash Basin) (Figure 4-1). No potable water supply lines are available to the area, with the nearest water supply line provided by the City of Roxboro, located at the intersection of Country Club Lane and Chub Lake Road, approximately 4.5 miles to the east from the Dunnaway Road entrance to the Plant. The NORR CSA guidance requires that subsurface utilities be mapped within 1,500 feet of the known extent of contamination in order to evaluate the potential for preferential 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 4-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx pathways. Locations of subsurface utilities in the Plant area to 1,500 feet beyond the basin are exhaustive and difficult to completely map with certainty. However, identification of piping near and around the ash basins was conducted by Stantec in 2014 and utilities around the Site were also included on a 2014 topographic map prepared by WSP Global, Inc. and are included in Appendix E to meet this NCDEQ requirement. Due to the depth of the groundwater in the area of the EAB and WAB area, there are no known subsurface utilities that would likely create preferential pathways for groundwater flow. 4.1 Summary of Receptor Survey Activities Surveys to identify potential receptors for groundwater including public and private water supply wells (including irrigation wells and unused or abandoned wells) and surface water features within a 0.5-mile radius of the EAB and WAB compliance boundaries have been reported to NCDEQ: Drinking Water Well and Receptor Survey – Roxboro Steam Electric Plant (SynTerra, 2014a), Supplement to Drinking Water Well and Receptor Survey – Roxboro Steam Electric Plant (SynTerra, 2014b), Update to Drinking Water Well and Receptor Survey – Roxboro Steam Electric Plant (SynTerra, 2016d). These reports are included in Appendix D. The Drinking Water Well and Receptor Survey - Roxboro Steam Electric Plant (SynTerra, 2014a) included the results of a review of publicly available data from NCDEQ, NC OneMap GeoSpatial Portal, Division of Water Resources (DWR) Source Water Assessment Program online database, Person County Geographic Information System, Environmental Data Resources, Inc. (EDR) Records Review, the United States Geological Survey (USGS) National Hydrography Dataset, as well as a vehicular survey along public roads located within 0.5 mile radius of the compliance boundary. The Supplement to Drinking Water Well and Receptor Survey- Roxboro Steam Electric Plant (SynTerra, 2014b) supplemented the initial report with additional information obtained from questionnaires completed by property owners who own property within the 0.5 mile radius of the ash basin compliance boundary. The report included a sufficiently scaled map showing the coal ash facility location, the boundary of the Site, the waste and compliance boundaries, all monitoring wells listed in the NPDES permit and the approximate location of identified water supply wells. A table presented available 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 4-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx information about identified wells including the owner's name, address of the well with parcel number, construction and usage data, and the approximate distance from the compliance boundary. A revision to the ash basin waste boundary and the proposed CCR impoundment compliance boundary incorporating the ash basin extension impoundments was presented to the NCDEQ DWR in August 2016 (Ash Basin Extension Impoundments and Discharge Canals Assessment Work Plan (SynTerra, 2016b). As a result, an updated receptor survey was conducted and provided in September 2016 (Update to Drinking Water Well and Receptor Survey) (SynTerra, 2016d). The updated survey included a review of the most recent available state, county and other resources and an additional field reconnaissance to observe potential water supply wells near the 0.5 mile radius of the revised EAB and WAB compliance boundaries. 4.2 Summary of Receptor Survey Findings No public or private drinking water wells or wellhead protection areas were found to be located downgradient of the ash basins. This finding was supported by field observations and a review of public records. Based on the known groundwater flow direction, none of the wells identified in the water well survey are located downgradient of the ash basins. The location and relevant information pertaining to suspected water wells located upgradient of the facility, within 0.5 mile of the EAB and WAB compliance boundaries, were included in the survey reports as required by the NORR and depicted on Figure 4-2. As required by G.S. 130A-309.211(c1) of House Bill 630 (HB630), Duke Energy evaluated the feasibility and costs of providing a permanent replacement water supply to eligible households. Households were eligible if any portion of a parcel of land crossed the 0.5 mile compliance line described in House Bill 630 and if the household currently used well water or bottled water (under Duke Energy’s bottled water program) as the drinking water source. Undeveloped parcels were identified but were not considered “eligible” because groundwater wells are not currently utilized as a drinking source. A Potable Water Programmatic Evaluation (Dewberry, 2016); (Appendix E) was conducted and consisted of a survey of eligible households and a preliminary engineering evaluation, cost estimate and schedule. The evaluation report included a listing and relevant information for households/properties within the survey area and maps depicting property locations including those properties for which a replacement water supply will be provided. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 4-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Public Water Supply Wells 4.2.1 A building materials manufacturing facility located offsite northeast of the plant cooling water intake canal and an elementary school located southwest of the Site have public water supply wells within 0.5-mile radius of the EAB and WAB compliance boundary. The building materials facility well is approximately 2,500 feet northeast of the EAB and is located beyond the cooling water intake canal of Hyco Lake. The Woodland Elementary School well, owned by the Person County School District, has two wells with reported depths of 280 feet bgs and 600 feet bgs, respectively. The school wells are located approximately 2,000 feet southwest of the WAB discharge canal and upgradient of the WAB compliance boundary. Private Water Supply Wells 4.2.2 The fractured bedrock aquifers in the north-central Piedmont, including in the rural areas surrounding the Roxboro Plant, are commonly used for water supply purposes. Drinking water is obtained from private groundwater wells by residents located on McGhees Mill Road, The Johnson Lane, Dunnaway Road, Archie Clayton Road, Daisy Thompson Road, and Semora Road (Figure 4-1). Several efforts have been made to locate and document the presence of and information related to private water supply wells in the vicinity of the Roxboro Plant. The September 2014 Drinking Water Well and Receptor Survey report indicated that no public or private drinking water wells or wellhead protection areas were found to be located downgradient of the ash basins; however, three public water supply and multiple private water supply wells have been identified within or in close proximity to the 0.5-mile off-set. SynTerra’s November 2014 report supplemented the initial report with information obtained from questionnaires sent to owners of property within the 0.5-mile radius of the compliance boundary. The questionnaires were designed to collect information regarding whether a water well or spring is present on the property, its use, and whether the property is serviced by a municipal water supply. If a well is present, the property owner was asked to provide information regarding the well location and construction information. The results from the previous survey and the questionnaires indicated approximately 58 wells might be located within or in close proximity to the survey area (reported wells, observed wells, and possible wells). The November 2014 and September 2016 update reports included a sufficiently scaled map showing the ash basin location, the facility property boundary, the waste and revised compliance boundaries, all monitoring wells, and the 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 4-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx approximate location of identified water supply wells. A table presented available information related to identified wells, including: the owner's name, the address of the well location with parcel number, construction and usage data, and the approximate distance of the well from the compliance boundary. A total of 102 private water supply wells were identified within a 0.5 mile radius of the EAB and WAB revised compliance boundaries. A summary of the water supply well information and locations is provided in Appendix D. 4.3 Private and Public Well Water Sampling NCDEQ coordinated sampling of 14 public and private water supply wells within a half-mile radius of the ash basins compliance boundary between April and September 2015. The two public water supply wells (DW-46 and DW-47 / RO-10-1 and RO-2) identified at the Woodland Elementary School were sampled in May 2015. Based on the analytical results, NCDEQ did not advise that an alternate water source be used for school water supply. The analytical data for the public and private water supply wells were provided in the 2015 CSA report as an appendix and are summarized in Appendix B, Table 1. A review of the analytical data for the private and public water supply wells indicated several constituents were detected above 2L or IMACs including: pH (6 wells) chloride (1 well) iron (2 wells) lead (1 well) manganese (2 wells) total dissolved solids (1 well) vanadium (13 wells) In comparison to statistically derived provisional background threshold values (PBTVs) (Section 10.0) several constituents were detected above PBTVs including: chloride (1 well) TDS (1 well), Lead (1 well), vanadium (7 wells) 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 4-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The exceedances of PBTVs in relation to water supply wells were further evaluated. First, the PBTVs have been developed using groundwater data from a set of five background wells from a geographically limited area, all located within the Roxboro Plant site. The geochemical data from these wells may not be representative across the broader area encompassed by the water supply wells (spread across approximately two square miles). Second, well construction may influence analytical results. For example, galvanized pipe could yield high zinc concentrations. Information concerning well construction and piping materials is important to have before attributing detections of metals solely to the geochemistry of the groundwater. Third, there is very limited information available about the wells (e.g., date of installation, drilling method, well depth, casing length, pump set depth, etc.). Many water supply wells in this part of the Piedmont are open-hole rock wells. A shallow surface casing is installed and then the well is drilled to a depth that may be as shallow as 40 or 50 feet or as deep as several hundred feet. When a groundwater sample is collected, it is unknown from what part of the bedrock aquifer the groundwater is drawn. Groundwater geochemistry in fractured bedrock aquifers can be quite variable. A fourth reason for considering the apparent exceedances of PBTVs in groundwater is that, as previously described, water wells in bedrock are typically installed as open-hole wells. Care must be taken when comparing geochemical data from these wells and comparing them to background concentrations derived from carefully drilled and installed groundwater monitoring wells with machine-slotted wells screens, proper filter pack installation, proper well development, and specific sample collection procedures employed. Finally, the geochemical signature of groundwater from the water supply wells was compared with the signature of groundwater from the source area using Piper diagrams (a graphical representation of major water chemistry using two ternary plots and a diamond plot showing the relative percentage of major cations and major anions in a sample). The geochemical nature of groundwater from the sampled water supply wells is very different from ash pore water and from groundwater beneath the basin (discussed in Section 10.0). Data from seven of the wells were plotted because data with a charge balance greater than 10 percent were omitted. All of the water supply wells plot consistently with the deep bedrock background wells and deep groundwater geochemical types of calcium-bicarbonate water type (Figure 4-3). In conjunction with the water supply well evaluation, groundwater samples have been collected by Duke from additional water supply wells during various time periods ranging from October 2016 to July 2017. The analytical data are summarized Appendix 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 4-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx B, Table 1. The analytical data indicates no exceedances of regulatory and background concentrations with the exception of TDS (one well) and vanadium (one well). The NCDEQ collected an additional groundwater sample from the shallow elementary school well (RO-10) on July 11, 2017. The analytical data indicated several constituents greater 2L/IMAC including manganese and TDS. As compared to PBTVs, TDS remained above background levels. The analytical data are provided in Appendix B, Table 1. 4.4 Numerical Capture Zone Analysis In December 2015, a numerical capture zone analysis for the Roxboro Site was conducted to evaluate potential impact of upgradient water supply pumping wells. The analysis employed MODPATH to interface with the MODFLOW flow model. MODPATH is a “particle tracking” model that traces groundwater flow lines from a starting position. MODPATH was used to trace groundwater flow lines around pumping wells to indicate where the water being pumped from the well originates (i.e., well capture zone analysis). The analysis for Roxboro indicates that well capture zones from wells located to the southeast, south and southwest of the Roxboro Plant are limited to the immediate vicinity of the well head and do not extend toward the ash basins. None of the particle tracks originating in the ash basins moved into the well capture zones (Figure 4-4). 4.5 Surface Water Receptors The Roxboro Plant has its own Non-Transient Non-Community Water System that pulls surface water from the cooling water intake canal for potable water production. Water treatment is a physical/chemical process using flocculation/sedimentation, sand and carbon filtration, and hypochlorite/polyphosphate chemical treatment. Potable water production is a batch process, in which potable water is processed a few times per week depending on need. On average, the potable water system produces approximately 50,000 gallons per week. In addition, surface water from the intake canal is used as cooling tower make-up water for the Plant operations. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 5-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY North Carolina is divided into distinct regions by portions of three physiographic provinces: the Atlantic Coastal Plain, the Piedmont, and the Blue Ridge. The Roxboro Plant is situated in the Piedmont physiographic province of north-central North Carolina. The Piedmont is generally characterized by mature, well-rounded hills and rolling ridges cut by small streams and drainages. The Piedmont in North Carolina is several hundred feet higher than in neighboring South Carolina and Virginia due to the Cape Fear Arch, an uplift feature that trends roughly along the Cape Fear River and continues through the Piedmont into the Appalachian Mountains (Rogers, 2006). The resulting geomorphology leads to river flow to the north or south instead of east (Rogers, 2006). The following sections contain a synopsis of geologic and hydrogeologic characteristics for the area. This section does not provide an exhaustive list or summary of the many important geologic research efforts that have been published on the region. This section provides summary information from research. 5.1 Regional Geology The Geologic Map of North Carolina shows a belt of metamorphic rock trending generally southwest to northeast across the area and characterized by strongly foliated felsic mica gneiss and schist and metamorphosed intrusive rocks (NCDNRCD, 1985). The rocks of the area near the Plant are described as biotite gneiss and schist with abundant potassic feldspar and garnet, and interlayered and gradational with calcic-silicate rock, sillimanite-mica schist and amphibolite. The gneiss contains small masses of granite rock. The felsic mica gneiss is described as being interlayered with biotite and hornblende schist. Later mapping generally confirms these observations and places the Roxboro Plant near the contact between the Inner Piedmont zone, characterized by the presence of biotite gneiss and schist, and the Charlotte Belt (or Charlotte Terrane), characterized by felsic mica gneiss (Dicken, Nicholson, Horton, Foose, & Mueller, 2007) (Figure 5-1). Bedrock at Roxboro is characterized by three primary rock types (USGS website, North Carolina geology): • Biotite gneiss and schist located under Hyco Lake and the northern half of the ash basins. The rocks are further described as inequigranular, locally abundant potassic feldspar and garnet; interlayered and gradational with 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 5-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx calc-silicate rock, sillimanite-mica schist, mica schist, and amphibolite. Contains small masses of granitic rock. • Felsic mica gneiss located in a narrow east to west band near the center of the ash basins. This rock type is interlayered with biotite and hornblende gneiss and schist. • Metamorphosed granitic rock (520-650 my) located under the southernmost portion of the ash basins. It is further describes as megacrystic, well foliated, locally contains hornblende; a fountain intrusive. A generalized geologic map of the Site is presented as Figure 5-2. Other researchers have conducted detailed investigations of the area and have provided additional description of the geology in detailed tectonic, structural, and litho- stratigraphic terms (Wilkins, Shell, & Hibbard, 1995); (Hibbard, Stoddard, Secor, & Dennis, 2002). One of the most important interpretations concerning the geologic nature of the region is the discovery and description of the Hyco shear zone, a tectonic boundary comprised of a ductile shear zone that sharply separates contrasting rocks of the Charlotte (Milton) and Carolina Terranes in north-central North Carolina and southern Virginia (Hibbard, Shell, Bradley, & Wortman, 1998). Hibbard and his co- authors (1998) describe the north-northeast trending Hyco shear zone as a terrane boundary separating the Piedmont (and locally, the Charlotte and Milton terranes) from the Carolina terrane. The Hyco shear zone was mapped as directly underlying Hyco Lake. The authors provide a detailed analysis of the structural nature of the Hyco shear zone and state their position concerning the timing and large-scale regional tectonic implications of their work (Hibbard, Shell, Bradley, & Wortman, 1998). 5.2 Regional Hydrogeology The upper portions of rocks in the Piedmont are typically fractured and weathered and are covered with unconsolidated soil and rock like material known as regolith. The regolith includes residual soil and saprolite zones and, where present, alluvium. Saprolite is formed by in-situ chemical weathering of bedrock. It is typically composed of clay and coarser granular material and reflects the texture and structure of the parent rock. For example, the weathering products of granitic rocks are quartz-rich and sandy textured. Rocks poor in quartz but rich in feldspar and ferro-magnesium minerals form a more clayey saprolite. The degree of weathering decreases with depth, and partially weathered rock (PWR) is commonly present near the top of the bedrock surface. The transition zone from the regolith and the PWR and competent bedrock is often gradational and difficult to differentiate. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 5-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Groundwater flow systems in the Piedmont are comprised of two interconnected hydrogeologic units: (1) residual soil/saprolite and weathered fractured rock (regolith and PWR) overlying (2) fractured crystalline bedrock (Heath, 1980); (Harned & Daniel, 1992). The regolith layer is weathered largely structureless residual soil that occurs near ground surface with the degree of weathering decreasing with depth. Residual soil grades into saprolite. Beneath the saprolite, partially weathered/fractured bedrock occurs with depth until competent bedrock is encountered. This mantle of residual soil, saprolite, and weathered/fractured rock (transition zone) is a hydrogeologic unit that covers and crosses various types of rock (LeGrand, 1988). This layer serves as the principal storage reservoir and provides a granular medium through which the recharge and discharge of water from the underlying fractured rock occurs (Harned & Daniel, 1992). Daniel & Dahlen (2002) provide a summary of the nature and occurrence of groundwater in fractured rock. Within fractured crystalline bedrock, fracture apertures, connectivity, etc. control groundwater movement and storage capacity. The bedrock is broken and displaced by faults and shear zones, some of which extend for miles. Joints, rock breaks without accompanying displacement, are common, and the joints typically occur in groups oriented in preferred directions. Weathering and erosion have resulted in fracturing in the form of stress-relief fractures, as well as expansion of existing fractures, and it is through these fractures that groundwater flows. Planes and bedding of metamorphic foliation, as well as breaks and folds in these rocks, are areas of higher permeability (Daniel & Dahlen, 2002). LeGrand’s (1988; 1989) conceptual model of the groundwater setting in the Piedmont incorporates the two-medium system described above into a single feature that is useful for the description of groundwater conditions. That feature is the surface drainage basin that contains a perennial stream (LeGrand, 1988). Each surface drainage basin is similar to adjacent basins and the conditions are generally repetitive from basin to basin. Within a basin, movement of groundwater is generally restricted to the area extending from the drainage divides to a perennial stream (Slope-Aquifer System; (LeGrand, 1988); (LeGrand, 1989); Figure 5-3). Freeze and Witherspoon’s (1967) model for regional groundwater flow centers on a large regional discharge area that will receive water from a groundwater basin except for shallow discharges into smaller perennial streams located closer to sub-regional recharge areas (Freeze & Witherspoon, 1967). Shallow groundwater near perennial streams will discharge into that stream. The crests of water table undulations represent natural groundwater divides within a slope-aquifer system and limit the area of influence of wells or contaminant plumes 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 5-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx located within their boundaries depending on the depth of the impacted groundwater. The concave topographic areas between the topographic divides may be considered as flow compartments that are open-ended down slope. Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation. Groundwater recharge occurs in areas of higher topography and groundwater discharge occurs in lowland areas bordering surface water bodies, wetlands, and floodplains (LeGrand, 2004). Average annual precipitation in the Piedmont ranges from 40 inches to 50 inches with a minimum of about 30 inches and a maximum of about 80 inches. Mean annual recharge in the Piedmont ranges from about 4 inches to under 10 inches (Daniel & Dahlen, 2002). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 6.0 SITE GEOLOGY AND HYDROGEOLOGY Geology beneath the Roxboro Plant can be classified into three units. Regolith (surficial soils, fill and reworked soil, alluvium, and saprolite) is the shallowest geologic unit. Saprolite is mostly thin (ranging from nonexistent to around 48 feet deep) and almost entirely unsaturated. This generalization is not consistent for certain locations beneath the ash basins, where a thin soil layer is noted. The thin to nonexistent saprolite zone across the central and northern portion of the Site is due to extensive excavation and reworking of surficial materials during Plant construction. A transition zone of partially weathered rock underlies the regolith (where present, the saprolite is the lowest portion of the regolith) and is generally continuous throughout the Roxboro Plant area. However, the transition zone at the Roxboro Site is comprised mostly of partially weathered rock that is gradational between saprolite and competent bedrock. The change from partially weathered rock to the third unit, competent bedrock, is subjective, and at the Roxboro Site, is defined by subtle changes in weathering, secondary staining and mineralization, core recovery, and the degree of fracturing in the rock. Typically, mildly productive fractures (providing water to wells) were observed within the top 50 feet to 75 feet of competent rock. In general, three hydrogeologic units or zones of groundwater flow can be described for the Site. The zone closest to the surface is the shallow or surficial flow zone encompassing saturated conditions, where present, in the residual soil, saprolite, or alluvium beneath the Site. A transition zone, encountered below the surficial zone and above the bedrock, is characterized primarily by partially weathered rock of variable thickness. The transition zone is not consistently saturated across the Site. The bedrock flow zone occurs below the transition zone and is characterized by the storage and transmission of groundwater in water-bearing fractures. Site investigations included installation of soil borings, collection of soil and rock cores, groundwater monitoring wells, borings in and through the ash basins, and installation of wells for the sampling of ash pore water. Physical and chemical properties of soil samples collected from the borings and wells are presented in Tables 6-1 and 6-2, respectively. The analytical methods used with solid and aqueous samples are presented in Table 6-3 and Table 6-4. Boring logs for CAMA-related monitoring installations are included in Appendix F. Primary technical objectives for the sampling locations included: the development of additional background data on groundwater quality; the determination of horizontal and vertical extent of impact to soil and groundwater; and the establishment of perimeter boundary conditions for groundwater modeling that will be used to develop a CAP. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 6.1 Site Geology The regional geologic setting for the Roxboro Plant is described in Section 5.0. A generalized geologic map for the Roxboro Plant area is included as Figure 5-2. The subsurface at the Site is composed of regolith/saprolite, a transition zone and bedrock. Each zone was not encountered at every boring location. Subsurface conditions varied with topography, parent rock, and Site infrastructure. The subsurface at Roxboro Plant is composed of regolith (including residual soils, fill and reworked soils, and alluvium). Each type of regolith material was not encountered at every boring location. Surficial soils consisting of silty sands or clays were usually encountered in the upper 20 feet which generally graded to saprolite. Alluvium was encountered at a few locations, such as ABMW-5 on the north side of the East Ash Basin. Saprolite is mostly thin (ranging from non-existent to around 48 feet deep) and almost entirely unsaturated for most portions of the site. This generalization is not consistent for the northern portions of the Site closest to Hyco Lake where a thicker saturated saprolite zone is present (e.g., GPMW-1S/D/BR cluster). The transition zone is mostly comprised of partially weathered rock that is gradational between saprolite and competent bedrock and is generally continuous throughout the Roxboro Plant area. The change from partially weathered rock to the third unit, competent bedrock, is subjective and at Roxboro Plant is defined by subtle changes in weathering, secondary staining and mineralization, core recovery, and the degree of fracturing in the rock. Bedrock in the area includes volcanic and sedimentary rocks that have been metamorphosed, intruded by coarse-grained granitic rocks, and subjected to regional structural deformation. The dominant rock type is crystalline bedrock consisting of biotite gneiss, felsic gneiss or granitic gneiss. Field observations determined that biotite gneiss was more common in the north/northwest portion of the Site, felsic gneiss in the central portion and a very hard granitic gneiss or granite in the south southeastern portion of the Site. The shallow bedrock is fractured; however, only mildly productive fractures (providing water to wells) were observed within the top 50 feet of competent rock. Soil Classification 6.1.1 Overburden (regolith) was encountered at the Site at depths ranging from 3 to 48 feet bgs. Surficial soils consisting of silty sands or clays were usually 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx encountered in the upper 20 feet which generally graded to saprolite. A partially-weather transition zone, when encountered, typically ranged from a 5 to 20 feet in thickness. The transition from surficial soils to saprolite and then to the transition zone was typically gradational. Mineralogical analysis of soil samples indicate that quartz and feldspar are the dominant minerals, with chlorite and biotite also occurring in significant amounts. Grain-size analyses of samples site-wide indicate most soils are classified as silty sands or clayey silts. Of the six grain-size analyses performed, all but one was found to be clayey, silty sands, some with gravel. One sample, collected from a low-lying area, was found to be clayey silt. Porosity of samples (as determined by laboratory analyses on undisturbed samples) collected from surficial soils at MW-15 was measured at 34.2 percent while soils from the transition zone had a porosity of 25.0 percent. Example of Regolith to Transition Zone Contact. MW-12BR (7-17’). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Example of Transition Zone to Rock Contact. MW-3BR (18-28’). The soils beneath the ash basins tended to be silts or clays underlain by saprolite which graded to partially-weathered rock or bedrock. Porosity of sands beneath the ash basins were determined to range from 20.9 to 24.1 percent. Soils across the Site, including those beneath the ash basins were found to have relatively low hydraulic conductivities as determined by laboratory analyses on undisturbed samples collected at ABMW-3, ABMW-4 and MW-15. Hydraulic conductivity in samples from the lower saprolite/transition zone was slightly higher. Grain size analyses, moisture content and other physical soil test results are summarized in Table 6-1. 6.1.2 Rock Lithology The Site is underlain by crystalline metamorphic rock, predominately gneiss. Biotite gneiss of the Inner Piedmont, felsic mica gneiss of the Charlotte and Minton Belts and granitic gneiss of the Eastern Slate Belt were observed in rock cores collected at monitoring well locations. Field observations determined that biotite gneiss was more common in the north/northwest portion of the Site, felsic gneiss in the central portion and a very hard granitic gneiss or granite in the south southeastern portion of the Site. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Granitic Gneiss with Common High Angle Fracture. MW-4BR (78-88’). Example of Biotite Gneiss Found Across Site. ABMW-1BR (98-108’). Thin section mineralogical analysis via x-ray diffraction was performed on six rock core samples selected from locations spanning the Roxboro Plant to represent the variations within observed lithology. X-ray fluorescence analyses of these samples indicate that oxides of aluminum and silicon are the predominant chemical constituents in the various rock types across the Site. The third greatest chemical component was iron oxide, ranging from 6.91 to 13.70 percent composition. Mineralogical analysis of Roxboro Plant transition zone and bedrock indicated that phyllosilicate and weathered clay phyllosilicate minerals were the predominant mineral composition in transition zone and bedrock. Chlorites and clay minerals (chiefly illite) along with amphibole and feldspars made up over 90% of Roxboro Plant rock core. These results correspond well with the lithology observed across the Plant, which was largely weathered biotite gneiss, felsic gneiss or granitic gneiss with areas of more mafic metavolcanic rocks. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Structural Geology 6.1.3 The metamorphic rock in the Site area trends generally southwest to northeast. Core samples collected during well installation exhibited strong foliation. Interlayering of gneiss with hornblende, granite and quartzite was observed. Exposed bedrock was observed to be dipping at high, near vertical angles in places. The core samples were often highly fractured, often with significant vertical fractures present. 6.2 Site Hydrogeology According to LeGrand (2004), the soil/saprolite regolith and the underlying fractured bedrock represent a composite water-table aquifer system. The regolith provides the majority of water storage in the Piedmont province, with porosities that range from 35 percent to 55 percent (Daniel & Dahlen, 2002). Calculated porosities specific to the Site are consistent with this range. Two major factors that influence the behavior of groundwater in the vicinity of the Site include the thickness (or occurrence) of saprolite/regolith and the hydraulic properties of underlying bedrock. Thickness of the regolith is directly related to topography, type of parent rock, and weathering. Topographic highs typically exhibit to thinner soil-saprolite zones, while topographic lows typically exhibit thicker soil-saprolite zones. Saprolite thickness at the Roxboro Plant ranges from 3 to 48 feet bgs. LeGrand (2004) makes the generalization that gneiss and schist, which are dominant rock types at the Site, yield thicker soils and moderate to relatively high fracture densities compared with the densities of unaltered igneous rocks such as granite. According to Daniel & Dahlen (2002), foliated rocks such as schist provide planes of weakness that facilitate fracturing at the onset of weathering. This weathering process can produce a relatively transmissive zone. Massive igneous/meta-igneous parent rocks such as granitic gneiss do not provide tightly spaced planes of weakness and are less susceptible to secondary porosity development due to weathering. Hydrogeologic conditions encountered above these rocks revealed less-distinct transition zones than those at mica schist locations. Porosity of the regolith is directly influenced by parent rock type based on susceptibility to weathering. As weathering advances to formation of clays from mica content, the relative permeability will be reduced. Hydrostratigraphic Layer Development 6.2.1 Hydrostratigraphic units were identified using the framework described by LeGrand (2004) where the soil/saprolite regolith and the underlying fractured bedrock represent a composite water-table aquifer system. Continuous core drilling techniques were employed to continually observe the subsurface for 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx saturated zones, weathered in-situ material, and characteristics of underlying parent rock that may contribute to a water bearing zone. Borings were advanced to a depth of 50 feet beyond the top of competent bedrock to define water bearing zones within, adjacent to, and underlying the ash basins. Determination of regolith saturation, transition zone thickness, and potential well yield were made in the field by the lead geologist. Three hydrostratigraphic units were identified at the Site which includes the shallow zone (alluvium and saprolite), transition zone, and fractured bedrock. However, in most cases, the saprolite zone is combined with the transition zone for purposes of discussion. No confining unit exists between the saprolite and transition zones and the boundary between the two is gradational. The saprolite, transition zone and bedrock aquifers are interconnected and the saprolite, where the saturated thickness is sufficient, acts as a reservoir for supplying groundwater to the transition zone which is connected to the fractures and joints of the bedrock. Due to its limited occurrence and extent, saprolite zone is considered part of the transition zone aquifer for this investigation. Localized to the ash basins, ash pore water acts as its own hydrogeologic feature prior to migration to another regime listed above. A description of each is provided in the following section. Hydrostratigraphic Layer Properties 6.2.2 Ash Pore Water The ash pore water unit consists of saturated ash material. Ash depths extend to a depth of 70 feet in the WAB and 80 feet in the EAB. Depth to water in the EAB is less than 10 feet bgs and less than 15 feet bgs in the WAB. Shallow/Surficial Zone The shallow/surficial flow zone consists of regolith (soil/saprolite) and alluvial material. This flow zone is not continuous across the Site; areas of saturated soil- saprolite were isolated and limited, typically occurring in low-lying and/or downgradient areas. Thickness of regolith is directly related to topography, type of parent rock, and geologic history. Topographically higher areas tend to contain thinner soil-saprolite zones, while topographic lows typically contain thicker soil-saprolite zones. The thickest section of alluvium was encountered on the north side of the East Ash Basin at AMBW-5, where the alluvium extended beneath the ash for approximately 30 feet before grading to saprolite and eventually bedrock at 93 feet bgs. Saprolite thickness at the Site ranged from 8 to 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 27 feet (MW-8BR). The alluvium and saprolite zones were generally unsaturated at the Site and no wells were set in this zone during the assessment. Transition Zone The transition zone consists of a relatively moderate permeability zone of partially weathered bedrock interbedded with saprolite and/or competent rock. Observations of core recovered from this zone included rock fragments, unconsolidated material, and highly oxidized bedrock material. This combination provides rock fragments that create a high-permeability zone on top of bedrock. This zone is generally unsaturated at the Site, however, saturated conditions were encountered and wells were set at MW-5, MW-6, MW-14, MW- 15, MW-18 and BG-01 locations. Transition zone wells are labeled with a “D” designation. Fractured Bedrock The fractured bedrock unit occurs within parent bedrock material. Geology at the Site is dominated by biotite, felsic or granitic gneiss. Bedrock wells are labelled with a “BR” designation. Lower bedrock wells are labelled with a “BRL” designation. Most bedrock wells installed during the 2015 CSA assessment yield low groundwater flow, often less than one gallon per minute (gpm) during development and often dewatered even at low flows. The exceptions were evident including MW-12BR, MW-13BR, MW-16BR and ABMW-1BR, which produced approximately 2.5 gpm during development. Four transects were selected for the Site to illustrate lithologic conditions in the vicinity of the ash basins. Section A-A’ show conditions in the West Ash Basin in relation to the upgradient area to the south, including the Woodland Elementary School, and the downgradient area to the north (Roxboro Plant) (Figure 6-1). Section B-B’ show conditions in the WAB in relation to the upgradient area to the south and the downgradient area to the north (WAB main dam and heated water discharge pond) (Figure 6-2). Section C-C’ depicts conditions across the EAB, lined landfill, and gypsum storage area in relation to the upgradient areas, including residential properties on Dunnaway Road, to the south and downgradient areas to the north, including the cooling water intake canal (Figure 6-3). Section D-D’ illustrates conditions across the EAB, lined landfill and the extension impoundment in relation to the upgradient areas, including residential properties along The Johnson Lane, to the south and downgradient 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-9 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx areas to the north, including the Roxboro plant and cooling tower pond (Figure 6-4). 6.3 Groundwater Flow Direction The groundwater table surface generally follows topography but varies based on Site- specific factors. The groundwater flow system at the Site serves both to store and provide a means for groundwater movement. The porosity of the regolith is largely controlled by pore space (primary porosity), whereas in bedrock porosity is largely controlled by the number, size and interconnection of fractures. As a result, the effective porosity in the regolith is normally greater than in the bedrock and thus the quantity of groundwater flow will be greater in the regolith. At the Roxboro Plant, saturated regolith was only observed in several locations nearest to Plant water features and Hyco Lake and the regolith is the least transmissive of the flow zones. The majority of groundwater across the Site appears to flow through the fractured bedrock and, to a lesser degree, in the transmission zone where saturated. Downgradient of the Roxboro Plant, groundwater gradients in the shallow flow zone are affected by man-made features (rail cuts, basins, stormwater run-off ditches, Plant water features) and Hyco Lake. At the Roxboro Plant, it is appropriate to combine the flow zones into one generalized flow map. In large portions of the subsurface beneath the Site, the regolith/saprolite and the transition zone is not saturated, and the shallow bedrock is the first and only zone where groundwater is encountered. Further, where there are saturated conditions in either regolith/saprolite or the transition zone, the difference between the water levels in wells in these zones, as compared to the level in adjacent bedrock wells, is minor. Water level measurements for all CAMA wells were collected during a 24-hour period on October 31, 2016 and April 10, 2017 to provide water level elevation data for dry and wet seasons (respectively) at the various flow systems observed at the Site. The wet and dry seasons for Roxboro were established based on precipitation data from the State Climate Office of North Carolina website, 2017. Historical water level data, including the October 31, 2016 and April, 10, 2017 events, are presented in Table 6-5. Individual water level maps for the saprolite and the transition zones were not made due to the limited occurrence of saturated conditions in those units. A generalized water level map for the bedrock aquifer, including the saprolite and transition zone hydrogeologic units, for the October 31, 2016 and April 10, 2017 event are included on Figures 6-5 and 6-6, respectively. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-10 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Groundwater flow within both the saprolite/transition zone and bedrock aquifers is to the north/northwest at the Site. Groundwater within the saprolite and transition zones follows the same flow patterns as the groundwater within bedrock. Localized groundwater high zones are centered around the ash basins, with radial flow in these areas. Recharge areas at the Site are located to the east and south. The groundwater flow regime of the Site is hydraulically bounded on the west and north by the Hyco Lake. Groundwater from the EAB and WAB flow north and west toward the Plant water features (heated water discharge pond, cooling tower intake pond and the cooling water intake canal). No significant changes in water levels or groundwater flow directions were noted in April 10, 2017 water level map from the October 31, 2016 water level map. As well, no significant change is noted as compared to the water level maps presented in previous reports. 6.4 Hydraulic Gradients Horizontal hydraulic gradients were derived for the April 10, 2017 water levels measurements in the saprolite/transition zone and fractured bedrock wells by calculating the difference in hydraulic head over the length of the flow path between two wells with similar well construction (e.g., wells within the same water-bearing unit). The following equation was used to calculate horizontal hydraulic gradient: i = dh / dl Where i is the hydraulic gradient; dh is the difference between two hydraulic heads (measured in feet); and dl is the flow path length between the two wells (measured in feet). Horizontal hydraulic gradients were calculated using data collected from monitoring well locations on April 10, 2017 (Table 6-6). The gradients ranged from 0.007 foot per foot (ft/ft) to 0.21 ft/ft. Downward vertical gradients were noted in most locations where companion transition zone and bedrock wells were installed; though some clusters exhibited upward gradient including CW-2/2D, CW-3/3D and MW-4 BR/BRL (Table 6-7). This observance indicates the WAB effluent discharge canal acts as a receiving groundwater feature. A comparison of water elevations in the ash basin pore water wells and bedrock wells indicate downward gradients with the exception of ABMW-2 and ABMW-6. Downward gradients were noted in most locations between transition zone and bedrock wells and between upper and lower bedrock wells. The vertical gradient 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-11 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx magnitude and direction is similar to vertical gradients presented in previous CSA reports. A potential vertical gradient distribution is visually presented on Figure 6-7. However, a significant downward vertical hydraulic gradient remains evident at the ABMW-05/05D well pair located on the northern berm of the EAB. The ABMW-05/05D well pair is installed at the confluence of the two natural drainage features that formed the EAB. A downward vertical gradient of 0.926 feet/feet was reported in the CAP 1 and 0.96 feet/feet in the CSA Supplement (July 2016). Recent water level measurements (April 2017) indicate a downward vertical gradient of 0.947 ft/ft, which is consistent with previous measurements. ABMW-05 is installed to the bottom portion of the East Ash Basin to a depth of 58 feet below ground surface. ABMW-05D is installed to a depth of approximately 91 feet bgs into the underlying clayey silts/silty clays comprising the confluence of the former drainage features. The hydraulic gradient differential may be a result of preferential drainage in the lower alluvial sediments of the former stream channel below the earthen embankment as compared to the permeability of the overlying ash materials indicated by ABMW-05. Groundwater flow within the alluvial sediments likely discharges to the adjacent Unit 3 cooling tower intake pond. Similarly for the WAB, significant downward vertical gradients were documented for the ABMW-03/03BR/BRL well cluster and the MW-5D/5BR well pair. During the April 2017 water level collection event a downward vertical gradient of 0.358 ft/ft was noted between ABMW-3 and ABMW-3BR and a gradient of 0.109 ft/ft (approximately half) was noted between ABMW-3BR and ABMW-3BRL. As well, a significant downward gradient has been observed at the MW-05D/MW-05BR well pair. In June 2015, the downward gradient was determined to be 0.361 ft/ft and similarly a downward gradient of 0.367 was observed in December 2015. During April 2017 event, a downward gradient of 0.377 ft/ft was noted. The hydraulic gradient difference is likely related to higher hydraulic conductivity values within the overlying ash materials evident in ABMW-03 and the saprolitic soil/ partially weathered rock present in MW-05D in contrast to the underlying mineralized fractured upper bedrock as reflected in ABMW-03BR/BRL and MW-05BR. 6.5 Hydraulic Conductivity Hydraulic conductivity values for the various hydrogeologic zones in which the wells are screened varied Site-wide as determined by the slug test method. Slug test field and analytical methods are discussed in Section 6.8. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-12 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Horizontal hydraulic conductivity of the ash basin wells range from 1.1 x 10-1 to 6.6 x 10- 5 cm/sec. with a geometric mean of 7.6 x 10-4 cm/sec. ABMW-5D, screened in saprolite below the East Ash Basin had a hydraulic conductivity geometric mean of 1.1 x 10-3. cm/sec. Wells screened in the transition zone range from 1.5 x 10-4 to 6.2 x 10-6 cm/sec with a geometric mean of 4.4 x 10-5 cm/sec. Wells screened in bedrock range from 6.3 x 10-2 to 1.4 x 10-6 cm/sec. with a geometric mean of 4.0 x 10-4 cm/sec. In-situ hydraulic conductivity results are summarized in Table 6-8. 6.6 Groundwater Velocity To calculate the velocity that water moves through a porous medium, the specific discharge, or Darcy flux, is divided by the effective porosity, ne. The result is the average linear velocity or seepage velocity of groundwater between two points. Groundwater flow velocities for the surficial and transition flow zones were calculated using Darcy's Law equation which describes the flow rate or flux of fluid through a porous media by the following formula: 𝑉𝑉𝑠𝑠=𝐾𝐾𝐾𝐾/𝑛𝑛e 𝑉𝑉𝑠𝑠 = seepage groundwater velocity, K = hydraulic conductivity i = the horizontal gradient, and ne = effective porosity. Effective porosities were calculated using laboratory testing and physical soil data presented in Table 6-1 (soils table) and estimating them on a Fetter-Bear diagram (Johnson, 1967). This technique provides a simple method to estimate specific yield; however, there are limitations to this method that may not provide an accurate determination of the specific yield of a single sample (Robson, 1993). Due to the limited occurrence of saturated regolith and transition zone at the Roxboro Plant, groundwater velocities were not calculated for surficial and transition zone flow zones. Groundwater velocities calculated for the four flow paths vary greatly. From MW-15BR to MW-9BR along the western portion of the Site, the velocities range from 0.95 to 12.28 feet per year. By comparison, the velocities along the flow path from MW- 13BR to MW-6BR, southeast to northwest through the central portion of the Site range from 41.72 to 536.72 feet per year. This large variation is reflective of the fracture pattern within the crystalline bedrock. At Roxboro, groundwater movement in the bedrock flow zone is primarily due to secondary porosity represented by fractures in the bedrock. Primary (matrix) porosity is negligible; therefore, it is not technically appropriate to calculate groundwater 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-13 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx velocity using effective porosity values and the method presented above. Bedrock fractures encountered at Roxboro tend to be isolated with low interconnectivity. Further, hydraulic conductivity values measure the fractures immediately adjacent to a well screen, not across the distance between two bedrock wells. Groundwater flow in bedrock fractures is anisotropic and difficult to predict, and velocities change as groundwater moves between factures of varying orientations, gradients, pressure, and size. For these reasons, bedrock groundwater velocities calculated using the seepage velocity equation are not representative of actual site conditions and were not calculated. For additional information on the movement of groundwater around and downgradient of the ash basins over time, refer to discussion concerning groundwater fate and transport modeling (Section 13.0). 6.7 Contaminant Velocity The degree of migration, retardation, and attenuation of constituents in the subsurface is a function of physical and chemical properties of the media through which the groundwater passes. Contaminant velocity depends on factors such as the rate of groundwater flow, the effective porosity of the aquifer material, and the soil-water partitioning coefficient, or Kd term. Soil samples were collected and analyzed for grain size, total porosity, soil sorption (Kd), and anions/cations to provide data necessary for completion of a fate and transport model. Constituents enter the ash basin system in both dissolved and solid phases, and those constituents may undergo phase changes that include dissolution, precipitation, adsorption, and desorption. Dissolved phase constituents may undergo these phase changes as they are transported in groundwater flowing through the basins. Phase changes are collectively addressed by specifying a linear soil-groundwater partitioning coefficient (sorption coefficient [Kd]). In the fate and transport model, the entry of constituents into the ash basins is represented by a constant concentration in the saturated zone (pore water) of the basin, and is continually replaced by infiltrating recharge from above. As previously described (Section 7.0), laboratory Kd terms were developed by University of North Carolina – Charlotte (UNCC) via column testing of 14 site-specific samples of soil. The methods used by UNCC and Kd results obtained from the testing are presented in Appendix C. The Kd data were used as an input parameter to evaluate constituent fate and transport through the subsurface. Boron is relatively mobile in groundwater and is associated with low Kd values. This is primarily because boron is mostly inert, has limited potential for sorption, and lacks an affinity to form complexes with other ions. In general, the low Kd measured for boron allows the constituent to move at the velocity as groundwater. The higher Kd values 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-14 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx measured for other constituents, like arsenic and cobalt, are consistent with the observed, limited migration of these constituents. Constituents like cobalt and arsenic have much higher Kd values and will move at a much slower velocity than groundwater as it sorbs onto surrounding soil. It should be noted that the fractured bedrock flow system is highly heterogeneous in nature and low permeability zones predominate. Geochemical mechanisms controlling the migration of constituents are discussed further in Section 13.0. Groundwater modeling to be performed in the CAP will include discussion of contaminant velocities for the modeled constituents. 6.8 Slug Test and Aquifer Test Results As previously discussed, hydraulic conductivity values for the various hydrogeologic zones in which the wells are screened varied Site-wide as determined by the slug test method conducted in accordance with GAP Section 7.1.4. Slug test field and analytical methods are in Appendix G and results are presented in Appendix C. Slug test data was analyzed for CAMA and other regulatory wells were screened across the surficial, transition, and bedrock zones throughout the Site. Horizontal hydraulic conductivity of the ash basin wells range from 1.1 x 10-1 to 6.6 x 10-5 cm/sec. with a geometric mean of 7.6 x 10-4 cm/sec. ABMW-5D, screened in saprolite below the East Ash Basin had a hydraulic conductivity geometric mean of 1.1 x 10-3. cm/sec. Wells screened in the transition zone range from 1.5 x 10-4 to 6.2 x 10-6 cm/sec with a geometric mean of 4.4 x 10-5 cm/sec. Wells screened in bedrock range from 6.3 x 10-2 to 1.4 x 10-6 cm/sec. with a geometric mean of 4.0 x 10-4 cm/sec. Undisturbed Shelby tube samples were collected from the East Ash Basin (AB-4) and background location, MW-15, for laboratory determination of porosity and hydraulic conductivity. The vertical hydraulic conductivity of the ash in the East Ash Basin was determined to range from 3.3 x 10-1 cm/sec at ABMW-4 (28’-30’) to 8.0 x 10-8 cm/sec at ABMW-4 (51’-53’). For the background location at MW-15, the hydraulic conductivity ranged from 1.7 x 10-7 cm/sec (11’-13 ‘) to 1.4 x 10-5 cm/sec (22’-24’) (Table 6-9). The vertical conductivities were calculated to be, on average, three to four orders of magnitude smaller than the horizontal results. These data indicate that lateral groundwater flow predominates over vertical flow at the Site. To evaluate the potential for hydraulic connectivity between the water bearing fractures in the bedrock monitoring wells and potential pumping effects from the Woodland Elementary School wells during school and summer activities, pressure transducers were installed in the four bedrock monitoring wells: BG-1BRL, BG-1BRLR, MW-31, and MW-32. Solinst Level Logger Model 3001® pressure transducers were activated from 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-15 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx April 20, 2017 to May 2, 2017 and June 20, 2017 to August 8, 2017 to coincide with drilling activities associated with BG-2BR. Data from pressure transducers accounted for a barometric pressure correction by installing a Solinst Barologger Edge 3001® in monitoring well BG-1BRLR and collecting barometric data from onsite station. Earth tides were also observed within the raw data and displayed a one centimeter oscillatory variation. Data loggers installed in monitoring wells BG-1BRL and BG-1BRLR detected drilling activities from BG-2BR on August 4, 2017 and August 5, 2017. On August 3, 2017, the water level increased within BG-1BRLR which could reflect drilling water entering into the fractured system while rock coring BG-02BR. On August 4, 2017, BG- 1BRL and BG-1BRLR pressure transducers detected a two foot decrease in the water levels which could represent a packer test conducted in borehole BG-2 from 219.5 feet to 240.8 feet bgs. Well development activities in BG-2BR were also detected in BG-1BRL and BG-1BRLR pressure transducers with the water table decreasing 1.5 feet. Pressure transducer observations within monitoring wells BG-1BRL and BG-1BRLR determine there is a hydraulic connection to BG-2BR. Pressure transducers in BG-1BRL, BG- 1BRLR, MW-31, and MW-32 did not detect pumping characteristics from the Woodland Elementary School wells greater than the tolerance level of 1 centimeter, which correlates to earth tide effects. Pressure transducer data is provided in Appendix C. 6.9 Fracture Trace Study Results Fracture trace analysis is a remote sensing technique used to identify lineaments on topographic maps and aerial photography that may correlate to locations of bedrock fractures exposed at the earth’s surface. Although fracture trace analysis is a useful tool for identifying potential fracture locations, and by extension, potential preferential pathways for infiltration and flow of groundwater near a site, results are not definitive. Lineaments identified as part of fracture trace analysis may or may not correspond to actual locations of fractures exposed at the surface, and if fractures are present, it cannot be determined from fracture trace analysis whether these are open or healed. Strongly linear features at the earth’s surface are commonly formed by weathering along steeply dipping to vertical fractures in bedrock. Morphological features such as narrow, sharp-crested ridges, narrow linear valleys, linear escarpments, and linear segments of streams otherwise characterized by dendritic patterns are examples. Linear variations in vegetative cover are also sometimes indicative of the presence of exposed fractures, though in many cases these result from unrelated human activity or other geological considerations (e.g., change in lithology). Straight (as opposed to curvilinear) features are commonly associated with the presence of steeply dipping fractures. Curvilinear features in some cases are associated with 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 6-16 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx exposed moderately-dipping fractures, but these also can be a result of preferential weathering along lithologic contacts, or along foliation planes or other geologic structure. As part of this study, only strongly linear features were considered, as these are far more commonly indicative of steeply dipping or vertical fractures. The effectiveness of fracture-trace analysis in the eastern United States, including in the Piedmont, is commonly hampered by the presence of dense vegetative cover, and often extensive land-surface modification owing to present and past human activity. Aerial- photography interpretation is most affected, as identification of small-scale features can be rendered difficult or impossible in developed areas. Fracture trace analysis was performed in the vicinity of the Roxboro Plant and no major faults or shear zones were identified (Figure 6-8). Fracture trace analyses indicated numerous fracture zones at the site, most trending south-southeast to north-northwest. Typical of the Piedmont, joint sets perpendicular to the southwest-northwest trend were also prevalent. The observations were corroborated with direct field observations and mapping of surface exposures in the area around Roxboro Plant and Hyco Lake. Measured (using a Brunton pocket transit) joint set orientations and dominant foliation trends in rocks near the Plant ranged from approximately N50E to N65E. Secondary joint sets were measured with northwest-southeast and north-south trend lines. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 7-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 7.0 SOIL SAMPLING RESULTS Soils samples were collected and tested in accordance with GAP (Section 7.1.1) and the analytical methods for testing soil are summarized in Table 6-3. Soils test data, including SPLP data, is included in Appendix B, Table 4. Soil borings were conducted in upgradient and downgradient areas of the ash basins in order to collect soil samples from the unsaturated zone and the zone of saturation for these areas (Figure 2-11 and Figure 2-12). Physical property testing of soil and saprolite indicate that Site soils are predominately silty or silty clayey sand or clayey silts (Table 6-1). Mineralogical determinations indicate feldspar, amphibole and chlorite quartz in soil samples from the Site. 7.1 Background Soil Data Ten upgradient monitoring well borings (MW-7BR, MW-8BR, MW-10BR, MW13BR, MW-14BR, MW-16, MW-17, and MW-18) were originally installed during 2015 CSA activities for use as background soil borings and monitoring wells. A background soil dataset based on the 2015 CSA data was provided to NCDEQ on May 26, 2017 for consideration of background soil concentrations. Additionally, the revised Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities (statistical methods document) (HDR and SynTerra, 2017) was provided to NCDEQ as a basis for determination. On July 7, 2017, NCDEQ provided a response letter for each Duke Energy coal ash facility that identified soil and groundwater data appropriate for inclusion in the statistical analysis to determine PBTVs for both media. NCDEQ requested that Duke Energy collect a minimum of 10 valid background samples, rather than the previously planned eight that was provided, prior to the determination of PBTVs for each constituent. In addition, soil samples meeting the following criteria are considered valid for use in statistical determinations of PBTVs: Sample was collected from a location that is not impacted by coal combustion residuals or coal associated materials; Sample was collected from a location that is not impacted by other potential anthropogenic sources of constituents; and, Sample was collected from the unsaturated zone, greater than one foot (ft) above the seasonal high water table elevation. NCDEQ determined samples collected from several locations/depths do not meet NCDEQ Inactive Hazardous Site Branch (IHSB) Guidance requirements; therefore, they 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 7-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx are not appropriate for use in determining PBTVs. The background soil dataset included laboratory reporting limits for antimony and thallium above the NCDEQ IHSB Preliminary Soil Remediation Goals (PSRG) Protection of Groundwater values (dated October 2016). NCDEQ requested the values for antimony and thallium be reported below the PSRG Protection of Groundwater (POG) values. To address these requirements, additional soil samples were collected from background locations on July 18, 2017 and July 19, 2017 (Figure 2-11 and Figure 2-12). Boring logs associated with the additional soil samples are included in Appendix F. The updated background dataset was provided to NCDEQ on August 28, 2017. NCDEQ responded on September 1, 2017 with a list of acceptable PBTVs for soil. The updated background dataset was screened for outliers prior to statistical determinations and provided to NCDEQ on August 28, 2017. Soil PBTVs were partially approved on September 1, 2017 (NCDEQ, September 2017, Appendix A). PBTV values were accepted for all constituents except manganese and nitrate (as N). PBTVs were recalculated and concurrence on values was achieved in a meeting on October 13, 2017 between NCDEQ, Duke Energy, and SynTerra. PBTVs for soil constituents were computed and are provided in Table 7-1. A background summary report for soils is included as Appendix H. 7.2 Facility Soil Data Soil samples were collected during CSA monitoring well installations. Comparison of soil analytical results with background is discussed below based on the area of the Site. Soil Beneath Ash Basin The contact between the ash and underlying soils in the ash basin borings was visually distinct. There was no visible evidence of substantial migration of ash into underlying soils or mixing of ash with those soils. Soil samples were collected below the ash/soil interface from seven boring/monitoring well locations within the ash basins (WAB: AB-1 through AB-3 and EAB: AB-4 through AB-7). Chromium was the only constituent detected at a concentration that exceeded the PSRG Industrial and POG in soil below both basins. Cobalt, iron, manganese and vanadium were detected in soil below both basins in exceedance of their respective PSRG POGs. Arsenic, barium, lead, mercury and selenium concentrations in the ash are significantly higher than in the underlying soils, indicating that these metals are relatively immobile. In comparison to PBTVs, only chromium and cobalt were detected in one location (AB-3: 12-14 feet bgs) in the EAB which exceeded the calculated PBTVs. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 7-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx SPLP was used to determine the ability of simulated rainwater to leach site-specific constituents out of the soil to groundwater. The 2L/IMAC standards are used for reference only of SPLP data; SPLP test results do not represent groundwater; therefore, comparison to 2L/IMAC is not required. The SPLP analysis revealed several constituents including: antimony, arsenic, barium, chromium, cobalt, iron, lead, manganese, nickel, nitrate, thallium, and vanadium were present at concentrations greater than the 2L or IMAC in the leachate from soil underlying the ash basins; however, only for chromium and vanadium did the leachate concentrations exceed the surficial groundwater PBTV. Cobalt, iron, manganese, and vanadium appear to be ubiquitous across the Roxboro Site in soils regardless of location (e.g., beneath ash, upgradient, downgradient) and tend to leach in concentrations that are often greater than the 2L/IMAC in the leachate even for soils not beneath the ash basins. Soil Beyond Waste Boundary and Within Compliance Boundary Soil samples were collected from monitoring well soil borings outside of the ash basin waste boundary (downgradient, sidegradient). Chromium was the only constituent that exceeded the PSRG Industrial and POG in these soil samples. Detected concentrations of cobalt, iron, manganese, and vanadium in multiple soil samples exceeded the PSRG POG. In comparison to PBTVs, chromium, cobalt and vanadium exceeded the soil PBTV in soil proximal (MW-2, MW-4) and/or downgradient (MW-3, MW-5, MW-6, MW-11) of the ash basins. SPLP results for soils beyond the waste boundary indicate that cobalt, iron, manganese, and vanadium readily leach from natural soils. The majority of detections were sporadic and inconsistent and did not indicate a source of soil impact beyond the ash basin waste boundary. Comparison of PWR and Bedrock Results to Background One sample was collected from the transition zone and analyzed as a soil sample. ABMW-1BR (83 – 85 feet bgs) was collected from weathered biotite gneiss. Chromium exceeded the PSRG Industrial and POG. Cobalt, iron, manganese and vanadium exceeded the PSRG POG. No constituents exceeded the PBTV. Secondary Sources Soil assessment data indicates that chromium and cobalt exceeded the PBTV in one soil sample from beneath the EAB; however, both constituents demonstrate that SPLP leachate concentrations exceed the surficial/transition zone groundwater PBTV. It appears that elevated concentrations of iron, manganese, and vanadium are present in Site areas not influenced by the ash basins and likely are associated with natural soil geochemistry. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 7-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Analysis of soil analytical data presented in Appendix B, Table 4 and Table 7-2 shows that only in a limited extent have constituents of interest (COIs) from the source mobilized and sorbed onto soils beneath the ash basins and downgradient locations. Arsenic, chromium, cobalt, iron, manganese, molybdenum, selenium, strontium, sulfate, and vanadium were detected at concentrations greater than their respective PBTVs or PSRGs, whichever higher. Figure 7-1 shows the exceeding data in relation to the EAB and the WAB. This analysis of soil demonstrates after mitigation of the ash basins, COIs remain in impacted soils and can potentially act as a secondary source though the distribution of COIs does not appear widespread beneath the ash basin areas. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 8-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 8.0 SEDIMENT RESULTS Eight sediment samples were collected during the 2015 CSA from locations beyond the EAB and WAB waste boundaries and multiple sediments samples were collected during the 2016 assessments of the ash basin extension impoundments and related effluent discharge canals (Figure 2-11 and Figure 2-12). Sediment analytical results are presented in Appendix B, Table 5. 8.1 Sediment/Surface Soil Associated with Areas of Wetness (AOWs) Sediment sampling at locations S-09, S-13, and S-14 were co-located with designated Areas of Wetness (AOWs). For these locations, solid material was collected at or near the point of emergence or flow of water. In most cases, the “sediment” that was collected was actually surface soil over which water originating at the AOW was flowing. A description of the AOW and the results of sediment analysis are provided below: S-09: Located at northwest end of the EAB extension impoundment near its junction with the EAB effluent discharge canal. Sediment was collected by hand from the edge of the impoundment. Boron, chromium, cobalt, and manganese concentrations exceeded the PSRG POG and soil PBTVs. S-13: Consists of two 72-inch diameter reinforced concrete pipe (RCP) culverts with discharge flow from the EAB effluent discharge canal. The location is northeast of the gypsum storage area, between the cooling water intake canal and the access road/railroad line. Sediment was collected by hand from below the RCP culverts. Manganese exceeded the PSRG POG and soil PBTVs. S-14: Located northwest of the gypsum storage area, in a storm water drainage system that directs flow to NPDES Outfall 003. Drainage from an area located north of the EAB, is directed to this storm water drainage ditch northwest of the gypsum storage area via an underground 36” diameter RCP. Flow emerges from a corrugated culvert at the bank of the drainage system northwest of the gypsum storage area. Sediment was collected by hand from below the corrugated pipe. Arsenic, cobalt, manganese, and selenium concentrations exceeded the PSRG POG and soil PBTVs. The detected concentrations of shallow sediment/inundated surface soils that are laterally restricted in areal extent do not indicate a source of impact to groundwater. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 8-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 8.2 Sediment in Major Water Bodies The sediment sampling locations were located at the confluence of stream channels to surface water bodies. For these locations, solid material was collected from the bottom of the stream channel by hand. Sediment samples were collected from the bed surface from sample locations SW-1 through SW-3. Samples SW-1, SW-2 and SW-3 were collected from the surface water features west of ash management areas between the Site and Hyco Lake (Figure 2-11). SW-1, SW-2 and SW-3: Located in in the stream sediments discharging to Hyco Lake. Chromium (SW-1, SW-2), cobalt (all locations), iron (all locations), manganese (all locations), and vanadium (all locations) were detected in exceedance of the respective PSRG POGs. None of the detected constituents exceeded a PBTV for soil with the exception of the following: chromium (SW-1, SW-2) cobalt (SW-2 and SW-3) manganese (SW-2 and SW-3) 8.3 Sediment Associated with Extension Impoundments/Effluent Discharge Canals During the 2015 CSA, the SW-4 and SW-5 locations were initially considered background sediment samples based on their proximity to natural undisturbed areas of the Site. However, the sample locations were determined to be approximate to the ponded water in the WAB extension impoundment prior to the construction of the filter dike. SW-4: Located in the Sargents Creek stream basin adjacent to the WAB extension impoundment. No constituents were detected in exceedance of PSRG POGs and PBTVs. SW-5: Located in a stream basin draining to the east finger of the WAB extension impoundment. Chromium and manganese were detected in exceedance of their respective PSRG POGs and PBTVs. In a letter dated July 8, 2016, the NCDEQ DWR requested that Duke Energy assess the distribution CCR at confirmed and potential disposal sites that included areas at the Roxboro Steam Electric Plant. The assessment was to determine if potential coal ash constituents in the ash basin extension impoundments and their discharge canals may 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 8-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx be an additional contributing source to groundwater. A component of the assessment was to collect and characterize sediment samples from each of the extension impoundments and their related effluent discharge canals. The assessment activities were conducted in the summer of 2016 through March 2017 and a documented in the Ash Basin Extension Impoundments and Discharge Canals Assessment Report – Roxboro Steam Electric Plant (SynTerra, 2016b) For the WAB extension impoundment, surficial sediment samples and cores were collected from seven locations in the impoundment (EF-1, EF-3, CW-1, CF-3, CF-5, WF- 1 and WF-3) using a direct push barge mounted GeoProbe with core samples collected to probe refusal. Six sediment samples (WDC-1 through WDC-6) were collected using a Ponar Dredge from the WAB effluent discharge canal. Ash thickness from 1 to 5 feet was observed within the impoundment, which was greatest near the filter dike, and from 1 to 1.5 feet within the effluent discharge canal. Analytical results for the sediment samples, as compared to PSRG POG and PBTVs, revealed arsenic, boron, chromium, cobalt, iron, manganese, mercury, selenium, and vanadium concentrations were greater than the POG and PBTVs in one or more sediment samples within the impoundment and the effluent discharge canal. With the exception of arsenic and selenium in the sediment samples, the SPLP analysis for sediment samples are consistent with SPLP analysis of soil, including background locations. For the EAB extension impoundment, four shallow sediment samples (NL-8, SL-8, CV- 2, and NL-4) and five deeper sediment cores (CL-2, CL-4, CL-6, CV-1, and CL-7) were collected. Shallow sediment was collected from the top six inches of the sediment using a Ponar dredge. Intact core samples were collected using the direct push barge mounted GeoProbe with core samples collected to probe refusal. Four sediment samples (EDC-1, EDC-2, EDC-3, and EDC-5) were collected from the effluent discharge canal using a clam shell sampler. Ash thickness from <1 to 20 feet was observed within the impoundment, which was greatest near the separator dike, and from <0.5 to 1 feet within the effluent discharge canal, which was greatest near the confluence of the impoundment and the effluent discharge canal. Analytical results for the sediment samples revealed antimony, arsenic, chromium, cobalt, iron, manganese, selenium, and vanadium concentrations were greater than the PSRG POG and PBTVs in one or more surficial and core sediment samples within the impoundment and the effluent discharge canal. With the exception of antimony, arsenic and selenium in the sediment samples, the SPLP analysis for sediment samples are consistent with SPLP analysis of soil, including background locations. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 8-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The detected concentrations of sediments in the extension impoundments and the effluent discharge canals, which are restricted within the features, may create a secondary source for impacts to groundwater. It is anticipated that sediment in the basin extension impoundments and discharge canals will be evaluated in the CAP. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 9-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 9.0 SURFACE WATER RESULTS The Roxboro ash basins are located in the north central portion of the Site and were constructed in former stream valleys. The streams receive groundwater recharge from upland areas to the southeast (WAB) and to the east-southeast (EAB) and from surface water runoff from the upland areas. Surface water runoff and rainfall infiltration at the ash basins are primarily directed to the WAB effluent discharge canal, via natural and man-made storm water conveyances, with discharge to the heated water discharge pond. Discharge from the heated water discharge pond is monitored through NPDES Outfall 003 to Hyco Lake. Surface water runoff to the EAB extension impoundment from upland areas to the east-southeast is conveyed to the cooling water intake canal via the EAB effluent discharge canal. Aqueous samples discussed within the following sections include three distinct types: 1) named surface waters, 2) AOWs, and 3) wastewater from the ash basins and related impoundments/effluent discharge canals. For the scope of this CSA, it is only appropriate to compare named surface waters to NCDENR Title 15A, Subchapter 02B Surface Water Standards (2B) because AOWs, wastewater and wastewater conveyances (effluent channels) are evaluated and governed wholly separate in accordance with the NPDES Program administered by NCDEQ DWR. This process is on-going in a parallel effort to the CSA and subject to change. Surface Water in Major Water Bodies During the 2015 CSA activities, surface water samples for water quality analysis were collected at stream locations along the Site boundary with Hyco Lake to the northwest (SW-1 through SW-3). The tributaries where SW-1, SW-2 and SW-3 were located are separated from the ash basins by a topographic ridge and groundwater divide (the WAB effluent discharge canal). Surface water analytical results are included in Appendix B, Table 2. The surface water sample locations are included on Figure 2-11. Surface Water Associated with AOWs Twelve AOWs have been identified and sampled routinely for monitoring purposes. The Roxboro Site is inspected semi-annually for the presence of existing and potentially new AOWs. Inspections include observations of the EAB and WAB along the toe of the dams; areas below full pond elevation for the EAB and WAB; between the ash basins and receiving waters; and drainage features associated with the basins including engineered channels. Per the interim administrative agreement, these inspections are governed by a Discharge Identification Plan (DIP) until the NPDES permit is issued. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 9-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx These AOWs include: Six engineered toe drains (S-01, S-02, S-03, S-04, S-07 and S-08) at the base of the WAB dam, Five AOW locations (S-09, S-13, S-14, S-18, S-21), Water from the southeast corner of the Unit #3 Cooling Tower Intake Pond (EAB-01); Water from the southwest corner of the WAB near the filter dike (WAB-01) Surface Water Associated with the Impoundments/Effluent Discharge Canals During the 2015 CSA activities, SW-4 and SW-5 water samples were collected at the upstream locations to the WAB southern extension impoundment in conjunction with the sediment sample locations previously described. A sixth sample location, SW-6 (unnamed tributary to the EAB extension impoundment) contained an insufficient amount of free water to sample. Water samples were collected from the EAB and WAB extension impoundments and related effluent discharge canals during the April and July 2016 assessment activities as documented in the Ash Basin Extension Impoundments and Discharge Canals Assessment Report – Roxboro Steam Electric Plant (SynTerra, 2016b). Six shallow water samples (WF- 2S, WF-4S, CF-2S, CF-4S, EF-2S and EF-4S) and six deep water samples (WF-2D, WF-4D, CF-2D, CF-4D, EF-2D and EF-4D) were collected from the WAB extension impoundment. Six water samples (WDC-1 through WDC-6) were collected from the WAB effluent discharge canal. For the EAB extension impoundment, four shallow water samples (CL-2S, CL-5S, CV-2 and CL-7) and two deep water samples (CL-2 and CL-5) were collected. Five water samples (EDC-1– EDC-5) were collected from the EAB effluent discharge canal. Water analytical results are included in Appendix B, Table 3. The water sample locations are included on Figure 2-11 and Figure 2-12. 9.1 Comparison of Exceedances to 2B Standards Water in the WAB extension impoundment and the effluent discharge canal is subject to NPDES discharge permit requirements associated with Outfall 002. Water in the heated water discharge pond, which also receives surface water from toe drains of the WAB main dam and AOW location S-18 and S-21, is subject to NPDES discharge permit requirements via Outfall #003 and is not considered waters of the state. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 9-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Water in the EAB extension impoundment and effluent discharge canal, which included water from AOW location S-09, is part of the EAB and is not considered waters of the state. However, the water in the EAB discharge canal does discharge to the cooling water intake canal, via S-13. As previously discussed, NCDEQ is considering the applicable mechanism to provide coverage for this area in the renewed NPDES permit. A review of historical surface water sample data from S-13 since August 2014 indicates no exceedances of constituents above a 2B standard with the exception of sulfate and chloride in one sample event conducted in October 2015. No exceedances of sulfate and chloride constituents above the 2B have been documented since October 2015. Surface water samples collected from stream discharges to Hyco Lake (SW-1, SW-2, and SW-3) indicate no exceedance of 2B with the exception of dissolved oxygen (DO). DO was detected in all three samples below the minimum DO levels. 9.2 Discussion of Results for Constituents Without Established 2B A 2B has not been established for a number of constituents. A summary of these results for COIs without 2B standards follows. Boron concentrations were detected in each AOW and surface water sample collected during the various assessments with the exception of upstream surface water samples SW-4 and SW-5 and the stream locations adjacent to Hyco Lake (SW-1 through SW-3). Detected concentrations were quite variable depending on location. For the WAB main dam toe drains, boron ranged from an average of 3940 µg/L (S-02) to 28,760 µg/L (S-08). The average boron concentration detected in S-13 is 1,357 µg/L. Cobalt was detected above 1 µg/L in the two deep water samples from the WAB extension impoundment; at S-9 (one occurrence); at S-13 (two occurrences); at S- 14 (two occurrences); S-18 (one occurrence); and one location in the WAB effluent discharge canal. Cobalt was not detected in the shallow water samples from the EAB extension impoundment and all but one effluent discharge canal samples. Cobalt was not detected in the upstream locations, SW-4 and SW-5; however, cobalt was detected in the background stream locations adjacent to Hyco Lake ranging from 1.12 µg/L (S-01) to 8 µg/L (S-03). Total chromium was detected in only a few of the samples and usually detected just above the laboratory reporting limit of 1 µg/L. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 9-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Iron was detected in each AOW and surface water sample collected during the assessments, including upgradient and background reference locations along Hyco Lake. Total iron concentrations were greater than dissolved iron concentrations for most samples with total iron concentrations approximately two to ten times higher than the dissolved concentrations. Manganese was detected in each AOW and surface water sample collected during the assessments including upgradient and background reference locations along Hyco Lake. The difference between total and dissolved manganese concentrations was generally negligible. Vanadium was detected in each AOW and surface water sample collected during the assessments including upgradient and background reference locations along Hyco Lake. Detected total concentrations of vanadium were generally two times higher than dissolved concentrations. 9.3 Discussion of Surface Water Results As previously described, prior to construction of the WAB, Sargents Creek was a perennial stream with headwaters that originate approximately 2 miles south-southeast of the WAB. The EAB was created in a smaller stream valley with headwaters located less than 2,000 feet east-southeast of the current ash basin footprint. Surface water from the upland areas of the former stream valleys flow into the extension impoundments with secondary flow contributions from smaller intermittent streams into the ash basins and/or the effluent discharge canals. Groundwater underlying the EAB and WAB flows north-northwest along the former stream valleys beneath and through the base of the dams into the facility heated water discharge pond (WAB) or the cooling tower intake pond (EAB) both of which flow to NPDES permitted outfall 003. Detected concentrations of constituents in AOW and surface water in the extension impoundments and effluent discharge canals are generally consistent with or higher than those detected in surface water from feeder streams as represented by SW-4 and SW-5 for the WAB extension impoundment. Boron concentrations are greatest in AOW and surface water near and proximate to the engineered toe drains. Piper diagrams, a graphical representation of major water chemistry using two ternary plots and a diamond plot for AOW and surface water are included as Figure 9-1. Shallow surface water samples collected from areas within the permitted NPDES wastewater treatment system (such as the EAB and WAB extension impoundments and associated effluent discharge canals) are characterized as calcium-sulfate water type. Surface water samples collected from Hyco Lake, deeper water samples from the 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 9-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx extension impoundments, and samples from the feeder streams to the WAB extension impoundment are characterized as calcium-bicarbonate water type. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 10.0 GROUNDWATER SAMPLING RESULTS This section provides a summary of groundwater analytical results for the most recent monitoring event (2Q2017) and discussion of historical data results and trends. A comprehensive table with all media analytical sampling results is provided in Appendix B, Table 1. As indicated in the comprehensive data table, at the request of NCDEQ, the groundwater results have been marked to indicate data points excluded for evaluation based on a measured turbidity greater than 10 Nephelometric Turbidity Unit (NTUs); high pH values that may indicate possible grout intrusion into the well screen; and data that may be auto-correlated because it was collected within 60 days of a previous sampling event. The most recent data collected is presented on the pertinent maps. One comprehensive round of groundwater sampling and analysis was conducted in June 2015 and the data included in the CSA report (SynTerra, 2015a). In addition, the following sampling and analysis events have been completed: Comprehensive Round – September 2015 (reported in CAP Part 1) Comprehensive Round – December 2015 (reported in CAP Part 2) Comprehensive Round – January 2016 (reported in CSA Supplement 1) Comprehensive Round – April 2016 (reported in CSA Supplement 1) Limited Round (fracture trace data gap wells) – June 2016 (reported in CSA Supplement 1) Comprehensive Round – July 2016 Comprehensive Round – September 2016 Comprehensive Round – November 2016 Comprehensive Round – January 2017 Limited Round (fracture trace wells; vertical assessment wells and ash basin extension impoundment wells) – June 2016 Limited Round (ash basin extension impoundment and discharge canal assessment wells) – February/March 2017 Comprehensive Round – April 2017 Limited Round (BG-2BR) – August 2017 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Groundwater sampling methods were in general accordance with the procedures described in the GAP (SynTerra, 2014c)and included in Appendix G Analytical data reports are included in Appendix I. A background summary report for groundwater is included as Appendix H. 10.1 Background Groundwater Concentrations Locations for background monitoring wells installed in 2015 for the initial CSA field effort were chosen based on the information available including the previously installed NPDES monitoring well network, horizontal distance from the waste boundary, the relative topographic and groundwater elevation difference compared to the nearest ash basin surface or pore water, and the calculated groundwater flow direction were considered to determine whether the locations represent background conditions. After the background wells were installed and a sufficient number of sample events conducted, statistical analysis was used to confirm the analytical results represented background conditions. The following monitoring wells have been approved by NCDEQ as background monitoring wells (Zimmerman to Draovitch, July 7, 2017; Appendix A). Background monitoring well locations are depicted on Figure 2-11 and Figure 2-12. BG-1 – Transition Zone MW-15D – Transition Zone MW-18D – Transition Zone BG-01BR – Bedrock MW-10BR – Bedrock MW-14BR – Bedrock MW-15BR - Bedrock MW-18BR - Bedrock BW-19BRL - Bedrock Monitoring well BG-1 is a transition zone well installed prior to 2015. Samples have been collected from this well since 2010, which is currently used as background well for NPDES and other monitoring programs. The well is located 2,000 feet southwest and hydraulically upgradient of the WAB. BG-01BR is located adjacent to BG-01 to monitor shallow water bearing fractures in the upper bedrock. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Monitoring well pair MW-15D and MW-15BR are located approximately 1,500 feet south-southwest and upgradient of the WAB. Monitoring well pair MW-18D and MW- 18BR are located approximately 2,800 feet south-southeast and upgradient of the WAB. This well pair was installed in similar geologic conditions are the MW-15D/BR well pair. MW-10BR is located approximately 1,300 feet southeast of the EAB and was installed to monitor the shallow bedrock fractures. MW-14BR is located approximately 2,000 feet northeast and upgradient of the EAB discharge canal. Monitoring well MW-19BRL is located approximately 1,600 feet upgradient of the East Ash Basin. It is also located on the east side of Dunnaway Road, approximately 2,400 feet west of its intersection with McGhee Mills Road. Background Dataset Statistical Analysis 10.1.1 The revised background groundwater datasets and statistically determined PBTVs are presented below. The current background monitoring well network consists of wells installed within the two flow zones – transition zone and fractured bedrock. Well locations are presented on Figure 2-11 and 2-12. For groundwater datasets with less than 10 valid samples available for determination of PBTVs, no formal upper tolerance limit (UTL) statistics were run and the PBTV for a constituent and groundwater flow system were computed to be either: The highest value, or If the highest value is above an order of magnitude greater than the geometric mean of all values, then the highest value should be considered an outlier and removed from further use and the PBTV is computed to be the second highest value. NCDEQ requested that the updated background groundwater dataset exclude data from the background data set due to one or more of the following conditions: Sample pH is greater than or equal to 8.5 standard units unless the regional NCDEQ office has determined an alternate background threshold pH for the Site; Sample turbidity is greater than or equal to 10 Nephelometric Turbidity Units (NTUs); 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Result is a statistical outlier identified for background sample data collected through second quarter 2017; Sample collection occurred less than a minimum 60 days between sampling events; and Non-detected results are greater than 2L/IMAC. Statistical determinations of PBTVs were performed in accordance with the revised Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities (statistical methods document (HDR and SynTerra, 2017). Background datasets provided to NCDEQ on May 26, 2017 were revised based on input from NCDEQ in the July 7, 2017 correspondence. The revised background datasets for each flow system used to statistically determine naturally occurring concentrations of inorganic constituents in groundwater are provided in Table 10-1. The following sections summarize the refined background datasets along with the results of the statistical evaluations for determining PBTVs. Transition Zone Flow Unit Three monitoring wells, BG-1, MW-15D and MW-18D, monitor background groundwater quality within the transition zone. PBTVs were calculated for all constituents monitored within the transition zone using formal UTL statistics. PBTVs for the transition zone flow layer are provided in Table 10-1. Chromium (total and hexavalent), iron, manganese, TDS, and vanadium currently have PBTVs greater than the 2L/IMAC. Bedrock Flow Unit Six monitoring wells (BG-1BR, MW-10BR, MW-14BR, MW-15BR, MW-18BR and MW-19BRL) monitor background groundwater quality within the upper fractured bedrock. PBTVs for the bedrock flow layer are provided in Table 10-1. Cobalt, iron, manganese, TDS, and vanadium currently have PBTVs greater than the 2L/IMAC. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Summary The calculated groundwater PBTVs were less than their applicable 2L/IMAC for both flow layers with the following exceptions: Chromium (total and hexavalent) in the transition zone: PBTV of 24.1 µg/L (Cr (total) / 16.1 µg/L (Cr (hex)) versus 2L of 10 µg/L. Cobalt in bedrock flow zones: PBTV 6.4 µg/L (bedrock) versus IMAC of 1 µg/L. Iron in both flow zones: PBTV of 1,173 µg/L (transition zone) and 4,227 µg/L (bedrock) versus 2L of 300 µg/L. Manganese in both flow zones: PBTV of 405 µg/L (transition zone) and 1,198 µg/L (bedrock) versus 2L of 50 µg/L. TDS in both flow zones: PBTV of 540 µg/L (transition zone) and 530 µg/L (bedrock) versus 2L of 500 µg/L. Vanadium in both flow zones: PBTV of 30.2 µg/L (transition zone) and 2.49 µg/L (bedrock) versus IMAC of 0.3 µg/L. pH in the transition zone: PBTV range of 6.3 to 7.6 SU (transition zone) and 6.8 to 8.3 SU (bedrock) versus 2L range of 6.5 to 8.5 SU. Groundwater PBTVs were calculated for the following constituents that do not have a 2L Standard, IMAC or Federal maximum containment level (MCL) established: alkalinity, bicarbonate, calcium, carbonate, magnesium, methane, potassium, sodium, sulfide, and TOC. Background threshold values will continue to be evaluated and adjusted over time as additional background data becomes available. Piper Diagrams (Comparison to Background) 10.1.2 A Piper diagram is a graphical representation of major water chemistry using two ternary plots and a diamond plot. One of the ternary plots shows the relative percentage of major cations in individual water samples and the other shows the relative percentage of the major anions. The apices of the cation plot are calcium, magnesium, and sodium plus potassium. The apices of the anion plot are sulfate, chloride, and carbonates. The two ternary plots are projected onto the diamond plot to represent the major ion chemistry of a water sample. The ion composition can be used to classify groundwater of particular character and chemistry into sub-groups known as groundwater facies. For this reason, the 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx diamond of the piper plot is sometimes referred to as the groundwater facies diamond. Percentages of major anions and cations are based on concentrations expressed in meq/L (EPRI, 2006). Plots of transition zone and bedrock groundwater including ash basin, downgradient and upgradient wells and background locations are shown on Figure 10-1 and Figure 10-2, respectively. Historical data from neighboring Orange County is presented by Cunningham and Daniel (2001) and serves as a useful comparison to those wells identified as background in this study. In Orange County, the groundwater is characterized as circumneutral calcium bicarbonate. Background wells in the transition zone fall within the same region as those studied in Cunningham and Daniel, supporting their selection as background. MW-18D results indicate a higher concentration of calcium at MW-18D resulting in this sample plotting on the margin of calcium bicarbonate water. In the bedrock, background groundwater is generally characterized as a calcium bicarbonate water type, while MW-18BR falls on the margin due to the observed concentration of calcium. 10.2 Downgradient Groundwater Concentrations The following is a summary of groundwater analytical data for areas associated with the EAB and WAB. The comprehensive groundwater analytical data table is included as Appendix B, Table 1. Monitoring Wells Beneath WAB 10.2.1 Monitoring wells ABMW-1BR, ABMW-2BR, ABMW-3BR, and ABMW-3BRL were installed beneath the WAB. These wells have one or more detected concentrations exceeding 2L/IMAC/PBTVs for the following constituents boron: ABMW-1BR (PBTV); ABMW-3BR (2L/PBTV); ABMW-3BRL (PBTV) sulfate: ABMW-2BR (PBTV); ABMW-3BR (2L/PBTV); ABMW-3BRL (2L/PBTV) TDS: ABMW-3BR (2L/PBTV); ABMW-3BRL (2L/PBTV) beryllium: ABMW-3BR (IMAC/PBTV) cobalt: ABMW-3BR (IMAC/PBTV); ABMW-3BRL (IMAC) iron: ABMW-1BR (2L/PBTV); ABMW-2BR (2L); ABMW-3BR (2L/PBTV); ABMW-3BRL (2L) manganese: ABMW-1BR (2L); ABMW-2BR (2L/PBTV); ABMW-3BR (2L/PBTV); ABMW-3BRL (2L) 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx nickel: ABMW-3BR (2L/PBTV) pH: ABMW-1BR (2L/PBTV), ABMW-3BR (2L/PBTV) strontium: ABMW-2BR (PBTV), ABMW-3BR (PBTV). No 2L established. vanadium: ABMW-1BR (IMAC); ABMW-2BR (IMAC); ABMW-3BR (IMAC); ABMW-3BRL (IMAC). All wells are below PBTV. Constituents including antimony, arsenic, chromium (total and hexavalent), molybdenum, radium/uranium (total), and thallium have not been detected in the wells below the WAB above 2L/IMAC, as applicable, and/or the respective PBTVs. Monitoring Wells Beneath EAB 10.2.2 Monitoring wells ABMW-4BR, ABMW-6BR, ABMW-7BR, and ABMW-7BRL were installed beneath the EAB. These wells have one or more detected concentrations exceeding 2L/IMAC/PBTVs for the following constituents boron: ABMW-7BR (2L/PBTV); ABMW-7BRL (PBTV) sulfate: ABMW-6BR (PBTV); ABMW-7BR (PBTV); ABMW-7BRL (2L/PBTV) strontium: ABMW-7BR (PBTV) TDS: ABMW-7BRL (2L/PBTV). All remaining wells below PBTV. cobalt: ABMW-4BR (IMAC). All wells below PBTV. iron: ABMW-4BR (2L/PBTV). All remaining wells below PBTV. manganese: ABMW-4BR (2L/PBTV); ABMW-6BR (2L/PBTV); ABMW-7BR (2L); ABMW-7BRL (2L) vanadium: All wells are above IMAC but below PBTV. Constituents including antimony, arsenic, beryllium, chromium (total and hexavalent), molybdenum, nickel, radium/uranium (total), and thallium have not been detected in the monitoring wells below the EAB above 2L/IMAC, as applicable, and/or the respective PBTVs. Saprolite/Transition Zone Downgradient Monitoring 10.2.3 Wells (WAB) Monitoring wells CW-2, CW-3, CW-4, CW-5, MW-1, MW-2, MW-5D, and MW- 6D are located directly downgradient of the WAB and within the Sargents Creek 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx stream valley. These wells have one or more detected concentrations exceeding 2L/IMAC/PBTVs for the following constituents: pH: CW-2 (2L/PBTV); CW-3 (2L/PBTV); CW-5 (2L); MW-1 (2L/PBTV); MW-2 (2L/PBTV); MW-5D (2L/PBTV); MW-6D (2L) boron: MW-5D (2L/PBTV); CW-5 (PBTV) sulfate: CW-2 (PBTV); CW-4 (PBTV); CW-5 (2L/PBTV); MW-1 (PBTV); MW-2 (PBTV); MW-5D (2L/PBTV); MW-6D (PBTV) TDS: CW-2 (2L); CW-3 (2L/PBTV); CW-4 (2L/PBTV); CW-5 (2L/PBTV); MW- 5D (2L/PBTV) chromium (total): CW-4 (2L/PBTV) cobalt: MW-2 (IMAC/PBTV); MW-5D (IMAC/PBTV) iron: CW-2 (2L/PBTV); CW-3 (2L); CW-4 (2L); MW-1 (2L/PBTV); MW-2 (2L/PBTV) manganese: CW-2 (2L); MW-1 (2L); MW-5D (2L/PBTV) molybdenum: CW-3 (PBTV); CW-4 (PBTV); MW-5D (PBTV) selenium: MW-1 (PBTV); MW-2 (PBTV) vanadium: CW-2 (IMAC/PBTV); CW-3 (IMAC); CW-4 (IMAC); CW-5 (IMAC/PBTV); MW-1 (IMAC); MW-2 (IMAC); MW-5D (IMAC); MW-6D (IMAC) Constituents including antimony, arsenic, beryllium, chromium (total and hexavalent), molybdenum, nickel, strontium, radium/uranium (total), and thallium have not been detected in the WAB downgradient wells above 2L/IMAC, as applicable, and/or the respective PBTVs. Saprolite/Transition Zone Downgradient Monitoring 10.2.4 Wells (EAB) Monitoring wells GMW-6, GPMW-1S/D, GPMW-2D, GPMW-3D and MW-22D are located directly downgradient of the EAB and/or the gypsum storage area. These wells have one or more detected concentrations exceeding 2L/IMAC/PBTVs for the following constituents: 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-9 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx pH: GMW-6 (2L/PBTV); GPMW-1S (2L); GPMW-3D (2L/PBTV); MW-22D (2L/PBTV) boron: GPM-6 (2L/PBTV); GPMW-1D (2L/PBTV); GPMW-1S (2L/PBTV); GPMW-3D (2L/PBTV); MW-22D (PBTV) strontium: GMW-6 (PBTV); GPMW-1D (PBTV); GPMW-1S (PBTV); GPMW- 2D (PBTV); GPMW-3D (PBTV); MW-22D (PBTV) sulfate: GMW-6 (2L/PBTV); GPMW-1D (2L/PBTV); GPMW-1S (2L/PBTV); GPMW-2D (2L/PBTV); GPMW-3D (2L/PBTV); MW-22 (2L/PBTV) TDS: GMW-6 (2L/PBTV); GPMW-1D (2L/PBTV); GPMW-1S (2L/PBTV); GPMW-2D (2L/PBTV); GPMW-3D (2L/PBTV); MW-22 (2L/PBTV) chromium (total): GMW-6 (2L/PBTV) cobalt: GPMW-1S (IMAC/PBTV); GPMW-2D (IMAC/PBTV); GPMW-3D (IMAC/PBTV); MW-22D (IMAC/PBTV) iron: GMW-6 (2L/PBTV); GPMW-2D (2L/PBTV); GPMW-3D (2L); MW-22D (2L) manganese: GMW-6 (2L/PBTV); GPMW-1D (2L); GPMW-1S (2L/PBTV); GPMW-2D (2L/PBTV); GPMW-3D (2L/PBTV); MW-22 (2L/PBTV) selenium: GMW-6(2L/PBTV); GPMW-1D (PBTV); GPMW-3D (2L/PBTV); MW-22 (2L/PBTV) vanadium: GMW-6 (IMAC); GPMW-1D (IMAC); GPMW-1S (IMAC); GPMW-2D (IMAC); GPMW-3D (IMAC); MW-22 (IMAC) Constituents including antimony, arsenic, beryllium, chromium (total and hexavalent), molybdenum, nickel, radium/uranium (total), and thallium have not been detected in the downgradient EAB and gypsum storage area wells above 2L/IMAC, as applicable, and/or the respective PBTVs. Bedrock Downgradient Monitoring Wells (WAB) 10.2.5 Bedrock wells downgradient of the WAB include CW-2D, CW-3D, MW-4BR, MW-4BRL, MW-5BR, MW-6BR, MW-9BR and MW-12BR. These wells have one or more detected concentrations exceeding 2L/IMAC/PBTVs for the following constituents: 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-10 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx pH: CW-2D (2L/PBTV); MW-4BR (2L/PBTV); MW-9BR (PBTV) strontium: CW-2D (PBTV); CW-3D (PBTV); MW-4BR (PBTV); MW-5BR (PBTV) sulfate: CW-2D (PBTV); MW-5BR (2L/PBTV) TDS: MW-5BR (2L/PBTV) antimony: MW-4BR (IMAC/PBTV) chromium (hexavalent): CW-2D (PBTV); MW-4BR (PBTV); MW-5BR (PBTV) chromium (total): CW-2D (2L/PBTV); MW-4BR (PBTV) cobalt: MW-4BRL (IMAC); MW-5BR (IMAC); MW-9BR (IMAC); MW-12BR (IMAC) iron: CW-2D (2L); CW-3D (2L); MW-5BR (2L); MW-6BR (2L); MW-9BR (2L); MW-12BR (2L) manganese: CW-3D (2L); MW-5BR (2L); MW-6BR (2L); MW-9BR (2L); MW- 12BR (2L) vanadium: CW-2D (IMAC/PBTV); CW-3D (IMAC/PBTV); MW-4BR (IMAC/PBTV); MW-4BRL (IMAC); MW-5BR (IMAC); MW-6BR (IMAC); MW-9BR (IMAC/PBTV); MW-12BR (IMAC) uranium (total): MW-5BR (PBTV) Constituents including antimony, arsenic, beryllium, chromium (total and hexavalent), molybdenum, nickel, radium/uranium (total), strontium, and thallium (except MW-12BR) have not been detected in the WAB downgradient wells above 2L/IMAC, as applicable, and/or the respective PBTVs. Bedrock Downgradient Wells (EAB) 10.2.6 Bedrock wells downgradient of the EAB include CW-1, GMW-10, GMW-11, GPMW-1BR, GPMW-2BR, GPMW-3BR, MW-1BR, MW-3BR, MW-11BR, MW- 22BR, and MW-27BR. These wells have one or more detected concentrations exceeding 2L/IMAC/PBTVs for the following constituents: 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-11 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx pH: CW-1 (2L/PBTV); GMW-10 (2L/PBTV); GMW-11 (2L/PBTV); GPMW- 1BR (PBTV); GPMW-2BR (PBTV); MW-1BR (PBTV); MW-3BR (2L/PBTV); MW-11BR (2L/PBTV); MW-22BR (PBTV) boron: GMW-10 (PBTV); GMW-11 (2L/PBTV); GPMW-1BR (2L/PBTV); GPMW-2BR (2L/PBTV); GPMW-3BR (PBTV); MW-1BR (2L/PBTV); MW-3BR (2L/PBTV); MW-22BR (PBTV) strontium: CW-1 (PBTV); GMW-11 (PBTV); GPMW-1BR (PBTV); GPMW- 2BR (PBTV); GPMW-3BR (PBTV); MW-1BR (PBTV); MW-3BR (PBTV); MW- 22BR (PBTV); MW-27BR (PBTV) sulfate: CW-1 (PBTV); GMW-10 (2L/PBTV); GMW-11 (2L/PBTV); GPMW- 1BR (2L/PBTV); GPMW-2BR (2L/PBTV); GPMW-3BR (2L/PBTV); MW-1BR (PBTV); MW-3BR (2L/PBTV); MW-22BR (2L/PBTV); MW-27BR (PBTV) TDS: GMW-10 (2L/PBTV); GMW-11 (2L/PBTV); GPMW-1BR (2L/PBTV); GPMW-2BR (2L/PBTV); GPMW-3BR (2L/PBTV); MW-1BR (2L/PBTV); MW- 3BR (2L/PBTV); MW-22BR (2L/PBTV); MW-27BR (2L/PBTV) chromium (hexavalent): GMW-11 (PBTV); MW-1BR (PBTV); MW-3BR (PBTV) chromium (total): GMW-10 (2L/PBTV); GMW-11 (2L/PBTV); GPMW-1BR (PBTV) cobalt: CW-1 (IMAC); GPMW-1BR (IMAC); MW-1BR (IMAC); MW-3BR (IMAC); MW-22BR (PBTV/IMAC) iron: CW-1 (2L); GMW-10 (PBTV/2L); GMW-11 (PBTV/2L); GPMW-1BR (2L); MW-1BR (2L); MW-3BR (2L); MW-11BR (2L); MW-22BR (2L) manganese: CW-1 (2L); GMW-10 (2L); GMW-11 (2L); GPMW-1BR (2L); GPMW-2BR (2L); MW-1BR (PBTV/2L); MW-3BR (2L); MW-11BR (2L); MW- 22BR (PBTV/2L); MW-27BR (2L) selenium: CW-1 (PBTV); GMW-10 (PBTV); GMW-11 (PBTV/2L); GPMW-1BR (PBTV); GPMW-2BR (PBTV); MW-1BR (PBTV); MW-3BR (PBTV); MW-22BR (PBTV) 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-12 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx vanadium: CW-1 (PBTV/IMAC); GMW-10 (PBTV/IMAC); GMW-11 (PBTV/IMAC); GPMW-1BR (PBTV/IMAC); GPMW-2BR (PBTV/IMAC); GPMW-3BR (IMAC); MW-1BR (PBTV/IMAC); MW-3BR (PBTV/IMAC); MW- 11BR (PBTV/IMAC); MW-22BR (IMAC); MW-27BR (IMAC) uranium (total): GPMW-1BR (PBTV); GPMW-2BR (PBTV); MW-1BR (PBTV); MW-3BR (PBTV/2L); MW-22BR (PBTV/2L) Constituents including antimony, arsenic, beryllium, chromium (total and hexavalent), molybdenum, nickel, radium, strontium, and thallium have not been detected in the EAB downgradient wells above 2L/IMAC, as applicable, and/or the respective PBTVs. Piper Diagrams (Comparison to Downgradient/ 10.2.7 Separate Flow Regime) The Piper Diagrams (Figures 10-1 to 10-3) display water chemistry for pore water and downgradient wells. Shallow downgradient locations characterized by calcium-magnesium-sulfate water type include: GPMW-01S, GPMW-01D, GPMW-02D, GPMW-03D, MW-05 and MW-22D. Four of these six wells indicated boron concentrations greater than 700 µg/L for the April 2017 sampling event. Locations that indicate potential mixing between background and impacted water include CW-05 and GMW-06. Compared to piper diagrams provided in the initial 2015 CSA, CW-05 has shifted toward the calcium bicarbonate water type, consistent with declining constituent concentrations observed at this well. Downgradient locations ABMW-05D, CW-02, CW-04, and MW-06 are characterized as calcium-bicarbonate type indicating little influence from source areas or a high degree of mixing with background groundwater. Three of these four wells contained boron concentrations below detection limit for the April 2017 sampling event. Bedrock downgradient locations characterized by calcium-magnesium-water type include: GMW-11, GPMW-01BR, GPMW-02BR, GPMW-03BR, MW-03BR, and GMW-08. Locations that indicate potential mixing between background and impacted groundwater include GMW-07, MW-05BR, and MW-22BR. Upgradient locations and downgradient wells CW-01, CW-02D, CW-03, GMW-10, MW- 04BR, MW-06BR, MW-07BR, MW-08BR, MW-11BR, MW-23BR, and MW-27BR are characterized as calcium bicarbonate water type, indicating little influence from source areas or a high degree of mixing with background groundwater. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-13 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 10.3 Site Specific Exceedances (Groundwater COIs) Site-specific COIs were developed by evaluating groundwater sampling results with respect to PBTVs, applicable regulatory standards, and additional regulatory input/requirements. The approach to determining those constituents which should be considered constituents of interest (COIs) for the purpose of this assessment is discussed in the following section. Provisional Background Threshold Values (PBTVs) 10.3.1 As presented in 2L .0202 (b)(3), “Where naturally occurring substances exceed the established standard, the standard shall be the naturally occurring concentration as determined by the Director”- the following report was provided to NCDEQ: Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities (HDR and SynTerra, 2017). NCDEQ (July 7, 2017) addressed each Duke Energy coal ash facility and identified soil and groundwater data appropriate for inclusion in the statistical analysis to determine provisional background threshold values (PBTVs) and provisional background threshold values (PBTVs). A revised and updated technical memorandum that summarized revised background groundwater datasets and statistically determined PBTVs for Roxboro Plant was submitted to NCDEQ on August 16, 2017. A list of NCDEQ-approved groundwater PBTVs were provided to Duke Energy on September 1, 2017 (Zimmerman to Draovitch; Appendix A). Applicable Standards 10.3.2 As part of CSA activities at the Site, multiple media including coal ash, ponded water in the ash basins, ash pore water, AOW, surface water, sediment, soil, and groundwater downgradient of the ash basins and in background areas have been sampled and analyzed for inorganic constituents. Based on comparison of the sampling results from the multiple media to applicable regulatory values, potential lists of COIs were developed in the 2015 CSA, CAPs and CSA Supplement. For the purpose of developing the groundwater COIs, constituent exceedances in downgradient groundwater of PBTVs and 2L or IMAC are considered a primary focus. Additionally, NCDEQ requested that hexavalent chromium be included as a COI at each CAMA-related site due to public interest and receptor wells. Molybdenum and strontium do not have 2L or IMACs standards established; however, these constituents are considered potential contaminants of concern with regards to CCR and are evaluated as potential COIs for the Site at the request of NCDEQ. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-14 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The following constituents do not have a 2L, IMAC, or Federal MCL established: alkalinity, bicarbonate, calcium, carbonate, magnesium, methane, potassium, sodium, sulfide, and TOC. Results from these constituents are useful in comparing water conditions across the Site. For example calcium is listed as a constituent for detection monitoring in Appendix III to 40 Code of Federal Register (CFR) Part 257. Although these constituents will be used to compare and understand groundwater quality conditions at the site, because there are no associated 2L, IMAC, or MCL these constituents are not evaluated as potential COIs for the Site. Additional Requirements 10.3.3 NCDEQ requested that figures be included in the CSA that depict groundwater analytical results for the constituents in 40 CFR 257, Appendix III detection monitoring and 40 CFR 257, Appendix IV assessment monitoring (CCR Rule) (USEPA, 2015). Detection monitoring constituents in 40 CFR 257 Appendix III are: Boron Calcium Chloride Fluoride (limited historical data, not on assessment constituent list) pH Sulfate TDS Constituents for assessment monitoring listed in 40 CFR 257 Appendix IV include: Antimony Arsenic Barium Beryllium Cadmium Chromium Cobalt 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-15 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Fluoride (limited historical data, not on assessment constituent list) Lead Lithium (not analyzed) Mercury Molybdenum Selenium Thallium Radium 226 and 228 combined Aluminum, copper, iron, manganese, and sulfide were originally included in the Appendix IV constituents in the draft rule; USEPA removed these constituents in the final rule. Therefore, these constituents are not included in the listing above; although, they are included as part of the current Interim Monitoring Plan (IMP). NCDEQ requested that vanadium be included as a COI. Roxboro Plant COIs 10.3.4 Exceedances of comparative values, the distribution of constituents in relation to the ash management areas, co-occurrence with CCR indicator constituents such as boron and sulfate, and likely migration directions based on groundwater flow direction are considered in determination of groundwater COIs. A constituent exceedance in an outlying area with no co-occurrence of boron or sulfate would likely not be considered reason to list the constituent as a COI. A constituent exceedance based on a single sampling event when previous results indicate a concentration trend below comparative values would likely not indicate inclusion as a COI. Based on site-specific conditions, observations, and findings, the following list of COIs has been developed for the Roxboro Plant: Antimony Boron Chromium (total) Chromium (hexavalent) Cobalt Iron Manganese 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 10-16 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Molybdenum pH Selenium Strontium Sulfate TDS Vanadium Uranium (total) Table 10-2 lists the COIs at the Roxboro Site along with the established PBTVs and associated 2L/IMACs. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 11.0 HYDROGEOLOGICAL INVESTIGATION Results from the hydrogeological assessment of the Roxboro site, summarized in this section, are primary components of the SCM4. Plume physical and chemical characterization is detailed below for each groundwater COI. The horizontal and vertical extent of constituent concentrations is presented on isoconcentration maps and cross sections. These descriptions are primarily based on the most recent available comprehensive groundwater sampling event (April 2017). 11.1 Plume Physical and Chemical Characterization Plume Physical Characterization 11.1.1 The groundwater plume is defined as any locations (in three-dimensional space) where groundwater quality is impacted by the ash basins. Other COIs (defined in Section 10.0) are used to help refine the extent and degree to which areas are impacted by groundwater from the ash basins. The comprehensive groundwater data table (Appendix B, Table 1) and an understanding of groundwater flow dynamics and direction (Section 6.3, Figures 6-5 to 6-6) were used to define the horizontal and vertical extent of the plume. As discussed in Section 13.2 (Geochemical Modeling), not all constituents with PBTV exceedances can be attributed to the ash basins. Naturally occurring groundwater contains varying concentrations of alkalinity, aluminum, bicarbonate, cadmium, carbonate, copper, lead, magnesium, methane, nickel, potassium, sodium, total organic carbon (TOC), and zinc. Sporadic and low-concentration exceedances of these constituents in the groundwater data do not necessarily demonstrate horizontal or vertical distribution in groundwater that indicates impact from the ash basins. Isoconcentration Maps The horizontal extent of the COI plume in each flow unit is interpreted in concentration isopleth maps (Figures 11-1 to 11-42). These maps use valid groundwater analytical data to spatially and visually define areas where groundwater concentrations are above the respective constituent PBTV and/or 2L/IMAC. 4 Pursuant to the CCR rule, owners and operators of CCR units must install the required groundwater monitoring system; develop the required groundwater sampling and analysis program to include selection of the statistical procedures to be used for evaluating groundwater monitoring data; and begin detection monitoring, which requires owners and operators to have a minimum of eight samples for each well and begin evaluating groundwater monitoring data for statistically significant increases over background levels for the constituents listed in Appendix III of 40 C.F.R. Part 257. These data need not be posted to Duke Energy’s publicly accessible Internet site until such time the annual groundwater monitoring and corrective action report required under the CCR rule becomes due. Although a portion of these data was utilized in this assessment for refinement of constituent distribution, these data are not included in this report because it was not public information as of the date of its completion. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Concentration versus Distance Plots Figures 11-43 and 11-46 depicts concentration versus distance from the source along the plume centerline for COIs for the WAB and the EAB, respectively. The graphs show constituent concentrations in source areas and downgradient locations to aid in understanding plume distribution. Concentrations of each COI represents March-April 2017 conditions. The wells used are consistent for each constituent represented. Within the source area for the West Ash Basin, the well cluster ABMW-3/3BR/3BRL was used. Downgradient well clusters MW- 5D/BR and CW-5, at approximately 800 feet from the source, and MW-6D/BR, at approximately 1,400 feet from the source, were used. For the EAB, the well cluster ABMW-7/BR/BRL was used as the source wells. Downgradient well GMW-6, at approximately 500 feet from the source, and GPMW-1S/D/BR, at approximately 1,300 feet from the source, were used. The graphs demonstrate that COI concentrations decrease dramatically from the source area to downgradient locations. Vertical Extent Cross-Sections The vertical extent of the plume extent is depicted in the cross-sectional views of the site (Figures 11-47 to 11-102). The cross-sectional transect lines A-A’, B-B’, C- C’ and D-D’ are depicted as an insert in each cross-section figure. Section A-A’ show conditions in the WAB in relation to the upgradient area to the south, including the Woodland Elementary School, and the downgradient area to the north (Roxboro Plant). Section B-B’ show conditions in the WAB in relation to the upgradient area to the south and the downgradient area to the north (WAB main dam and heated water discharge pond. Section C-C’ depicts conditions across the EAB, lined landfill, and gypsum storage area in relation to the upgradient areas, including residential properties on Dunnaway Road, to the south and downgradient areas to the north, including the cooling water intake canal. Section D-D’ illustrates conditions across the EAB, lined landfill and the extension impoundment in relation to the upgradient areas, including residential properties along The Johnson Lane, to the south and downgradient areas to the north, including the Roxboro plant and cooling tower pond. COIs have been contoured in the cross-sectional depictions. Constituent isopleths reflect values above the PBTV and the 2L/IMAC standard, as applicable. The horizontal and vertical extent of the plume has been defined. Further, it can be concluded that monitoring wells across the site are appropriately placed and 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx screened to the correct elevations to monitor groundwater quality. Monitoring wells installed for other regulatory programs have added additional details about the orientation and extent of the downgradient plume and have helped refine an understanding of the vertical and horizontal distribution of the plume. Plume Chemical Characterization 11.1.2 Plume chemical characterization is detailed below for each COI. Analytical results are based on the March-April 2017 groundwater sampling event. The range of detected concentrations is presented with the number of detections for the sampling event. Descriptions of the COIs identified for the Roxboro Site are also provided. Antimony Detected Range: 0.64 µg/L – 2.85 µg/L; Number of Detections/Total Samples: 16/586 Concentrations in 13 samples exceeded the PBTV (three transition zone and 10 bedrock locations). Concentrations in 13 samples exceeded the IMAC. Antimony exceeds both the PBTV and IMAC in the transition zone and bedrock groundwater at the site. Three back ground well locations exceeded the PBTV and IMAC standard. Antimony is a silvery-white, brittle metal. In nature, antimony combines with other elements to form antimony compounds. Small amounts of antimony are naturally present in rocks, soils, water, and underwater sediments. Only a few ores of antimony have been encountered in North Carolina. Antimony has been found in combination with other metals, and is found most commonly in Cabarrus County and other areas of the Carolina Slate Belt (Chapman, Cravotta, III, Szabo, & Lindsey, 2013). In a USGS study of naturally occurring trace minerals in North Carolina, 57 private water supply wells were sampled to obtain trace mineral data. Of the wells sampled, no wells contained antimony above the USEPA primary MCL (Chapman, Cravotta, III, Szabo, & Lindsey, 2013). Antimony is compared to an IMAC since no 2L Standard has been established for this constituent by NCDEQ. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Boron Detected Range: 5.3 µg/L – 5,350 µg/L; Number of Detections/Total Samples: 209/736 Concentrations in 197 samples exceeded the PBTV (70 transition zone and 127 bedrock samples). Concentrations in 117 samples exceeded the 2L. Boron exceeds both the PBTV and 2L in saprolite/transition zone and bedrock groundwater at the site. One background bedrock location exceeded the PBTV. Boron is a trace element in the crust, with estimated concentrations ranging from as little as 1 mg/kg in mafic igneous rocks to hundreds of milligrams per kilogram in clay rich rocks (Parker, 1967). It occurs only in the trivalent form (B+3) and is concentrated in sedimentary rocks (Urey & Mem, 1953). This observation indicates that a mechanism exists to concentrate boron in minerals because the oceans could dissolve all of the boron estimated to be present in the crust (Fleet, 1965). Fleet (1965) presents both biogenic and mineralogical processes to account for the preferential concentration of boron in the crust. Boron is a micronutrient (Goldberg, 1997) that is concentrated in plant tissue, including the plants from which coal formed. While boron is relatively abundant on the earth’s surface, boron and boron compounds are relatively rare in all geological provinces of North Carolina. Natural sources of boron in the environment include volatilization from seawater, geothermal vents, and weathering of clay-rich sedimentary rocks. Total contributions from anthropogenic sources are less than contributions from natural sources. Anthropogenic sources of boron include agriculture, refuse, coal and oil burning power plants, by-products of glass manufacturing, and sewage and sludge disposal (EPRI, 2005) Because boron is associated with the carbon (fuel) in coal, it tends to volatilize during combustion and subsequently condense onto fly ash as a soluble borate salt (Dudas, 1981). Boron leaches readily (up to 50 percent of total present) and rapidly from fly ash (Cox, Lundquist, Przyjazny, & Schmulbach, 1978). Boron is considered a marker COI for coal ash because boron is rarely associated with other types of industrial waste products. Fleet describes sorption of boron by clays as a two-step process. Boron in solution is likely to be in the form of the borate ion (B(OH)4-). The initial sorption 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx occurs onto a charged surface. Observations that boron does not tend to desorb from clays indicates that it migrates rapidly into the crystal structure, most likely in substitution for aluminum. Goldberg et al. (1996) determined that boron sorption sites on clays appear to be specific to boron. For this reason, there is no need to correct for competition for sorption sites by other anions in transport models (Goldberg, Forster, Lesch, & Heick, 1996). Goldberg (1997) lists aluminum and iron oxides, magnesium hydroxide, clay minerals, calcium carbonate (limestone), and organic matter as important sorption surfaces in soils (Goldberg, 1997). Boron sorption on oxides is diminished by competition from numerous anions. Boron solubility in groundwater is controlled by adsorption reactions rather than by mineral solubility. Goldberg concludes that chemical models can effectively replicate boron adsorption data over changing conditions of boron concentration, pH, and ionic strength. Chromium Detected Range: 0.52 µg/L – 824 µg/L; Number of Detections/Total Samples: 223/810 Concentrations in 5 samples exceeded the PBTV (transition zone only). Concentrations in 50 samples exceeded the 2L. Chromium exceeds both the PBTV and 2L in transition zone and bedrock groundwater at the site. Chromium exceeds the PBTV in 13 background wells and one upgradient well and exceeded the 2L in 13 background wells. Chromium is a blue-white metal found naturally occurring in combination with other substances. It occurs in rocks, soils, plants, and volcanic dust and gases (EPRI, 2008a). Background concentrations of chromium in groundwater generally vary according to the media in which they occur. Most chromium concentrations in groundwater are low averaging less than 1.0 µg/L worldwide. Chromium tends to occur in higher concentrations in felsic igneous rocks (such as granite and metagranite) and ultramafic igneous rocks; however, it is not a major component of the igneous or metamorphic rocks found in the North Carolina Piedmont or the Blue Ridge (Chapman, Cravotta, III, Szabo, & Lindsey, 2013). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at UNC analyzed 1,898 private well water samples 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx in Gaston and Mecklenburg Counties. The samples were tested by the North Carolina State Laboratory of Public Health from 1998 to 2012. The average chromium concentrations were 5.1µg/L and 5.2 µg/L in Gaston and Mecklenburg Counties respectively. Hexavalent Chromium Detected Range: 0.027 µg/L – 13.1 µg/L; Number of Detections/Total Samples: 208/358 Concentrations in 73 samples exceeded the PBTV (bedrock only). Concentrations in 4 samples exceeded the 2L. Hexavalent chromium exceeds both the PBTV and 2L in the transition zone groundwater at the site. Hexavalent chromium exceeds the bedrock PBTV in five upgradient and two background location and exceeds the 2L in four background transition zone locations. Chromium can also occur in the +III oxidation state, depending on pH and redox conditions. Cr (VI) is the dominant form of chromium in shallow aquifers where aerobic conditions exist. Cr(VI) can be reduced to Cr(III) by soil organic matter, S2- and Fe2+ ions under anaerobic conditions often encountered in deeper groundwater. Major Cr(VI) species include chromate (CrO4 2-) and dichromate (Cr2O7 2-) which precipitate readily in the presence of metal cations (especially Ba2+, Pb2+, and Ag+). Chromate and dichromate also adsorb on soil surfaces, especially iron and aluminum oxides. Cr(III) is the dominant form of chromium at low pH. Chromium mobility depends on sorption characteristics of the soil, including clay content, iron oxide content, and the amount of organic matter present. Chromium can be transported by surface runoff to surface waters in its soluble or precipitated form. Soluble and unabsorbed chromium complexes can leach from soil into groundwater. The leachability of Cr(VI) increases as soil pH increases. Most of chromium released into natural waters is particle associated, however, and is ultimately deposited into the sediment (Smith, Means, Chen, & others, 1995). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Cobalt Detected Range: 0.11 µg/L – 755 µg/L; Number of Detections/Total Samples: 126/489 Concentrations in 35 samples exceeded the PBTV (19 in the transition zone/scapolite and 16 in bedrock only). Concentrations in 119 samples exceeded the 2L. Cobalt exceeds both the PBTV and IMAC in the saprolite/transition zone and bedrock groundwater at the site. Cobalt exceeds the PBTV and the IMAC in four background transition zone locations and in seven background bedrock locations. Cobalt detected in groundwater downgradient of the ash basin including exceedances of PBTV and IMAC in surficial and bedrock groundwater. Cobalt is a base metal that exhibits geochemical properties similar to iron and manganese, occurring as a divalent and trivalent ion. Cobalt can occur as Co-1. In terms of distribution in the crust, all three metals exhibit a strong affinity for mafic igneous and volcanic rocks and deep-sea clays (Parker, 1967) Cobalt occurs in clay minerals and substitutes into the pyrite crystal structure. There is also evidence that it is organically bound in coal (Finkelman, 1995). Izquierdo and Querol (2012) report limited leaching of cobalt from coal, attributing this observation to incorporation into iron oxide minerals. The concentration of cobalt in surface and groundwater in the United States is generally low— between 1 and 10 parts of cobalt in 1 billion parts of water (ppb) in populated areas. The concentration may be hundreds or thousands times higher in areas that are rich in cobalt containing minerals or in areas near mining or smelting operations. In most drinking water, cobalt levels are less than 1 to 2 ppb (USGS, 1973). Cobalt is compared to IMAC since no 2L standard has been established for this constituent by NCDEQ. Iron Detected Range: 10 µg/L – 88,100 µg/L; Number of Detections/Total Samples: 723/808 Concentrations in 68 samples exceeded the PBTV (36 in the saprolite/transition zone and 32 in the bedrock). Concentrations in 306 samples exceeded the 2L. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Iron exceeds both the PBTV and 2L in saprolite/transition zone, and bedrock groundwater at the site. Iron exceeds the PBTV and 2L in one background transition zone location and in five bedrock locations. Iron exceeds the 2L in 59 background locations and 10 upgradient locations. Iron is a naturally occurring element that may be present in groundwater from the erosion of natural deposits (NCDHHS, 2010). A 2015 study by NCDEQ (Summary of North Carolina Surface Water Quality Standards 2007-2014) found that while concentrations vary regionally, “iron occurs naturally at significant concentrations in the groundwaters of NC,” with a statewide average concentration of 1320 µg/L. Iron is estimated to be the fourth most abundant element in the Earth’s crust at approximately 5 percent by weight (Parker, 1967). Only Oxygen (46.60 weight percent), silicon (27.72 weight percent), and aluminum (8.13 weight percent) occur in higher concentrations. Iron occurs in divalent (ferrous, Fe+2), trivalent (ferric, Fe+3), hexavalent (Fe+6), and Fe-2 oxidation states. Iron is a common mineral-forming element, occurring primarily in mafic (dark colored) minerals including micas, pyrite (iron disulfide), and hematite (iron oxide), as well as in reddish-colored clay minerals. Clay minerals and pyrite are common impurities in coal. Under combustion conditions in a coal-fired boiler, clay minerals would be dehydrated to mullite or gibbsite, possibly liberating iron, and pyrite would oxidize to hematite or magnesioferrite. Research summarized by Izquierdo and Querol (2012) indicates that iron leaching from coal ash is on the order of 1 percent of the total iron present due to the low pH required to solubilize iron minerals. Despite the low apparent mobilization percentage, iron is often one of the COIs detected in the highest concentrations in ash pore water. Ferric iron is soluble at pH less than 2 at typical surface conditions (25°C and 1 atmosphere total pressure (Schmidt, 1962). For this reason, dissolved iron in surficial waters is typically oxidized to the trivalent state resulting in formation of ferric iron oxide flocculation that exhibits a characteristic reddish tint. Manganese Detected Range: 0.55 µg/L – 30,000 µg/L; Number of Detections/Total Samples: 572/764 Concentrations in 67 samples exceeded the PBTV (27 in the saprolite/transition zone and 40 in the bedrock). Concentrations in 359 samples exceeded the 2L. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-9 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Manganese exceeds both the PBTV and 2L in the saprolite/transition zone and bedrock groundwater at the site. Manganese exceeds the PBTV and 2L in five background transition zone locations and two bedrock locations (one background and one upgradient). Manganese exceeds the 2L in 59 background locations and 24 upgradient locations. Manganese is a naturally occurring silvery-gray transition metal that resembles iron but is more brittle and is not magnetic. It is found in combination with iron, oxygen, sulfur, or chlorine to form manganese compounds. High manganese concentrations are associated with silty soils, and sedimentary, unconsolidated, or weathered lithologic unit and low concentrations are associated with non- weathered igneous bedrock and soils with high hydraulic conductivity (Gillespie, 2013); (Polizzotto, et al., 2015). Manganese is most readily released to the groundwater through the weathering of mafic or siliceous rocks (Gillespie, 2013). When manganese-bearing minerals in saprolite, such as biotite, are exposed to acidic weathering, the metal can be liberated from the host mineral and released to groundwater. It then migrates through pre-existing fractures during the movement of groundwater through bedrock. If this aqueous-phase manganese is exposed to higher pH in the groundwater system, it will precipitate out of solution. This results in preferential pathways becoming “coated” in manganese oxides and introduces a concentrated source of manganese into groundwater (Gillespie, 2013). Manganese(II) in suspension of silt or clay is commonly oxidized by microorganisms present in soil, leading to the precipitation of manganese minerals (ATSDR, 2012). Roughly 40 percent to 50 percent of North Carolina wells have manganese concentrations higher than the state drinking water standard (Gillespie, 2013). Concentrations are spatially variable throughout the state, ranging from less than 0.01 mg/L to more than 2 mg/L. This range of values reflects naturally derived concentrations of the constituent and is largely dependent on the bedrock’s mineralogy and extent of weathering (Gillespie, 2013). Manganese is estimated to be the 12th most abundant element in the crust (0.100 weight percentage, (Parker, 1967)). Manganese exhibits geochemical properties similar to iron with Mn+7, Mn+6, Mn+4, Mn+3, Mn+2, and Mn-1 oxidation states. Manganese substitutes for iron in many minerals. Similar to iron, manganese leaching from coal ash is limited to less than 10 percent of the total manganese present due to the low pH required to solubilize manganese minerals (Izquierdo & Querol, 2012). Despite the low apparent mobilization percentage, manganese can be detected in relatively high concentrations in ash pore water. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-10 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Molybdenum Detected Range: 0.52 µg/L – 71.1 µg/L; Number of Detections/Total Samples: 324/489 Concentrations in 36 samples exceeded the PBTV (33 in the transition zone and three in the bedrock). Molybdenum exceeded the PBTV in transition zone and bedrock groundwater at the site. Molybdenum exceeded the PBTV in six transition zone background locations and 2 bedrock background locations. Molybdenum is a trace element that exists predominantly as Mo(IV) and Mo(VI). As a free metal, it is silvery gray, although it does not occur in this form in nature. It is mined for use in alloys. Molybdenum commonly forms oxyanions in groundwater that are affected by redox and pH (Ayotte, Gronbert, & Apodaca, 2011). Molybdenum has been observed to leach less from coal cleaning rejects in acidic than neutral conditions, unlike many other metals (Jones & Ruppert, 2017). Molybdenum has been shown to become more mobile in procedures that use deionized water as a leachate, which may be similar to actual disposal conditions unlike many other coal ash elements that are more mobile when subjected to weak acid (Jones & Ruppert, 2017). Selenium Detected Range: 0.84 µg/L – 416 µg/L; Number of Detections/Total Samples: 178/810 Concentrations in 170 samples exceeded the PBTV (57 in the saprolite/transition zone and 113 in the bedrock). Concentrations in 70 samples exceeded the 2L. Selenium exceeds both the PBTV and 2L in the saprolite/ transition zone and bedrock groundwater at the site. Selenium exceeds the PBTV in three transition zone background locations, two bedrock background locations and five upgradient bedrock locations. Selenium is a semi-metallic gray metal that commonly occurs naturally combined with rocks and soil. It is common to find trace amounts of selenium in food, drinking water, and air-borne dust. Over geologic time, selenium has been introduced to the earth’s surface and atmosphere through volcanic emissions and igneous extrusions. Weathering and transport partition the element into residual soils, where it is available for plant uptake, or to the aqueous 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-11 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx environment, where it may remain dissolved, enter the aquatic food chain, or redeposit within a sedimentary rock such as shale (EPRI 2008). Groundwater containing selenium is typically the result of either natural processes or industrial operations. Naturally, selenium’s presence in groundwater is from leaching out of selenium-bearing rocks. It is most common in shale ranging from 0.6 to 103 mg/kg. Anthropogenically, selenium is released as a function of the discharge from petroleum and metal refineries and from ore mining and processing facilities. Ore mining may enhance the natural erosive process by loosening soil, creating concentrations in erodible tailings piles, and exposing selenium containing rock to runoff (Martens, 2002); (USEPA, 2017c). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at UNC analyzed 399 private well water samples in Stokes and Rockingham counties from 1998-2010. The values ranged from 2.5 to 26 µg/L, and no samples exceeded the 50 µg/L primary MCL for selenium (NCDHHS, 2010). The mean concentration in both counties was 2.7 µg/L. pH Detected Range: 5.1 units – 12.9 units; Number of Detections/Total Samples: 804/804 Concentrations in 298 samples exceeded the PBTV (33 in the saprolite/transition zone and 265 in the bedrock). pH exceeds the PBTV in the saprolite/ transition zone and bedrock groundwater at the site. pH exceeds the PBTV in three background transition zone locations, two bedrock background locations and 31 upgradient bedrock locations. The pH scale is used to measure acidity or alkalinity. A pH value of 7 indicates neutral water. A value lower than the USEPA-established secondary maximum contaminant level (SMCL) range (<6.5 Standard Units) is associated with a bitter, metallic tasting water, and corrosion. A value higher than the SMCL range (>8.5 Standard Units) is associated with a slippery feel, soda taste, and deposits in the water (USEPA, 2017b). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at UNC analyzed 618 private well water samples for pH in Cleveland and Rutherford Counties. The samples were analyzed by the North Carolina State Laboratory of Public Health from 1998 – 2012. This study 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-12 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx found that 16.9% of wells in Cleveland County and 20.3% of wells in Rutherford County had a pH result outside of the USEPA’s SMCL range. Using the USGS National Uranium Resource Evaluation (NURE) database, all pH tests within a 20-mile radius of CSS are shown on Figure 11-65; with a pH range from 5.1 to 8.7. Strontium Detected Range: 64 µg/L – 6,320 µg/L; Number of Detections/Total Samples: 472/475 Concentrations in 221 samples exceeded the PBTV (21 in the saprolite/transition zone and 200 in the bedrock). Strontium exceeds the PBTV in the saprolite/ transition zone, and bedrock groundwater at the site. Strontium exceeds the PBTV in three background transition zone locations, eight background bedrock locations and 30 upgradient bedrock locations. Strontium is a soft silver-yellow alkaline earth metal. It is highly chemically reactive and forms a dark oxide layer when it interacts with air. It is chemically similar to Ca and replaces Ca or K in igneous rocks in minor amounts. Strontium is generally present in low concentrations in surface waters but may exist in higher concentrations in some groundwater (Hem, 1985). Strontium is present as a minor coal and coal ash constituent. Strontium has been observed to leach from coal cleaning rejects more in neutral conditions than acidic, unlike many other metals (Jones & Ruppert, 2017). It has been shown to behave conservatively in surface waters downstream of coal plants (Ruhl, et al., 2012). Sulfate Detected Range: 0.1 µg/L – 3,400 µg/L; Number of Detections/Total Samples: 801/809 Concentrations in 380 samples exceeded the PBTV (168 in the saprolite/transition zone and 212 in the bedrock). Concentrations in 155 samples exceeded the 2L. Sulfate exceeds both the PBTV and 2L in saprolite/transition zone and bedrock groundwater at the site. Sulfate exceeds the PBTV in four background transition zone locations. Sulfate exceeds both the PBTV and 2L 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-13 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx in two background bedrock locations and exceeds the PBTV in four upgradient bedrock locations two of which also exceed the 2L. Sulfate is a naturally occurring substance found in minerals, soil, and rocks. It is present in ambient air, groundwater, plants, and food. Primary natural sources of sulfate include atmospheric deposition, sulfate mineral dissolution, and sulfide mineral oxidation. The principal commercial use of sulfate is in the chemical industry. Sulfate is discharged into water in industrial wastes and through atmospheric deposition (USEPA, 2003). Anthropogenic sources include coal mines, power plants, phosphate refineries, and metallurgical refineries. While sulfate has an SMCL, and no enforceable maximum concentration set by the USEPA, ingestion of water with high concentrations of sulfate may be associated with diarrhea, particularly in susceptible populations, such as infants and transients (USEPA, 2012). However, adults generally become accustomed to high sulfate concentrations after a few days. It is estimated that about 3 percent of the public drinking water systems in the United States may have sulfate concentrations of 250 mg/L or greater (Miao, Brusseau, Carroll, & others, 2012). Sulfate is on the list of enforced regulated contaminates that may cause cosmetic effects or aesthetic effects in drinking water (USEPA, 2017c). TDS Detected Range: 54 µg/L – 4,300 µg/L; Number of Detections/Total Samples: 806/810 Concentrations in 221 samples exceed both the PBTV and the 2L (83 in the saprolite/transition zone and 138 in the bedrock). Concentrations in 246 samples exceeded the 2L. TDS exceeds both the PBTV and 2L in saprolite/transition zone and bedrock groundwater at the site. TDS exceeds both the PBTV and 2L in seven background transition zone locations and exceeds the 2L in a total of nine transition zone background locations. TDS exceeds both the PBTV and 2L in ten bedrock background locations and exceeds the 2L at 14 locations. TDS exceeds the 2L in 17 background location (nine transition zone and 8 bedrock locations) and in six upgradient bedrock locations. Groundwater contains a wide variety of dissolved inorganic constituents as a result of chemical and biochemical interactions between the groundwater and the elements in the soil and rock through which it passes. Total Dissolved Solids 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-14 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx (TDS) mainly consist of cation and anion particles (e.g., calcium, chlorides, nitrate, phosphorus, iron, sulfur, and others) that can pass through a 2 micron filter (USEPA, 1997). TDS is therefore a measure of the total amount of dissolved ions in the water, but does not identify specific constituents or explain the nature of ion relationships. TDS concentrations in groundwater can vary over many orders of magnitude and generally range from 0 – 1,000,000 µg/L. The ions listed below are referred to as the major ions as they make up more than 90 percent of the TDS in groundwater. TDS concentrations resulting from these constituents are commonly greater than 5,000 µg/L (Freeze & Cherry, 1979). Sodium (Na+) Magnesium (Mg2+) Calcium (Ca2+) Chloride (Cl-) Bicarbonate (HCO3-) Sulfate (SO42-) Minor ions in groundwater include: boron, nitrate, carbonate, potassium, fluoride, strontium, and iron. TDS concentrations resulting from minor ions typically range between 10 – 1,000 µg/L (Freeze & Cherry, 1979). Trace constituents make up an even smaller portion of TDS in groundwater and include: aluminum, antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, lead, manganese, nickel, selenium, thallium, vanadium, and zinc among others. TDS concentrations resulting from trace constituents are typically less than 100 µg/L (Freeze & Cherry, 1979). In some cases, contributions from anthropogenic sources can cause some of the elements listed as minor or trace constituents to occur as contaminants at concentration levels that are orders of magnitude above the normal ranges indicated above. TDS in water supplies originate from natural sources, sewage, urban and agricultural run-off, and industrial wastewater. Salts used for road de-icing can also contribute to the TDS loading of water supplies. Concentrations of TDS from natural sources have been found to vary from less than 30 mg/L to as much as 6,000 mg/L. Water containing more than 2,000 – 3,000 mg/L TDS is generally too salty to drink (the TDS of seawater is approximately 35,000 mg/L) (Freeze & Cherry, 1979). Reliable data on possible health effects associated with the ingestion of TDS in drinking water are not available (WHO, 1996). TDS is on the 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-15 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx list of “National Secondary Drinking Water Regulations” which are non-enforced regulated contaminates that may cause cosmetic effects or aesthetic effects in drinking water (USEPA, 2017b). In the April 2015 CCR Rule, the USEPA listed TDS as an indicator constituent (along with boron, calcium, chloride, fluoride, pH, and sulfate). USEPA defines indicator constituents as those that are present in CCR and would rapidly move through the surface layer, relative to other constituents, and thus provide an early detection of whether contaminants are migrating from the CCR unit (USEPA CCR Rule, 2015). Vanadium Detected Range: 0.3 µg/L – 41.5 µg/L; Number of Detections/Total Samples: 423/482 Concentrations in 133 samples exceed both the PBTV and the IMAC (11 in the transition zone and 122 in the bedrock). Concentrations in 296 samples exceeded the IMAC. Vanadium exceeds both the PBTV and IMAC in saprolite/transition zone and bedrock groundwater at the site. Vanadium exceeds the IMAC in 37 background bedrock locations and 55 upgradient bedrock locations. Vanadium exceeds both the IMAC and the PBTV in 3 background bedrock locations and 33 upgradient bedrock locations. Exceedances of the IMAC of 0.0003 mg/L were detected in samples from each of the ash pore well locations; and in most groundwater samples, including background locations. Vanadium is estimated to be the 22nd most abundant element in the crust (0.011 weight percent, (Parker, 1967). Vanadium occurs in four oxidation states (V+5, V+4, V+3, and V+2). It is a common trace element in both clay minerals and plant material. The National Uranium Resource Evaluation (NURE) program was initiated by the Atomic Energy Commission in 1973 with a primary goal of identifying uranium resources in the United States (Smith S. M., 2016). The Hydrogeochemical and Stream Sediment Reconnaissance program (initiated in 1975) was one component of NURE. Planned systematic sampling of the entire United States began in 1976 under the responsibility of four Department of Energy national laboratories. Samples were collected from 5,178 wells across 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-16 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx North Carolina. Of these, the concentration of vanadium was equal to or higher that the former IMAC of 0.0003 mg/L in 1,388 well samples (27 percent). Uranium (total) Detected Range: 0.000201 µg/L – 0.0436 µg/L; Number of Detections/Total Samples: 218/271 Concentrations in 35 samples exceed the PBTV in the bedrock. Concentrations in 5 bedrock samples exceeded the MCL. Uranium exceeds both the PBTV and MCL in the bedrock groundwater at the site. Uranium exceeds both the PBTV and MCL in one background bedrock location. Uranium exceeds the PBTV in three background bedrock locations and two upgradient bedrock locations. Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is the 51st element in order of abundance in the Earth's crust. Uranium is also the highest-numbered element to be found naturally in significant quantities on Earth and is almost always found combined with other elements. The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics. Uranium is more plentiful than antimony, tin, cadmium, mercury, or silver, and it is about as abundant as arsenic or molybdenum. Uranium is found in hundreds of minerals, including uraninite (the most common uranium ore), carnotite, autunite, uranophane, torbernite, and coffinite. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores. 11.2 Pending Investigation(s) Additional metal oxy-hydroxide phases of iron (HFO) and aluminum (HAO) data are needed to support geochemical modeling conducted as part of the CAP. Soil and rock samples from previously installed borings or from additionally drilled boreholes along the primary groundwater flow transect will be used. The samples will be located: Background/Upgradient Directly beneath ash basins Downgradient location, north of the ash basins 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 11-17 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The samples will be collected at vertical intervals that coincide with nearby well screen elevations. Analysis results of collected samples will be used to improve input parameters for the updated geochemical model. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 12-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 12.0 RISK ASSESSMENT A baseline human health and ecological risk assessment was performed in 2016 as a component of CAP Part 2 (SynTerra, 2016a). The risk assessment characterized potential effects on humans and wildlife exposed to coal ash constituents present in environmental media for the purpose of aiding corrective active decisions. Implementation of corrective action is intended to achieve future site conditions protective of human health and the environment, as required by CAMA. This update to the risk assessment evaluates groundwater and surface water results collected since the 2016 risk assessment (November 2015 to June 2017) in order to confirm or update risk conclusions in support of remedial actions. Data used in the 2016 risk assessment included groundwater, surface water, sediment, AOW water and soil collected from March 26, 2015 through September 16, 2015. This update to the risk assessment uses sampling locations described in Section 3.2 of the 2016 document, unless otherwise noted below. As previously noted, AOW locations are outside the scope of this risk assessment because AOWs, wastewater, and wastewater conveyances (effluent channels) are being evaluated and governed wholly separate in accordance with the NPDES Program administered by NCDEQ DWR. This process is on-going in a parallel effort to the CSA and subject to change. No new sediment or soil samples, with exception of background soils, have been collected that are applicable to the 2016 risk assessment, therefore risk estimates associated with those media have not been re-evaluated. As part of the 2016 risk assessment, human health and ecological conceptual site models (CSMs) were developed to guide identification of exposure pathways, exposure routes, and potential receptors for evaluation in the risk assessment. The CSMs (CAP 2, Appendix F, Figures 2-2 and 2-4) describe the sources and potential migration pathways through which groundwater beneath the ash basins may have transported coal ash constituents to other environmental media (receiving media) and, in turn, to potential human and ecological receptors. Exposure scenarios and exposure areas were presented in detail in the 2016 CAP Part 2 risk assessment. This risk assessment update included the following: Identification of maximum constituent concentrations for groundwater and surface water 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 12-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Inclusion of new groundwater and surface water data to derive overall average constituent concentrations for exposure areas Comparison of new maximum constituent concentrations (November 2015 to June 2017) to the risk assessment human health and ecological screening values Comparison of new maximum constituent concentrations (November 2015 to June 2017) to human health Risk-Based Concentrations (RBC) Where applicable, incorporation of new maximum constituent concentrations into wildlife Average Daily Dose (ADD) calculations for comparison to ecological Toxicity Reference Values (TRVs) Evaluation of new groundwater and surface water data and the influence on the 2016 risk assessment are summarized below by exposure areas at the Roxboro Site (Figures 12-1 and 12-2). 12.1 Human Health Screening Summary On-Site Groundwater - Bedrock and Transition Zone Aquifer Groundwater sample locations included in the assessment were: ABMW-1BR through ABMW-4BR, ABMW-5D, ABMW-6BR, ABMW-7BR, CW-1 through CW-5, CW-2D, CW- 3D, GMW-6 through GMW-11, MW-1BR through MW-12BR, MW-5D and MW-6D. These wells were evaluated because they represent the potential trespasser/worker exposure area as determined in the 2016 risk assessment. Groundwater analytical results are included in Appendix B, Table 1. No maximum detected constituent concentrations (November 2015 to June 2017) exceed human health RBCs; therefore, no potential risks to humans exposed to on-site groundwater were indicated. Surface Water - Hyco Lake The 2016 risk assessment identified potential risks under a hypothetical recreational and subsistence fisher scenario exposed to cobalt in fish tissue modeled from surface water concentrations. The risks were overestimated because of very conservative assumptions in the exposure models. The Hyco Lake exposure area included surface water samples SW-01, SW-02, and SW-03, collected west of the WAB along the eastern shore of the reservoir. According to the groundwater plume boundary and flow direction, the Hyco Lake exposure area is not influenced by groundwater affected by the ash basins. No potential unacceptable risks to wildlife exposed to surface water in Hyco Lake were identified. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 12-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 12.2 Ecological Screening Summary Based on groundwater flow direction and plume delineation, no surface water bodies appear to be affected by constituent migration in groundwater from the ash basins. Thus, ecological risks were not evaluated as part of this update. 12.3 Private Well Receptor Assessment Update An independent study was conducted that evaluated 2015 groundwater data collected from three groundwater datasets: private wells data collected by NCDEQ within close proximity (<0.5 miles) of the Roxboro Plant, private well data collected by NCDEQ from areas identified as background locations, and groundwater data collected from 26 wells within a 2 to 10 mile radius of the Roxboro Plant (CAP 2, Section 5.7; (Haley & Aldrich, 2015). Pertinent observations presented in the study included: Boron and other potential coal ash constituents were detected at concentrations less than screening levels, with the exception of lead in one well. The concentration of lead was not confirmed by additional samples from this well. Hexavalent chromium was detected in some of the private well samples at levels greater than the DHHS screening level but consistent with background concentrations, Vanadium concentrations detected in private well samples were consistent with background concentrations; and Groundwater flow paths from the Roxboro coal ash management areas not in the direction of residential areas. The Haley & Aldrich report concluded that the constituents detected in the private wells sampled by NCDEQ are consistent with regional background and do not indicate impact from constituents derived from coal ash. Recent (2017) results from water supply wells did not indicate human health risks to off-site residents potentially exposed to groundwater associated with the ash basins. Cobalt exceeded IMAC in one well at 3.74 µg/L, which is below the bedrock background threshold value of 11 µg/L. Lead was detected in one water supply well at 40.3 µg/L. Detected concentrations of manganese were below the bedrock background threshold value of 1,196 µg/L with exception of one sample. While several wells exceeded IMAC for vanadium, all detected vanadium concentrations were less than PBTV. As determined, water supply wells are located upgradient of the Roxboro Plant 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 12-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx ash basins. Based on these observations, there are no indications that potential risks to off-site residences exposed to groundwater exist. 12.4 Risk Assessment Update Summary Based on review and analysis of groundwater and surface water data, there is no evidence of risks to humans and wildlife at the Roxboro Site attributed to CCR constituent migration in groundwater from the ash basins. This update to the human health and ecological risk assessment supports a risk classification of “Low” for the EAB and WAB. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 13.0 GROUNDWATER MODELING RESULTS Groundwater flow, and transport, and geochemical models are being developed to simulate movement of constituents of interest (COI) through the subsurface to support the evaluation and design of remedial options at the sites. The models will provide insights into: 1. COI Mobility: Geochemical processes affecting precipitation, adsorption and desorption onto solids will be simulated based on lab data and thermodynamic principles to predict partitioning and mobility in groundwater. 2. COI Movement: Simulations of the groundwater flow system will be combined with estimates of source concentrations, sorption, effective porosity, and dispersion to predict the paths and rates of constituent movement at the field scale. 3. Scenario Screening: The flow, transport and geochemical models will be adjusted to simulate how various ash basin closure design options and groundwater remedial technologies will affect the short-term and long-term distribution of COIs. 4. Design: Model predictions will be used to help design basin closure and groundwater corrective action strategies in order to achieve compliance with 2L and/or PBTV in a reasonable cost and timeframe. The groundwater flow model linked with the transport model will be used to establish transport predictions that best represent observed conditions at the site particularly for the constituents, such as boron, that tend to be negligibly affected by geochemical processes. The geochemical model information will provide insight into the complex processes that influence constituent mobility, which will be used to refine constituent sorption within the transport model. Once the flow, transport and geochemical models for the site accurately reproduce observed site conditions, they can be used as predictive tools to evaluate the conditions that will result from various remedial options for basin closure (No Change, Cap-in-Place or Ash Removal) and potential subsequent passive or active groundwater remedial technologies. The site-specific groundwater flow and transport models and the site-specific geochemical models are currently being updated for use in the CAP. The CAP will further discuss the purpose and scope of both the groundwater and geochemical models. It will detail model development, calibration, assumptions and limitations. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The CAP will also include a detailed remedial option evaluation, based on observed conditions and the results of predictive modeling. The evaluation of the potential remedial options will include comparisons of predictive model results for long-term source concentration and plume migration trends toward potential receptors. The model predictions will be used in combination with other evaluation criteria to develop the optimal approach for basin closure and groundwater remediation. The following sections provide a brief summary of modeling efforts completed to date at Roxboro. 13.1 Summary of Fate and Transport Model Results A groundwater flow and transport model was developed to gain an understanding of COI migration after closure of the ash basins at the Roxboro Plant. The initial groundwater model in the CAP Part 1 (SynTerra, 2015b) included a calibrated steady- state flow model of June 2015 conditions; a calibrated historical transient model of constituent transport to June 2015 conditions; and three potential basin closure scenarios. Those basin closure simulation scenarios included: No change in site conditions (basins remain open, as is) Cap-in-place Ash removal (excavation) The initial model used arsenic, boron, manganese, and sulfate as primary COIs. As part of the CAP Part 2 (SynTerra, 2016a), the model was revised to only include boron and manganese and the model predictive time was extended from 30 years to 100 years. The revised model in the CAP Part 2 (SynTerra, 2016a) included a calibrated steady-state flow model of June 2015 conditions; a calibrated historical transient model of constituent transport to June 2015 conditions; and two potential basin closure scenarios. Those basin closure simulation scenarios included: No change in site conditions (basin remains open, as is) Cap-in-place The flow and transport model is currently being updated as a part of the final CAP and will include: development of a calibrated steady-state flow model that includes data available through November 2017; development of a historical transient model of constituent transport; and predictive simulations of basin closure plus groundwater corrective action scenarios. The updated fate and transport model will consider arsenic, boron, and possibly additional COIs that are hydraulically driven. Predictive 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx simulations will have simulation times that continue until modeled COIs concentrations are below the 2L standard at the compliance boundary. The following sections provide a brief summary of the groundwater modeling that was presented in the CAP Part 2 and a general outline for the updated modeling effort. The summary of the groundwater modeling presented in the CAP Part 2 was compiled to address specific questions regarding model set-up and calibration. A complete updated groundwater flow and transport model report is being developed and will be submitted as part of the updated CAP. The model was developed using the MODFLOW-NWT version (Niswonger, Panday, & Motomu, 2011). This version provides improved numerical stability and accuracy for modeling problems within a variable water table. The improved numerical stability and accuracy can provide better estimates of the water table fluctuations that result from ash basin operating conditions and potential closure and groundwater corrective action activities. MT3DMS was used to simulate fate and transport of selected COIs. MT3DMS uses the groundwater flow field from MODFLOW to simulate 3D advection and dispersion of the dissolved COIs, including the effects of retardation due to the soil matrix adsorption of COIs. Flow Model Construction 13.1.1 The flow and transport model was built through a series of steps. The first step was to build a three-dimensional (3D) model of the Site hydrostratigraphy based on the SCM. The next steps were to determine the model dimensions and the construction of the numerical grid. The numerical grid was then populated with flow parameters, which were calibrated in the steady-state flow model. Once the flow model was calibrated, the flow parameters were used to develop a transient model of the historical flow patterns at the site. The historical flow model was then used to provide the time-dependent flow field for the constituent transport simulations. Generally, the model geometry will not be substantially modified for the updated model. Hydraulic parameters such as hydraulic conductivity values may be adjusted within reasonable site-specific ranges to achieve hydraulic head calibration error below 10 percent. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Flow Model Domain and Grid Layers The model has dimensions of approximately four miles-by-three miles, with the ash basin at the center of the model domain. The long axis of the model domain was oriented N30E so it was generally parallel to the axis of Hyco Lake. The NW corner of this region was underlain by Hyco Lake and the model was set as inactive to the west of the approximate center of the lake. This configuration was selected so that most of the NW and SW sides of the model were bounded by Hyco Lake. The distance to the SE and NE boundaries of the model were made large relative to the area of interest in order to minimize the influence of outer model boundary conditions. The shortest distance between the ash basins and a model boundary is approximately one mile. The hydrostratigraphic model consists of six units: ash, saprolite, transition zone, upper bedrock (upper fractured rock), middle bedrock (middle fractured rock), and lower bedrock (lower rock). The units were determined by interpolating boring log data from historical data, the various CSA activities, and the CAP reports (SynTerra, 2015b); (SynTerra, 2016a). The hydrostratigraphic model was developed using “Solids” in GMS and was subdivided into five solids. A computational mesh (numerical grid) was then developed based on these solids: ash, saprolite, transition zone, fractured rock, and lower rock. The numerical grid consists of rectangular blocks arranged in columns, rows, and layers. There are 299 columns, 198 rows, and 15 layers. The maximum width of the columns and rows is 100 feet. The size of the grid blocks is approximately 50 feet by 50 feet in the vicinity of the ash basins. The horizontal dimension of some of the grid blocks is as small as 25 feet in the vicinity of the dams. The grid consists of 15 layers representing the six hydrostratigraphic units. It is expected that the updated model will use similar grid spacing. Hydrostratigraphic layer Grid layer Ash 1-4 Saprolite 5 Transition zone 6-7 Upper fractured rock 8-10 Middle fractured rock 11-12 Lower Rock 13-15 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Flow Model Boundary Conditions The western and northern boundaries of the model include parts of Hyco Lake. The heads in the upper layer in this area was set to the stage of the lake (408 mean sea level. The boundaries on the south and east sides of the model are independent of a definitive hydrologic feature. A constant head boundary condition with the head set at 3 feet above the top of the saprolite layer was used along these boundaries. This boundary condition forces the water table to be in the top of the saprolite along the south and east boundaries, which is a reasonable approximation of the expected conditions. The constant head boundary condition extends along the upland areas, but it is terminated within a few hundred feet of the locations of streams or lakes. This is because streams or lakes that intersect the boundary are defined by their own boundaries conditions (as either constant head or drain-type boundaries). This creates short intervals of no-flow conditions between streams or lakes and the uplands. The constant head boundary condition was assigned to layers 5-10, which is where most of the flow occurs. The underlying layers were set to no-flow. Sources and Sinks Water can enter or leave the model through the use of sources and sinks. MODFLOW uses point sources/sinks as well as aerial sources/sinks. Point sources/sinks include rivers, wells, drains, and general head. Aerial sources/sinks considered are limited to recharge. Source (Recharge) Model recharge sources include: Recharge that infiltrates through the EAB and WAB (set to approximately 3x ambient) Rainwater that infiltrates in the upland areas (6.5 inches/year) (Precipitation in developed areas of the Site (set to near zero; assumes most will run off). Constant head boundaries (Large areas of ponded water, such as the ash basins and Hyco Lake, were represented as specific head boundaries and recharge was set to zero.) 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx EAB and WAB, Hyco Lake, water bodies within the plant Channels through the ash basins Model Sinks (Drains) Model sinks include: Streams within the model domain EAB and WAB effluent discharge canals EAB and WAB, Hyco Lake water bodies within the plant Channels through the ash basins Streams within the model domain were set as drains. Drains are only allowed to gain (remove) water from the model. The EAB and WAB, lakes, water bodies and channels were set as ether a constant head or a specified and can ether remove water or add water to the model. Water Supply Wells Approximately 63 domestic wells were previously identified within the compliance boundary of the Roxboro Plant (SynTerra, 2014a). Additional wells were identified based on the updated compliance boundary which will be added to the updated model that will be presented in the updated CAP. Two wells are used as the water supply for the Woodland Elementary School to the southwest of the plant, and another well is used by a building materials facility located to the northeast of the Site. The school wells were set at a discharge of 1,870 gallons/day and the building materials well was set at 3,740 gallons per day. The average daily use for the domestic wells was set at a discharge of 375 gallons per day (USEPA, 2017a). Hydraulic Conductivity The horizontal hydraulic conductivity and the horizontal-to-vertical hydraulic conductivity anisotropy ratio (anisotropy) are the main variable hydraulic parameters in the model. The distribution of those parameters is based primarily on the model hydrostratigraphy, with some local variations. The values can be adjusted during the calibration process to provide a best fit for observing water levels in wells. Initial estimates of parameters were based on literature values, results of slug and core testing, and simulations performed using a preliminary flow model. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Streams and Lake Hydraulic Parameters Hyco Lake, and other water bodies within the plant were represented as constant head boundaries. These features were assumed to be at the same stage as Hyco Lake. Hyco Lake full pool is 410 feet mean sea level but at the time of model calibration the lake was not at full pool; therefore, a value of 408 feet mean sea level was used for the stage in the model. The EAB and the WAB were represented by simulating the observed surface water as specified head and applying recharge based on estimates from the current land cover. This approach treats the ash basins in the same way as other hydrogeologic components in the model, and it was selected as the best approach to characterize current conditions. The historical (1977) stage of the water in the ash basins appears to be similar to water levels observed in wells presently. Drains and specified heads where set with a conductance of 100 square feet per day (ft2/day). Their heads were set to correspond to water levels observed in nearby wells. Flow Model Calibration Targets The steady state flow model calibration data for June 2015 were presented in the CAP, Part 2. In the final CAP, calibration target data will be incorporated by taking the mean of the hydraulic head data for each well and applying a standard deviation to reflect the seasonal changes in the hydraulic heads. Hydraulic head data will include measurements until November 2017. Mass Balance The previous model had a mass balance error of well below 1%. The updated model will have a similar numerical accuracy. Flow Model Sensitivity Analysis A parameter sensitivity analysis for the preliminary calibrated model showed the highest degree of sensitivity to upland recharge and hydraulic conductivities (in the transition zone and saprolite stratigraphic units). The model was only weakly sensitive to the hydraulic conductivities of the ash, deep bedrock, and hydraulic conductivity of the dams and to the pumping rate of the domestic wells. Since no major elements within the model are to be changed, there is no need to perform additional sensitivity testing. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Particle Tracking A primary concern is the potential impact to domestic and public wells from COIs emanating from the Site. The final calibrated groundwater flow model will be used to assess potential impacts by considering pumping from domestic and public wells within the model domain. Flow Model Assumptions and Limitations The groundwater model is currently being updated/refined and assumptions and limitations will be subject to change. Based on the preliminary modeling results, the assumptions and limitations included the following: The steady-state flow model was calibrated to hydraulic heads measured in monitoring wells in June 2015. The model was not calibrated to transient water levels over time, recharge, or river flow. MODFLOW simulates flow through porous media. A single domain MODFLOW modeling approach for simulating flow in the primary porous groundwater zones and bedrock was used for contaminant transport. Flow in fractured bedrock is simulated using the equivalent porous media approximation. For the purposes of numerical modeling and comparing predictive scenarios, it was previously assumed that basin closure would be completed in 2015. A similar assumption will be used in the updated model. Predictive simulations were performed and steady-state flow conditions were assumed from the time that the ash basin was placed in service through the current time until the end of the predictive simulations (2115). The uncertainty in model parameters and predictions has not been quantified; therefore, the error in model predictions is not known. It was assumed the model results are suitable for a relative comparison of closure scenario options. Residential wells for which well construction records could not be obtained were assumed to be completed in the upper bedrock. Transport Model Construction 13.1.2 Modular 3-D Transport Multi-Species (MT3DMS) is being used to simulate constituent transport. MT3DMS simulates 3D advection and dispersion of the dissolved COIs, including the effects of retardation due to the soil matrix 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-9 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx adsorption of COIs based on flow fields established by MODFLOW. The initial model used boron and arsenic as primary modeling constituents. The updated fate and transport modeling will focus on arsenic, boron, and possibly additional COIs that are hydraulically driven. Other constituents will be considered in geochemical modeling. Transport Model Parameters The key transport model parameters (besides the flow field) are the constituent source concentrations in the ash basins and the constituent soil-water distribution coefficients (Kd). Secondary parameters are the longitudinal, transverse, and vertical dispersivity, and the effective porosity. Transport Model Boundary Conditions In the current model, the transport model boundary conditions are “no flow” on the exterior edges of the model. Infiltrating rainwater is assumed to be clean and enters with zero concentration from the top of the model. An exception is beneath parts of the unlined portions of the landfill and the eastern end of the gypsum pile. The concentration is fixed at the geometric mean concentration at the water table to represent mass that has been dissolved from the ash during infiltration. All of the constant head water bodies have a fixed concentration of zero. As water containing dissolved constituents enters these zones, the dissolved mass is removed from the model. In the current model, the concentrations from the June 2015 sampling event were set as boundary conditions within the ash basin. These values will be updated to use the concentration data up through the November 2017 sampling event. Transport Model Sources and Sinks Transport model sources include: The ash basins are considered the source of COIs in the model. The sources are simulated by applying a constant COI concentration within the cells of the ash basins and were applied to layers 1 through 4 which represent the ash. This allows infiltrating water to carry dissolved constituents from the ash pore water into the groundwater underneath the ash basin. Chemical analyses from nine wells were used to characterize the distribution of COI concentration within the ash basins, and the source concentration is used as a calibration parameter in the transport simulations. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-10 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx COIs in the area of the unlined portion of the landfill were specified at the water table. As the COIs migrate beneath and away from the coal ash, zones of soil and fractured rock become impacted. These impacted zones can serve as secondary sources, and are fully accounted for in the transport models. For simulations that involve ash excavation, the constant concentration sources in the ash zones are removed, but the secondary sources in the impacted soil and fractured bedrock remain. The longevity of these secondary sources depends on the COI Kd, and on the degree of flushing by infiltration and groundwater flow. Transport model sinks include: Lakes Streams/rivers Other AOW and engineered drains Transport Model Calibration Targets and Sensitivity The initial transport model calibration targets were COI concentrations measured in monitoring wells in June 2015. The updated model calibration targets will include COIs concentrations measured in monitoring wells in 2017. Constituents considered for the next fate and transport model will include boron, arsenic and possibly other COIs. COIs not amenable to simulation in the fate and transport model will be addressed in the geochemical model. Transport Simulation The updated model will be calibrated to include data through November 2017 and will extend until modeled COI concentrations are below the 2L standard at the compliance boundary. The following is a summary of the basin closure options modeled: No Action – Leave the ash basin in place to evaluate whether groundwater quality would be restored by natural attenuation under current conditions. Cap-in-Place – Grade the ash and place an engineered low permeability cover system to reduce infiltration of surface water. This scenario assumes that the ash under the cap will be dewatered. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-11 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Ash Removal – Remove the ash from the basin. This scenario assumes that the ground surface would be restored to its initial grade (prior to construction of the ash basin). The distribution of recharge, locations of drains, and distribution of material will be modified to represent the different basin closure options. The results of these simulations will be included as part of the updated CAP submittal. Summary of Flow and Transport Modeling Results To 13.1.3 Date The simulated June 2015 concentration distributions described in the CAP 1 (SynTerra, 2015b) were used as initial conditions in a predictive simulation of future flow and transport at the Site. Predictive simulations of future flow and transport for arsenic, boron, manganese, and sulfate under the existing conditions (“no action”), cap-in-place, and complete ash removal scenarios were run. The initial model ran simulations were run for 30 years (presented in the CAP Part 1). The updated model extended predictive simulations to 100-years (presented in the CAP Part 2) for boron and manganese and was limited to “no action” and cap-in-place. A summary of the basin closure options include: No Action In the CAP Part 1 report (SynTerra, 2015b) simulated arsenic concentrations beneath the ash basin within the transition zone expanded laterally by a few 100 feet from 2015 to 2045. However, simulated concentrations within the fractured bedrock remain below the 2L standard from 2015 to 2045. The CAP Part 2 results for the No Action scenario (SynTerra, 2016a) indicate the 2115 simulation are similar to the 2045 conditions and predict that the boron plumes increase laterally and vertically downward, and increase in concentration. This pattern occurs within the modeled saprolite, transition zone, and fractured bedrock layers. The West Ash Basin boron plume within the fractured bedrock has expanded in size; however the boron plume migrates east from the WAB effluent channel. The middle fracture bedrock layer (layer 11) illustrates two new boron plumes within the WAB and three new plumes within the EAB, thus showing a downward migration. The CAP Part 2 simulations of manganese are similar to boron as the plume extent expands laterally and vertically downward (SynTerra, 2016a). The extent 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-12 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx of the manganese plumes within the saprolite and transition zone are similar to the 2045 simulations. The manganese plume expands within the upper and middle fractured bedrock layers in both East and West Ash Basins. The concentration within the middle fractured bedrock under the East Ash Basin increased from 2045 to 2115 In the CAP Part 1 report (SynTerra, 2015b) simulated sulfate and the results are similar to boron and manganese where the plume expands laterally and vertically downward, and increases in concentration from 2015 to 2045. However, the extent of the migration is less than 100 feet and in some cases it is hard to distinguish a change within the time steps. In addition, there is no significant new bedrock impacts in the 2045 simulation that is not already present in the 2015 simulations. Cap-In-Place In the CAP Part 1 report (SynTerra, 2015b) simulated arsenic concentrations and shape are essentially the same from 2015 to 2045. The results of the CAP Part 2 (SynTerra, 2016a) cap-in-place (engineered capping system) simulation depict zones of boron that increase in concentration and size from 2045 to 2115. However the magnitude of the increase is less than those simulated for the No Action scenario. Within the saprolite layer in the WAB area the concentration increases; however, like the EAB, the 2L plume stabilizes in size. At the western edge of the EAB, the boron plume slightly increases in size; however, decreases in concentration in the saprolite layer. Within the simulated transition zone and fractured bedrock, the concentrations decreased, but 2L plume slightly expanded in size. In the CAP Part 2 (SynTerra, 2016a) the size and shape of the simulated manganese plume decreases in size within the saprolite, transition zone and bedrock layers. The simulation predicted the manganese zone to the south of the EAB receded 2,050 ft within the bedrock layer. The CAP Part 1 modeling report did not describe results of sulfate; however model results indicate that sulfate is decreasing in size and concentration within the transition zone and fractured bedrock on the EAB and WAB. The results of the CAP Part 2 modeling do not substantially alter the conclusions presented in CAP Part 1. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-13 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 13.2 Summary of Geochemical Model Results The Roxboro Site geochemical model investigates how variations in geochemical parameters affect movement of constituents through the subsurface. The geochemical site conceptual model (SCM) will be updated as additional data and information associated with Site constituents, conditions, or processes are developed. The geochemical modeling approach presented in the following sections was developed using laboratory analytical procedures and computer simulations to understand the geochemical conditions and controls on groundwater concentrations at the Roxboro Plant in order to predict how remedial action and/or natural attenuation may occur at the site and avoid unwanted side effects. The final geochemical model will be presented in the updated CAP. Model Construction 13.2.1 The geochemical model in the CAP Part 2 (SynTerra, 2016a) included: EH-pH (Pourbaix) diagrams showing potential stable chemical phases of the aqueous electrochemical system, calibrated to encompass conditions at the Site, Sorption model where the aqueous speciation and surface complexation are modeled using the USGS geochemical modeling program PHREEQC, Simulations of the anticipated geochemical speciation that would occur for each COI in the presence of adsorption to soils and in response to changes in EH and pH, and Attenuation calculations where the potential capacity of aquifer solids to sequester constituents of interest were estimated. Laboratory Determination of Distribution Coefficient SynTerra retained researchers from the University of North Carolina at Charlotte (UNCC) to determine site-specific distribution coefficients (Kd) for the primary hydrostratigraphic units. The UNCC Soil Sorption Evaluation and Addendum to the UNCC Soil Sorption Evaluation reports are provided in Appendix C. Selected soil samples were analyzed using batch and column experiments to determine Kd values for COIs (Table 13-1). In addition to these analyses, metal oxy-hydroxide phases of iron (HFO), manganese (HMO), and aluminum (HAO) in soils were measured. HFO, HMO, and HAO are considered to be the most important surface reactive phases for cationic and anionic constituents in many subsurface environments (Ford, W., & Puls, 2007). Quantities of these phases in soil can thus be considered a proxy for the presence of ferrihydrite (HFO) and 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-14 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx gibbsite (HAO) which can be used to model COI sorption capacity for a given soil (Dzombak & Morel, 1990); (Karamalidis & Dzombak, 2010). Geochemical Model Construction To examine the sorption behavior of multiple ions of interest in the subsurface environment surrounding coal-fired power plants, a combined aqueous speciation and surface complexation model was developed using the USGS geochemical modeling program PHREEQC. Equilibrium constants for aqueous speciation reactions were taken from the USGS WATEQ4F database. This database contained the reactions for most elements of interest except for Co, Sb, V, and Cr. Constants for aqueous reactions and mineral formation for these elements were taken from the MINTEQ v4 database which is also issued with PHREEQC. The constants were all checked to provide a self-consistent incorporation into the revised database. The source of the MINTEQ v4 database is primarily the well-known NIST 46 database (Martell & Smith, 2001). Sorption reactions were modeled using a diffuse double layer surface complexation model. For self-consistency in the sorption model, a single database of constants was used as opposed to searching out individual constants from literature. The diffuse double layer model describing ion sorption to HFO and HAO was selected for this effort (Dzombak & Morel, 1990); (Karamalidis & Dzombak, 2010). Geochemical Controls on COI As described in previous geochemical model reports (SynTerra, 2015b); (SynTerra, 2016a), pH, EH, and solubility are the primary geochemical parameters affecting constituent mobility. In the updated geochemical model planned to be submitted in 2018 as part of the CAP, hydraulically significant flow transects will be used to evaluate our conceptual model of COI mobility in the subsurface. It will compare trends in the concentrations of COIs along transects with the model output to verify that the conceptual and qualitative models can predict COI behavior. Then the model can be used to evaluate the potential impacts of remediation activities. The model will relate the COI concentrations observed in groundwater along flow transects to key geochemical parameters influencing constituent mobility (i.e., EH, pH, and saturation/solubility controls). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-15 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Geochemical Model Assumptions Several key assumptions will be applied to the planned geochemical modeling effort: 1) The thermochemical sorption constant reactions describe ion sorption to ferrihydrite and gibbsite (HFO and HAO). 2) The model will use the same or more conservative site density assumptions as those used by Dzombak and Morel (1990) and Karamalidis and Dzombak (2010) to constrain the surface sites. HAO and HFO (i.e., gibbsite and ferrihydrite) are used as the primary reactive minerals due to the availability of surface complexation reactions. Differences between the sorption behaviors at each site will be primarily due to 1) differences in the pH, EH, and ion concentrations at each site, and 2) differences in the extractable iron and aluminum concentrations from Site specific solids. Additional reactive minerals will be incorporated into the model as needed on a Site specific basis Updated Geochemical Model Development The updated geochemical site investigation to accompany the CAP will develop parameters for each aquifer or geologically derived flow zone (geozone) by considering the bulk densities, porosities, and hydraulic gradients used in the fate and transport model. These parameters are used to constrain the sorption site concentrations in the model input and will be incorporated in the 1-D ADVECTION model to accompany the capacity simulations. The objective of these capacity simulations is to determine the mass balance on iron and aluminum sorption sites when simulating flow through a fixed region. Input and initial iron and aluminum concentrations will be fixed based on site-specific data. Thus, the model will be able to simulate the stability of the HFO and HAO phases assumed to control constituent sorption. The final geochemical model report will include a site specific discussion of: The model description, The purpose of the geochemical model, Modeling results with comparison to observed conditions, COI sensitivity to pH, EH, iron/aluminum oxide content, and Model limitations. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-16 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The updated geochemical modeling will also present multiple methods of determining constituent mobility at the Site. Aqueous speciation, surface complexation, and solubility controls will be presented in the revised report. These processes will be modeled using: Pourbaix diagrams created with the Geochemist Workbench v10 software using site-specific minimum and maximum constituent concentrations. PHREEQC’s combined aqueous speciation and surface complexation model and the 1-D ADVECTION function to gain a comprehensive understanding of current geochemical controls on the system and evaluate how potential changes in the geochemical system might affect constituent mobility in the future. Summary of Geochemical Model Results To Date 13.2.2 The geochemical model developed in this work considers changes in oxidation state for redox active constituents of interest (Se, As, Fe, V, Mn, Cr, Co, S) and changes in chemical speciation. PHREEQC model predicts: Arsenic - As(V) as the dominant oxidation state of arsenic. As(III) is the dominant species measured in groundwaters. This is due to the stronger sorption of As(V). This results in the relatively lower Kd values predicted for arsenic in the model. Boron - Boron exists only in the B(III) oxidation state. PHREEQC predicted Kd values for boron are low. Predicted values are slightly lower, but generally consistent, with the values chosen for reactive transport modeling and those measured in batch laboratory experiments. Chromium - Cr(III) is the dominant oxidation state. Cr(III) readily sorbs to mineral surfaces as the pH increases. Cr (VI) however, is weakly sorbing and decreases sorption as the pH increases. Kd for Cr (III) is relatively high while the Kd for Cr (VI) is relatively low. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-17 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Manganese - Manganese is predominantly present as Mn2+. Sorption of Mn(II) is generally weak and yields low Kd values. Manganese bearing soil minerals could occur given sufficiently high manganese concentrations and high pH/EH conditions which may play a role on controlling the movement of manganese in the subsurface. Cobalt - The dominant cobalt species predicted by the PHREEQC model is Co2+. Redox potential exhibits relatively little influence on Co2+. Overall, cobalt is expected to exhibit minimal transport in these systems (high Kd) relative to more mobile species. Selenium – The geochemical behavior of selenium is highly dependent on the EH of the groundwater. The PHREEQC model predictions show Se(IV) as the dominant species under approximately neutral pH conditions but the fraction of Se(VI) increases with increasing pH and EH. Overall the range of Kd values predicted by PHREEQC agrees with the values determined experimentally from batch sorption tests. Vanadium - Vanadium can exist in multiple oxidation states including V(III), V(IV), and V(V) under the groundwater conditions at the site. The majority of vanadium is expected to exist as pentavalent V(V) which exhibits moderate sorption. Predicted Kd values are highly dependent on the pH of the groundwater. 13.3 Groundwater to Surface Water Pathway Evaluation Regulation 2L requires that groundwater discharge will not possess contaminant concentrations that would result in violations of standards for surface waters contained in 2B .0200. Hyco Lake is the main surface water body located near the Roxboro ash basins. However, as stated in Section 9.0, the Roxboro ash basins are located in former stream valleys that receive groundwater recharge from upland areas to the southeast (WAB) and to the east-southeast (EAB) and from surface water runoff from the upland areas. Surface water runoff and rainfall infiltration at the ash basins are primarily directed to the WAB effluent discharge canal, via natural and man-made storm water conveyances, with discharge to the heated water discharge pond. Surface water runoff to the EAB extension impoundment from upland areas to the east-southeast is conveyed to the cooling water intake canal via the EAB effluent discharge canal. Groundwater from the ash basins flow north and west toward the Plant water features (heated water discharge pond, cooling tower intake pond and the cooling water intake canal). Discharge from 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 13-18 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx the plant water features ultimately discharge to Hyco through NPDES Outfall 003. Therefore, surface water and groundwater from the EAB, WAB and related conveyances do not directly discharge to surface waters regulated by 2B .0200. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 14.0 SITE ASSESSMENT RESULTS 14.1 Nature and Extent of Contamination The site assessment described in the CSA presents the results of investigations required by CAMA and 2L regulations. Ash basin pore water was determined to be a source of impact to groundwater. The site assessment investigated the Site hydrogeology, determined the direction of groundwater flow from the ash basins, and determined the horizontal and vertical extent of impacts to groundwater and soil sufficient to proceed with preparation of a CAP. Constituents of Interest COIs in groundwater identified as being associated with the Roxboro Plant ash basins include antimony, boron, chromium, hexavalent chromium, cobalt, iron, manganese, molybdenum, pH, selenium, strontium, sulfate, TDS, uranium and vanadium. Groundwater COIs migrate laterally and vertically into and through regolith, the regolith/bedrock transition zone, shallow bedrock and deep bedrock. Regolith at the Roxboro Site is generally thin and unsaturated. The regolith/bedrock transition zone, where saturated, and shallow bedrock fractures contain the first occurrence of groundwater. Constituent migration in groundwater occurs at variable rates depending on constituent sorption properties and geochemical conditions (e.g., redox state, pH, etc.). Some COIs, such as boron, readily solubilize and migrate with minimal retention. In contrast, some COIs such as arsenic readily adsorb to aquifer materials, do not readily solubilize, and thus are relatively immobile. Hydrogeologic Conditions Site hydrogeologic conditions were evaluated by installing and sampling groundwater monitoring wells and piezometers; conducting in-situ hydraulic tests; sampling soil for physical and chemical testing; and sampling surface water, AOW, and sediment samples. Monitoring wells were completed in each hydrostratigraphic unit. The groundwater flow system serves to store and provide a means for groundwater movement. The porosity of the regolith is largely controlled by pore space (primary porosity); whereas, in bedrock, the effective porosity is largely secondary and controlled by the number, size, and interconnection of fractures. The nature of groundwater flow across the Site is based on the character and configuration of the ash basins relative to specific Site features such as manmade and natural drainage features, engineered drains, streams, and lakes; hydraulic boundary conditions; and subsurface media properties. The majority of groundwater flow across the Site flows through the transition zone and upper bedrock. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx The EAB and WAB occupy former stream valleys. The position, geometry, topography, and hydrogeologic character of the ash basins, the former stream valleys to the Hyco River in which the basins were constructed, and Hyco Lake are the primary influences on groundwater flow and constituent transport at the Site. The former natural drainage features generally trend southeast to northwest across the site. The ash basins are separated by a northwest-southeast trending topographic ridge. Groundwater flow across the site is generally from upland areas south and southeast (recharge areas) toward Hyco Lake which is situated to the north/northwest. Localized areas of groundwater discharge to plant water features occur from the two ash basins and the topographic ridge separating the basins. There are few substantive differences in water level among wells completed in the different flow zones across the Site (shallow/surficial, transition zone, bedrock), and lateral groundwater movement predominates over vertical movement. The vertical gradients are near equilibrium across the Site except near the ash basin dams and the discharge canals, indicating that there is no distinct horizontal confining layer beneath the Roxboro site. The horizontal gradients, hydraulic conductivity, and AOW velocities indicate that most of the groundwater transport occurs through the transition zone and bedrock, as most of the regolith encountered is largely unsaturated. Groundwater flow directions and the overall morphology of the potentiometric surface vary little from “dry” to “wet” seasons. Water levels do fluctuate up and down with significantly increased or decreased precipitation, but the general groundwater flow directions do not change due to seasonal changes in precipitation. Generally, upward vertical gradients predominate on the north side of the Plant, including the ash basin areas, while downward (recharge) gradients are more prevalent in the southern and eastern portions of the property into the former stream valleys. Horizontal and Vertical Extent of Impact As stated in Section 11.0, the groundwater plume is defined as any location (in three- dimensional space) where groundwater quality is impacted by the ash basins. Naturally occurring groundwater contains varying concentrations of a number of constituents (e.g., alkalinity, aluminum, magnesium, sodium, zinc, etc.). Concentrations greater than the current PTBVs in groundwater do not necessarily demonstrate distribution of groundwater that has been impacted by the ash basins. As additional background data becomes available, the variability will be better defined. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx At Roxboro, boron, sulfate and TDS are key indicators of CCR impacts in groundwater and are detected at concentrations greater than the 2L values downgradient of the ash basins. WAB – Boron, sulfate and TDS are detected greater than 2L in bedrock monitoring wells underlying the ash basin and in downgradient transition zone wells. Boron was not detected above background levels in the downgradient bedrock wells; however, sulfate and TDS were detected above 2L in one downgradient bedrock well. The heated water discharge pond lies immediately adjacent to the WAB downgradient monitoring wells. CCR constituents are generally not detected in groundwater upgradient of the WAB, discharge canal and the extension impoundment with the exception of two wells screened in deeper bedrock fractures southwest of the ash basin. Assessment of the area further to the southwest and upgradient of this area in similar deep fracture zones indicates background conditions. EAB – CCR constituents including boron, sulfate and TDS are detected above 2L in the bedrock monitoring wells underlying the ash basin and in several downgradient saprolite/transition zone and bedrock monitoring wells, including wells downgradient and proximal to the gypsum storage area adjacent to the cooling water intake canal. No CCR constituents are detected upgradient of the EAB, discharge canal and the extension impoundment. 14.2 Maximum COC Concentrations Changes in COI concentrations over time are included as time-series graphs (Figures 14-1 through 14-42). The maximum historical detected COI concentrations in groundwater for ash pore water or wells directly beneath the EAB, WAB and non-ash basin groundwater are included below. Also listed is the range of PBTVs for the surficial/transition zone, and bedrock flow units: EAB Antimony – Ash Basin: 6.09 µg/L (ABMW-07); Outside Basin: 1.67 µg/L (MW- 23BR); PBTV range: Not Detected in background samples. Boron - Ash Basin: 40,500 µg/L (ABMW-04); Outside Basin: 5,350 µg/L (GMW- 08); PBTV range: Not Detected in background samples. Chromium – Ash Basin: 10 µg/L (ABMW-04BR); Outside Basin: 824 µg/L (GMW- 07); PBTV range: 3.61µg/L – 24.1 µg/L. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Chromium (hexavalent) – Ash Basin: 10.5 µg/L (ABMW-04); Outside Basin: 3.8 µg/L (GPMW-02D); PBTV range: 0.19 µg/L – 16.1 µg/L. The Ash Basin value is suspect since the highest total chromium value at this location was 2.56 µg/L. The Outside Basin value is questionable since GPMW-02D is associated with both the Gypsum Storage Area and EAB. Cobalt – Ash Basin: 6.45 µg/L (ABMW-04); Outside Basin: 13.6 µg/L (MW-22D); PBTV range: Not detected (transition zone) – 6.4 µg/L. Iron – Ash Basin: 58,400 µg/L (ABMW-04); Outside Basin: 88,100 µg/L (GPMW- 02D); PBTV range: 1,173 µg/L – 4,227 µg/L. The Outside Basin value related to GPMW-02D is likely an artifact of natural degradation of remnant organic material in the former low-lying topographic low associated with the Gypsum Storage Area. Manganese – Ash Basin: 9,190 µg/L (ABMW-04); Outside Basin: 5,670 µg/L (GPMW-02D); PBTV range: 405 µg/L – 1,198 µg/L. The Outside Basin value is questionable because GPMW-02D is associated with both the Gypsum Storage Area and EAB. Molybdenum – Ash Basin: 1,690 µg/L (ABMW-07); Outside Basin: 18 µg/L (MW- 17BR); PBTV range: 4.17 µg/L – 35.2 µg/L. pH - Ash Basin: 6.6 SU (ABMW-06BR) – 9.6 SU (ABMW-07); Outside Basin: 5.4 SU (MW-22D) – 12.9 SU (MW-23BR); PBTV range: 6.3 – 8.3 SU. Selenium – Ash Basin: 1.82 µg/L (ABMW-04); Outside Basin: 416 µg/L (MW- 22D); PBTV range: 1 µg/L – 1.78 µg/L. Strontium - Ash Basin: 13,600 µg/L (ABMW-06); Outside Basin: 6,320 µg/L (MW- 23BR); PBTV range: 232 µg/L – 760 µg/L. Sulfate – Ash Basin: 2,200 mg/L (ABMW-04); Outside Basin: 1,720 mg/L (GMW- 10); PBTV range: 37 mg/L – 73.5 mg/L. TDS – Ash Basin: 3,800 mg/L (ABMW-04); Outside Basin: 2,400 mg/L (MW- 03BR); PBTV range: 530 mg/L – 540 mg/L. Uranium – Ash Basin: 0.0341 µg/mL (ABMW-04); Outside Basin: 0.0436 µg/mL (MW-03BR); PBTV range: 0.00324 µg/mL – 0.00516 µg/mL Vanadium – Ash Basin: 19.1 µg/L (ABMW-07): Outside Basin: 25.4 µg/L (CW- 01); PBTV range: 2.49 µg/L – 30.2 µg/L.. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx WAB Antimony – Ash Basin: 7.07 µg/L (ABMW-01); Outside Basin: 2.85 µg/L (MW- 04BR); PBTV range: Not Detected in background samples. Boron - Ash Basin: 12,900 µg/L (ABMW-01); Outside Basin: 957 µg/L (MW-05D); PBTV range: Not Detected in background samples with the exception of BG- 1BRLR at 101 µg/L. Chromium – Ash Basin: 69.7 µg/L (ABMW-03BRL); Outside Basin: 29.6 µg/L (CW-04); PBTV range: 3.61µg/L – 24.1 µg/L. Chromium (hexavalent) – Ash Basin: 5.5 µg/L (ABMW-02); Outside Basin: 7.1 µg/L (MW-02BR); PBTV range: 0.19 µg/L – 16.1 µg/L. Cobalt – Ash Basin: 755 µg/L (ABMW-03BR); Outside Basin: 5.27 µg/L (MW- 02BR); PBTV range: Not detected (transition zone) – 6.4 µg/L. Iron – Ash Basin: 310,000 µg/L (ABMW-03); Outside Basin: 24,500 µg/L (MW- 02BR); PBTV range: 1,173 µg/L – 4,227 µg/L. Manganese – Ash Basin: 3,000 µg/L (ABMW-03BR); Outside Basin: 1,870 µg/L (MW-02BR); PBTV range: 405 µg/L – 1,198 µg/L. Molybdenum – Ash Basin: 2,540 µg/L (ABMW-01); Outside Basin: 71.1 µg/L (BG-1BRLR); PBTV range: 4.17 µg/L – 35.2 µg/L. pH - Ash Basin: 3.2 SU (ABMW-03) – 12.1 SU (ABMW-02BR); Outside Basin: 5.4 SU (MW-02) – 9.7 SU (MW-04BR); PBTV range: 6.3 – 8.3 SU. Selenium – Ash Basin: 9.6 µg/L (ABMW-01); Outside Basin: 11.2 µg/L (MW-01); PBTV range: 1 µg/L – 1.78 µg/L. Strontium - Ash Basin: 2,740 µg/L (ABMW-02BR); Outside Basin: 1,010 µg/L (BG-1BRLR); PBTV range: 232 µg/L – 760 µg/L. Sulfate – Ash Basin: 3,400 mg/L (ABMW-03BR); Outside Basin: 873 mg/L (CW- 05); PBTV range: 37 mg/L – 73.5 mg/L. TDS – Ash Basin: 4,300 mg/L (ABMW-03BR); Outside Basin: 1,510 mg/L (CW- 05); PBTV range: 530 mg/L – 540 mg/L. Uranium – Ash Basin: 0.00212 µg/mL (ABMW-03BR); Outside Basin: 0.0385 µg/mL (BG-1BRLR); PBTV range: 0.00324 µg/mL – 0.00516 µg/mL. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Vanadium – Ash Basin: 107 µg/L (ABMW-01): Outside Basin: 41.5 µg/L (CW-05); PBTV range: 2.49 µg/L – 30.2 µg/L. 14.3 Contaminant Migration and Potentially Affected Receptors Contaminant Migration Assessment results indicate that groundwater impacts from ash pore water is limited to beneath the ash basins and downgradient in the areas between the ash basins and the internal plant water features (the heated water discharge pond, the cooling tower pond, cooling tower intake pond, and the cooling water intake canal). The pore water in the ash basins is the source of constituents for groundwater impacted above 2L/IMAC or PBTVs in the vicinity of the ash basins. Pore water analytical results are compared to 2L and/or IMAC for reference purposes only. The ash basins are permitted wastewater systems; therefore, comparison of pore water within the wastewater treatment residuals (ash) to 2B or 2L/IMAC is not required. Gradients measured within the ash basins support the interpretation that ash pore water mixes with shallow/surficial groundwater and migrates downward into the transition zone. Continued vertical migration of groundwater downgradient of the ash basin is also evidenced by detected constituent concentrations. Ash basin constituents become dissolved in groundwater that flows in response to hydraulic gradients. Groundwater migrates under diffuse flow conditions in the aquifer in the direction of the prevailing gradient. As constituents enter the transition zone and fractured bedrock flow systems, the rate of constituent transport has the potential to increase owing to the higher transmissive nature of those flow zones. Groundwater flow is the primary mechanism for migration of constituents to the environment. The hydrogeologic characteristics of the ash basin environment are the primary control mechanisms on groundwater flow and constituent transport. The stream valley in which the ash basins were constructed is a distinct slope-aquifer system in which flow of groundwater into the ash basins and out of the ash basins is restricted to the local flow regime. At Roxboro, groundwater movement in the bedrock flow zone is due primarily to secondary porosity represented by fractures in the bedrock. Primary (matrix) porosity is negligible; therefore, it is not technically appropriate to calculate groundwater velocity using effective porosity values. Bedrock fractures encountered at Roxboro tend to be isolated with low interconnectivity. Groundwater flow in bedrock fractures is anisotropic and difficult to predict, and velocities change as groundwater moves 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx between factures of varying orientations, gradients, pressure, and size. However, the direction of groundwater flow toward a discharge zone will be consistent. COIs migrate laterally and vertically into and through regolith, transition zone, and shallow and deeper bedrock. Constituent migration in groundwater occurs at variable rates depending on constituent sorption properties and geochemical conditions (e.g., redox state, pH, etc.). Some COIs, such as boron, readily solubilize and migrate with minimal retention. In contrast, some COIs such as arsenic readily adsorb to aquifer materials, do not readily solubilize, and thus are relatively immobile. Figures 14-43 to 14-69 graphically depict the most recent valid COI groundwater analytical concentrations for monitoring wells. The figures are colored-coded to visually depict whether analytical concentrations seem to be increasing, decreasing, stable, or a trend could not be determined. The vast majority of figures show concentrations for most COIs are stable, with a few notable exceptions. Figure 14-45 shows concentrations of boron potentially increasing along the plume centerline within the ash pore water wells in the WAB (ABMW-1 and ABMW-2) and the EAB (ABMW-5). For boron, concentrations seem to be increasing in monitoring well ABMW-7BR screened in the bedrock under the EAB and downgradient wells, MW-22D and MW- 22BR. For sulfate, concentrations seem to be increasing in ash pore and in transition zone and bedrock wells downgradient of the ash basins (Figure 14-63). COIs in groundwater identified as being associated with the WAB and EAB, impoundments, and effluent discharge canals include antimony, boron, chromium, hexavalent chromium, cobalt, iron, manganese, molybdenum, pH, selenium, strontium, sulfate, TDS, uranium and vanadium. The most recent concentrations of COIs in soil, sediment, surface waters, AOWs, and groundwater are provided on Figures 14-70 through 14-75. Potentially Affected Receptors The human health and ecological risk assessment was performed in 2016 as a component of the CAP, Part 2 (SynTerra, 2016a), concluding that no unacceptable risks to humans resulted from hypothetical exposure to constituents detected in the ash basin area. Based on review and analysis of groundwater and surface water data collected since completing the human health and ecological risk assessment in 2016, there is no evidence of potential risks to humans and wildlife at the Roxboro Site. Water Supply Wells Results from private water supply wells did not indicate human health risks to off-site residents potentially exposed to groundwater associated with the ash basins. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx No public or private drinking water wells, supply wells or wellhead protection areas were found to be located downgradient of the ash basins. Private water supply wells are located to the east and southeast on Dunnaway Road, The Johnson Road and Archie Clayton Road and to the south on Daisy Thompson Road and Semora Road (NC Highway 57). Two public water supply wells (Woodland Elementary School) are located to the southwest along Semora Road. Some of the wells are within a one-half-mile radius of the site and others are outside of one-half-mile. NCDEQ coordinated sampling of private water supply wells in 2015. A review of the analytical data for the private and public water supply wells indicated several constituents (iron, manganese, and vanadium) were detected above 2L/IMAC; though the detected concentrations are below statistically derived background concentrations and not attributable to the ash basins. The private and school wells are located upgradient of the Roxboro Plant ash basins. Concentrations of analyzed constituents exceeded the respective PBTVs for a number of private water supply wells; however, these data should be interpreted with caution for the reasons described below: Well construction, equipment, and materials, such as pumps and casings, may influence analytical results. There is very limited information available about the sampled wells. It is likely the wells were constructed with metal casings and piping that will influence sample water quality. Groundwater geochemistry in fractured bedrock aquifers can be quite variable and the background data set is very limited. The geologic conditions affecting the water supply wells will vary from the site background wells. A numerical capture zone analysis for the Roxboro Site was conducted to evaluate potential impact of upgradient water supply pumping wells. The analysis indicated that capture zones from water supply wells are limited to the immediate vicinity of the well head and do not extend toward the ash basins. None of the particle tracks originating in the ash basins moved into the well capture zones. The geochemical signature of groundwater from the private wells was compared with the signature of groundwater from the source areas using Piper diagrams. The geochemical nature of groundwater from the 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 14-9 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx sampled private wells is very different from ash pore water and from groundwater beneath the basin. It is concluded that there is no impact to the private water supply wells that are located upgradient from the EAB and WAB. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 15.0 CONCLUSIONS AND RECOMMENDATIONS A discussion of preliminary corrective action alternatives that may be appropriate to consider during the updated CAP development are presented in this section. 15.1 Overview of Site Conditions at Specific Source Areas CCR material and pore water in the ash basins were determined to be a source of impact to groundwater. Boron, sulfate and TDS are key indicators of CCR impacts in groundwater and are detected at concentrations greater than the 2L associated with the ash basins. For the WAB, boron, sulfate, and TDS are detected greater than 2L in bedrock monitoring wells underlying the ash basin and in downgradient transition zone wells. Boron was not detected above background levels in the downgradient bedrock wells; however, sulfate and TDS were detected above 2L in one downgradient bedrock well. CCR constituents are generally not detected in groundwater upgradient of the WAB, discharge canal and the extension impoundment with the exception of two wells screened in deeper bedrock fractures southwest of the ash basin. Assessment of the area further to the southwest and upgradient of this area in similar deep fracture zones indicates background conditions. For the EAB, boron, sulfate, and TDS are detected above 2L in the bedrock monitoring wells underlying the ash basin and in several downgradient saprolite/transition zone and bedrock monitoring wells, including wells downgradient and proximal to the gypsum storage area adjacent to the cooling water intake canal. No CCR constituents are detected upgradient of the EAB, discharge canal and the extension impoundment. 15.2 Revised Site Conceptual Model Site Conceptual Models (SCMs) are developed to be a representation of what is known or suspected about a site with respect to contamination sources, release mechanisms, transport, and fate of those contaminants. SCMs can be a written and/or be a graphic presentation of site conditions to reflect the current understanding of the site, identify data gaps, and be updated as new information is collected throughout the project. SCMs can be utilized to develop understanding of the different aspects of site conditions, such as a hydrogeologic conceptual site model, to help understand the site hydrogeologic condition affecting groundwater. SCMs can also be used in a risk assessment to understand contaminant migration and pathways to receptors. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx In the initial site conceptual hydrogeologic model presented in the Work Plan dated December 30, 2014, the geological and hydrogeological features influencing the movement, chemical, and physical characteristics of contaminants were related to the Piedmont hydrogeologic system present at the site. A hydrogeological site conceptual model was developed from data generated during previous assessments, existing groundwater monitoring data, and CSA activities. The Roxboro Plant utilizes two ash basins (surface impoundments), the EAB and the WAB, for the management of CCR material generated from the Plant’s historic coal combustion. Assessment results indicate the thickness of CCR in the EAB is approximately 55 to 80 feet and in the WAB is approximately 80 feet with residual CCR present in the related extension impoundments and effluent discharge canals. Assessment findings determined that CCR accumulated in the ash basins is the primary source of impact to groundwater. Leached CCR constituents present in soil directly underlying the ash basins and localized areas downgradient of the ash basins potentially act as secondary sources to groundwater impacts. The EAB and WAB occupy former stream valleys. Each stream valley in which the ash basins were constructed is a distinct slope-aquifer system in which flow of groundwater into and out of the ash basins is restricted to the local flow regime. Groundwater from the ash basins flow north and west toward the Plant water features (heated water discharge pond, cooling tower intake pond and the cooling water intake canal). Recharge areas at the site are located in upland areas to the east and the south. Site-specific groundwater constituents of interest (COIs) were developed by evaluating groundwater sampling results with respect to 2L/IMAC and PBTVs, and additional regulatory input/requirements. The distribution of constituents in relation to each ash basin, co-occurrence with CCR indicator constituents such as boron, and likely migration directions based on groundwater flow direction were considered in determination of groundwater COIs. Wells monitoring the bedrock flow unit were installed beneath the ash basins. Wells completed in the bedrock zone beneath the WAB and EAB have PBTV and 2L/IMAC exceedances for boron, cobalt, iron, manganese, sulfate, TDS and vanadium. Boron is a key indicator of CCR groundwater impacts. Sulfate and TDS also indicate impact. For the WAB, boron, sulfate and TDS are detected greater than 2L in downgradient transition zone wells. Boron was not detected above background levels in the downgradient bedrock wells; however, sulfate and TDS were detected above 2L in one downgradient bedrock well. For the EAB, CCR constituents including boron, 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx sulfate and TDS are detected above 2L in several downgradient saprolite/transition zone and bedrock monitoring wells, including wells downgradient and proximal to the gypsum storage area adjacent to the cooling water intake canal. CCR constituents are generally not detected in groundwater upgradient of the WAB, discharge canal and the extension impoundment with the exception of two wells screened in deeper bedrock fractures southwest of the ash basin. Assessment of the area further to the southwest and upgradient of this area in similar deep fracture zones indicates background conditions. No CCR constituents are detected upgradient of the EAB, discharge canal and the extension impoundment. Water in the WAB extension impoundment and the effluent discharge canal is subject to NPDES discharge permit requirements associated with Outfall 002. Water in the heated water discharge pond, which also receives surface water from toe drains of the WAB main dam and AOW locations, is subject to NPDES discharge permit requirements via Outfall #003 and is not considered waters of the state. Water in the EAB extension impoundment and effluent discharge canal, which included water from AOW locations, is part of the EAB and is not considered waters of the state. However, the water in the EAB discharge canal does discharge to the cooling water intake canal. As previously discussed, NCDEQ is considering the applicable mechanism to provide coverage for this area in the renewed NPDES permit. The SCM will continue to be refined following evaluation of the completed groundwater models to be presented in the CAP and additional information obtained in subsequent data collection activities. 15.3 Interim Monitoring Program An Effectiveness Monitoring Program (EMP) is required by CAMA §130A-309.209 (b)(1)e. The EMP for the Roxboro Plant is anticipated to begin once the basin closure and groundwater CAP have been implemented. In the interim, an IMP has been developed at the direction of NCDEQ. The IMP is designed to monitor near-term groundwater quality changes. The CAP, and a proposed EMP, will be submitted at a future date; therefore, this section presents details for the IMP only. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx IMP Implementation 15.3.1 An IMP has been implemented in accordance with NCDEQ correspondence (NCDEQ, May 1, 2017) that provided an approved “Revised Roxboro Steam Electric Plant Interim Monitoring Plan.” Sampling will be conducted quarterly until approval of the CAP or as otherwise directed by NCDEQ. Groundwater samples will be collected using low-flow sampling techniques in accordance with the Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater Assessment Program, North Carolina, June 10, 2015 (Appendix G) conditionally approved by NCDEQ in a June 11, 2015 email with an attachment summarizing their approval conditions. Samples will be analyzed by a North Carolina certified laboratory for the parameters listed in Table 15-1. The table includes targeted minimum detection limits for each listed constituent. Analytical parameters and detection limits for each media were selected so the results could be used to evaluate the effectiveness of a future remedy, conditions within the aquifer that may influence the effectiveness of the remedy, and migration of constituents related to the ash basin. Laboratory detection limits for each constituent are targeted to be at or below applicable regulatory values (i.e., 2L, IMAC, or 2B). Monitoring wells and surface water locations that will be sampled for radionuclides and monitored as part of the IMP are included in Table 15-2. IMP Reporting 15.3.2 Currently, data summary reports – comprised of analytical results received during the previous month – are submitted to NCDEQ by the 15th of the month. In addition, NCDEQ (May 1, 2017) directed that an annual IMP report be submitted by April 30 of the following year of data collection. The reports shall include materials that provide “an integrated, comprehensive interpretation of site conditions and plume status.” The initial report was to be submitted to NCDEQ no later than April 30, 2018; however, the October 19, 2017 correspondence provides that the required date for an annual monitoring report will be extended to a date in 2018 to be determined later. 15.4 Preliminary Evaluation of Corrective Action Alternatives Closure of the ash basin is required by 2024 under CAMA (Intermediate Risk). The updated risk assessment (Section 12.0) has determined there is no imminent risk to human health or the environment due to groundwater, surface water, or sediment impacts. Groundwater in the bedrock flow unit used for private drinking water supply in the area is not impacted. In the ash basin locations where soil samples could be 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx collected, analytical results indicate a few, limited detections of COIs above PBTVs. If needed, groundwater and surface water can be remediated over time using a variety of approaches and technologies. Groundwater modeling has indicated closure by excavation compared to a cap-in-place closure does not substantively accelerate groundwater clean-up. For basin closure, ash dewatering and reduction of infiltrating water will have the greatest positive impact on groundwater and surface water quality downgradient of the ash basin. Closure design can augment an overall groundwater corrective action scenario including cap in place which will be evaluated in the CAP. Therefore, a “low” groundwater risk classification is recommended. This preliminary evaluation of corrective action alternatives is included to provide insight into the groundwater update CAP preparation process. This preliminary evaluation is based on data available and the current understanding of regulatory requirements for the Site. It is assumed a source control measure of either implementation of an engineered capping system (cap-in-place) to minimize infiltration, or excavation, or a combination of the two, will be designed following completion of the risk classification process. The groundwater currently presents minimal, if any, risk to receptors. A low risk classification and closure via a cap-in- place scenario are considered viable. Potential groundwater remedial strategies are being considered as part of the closure design. CAP Preparation Process 15.4.1 The CAP preparation process is designed to identify, describe, evaluate, and select remediation alternatives with the objective of bringing groundwater quality to levels that meet applicable standards, to the extent that the objective is economically and technologically feasible, in accordance with 2L .0106 Corrective Action. Sections (h), (i), and (j) regarding CAP preparation read as follows: (h) Corrective action plans for restoration of groundwater quality, submitted pursuant to Paragraphs (c), (d), and (e) of this Rule shall include: (1) A description of the proposed corrective action and reasons for its selection; (2) Specific plans, including engineering details where applicable, for restoring groundwater quality; (3) A schedule for the implementation and operation of the proposed plan; and (4) A monitoring plan for evaluating the effectiveness of the proposed corrective action and the movement of the contaminant plume. (i) In the evaluation of corrective action plans, the Secretary shall consider the extent of any violations, the extent of any threat to human health or safety, the extent of damage or potential adverse impact to the environment, technology available to 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx accomplish restoration, the potential for degradation of the contaminants in the environment, the time and costs estimated to achieve groundwater quality restoration, and the public and economic benefits to be derived from groundwater quality restoration. (j) A corrective action plan prepared pursuant to Paragraphs (c), (d), or (e) of this Rule shall be implemented using a remedial technology demonstrated to provide the most effective means, taking into consideration geological and hydrogeological conditions at the contaminated site, for restoration of groundwater quality to the level of the standards. Corrective action plans prepared pursuant to Paragraphs (c) or (e) of this Rule may request an exception as provided in Paragraphs (k), (l), (m), (r), and (s) of this Rule. To meet these requirements and to provide a comprehensive evaluation, it is anticipated that the CAP will include: Corrective action objectives and evaluation criteria Technology assessment Formulation of remedial action alternatives Analysis, modeling, selection, and description of selected remedial action alternative(s) Conceptual design elements, including identification of pre-design testing such as pilot studies Monitoring requirements and performance metrics Implementation schedule The following Site conditions significantly limit the effectiveness of a number of possible technologies. The COIs in groundwater flow primarily through the transition zone and upper fractured bedrock. The formations are very heterogeneous with anisotropic flow conditions. The preliminary screening of potential groundwater corrective action follows: Source control by capping in place or excavation, and monitored natural attenuation, will be vital components to the CAP. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Groundwater migration barriers. The lateral extent potentially required, along with the depth and heterogeneity of the transition zone and bedrock, may limit the feasibility of this technology. In-situ chemical immobilization. This technology has not been demonstrated to be effective for the primary COI, boron. It may be applicable for other COIs. Permeable reactive barrier. Similar to in-situ chemical immobilization, permeable reactive barrier technology has not been demonstrated to be effective for boron; however, if may be applicable for other COIs. Groundwater extraction. Given Site conditions, preliminary screening of potentially applicable technologies indicates that some form of groundwater extraction could potentially be a viable choice as a key element of groundwater corrective action in combination with source control and monitored natural attenuation (MNA). However, limitations of pump and treat, including desorption, should be considered. Further analysis is required and will be addressed in the updated CSA. Potentially viable options will be further evaluated in the CAP with updated fate and transport and geochemical modeling. Summary 15.4.2 This preliminary evaluation of corrective action alternatives is intended to provide insight into the updated CAP preparation process, as outlined in 2L. It is based on data available and the current regulatory requirements for the site. It addresses potentially applicable technologies and remedial alternatives. Potential approaches are based on the currently available information about site hydrogeology and COIs. In general, three hydrogeologic units or zones of groundwater flow can be described for the site: shallow/surficial zone, transition zone, and bedrock flow zone. The site COIs include a list of common coal ash related metals - such as boron. If required, potentially applicable technologies to supplement source control and MNA include groundwater extraction technologies such as conventional vertical wells, angle-drilled and horizontal wells. All of these extraction technologies could be augmented with fracturing of the bedrock formation. Migration barriers, insitu chemical immobilization, and permeable reactive barriers are also identified as potentially applicable remedial action alternatives. In the event that 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 15-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx extracted groundwater may require treatment prior to discharge, several water treatment technologies for the relevant COIs would be evaluated, including pH adjustment, metals precipitation, ion exchange, permeable membranes, and adsorption technologies. The CAP will further evaluate basin closure options to reduce the potential impacts to human health or the environment; short- and long-term effectiveness, implementability, and potential for attenuation of contaminants; time and cost to achieve restoration; public and economic benefits; and compliance with applicable laws and regulations. The CAP evaluation process will be used to determine which approach, or combination of approaches, will be most effective. Modeling will also be used to evaluate the various options prior to selection. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-1 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx 16.0 REFERENCES ASTM. (2014). E1689-95: Standard Guide for Developing Conceptual Site Models for Contaminated Sites. ATSDR. (2012). Toxicological profile for Manganese. Atlanta: U.S. Department of Health and Human Services, Public Health Service. Ayotte, J. D., Gronbert, J. M., & Apodaca, L. E. (2011). Trace Elements and Radon in Groundwater Across the United States 1992-2003. U.S. Geological Survey Scientific Investigations Report 2011-5059. Bowman, J. D. (2010). The Aaron Formation: Evidence for a New Lithotectonic Unit in Carolina. North Central North Carolina. North Carolina State University. Raleigh, North Carolina: unpublished M.S. thesis. Bowman, J., Hibbard, J., & Miller, B. (2013, November 8). The Virgilina sequence redefined, north-central North Carolina, in One Arc, Two Arcs, Old Arc, New Arc – The Carolina Terrane in Central North Carolina. Carolina Geological Society. Butler, J., & Secor, D. (1991). The Central Piedmont, in the Geology of the Carolinas. In J. W. Horton, & V. A. Zullo (Eds.), The geology of the Carolinas: Carolina Geological Society fiftieth anniversary volume (1 ed.). Knoxville, TN: Univ. of Tennessee Press. Carpenter, A. P. (1976). Metallic mineral deposits of the Carolina Slate Belt. North Carolina. (84). Chapman, M. J., Cravotta, III, C. A., Szabo, Z., & Lindsey, B. D. (2013). Naturally occurring contaminants in the Piedmont and Blue Ridge crystalline-rock aquifers and Piedmont Early Mesozoic basin siliciclastic-rock aquifers, eastern United States, 1994– 2008. United States Geological Survey, Water Resources Investigations Report 00- 4286. Cox, J., Lundquist, G., Przyjazny, A., & Schmulbach, C. (1978). Leaching of boron from coal ash. Environmental Science & Technology, 12(6), 722-723. Cunningham, W. L., & Daniel, C. L. (2001). Investigation of ground-water availability and quality in Orange County, North Carolina. North Carolina: U.S. Dept. of the Interior, U.S. Geological Survey ; Branch of Information Services. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-2 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Daniel, C. C., & Dahlen, P. R. (2002). Preliminary hydrogeologic assessment and study plan for a regional ground-water resource investigation of the Blue Ridge and Piedmont provinces of North Carolina. Raleigh, North Carolina: U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 02–4105. Dennis, A. J., & Shervais, J. W. (1991). Arc rifting of the Carolina terrane in northwestern South Carolina. (Vol. 45). Geological Society of America. Dennis, A. J., & Shervais, J. W. (1996). The Carolina terrane in northwestern South Carolina: Insights into the development of an evolving island arc. Avalonian And Related Peri-Gondwana Terranes Of The Circum-North Atlantic, Special Paper 304, 237-156. (D. Nance, & M. Thompson, Eds.) Boulder, Colorado: Geological Society of America. Dewberry. (2016). Mayo Steam Station Phase II Potable Water Programmatic Evaluation - October 27, 2016. Roxboro, NC. Dewberry. (2016). Potable water programmatic evaluation - October . Dicken, C., Nicholson, S., Horton, J., Foose, M., & Mueller, J. (2007). Preliminary integrated geologic map databases for the United States – Alabama, Florida, Georgia, Mississippi, North Carolina, And South Carolina. Version 1.1. Dudas, M. (1981). Long-term leachability of selected elements from fly ash. Environmental Science & Technology, 15(7), 840-843. Duke Energy. (2017). Retrieved October 20, 2017, from Duke Energy: https://www.duke-energy.com/_/media/pdfs/our-company/ash- management/duke-energy-ash-metrics.pdf?la=en Dzombak, D., & Morel, M. (1990). Surface complexation modeling: Hydrous ferric oxide. New York, NY: Wiley-Interscience Publication. EPRI. (1993). Physical and Hydraulic Properties of Fly Ash and Other By-Products From Coal Combustion. Palo Alto, CA. TR-101999: Electric Power Research Institute. EPRI. (1994). A Field and Laboratory Study of Solute Release from Sluices Fly Ash. Palo Alta, CA: Electric Power Research Institute. EPRI. (1995). Coal ash disposal manual: Third edition. Palo Alto, CA: Electric Power Research Institute, TR-104137. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-3 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx EPRI. (2005). Chemical Constituents in Coal Combustion Product. Palo Alto, CA: Electric Power Research Institute. Technical Report 1005258. EPRI. (2005). Chemical Constituents in Coal Combustion Product Leachate: Boron. Palo Alto: Electric Power Research Institute. EPRI. (2006). Groundwater Remediation of Inorganic Constituents at Coal Combustion Product Management Site: Overview of Technologies, Focusing on Permeable Reactive Barriers. Palo Alto, CA: Electric Power Research Institute; 1012584. EPRI. (2006). Groundwater Remediation of Inorganic Constituents at Coal Combustion Product Management Site: Overview of Technologies, Focusing on Permeable Reactive Barriers. Palo Alto, CA: Electric Power Research Institute. EPRI. (2008a). Chemical Profile: Chromium. Electric Power Research Institute, Palo Alto, CA, and Hydro One Networks, Inc., Toronto, Canada: 2008. 1014622. EPRI. (2008a). Toxics Release Inventory. Chemical Profile: Arsenic. Palo Alto, CA: Electric Power Research Institute. EPRI. (2008b). Toxics Release Inventory. Chemical Profile: Selenium. Palo Alto, CA: Electric Power Research Institute. EPRI. (2008b). Toxics Release Inventory. Chemical Profile: Barium. Palo Alto, CA: Electric Power Research Institute. EPRI. (2008c). Chemical Profile: Chromium. Electric Power Research Institute, Palo Alto, CA, and Hydro One Networks, Inc., Toronto, Canada: 2008. 1014622. EPRI. (2010). Comparison of coal combustion products to other common materials. Palo Alto, CA: Electric Power Research Institute, TR-1020556. Finkelman, R. (1995). Modes of occurrence of environmentally-sensitive trace elements in coal. In D. Swaine, & F. Goodzarzi, Environmental Aspects of Trace Elements in Coal (pp. 24-50). Kluwer Academic Publishers. Fleet, M. (1965). Preliminary investigations into the sorption of boron by clay minerals. Clay Minerals, 6(1): 3-16. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-4 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Ford, R. G., W., R. T., & Puls, R. W. (2007). Monitored Natural Attenuation of Inorganic Contaminants in Ground Water. Cincinnati, OH: National Risk Management Research Laboratory, U.S. EPA. Freeze, R. A., & Cherry, J. A. (1979). Groundwater. Englewood Cliffs, NJ: Prentice-Hall. Freeze, R., & Witherspoon, P. (1967). Theoretical analysis of regional groundwater flow. 2. Effect of water-table configuration and subsurface permeability variation. Water Resources Research, 3(2): 623-624. Fruchter, J. S., Rai, D., & Zachara, J. M. (1990). Identification of solubility-controlling solid phases in a large fly ash field lysimeter. Environmental Science and Technology, 24(8), 1173-1179. Gillespie, E. (2013). Characterizing the Sources and Variability of Manganese in Well Water of the North Carolina Piedmont. International Conference on the Biogeochemistry of Trace Elements. Glover, L., & Sinha, A. (1973). The Virgilina deformation, a late precambrian to early cambrian (?) orogenic event in the central piedmont of Virginia and North Carolina. American Journal of Science, 273(A): 234-251. Goldberg, S. (1997). Reactions of boron with soils. Plant and Soil, 193: 35-48. Goldberg, S., Forster, H., Lesch, S., & Heick, E. (1996). Influence of anion competition on boron adsorption by clays and soils. Soil Science, 161 (2): 99-103. Goodarzi, F., Huggins, F., & Sanei, H. (2008). Assessment of elements, speciation of As, Cr, Ni and emitted Hg for a Canadian power plant burning bituminous coal. International Journal of Coal Geology, 74(1): 1-12. Haley & Aldrich. (2015). Evaluation of NC DEQ private well data, volumes 1 and 2. Harned, D., & Daniel, C. (1992). The transition zone between bedrock and regolith: Conduit for contamination? In Daniel, C.C., White, R., and Stone, P., eds., Groundwater in the Piedmont, Proceedings of a Conference on Ground Water in the Piedmont of the Eastern United States, Charlotte, N.C., Oct. 16-18, 1989. Clemson, SC: Clemson University (336-348). 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-5 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Harris, C., & Glover, L. (1985). The virgilina deformation: Implications of stratigraphic correlation in the Caroina Slate Belt. Carolina Geological Society, Guidebook for 1985 Annual Meeting. Harris, C., & Glover, L. (1988). The regional extent of the ca. 600 Ma Virgilina deformation: Implications for stratigraphic correlation in the Carolina terrane. The Geological Society of America, 100(2): 200-217. HDR and SynTerra. (2017). Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities. HDR Engineering, Inc. and SynTerra Corporation. Heath, R. (1980). Basic elements of groundwater hydrology with reference to conditions in North Carolina. United States Geological Survey, Open-File Report: 80-44. Hem, J. D. (1985). Study and Interpretation of the Chemical Characteristics of Natural Water. United States Geological Survey Water-Supply Paper 2254. Hem, J. D. (1985). Study and Interpretation of the Chemical Characteristics of Natural Water. United States Geological Survey, Water-Supply Paper 2254. Hibbard, J., Shell, G., Bradley, P., & Wortman, G. (1998). The Hyco shear zone in North Carolina and southern Virginia; implications for the Piedmont Zone-Carolina Zone boundary in the Southern Appalachians. American Journal of Science, 298(2): 85-107. Hibbard, J., Stoddard, E., Secor, D., & Dennis, A. (2002). The Carolina zone: Overview of Neoproterozoic to early Paleozoic Peri-Gondwanan terranes along the eastern flank of the southern Appalachians. Earth Science Reviews, 57(3): 299-339. Hurlbut, C. S. (1971). Dana's manual of mineralogy (18 ed.). John Wiley & Sons Inc. Izquierdo, M., & Querol, X. (2012). Leaching behaviour of elements from coal combustion fly ash : An overview. International Journal of Coal Geology, 94. 54-56. Johnson, A. (1967). Specific yield : compilation of specific yields for various materials (Vols. 1662-D). Washington: Geological Survey water-supply paper. Jones, K. B., & Ruppert, L. F. (2017, February). Leaching of trace elements from Pittsburgh coal mill rejects compared with coal combustion products from a coal- 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-6 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx fired power plant in Ohio, USA. United States Geological Survey Bulletin, 171, 130- 141. Jurgens, B., McMahon, P., Chapelle, F., & Eberts, S. (2009). An Excel® workbook for identifying Redox processes in ground water. Retrieved from U.S. Geologic Survey Open-File Report. 2009-1004: Available at: https://pubs.usgs.gov/of/2009/1004/ Karamalidis, A., & Dzombak, D. (2010). Surface Complexation Modeling: Gibbsite. Hobboken, NJ: John WIley and Sons, Inc. Kunesh, C. (1978). Barium. (M. Grayson, & D. Eckroth, Eds.) Kirk-Othmer encyclopedia of chemical technology, Vol. 3, pp. 457–463. Laney, F. (1917). The geology and ore deposits of the Virgilina district of Virginia and North Carolina. Virginia Geological Survey and the North Carolina Geological and Economic Survey, Bulletin, (XIV). LeGrand, H. (1988). Region 21, Piedmont and Blue Ridge. In: J. Black, J. Rosenshein, P. Seaber, ed. Geological Society of America, 0-2, (pp. 201-207). LeGrand, H. (1989). A conceptual model of ground water settings in the Piedmont region, in groundwater in the Piedmont. In: Daniel C., White, R., Stone, P., ed. Ground Water in the Piedmont of the Eastern United States (pp. 317-327). Clemson, SC: Clemson University. LeGrand, H. (2004). A master conceptual model for hydrogeological site characterization in the Piedmont and Mountain Region of North Carolina: A guidance manual. North Carolina Department of Environment and Natural Resources, Division of Water Quality, Groundwater Section, Raleigh, NC, 55. Martell, A. E., & Smith, R. M. (2001). Critical Stability Constants. Gaithersburg, MD: National Institute of Standards. Martell, A. E., & Smith, R. M. (2001). Critical Stability Constants. National Institute of Standards. Martens, D. A. (2002). Selenium. In E. o. Science. New York: Marcel Dekker. Miao, Z., Brusseau, M. L., Carroll, K. C., & others. (2012). Environ Geochem Health. 34:539. https://doi.org/10.1007/s10653-011-9423-1. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-7 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Miner, S. (1969). Air pollution aspects of barium and its compounds. Bethesda: Litton Systems. NCDENR. (2015). Classifications and water quality standards applicable to the surface waters of North Carolina (pending approval of 2007-2014 Triennial review). Raleigh: North Carolina Administrative Code Title 15A, Subchapter 02B. NCDHHS. (2010). Concentration of Iron Detected in NC Private Well Water, Average 1998-2010 and Average 2010. Well Water & Health. University of North Carolina Superfund Research Program. NCDHHS. (2010). Concentration of Selenium Detected in NC Private Well Water, Average 1998-2010 and Average 2010. Well Water & Health. University of North Carolina Superfund Research Program. NCDHHS. (2010a). Concentration of Barium Detected in NC Private Well Water, Average 1998-2010 and Average 2010. Well Water & Health. University of North Carolina Superfund Research Program. NCDHHS. (2010b). Concentration of Iron Detected in NC Private Well Water, Average 1998-2010 and Average 2010. Well Water & Health. University of North Carolina Superfund Research Program. NCDNRCD. (1985). Geological map of North Carolina. North Carolina Geological Survey, Division of Land Resources. Niswonger, R., Panday, S., & Motomu, I. (2011). MODFLOW-NWT, A Newton formulation for MODFLOW-2005. In Techniques and Methods 6-A37 (pp. 1-44). Reston, Virginia: Chapter 37 of Section A, Book 6: U.S. Geological Survey. NOAA. (2013). Regional climate trends and scenarios for the U.S. national climate assessment. Part 2. Climate of the southeast U.S. Washington, D.C.: National Oceanic and Atmospheric Administration - U.S. Department of Commerce. Parker, R. (1967). Chapter D. composition of the Earth's crust. Geological survey paper 440-D. In Data of Geochemistry. 6th ed. Washington, D.C.: U.S. Government Printing Office, 1967. Polizzotto, M., Amoozegar, A., Austin, R., Bolich, R., Bradley, P., Duckworth, O., et al. (2015). Surface and Subsurface Properties Regulating Manganese Contamination of 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-8 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx Groundwater in the North Carolina Piedmont. Water Resources Research Institute of The University of North Carolina. Pollock, J., Hibbard, J., & Sylvester, P. (2010). Depositional and tectonic setting of the Neoproterozoic-early Paleozoic rocks of the Virgilina sequence and Albemarle Group, North Carolilna. In R. Tollo, M. Batholomew, J. Hibbard, & P. Karabinos, From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region (pp. 1-34). Geological Society of America, 206. Robson, S. (1993). Techniques for estimating specific yield and specific retention from grain- size data and geophysical logs from clastic bedrock aquifers. U.S. Geological Survey, Water-Resources Investigation Report 93-4198, 19p. Rogers, J. (2006). Chapter 2 - The Carolina Slate Belt. In V. Steponaitis, J. Irwin, T. McReynolds, & C. Moore, Stone Quarries and Sourcing in the Carolina Slate Belt (pp. 10-15). Chapel Hill, NC: University of North Carolina Research Laboratories of Archaeology, Research Report 25. Ruhl, L., Vengosh, A., Dwyer, G. S., Hsu-Kim, H., Schwartz, G., Romanski, A., et al. (2012, September 30). The Impact of Coal Combustion Residue Effluent on Water Resources: A North Carolina Example. Environmental Science and Technology, 12226-12233. Samson, S., Hibbard, J., & Wortman, G. (1995). Nd isotopic evidence for juvenile crust in the Carolina terrance, southern Appalachians. Contributions to Mineralogy and Petrology; 121(2), 171-184. Schmidt, H. (1962). Equilibrium diagrams for minerals at low temperature and pressure. The Geological Club of Harvard, 199. Smith, L. A., Means, J. L., Chen, A., & others. (1995). Remedial Options for Metals- Contaminated Sites. Boca Raton, FL: Lewis Publishers. Smith, S. M. (2016). National Geochemical Database. Retrieved October 20, 2017, from USGS: https://pubs.usgs.gov/of/1997/ofr-97-0492/ State Climate Office. (2017). Retrieved October 2017, from www.nc- climate.ncsu.edu/climate/ncclimate.html SynTerra. (2014a). Drinking water well and receptor survey - Mayo Steam Electric Plant - September 2014. Roxboro, NC. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-9 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx SynTerra. (2014a). Drinking water well and receptor survey - Roxboro Steam Electric Plant - September 2014. Semora, NC. SynTerra. (2014b). Supplement to drinking water well and receptor survey - Mayo Steam Electric Plant - November 2014. Roxboro, NC. SynTerra. (2014b). Supplement to drinking water well and receptor survey - Roxboro Steam Electric Plant - November 2014. Semora, NC. SynTerra. (2014c). Proposed groundwater assessment work plan for Mayo Steam Electric Plant (Revision 1) - December 30, 2014. Roxboro, NC. SynTerra. (2014c). Proposed groundwater assessment work plan for Roxboro Steam Electric Plant (Revision 1) - December 30, 2014. SynTerra. (2015a). Comprehensive site assessment report - Mayo Steam Electric Plant - September 2, 2015. Roxboro, NC. SynTerra. (2015a). Comprehensive site assessment report, Roxboro Steam Electric Plant - September 2, 2015. Semora, NC. SynTerra. (2015b). Corrective action plan - part 1: Mayo Steam Electric Plant - December 1, 2015. Roxboro, NC. SynTerra. (2015b). Corrective action plan, part 1 - Roxboro Steam Electric Plant - December 1, 2015. Semora, NC. SynTerra. (2016a). Corrective action plan - part 2: Mayo Steam Electric Plant - February 29, 2016. Roxboro, NC. SynTerra. (2016a). Corrective action plan, part 2 - Roxboro Steam Electric Plant - February 29, 2016. Semora, NC. SynTerra. (2016b). Ash basin extension impoundments and discharge canals assessment report - Roxboro Steam Electric Plant - May 2017. Semora, NC. SynTerra. (2016b). Comprehensive site assessment, supplement 1 - Mayo Steam Electric Plant - July 7, 2016. Roxboro, NC. SynTerra. (2016c). Comprehensive site assessment, supplement 1 - Roxboro Steam Electric Plant - August 1, 2016. Semora, NC. 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-10 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx SynTerra. (2016c). Update to drinking water well and receptor survey - Mayo Steam Electric Plant - September 2016. Roxboro, NC. SynTerra. (2016d). Update to drinking water well and receptor survey - Roxboro Steam Electric Plant - September 2016. Semora, NC. Urey, H., & Mem, R. (1953). On the concentration of certain elements at the earth's surface. In Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (pp. 281-292). The Royal Society Publishing, 219(1138). USEPA. (1997). Ecological risk assessment guidance for superfund: Process for designing and conducting ecological risk assessments. Edison, NJ: U.S. Environmental Protection Agency, Environmental Response Team. EPA 540-R-97-006. USEPA. (2003). Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on Sulfate. Washington: U.S. Environmental Protection Agency, EPA 822- R-03-007. USEPA. (2007). Monitored natural attenuation of inorganic contaminants in ground water technical basis for assessment, volume I, October 2007. United States Environmental Protection Agency. EPA/600/R-07/139. USEPA. (2012). Sulfate in Drinking Water. Retrieved from URL: http://water.epa.gov/drink/contaminants/unregulated/sulfate.cfm USEPA. (2012). Sulfate in Drinking Water. Retrieved from EPA: http://water.epa.gov/drink/contaminants/unregulated/sulfate.cfm USEPA. (2015). Disposal of Coal Combustion Residual From Electric Utilities: Final Rule - April 17, 2015. Code of Federal Register, Vol. 80(No. 74). USEPA. (2017a). National recommended water quality criteria for aquatic life. Retrieved October 20, 2017, from EPA: https://www.epa.gov/wqc/national-recommended- water-quality-criteria-aquatic-life-criteria-table#altable USEPA. (2017a). Watersense. Retrieved October 2017, from EPA: http://www.epa.gov/watersense/pubs/indoor.html USEPA. (2017b). Secondary Drinking Water Regulations: Guidance for Nuisance Chemicals. Retrieved October 2017, from EPA: 2017 Comprehensive Site Assessment Update October 2017 Roxboro Steam Electric Plant SynTerra Page 16-11 P:\Duke Energy Progress.1026\107. Roxboro Ash Basin GW Assessment Plan\CSA Update Oct 2017\Roxboro CSA October 2017 Report.docx https://www.epa.gov/dwstandardsregulations/secondary-drinking-water- standards-guidance-nuisance-chemicals USEPA. (2017c). National recommended water quality criteria for aquatic life. Retrieved October 20, 2017, from EPA: https://www.epa.gov/wqc/national-recommended- water-quality-criteria-aquatic-life-criteria-table#altable USEPA. (2017c). Watersense. Retrieved October 2017, from EPA: http://www.epa.gov/watersense/pubs/indoor.html USEPA. (October 2007). Monitored natural attenuation of inorganic contaminants in ground water technical basis for assessment, volume I. United States Environmental Protection Agency. EPA/600/R-07/139. USGS. (1973). United States Mineral Resources. United States Government Printing Office. WHO. (1996). Guidelines for drinking-water quality: Health criteria and other supporting information. (2nd, Ed.) Vol. 2. Wilkins, J., Shell, G., & Hibbard, J. (1995). Geologic contrasts across the central Piedmont suture in north-central North Carolina. Field Trip Guide for the 1995 Carolina Geological Society Annual Meeting: Geology of the Western Part of the Carolina Terrance in Northwestern South Carolina, 37, pp. 25-32. Wortman, G., Samson, S., & Hibbard, J. (2000). Precise U-Pb Zircon constraints on the earliest magmatic history of the Carolina Terrance. The Journal of Geology, 108(3), 321-338. Zhang, D. (2013). Ultra-supercritical coal power plants: Materials, technologies and optimisation. Sawston, Cambridge, UK: Woodhead Publishing.