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Home My WebLink AboutNC0024406_2017 Final CSA Updated_201710312017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 11.3 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 were not evaluated. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx WORK PERFORMED BY OTHERS • HDR Engineering, Inc. (HDR) of the Carolinas prepared the reports referenced herein under contract to Duke Energy. • The reports were sealed by licensed geologists or engineers as required by the North Carolina Board for Licensing of Geologists or Board of Examiners for Engineers and Surveyors. • The evaluations of hydrogeologic conditions and other information provided in this updated Comprehensive Site Assessment (CSA) are based in part on the work contained in the HDR documents and on sampling activities performed by Pace Analytical Services after the submittal of the HDR documents. The evaluations described in this paragraph meet requirements detailed in 15A NCAC 02L .0106(g). • SynTerra relied on information from the HDR reports as being correct. SynTerra has proofread boring logs; monitoring well installation records; and data tables presenting chemical, physical, and hydraulic properties of ash, soil, rock, groundwater, and surface water, and has made corrections where mistakes were found. SynTerra did not perform additional validation activities concerning the HDR reports. SynTerra has found no reason to question geological interpretations of site hydrostratigraphic information and other information in the HDR reports. • The seal of the licensed geologist for this CSA applies to activities conducted and interpretations derived after the HDR reports were submitted. This submittal relies on the professional work performed by HDR and references that work. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx EXECUTIVE SUMMARY ES.1 Source Information Duke Energy Carolinas, LLC (Duke Energy) owns and operates the Belews Creek Steam Station (BCSS), which is located on Belews Reservoir in Belews Creek, Stokes County, North Carolina. The 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. 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. BCSS began operation in 1974 as a coal-fired generating station and currently operates two coal-fired units. Prior to 1984, BCSS has disposed of coal combustion residuals (CCR) from the coal combustion process in the ash basin located across Pine Hall Road to the west-northwest of the station. The ability to sluice fly ash to the ash basin is available but is limited to certain situations (i.e. unit startup/shutdown, equipment maintenance and service) but is primarily disposed in permitted landfills located at the site. The station’s ash basin consists of a single cell impounded by an earthen main dam located on the north end of the ash basin and an embankment dam located in the northeast portion of the basin. The ash basin main dam was constructed from 1970 to 1972 and is located approximately 3,200 feet northwest of the BCSS powerhouse. The North Carolina Department of Environmental Quality (NCDEQ) Division of Water Resources (DWR) currently permits discharge from the ash basin under the National Pollutant Discharge Elimination System (NPDES) Permit NC0024406. The discharge from the ash basin is through a concrete discharge tower located in the northwest portion of the ash basin. The concrete discharge tower drains through a 21-inch inside diameter high-density polyethylene (HDPE) conduit for approximately 1,600 feet and then discharges into a concrete flume box. From the flume box the discharge is routed through the designated effluent channel that flows northwest to the Dan River. The ash basin originally discharged to Belews Reservoir through a concrete discharge tower located at the northeast end of the ash basin. Assessment results indicate the thickness of CCR in the ash basin ranges from a few feet to approximately 66 feet. Assessment findings determined that CCR accumulated in the ash basin is the primary source of impact to groundwater. The inferred general extent of constituent migration in groundwater based on evaluation of concentrations greater than both site background and groundwater quality standards is shown on 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 has not conducted emergency responses because groundwater impacts from the ash basin do not present an imminent and substantial threat to the environment requiring emergency response. A Settlement Agreement between NCDEQ and Duke Energy signed on September 29, 2015, requires accelerated groundwater remediation to be implemented at sites that demonstrate off-site groundwater impacts. Assessment information indicates the potential for off-site groundwater impact northwest of the BCSS ash basin toward an undeveloped 2.23-acre parcel (hereafter referred to as Parcel A) not owned by Duke Energy. A groundwater extraction system, located between the ash basin and the southeast side of Parcel A, is designed and will be installed to control groundwater flow from the ash basin prior to migration toward Parcel A. The 100% Basis of Design (BOD) report was submitted to NCDEQ on September 1, 2017. In preparation for the ash basin closure, a dry bottom ash handling system, new retention basins, and wastewater treatment systems are being designed and constructed. The reduction of inflows to the basin is an initial abatement measure. ES.3 Receptor Information In accordance with NCDEQ direction, CSA receptor survey activities include 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. ES.3.1 Public Water Supply Wells One public water supply well was identified within a 0.5-mile radius of the ash basin compliance boundary. It is located at the Withers Chapel United Methodist Church (UMC) located offsite approximately 1,750 feet (0.3 miles) northeast of the BCSS ash basin, in an area hydraulically upgradient from groundwater flow associated with the ash basin. ES.3.2 Private Water Supply Wells Approximately 50 private water supply wells (including irrigation wells and unused wells) were identified within a 0.5-mile radius of the ash basin compliance boundary. The private water supply wells are located hydraulically upgradient or sidegradient from the ash basin. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Private water supply wells are assumed to be open borehole bedrock wells. The water supply well data does not reflect characteristic ash basin constituents. Constituent concentrations in bedrock groundwater directly downgradient of the ash basin are less than 2L with the exception of manganese, which appears to be due to geochemical conditions. The water chemistry signature of the water supply wells is similar to the background bedrock wells at the site. Although several water supply well concentrations reported are greater than the site specific provisional background threshold values (PBTVs), the concentrations are within the background concentration range for similar Piedmont geologic settings. ES.3.3 Surface Water Bodies Several surface water bodies flow from the topographic divide along Middleton Loop Road toward the Dan River within a 0.5-mile radius of the ash basin. Belews Reservoir is also located within the 0.5-mile receptor survey radius. Surface water intakes include two from Belews Reservoir for BCSS plant operations and for water trucks at the Craig Road Landfill. A backup intake is located on the Dan River. The surface water intakes are for non-potable uses. ES.3.4 Human and Ecological Receptors A baseline human health and ecological risk assessment was performed in 2016 as a component of Corrective Action Plan (CAP) 2 (HDR, 2016). Water supply well data collected since the risk assessment was completed indicates several wells located to the west-southwest and northeast of the ash basin had concentrations of chromium, cobalt, iron, manganese, vanadium that exceeded their respective water quality standards, however all reported concentrations were less than their respective EPA risk-based tap water screening levels. As previously noted, the wells are located upgradient or a sufficient distance sidegradient to not be impacted by groundwater migration from the ash basin. The ecological risk assessment considered surface water data associated with Belews Reservoir beyond the extent of constituent migration in groundwater from the ash basin. As such, the findings for the Belews Reservoir do not imply adverse effects associated with groundwater to surface water migration from the ash basin. This exposure route will be further evaluated through direct surface water sampling and predictive modeling as part of the CAP. To date, 2B and EPA water quality criteria have not been exceeded in waters proximal to areas of groundwater impact. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx ES.3.5 Land Use The area surrounding BCSS generally consists of residential properties, farm land, undeveloped land, and Belews Reservoir. Properties located within the 0.5- mile radius of the BCSS ash basin compliance boundary generally consist of residential properties located to the southwest and residential farm land northeast, north, and west. Duke Energy property is located to the north, northwest, south, and east with Belews Reservoir to the south and east. 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 basin. ES.4.1 Background Concentration Determinations Naturally occurring background concentrations, Provisional Background Threshold Values (PBTVs), were determined using statistical analysis for both soil and groundwater at the site. Statistical determinations of 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 network consists of wells installed within three flow layers – shallow, deep (transition zone), and fractured bedrock. Background datasets were used to statistically determine naturally occurring concentrations of inorganic constituents in soil and groundwater. 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 2L/IMACs and PBTVs, and additional regulatory input/requirements. The distribution of constituents in relation to the ash basin, co-occurrence with CCR indicator constituents such as boron, and likely migration directions based on groundwater flow direction are considered in determination of groundwater COIs. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx The following list of groundwater COIs has been developed for BCSS: Antimony Iron Arsenic Manganese Barium Molybdenum Beryllium pH Boron Selenium Cadmium Strontium Chloride Sulfate Chromium (hexavalent) TDS (Total Dissolved Solids) Chromium (total) Thallium Cobalt Vanadium Boron is a CCR-derived constituent in groundwater and is detected at concentrations greater than the 2L standard beneath and downgradient of the ash basin. Boron is not detected in background groundwater. The horizontal extent of boron concentrations greater than 2L approximates the leading edge of the CCR-derived plume from the source areas (Figure ES-1). Boron is detected in groundwater at concentrations greater than 2L in the shallow flow layer primarily north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance boundary. In the deep flow layer boron concentrations greater than 2L occur beneath the ash basin and the Pine Hall Road Landfill, north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance boundary. Boron concentrations greater than 2L are also reported west of the Structural Fill, which is south of the ash basin and topographic divide along Pine Hall Road. The boron south of Pine Hall Road appears to be related to the Structural Fill where an assessment is ongoing. Boron concentrations less than 2L have been reported in the bedrock flow layer with the exception of a grout contaminated well beneath the ash basin main dam. Beryllium, chloride, chromium, cobalt, manganese, and thallium are also constituents detected in groundwater greater than background and 2L/IMAC near or beyond the compliance boundary. The interpreted extent of beryllium concentrations greater than background and the IMAC is beyond the compliance boundary in the shallow and deep flow layers. Beryllium was not reported at a concentration greater than the IMAC in the bedrock flow layer. The interpreted extent of chloride concentrations greater than 2L at and beyond the compliance 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx boundary is in the shallow and deep flow layers. Chloride was not reported at a concentration greater than 2L in the bedrock flow layer. The interpreted extent of chromium concentrations greater than 2L at and beyond the compliance boundary is in the shallow and deep flow layers. Chromium was not reported at a concentration greater than 2L in the bedrock flow layer. The interpreted extent of cobalt concentrations greater than IMAC at and beyond the compliance boundary is in the shallow flow layer only. Cobalt exceedances were not reported in the deep and bedrock flow layers. The interpreted extent of manganese concentrations greater than 2L at and beyond the compliance boundary is in the shallow, deep, and bedrock flow layers. The interpreted extent of thallium concentrations greater than the IMAC at and beyond the compliance boundary is in the shallow and deep flow layers. Thallium was not reported at a concentration greater than 2L in the bedrock flow layer. The bedrock aquifer is generally the source of water for supply wells in the area. As outlined above, the bedrock aquifer has not been impacted by CCR constituent migration from the ash basin with the exception of a grout contaminated well beneath the ash basin main dam. The manganese concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. In ash basin locations where soil samples were collected beneath the ash, analytical results indicate arsenic and selenium concentrations greater than PBTVs and PSRGs for POG are present. Strontium was also reported in five of the soil samples collected beneath the ash basin at concentrations greater than the background concentration. There is no PSRG POG for strontium. No other COIs were detected in soil beneath the ash basin at concentrations greater than PBTVs or PSRG POGs. ES.4.3 Maximum Contaminant Concentrations (Source Information) The source areas at BCSS include CCR material in the ash basin including the former chemical pond and the Pine Hall Road Landfill. Ash pore water samples collected from wells installed within the ash basin and screened in the ash layer 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Soil samples collected below the ash/soil interface from locations within the ash basins indicate arsenic, selenium, and strontium reported at concentrations greater than their respective PSRG Protection of Groundwater (POG) and/or soil PBTV values. ES.4.4 Site Geology and Hydrogeology Based on the site investigation, the groundwater system in natural materials (soil, soil/saprolite, and bedrock) at the BCSS site is consistent with the regolith- fractured rock system and is an unconfined, connected aquifer system. Regolith is underlain by a transition zone (TZ) of weathered rock which transitions to competent bedrock. The groundwater system at the BCSS site is divided into three flow layers referred to in this report as the shallow, deep (TZ), and bedrock layers, so as to distinguish unique characteristics of the connected aquifer system. The shallow flow layer generally consists of surficial material such as soil and fill. The deep flow layer includes both saprolite and weathered rock, while the bedrock layer is competent bedrock with limited fractures. A topographic and hydrologic divide (highest topographic portion of the Site) is generally located along Pine Hall Road south of the ash basin. Groundwater flow contours developed from water level elevations measured in the shallow, deep and bedrock wells indicate groundwater flow from the ash basin is generally to the north and northwest toward the Dan River and to the east toward Belews Reservoir. ES.5 Conclusions and Recommendations The investigation described in the CSA presents the results of the assessments required by CAMA and 2L. The ash basin was determined to be a source of the groundwater contamination. The BCSS ash basin is currently designated as “Intermediate” risk under CAMA, requiring closure of the ash basin by 2024. However, groundwater and surface water quality data provide no indications of potential risk to human and wildlife receptors related to constituent migration through the groundwater pathway from the ash basin. These findings support a proposed “low” risk classification. Impacts to soil were determined to be limited to a shallow interval below the ash. Soil samples collected from below the ash basin exhibited concentrations greater than POG PSRGs and/or PBTVs for arsenic, selenium and strontium. Those shallow soil impacts are anticipated to be addressed through basin closure and the CAP. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Boron, beryllium, chloride, chromium, cobalt, manganese, and thallium are the primary constituents detected in groundwater greater than PBTVs and 2L/IMAC near or beyond the compliance boundary. The interpreted extent of exceedances are within the shallow and/or deep flow layers with the exception of manganese. The bedrock aquifer is generally the source of water for supply wells in the area. As outlined above, the bedrock aquifer has not been impacted by CCR constituent migration from the ash basin with the exception of a grout contaminated well beneath the ash basin main dam. The manganese concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. A preliminary evaluation of groundwater corrective action alternatives is included in this CSA to provide insight into the CAP preparation process. For BCSS, the primary source control (closure) methods anticipated to be evaluated in the CAP are: Dewater the ash within the basin 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 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 basin to groundwater will have the greatest positive impact on groundwater and surface water quality downgradient of the ash basin. 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 basin. Groundwater corrective action by monitored natural attenuation (MNA) is anticipated to be a remedy further evaluated in the CAP. As warranted, a number of viable groundwater remediation technologies such as phytoremediation, groundwater extraction, or hydraulic barriers may be evaluated based upon short-term and long-term effectiveness, feasibility, and 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ES-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 Belews Creek Steam Station SynTerra Page i P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.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-2 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-7 ES.5 CONCLUSIONS AND RECOMMENDATIONS ................................................ ES-7 1.0 INTRODUCTION ......................................................................................................... 1-1 Purpose of Comprehensive Site Assessment ........................................................ 1-1 1.1 Regulatory Background ........................................................................................... 1-2 1.2 Notice of Regulatory Requirements (NORR) ............................................... 1-2 1.2.1 Coal Ash Management Act Requirements .................................................... 1-3 1.2.2 Approach to Comprehensive Site Assessment ..................................................... 1-4 1.3 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 Technical Objectives ................................................................................................. 1-5 1.4 Previous Submittals .................................................................................................. 1-6 1.5 2.0 SITE HISTORY AND DESCRIPTION ..................................................................... 2-1 Site Description, Ownership and Use History ...................................................... 2-1 2.1 Geographic Setting, Surrounding Land Use, Surface Water Classification ..... 2-2 2.2 CAMA-related Source Areas ................................................................................... 2-4 2.3 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx TABLE OF CONTENTS CONTINUED SECTION PAGE Other Primary and Secondary Sources .................................................................. 2-5 2.4 Summary of Permitted Activities ........................................................................... 2-6 2.5 History of Site Groundwater Monitoring .............................................................. 2-8 2.6 Ash Basin ............................................................................................................ 2-8 2.6.1 Landfill Groundwater Monitoring ................................................................. 2-9 2.6.2 Ash Basin CAMA Monitoring ....................................................................... 2-10 2.6.3 Summary of Assessment Activities ...................................................................... 2-11 2.7 Summary of Initial Abatement, Source Removal or other Corrective Action 2-13 2.8 3.0 SOURCE CHARACTERISTICS ................................................................................. 3-1 Coal Combustion and Ash Handling System ....................................................... 3-1 3.1 General Physical and Chemical Properties of Ash .............................................. 3-2 3.2 Site-Specific Coal Ash Data ..................................................................................... 3-5 3.3 4.0 RECEPTOR INFORMATION ..................................................................................... 4-1 Summary of Receptor Survey Activities................................................................ 4-2 4.1 Summary of Receptor Survey Findings ................................................................. 4-3 4.2 Public Water Supply Wells .............................................................................. 4-4 4.2.1 Private Water Supply Wells ............................................................................ 4-4 4.2.2 Private and Public Well Water Sampling .............................................................. 4-5 4.3 Numerical Well Capture Zone Analysis ............................................................... 4-8 4.4 Surface Water Receptors .......................................................................................... 4-8 4.5 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY ............................................... 5-1 Regional Geology ...................................................................................................... 5-1 5.1 Regional Hydrogeology ........................................................................................... 5-2 5.2 6.0 SITE GEOLOGY AND HYDROGEOLOGY ............................................................ 6-1 Site Geology ............................................................................................................... 6-2 6.1 Soil Classification .............................................................................................. 6-2 6.1.1 Rock Lithology .................................................................................................. 6-4 6.1.2 Structural Geology ............................................................................................ 6-4 6.1.3 Soil and Rock Mineralogy and Chemistry .................................................... 6-5 6.1.4 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page iii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx TABLE OF CONTENTS CONTINUED SECTION PAGE Geologic Mapping ............................................................................................. 6-6 6.1.5 Effects of Geologic Structure on Groundwater Flow ................................... 6-7 6.1.6 Site Hydrogeology .................................................................................................... 6-7 6.2 Hydrostrographic Layer Development ......................................................... 6-7 6.2.1 Hydrostrographic Layer Properties ............................................................... 6-8 6.2.2 Groundwater Flow Direction .................................................................................. 6-9 6.3 Hydraulic Gradient ................................................................................................. 6-10 6.4 Hydraulic Conductivity ......................................................................................... 6-11 6.5 Groundwater Velocity ............................................................................................ 6-12 6.6 Contaminant Velocity ............................................................................................. 6-13 6.7 Slug Test and Aquifer Test Results....................................................................... 6-14 6.8 Fracture Trace Study Results (if applicable) ....................................................... 6-15 6.9 Methods ............................................................................................................ 6-15 6.9.1 Results ............................................................................................................... 6-16 6.9.2 7.0 SOIL SAMPLING RESULTS ...................................................................................... 7-1 Background Soil Data ............................................................................................... 7-1 7.1 Facility Soil Data ....................................................................................................... 7-2 7.2 8.0 SEDIMENT RESULTS ................................................................................................. 8-1 Sediment/Surface Soil Associated with AOWs .................................................... 8-1 8.1 Sediment in Major Water Bodies ............................................................................ 8-3 8.2 9.0 SURFACE WATER RESULTS .................................................................................... 9-5 Comparison of Exceedances to 2B Criteria ........................................................... 9-8 9.1 Discussion of Results for Constituents Without Established 2B ........................ 9-9 9.2 Discussion of Surface Water Results .................................................................... 9-12 9.3 10.0 GROUNDWATER SAMPLING RESULTS ............................................................ 10-1 Background Groundwater Concentrations ......................................................... 10-2 10.1 Background Dataset Statistical Analysis ..................................................... 10-4 10.1.1 Piper Diagrams (Comparison to Background) ........................................... 10-6 10.1.2 Downgradient Groundwater Concentrations ..................................................... 10-7 10.2 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page iv P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx TABLE OF CONTENTS CONTINUED SECTION PAGE Piper Diagrams (Comparison to Downgradient/ Separate Flow Regime)10-10.2.1 12 Site-Specific Exceedances (Groundwater COIs) ............................................... 10-13 10.3 Provisional Background Threshold Values (PBTVs) ............................... 10-13 10.3.1 Applicable Standards ................................................................................... 10-13 10.3.2 Additional Requirements ............................................................................. 10-14 10.3.3 BCSS Groundwater COIs ............................................................................. 10-15 10.3.4 Water Supply Well Groundwater Concentrations and Exceedances ............ 10-17 10.4 11.0 HYDROGEOLOGICAL INVESTIGATION .......................................................... 11-1 Plume Physical Characterization .......................................................................... 11-1 11.1 Plume Chemical Characterization ........................................................................ 11-4 11.2 Pending Investigations ......................................................................................... 11-25 11.3 12.0 RISK ASSESSMENT .................................................................................................. 12-1 Human Health Screening Summary .................................................................... 12-2 12.1 Ecological Screening Summary ............................................................................. 12-3 12.2 Private Well Receptor Assessment Update ......................................................... 12-3 12.3 Risk Assessment Update Summary ..................................................................... 12-5 12.4 13.0 GROUNDWATER MODELING RESULTS ........................................................... 13-1 Summary of Fate and Transport Model Results................................................. 13-2 13.1 Flow Model Construction .............................................................................. 13-3 13.1.1 Transport Model Construction ..................................................................... 13-7 13.1.2 Summary of Flow and Transport Modeling Results To Date .................. 13-9 13.1.3 Summary of Geochemical Model ....................................................................... 13-12 13.2 Model Construction ...................................................................................... 13-12 13.2.1 Summary of Geochemical Model Results To Date ................................... 13-16 13.2.2 Groundwater to Surface Water Pathway Evaluation ...................................... 13-16 13.3 14.0 SITE ASSESSMENT RESULTS ................................................................................ 14-1 Nature and Extent of Contamination ................................................................... 14-1 14.1 Maximum Constituent Concentrations ............................................................... 14-6 14.2 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page v P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx TABLE OF CONTENTS CONTINUED SECTION PAGE Contaminant Migration and Potentially Affected Receptors ........................... 14-7 14.3 15.0 CONCLUSIONS AND RECOMMENDATIONS ................................................. 15-1 Overview of Site Conditions at Specific Source Areas ...................................... 15-1 15.1 Revised Site Conceptual Model ............................................................................ 15-2 15.2 Interim Monitoring Program ................................................................................. 15-4 15.3 IMP Implementation ....................................................................................... 15-4 15.3.1 IMP Reporting ................................................................................................. 15-5 15.3.2 Preliminary Evaluation of Corrective Action Alternatives............................... 15-5 15.4 CAP Preparation Process ............................................................................... 15-6 15.4.1 Summary .......................................................................................................... 15-8 15.4.2 16.0 REFERENCES ............................................................................................................... 16-1 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page vi P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.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 Site Layout Map Figure 2-2 1951 Aerial Photograph Figure 2-3 1966 Aerial Photograph Figure 2-4 1971 Aerial Photograph Figure 2-5 1977 Aerial Photograph Figure 2-6 Site Features Map Figure 2-7 Belews Creek Plant Vicinity Map Figure 2-8 Pre-Ash Basin USGS Topo Map Figure 2-9 Surface Water Bodies Figure 2-10 Sample Location Map Figure 2-11 Belews Creek Steam Station Flow Schematic Diagram 3.0 Source Characteristics Figure 3-1 Photo of Fly Ash and Bottom Ash Figure 3-2 Elemental Composition for Bottom Ash, Fly Ash, Shale, and Volcanic Ash Figure 3-3 Coal Ash TCLP Leachate Concentration vs Regulatory Limits 4.0 Receptor Information Figure 4-1 USGS Map with Water Supply Wells Figure 4-2 Water Supply Well Locations Figure 4-3 Piper Diagram Water Supply Wells 5.0 Regional Geology and Hydrogeology Figure 5-1 Tectonostratigraphic Map of the Southern and Central Appalachians Figure 5-2 Regional Geologic Map Figure 5-3 Piedmont Slope-Aquifer System 6.0 Site Geology Figure 6-1 Site Geologic Map Figure 6-2 Site Cross Section Locations Figure 6-3 General Cross Section A-A' Figure 6-4 General Cross Section B-B' Figure 6-5 General Cross Section C-C' 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page vii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 6-6 Shallow Water Level Map April 2017 - Wet Season Figure 6-7 Shallow Water Level Map September 2016 - Dry Season Figure 6-8 Deep Water Level Map April 2017 - Wet Season Figure 6-9 Deep Water Level Map September 2016 - Dry Season Figure 6-10 Bedrock Water Level Map April 2017 - Wet Season Figure 6-11 Bedrock Water Level Map September 2016 - Dry Season Figure 6-12 Potential Vertical Gradient Between Shallow, Deep, and Bedrock Zones Figure 6-13 Topographic Lineaments and Rose Diagram Figure 6-14 Aerial Photography Lineaments and Rose Diagram 7.0 Soil Sampling Results Figure 7-1 Potential Secondary Source Soil Analytical Results 9.0 Surface Water Results Figure 9-1 Piper Diagram - AOWs Figure 9-2 Piper Diagram - Surface Water and Waste Water 10.0 Groundwater Sampling Results Figure 10-1 Piper Diagram - Shallow Groundwater Figure 10-2 Piper Diagram - Deep Groundwater Figure 10-3 Piper Diagram - Bedrock Groundwater Figure 10-4 Generalized Well Construction Diagram Figure 10-5 Isoconcentration Map - Antimony In Shallow Groundwater Figure 10-6 Isoconcentration Map - Antimony In Deep Groundwater Figure 10-7 Isoconcentration Map - Antimony In Bedrock Groundwater Figure 10-8 Isoconcentration Map - Arsenic In Shallow Groundwater Figure 10-9 Isoconcentration Map - Arsenic In Deep Groundwater Figure 10-10 Isoconcentration Map - Arsenic In Bedrock Groundwater Figure 10-11 Isoconcentration Map - Barium In Shallow Groundwater Figure 10-12 Isoconcentration Map - Barium In Deep Groundwater Figure 10-13 Isoconcentration Map - Barium In Bedrock Groundwater Figure 10-14 Isoconcentration Map - Beryllium In Shallow Groundwater Figure 10-15 Isoconcentration Map - Beryllium In Deep Groundwater Figure 10-16 Isoconcentration Map - Beryllium In Bedrock Groundwater Figure 10-17 Isoconcentration Map - Boron In Shallow Groundwater Figure 10-18 Isoconcentration Map - Boron In Deep Groundwater Figure 10-19 Isoconcentration Map - Boron In Bedrock Groundwater Figure 10-20 Isoconcentration Map - Cadmium In Shallow Groundwater Figure 10-21 Isoconcentration Map - Cadmium In Deep Groundwater 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page viii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 10-22 Isoconcentration Map - Cadmium In Bedrock Groundwater Figure 10-23 Isoconcentration Map - Chloride In Shallow Groundwater Figure 10-24 Isoconcentration Map - Chloride In Deep Groundwater Figure 10-25 Isoconcentration Map - Chloride In Bedrock Groundwater Figure 10-26 Isoconcentration Map - Chromium (VI) and Chromium (Total) In Shallow Groundwater Figure 10-27 Isoconcentration Map - Chromium (VI) and Chromium (Total) In Deep Groundwater Figure 10-28 Isoconcentration Map - Chromium (VI) and Chromium (Total) In Bedrock Groundwater Figure 10-29 Isoconcentration Map - Chromium (VI) In Shallow Groundwater Figure 10-30 Isoconcentration Map - Chromium (VI) In Deep Groundwater Figure 10-31 Isoconcentration Map - Chromium (VI) In Bedrock Groundwater Figure 10-32 Isoconcentration Map - Cobalt In Shallow Groundwater Figure 10-33 Isoconcentration Map - Cobalt In Deep Groundwater Figure 10-34 Isoconcentration Map - Cobalt In Bedrock Groundwater Figure 10-35 Isoconcentration Map - Iron In Shallow Groundwater Figure 10-36 Isoconcentration Map - Iron In Deep Groundwater Figure 10-37 Isoconcentration Map - Iron In Bedrock Groundwater Figure 10-38 Isoconcentration Map - Manganese In Shallow Groundwater Figure 10-39 Isoconcentration Map - Manganese In Deep Groundwater Figure 10-40 Isoconcentration Map - Manganese In Bedrock Groundwater Figure 10-41 Isoconcentration Map - Molybdenum In Shallow Groundwater Figure 10-42 Isoconcentration Map - Molybdenum In Deep Groundwater Figure 10-43 Isoconcentration Map - Molybdenum In Bedrock Groundwater Figure 10-44 Isoconcentration Map - Selenium In Shallow Groundwater Figure 10-45 Isoconcentration Map - Selenium In Deep Groundwater Figure 10-46 Isoconcentration Map - Selenium In Bedrock Groundwater Figure 10-47 Isoconcentration Map - Strontium In Shallow Groundwater Figure 10-48 Isoconcentration Map - Strontium In Deep Groundwater Figure 10-49 Isoconcentration Map - Strontium In Bedrock Groundwater Figure 10-50 Isoconcentration Map - Sulfate In Shallow Groundwater Figure 10-51 Isoconcentration Map - Sulfate In Deep Groundwater Figure 10-52 Isoconcentration Map - Sulfate In Bedrock Groundwater Figure 10-53 Isoconcentration Map - Total Dissolved Solids In Shallow Groundwater Figure 10-54 Isoconcentration Map - Total Dissolved Solids In Deep Groundwater 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page ix P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 10-55 Isoconcentration Map - Total Dissolved Solids In Bedrock Groundwater Figure 10-56 Isoconcentration Map - Thallium In Shallow Groundwater Figure 10-57 Isoconcentration Map - Thallium In Deep Groundwater Figure 10-58 Isoconcentration Map - Thallium In Bedrock Groundwater Figure 10-59 Isoconcentration Map - Vanadium In Shallow Groundwater Figure 10-60 Isoconcentration Map - Vanadium In Deep Groundwater Figure 10-61 Isoconcentration Map - Vanadium In Bedrock Groundwater Figure 10-62 Isoconcentration Map - pH In Shallow Groundwater Figure 10-63 Isoconcentration Map - pH In Deep Groundwater Figure 10-64 Isoconcentration Map - pH In Bedrock Groundwater 11.0 Hydrogeological Investigation Figure 11-1 COI vs. Distance- Antimony, Arsenic, Barium, Beryllium, Boron, Cadmium, Chloride Figure 11-2 COI vs. Distance- Chromium and Chromium (VI), Cobalt, Iron, Manganese, Molybdenum, Selenium, Strontium Figure 11-3 COI vs. Distance- Sulfate, Thallium, Total Dissolved Solids, Vanadium, pH Figure 11-4 Antimony Analytical Results - Cross Section A-A' Figure 11-5 Antimony Analytical Results - Cross Section B-B' Figure 11-6 Antimony Analytical Results - Cross Section C-C' Figure 11-7 Arsenic Analytical Results - Cross Section A-A' Figure 11-8 Arsenic Analytical Results - Cross Section B-B' Figure 11-9 Arsenic Analytical Results - Cross Section C-C' Figure 11-10 Barium Analytical Results - Cross Section A-A' Figure 11-11 Barium Analytical Results - Cross Section B-B' Figure 11-12 Barium Analytical Results - Cross Section C-C' Figure 11-13 Beryllium Analytical Results - Cross Section A-A' Figure 11-14 Beryllium Analytical Results - Cross Section B-B' Figure 11-15 Beryllium Analytical Results - Cross Section C-C' Figure 11-16 Boron Analytical Results - Cross Section A-A' Figure 11-17 Boron Analytical Results - Cross Section B-B' Figure 11-18 Boron Analytical Results - Cross Section C-C' Figure 11-19 Cadmium Analytical Results - Cross Section A-A' Figure 11-20 Cadmium Analytical Results - Cross Section B-B' Figure 11-21 Cadmium Analytical Results - Cross Section C-C' Figure 11-22 Chloride Analytical Results - Cross Section A-A' Figure 11-23 Chloride Analytical Results - Cross Section B-B' 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page x P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 11-24 Chloride Analytical Results - Cross Section C-C' Figure 11-25 Chromium (VI) Analytical Results - Cross Section A-A' Figure 11-26 Chromium (VI) Analytical Results - Cross Section B-B' Figure 11-27 Chromium (VI) Analytical Results - Cross Section C-C' Figure 11-28 Chromium Analytical Results - Cross Section A-A' Figure 11-29 Chromium Analytical Results - Cross Section B-B' Figure 11-30 Chromium Analytical Results - Cross Section C-C' Figure 11-31 Cobalt Analytical Results - Cross Section A-A' Figure 11-32 Cobalt Analytical Results - Cross Section B-B' Figure 11-33 Cobalt Analytical Results - Cross Section C-C' Figure 11-34 Iron Analytical Results - Cross Section A-A' Figure 11-35 Iron Analytical Results - Cross Section B-B' Figure 11-36 Iron Analytical Results - Cross Section C-C' Figure 11-37 Manganese Analytical Results - Cross Section A-A' Figure 11-38 Manganese Analytical Results - Cross Section B-B' Figure 11-39 Manganese Analytical Results - Cross Section C-C' Figure 11-40 Molybdenum Analytical Results - Cross Section A-A' Figure 11-41 Molybdenum Analytical Results - Cross Section B-B' Figure 11-42 Molybdenum Analytical Results - Cross Section C-C' Figure 11-43 pH Analytical Results - Cross Section A-A' Figure 11-44 pH Analytical Results - Cross Section B-B' Figure 11-45 pH Analytical Results - Cross Section C-C' Figure 11-46 Selenium Analytical Results - Cross Section A-A' Figure 11-47 Selenium Analytical Results - Cross Section B-B' Figure 11-48 Selenium Analytical Results - Cross Section C-C' Figure 11-49 Strontium Analytical Results - Cross Section A-A' Figure 11-50 Strontium Analytical Results - Cross Section B-B' Figure 11-51 Strontium Analytical Results - Cross Section C-C' Figure 11-52 Sulfate Analytical Results - Cross Section A-A' Figure 11-53 Sulfate Analytical Results - Cross Section B-B' Figure 11-54 Sulfate Analytical Results - Cross Section C-C' Figure 11-55 Thallium Analytical Results - Cross Section A-A' Figure 11-56 Thallium Analytical Results - Cross Section B-B' Figure 11-57 Thallium Analytical Results - Cross Section C-C' Figure 11-58 TDS Analytical Results - Cross Section A-A' Figure 11-59 TDS Analytical Results - Cross Section B-B' Figure 11-60 TDS Analytical Results - Cross Section C-C' Figure 11-61 Vanadium Analytical Results - Cross Section A-A' 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xi P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 11-62 Vanadium Analytical Results - Cross Section B-B' Figure 11-63 Vanadium Analytical Results - Cross Section C-C' Figure 11-64 Regional Groundwater Quality - Chloride Figure 11-65 Regional Groundwater Quality - pH Figure 11-66 Thallium Distribution in Soil 12.0 Screening-Level Risk Assessment Figure 12-1 Ecological Exposure Areas 14.0 Discussion - Assessment Results Figure 14-1 Time vs Concentration - Antimony in Shallow Zone Figure 14-2 Time vs Concentration - Antimony in Deep Zone Figure 14-3 Time vs Concentration - Antimony in Bedrock Zone Figure 14-4 Time vs Concentration - Antimony Pine Hall Road Landfill Figure 14-5 Time vs Concentration - Arsenic in Shallow Zone Figure 14-6 Time vs Concentration - Arsenic in Deep Zone Figure 14-7 Time vs Concentration - Arsenic in Bedrock Zone Figure 14-8 Time vs Concentration - Arsenic Pine Hall Road Landfill Figure 14-9 Time vs Concentration - Barium in Shallow Zone Figure 14-10 Time vs Concentration - Barium in Deep Zone Figure 14-11 Time vs Concentration - Barium in Bedrock Zone Figure 14-12 Time vs Concentration - Barium Pine Hall Road Landfill Figure 14-13 Time vs Concentration - Beryllium in Shallow Zone Figure 14-14 Time vs Concentration - Beryllium in Deep Zone Figure 14-15 Time vs Concentration - Beryllium in Bedrock Zone Figure 14-16 Time vs Concentration - Beryllium Pine Hall Road Landfill Figure 14-17 Time vs Concentration - Boron in Shallow Zone Figure 14-18 Time vs Concentration - Boron in Deep Zone Figure 14-19 Time vs Concentration - Boron in Bedrock Zone Figure 14-20 Time vs Concentration - Boron Pine Hall Road Landfill Figure 14-21 Time vs Concentration - Cadmium in Shallow Zone Figure 14-22 Time vs Concentration - Cadmium in Deep Zone Figure 14-23 Time vs Concentration - Cadmium in Bedrock Zone Figure 14-24 Time vs Concentration - Cadmium Pine Hall Road Landfill Figure 14-25 Time vs Concentration - Chloride in Shallow Zone Figure 14-26 Time vs Concentration - Chloride in Deep Zone Figure 14-27 Time vs Concentration - Chloride in Bedrock Zone Figure 14-28 Time vs Concentration - Chloride Pine Hall Road Landfill Figure 14-29 Time vs Concentration - Chromium and Chromium (VI) in Shallow Zone 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 14-30 Time vs Concentration - Chromium and Chromium (VI) in Deep Zone Figure 14-31 Time vs Concentration - Chromium and Chromium (VI) in Bedrock Zone Figure 14-32 Time vs Concentration - Chromium Pine Hall Landfill Figure 14-33 Time vs Concentration - Cobalt in Shallow Zone Figure 14-34 Time vs Concentration - Cobalt in Deep Zone Figure 14-35 Time vs Concentration - Cobalt in Bedrock Zone Figure 14-36 Time vs Concentration - Cobalt Pine Hall Landfill Figure 14-37 Time vs Concentration - Iron in Shallow Zone Figure 14-38 Time vs Concentration - Iron in Deep Zone Figure 14-39 Time vs Concentration - Iron in Bedrock Zone Figure 14-40 Time vs Concentration - Iron Pine Hall Landfill Figure 14-41 Time vs Concentration - Manganese in Shallow Zone Figure 14-42 Time vs Concentration - Manganese in Deep Zone Figure 14-43 Time vs Concentration - Manganese in Bedrock Zone Figure 14-44 Time vs Concentration - Manganese Pine Hall Landfill Figure 14-45 Time vs Concentration - Molybdenum in Shallow Zone Figure 14-46 Time vs Concentration - Molybdenum in Deep Zone Figure 14-47 Time vs Concentration - Molybdenum in Bedrock Zone Figure 14-48 Time vs Concentration - Molybdenum Pine Hall Landfill Figure 14-49 Time vs Concentration - pH in Shallow Zone Figure 14-50 Time vs Concentration - pH in Deep Zone Figure 14-51 Time vs Concentration - pH in Bedrock Zone Figure 14-52 Time vs Concentration - pH Pine Hall Landfill Figure 14-53 Time vs Concentration - Selenium in Shallow Zone Figure 14-54 Time vs Concentration - Selenium in Deep Zone Figure 14-55 Time vs Concentration - Selenium in Bedrock Zone Figure 14-56 Time vs Concentration - Selenium Pine Hall Landfill Figure 14-57 Time vs Concentration - Strontium in Shallow Zone Figure 14-58 Time vs Concentration - Strontium in Deep Zone Figure 14-59 Time vs Concentration - Strontium in Bedrock Zone Figure 14-60 Time vs Concentration - Strontium Pine Hall Landfill Figure 14-61 Time vs Concentration - Sulfate in Shallow Zone Figure 14-62 Time vs Concentration - Sulfate in Deep Zone Figure 14-63 Time vs Concentration - Sulfate in Bedrock Zone Figure 14-64 Time vs Concentration - Sulfate Pine Hall Landfill Figure 14-65 Time vs Concentration - TDS in Shallow Zone Figure 14-66 Time vs Concentration - TDS in Deep Zone Figure 14-67 Time vs Concentration - TDS in Bedrock Zone 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xiii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 14-68 Time vs Concentration - TDS Pine Hall Landfill Figure 14-69 Time vs Concentration - Thallium in Shallow Zone Figure 14-70 Time vs Concentration - Thallium in Deep Zone Figure 14-71 Time vs Concentration - Thallium in Bedrock Zone Figure 14-72 Time vs Concentration - Thallium Pine Hall Landfill Figure 14-73 Time vs Concentration - Vanadium in Shallow Zone Figure 14-74 Time vs Concentration - Vanadium in Deep Zone Figure 14-75 Time vs Concentration - Vanadium in Bedrock Zone Figure 14-76 Time vs Concentration - Vanadium Pine Hall Landfill Figure 14-77 Groundwater Concentration Trend Analysis - Antimony All Flow Layers and AOWs Figure 14-78 Groundwater Concentration Trend Analysis - Arsenic All Flow Layers and AOWs Figure 14-79 Groundwater Concentration Trend Analysis - Barium All Flow Layers and AOWs Figure 14-80 Groundwater Concentration Trend Analysis - Beryllium All Flow Layers and AOWs Figure 14-81 Groundwater Concentration Trend Analysis - Boron All Flow Layers and AOWs Figure 14-82 Groundwater Concentration Trend Analysis - Cadmium All Flow Layers and AOWs Figure 14-83 Groundwater Concentration Trend Analysis - Chloride All Flow Layers and AOWs Figure 14-84 Groundwater Concentration Trend Analysis - Chromium (VI) All Flow Layers and AOWs Figure 14-85 Groundwater Concentration Trend Analysis - Chromium (Total) All Flow Layers and AOWs Figure 14-86 Groundwater Concentration Trend Analysis - Cobalt All Flow Layers and AOWs Figure 14-87 Groundwater Concentration Trend Analysis - Iron All Flow Layers and AOWs Figure 14-88 Groundwater Concentration Trend Analysis - Manganese All Flow Layers and AOWs Figure 14-89 Groundwater Concentration Trend Analysis - Molybdenum All Flow Layers and AOWs Figure 14-90 Groundwater Concentration Trend Analysis - pH All Flow Layers and AOWs 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xiv P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF FIGURES CONTINUED Figure 14-91 Groundwater Concentration Trend Analysis - Selenium All Flow Layers and AOWs Figure 14-92 Groundwater Concentration Trend Analysis - Strontium All Flow Layers and AOWs Figure 14-93 Groundwater Concentration Trend Analysis - Sulfate All Flow Layers and AOWs Figure 14-94 Groundwater Concentration Trend Analysis - Total Dissolved Solids All Flow Layers and AOWs Figure 14-95 Groundwater Concentration Trend Analysis - Thallium All Flow Layers and AOWs Figure 14-96 Groundwater Concentration Trend Analysis - Vanadium All Flow Layers and AOWs Figure 14-97 Comprehensive Groundwater Data Figure 14-98 Comprehensive Surface Water and Seep Data Figure 14-99 Comprehensive Soil and Sediment Data 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xv P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF TABLES 2.0 Site History and Description Table 2-1 Well Construction Data Table 2-2 Compliance Monitoring Wells Table 2-3 Summary of Onsite Environmental Incidents 3.0 Source Characteristics Table 3-1 Range (10th percentile - 90th percentile) in Bulk Composition of Fly Ash, Bottom Ash, Rock, and Soil (Source: EPRI 2009a) Table 3-2 Soil/Material Properties for Ash, Fill, Alluvium, and Soil/Saprolite Table 3-3 Regional Background Soil SPLP data 4.0 Receptor Information Table 4-1 Public and Private Water Supply Wells within 0.5-mile Radius of Ash Basin Compliance Boundary' Table 4-2 Property Owner Addresses Contiguous to the Ash Basin Waste Boundary Table 4-3 Private Water Supply Analytical Results Table 4-4 Piedmont Groundwater Background Threshold Values 6.0 Site Geology Table 6-1 Soil Mineralogy Results Table 6-2 Soil Chemistry Results - Oxides Table 6-3 Soil Chemistry Results - Elemental Table 6-4 Solid Matrix Parameters and Analytical Methods for Soil, Ash, and Rock Parameters and Constituent Analysis - Analytical Methods Table 6-5 Ash Basin Surface Water, Pore water and Seep Parameters and Analytical Methods Table 6-6 Transition Zone Mineralogy Table 6-7 Oxide Composition of Transition Zone Samples Table 6-8 Elemental Composition of Transition Zone Samples Table 6-9 Whole Rock Chemistry Results - Oxides Table 6-10 Whole Rock Chemistry Results - Elemental Table 6-11 Petrographic Analysis Summary Table 6-12 Historic and Recent Water Level Measurements Table 6-13 Horizontal Groundwater Gradients and Flow Velocities Table 6-14 Vertical Hydraulic Gradients Table 6-15 Hydrostratigraphic Layer Properties - Horizontal Hydraulic Conductivity Table 6-16 Hydrostratigraphic Layer Properties - Vertical Hydraulic Conductivity 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xvi P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF TABLES CONTINUED Table 6-17 In-Situ Hydraulic Conductivity Results Table 6-18 Estimated Effective Porosity/Specific Yield and Specific Storage for Upper Hydrostratigraphic Units (A, F, S, M1, and M2) Table 6-19 Total Porosity, Secondary (Effective) Porosity/Specific Yield, and Specific Storage for Lower Hydrostratigraphic Units (TZ and BR) Table 6-20 Field Permeability Test Results Table 6-21 Historic Laboratory Field Permeability Test Results 7.0 Soil Sampling Results Table 7-1 Unsaturated Background Soil Data Summary Table 7-2 Provisional Background Threshold Values for Soil 10.0 Groundwater Sampling Results Table 10-1 Background Groundwater Results Through April 2017 Table 10-2 Groundwater Provisional Background Threshold Values Table 10-3 State and Federal Standards for COIs 11.0 Hydrogeological Investigation Table 11-1 Private Well Sample Results 13.0 Groundwater Modeling Results Table 13-1 Summary of Kd Values from Batch and Column Studies 15.0 Conclusions and Recommendations Table 15-1 Groundwater Interim Monitoring Program Analytical Methods Table 15-2 Interim Monitoring Program List 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xvii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF APPENDICES Appendix A Regulatory Correspondence DEQ Expectations Document (July 18, 2017) Completed DEQ CSA Update Expectations Check List NCDENR NORR Letter (August 13, 2014) Revised Interim Monitoring Plans for 14 Duke Energy Facilities (October 19, 2017) NCDEQ Background Dataset Review (July 7, 2017) NCDEQ Background Dataset Review (September 1, 2017) NCDEQ Background Threshold Value Approval Attachments (September 1, 2017) Appendix B Comprehensive Data Table Appendix B Notes Table 1 - Groundwater Results Table 2 - Surface Water Results Table 3 - AOW and WW Results Table 4 - Soil and Ash Results Table 5 - Sediment Results Table 6 - SPLP Results Appendix C Site Assessment Data HDR CSA Appendix H Soil Physical Lab Reports Mineralogy Lab Reports Slug Test Procedure Slug Test Reports Historic Permeability Data Field Permeability Data Fetter-Bear Diagrams – Porosity Historic Porosity Data Estimated Seasonal High Groundwater Elevations Calculation HDR CSA Supplement 2 Slug Test Report UNCC Soil Sorption Evaluation Addendum to the UNCC Soil Sorption Evaluation Appendix D Receptor Surveys Updated Receptor Survey Report Supplement to Drinking Water Well and Receptor Survey Drinking Water Supply Well and Receptor Survey Dewberry Report – Permanent Water Supply Proposal to DEQ 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xviii P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF APPENDICES CONTINUED Appendix E Supporting Documents Stantec Report WSP Maps Appendix F Boring Logs, Construction Diagrams, and Abandonment Records Well Boring Logs Well Construction Records Well Abandonment Records Soil Sample and Rock Core Photos Appendix G Methodology Source Characterization Soil and Rock Characterization Surface water and sediment characterization Groundwater characterization Field, Sampling, and Data analysis Quality Assurance / Quality Control Appendix H Background Determination Belews Creek 2017 CSA PBTV Report HDR Background Determination Report Appendix I Lab Reports Water Supply Wells 2015 Round 2 - Surface Water Round 2 - September 2015 Round 3 - November 2015 Round 4 - December 2015 Round 5 - March and April 2016 Round 6 - May 2016 Round 7 - September 2016 Round 8 - November 2016 Round 9 - January 2017 Round 10 - April 2017 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xix P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF ACRONYMS 2B NCDENR Title 15A, Subchapter 02B. Surface Water and Wetland Standards 2L NCDENR Title 15A, Subchapter 02L. Groundwater Classification and Standards ADD Average Daily Dose AOW Area of Wetness ASTM American Society for Testing and Materials BCSS Belews Creek Steam Station BGS Below Ground Surface BOD Basis of Design BR Bedrock CAMA Coal Ash Management Act CAP Corrective Action Plan CCR Coal Combustion Residuals CFR Code of Federal Register CM/SEC Centimeters per second COI Constituent of Interest CSA Comprehensive Site Assessment DO Dissolved Oxygen DOE Department of Energy Duke Energy Duke Energy Carolinas, LLC DWM Division of Waste Management EDR Environmental Database Resources, Inc. EMP Effectiveness Monitoring Program EPC Exposure Point Concentration EPD Environmental Protection Division EPRI Electric Power Research Institute FGD Flue Gas Desulfurization GAP Groundwater Assessment Work Plan GIS Geographic Information System GPD Gallons Per Day GTB Geotechnical Borings HAO Hydrous Aluminum Oxide HB Highway Business District HDPE High-Density Polyethylene HFO Hydrous Ferric Oxide HSSR Hydrogeochemical and Stream Sediment Reconnaissance 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xx P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF ACRONYMS CONTINUED IAP Interim Action Plan IMAC Interim Maximum Allowable Concentration IMP Interim Monitoring Plan Kd Sorption Coefficient LOAEL Lowest Observed Adverse Effects Level MCL Maximum Contaminant Level Mg/kg Milligrams per Kilogram Mg/L Milligrams per liter MGD Million Gallons per Day Mil Thousandths of Inch mm Millimeter MNA Monitored Natural Attenuation MRL Method Reporting Limit MT3DMS Modular 3-D Transport Multi-Species MW Megawatts NAVD 88 North American Vertical Datum of 1988 NCAC North Carolina Administrative Code NCDENR North Carolina Department of Environment and Natural Resources NCDEQ North Carolina Department of Environmental Quality NCDHHS North Carolina Department of Health and Human Services NORR Notice of Regulatory Requirements NPDES National Pollutant Discharge Elimination System NSDWRs National Secondary Drinking Water Regulations NURE National Uranium Resource Evaluation PBTV Provisional Background Threshold Value *Define on p. ES-4 Plant/Site Belews Creek Steam Station PMCL Primary Maximum Contaminant Level POG Protection of Groundwater PPB Parts per billion PPBC Proposed Provisional Background Concentrations PSRG Preliminary Soil Remediation Goal PWR Partially Weathered Rock RBC Risk-Based Concentrations REC Recovery RQD Rock Quality Designation RSL Regional Screening Levels S.U. Standard Units 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page xxi P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx LIST OF ACRONYMS CONTINUED SCM Site Conceptual Model SMCL Secondary Maximum Contaminant Level SPLP Synthetic Precipitation Leaching Procedure SW Surface Water SWAP Source Water Assessment Program TCLP Toxicity Characteristic Leaching Procedure TDS Total Dissolved Solids TOC Total Organic Carbon TRVs Toxicity Reference Values TZ Transition Zone UMC United Methodist Church UNC University of North Carolina UNCC University of North Carolina at Charlotte USEPA United States Environmental Protection Agency USCS Unified Soil Classification System USDA U.S. Department of Agriculture USGS United States Geological Survey UTL Upper Tolerance Limit Work Plan Groundwater Assessment Work Plan 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 1-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 1.0 INTRODUCTION Duke Energy Carolinas, LLC (Duke Energy) owns and operates the Belews Creek Steam Station (BCSS), which is located on Belews Reservoir in Belews Creek, Stokes County, North Carolina (Figure 1-1). BCSS began operation in 1974 as a coal-fired generating station and currently operates two coal-fired units with 2,240 megawatt capacity of generation. Coal combustion residuals (CCR) have historically been managed in the Site’s ash basin (surface impoundment) located north of Pine Hall Road to the west- northwest of the station. CCR were initially deposited in the ash basin by hydraulic sluicing operations. In 1984, BCSS converted from a wet to a dry fly ash handling system. However, the ability to sluice to the ash basin was still available, but limited to certain situations (i.e. unit startup/shutdown, equipment maintenance and service). A 100% dry ash handling system is currently being constructed onsite. Discharge from the ash basin to the Dan River is permitted by the North Carolina Department of Environmental Quality (NCDEQ)1 Division of Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES) Permit NC0024406. Purpose of Comprehensive Site Assessment 1.1 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 basin. 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 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. The NCDEQ Expectations Document (July 18, 2017) and the completed NCDEQ CSA Update Expectations Check List are included in Appendix A: Review of baseline assessment data collected and reported as part of CSA activities; 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 Belews Creek Steam Station SynTerra Page 1-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx A summary of NPDES and Coal Ash Management Act (CAMA) groundwater monitoring information; A summary of potential receptors including analytical 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. Regulatory Background 1.2 The North Carolina Coal Ash Management Act of 2014 (CAMA) 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 (NORR) 1.2.1 On August 13, 2014, 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 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 1-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 1-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Approach to Comprehensive Site Assessment 1.3 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 the site assessment provide information to meet the requirements of North Carolina regulation 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. 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; Sections 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 Section 7.0, 8.0, and 14.0 (5) Geological and hydrogeological features influencing the movement, chemical, and physical character of the contaminants. Section 6.0, 11.0, and 15.0 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 1-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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” (USEPA, October 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 presented in Section 14.0. The Site Conceptual Model is used to integrate site information, identify data gaps, and determine whether additional information is needed at the site. The model is also used to facilitate selection of remedial alternatives and evaluate the potential effectiveness of remedial actions in reducing the exposure of environmental receptors to contaminants (ASTM, 2014). Technical Objectives 1.4 The rationale for CSA activities fall into one of the following categories: Determine the range of background 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 1-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Provide source area information including ash pore water chemistry, physical and hydraulic properties, CCR thickness and residual saturation within the ash basin. Address soil chemistry in the vicinity of the ash basin (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. Previous Submittals 1.5 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 – Belews Creek Steam Station Ash Basin (HDR Engineering, Inc. of the Carolinas (HDR, 2015a). Corrective Action Plan Part 1 – Belews Creek Steam Station Ash Basin (HDR, 2015b). Corrective Action Plan Part 2 (included CSA Supplement 1 as Appendix A) – Belews Creek Steam Station Ash Basin (HDR, 2016d). Comprehensive Site Assessment Supplement 2 – Belews Creek Steam Station Ash Basin (HDR, 2016c). Basis of Design Report (100% Submittal) – Belews Creek Steam Station (SynTerra, 2017a). 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 2.0 SITE HISTORY AND DESCRIPTION An overview of the BCSS setting and operations is presented in the following sections. Site Description, Ownership and Use History 2.1 The BCSS site is located on the north side of Belews Reservoir on Pine Hall Road in Belews Creek, Stokes County, North Carolina. BCSS is one of Duke Energy's largest coal-burning power plants in the Carolinas. BCSS is a two-unit coal-fired electricity generating plant with a capacity of 2,240 megawatts (MW). The BCSS site, including the station and supporting facilities, is approximately 700 acres (Figure 2-1). The BCSS site lies within a 6,100 acre parcel owned by Duke Energy, of which, Belews Reservoir comprises 3,800 acres and extends into Rockingham, Guilford and Forsyth counties. Based on a review of available historical aerial photography, the Site consisted of a combination of agricultural land, rural residential, and woodlands prior to the impoundment of Belews Creek for the formation of Belews Reservoir. Aerial photographs from 1951, 1966, 1971, and 1977 are presented as Figures 2-2, 2-3, 2- 4, and 2-5, respectively. The station began commercial operations in 1974 with Unit 1 (1,120 MW) followed by Unit 2 (1,120 MW) in 1975. Four generators are present at BCSS, including two low pressure generators and two high pressure/intermediate pressure generators. Cooling water for BCSS is provided by Belews Reservoir. The air pollution control system for the coal-fired units at BCSS includes a selective catalytic reducer to remove nitrogen oxide emissions, an electrostatic precipitator that removes fly ash, and the units have low nitrogen oxide burners in the boiler. A Flue Gas Desulfurization (FGD) system is active at BCSS. The FGD system directs flue gas into an absorber where limestone (calcium carbonate) slurry is sprayed. Sulfur dioxide in the flue gas reacts with the limestone slurry to produce calcium sulfate, or gypsum. Gypsum is primarily sold for re-use or managed in the on-site NCDEQ Division of Waste Management (DWM) approved FGD Residue Landfill (Permit No. 8505). The BCSS ash basin is located across Pine Hall Road to the northwest of the station and is generally bounded by an earthen dam and a natural ridge to the north, Middleton Loop Road to the west, and Pine Hall Road to the south and east (Figure 2-1). Middleton Loop Road and Pine Hall Road are located along topographic divides. Topography to the west of Middleton Loop Road and north of the earthen dam and natural ridge generally slopes downward toward the Dan River. Topography to the south and east of Pine Hall Road generally slopes downward toward Belews Reservoir. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Other areas of the site are occupied by facilities supporting the production or transmission of power, including a switchyard, substation, and associated transmission lines. A former chemical holding pond (the pond has been drained and the valve left open to allow surface flow of storm water through) is located in the southeast end of the ash basin. The drained pond is now part of the ash basin. The closed Pine Hall Road Landfill (NCDEQ Permit No. 8503) is located south of the ash basin and north of Pine Hall Road. An structural fill constructed using fly ash generated from BCSS under the structural fill rules found in 15A NCAC 13B .1700 is located south of the ash basin on the south side of Pine Hall Road. The structural fill was approved by the NCDEQ DWM (Permit No. CCB0070). The Craig Road Landfill (NCDEQ Permit No. 8504) and the FGD Residue Landfill (NCDEQ Permit No. 8505) are located south of the ash basin on the south side of Belews Reservoir. Site features are shown on Figure 2-6. Geographic Setting, Surrounding Land Use, Surface Water 2.2 Classification The BCSS site is situated in a rural area along Belews Reservoir in Stokes County, North Carolina. A description of the physical setting for BCSS is provided in the following sections. Geographic Setting The surrounding area around BCSS generally consists of residential properties, farm land, undeveloped land, and Belews Reservoir (Figure 2-7). Natural topography at the BCSS site ranges from an approximate high elevation of 878 feet (NAVD 88) southeast of the ash basin near the intersection of Pine Hall Road and Middleton Loop Road to an approximate low elevation of 646 feet at the base of the earthen dike located at the north end of the ash basin. The ash basin designated effluent channel extends from the base of the ash basin dam and flows approximately 4,400 feet from southeast to northwest where it enters the Dan River. The elevation at the discharge point of the tributary to the Dan River is approximately 578 feet. The elevation of Belews Reservoir is approximately 725 feet. A 1962 United States Geological Survey (USGS) topographic map depicting the site prior to construction of the ash basin features is shown on Figure 2-8. The Pine Hall Road Landfill is located upgradient to the ash basin and is just north of the Pine Hall Road topographic divide. The BCSS structural fill is located south of the BCSS ash basin and Pine Hall Road. Refer to Section 3.1 for a detailed description of the BCSS ash basin and other ash storage facilities. Surrounding Land Use Properties located within the 0.5-mile radius of the BCSS ash basin compliance boundary generally consist of residential properties located to the southwest and 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx residential farm land northeast, north, and west. Duke Energy property is located to the north, northwest, south, and east with Belews Reservoir beyond to the south and east. A review of deed information for properties surrounding the BCSS site indicates most of these properties do not currently have a Stokes County zoning designation. The Duke Energy property is zoned Light Manufacturing District (M-1) where the principal use is for light manufacturing and warehousing which normally seek locations on large tracts of land where the operations involved do not detract from the development potential of nearby undeveloped properties. Another parcel located north of the Dan River from the BCSS site is also zoned M-1 and is owned by a pipe and brick company. The only other zoned parcel in the vicinity of the BCSS site is located on the south side of Pine Hall Road and west of the Pine Hall Road Landfill. This property is zoned Highway Business District (HB) which allows the property to be used for retail trade establishments and the provision of services to the traveling public. Meteorological Setting In summer, the average temperature in Stokes County is 74°F, and the average daily maximum temperature is 85°F (USDA-NRCS 1995). In winter, the average temperature is 37°F, and the average daily minimum temperature is 25°F. The total annual precipitation in Stokes County is 45 inches, with approximately half (24 inches) occurring from April through September. Thunderstorms occur approximately 46 days each year (U.S. Department of Agriculture, 1995). The average relative humidity in midafternoon is approximately 55 percent, with humidity reaching higher levels at night. The prevailing wind is from the southwest, and average wind speed is highest (9 miles per hour) in spring (U.S. Department of Agriculture, 1995). Surface Water Classification The BCSS site drains to the Dan River which is part of the Roanoke River watershed. The Site is located between Belews Reservoir to the south and the Dan River to the north. The ash basin designated effluent channel extends from the base of the ash basin dam and flows northwards through Duke Energy property where it discharges to the Dan River (NPDES outfall 003). This feature was designated as a designated effluent channel by the State of North Carolina in the 1980’s when the ash pond discharge was redirected from Belews Reservoir to the Dan River. Surface water classifications in North Carolina are defined in 15A NCAC 02B.0101(c). The surface water classification for the Dan River and Belews Reservoir in the vicinity of the BCSS site is Class WS-IV and Class WS-IV–C, respectively. Class WS-IV waters are protected as water supplies which are generally in moderately to highly developed watersheds. Class C waters are protected for uses such as secondary recreation, fishing, 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx wildlife, fish consumption, aquatic life including propagation, and survival. Surface water features located on the site are shown on Figure 2-9. No residential potable water supply lines are available to the area, with the nearest residential water supply line, provided by the Town of Walnut Cove, located at the intersection of Martin-Luther King Jr. Road and Crestview Drive, approximately 4.5 miles to the west from the Duke Power Steam Plant Road entrance to the Station. BCSS is supplied with potable water from water lines originating south of the plant by the City of Winston-Salem. No surface water intakes, other than the intake used to pump water from Belews Reservoir for BCSS plant operations, the intake on Belews Reservoir to pump water for water trucks at the Craig Road Landfill, and the backup intake on the Dan River, are located in the vicinity of BCSS either in Belews Reservoir or in the Dan River. CAMA-related Source Areas 2.3 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 BCSS, the groundwater assessment was conducted for the ash basin CCR surface impoundment, including the former chemical pond and the Pine Hall Road Landfill (NCDEQ Permit No. 8503-INDUS). Figure 2-10 shows all sample locations regarding assessment activities. Collectively, the ash basin, the former chemical pond, and the Pine Hall Road Landfill are referred to herein as ash management areas. The BCSS ash basin consists of a single cell impounded by an earthen dam located on the north end of the ash basin. The dam is approximately 2,000 feet long and a maximum of approximately 140 feet high. The top of the dam is at elevation 770 feet and the crest is 20 feet wide. The ash basin was constructed from 1970 to 1972 and is located approximately 3,200 feet northwest of the BCSS powerhouse. The area contained within the ash basin waste boundary is approximately 283 acres. The full pond elevation of the BCSS ash basin is approximately 750 feet. The full pond capacity of the ash basin is estimated to be 17,656,000 cubic yards (cy). The Pine Hall Road Landfill received a permit to operate on December 10, 1984 and a subsequent expansion (Phase I Expansion) was permitted in 2003. The unlined landfill is a monofill that was permitted to receive fly ash from the combustion of coal at BCSS. The total footprint of the landfill is approximately 52 acres. The placement of ash 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx within the Phase I expansion was discontinued prior to March 2008. A total of approximately 8,500,000 cubic yards (cy) of ash was placed within the Pine Hall Road Landfill between December 1984 and March 2008. More detailed discussion of the ash management areas is provided in Section 3.0 of this report. Regulation 15A NCAC 02L .0106 (f)(4) requires that the secondary sources that could be potential continuing sources of possible pollutants to groundwater be addressed in the CAP. At the BCSS, the soil located below the ash basin 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. Other Primary and Secondary Sources 2.4 CSA activities, as outlined in the NCDENR NORR letter, included an assessment of the horizontal and vertical extent of constituents related to the ash management areas observed at concentrations greater than the 2L Standards/Interim Maximum Allowable Concentrations (IMACs) or background concentrations. If the CSA indicates constituent exceedances are related to sources other than the CCR impoundments, these sources will be addressed as part of a separate process in compliance with the requirements of 2L. Per the approved CSA work plan, ash used in the structural fill was not considered part of the source area and was not evaluated during the CSA. Based on exceedances from an area of wetness (AOW) location (S-9) south of the ash basin and west of the structural fill, monitoring wells GWA-23S and GWA-23D were installed and sampled as part of the CAMA Round 5 sampling event (April 2016). Exceedances and concentrations of the constituents in GWA-23S and GWA-23D were similar, indicating that the concentrations were from the same source. This comparison of the elevation of the screen in GWA-23S and the ash basin full pond elevation indicate that the source of the exceedances in GWA-23S is not the ash basin. Although the bottom of screen elevation for GWA-23D (754.96 to 749.96 feet) is lower than the former chemical treatment pond area historical elevation (772 feet), based on the similar nature of the exceedances, it is likely that the same source is the cause of the exceedances in both GWA-23S and GWA-23D. The approximate elevation for AOW S-9 is 792 feet, which is greater than water elevations in the ash pond and the former chemical treatment pond. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx The exceedances in GWA 23S/D are consistent with constituents associated with coal ash and a potential source could be the nearby structural fill. As the structural fill was constructed under the NCDEQ Division of Waste Management (DWM) structural fill rules found in 15A NCAC 13B .1700 (Permit No. CCB0070), Duke Energy notified DWM of these exceedances and an assessment is ongoing at the BCSS structural fill. The assessment results will be reported to the NCDEQ DWM. See Section 2.7 for a detailed description of the assessment activities with regards to the structural fill. Summary of Permitted Activities 2.5 Duke Energy is authorized to discharge wastewater from the BCSS ash basin to the Dan River (outfall 003). This discharge is in accordance with NPDES Permit NC0024406, which was renewed on November 1, 2012 and expired on February 28, 2017. A draft renewal permit (NC0024406) was submitted to NCDEQ on September 9, 2016. BCSS is currently operating under the expired permit. The renewal permit is proposed to expire three years after its effective date. As part of the permit renewal, the facility identified seeps and collected seep samples. The seeps were incorporated into the permit as outfalls where appropriate. The draft NPDES permit proposes to require surface water monitoring, including continued sampling of seep outfalls, as part of the permit conditions. The current NPDES flow diagram from the permit application for BCSS is provided in Figure 2-11. Current approximate quantities of inflows into the ash basin include 2.7 million gallons per day (MGD) from the ash sluice, 4.2 MGD from the yard holding sump, 0.7 MGD from the coal yard sumps, 0.7 MGD from the FGD wastewater treatment lagoons, 0.46 MGD of stormwater, less than 0.19 MGD from the consolidated sump system, 0.03 MGD from the chemical holding pond, 0.019 MGD from the west holding sump. The contributing sources to these inflows are depicted on Figure 2-9. There are four solid waste facilities associated with BCSS: the active Craig Road Landfill (NCDEQ Permit No. 8504 - INDUS), the active FGD Landfill (NCDEQ Permit No. 8505 - INDUS), a closed structural fill (NCDEQ Permit No. CCB0070), and the closed Pine Hall Road Landfill (NCDEQ Permit No. 8503 - INDUS). The Craig Road Landfill, FDG Landfill and the structural fill are located south of the ash basin and are not hydrogeologically connected to the ash basin (although leachate collected from the landfill facilities are routed to the ash basin). The Pine Hall Road Landfill is located on the south side of the ash basin and north side of Pine Hall Road and is hydrogeologically connected to the ash basin (Figure 2-10). The Pine Hall Road Landfill was closed in December 2008. The landfill was permitted to accept fly ash from Belews Creek Steam Station operations. The landfill was originally 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx permitted in 1983. The original landfill was unlined and was permitted with a soil cap one foot thick on the side slopes and two feet thick on flatter areas. A subsequent expansion (Phase I Expansion) was permitted in 2003. This phase was also unlined but was a synthetic cap system was applied at closure. After groundwater exceedances were observed in wells installed near the landfill, the placement of additional ash in the landfill stopped. The closure design was changed to utilize an engineered cover system for a portion of the landfill. The engineered cover system consists of a 40-mil linear low- density polyethylene geomembrane, a geonet composite, 18 inches of compacted soil, and 6 inches of vegetative soil cover. The engineered cover system was installed over a 37.9-acre area. An adjacent 14.5-acre area, located to the northeast, had additional soil cover applied and was graded to improve surface drainage. The construction of the engineered cover system and additional soil cover on the 14.5-acre area was completed in December 2008. The Craig Road Landfill is permitted to receive CCR and other operational waste material Phase 1 and 2 of the landfill were constructed with an engineered liner system consisting of a leachate collection system, underlain by a high-density polyethylene (HDPE) geomembrane liner, underlain by a geo-synthetic clay liner. The waste boundary contains an area of approximately 67.1 acres. Phase 1 began accepting waste in February 2008. Phase 2 began accepting waste in June 2014. The FGD residue landfill is permitted to receive CCR and other operational waste material; however Duke only places FGD residue (gypsum) from BCSS operations in this landfill. The FGD residue landfill is located south of the Belews Creek plant on land between two arms of the Belews Reservoir. The West Belews Creek arm of the reservoir is located west of the landfill site and the East Belews Creek arm of the reservoir is located east of the site. Craig Road is located to the west of the landfill. The landfill consists of four cells contained in an area of approximately 24 acres. The adjacent stormwater basin occupies an area of approximately 2.4 acres and is used to manage leachate and stormwater collected from the landfill and discharged to the ash basin. The landfill has an engineered liner system consisting of a leachate collection system, underlain by a high-density polyethylene (HDPE) geomembrane liner, underlain by a geo-synthetic clay liner. The structural fill (see Figure 2-10) comprised of compacted fly ash was constructed southeast of the ash basin. The structural fill is located south of the Pine Hall Road topographic divide, and therefore, groundwater flow beneath the fill should be predominantly away from the ash basin towards Belews Reservoir. This structural fill 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx was constructed under the structural fill rules found in 15A NCAC 13B .1700. The Notification of the Beneficial Use Structural Fill was submitted by Duke Energy to NCDENR on May 7, 2003. Approximately 968,000 cy of ash were placed within the structural fill from February 2004 to the last ash placement in July 2009. An engineered cap similar to that previously described for the Pine Hall Road Landfill was constructed over the structural fill in 2012. The structural fill is currently used as an equipment/material staging area and overflow parking. The structural fill was not considered part of the source area and was not evaluated by the CSA. History of Site Groundwater Monitoring 2.6 The following sections discuss groundwater monitoring activities conducted association with the BCSS ash basin. 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 Figure 2-4. Construction details for site monitoring wells are provided in Table 2-1. The following sections discuss groundwater monitoring activities prior to CSA activities through current CAMA assessment activities. Ash Basin 2.6.1 Voluntary Groundwater Monitoring Voluntary monitoring wells MW-101S, MW-101D, MW-102S, MW-102D, MW- 103S, MW-103D, MW-104S, and MW-104D were installed by Duke Energy in 2006 as part of a voluntary monitoring system. The voluntary wells are shown on Figure 2-10. Duke Energy performed voluntary groundwater monitoring around the BCSS ash basin from November 2007 until May 2010. During this period, the voluntary groundwater monitoring wells were sampled biannually and the analytical results were submitted to NCDENR DWR. Monitoring wells MW-102S and MW-102D were abandoned as a result of reinforcement construction activities at the ash basin dam in 2015. Samples have been collected from monitoring wells MW-103S/D and MW-104S/D since July 2015 as part of groundwater assessment efforts. No samples are currently being collected from the other voluntary wells. NPDES Groundwater Monitoring Groundwater monitoring as required by BCSS NPDES permit NC0024406 began in January 2011 as described in NPDES Permit Condition A (10), effective November 1, 2012. Groundwater monitoring events are conducted three times a year (January, May, and September). Compliance groundwater monitoring is continuing in accordance with the draft NPDES permit (NC0024406). 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Locations for the compliance groundwater monitoring wells were approved by the NCDENR DWR. The compliance groundwater monitoring system for the BCSS ash basin consists of the following monitoring wells: MW-200S, MW-200D, MW-201D, MW-202S, MW-202D, MW-203S, MW-203D, MW-204S, and MW- 204D (shown on Figure 2-10 and Table 2-2). All the compliance monitoring wells were installed in December 2010. The compliance groundwater monitoring is performed in addition to the normal NPDES monitoring of the discharge flows from the ash basin. With the exception of monitoring wells MW-202S and MW-202D, the ash basin compliance monitoring wells were installed at or near the compliance boundary. Monitoring wells MW-200S and MW-200D are located to the north of the ash basin dike. Monitoring well MW-201D is located west of Pine Hall Road near the former ash basin discharge canal. Monitoring wells MW-203S, MW-203D, MW- 204S, and MW-204D are located west of the ash basin along Middleton Loop Road. Landfill Groundwater Monitoring 2.6.2 Groundwater monitoring is conducted at the three permitted BCSS landfills (Pine Hall Road, Craig Road, and FGD Residue) in accordance with permit requirements. Monitoring is performed twice per year per an established schedule at each landfill. Pine Hall Road Landfill – The groundwater monitoring system currently consists of 13 monitoring wells and two surface water sample locations. Twelve wells are screened in the residual soil/saprolite layer and one well (MW-1D) is screened in fractured bedrock. Groundwater monitoring wells MW-1, MW-2, MW-3, MW-4, and MW-5 were installed in 1989. Monitoring well MW-3 was confirmed to monitor background groundwater quality in CAP 1. The initial twice per year groundwater sampling was performed at these wells in October 1989. Monitoring wells MW-6, MW2-7, MW2-9, OB-4, OB-5, and OB-9 were installed, and monitoring initiated, as part of the site investigation for the Phase 1 Expansion and subsequent investigation of groundwater exceedances from 2000 to 2004. Monitoring wells MW-1D and MW-7 were installed after installation of the engineered cap in 2008. Groundwater monitoring is performed in April and October per the landfill Water Quality Monitoring Plan. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-10 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Craig Road Landfill – The groundwater monitoring system currently consists of 17 monitoring wells, six surface water sample locations and three leachate sample locations. Monitoring well CRW-10 was confirmed to monitor background water quality in CAP 1. Monitoring wells were installed to monitor the transition zone (TZ) between the saprolite/partially weathered rock zone and bedrock. The initial twice per year groundwater sampling event was performed in January 2007 prior to initial placement of waste in February 2008. Groundwater monitoring is performed in January and July per the landfill Water Quality Monitoring Plan. FGD Residue Landfill – The groundwater monitoring system currently consists of 12 monitoring wells, one surface water sample location and one leachate sample location. Wells BC-23A and BC-28 were confirmed to monitor background groundwater quality in CAP 1. The monitoring wells were installed to monitor groundwater quality in the residual soil/saprolite layer. The initial twice per year groundwater sampling event was performed in November 2007 prior to initial waste placement in April 2008. Groundwater monitoring is performed in May and November per the landfill Water Quality Monitoring Plan. Ash Basin CAMA Monitoring 2.6.3 One hundred nine (109) groundwater wells were installed as part of this assessment (Figure 2-10). Eighteen (18) existing voluntary and compliance wells have been included in assessment activities. Nine background (BG) monitoring wells BG-1S/D, BG-2S/D/BR/BRA, BG-3S/D and MW-202BR have been installed to evaluate background water quality in the shallow, deep and bedrock flow regimes. Two existing background compliance monitoring wells MW-202 S/D, are also sampled for assessment activities. Thirty-one (31) groundwater monitoring wells were installed in locations anticipated to be upgradient of the ash basin: GWA-4S/D, GWA-5S/SA/D/BR2, GWA-6S/D, GWA-7S/SA/D, GWA-8S/D, GWA-9S/D/BR, GWA-12S/D/BR, GWA- 16S/D/DA/BR, GWA-17S/D, GWA-23S/D, GWA-25BR, GWA-26S/D/BR MW- 201BR and MW-203BR. These groundwater monitoring wells were installed to evaluate groundwater quality upgradient of the ash basin and to confirm groundwater flow direction. Eight upgradient voluntary and compliance monitoring wells are also sampled for assessment activities MW-104S/D/BR, MW-201D, MW-203S/D, and MW-204S/D. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-11 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Twenty-eight (28) groundwater monitoring wells were installed within the waste boundary: AB-1S/D/BR, AB-2S/SA/D, AB-3S/D, AB-4S/SL/D/BR/BRD, AB- 5S/SL/D, AB-6S/SL/D, AB-7S/D, AB-8S/SL/D and AB-9S/D/BR/BRD. These groundwater monitoring wells were installed to evaluate groundwater quality within the pore water, TZ, upper bedrock, and deeper bedrock zones. Monitoring wells AB-1S/D/BR, AB-2S/SA/D, and AB-3S/D were installed at the crest of the ash basin dam. Monitoring wells AB-9S/D/BR/BRD were installed at the crest of the chemical pond dike. The rest of the monitoring wells within the waste boundary were installed in the ash basin. Thirty-nine (39) groundwater monitoring wells were installed outside and downgradient of the ash basin footprint. The downgradient monitoring wells include the following: GWA-1S/D/BR, GWA-2S/D, GWA-3S/D, GWA-10S/DA, GWA-11S/D, GWA-18S/SA/D, GWA-19S/SA/D/BR, GWA-20S/SA/D/BR, GWA- 21S/D, GWA-22S/D, GWA-23S/D, GWA-24S/D/BR, GWA-25BR, GWA-26S/D/BR, GWA-27S/D/BR, GWA-30S/D, GWA-31S/D, GWA-32S/D and MW-200BR. These groundwater monitoring wells were installed to evaluate groundwater quality within the shallow, TZ, and bedrock zones downgradient of the ash basin. Eight existing downgradient voluntary and compliance monitoring wells downgradient of the ash basin were also sampled: MW-101S/D, MW-102S/D, MW-103S/D, and MW-200S/D. Summary of Assessment Activities 2.7 Ash Basin With the exception of the voluntary and compliance well groundwater monitoring described above, no other known groundwater investigations or environmental site assessments have been conducted at the BCSS ash basin prior to implementation of the CAMA Groundwater Assessment Work Plan (HDR, 2014). Solid Waste Facilities Duke Energy was notified in a letter dated November 9, 2011 from NCDENR Division of Waste Management (DWM) that exceedances of the 2L Standards were reported in samples collected from review boundary groundwater monitoring wells at the Pine Hall Road Landfill which is located to the south and upgradient of the ash basin. HDR prepared and submitted an assessment to the NCDENR Division of Waste Management for exceedances of 2L Standards at this landfill (HDR, 2012). The report assessed 2L Standard exceedances at wells MW-3 and MW-6 and found those exceedances to be attributed to naturally occurring conditions. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-12 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx The assessment report reviewed the location of wells and surface water sample locations with exceedances of 2L Standards (MW-4, MW-7, MW2-7, MW2-9, SW-1A, and SW-2) and found that the hydrologic boundaries and the groundwater flow at the site was such that the groundwater at these locations was flowing to the ash basin. The report also concluded that with the reduced infiltration, due to the engineered cover system installed in 2008, the groundwater concentration of constituents attributable to fly ash in these wells will likely continue to decrease over time. There have been groundwater assessments associated with the Craig Road Landfill and FGD Residue Landfill located south of the ash basin on the south side of Belews Reservoir. There is no hydrogeologic connection between these two landfills and the ash basin therefore details related to these assessment and their findings are not included in this report. Structural Fill Per the approved CSA work plan, ash used in the structural fill was not considered part of the source area and was not evaluated during the CSA. Based on exceedances from AOW S-9 south of the ash basin and west of the structural fill, monitoring wells GWA- 23S and GWA-23D were installed and sampled as part of the CAMA Round 5 sampling event (April 2016). Exceedances and concentrations of the constituents in GWA-23S and GWA-23D were similar, indicating that the concentrations were from the same source. The exceedances in GWA 23S/D are consistent with constituents associated with coal ash and a potential source could be the nearby structural fill. As the structural fill was constructed under the NCDEQ DWM structural fill rules found in 15A NCAC 13B .1700 (Permit No. CCB0070), Duke Energy notified DWM of these exceedances. A Proposed Groundwater Assessment Monitoring Plan was prepared and submitted to the NCDEQ DWM in November 2016. The monitoring plan included proposed monitoring well installation locations, and soil sample and surface water sample locations. The structural fill assessment is ongoing at BCSS. To date five monitoring wells (SFMW-1D, SFMW-2D, SFMW-3D, SFMW-4D, and SFMW-5D) have been installed around the structural fill (Figure 2-10). The monitoring well and surface water samples have been collected and the results are pending. The results of the structural fill assessment will be reported to the NCDEQ DWM under separate cover. Other Site Locations Between 1991 and 2017, environmental incidents (i.e., releases) occurred at the BCSS site that initiated notifications to NCDEQ. The historical incidents generally consisted of releases of motor/lubrication or transformer oil (including illegal dumping by unknown 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-13 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx parties) that had potential to impact soil and groundwater at the site. A summary of the historical on-site environmental incidents is provided in Table 2-3. Summary of Initial Abatement, Source Removal or other 2.8 Corrective Action A Settlement Agreement between NCDEQ and Duke Energy signed on September 29, 2015, requires accelerated remediation to be implemented at sites that demonstrate off- site groundwater impacts. Historical and 2015 CSA assessment information indicates the potential for off-site groundwater impact northwest of the BCSS ash basin in the area of the 2.23-acre parcel (hereafter Parcel A) not owned by Duke Energy. Constituents associated with coal ash pore water have been identified within groundwater in shallow (saprolite) and deep (transition zone between saprolite and competent bedrock) flow layers between the ash basin and Parcel A and downgradient of Parcel A. Groundwater in shallow and deep layers near Parcel A flows north and northwest toward the Dan River (located approximately 2,500 feet downstream of parcel A). Groundwater monitoring wells delineating concentrations in this area are located on Duke Energy property. The compliance boundary coincides with the southeast property line of Parcel A. Duke Energy provided an Accelerated Remediation Summary report to NCDEQ on February 17, 2016 which supplemented and updated information included with the CAP Part 2. In correspondence dated March 28, 2016, NCDEQ acknowledged receipt of the Remediation Summary and requested additional information. NCDEQ conditionally approved the Interim Action Plan (IAP) in a letter dated July 22, 2016 with the condition (among others) that a Basis of Design (BOD) Report be submitted for review. Duke Energy provided a response to the conditional approval letter on September 9, 2016. In follow-up, the Table of Contents for the Basis of Design report was adjusted by NCDEQ in a letter dated September 27, 2016. Interim action activities associated with Parcel A consisted of pilot testing with the potential of installing a groundwater extraction system along the northwest corner of the ash basin. Specific objectives outlined in the Interim Action Plan (HDR, 2016) were: Acquire Parcel A. This activity is no longer being pursued by Duke Energy. Conduct initial aquifer tests to evaluate feasibility and aid in the preliminary design of a groundwater extraction system and/or subsurface barrier wall. Recently completed aquifer tests indicate groundwater extraction is a viable remedial alternative at BCSS. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 2-14 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Initiate preliminary design of a groundwater extraction system. Initiate permitting for a groundwater extraction system. Implementation of a groundwater extraction system located between the ash basin and the southeast side of Parcel A will reduce groundwater flow from the ash basin prior to migration toward Parcel A. The primary objective of the groundwater extraction system is to reduce groundwater migration of source area constituents from the ash basin towards the 2.23-acre parcel and achieve a hydraulic boundary proximal to the extraction well network. The following BOD reports have been submitted to date. The purpose of the BOD reports are to provide a system layout and sizing of system components including wells, piping, pumps, discharge system with control system capabilities and power requirements. A 30 % BOD report was submitted to NCDEQ on December 21, 2016 and review comments were received on February 1, 2017. A 60% BOD report was submitted on April 10, 2017 and review comments were received on June 30, 2017. The 100% BOD report was submitted to NCDEQ DWR on September 1, 2017. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 3-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 3.0 SOURCE CHARACTERISTICS For purposes of this assessment, the source area is defined by the ash waste boundary as depicted on Figure 2-1. For the BCSS site, sources include the ash basin, Pine Hall Road Landfill, and the former chemical pond. Coal Combustion and Ash Handling System 3.1 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. BCSS historically produced approximately 650,000 tons of ash per year although in recent years, this number has decreased to approximately 450,000 tons per year. Note that these quantities are an estimate based on generation rates, outages, coal mineralogy, and other factors. Coal ash residue from the coal combustion process has historically been disposed of in the ash basin. Prior to 1984, fly ash and bottom ash generated at the station was sluiced to the ash basin. The Pine Hall Road Landfill was permitted in 1983 when the station converted to dry handling of fly ash. Fly ash is still occasionally sluiced to the ash basin during startup or maintenance activities. Ash Basin The station’s ash basin consists of a single cell impounded by two earthen dams located on the north end of the ash basin and an embankment dam located in the northeast portion of the basin along Pine Hall Rd. The main dam is approximately 2,000 feet long and a maximum of approximately 140 feet high. The top of the dam is at elevation 770 feet and the crest is 20 feet wide. The ash basin was constructed from 1970 to 1972 and is located approximately 3,200 feet northwest of the BCSS powerhouse. The area contained within the ash basin waste boundary is approximately 283 acres (shown on Figure 2-1). The normal operating elevation of the BCSS ash basin pond is 750 feet, while full pond elevation is approximately 768.2 feet. The full pond capacity of the ash basin is estimated to be 17,656,000 cubic yards (cy). The ash basin is operated as an integral part of the station’s wastewater treatment system, which receives flows from the ash removal system, BCSS powerhouse and yard sumps, coal yard sumps, stormwater, landfill leachate, and treated FGD wastewater. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 3-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx During station operations, inflows to the ash basin are highly variable due to the cyclical nature of station operations. Inflows from the station to the ash basin are discharged into the southeast portion of the ash basin. The discharge from the ash basin is through a concrete discharge tower located in the northwest portion of the ash basin. The concrete discharge tower drains through a 21- inch-inside diameter high-density polyethylene (HDPE) conduit for approximately 1,600 feet and then discharges into a concrete flume box. The ash basin pond elevation is controlled by the use of concrete stop logs in the discharge tower. The discharge is to the designated effluent channel that flows northwest to the Dan River. The discharge from the ash basin is permitted by the NCDEQ DWR under NPDES Permit NC0024406. The ash basin originally discharged to Belews Reservoir through a concrete discharge tower located at the east end of the ash basin. Due to water quality issues in Belews Reservoir, in 1984 the original discharge was closed current discharge tower was constructed. The original discharge tower was filled with flowable fill in the mid 1990’s. Duke Energy permanently closed the original discharge tower with cementitious grout in 2015 to avoid potential inadvertent discharges to Belews Reservoir. Pine Hall Road Landfill The Pine Hall Road Landfill (NCDENR Permit No. 8503 - INDUS) received a permit to operate on December 10, 1984 and a subsequent expansion (Phase I Expansion) was permitted in 2003. The unlined landfill was permitted to receive fly ash from the combustion of coal at BCSS. The total footprint of the landfill is approximately 67.2 acres. A total of approximately 8,500,000 cubic yards (cy) of ash was placed within the Pine Hall Road Landfill between December 1984 and March 2008. Structural Fill An unlined structural fill comprised of compacted fly ash was constructed southeast of the ash basin. The structural fill is located south of the Pine Hall Road topographic divide and, therefore, groundwater flow beneath the fill should be predominantly away from the ash basin towards Belews Reservoir. The structural fill is not considered part of the source area evaluated by this CSA. Approximately 968,000 cy of ash were placed within the structural fill. General Physical and Chemical Properties of Ash 3.2 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 3-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Physical Properties Approximately 70 to 80 percent of the ash produced during coal combustion is fly ash (EPRI, January 1995). 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, January 1995). Based on published literature not specific to the BCSS site, the specific gravity of fly ash typically ranges from 2.1 to 2.9, and the specific gravity of bottom ash typically ranges 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 sand-gravel with a similar gradation, grain size distribution, and density (EPRI, January 1995). Chemical Properties In general, 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, 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 historical specific coal sources used at BCSS are bituminous coal from Northern Appalachia and Central Appalachia. 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 (which is considered representative of the ash at BCSS) 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 resistant 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 3-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx the glassy spheres. These surface condensates consist of soluble salts (e.g. calcium (Ca2+), sulfate (SO42-), metals (copper (Cu), zinc (Zn)), and other minor elements (e.g. boron (B), selenium (Se), and arsenic (As)) (EPRI 1995). The major elemental composition of fly ash (approximately 95 percent by weight) is composed of mineral oxides of silicon, aluminum, iron, calcium. Oxides of magnesium, potassium, titanium and sulfur comprise approximately 4 percent by weight (EPRI, January 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 with pH levels ranging from approximately 5 to 10 on contact with water. 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 (EPRI, 2010) reports that 64 samples of coal combustion products (including fly ash, bottom ash, and FGD residue) from 50 different power plants were subjected to EPA Method 1311 Toxicity Characteristic Leaching Procedure (TCLP) leaching and no TCLP result exceeded the TCLP hazardous waste limit. Figure 3-3 provides the results of that testing. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 3-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Site-Specific Coal Ash Data 3.3 Source characterization was performed to identify the physical and chemical properties of the ash in the source areas. 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 collection and analysis of associated solid matrix and aqueous samples. Ash samples were collected for analysis of physical characteristics (e.g., grain size, porosity, etc.) to provide data for evaluation of retention/transport properties within and beneath the ash basin. Ash samples were collected for analysis of chemical characteristics (e.g., total inorganics, leaching potential, etc.) to provide data for evaluation of constituent concentrations and distribution. Samples were collected in general accordance with the Work Plan. Groundwater monitoring wells were installed inside the waste boundary of the ash basin as part of the 2015 CSA investigation. In the boring and monitoring wells performed within the Ash Basin ash was encountered at varying intervals, from 18 to 66 feet below ground surface; auger refusal was encountered between approximately 68 to 88 feet below ground surface (bgs) indicating competent rock. Water levels ranged from approximately 3.4 to 7.6 feet bgs, causing ash to be saturated. Ash was not observed in borings outside the ash basin. Laboratory results of ash samples are presented in Appendix B, Table 4. Physical Properties of Ash Physical properties (grain size, specific gravity, and moisture content) were performed on seven fly ash samples from the ash basin. Physical properties were measured using ASTM methods, lab reports are provided in Appendix C. Ash is generally characterized as a non-plastic silty (medium to fine) sand or silt. Compared to soil, fly ash exhibits a lower specific gravity with two values reported from AB-6GTB (1.7) and AB-7SL (2.2). Moisture content of the fly ash samples ranges from 11.2 to 65.4% (Table 3-2). Ash was generally described as gray to dark gray, non-plastic, loose to medium density, dry to wet, fine- to coarse-grained sandy silt texture. Chemical Properties of Ash Ash samples were collected during the installation of the monitoring wells inside the waste boundary of the ash basin as part of the 2015 CSA investigation. Concentrations 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 3-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx of arsenic, boron, chromium, cobalt, iron, manganese, selenium, and vanadium were reported above soil background concentrations and the North Carolina Preliminary Soil Remediation Goals (PSRGs) for Industrial Health and/or Protection of Groundwater for ash samples collected within the ash basin waste boundary (Appendix B, Table 4). In addition to total inorganic testing of ash samples, seven ash samples collected from borings completed within the ash basin were analyzed for leachable inorganics using Synthetic Precipitation Leaching Procedures (SPLP) (Appendix B, Table 6). The purpose of the SPLP testing is to evaluate the leaching potential of constituents that may result in impacts to groundwater above the 2L Standards or IMACs. The results of the SPLP analyses indicated that antimony, arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium exceeded their respective 2L Standard or IMAC. Although SPLP analytical results are being compared to the 2L Standards or IMAC, these samples do not represent groundwater samples and the 2L Standards and IMACs are not applicable to the results (presented for comparative purposes only). Background soil SPLP data collected from various sites in the Piedmont is presented as Table 3-3. The following metals leach from naturally occurring soils in similar geologic settings at concentrations greater than 2L or IMAC: barium, chromium, cobalt, iron, manganese, nickel, thallium, and vanadium. 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. Nine pore water monitoring wells (AB-4S, AB-4SL, AB- 5S, AB-5SL, AB-6S, AB-6SL, AB-7S, AB-8S, and AB-8SL) were installed within the ash basin waste boundary and were screened within the ash layer. Since installation as part of the first 2015 CSA, these wells have been sampled eight times up to the second quarter of 2017 as part of the CAMA monitoring program. Concentrations of antimony, arsenic, beryllium, boron, chloride, chromium, cobalt, iron, manganese, selenium, sulfate, thallium, vanadium, and total dissolved solids (TDS) have been reported above the background groundwater concentration range and 2L Standards or IMACs in pore water samples collected from wells within the ash basin. The pore water sampling results show a decrease in constituent concentrations at some locations with most locations showing stable concentrations. No significant increases in constituent concentrations were observed. Pore water sample locations and results are shown on Figure 2-10 and are listed in (Appendix B, Table 1). Piper diagrams have been prepared for groundwater results from BCSS monitoring wells and are discussed in Section 10.0. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 3-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Relative redox conditions were determined using an assignment of redox conditions based on concentrations of dissolved oxygen (O2), nitrate (NO3–), manganese (Mn2+), iron (Fe2+), sulfate (SO42–), and sulfide (sum of dihydrogen sulfide [aqueous H2S], hydrogen sulfide [HS–], and sulfide [S2–])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. The ash pore water is generally anoxic to mixed (oxic-anoxic). Ash pore water at BCSS for AB-4S, AB-7S, and AB-8S resembles bituminous coal ash leachate water from EPRI’s 2006 study which is a calcium-magnesium-sulfate water type. In comparison, BCSS ash pore water from AB-6S and AB-8SL have an elevated bicarbonate component. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.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. Refer to Section 12.0 for a discussion of ecological receptors. The NORR CSA receptor survey guidance requirements include listing and depicting all water supply wells, public or private, including irrigation wells and unused wells unless such wells have been properly abandoned in accordance with 15A NCAC 2C .0113, 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, NCDEQ DWR acknowledged the difficulty with determining the known extent of contamination at this time and stated that they expected all drinking water wells located 2,640 feet (0.5-mile) downgradient from the established compliance boundary to be documented in the CSA reports as specified in the CAMA requirements. Water supply well locations near BCSS are depicted on the USGS map (Figure 4-1). 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 (Table 4-1). Properties located within the 0.5-mile radius of the BCSS ash basin compliance boundary generally consist of residential properties located to the southwest and residential farm land northeast, north, and west. Duke Energy property is located to the north, northwest, south, and east with Belews Reservoir beyond to the south and east (Figure 4-2). No residential potable water supply lines are available to the area, with the nearest residential water supply line, provided by the Town of Walnut Cove, located at the intersection of Martin-Luther King Jr. Road and Crestview Drive, approximately 4.5 miles to the west from the Duke Power Steam Plant Road entrance to the Station. BCSS plant is supplied with potable water from the City of Winston-Salem. The water line enters the property from the south along Craig Road and does not extend beyond that location. NORR CSA guidance requires that subsurface utilities are to be mapped within 1,500 feet of the known extent of contamination in order to evaluate the potential for 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx preferential pathways. Identification of piping near and around the ash basin was conducted by Stantec in 2014 and 2015 and utilities around the Site were also included on a 2015 topographic map by WSP USA, Inc. (Appendix E). It is anticipated that any underground utilities present at the site would not act as potential preferential pathways for contaminant migration through underground utility corridors to water supply well receptors. The flow of groundwater from the ash basin is north toward the Dan River. Summary of Receptor Survey Activities 4.1 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 Site compliance boundary have been reported to NCDEQ: Drinking Water Well and Receptor Survey – Belews Creek Steam Station (HDR, 2014), Supplement to Drinking Water Well and Receptor Survey – Belews Creek Steam Station (HDR, 2014), Comprehensive Site Assessment Report – Belews Creek Steam Station Ash Basin, (HDR, 2015a), Drinking Water Well and Receptor Survey – Belews Creek Steam Station (HDR, 2014). The first report submitted in September 2014 (Drinking water Well and Receptor Survey, HDR) included the results of a review of publicly available data from NCDEQ, NC OneMap GeoSpatial Portal, DWR Source Water Assessment Program (SWAP) online database, county Geographic Information System (GIS), 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 (Appendix D). The second report submitted in November 2014 (Supplement to Drinking Water Well and Receptor Survey, HDR) 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 compliance boundary(Appendix D). 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. Table 4-2 presents available information about identified wells including the owner's name, address of the 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx well with parcel number, construction and usage data, and the approximate distance from 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 51 wells might be located within or in close proximity to the survey area (public wells, assumed private wells, field identified private wells, and recorded private wells). Summary of Receptor Survey Findings 4.2 No public or private drinking water wells or wellhead protection areas were found to be located downgradient of the ash basin. This finding was supported by field observations, a review of public records and groundwater flow direction. The location and relevant information pertaining to suspected water wells located upgradient or sidegradient of the facility, within 0.5 miles of the compliance boundary, were included in the survey reports as required by the NORR. 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, November 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. Base on the report, 19 of the 58 households surrounding BCSS have been recommended for installation of an individual filtration system. A total of 51 water supply wells were identified within a 0.5-mile radius of the ash basin compliance boundary. Thirty-nine (39) private water supply wells were identified within a 0.5-mile radius of the ash basin compliance boundary. The Stokes County Department, Division of Environmental Health had records for 20 of the 39 private water supply wells. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Eleven additional private water supply wells are assumed at residences located within a 0.5-mile radius of the ash basin compliance boundary, based on the lack of public water supply in the area and proximity to other residences that have private wells. One public water supply well was identified within a 0.5-mile radius of the ash basin compliance boundary. No wellhead protection areas were identified within a 0.5-mile radius of the ash basin compliance boundary. Several surface water bodies that flow from the topographic divide along Middleton Loop Road toward the Dan River were identified within a 0.5-mile radius of the ash basin. Public Water Supply Wells 4.2.1 One public supply well was located during the receptor survey within 0.5-mile radius of the ash basin compliance boundary. The Withers Chapel United Methodist Church (UMC) public water supply well is approximately 1,750 feet (0.3 miles) northeast of the ash basin. Private Water Supply Wells 4.2.2 A total of 50 private water supply wells were identified within the 0.5-mile radius of the ash basin compliance boundary; most northeast of the ash basin along Pine Hall Road and Middleton Loop, and west and southwest of the ash basin along Middleton Loop, Old Plantation Road, Pine Hall Road, and Martin Luther King Jr. Road. Several efforts have been made to locate and document the presence of and information related to private water supply wells in the vicinity of BCSS. Duke Energy submitted a Drinking Water Well and Receptor Survey report in September 2014, and subsequently submitted a supplement to the receptor survey in November 2014. The 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 receptor surveys and the questionnaires indicated that one 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx public water supply wells and 50 private water supply wells were in use within 0.5 miles of the BCSS ash basin compliance boundary. The receptor survey reports included a sufficiently scaled map showing the ash basin location, the facility property boundary, the waste and compliance boundaries, all monitoring wells, and the 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. Private and Public Well Water Sampling 4.3 Between February and July 2015, NCDEQ arranged for independent analytical laboratories to collect and analyze water samples obtained from private wells identified during the Well Survey, if the owner agreed to have their well sampled. At the time of the 2015 CSA report, NCDEQ had collected and analyzed a total of 7 groundwater samples from 7 private water supply wells within a 0.5 mile radius of the BCSS ash basin compliance boundary. The analytical data was provided in the 2015 CSA report as an appendix. NCDEQ continued to collect and analyze samples from water supply wells within a 0.5 mile radius of the BCSS ash basin compliance boundary during 2015 and early 2016. A total of 36 samples from 36 private monitoring wells were collected by NCDEQ. Duke Energy collected samples from private water supply wells in 2016 and 2017 after the NCDEQ sampling effort. Sample IDs in the 1000 and 2000 range were sampled by Duke Energy. Table 4-3 provides tabulated results, provided by Duke Energy, for the NCDENR and Duke Energy sampling results as well as identified exceedances of 2L Standards, IMACs, and/or other regulatory limits. For many of the wells sampled in this program, as with standard practice, samples were split for analysis by Duke Energy’s certified (North Carolina Laboratory Certification #248) laboratory. The results were judged by Duke Energy to be substantially the same as the NCDENR results; however the analysis of determining potential groundwater impact focuses on NCDENR results. A review of the analytical data for the water supply wells indicated several constituents were detected above 2L or IMACs including pH (19 wells), arsenic (six wells), chromium (one well), cobalt (one well), iron (five wells), manganese (six wells), and vanadium (ten wells). Concentrations of analyzed constituents exceeded their 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx respective bedrock provisional background threshold values (PBTVs) for a number of private water supply wells (data/values biased by the presence of high turbidity are excluded) including: Arsenic – 23 wells Barium – 18 wells Beryllium – 1 well Cadmium – 4 wells Calcium – 25 wells Chromium (hexavalent) – 8 wells Chromium (total) – 1 well Copper – 19 wells Iron – 10 wells Lead – 36 wells Magnesium – 20 wells Manganese – 14 wells Molybdenum – 7 wells Nickel – 1 well Selenium – 2 wells Sodium – 1 well Sulfate – 9 wells TDS – 10 wells Vanadium – 10 wells Zinc – 25 wells The exceedances of PBTVs in private water wells was further evaluated. First, the bedrock PBTVs have been developed using groundwater data from two background bedrock wells located on the BCSS site. The geochemical data from these wells may not be representative across the broader area encompassed by the private water supply wells surrounding the site. 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, as described, private 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 well screens, proper filter pack installation, proper well development, and proper sample collection procedures employed. Fourth, 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 private 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Based on the bedrock groundwater flow direction at the site (Figures 6-10 and 6-11, discussed in Section 6.3) private water supply wells located west of the ash basin along Old Plantation Road (WSWs samples BC2019-RAW, BC2 Well 1, BC2 Well 2, BC-1007, BC4, BC4A and BC4B) are located sidegradient and in relative proximity to the ash basin. The remaining water supply wells identified in the area are located upgradient or sidegradient substantially beyond the expected flow zone of the BCSS ash basin. Analytical data is not available for water supply well BC4. The turbidity reading in BC4 Well B at the time of sampling was 19.3 NTU, therefore the data is not considered valid, and is not evaluated. Iron was reported at concentrations which exceed the bedrock PBTV (228 µg/L) and the 2L standard (300 µg/L) in water supply well samples BC-1007, BC2 Well 1, BC2 Well 2, and BC2019-RAW. However, the iron concentrations in these water supply wells are within the background concentration range for similar Piedmont geologic settings (Table 4-4). Vanadium was reported at a concentration greater than the IMAC but less than the bedrock PBTV in water supply well sample BC2019-RAW, and greater than the IMAC and PBTV in BC4 Well A. However, the vanadium concentrations in these water supply wells are within the background concentration range for similar Piedmont geologic settings (Table 4-4). Boron was not detected in any of these water supply wells sampled sidegradient of the ash basin along Old Plantation Road. A Piper diagram for water supply well data compared to ash basin pore water, background bedrock monitoring wells and bedrock monitoring wells located downgradient of the ash basin (between the ash basin and the private water supply wells) is presented as Figure 4-3. Observations based on the diagram include: Water supply wells are characterized as calcium bicarbonate water type, consistent with samples collected from the background bedrock well at BCSS. Monitoring well MW-203BR (located between the ash basin and the private water supply wells to the west) plots along with background well BG-2BR, indicating this well is likely representative of unimpacted groundwater. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Monitoring well GWA-9BR (located between the ash basin and the private water supply wells to the west) plots between calcium-magnesium sulfate type water and calcium bicarbonate water, a result of the concentration of chloride (52.7 mg/L) relative to the concentration of sulfate and may indicate potential mixing with source area groundwater. A more thorough evaluation of piper diagrams related to ash pore water, downgradient groundwater, and background conditions is provided in Section 10 of this report. The water quality signature of the water supply wells is similar to the background bedrock well data at the site indicating that these wells reflect natural background conditions. See Section 10.1 for background concentrations determined through statistical analysis. Numerical Well Capture Zone Analysis 4.4 In BCSS CAP 2 (HDR, 2016d), potential constituent of interest (COI) impacts to private water supply wells located within the model domain were evaluated through particle tracking simulations by applying a constant pumping rate of 400 gallons per day in each well, which represents the average household usage per United States Environmental Protection Agency (USEPA) Water Sense Partnership Program (USEPA, 2015). Reverse particle tracking was conducted for private water supply wells within the model domain. The reverse particle tracks did not reach the BCSS Compliance Boundary, indicating the water supply wells located beyond the compliance boundary did not have ash-related impacts (Figure 4-2). Surface Water Receptors 4.5 The Site is located in the Roanoke River watershed. The site is located between Belews Reservoir to the south and the Dan River to the north. Groundwater influenced by the ash basin flows north toward to the ash basin designated effluent channel that extends from the base of the ash basin dam and flows northwards through Duke Energy property discharging to the Dan River (NPDES outfall 003). Surface water classifications in North Carolina are defined in 02B. 0101 (c). The surface water classification for the Dan River and Belews Reservoir in the vicinity of the BCSS site is Class WS-IV and Class WS-IV–C, respectively. Class WS-IV waters are protected as water supplies which are generally in moderately to highly developed watersheds. Class C are waters protected for uses such as secondary recreation, fishing, wildlife, fish consumption, aquatic life including propagation, and survival. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 4-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx No surface water intakes, other than the intake used to pump water from Belews Reservoir for BCSS plant operations, the intake on Belews Reservoir to pump water for water trucks at the Craig Road Landfill, and the backup intake for cooling lake makeup water on the Dan River, are located in the vicinity of BCSS either in Belews Reservoir or in the Dan River. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 5-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY North Carolina lies within three physiographic provinces of the southeastern United States: the Coastal Plain, Piedmont, and Blue Ridge (Fenneman, 1938). The BCSS site is located in the Piedmont province. The Piedmont province is bounded to the east and southeast by the Atlantic Coastal Plain and to the west by the escarpment of the Blue Ridge Mountains, with a width ranging from 150 miles to 225 miles in the Carolinas (LeGrand, 2004). A discussion of geology and hydrogeology relevant to the BCSS site is provided below. Regional Geology 5.1 The topography of the Piedmont region is characterized by low, rounded hills and long, rolling, northeast-southwest trending ridges (Heath R. C., 1984). Stream valley to ridge relief in most areas ranges from 75 feet to 200 feet. Along the Coastal Plain boundary, the Piedmont region rises from an elevation of 300 feet above mean sea level, to the base of the Blue Ridge Mountains at an elevation of 1,500 feet (LeGrand, 2004), (Daniel & Dahlen, 2002). The BCSS site is within the Milton terrane, one of a number of tectonostratigraphic terranes that have been defined in the southern and central Appalachians. It is bounded on the northwest by the Dan River Basin and Sauratown Mountains Anitclinorium and on the southeast by the Carolina terrane of the larger Carolina superterrane (Figure 5-1; (Horton, Jr., Drake, Jr., & Rankin, 1989); (Hibbard, Stoddard, Secor, & Dennis, 2002); (Hatcher, Jr., Bream, & Merschat, 2007)). A geologic map of the area around the BCSS site is provided as Figure 5-2. The Milton terrane is characterized by strongly foliated gneisses and schists, commonly with distinct compositional layering and felsic composition; quartzite, calc-silicate gneiss, and marble are minor units (Carpenter III, 1982); (Butler & Secor, 1991). The available evidence suggest that the rocks of the Milton terrane are mainly Precambrian in age and were metamorphosed and deformed during the early to late Paleozoic (Butler & Secor, 1991)). The majority of the rocks in the belt are metamorphosed to the sillimanite and kyanite grade of amphibolite metamorphism (Butler & Secor, 1991). A steep metamorphic gradient occurs along the southeastern boundary where the grade decreases to the chlorite zone of greenschist metamorphism in the adjacent Carolina terrane (Butler & Secor, 1991). This boundary with the Carolina terrane is also a lithologic discontinuity and is marked locally with sheared rocks (Carpenter III, 1982). The southwestern boundary of the belt is placed where the gneiss and schist units give way to the dominant non-layered mafic and felsic intrusive rocks of the Charlotte terrane (Butler J. R., 1980). 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 5-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx The Dan River Triassic Basin (Danville Basin in Virginia) is one of several exposed rift basins that form two parallel belts that strike northeasterly within the Piedmont province. The basins are aligned subparallel to the Appalachian terranes (Figure 5-1) and formed along pre-existing zones of faulting and then subsided during a period of crustal stretching (Olsen, Froelich, Daniels, Smoot, & Gore, 1991). The Dan River Basin is located in the western belt of rift basins and is bounded on the southeast by the Milton terrane and on the northwest by the Sauratown Mountains Anticlinorium and the Smith River allochthon (Figure 5-1; (Horton, Jr., Drake, Jr., & Rankin, 1989); (Hibbard, Stoddard, Secor, & Dennis, 2002); (Hatcher, Jr., Bream, & Merschat, 2007)). The Sauratown Mountains Anticlinorium consists of four stacked thrust sheets and subsequent erosion has exposed a complex, multitiered window or exposure of these thrust sheets (Horton & McConnell, 1991). A complex sequence of interlayered and faulted calc-silicate gneiss, biotite-augen gneiss, quartz-feldspar gneiss, epidosite, and amphibolite characterize the anticlinorium (Horton & McConnell, 1991). The Smith River allochthon consists predominately of biotite gneiss in North Carolina (Horton & McConnell, 1991). The fractured bedrock is overlain by a mantle of unconsolidated material known as regolith. The regolith includes residual soil and saprolite zones and, where present, alluvial deposits. Saprolite, the product of chemical weathering of the underlying bedrock, is typically composed of clay and coarser granular material and reflects the texture and structure of the rock from which it was formed. The weathering products of granitic rocks are quartz-rich and sandy textured. Rocks poor in quartz and rich in feldspar and ferro-magnesium minerals form a more clayey saprolite (LeGrand, 2004). 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. Regional Hydrogeology 5.2 The groundwater system in the Piedmont Province, in most cases, is comprised of two interconnected layers, or mediums: 1) residual soil/saprolite and weathered fractured rock (regolith) overlying 2) fractured crystalline bedrock (Heath R. , 1980); (Harned & Daniel, 1992). The regolith layer is a thoroughly weathered and structureless residual soil that occurs near the ground surface with the degree of weathering decreasing with depth. The residual soil grades into saprolite, a coarser grained material that retains the structure of the parent bedrock. Beneath the saprolite, partially weathered/fractured bedrock occurs with depth until sound bedrock is encountered. This mantle of residual soil, saprolite, and weathered/fractured rock is a hydrogeologic unit that covers and crosses various types of rock (LeGrand, 1988). This layer serves as the shallow 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 5-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx unconfined groundwater system and provides an intergranular medium through which the recharge and discharge of water from the underlying fractured rock occurs. Within the fractured crystalline bedrock layer, the fractures control both the hydraulic conductivity and storage capacity of the rock mass. A transition zone (TZ) at the base of the regolith has been interpreted to be present in many areas of the Piedmont. Harned and Daniel (1992) describe the TZ as consisting of partially weathered/fractured bedrock and lesser amounts of saprolite that grades into bedrock. They also describe the TZ as “being the most permeable part of the system, even slightly more permeable than the soil zone” (Harned & Daniel, 1992). Harned and Daniel (1992) suggested the zone may serve as a conduit of rapid flow and transmission of contaminated water. Until recently, most of the information supporting the existence of the TZ was qualitative based on observations made during the drilling of boreholes and water- wells, although some quantitative data is available for the Piedmont region (Stewart, 1964a); (Nutter & Otton); (Harned & Daniel, 1992). Using a database of 669 horizontal conductivity measurements in boreholes at six locations in the Carolina Piedmont, Schaeffer (Schaeffer, 2014a) statistically showed that a TZ of higher hydraulic conductivity exists in the Piedmont groundwater system when considered within Harned and Daniel’s (1992) two types of bedrock conceptual framework. The TZ is comprised of partially weathered rock, open, steeply dipping fractures, and low angle stress relief fractures, either singly or in various combinations below refusal (auger, roller cone, or casing advancer; (Schaeffer, 2011); (2014b). The TZ has less advanced weathering relative to the regolith and generally the weathering has not progressed to the development of clay minerals that would decrease the permeability of secondary porosity developed during weathering, (i.e., new fractures developed during the weathering process, and /or the enhancement of existing fractures). The characteristics of the TZ can vary widely based on the interaction of rock type, degree of weathering, degree of systematic fracturing, presence of stress-relief fracturing, and the general characteristics of the bedrock (foliated/layered, massive, or in between). The TZ is not a continuous layer between the regolith and bedrock; it thins and thickens within short distances and is absent in places (Schaeffer, 2011); (2014b). The absence, thinning, and thickening of the TZ is related to the characteristics of the underlying bedrock (Schaeffer, 2014b). The TZ may vary due to different rock types and associated rock structure. Harned and Daniel divided the bedrock into two conceptual models: 1) foliated/layered (metasedimentary and metavolcanic sequences) and 2) massive/plutonic (plutonic and metaplutonic complexes) structures (Harned & Daniel, 1992). Strongly foliated/layered rocks are thought to have a well-developed TZ due to the breakup and weathering 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 5-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx along the foliation planes or layering, resulting in numerous rock fragments (Harned & Daniel, 1992). More massive/plutonic rocks are thought to develop an indistinct TZ because they do not contain foliation/layering and tend to weather along relatively widely spaced fractures (Harned & Daniel, 1992). Schaeffer (Schaeffer, 2014a) proved Harned and Daniel’s (Harned & Daniel, 1992) hypothesis that foliated/layered bedrock would have a better developed transition zone than plutonic/massive bedrock. The foliated/layered bedrock transition zone has a statistically significant higher hydraulic conductivity than the massive/plutonic bedrock transition zone (Schaeffer, 2014a). LeGrand’s (1988); (1989) conceptual model of the groundwater setting in the Piedmont, applicable to the BCSS site, incorporates the Daniel and Harned (1992) two-medium regolith/bedrock system into an entity that is useful for the description of groundwater conditions. That entity is the surface drainage basin that contains a perennial stream (LeGrand, 1988). Each 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; Figure 5-3; (LeGrand, 1988); (1989); (2004). Rarely does groundwater move beneath a perennial stream to another more distant stream or across drainage divides (LeGrand, 1989). The crests of the water table underneath topographic drainage divides represent natural groundwater divides within the slope-aquifer system and may limit the area of influence of wells or contaminant plumes located within their boundaries. The concave topographic areas between the topographic divides may be considered as flow compartments that are open-ended down slope. Therefore, the groundwater system is a two-medium system restricted to the local drainage basin. The groundwater occurs in a system composed of two interconnected layers: residual soil/saprolite and weathered rock overlying fractured crystalline rock separated by the TZ. Typically, the residual soil/saprolite is partially saturated and the water table fluctuates within it. Water movement is generally preferential through the weathered/fractured and fractured bedrock of the TZ (i.e., enhanced permeability zone). The character of such layers results from the combined effects of the rock type, fracture system, topography, and weathering. Topography exerts an influence on both weathering and the opening of fractures, while the weathering of the crystalline rock modifies both transmissive and storage characteristics. The igneous and metamorphic bedrock in the Piedmont consists of interlocking crystals and primary porosity is very low, generally less than 3 percent. Secondary porosity of crystalline bedrock due to weathering and fractures ranges from 1 to 10 percent (Freeze & Cherry, 1979); but, porosity values of 1 to 3 percent are more typical (Daniel III & Sharpless). Daniel (1992) reported that the porosity of the regolith ranges from 35 to 55 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 5-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx percent near land surface but decreases with depth as the degree of weathering decreases. In natural areas, groundwater flow paths in the Piedmont are almost invariably restricted to the zone underlying the topographic slope extending from a topographic divide to an adjacent stream. Under natural conditions, the general direction of groundwater flow can be approximated from the surface topography (LeGrand, 2004). Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation. Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains (LeGrand, 2004). Average annual precipitation contributing to recharge in the Piedmont ranges from 42 to 46 inches. Mean annual recharge in the Piedmont ranges from 4.0 to 9.7 inches per year (Daniel, 2001). 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 6.0 SITE GEOLOGY AND HYDROGEOLOGY Geology beneath the BCSS site can be classified into three units. Regolith (surficial soils, fill and reworked soil, and saprolite) is the shallowest geologic unit. 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 BCSS site. The third unit, competent bedrock, is defined by rock core recovery, RQD and the degree of fracturing in the rock. Typically, mildly productive fractures (providing water to wells) were observed within the top 50 feet of competent rock. In general, three hydrogeologic units or zones of groundwater flow can be described for the BCSS Site. The zone closest to the surface is the shallow flow layer encompassing saturated conditions, where present, in the residual soil or saprolite beneath the Site. A transition zone (deep flow layer) is encountered below the shallow flow layer and above the bedrock, is characterized primarily by partially weathered rock of variable thickness. The bedrock flow layer occurs below the transition zone and is characterized by the storage and transmission of groundwater in water-bearing fractures. Site investigations included performing soil borings, collection of soil and rock cores, groundwater monitoring wells, borings installed in the ash basin 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 through 6-3, respectively. The analytical methods used with solid and aqueous samples are presented in Table 6-4 and Table 6- 5. Table 2-1 summarizes the well construction data for CAMA-related wells and piezometers at the Site. Strategic locations for anchoring flow path transects were selected. Boring logs, well construction records and well abandonment records 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. The BCSS ash basin acts as a bowl-like feature which groundwater flows towards. Groundwater then flows from the basin to the east, northeast, northwest but primarily north towards the Dan River. Groundwater at the Site flows away from the topographic and hydrologic divide (highest topographic portion of the Site) generally located along Pine Hall Road to the north towards the ash basin and south towards Belews Reservoir. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Three transects were selected to illustrate flow path conditions in the vicinity of the ash basin. Section A-A’ is a transverse section through the ash basin, parallel to groundwater flow. Section B-B’ illustrates conditions perpendicular to groundwater flow, traversing from west to east across the site. Section C-C’ is a traverse south to north along the western edge of the ash basin. Site Geology 6.1 The BCSS site and its associated ash basin are located in the Milton terrane. The Milton terrane is characterized by strongly foliated gneisses and schists, commonly with distinct compositional layering and felsic composition; quartzite, calc-silicate gneiss, hornblende gneiss and schist, and marble are minor units (Carpenter III, 1982); (Butler & Secor, 1991); (Schaeffer, 2001)). The majority of the rocks in the belt are metamorphosed to the sillimanite and kyanite grade of amphibolite metamorphism (Butler & Secor, 1991). The Dan River Triassic Basin is located approximately 3,000 feet north of the site. Geologic units mapped in the vicinity of the site include alluvium, terrace deposits, sedimentary rocks of the Dan River Basin, a diabase dike, and felsic gneisses and schists with interlayered hornblende gneiss and schist (Figure 6-1; Schaeffer 2001). The alluvium consists of unconsolidated sand, silt, and clay with occasional sub-rounded to well-rounded pebbles and cobbles. The terrace deposits consist of unconsolidated sand, silt, and clay with pebbles and cobles of quartz. In places, the terrace deposits are comprised of large angular quartz fragments in a red matrix of sand, silt, and clay. The diabase occurs in a long, relatively thin dike. The rocks of the Milton terrane in the area include interlayered augen gneiss, quartz-feldspar gneiss, flaser gneiss, “button” mica schist, and with interlayers of hornblende gneiss and schist (Schaeffer, 2001). The installed well and sample locations are shown in Figure 2-10. Soil Classification 6.1.1 Regolith was encountered from a depth range of a few inches to 66 feet at BCSS outside the ash basin. Beneath the ash basin soil samples were collected from 28 to 81.5 feet. The following soils/materials were encountered in the boreholes: Ash – Ash was encountered in borings advanced within the ash basin. Ash was generally described as gray to dark gray, non-plastic, loose to medium dense, dry to wet, fine- to coarse-grained, consistent with fly ash and bottom ash. Fill – Fill material was used in the construction of the ash basin dikes and dam, and generally consisted of re-worked silts, clays, and sands that 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx were borrowed from the site and re-distributed to other areas. Fill was generally classified as silty sand, clay with sand, clay, and sandy clay on the boring logs. Residuum (Residual soils) – Residuum is the in-place weathered soil that consists primarily of silt with sand, clayey sand, sandy clay, clay with gravel, and clayey silts. Residuum varied in thickness and was relatively thin compared to the thickness of saprolite. Saprolite/Weathered Rock – Saprolite is soil developed by in-place weathering of rock that retains remnant bedrock structure. Saprolite consisted primarily of medium dense to very dense silty sand, sandy silt, sand, sand with gravel, sand with clay, clay with sand, and clay. Sand particle size ranged from fine to coarse-grained. Much of the saprolite was micaceous. Alluvial deposits were not encountered in any of the new boreholes or in any of the historic boreholes in the area of the BCSS ash basin. Alluvial deposits were mapped downstream of the ash basin main dam and along the Dan River (Figure 6-1). Geotechnical index property testing of the above soil/materials was performed for disturbed and undisturbed samples in accordance with ASTM standards. Thirty-six undisturbed ('Shelby Tube') samples were submitted for geotechnical index testing. Index property testing for undisturbed samples comprised Unified Soil Classification System (USCS) classification (ASTM, 2001)), natural moisture content (ASTM, 2010), Atterberg Limits (ATSM, 2010), grain size distribution, including sieve analysis and hydrometer (ASTM, 2007), total porosity calculated from specific gravity (ASTM, 2010), and hydraulic conductivity (ASTM, 2010). One undisturbed sample was unable to receive the full suite of index property tests due to low recovery, wax and gravel mixed in the tube, loose material, or damaged tubes. Eighteen disturbed ('Split Spoon,' or 'Jar') samples received grain size distribution with hydrometer (ASTM, 2007), and natural moisture content (ASTM, 2010). Results from the geotechnical property testing show background soil samples collected at BCSS range from silty sand to sandy silt. Natural moisture content in the background soil samples is as low as 15.2% (sandy silt) and as high as 40.3% (silty sand). Specific gravity values for the background soil samples are between 2.597 and 2.753. High levels of fine sand, silt, and clay are present in all 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx background soil samples, while low levels of gravel are present in the silty sand samples. Soil samples collected from downgradient boreholes are characterized as silty sand to sandy silt. Downgradient soil samples have natural moisture content levels from 12.2% to 38.7%. Similar to the background soil samples, the downgradient soil samples have a specific gravity range of 2.6 to 2.764. While the downgradient samples are mainly comprised of fine sand, silt and clay, fine gravel is also present in many of the samples. All soil property results are shown in Table 3-2. Rock Lithology 6.1.2 The main rock types in the immediate vicinity of the ash pond are mica schist, schistose mica gneiss, augen gneiss, flaser gneiss, quartz-feldspar gneiss, biotite gneiss, and hornblende schist and gneiss. The mica schist is coarse-grained, well foliated, “button” schist composed of muscovite and quartz with pinhead garnets. Interlayered with the “button” schist are layers of mica schist (non- “button”) and fine- to medium-grained schistose mica gneiss. The augen gneiss is a fine- to medium-grained rock with a well-developed foliation that wraps around conspicuous pods or “eyes” of feldspar and to a lesser extent quartz. They are comprised mainly of quartz, feldspar, and mica. The flaser gneiss consists of small lenses or granular materials (quartz-feldspar-mica) separated by wavy ribbons and streaks of finely crystalline, foliated materials (primarily mica). The quartz-feldspar gneiss is a medium- to coarse-grained, foliated, normally mica-poor rock although some massive varieties (less foliated) have up to 15 percent muscovite. The biotite gneiss is fine- to medium-grained, banded rock consisting of alternating layers of biotite-rich zones and quartz/feldspar-rich zones. The hornblende gneiss and schist is a fine- to coarse-grained, dark colored rock composed of hornblende, biotite, and plagioclase. It is semi-massive to well- foliated and occurs as interlayers in the predominantly felsic rock sequence. A diabase dike has been mapped from the right abutment of the main ash basin dike and extends to the north cutting across the above rock types and the sedimentary rocks of the Dan River Basin. The diabase dike is fine- to medium- grained and consists of pyroxene, hornblende, and plagioclase with minor amounts of olivine (Schaeffer, 2001). Structural Geology 6.1.3 All the rock types are interlayered and the felsic rocks grade laterally and vertically into each other. The contacts of the hornblende gneiss/schist with the felsic rock are generally sharp. Compositional layer is generally parallel to the strongly developed foliation. The orientation of foliation is relatively consistent 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx throughout the area (N72E; 56SE). The presence of “button” schist, augen gneiss, and flaser gneiss indicates that the rocks have been strongly deformed and sheared during at least two episodes of isoclinal folding (Schaeffer, 2001); “buttons” are formed by the intersection of two, nearly parallel, axial planar foliations). The deformation related to folding was ductile, although the presence of thin layers of flaser gneiss indicates that some of the deformation occurred under semi-brittle to brittle conditions (Schaeffer, 2001). Data on the orientation of fractures in the underlying bedrock in the area is sparse due to relatively poor bedrock exposures. Schaeffer (2001) observed three joint sets in outcrops: (1) N20-40W with steep dips (>70o), (2) N to N20E with steep dips (>70o); and (3) a set sub-parallel to layering/foliation N60-75E with dips ranging from 30o to vertical. Very few joints are present in the mica schist. In contrast, the gneissic rocks tend to have more fractures, and the hornblende gneisses and schists have few fractures associated with them compared to the felsic rocks (Schaeffer, 2001). The joints are generally clay-filled in the saprolite/weathered zone above the transition zone (Schaeffer, 2001). Soil and Rock Mineralogy and Chemistry 6.1.4 Soil mineralogy and chemistry analyses are complete and the results are shown in Table 6-1 (mineralogy), Table 6-2 (chemistry, % oxides), and Table 6-3 (chemistry, elemental composition). Completed laboratory analyses of the mineralogy and chemical composition of TZ materials are presented in Tables 6- 6 (mineralogy), 6-7 (chemistry, % oxides), and 6-8 (chemistry, elemental). Rock chemistry results are presented in Table 6-9 (chemistry, % oxides) and Table 6- 10 (chemistry, elemental). All mineralogy reports can be found in Appendix C. The petrographic analysis of seven rock samples (thin-sections) are presented in Table 6-11 (mineralogy). The mineralogical analyses of BCSS soils varied slightly between 23 boring locations but mineralogical composition indicates the dominant minerals in the soils are quartz, feldspar (both alkali and plagioclase feldspars), kaolinite, illite, and muscovite/illite. Other minerals identified include vermiculite/illite, biotite, smectite, chlorite, and amorphous smectites, mica, and iron oxide/hydroxide. Mineralogy results from six TZ samples are comparable to the soil results. The dominant minerals remain quartz, feldspar (both alkali and plagioclase feldspars), illite, kaolinite, and biotite. At BG-2D, a background well located northeast of the ash basin with 55 feet of saprolitic regolith, the mineral assemblage consisted of predominately quartz 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx and clay minerals with 65% quartz, 15% kaolinite, 5% plagioclase feldspar, and 5% vermiculite 5% chlorite, 3% smectite and 2% mica. In comparison, the mineralogical data at AB-3D from a sample recovered from 50 feet in saprolitic regolith below the ash basin includes a similar mineralogical composition of 74% quartz, 10% kaolinite, 2% plagioclase feldspar, and 3% vermiculite, 1% smectite and 10% mica. The similarities in extent of saprolitic depths at boring locations and mineralogical composition suggest uniform regolith conditions across the site. Elemental chemistry of BCSS soils shows highest concentrations of zinc, vanadium, strontium and tin. Other elements identified in most samples are chromium, copper, cobalt, lead and nickel. Elemental chemistry results for all samples from both the TZ and whole rock samples indicate uniform highest concentrations of cerium, zinc, gallium, and lanthanum compared to other elements analyzed. Other elements identified in most samples are copper, cobalt, nickel and lead. The whole rock chemistry of GWA-2D shows the highest concentrations of each element analyzed compared to the other samples collected at BCSS. This location, northeast of the ash basin, shows arsenic concentrations of 17 ppm in the TZ and 24 ppm in bedrock which are elevated relative to all other samples which range from 1 to 9 ppm of Arsenic. Oxide results from each layer show SiO2, Al2O3, and Fe2O3 as the three dominate oxide compositions for all samples analyzed at BCSS: Soil oxide composition: SiO2 (47.20% - 74.97%), Al2O3 (12.18% -26.40%), and Fe2O3 (2.78% - 12.00%) Transition zone oxide composition: SiO2 (64.92% - 72.01%), Al2O3 (13.17% - 16.65%), and Fe2O3 (2.96% - 6.39%) Whole rock oxide composition: SiO2 (63.4% - 74.3%), Al2O3 (15.4% - 21.7%) and Fe2O3 (2.5% - 8.0%) Results also indicate a significant composition of MnO from both the BCSS soils and transition zone with ranges from 0.03% to 0.10% for soils and 0.05% to 0.14% for transition zone. Geologic Mapping 6.1.5 Duke Engineering & Services (2001) and Schaeffer (2001) prepared a detailed geologic map of the area surrounding the BCSS ash basin for expansion of an existing on-site landfill as shown on Figure 6-1. The rock(s) encountered in the 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx boreholes for the monitoring wells and pre-existing wells are shown on Figure 6- 1. Effects of Geologic Structure on Groundwater Flow 6.1.6 The most important effects of structural geology on groundwater flow would be preferential flow along the contacts (~N72E) and along the joints within the bedrock. The north-trending diabase dike could either form a barrier to flow or a flow path depending on its degree of fracturing and weathering both of which are not known. A non-fractured diabase dike would be a flow barrier and would direct groundwater flow along its contact. A fractured, weathered dike could act as a flow channel. The extent of the diabase dike under the ash to the south of the main dam is not known, but it does not extend south of the ash basin based on the geologic mapping (Figure 6-1) Site Hydrogeology 6.2 According to LeGrand, the soil/saprolite regolith and the underlying fractured bedrock represent a composite water-table aquifer system (LeGrand 2002). The regolith provides the majority of water storage in the Piedmont province, with porosities that range from 35 to 55 percent (Daniel & Dahlen, 2002). Calculated porosities specific to the Site (43.4% to 47.3%)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. Saprolite thickness varies across the Site but is generally thickest in upgradient areas (20 to 60 feet for GWA-8S and MW-202S) and thins in downgradient areas near the Dan River (5 to 12 feet for GWA-24S and MW-200s). Based on the site investigation, the groundwater system in natural materials (soil, soil/saprolite, and bedrock) at the BCSS site is consistent with the regolith-fractured rock system and is an unconfined, connected aquifer system as discussed in Section 5.2. Regolith is underlain by a transition zone (TZ) of weathered rock which transitions to competent bedrock. The groundwater system at the BCSS site is divided into three flow layers referred to in this report as the shallow, deep (TZ), and bedrock layers, so as to distinguish unique characteristics of the connected aquifer system. Hydrostrographic Layer Development 6.2.1 The hydrostratigraphic classification system of Schaeffer (Schaeffer, 2014a) was used to evaluate natural system hydrostratigraphic layer properties. The classification system is based on Standard Penetration Testing values (N) and the Recovery (REC) and Rock Quality Designation (RQD) collected during the drilling and logging of the boreholes (Borehole/Well logs in Appendix F). The 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Schaeffer classification system uses of the terms M1 and M2 to classify saprolite material with the M2 designation indicating greater competency. A transition zone of weathered, fractured rock is delineated between overlying saprolite and underlying bedrock based on rock core recovery (REC) and rock quality designation (RQD). The bedrock zone is classified as having REC>85% and RQD>50%. For discussion purposes, hydrostratigraphic units will be recognized in the text and supporting documents as follows: Shallow Unit – Alluvium/Saprolite (S wells) Deep Unit – Saprolite and weathered rock (D wells) Bedrock Unit – Sound rock, relatively unfractured (BR wells) The shallow zone generally corresponds to the M1 unit and the deep zone incorporates the M2 and weathered, fractured rock layers. Bedrock is identified per the REC and RQD criteria. The designations ash, fill, saprolite, transition zone and bedrock are used on the geologic cross-sections with locations shown on Figure 6-2. Generalized cross sections are presented in Figures 6-3 to 6-5 showing site geology and groundwater flow directions. Hydrostrographic Layer Properties 6.2.2 Ash Pore water The ash pore water unit consists of saturated ash material. Ash depths range from a few feet to approximately 66 feet. The full pond elevation of the BCSS ash basin is approximately 750 feet, yielding approximately 55 feet of saturated ash in the thickest ash locations. Shallow Flow Layer The shallow flow layer consists of regolith (soil/saprolite) material. Thickness of regolith is directly related to topography, type of parent rock, and geologic history. Topographic highs tend to exhibit thinner soil-saprolite zones, while topographic lows typically contain thicker soil-saprolite zones. Wells within the shallow flow layer that are installed within shallow wells contain an “S” designation. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Deep Flow Layer The deep flow layer (transition zone) consists of a relatively transmissive zone of partially weathered bedrock. Observations of core recovered from this zone included rock fragments, unconsolidated material, and highly oxidized bedrock material. Deep flow layer wells are labeled with a “D” designation. Bedrock Flow Layer The fractured bedrock unit occurs within competent bedrock. Bedrock in the immediate vicinity of the ash basin are mica schist, schistose mica gneiss, augen gneiss, flaser gneiss, quartz-feldspar gneiss, biotite gneiss, and hornblende schist and gneiss. The majority of water producing fracture zones was found within 50 feet of the top of competent rock. Water-bearing fractures encountered are only mildly productive (providing water to wells). Bedrock wells are labeled with a “BR” designation. Groundwater Flow Direction 6.3 Based on the CSA site investigation, groundwater flow is generally to the north and northwest in the direction of the Dan River. Groundwater also flows south of the topographic ridge, which follows Pine Hall Road, towards Belews Reservoir. Voluntary, compliance, and groundwater assessment monitoring wells were gauged for depth to water within a 24- hour period during comprehensive groundwater elevation measurement events on September 20, 2016 and April 3, 2017 to provide water level elevation data for dry and wet season (respectively) at the Site. Depth to water measurements were subtracted from surveyed top of well casing elevations to produce groundwater elevations in shallow, deep, and bedrock monitoring wells (Table 6-12). Groundwater flow direction was estimated by contouring these groundwater elevations. Groundwater flow at the BCSS follows the local slope aquifer system (Figure 5-3), as described by LeGrand (LeGrand, 2004)). In general, groundwater within the shallow wells (S), wells in the TZ (D), and wells in fractured bedrock (BR) flows northerly from the ash basin toward the Dan River. A groundwater divide is located approximately along Pine Hall and to the west of the ash basin along Middleton Loop Road. Another groundwater divide exists north of the ash basin along a ridgeline that extends from the east dike abutment toward the northeast. These groundwater divides generally correspond to the topographic divides in these locations. The predominant direction of groundwater flow from the ash basin is in a northerly direction toward the valley where the designated effluent channel flows from the base of the ash basin dam northwest to the Dan River and to the east toward Belews Reservoir. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-10 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx During full-operations (prior to dry ash handling) sluicing to the basin would have had an impact contaminant inputs to the basin. As fly ash production moved to a dry process (1984) the basin water input would have decreased as containment load would have begun to decrease. Beginning in 2018 basin water input should decrease and therefore further reduce containment load. With bulk water removal through dewatering, recharge and containment loading should return to pre-development levels, including groundwater flow patterns. The shallow, deep and bedrock water level maps during September 2016 and April 2017 are included as Figures 6-6 through 6-11. Hydraulic Gradient 6.4 Horizontal hydraulic gradients were derived for April 2017 water levels measurements in the shallow, TZ, 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) Applying this equation to wells installed during the CSA activities yields the following average horizontal hydraulic gradients (measured in feet/foot): Shallow wells: 0.009 ft/ft Deep wells: 0.010 ft/ft Bedrock wells: 0.019 ft/ft Generally horizontal gradients in the ash basin range from 0.002 to 0.004 ft/ft. Horizontal gradients outside the waste boundary range from 0.006 to 0.035 ft/ft. The hydraulic gradient south of the ash basin (GWA-12BR to MW-202BR) and northwest of the dam (GWA-16S to GWA-11S) is likely due to the much higher relief between the basin and downgradient areas. A summary of horizontal hydraulic gradient calculations is presented in Table 6-13. Vertical hydraulic gradients were calculated by taking the difference in groundwater elevation in a deep and shallow well pair over the difference in total well depth of the 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-11 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx deep and shallow well pair. A positive output indicates downward flow and a negative output indicates upward flow. Vertical gradient calculations for 32 shallow and deep well pair locations and 9 deep to bedrock well pair locations, were used to calculate vertical hydraulic gradient across the site. Applying this calculation to wells installed during the CSA activities yields the following average vertical hydraulic gradients (measured in feet/foot): Shallow to Deep wells: 0.0195 ft/ft Deep to Bedrock wells: 0.0967 ft/ft Based on review of the results, vertical gradients were mixed across the site but with more locations showing downward gradient values. More upward values were noted south of the ash basin and the topographic high of Pine Hall Road near Belews Reservoir (GWA-12, GWA-23, and BG-3 locations), downgradient of the basin near the Dan River (GWA-30 and GWA-31) and northeast of the basin (BG-2). Vertical gradient calculations are summarized in Table 6-14 and shown in Figure 6-12. Hydraulic Conductivity 6.5 Hydraulic conductivity (slug) tests were completed in monitoring wells. Slug tests were performed to meet the requirements of the May 31, 2007 NCDENR Memorandum titled, Performance and Analysis of Aquifer Slug Tests and Pumping Tests Policy. Water level change during the slug tests was recorded by a data logger. The slug test was performed for no less than 10 minutes, or until such time as the water level in the test well recovered 95 percent of its original pre-test level, whichever occurred first. Slug tests were terminated after 60 minutes even if the 95 percent pre-test level was not achieved. Slug test field data was analyzed using the Aqtesolv (or similar) software and the Bouwer and Rice method. These previously reported horizontal and vertical groundwater conductivity results are presented in Table 6-15 and 6-16. Additionally, in situ hydraulic conductivities were calculated using slug test results reported in CSA Supplement 2 (HDR, 2016c) (Appendix C) to determine groundwater velocity by grouping hydraulic conductivity (slug) test data into their respective hydrostratigraphic units and calculating the geometric mean, maximum and minimum. Hydrostratigraphic layers are defined in Section 11.1. Hydraulic conductivity values for wells screened in saprolite have a geometric mean of 2.65 x 10-4 cm/sec. Hydraulic conductivity values for wells screened in the transition zone have a geometric mean of 7.91 x 10-5 cm/sec. These measurements reflect the dynamic nature of the transition zone, where hydrologic properties can be heavily influenced by the formation of clays and other weathering by-products. Hydraulic conductivity results for bedrock wells 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-12 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx across the Site have a geometric mean of 2.76 x 10-5 cm/sec . The hydraulic conductivity measurements in bedrock wells can be regarded as a generalized representation of the localized bedrock fractures in specific areas of a well cluster. In situ horizontal hydraulic conductivity values for each hydrostratigraphic unit established are in Table 6-17. Groundwater Velocity 6.6 To calculate the velocity that water moves through a porous media, 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 = Ki/ne 𝑣𝑣𝑠𝑠 = seepage velocity, K = horizontal hydraulic conductivity, i = the horizontal hydraulic gradient; and ne = effective porosity. Seepage velocities for groundwater were calculated using horizontal hydraulic gradients established by grouping hydraulic conductivity (slug) test data into their respective hydrostratigraphic units and calculating the geometric mean, maximum and minimum. Horizontal hydraulic conductivity values for each hydrostratigraphic unit established in Table 6-17, and effective porosity values established in Tables 6-18 and 6-19. Hydrogeologic porosity reports are provided in Appendix C. Hydrostratigraphic layers are defined in Section 11.1. Average groundwater seepage velocity results are summarized in Table 6-13. At BCSS, 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 velocity using effective porosity values and the method presented above. Bedrock fractures encountered at BCSS 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-13 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 Basin over time, refer to discussion concerning groundwater fate and transport modeling (Section 13.0). Contaminant Velocity 6.7 Migration, retardation, and attenuation of COIs in the subsurface is a factor of both physical and chemical properties of the media in which the groundwater passes. Soil samples were collected and analyzed for grain size, total porosity, soil sorption (Kd), and anions/cations to provide data necessary for completion of the three-dimensional groundwater model discussed in Section 13. The pore water in the ash basin is the source of constituents reported greater than background concentrations, 2L standards, and IMACs in groundwater samples in the vicinity of the ash basins. Gradients measured within the ash basin support the interpretation that ash pore water mixes with shallow/surficial groundwater and migrates downward into the transition zone and bedrock flow zones. Continued vertical migration of groundwater is also evidenced by detected constituent concentrations. 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 a similar velocity to groundwater. The higher Kd values measured for the remaining metals, like thallium and cobalt, agree with the limited migration of these constituents. Constituents like cobalt and thallium have much higher Kd values, and will move at a much slower velocity than groundwater as it sorbs onto surrounding soil. Groundwater migrates under diffuse flow conditions in the shallow and deep aquifer in the direction of the prevailing gradient. As constituents enter the transition zone material, the rate of constituent transport has the potential to increase from 7.66 x10-6 cm/sec in the shallow zone to 1.62 x10-05 cm/sec in transition zone, as demonstrated by groundwater seepage velocity results (Table 6-13). It should be noted that the fractured bedrock flow system is highly heterogeneous in nature and high permeability zones with a geomean in situ horizontal conductivity of 0.00003 cm/sec observed, but these hydraulic conductivity measurements measure the fractures immediately adjacent to a well screen, not across the distance between two bedrock wells and cannot be applied across the entire Site. Geochemical mechanisms controlling the migration of 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-14 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx constituents are discussed further in Section 13. Groundwater modeling to be performed for the updated CAP will include a discussion of contaminant velocities for the modeled constituents. Slug Test and Aquifer Test Results 6.8 In-situ horizontal (open hole) and vertical (flush bottom) permeability tests, either falling or constant head as appropriate for field conditions, were performed in each of the hydrostratigraphic units above refusal, ash, fill, and soil/saprolite. In-situ borehole horizontal permeability tests, either falling or constant head tests as appropriate for field conditions, were performed just below refusal in the first 5 feet of a rock cored borehole (TZ, if present). The flush bottom test involves advancing the borehole through the overburden with a casing advancer until the test interval is reached. The cutting tool is removed from the casing and the casing is filled with water to the top and the water level drop in the casing is measured over 60 minutes. In the open hole test, after the top of the test interval is reached, the cutting tool but not the casing, is advanced an additional number of feet (five feet in the majority of tests) and water level drop in the casing is measured over 60 minutes. The constant head test is similar except the water level is kept at a constant level in the casing and the water flow-in is measured over 60 minutes. The constant head test was only used when the water level in the borehole was dropping too quickly back to the static water level such that the time interval was insufficient to calculate the hydraulic conductivity. The results from the field permeability testing are summarized in Table 6-20 and the worksheets are provided in Appendix C. Packer tests (shut-in and pressure tests) were conducted in a minimum of five boreholes. The shut-in test is performed by isolating the zone between the packers (in effect, a piezometer) and measuring the resulting water level over time until the water level is stable. The shut-in test provides an estimate of the vertical gradient during the test interval. The pressure test involves forcing water under pressure into rock through the walls of the borehole providing a means of determining the apparent horizontal hydraulic conductivity of the bedrock. Each interval is tested at three pressures with three steps of 20 minutes up and two steps of 5 minutes back down. The pressure test results are summarized in Table 6-20 and the shut-in and packer tests worksheets are provided in Appendix C. Where possible, tests were conducted at borehole locations specified in the Work Plan and at test intervals based on site-specific conditions at the time of the groundwater assessment work. The U.S. Bureau of Reclamation test method and calculation 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-15 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx procedures, as described in Chapter 10 of their Ground Water Manual (1995), were used for the field permeability and packer tests. Historic field permeability and packer/pressure test data for the BCSS site are presented in Table 6-21. Fracture Trace Study Results (if applicable) 6.9 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 hence 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. Healed fractures intruded by diabase are common in the vicinity of the site. Strong 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 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. Methods 6.9.1 Available geologic maps for the area were consulted prior to performance of aerial-photography and topographic-map interpretation, to identify lithologies and geologic structure in the area that can control fracture occurrence and 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-16 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx orientations. Topographic-map interpretation was performed over an area of approximately 22 square miles, and aerial-photography interpretation was performed over an area of approximately 5 square miles. Topographic-map interpretation involved examination of the Belews Creek, N.C. 1:24,000-scale USGS 7.5-minute topographic quadrangle. A digital copy of the quadrangle was obtained and viewed on a monitor at up to 7x magnification. Lineaments identified were plotted directly on the digital images. Photography provided for review included 1”= 600’ scale, 9 x 9 inch black-and- white (grayscale) contact prints dated April 17, 2014.The photography was examined using a Lietz Sokkia MS-27 mirror stereoscope with magnifying binocular eyepiece. Lineaments identified on the photographs were marked on hard copies of scanned images (600dpi resolution), and subsequently compiled onto a photomosaic base. Results 6.9.2 Lineaments identified from topographic maps are shown and lineament trends indicated by a rose diagram are included on Figure 6-13. A total of 35 topographic lineaments were identified across the study area, mainly north, west, and southwest of the site. The prevalent trend is toward the northwest, with subsidiary trends toward the north, northeast, and west-northwest. The north and northwest trending lineaments are in general agreement with orientations of Triassic diabase dikes and with the N20-40W and N-N20E joint sets discussed in Section 6.1.3. The northeast and west-northwest trending lineaments correlate well with foliation and joint trends in the Milton terrane rocks that underlie the study area (Figure 6-1). Lineaments identified from aerial photography are shown and lineament trends indicated by a rose diagram are included on Figure 6-14. A total of 25 lineaments were identified. These were primarily in the form of linear morphological highs, linear morphological lows (linear stream valleys, ravines, and gullies), and light- colored linear outcrops of the Milton terrane rocks. Generally, the lineament trends from the aerial photography correlate with those identified from topographic-map interpretation. Relatively fewer northwest- trending lineaments, and more north-trending lineaments (both being subparallel to regional diabase dike orientations) were identified on aerial photography. Few west-northwest trending lineaments were identified, and northeast trending lineaments identified on aerial photography are oriented 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 6-17 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx primarily N25E as opposed to N40E for those identified from topographic-map interpretation. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 7-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 7.0 SOIL SAMPLING RESULTS Soil, PWR, and bedrock samples were collected from background locations, beneath the ash basin, and from locations beyond the waste boundary. The purpose of soil and rock characterization is to evaluate the physical and geochemical properties in the subsurface with regard to COI presence, retardation, and migration. Soil and rock sampling was performed in general accordance with the procedures described in the Work Plan utilized for groundwater assessment activities. Refer to Appendix G for a detailed description of these methods and Appendix G for field and sampling quality control / quality assurance protocols. Table 6-4 summarizes the parameters and constituent analytical methods for soil, PWR, and bedrock samples collected. Total inorganic results for background soil, PWR, and bedrock samples can be found in Appendix B, Table 4. Soil borings were conducted in upgradient and downgradient (laterally and vertically) areas of the ash basins in order to collect soil samples from the unsaturated zone and the zone of saturation for these areas (Figure 2-10). Cross-section transects are presented in plan view on Figure 6-2 and with vertical distribution COIs along each transect depicted on Figures 11-4 through 11-63. BCSS does not have SPLP results for background soil samples. Regional background soil SPLP results are averaged for comparison and are presented in Table 3-3. Although SPLP analytical results are being compared to the 2L Standards or IMAC, these samples do not represent groundwater samples. Background Soil Data 7.1 Because some COIs are naturally occurring in soil and are present in the source areas, establishing background concentrations is important for determining whether releases have occurred from the source areas. Background (BG) boring locations were identified based on the Site Conceptual Model at the time the Work Plan was submitted and approved. The background locations (BG-1, BG-2, BG-3 and GWA-12) were chosen in areas believed not to be impacted by CCR leachate based on existing knowledge of the site and topographically upgradient of the ash basin. Based on the groundwater contours shown in Figures 6-6 through 6-11, and the Site Conceptual Model, the background locations are considered to be hydrologically upgradient of the ash basin. As a result, the background boring locations are considered to be representative of background soil and rock conditions at the BCSS site. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 7-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx An updated background soil dataset was provided to NCDEQ for BCSS on May 26, 2017. 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. On July 7, 2017, NCDEQ provided a response letter (Zimmerman to Draovitch, July 7, 2017) for each Duke Energy coal ash facility that identified soil and groundwater data appropriate for inclusion in the statistical analysis to determine provisional background threshold values (PBTVs) for both media (Appendix A). As outlined in the NCDEQ July 7, 2017 letter, Duke Energy was required to provide PBTVs for each media within 30 days from receipt of the NCDEQ letter for facilities submitting CSAs by October 31, 2017. NCDEQ requested that Duke Energy collect a minimum of 10, rather than the previously planned eight, valid background samples prior to the determination of PBTVs for each constituent. The background dataset provided to NCDEQ on May 26, 2017 included pooled soil samples collected from multiple depth intervals. Only samples collected from background locations at depth intervals greater than one foot above the seasonal high water table were included in the dataset. The background soil dataset has been further revised from the May 26, 2017 submittal based on input from NCDEQ in the July 7, 2017 letter. Additional soil samples were collected on July 26, 2017 to satisfy the minimum number of soil samples and to provide values for antimony, selenium and thallium below the PSRG Protection of Groundwater values (Figure 2-10). The dataset was screened for outliers once the additional samples were included in the dataset Table 7-1. The soil background dataset and PBTVs were sent to NCDEQ in an Updated Background Threshold Values for Soil Technical Memorandum dated August 30, 2017 and approved by NCDEQ DWR in a response letter (Zimmerman to Draovitch) dated September 1, 2017 (Appendix A). PBTVs for soil constituents are provided in Table 7-2. Boring logs associated with the additional soil samples are included in Appendix F. Facility Soil Data 7.2 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 the Ash Basin Soil samples within the ash basin waste boundary (including dams) were obtained from AB-1S, AB-2D/GTB, AB-3S/D, AB-4D, AB-5D, AB-6D/GTB, AB-7D, AB-8D, and AB- 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 7-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 9S/D. The range of constituent concentrations in soils beneath the ash basin and within the waste boundary, along with a comparison to soil PBTVs is provided in Appendix B, Table 4. Geotechnical borings (GTB) were utilized at the BCSS site to supplement soil data needs in a temporary boring used only for collection purposes (i.e., no monitoring wells were installed at these locations). Although some constituent levels were measured above Industrial preliminary soil remediation goals (PSRG) and PSRG for protection of groundwater (POG) standards in soil samples beneath the basin, when compared to the Site’s PBTVs most constituent levels appeared to be similar to calculated soil background values for the Site. For soil samples below the ash, arsenic and chromium were reported at concentrations that exceeded the Industrial PSRG. Arsenic, boron, chromium, cobalt, iron, manganese, selenium and vanadium had reported values above the PSRG for POG. All soil samples beneath the ash basin that had PSRG exceedances were greater than or equal to those in the ash. Boron concentrations were not detected greater than the PSRG values or the Site PBTV (17 mg/kg) below the ash basin. Of the PSRG exceedances, concentrations of six arsenic samples and one selenium sample exceeded the respective PBTV for the Site. The exceedances are depicted on Figure 7-1. Soil sample test results indicate shallow impacts to the soil beneath the ash basin Soil Beyond the Waste Boundary Soil samples outside the waste boundary were obtained from GWA-1S, GWA-2D, GWA-3S/D, GWA-4S, GWA-5S/GTB, GWA-6S, GWA-7S, GWA-8D, GWA-9S/GTB, GWA-10D, GWA-11D, GWA-12D, MW-200BR, MW-203BR, and SB-3. The range of constituent concentrations in soils outside the waste boundary, along with a comparison to the range of reported background soil concentrations, is provided in Appendix B, Table 4. Constituent concentrations for soils outside the waste boundary tend to be similar to background soil concentrations for all constituents with the exception of barium and cobalt (but are within one order of magnitude). The barium concentration at GWA- 9GTB (a geotechnical boring located near the GWA-9 well cluster) and cobalt concentrations at SB-3 for the singular soil sample were above the POG PSRGs and account for the upper ranges for these constituents. All other barium and cobalt concentrations obtained outside the waste boundary were similar to those measured at background locations. Additionally, arsenic and chromium had concentrations above the Industrial PSRG in several soil sample locations. Detected concentrations of arsenic, chromium, cobalt, iron, manganese, selenium and vanadium in multiple locations exceeded the PSRG for 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 7-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx POG. Several of the arsenic and iron soil concentrations that exceeded PSRG standards also exceeded the PBTV. Three locations, GWA-6S (68.5-70), GWA-9S (50-52) and GWA- 11D (55-55.4), had concentrations of iron that exceeded the PBTV. Locations GWA-6S (68.5-70) exceeded the PBTV for chromium and GWA-7S (30-31.5) exceeded the PBTV for selenium. Concentrations of boron from wells beyond the compliance boundary did not exceed PSRG values and only two locations exceeded the PBTV at GWA-6S and MW-200BR. The majority of exceedances are sporadic and do not indicate the ash basin as a source of soil impacts beyond the waste boundary. Comparison of PWR and Bedrock Results to Background Samples were obtained from locations ouside the waste boundary; two PWR samples at BG-1S and GWA-3D, and three bedrock samples at BG-2D, MW-200BR, and MW- 203BR,. The range of constituent concentrations in PWR and bedrock samples outside the waste boundary, along with a comparison to the reported PBTV, is provided in Appendix B, Table 4. Chromium exceeded the Industrial PSRG and POG for two of the rock samples. Arsenic, iron, manganese, and vanadium exceeded the PSRG POG in four of the samples. Of the PSRG exceedances, the chromium concentration from MW-203BR is the only exceedance above the PBTV (41.09 mg/kg). Secondary Sources Soil samples were collected during assessment activities from areas beneath the ash basin, and outside the ash basin and within the compliance boundary. Concentrations of arsenic, barium, chloride, chloride, chromium, cobalt, iron, selenium, strontium and vanadium in soils were found to be greater than the POG PSRGs or PBTV for one or more sample locations. Soils beneath the ash basin were found to have exceedances of the POG PSRGs and/or PBTVs limited to a shallow interval beneath the basin. Arsenic, selenium and strontium exceeded the PBTV in at least one soil sample beneath the ash basin. Constituent concentrations often decrease with depth in borings beneath the ash basin. Constituent occurrences in areas outside the ash basin may exceed site-specific PBTVs but elevated concentrations of chromium, iron, strontium and vanadium in areas upgradient of the ash basin (GWA-6S, GWA-7S and GWA-8D) are not influenced by the ash basin and associated with natural soil geochemistry. Saturation and other factors may also affect constituent occurrence in the samples. Geochemical modeling which will be included in the CAP is anticipated to help in determining constituent association with coal ash and an appropriate site remedy if necessary. The locations to be evaluated for site remedy are depicted on Figure 7-1. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 8-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 8.0 SEDIMENT RESULTS Sediment samples were collected from 19 locations beyond the perimeter of the ash basin (Figure 2-10) during and after the 2015 CSA field effort. Sediment sampling procedures and variances are provided in Appendix G and analytical results are presented in Appendix B, Table 5. Sediment/Surface Soil Associated with AOWs 8.1 Eleven of the 19 sediment sampling locations were co-located with designated Areas of Wetness (AOWs). The “sediment” that was collected was actually surface soil over which water at the AOW was flowing or seeping. Sediment samples were collected on October 5 and 8, 2015 (Round 2). Four of the 19 sediment sample locations were co-located with NCDENR March 2014 water sample locations (BCSW-007, BCSW-008, BCSW-018A, and BCSW019). These locations are stormwater outfalls to Belews Reservoir. It is assumed that the sediment collected from these locations was actually surface soil over which water was flowing or seeping. Sediment samples were collected on October 5, 2015 (Round 2). The remaining 4 sediment samples were collected beneath Belews Reservoir and are discussed in Section 8.2. The sediment sample results were compared to North Carolina PSRGs for POG, and are presented in Appendix B, Table 5. Sediment sample locations are shown on Figure 2- 10. A description of AOWs S-1 through S-11 and the results of sediment analysis are provided below, as well as the results of sediment analysis for locations BCSW-007, BCSW-008, BCSW-018A, and BCSW-019: S-1: Steady flow emerging from several springs within channel that appears to follow natural topography that trends away from a ridge separating the ash basin from the apparent drainage area. Sediment was collected from the channel. No constituents exceeded their PBTVs for soil. Cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. S-2: Steady flow within ravine channel that appears to follow natural topography that trends away from a ridge separating the ash basin from the apparent drainage area. Flow is continuous but occasionally it disappears and reappears from the ground surface. Sediment was collected from the channel. No constituents exceeded their PBTVs for soil. Arsenic, chromium, cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 8-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx S-3: Steady continuous flow within ravine channel appears to follow natural topography that trends away from a ridge separating the ash basin from the apparent drainage area. Sediment was collected from the channel. The concentration of arsenic exceeds the soil PBTV. Arsenic, chromium, cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. S-4: Steady continuous flow within ravine channel appears to follow natural topography that trends away from a ridge separating the ash basin from the apparent drainage area. Sediment was collected from channel. No PSRG values are established for strontium and this is the only constituent that exceeded the PBTV at this location. Chromium, cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. S-5: Steady continuous flow within ravine channel appears to follow natural topography that trends away from a ridge separating the ash basin from the apparent drainage area. Sediment was collected from the channel. The concentration of arsenic exceeds the soil PBTV. Arsenic, chromium, cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. Boron was detected in this sample. S-6: Moderate flow of clear water emerging from toe of dam below the ash basin former outfall and berm. Sediment collected from the channel. Concentrations of nickel, strontium, sulfate and zinc exceed their soil PBTVs. Chromium, cobalt, iron, manganese, selenium and vanadium concentrations exceeded their PSRGs for POG. Boron was detected in this sample. S-7: Low flow wide area with shallow water depth. Sediment collected beneath inundated area. The concentration of arsenic exceeds the soil PBTV. Arsenic, chromium, cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. S-8: Well defined stream approximately 2.5 feet wide and 3 to 4 inches deep on average with a sandy substrate. Sediment was collected from stream bed. No constituents exceeded their soil PBTVs. Chromium, iron, manganese and vanadium concentrations exceeded the PSRG for POG. Boron was detected in this sample. S-9: Steady trickle to moderately flow clear water stream. Sediment was collected from the stream bed. No constituents exceeded their soil PBTVs. Chromium, iron, manganese and vanadium concentrations exceeded the PSRG for POG. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 8-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx S-10: Flow emerging from downstream terminus of wetland areas on west side of the base of the ash basin dam. Sediment was collected from the channel. The concentrations of arsenic and strontium exceed their soil PBTVs. Arsenic, chromium, cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. Boron was detected in this sample. S-11: Flow originates from piping that captures flow from main ash basin dam. Sediment collected from channel. Aluminum, arsenic and nickel concentrations exceeded their soil PBTVs. Arsenic, chromium, cobalt, iron, manganese and vanadium concentrations exceeded their PSRGs for POG. Boron was detected in this sample. BCSW-007: Sample is located southeast of the ash basin and the plant near Belews Reservoir. Copper, barium, nickel, selenium and strontium concentrations exceeded their respective soil PBTVs. Arsenic, chromium, cobalt, iron, manganese, selenium and vanadium concentrations exceeded their PSRGs for POG. BCSW-008: Sample is located west of the FGD Residue Landfill near Belews Reservoir. No PSRG values are established for sulfate and this is the only constituent that exceeded the PBTV at this location. Chromium, cobalt, iron, manganese, selenium and vanadium concentrations exceeded their PSRGs for POG. Boron was detected in this sample. BCSW-018A: Sample is located southeast of the structural fill near Belews Reservoir. No constituents exceeded their PBTVs. Chromium, cobalt, iron, manganese, selenium and vanadium concentrations exceeded their PSRGs for POG. BCSW-19: Sample is located south of the ash basin downgradient from AOW location S-9. No constituents exceeded their soil PBTVs. Chromium concentration exceeded both the Industrial PSRG and POG. Cobalt, iron, manganese and vanadium concentrations exceeded the PSRG POG. Boron was detected in this sample. Sediment in Major Water Bodies 8.2 Sediment samples were collected coincidentally with the surface water samples along the shore line of the Dan River (SD-DR-U and SD-DR-D) and Belews Reservoir (SD-BL- U and SD-BL-D) during CSA sampling Round 1 (July 2015). 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 8-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Sediment samples were analyzed in accordance with the constituent and parameter list used for soil and rock characterization (Table 6-4). In the absence of NCDEQ sediment criteria, the sediment sample results were compared to North Carolina PSRGs and soil PBTVs, and are presented in Appendix B, Table 5. Sediment sample locations are shown on Figure 2-10. Exceedances of the PSRGs for POG in the sediment samples included chromium (SD- DR-U, SD-DR-D, and SD-BL-U), cobalt (SD-DR-D), iron (all samples), manganese (SD- DR-U, SD-DR-D, and SD-BL-D), selenium (SD-DR-D), and vanadium (all samples). Sample SD-DR-D exceeded the PBTV for chloride where no PSRG value has been established. Sample SD-DR-U had four exceedances (chromium, iron, manganese, and vanadium) while the downstream sample had seven exceedances (arsenic, chromium, cobalt, iron, manganese, selenium, and vanadium). Sample SD-DR-D also had boron detected in the sample. Sample SD-BL-U had three exceedances (chromium, iron and vanadium) while the downstream sample had four exceedances (chromium, iron, manganese and vanadium). None of the PSRG exceedances were greater than the PBTVs. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 9.0 SURFACE WATER RESULTS The BCSS ash basin is located in the central part of the BCSS site and receives surface water runoff and groundwater recharge from upland areas south of the basin. Groundwater from the ash basin flows downgradient of the ash basin dam predominately through the designated effluent channel, discharging to the Dan River (NPDES outfall 003). Surface water analytical results associated with samples collected from the Dan River and Belews Reservoir are included in Appendix B, Table 2. The surface water sample locations are included on Figure 2-10. Aqueous matrix parameters and analytical methods are shown on Table 6-5. As shown Figures 10-5 to 10-64, the extent of groundwater migration from the ash basin at concentrations greater than background and 2L extend downgradient of the ash basin but do not reach the Dan River or Belews Reservoir. Therefore, the surface water data reflect contributions from sources other than groundwater migration from the ash basin. Water samples discussed within the following sections include four distinct types: 1) ash basin wastewater and wastewater conveyance (effluent channels), 2) areas of wetness (AOWs), 3) industrial stormwater, and 4) named surface waters. For this CSA, it is pertinent that a comparison with NCDENR Title 15A, Subchapter 02B. Surface Water and Wetland Standards (2B) standards includes only sample results from named surface waters. AOWs, wastewater and wastewater conveyances (effluent channels), and industrial storm water are evaluated and regulated 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. Ash Basin Water Samples Water samples (SW-1, SW-1A, SW-2, and SW-AB1 through SW-AB9) were collected from water ponded within the ash basin. Sample SW-10 is located downstream of the ash basin main dam in the designated effluent channel. This sample is also considered to be representative of ash basin water. The ash basin water is not considered surface water or groundwater and the results are presented for discussion purposes only. Ash basin water sample locations are shown on Figure 2-10 and analytical results are listed in Appendix B, Table 3. Belews Creek Area of Wetness (AOW) Sample Locations Sixteen AOWs (S-1 through S-16) have been identified and sampled routinely for monitoring purposes. Eleven AOWs (S-1 through S-11) were identified and sampled as 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx part of the 2015 CSA. The BCSS site is inspected semi-annually for the presence of existing and potentially new AOWs along the Belews Reservoir shoreline, downgradient of the ash basin, including observations by boat and by land. Inspections by land included observations of the ash basin along toe of the dikes; areas below full pond elevation for the ash basin; between the ash basin and receiving waters; and drainage features associated with the basin including engineered channels. Per the interim administrative agreement, these inspections are governed by the Discharge Identification Plan (DIP) until the NPDES permit is issued. AOW locations S-12, S-13, S- 14, S-15, and S-16 were identified after the 2015 CSA sampling effort. These locations are being evaluated for separately in accordance with the NPDES permit and do not have applicable criteria. The analytical results of these samples are for discussion purposes only. AOW sample locations are shown on Figure 2-10 and analytical results are listed in Appendix B, Table 3. Dan River and Belews Reservoir Sample Locations Dan River sample SW-DR-BG collected upstream of the confluence of the ash basin designated effluent channel (outfall 003) with the Dan River outside of the Duke Energy property boundary is considered to be representative of background surface water quality conditions in the river. Dan River sample SW-DR-U was collected immediately upstream of the confluence of the ash basin designated effluent channel (outfall 003) with the Dan River and sample SW-DR-D was collected immediately downstream of the confluence. Sample SW-DR-U has had contaminant concentrations reported as being greater than the background surface water sample (and reported 2B surface water standard exceedances), which suggests that there may be influence from the ash basin at this location along the Dan River. However, contaminant concentrations detected in SW- DR-U were similar to those in sample 003, collected at the ash basin discharge structure flume in the designated effluent channel, indicating that the location of sample SW-DR- U may be too close to the designated effluent channel to reflect actual water quality in the Dan River. Eleven additional water samples (S-003-D, S-2-D, S-3-D, S-5-D, SW-DR-1, SW-DR-2, SW-DR-3, SW-DR-4, SW-DR-BG, SW-DR-D and SW-DR-UA) were collected from the Dan River in September 2017 to refine the understanding the potential source of 2B exceedances detected in the river at SW-DR-U. Surface water samples (SW-DR-U, SW-DR-D and SW-DR-BG) were intended to be collected from the Dan River from there previously sampled locations as conditions 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx permitted. Surface water sample SW-DR-U was inadvertently collected further upstream than intended and therefore has been identified as a unique sample location (SW-DR-UA). Samples S-2-D, S-3-D, S-5-D were collected downstream of their respective AOW sample locations from the streams prior to their confluence with the Dan River. Sample S-003-D was collected downstream of sample 003 from the designated effluent channel at the confluence with the Dan River. These sample results do not have applicable criteria and the analytical results of these samples are for discussion purposes only. Surface water samples SW-DR-1, SW-DR-2, SW-DR-3, and SW-DR-4 were collected from the Dan River between the stream channels to evaluate whether the tributaries were potentially influencing water quality in the Dan River. Upstream and downstream surface water samples were collected from Belews Reservoir (SW-BL-U and SW-BL-D). The upstream sample location (SW-BL-U), on the south shore of Belews Reservoir upstream of the Craig Road Landfill, is considered to be representative of background surface water quality conditions in the lake. The downstream Belews Reservoir sample location (SW-BL-D), located west of a boat ramp on the north shore of Belews Reservoir, is considered to be downstream of potential impacts from the ash basin. NCDEQ Sample Locations NCDENR collected water samples from 13 locations at BCSS during March 2014 (Figure 2-10). Analytical results are provided in Appendix B, Table 3. The locations and analytical results from this sampling event were provided by NCDEQ to Duke Energy and are assumed to be accurate. Prior to the dam reinforcement construction activities, water from the ash basin embankment and foundation was captured in a series of horizontal drains (HD) and engineered flumes (TF) before being routed through a Parshall flume for NCDEQ Dam Safety flow monitoring at the toe of the dam (ABW). Water sample identifiers and location relative to former and current site features are: TF-1, TF-2, TF-3, HD-07A, HD-09, HD-10, HD-11A, HD-21, HD-22, HD-24, HD- 25, HD-26, HD-27, ABW (base of ash basin dam; primarily monitoring discharge from toe drains installed within the structural fill of the embankment dam) 003 (ash basin discharge structure flume) BCWW-002 (FGD wastewater treatment plant effluent) 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx BCSW-018A and BCSW-019 (stormwater outfalls adjacent to railroad tracks near Belews Reservoir) BCSW-08 (stormwater outfall adjacent to FGD Landfill) Samples TF-1, TF-2, TF-3, HD-07A, HD-09, HD-10, HD-11A, HD-21, HD-22, HD-24, HD-25, HD-26, HD-27 and ABW, are representative of ash basin water, the sample results do not have applicable criteria and are presented for discussion purposes only. As a result of dam reinforcement activities, the embankment drainage system is now connected to a single discharge point. Therefore, monitoring the previous toe drainage locations is no longer possible. Sample BCWW-002 was collected from the FGD wastewater treatment plant effluent and is wastewater and therefore is not evaluated with regards to exceedances of regulatory standards or background concentrations. Samples BC-018A, BCSW-019, and BCSW-08 are stormwater outfalls and these locations do not have applicable criteria and are presented for discussion purposes only. Comparison of Exceedances to 2B Criteria 9.1 The following surface water sample locations occur in the Dan River and are compared to 2B (Class WS-IV) values. SW-DR-BG, S-2D, SW-DR-1, S-3D, SW-DR-2, S-5D, SW-DR-3, SW-DR-UA, SW- DR-U, SW-DR-D, and SW-DR-4. The following surface water sample locations occur in Belews Reservoir and are compared to 15A NCAC 02B (Class C) values. SW-BL-U and SW-BL-D SW-DR-BG and SW-BL-U are considered background surface water quality locations with regards to the downgradient samples collected on the Dan River (SW-DR-1, SW- DR-2, SW-DR-3, SW-DR-UA, SW-DR-U, SW-DR-D, and SW-DR-4) and from Belews Reservoir (SW-BL-D), respectively. Therefore, in addition to comparing downstream surface water results with the 2B standards they are also compared with the background surface water location results. The background surface water concentrations have not been statistically derived or approved by NCDEQ and are for discussion purposes only. Analytical results with the dissolved phase concentrations greater than their associated total reportable concentrations are not included in the assessment as they are considered invalid. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Data presented below lists the sample ID, the constituent that has been reported with a 2B exceedance, and the number of reported 2B exceedances over the number of sampling events in parenthesis: Dan River Samples SW-DR-BG: (Dan River background sample): No 2B exceedances (0/2) SW-DR-1: No 2B exceedances (0/1) SW-DR-2: No 2B exceedances (0/1) SW-DR-3: No 2B exceedances (0/1) SW-DR-UA: No 2B exceedances (0/1) SW-DR-U: pH (1/8), Turbidity (2/8), DO (1/8), Chloride (1/8), Selenium (2/8), TDS (2/8), Dissolved Cadmium (1/8), Dissolved Lead (1/8) SW-DR-D: pH (1/9), Turbidity (2/9), Chloride (2/9), Selenium (2/9), TDS (3/9), Dissolved Cadmium (1/8), Dissolved Lead (1/8) SW-DR-4: No 2B exceedances Sample results from the Dan River indicate that field parameters (turbidity, pH, and DO), total concentrations of chloride, selenium, and TDS, dissolved concentrations (cadmium and lead) have been reported as being greater than 2B values on one or two occasions, but not consistently. Belews Reservoir Samples No 2B exceedance have been reported in the samples (SW-BL-U and SW-BL-D) collected from Belews Reservoir over the period of monitoring. Discussion of Results for Constituents Without Established 2B 9.2 A 2B standard has not been established for a number of constituents. A summary of results for select constituents without 2B standards follows. The results are compared with the background surface water data. The background surface water concentrations have not been statistically derived or approved by NCDEQ and are for discussion purposes only. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-10 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Dan River Samples Antimony was not detected in the Dan River background sample at a concentration greater than the MDL (<0.5 µg/L to 1 µg/L). The reported antimony concentrations in the downgradient sample location have been within the range of the reported background concentrations. Boron has not been detected in the Dan River background sample or upstream of the effluent channel confluence. Concentrations of boron at SW-DR-U, SW-DR- D, and SW-DR-4 have been greater than background. Cobalt was reported in the Dan River background sample at a concentration of 0.14 µg/L. During the second sampling event of the background location cobalt was not detected at the MDL (<1 µg/L). Concentrations of cobalt at SW-DR-U and SW-DR-D have exceeded the background concentration range for cobalt. Cobalt has not been detected at the remaining sample locations. Chromium was not detected in the Dan River background sample at a concentration greater than the MDL (<0.5 to <1 µg/L). Concentrations of chromium at SW-DR-U and SW-DR-D have exceeded the background concentration range for chromium. Chromium has not been detected at the remaining sample locations. Hexavalent chromium concentrations were reported at 0.06 µg/L at the Dan River background sample location. Concentrations of hexavalent chromium at SW-DR-3, SW-DR-4, and SW-DR-U have exceeded the background concentration for chromium. The remaining sample locations have had concentrations reported as being less than the background concentration. Iron concentrations range from 459 µg/L to 589 µg/L at the Dan River background sample location. Concentrations of iron at SW-DR-D and SW-DR-U have exceeded the background concentration range for iron. The remaining sample locations have had concentrations reported as being less than the background concentration range. Manganese concentrations range from 51.2 µg/L to 65 µg/L at the Dan River background sample location. Concentrations of manganese at SW-DR-D and SW-DR-U have exceeded the background concentration range for manganese. The remaining sample locations have had concentrations reported as being less than the background concentration range. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-11 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Thallium was not detected at the Dan River background sample at a concentration greater than the MDL (<0.1 to <0.2 µg/L). Concentrations of thallium at SW-DR-D and SW-DR-U have exceeded the background concentration range for thallium. Thallium has not been detected at the remaining sample locations. Vanadium concentrations were reported at 1 µg/L at the Dan River background sample location. Concentrations of vanadium at SW-DR-2, SW-DR-3, SW-DR-4, SW-DR-D and SW-DR-U have exceeded the background concentration for vanadium. The remaining sample locations have had concentrations reported as being less than the background concentration. Belews Reservoir Samples Antimony concentrations range from 0.1 µg/L to <0.5 µg/L in the Belews Reservoir background sample location. The reported antimony concentrations at the downgradient sample location have been within the range of the reported background concentrations. Boron concentrations range from 25.4 µg/L to 71 µg/L in the Belews Reservoir background sample location. The reported downgradient boron concentrations have generally been in the range of the background concentrations with the exception of one sampling event with a result of 72 µg/L. Cobalt concentrations range from 0.01 µg/L to <0.5 µg/L in the Belews Reservoir background sample location. The reported cobalt concentrations at the downgradient sample location have been within the range of the reported background concentrations. Chromium concentrations range from 0.097 µg/L to 0.37 µg/L in the Belews Reservoir background sample location. The reported downgradient chromium concentrations have generally been in the range of the background concentrations with the exception of two sampling events with results of 0.38 and 0.7 µg/L. Hexavalent chromium concentrations range from 0.026 µg/L to 0.12 µg/L in the Belews Reservoir background sample location. The reported hexavalent chromium concentrations at the downgradient sample location have been within the range of the reported background concentrations. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-12 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Iron concentrations range from 39.7 µg/L to 235 µg/L in the Belews Reservoir background sample location. The reported iron concentrations at the downgradient sample location have been within the range of the reported background concentrations. Manganese concentrations range from 6.2 µg/L to 24.3 µg/L in the Belews Reservoir background sample location. The reported manganese concentrations at the downgradient sample location have been within the range of the reported background concentrations. Thallium concentrations range from 0.018 µg/L to <0.1 µg/L in the Belews Reservoir background sample location. The reported thallium concentrations at the downgradient sample location have been within the range of the reported background concentrations. Vanadium concentrations range from 0.48 µg/L to 0.89 µg/L in the Belews Reservoir background sample location. The reported downgradient vanadium concentrations have generally been in the range of the background concentrations with the exception of two sampling events with results of 0.94 and 1 µg/L. Discussion of Surface Water Results 9.3 Dan River Dan River samples SW-DR-U and SW-DR-D have had reported 2B exceedances of turbidity, pH, DO, chloride, selenium, TDS, dissolved cadmium, and dissolved lead. The 2B exceedances have all been greater than the concentrations reported in background sample SW-DR-BG, which does not have any 2B exceedances reported. Dan River sample SW-DR-U was collected immediately upstream of the confluence of the ash basin designated effluent channel with the Dan River, and sample SW-DR-D was collected immediately downstream of the confluence. Water samples SW-DR-1, SW-DR-2, SW-DR-3, and SW-DR-UA were collected from the Dan River in September 2017 between background sample location SW-DR-BG and the SW-DR-U location to refine the understanding the potential source of 2B exceedances reported at SW-DR-U. Exceedances of the 2B standards were not reported in any of the surface water samples collected between SW-DR-BG and SW-DR-UA. A sample was inadvertently not collected from SW-DR-U during the September 2017 sampling event; however it 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-13 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx appears that the 2B exceedances reported in SW-DR-U (and SW-DR-D) are a result of the proximity to the designated effluent channel (outfall 003). The sampling results do not suggest that the reported 2B exceedances in the Dan River are a result of influence from the ash basin. Belews Reservoir No 2B exceedance have been reported in the samples (SW-BL-U and SW-BL-D) collected from Belews Reservoir over the period of monitoring. Based on the available data for the upstream and downstream Belews Reservoir samples the BCSS ash basin is not the source of 2B exceedances in Belews Reservoir. To help determine potential routes of exposure and receptors related to the ash basin, additional surface water samples will be collected from Belews Reservoir and the Dan River near the stream/river bank most likely to be impacted by potentially contaminated groundwater discharge. The additional surface water sampling effort is described in detail in Section 11.3. Piper diagrams, a graphical representation of major water chemistry using two ternary plots and a diamond plot, for AOWs and surface water are included as Figure 9-1 and 9-2. 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. Piper diagrams for groundwater monitoring wells are presented and discussed in more detail in Section 10.0. Piper diagram for AOWs, engineered drains below the dam and surface water locations compared to background surface water (SW-DR-BG) concentrations are presented as Figure 9-1 and 9-2. Observations based on the diagram include: Waters at BCSS are predominately characterized as calcium-chloride bicarbonate water type, with AOW samples from locations S-1, S-8, S-12, S-13, S-15, and surface water locations SW-BL-D and SW-DR-U consistent with those of background waters at BCSS. Upgradient AOW S-9 exhibits higher relative concentrations of sulfate compared with other AOW water types. This location is south of the ash basin and the topographic ridge that divides groundwater flow north and south. The unique water type may be associated with impact from the structural fill. An assessment of the structural fill is ongoing. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 9-14 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Locations S-2, S-4, S-6/ S-6-BL, S-9, S-10 and S-11 indicate potential mixing between background water and impacted AOW waters. Outfall locations and surface water collected from engineered drains below the dam are representative of impacted surface water. Water type from those locations are characterized as chloride-sodium and chloride-bicarbonate. Higher concentrations of chloride relative to the concentration of sulfate indicate mixing of source area water with different basin sources; however the ash basin shows higher concentrations of chloride in water samples than waters that may be influenced from other basins on site. Samples BCSW-008 and BCSW-019 are upgradient of the ash basin and show less chloride impact in water samples. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 10.0 GROUNDWATER SAMPLING RESULTS This section provides a summary of groundwater analytical results for the most recent monitoring event through April 2017 (2Q2017) with discussion of historical data result and trends. A comprehensive table with all media analytical sampling results is provided in Appendix B, Table 1. Most recent and historical groundwater laboratory reports are presented in Appendix I. The current monitoring well network at the site is presented on Figure 2-10. As indicated on the comprehensive data table, for groundwater results, the results have been marked to indicate data points excluded based on a measured turbidity greater than 10 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 available through April 2017 is shown on the pertinent maps. Background data were screened to eliminate outliers. One comprehensive round of sampling and analysis was conducted prior to and reported in the August 2015 CSA. In addition, the following groundwater sampling and analysis events have been completed: Round 2 - September 2015 (reported in the CAP Part 1) Round 3 - November 2015 (background wells only, reported in the CSA Supplement 1 as part of the CAP Part 2 report) Round 4 - December 2015 (background wells only, reported in the CSA Supplement 1 as part of the CAP Part 2) Round 5 – March and April 2016 (72 groundwater monitoring wells, reported in the CSA Supplement 2) Round 6 - May 2016 Round 7 - September 2016 Round 8 - November 2016 Round 9 - January 2017 Round 10 - April 2017 Following CAP approval but prior to final closure, an Interim Monitoring Plan (IMP) has been proposed. The IMP is designed to supplement the compliance monitoring 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx program established as part of the Site NPDES permit. The IMP is designed to monitor near-term groundwater quality changes until the basin closure process has been completed. Monitoring of Site groundwater monitoring wells and surface water locations has been conducted since 2015; although, an approved IMP was not finalized until October 2017. Agreement between NCDEQ and Duke Energy was reached on a list of specific wells to be included in the BCSS IMP (NCDEQ, October 19, 2017) with monitoring to begin during the third calendar quarter of 2017 and culminating in an annual IMP report in April of the following year of monitoring. Additional details concerning the IMP are presented in Section 14.0. Groundwater sampling methods and the rationale for sampling locations were in general accordance with the procedures described in the GAP (HDR, 2014). Variances from the proposed well installation locations, methods, quantities, and well designations are presented in Appendix G. As described in the approved Work Plan, both unfiltered and filtered (0.45 um filter) samples were collected for analyses of constituents whose results may be biased by the presence of turbidity. Unless otherwise noted, concentration results discussed are for the unfiltered samples and represent total concentrations. Background Groundwater Concentrations 10.1 Locations for background monitoring wells installed in 2015 for the initial CSA field effort were chosen based on the information available. The previously installed NPDES monitoring well network provided a rudimentary groundwater water level map. Using those maps, topographic maps, and hydrogeologic expertise, it was determined locations northeast of the ash basin, and south of the topographic/hydrologic divide generally along Pine Hall Road were upgradient and/or background. After the background wells were installed and sampled a sufficient number of tables, 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, Note: NCDEQ incorrectly identifies MW-202D as BG-202D in the letter): BG-2S – Shallow BG-3S – Shallow MW-3 – Shallow MW-202S – Shallow 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx BG-1D – Deep (transition zone) BG-3D – Deep (transition zone) MW-202D – Deep (transition zone) BG-2BR-A – Bedrock MW-202BR – Bedrock Eight background (BG) monitoring wells BG-1S/D, BG-2S/D/BR, BG-3S/D, and MW- 202BR were proposed and installed during the 2015 CSA activities to evaluate background water quality in the shallow (S wells), deep (D wells), and bedrock (BR wells) flow regimes. This was in addition to the two existing NPDES background compliance monitoring wells MW-202S and MW-202D, the Pine Hall Road Landfill background monitoring well MW-3, the Craig Road Landfill background monitoring well CRW-10, and the FGD Residue Landfill background monitoring wells BC-23A and BC-28. Evaluation of the suitability of each of these locations for background purposes was conducted as part of the CAP 1 (Appendix H) and in technical memoranda (December 12, 2016 and May 26, 2017). Factors such as 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. Based on these criteria, the BC-23A, BC-28, and CRW-10 locations were determined to be installed in a different geologic environment than the ash basin. These monitoring wells are located more than one mile southeast of the ash basin and were removed from the background dataset. Monitoring well BG-1S has had insufficient water to sample the well during every monitoring event and therefore is not included in the background dataset. Elevated pH due to grout contamination negated the use of the data collected from monitoring well BG-2BR. On March 28, 2017 monitoring well BG-2BR was replaced with background monitoring well BG-2BR-A. A Piper diagram, also referred to as a tri-linear 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 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 pore water, shallow, deep, and bedrock groundwater including background locations are shown on Figure 10-1, Figure 10-2, and Figure 10-3. 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 three flow zones – shallow, deep, and bedrock. Well locations are presented on Figure 2-10. For the bedrock groundwater dataset, less than 10 valid samples were available for determination of PBTVs. Therefore, no formal upper tolerance limit (UTL) statistics were run and the PBTV for the constituents in the bedrock 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 was considered an outlier and removed from further use and the PBTV was 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 (S.U.) 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); Result is a statistical outlier identified for background sample data presented to NCDEQ on May 26, 2017; 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Shallow Flow Layer Four monitoring wells – BG-2S, BG-3S, MW-202S, and MW-3 – monitor background groundwater quality within the shallow flow layer. NCDEQ indicated in the July 7, 2017 letter that these shallow wells were retained for use in development of PBTVs. The shallow flow layer dataset is presented in Table 10-1. The background groundwater dataset meets the minimum requirement of 10 samples for all constituents. PBTVs were calculated for constituents monitored within the shallow flow zone using formal UTL statistics. PBTVs for the shallow flow layer are provided in Table 10-2. Deep Flow Layer Four monitoring wells – BG-1D, BG-2D, BG-3D, and MW-202D—monitor background groundwater quality within the deep flow layer. NCDEQ indicated in the July 7, 2017 letter that these deep wells were retained for use in development of PBTVs. The deep flow layer dataset is presented in Table 10-1. The background groundwater dataset meets the minimum requirement of 10 samples for all constituents. PBTVs were calculated for constituents monitored within the deep flow layer using formal UTL statistics. PBTVs for the deep flow layer are presented in Table 10-2. Bedrock Flow Layer Two wells, BG-2BR-A and MW-202BR, monitor background groundwater quality within the bedrock flow layer. NCDEQ indicated in the July 7, 2017 letter that these bedrock wells were retained for use in development of PBTVs. The bedrock flow layer dataset is presented in Table 10-1. Currently, the dataset for bedrock does not meet 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx the minimum requirement of 10 samples. PBTVs for constituents in bedrock were computed to be either the maximum value, or, if the maximum value was above an order of magnitude greater than the geometric mean of all values, the second highest value. PBTVs for the bedrock flow layer are presented in Table 10-2. Summary The calculated groundwater PBTVs were less than their applicable 2L Standards or IMACs for all flow layers with the following exceptions: Cobalt in the deep flow layer (PBTV of 1.6 µg/L, IMAC = 1 µg/L) Iron in the shallow flow layer (PBTV of 750 µg/L, 2L = 300 µg/L) Vanadium in all flow layers (shallow PBTV of 1.33 µg/L, deep PBTV of 1.45 µg/L, and bedrock PBTV 0.82 µg/L, IMAC = 0.3 µg/L) pH in all flow layers (shallow PBTV range of 5.1 to 6.0 SU, deep PBTV range of 5.2 to 7.0 SU, bedrock PBTV range of 6.3 to 6.5 SU, 2L range = 6.5 to 8.5 SU) Groundwater PBTVs were also calculated for the following constituents that do not have a 2L Standard, IMAC or Federal MCL established: alkalinity, bicarbonate, calcium, carbonate, magnesium, methane, potassium, sodium, sulfide, and total organic carbon (TOC). Piper Diagrams (Comparison to Background) 10.1.2 A Piper diagram, also referred to as a trilinear 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 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 shallow, deep, and bedrock groundwater including background locations are shown on Figure 10-1, Figure 10-2, and Figure 10-3. All background monitoring well locations are depicted on Figure 2-10. A generalized well construction diagram for assessment wells is shown in Figure 10-4. Well installation 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx procedures are documented in Appendix G. Boring logs and Soil Sample and Rock Core Photographs are provided in Appendix F. Background water types at BCSS are consistent with findings from a five year study of groundwater flow and quality conducted at the Upper Piedmont Research Station, located in a similar geologic setting approximately 22 miles northeast of the Site (Huffman, et al., 2006). Samples collected from background wells at BCSS generally indicate calcium, sodium, or potassium bicarbonate water. Downgradient Groundwater Concentrations 10.2 In order to best reflect current conditions at the site, the second quarter 2017 groundwater sample results are the focus for data evaluation in this report. Results from prior events are incorporated in data evaluation and summarized as appropriate. The second quarter 2017 data is the primary dataset used for generating isoconcentration maps and graphical representation of data such as Piper diagrams. Monitoring wells AB-1S, AB-2S, and AB-3S are located within the ash basin main dam. Monitoring wells MW-101S (abandoned) and MW-102S (abandoned) are located near the toe of the ash basin main dam. These wells are located within the ash basin waste boundary. Monitoring well AB-9S is located within the dam at the chemical pond. The wells are not screened within ash and are therefore not considered pore water wells; however, due to their location within the ash basin waste boundary they are not categorized and evaluated as downgradient wells as the constituent concentrations reported in these wells are expected to be more representative of ash basin water than downgradient groundwater conditions. Groundwater isoconcentration contours with respect to each COI are depicted in Figures 10-5 through 10-63. The isoconcentration maps present COI data in the shallow, deep, and bedrock flow units. Measurements of pH indicated a number of locations with pH less than the 2L lower limit of 6.5, or higher than the 2L upper limit of 8.5. In general, elevated pH measurements are interpreted as the result of grout contaminated wells and in accordance with DEQ guidance, the associated groundwater samples are not used for evaluation of constituent concentrations. Antimony Antimony PBTV and IMAC exceedances were not reported downgradient of the ash basin in the shallow flow layer and are generally located at the southern end of the ash basin. In the deep flow layer the downgradient IMAC exceedances are limited to 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx beneath the southern end of the ash basin and in the vicinity of monitoring well GWA- 9D, near the southwest corner of the basin. No downgradient IMAC exceedances are reported in the bedrock flow layer. Arsenic Arsenic 2L exceedances in the shallow flow layer are limited to within the footprint of the ash basin and not downgradient. Two isolated areas exceeding the 2L standard in the deep flow layer are located north of the ash basin main dam, one inside and one outside of the waste boundary and within the compliance boundary. One bedrock downgradient exceedance of arsenic is located beneath the south end of the ash basin at AB-9BR. Barium One area of barium 2L exceedances was reported northwest and downgradient of the ash basin, outside of the compliance boundary at GWA-19SA; however, no exceedances were reported within the footprint of the basin or between the basin and the well. This well has historical barium 2L exceedances. No barium exceedances were reported in in the deep or bedrock flow layers. Beryllium Beryllium IMAC exceedances are located at and beyond the compliance boundary northwest of and downgradient of the ash basin. Downgradient beryllium exceedances in the deep flow layer are located north of the ash basin main dam, within the compliance boundary at MW-103D, and northwest of the ash basin beyond the compliance boundary at GWA-21D. No beryllium IMAC exceedances were reported in the bedrock flow layer. Boron Downgradient boron exceedances of 2L in the shallow flow layer are primarily located north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance boundary, and west of the structural fill at GWA-23S. In the deep flow layer boron exceedances are located beneath the ash basin and the Pine Hall Road Landfill, north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance boundary. Boron exceedances are also reported south of the topographic divide along Pine Hall Road, west of the structural fill. These exceedances are not related to the ash basin and a separate assessment of the structural fill is ongoing. There are no boron exceedances reported in the bedrock flow layer in wells that are not grout contaminated. Monitoring wells GWA-19BR, GWA-20BR, and GWA-27BR are located northwest of the ash basin. These wells are grout contaminated (high pH) and their 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx data is not considered valid. The boron concentrations reported in these monitoring wells are similar to the boron background concentration. Cadmium There are no cadmium 2L exceedances in the shallow flow layer. Downgradient cadmium exceedances in the deep flow layer are located north of the ash basin main dam within the compliance boundary, northwest of the ash basin at GWA-20D, located at the compliance boundary, and at OB-9 adjacent to the Pine Hall Road Landfill. There are no cadmium 2L exceedances reported in the bedrock flow layer. Chloride Downgradient chloride 2L exceedances in the shallow flow layer are located north of the ash basin main dam within the compliance boundary, and northwest of the ash basin, at and beyond the compliance boundary. Downgradient chloride 2L exceedances in the deep flow layer are located beneath the north end of the ash basin and north of the ash basin main dam within the compliance boundary, and northwest of the ash basin, at and beyond the compliance boundary. No 2L exceedances of chloride were reported in the bedrock flow layer. Chromium Downgradient 2L exceedances of chromium in the shallow flow layer are located east/northeast of the ash basin, beyond the compliance boundary at GWA-3S, north of the ash basin main dam, within the compliance boundary, and north/northwest of the ash basin, beyond the compliance boundary. Downgradient exceedances in the deep flow layer are located beneath the ash basin, west of the ash basin at GWA-16DA, located at the compliance boundary, at GWA-11D and GWA-10DA, northwest of the ash basin beyond the compliance boundary and at GWA-1D, located north of the ash basin at the compliance boundary. No chromium exceedances were reported in the in the bedrock flow layer with the exception of background monitoring well BG-2BRA. Hexavalent Chromium No hexavalent chromium exceedances of the 2L standard for total chromium were reported in the shallow, deep or bedrock flow layers. Exceedances of the PBTV were not reported in the shallow flow layer. Exceedances of the deep flow layer PBTV were reported beneath the ash basin, and southeast and east of the ash basin, and west of the structural fill. Exceedances of the bedrock flow layer PBTV were reported beneath the southern end of the ash basin at AB-4BR and southwest of the ash basin at the compliance boundary at monitoring well MW-203BR. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-10 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Cobalt Downgradient cobalt IMAC exceedances in the shallow flow layer are located northeast, north, northwest, and west of the ash basin, at or beyond the compliance boundary, and southwest of the Pine Hall Road Landfill. Exceedances of the deep flow layer PBTV are located beneath the ash basin, and north, northwest, and west of the ash basin, at or beyond the compliance boundary. No IMAC exceedances in the bedrock flow layer were reported. Iron Downgradient exceedances of the established iron PBTV in the shallow flow layer, which is greater than 2L, are located northeast, north, northwest, and west of the ash basin, at or beyond the compliance boundary and west of the structural fill. Iron exceedances of the 2L standard in the deep flow layer are located beneath the ash basin and north, northwest, west and southeast of the ash basin, at or beyond the compliance boundary, and west of the structural fill. There is one downgradient iron exceedances of the 2L standard at monitoring well AB-9BR beneath the southern end of the ash basin. Manganese Downgradient manganese exceedances of the 2L standard in the shallow flow layer are located east, northeast, north, northwest, and west of the ash basin, at or beyond the compliance boundary, and west of the structural fill. Manganese exceedances of the 2L standard in the deep flow layer are located beneath the ash basin, east, north, northwest, west and southeast of the ash basin, at or beyond the compliance boundary, and west of the structural fill. Manganese downgradient exceedances in the bedrock flow layer are located beneath the ash basin, north and southwest of the ash basin, at or beyond the compliance boundary, and west of the structural fill. Molybdenum Downgradient exceedances of the molybdenum PBTV in the shallow flow layer are located northeast of the ash basin, beyond the compliance boundary at monitoring well GWA-3S, and north of the ash basin near the compliance boundary at GWA-1S. Molybdenum exceedances of the PBTV in the deep flow layer are located beneath the ash basin, northeast of the ash basin, within the compliance boundary, and northwest, west and southeast of the ash basin, at or beyond the compliance boundary, beneath the Pine Hall Road Landfill, and west of the structural fill. Molybdenum exceedances of the PBTV in the bedrock flow layer are located beneath the ash basin, east, northwest, and west, of the ash basin, at or beyond the compliance boundary, and west of the structural fill. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-11 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Selenium Downgradient 2L exceedances of selenium in the shallow flow layer are located north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance boundary. Exceedances of the selenium 2L standard in the deep flow layer are limited to beneath the south end of the ash basin and beneath the Pine Hall Road Landfill. There are no 2L exceedances of selenium in the bedrock flow layer. Strontium Downgradient exceedances of the established strontium PBTV in the shallow flow layer are located east, north, northwest, and west of the ash basin at or beyond the compliance boundary, and west of the structural fill. Exceedances of the strontium PBTV in the deep flow layer are located beneath the southern end and upgradient of the ash basin and east, northeast, north, northwest, and west of the active ash basin, at or beyond the compliance boundary, and west of the structural fill. Exceedances of the strontium PBTV in the bedrock flow layer are located beneath the southern end of the ash basin and east of the ash basin, within or near the compliance boundary, and north of the ash basin beyond the compliance boundary. Sulfate There are no downgradient 2L exceedances of sulfate in the shallow flow layer, sulfate exceedances are located within the basin and west of the structural fill. Sulfate 2L exceedances in the deep flow layer are limited to beneath the south end of the ash basin, adjacent to the Pine Hall Road Landfill, and west of the structural fill. These exceedances are not related to the ash basin and a separate assessment of the structural fill is ongoing. There are no sulfate 2L exceedances in the bedrock flow layer. TDS Downgradient 2L exceedances of TDS in the shallow flow layer are located north and northwest of the ash basin, within or at or beyond the compliance boundary, and west of the structural fill. TDS exceedances in the deep flow layer are located adjacent to the Pine Hall Road Landfill and beneath the ash basin main dam, and north of the ash basin, within the compliance boundary, northwest of the ash basin at or beyond the compliance boundary, and west of the structural fill. These exceedances are not related to the ash basin and a separate assessment of the structural fill is ongoing. There are no downgradient exceedance of TDS in the bedrock flow layer. Thallium Downgradient exceedances of the thallium IMAC in the shallow flow layer are located southeast, north, and northwest of the ash basin, at or beyond the compliance 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-12 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx boundary. Thallium exceedances of the IMAC in the deep flow layer are located beneath the north end of the ash basin, and north of the ash basin within the compliance boundary, and northwest of the ash basin, at and beyond the compliance boundary. There are no exceedances of the thallium IMAC in the bedrock flow layer. Vanadium No downgradient exceedances of the vanadium PBTV are located in the shallow flow layer. PBTV exceedances are generally located within the footprint of the ash basin. Exceedances of the PBTV in the deep flow layer are located beneath the ash basin, and southeast, east, northeast, north, and northwest of the ash basin, at or beyond the compliance boundary. Exceedances of the PBTV in the bedrock flow layer are located beneath the ash basin. Piper Diagrams (Comparison to Downgradient/ 10.2.1 Separate Flow Regime) A 2006 EPRI study of 40 ash leachate water samples collected from 20 different coal ash landfills and impoundments characterized bituminous coal ash leachate as calcium-magnesium-sulfate water type and subbituminous coal ash leachate as sodium-calcium-sulfate water type. Ash pore water at BCSS for AB-4S, AB-7S, and AB-8S resembles bituminous coal ash leachate water from EPRI’s 2006 study which is a calcium-magnesium-sulfate water type. In comparison, BCSS ash pore water from AB-6S and AB-8SL have an elevated bicarbonate component. Shallow downgradient locations characterized by calcium-magnesium-sulfate water type include: AB-1S, AB-3S, GWA-1S, GWA-11S, GWA-20SA, and GWA- 21S . Five of these six wells indicated boron concentrations greater than 700 µg/L for the April 2017 sampling event. GWA-31S indicates potential mixing between background and impacted water. Downgradient location GWA-2S is characterized as sodium-potassium-bicarbonate type indicating little influence from source areas or a high degree of mixing with background groundwater. Both GWA-31S and GWA-2S contained boron concentrations below the detection limit of 50 µg/L for the April 2017 sampling event. AB-6SL, GWA-10S, GWA- 19SA, GWA-23S, GWA-30S, GWA-32S, MW-1, MW-103S, MW-104S, GWA-12S, BG-2S, and BG-3S exhibit ion charge balance of greater than 10% (10.192% to 66.664%) and are therefore not represented on the piper diagram. Deep groundwater locations characterized by calcium-magnesium-sulfate type water include: AB-1D, AB-2D, AB-3D, GWA-1D, GWA-11D, GWA-20D, GWA- 21D, GWA-24D, and MW-103D. Locations that indicate potential mixing 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-13 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx between background groundwater and impacted groundwater include GWA-9D and GWA-32D. Downgradient locations GWA-2D and GWA-18D are characterized as calcium-bicarbonate type water consistent with unimpacted background water. MW-200BR, MW-203BR, and BG-2BRA are characterized as calcium-bicarbonate type water, consistent with background groundwater. No bedrock locations are characterized as calcium-magnesium-sulfate type water. Plots of shallow, deep, and bedrock groundwater locations are shown on Figure 10-1, Figure 10-2, and Figure 10-3. All monitoring well locations are depicted on Figure 2-10. Boring logs and Soil Sample and Rock Core Photographs are provided in Appendix F. Site-Specific Exceedances (Groundwater COIs) 10.3 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 COIs for the purpose of evaluating a site remedy is discussed in the following section. Provisional Background Threshold Values (PBTVs) 10.3.1 Addressing 15A NCAC 02L .0202 (b)(3) — “Where naturally occurring substances exceed the established standard, the standard shall be the naturally occurring concentration as determined by the Director” — HDR and SynTerra (May 2017) provided the following report to NCDEQ: Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities. 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 PBTVs. A revised and updated technical memorandum that summarized revised background groundwater datasets and statistically determined PBTVs for BCSS 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). The Proposed Naturally Occurring (Reference Background) Concentrations In Groundwater and Soil for BCSS (SynTerra, 2017) report is provided in Appendix H. Applicable Standards 10.3.2 As part of CSA activities at the Site, multiple media including coal ash, ponded water in the ash basis, ash pore water, AOWs, soil, and groundwater 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-14 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx downgradient of the ash basin 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. Although the COI list has been developed based on site-specific conditions and observations, certain constituents, such as boron and sulfate, may be listed as COIs at all sites based on their usefulness as indicators of coal ash influence. Additionally, NCDEQ requested that hexavalent chromium be included as a COI at each CAMA-related site due to due to public interest associated with drinking water supply wells. Molybdenum and strontium do not have 2L standards, IMACs, or 2B 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. The following constituents do not have a 2L standard, 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 Registry (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 standards, IMACs, or MCLs, 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 (USEPA CCR Rule, 2015). Detection monitoring constituents in 40 CFR 257 Appendix III are: Boron Calcium Chloride Fluoride (limited historical data, not on assessment constituent list) pH 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-15 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Sulfate Total dissolved solids (TDS) Constituents for assessment monitoring listed in 40 CFR 257 Appendix IV include: Antimony Arsenic Barium Beryllium Cadmium Chromium Cobalt 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 Implementation Monitoring Plan (IMP). In addition, NCDEQ requested that vanadium be included. BCSS Groundwater COIs 10.3.4 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-16 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Based on an evaluation of criteria described above, and based on site-specific conditions, observations, and findings, the following list of groundwater COIs have been initially developed for BCSS: Antimony Arsenic Barium Beryllium Boron Cadmium Chloride Chromium (total) Chromium (hexavalent) Cobalt Iron Manganese Molybdenum pH Selenium Strontium Sulfate Thallium TDS Vanadium Table 10-3 lists the COIs at BCSS along with their associated NC 2L Groundwater Standards, IMACs, and federal drinking water standards (Primary Maximum Contaminant Levels [MCLs] and Secondary Maximum Contaminant Levels [SMCLs]). NC 2L Standards are established by NCDEQ, whereas federal 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 10-17 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx MCLs and SMCLs are established by the USEPA. Primary MCLs are legally enforceable standards for public water supply systems set to protect human health in drinking water. Secondary MCLs are non-enforceable guidelines set to account for aesthetic considerations, such as taste, color, and odor (USEPA, 2014). Water Supply Well Groundwater Concentrations and 10.4 Exceedances Water supply well sampling results can be found in Table 4-3, provided by Duke Energy, for the NCDENR and Duke Energy sampling results as well as identified exceedances of 2L Standards, IMACs, and/or other regulatory limits. The analysis of determining potential groundwater impact focuses on NCDENR results. A review of the analytical data for the water supply wells indicated several constituents were reported at concentrations greater than 2L or IMACs including pH (19 wells), arsenic (six wells), chromium (one well), cobalt (one well), iron (five wells), manganese (six wells), and vanadium (ten wells). Concentrations of analyzed constituents exceeded their respective bedrock PBTVs for a number of private water supply wells (data/values biased by the presence of high turbidity are excluded) including: Arsenic – 23 wells Barium – 18 wells Beryllium – 1 well Cadmium – 4 wells Calcium – 25 wells Chromium (hexavalent) – 8 wells Chromium (total) – 1 well Copper – 19 wells Iron – 10 wells Lead – 36 wells Magnesium – 20 wells Manganese – 14 wells Molybdenum – 7 wells Nickel – 1 well Selenium – 2 wells Sodium – 1 well Sulfate – 9 wells TDS – 10 wells Vanadium – 10 wells Zinc – 25 wells 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 11.0 HYDROGEOLOGICAL INVESTIGATION Results of the hydrological investigation summarized in this section are primary components of the Site Conceptual Model.2 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 groundwater sampling event (April 2017). Plume Physical Characterization 11.1 Boron is the primary CCR-derived constituent in groundwater and is detected at concentrations greater than the NC 2L standard beneath the ash basin and the Pine Hall Road Landfill and downgradient of the ash basin (north and northwest). Boron is not detected in background groundwater. Boron, in its most common forms, is soluble in water, and boron has a very low Kd value, making the constituent highly mobile in groundwater. Therefore, the presence/absence of boron in groundwater provides a close approximation of the distribution of CCR-impacted groundwater. The detection of boron at concentrations in groundwater greater than applicable 2L standards and PBTVs best represents the leading edge of the CCR-derived plume moving downgradient from the source area (ash basin and Pine Hall Road Landfill). The groundwater plume is defined as any locations (in three-dimensional space) where groundwater quality is impacted by the ash basin. 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 basin. The comprehensive groundwater data table (Appendix B, Table 1) and an understanding of groundwater flow dynamics and direction (Section 6.3, Figure 6-6 to 6-11) 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 basin. 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- 2 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 Belews Creek Steam Station SynTerra Page 11-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 basin. The horizontal extent of the plume in each flow layer is depicted in concentration isopleth maps (Figure 10-5 to 10-63). These maps use groundwater analytical data to spatially and visually define areas where groundwater concentrations are above the respective constituent PBTV and/or 2L/IMAC. The leading edge of the plume, the farthest downgradient edge, is represented by groundwater concentrations in the wells in each flow layer. In the bedrock flow layer, boron is reported in downgradient well MW-200BR, located north of the ash basin main dam at the compliance boundary at a concentration greater than the PBTV and less than the 2L standard. Boron is also detected in the bedrock flow layer at monitoring well GWA-20BR, located northwest of the ash basin at a concentration similar to the PBTV and less than the 2L standard. Boron is also detected in the bedrock flow layer at monitoring well OB-9, located north/northwest of the Pine Hall Road Landfill at a concentration greater than the PBTV and less than the 2L standard. The leading edge of the bedrock boron plume is interpreted to be at or just beyond these monitoring wells. The remaining bedrock downgradient wells did not have boron detected. In the deep flow layer, boron results in the monitoring wells located within the compliance boundary on the east and southeast sides of the ash basin are non-detect. On the north side of the ash basin, boron is reported in downgradient well MW-200D, located north of the ash basin main dam at the compliance boundary at a concentration greater than the PBTV and less than the 2L standard. Northwest of the ash basin, boron is reported at a concentration greater than the 2L standard at monitoring well GWA-27D located beyond the compliance boundary. 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 distribution of the plume. The boron concentrations reported in monitoring wells GWA-10DA, GWA-31D, and GWA-30D are non-detect. These wells are located beyond GWA-21D and the leading edge of the boron plume is expected to be generally between GWA-27D and this set of wells. Boron results exceed the 2L standard beneath the Pine Hall Road Landfill in the deep flow layer, but are non-detect at the compliance boundary. The leading edge of the boron plume in the shallow flow layer east of the ash basin is generally at the compliance boundary. North of the ash basin main dam and northwest of the ash basin, the boron plume in the shallow flow layer extends to beyond the compliance boundary. The boron concentration is non-detect in monitoring wells GWA-30S and GWA-31S which define the leading edge of the boron plume in the shallow flow layer. West of the ash basin the boron concentrations are non-detect or less than the PBTV at the compliance 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx boundary. As described in Section 6.0, there is no hydrogeologic confining unit at BCSS; therefore, under these unconfined conditions, groundwater moves freely across each layer shown in a vertical gradient map (Figure 6-12). Figures 11-1 through 11-3 depict concentration versus distance from the source along the plume centerline for COIs. Concentrations of each COI were measured from sampling in April-May 2017. The wells used are consistent for each constituent represented. Within the source area, well AB-4S was used for the shallow flow layer, well AB-4D was used for the deep flow layer, and well AB-4BR was used for the bedrock flow layer. At the compliance boundary, downgradient of the ash basin main dam, GWA-1S was used for the shallow flow layer, MW-200D was used for the deep flow layer, and MW-200BR was used in the bedrock flow layer. The wells at or beyond the compliance boundary downgradient of the ash basin main dam are MW-200S for the shallow flow layer, GWA-24D for the deep flow layer, and GWA-24BR for the bedrock flow layer. While PBTV values could not be distinguished on these graphs because values differ by flow unit, the graphs show constituent concentrations in source areas and downgradient and aid in understanding plume distribution. The vertical extent of the plume extent is depicted in the cross-sectional views of the site (Figures 6-2 and 11-4 to 11-63). Cross-section A-A’ is a transect of the ash basin and the plume, along the plume centerline, from south to north. There are 29 CAMA wells, 2 geotechnical borings, and two wells from other regulatory programs along the centerline. These wells represent background, source area, and downgradient locations relative to the ash basin. Cross-section B-B’ is a transect perpendicular to the plume centerline. There are 25 CAMA wells and 3 geotechnical borings along the transect. These wells are background, source area, downgradient, and sidegradient locations relative to the ash basin. Cross-section C-C’ is a transect parallel to Middleton Loop Road requested by DEQ. There are 29 CAMA wells and 3 wells from other regulatory programs along the transect. The well screens in the CAMA wells accurately monitor groundwater conditions and impact to the shallow and deep flow layers. Likewise, as has been demonstrated with the installation of deeper bedrock well AB-4BRD beneath the ash basin (AB-9BRD is grout contaminated and the data is not usable), impact to the bedrock flow unit is confined to the top approximately 100-140 feet of fractured bedrock. The vertical extent of the plume is best represented by groundwater concentrations in bedrock wells beneath and downgradient of the ash basin. Boron is present in the saprolite beneath the ash basin, extending into the bedrock beneath the ash basin main 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx dam. Boron concentrations are less than the 2L standard approximately 300 feet downgradient of the toe of the ash basin main dam, prior to the MW-200 well nest. As groundwater under the ash basin flows north toward the ash basin dam, the hydraulic impact of the ash basin dam and the hydraulic head exerted by the ash basin water, forces groundwater downward into the bedrock, which increases hydraulic pressure in the bedrock aquifer. In general, the pressures in the bedrock just downgradient of the base of the dam become greater than in the transition zone or surficial aquifers as indicated by the artesian conditions encountered at monitoring well MW-200BR located along the designated effluent channel. Groundwater elevations are not available to calculate vertical gradients in the well clusters installed near and along the base of the dam. A downward gradient exists to the east and west of the designated effluent channel downgradient of the dam. As groundwater and the plume migrate in the downgradient direction, unimpacted groundwater enters the system from upgradient recharge areas to the west and east, mitigating the concentration of some COIs (e.g., boron). 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 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 11.2 Plume chemical characterization is detailed below for each COI. Analytical results are based on the 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 BCSS are also provided. Samples that have turbidity >10 NTUs or pH greater than 9.0 (indicative of grout contamination in the well) have been removed from the data set. Antimony Reported Range: 0.1 µg/L – 26.2 µg/L; Number of Detections/Total Samples: 33/94 Concentrations in 12 samples exceeded the PBTV. Concentrations in 7 samples exceeded the IMAC. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Antimony exceeds the PBTV and IMAC in ash basin pore water groundwater beneath the ash basin, transition zone downgradient of the ash basin. 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. Arsenic Reported Range: 0.041 µg/L – 227 µg/L; Number of Detections/Total Samples: 83/94 Concentrations in 36 samples exceeded the PBTV. Concentrations in 12 samples exceeded the 2L. Arsenic exceeds the PBTV and 2L in pore water, transition zone and bedrock groundwater beneath the ash basin and downgradient shallow and bedrock groundwater. Arsenic soil concentrations from 52 samples beneath the ash basin and downgradient of the ash basin exceed the PSRG for POG value; 35 samples exceed the PBTV. Arsenic is a trace element in the crust, with estimated concentrations ranging from less than one mg/kg in mafic igneous rocks to 13 mg/kg in clay rich rocks (Parker, 1967). It occurs in multiple valence states (As5+, As3+, and As3-). Arsenic in coal occurs primarily in pyrite (iron sulfide, with arsenic replacing iron in the crystal structure) (Finkelman, 1995). Arsenic condenses on fly ash as arsenate (As5+) (Goodarzi, Huggins, & Sanei, 2008). Leaching tests on ash indicate that trace quantities up to 50 percent of the arsenic present can be leached. In addition to the solubility of the source, the concentration of calcium and presence of oxides appear to limit the mobility of arsenic (Izquierdo & Querol, 2012). The 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx USEPA estimates that the amount of natural arsenic released into the air as dust from the soil is approximately equal to the amount of arsenic released by all human activities (EPRI, 2008b). Barium Reported Range: 0.918 µg/L – 746 µg/L; Number of Detections/Total Samples: 89/94 Concentrations in 63 samples exceeded the PBTV. Concentrations in 1 sample exceeded the 2L in downgradient shallow groundwater. Barium exceeds the PBTV in all flow units beneath the ash basin and downgradient of the ash basin. Barium is a naturally occurring component of minerals that are found in small, but widely distributed amounts in the earth’s crust (Kunesh, 1978); (Miner, 1969). Two forms of barium, barium sulfate (barite) and barium carbonate (witherite), are often found in nature as ore deposits. Barium enters the environment naturally through the weathering of rocks and minerals. Anthropogenic releases are primarily associated with industrial processes. Barium is sometimes found naturally in drinking water and food. However, because the dominant naturally occurring barium compounds (barium sulfate and barium carbonate) have a low to moderate solubility in water under most conditions, the amount of barium found in drinking water is typically small. Barium compounds such as barium acetate, barium chloride, barium hydroxide, barium nitrate, and barium sulfide dissolve more easily in water than barium sulfate and barium carbonate, but because they are not commonly found in nature, they do not usually occur in drinking water unless the water is contaminated by barium compounds that are released from waste sites (EPRI, 2008b). Barium is naturally released into the air by soils as they erode and is released into the soil and water by eroding rocks. Barium released into the air by human activities comes mainly from barium mines, metal production facilities, and industrial boilers that burn coal and oil (EPRI, 2008b). The leachability of barium has been found to be relatively independent of pH but is controlled instead by the presence of calcium with which it competes for sulfate (Fruchter et al., 1990). In an overview of leachability studies found in the International Journal of Coal 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Geology, the mobility of barium typically ranged from 0.02 to 2 percent (Izquierdo & Querol, 2012). Regional metamorphic grade greenschist to upper amphibolite in the Piedmont’s King’s Mountain Belt contains deposits of barium sulfate (barite). Barium is especially common as concretions and vein fillings in limestone and dolostone, which are not common geologic facies in North Carolina; however, at various times in the past century and a half, the Carolinas have been major producers of barite (USEPA, 2014). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at the University of North Carolina (UNC) analyzed 1,898 private well water samples in Gaston and Mecklenburg Counties. The samples were tested by the North Carolina State Laboratory of Public Health from 1998-2012. This study found an average barium concentration of 50 µg/L. No samples exceeded the 2,000 µg/L Primary Maximum Contaminant Level (PMCL) for barium (NC DHHS, 2010). Beryllium Reported Range: 0.012 µg/L – 11.5 µg/L; Number of Detections/Total Samples: 69/94 Concentrations in 16 samples exceeded the PBTV. Concentrations in 7 samples exceeded the IMAC. Beryllium exceeds the PBTV and 2L in pore water and transition zone groundwater beneath the ash basin. Beryllium detected in groundwater in all three flow units downgradient of the ash basin including exceedance of PBTV and 2L in surficial and transition zone groundwater. Beryllium is a hard, gray metal that is very lightweight. In nature, it combines with other elements to form beryllium compounds. Small amounts of these compounds are naturally present in soils, rocks, and water. Emeralds and aquamarines are gem-quality examples of a mineral (beryl) that is a beryllium compound. Beryllium combines with other metals to form mixtures called alloys. Beryllium and its alloys are used to construct lightweight aircraft, missile, and satellite components. Beryllium is also used in nuclear reactors and weapons, X-ray 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx transmission windows, heat shields for spacecraft, rocket fuel, aircraft brakes, bicycle frames, precision mirrors, ceramics, and electrical switches (EPRI, 2008c). Most of the beryl occurring in North Carolina is along the south and southwest sides of the Blue Ridge Mountains. The most notable mines include the Biggerstaff, Branchand, and Poteat mines in Mitchell County; the Old Black mine in Avery County; and the Ray mine in Yancey County. The beryl forms golden or pale-green well-formed prismatic crystals ranging in size from a fraction of an inch to about 3 inches in diameter. It is generally found near the cores of bodies of pegmatites of moderate size that contain considerable amounts of perthitic microcline. Production has been negligible, and no regular production appears possible. Green beryl (aquamarine and emerald) was mined commercially many years ago at the Grassy Creek emerald mine and the Grindstaff emerald mine on Crabtree Mountain in Mitchell County. The Ray mine in Yancey County has also produced some golden beryl and aquamarine (Brobst, 1962). Beryllium- containing minerals are also common in granites and pegmatites throughout the Piedmont; however, to a lesser degree than the Blue Ridge Mountains Province (Brobst, 1962). Beryllium is concentrated in silicate minerals relative to sulfides and in feldspar minerals relative to ferromagnesium minerals. The greatest known naturally occurring concentrations of beryllium are found in certain pegmatite bodies. Beryllium is not likely to be found in natural water above trace levels due to the insolubility of oxides and hydroxides at the normal pH range (Brobst, 1962). In groundwater, beryllium concentrations are compared to IMAC since no 2L Standard has been established for this constituent by NCDEQ. Boron Reported Range: 25.3 µg/L – 26,700 µg/L; Number of Detections/Total Samples: 53/94 Concentrations in 38 samples exceeded the PBTV. Concentrations in 23 samples exceeded the 2L. Boron exceeds the PBTV and 2L in pore water and transition zone groundwater beneath the ash basin. Boron detected in groundwater in all three flow units downgradient of the ash basin including exceedance of PBTV and 2L in surficial and transition zone groundwater. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Soil concentrations beneath the ash basin exceed the PBTV and PSRG for POG value. 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 (B3+) 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. Boron is the primary component of a few minerals including tourmaline, a rare gem mineral that forms under high temperature and pressure (Hurlbut, 1971). The remaining common boron minerals, including borax that was mined for laundry detergent in Death Valley, California, form from the evaporation of seawater in deposits known as evaporites. For this reason, boron mobilized into the environment will remain in solution until incorporation into plant tissue or adsorption by a mineral. 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-10 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx sorption 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 (1997) lists aluminum and iron oxides, magnesium hydroxide, clay minerals, calcium carbonate (limestone), and organic matter as important sorption surfaces in soils. 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. Cadmium Reported Range: 0.051 µg/L – 3.3 µg/L; Number of Detections/Total Samples: 29/94 Concentrations in 6 samples exceeded the PBTV. Concentrations in 2 samples exceeded the 2L in the transition zone downgradient of the ash basin. Historic detections show concentrations increasing for pore water beneath the ash basin. Historic detections are stable for the two locations that exceed the 2L. Cadmium is generally characterized as a soft, ductile, silver-white or bluish- white metal, and is listed as 64th in relative abundance amongst the naturally occurring elements. Cadmium is found principally in association with zinc sulfide based ores and, to a lesser degree, as an impurity in lead and copper ores. It is also found in sedimentary rocks at higher levels than in igneous or metamorphic rocks, with the exception of the nonferrous metallic ores of zinc, lead and copper (WHO 2011). Cadmium often co-occurs with zinc minerals like sphalerite, and can substitute in the sphalerite crystal structure during weathering (USGS 1985). Cadmium is found throughout the environment from natural sources and processes such as the erosion and abrasion of rocks and soils and from singular events such as forest fires and volcanic eruptions (USGS 1985). 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-11 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Cadmium occurs sporadically in the auriferous parts of the North Carolina Charlotte and Carolina Slate Belts. Cadmium is widespread in the Carolina Slate Belt, but is found in the Charlotte Belt only near its southeastern boundary. A cluster of cadmium sites marks the mineralized district in the northeast corner of the Carolina Slate Belt, where cadmium was found in all zinc-rich samples. The solubility of cadmium in water is influenced to a large degree by its acidity; suspended or sediment-bound cadmium may dissolve when there is an increase in acidity. In natural waters, cadmium is found mainly in bottom sediments and suspended particles (WHO 2011). Contamination of drinking water may occur as a result of the presence of cadmium as an impurity in the zinc of galvanized pipes or cadmium-containing solders in fittings, water heaters, water coolers and taps. Levels of cadmium could be higher in areas supplied with soft water of low pH, as this would tend to be more corrosive in plumbing systems containing cadmium. Cadmium is used in battery production, dye and pigment manufacturing, coatings and plating, as a stabilizing agent in plastic production, nonferrous alloys, and photovoltaic devices (WHO 2011). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at UNC analyzed private well water samples tested by the North Carolina State Laboratory of Public Health from 1998-2010. Summary statistics for the 399 wells tested in Stokes and Rockingham counties are included in Table 11-1. The average cadmium concentrations were 0.5 µg/L and 0.6 µg/L in Stokes and Rockingham counties, respectively. Chloride Reported Range: 0.67 µg/L – 884 µg/L; Number of Detections/Total Samples: 94/94 Concentration in 32 samples exceeds the PBTV. Concentrations in 11 samples exceeded the 2L. Exceedances of 2L occur in the pore water and transition zone beneath the ash and shallow and transition zone groundwater downgradient of the ash basin. Historic detections are show stable or decreasing concentrations and include some exceedances of PBTVs in surficial, transition zone and bedrock groundwater downgradient of the ash basin. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-12 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Chloride is a major ion, and occurs widely as a salt of sodium (NaCl), potassium (KCl), and calcium (CaCl2). Oceans typically contain about 19,000 mg/L of chloride (Feth 1981). Elevated levels of chloride may occur in groundwater as a result of sea water intrusion, or erosion of halite (U.S. Geological Survey, 2009). The USEPA has not established an MCL for chloride because it is not known to have adverse effects on human health. An SMCL of 250 mg/L has been established for chloride because of taste and corrosive considerations. The taste threshold for chloride depends on the associated cation. A study by Lockhart (1955) found that people detected a salty taste in water at 210, 310, and 222 mg/L from the respective sodium, potassium, and calcium salts. The taste of coffee is affected when brewed with water containing chloride concentrations ranging from 400-530 mg/L, depending on the corresponding cation (Lockhart 1955). Chloride concentrations above 250 mg/L in drinking water may cause corrosion in water distribution systems (McConnell & Lewis, 1972). Using the USGS National Uranium Resource Evaluation (NURE) database, all chloride groundwater test results within a 20-mile radius of the BCSS site are shown on Figure 11-64. These samples were taken at depths ranging from 20 to 500 ft bgs, and the chloride concentrations range from below detection limits to 55.7 mg/L. Chromium Reported Range: 0.098 µg/L – 289 µg/L; Number of Detections/Total Samples: 79/94 Concentrations in 14 samples exceeded the PBTV. Concentrations in 7 samples exceeded the 2L in the shallow and transition zone downgradient of the ash basin, and at one background location. Historic detections are inconsistent but include some 2L exceedances and in surficial and transition zone groundwater downgradient of the ash basin. Chromium soil concentrations from 79 samples beneath the ash basin and downgradient of the ash basin exceed the PSRG for POG value, only 13 samples exceed the PBTV. 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-13 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 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 5.2µg/L in Gaston and Mecklenburg Counties respectively. Hexavalent Chromium Reported Range: 0.0092 µg/L – 8.3µg/L; Number of Detections/Total Samples: 56/94 Concentrations in 14 samples exceeded the PBTV. Hexavalent chromium exceeds the PBTV in transition zone and bedrock groundwater beneath the ash basin; Hexavalent chromium exceeds the PBTV in transition zone groundwater upgradient and sidegradient of the ash basin; and bedrock groundwater downgradient. Hexavalent chromium exceeds the PBTV in transition zone in groundwater south of the ash basin’s topographic ridge, west of the structural fill. Historic detections are inconsistent but include some PBTV exceedances and in the transition zone groundwater beneath the ash basin and sidegradient and downgradient of the ash basin. 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 (CrO42-) and dichromate 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-14 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx (Cr2O72-) 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 unadsorbed 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 et al., 1995). Cobalt Reported Range: 0.019 µg/L – 85.6 µg/L; Number of Detections/Total Samples: 83/94 Concentrations in 31 samples exceeded the PBTV. Concentrations in 32 samples exceeded the IMAC. Three samples above IMAC in the transition zone are below the PBTV Cobalt exceeds the PBTV and IMAC in pore water and transition zone groundwater beneath the ash basin. Cobalt exceeds the PBTV and IMAC in shallow and transition zone groundwater downgradient of the ash basin. Historic detections generally show decreasing concentrations overtime except at locations northwest of the ash basin. Soil concentrations beneath the ash basin and downgradient of the ash basin exceed the PSRG for POG value but only one location (SB-03) exceeds the PBTV. Cobalt is a base metal that exhibits geochemical properties similar to iron and manganese, occurring as a divalent and trivalent ion. Cobalt can also 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-15 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 (U.S. Geological Survey, 1973). Cobalt is compared to IMAC since no 2L standard has been established for this constituent by NCDEQ. Iron Reported Range: 1.91 µg/L – 88,300 µg/L; Number of Detections/Total Samples: 83/94 Concentrations in 24 samples exceeded the PBTV. Concentrations in 38 samples exceeded the 2L. Iron exceeds the PBTV and 2L in pore water, transition zone, and bedrock groundwater beneath the ash basin. Iron detected in groundwater downgradient of the ash basin including exceedances of PBTV and 2L in shallow and transition zone groundwater. All 119 soil samples concentrations beneath the ash basin and downgradient of the ash basin exceed the PSRG for POG value but only 9 locations exceeds the PBTV. Iron is a naturally occurring element that may be present in groundwater from the erosion of natural deposits (NC DHHS, 2010). A 2015 study by DENR (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 1,320 µg/L. Iron is estimated to be the fourth most abundant element in the Earth’s crust at approximately five 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, Fe2+), trivalent (ferric, Fe+3), hexavalent (Fe6+), and Fe2- 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-16 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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, Schmitt, 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 Reported Range: 1.73 µg/L – 11,600 µg/L; Number of Detections/Total Samples: 89/94 Concentrations in 61 samples exceeded the PBTV. Concentrations in 47 samples exceeded the 2L. Manganese exceeds the PBTV and 2L in pore water, transition zone, and bedrock groundwater beneath the ash basin. Manganese detected in groundwater downgradient of the ash basin including exceedances of PBTV and 2L in shallow, transition zone and bedrock groundwater. Historic detections generally show decreasing concentrations overtime for each flow layer except at locations northwest of the ash basin. Manganese concentrations from 98 soil samples concentrations beneath the ash basin and downgradient of the ash basin exceed the PSRG for POG value but no samples exceed the PBTV. 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-17 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 40-50% 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 twelfth most abundant element in the crust (0.100 weight percent, (Parker, 1967). Manganese exhibits geochemical properties similar to iron with Mn7+, Mn6+, Mn4+, Mn3+, Mn2+, and Mn1- 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. Molybdenum Reported Range: 0.12 µg/L – 3,460 µg/L; Number of Detections/Total Samples: 59/94 Concentrations in 25 samples exceeded the PBTV. Molybdenum exceeds the PBTV in pore water, transition zone and bedrock groundwater beneath the ash basin. Molybdenum detected in groundwater downgradient of the ash basin including exceedances of PBTV in shallow, transition zone and bedrock groundwater. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-18 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Mo commonly forms oxyanions in groundwater that are affected by redox and pH (Ayotte, Gronbert, & Apodaca, 2011). Mo has been observed to leach less from coal cleaning rejects in acidic than neutral conditions, unlike many other metals (Jones & Ruppert, 2017). Mo has been shown to become more mobile in procedures that use deionized water as a leachant, 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). pH Detected Range: 4.2 -11.1 S.U. in 94 samples Concentrations in 39 samples exceeded the PBTV. Concentrations in 65 samples exceeded the 2L. pH exceeds the PBTV and 2L in pore water, transition zone and bedrock groundwater beneath the ash basin. pH downgradient of the ash basin exceeds the PBTV and 2L were observed in shallow, transition zone, and bedrock groundwater. 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 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, 2013c). 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 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 (Table 11-1). Using the USGS 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-19 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Selenium Reported Range: 0.122 µg/L – 300 µg/L; Number of Detections/Total Samples: 31/94 Concentrations in 23 samples exceeded the PBTV. Selenium exceeds the PBTV in pore water and transition zone beneath the ash basin. Selenium reported in groundwater downgradient of the ash basin including exceedances of PBTV in shallow and transition zone groundwater. Selenium concentrations from 31 soil samples beneath the ash basin and downgradient of the ash basin exceed the PSRG for POG value but only 9 samples exceed the PBTV. 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 environment, where it may remain dissolved, enter the aquatic food chain, or redeposit within a sedimentary rock such as shale (Institute, 2008a). 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 2014). 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-20 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx (NCDHHS, 2010). The mean concentration in both counties was 2.7 µg/L. The selenium summary statistics from this study are reported in Table 11-1. Strontium Reported Range: 3.3 µg/L – 4,450 µg/L; Number of Detections/Total Samples: 83/94 Concentrations in 41 samples exceeded the PBTV. Strontium exceeds the PBTV in pore water, transition zone, and bedrock groundwater beneath the ash basin. Strontium detected in groundwater downgradient of the ash basin including exceedances of PBTV in shallow, transition zone, and bedrock groundwater. Historic detections generally show decreasing or stable concentrations overtime for each flow layer except at locations northwest of the ash basin. 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). Sr is present as a minor coal and coal ash constituent. Sr 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 Reported Range: 0.0454 µg/L – 1,540 µg/L; Number of Detections/Total Samples: 82/94 Concentrations in 36 samples exceeded the PBTV. Concentrations in 6 samples exceed 2L. Sulfate exceeds the PBTV and 2L in pore water beneath the ash basin; and transition zone groundwater downgradient of the basin. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-21 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Sulfate detected in groundwater downgradient of the ash basin including exceedances of PBTV in shallow, transition zone, and bedrock groundwater. Historical exceedances generally show decreasing concentrations both beneath the ash basin and downgradient of the ash basin except west of the structural fill where concentrations are increasing overtime. 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 (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% 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, 2012). In the Piedmont and Blue Ridge Aquifers chapter of the USGS Ground Water Atlas of the United States, the groundwater of this region as a whole is described as “generally suitable for drinking…but iron, manganese, and sulfate locally occur in objectionable concentrations,” (U.S. Geological Survey, 1997). Thallium Reported Range: 0.016 µg/L – 8.39 µg/L; Number of Detections/Total Samples: 42/94 Concentrations in 22 samples exceeded the PBTV. Thallium exceeds the PBTV in pore water and transition zone beneath the ash basin. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-22 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Thallium reported in groundwater downgradient of the ash basin including exceedances of PBTV in shallow and transition zone groundwater. Pure thallium is a soft, bluish white metal that is widely distributed in trace amounts in the earth's crust. In its pure form, it is odorless and tasteless. It can be found in pure form or mixed with other metals in the form of alloys. It can also be found combined with other substances such as bromine, chlorine, fluorine, and iodine to form salts (Institute, 2008c). Traces of thallium naturally exist in rock and soil. As rock and soil is eroded, small amounts of thallium end up in groundwater. In a USGS study of trace metals in soils, the variation in thallium concentrations in A (i.e., surface) and C (i.e., substratum) soil horizons was estimated across the United States. The overall thallium concentrations range from <0.1 mg/kg to 8.8 mg/kg. North Carolina concentrations from this study are depicted in Figure 11-66. Thallium is compared to an IMAC since no 2L Standard has been established for this constituent. In a study by the Georgia Environmental Protection Division (EPD) of the Blue Ridge Mountain and Piedmont aquifers, 120 sites were sampled for various constituents. Thallium was not detected at any of these sites (Method Reporting Limit (MRL)=1 µg/L) (Donahue & Kibler, 2007). TDS Reported Range: 21 µg/L – 2,600 µg/L; Number of Detections/Total Samples: 90/94 Concentrations in 43 samples exceeded the PBTV. Concentrations in 18 samples exceeded the 2L. TDS exceeds the PBTV in pore water, transition zone, and bedrock groundwater beneath the ash basin. 2L exceedances occur in the pore water, transition zone and bedrock groundwater. TDS detected in groundwater downgradient of the ash basin including exceedances of PBTV and 2L in shallow, transition zone and bedrock groundwater. Groundwater contains a wide variety of dissolved inorganic constituents as a result of chemical and biochemical interactions between the groundwater and 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-23 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx the elements in the soil and rock through which it passes. Total Dissolved Solids (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 & 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-24 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 list of “National Secondary Drinking Water Regulations” (NSDWRs) which are non-enforced regulated contaminates that may cause cosmetic effects or aesthetic effects in drinking water (USEPA, 2013c) 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 Reported Range: 0.093 µg/L – 948 µg/L; Number of Detections/Total Samples: 84/94 Concentrations in 17 samples exceeded the PBTV. Concentrations in 64 samples exceeded the IMAC. Vanadium exceeds the PBTV and IMAC in pore water, transition zone, and bedrock groundwater beneath the ash basin. Vanadium exceeds the PBTV and IMAC in shallow, transition zone, and bedrock groundwater downgradient the ash basin. Historic detections generally show stable or decreasing concentrations overtime for each flow layer beneath the ash basin and downgradient the ash basin. Vanadium concentrations from 108 soil samples beneath the ash basin and downgradient of the ash basin exceed the PSRG for POG value but only 9 samples exceed the PBTV. Vanadium is widely distributed in the earth’s crust at an average concentration of 100 ppm (approximately 100 mg/kg), similar to that of zinc and nickel. Vanadium is the 22nd most abundant element in the earth’s crust (Institute, 2008d). V(V) and V(IV) are the most important species in natural water, with V(V) likely the most abundant under environmental conditions (Wright & Belitz, 2010). Vanadium is compared to IMAC since no 2L standard has been established for this constituent by NCDEQ. Vanadium is estimated to be the 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-25 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 22nd most abundant element in the crust (0.011 weight percent, (Parker, 1967). Vanadium occurs in four oxidation states (V5+, V4+, V3+, and V2+). 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, 2006). The Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) 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 (DOE) national laboratories. Samples were collected from 5,178 wells across North Carolina. Of these, the concentration of vanadium was equal to or higher than the IMAC in 1,388 well samples (27 percent). Pending Investigations 11.3 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: Directly beneath the ash basin Downgradient locations north of the ash basin Downgradient locations northwest of the ash basin 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. To help determine potential routes of exposure and receptors related to the ash basin, additional surface water samples will be collected from Belews Reservoir and the Dan River near the stream/river bank most likely to be impacted by potentially contaminated groundwater discharge. Surface water samples to be collected in Belews Reservoir will include three upgradient sample locations and one downgradient sample location. Additionally, three samples will be collected from locations at the point of convergence with Belews Reservoir and AOW streams (S-6, S-7, S-13 and S-14) and the stream downgradient of wells GWA-4S/D. Surface water samples from the Dan River will include three background locations; two in the Dan River and one in the tributary stream, Town Fork Creek. Four additional samples will be collected downgradient of background locations. Locations will be sampled at a frequency and at the same 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 11-26 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx physical location to allow an assessment with 15A NCAC 02B water quality standards. At each location, two samples will be collected within one hour to be evaluated for acute instream metals standards and the remaining two samples will be collected within the following 95 hours to be evaluated, using an average of a minimum of four samples, for chronic instream metals standards. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 12-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 12.0 RISK ASSESSMENT A baseline human health and ecological risk assessment was performed in 2016 as a component of CAP Part 2 for the Belews Creek Steam Station (HDR, 2016d). 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 January 2011 through October 2015 (HDR, 2016). This update to the risk assessment uses sampling locations described in Section 3.2 of the 2016 document, unless otherwise noted. As previously noted, AOW locations are outside the scope of this risk assessment because AOWs, wastewater, and wastewater conveyances (effluent channels) are permitted under 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 Part 2, Appendix F, Figures 2-3 and 2-4) describe the sources and potential migration pathways through which groundwater beneath the ash basin 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 Sections 2 and 5 of the 2016 risk assessment (CAP Part 2, Appendix F). This risk assessment update included the following: Identification of maximum constituent concentrations for groundwater and surface water Inclusion of new groundwater and surface water data to derive overall average constituent concentrations for exposure areas 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 12-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Comparison of new maximum constituent concentrations to the 2016 risk assessment human health and ecological screening values Comparison of new maximum constituent concentrations to site-specific 2016 human health Risk-Based Concentrations (RBC) 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 collected since the 2016 risk assessment and their influence on potential risks are summarized below by exposure area (Figure 12-1). Human Health Screening Summary 12.1 On-Site Groundwater Groundwater sample locations included in the assessment were: MW-102S through MW-204D, GWA-1S through GWA-17D and AB-1S through AB-9D, excluding ash pore water wells. 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. New maximum concentrations of antimony, arsenic, beryllium, hexavalent chromium, nickel, and selenium were detected that exceeded human health risk screening values; however, no values exceeded respective site-specific RBCs. There is no evidence these constituents pose human health risks from groundwater exposure. On-Site Surface Water Surface water sample locations included in the 2016 risk assessment were: SW-BL-D, SW-DR-D and SW-DR-U (Figure 12-1). The sample location SW-DR-D is adjacent to NPDES outfall 003 discharging ash sluice and FGD wastewater and is not representative of Dan River conditions downstream of plant operations. Thus, SW-DR- D is influenced by the NPDES outfall and not a subject of CAMA. Results for the surface water sample locations are included in Appendix B, Table 2. New maximum concentrations of boron, cobalt, manganese, molybdenum, and thallium exceeded on-site surface water risk screening values. Concentrations of boron, manganese and molybdenum did not exceed respective RBCs; therefore, no risks to 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 12-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx humans (trespasser/worker) exposed to these constituents in on-site surface water were identified. New maximum concentrations for cobalt (7.8 µg/L) and thallium (1.1 µg/L) were detected at SW-DR-U on the Dan River. The 2016 risk assessment identified potential risk under a hypothetical recreational and subsistence fisher scenario exposed to thallium in fish tissue modeled from surface water concentrations. Similarly, the 2016 risk assessment identified potential risk under a hypothetical subsistence fisher scenario exposed to cobalt in modeled fish tissue. The risks were likely overestimated because of very conservative assumptions in the exposure models. Concentrations of cobalt and thallium have decreased in subsequent sampling events and have not exceeded the respective human health screening levels of 1 µg/L (cobalt) and 0.2 µg/L (thallium) in the two most recent sampling events at SW-DR-U. Thus, there is no evidence of potential risks under the hypothetical fisher scenario from exposure to cobalt and thallium at SW-DR-U. Ecological Screening Summary 12.2 Exposure Area 3 – Surface Water One surface water sample location was included in the assessment for Ecological Exposure Area 3: SW-BL-D in Belews Reservoir (Figure 12-1). Results for the surface water sample location are included in Appendix B, Table 2. The 2016 risk assessment resulted in no LOAEL-based HQ greater than unity in Exposure Area 3 surface water for the ecological receptors evaluated. A new maximum concentration of cobalt exceeded the surface water ecological risk screening value. The concentration cobalt did not affect wildlife ADDs to the extent that the TRV was exceeded (HQ<1). No evidence of risks to ecological receptors exposed to cobalt in Exposure Area 3 surface water identified. In addition, Belews Reservoir is considered beyond the extent of constituent migration in groundwater from the ash basin. Private Well Receptor Assessment Update 12.3 An independent study was conducted that evaluated 2015 groundwater data collected from 24 private drinking water wells within close proximity of the Belews Creek Steam Station (HDR 2016; Haley & Aldrich, 2015). Pertinent observations presented in the study included: Groundwater flow paths from BCSS CAMA areas are not in the direction of private wells. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 12-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx The concentration of boron and other potential coal ash indicators were low and not above screening levels in the private wells sampled by NCDEQ with three exceptions. Cobalt, molybdenum and arsenic were above the state screening levels, DHHS screening level and the 2L, respectively. Hexavalent chromium and vanadium were detected in some wells above their respective DHHS screening levels, but at concentrations consistent with regional background. Recent (2017) results from off-site private water supply wells sampled since the Haley & Aldrich assessment (2015) were compared to 2L, as well as U.S. EPA’s Maximum Contaminant Levels (MCL) and tap water Regional Screening Levels (RSL). Key observations from evaluation of the private well groundwater data include: Concentrations of boron were consistent with previous observations. Arsenic exceeded the 2L of 10 µg/L in samples collected from six wells (BC17, BC20, BC30, BC32, BC34, BC35). Due to their distance from the ash basin and based on groundwater flow to the north, these wells are not considered to be impacted by the ash basin. Chromium exceeded the 2L of 10 µg/L in samples collected from one location (BC33), although chromium concentrations were less than the MCL and tap water RSL. Cobalt exceeded the 2L of 1 µg/L at one location (BC23-5); however, the concentration was less than the tap water RSL of 6 mg/L. Iron exceeded the 2L of 300 µg/L in samples collected from 15 locations, but was less than the tap water RSL of 14,000 µg/L. Manganese exceeded the 2L of 50 µg/L in samples collected from seven locations, but was less than the tap water RSL of 430 µg/L at all locations. Vanadium exceeded 2L in samples collected from 22 locations, but was less than the tap water RSL at all locations. While several wells located to the west-southwest and northeast of the ash basin had concentrations of chromium, cobalt, iron, manganese, vanadium that exceeded their respective 2L, all detected concentrations were less than their respective tap water RSLs. Based on the bedrock groundwater flow direction at the site (Figures 6-10 and 6-11, discussed in Section 6.3) private water supply wells located west of the ash basin along 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 12-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Old Plantation Road (BC2019-RAW, BC2 Well 1, BC2 Well 2, BC-1007, BC4, BC4A and BC4B) are located sidegradient to the ash basin. The remaining water supply wells identified in the area are located upgradient or sidegradient substantially beyond the expected flow zone of the BCSS ash basin. The water supply wells do not show indications of being impacted by the ash basin. The water chemistry signature of the water supply wells is similar to the background bedrock wells at the site. Although several water supply wells exceeded the site specific BTVs, concentrations in these water supply wells are within the background concentration range for similar Piedmont geologic settings. Risk Assessment Update Summary 12.4 Based on review and analysis of groundwater and surface water data, there is no evidence of risks to humans and wildlife at BCSS attributed to CCR constituent migration in groundwater from the ash basins. This update to the human health and ecological risk assessment supports a proposed NCDEQ Risk Classification of “Low”. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.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 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 are 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 Belews Creek Steam Station SynTerra Page 13-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.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 BCCS. Summary of Fate and Transport Model Results 13.1 The initial groundwater flow and transport model was developed by HDR in conjunction with University of North Carolina at Charlotte (UNCC) to gain an understanding of COI migration after closure of the ash basin at the BCCS. The initial groundwater model presented in the CAP Part 1 (HDR, 2015b) included a calibrated steady-state flow model of July 2015 conditions; a calibrated historical transient model of constituent transport to match June/July 2015 conditions; and three potential basin closure scenarios. Those basin closure simulation scenarios included: No change in site conditions (basin remains open, as is) Cap-in-place Ash removal (excavation) The initial model used arsenic, beryllium, boron, chloride, chromium, chromium VI, cobalt, and thallium as primary modeling constituents. In addition, the remedial alternative evaluation simulations were run to a total time of 250 years. The revised model in the CAP Part 2 (HDR, 2016d) included a calibrated steady-state flow model of June 2015 conditions; a calibrated historical transient model of constituent transport to June/July 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 As a portion of interim remedial action at the site the flow and transport model was revised. The revised model was focused on evaluating hydraulic impacts to the northwest corner of the ash basin for the interim remedial action. The results of the model were presented as Appendix C of the Basis of Design Report for the Interim 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Action Plan (SynTerra, 2017a). The model was revised by HDR which included: expanding the grid; modifications to the layering; refinements to hydraulic conductivity; modification of the sorption coefficient (Kd) based on geochemical modeling; adjustment of source pore water concentrations; and incorporation of proposed provisional background concentrations (PPBC). SynTerra used the updated HDR model and simulated four extraction wells to evaluate the hydraulic impacts to the northwest corner of the ash basin. The flow and transport model is currently being modified as a part of the updated 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 boron, and additional COIs that are hydraulically driven. Predictive simulations will have simulation times that continue until modeled COI concentrations are below the 2L standard/IMAC 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Hydraulic parameters such as hydraulic conductivity values may be adjusted within reasonable site-specific conditions to achieve hydraulic head calibration error below 10%. Flow Model Domain and Grid Layers The HDR model has dimensions of approximately 11,000 feet north to south, 10,000 feet east to west, with the ash basin at the center of the model domain. The model domain was not rotated, but is parallel to the Dan River. The hydrostratigraphic model consists of five units: ash/dam/fill material, soil/saprolite, saprolite, transition zone and fractured bedrock. Those units were determined by interpolating boring log data from historical data, the CSA, and the CAP reports (HDR, 2015a), (2015b), (2016). The numerical grid consists of rectangular blocks arranged in columns, rows, and layers. The model was developed using a 40-foot by 40-foot grid. The grid consists of 11 layers representing the five hydrostratigraphic units. It is expected grid layers and spacing will be adjusted for in the updated model. Flow Model Boundary Conditions The northwest model boundary which represents the Dan River was set to a specified head within the fractured bedrock. Drain features such as the small catchments to the west of the site and the unnamed stream downgradient of the ash basin dam were applied as hydraulic boundaries. The ash basin pond and Hydrostratigraphic layer Grid layer Ash/Dam/Fill 1-4 M1 Soil/Saprolite 5-6 M2 Saprolite 7 Transition Zone 8-9 Fractured Bedrock 10-11 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx other small water bodies within the model domain were also set as constant head boundaries. Sources and Sinks Water can enter the model 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 in the current model include: Recharge outside of the ash basin ranges from 3 to 9 inches per year. Rainwater that infiltrates Constant head boundaries Model Sinks (Drains) Model sinks in the current model include: Streams within the model domain Constant head boundaries AOWs (14 with measurable flow) Water Supply Wells A total of 6 domestic supply wells have been identified within the model domain of the CAP Part 2 model (HDR, 2016). The average daily use for domestic wells was set at a discharge of approximately 400 gallons per day (USEPA, 2015). The model domain will be expanded to include additional domestic and public supply wells. 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Streams and Lake Hydraulic Parameters The ash basin was represented as a specific head boundary. The stage of the ash pond was set at 750 feet. 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 through 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 flow model sensitivity analysis was conducted by varying the recharge rates and hydraulic conductivities in the shallow and transition zones. The change to the Normalized Root Mean Square of the Error was observed. The model was most sensitive to varying horizontal hydraulic conductivity within the shallow zone, followed by recharge outside the basin, then recharge to the ash basin. The model was least sensitive to varying vertical hydraulic conductivity of the shallow zone and transition zone. Since no major elements within the model are to be changed, there is no need to perform additional sensitivity testing. 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 refined therefore the assumptions and limitations are subject to change. Based on the preliminary modeling results, the assumptions and limitations include the following: 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx The steady-state flow model was calibrated to hydraulic heads measured in monitoring wells in July 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. In the fate and transport model found in the Appendix C of the Basis of Design Report for the Interim Action Plan (SynTerra, 2017a) Belews Lake and the Dan River were modeled as constant head boundaries in the numerical model. It was not possible to assess the effects of pumping wells or other groundwater sinks that are near the Dan River. However, this boundary condition can be modified to allow for groundwater remediation simulations. Residential wells were assumed to be completed in one of three bedrock model layers. 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 adsorption of COIs based on flow fields established by MODFLOW. The initial model used arsenic, beryllium, boron, chloride, chromium, chromium VI, cobalt, and thallium as primary modeling constituents. The updated fate and transport 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx modeling will focus on boron and additional COIs that are hydraulically driven. Other constituents will be considered using the geochemical model. Transport Model Parameters The key transport model parameters (besides the flow field) are the constituent source concentrations in the ash basin 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. Contaminants are assumed to leave the model when they reach a drain or are removed by flow that enters a constant head boundary. 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 fourth quarter 2017 sampling event. Transport Model Sources and Sinks Transport model sources include: The ash basin is the source of COIs in the model. The sources are simulated by applying a constant COI concentration within the cells of the ash basin 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. 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: 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Streams Drain Boundaries Transport Model Calibration Targets and Sensitivity The initial transport model calibration targets were COI concentrations measured in monitoring wells in June/July 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 and 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 fourth quarter 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 to be modeled: No Action – Leave the ash basin as is 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. 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 installation of a groundwater extraction system (or other contemplated groundwater corrective system(s)). The distribution of recharge, locations of drains, and distribution of material will be modified to represent possible 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 update model (presented in Appendix C of the Basis of Design Report for the Interim Action Plan (SynTerra, 2017a)) predicts that ten extraction wells 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-10 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx within the transition zone (model layer 6) will lower groundwater levels more than 5 to 10 feet along the extraction system axis. Modeling of boron shows little effect after pumping for six months. Pumping simulations for longer period (five year) demonstrates a slight reduction of boron concentrations along the extraction system axis. The simulated June/July 2015 concentration distributions described in the CAP 1 (UNCC) (HDR, 2016d) were used as initial conditions in a predictive simulation of future flow and transport at the Site and modeled arsenic, beryllium, boron, chloride, chromium, cobalt, hexavalent chromium, and thallium. Predictive simulations of future flow and transport for (CAP 2 (UNCC) (HDR, 2016d) used the same COIs from CAP Part 1 modeling simulations. The “no action”, Cap-in- place, and ash removal scenarios were run for a 250-year projection. Site wide simulation data for the modified model will be presented in the updated CAP. No action The CAP 1 (UNCC) (HDR, 2015b) groundwater simulations indicated arsenic at the compliance boundary north of the dam will exceed the 2L standard. Simulated beryllium, cobalt and thallium are predicted to exceed IMAC at the compliance boundary within all three aquifer zones west of the dam and in bedrock north of the dam by 2115. Boron simulations are above the 2L standard at the compliance boundary north of the dam within the shallow, deep, and bedrock zones by 2115. Chromium is predicted to exceed the 2L standard at the compliance boundary north and west of the dam within the shallow, deep, and bedrock zones. The hexavalent chromium simulation shows well AB-2S is above the DHHS HSL standard, however is not above the DHHS HSL at the compliance boundary within all three groundwater zones. The CAP 2 (UNCC) (HDR, 2016) modeling scenario consists of modeling each COI using the calibrated model for steady-state flow and transient transport under the Existing Conditions scenario across the site to estimate when steady state concentrations are reached at the Compliance Boundary. The model indicates that arsenic, chloride, and chromium remain less than the 2L Standard north and west of the dam in shallow, deep, and bedrock zones by 2115. In 2115, boron is predicted to exceed the 2L Standard at the compliance boundary north of the dam, but not west of the dam. Simulated beryllium will continue to be below the IMAC at the compliance boundary after 100 years in all groundwater 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-11 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx zones. Simulated cobalt is predicted to exceed IMAC at the compliance boundary within all three aquifer zones north of the dam, but not west of the dam by 2115. Simulated thallium is predicted to exceed IMAC at the compliance boundary within all three aquifer zones due to a higher input concentration. After 100 years, hexavalent chromium is predicted to be greater than the NCDHHS HSL at the compliance boundary in all groundwater zones due to higher background concentration inputs. Cap-in-place The Cap-in-place scenario presented in the CAP 1 (UNCC) (HDR, 2015b) simulates the effects of placing an engineered cap over the ash basin. The model assumes the pond is drained and covered and has an applied recharge of zero. Simulations indicated arsenic north of the dam will exceed the 2L standard within the transition zone and bedrock at the compliance boundary, but decreases in the shallow aquifer. Simulated beryllium is below the 2L standard at the compliance boundary within the shallow, deep, and bedrock zones prior to 2115. Simulated boron north of the dam exceeds the 2L standard initially then dramatically declines and remains below standard within the shallow, deep, and bedrock zones around 5 to 35 years after 2015. Chromium has the same prediction as the No action scenario where the concentrations exceed the 2L standard at the compliance boundary to the north and west of the dam within the shallow, deep, and bedrock zones. The hexavalent chromium simulation is similar to the No Action and Excavation scenarios. The simulation shows well AB-2S is above the DHHS HSL standard for hexavalent chromium, however is not above the DHHS HSL at the compliance boundary within all three groundwater zones. Simulated cobalt and thallium are predicted to exceed IMAC at the compliance boundary within all three aquifer zones west of the dam and in bedrock north of the dam by 2115. The CAP 2 (UNCC) (HDR, 2016d) modeling scenario consists of modeling each COI using the calibrated model for steady-state flow and transient transport under the Cap-in-place scenario at the site to estimate when steady state concentrations are reached at the Compliance Boundary. The model indicates that arsenic, chloride, and chromium remain less than the 2L Standard north and west of the dam in shallow, deep, and bedrock zones by 2115. In 2115, boron is predicted to exceed the 2L Standard in the shallow, deep and bedrock zones. Simulated beryllium, will continue to be below the IMAC at the compliance boundary after 100 years in all groundwater zones. Similar to the No action simulation, cobalt and thallium are predicted to exceed IMAC at the compliance boundary within all three aquifer zones north of the dam by 2115. After 100 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-12 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx years, hexavalent chromium is predicted to be greater than the NCDHHS HSL at the compliance boundary in all groundwater zones due to higher background concentration inputs. Excavation Scenario The Excavation scenario presented in the CAP 1 (UNCC) (HDR, 2015b) simulates the effects of removing the ash basins, the dikes, and ash storage areas at the beginning of this scenario. Simulated arsenic concentrations decrease below the 2L standard at the compliance boundary within all three groundwater zones prior to 2115. Simulated beryllium concentrations are similar to the Cap-in-place results where it is below the 2L standard in the shallow, deep, and bedrock zones. The simulated boron behavior is similar to the Cap-in-place scenario where boron north of the dam exceeds the 2L standard initially then dramatically declines and remains below standard within all three groundwater zones around 5 to 35 years after 2015. Unlike the No action and Cap-in-place scenarios, simulated chromium concentrations decrease below the 2L standard at the compliance boundary in the shallow, deep, and bedrock zones before 2115. The hexavalent chromium simulation is similar to the No Action and Cap-in-place scenarios. The simulation shows well AB-2S is above the DHHS HSL standard for hexavalent chromium, however is not above the DHHS HSL at the compliance boundary within all three groundwater zones. Simulated cobalt is predicted to exceed IMAC at the compliance boundary north of the dam by 2115. Thallium is predicted to decrease below the IMAC at the compliance boundary within the shallow, deep, and bedrock zones. Summary of Geochemical Model 13.2 The Belews Creek 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 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 (HDR, 2016) included: 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-13 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. A focused geochemical model was presented in Appendix D of the Basis of Design Report for the Interim Action Plan (SynTerra, 2017a). This model was limited to the northwest corner of the ash basin. Laboratory Determination of Distribution Coefficient HDR 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 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-14 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 by Dzomback and Morel (1990) and Karamalidis and Dzomback (2010), respectively, was selected for this effort. Geochemical Controls on COI As described in previous geochemical model reports (HDR, 2016), pH, Eh, and solubility are the primary geochemical parameters affecting constituent mobility. In the updated geochemical model that will be submitted in 2018 as part of the CAP, hydraulically significant flow transects will be used to evaluate the 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). 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-15 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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. Groundwater concentrations and initial solid phase 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 updated 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. 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-16 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Summary of Geochemical Model Results To Date 13.2.2 The relationship between aqueous and sorbed COI concentrations is an equilibrium process. However, redox conditions vary widely across the site indicating the site soils (ash) may not have reached equilibrium with the groundwater which may affect the results of the model. The geochemical model results presented in the CAP Part 2 (HDR, 2016) verified the geochemical behavior of the constituents of interest. Constituents found to be relatively mobile with low distribution coefficients included barium and antimony. Low distribution coefficients were predicted for some additional species such as boron, cobalt, iron, manganese, and nickel. High distribution coefficients indicating low mobility were found for arsenic, beryllium, and chromium. Intermediate to high distribution coefficients indicating variable to low mobility were found for selenium, sulfate, and vanadium. Groundwater to Surface Water Pathway Evaluation 13.3 Regulation 15A NCAC 02L requires that groundwater discharge will not possess constituent concentrations that would result in exceedances of standards for surface waters contained in 15A NCAC 02B .0200. The BCSS ash basin is located south of the Dan River, and north and west of Belews Reservoir. The Dan River represents a groundwater discharge feature for the ash basin. Belews Reservoir represents a groundwater receptor east of the ash basin. Dan River Dan River samples SW-DR-U and SW-DR-D have had reported 2B exceedances of turbidity, pH, DO, chloride, selenium, TDS, dissolved cadmium, and dissolved lead. The 2B exceedances have all been greater than the concentrations reported in background sample SW-DR-BG, which does not have any 2B exceedances reported. Dan River sample SW-DR-U was collected immediately upstream of the confluence of the ash basin designated effluent channel with the Dan River, and sample SW-DR-D was collected immediately downstream of the confluence. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 13-17 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Water samples SW-DR-1, SW-DR-2, SW-DR-3, and SW-DR-UA were collected from the Dan River in September 2017 between background sample location SW-DR-BG and the SW-DR-U location to refine the understanding the potential source of 2B exceedances reported at SW-DR-U. Exceedances of the 2B standards were not reported in any of the surface water samples collected between SW-DR-BG and SW-DR-UA. A sample was inadvertently not collected from SW-DR-U during the September 2017 sampling event; however it appears that the 2B exceedances reported in SW-DR-U (and SW-DR-D) are a result of the proximity to the designated effluent channel (outfall 003). The sampling results do not suggest that the reported 2B exceedances in the Dan River are a result of influence from the ash basin. Belews Reservoir No 2B exceedance have been reported in the samples (SW-BL-U and SW-BL-D) collected from Belews Reservoir over the period of monitoring. Based on the available data for the upstream and downstream Belews Reservoir samples and the known COI distribution in groundwater the BCSS ash basin is not the source of 2B exceedances in Belews Reservoir. As shown on Figures 10-5 to 10-64, the extent of groundwater migration from the ash basin at concentrations greater than background and 2L extend downgradient of the ash basin but do not reach the Dan River or Belews Reservoir. Therefore, the surface water data reflect contributions from sources other than groundwater migration from the ash basin. To help determine potential routes of exposure and receptors related to the ash basin, additional surface water samples will be collected from Belews Reservoir and the Dan River near the stream/river bank most likely to be impacted by potentially contaminated groundwater discharge. The additional surface water sampling effort is described in detail in Section 11.3. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 14.0 SITE ASSESSMENT RESULTS Nature and Extent of Contamination 14.1 The site assessment described in the CSA presents the results of investigations required by CAMA and 2L regulations. The 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 basin, 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 BCSS ash basin include antimony, arsenic, barium, beryllium, boron, cadmium, chloride, chromium, hexavalent chromium, cobalt, iron, manganese, molybdenum, pH, selenium, strontium, sulfate, thallium, TDS, and vanadium. COIs migrate laterally and vertically into and through regolith, the transition zone, and shallow 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. Hydrogeologic Conditions Site hydrogeologic conditions were evaluated by installing and sampling groundwater monitoring wells; 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 basin 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 groundwater flow across the Site appears to flow through the interconnected flow layers. Four hydrostratigraphic layers were identified at the BCSS and were evaluated during the CSA: 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Ash – The ash pore water unit consists of saturated ash material. Observed ash depths range from a few feet to approximately 66 feet. Shallow – The shallow flow layer consists of soil and saprolite material that overlie the transition zone and bedrock. Alluvial deposits were not encountered in any of the boreholes in the area of the BCSS ash basin. Where present, the first occurrence of groundwater is generally represented by this layer. Deep (Transition Zone) – The deep (TZ) flow regime is a relatively transmissive zone of partially weathered bedrock comprised of rock fragments, unconsolidated material, and highly oxidized bedrock. This unit lies directly above competent bedrock; although, the change of transition zone material into bedrock can be indistinct and characterized by subtle differences in secondary mineralization, weathering, rock quality/competency, and fracture density. Fractured Bedrock – Secondary porosity through weathering and subsequent fracturing of bedrock control groundwater flow through the deepest hydrostratigraphic unit beneath BCSS. Water-bearing fractures are minimally productive. The BCSS ash basin acts as a bowl-like feature towards which groundwater flows from the basin to the east, northeast, north, and northwest. Groundwater primarily flows north toward the Dan River. Groundwater at the Site flows away from the topographic and hydrologic divide (highest topographic portion of the Site) generally located along Pine Hall Road to the north and south. The flow of ponded water within the ash basin is controlled laterally by groundwater flow that enters the basin from the south and is controlled downgradient (north) by the ash basin main dam and the NPDES outfall/discharge. The head created by the ash pore water creates a slight mounding effect that influences the groundwater flow direction in the immediate vicinity of the ash basin. In summary, there are no substantive differences in water level among wells completed in the different flow zones across the Site (shallow; deep; bedrock), and generally lateral groundwater movement predominates over vertical movement. The vertical gradients are near equilibrium across the Site indicating that there is no distinct horizontal confining layer beneath the Site. The horizontal gradients, hydraulic conductivity, and seepage velocities indicate that most of the groundwater transport occurs through the transition zone and bedrock, as most of the regolith encountered downgradient of the basin is thin and less likely to be saturated. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 overall groundwater flow direction does not change due to seasonal changes in precipitation. Horizontal gradients in the ash basin range from 0.002 to 0.006 ft/ft. The ash basin gradients are low compared to downgradient areas likely due to the low relief in the basin. Horizontal gradients along the southern portion of the Site downgradient of the topographic ridge are highest (0.035 ft/ft). The gradient is influenced by the steep relief in the southern portion of the property as the area slopes down to Belews Reservoir. Horizontal gradients along the north, northwest end of the Site range from 0.004 to 0.025 ft/ft. The hydraulic gradient in the northern portion of the Site is influenced by the higher relief between this area and the ash basin dam. Vertical gradients in saprolite, transition zone and bedrock wells are near equilibrium, indicating that there is no distinct horizontal confining layer beneath BCSS. Generally, upward vertical gradients predominate on the northeast and south side of the Site near Belews Reservoir, and include areas of the ash basin for deep and bedrock zones, while downward (recharge) gradients are more prevalent in the north and northwest portion of the property. Horizontal and Vertical Extent of Impact Boron is a CCR-derived constituent in groundwater and is detected at concentrations greater than the NC 2L standard beneath the ash basin and the Pine Hall Road Landfill and downgradient of the ash basin (north and northwest). Boron is not detected in background groundwater. Boron, in its most common forms, is soluble in water, and boron has a very low Kd value, making the constituent highly mobile in groundwater. Therefore, the presence/absence of boron in groundwater provides a close approximation of the distribution of CCR-impacted groundwater. The detection of boron at concentrations in groundwater greater than applicable 2L standards and PBTVs best represents the leading edge of the CCR-derived plume moving downgradient from the source area (ash basin and Pine Hall Road Landfill). As previously described, the groundwater plume is defined as any locations (in three- dimensional space) where groundwater quality is impacted by the ash basin. 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 impacts from the ash basin. The leading edge of the plume, the farthest downgradient edge, is represented by groundwater concentrations in the wells in each flow layer. In the bedrock flow layer, boron is reported in downgradient well MW-200BR, located north of the ash basin main dam at 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx the compliance boundary at a concentration greater than the PBTV and less than the 2L standard. Further downgradient boron has not been detected in wells MW-24D/BR. Boron is also detected in the bedrock flow layer at monitoring well GWA-20BR, located northwest of the ash basin at a concentration greater than the PBTV and less than the 2L standard. Boron is also detected in the bedrock flow layer at monitoring well OB-9, located north/northwest of the Pine Hall Road Landfill at a concentration greater than the PBTV and less than the 2L standard. The leading edge of the bedrock boron plume is interpreted to be at or just beyond these monitoring wells. The remaining bedrock downgradient wells did not have boron detected. In the deep flow layer (transition zone), boron results in the monitoring wells located within the compliance boundary on the east and southeast sides of the ash basin are non-detect. On the north side of the ash basin boron is reported in downgradient well MW-200D, located north of the ash basin main dam at the compliance boundary at a concentration greater than the PBTV and less than the 2L standard. Northwest of the ash basin, boron is reported at a concentration greater than the 2L standard at monitoring well GWA-27D located beyond the compliance boundary. 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 distribution of the plume. The boron concentrations reported in monitoring wells GWA-10DA, GWA-31D, and GWA-30D are non-detect. These wells are located beyond GWA-21D and the leading edge of the boron plume is expected to be generally between GWA-27D and this set of wells. Boron results exceed the 2L standard beneath the Pine Hall Road Landfill in the deep flow layer, but are non-detect at the compliance boundary. The leading edge of the boron plume in the shallow flow layer east of the ash basin is generally at the compliance boundary. North of the ash basin main dam and northwest of the ash basin, the boron plume in the shallow flow layer extends to beyond the compliance boundary. The boron concentration is non-detect in monitoring wells GWA-30S and GWA-31S which define the leading edge of the boron plume in the shallow flow layer. West of the ash basin the boron concentrations are non-detect or less than the PBTV at the compliance boundary. Surface water samples north of the basin from AOWs S-10 and S-11 show boron concentrations above the 2L standard, ranging 4,960 to 10,800 µg/L. Nearby wells MW-200S/D/BR have boron detected below the 2L standard. The boron concentration is non-detect in surface waters northwest of the basin (AOWs S-1, S-3 through S-5), however S-2 has boron detected below the 2L standard. Upgradient of S-2, wells GWA-31S/D have no detections of boron but further upgradient wells GWA-19S/D/BR shows boron detected only in the shallow layer and 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx above the 2L standard. Wells GWA-21S/D, upgradient of S-3 and S-4, shows boron detected below the 2L standard and wells GWA-30S/D, upgradient of S-5, have no detections of boron. Beryllium, chloride, chromium, cobalt, manganese, and thallium are also constituents detected in groundwater greater than background and 2L/IMAC near or beyond the compliance boundary. The interpreted extent of beryllium concentrations greater than background and the IMAC is beyond the compliance boundary in the shallow and deep flow layers. Beryllium was not reported at a concentration greater than the IMAC in the bedrock flow layer. The interpreted extent of chloride concentrations greater than 2L at and beyond the compliance boundary is in the shallow and deep flow layers. Chloride was not reported at a concentration greater than 2L in the bedrock flow layer. The interpreted extent of chromium concentrations greater than 2L at and beyond the compliance boundary is in the shallow and deep flow layers. Chromium was not reported at a concentration greater than 2L in the bedrock flow layer. The interpreted extent of cobalt concentrations greater than IMAC at and beyond the compliance boundary is in the shallow flow layer only. Cobalt exceedances were not reported in the deep and bedrock flow layers. The interpreted extent of manganese concentrations greater than 2L at and beyond the compliance boundary is in the shallow, deep, and bedrock flow layers. The interpreted extent of thallium concentrations greater than the IMAC at and beyond the compliance boundary is in the shallow and deep flow layers. Thallium was not reported at a concentration greater than 2L in the bedrock flow layer. The bedrock aquifer is generally the source of water for supply wells in the area. As outlined above, the bedrock aquifer has not been impacted by CCR constituent migration from the ash basin with the exception of a grout contaminated well beneath the ash basin main dam. The manganese concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. The surficial and transition zone flow units at Belews Creek— beneath and downgradient of the ash basin — are impacted by CCR-derived constituents; however, these units are not vertically extensive. Impact to the bedrock flow unit beneath the basin is observed, approximately, to the top 50 – 60 feet of fractured bedrock. The vertical extent of the plume is represented by groundwater concentrations in bedrock wells beneath and downgradient of the ash basin. AB-4BR, drilled to a depth of 144 feet bgs, contains no boron or manganese concentrations above 2L or the PBTV. However AB-9BR, drilled to 137 feet bgs has same absence of boron but has manganese detected above the 2L. Groundwater in the transition zone beneath the basin is impacted. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx As groundwater under the ash basin flows north, northwest toward the ash basin dam, the hydraulic impact of the ash basin dam and the hydraulic head exerted by the ash basin water forces groundwater downward into the bedrock, which increases hydraulic pressure in the bedrock aquifer. Wells completed in surficial, transition zone, and bedrock proximate to the north and northwest side of the ash basin dam are impacted by COIs. As groundwater and the plume migrate in the downgradient direction north of the basin, unimpacted groundwater enters the system from upgradient recharge areas to the west and east mitigating the concentration of some COIs (e.g., boron). Boron is present in groundwater downgradient of the ash basin on the Site in concentrations that exceed the 2L in both the shallow and transition zones. In bedrock boron is detected at only MW-200BR, based on data from wells positioned downgradient from the ash basin and off the Site property. Concentrations are below 2L for this location. Surface water flowing off the Site property north and northwest of the basin through AOWs S-2, S-10 and S-11 contain boron above 2L. The concentrations of boron at these locations have stayed relatively stable the past two years. Maximum Constituent Concentrations 14.2 Changes in COI concentrations over time are included as time-series graphs (Figures 14-1 through Figure 14-76). The maximum historical detected COI concentrations in groundwater for ash pore water or wells directly beneath the ash basin and non-ash basin groundwater are included below: Antimony – Ash Basin: 12.3 µg/L (AB-08SL); Outside Basin: 98,500 µg/L (OB-4) Arsenic – Ash Basin: 494 µg/L (AB-08SL); Outside Basin: 91.8 µg/L (OB-4) Barium – Ash Basin: 348 µg/L (AB-08SL); Outside Basin: 836 µg/L (GWA-19SA) Boron - Ash Basin: 21,900 µg/L (AB-04S); Outside Basin: 44,600 µg/L (OB-4) Beryllium - Ash Basin: 0.24 µg/L (AB-04S); Outside Basin: 11.5 µg/L (GWA-11S) Chloride– Ash Basin: 884 µg/L (AB-7S); Outside Basin: 499 µg/L (GWA-20SA) Cadmium – Ash Basin: 1.9 µg/L (AB-7S); Outside Basin: 18.72 µg/L (OB-4) Chromium – Ash Basin: 15.8 µg/L (AB-1S); Outside Basin: 269 µg/L (GWA-3S) Chromium (hexavalent) – Ash Basin: 5.5 µg/L (AB-08SL); Outside Basin: 8.3 µg/L (GWA-23D) Cobalt – Ash Basin: 271 µg/L (AB-7S); Outside Basin: 413 µg/L (MW-102S) 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Iron – Ash Basin: 137,000 µg/L (AB-08SL); Outside Basin: 92,200µg/L (MW-103S) Manganese – Ash Basin: 15,400 µg/L (AB-2D); Outside Basin: 2,300 µg/L (MW- 102S) Molybednum – Ash Basin: 3,460 µg/L (AB-4SL); Outside Basin: 22.3 µg/L (GWA- 6D) pH - Ash Basin: 3.9 (AB-7S) – 11.5 (AB-4SL); Outside Basin: 4.1 (GWA-10S) – 8.8 (GWA-20BR) Nickle – Ash Basin: 174 µg/L (AB-7); Outside Basin: 139 µg/L (GWA-3S) Radium (combined 226+228): 9.11 pCi/L (AB-2D); Outside Basin: 11.91 pCi/L (GWA-10S) Selenium - Ash Basin: 205 µg/L (AB-7S); Outside Basin: 401 µg/L (OB-9) Strontium - Ash Basin: 5,600 µg/L (AB-5SL); Outside Basin: 1,040 µg/L (GWA- 20D) Sulfate – Ash Basin: 637 mg/L (AB-7S); Outside Basin: 1,746 mg/L (OB-4) TDS – Ash Basin: 2,430 mg/L (AB-5SL); Outside Basin: 2,839 mg/L (OB-4) Thallium – Ash Basin: 5.5 µg/L (AB-8S); Outside Basin: 25.8 µg/L (OB-4) Vanadium – Ash Basin: 948 µg/L (AB-4S): Outside Basin: 213 µg/L (OB-4) Exceedances of PBTV soil concentrations are limited to only a few locations outside of the footprint of the ash basin. Concentrations of arsenic exceeding the PBTV are concentrated in areas north of the ash basin (GWA-1 and GWA-2) and northwest of the ash basin (GWA-9, GWA-10 and GWA-11). A few locations have iron concentrations that exceed the PBTV but appear spatially inconsistent beyond the ash basin footprint. Contaminant Migration and Potentially Affected Receptors 14.3 Contaminant Migration 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx flow will be greater in the regolith. At the Site, all hydrogeologic zones are saturated, however downgradient of the basin closer to the Dan River the regolith is observed to become thinner and less saturated (MW-24S). Across the site the regolith is the least transmissive of the flow zones. The majority of groundwater across the Site appears to flow through the transition zone and bedrock. Figures 14-77 to 14-96 show the most recent COI groundwater analytical concentrations for CAMA monitoring wells. The figures are color-coded to visually depict whether analytical concentrations are 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. Figures 14-81 and 14-92 show concentrations of boron and strontium increasing downgradient, northwest of the ash basin. For boron, concentrations are increasing in monitoring wells screened in the shallow zone and transition zone, downgradient of the ash basin. Figures 14-79 and 14-80 show similar temporal trends between barium and beryllium, with increasing concentrations north, northwest of the ash basin. Figure 14-87 and 14-88 show iron and manganese decreasing in many wells downgradient and outside of the ash basin across the site, which could be attributable to the wells stabilizing after a period of time has passed since well installation. The pore water in the ash basin is the source of constituents detected above 2L in groundwater samples in the vicinity of the ash basin. Gradients measured within the ash basin 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 north, northwest in response to hydraulic gradients, with potential mixing of source area groundwater and regional groundwater along side-gradients east and west of the ash basin. Groundwater migrates under diffuse flow conditions in the surficial 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. Groundwater flow is the primary mechanisms 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 basin acts as a bowl- like feature toward which groundwater flows from all directions except from the north. The valley in which the ash basin was constructed follows the slope-aquifer system, where flow of groundwater into the ash basin and out of the ash basin is restricted to the local flow regime. Shallow groundwater and surface water flow from the ash basin 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx is funneled into a natural valley with engineered structures to capture northerly flow from the dam and eventually discharges into the Dan River as a permitted outfall. Groundwater also flows northwest from the ash basin into several natural valleys which also flow to the north of the property discharging into the Dan River. Boron is present in groundwater in both the north and northwest valleys extending from the ash basin at concentrations that exceed the 2L. Downgradient of the ash basin to the northwest, boron concentrations above 2L extend outside the compliance boundary. At BCSS, 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 and the method presented above. Bedrock fractures encountered at Belews Creek 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. Recent concentrations of COIs in groundwater, surface water, and AOWs are provided on Figures 14-97 and 14-98. Recent concentrations of COIs in solid media, as well as available geochemical properties of soils and sediments, are provided on Figure 14-99. Potentially Affected Receptors A baseline human health and ecological risk assessment was performed in 2016. An update to the risk assessment has been completed (Section 12.0). The update evaluated recent analytical data for their potential to influence 2016 risk assessment conclusions. Human The 2016 risk assessment estimated potential risks under a hypothetical subsistence fisher scenario exposed to thallium and cobalt in fish tissue modeled from surface water concentrations, and potential risks from thallium under a hypothetical recreational fisher scenario. The risks were likely overestimated because of very conservative assumptions in the exposure models. Concentrations of cobalt and thallium have decreased in subsequent sampling events and have not exceeded the respective human health screening levels of 1 µg/L (cobalt) and 0.2 µg/L (thallium) in the two most recent sampling events at SW-DR-U. Thus, there is no evidence of potential risks under the hypothetical fisher scenario from exposure to cobalt and thallium. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-10 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Ecological One surface water sample location was included in the assessment for Ecological Exposure Area 3: SW-BL-D in Belews Reservoir . A new maximum concentration of cobalt did not result in a wildlife hazard quotient greater than unity (1); therefore there is no evidence of risks to ecological receptors exposed to cobalt at the SW-BL-D sample location. In addition, Belews Reservoir is considered beyond the extent of constituent migration in groundwater from the ash basin. Water Supply Wells 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: There is very limited information available about the sampled wells. It is likely the wells were constructed as open-hole bedrock wells. Groundwater geochemistry in fractured bedrock aquifers can be quite variable. PBTVs were developed using groundwater data from a set of two background monitoring wells all located on the Site. The geochemical data from these wells may not be representative across the broader area encompassed by the 50 private water supply wells and one public water supply well. Well construction, pump, piping, and well materials may influence analytical results. A numerical capture zone analysis for the BCSS Site was conducted to evaluate potential impact of upgradient water supply pumping wells. None of the particle tracks originating in the ash basin moved into the well capture zones. Based on the bedrock groundwater flow direction at the site (Figures 6-10 and 6-11, discussed in Section 6.3) private water supply wells located west of the ash basin along Old Plantation Road (WSWs samples BC2019-RAW, BC2 Well 1, BC2 Well 2, BC-1007, BC4, BC4A and BC4B) are located sidegradient of the ash basin. The remaining water supply wells are located in upgradient or a sufficient distance sidegradient to not be impacted by groundwater migration from the ash basin. Analytical data is not available for water supply well BC4. The turbidity reading in BC4 Well B at the time of sampling was 19.3 NTU, therefore the data is not considered valid, and is not evaluated. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-11 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Iron was reported at concentrations which exceed the bedrock PBTV (228 µg/L) and the 2L standard (300 µg/L) in water supply well samples BC-1007, BC2 Well 1, BC2 Well 2, and BC2019-RAW. However, the iron concentrations in these water supply wells are within the background concentration range for similar Piedmont geologic settings. Vanadium was reported at a concentration greater than the IMAC but less than the bedrock PBTV in water supply well sample BC2019-RAW, and greater than the IMAC and PBTV in BC4 Well A. However, the vanadium concentrations in these water supply wells are within the background concentration range for similar Piedmont geologic settings. Boron was not detected in any of these water supply wells sampled sidegradient of the ash basin. A Piper diagram for water supply well data compared to ash basin pore water, background bedrock monitoring wells and bedrock monitoring wells located downgradient of the ash basin (between the ash basin and the private water supply wells) is presented as Figure 4-3. Observations based on the diagram include: Water supply wells are characterized as calcium bicarbonate water type, consistent with samples collected from the background bedrock well at BCSS. Monitoring well MW-203BR (located between the ash basin and the private water supply wells to the west) plots along with background well BG-2BR, indicating this well is likely representative of unimpacted groundwater. Monitoring well GWA-9BR (located between the ash basin and the private water supply wells to the west) plots between calcium-magnesium sulfate type water and calcium bicarbonate water, a result of the concentration of chloride (52.7 mg/L) relative to the concentration of sulfate and may indicate potential mixing with source area groundwater. The signature of the water supply wells is similar to the background bedrock well at the site indicating that these wells are not impacted by the source area water. Surface Waters As shown Figures 10-5 to 10-64, the extent of groundwater migration from the ash basin at concentrations greater than background and 2L extend downgradient of the ash basin but do not reach the Dan River or Belews Reservoir. Therefore, the surface water data reflect contributions from sources other than groundwater migration from the ash basin. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 14-12 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx In the Dan River, exceedances of the 2B standards were not reported in any of the surface water samples collected between SW-DR-BG and SW-DR-UA. A sample was inadvertently not collected from SW-DR-U during the September 2017 sampling event, however it appears that the 2B exceedances reported in SW-DR-U (and SW-DR-D) are a result of the proximity to the designated effluent channel (outfall 003). The sampling results do not suggest that the reported 2B exceedances in the Dan River are a result of influence from the ash basin. No 2B exceedance have been reported in the samples (SW-BL-U and SW-BL-D) collected from Belews Reservoir over the period of monitoring. Based on the available data for the upstream and downstream Belews Reservoir samples the BCSS ash basin is not the source of 2B exceedances Belews Reservoir. To help determine potential routes of exposure and receptors related to the ash basin, additional surface water samples will be collected from Belews Reservoir and the Dan River near the stream/river bank most likely to be impacted by potentially contaminated groundwater discharge. The additional surface water sampling effort is described in detail in Section 11.3. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.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. Overview of Site Conditions at Specific Source Areas 15.1 The horizontal and vertical extent of exceedances has been defined (Figure ES-1) sufficiently for preparation of the CAP. Boron exceedances in the shallow flow layer are primarily located north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance boundary. In the deep flow layer boron exceedances are located beneath the ash basin and the Pine Hall Road Landfill, north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance boundary. Boron exceedances are also reported south of the topographic divide along Pine Hall Road, west of the structural fill. These exceedances are not related to the ash basin and a separate assessment of the structural fill is ongoing. There are no boron exceedances reported in the bedrock flow layer in monitoring wells that are not grout contaminated (high pH). Beryllium, chloride, chromium, cobalt, manganese, and thallium are also constituents detected in groundwater greater than background and 2L/IMAC near or beyond the compliance boundary. The interpreted extent of beryllium concentrations greater than background and the IMAC is beyond the compliance boundary in the shallow and deep flow layers. Beryllium was not reported at a concentration greater than the IMAC in the bedrock flow layer. The interpreted extent of chloride concentrations greater than 2L at and beyond the compliance boundary is in the shallow and deep flow layers. Chloride was not reported at a concentration greater than 2L in the bedrock flow layer. The interpreted extent of chromium concentrations greater than 2L at and beyond the compliance boundary is in the shallow and deep flow layers. Chromium was not reported at a concentration greater than 2L in the bedrock flow layer. The interpreted extent of cobalt concentrations greater than IMAC at and beyond the compliance boundary is in the shallow flow layer only. Cobalt exceedances were not reported in the deep and bedrock flow layers. The interpreted extent of manganese concentrations greater than 2L at and beyond the compliance boundary is in the shallow, deep, and bedrock flow layers. The interpreted extent of thallium concentrations greater than the IMAC at and beyond the compliance boundary is in the shallow and deep flow layers. Thallium was not reported at a concentration greater than 2L in the bedrock flow layer. The bedrock aquifer is generally the source of water for supply wells in the area. As outlined above, the bedrock aquifer has not been impacted by CCR constituent 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-2 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx migration from the ash basin. The manganese concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. In ash basin locations where soil samples were collected beneath the ash, analytical results indicate arsenic and selenium concentrations greater than PBTVs and PSRGs for POG are present. Strontium was also reported in five of the soil samples collected beneath the ash basin at concentrations greater than the background concentration. There is no PSRG POG for strontium. No other COIs were detected in soil beneath the ash basin at concentrations greater than PBTVs or PSRG POGs. Revised Site Conceptual Model 15.2 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. 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 SCM was developed from data generated during previous assessments, existing groundwater monitoring data, and CSA activities. The BCSS ash basin is located in the central part of the BCSS site and receives surface water runoff and groundwater recharge from upland areas south of the basin. Assessment results indicate the thickness of CCR in the ash basin ranges from a few feet to approximately 66 feet. Assessment findings determined that pore water in the ash basin is the primary source of impact to groundwater. As previously discussed, residual concentrations of arsenic, selenium and strontium in soil beneath the ash basin may also represent a secondary source. The ash basin discharges pore water to the subsurface beneath the basin. Groundwater from the ash basin flows downgradient of the ash basin dam predominately through the designated effluent channel, discharging to the Dan River (NPDES outfall 003). Groundwater in the vicinity of the ash basin also flows to the northwest towards the 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-3 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Dan River and to the east towards Belews Reservoir. Horizontal migration of groundwater at the site is generally controlled by topographic divides along Pine Hall Road to the south and east of the ash basin and along Middleton Loop Road to the west of the ash basin. These topographic divides generally function as groundwater divides, although groundwater flow across topographic divides may be possible based on hydraulic head conditions from the ash basin and the existence of preferential flow paths within the shallow and/or deep flow layers. The horizontal and vertical extent of exceedances has been sufficiently defined for preparation of the updated CAP. Seventeen constituents were reported at concentrations greater than their corresponding background concentration range, 2L or IMACs in one or more pore water samples. In groundwater, the maximum COI concentrations occur in the shallow and deep flow layers. The maximum concentrations are located northwest, downgradient of the ash basin. Concentrations of boron, cobalt, iron, manganese, sulfate, TDS are also observed west of the Structural Fill. The extent of constituent migration in groundwater at concentrations greater than site background and groundwater quality standards is shown on Figure ES-1. Boron and additional COI exceedances in the shallow and deep flow layers are primarily located north of the ash basin main dam, within the compliance boundary, and northwest of the ash basin, at or beyond the compliance. The bedrock aquifer is generally the source of water for supply wells in the area. As outlined above, the bedrock aquifer has not been impacted by CCR constituent migration from the ash basin. The manganese concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. Constituent concentrations in bedrock groundwater directly downgradient of the ash basin are less than 2L with the exception of manganese, which appears to be due to geochemical conditions. The water chemistry signature of the water supply wells is similar to the background bedrock wells at the site. Although several water supply well concentrations reported are greater than the site specific PBTVs, the concentrations are within the background concentration range for similar Piedmont geologic settings. Monitoring wells GWA-19BR, GWA-20BR, and GWA-27BR are located northwest of the ash basin. These wells are grout contaminated (high pH) and their data is not considered valid. The boron concentrations reported in these monitoring wells are similar to the boron background concentration. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-4 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx As shown Figures 10-5 to 10-64, the extent of groundwater migration from the ash basin at concentrations greater than background and 2L extend downgradient of the ash basin but do not reach the Dan River or Belews Reservoir. Therefore, the surface water data reflect contributions from sources other than groundwater migration from the ash basin. The ecological risk assessment considered surface water data associated with Belews Reservoir beyond the extent of constituent migration in groundwater from the ash basin. As such, the findings for the Belews Reservoir do not imply adverse effects associated with groundwater to surface water migration from the ash basin. This exposure route will be further evaluated through direct surface water sampling and predictive modeling as part of the CAP. To date, 2B and EPA water quality criteria have not been exceeded in waters proximal to areas of groundwater impact. The SCM will continue to be refined following evaluation of the completed groundwater model in the CAP and additional information obtained in subsequent data collection activities. Interim Monitoring Program 15.3 An Effectiveness Monitoring Program (EMP) is required by CAMA §130A-309.209 (b)(1)e. The EMP for BCSS will begin once the basin closure and groundwater CAP have been implemented. In the interim, and Interim Monitoring Plan (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 of the IMP only. IMP Implementation 15.3.1 An IMP has been implemented in accordance with NCDEQ correspondence (NCDEQ, October 19, 2017) that provided an approved “Revised Interim Monitoring Plans for 14 Duke Energy Facilities” (Appendix A). Sampling will be conducted quarterly until approval of the CAP or as otherwise directed by NCDEQ. These events will be conducted in conjunction with the NPDES triennial monitoring with a fourth sampling event added to provide four rounds of sampling during the year. 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. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-5 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 and monitored as part of the IMP, as approved in NCDEQ correspondence (NCDEQ, October 19, 2017; Appendix A), 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 on a monthly basis. 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 IMP Report is to be submitted to NCDEQ no later than April 30, 2018. Preliminary Evaluation of Corrective Action Alternatives 15.4 Closure of the ash basin is required by 2024 under CAMA (Intermediate Risk). The updated risk assessment (Section 12.0) has determined there are indications that potential risks to humans and wildlife at the Belews Creek site. Risk calculations using new results will be required to estimate potential risks posed by newly detected constituents and constituents detected at greater concentrations since completing the 2016 risk assessment. Groundwater in the bedrock flow unit, typically used for private drinking water supply wells in the region, is impacted. In locations beneath the ash basin where soil samples could be collected, analytical results indicate shallow impacts of COIs above PBTVs. If needed, groundwater and surface water can be remediated over time using a variety of approaches and technologies. The updated groundwater model (presented in Appendix C of the Basis of Design Report for the Interim Action Plan (SynTerra, 2017)) predicts that ten extraction wells within the transition zone (model layer 6) will lower groundwater levels for more than 5 to 10 feet along the extraction system axis, with hydraulic impacts to northwest corner of the ash basin. 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-6 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Site wide simulation data for the updated model extended out until such time as compliance with 2L at the compliance boundary is achieved will be presented in the updated CAP. This preliminary evaluation of corrective action alternatives is included to provide insight into the groundwater 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 capping the ash basin and minimizing 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, in addition to the groundwater extraction system currently being installed. CAP Preparation Process 15.4.1 The CAP preparation process is designed to identify, describe, evaluate, and select remediation alternatives. Those alternatives will have 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 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 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-7 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 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 complete CAP will include: Descriptions of site conditions Corrective action objectives and evaluation criteria Technology assessment Formulation of complete remedial action alternatives Analysis, selection, and description of a complete remedial action alternative 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 area that may require groundwater remediation is between the toe of the basin dam and the compliance boundary to the north. The COIs that may potentially need to be addressed are predominantly found in the downgradient bedrock formations. Groundwater flow is primarily through the upper fractured bedrock unit and the highly heterogeneous bedrock transition zone. The formations in question appear to be significantly heterogeneous and appear to create anisotropic flow conditions. The preliminary screening of potential groundwater corrective action follows: 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-8 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx Source control by capping in place or excavation, and monitored natural attenuation, will be vital components to the CAP. Groundwater migration barriers. The lateral extent potentially required, along with the depth and heterogenitity of the transition zone and bedrock, may limit the feasibility of this technology. Insitu 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. 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 MNA. However, further analysis is required and will be addressed in the updated CAP. 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 revised CAP preparation process, as outlined in 2L. It is based on data currently available and on the current understanding of regulatory requirements for the site. It addresses potentially applicable technologies and remedial alternatives. Potential approaches are based on the currently available information about site geology/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 and manganese. If required, the potentially applicable technologies to supplement source control and MNA include several groundwater extraction technologies such as conventional vertical wells, along with angle-drilled and horizontal wells. All of 2017 Comprehensive Site Assessment Update October 2017 Belews Creek Steam Station SynTerra Page 15-9 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx these extraction technologies could also be augmented with fracturing of the bedrock formation. Migration barriers, in-situ chemical immobilization, and permeable reactive barriers are also identified as potentially applicable remedial action alternatives. In the event that 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 Belews Creek Steam Station SynTerra Page 16-1 P:\Duke Energy Carolinas\20. BELEWS CREEK\CSA UPDATE OCT 2017\Belews Creek CSA October 2017 FINAL.docx 16.0 REFERENCES ASTM. (2001). D2487; Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). West Conshohocken, PA: ASTM International, DOI:10.1520/D2487-11. ASTM. (2007). D422; Standard Test Method for Particle Size Analysis of Soils. West Conshohocken, PA: ASTM International, DOI:10.1520/D0422-63R07. ASTM. (2010a). D2216; Standard Test Methods for Laboratory Determination of Water (Moisture) Conent of Soil and Rock by Mass. West Conshohocken, PA: ASTM International, DOI: 10.1520/ D2216-10. ASTM. (2010b). D5084; Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter. 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