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HomeMy WebLinkAboutNC0005088_FINAL_CSA_Report_201801312018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.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 of the CSA report. Continued groundwater monitoring at the Site is planned. Item 2. Imminent hazards to human health and the environment have been evaluated. The NCDEQ data associated with nearby water supply wells is provided herein and is being evaluated. Item 5. The groundwater assessment plan for the CSA as approved by NCDEQ was specifically developed to assess the coal ash management areas of the facility for the purposes of developing a corrective action plan for groundwater. Other areas of possible contamination on the property, if noted, are anticipated to be evaluated separately. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.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. • 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx EXECUTIVE SUMMARY ES.1 Source Information Duke Energy Carolinas, LLC (Duke Energy) owns and operates the Cliffside Steam Station (CSS), which is located on the Broad River in Mooresboro, in Rutherford and Cleveland Counties, North Carolina. This Comprehensive Site Assessment (CSA) update was conducted to refine and expand the understanding of subsurface conditions and evaluate the extent of impacts from historical management of coal ash in accordance with the North Carolina Coal Ash Management Act (CAMA). 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. Available groundwater data from monitoring wells associated with the Federal Coal Combustion Residuals Rule (CCR Rule) compliance program are also considered in data interpretations. However, the CCR data has not been as thoroughly evaluated as the CAMA data due to the CCR data only becoming available as of mid- January 2018. For example, analytical results from CCR Rule-specific monitoring wells are included on isoconcentration maps and analytical summary tables, but not integrated into detailed mathematical analysis, such as piper plots, box-and-whisker plots or background statistical calculations. CSS began operation in 1940 as a coal-fired generating station and currently operates two coal-fired units. CSS managed coal combustion residuals (CCR) from the coal combustion process in unlined Units 1-4 inactive ash basin from 1957 until 1977 when it reached capacity; and in the unlined Unit 5 inactive ash basin beginning in 1972 until it was retired in 1980 when it reached full capacity. The Units 1-4 inactive ash basin was located immediately east of the retired Units 1-4. The basin has been excavated and the final grading of the area is in progress. The Unit 5 inactive ash basin is located on the western portion of the site, west and southwest of Units 5 and 6. The active ash basin is located on the eastern portion of the site, east and southeast of Units 5 and 6. Construction of the active ash basin occurred in 1975 and it began receiving sluiced ash from Unit 5. The active ash basin expanded in 1980 to its current footprint and continues to receive sluiced bottom ash from Unit 5 and Unit 6 in addition to other waste streams. The fly ash at CSS is currently dry handled. The active ash basin is unlined and consists of a single cell impounded by a main dam on the north, adjacent to the Broad River (downstream dam) and an embankment dam located to the west of the ash basin adjacent to Suck Creek (upstream dam). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx An unlined dry ash storage area, which is split into an eastern and western portion, is also located within the northwestern portion of the active ash basin waste boundary. This ash storage area was likely created when ash was removed from the active ash basin in the 1980s to provide additional capacity for sluiced ash. The eastern portion of the ash storage area may also contain soil from the active ash basin embankment dam construction. Duke Energy also operates a Coal Combustion Products (CCP) Landfill in accordance with the North Carolina Department of Environmental Quality (NCDEQ) Industrial Solid Waste Permit No. 81-06. The landfill, constructed with an engineered liner and leachate collection system, is permitted to receive fly ash, bottom ash, boiler slag, coal mill rejects/pyrites, flue gas desulfurization sludge, gypsum, leachate basin sludge, non- hazardous sandblast material, limestone, lime, ball mill rejects, coal, carbon, sulfur pellets, cation and anion resins, sediment from sumps, cooling tower sludge, filter bags, conditioning agents (e.g. lime kiln dust), soil material that contains any of the above material and soil used for operations), incidental amounts of geotextile used in the management of CCP’s, and vacuum truck waste. The landfill is located approximately 1,800 feet southwest of the Unit 5 inactive ash basin, south of Duke Power Road. The NCDEQ Division of Water Resources (DWR) currently permits discharge from the active ash basin to receiving waters designated as the Broad River under the National Pollutant Discharge Elimination System (NPDES) Permit NC0005088. The outlet for the active ash basin (NPDES Outfall 002) is a reinforced concrete pipe (RCP) located in the northwest corner of the basin. Assessment results indicate the thickness of CCR in the active ash basin ranges from a few feet to approximately 73 feet. Within Units 1-4 inactive ash basin CCR thickness ranged from a few feet to approximately 37 feet prior to excavation, and to 67 feet in Unit 5 inactive ash basin. The ash storage area has a CCR thickness from 7 feet to 57 feet. Portions of ash within the active ash basin, the Unit 5 inactive ash basin, and the ash storage area are saturated. The Units 1-4 inactive ash basin has been excavated. Assessment findings determined that CCR accumulated in the ash basins is the primary source of impact to groundwater. The inferred extent of constituent migration in groundwater at concentrations greater than site background and groundwater quality standards is shown on Figure ES-1. A detailed evaluation of constituent migration is included in this CSA update report. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx ES.2 Initial Abatement and Emergency Response Duke Energy has not conducted emergency responses because groundwater impacts from the ash basins do not present an imminent hazard to human health or the environment requiring emergency response. Duke Energy recommended full excavation of the Units 1-4 inactive ash basin. Excavation of the basin began in October 2015 and concluded in March 2017 with the exception of minor ash removal that is still ongoing at the interior slopes of the dam. Approximately 450,000 tons of ash and comingled soil material was removed from the basin and relocated in the existing lined Cliffside CCP Landfill. Two lined basins and a wastewater treatment plant will be constructed within the footprint of the basin to treat plant flows when the active ash basin is taken offline in the future. ES.3 Receptor Information In accordance with NCDEQ direction, CSA receptor survey activities include listing and depicting water supply wells (public or private, including irrigation wells and unused wells) and surface water bodies within a 0.5-mile radius of the ash basin compliance boundaries. During the timeframe of the receptor survey, a compliance boundary was assumed around the Unit 5 inactive ash basin and the Units 1-4 inactive ash basin as well as the compliance boundary around the active ash basin and the ash storage area. In 2017, the compliance boundary was revised and therefore the receptor survey covered a broader area than would be within 0.5 miles of the current compliance boundary. ES.3.1 Public Water Supply Wells No public water supply wells (including irrigation wells and unused wells) or wellhead protection areas were identified within a 0.5-mile radius of the CSS ash basin compliance boundaries. ES.3.2 Private Water Supply Wells A total of 71 private water supply wells were identified within the 0.5-mile radius of the ash basin compliance boundaries; most south, southeast, east, and northeast of the active ash basin off of McCraw Road, Prospect Church Road, Fox Place, and Riverfront Drive, west and southwest of the Unit 5 inactive ash basin along Duke Power Road, US-221 Alt, and Old US-221A, and north of the Broad River. 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 flowing toward the Broad River. The water chemistry signature of 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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. The data does not indicate that offsite private water supply wells have been impacted by the active ash basin, Unit 5 inactive ash basin, the Units 1-4 inactive ash basin or the ash storage area at the CSS site. ES.3.3 Surface Water Bodies The Site is located in the Broad River watershed. The North Carolina portion of the Broad River Basin encompasses approximately 1,513 square miles in all or in part of eight counties. It straddles the southeastern corner of the Blue Ridge eco- region and the southwestern portion of the Piedmont eco-region. The site is located south of and adjacent to the Broad River. Groundwater at the site primarily flows horizontally toward the north and discharges to the Broad River. Groundwater flow to the west of the active ash basin and east of Unit 6 is towards Suck Creek which discharges to the Broad River. Surface water classifications in North Carolina are defined in 15A NCAC 02B . 0101(c). The surface water classifications for the Broad River and Suck Creek in the vicinity of the CSS site are Class WS-IV. Class WS-IV waters are protected as water supplies which are generally in moderately to highly developed watersheds. No surface water intakes, other than the intake used to pump water for plant operations are located in the vicinity of CSS in the Broad River. ES.3.4 Land Use The area surrounding CSS generally consists of residential properties, undeveloped land, and the Broad River. Properties in Cleveland County are primarily comprised of the CSS and residential properties to the south, east, and northeast of CSS. Properties located to the west along Hwy 221A and northwest across the Broad River in Rutherford County are zoned rural residential including CSS, which is identified as average rural. No changes in land use surrounding CSS are expected. ES.4 Human Health and Ecological Risk Assessment An update to the 2016 human health and ecological risk assessment was conducted. There is no evidence of unacceptable risks to humans exposed to groundwater on-site. Limited potential for unacceptable risks to humans was estimated for the hypothetical recreational and subsistence fisher due to the surface water derived estimate of cobalt concentration in fish tissue. Limited potential for unacceptable risks to birds and mammals was consistent with the 2016 assessment. Fisher risks were overestimated in 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx the risk assessment based on conservative exposure model assumptions. This update to the human health and ecological risk assessment supports a risk classification of “low” for groundwater related consideration. ES.5 Sampling/Investigation Results This CAMA CSA includes evaluations of the hydrogeological and geochemical properties of soil and groundwater at multiple depths and distances from the ash management areas. ES.5.1 Background Concentration Determinations Naturally occurring background concentrations were determined using statistical analysis for both soil and groundwater. 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 bedrock. As of October 11, 2017, DEQ approved a number of the statistically derived background values, however others are still under evaluation and thus considered preliminary at this time. Therefore, it is understood that valid background data may be greater than the currently calculated PBTVs due to the limited dataset currently available and the statistical nature of the determination. The statistically derived background threshold values will continue to be adjusted as additional data become available. ES.5.2 Nature and Extent of Contamination Site-specific groundwater constituents of interest (COIs) were developed by evaluating groundwater sampling results with respect to 2L/Interim Maximum Allowable Concentrations (IMACs) and PBTVs. The distribution of constituents in relation to the ash basins and ash storage area, 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The following list of groundwater COIs has been developed for CSS: Arsenic Strontium Boron Sulfate Chromium (hexavalent) TDS (Total Dissolved Solids) Chromium (total) Thallium Cobalt Vanadium Iron Total uranium Manganese Total radium pH In the following discussion of the nature and extent of contamination, exceedances are defined as concentrations greater than the 2L/IMAC, except when the PBTV is greater than the 2L/IMAC, or there is no 2L/IMAC established for the constituent. In these cases, the PBTV is used to determine constituent exceedances. The general extent of constituent exceedances in groundwater for all flow zones are shown on Figure ES-1. Active Ash Basin The leading edge of the boron plume in the shallow flow layer is located southwest of the basin and discharges to Suck Creek. The north end of the boron 2L exceedances plume intersects with the western portion of the ash storage area and extends toward the Broad River. In the eastern portion of the ash basin there is one boron exceedance located at the downstream dam. In the deep flow layer, boron 2L exceedances are limited to the west side of the basin, and the toe of the upstream dam within the compliance boundary. In the bedrock flow layer, boron is not reported in any of the wells at a concentration greater than the 2L standard. Boron is reported at a concentration greater than the PBTV at the toe of the upstream dam, west of the active ash basin and north and northeast of the downstream dam, near the Broad River. The remaining bedrock downgradient well locations did not have boron detected. Chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are also constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. The extent of exceedances of chromium is confined to the shallow layer, at the downstream dam extending near or beyond the compliance boundary. Chromium exceedances were not reported in the deep or bedrock flow layers. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The extent of exceedances of cobalt near or beyond the compliance boundary are limited to north of the ash basin downstream dam in the shallow flow layer and southeast of the basin in the bedrock flow layer. Cobalt exceedances in the bedrock flow layer are reported southeast and north of the ash basin. Cobalt exceedances are also detected near the waste boundary in the shallow and deep flow layers near the upstream dam. The extent of exceedances of iron in the shallow and deep flow layers is downgradient northwest and north of the basin and within or near the waste boundary at the upstream dam. The exceedances of iron reported north of the active ash basin downstream dam are detected near or beyond the compliance boundary. In the bedrock flow layer iron exceedances are reported at two wells within the waste boundary. The extent of exceedances of manganese in the shallow flow layer is at locations beneath the southern end of the basin, at the upstream dam within the compliance boundary. Shallow manganese exceedances near or beyond the compliance boundary were detected north of the active ash basin downstream dam. Manganese exceedances in the deep flow layer were reported northwest of the active ash basin within the compliance boundary and west and north of the active ash basin near or beyond the compliance boundary. Manganese exceedances are also reported in the bedrock flow layer beneath the active ash basin and near or beyond the compliance boundary north of the active ash basin. The extent of exceedances of strontium in the shallow flow layer is beneath the active ash basin within the waste boundary, and near or beyond the compliance boundary north of the basin near the downstream dam. Exceedances of strontium in the deep flow layer are located northwest of the ash basin at the upstream dam and near or beyond the compliance boundary west and north of the active ash basin. Bedrock flow layer exceedances are located near the upstream dam and near or beyond the compliance boundary north of the downstream dam. The extent of exceedances of sulfate is limited to the shallow flow layer, north of the active ash basin within the waste boundary, between the basin and the ash storage area. Sulfate exceedances were not detected in the deep or bedrock flow layers. The extent of exceedances of thallium in the shallow flow layer is within the compliance boundary west and northwest of the active ash basin. Thallium exceedances are detected in the deep flow layer at the north end of the ash basin 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx near the ash storage area. Thallium exceedances were not reported in the bedrock flow layer. The extent of TDS exceedances in the shallow flow layer are located north of the active ash basin within the waste boundary, between the basin and the ash storage area. TDS exceedances were reported in the deep flow layer northwest of the active ash basin near the upstream dam within the compliance boundary. TDS exceedances were not reported in the bedrock flow layer. The extent of exceedances of vanadium in the shallow flow layer is located beneath the basin and north of the basin between the basin and the ash storage area. Vanadium exceedances in the deep flow layer are detected beneath the basin and at the upstream dam within the compliance boundary, and near or beyond the compliance boundary northeast of the downstream dam. A vanadium concentration equal to the PBTV in the bedrock flow layer was reported at one well upgradient and east of the active ash basin. A vanadium exceedance was detected within the compliance boundary near the active ash basin downstream dam. For soil samples below the ash in the active ash basin, boron, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium had reported values greater than the preliminary soil remediation goals (PSRG) for protection of groundwater (POG). Although some constituent levels were measured above PSRG for POG standards in soil samples beneath the basin, when compared to the Site’s PBTVs, most constituent concentrations are similar to calculated soil background values, with the exception of boron, cobalt, and manganese. Soil sample analytical results indicate shallow impacts to the soil beneath the active ash basin. Units 1-4 Inactive Ash Basin In the deep flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Units 1-4 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard upgradient and adjacent to the basin, and downgradient of the basin. In the bedrock flow layer, boron is not reported in the monitoring wells adjacent to or beneath the former Units 1-4 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx but less than the 2L standard upgradient and adjacent to the basin, and beneath the basin. Arsenic, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are also constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. An arsenic exceedance in the shallow flow layer is reported near or beyond the northern waste boundary. Arsenic exceedances were not reported in the deep or bedrock flow layers. The extent of exceedances of chromium in the shallow flow layer is located upgradient of the Units 1-4 inactive ash basin and at a location near or beyond the waste boundary north of the basin. Chromium exceedances in the deep flow layer are located north of the basin, near and beyond the waste boundary. Chromium exceedances were not reported in the bedrock flow layer. The extent of exceedances of cobalt in the shallow flow layer is limited to one well location beneath the Units 1-4 inactive ash basin. Cobalt exceedances were not reported in the deep or bedrock flow layers. The extent of iron exceedances in the shallow and deep flow layers are located beneath the Units 1-4 inactive ash basin and near and beyond the northern and eastern waste boundary, and upgradient of the basin. Iron exceedances were not reported in the bedrock flow layer. The extent of exceedances of manganese in the shallow, deep and bedrock flow layers is north of the Units 1-4 inactive ash basin, near or beyond the waste boundary, and south of the basin at upgradient locations. The extent of exceedances of strontium in the shallow, deep and bedrock flow layers is beneath the Units 1-4 inactive ash basin, north of the basin near and beyond the waste boundary and at upgradient locations south of the basin. The extent of exceedances of sulfate exceedances in the shallow, deep and bedrock flow layers is at upgradient locations south of the ash basin. Sulfate exceedances are not detected beneath or downgradient of the basin. The extent of exceedances of thallium at the Units 1-4 inactive ash basin in the shallow flow layer is located near or beyond the northeast and northwest waste boundary. Thallium exceedances were not reported in the deep or bedrock flow layers. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The extent of exceedances of TDS in the shallow flow layer is located within the Units 1-4 inactive ash basin waste boundary. The exceedances reported in the deep and bedrock flow layers are upgradient, south of the basin. The extent of exceedances of vanadium in the shallow, deep and bedrock flow layer is downgradient near or beyond the northeast and northwest waste boundaries and at isolated upgradient locations in the shallow and bedrock flow layers. For soil samples below the ash, arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium had reported values greater than the PSRG for POG. Although some constituent levels were measured above the PSRG for POG standards in soil samples beneath the basin, when compared to the Site’s PBTVs most constituent concentrations are similar to calculated soil background values, with the exception of arsenic and chromium which had several PBTV exceedances reported. Soil sample analytical results indicate shallow impacts to the soil beneath the Units 1-4 inactive ash basin. Unit 5 Inactive Ash Basin In the shallow flow layer, boron is not reported in the monitoring wells downgradient of the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron was reported at concentrations greater than the PBTV at wells adjacent to the basin and downgradient of the basin. Boron in the deep flow layer is reported at a concentration greater than the PBTV and the 2L standard beneath the northern waste boundary, but not downgradient of the basin. In the bedrock flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV beneath the basin and downgradient of the basin. Arsenic, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. Arsenic exceedances were not reported in the shallow flow layer at the Unit 5 inactive ash basin. The extent of exceedances of arsenic in the deep and bedrock flow layers is an isolated location beneath the western portion of the basin within the waste boundary. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Chromium exceedances in the shallow flow layer is limited to an isolated location east of and sidegradient of the Unit 5 inactive ash basin, beyond the waste boundary. Chromium exceedances in the deep flow layer were detected near or beyond the eastern waste boundary, including one sidegradient location. Chromium exceedances were not reported in the bedrock flow layer. Cobalt exceedances in the shallow and deep flow layers are located near or beyond the waste boundary north of and east of the Unit 5 inactive ash basin as well as an isolated location in the shallow flow layer east of and sidegradient of the basin waste boundary. Cobalt exceedances in the bedrock flow layer are located beneath the basin, and north of the basin, near or beyond the waste boundary. The extent of exceedances of iron in the shallow and deep flow layers is within the Unit 5 inactive ash basin waste boundary and north of the basin, near or beyond the waste boundary. One iron exceedance was reported south of and upgradient of the basin, beyond the waste boundary in the bedrock flow layer. The extent of exceedances of manganese in the shallow flow layer is within the waste boundary, and north and east, near or beyond the waste boundary. Manganese exceedances in the deep flow layer are located beneath the basin, and north, west, and east of the basin, near or beyond the waste boundary. Manganese in the bedrock flow layer is detected beneath the basin, and northeast of the ash basin beyond the waste boundary. The extent of exceedances of strontium in the shallow flow layer are located within the Unit 5 inactive ash basin, and at locations east and north of the basin, near and beyond the waste boundary, including locations sidegradient of the basin. Strontium exceedances in the deep flow layer are located beneath the basin and at locations west, north and east of the basin, near and beyond the waste boundary. In the bedrock flow layer strontium exceedances are reported beneath the basin and beyond the waste boundary, northeast of the ash basin. The extent of exceedances of sulfate in the shallow flow layer is within, near, and beyond the waste boundary southeast of the ash basin. Sulfate exceedances are detected east and north of the Unit 5 inactive ash basin, near and beyond the waste boundary in the deep flow layer. An isolated sulfate exceedance is reported in the bedrock flow layer, beyond the waste boundary north of the basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The exceedances of thallium in the shallow flow layer are located near and beyond the waste boundary, north and east of the Unit 5 inactive ash basin. Thallium in the deep flow layer is detected near or beyond the northern and eastern waste boundaries. A thallium exceedance was reported at isolated location beneath the western portion of the basin. The extent of exceedances of TDS in the shallow flow layer is near and beyond the waste boundary, east of the Unit 5 inactive ash basin. TDS exceedances in the deep flow layer are located near and beyond the waste boundary, east and north of the basin. An isolated TDS exceedance was reported north of ash basin, beyond the waste boundary. The extent of exceedances of vanadium in the shallow flow layer are located within the waste boundary, north of the Unit 5 inactive as basin near or beyond the waste boundary, and northeast of the basin, near and beyond the waste boundary. Vanadium exceedances in the deep flow layer are located beneath the basin, and southeast, northeast, north and northwest, near and beyond the waste boundary. Exceedances of vanadium in the bedrock flow layer are limited to an isolated area northeast of the basin, near or beyond the waste boundary. For the one soil sample below the ash, arsenic, chromium, cobalt, iron, manganese, and vanadium had reported values greater than the PSRG for POG. Although some constituent levels were measured above the PSRG for POG standards when compared to the Site’s PBTVs, most constituent concentrations are similar to calculated soil background values for the Site, with the exception of arsenic. Soil sample analytical results indicate shallow impacts to the soil beneath the Unit 5 inactive ash basin. Ash Storage Area The leading edge of the boron plume in the shallow flow layer north of the ash storage area is located north of the western portion of the ash storage area near the Broad River. Boron 2L exceedances in the shallow flow layer are not reported in the eastern portion of the ash storage area with one exception at the southern waste boundary. In the deep flow layer, boron 2L exceedances are limited to beneath the western portion of the ash storage area. In the bedrock flow layer, boron is not reported in any of the wells at a concentration greater than the 2L standard but is reported at a concentration 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-13 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx greater than the PBTV downgradient of the western portion of the ash storage area. Boron was not detected in the remaining bedrock downgradient wells. Chromium, cobalt, manganese, strontium, sulfate, thallium, TDS and vanadium are also constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. Chromium exceedances are limited to one location within the ash storage area waste boundary in the shallow flow layer. Chromium exceedances were not detected in the deep or bedrock flow layers associated with the ash storage area. The extent of cobalt exceedances in the shallow flow layer is located within the western portion of the ash storage area, and beyond the waste boundary within the compliance boundary. Cobalt exceedances were not detected in the deep flow layer. An isolated exceedance in the bedrock flow layer was reported beyond the waste boundary and within the compliance boundary downgradient of the western portion of the ash storage area. The extent of exceedances of manganese in the shallow flow, deep and bedrock flow layer are near or beyond the compliance boundary, north of the western portion of the ash storage area. The extent of exceedances of strontium in the shallow, deep and bedrock flow layers are located near or beyond the compliance boundary, downgradient of the western portion of the ash storage area. The extent of exceedances of sulfate in the shallow flow layer near or beyond the compliance boundary are located downgradient of the western portion of the ash storage area. No sulfate exceedances were reported in the deep or bedrock flow layers associated with the ash storage area. The extent of exceedances of thallium in the shallow flow layer is near or beyond the compliance boundary, downgradient of the western portion of the ash storage area. Thallium exceedances were not reported near or beyond the compliance boundary in the deep or bedrock flow layers. The extent of exceedances of TDS in the shallow flow layer is near or beyond the compliance boundary, downgradient of the western portion of the ash storage area. TDS exceedances were not reported near or beyond the compliance boundary in the deep or bedrock flow layers. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-14 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Vanadium exceedances were not reported near or beyond the compliance boundary in the shallow or deep flow layers. An isolated exceedance beyond the waste boundary and within the compliance boundary was reported north of the western portion of the ash storage area. For soil samples below the ash, chromium, iron, and vanadium had reported values greater than the PSRG for POG. Although some constituent levels were measured above PSRG for POG standards in soil samples beneath the ash storage area, when compared to the Site’s PBTVs the concentrations were less than the calculated soil background values for the Site. Soil sample analytical results do not indicate impacts to the soil beneath the ash storage area. ES.5.3 Maximum Contaminant Concentrations (Source Information) The source areas at CSS include CCR material in the active ash basin, the former Units 1-4 inactive ash basin, Unit 5 inactive ash basin and the ash storage area. Ash pore water samples collected from wells installed within the ash basins and screened in the ash layer have been monitored since 2015 unless abandoned due to closure activities. The ash pore water and shallow downgradient well data generally represent the maximum concentrations for the source areas. The ash pore water concentrations 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 used for source area information only. The greatest concentrations of COIs in the active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage area were generally reported in ash porewater samples and downgradient shallow monitoring wells near the waste boundaries. Soil samples collected below the ash/soil interface from locations within the ash basins indicate arsenic, boron, chromium, cobalt, and manganese reported at concentrations greater than their respective PSRG for POG and/or soil PBTV values. This indicates areas of soil as a potential secondary source to groundwater. ES.5.4 Site Geology and Hydrogeology Based on the site investigation, the groundwater system in natural materials (soil, soil/saprolite, and bedrock) at the CSS 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-15 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx competent bedrock with mildly productive fractures in the top 50 feet of bedrock. The groundwater system at the CSS 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 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. In general, groundwater within the shallow, deep (transition zone), and fractured bedrock flow layers flows northerly from the ash basin toward the Broad River. A groundwater divide is located approximately along Duke Power Road to the south. This groundwater divide generally corresponds to the topographic divide. The predominant direction of groundwater flow from the ash basins and ash storage area is in a northerly direction toward the Broad River. In the shallow and deep flow layers to the west of the active ash basin and east of Unit 6, groundwater flow is generally toward Suck Creek and on to the Broad River. ES.6 Conclusions and Recommendations The investigation described in the CSA presents the results of the assessments required by CAMA. The ash basins and ash storage area were determined to be a source of the groundwater contamination. During the CSA an area of exceedances that appears not to be associated with the identified source areas (active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage area), is located east of Unit 6 and west of Suck Creek. CCR has not historically been disposed of in this area of the site and the source of the reported exceedances is unknown. It is anticipated that this additional source area will be further assessed along a separate timeline than the CAMA units. Impacts to soil were determined to be limited to a shallow interval below the active ash basin, Units 1-4 inactive ash basin and Unit 5 inactive ash basin. Soil samples collected from below the ash basins 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. Soil sample test results do not indicate shallow impacts to the soil beneath the ash storage area greater than the calculated PBTVs. Sediment concentrations in Suck Creek were less than respective 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-16 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx PBTVs and therefore do not appear to represent additional secondary source contributions associated with the ash basin. For the active ash basin, boron, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS, and vanadium are the primary constituents detected in groundwater greater than 2L/IMAC and/or PBTVs where no 2L/IMAC is established, near or beyond the compliance boundary. The groundwater beneath the active ash basin flows north towards the Broad River or towards Suck Creek and then to the Broad River. The northern downgradient compliance boundary is at the shore of the Broad River. The surface water results collected from Suck Creek and the Broad River do not indicate that impacted groundwater associated with the active ash basin is causing 2B standard exceedances in the Broad River. For the Units 1-4 inactive ash basin, boron, arsenic, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are the primary constituents detected in groundwater greater than 2L/IMAC and/or PBTVs where no 2L/IMAC is established, near or beyond the waste boundary and/or beneath the ash basin. The groundwater beneath the Units 1-4 inactive ash basin flows north towards the Broad River. There is not an established compliance boundary at the basin and the waste boundary is near the shore of the Broad River. The surface water results collected from the Broad River indicate that impacted groundwater associated with the Units 1-4 inactive ash basin is not causing 2B standard exceedances in the Broad River. For the Unit 5 inactive ash basin, boron, arsenic, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are the primary constituents detected in groundwater greater than 2L/IMAC and/or PBTVs where no 2L/IMAC is established, near or beyond the waste boundary and/or beneath the ash basin. The groundwater beneath the Unit 5 inactive ash basin flows north towards the Broad River. There is not an established compliance boundary at the basin. The surface water results collected from the Broad River indicate that impacted groundwater associated with the Unit 5 inactive ash basin is not causing 2B standard exceedances in the Broad River. For the ash storage area, boron, cobalt, manganese, strontium, sulfate, thallium, and TDS are the primary constituents detected in groundwater greater than 2L/IMAC and/or PBTVs where no 2L/IMAC is established, near or beyond the compliance boundary. The groundwater beneath the ash storage area flows north towards the Broad River. The northern downgradient compliance boundary is at the shore of the Broad River. The surface water results collected from the Broad River indicate that impacted groundwater associated with the ash storage area is not causing 2B standard exceedances in the Broad River. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-17 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The extent of exceedances are within the shallow and/or deep flow layers with the exception of manganese and strontium in areas beneath and downgradient of the Unit 5 inactive ash basin, the Units 1-4 inactive ash basin, and the active ash basin and the ash storage area; arsenic at an isolated location beneath the Unit 5 inactive ash basin; sulfate and TDS at an isolated location downgradient of the Unit 5 inactive ash basin; sulfate and TDS at an isolated location east of Unit 6 and west of Suck Creek, and cobalt, iron, and vanadium at isolated locations across the site. The bedrock aquifer is generally the source of water for supply wells in the area. There are no supply wells located downgradient of the source areas. Multiple lines of evidence suggest the supply well data represent naturally occurring background concentrations. The CSS ash basin is currently designated as “Intermediate” risk under CAMA, requiring closure of the ash basin by 2024. Based on review and analysis of groundwater and surface water data, no evidence of unacceptable risks from exposure to groundwater on-site exists. Limited potential for unacceptable risks to humans was estimated for exposure to cobalt under the recreational and subsistence fisher scenarios. Limited evidence of potential risks to wildlife exists for the CSS Site. Conclusions of the risk assessment update remain consistent with the conclusions presented in the 2016 risk assessment, with the addition of limited potential risk for exposure to cobalt under the recreational and subsistence fisher scenarios. This update to the human health and ecological risk assessment supports a risk classification of “low” for groundwater related consideration. A "Low" risk classification and closure via a cap-in-place scenario are considered appropriate for the active ash basin, the Unit 5 inactive ash basin and the ash storage area, as alternative water supplies are being provided in accordance with G.S. 130A-309.213.(d)(1) of House Bill 630. The Units 1-4 inactive ash basin has been excavated. The updated CAP will evaluate potential groundwater remedial strategies in addition to closure options. A preliminary evaluation of groundwater corrective action alternatives is included in this CSA to provide insight into the CAP preparation process. For CSS, the primary source control (closure) methods anticipated to be evaluated in the CAP include but are not limited to: 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ES-18 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The source control (closure) options will be evaluated in the CAP based upon technical and economical 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 (including overall environmental costs and sustainability) associated with various options. For basin closure, preliminary modeling indicates reduction of the amount of water migrating from the basin to groundwater will have a positive impact on groundwater and surface water quality downgradient of the ash basins. If a “Low” risk classification is determined, a well- designed capping system can be expected to minimize ongoing migration to groundwater. In addition to source control measures, the CAP will evaluate measures to address groundwater conditions associated with the ash basins. Groundwater corrective action by monitored natural attenuation (MNA) is anticipated to be a remedy further evaluated in the CAP. 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, implementability, cost, and sustainability. Results of the evaluation, including groundwater flow and transport modeling, and geochemical modeling, will be used for remedy selection in the CAP. 148 RIVER STREET, SUITE 220 GREENVILLE, SOUTH CAROLINA 29601 PHONE 864-421-9999 www.synterracorp.com PROJECT MANAGER: LAYOUT: DRAWN BY: SCOTT SPINNER DATE:ADAM FEIGL ES1 10/09/2017 01/23/2018 4:39 PM P:\Duke Energy Progress.1026\00 GIS BASE DATA\Cliffside\Mapdocs\CSA_Supplement_2\CSM3D\Cliff_3D_ES1_v2.dwg FIGURE ES-1 APPROXIMATE EXTENT OF IMPACTS CLIFFSIDE STEAM STATION DUKE ENERGY CAROLINAS, LLC MOORESBORO, NORTH CAROLINA VISUAL AID ONLY - DEPICTION NOT TO SCALE CAROLINAS TRANSITION ZONE NORTH ASH BASIN WASTE BOUNDARY GENERALIZED GROUNDWATER FLOW DIRECTION APPROXIMATE LANDFILL AND ASH STORAGE WASTE BOUNDARIES NOTE: 1.OCTOBER, 2016 AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON DECEMBER 7, 2017. AERIAL DATED OCTOBER 8, 2016. 2.STREAMS OBTAINED FROM AMEC FOSTER WHEELER NRTR, MAY 2015. 3.GENERALIZED GROUNDWATER FLOW DIRECTION BASED ON SEPTEMBER 11, 2017 WATER LEVEL DATA. 4.PROPERTY BOUNDARY PROVIDED BY DUKE ENERGY. 5.GENERALIZED AREAL EXTENT OF MIGRATION REPRESENTED BY NCAC 02L EXCEEDANCES OF MULTIPLE CONSTITUENTS IN MULTIPLE FLOW ZONES. WATER SUPPLY WELL LOCATION DUKE ENERGY PROPERTY BOUNDARY LEGEND AREA OF CONCENTRATION IN GROUNDWATER ABOVE NC2L (SEE NOTE 5) STREAM WITH FLOW DIRECTION BROAD RIVER HIG H W A Y 221 ALT CCP LANDFILL DUKE POWER RD SURFICIAL M C C R A W R D WHEL C H E L R D BEDROCK BROAD R I V E R SUC K C R E E K UNIT 6 UNIT 5 CLIFFSIDE STEAM STATION UNITS 1-4 INACTIVE ASH BASIN ASH STORAGE AREAUNIT 5 INACTIVE ASH BASIN ACTIVE ASH BASIN 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page i P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx TABLE OF CONTENTS SECTION PAGE ES.1 SOURCE INFORMATION ....................................................................................... ES-1 ES.2 INITIAL ABATEMENT AND EMERGENCY RESPONSE ................................ ES-3 ES.3 RECEPTOR INFORMATION .................................................................................. ES-3 ES.3.1 Public Water Supply Wells ................................................................................... ES-3 ES.3.2 Private Water Supply Wells ................................................................................. ES-3 ES.3.3 Surface Water Bodies ............................................................................................. ES-4 ES.3.4 Land Use .................................................................................................................. ES-4 ES.4 HUMAN HEALTH AND ECOLOGICAL RISK ASSESSMENT ...................... ES-4 ES.5 SAMPLING/INVESTIGATION RESULTS .......................................................... ES-5 ES.5.1 Background Concentration Determinations ...................................................... ES-5 ES.5.2 Nature and Extent of Contamination .................................................................. ES-5 ES.5.3 Maximum Contaminant Concentrations (Source Information) .................... ES-14 ES.5.4 Site Geology and Hydrogeology ....................................................................... ES-14 ES.6 CONCLUSIONS AND RECOMMENDATIONS .............................................. ES-15 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 .................................................... 1-2 1.2.2 Coal Combustion Residuals Rule (CCR Rule) .............................................. 1-4 1.2.3 Approach to Comprehensive Site Assessment ..................................................... 1-5 1.3 NORR Guidance ................................................................................................ 1-5 1.3.1 USEPA Monitored Natural Attenuation (MNA) Tiered Approach .......... 1-6 1.3.2 ASTM Conceptual Site Model Guidance ....................................................... 1-6 1.3.3 Technical Objectives ................................................................................................. 1-6 1.4 Previous Submittals .................................................................................................. 1-7 1.5 2.0 SITE HISTORY AND DESCRIPTION ..................................................................... 2-1 Site Description, Ownership, and Use History..................................................... 2-1 2.1 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx TABLE OF CONTENTS (CONTINUED) Geographic Setting, Surrounding Land Use, and Surface Water Classification .. 2.2 ..................................................................................................................................... 2-3 CAMA-related Source Areas ................................................................................... 2-5 2.3 Other Primary and Secondary Sources .................................................................. 2-6 2.4 Summary of Permitted Activities ........................................................................... 2-7 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 ...................................................................... 2-13 2.7 Summary of Initial Abatement, Source Removal, and other Corrective Action .. 2.8 ................................................................................................................................... 2-14 3.0 SOURCE CHARACTERISTICS ................................................................................. 3-1 Coal Combustion and Ash Handling System ....................................................... 3-1 3.1 General Physical and Chemical Properties of Ash............................................... 3-5 3.2 Site-Specific Coal Ash Data ..................................................................................... 3-7 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 .............................................................................. 4-5 4.2.1 Private Water Supply Wells ............................................................................ 4-5 4.2.2 Private and Public Well Water Sampling .............................................................. 4-5 4.3 Numerical Well Capture Zone Analysis ............................................................... 4-9 4.4 Surface Water Receptors .......................................................................................... 4-9 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 ............................................................................................................... 6-3 6.1 Soil Classification .............................................................................................. 6-3 6.1.1 Rock Lithology .................................................................................................. 6-5 6.1.2 Structural Geology ............................................................................................ 6-5 6.1.3 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page iii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx TABLE OF CONTENTS (CONTINUED) Soil and Rock Mineralogy and Chemistry .................................................... 6-6 6.1.4 Geologic Mapping ............................................................................................. 6-8 6.1.5 Effects of Geologic Structure on Groundwater Flow ................................... 6-8 6.1.6 Site Hydrogeology .................................................................................................... 6-9 6.2 Hydrostratigraphic Layer Development ....................................................... 6-9 6.2.1 Hydrostratigraphic Layer Properties ........................................................... 6-10 6.2.2 Groundwater Flow Direction ................................................................................ 6-12 6.3 Hydraulic Gradient ................................................................................................. 6-13 6.4 Hydraulic Conductivity ......................................................................................... 6-15 6.5 Groundwater Velocity ............................................................................................ 6-15 6.6 Contaminant Velocity ............................................................................................. 6-16 6.7 Slug Test and Aquifer Test Results ...................................................................... 6-17 6.8 Fracture Trace Study Results ................................................................................. 6-18 6.9 Methods ............................................................................................................ 6-19 6.9.1 Results ............................................................................................................... 6-20 6.9.2 7.0 SOIL SAMPLING RESULTS ...................................................................................... 7-1 Background Soil Data ............................................................................................... 7-1 7.1 Facility Soil Data ....................................................................................................... 7-3 7.2 Secondary Sources .................................................................................................... 7-7 7.3 White Material at Toe of Unit 5 Inactive Ash Basin Dam ................................... 7-8 7.4 8.0 SEDIMENT RESULTS ................................................................................................. 8-1 Sediment/Surface Soil Associated with AOWs .................................................... 8-1 8.1 Sediment in Major Water Bodies ............................................................................ 8-5 8.2 9.0 SURFACE WATER RESULTS .................................................................................... 9-1 Comparison of Exceedances to 2B Standards ....................................................... 9-4 9.1 Discussion of Results for Constituents Without Established 2B ........................ 9-6 9.2 Discussion of Surface Water Results ...................................................................... 9-9 9.3 10.0 GROUNDWATER SAMPLING RESULTS ............................................................ 10-1 Background Groundwater Concentrations ......................................................... 10-2 10.1 Background Dataset Statistical Analysis ..................................................... 10-3 10.1.1 Piper Diagrams (Comparison to Background) ........................................... 10-6 10.1.2 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page iv P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx TABLE OF CONTENTS (CONTINUED) Downgradient Groundwater Concentrations..................................................... 10-6 10.2 Piper Diagrams (Comparison to Downgradient/ Separate Flow Regime) .... 10.2.1 .......................................................................................................................... 10-19 Site-Specific Exceedances (Groundwater COIs) ............................................... 10-24 10.3 Provisional Background Threshold Values (PBTVs) ............................... 10-24 10.3.1 Applicable Standards ................................................................................... 10-24 10.3.2 Additional Requirements ............................................................................. 10-25 10.3.3 CSS Groundwater COIs ............................................................................... 10-26 10.3.4 Water Supply Well Groundwater Concentrations and Exceedances ............ 10-27 10.4 11.0 HYDROGEOLOGICAL INVESTIGATION .......................................................... 11-1 Plume Physical Characterization .......................................................................... 11-1 11.1 Plume Chemical Characterization ...................................................................... 11-12 11.2 Pending Investigations ......................................................................................... 11-28 11.3 12.0 RISK ASSESSMENT .................................................................................................. 12-1 Human Health Screening Summary .................................................................... 12-2 12.1 Ecological Screening Summary ............................................................................. 12-4 12.2 Private Well Receptor Assessment Update ......................................................... 12-6 12.3 Risk Assessment Update Summary ..................................................................... 12-7 12.4 13.0 GROUNDWATER MODELING RESULTS........................................................... 13-1 Summary of Flow and Transport Model Results ............................................... 13-2 13.1 Summary of Geochemical Model Results ........................................................... 13-3 13.2 14.0 SITE ASSESSMENT RESULTS ................................................................................ 14-1 Nature and Extent of Contamination ................................................................... 14-1 14.1 Maximum Constituent Concentrations ............................................................. 14-16 14.2 Contaminant Migration and Potentially Affected Receptors ......................... 14-19 14.3 15.0 CONCLUSIONS AND RECOMMENDATIONS ................................................. 15-1 Overview of Site Conditions at Specific Source Areas ...................................... 15-2 15.1 Revised Site Conceptual Model ............................................................................ 15-9 15.2 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page v P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx TABLE OF CONTENTS (CONTINUED) Interim Monitoring Program ............................................................................... 15-11 15.3 IMP Implementation ..................................................................................... 15-11 15.3.1 IMP Reporting ............................................................................................... 15-12 15.3.2 COIs for Monitored Natural Attenuation at Site Specific Source Areas ....... 15-12 15.4 Preliminary Evaluation of Corrective Action Alternatives............................. 15-15 15.5 CAP Preparation Process ............................................................................. 15-16 15.5.1 Summary ........................................................................................................ 15-17 15.5.2 16.0 REFERENCES ............................................................................................................... 16-1 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page vi P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF TABLES 2.0 Site History and Description Table 2-1 Well Construction Data Table 2-2 NPDES Groundwater Monitoring Requirements 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 Cliffside Steam Station Ash Basin Compliance Boundary Table 4-2 Property Owners 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 Chemial Properties of Soil Table 6-3 Soil, Sediment, and Ash Analytical Methods Table 6-4 Ash Pore Water, Groundwater, Surface Water, and AOW Analytical Methods Table 6-5 Transition Zone Mineralogy Results Table 6-6 Chemical Properties of Transition Zone Table 6-7 Chemical Properties of Whole Rock Table 6-8 Cliffside Petrographic Analysis Summary Table 6-9 Historical Water Level Measurements Table 6-10 Horizontal Groundwater Gradients and Velocities Table 6-11 Vertical Hydraulic Gradients Table 6-12 In-Situ Hydraulic Conductivities Table 6-13 Hydrostratigraphic Layer Properties - Horizontal Hydraulic Conductivity Table 6-14 Hydrostratigraphic Layer Properties - Vertical Hydraulic Conductivity Table 6-15 Estimated (Effective) Porosity/Specific Yield, and Specific Storage for Upper Hydrostratigraphic Units (A, F, S, M1, and M2) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page vii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF TABLES (CONTINUED) Table 6-16 Total Porosity, Secondary (Effective) Porosity/Specific Yield, and Specific Storage for Lower Hydrostratigraphic Units (TZ and BR) Table 6-17 Total Porosity for Upper Hydrostratigraphic Units (A, F, S, M1, and M2) Table 6-18 Field Permeability Test Results Table 6-19 Historic Field Permeability Test Results Table 6-20 Laboratory Permeability Test Results Table 6-21 Historic Laboratory Permeability Test Results 7.0 Soil Sampling Results Table 7-1 Provisional Background Threshold Values for Soil Table 7-2 Potential Secondary Source Soil Analytical Results 10.0 Groundwater Sampling Results Table 10-1 Provisional Background Threshold Values for Groundwater Table 10-2 State and Federal Standards for Constituents of Interest 11.0 Hydrogeological Investigation Table 11-1 Data Inventory Summary 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 Sampling Parameters and Analytical Methods Table 15-2 Interim Monitoring Program Sample Locations 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page viii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.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 Vicinity Map Figure 2-2 1959 USGS Topographic Map Figure 2-3 1971 USGS Topographic Map Figure 2-4 1955 Aerial Photograph Figure 2-5 1964 Aerial Photograph Figure 2-6 1976 Aerial Photograph Figure 2-7 1979 Aerial Photograph Figure 2-8 NPDES Water Flow Diagram Figure 2-9 NPDES Water Flow Diagram Post Outfall 005 Operation Figure 2-10 Site Layout 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 Figure 3-4 Piper Diagram - Ash Pore Water Active Ash Basin Figure 3-5 Piper Diagram - Ash Pore Water Units 1-4 Inactive Ash Basin Figure 3-6 Piper Diagram - Ash Pore Water Unit 5 Inactive Ash Basin 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 Active Ash Basin Figure 4-4 Piper Diagram - Water Supply Wells Unit 5 Inactive Ash Basin 5.0 Regional Geology and Hydrogeology Figure 5-1 Regional Geologic Map Figure 5-2 Site Geologic Map Figure 5-3 Piedmont Slope-Aquifer System 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page ix P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) 6.0 Site Geology Figure 6-1 Cross Section Location Map Figure 6-2 General Cross Section A-A' Figure 6-3 General Cross Section B-B' Figure 6-4 General Cross Section C-C' Figure 6-5 General Cross Section D-D' Figure 6-6 General Cross Section E-E' Figure 6-7 General Cross Section F-F' Figure 6-8 General Cross Section G-G' Figure 6-9 General Cross Section H-H' Figure 6-10 General Cross Section I-I' Figure 6-11 General Cross Section J-J' Figure 6-12 General Cross Section K-K' Figure 6-13 General Cross Section L-L' Figure 6-14 General Cross Section M-M' Figure 6-15 Shallow Water Level Map - August 27, 2015 Figure 6-16 Shallow Water Level Map - February 10, 2017 Figure 6-17 Deep Water Level Map - August 27, 2015 Figure 6-18 Deep Water Level Map - February 10, 2017 Figure 6-19 Bedrock Water Level Map - August 27, 2015 Figure 6-20 Bedrock Water Level Map - February 10, 2017 Figure 6-21 Shallow Water Level Map - August 27, 2015 - Units 1 -4 Inactive Ash Basin Figure 6-22 Shallow Water Level Map - February 10, 2017 - Units 1-4 Inactive Ash Basin Figure 6-23 Potential Vertical Gradient Between Shallow, Deep, and Bedrock Zones Figure 6-24 Topographic Lineaments and Rose Diagram Figure 6-25 Aerial Photography Lineaments and Rose Diagram 7.0 Soil Sampling Results Figure 7-1 Potential Secondary Source - Soil Analytical Results Figure 7-2 Detailed Secondary Source Map - Units 1 -4 Inactive Ash Basin 9.0 Surface Water Results Figure 9-1 Detailed Thallium Map – Active Ash Basin – Groundwater Surface Water Results Figure 9-2 Piper Diagram - Surface Waters 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page x P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) 10.0 Groundwater Sampling Results Figure 10-1 Piper Diagram - Active Ash Basin Shallow Groundwater Figure 10-2 Piper Diagram - Active Ash Basin Deep Groundwater Figure 10-3 Piper Diagram - Active Ash Basin Bedrock Groundwater Figure 10-4 Piper Diagram - Units 1-4 Inactive Ash Basin Shallow Groundwater Figure 10-5 Piper Diagram - Units 1-4 Inactive Ash Basin Deep Groundwater Figure 10-6 Piper Diagram - Units 1-4 Inactive Ash Basin Bedrock Groundwater Figure 10-7 Piper Diagram - Unit 5 Inactive Ash Basin Shallow Groundwater Figure 10-8 Piper Diagram - Unit 5 Inactive Ash Basin Deep Groundwater Figure 10-9 Piper Diagram - Unit 5 Inactive Ash Basin Bedrock Groundwater Figure 10-10 Piper Diagram - Ash Storage Area Shallow Groundwater Figure 10-11 Piper Diagram - Ash Storage Area Deep Groundwater Figure 10-12 Piper Diagram - Ash Storage Area Bedrock Groundwater 11.0 Hydrogeological Investigation Figure 11-1 Isoconcentration Map - pH in Shallow Groundwater Figure 11-2 Isoconcentration Map - pH in Deep Groundwater Figure 11-3 Isoconcentration Map - pH in Bedrock Groundwater Figure 11-4 Isoconcentration Map - Arsenic in Shallow Groundwater Figure 11-5 Isoconcentration Map - Arsenic in Deep Groundwater Figure 11-6 Isoconcentration Map - Arsenic in Bedrock Groundwater Figure 11-7 Isoconcentration Map - Boron in Shallow Groundwater Figure 11-8 Isoconcentration Map - Boron in Deep Groundwater Figure 11-9 Isoconcentration Map - Boron in Bedrock Groundwater Figure 11-10 Isoconcentration Map - Total Chromium in Shallow Groundwater Figure 11-11 Isoconcentration Map - Total Chromium in Deep Groundwater Figure 11-12 Isoconcentration Map - Total Chromium in Bedrock Groundwater Figure 11-13 Isoconcentration Map - Hexavalent Chromium in Shallow Groundwater Figure 11-14 Isoconcentration Map - Hexavalent Chromium in Deep Groundwater Figure 11-15 Isoconcentration Map - Hexavalent Chromium in Bedrock Groundwater Figure 11-16 Isoconcentration Map - Cobalt in Shallow Groundwater Figure 11-17 Isoconcentration Map - Cobalt in Deep Groundwater Figure 11-18 Isoconcentration Map - Cobalt in Bedrock Groundwater Figure 11-19 Isoconcentration Map - Iron in Shallow Groundwater Figure 11-20 Isoconcentration Map - Iron in Deep Groundwater Figure 11-21 Isoconcentration Map - Iron in Bedrock Groundwater 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xi P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) Figure 11-22 Isoconcentration Map - Manganese in Shallow Groundwater Figure 11-23 Isoconcentration Map - Manganese in Deep Groundwater Figure 11-24 Isoconcentration Map - Manganese in Bedrock Groundwater Figure 11-25 Isoconcentration Map - Strontium in Shallow Groundwater Figure 11-26 Isoconcentration Map - Strontium in Deep Groundwater Figure 11-27 Isoconcentration Map - Strontium in Bedrock Groundwater Figure 11-28 Isoconcentration Map - Sulfate in Shallow Groundwater Figure 11-29 Isoconcentration Map - Sulfate in Deep Groundwater Figure 11-30 Isoconcentration Map - Sulfate in Bedrock Groundwater Figure 11-31 Isoconcentration Map - Thallium in Shallow Groundwater Figure 11-32 Isoconcentration Map - Thallium in Deep Groundwater Figure 11-33 Isoconcentration Map - Thallium in Bedrock Groundwater Figure 11-34 Isoconcentration Map - Total Dissolved Solids in Shallow Groundwater Figure 11-35 Isoconcentration Map - Total Dissolved Solids in Deep Groundwater Figure 11-36 Isoconcentration Map - Total Dissolved Solids in Bedrock Groundwater Figure 11-37 Isoconcentration Map - Vanadium in Shallow Groundwater Figure 11-38 Isoconcentration Map - Vanadium in Deep Groundwater Figure 11-39 Isoconcentration Map - Vanadium in Bedrock Groundwater Figure 11-40 Isoconcentration Map - Total Uranium in Shallow Groundwater Figure 11-41 Isoconcentration Map - Total Uranium in Deep Groundwater Figure 11-42 Isoconcentration Map - Total Uranium in Bedrock Groundwater Figure 11-43 Isoconcentration Map - Total Radium in Shallow Groundwater Figure 11-44 Isoconcentration Map - Total Radium in Deep Groundwater Figure 11-45 Isoconcentration Map - Total Radium in Bedrock Groundwater Figure 11-46 Concentration Versus Distance from Source - pH, Arsenic, Boron, Chromium (VI), Chromium, Cobalt, and Iron - Active Ash Basin - Upstream Dam (Sheet 1 of 3) Figure 11-47 Concentration Versus Distance from Source - Manganese, Strontium, Sulfate, Total Dissolved Solids, Thallium, and Vanadium - Active Ash Basin - Upstream Dam (Sheet 2 of 3) Figure 11-48 Concentration Versus Distance from Source - Radium and Uranium - Active Ash Basin - Upstream Dam (Sheet 3 of 3) Figure 11-49 Concentration Versus Distance from Source - pH, Arsenic, Boron, Chromium (VI), Chromium, Cobalt, and Iron - Active Ash Basin - Downstream Dam (Sheet 1 of 3) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) Figure 11-50 Concentration Versus Distance from Source - Manganese, Strontium, Sulfate, Total Dissolved Solids, Thallium, and Vanadium - Active Ash Basin - Downstream Dam (Sheet 2 of 3) Figure 11-51 Concentration Versus Distance from Source - Radium and Uranium - Active Ash Basin - Downstream Dam (Sheet 3 of 3) Figure 11-52 Concentration Versus Distance from Source - pH, Arsenic, Boron, Chromium (VI), Chromium, Cobalt, and Iron - Ash Storage Area (Sheet 1 of 3) Figure 11-53 Concentration Versus Distance from Source - Manganese, Strontium, Sulfate, Total Dissolved Solids, Thallium, and Vanadium - Ash Storage Area (Sheet 2 of 3) Figure 11-54 Concentration Versus Distance from Source - Ash Storage Area (Sheet 3 of 3) Figure 11-55 Concentration Versus Distance from Source - pH, Arsenic, Boron, Chromium (VI), Chromium, Cobalt, and Iron - Units 1-4 Inactive Ash Basin (Sheet 1 of 3) Figure 11-56 Concentration Versus Distance from Source - Manganese, Strontium, Sulfate, Total Dissolved solids, Thallium, and Vanadium - Units 1-4 Inactive Ash Basin (Sheet 2 of 3) Figure 11-57 Concentration Versus Distance from Source - Units 1-4 Inactive Ash Basin (Sheet 3 of 3) Figure 11-58 Concentration Versus Distance from Source - pH, Arsenic, Boron, Chromium (VI), Chromium, Cobalt, and Iron - Unit 5 Inactive Ash Basin (Sheet 1 of 3) Figure 11-59 Concentration Versus Distance from Source - Manganese, Strontium, Sulfate, Total Dissolved Solids, Thallium, and Vanadium - Unit 5 Inactive Ash Basin (Sheet 2 of 3) Figure 11-60 Concentration Versus Distance from Source - Radium and Uranium - Unit 5 Inactive Ash Basin (Sheet 3 of 3) Figure 11-61 Arsenic Analytical Results - Cross Section A-A' Figure 11-62 Boron Analytical Results - Cross Section A-A' Figure 11-63 Hexavalent Chromium Analytical Results - Cross Section A-A' Figure 11-64 Total Chromium Analytical Results - Cross Section A-A' Figure 11-65 Cobalt Analytical Results - Cross Section A-A' Figure 11-66 Iron Analytical Results - Cross Section A-A' Figure 11-67 Manganese Analytical Results - Cross Section A-A' Figure 11-68 pH Analytical Results - Cross Section A-A' 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xiii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) Figure 11-69 Total Radium Analytical Results - Cross Section A-A' Figure 11-70 Strontium Analytical Results - Cross Section A-A' Figure 11-71 Sulfate Analytical Results - Cross Section A-A' Figure 11-72 Total Dissolved Solids Analytical Results - Cross Section A-A' Figure 11-73 Thallium Analytical Results - Cross Section A-A' Figure 11-74 Total Uranium Analytical Results - Cross Section A-A' Figure 11-75 Vanadium Analytical Results - Cross Section A-A' Figure 11-76 Arsenic Analytical Results - Cross Section H-H' Figure 11-77 Boron Analytical Results - Cross Section H-H' Figure 11-78 Hexavalent Chromium Analytical Results - Cross Section H-H' Figure 11-79 Total Chromium Analytical Results - Cross Section H-H' Figure 11-80 Cobalt Analytical Results - Cross Section H-H' Figure 11-81 Iron Analytical Results - Cross Section H-H' Figure 11-82 Manganese Analytical Results - Cross Section H-H' Figure 11-83 pH Analytical Results - Cross Section H-H' Figure 11-84 Total Radium Analytical Results - Cross Section H-H' Figure 11-85 Strontium Analytical Results - Cross Section H-H' Figure 11-86 Sulfate Analytical Results - Cross Section H-H' Figure 11-87 Total Dissolved Solids Analytical Results - Cross Section H-H' Figure 11-88 Thallium Analytical Results - Cross Section H-H' Figure 11-89 Total Uranium Analytical Results - Cross Section H-H' Figure 11-90 Vanadium Analytical Results - Cross Section H-H' Figure 11-91 Arsenic Analytical Results - Cross Section K-K' Figure 11-92 Boron Analytical Results - Cross Section K-K' Figure 11-93 Hexavalent Chromium Analytical Results - Cross Section K-K' Figure 11-94 Total Chromium Analytical Results - Cross Section K-K' Figure 11-95 Cobalt Analytical Results - Cross Section K-K' Figure 11-96 Iron Analytical Results - Cross Section K-K' Figure 11-97 Manganese Analytical Results - Cross Section K-K' Figure 11-98 pH Analytical Results - Cross Section K-K' Figure 11-99 Total Radium Analytical Results - Cross Section K-K' Figure 11-100 Strontium Analytical Results - Cross Section K-K' Figure 11-101 Sulfate Analytical Results - Cross Section K-K' Figure 11-102 Total Dissolved Solids Analytical Results - Cross Section K-K' Figure 11-103 Thallium Analytical Results - Cross Section K-K' Figure 11-104 Total Uranium Analytical Results - Cross Section K-K' Figure 11-105 Vanadium Analytical Results - Cross Section K-K' Figure 11-106 Arsenic Analytical Results - Cross Section L-L' 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xiv P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) Figure 11-107 Boron Analytical Results - Cross Section L-L' Figure 11-108 Hexavalent Chromium Analytical Results - Cross Section L-L' Figure 11-109 Total Chromium Analytical Results - Cross Section L-L' Figure 11-110 Cobalt Analytical Results - Cross Section L-L' Figure 11-111 Iron Analytical Results - Cross Section L-L' Figure 11-112 Manganese Analytical Results - Cross Section L-L' Figure 11-113 pH Analytical Results - Cross Section L-L' Figure 11-114 Total Radium Analytical Results - Cross Section L-L' Figure 11-115 Strontium Analytical Results - Cross Section L-L' Figure 11-116 Sulfate Analytical Results - Cross Section L-L' Figure 11-117 Total Dissolved Solids Analytical Results - Cross Section L-L' Figure 11-118 Thallium Analytical Results - Cross Section L-L' Figure 11-119 Total Uranium Analytical Results - Cross Section L-L' Figure 11-120 Vanadium Analytical Results - Cross Section L-L' Figure 11-121 Solid Phase - Groundwater Interaction Data Map 12.0 Screening-Level Risk Assessment Figure 12-1 Human Health and Ecological Exposure Areas 14.0 Discussion - Assessment Results Figure 14-1 Time versus Concentration Arsenic in Background Figure 14-2 Time versus Concentration Arsenic for the Active Ash Basin (Sheet 1 of 2) Figure 14-3 Time versus Concentration Arsenic for the Active Ash Basin (Sheet 2 of 2) Figure 14-4 Time versus Concentration Arsenic for the Units 1-4 Inactive Ash Basin Figure 14-5 Time versus Concentration Arsenic for the Unit 5 Inactive Ash Basin Figure 14-6 Time versus Concentration Boron in Background Figure 14-7 Time versus Concentration Boron for the Active Ash Basin (Sheet 1 of 2) Figure 14-8 Time versus Concentration Boron for the Active Ash Basin (Sheet 2 of 2) Figure 14-9 Time versus Concentration Boron for the Units 1-4 Inactive Ash Basin Figure 14-10 Time versus Concentration Boron for the Unit 5 Inactive Ash Basin Figure 14-11 Time versus Concentration Total and Hexavalent Chromium In Background Figure 14-12 Time versus Concentration Total and Hexavalent Chromium for the Active Ash Basin (Sheet 1 of 2) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xv P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) Figure 14-13 Time versus Concentration Total and Hexavalent Chromium for the Active Ash Basin (Sheet 2 of 2) Figure 14-14 Time versus Concentration Total and Hexavalent Chromium for the Units 1-4 Inactive Ash Basin Figure 14-15 Time versus Concentration Total and Hexavalent Chromium for the Unit 5 Inactive Ash Basin Figure 14-16 Time versus Concentration Cobalt in Background Figure 14-17 Time versus Concentration Cobalt for the Active Ash Basin (Sheet 1 of 2) Figure 14-18 Time versus Concentration Cobalt for the Active Ash Basin (Sheet 2 of 2) Figure 14-19 Time versus Concentration Cobalt for the Units 1-4 Inactive Ash Basin Figure 14-20 Time versus Concentration Cobalt for the Unit 5 Inactive Ash Basin Figure 14-21 Time versus Concentration Iron in Background Figure 14-22 Time versus Concentration Iron for the Active Ash Basin (Sheet 1 of 2) Figure 14-23 Time versus Concentration Iron for the Active Ash Basin (Sheet 2 of 2) Figure 14-24 Time versus Concentration Iron for the Units 1-4 Inactive Ash Basin Figure 14-25 Time versus Concentration Iron for the Unit 5 Inactive Ash Basin Figure 14-26 Time versus Concentration Manganese in Background Figure 14-27 Time versus Concentration Manganese for the Active Ash Basin (Sheet 1 of 2) Figure 14-28 Time versus Concentration Manganese for the Active Ash Basin (Sheet 2 of 2) Figure 14-29 Time versus Concentration Manganese for the Units 1-4 Inactive Ash Basin Figure 14-30 Time versus Concentration Manganese for the Unit 5 Inactive Ash Basin Figure 14-31 Time versus Concentration pH in Background Figure 14-32 Time versus Concentration pH for the Active Ash Basin (Sheet 1 of 2) Figure 14-33 Time versus Concentration pH for the Active Ash Basin (Sheet 2 of 2) Figure 14-34 Time versus Concentration pH for the Units 1-4 Inactive Ash Basin Figure 14-35 Time versus Concentration pH for the Unit 5 Inactive Ash Basin Figure 14-36 Time versus Concentration Radium in Background Figure 14-37 Time versus Concentration Radium for the Active Ash Basin Figure 14-38 Time versus Concentration Radium for the Unit 5 Inactive Ash Basin Figure 14-39 Time versus Concentration Strontium in Background Figure 14-40 Time versus Concentration Strontium for the Active Ash Basin (Sheet 1 of 2) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xvi P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) Figure 14-41 Time versus Concentration Strontium for the Active Ash Basin (Sheet 2 of 2) Figure 14-42 Time versus Concentration Strontium for the Units 1-4 Inactive Ash Basin Figure 14-43 Time versus Concentration Strontium for the Unit 5 Inactive Ash Basin Figure 14-44 Time versus Concentration Sulfate in Background Figure 14-45 Time versus Concentration Sulfate for the Active Ash Basin (Sheet 1 of 2) Figure 14-46 Time versus Concentration Sulfate for the Active Ash Basin (Sheet 2 of 2) Figure 14-47 Time versus Concentration Sulfate for the Units 1-4 Inactive Ash Basin Figure 14-48 Time versus Concentration Sulfate for the Unit 5 Inactive Ash Basin Figure 14-49 Time versus Concentration Total Dissolved Solids in Background Figure 14-50 Time versus Concentration Total Dissolved Solids for the Active Ash Basin (Sheet 1 of 2) Figure 14-51 Time versus Concentration Total Dissolved Solids for the Active Ash Basin (Sheet 2 of 2) Figure 14-52 Time versus Concentration Total Dissolved Solids for the Units 1-4 Inactive Ash Basin Figure 14-53 Time versus Concentration Total Dissolved Solids for the Unit 5 Inactive Ash Basin Figure 14-54 Time versus Concentration Thallium in Background Figure 14-55 Time versus Concentration Thallium for the Active Ash Basin (Sheet 1 of 2) Figure 14-56 Time versus Concentration Thallium for the Active Ash Basin (Sheet 2 of 2) Figure 14-57 Time versus Concentration Thallium for the Units 1-4 for the Active Ash Basin Figure 14-58 Time versus Concentration Thallium for the Unit 5 for the Active Ash Basin Figure 14-59 Time versus Concentration Uranium in Background Figure 14-60 Time versus Concentration Uranium for the Active Ash Basin Figure 14-61 Time versus Concentration Uranium for the Units 1-4 Inactive Ash Basin Figure 14-62 Time versus Concentration Uranium for the Unit 5 Inactive Ash Basin Figure 14-63 Time versus Concentration Vanadium in Background Figure 14-64 Time versus Concentration Vanadium for the Active Ash Basin (Sheet 1 of 2) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xvii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF FIGURES (CONTINUED) Figure 14-65 Time versus Concentration Vanadium for the Active Ash Basin (Sheet 2 of 2) Figure 14-66 Time versus Concentration Vanadium for the Units 1-4 Inactive Ash Basin Figure 14-67 Time versus Concentration Vanadium for the Unit 5 Inactive Ash Basin Figure 14-68 Groundwater Concentration Trend Analysis - pH In All Flow Layers Figure 14-69 Groundwater Concentration Trend Analysis - Arsenic In All Flow Layers Figure 14-70 Groundwater Concentration Trend Analysis - Boron In All Flow Layers Figure 14-71 Groundwater Concentration Trend Analysis - Hexavalent Chromium In All Flow Layers Figure 14-72 Groundwater Concentration Trend Analysis - Total Chromium In All Flow Layers Figure 14-73 Groundwater Concentration Trend Analysis - Cobalt In All Flow Layers Figure 14-74 Groundwater Concentration Trend Analysis - Iron In All Flow Layers Figure 14-75 Groundwater Concentration Trend Analysis - Manganese In All Flow Layers Figure 14-76 Groundwater Concentration Trend Analysis - Strontium In All Flow Layers Figure 14-77 Groundwater Concentration Trend Analysis - Sulfate In All Flow Layers Figure 14-78 Groundwater Concentration Trend Analysis - Total Dissolved Solids In All Flow Layers Figure 14-79 Groundwater Concentration Trend Analysis - Thallium In All Flow Layers Figure 14-80 Groundwater Concentration Trend Analysis - Vanadium In All Flow Layers Figure 14-81 Comprehensive Soil and Sediment Data Figure 14-82 Detailed Units 1-4 Inactive Ash Basin Comprehensive Soil Data Figure 14-83 Comprehensive Groundwater Data Figure 14-84 Comprehensive Surface Water and Area of Wetness Data 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xviii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF APPENDICES Appendix A Regulatory Correspondence NCDEQ Expectations Document (July 18, 2017) Completed NCDEQ CSA Update Expectations Check List NCDENR NORR Letter (August 13, 2014) NCDEQ Background Location Approvals (October 11, 2017) NCDEQ Background Dataset Review (July 7, 2017) NCDEQ PBTV Approval Attachments (October 11, 2017) NCDEQ Correspondence – Revised Interim Monitoring Plan (October 19, 2017) Appendix B Comprehensive Data Table Comprehensive Data Table Notes Table 1 - Groundwater Analytical Results Table 2 - Surface Water Analytical Results Table 3 - AOW Analytical Results Table 4 - Soil and Ash Analytical Results Table 5 - Sediment Analytical Results Table 6 - SPLP Analytical Results Table 7 - CCR Analytical Results Appendix C Site Assessment Data HDR CSA Appendix H – Hydrogeological Investigation 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 / Slug Test Results UNCC Soil Sorption Evaluation – HDR CAP 1 Appendix D Addendum to the UNCC Soil Sorption Evaluation – HDR CAP 2 Appendix C 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xix P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF APPENDICES (CONTINUED) Appendix D Receptor Surveys Drinking Water Well and Receptor Survey Report – September 30, 2014 (HDR) Supplement to Drinking Water Supply Well and Receptor Survey – November 6, 2014 (HDR) Update to Drinking Water Well and Receptor Survey - HDR CSA Appendix B Dewberry Report – Permanent Water Supply Proposal to DEQ Appendix E Supporting Documents Stantec Report WSP Maps Appendix F Boring Logs, Construction Diagrams, and Abandonment Records Boring Logs Well Construction Records Well Abandonment Records Appendix G Sample Characterization Source Characterization – HDR CSA Appendix C Soil and Rock Characterization – HDR CSA Appendix D Surface Water and Sediment Characterization – HDR CSA Appendix F Groundwater Characterization – HDR CSA Appendix G Includes Duke Low Flow Sampling Plan Field, Sampling, and Data Analysis Quality Assurance / Quality Control - HDR CSA Appendix E Mineralogical Characterization of Soil and Rock Appendix H Background Determination Cliffside Steam Station 2018 CSA PBTV Report Appendix I Lab Reports HDR CSA Lab Reports - Appendix K HDR CSA Supplement 2 Lab Reports - Appendix C HDR CAP Part 2, Appendix A - CSA Supplement 1 Lab Reports - Attachment 4 2016 Quarter 2 Lab Reports 2016 Quarter 3 lab Reports 2016 Quarter 4 Lab Reports 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xx P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF APPENDICES (CONTINUED) Appendix I Lab Reports (continued) 2017 Quarter 1 Lab Reports 2017 Quarter 2 Lab Reports 2017 Quarter 3 Lab Reports Appendix J Risk Assessment Baseline Human Health and Ecological Risk Assessment - HDR CAP Part 2 Appendix F 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xxi P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.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 AMEC AMEC Foster Wheeler AOW Area of Wetness ASTM American Society for Testing and Materials bgs Below Ground Surface BR Bedrock CAMA Coal Ash Management Act CAP Corrective Action Plan CCP Coal Combustion Products CCR Coal Combustion Residuals CFR Code of Federal Register cm/sec Centimeters per second COI Constituent of Interest CSA Comprehensive Site Assessment CSM Conceptual Site Model CSS Cliffside Steam Station DIP Discharge Inspection Plan DO Dissolved Oxygen DOE Department of Energy Duke Energy Duke Energy Carolinas, LLC DWM Division of Waste Management DWR Division of Water Resources EDR Environmental Database Resources, Inc. EDS Energy Dispersive X-ray Spectroscopy EMP Effectiveness Monitoring Program EPD Environmental Protection Division EPRI Electric Power Research Institute ESV Ecological Screening Value FGD Flue Gas Desulfurization GAP Groundwater Assessment Work Plan GIS Geographic Information System gpd Gallons Per Day GTB Geotechnical Borings HAO Hydrous Aluminum Oxide 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xxii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF ACRONYMS (CONTINUED) HFO Hydrous Ferric Oxide HQ Hazard Quotients HSSR Hydrogeochemical and Stream Sediment Reconnaissance IMAC Interim Maximum Allowable Concentration IMP Interim Monitoring Plan Kd Sorption Coefficient LOAEL Lowest Observed Adverse Effects Level LQS Land Quality Section MCL Maximum Contaminant Level mg/kg Milligrams per Kilogram mg/L Milligrams per liter mgd Million Gallons per Day mm Millimeter MNA Monitored Natural Attenuation MRL Method Reporting Limit MRO Mooresville Regional Office MT3DMS Modular 3-D Transport Multi-Species MW Megawatts NCAC North Carolina Administrative Code NCDENR North Carolina Department of Environment and Natural Resources NCDEQ/DEQ North Carolina Department of Environmental Quality NCDHHS North Carolina Department of Health and Human Services NOD Notice of Deficiency 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 Plant/Site Cliffside Steam Station POG Protection of Groundwater PPBC Proposed Provisional Background Concentrations PSRG Preliminary Soil Remediation Goal PWR Partially Weathered Rock RBC Risk-Based Concentrations REC Rock Core Recovery RQD Rock Quality Designation RSL Regional Screening Levels S.U. Standard Units 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page xxiii P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx LIST OF ACRONYMS (CONTINUED) SCM Site Conceptual Model SEM Scanning Electron Microscopy SMCL Secondary Maximum Contaminant Level SPLP Synthetic Precipitation Leaching Procedure SWAP Source Water Assessment Program TCLP Toxicity Characteristic Leaching Procedure TDS Total Dissolved Solids TOC Total Organic Carbon TRV Toxicity Reference Value TZ Transition Zone 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 1-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 1.0 INTRODUCTION Duke Energy Carolinas, LLC (Duke Energy) owns and operates the Rogers Energy Complex (henceforth referred to as the Cliffside Steam Station (CSS), or the site), which is located in Mooresboro, Rutherford and Cleveland Counties, North Carolina. CSS began operation in 1940 as a coal-fired generating station. Units 1 through 4 were retired in October 2011, and currently only Units 5 and 6 are in operation at CSS. The coal ash residue and other liquid discharges from coal combustion processes at CSS have historically been managed in CSS ash basins, which consist of the active ash basin, the Units 1-4 inactive ash basin, and the Unit 5 inactive ash basin. Discharge from the active ash basin is currently permitted by the North Carolina Department of Environmental Quality (NCDEQ) Division of Water Resources (DWR) under National Pollutant Discharge Elimination System (NPDES) Permit NC0005088. 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 in accordance with CAMA. This CSA update contains an assessment of Site conditions based on a comprehensive interpretation of geologic and sampling results from the initial CSA 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 in accordance with CAMA. Data associated with monitoring wells installed for the purpose of compliance with 40 C.F.R. § 257.90 (the CCR Rule) is provided as information. Groundwater data collected for the purpose of compliance with the CCR Rule will be evaluated in accordance with the requirements and schedule provided therein. This CSA update was prepared in response to an NCDEQ request and in conformance with the most recently updated CSA table of contents provided by NCDEQ to Duke Energy on September 29, 2017. This submittal includes the following information: Review of baseline assessment data collected and reported as part of CSA activities A summary of NPDES and Coal Ash Management Act (CAMA) groundwater monitoring information A summary of potential receptors including analytical results from water supply wells 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 1-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 Definition of horizontal and vertical extent of CCR constituents in soil and groundwater based on NCDEQ-approved background concentrations; and 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 Coal Combustion Residuals (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 boundaries, and a CSA was conducted for each facility. The NORR letter is included in Appendix A. Coal Ash Management Act Requirements 1.2.2 The Coal Ash Management Act (CAMA) of 2014 — General Assembly of North Carolina Senate Bill 729 Ratified Bill (Session 2013) (SB 729) requires that ash from Duke Energy coal plant sites located in North Carolina either (1) be excavated and relocated to fully lined storage facilities or (2) go through a classification process to determine closure options and schedule. Closure options can include a combination of excavating and relocating ash to a fully 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 1-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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. 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 1-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx (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. Coal Combustion Residuals Rule (CCR Rule) 1.2.3 On April 17, 2015, the United States Environmental Protection Agency (USEPA) published 40 Code of Federal Regulations (CFR) Parts 257 and 261: Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals from Electric Utilities; Final Rule (USEPA, 2015). This regulation addresses the safe disposal of coal combustion residuals (CCR) as solid waste under Subtitle D of the Resource Conservation and Recovery Act (RCRA) and is referred to herein as the CCR Rule. The CCR Rule became effective on October 19, 2015. The rule provides national minimum criteria for “the safe disposal of CCR in new and existing CCR landfills, surface impoundments, and lateral expansions, design and operating criteria, groundwater monitoring and corrective action, closure requirements and post closure care, and recordkeeping, notification, and internet posting requirements. Monitoring wells have been installed and monitored in accordance the CCR Rule. The most recent data available from the CCR groundwater monitoring well network is provided on isoconcentration maps and cross-sections herein. The CCR Rule data will otherwise be evaluated in accordance with the requirements and schedule outlined therein. The Final Rule establishes requirements for a phased groundwater monitoring program consisting of detection monitoring and, if necessary, assessment monitoring and corrective action. The first phase of monitoring to comply with the CCR Rule is to include at least eight rounds of Detection Monitoring for Appendix III and Appendix IV constituents (described below) prior to October 2017. This Detection Monitoring may be followed by Assessment Monitoring. The USEPA considers several parameters to be leading indicators that provide an early detection of whether constituents are migrating from a CCR unit (i.e., Appendix III constituents). Appendix III constituents include: boron, calcium, chloride, fluoride, pH, sulfate, and total dissolved solids. If sampling results from the Detection Monitoring phase indicate that there are statistically significant increases over background concentrations for Appendix III constituents, the Final Rule requires the facility (or Site) to begin Assessment 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 1-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Monitoring. The parameters required for Assessment Monitoring are antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, fluoride, lead, lithium, mercury, molybdenum, radium 226 and 228 (combined), selenium, and thallium (USEPA, April 2015; Appendix IV constituents). If the results of assessment monitoring indicate that corrective action may be warranted, the CCR Rule requires additional assessment of corrective measures and potentially corrective action monitoring. Approach to Comprehensive Site Assessment 1.3 The CSA conducted in accordance with CAMA has been performed to meet NCDEQ requirements associated with potential site remedy selection. The following components were used 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 1-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx USEPA Monitored Natural Attenuation (MNA) Tiered 1.3.2 Approach The assessment data is compiled in a manner to be consistent with “Monitored Natural Attenuation of Inorganic Contaminants in Groundwater” (USEPA, 2007). The tiered analysis approach discussed in this guidance document is designed to align site characterization tasks to reduce uncertainty in remedy selection. The tiered assessment data collection includes information to evaluate: Active contaminant removal from groundwater and dissolved plume stability The mechanisms and rates of attenuation The long-term capacity for attenuation and stability of immobilized contaminants Anticipated performance monitoring needs to support the selected remedy ASTM Conceptual Site Model Guidance 1.3.3 The American Society for Testing and Materials (ASTM) E1689-95 generally describes the major components of conceptual site models, including an outline for developing models. To the extent possible, this guidance was incorporated into preparation of the Site Conceptual Model (SCM) 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 1-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Provide source area information, including ash pore water chemistry, physical and hydraulic properties, and CCR thickness and residual saturation within the ash basins. Address soil chemistry in the vicinity of the ash basins (horizontal and vertical extent of CCR leachate constituents in soil) compared with 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 – Cliffside Steam Station Ash Basin (HDR, 2015a) Corrective Action Plan Part 1 – Cliffside Steam Station Ash Basin (HDR, 2015b) Corrective Action Plan Part 2 (included CSA Supplement 1 as Appendix A) – Cliffside Steam Station Ash Basin (HDR, 2016b) Comprehensive Site Assessment Supplement 2 – Cliffside Steam Station Ash Basin (HDR, 2016c) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 2.0 SITE HISTORY AND DESCRIPTION An overview of the CSS setting and operations is presented in the following sections. Site Description, Ownership, and Use History 2.1 The CSS site is located in Mooresboro, in Rutherford and Cleveland Counties, North Carolina. The CSS site occupies approximately 1,000 acres and is owned by Duke Energy (Figure 2-1). Figure 2-2 is the 1959 USGS topographic map of a majority of the site with the exception of the eastern portion of the property. The topographic map identifies the Units 1-4 power plant and depicts Suck Creek in its flow path prior to the diversion of the creek during construction of the active ash basin. Figure 2-3 is the 1971 USGS topographic map of the eastern portion of the site. This figure depicts the site prior to the construction of the active ash basin and Suck Creek in its flow path prior to construction of the active ash basin. Based on a review of available historical aerial photography, the Site consisted of rural residential (assumed to be housing for plant workers) and woodlands as early as 1955. This photo does not depict any of the ash basins. In the 1964 aerial photo the Units 1-4 inactive ash basin is visible. In the 1976 aerial photo the Unit 5 inactive ash basin is present and it appears construction has begun on the active ash basin. Suck Creek is visible in its original location prior to diversion as well as the relocation channel during the construction of the basin. The residential properties are no longer visible in this photograph. The 1979 photograph shows an active Unit 5 ash basin, and the completed active ash basin with Suck Creek relocated. Aerial photographs from 1955, 1964, 1976, and 1979 are presented as Figures 2-4, 2-5, 2-6, and 2-7, respectively. CSS is a coal-fired electricity generating facility with a current capacity of 1,381 megawatts (MW). The station began commercial operations in July 1940 with Units 1, 2, 3, and 4 (198 MW total). Unit 5 (556 MW) began operations in 1972, increasing the total plant capacity to 754 MW. Construction of Unit 6, an 825 MW clean-coal unit, began in 2008, and the unit began commercial operations in 2012. Units 1 through 4 were retired from service in October 2011, and Units 5 and 6 continue to operate and use the active ash basin. Unit 5 operates with wet bottom ash and dry fly ash handling. Unit 6 operates with dry bottom ash and dry fly ash handling. The CSS ash basin system, located both west and east-southeast from the station and adjacent to the Broad River, consists of an active ash basin, the former Units 1-4 inactive ash basin, and the Unit 5 inactive ash basin. An ash storage area is located within the ash basin system waste boundary. The Units 1-4 inactive ash basin is located immediately east of the retired Units 1-4. It was constructed in 1957 and began operations the same year. The Units 1- 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 4 ash basin was retired in 1977 once it reached capacity. However, stormwater ponds were constructed on top of the retired basin and continued to operate until the basin was excavated. The Unit 5 inactive ash basin is located on the western portion of the site, west and southwest of Units 5 and 6. The Unit 5 inactive ash basin is currently used as a laydown yard for the station. This ash basin was constructed in 1970 (in advance of Unit 5 operations) and received sluiced ash from Unit 5 starting in 1972 until it was retired in 1980 when it reached full capacity. It is currently covered with a layer of topsoil and is stable with vegetation. The basin currently receives stormwater from a localized drainage area. The stormwater is discharged out of NPDES stormwater outfall SW009. The active ash basin is located on the eastern portion of the site, east and southeast of Units 5 and 6. Construction of the active ash basin occurred in 1975, and it began receiving sluiced ash from Unit 5. The active ash basin, expanded in 1980 to its current footprint, continues to receive sluiced bottom ash from Unit 5 in addition to other waste streams identified below. An unlined dry ash storage area, which is split into eastern and western portions, is also located within the northwestern portion of the active ash basin waste boundary. This ash storage area was probably created when ash was removed from the active ash basin in the 1980s to provide additional capacity for sluiced ash. The eastern portion of the ash storage area may be a spoils area remnant of soil from embankment dam construction. The active ash basin, an integral part of the station’s wastewater treatment system, historically received inflows from the ash removal system, station yard drain sump, stormwater flows, station wastewater, and other permitted discharges. Currently, the Unit 5 ash removal system and the station yard drainage system are routed through high density polyethylene pipe sluice lines into the active ash basin. Inflows to the active ash basin are variable based on Unit 5 and Unit 6 operations. Duke Energy also operates the Coal Combustion Products (CCP) Landfill in accordance with the NCDEQ Industrial Solid Waste Permit No. 81-06. The landfill, constructed with an engineered liner and leachate collection system, is permitted to receive fly ash, bottom ash, boiler slag, coal mill rejects/pyrites, flue gas desulfurization sludge, gypsum, leachate basin sludge, non-hazardous sandblast material, limestone, lime, ball mill rejects, coal, carbon, sulfur pellets, cation and anion resins, sediment from sumps, cooling tower sludge, filter bags, conditioning agents (e.g. lime kiln dust), soil material that contains any of the above material and soil used for operations), incidental 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx amounts of geotextile used in the management of CCP’s, and vacuum truck waste. The landfill is located approximately 1,800 feet southwest of the Unit 5 inactive ash basin, northeast of the intersection of Old U.S. Highway 221A and Ballenger Road. Site features are shown on Figure 2-6. Geographic Setting, Surrounding Land Use, and Surface Water 2.2 Classification The CSS site is situated in a rural area along the Broad River in Rutherford and Cleveland Counties, North Carolina. A description of the physical setting for CSS is provided in the following sections. Geographic Setting The area surrounding CSS generally consists of residential properties, undeveloped land, and the Broad River (Figure 2-7). McCraw Road (Duke Power Road) runs from northwest to southeast in the vicinity of the Site. Suck Creek, located west of the active ash basin, transects the Site generally from south to north, discharging to the Broad River. Topography at the CSS site ranges from approximate high elevations of 832 feet southwest of the active ash basin, 848 feet west of the Unit 5 inactive ash basin, and 856 feet southwest of the Unit 5 inactive ash basin to a low elevation of 664 feet at the interface with the Broad River on the northern extent of the Site. Overall topography generally slopes from south-to-north with an elevation difference of approximately 190 feet over an approximate distance of 4,000 feet. Surface water drainage generally follows site topography and flows from the south to the north across the Site except where natural drainage patterns have been modified by the ash basin or other construction. Unnamed drainage features are located near the western and eastern edges of the Site and generally flow north to the Broad River. Suck Creek transects the site from south to north, discharging to the Broad River. The approximate pond elevation for the active ash basin is 762 feet. The elevation of the Broad River at the Site is approximately 656 feet. Surrounding Land Use The area surrounding CSS generally consists of residential properties, undeveloped land, and the Broad River (Figure 2-5). Properties in the Town of Boiling Springs, Cleveland County, are primarily zoned heavy and light industrial, and residential properties to the south, east, and northeast of CSS are zoned residential. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Properties located to the west along Hwy 221A and northwest across the Broad River in Rutherford County are zoned rural residential including CSS, which is identified as average rural. The Town of Forest City does not quantify zoning outside the city limits. Meteorological Setting Rutherford County The yearly average daily maximum temperature in Rutherford County is 70.4°F, and the average daily maximum temperature ranges from 89.5°F in July to 48.7°F in January (USDA-NRCS, 1997). The yearly average minimum temperature is 44.8°F, and the average daily minimum temperature ranges from 64.2°F in July to 25.2°F in January. The total average annual precipitation in Rutherford County is 51 inches, with more than half of the rainfall (27 inches) occurring from April through September. Thunderstorms occur approximately 45 days each year. The average relative humidity in midafternoon is approximately 60 percent, with humidity reaching higher levels at night. The prevailing wind is from the northwest, and average wind speed is highest (10 miles per hour) in winter. Cleveland County During summer, the average temperature in Cleveland County is 75.5°F, and the average daily maximum temperature is 87°F (USDA-NRCS, 2006). During winter, the average temperature is 41.1°F and the average daily minimum temperature is 29.5°F. The total annual precipitation in Cleveland County is 48.09 inches, with more than half of the rainfall (28 inches) occurring from April through October. Thunderstorms occur approximately 41 days each year. The average relative humidity in midafternoon is approximately 54 percent, with humidity reaching higher levels at night. The prevailing wind is from the northeast, and average wind speed is highest (9 miles per hour) in spring. Surface Water Classification The CSS site drains north to the Broad River, which is part of the Broad River watershed. Surface water classifications in North Carolina are defined in 15A NCAC 02B.0101(c). Suck Creek, a tributary of the Broad River, transects the Site flowing from the south to the north into the Broad River. The surface water classification for the Broad River and Suck Creek in the vicinity of the CSS site is Class WS-IV. Class WS-IV waters are protected as water supplies, which are generally in moderately to highly 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx developed watersheds. Surface water features located on the Site are shown on Figure 2-10 The Grassy Pond Water Company (GPWC) has existing potable water supply lines that serve CSS, as well as residences to the west, south, and east of the Site. To the west, water lines run along US-221 Alt and Old US-221A. Water lines also run along McCraw Road (Duke Power Road) south and east of CSS. The location of the water lines in the vicinity of the site are included in the Cliffside Steam Station Phase II Potable Water Programmatic Evaluation (Dewberry, November 1, 2016) included in Appendix D. No surface water intakes, other than the intake used to pump water for plant operations, are located in the vicinity of CSS in the Broad 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 (General Statute §130A-309.201). At CSS, the groundwater assessment was conducted for the former Units 1-4 inactive ash basin, the Unit 5 inactive ash basin, and the active ash basin CCR surface impoundments, including the ash storage area. Figure 2-10 shows all sample locations regarding assessment activities. Collectively, the active ash basin, the Units 1 -4 inactive ash basin, the Unit 5 inactive ash basin, and the ash storage area are CAMA-related source areas and are referred to herein as ash management areas. The Units 1-4 ash basin dam was constructed in 1957, and operations began there the same year. The Units 1-4 basin was retired in 1977 once it reached capacity, although five small settling cells continued to exist on the western portion of the footprint. The contents of the settling cells were pumped to the active ash basin until the fall of 2016 when they were decommissioned. Excavation of the Units 1-4 inactive ash basin began in October 2015 and concluded in March 2017 with the exception of minor ash removal that is still ongoing at the interior slopes of the dam. Two lined basins and a wastewater treatment plant will be constructed within the footprint of the basin to treat plant flows as the active ash basin is taken offline in the future. The Unit 5 ash basin main dam and saddle dam were constructed in 1970, in advance of Unit 5 operation. The Unit 5 ash basin received inflows from Unit 5 operations starting in 1972 and until it was retired in 1980 once it reached capacity. The Unit 5 inactive ash basin is located on the western portion of the Site, west and southwest of Units 5 and 6. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The basin, which receives only stormwater from the drainage area, was made inactive in 1980 and is used as a laydown yard for the station. Construction of the active ash basin began in 1975 and was expanded in 1980 to its current footprint. The active ash basin is located on the eastern portion of the Site, east and southeast of Units 5 and 6. The unlined dry ash storage area (eastern and western portions) is located within the northwestern portion of the active ash basin and south of the Broad River as depicted in a Duke Energy ash basin engineering drawing. This storage area was likely created when ash was removed from the active ash basin in the 1980s to provide additional capacity for sluiced ash. 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 CSS, 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. Sediment samples collected at AOW and water sample locations also indicate impacts to soil greater the PBTVs and PSRGs for POG and could be considered a potential CAMA-related secondary source. 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, those sources will be addressed as part of a separate process in compliance with the requirements of 2L. On November 16, 2015 while conducting a field reconnaissance in preparation of a U.S. Army Corps of Engineers site wetlands jurisdictional determination, Duke Energy personnel noticed some raised areas on undeveloped land northwest of the Unit 5 Switchyard. Duke Energy personnel determined that the raised areas exhibited visual characteristics of ash and reported the historical ash disposal area to NCDEQ. An assessment of the coal combustion disposal area across the Broad River is ongoing. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Monitoring wells have been installed (Figure 2-10) and the results of the sampling and additional assessment of this area will be provided under separate cover. During the CSA assessment an area of exceedances was identified that appears not to be associated with the CAMA-related source areas (active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage area). This area is located east of Unit 6 and west of Suck Creek. Details regarding the exceedances reported in this area are included in Section 10.2. Summary of Permitted Activities 2.5 Duke Energy is authorized to discharge wastewater from CSS to receiving waters designated as the Broad River in accordance with NPDES Permit NC0005088. This permit was last issued on March 1, 2011, and expired July 31, 2015. A permit renewal application was submitted to NCDEQ DWR on January 28, 2015, followed by several updates to the application. CSS continues to operate under the administratively extended permit. Renewal of the permit is pending. As part of the permit renewal, the facility identified seeps and provided the analytical results of collected seep samples. NCDEQ is considering the appropriate regulatory mechanism to regulate seeps. The current NPDES flow diagram for CSS is provided in Figure 2-8. The NPDES flow diagram from the permit application for CSS is provided in Figure 2-9. Current approximate quantities of inflows into the active ash basin include 9.97 million gallons per day (MGD) from the yard drainage basin, 1.1 MGD from stormwater, and 1.8 MGD from the ash sluice for Unit 5. The contributing sources to those inflows are depicted on Figure 2-10. There is one solid waste facility associated with CSS: the active Rogers Energy Complex Coal Combustion Products (CCP) Landfill (NCDEQ Permit No. 8106 - INDUS). The CCP Landfill is located south of the Unit 5 inactive ash basin on the south side of McCraw Road (Figure 2-10). The CCP landfill, constructed with an engineered liner and leachate collection system, is permitted to receive fly ash, bottom ash, boiler slag, coal mill rejects/pyrites, flue gas desulfurization sludge, gypsum, leachate basin sludge, non-hazardous sandblast material, limestone, lime, ball mill rejects, coal, carbon, sulfur pellets, cation and anion resins, sediment from sumps, cooling tower sludge, filter bags, conditioning agents (e.g. lime kiln dust), soil material that contains any of the above material and soil used for operations), incidental amounts of geotextile used in the management of CCP’s, and vacuum truck waste. The landfill is located southwest of the Cliffside Steam Station, northeast of the intersection of Old U.S. Highway 221A and Ballenger Road. Waste 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx placement began in Phase I of the landfill on October 24, 2010. Phase I has a footprint of approximately 23 acres. Construction of Phase II was completed in early 2016 and has a footprint of approximately 15 acres. The CSS operates under Title V Air Permit Number 04044T39. An active Underground Storage Tank on the property is operated under NCDENR UST Permit No. 0-008944 The station has an Asbestos Non Schedule Abatement Permit Number: NC24923. The current NPDES Industrial Stormwater Permit, NCS000571, became effective on October 1, 2015. The permit expires on September 30, 2020. History of Site Groundwater Monitoring 2.6 The following sections discuss groundwater monitoring activities conducted at the CSS ash basins. The location of the ash basin voluntary and compliance monitoring wells, the CSA wells, the approximate ash basin waste boundaries, and the compliance boundaries 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 Monitoring wells were installed by Duke Energy in 1995/1996, 2005, and 2007 as part of the voluntary monitoring system for groundwater near the active ash basin. Monitoring wells CLMW-1, CLMW-2, CLMW-3S, CLMW-3D, CLMW-4, CLMW-5S, and CLMW-6 were installed in 1995 and 1996. Monitoring wells MW-8S, MW-10S, and MW-11S were installed in 2005. Monitoring wells MW- 2D, MW-4D, MW-8D, MW-10D, and MW-11D were installed in 2007. In addition, MW-2D-A was installed in 2011 to replace MW-2D. The existing voluntary wells are shown in Figure 2-10. Duke Energy implemented enhanced voluntary groundwater monitoring around the CSS active ash basin from August 2008 until August 2010. During that period, the voluntary groundwater monitoring wells were sampled two times per year and the analytical results were submitted to NCDENR DWR. Samples continue to be collected from some of the voluntary wells as part of the IMP. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx NPDES Groundwater Monitoring Groundwater monitoring as required by CSS NPDES permit NC0005088 began in April 2011 as described in NPDES Permit Condition A (11), Version 1.1, effective June 15, 2011. Groundwater monitoring events are conducted three times a year (April, August, and December). Compliance groundwater monitoring is continuing in accordance with the expired NPDES permit (NC0005088). Locations for the compliance groundwater monitoring wells were approved by the NCDENR DWR. The compliance groundwater monitoring system for the CSS active ash basin consists of the following monitoring wells: MW-20D, MW- 20DR, MW-21D, MW-22DR, MW-23D, MW-23DR, MW-24D, MW-24DR, and MW-25DR (shown on Figure 2-10 and Table 2-2). The compliance monitoring wells were installed in 2010 and 2011. 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-24D, MW-24DR, and MW-25DR the ash basin monitoring wells were installed at or within the CSS active ash basin compliance boundary. Monitoring wells MW-21D and MW-22DR are located to the east of the active ash basin, adjacent to the Duke Energy property boundary. Monitoring wells MW-20D and MW-20DR are located to the north of the active ash basin main dam, adjacent to the Broad River. Monitoring wells MW-23D and MW-23DR are located on the opposite side of Suck Creek west of the active ash basin, and monitoring well MW-25DR is located to the north of the ash basin across the Broad River. Monitoring wells MW-24D and MW-24DR are located approximately 150 feet outside of the most southern portion of the compliance boundary and represent background conditions. Landfill Groundwater Monitoring 2.6.2 Groundwater monitoring is conducted at the CSS Coal Combustion Products (CCP) Landfill in accordance with permit requirements. Monitoring is performed twice per year at the landfill per an established schedule. The groundwater monitoring system currently consists of 13 monitoring wells, three surface water sample locations, and one leachate sample location. Monitoring wells CCPMW-1S and CCPMW-1D were determined to monitor background water quality in CSS CAP 1. Monitoring wells were installed to 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx monitor constituent concentrations in the saprolite, the transition zone (TZ), and bedrock. The initial groundwater sampling event was performed in February 2010 prior to initial placement of waste in October 2010. Groundwater monitoring is performed in April and October per the landfill Water Quality Monitoring Plan. Ash Basin CAMA Monitoring 2.6.3 Over one hundred and fifty groundwater wells were installed as part of this assessment (Figure 2-10). Twenty-five (25) existing voluntary and compliance monitoring wells associated with the active ash basin, 16 compliance monitoring wells associated with the CCP Landfill, and sixty four (64) wells associated with the CCR rule have been included in assessment activities. Background monitoring wells have been installed to evaluate background water quality in the shallow, deep, and bedrock flow regimes. Monitoring wells BG-1S, MW-30S, and MW-32S were installed to monitor background groundwater quality within the shallow flow layer. Wells GWA-24S, GWA-25S, and GWA-30S were evaluated and their samples were found to represent background water quality in the shallow flow layer. Existing CCP landfill compliance monitoring well CCPMW-1S is also sampled to monitor background groundwater quality in the shallow flow layer, for a total of seven shallow background monitoring wells. Monitoring wells BG-1D and MW-32D were installed to monitor background groundwater quality within the deep flow layer. Well GWA-24D was evaluated and found to represent background water quality in the deep flow layer. Active ash basin compliance monitoring well MW-24D is also sampled to monitor background groundwater quality in the deep flow layer for a total of four deep background monitoring wells. Monitoring well MW-32BR was installed to monitor background groundwater quality in the bedrock flow layer. Monitoring wells GWA-24BR, GWA-30BR, and MW-22BR were evaluated and found to represent background groundwater quality within the bedrock flow layer. Active ash basin compliance monitoring wells MW-22DR and MW-24DR and CCP landfill monitoring well CCPMW-1D are also sampled to monitor background groundwater quality in the bedrock flow layer for a total of seven bedrock background monitoring wells. A total of 21 wells (AB-1S/D, AB-2S/D, AB-3S/SL/I/BRU, AB-4S/SL/D/BR, AB- 5S/BRU/BR, AB-6S/D/BR, and GWA-20S/D/BR) were installed within the active ash basin waste boundary during the initial 2015 well installations. Locations 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx AB-3, AB-4, AB-5, and AB-6 were installed to evaluate groundwater quality within the pore water in the basin, and within the saprolite, transition zone and bedrock flow layers beneath the basin. Locations AB-1, AB-2, and GWA-20 were installed to evaluate groundwater quality in the saprolite and transition zone in the embankment dams associated with the active ash basin. Wells MW-8S/D were existing voluntary monitoring wells installed in the embankment dam associated with the basin that are also sampled for assessment activities. Twelve (12) monitoring wells (IB-1S/D, IB-2S-SL/AL/I/BRU, IB-4S-SL/D/BR, and IB-3S/D) were installed within the Units 1-4 inactive ash basin waste boundary during the initial 2015 well installations. Locations IB-1, IB-2, and IB-4 were installed to evaluate groundwater quality within the ash pore water in the basin, and within the saprolite, transition zone and bedrock flow layers beneath the basin. The wells at IB-3 was installed to evaluate groundwater quality in the saprolite and transition zone in the embankment dam associated with the Units 1-4 inactive ash basin. Monitoring wells IB-1S/D, IB-2S-SL/AL/I/BRU, IB-4S- SL/D/BR, and IB-3S/D were abandoned to facilitate excavation of the Units 1-4 inactive ash basin. Nineteen (19) monitoring wells (U5-1S/D, U5-2S-SL/D/BR, U5-3S/D, U5-4S/D/BR, U5-5D, U5-6S/D, U5-7S/SL/D, U5-8S/D/BR) were installed within the Unit 5 inactive ash basin waste boundary during the initial 2015 well installations. Locations U5-1, U5-2, U5-5, U5-7, and U5-8 were installed to evaluate groundwater quality within the ash basin pore water, and within the saprolite and transition zone beneath the basin. The U5-7 cluster of wells has since been abandoned. Locations U5-3, U5-4, and U5-6 were installed to evaluate groundwater quality in the saprolite and transition zone in the embankment dams associated with the Unit 5 inactive ash basin. Fourteen (14) monitoring wells (AS-1S/D, AS-2S/D/BR, AS-3BRU, AS-4S/D, AS- 6S/D/BR, AS-7S/D/BR) were installed within the ash storage area waste boundary to evaluate groundwater quality within the ash basin pore water, and within the saprolite, and transition zone beneath the storage area during the initial 2015 well installations. A total of 26 groundwater monitoring wells were installed outside the waste boundary and within the compliance boundary of the active ash basin during the initial 2015 well installations to evaluate the impact of the basin on groundwater quality outside the waste boundary. Those monitoring wells include GWA- 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 21S/BRU/BR, GWA-22S/BRU, GWA-23D, GWA-25D, GWA-26S/D, GWA- 27D/DA/BR, GWA-28S/BRU/BR, GWA-33S/D/BR, GWA-39S , GWA-40S, GWA- 42S, GWA-43S/D, GWA-46D, GWA-47D, and GWA-48BR. Wells installed beyond the active ash basin compliance boundary are BG-1S/D/BR/BRA and GWA-44S/D/BR. Wells CLMW-1, CLMW-2, CLMW-3D, CLMW-3S, CLMW-4, CLMW-5S, CLMW-6, MW-4D, MW-7D, MW-10S/D, and MW-11S/D were existing voluntary monitoring wells; and wells MW-20D/BR, MW-21D/BR, and MW-23S/D/BR were existing active ash basin compliance monitoring wells. Those preexisting monitoring wells are also sampled for assessment activities. A total of 15 groundwater monitoring wells were installed outside the waste boundary of the former Units 1-4 inactive ash basin to evaluate the impact of the basin on groundwater quality outside the waste boundary during the initial 2015 well installations. Those monitoring wells include GWA-10S/D, GWA-11S/BRU, GWA-12S/BRU, GWA-13BR, GWA-14S/D/BR, and GWA-29D/BR/BRA, and GWA-38S/D. A total of 42 groundwater monitoring wells were installed outside the waste boundary of the Unit 5 inactive ash basin to evaluate the impact of the basin on groundwater quality outside the waste boundary during the initial 2015 well installations. Those monitoring wells include GWA-1BRU, GWA-2S/BRU/BR, GWA-3D, GWA-4S/D, GWA-5S/BRU, GWA-6S/D, GWA-30BRU, GWA- 31D/BR/BRA, GWA-35S/D, GWA-36S/BRU, MW-34S/BRU, MW-36S/BRU, MW- 38S/D/BR, MW-40S/BRU, MW-42S/D/DA, BG-2D, GWA-34S, GWA-37S/D, GWA- 45S/D, MW-30S/D, MW-32BR, and GWA-32D/BR. One existing compliance groundwater monitoring well, MW-25DR, and one existing voluntary monitoring well, MW-2DA, located outside of the ash storage area waste boundary are sampled to supplement groundwater quality data for this groundwater assessment. CCP Landfill monitoring wells CCPMW-1S/D, CCPMW-2S/D, CCPMW-3S/D, CCPMW-4, CCPMW-5, CCPMW-6S/D, CCPTW-1D, CCPTW-1S, CCPTW-2, and surface water locations CCPSW-1, CCPSW-2, CCPSW-3, are sampled as part of the landfill compliance monitoring program. CCPMW-1S/D are also background monitoring wells for the Site as well as the landfill. Additional monitoring wells have been installed since the 2015 initial installation activities to assess the horizontal and vertical extent of reported exceedances, and 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-13 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx to replace wells that were grout contaminated, had insufficient water volume, high turbidity, or were damaged and unable to be sampled. 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 were conducted at the CSS ash basins prior to implementation of the CAMA Groundwater Assessment Work Plan (HDR, 2014b). Coal Combustion Disposal Area Across the Broad River On November 16, 2015, while conducting a field reconnaissance in preparation of a U.S. Army Corps of Engineers site wetlands jurisdictional determination, Duke Energy personnel noticed some unnatural looking raised areas on undeveloped land northwest of the Unit 5 Switchyard (Figure 2-10). Duke Energy personnel determined that the raised areas exhibited visual characteristics of ash and reported the historical ash disposal area to NCDEQ. The NCDEQ issued a letter to Mr. Harry Sideris of Duke Energy, dated July 8, 2016, requiring that additional assessment of this area be conducted in accordance with the NCDENR NORR letter dated August 13, 2014, and CAMA of 2014. A proposed GAP was developed and submitted to NCDEQ on August 19, 2016, and conditionally approved by NCDEQ in a letter to Mr. Harry Sideris of Duke Energy dated November 23, 2016, which was revised in a letter dated December 2, 2016. A revised GAP was submitted to NCDEQ on May 12, 2017. The assessment of the coal combustion disposal area across the Broad River is ongoing. Monitoring wells have been installed (Figure 2-10), and the results of the sampling and additional assessment of this area will be provided under separate cover. Other Site Locations From 1988 to 2017, environmental incidents (i.e., releases) occurred at the CSS site that initiated notifications to NCDEQ. The historical incidents generally consisted of fuel oil releases associated with fuel storage tanks and/or associated piping, hydraulic oil spills, and stormwater and leachate releases to surface water. A summary of the historical on- Site environmental incidents is provided in Table 2-3. On March 5, 2014, NCDENR issued a Notice of Deficiency (NOD) associated with conditions observed at the toe of the Unit 5 inactive ash basin; specifically, “a grain-like 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 2-14 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx substance, white and gray in color, was observed originating from several seepage and boil locations at the toe of the dam”. Duke Energy submitted the Cliffside Steam Station, Inactive ash basin #5 Main Dam (RUTHE-070), Characterization of White Material Observed in Seepage report dated April 11, 2014 to NCDENR. The report presented the results of the characterization of the white material observed in the seepage. A summary of the findings from the April 2014 report, observations at the toe of the Unit 5 inactive ash basin, and a discussion of groundwater and seepage data that might have implications relevant to the white material are included in Section 7.0. That information was previously presented in the 2015 CSA report. Summary of Initial Abatement, Source Removal, and other 2.8 Corrective Action No imminent hazard to human health or the environment of the environment has been identified; therefore, initial abatement and emergency response actions have not been required. Duke Energy recommended excavation of the Units 1-4 inactive ash basin. Excavation of the basin began in October 2015 and concluded in March 2017 with the exception of minor ash removal that is still ongoing at the interior slopes of the dam. Approximately 450,000 tons of ash and comingled soil material was removed from the basin and relocated in the existing lined Cliffside CCP Landfill. Two lined basins and a wastewater treatment plant will be constructed within the footprint of the basin to treat plant flows as the active ash basin is taken offline in the future. Proposed corrective action will be outlined in the updated CAP. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 3.0 SOURCE CHARACTERISTICS For purposes of this assessment, the source areas are defined by the ash waste boundaries as depicted on Figure 2-1. For the CSS site, sources include the active ash basin, the former Units 1-4 inactive ash basin, the Unit 5 inactive ash basin, and the ash storage area. 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. Coal ash residue from the coal combustion process produced by Units 1-4 was historically managed in the Units 1-4 inactive ash basin. Coal ash residue from Unit 5 was historically managed in the Unit 5 inactive ash basin until that basin reached capacity and the discharge was re-routed to the active ash basin. Fly ash from the electrostatic precipitators was collected in hoppers. Bottom ash and boiler slag were collected in the bottom of the boilers. After collection, both fly ash and bottom ash/boiler slag were sluiced to the ash basins using conveyance water withdrawn from the Broad River. Sluice lines are used to convey the water/ash slurry and other flows to the basin. Fly ash from Unit 5 and both bottom ash and fly ash produced by Unit 6 is dry handled and disposed of in the on-Site lined NCDEQ-permitted CCP landfill as well as FGD gypsum that is produced from both Unit 5 and Unit 6. Refer to Figure 2-10 for a depiction of these features. CSS currently produces approximately 275,000 tons of ash per year. During operation of the coal-fired units, the ash basins received variable inflows from the ash removal system and other permitted discharges. Currently, the active ash basin receives variable inflows from the Unit 5 fly ash handling system, Unit 5 bottom ash handling system, cooling tower blowdown, stormwater runoff from yard drainage, coal pile runoff, gypsum pile runoff, limestone pile runoff, landfill leachate, and wastewater streams generated from emission monitoring equipment, precipitators, and Selective Catalytic Reduction (SCR) Unit. The active ash basin also receives treated sanitary wastewater, miscellaneous cleaning wastes, domestic package plant wastewater (through the yard sumps) and water treatment system wastes (filter backwash, demineralizer regeneration waste, reverse osmosis rinse water, and clarifier solids). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Duke Energy is in the process of evaluating alternatives for removing those flows from the ash basin to allow total decommissioning of the ash basins on-Site. Active Ash Basin The active ash basin is located approximately 1,700 feet to the east-southeast of CSS Units 5 and 6 and adjacent to the Broad River as shown in Figure 2-10. The active ash basin is an unlined basin impounded by earthen dams located between the west portion of the basin and Suck Creek and between the northeast portion of the basin and the Broad River. The waste boundary associated with the active ash basin, including associated dams and the ash storage areas, is approximately 117 acres in area. The approximate maximum pond elevation of the active ash basin is 770 feet. The active ash basin contains approximately 5,400,000 tons of ash. The main section of the pond is maintained at an elevation below 765 feet to have extra storage capacity during a significant flood event. The active ash basin was constructed in two phases. The first phase consisted of excavation of the Suck Creek diversion canal and construction of the upstream dam to an elevation of 745 feet and the downstream dam to an elevation of 725 feet. The first phase began in 1974 and was completed in 1975. The second phase consisted primarily of raising both dams to an elevation of 775 feet. The downstream dam was raised in two stages, with the first stage involving construction of the dam to a temporary elevation of 737 feet sometime in late 1979. The second stage construction was essentially completed in late 1980. In 2012, ash from within the southern portion of the active ash basin was removed and placed dry within an upland portion of the ash basin footprint in order to create a settling cell. The ash that was stacked northwest of the settling cell was covered with a soil layer and is currently well-vegetated. The active ash basin was formed by construction of two earth fill dams across Suck Creek bracketing a nearly mile-long meandering reach of the natural stream valley. At the upstream dam, Suck Creek was diverted through a canal and away from the ash basin to the Broad River, its present-day configuration. The maximum height of the upstream dam is about 60 feet above the exterior toe and about 65 feet above the interior toe and has a crest length of 890 feet. The active ash basin downstream dam, located just upstream of the original confluence of Suck Creek with the Broad River, has a maximum height of about 120 feet above the downstream toe and has a crest length of 876 feet. Both dams were designed to have 15-foot-wide crests at an elevation of 775 feet. The primary borrow area for construction of the embankment dams was material from within the basin footprint. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The outlet for the active ash basin (NPDES Outfall 002) is a reinforced concrete pipe (RCP) located in the northwest corner of the basin. The active ash basin receives variable inflows from the Unit 5 fly ash handling system, Unit 5 bottom ash handling system, cooling tower blowdown, stormwater runoff from yard drainage, coal pile runoff, gypsum pile runoff, limestone pile runoff, landfill leachate, and wastewater streams generated from emission monitoring equipment, precipitators, and Selective Catalytic Reduction Unit. The active ash basin also receives treated sanitary wastewater, miscellaneous cleaning wastes, domestic package plant wastewater (through the yard sumps) and water treatment system wastes (filter backwash, demineralizer regeneration waste, reverse osmosis rinse water, and clarifier solids). Ash Storage Area An unlined dry ash storage area is located north and adjacent to the active ash basin. This heavily vegetated area consists of an eastern and a western portion. Both the eastern and western portions are located between the active portion of the ash basin and the Broad River. The ash located in the storage area was probably removed from the active ash basin during the 1980s. The combined ash storage area footprint is approximately 15 acres and reportedly contains approximately 170,000 cubic yards of ash material. Units 1-4 Inactive ash basin The Units 1-4 inactive ash basin previously received inflows from Units 1-4 operation, primarily sluiced bottom ash and fly ash. The upstream, western portions of the ash basin were formerly converted into holding cells for storm and plant process water. Water from those holding cells was pumped to the active ash basin to the east. The impounded ash material within the inactive basin was previously capped with a soil cover approximately 2 feet thick. The Units 1-4 inactive ash basin was an unlined basin impounded by an earthen dam located along the north and northeast side of the basin. The waste boundary associated with the Units 1-4 inactive ash basin was approximately 14.5 acres in area and the basin formerly contained approximately 450,000 tons of ash material. The Units 1-4 inactive ash basin dam is an L-shaped earth fill embankment with an overall length of about 1,480 feet along the crest. The dam was originally designed to have a 15-foot wide crest at an elevation of 706 feet, with a maximum height of approximately 38 feet above the downstream toe. The final crest elevation after the excavation project is complete is projected to be approximately 686 feet. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The outlet for the Units 1-4 inactive ash basin was a reinforced concrete drainage tower with bottom discharge into a 30-inch diameter corrugated metal pipe (CMP), which extended approximately 180 feet (horizontally) through the base of the embankment at a skewed section located near the east end of the dam. The outlet pipe has been grouted and Duke plans for it to be removed. Stormwater currently entering the basin is evacuated by pumping, and permanent pumps are planned to route water to the future wastewater treatment plant and out through a new discharge pipe to the Broad River. Unit 5 Inactive ash basin The Unit 5 inactive ash basin is located approximately 1,000 feet to the southwest of Unit 5 and approximately 1,000 feet west of Unit 6, south of the Broad River (Figure 2- 10). The Unit 5 inactive ash basin is an unlined basin impounded by two earthen dams located along the north and northeast sides of the basin. The waste boundary associated with the Unit 5 inactive ash basin, including its dams, is approximately 58 acres in area. The Unit 5 inactive ash basin contains approximately 806,000 tons of ash material. The majority of the Unit 5 inactive ash basin footprint is currently used as a laydown area. The Unit 5 inactive ash basin dams are earth fill embankments. The main and saddle dams are the principal embankments that form this ash basin (Figure 2-10). The crest of the main dam is generally oriented in an east-west direction and parallels the flow of the Broad River to the north. The crest of the saddle dam is generally oriented in a southeast-northwest direction, and the Unit 5 cooling towers are located immediately northwest. The dams were designed to have 20-foot-wide crests at an elevation of 767 feet. The main dam is about 1,460 feet long at the crest and has a maximum height of about 97 feet above the toe of the downstream slope. The saddle dam is approximately 590 feet long at the crest and has a maximum height of about 42 feet above the downstream toe. The outlet for this basin is a reinforced concrete drainage tower with bottom discharge into a 60-inch diameter RCP that extends approximately 500 feet (horizontally) through the left abutment of the main dam (Figure 2-10). The Unit 5 ash basin and dam construction was completed in 1970, and the basin began receiving inflows with Unit 5 startup in 1972. The basin quickly reached its capacity and was retired in 1980, and a soil layer was placed across the footprint. The majority of the Unit 5 inactive ash basin footprint is currently used as a laydown area, and precipitation that falls within the ash basin drainage area is conveyed through the outlet structure. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Coal Combustion Products (CCP) Landfill Duke Energy owns and operates the Cliffside Steam Station Coal Combustion Products (CCP) Landfill (NCDEQ Division of Waste Management [DWM]), Solid Waste Section Permit No. 8106-INDUS-2009). The CCP landfill is located nearly a mile southwest of the CSS on Duke Energy property and is situated completely within Rutherford County. The CCP landfill is northeast of the intersection of Old U.S. Highway 221A and Ballenger Road. The landfill is permitted to receive fly ash, bottom ash, boiler slag, coal mill rejects/pyrites, flue gas desulfurization sludge, gypsum, leachate basin sludge, non-hazardous sandblast material, limestone, lime, ball mill rejects, coal, carbon, sulfur pellets, cation and anion resins, sediment from sumps, cooling tower sludge, filter bags, conditioning agents (e.g. lime kiln dust), soil material that contains any of the above material and soil used for operations), incidental amounts of geotextile used in the management of CCP’s, and vacuum truck waste generated by Duke Energy North Carolina coal-fired facilities, including from Cliffside Steam Station. Waste was first placed into the landfill on October 24, 2010. For construction of the CCP Landfill five phases encompassing 86 acres are planned. Phase I, which has been constructed, encompasses 23.3 acres of the southwestern corner of the landfill footprint. The estimated gross capacity of Phase I is 2,415,000 cubic yards. Phase II, completed in early 2016, encompasses 15.3 acres immediately north of the Phase I footprint. The estimated gross capacity of Phase II is 1,922,000 cubic yards. The entire landfill facility is projected to have a combined capacity of 13,343,000 cubic yards of waste when complete. The landfill was constructed with a leachate collection and removal system and an engineered liner system. Phase I and II contact stormwater and leachate are collected in the leachate collection pipe system and then pumped for treatment in the station’s active ash basin. Analytical results of the CCP Landfill leachate sampling are presented in Table 3 in Appendix B. The approximate boundary of the CCP Landfill Phases I and II is shown in Figure 2-10. 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. Physical Properties Approximately 70 percent to 80 percent of the ash produced during coal combustion is fly ash (EPRI, 1993). Typically 65 percent 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 percent to 30 percent of ash produced is 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 mm to 0.05 mm. In general, bottom ash has a grain size distribution similar to that of fine gravel to medium sand (EPRI, 1995). Based on published literature not specific to the CSS 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 sand gravel with similar gradation, grain size distribution, and density (EPRI, 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, and titanium) make up an additional 8 percent, while trace constituents account for less than 1 percent. The following constituents are considered to be trace elements: arsenic, barium, cadmium, chromium, lead, mercury, selenium, copper, manganese, nickel, lead, vanadium, and zinc (EPRI, 2010). The historical specific coal source generally used at CSS is bituminous coal from 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 CSS. The photograph shows 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 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, and calcium. Oxides of 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx magnesium, potassium, titanium, and sulfur comprise approximately 4 percent by weight (EPRI, 1995). Trace elemental composition typically is approximately 1 percent by weight and may include arsenic, antimony, barium, boron, cadmium, chromium, copper, manganese, mercury, nickel, lead, selenium, silver, thallium, zinc, and other elements. For comparison, Figure 3-2 shows the elemental composition of fly ash and bottom ash compared with typical values for shale and volcanic ash. Table 3-1 shows the bulk composition of fly ash and bottom ash compared with typical values for soil and rock. In addition to these constituents, fly ash may contain unburned carbon. Bituminous coal ash typically yields slightly acidic to alkaline solutions 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 others control the chemical concentration of the resultant solution. Constituents that are held on the glassy surfaces of fly ash such as boron, arsenic, and selenium may initially leach more readily than other constituents. As noted in Table 3-1, aluminum, silicon, calcium, and iron represent the larger fractions of fly ash by weight. Calcium and iron may limit the release of arsenic by forming calcium-arsenic precipitates. Formation of iron hydroxide compounds may also sequester arsenic and retard or prevent release of arsenic to the environment. Similar processes and reactions may affect other constituents of concern; however, certain constituents such as boron and sulfate will likely remain highly mobile. In addition to the variability that might be seen in the mineralogical composition of the ash, based on different coal types, different age of ash in the basin, etc., it is anticipated that the chemical environment of the ash basin varies over time, distance, and depth. EPRI (2010) reports that 64 samples of coal combustion products (including fly ash, bottom ash, and flue gas desulfurization (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 (EPRI, 2010). 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx to better understand impacts to soil and groundwater from the source area and will also be used 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 basins. 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 active ash basin, ash was encountered at varying intervals, from a few feet below ground surface (bgs) to 73 feet bgs; auger refusal was encountered from approximately 64 feet bgs to 115 feet bgs, indicating transition zone or bedrock. Water levels ranged from approximately 4.3 feet bgs to 34.0 feet bgs. In the Units 1-4 inactive ash basin, ash was encountered at varying intervals, from a few feet bgs to 50 feet bgs; auger refusal was encountered from approximately 44 feet bgs to 92 feet bgs. Water levels ranged from approximately 14 bgs to 33 feet bgs. In the Unit 5 inactive ash basin, ash was encountered at varying intervals, from 9.5 feet bgs to 67 feet bgs; auger refusal was encountered from approximately 67 feet bgs to 70 feet bgs. Water levels ranged from approximately 30 feet bgs to 55 feet bgs. In the ash storage area, ash was encountered at varying intervals, from 7 feet bgs to 57 feet bgs; auger refusal was encountered from approximately 46 feet bgs to 68 feet bgs. Water levels ranged from approximately 30 feet bgs to 78 feet bgs. Ash was not observed in borings outside the ash basins or ash storage area. Laboratory results of ash samples are presented in Appendix H, Table 3. Physical Properties of Ash Physical properties (grain size, specific gravity, and moisture content) were performed on seven ash samples. Physical properties were measured using ASTM methods; lab reports are provided in Appendix H. Ash is generally characterized as a non-plastic silty (medium to fine) sand or silt. Compared to soil, ash exhibits a lower specific gravity with two values reported from AB-6GTB (1.7) and AB-7SL (2.2). Moisture 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx content of the ash samples ranges from 11.2 percent to 65.4 percent (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 basins as part of the 2015 CSA investigation. Concentrations 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 Protection of Groundwater (POG) for ash samples collected within the ash basin waste boundary (Appendix E). Although ash analytical results are being compared with the PSRGs, these samples do not represent soil samples (for comparative purposes only). In addition to total inorganic testing of ash samples, six ash samples collected from borings completed within the ash basin were analyzed for leachable inorganics using Synthetic Precipitation Leaching Procedures (SPLP) (Appendix E). 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 with the 2L Standards or IMAC, these samples do not represent groundwater samples (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. Twelve pore water monitoring wells (AB-3S, AB-3SL, AB-4S, AB-4SL, AB-5S, AB-6S, IB-1S, IB-2S-SL, IB-3S, IB-4S-SL, U5-7S, and U5-7SL) were installed within the ash basin waste boundaries and were screened within the ash layer. Since their installation as part of the first 2015 CSA, those wells have been sampled as many as 12 times (IB-3S was sampled as part of the Units 1-4 inactive ash basin closure sampling in addition to CAMA and is now abandoned) up to the third quarter of 2017. Concentrations of antimony, arsenic, boron, cadmium, chromium, cobalt, iron, manganese, nickel, sulfate, thallium, total dissolved solids (TDS), and vanadium have been reported above the background groundwater concentration range and 2L 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 3-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Standards or IMACs in pore water samples collected from wells within the ash basins. Although pore water results are being compared with the 2L Standards or IMAC, these samples do not represent groundwater samples (for comparative purposes only). The pore water sampling results show fluctuating concentrations for some constituents in some wells. Piper diagrams have been prepared for groundwater results from CSS monitoring wells (Figures 3-4, 3-5, and 3-6) and are discussed in Section 10.0. Piper diagrams for ash pore water well data from the active ash basin, Units 1-4 inactive ash basin and Unit 5 inactive ash basin compared with data from background shallow and deep monitoring wells are presented as Figure 3-4 to 3-6. Observations based on the diagrams include: Ash pore water wells from each basin are generally characterized as sodium- calcium-sulfate water type which is consistent with data presented in EPRI (EPRI, 2006). Background shallow and deep wells show less percent of calcium and sulfate than ash pore water wells, and plot generally as calcium-sodium-bicarbonate type. Ash pore monitoring well AB-4SL is located in the active ash basin. Concentrations of bicarbonate were higher at this location relative to sulfate and chloride, plotting away other ash pore water wells within the active ash basin. All other ash pore water wells plot within the sodium-calcium-sulfate water type and are distinct from background wells. Ash pore monitoring well U5-7S is located in Unit 5 inactive ash basin and abandoned in July 2016. Concentrations of bicarbonate were higher at this location relative to sulfate and chloride, plotting distinctively from U5-7SL which plots within the sodium-calcium-sulfate water type observed in other Site basins. 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 chemistry signature of the ash pore water wells is unique compared to background shallow and deep well data at the Site and aligns with ash pore water data presented in EPRI (EPRI, 2012), indicating that these wells represent source related water chemistry and can be used for comparison to downgradient wells and water supply wells. See Section 10.1 for background concentrations determined through statistical analysis. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.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 in determining the known extent of contamination at this time and stated that it expected all drinking water wells located 2,640 feet (0.5 mile) downgradient from the established compliance boundaries to be documented in the CSA reports as specified in the CAMA requirements. Water supply well locations near CSS are depicted on the shown on a USGS receptor map (Figure 4-1). The identified water supply wells are also show on an aerial photograph (Figure 4-2). 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). The compliance boundary used for the receptor surveys were the pre-2017 compliance boundary which included the Units 1-4 inactive ash basin and the Unit 5 inactive ash basin, as well as the active ash basin and the ash storage area. Properties located within the 0.5-mile radius of the pre-2017 CSS ash basin compliance boundaries generally consist of residential properties, undeveloped land, and the Broad River. Properties in the Town of Boiling Springs, Cleveland County, are primarily comprised of CSS, and residential properties to the south, east, and northeast. Properties located to the west along Hwy 221A and northwest across the Broad River in Rutherford County include residential properties. The Grassy Pond Water Company (GPWC) has existing potable water supply lines that serve CSS, as well as residences to the west, south, and east of the Site. To the west, water lines run along US-221 Alt and Old US-221A. Water lines also run along McCraw Road (Duke Power Road) south and east of CSS. The location of the water lines in the 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx vicinity of the site are included in the Cliffside Steam Station Phase II Potable Water Programmatic Evaluation (Dewberry, November 1, 2016) included in Appendix B. The water intake on the Broad River for the Grassy Pond Water Company is located at 1661 Baber Road, Rutherfordton, North Carolina, greater than 10 miles upstream of CSS. The closest downstream surface water intake identified downstream of CSS on the Broad River is the Gaffney Water Treatment Plant located at 1271 Filter Plant Road, Gaffney, South Carolina, greater than 10 miles downstream of CSS. 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 preferential pathways. Identification of piping near and around the ash basins was conducted by Stantec in 2015 and utilities around the Site were also included on a 2015 topographic map by WSP USA, Inc. (Appendix B). The dams contain engineered drainage features associated with dam drainage and stability. These features are internal or adjacent to the dams and are not included in the underground utility mapping. The underground piping and drains on the CSS site appear to be designed to convey water from various portions of the site toward the Broad River or Suck Creek. 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 pre-2017 Site compliance boundaries, have been reported to NCDEQ: Drinking Water Well and Receptor Survey – Cliffside Steam Station (HDR, 2014a) Supplement to Drinking Water Well and Receptor Survey – Cliffside Steam Station (HDR, 2014c) Comprehensive Site Assessment Report – Cliffside Steam Station Ash Basin, (HDR, 2015a) Draft Drinking Water Well and Receptor Survey – Cliffside Steam Station (HDR, 2016b) The first report submitted in September 2014 (Drinking water Well and Receptor Survey, (HDR, 2014a)) 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, and the United States Geological Survey (USGS) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx National Hydrography Dataset, as well as a vehicular survey along public roads located within a 0.5-mile radius of the pre-2017 compliance boundaries (Appendix C). The second report submitted in November 2014 (Supplement to Drinking Water Well and Receptor Survey, (HDR, 2014c) 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 pre-2017 compliance boundaries. 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 well with parcel number, construction and usage data, and the approximate distance from the compliance boundaries. 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 71 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 line representing 0.5-mile from the compliance boundary 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 used as a drinking source. In response to House Bill 630, a Potable Water Programmatic Evaluation (Dewberry, November 2016; Appendix B) was conducted. The evaluation consisted of a survey of eligible households and a 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 or filtration system will be provided. Based on the report, 64 households surrounding CSS have been recommended for either connection to a public water supply or the installation of an individual filtration system, and two households for water filtration systems only. The evaluation report included the following: A total of 71 water supply wells were identified within a 0.5-mile radius of the pre-2017 ash basin compliance boundaries. Forty-two (42) private water supply wells were confirmed to be located on properties within a 0.5-mile radius of the pre-2017 ash basin compliance boundaries based on information provided in returned water supply well questionnaires. Those wells are identified as “reported” private water supply wells. Twenty-three (23) private water supply wells were identified within a 0.5-mile radius of the CSS ash basin pre-2017 compliance boundaries during the Site reconnaissance. Those wells are identified as “field identified” private water supply wells. Six (6) additional private water supply wells are assumed at residences located within a 0.5-mile radius of the CSS ash basin pre-2017 compliance boundaries, based on the lack of public water supply in the area and on proximity to other residences that have private wells. Those six wells are identified as “assumed” private water supply wells, as questionnaires for those wells were not received. No public water supply wells (including irrigation wells and unused wells) were identified within a 0.5-mile radius of the CSS ash basin pre-2017 compliance boundaries. No public water supply wells (including irrigation wells and unused wells) were identified within a 0.5-mile radius of the CSS ash basin pre-2017 compliance boundaries. Several surface water bodies that flow toward the Broad River were identified within a 0.5-mile radius of the ash basin pre-2017 compliance boundaries. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Public Water Supply Wells 4.2.1 No public water supply wells (including irrigation wells and unused wells) or wellhead protection areas were identified within a 0.5-mile radius of the CSS ash basin pre-2017 compliance boundaries. Private Water Supply Wells 4.2.2 A total of 71 private water supply wells were identified within the 0.5-mile radius of the ash basin pre-2017 compliance boundaries; most of the 71 were south, southeast, east, and northeast of the active ash basin off of McCraw Road, Prospect Church Road, Fox Place, and Riverfront Drive, west and southwest of the Unit 5 inactive ash basin along Duke Power Road, US-221 Alt, and Old US- 221A, and north of the Broad River. Several efforts have been made to locate and document the presence of, and information related to, private water supply wells in the vicinity of CSS. 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 pre-2017 compliance boundaries. 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 42 private water supply wells were in use within 0.5 miles of the CSS ash basin pre- 2017 compliance boundaries. The receptor survey reports included a sufficiently scaled map showing the ash basin locations, the facility property boundary, the waste and pre-2017 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 pre-2017 compliance boundaries. Private and Public Well Water Sampling 4.3 NCDEQ arranged for independent analytical laboratories to collect and analyze water samples from private wells identified during the Well Survey, if the owner agreed to have their well sampled. Those activities occurred from February 2015 to July 2015. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx At the time of the 2015 CSA report, NCDEQ had collected and analyzed a total of 23 groundwater samples from 21 private water supply wells within a 0.5-mile radius of the CSS ash basin pre-2017 compliance boundaries. 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 CSS ash basin pre-2017 compliance boundaries during 2015 and early 2016. An additional three samples from three private water supply 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 C1000 range were sampled by Duke Energy. Four water supply well sample results from 2014 are also included in the data set. Table 4-3 provides tabulated results, provided by Duke Energy, for the NCDENR and Duke Energy sampling and identifies 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 reported exceeding 2L or IMACs, including pH (14 wells), chromium (one well), cobalt (two wells), iron (15 wells), manganese (four wells), and vanadium (four wells). Concentrations of analyzed constituents exceeded their 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). The PBTV exceedances of manganese and vanadium also exceed their 2L and IMAC as the PBTV value is greater than the standard for these two constituents. Arsenic – 4 wells Barium – 14 wells Calcium – 9 wells Chromium (hexavalent) – 8 wells Chromium (total) – 1 well Copper – 11 wells Lead – 4 wells Magnesium – 10 wells Manganese – 2 wells Molybdenum – 1 well Nickel – 2 wells Selenium – 1 well Sodium – 6 wells Sulfate – 1 well TDS – 1 well Vanadium – 4 wells Zinc – 11 wells 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The exceedances of PBTVs, 2L, and IMACs in private water wells were further evaluated. First, the bedrock PBTVs have been developed using groundwater data from four background bedrock wells located on the CSS site. The geochemical data from those 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 those wells with 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 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. It is also common for wells in the Piedmont to be bored and installed within residuum (soil or saprolite) or transition zone material partially weathered rock (PWR) above bedrock and using bedrock PBTVs for comparison may not be appropriate. Groundwater geochemistry in residuum, PWR, and fractured bedrock aquifers can be quite variable. Boring logs for these private wells are not available, so lithologic information at each location is unknown. Fifth, regional geology is different beyond the plant boundary and can result in different background groundwater conditions. Based on the bedrock groundwater flow direction at the Site (Figures 6-15 and 6-23), groundwater flow in the area around CSS is consistent with the model of groundwater flow in the Piedmont as described in Section 5.2. This conceptual model of groundwater flow (LeGrand, 1988) (LeGrand, 1989) describes each distinct Piedmont surface drainage basin as similar to adjacent basins with the conditions generally repetitive from basin to basin. Within a basin, movement of groundwater is generally 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx restricted to the area extending from the drainage divide to a perennial stream (Slope- Aquifer System). Near CSS, off-site private water supply wells are located upgradient of the ash basins or are situated in distinct drainage basins/slope-aquifer systems separate from the Site and the ash basins, north of the Broad River. Further, groundwater flow from the active ash basin is to the north and northwest, and the closest private wells are situated to the south, east, and northeast; groundwater flow from the Unit 5 inactive ash basin is to the north and the closest water supply wells are situated to the southwest. The remaining water supply wells identified in the area are located substantially beyond the expected flow zone of the CSS ash basins and/or north of the Broad River. Piper diagrams for water supply wells, with available water chemistry data, and background bedrock monitoring wells are compared with ash pore water data and downgradient bedrock monitoring well data from the active ash basin and Unit 5 inactive ash basin and are presented as Figure 4-3 and 4-4. These basins are near the property boundary, and water supply wells are located south and east of the basins. Observations based on the diagram include: Water supply wells are characterized as calcium-sodium-bicarbonate water type, consistent with samples collected from the background bedrock well at CSS. Water supply well C-1002 (located southeast of the active ash basin) shows higher concentrations of sulfate and chloride relative to bicarbonate compared to other water supply wells. This water supply well location plots nearby background location MW-32BR, located south of the Unit 5 inactive ash basin, suggesting water chemistry upgradient of the ash basin may be variable. From the active ash basin, downgradient bedrock monitoring wells GWA-21BR and MW-20DR (located north of the ash basin between the basin and the Broad River) plot along with background wells BG-1BR, MW-24DR and MW-32BR indicating these downgradient wells are likely representative of unimpacted groundwater within the bedrock flow layer. From Unit 5 inactive ash basin, downgradient bedrock monitoring wells GWA- 31BR and MW-38BR, located northeast and north of the basin, plot with ash pore water locations U5-7S and U5-7SL indicating potential mixing with impacted source area groundwater. Bedrock monitoring well U5-2BR, located in bedrock beneath the southwest extension of the ash basin, plots with background and water supply well water chemistry results. This suggests bedrock groundwater south of the basin is upgradient and unimpacted by source area groundwater, 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx and is consistent with north, northeast groundwater flow direction from the ash basin. See Section 6.3 for groundwater flow direction. 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 chemistry signature of the water supply wells with available water chemistry data 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 CSS CAP 2 (HDR, 2016b), 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, according to the United States Environmental Protection Agency (USEPA) Water Sense Partnership Program (USEPA, 2015b). Reverse particle tracking was conducted for private water supply wells within the model domain. The reverse particle tracks did not reach the CSS compliance boundary, indicating the water supply wells located beyond the compliance boundary did not have ash-related impacts. Surface Water Receptors 4.5 The Site is located in the Broad River watershed. The North Carolina portion of the Broad River Basin encompasses approximately 1,513 square miles in all or in part of eight counties. It straddles the southeastern corner of the Blue Ridge eco-region and the southwestern portion of the Piedmont eco-region. The Site is located south of, and adjacent to, the Broad River. Groundwater at the Site flows horizontally generally toward the north and discharges to the Broad River. Groundwater flow to the west of the active ash basin and east of Unit 6 is generally toward Suck Creek, which discharges to the Broad River. Surface water classifications in North Carolina are defined in 02B. 0101 (c). The surface water classifications for the Broad River and Suck Creek in the vicinity of the CSS site are Class WS-IV. Class WS-IV waters are protected as water supplies which are generally in moderately to highly developed watersheds. No surface water intakes, other than the intake used to pump water for plant operations, are located in the vicinity of CSS in the Broad River. The water intake on the Broad River for the Grassy Pond Water Company is located at 1661 Baber Road, Rutherfordton, North Carolina, greater than 10 miles upstream of CSS. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 4-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The closest downstream surface water intake identified downstream of CSS on the Broad River is the Gaffney Water Treatment Plant located at 1271 Filter Plant Road, Gaffney, South Carolina, greater than 10 miles downstream of CSS. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 5-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.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 CSS 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 CSS 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, 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), Daniels 2002). The CSS site is the Inner Piedmont within the Cat Square terrane, one of a number of tectonostratigraphic terranes that have been defined in the southern and central Appalachians (Figure 5-1); (Horton, Jr., Drake, Jr., & Rankin, 1989); (Hibbard, Stoddard, Secor, & Dennis, 2002); (Hatcher, Jr., Bream, & Merschat, 2007); (Hatcher, Jr., Bream, & Merschat, 2007). The Cat Square terrane is bounded by the younger-over-older Brindle Creek fault to the west that places the terrane over the Tugaloo terrane of the Inner Piedmont and the Central Piedmont suture to the east (Hatcher, Jr., Bream, & Merschat, 2007). It consists of metasedimentary rocks (sillimanite mica schist and gneiss, and biotite gneiss) intruded by granitoid plutons. Subordinate layers and lenses of quartz schist, micaceous quartzite, and calc-silicate rocks are present within the metasedimentary sequence. Rare mafic and ultramafic rocks occur in portions of the eastern Cat Square terrane. The terrane is characterized by gently dipping structures and low-angle thrust faulting and sillimanite and higher amphibolite grade metamorphism (Hatcher, Jr., Bream, & Merschat, 2007). A geologic map of the area around the Cliffside Steam Station is shown in Figure 5-2.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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 5-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 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 (1989) 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, 1964); (Stewart, Callahan, & Carter, 1964); (Nutter & Otton); (Harned & Daniel, 1992). Using a database of 669 horizontal conductivity measurements in boreholes at six locations in the Carolina Piedmont, (Schaeffer, 2009); (Schaeffer, 2014) 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 (Harned & Daniel, 1992). 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 5-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx (auger, roller cone, or casing advancer; (Schaeffer, 2011); (Schaeffer, 2014)). 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); (Schaeffer, 2014). The absence, thinning, and thickening of the TZ is related to the characteristics of the underlying bedrock (Schaeffer, 2014). The TZ may vary due to different rock types and associated rock structure. Harned and Daniel (1992) divided the bedrock into two conceptual models: 1) foliated/layered (metasedimentary and metavolcanic sequences) and 2) massive/plutonic (plutonic and metaplutonic complexes) structures. Strongly foliated/layered rocks are thought to have a well-developed TZ due to the breakup and weathering 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 (2014) proved Harned and Daniel’s (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, 2014). LeGrand’s (1988; 1989) conceptual model of the groundwater setting in the Piedmont, applicable to the CSS site, incorporates the Daniel and Harned (1989) two-medium regolith/bedrock system into an entity that is useful for the description of groundwater conditions (LeGrand, 1988) (LeGrand, 1989). 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) (LeGrand, 1989) (LeGrand, 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 might limit the area 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 5-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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, which 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 percent to 10 percent (Freeze & Cherry, 1979); but porosity values of 1 percent to 3 percent are more typical (Daniel III & Sharpless, 1981-1983). Daniel (1990) reported that the porosity of the regolith ranges from 35 percent to 55 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 inches to 46 inches. Mean annual recharge in the Piedmont ranges from 4.0 inches per year to 9.7 inches per year (Daniel, 2001). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 6.0 SITE GEOLOGY AND HYDROGEOLOGY Geology beneath the CSS 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). The third unit, competent bedrock, is defined by rock core recovery, rock quality designation (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 CSS 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), 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, and borings installed in the ash basin for the sampling of ash pore water. Mineralogy of soil samples collected from the borings is presented in Table 6-1, and chemical properties of the soil samples are presented in Table 6-2. The analytical methods used with solid and aqueous samples are presented in Table 6-3 and Table 6-4. Table 2-1 summarizes the well construction data for CAMA-related wells and piezometers at the Site. Boring logs, well construction records, and well abandonment records for CAMA-related monitoring installations as well as CCR well installation logs and construction records are included in Appendix G. 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 CSS ash basins act as bowl-like features toward which groundwater flows. Groundwater then flows from the basins primarily north toward the Broad River, and in the case of the active ash basin, also to the west toward Suck Creek. Groundwater at the Site flows away from the topographic and hydrologic divide (highest topographic portion of the Site) generally located along McCraw (Duke Power Road), south of the ash basins, to the north toward the ash basins and the Broad River. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Thirteen (13) transects were selected to illustrate geologic units and flow path conditions in the vicinity of the ash basins (Figure 6-1 through Figure 6-14).The transect locations and descriptions are: Section A-A’ is transverse through the active ash basin, parallel to groundwater flow. Section B-B’ is perpendicular to groundwater flow that parallels the Broad River downgradient of the Units 1-4 inactive ash basin, the ash storage area, and the active ash basin. Section C-C’ is parallel to groundwater flow to the west of Suck Creek, traversing the Units 1-4 inactive ash basin. Section D-D’ illustrates conditions perpendicular to groundwater flow, traversing from west to east across the Unit 5 inactive ash basin. Section E-E’ is parallel to groundwater flow through the central portion of the Unit 5 inactive ash basin. Section F-F’ is a traverse through the northern and central portions of the ash storage area and the north end of the active ash basin, perpendicular to groundwater flow. Section G-G’ is a traverse perpendicular to groundwater flow through the central portion of the Units 1-4 inactive ash basin. Section H-H’ is parallel to groundwater flow through the central portion of the Units 1-4 inactive ash basin. Section I-I’ is a traverse perpendicular to groundwater flow from the middle of the eastern portion of the ash storage area to the west side of the western portion of the ash storage area. Section J-J’ is parallel to groundwater flow through the western portion of the ash storage area. Section K-K’ illustrates conditions perpendicular to groundwater flow, traversing from west to east across the active ash basin. Section L-L’ is a traverse through the eastern portion of the Unit 5 inactive ash basin, parallel to groundwater flow. Section M-M’ is parallel to groundwater flow through the western portion of the Unit 5 inactive ash basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Site Geology 6.1 The CSS site is located in the Cat Square terrane of the Inner Piedmont terrane. The Cat Square terrane consists of Ordovician to Devonian age, high grade (sillimanite grade) metamorphic rocks, including orthogneiss and paragneiss with later granitic intrusions (Hatcher, Jr., Bream, & Merschat, 2007). The Cat Square terrane, within the approximate latitude of the Site, is bounded to the west and northwest by the Tugaloo terrane (also part of the Inner Piedmont) and the Carolina terrane to the east and southeast. The Brindle Creek Fault separates the Tugaloo terrane from the Cat Square terrane and is approximately 10 miles northwest of the site. The site location and well locations are overlain on the Geologic Map of the Charlotte 1˚ x 2˚ Quadrangle, North Carolina and South Carolina (Goldsmith, Milton, & Horton, Jr., 1988). This map, while accurate in rock description and mapping of contacts, does not identify the Tugaloo and Cat Square terranes of the Inner Piedmont since the 1988 publication of the map predates the identification of these terranes. Field mapping and use of the borehole data confirm the geologic units and location of contacts of the units with only a slight variation of the contact of the mapped units based on borehole and field mapping data. The updated bedrock geologic map with the Site and boring locations is presented in Figure 5-2. Based on the location of the Site, the bedrock is composed of biotite gneiss (CZbg) and sillimanite schist (CZss) units. Granite (OCsg), located north of the Site, was not encountered at the Site in the boreholes. The installed well and sample locations are shown in Figure 2-10. Soil Classification 6.1.1 Soil conditions encountered in the borings showed minimal variation across the Site. Residual soil consists of clayey sand (SC), silty sand (SM), silty sand with gravel (SM), micaceous silty sand (SM), and gravel with silt and sand (GP). The following soils/materials were encountered in the boreholes: Ash – Ash was encountered in borings advanced within the active ash basin, the Units 1-4 inactive ash basin, the Unit 5 inactive ash basin, and the ash storage area. Ash was generally described as gray to dark gray with, non-plastic, dry to wet and silty to sandy texture, consistent with fly ash and bottom ash. Fill – Fill material generally consisted of reworked silts, clays, and sands that were borrowed from one area of the site and redistributed to other areas. Fill was generally classified as silty sand, clayey sand, and sand with clay and gravel in the boring logs. Fill was used in the construction of dikes and as cover for ash storage areas. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Alluvium – Alluvium is unconsolidated soil and sediment that has been eroded and redeposited by streams and rivers. Alluvium may consist of a variety of materials ranging from silts and clays to sands and gravels. During Site construction and plant operation, alluvial deposits have been removed or covered. Alluvium was encountered in borings along the Broad River during the project subsurface exploration activities and during geologic mapping. Designations between alluvium and fill are approximate and were challenging to distinguish due to the similarities in material. Residuum (Residual soils) – Residuum is the in-place weathered soil that consists primarily of micaceous silty sand, micaceous silt, and clayey sand. This unit was relatively thin at the Site. Designations between residuum and fill are approximate and were challenging to distinguish due to the similarities in material. Saprolite/Weathered Rock – Saprolite is soil developed by in-place weathering of rock that retains remnant bedrock structure. Saprolite consists primarily of dense to very dense silty sand and silty sand with gravel noted as micaceous in some boring logs and not noted as micaceous in others. The primary distinction from residuum is that saprolite typically retains some structure (e.g., mineral banding) from the parent rock. Saprolite thickness varies across the Site from a very thin mantle where bedrock is near the surface to as much as 72 feet in other areas. Geotechnical index property testing of the above soil/materials was performed for disturbed and undisturbed samples in accordance with American Society of Testing and Materials (ASTM) standards. Thirty-six (36) undisturbed (“Shelby Tube”) samples were submitted for geotechnical index testing. Index property testing for undisturbed samples included Unified Soil Classification System (USCS) classification ASTM D 2487 (ASTM, 2001), natural moisture content ASTM D 2216 (ASTM, 2010a), Atterberg Limits ASTM D 4318 (ASTM, 2010c), grain size distribution - sieve analysis and hydrometer ASTM D 422 (ASTM, 2007), total porosity calculated from specific gravity ASTM D 854 (ASTM, 2010d), and hydraulic conductivity ASTM D 5084 (ASTM, 2010b). The full suite of index property tests could not be applied to two undisturbed samples due to low recovery, wax and gravel mixed in the tube, loose material, or damaged tubes. Twenty-two (22) disturbed (“Split Spoon”, or ”Jar”) samples received grain size 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx distribution with hydrometer ASTM D 422 (ASTM, 2007) and natural moisture content ASTM D 2216 (ASTM, 2010a). Results from the CSS geotechnical property testing show background soil and saprolite samples range from silty sand to clayey sand. Natural moisture content in the background soil samples is as low as 11.6 percent (clayey sand) and as high as 17.6 percent (silty sand). Specific gravity values for the background soil samples are between 2.58 and 2.71. High levels of fine sand, silt, and clay are present in background soil samples from BG-1 and BG-2 locations. Samples from locations GWA-30 and GWA-32 have relative equal amounts of sand and clay and little composition variation with depth. The amount of gravel is low for all background soil samples. Soil, saprolite, and weathered rock samples collected from beneath the ash basin and downgradient of the basins are characterized primarily as silty sand or gravel with sand and silt. Natural moisture content levels range from 2.4 percent to 39.4 percent. Similar to the background soil samples, the downgradient soil samples have a specific gravity range of 2.55 to 2.73. While the downgradient samples are mainly comprised of fine to medium sand (>50%), the percentage of silt and clay varies between locations; fine gravel is also present in many of the samples, such as samples collected from the GWA- 23 location. Soil property results are shown in Table 3-2. Rock Lithology 6.1.2 The bedrock at the Site consists of biotite gneiss and sillimanite schist. The biotite gneiss contains subordinate zones of quartzite, quartz feldspar gneiss, and mica schist. Figure 5-2 shows the extent of each unit. The biotite gneiss is predominantly gray to dark gray, fine to medium grained with some coarse grained zones, thinly to medium banded, and consists of quartz, plagioclase, biotite, and minor amounts of muscovite and garnet. The sillimanite schist is gray to light gray, fine to medium grained and consists of sillimanite, muscovite, quartz, and subordinate amounts of feldspar. It generally occurs as interlayers in the biotite gneiss. Structural Geology 6.1.3 The Inner Piedmont, including the Cat Square terrane, has been subjected to intense deformation due to dextral transpression along a south moving orogenic belt at the convergent margin of the terrane and the Laurentian margin (Dennis, 2007). Deformation includes a pervasive foliation, folding that includes recumbent folds/nappe structures, and shear zones. Sinistral tranpression associated with accretion of the Carolina terrane (Wortman, Samson, & Hibbard, 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 2000) to the southeast has also had an effect on the geologic structure in the Cat Square terrane. This multi-phase deformation occurred primarily as ductile deformation and has resulted in complex structural components in the bedrock. Rock core data indicates a dominant 10- to 20- degree dipping foliation in both the biotite gneiss and sillimanite schist. The dip direction of the foliation cannot be determined from the borehole data. A number of shear zones ranging from, 0.1 to 0.5 feet thick along foliation were noted in boring MW-34BRU. Some of these shear zones are noted to have pyrite within the zone. Data from the rock cores also show two predominant joint sets; a 40- to 50- degree dipping set and a horizontal to sub-horizontal set. Less predominant sets of 20- to 30- degree dipping joints and joints along foliation planes were noted. Based on the degree of folding in Inner Piedmont, the 20- to 30- degree dipping joints, sub-horizontal joints, and joints along foliation may be the same joint set and related to the dominate foliation. An apparently less pervasive sub-vertical set is observed but is likely due to vertical boreholes being less likely to intercept sub-vertical joints. All of the joint sets are described as having iron oxide and some manganese oxide staining, which is an indication of groundwater flow along the joint sets. The degree of openness of the joint is difficult to assess from rock core since the core is often broken at a joint and no longer retains its actual aperture. 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, percentages of oxides, and elemental composition). Completed laboratory analyses of the mineralogy and chemical composition of TZ materials are presented in Tables 6-5 (mineralogy), Table 6-6 (chemistry, percentages of oxides, and elemental composition). Rock chemistry results are presented in Table 6-7 (chemistry, percentages of oxides, and elemental composition). All mineralogy reports can be found in Appendix H. The petrographic analysis of rock samples (thin sections) are presented in Table 6-8 (mineralogy). The mineralogical analyses of CSS soils varied between boring locations, but mineralogical composition indicates the dominant minerals in the soils are quartz, feldspar (both alkali and plagioclase feldspars), and muscovite/illite. Soils exhibiting a higher degree of weathering show an increase in kaolinite with a higher percentage of amorphous phase (lacking distinct crystalline structure). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Other minerals identified include chlorite, biotite, gibbsite, calcite, dolomite, hornblende/ amphibole, pyrite, ilmenite, mullite, and goethite. The major oxides in the soils are SiO2 (48.10% - 69.43%), Al2O3 (18.25% - 26.31%), and Fe2O3 (1.33% - 8.76%). MnO ranges from 0.02% to 0.11%. Major transition zone minerals are quartz, illite, biotite, kaolinite, and feldspar. The major oxides are SiO2 (59.0% - 61.3%), Al2O3 (27.5% - 28.7%), and Fe2O3 (7.0% - 8.2%). The major oxides in the rock samples are SiO2 (59.27% - 70.36%), Al2O3 (15.54% - 20.4%), and Fe2O3 (1.50% - 7.22%). The high SiO2 in the bedrock samples is consistent with the sedimentary origin of the samples. At BG-1D, a background well located south of the active ash basin, the mineral assemblage of a sample collected 35 feet bgs consisted of predominately quartz and clay minerals with 12 percent quartz, 7 percent kaolinite, 29 percent muscovite, and 52 percent illite. In comparison, the mineralogical data at AB-3D from a sample recovered from 40 feet to 45 feet in saprolitic regolith below the Unit 5 inactive ash basin contains a similar mineralogical composition of 19 percent quartz, 10 percent chlorite, 3 percent gibbsite, 2 percent amphibole, 25 percent muscovite, and 37 percent illite. The similarities in extent of saprolitic depths at boring locations and mineralogical composition suggest uniform regolith conditions across the Site. Elemental chemistry of CSS soils shows highest concentrations of cerium, nickel, and zinc. Other elements identified as being at high concentrations in most samples are cobalt, copper, lanthanum, lead, and zirconium. Elemental chemistry results for all samples from both the TZ and whole rock samples indicate highest concentrations of cerium, nickel, lead, and zinc compared with other elements analyzed. Other elements identified in higher concentrations are cobalt, copper, gallium, lanthanum and zirconium. Oxide results from each layer show SiO2, Al2O3, and Fe2O3 as the three dominant oxide compositions for all samples analyzed at CSS: Soil oxide composition: SiO2 (48.10% - 69.43%), Al2O3 (18.25% -26.31%), and Fe2O3 (1.33% - 8.76%) Transition zone oxide composition: SiO2 (59.0% - 61.3%), Al2O3 (27.5% - 28.7%), and Fe2O3 (7.0% - 8.2%) Whole rock oxide composition: SiO2 (59.27% - 70.36%), Al2O3 (15.54% - 20.4%) and Fe2O3 (1.5% - 7.22%) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Geologic Mapping 6.1.5 Geologic mapping was conducted in April 2015 at the Site and within a 2-mile radius of the Site. A Brunton compass was used to measure to the orientation (strike and dip) of structures, including foliation, joints, fold axis, and shear zones observed in rock outcrops. Figure 5-2 shows the location and orientation of foliation and joints mapped. The availability of outcrop was a limiting factor in characterizing the complex nature of folding and deformation. The major structures observed during mapping consist of: Sub-vertical, continuous, very widely spaced joints striking approximately N83E and dipping ~75 degrees to the south-southeast. Foliation ranging in dip from 4 degrees to 29 degrees and ranging in dip direction from 0 degrees to 34 degrees. Joint set striking N83W dipping 77 degrees to NE. Joint set striking N40W dipping 75 degrees to NE. Joint set striking N8W dipping 80 degrees to ENE. An anticlinal structure with a fold axis striking N55W and a plunge of 5 degrees to 8 degrees to the southwest. This structure was mapped at the steam plant at a large outcrop apparently excavated as part of the plant construction. Within the overall anticlinal structure, there was one recumbent fold noted and one tight “S” fold. These types of folds are assumed to exist within the bedrock throughout the Site, but the persistence and intensity of folding cannot be quantified in detail. The variation in foliation orientations presented in Figure 5-1 is evidence of the complex structure of the bedrock. Effects of Geologic Structure on Groundwater Flow 6.1.6 Due to the fact that rock deformation in the form of complex folding occurred primarily in ductile (pressure and temperature) conditions, there are not significant discontinuities associated with this folding that result in open discontinuities. Shear zones that have mineralization may be prone to preferential weathering resulting in potential higher conductivity flow paths. Since our investigation did not identify any shear zones in outcrop, and shear zones noted in rock cores are not oriented, it is difficult to quantify the potential affect of shear zones on groundwater flow. The significant structure with respect to groundwater movement include the joint sets discussed in the previous section that were observed to be very continuous and crosscutting of fold 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx structures and fractures that have formed along foliation in brittle (pressure and temperature) conditions. Site Hydrogeology 6.2 According to LeGrand, the soil/saprolite regolith and the underlying fractured bedrock represent a composite water-table aquifer system (LeGrand, 2004). The regolith provides the majority of water storage in the Piedmont province, with porosities that range from 35 percent to 55 percent (Daniel & Dahlen, 2002). Calculated total porosities specific to the Site (41.7% to 45.3%) 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 and sidegradient areas with saprolite as deep as 62 feet to 70 feet at BG-1 and GWA-24, and west of the Unit 5 inactive ash basin with saprolite as deep as 45 feet to 82 feet at GWA- 36, GWA-37, and GWA-38. The saprolite layer thins in downgradient areas near the Broad River with saprolite as deep as 4 feet to 13 feet at GWA-32, GWA-23 and GWA- 22). Based on the Site investigation, the groundwater system in natural materials (soil, soil/saprolite, and bedrock) at the CSS site is consistent with the regolith-fractured rock system and is an unconfined, connected aquifer system as discussed in Section 5.2. The groundwater system at the CSS 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. Hydrostratigraphic Layer Development 6.2.1 The hydrostratigraphic classification system of Schaeffer (Schaeffer, 2014) was used to evaluate natural system hydrostratigraphic layer properties. The classification system is based on Standard Penetration Testing values (N) and the rock core recovery (REC) and rock quality designation (RQD) collected during the drilling and logging of the boreholes (Borehole/Well logs in Appendix G). The Schaeffer classification system uses 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 REC and RQD. The bedrock zone is classified as having REC of greater than 85 percent and RQD of greater than 50 percent. For discussion purposes, hydrostratigraphic units will be recognized in the text and supporting documents as follows: 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Shallow Unit – Alluvium/Saprolite (S wells) Deep Unit – Saprolite and weathered rock (D and BRU 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 6-1. Generalized cross- sections are presented in Figures 6-2 through Figure 6-14 showing site geology and groundwater flow directions. Hydrostratigraphic Layer Properties 6.2.2 Ash Pore Water Ash pore water units in the active ash basin, former Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage area consist of saturated ash material. The full pond elevation of the active ash basin is approximately 770 feet but can be as low as 765 feet for extra storage capacity during flood events. Of the seven boring locations within the active ash basin waste boundary, only locations AB-3, AB-4, AB-5, and AB-6 contained ash. Ash depths in the active basin range from a few feet to approximately 73 feet in the thickest ash location (AB-3 location) and to approximately 37 feet in the shallowest ash location (AB-5 location). Ground elevations in the active ash basin range from approximately 793 to 768 feet (AB-3 and AB-5 locations respectively). The elevation of static water levels in the basin, averaged from wells screened in ash pore water, is approximately 762 feet. The static water levels of ash pore water yield approximately 31 feet of saturated ash in the shallowest ash locations and 42 feet of saturated ash in the thickest ash locations. During CSA activities, three of the four boring locations, IB-1, IB-2 and IB-4, encountered ash within the Units 1-4 inactive ash basin waste boundary. Ash thickness ranged from a few feet to approximately 37 feet in the thickest ash location (IB-4 location) and 43.5 feet to 50 feet in the thinnest ash location (IB-1 location). Prior to excavation, the ground surface in the inactive ash basin was approximately 698 feet. Static water level elevations in the inactive basin range 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx from 666 to 684 feet. The static water levels yielded approximately 7 feet to 20 feet of saturated ash within Units 1-4 inactive ash basin prior to excavation. Of the eight boring locations within the Unit 5 inactive ash basin waste boundary, ash was encountered only at the U5-2 and U5-7 locations. Ash depths range from approximately 38.5 feet to 66.5 feet in the thinnest ash location (U5-2 location) and 9.5 feet to 67 feet in the thickest ash location (U5-7 location). Ground elevations in the Unit 5 inactive ash basin range from approximately 791 feet at the U5-2 location to 767 feet at the U5-7 location. The elevation of static water levels in the inactive ash basin is approximately 737 feet, and saturated ash in Unit 5 inactive ash basin ranges from 13 feet to 37 feet in thickness. Of the five boring locations within the ash storage area waste boundary, ash was only encountered in the AS-1 and AS-7 locations. Ash depths range from approximately 32 feet to 57 feet in the thinnest ash location (AS-1 location) and 7 feet to 48 feet in the thickest ash location (AS-7 location). Ground elevations in the ash storage area range from approximately 807 feet at AS-1 to 740 feet at AS- 7. Static water level elevations in the ash storage area from wells screened in ash pore water are approximately 730 feet at AS-1 and 710 feet at AS-7. The static water levels at these locations yield no saturated ash at AS-1 and approximately 18 feet of saturated ash at AS-7. 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. Shallow flow layer wells are labeled with an “S” designation. 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. Upper bedrock wells are also considered part of this flow layer. These wells are screened in the upper 5 feet of competent bedrock where no transition zone was observed. The upper bedrock wells are labeled with a “BRU” designation. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Bedrock Flow Layer The fractured bedrock unit occurs within competent bedrock. Bedrock around the site consists of biotite gneiss and sillimanite schist. The biotite gneiss is predominantly gray to dark gray, fine to medium grained with some coarse grained zones, thinly to medium banded, and consists of quartz, plagioclase, biotite, and minor amounts of muscovite and garnet. The sillimanite schist is gray to light gray, fine to medium grained and consists of sillimanite, muscovite, quartz, and subordinate amounts of feldspar. It generally occurs as interlayers in the biotite gneiss. The majority of water producing fracture zones were found within 50 feet of the top of competent rock. Bedrock wells are labeled with a “BR” designation. Groundwater Flow Direction 6.3 Based on the CSA site investigation, groundwater flow within the shallow wells (S), transition zone (D) wells, and wells in fractured bedrock (BR) flow from south to north, toward the Broad River. The groundwater flow in the shallow and deep wells to the west of the active ash basin and east of Unit 6 flow generally toward Suck Creek and on to the Broad River. 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 August 27, 2015 and February 10, 2017 as well as the other sampling events over the period of monitoring. The August event provided water-level elevation data for the dry season, and the February event provided water-level elevation data for the wet season. The events also provided data related to pre- and post-excavation of the Units 1-4 inactive ash basin. Depth-to-water measurements were subtracted from surveyed top-of-well casing elevations to determine groundwater elevations in shallow, deep, and bedrock monitoring wells (Table 6-9). Groundwater flow direction is estimated by contouring those groundwater elevations. Groundwater flow at CSS 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 Broad River. A groundwater divide is located approximately along McCraw Road (Duke Power Road) to the south. That groundwater divide generally corresponds to the topographic divides at this location. The predominant direction of groundwater flow from the ash basins is in a northerly direction toward the Broad River and in the shallow and deep flow layers to the west of the active ash basin and east of Unit 6 flow toward Suck Creek and on to the Broad River. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-13 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The shallow, deep, and bedrock water level maps during August 2015 and February 2017 are included as Figures 6-15 through Figure 6-23. Hydraulic Gradient 6.4 Horizontal hydraulic gradients were derived for August 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 a representative set of wells at the Site yields the following average horizontal hydraulic gradients (measured in feet/foot): Shallow wells: 0.093 ft/ft Deep wells: 0.061 ft/ft Bedrock wells: 0.030 ft/ft In general, horizontal gradients across the Site are consistent within each flow layer, with the least variability observed in the bedrock flow layer. Beneath the active ash basin (AB-3SL to AB-4SL) a hydraulic gradient of 1.0 x10-3 ft/ft is observed and is within range of other shallow layer gradients outside of the ash basin. Monitoring wells furthest north of the basins, and nearest the Broad River show higher horizontal gradients. This is likely due to the higher relief between the southern basins and northern shorelines downgradient. Horizontal gradients outside any basin’s waste boundary range from 1.35 x10-1 to 2.8x10-2 ft/ft. This range comes from gradients observed in well pairs MW-11S to GWA-22S, MW-11D to GWA-20D, and MW-22BR to AB-5BR. The highest gradients are observed in the shallow flow layer from wells MW-11S to GWA-22S, and the lowest gradients are observed in the deep flow layer from wells MW-22BR to AB-5BR. The hydraulic gradient calculated for the shallow well pair is due to higher relief north of the active ash basin compared to the deep well pair located east of the basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-14 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx A horizontal gradient in the Units 1-4 inactive ash basin had a value of 1.8 x 10-2 ft/ft calculated from wells GWA-14S to GWA-11S. The hydraulic gradient considers water flowing from an upgradient location to the downgradient location just north of the Units 1-4 inactive ash basin where there is higher relief between the basin and the Broad River. Generally, horizontal gradients in the Unit 5 inactive ash basin range from 5.4 x10-2 to 6.3 x 10-2 ft/ft high. The hydraulic gradients in the shallow and deep layers north and northwest of the Unit 5 inactive ash basin (U5-1S to MW-36S and U5-5D to MW-38D) is likely due to the much higher relief between the basin and the Broad River shoreline. Generally, horizontal gradients in the ash storage area range from 8.3 x10-2 to 8.6 x10-2 ft/ft calculated from wells AS-1SB to AS-2S and AS-4S to AS-5S. There was little difference observed between the deep flow layer gradient and the bedrock gradient for groundwater near the ash storage area. A summary of horizontal hydraulic gradient calculations is presented in Table 6-10. Vertical hydraulic gradients were calculated by taking the difference in groundwater elevation in a deep and shallow well pair over the difference in bottom of the screen elevations of the deep and shallow well pair using the August 2017 groundwater elevation data. A positive output indicates downward flow, and a negative output indicates upward flow. Vertical gradient calculations for 44 shallow and deep well pair locations and 19 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): Ash Pore to Shallow wells: 0.005 ft/ft Shallow to Deep wells: 0.077 ft/ft Deep to Bedrock wells: 0.289 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 Table 6-11 values were noted northeast and east of the active ash basin near the Broad River (GWA-12, GWA-23, and BG-3 locations) indicating the river as a receiving water body, and at upgradient background locations (MW-24 and BG-1). Vertical gradient calculations are summarized in Table 6-11 and shown in Figure 6-24. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-15 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Hydraulic Conductivity 6.5 Hydraulic conductivity (slug) tests were completed using 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 6-13 and Table 6-14. Additionally, in-situ hydraulic conductivities were calculated using slug test results reported in the 2015 CSA (HDR, 2015a) and the 2016 CSA Supplement (HDR, 2016c) (Appendix C) to determine groundwater velocity by grouping hydraulic conductivity (slug) test data into their respective hydrostratigraphic units. The geometric mean for hydrostratigraphic unit was used for calculating velocity. Hydrostratigraphic layers are defined in Section 11.1. Hydraulic conductivity values for wells screened in ash have a geometric mean of 1.98 x10-03 cm/sec. Hydraulic conductivity values for wells screened in saprolite have a geometric mean of 1.09 x10-03 cm/sec. Hydraulic conductivity values for wells screened in the deep flow zone have a geometric mean of 2.41 x 10-4 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 throughout the Site have a geometric mean of 3.02x 10-4 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 6-12. Groundwater Velocity 6.6 To calculate the velocity at which 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-16 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 are presented in Table 6-13, and effective porosity values are presented in Table 6-15 and Table 6-16. 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 6-10. At CSS, 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 CSS tend to be isolated with low interconnectivity. Further, hydraulic conductivity values measure the fractures immediately adjacent to a well screen, not across the distance between two bedrock wells. Groundwater flow in bedrock fractures is anisotropic and difficult to predict, and velocities change as groundwater moves between factures of varying orientations, gradients, pressure, and size. For additional information on the movement of groundwater around and downgradient of the ash basins over time, refer to discussion concerning groundwater fate and transport modeling (Section 13.0). 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-17 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The pore water in the ash basins 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 basins 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 they 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 4.17 x10-5 cm/sec in the shallow zone to 2.15 x10-04 cm/sec in transition zone, as demonstrated by groundwater seepage velocity results (Table 6-10). 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 3.02 x10-04 cm/sec were 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 throughout the entire Site. Geochemical mechanisms controlling the migration of 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). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-18 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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, 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 (5 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 6-18, 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 6-17 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 procedures, as described in Chapter 10 of their Ground Water Manual (2nd Edition), were used for the field permeability and packer tests (U.S. Bureau of Reclamation, 1995). Historic field permeability and packer/pressure test data for the CSS site are presented in Table 6-18. Fracture Trace Study Results 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-19 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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. 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 of the area were consulted prior to performance of aerial photography and topographic map interpretation to identify lithologies and structures in the area, and likely fracture orientations. Both low-altitude aerial photography provided by Duke Energy (from WSP Global, Inc.) covering approximately 4.7 square miles and USGS 1:24000 scale topographic maps covering an area of approximately 19 square miles were examined. Maps examined included portions of the USGS 7.5’ N.C.-S.C. and Boiling Springs South N.C.-S.C. (1:24,000 Scale) topographic quadrangles. Digital copies of the quadrangles were obtained and viewed on a monitor at up to 7x magnification. Lineaments identified were plotted directly on the digital images. Lineaments identified from topographic map are shown and lineament trends indicated by a rose diagram are included on Figure 6-24. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 6-20 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Photography provided for review included 1”=600’ scale, 9-inch by 9-inch black- and-white (grayscale) contact prints dated April 14, 2014. Stereo coverage was complete across the area shown on Figure 6-25. 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. Rose diagrams were prepared for lineament trends identified from both aerial- photography and topographic-map interpretation and are included as inserts on the respective figures. Results 6.9.2 A total of 21 well-defined lineaments are apparent in the study area. Trends are predominantly toward the east-northeast and north-northwest. A prominent feature of more than a mile in length along Suck Creek is coincident with a north- northeast trending segment of a fold (synform) axis that transects the area, and may indicate the presence of well-developed axial-planar cleavage in this part of the study area. Similarly, discontinuous but strong northeast-trending lineaments in the lower reaches of Ashworth Creek may have developed along an axial-planar cleavage associated with an antiform that trends through the area. East-northeast lineaments along the Broad River west of the Site, and along Second Broad River to the north and northwest, appear to have developed along contacts between the metamorphic sequence and granitic intrusives. Lineaments identified from aerial photography are shown and lineament trends indicated by a rose diagram are included on Figure 6-25. Extensive alteration of the land surface in the study area has greatly impacted the ability to identify small scale lineaments on aerial photography with confidence. Results of aerial-photography interpretation were inconclusive. Five lineaments were identified as shown on Figure 6-25. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 7.0 SOIL SAMPLING RESULTS Soil, PWR, and bedrock samples were collected from background locations, from beneath the ash basins, 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. Refer to Appendix G for a detailed description of these methods and for field and sampling quality control / quality assurance protocols. Appendix G also summarizes the soil and rock sampling plan used for groundwater assessment activities. 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 F. 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). 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, MW-30, and MW-32) 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 6-15 through 6-23, and on 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 CSS site. An updated background soil dataset for CSS was provided to NCDEQ on May 26, 2017. That background dataset included pooled soil samples collected from multiple depth intervals. Only samples collected from background locations at depth intervals greater than 1 foot above the seasonal high water table were included in the dataset. 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 use in determining provisional background threshold values (PBTVs) for both media (Appendix A). NCDEQ also requested that Duke Energy collect a minimum of 10, rather than the previously planned eight, valid background samples before determining PBTVs for each constituent. The background soil dataset was revised from the May 26, 2017 submittal based on input from NCDEQ in the July 7, 2017 letter. The revised background soil dataset satisfied the minimum requirement that 10 samples be used in statistical determination of PBTVs for all constituents except antimony and thallium. NCDEQ provided a response letter (Zimmerman to Draovitch, October 11, 2017) for 10 of the Duke Energy facilities. The letter approved PBTVs for the James E. Rogers Energy Complex (CSS). For all of Duke Energy’s calculated PBTVs that DWR found acceptable, DWR approved the values. If DWR did not find the PBTVs calculated by Duke Energy to be acceptable, justification was provided along with PBTVs for soil initially approved by NCDEQ DWR, as well as those that were revised and approved, are the background soil values used for comparison in this CSA report. DWR recognizes that as new data is gathered, the approved PBTVs may be refined. Thus, there will be periodic review of the data and recalculation of the PBTVs. Additional soil samples were collected on October 17 and 19, 2017, to satisfy the requirement concerning the minimum number of soil samples and to provide values for antimony and thallium less than the PSRG Protection of Groundwater values (Figure 2- 10). The dataset was screened for outliers once the additional samples were included in the dataset. The soil background dataset and updated PBTVs are included in Appendix H. PBTVs for soil constituents are provided in Table 7-1. Boring logs associated with the additional soil samples are included in Appendix F. Background SPLP Results SPLP results for background soil samples can be found in Appendix B, Table 6. Although SPLP analytical results are being compared with the 2L Standards or IMAC, these samples do not represent groundwater samples (for comparative purposes only). The SPLP analysis revealed three constituents (cobalt, iron, and vanadium) reported at concentrations greater than the 2L or IMAC in the leachate from background soil. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Facility Soil Data 7.2 Soil samples were collected during CSA monitoring well installations. Comparison of soil analytical results with background is discussed below. Soil Beneath the Ash Basins Active Ash Basin Soil samples collected beneath the ash in the active ash basin include AB-4BR (43.5-45), AB-5BRU (38.5-40), AB-5BRU (43.5-45), and AB-6D (48.5-50). The range of constituent concentrations in soils beneath the ash basin with a comparison to soil PBTVs is provided in Appendix B, Table 4. SPLP was not run on any of the soil samples collected beneath the active ash basin. For soil samples collected below the ash, boron, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium had reported values greater than the preliminary soil remediation goals (PSRGs) for protection of groundwater (POG). Although some constituent levels were measured as being greater than the PSRG for POG, when compared with the Site’s PBTVs most constituent concentrations appeared to be similar to calculated soil background values for the Site, with the exception of boron, cobalt, and manganese. Soil samples had boron concentrations reported greater than the PSRG for POG standard (47.1 mg/kg and 47.3 mg/kg) of 45 mg/kg and greater than the PBTV of 1.82 mg/kg. One soil sample had a cobalt concentration result of 600 mg/kg compared to the PBTV of 43 mg/kg. One soil sample had a manganese result of 18,600 mg/kg compared to the PBTV of 1,421 mg/kg. The exceedances are presented on Figure 7-1. Soil sample test results indicate these limited shallow impacts to the soil beneath the active ash basin. Units 1-4 Inactive Ash Basin Soil samples collected beneath the ash in the Units 1-4 inactive ash basin during the CSA were collected from borings at locations IB-2, IB-3, and IB-4. Soil samples were also collected from residual soils after the ash had been removed from the basin in general accordance with the Excavation Soil Sampling Plan, Rogers Energy Complex, Units 1-4 Inactive Ash Basin for Ash Basin Excavation, North Carolina Ash Basin Closure (Duke Energy, 2017). This soil sampling excavation plan was developed to satisfy the requirements presented in CCR Surface Impoundment Closure Guidelines for Protection of Groundwater (Zimmerman, 2016). Those samples have “S” prefixes and their depth bgs (post ash excavation) is in the sample ID in parentheses. The samples were collected on a grid system from beneath the excavated basin. Two lined retention 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx basins will be constructed in a portion of the footprint of the basin, so Scenario 1 soil sampling criteria from the above referenced guidelines was applied for the S-100 series of samples located in those areas (discrete surface samples collected from the first 6 inches of soil only). The range of constituent concentrations in soils beneath the ash basin with a comparison to soil PSRGs for POG and PBTVs is provided in Appendix B, Table 4. Post-excavation soil data indicate some constituents at concentrations greater than the PSRG for POG standards in soil beneath the basin; however, when compared with the Site’s PBTVs most constituent concentrations appeared to be similar, with exceptions of arsenic and chromium. The post-excavation exceedances are depicted on Figure 7-2. Soil sample test results indicate shallow impacts to the soil remain beneath the Units 1-4 inactive ash basin. SPLP was used to determine the ability of simulated rainwater to leach Site-specific constituents out of the soil to groundwater. SPLP test results do not represent groundwater; therefore, their comparison to 2L/IMAC is for discussion purposes only. The SPLP results in the soil beneath the ash basin indicated antimony, arsenic, chromium, cobalt, hexavalent chromium, iron, lead, manganese, nickel, selenium, thallium, and vanadium leaching from soils beneath the Units 1-4 inactive ash basin at concentrations greater than the 2L/IMAC. Unit 5 Inactive Ash Basin The soil sample collected beneath the ash in the Unit 5 inactive ash basin was U5-7D (70). The range of constituent concentrations in soil beneath the ash basin with a comparison to soil PBTVs is provided in Appendix B, Table 4. SPLP was not run on any of the soil samples collected beneath the Unit 5 inactive ash basin. Arsenic, chromium, cobalt, iron, manganese, and vanadium had reported values greater than the PSRG for POG. Although some constituent levels were greater than the PSRG for POG in the soil sample beneath the basin, when compared to the Site’s PBTVs, most constituent concentrations appeared to be similar to calculated soil background values, with the exception of arsenic. Arsenic had a reported concentration of 15.7 mg/kg with a calculated PBTV of 4.88 mg/kg. The exceedances are presented on Figure 7-1. Soil sample test results indicate shallow impacts to the soil beneath the Unit 5 inactive ash basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Ash Storage Area Soil samples collected beneath the ash in the ash storage area include AS-1D (68.5-70) and AS-7BR (56.5-58.5). The range of constituent concentrations in soils beneath the ash storage area with a comparison to soil PBTVs is provided in Appendix B, Table 4. Chromium, iron, and vanadium had reported values greater than the PSRG for POG; however, when compared to the Site’s PBTVs, the concentrations were less than the soil background values.. Soil sample test results do not indicate shallow impacts to the soil beneath the ash storage area greater than the calculated PBTVs. The SPLP sample results indicated no exceedances of the 2L/IMAC in soil beneath the ash storage area. SPLP test results do not represent groundwater; therefore, the comparison to 2L/IMAC is for discussion purposes only. Soil Beyond the Waste Boundary Active Ash Basin Soil samples outside the active ash basin waste boundary were obtained from boring locations GWA-21, GWA-22, GWA-23, GWA-24, GWA-25, GWA-26, GWA-27, GWA-28, MW-21, and MW-22. The range of constituent concentrations in soils outside the active ash basin waste boundary, along with a comparison to the range of reported background soil concentrations, is provided in Appendix B, Table 4. Reported concentrations of arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium in multiple locations exceeded the PSRG for POG. Constituent concentrations for soils outside the waste boundary were less than or similar to their PBTVs for all constituents with the exception of cobalt (but are within one order of magnitude). The cobalt concentrations at GWA-27D were reported at 73.3 mg/kg and 73.8 mg/kg with a calculated PBTV for cobalt of 43 mg/kg. These soil samples were collected from unsaturated soil above the water table downgradient of the active ash basin and the exceedances do not indicate the ash basin is a source of cobalt concentrations in soil beyond the waste boundary. Units 1-4 Inactive Ash Basin Soil samples outside the Units 1-4 inactive ash basin waste boundary were obtained from boring locations GWA-10, GWA-11, GWA-12, GWA-13, GWA-14, GWA-29, and GWA-33. The range of constituent concentrations in soils outside the Units 1-4 inactive 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx ash basin waste boundary, along with a comparison to the range of reported background soil concentrations, is provided in Appendix B, Table 4. Reported concentrations of arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium in multiple locations exceeded the PSRG for POG. Constituent concentrations for soils outside the waste boundary were less than or similar to their PBTVs for all constituents with the exception of arsenic and chromium. The arsenic concentrations greater than the PBTVs, located downgradient and sidegradient of the inactive ash basin indicate that impacted groundwater may be contributing to soil impacts beyond the waste boundary. The chromium concentrations greater than the PBTVs are located upgradient and sidegradient of the inactive ash basin; therefoere, the inactive ash basin is probably not the source of chromium concentrations in soil reported beyond the waste boundary. Unit 5 Inactive Ash Basin Soil samples outside the Unit 5 inactive ash basin waste boundary were obtained from boring locations GWA-1, GWA-2, GWA-3, GWA-4, GWA-5, GWA-6, GWA-30, GWA- 31, GWA-32, MW-34, MW-36, MW-38, MW-40, and MW-42. The range of constituent concentrations in soils outside the Unit 5 inactive ash basin waste boundary, along with a comparison to the range of reported background soil concentrations, is provided in Appendix B, Table 4. Reported concentrations of arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium in multiple locations exceeded the PSRG for POG. Constituent concentrations for soils outside the waste boundary were less than or similar to their PBTVs for all constituents with the exception of arsenic and chromium. The one arsenic concentration (7.7 mg/kg) greater than the PBTV (4.88 mg/kg) is located downgradient of the ash basin and does not indicate the ash basin as a source of arsenic soil impacts beyond the waste boundary as the sample was collected 4 feet bgs and is unsaturated. The chromium concentrations greater than the PBTVs are located downgradient and sidegradient of the ash basin below the water table and indicate the ash basin may contribute to the soil concentrations reported beyond the waste boundary. Ash Storage Area Soil samples outside the ash storage area waste boundary were obtained from AS-2D (25) and AS-2D (31). The range of constituent concentrations in soils outside the ash 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx storage area waste boundary, along with a comparison to the range of reported background soil concentrations, is provided in Appendix B, Table 4. Reported concentrations of chromium, cobalt, iron, manganese, and vanadium exceeded the PSRG for POG in one or both of the soil samples. Constituent concentrations that exceeded the PSRG for POG are less than the respective PBTVs. The exceedances do not indicate the ash storage area is a source of reported soil concentrations beyond the waste boundary. Comparison of PWR and Bedrock Results to Background Samples were obtained from locations ouside the waste boundary: three PWR samples at GWA-13, GWA-29, and MW-32 and 13 bedrock samples at GWA-1, GWA-3, GWA- 22, GWA-23, GWA-28, GWA-29, GWA-32, GWA-33, MW-32, and MW-34. The range of constituent concentrations in PWR and bedrock samples outside the waste boundary, along with a comparison to the reported soil PBTVs, is provided in Appendix B, Table 4. The arsenic concentration exceeded the PSRG for POG in one bedrock sample, and the selenium concentration in one PWR sample exceeded the PSRG for POG. Chromium, cobalt, iron, manganese, and vanadium concentrations exceeded the PSRG for POG in several of the samples. Of the PSRG exceedances, the arsenic concentration from MW-34BRU is the only exceedance greater than its respective PBTV. Secondary Sources 7.3 Soil samples were collected during assessment activities from areas beneath the ash basins and ash storage area, and outside the ash basins and ash storage area within the compliance boundary. Soils beneath the active ash basin were found to have exceedances of the POG PSRGs and PBTVs in shallow intervals beneath the basin, although most constituent concentrations appeared to be similar to calculated soil background values. The exceptions were boron, cobalt, and manganese. Soil sample test results indicate shallow impacts to saturated soil beneath the active ash basin. Soils beneath the Units 1-4 inactive ash basin were found to have exceedances of the POG PSRGs and PBTVs in the shallow intervals beneath the basin, although most constituent concentrations appeared to be similar to calculated soil background values. Concentrations of arsenic and chromium were exceptions, with several exceedances of the PBTVs reported. Soil sample test results indicate shallow impacts to the soil beneath the Units 1-4 inactive ash basin after ash excavation. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Soils beneath the Unit 5 inactive ash basin were found to have exceedances of the POG PSRGs and PBTVs. When compared to the Site’s PBTVs, most constituent concentrations appeared to be similar to calculated soil background values, with the exception of arsenic. Soil sample test results indicate shallow impacts to the soil beneath the Unit 5 inactive ash basin. When compared to the Site’s PBTVs, the soil sample concentrations reported were less than the calculated soil background values. Soil sample test results do not indicate shallow impacts to the soil beneath the ash storage area greater than the calculated PBTVs. White Material at Toe of Unit 5 Inactive Ash Basin Dam 7.4 On March 5, 2014, NCDENR, Division of Energy, Mineral and Land Resources, Land Quality Section (LQS) issued a Notice of Deficiency (NOD) associated with conditions observed at the toe of the Unit 5 inactive ash basin main dam. As stated in the NOD, the dam was inspected on March 1 and 4, 2014, by personnel from the LQS. During these inspections, the following conditions were noted. Several seepage and boil locations have been historically noted at the toe of the dam beyond the rip rap, with clear flow and iron oxide discoloration of the ground surface. During this inspection, a grain-like substance, white and gray in color, was observed originating from several seepage and boil locations at the toe of the dam, in addition to the clear flow. The white material at the toe of the dam, water seeping at the toe of the dam, and ash from the Unit 5 inactive ash basin were collected. A report providing the results and findings regarding the white material was prepared and submitted to the NCDENR Division of Energy, Mineral and Land Resources. The characterization found that the white material was not ash and was likely the product of a precipitation reaction as a result of the geochemical activity in the ash basin. Scanning electron microscopy (SEM) results of the ash sample showed the morphology of the ash sample was largely glassy spheres, as is typical for ash and for fly ash in particular. The white material did not exhibit similar spherical morphology as was observed in the ash sample. Energy dispersive X-ray spectroscopy (EDS) results for the ash sample showed it to be rich in aluminum oxide and silica, but with a much larger silica proportion than was observed in the white material. Based on the results of the SEM/EDS analysis of the ash and white material, these samples did not appear to be the same substance. The white material was characterized by SEM/EDS as being rich in aluminum oxide and silica, possibly an aluminum silicate (i.e. a type of clay). The exact origin of this white material is uncertain; however, it is 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 7-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx likely that the white material is the product of a precipitation reaction as a result of the geochemical activity in the ash basin. As seepage emerges at the toe of the dam, the geochemical conditions change, producing the white material as a precipitate. Duke Energy’s consultant for regular (generally weekly) inspections of the Unit 5 inactive ash basin main dam was Amec Foster Wheeler (Amec). Inspection reports prepared by Amec documenting inspections from August 29, 2014 to July 21, 2015 were reviewed for notation of observations of the white material in the seepage water at the toe of the dam. The Amec reports prior to September 11, 2014 do not report observation of the white material. The white material was consistently observed and noted in reports from September 11, 2014 to July 21, 2015, with the exception of the January 28, 2015 and February 19, 2015, reports in which the white material was not observed. The quantity of white material was noted as being consistent until the February 4, 2015 report, when it was noted as being observed in less quantity than had previously been observed. Observed quantities apparently were consistent from February 4, 2015, to July 21, 2015, as no mention of additional or less quantity was noted. AOW inspections have been conducted semi-annually at CSS since November 2015. As part of the inspections, visual observations and conditions are noted for each of the AOWs. During the AOW inspections conducted on November 18, 2015, April 27, 2016, October 11, 2016, and April 13, 2017, at the toe of the Unit 5 inactive ash basin main dam the white material has not been noted as being present at AOWs 18 or 19. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 8-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 8.0 SEDIMENT RESULTS Sediment samples were collected from 34 locations beyond the perimeter of the ash basin (Figure 2-10) during the 2015 CSA field effort. Sediment sampling procedures and variances are provided in Appendix G, and analytical results are presented in Appendix E. Sediment/Surface Soil Associated with AOWs 8.1 Twenty-two (22) of the 34 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 in June and July, 2015. Nine of the 34 sediment sample locations were co-located with NCDENR March 2014 water sample locations CLFSP-051, CLFSP-058, CLFSP-059, CLFSP-061, CLFSTR-065, CLFTD-004, CLFTD-005, CLFTD-052, and CLFWW-057. (Sediment location CLFTD0056, at the toe of the active ash basin downstream dam, was inadvertently identified as CLFWW057 during the sampling event). 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 in June and July, 2015. The remaining three sediment samples were collected within Suck Creek and are discussed in Section 8.2. The sediment sample results were compared with North Carolina PSRGs for POG and soil PBTVs (Appendix B, Table 5). Sediment sample locations are shown on Figure 2- 10. A description of AOWs S-1 through S-20 and S-22, and the results of sediment analysis are provided below, as well as the results of sediment analysis for locations CLFSP-051, CLFSP-058, CLFSP-059, CLFSP-061, CLFSTR-065, CLFTD-004, CLFTD-005, CLFTD-052, and CLFWW-057: S-1: Is a steady stream with relatively high flow volume within well-defined tributary to the Broad River northwest of the Unit 5 inactive ash basin. AOW is downgradient of the confluence of two streams that flow onto Duke property. One of those two streams may emerge from a spring at a terracotta pipe on the west side of the Unit 5 inactive ash basin, approximately 1,500 feet south of the AOW S-01 sign. Sediment was collected from the channel. Concentrations did not exceed the PBTVs. S-2: Is a stream flow through wetland area at base (north side) of Unit 5 inactive ash basin dike approximately 50 feet down river from the Unit 5 inactive ash basin discharge canal. Flow has defined 1- to 2-foot wide channel that increases 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 8-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx with depth closer to river. Sediment was collected from the channel. Cobalt and selenium concentrations exceeded their respective PBTVs and their PSRGs for POG. Cobalt was reported at a maximum concentration of 81.6 mg/kg (PBTV is 43 mg/kg and PSRG for POG is 0.9 mg/kg) and selenium was reported at a maximum concentration of 26.7 mg/kg (PBTV is 8.3 mg/kg and PSRG for POG is 2.1 mg/kg). S-3: Is a steady and moderate flow from stream and pooled area along the discharge canal between the Units 1-4 inactive ash basin and the active ash basin near its confluence with the Broad River just downstream of the low head dam on the Broad River. Sediment was collected from the channel. Concentrations did not exceed the respective PBTVs. S-4: Is seepage from the bank downgradient of the active ash basin to a channel flowing toward the Broad River. Sediment was collected from the bank. Concentrations did not exceed the respective PBTVs. S-5: Is seepage emerging from an area approximately 8 inches wide at a sandy beach along the bank of the Broad River and base of the active ash basin. Sediment was collected from the channel. Concentrations did not exceed the respective PBTVs. S-6: Is a steady stream with moderate flow volume within well-defined channel at toe drain for the active ash basin dam, near the confluence with the Broad River. Sediment was collected from the channel. Concentrations did not exceed the respective PBTVs. S-7: Is a steady, clear, and braided stream that flows onto Duke Energy property from offsite. AOW is within a relatively level area behind floodplain banks of the Broad River northeast of the active ash basin in the northeast corner of the Duke Energy property. Sediment collected from the beneath the flowing water in the flat area. Concentrations did not exceed the respective PBTVs. S-8: Is a steady and clear stream flow within unnamed tributary that flows along a southern portion of the active ash basin toward Suck Creek. Tributary is dry until approximately 150 yards upstream of AOW sign, where flow emerges within the stream channel banks. Sediment was collected from stream bed. Concentrations did not exceed the respective PBTVs. S-9: Is seepage from the bank and within former concrete spillway that flows toward east side of Suck Creek near waterfall downstream of bridge, before confluence with the Broad River. Source is diffuse from a few areas near waterfall structure and flow is minimal. Sediment was collected from beneath 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 8-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx the diffuse flow. The manganese result concentration (1,570 mg/kg) exceeded its PBTV (1,421 mg/kg) and the PSRG for POG (65 mg/kg). S-10: Is seepage from at least three observable areas spanning approximately 15 feet along the Broad River banks near the water level at base of Units 1-4 inactive ash basin. Sediment was collected from the bank. The arsenic concentration (250 mg/kg) exceeded its PBTV (4.88 mg/kg) and the PSRG for POG (5.8 mg/kg). S-11: Is seepage that may emerge from sandy bank below riprap along a broad area approximately 15 feet wide at the Broad River, downgradient of the Units 1- 4 inactive ash basin. Sediment collected from the bank. Arsenic and cobalt concentrations exceeded the PBTVs and the PSRGs for POG. Arsenic was reported at a concentration of 310 mg/kg (PBTV is 4.88 mg/kg and PSRG for POG is 5.8 mg/kg) and cobalt was reported at a concentration of 45.2 mg/kg (PBTV is 43 mg/kg and PSRG for POG is 0.9 mg/kg). S-12: Is seepage emerging from two distinct channels along the Broad River bank below the active ash basin. The channels do not merge and both infiltrate ground with no over land flow to river. Sediment collected from the channel. Concentrations did not exceed the respective PBTVs. S-13: Is seepage emerging from an area approximately 2 feet wide along the Broad River bank and approximately 6 feet up the bank from the low flow river stage downgradient of the Units 1-4 inactive ash basin dike. Sediment collected from beneath the seepage. The arsenic concentration (8.3 mg/kg) exceeded its PBTV (4.88 mg/kg) and the PSRG for POG (5.8 mg/kg). S-14: Is seepage that may collect from a broad area at the toe (west side) of active ash basin dike. Sediment collected from beneath the seepage. Concentrations did not exceed the respective PBTVs. S-15: Is seepage that may collect from a broad area at toe (west side) of active ash basin and has potential to flow within a poorly defined channel toward Suck Creek. Sediment collected from the channel. Concentrations did not exceed the respective PBTVs. S-16: Is stagnant water that collects in a broad area along the toe of the active ash basin upstream dam. Sediment collected from beneath the pooled water. Concentrations did not exceed the respective PBTVs. S-17: Is an area where flow may emerge from banks of Broad River downgradient of the Unit 5 inactive ash basin main dam. Sediment collected 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 8-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx from the bank. The cobalt concentration (95.8 mg/kg) exceeded its PBTV (43 mg/kg) and the PSRG for POG (0.9 mg/kg). S-18: Is a broad seepage area along large portion on the east side of the toe of the Unit 5 inactive ash basin main dam. Sediment collected from beneath the seepage area. Cobalt and iron concentrations exceeded their respective PBTVs and their PSRGs for POG. Cobalt was reported at a concentration of 88.3 mg/kg (PBTV is 43 mg/kg and PSRG for POG is 0.9 mg/kg) and iron was reported at a concentration of 432,000 mg/kg (PBTV is 75,162 mg/kg and PSRG for POG is 150 mg/kg). S-19: Is a broad seepage area in central portions of the toe of Unit 5 inactive ash basin main dam. Flow converges to a single channel at S-19. Sediment collected from the channel. The cobalt concentration (50.4 mg/kg) exceeded its PBTV (43 mg/kg) and the PSRG for POG (0.9 mg/kg). S-20: Is a pooled area near the toe of the Unit 5 inactive ash basin saddle dam. Sediment collected from beneath the pooled area. Concentrations did not exceed the respective PBTVs. S-22: Is a steady and moderate flow within engineered drainage system that collects water at base of toe drain on the north side of the active ash basin main dam and flows toward the Broad River. Sediment collected from the channel. Concentrations did not exceed the respective PBTVs. CLFSP-051: The sample located north of the Units 1-4 inactive ash basin near the Broad River. The arsenic concentration (51.4 mg/kg) exceeded its PBTV (4.88 mg/kg) and the PSRG for POG (5.8 mg/kg). CLFSP-058: The sample is located northwest of the active ash basin downstream dam near the Broad River. Concentrations did not exceed the respective PBTVs. CLFSP-059: The sample is located north of the western portion of the ash storage area near the Broad River. Concentrations did not exceed the respective PBTVs. CLFSP-061: The sample is located west of the active ash basin upstream dam near Suck Creek. Concentrations did not exceed the respective PBTVs. CLFSTR-065: The sample is located northeast of the active ash basin downstream dam near the Broad River. Concentrations did not exceed the respective PBTVs. CLFTD-004: The sample is located north of the Unit 5 inactive ash basin main dam near the Broad River. The arsenic, cobalt, iron, manganese, nickel, and selenium concentrations exceeded the PBTVs. Arsenic was reported at 18.5 mg/kg (PBTV is 4.88 mg/kg and PSRG for POG is 5.8 mg/kg). Cobalt was 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 8-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx reported at 926 mg/kg (PBTV is 43 mg/kg and PSRG for POG is 0.9 mg/kg). Iron was reported at 104,000 mg/kg (PBTV is 75,162 mg/kg and PSRG for POG is 150 mg/kg). Manganese was reported at 8,840 mg/kg (PBTV is 1,420 and PSRG for POG is 65 mg/kg). Nickel was reported at 158 mg/kg (PBTV is 66.2 mg/kg and PSRG for POG is 130 mg/kg). Selenium was reported at 38.1 mg/kg (PBTV is 8.3 mg/kg and PSRG for POG 2.1 mg/kg). CLFTD-005: The sample is located north of the Unit 5 inactive ash basin main dam. The boron and iron concentrations also exceeded their respective PBTVs. Boron was reported at a concentration of 374 mg/kg (PBTV is 1.82 mg/kg and PSRG for POG is 45 mg/kg) and iron was reported at a concentration of 330,000 mg/kg (PBTV is 75,162 mg/kg and PSRG for POG is 150 mg/kg). CLFTD-052: The sample is located north of the Units 1-4 inactive ash basin near the Broad River. The arsenic concentration (33.2 mg/kg) exceeded its PBTV (4.88 mg/kg) and the PSRG for POG (5.8 mg/kg). CLFWW-057: The sample is located north of the active ash basin downstream dam near the Broad River. Concentrations did not exceed the respective PBTVs. Sediment beneath the AOWs and water sample locations were found to have exceedances of the PSRGs for POG and PBTVs. When compared to the Site’s PBTVs, most constituent concentrations appeared to be similar to calculated soil background values for the Site, with the exception of concentrations of arsenic, boron, cobalt, iron, manganese, and selenium. Soil sample test results indicate impacts to saturated soil below these AOWs and water sample locations. Sediment in Major Water Bodies 8.2 Sediment samples were collected concurrently with the surface water samples along the shore line of Suck Creek (SW-02, SW-03, and SW-04) during June 2015. Sediment samples were analyzed in accordance with the constituent and parameter list used for soil and rock characterization (Table 6-3). In the absence of NCDEQ sediment criteria, the sediment sample results were compared with North Carolina PSRGs for POG and soil PBTVs (Appendix B, Table 5). Sediment sample locations are shown on Figure 2-10. Sediment sample location SW-2, upstream of the active ash basin is considered a background location on Suck Creek in relation to the active ash basin. Chromium, iron, and vanadium were reported in all the three sediment samples collected from Suck Creek at concentrations greater than the PSRG for POG. Manganese was reported in sediment samples SW-3 and SW-4 at concentrations greater 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 8-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx than the PSRG for POG. All of the reported PSRG for POG exceedances were less than their respective soil PBTVs, indicating that the sediment is not impacted by the CAMA- related source areas. Sediment samples have not been collected from the Broad River. This is considered a data limitation and is discussed in more detail in Section 11. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 9.0 SURFACE WATER RESULTS The CSS ash basins and ash storage area receive surface water runoff and groundwater recharge from upland areas south of the basins and storage area. Groundwater from the ash basins and ash storage area flows downgradient predominantly to the Broad River. In the central portion of the Site, groundwater flows from the active ash basin westward to Suck Creek and on to the Broad River. Surface water analytical results associated with samples collected from the Broad River and Suck Creek 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 6-4. Water samples discussed within the following sections include four distinct types: 1) ash basin wastewater and wastewater conveyance (discharge canals), 2) areas of wetness (AOWs), 3) industrial storm water, and 4) named surface waters. For this CSA, it is pertinent that a comparison with NCDENR Title 15A, Subchapter 02B is made. Surface Water and Wetland Standards (2B) includes only sample results from named surface waters. AOWs, wastewater and wastewater conveyances (discharge channels), and industrial storm water are evaluated and regulated in accordance with the NPDES Program administered by NCDEQ DWR. This process, an on-going effort parallel to that of the CSA, is subject to change. Ash Basin Water Samples Water samples (Active Ash Pond, SW-5, and SW-7) were collected from water ponded within the active ash basin. Sample CLFWW-057 was collected from the active ash basin discharge pipe prior to entering the Broad River. Sample SW-1 was collected from the ponded water in the southwest corner of the Unit 5 inactive ash basin. The ash basin water is not considered surface water or groundwater, and the results are presented for source information purposes only. Ash basin water sample locations are shown on Figure 2-10, and analytical results are listed in Appendix B, Table 3. Cliffside Area of Wetness (AOW) Sample Locations Thirty-four (34) AOWs (S-1 through S-19, S-19A, S-20 through S-24, S-26 through S-32, S-34, and S-35) have been identified and sampled for monitoring purposes. AOW locations S-25 and S-33 have historically not had enough volume to collect a sample and results are not available for these two locations. Nineteen (19) AOWs were identified and sampled as part of the 2015 CSA activities. The CSS site is inspected by boat and by land semi-annually for the presence of existing and potentially new AOWs along the shore of the Broad River downgradient of the ash basins. Observations include areas of the ash basins along the toe of the dikes, areas below full pond elevation, between the 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx ash basin and receiving waters (including Suck Creek and the Broad River), and drainage features associated with the basins, 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-19A, S-23, S-24, S-26 through S-32, S-34, and S-35 were identified after the 2015 CSA field work. The AOW locations are being evaluated separately in accordance with the NPDES permit and constituent concentrations from those locations are not being compared with 2B Standards. 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. Suck Creek and Broad River Sample Locations Suck Creek Surface water samples were collected from Suck Creek, which generally flows south to north, between the active ash basin, and the ash storage area and the Units 1-4 inactive ash basin. The samples were collected at locations SW-2, SW-3, and SW-4 during the 2015 CSA and again in 2017 (Figure 2-10). Sample location SW-2 is upstream of the ash basins and ash storage area and is considered to be a background surface water sample location. Surface water sample location SW-3 is located west of the toe of the active ash basin upstream dam. Surface water sample SW-4 is located northwest of the active ash basin before the confluence with the Broad River. Surface water samples are also routinely collected from surface water sample locations CCPSW-1 and CCPSW-2 on Suck Creek as part of the CCP Landfill monitoring program. Those locations, south of Duke Power Road, are considered to be background surface water sample locations relative to the ash basins and ash storage area. For groundwater corrective action to be implemented under 15A North Carolina Administrative Code (NCAC) .02L .0106(l), groundwater discharge to surface water cannot result in violations of standards for surface waters contained in 15A NCAC 2B .0200. In response to electronic correspondence with NCDEQ, Duke Energy submitted a work plan dated November 28, 2016, for surface water sampling to demonstrate compliance with 15A NCAC 2B .0200. Subsequently, NCDEQ provided comments to the proposed plan in a letter dated December 20, 2016. During the week of January 30 to February 5, 2017, surface water samples were collected from locations within Suck Creek (and the Broad River) where groundwater flowing from CAMA-related source areas might cause 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx exceedances of NCAC 2B water quality standards. Sample collection was conducted during low or base flow conditions to evaluate both acute and chronic water quality. Surface water samples were collected from Suck Creek during the January/February 2017 surface water sampling event from locations SW-SC-01, SW-SC-02, and SW-SC-03, located west of the active ash basin; from SW-SC-04, SW-SC-05, and SW-SC-06, located west of the active ash basin upstream dam; and from SW-SC-07, located near the confluence with the Broad River. The results of the sampling indicated that at most locations downgradient and/or adjacent to the ash basins, constituent concentrations, where detected, are consistent with results from background locations. Broad River Surface water samples were not collected from the Broad River during the 2015 CSA field activities. Based on recommendations in the CAP, surface water samples were collected from SW- 9, located upstream from the Site and considered to represent background water quality in the Broad River, and from locations SW-10A, SW-10B, and SW-10C, located east and downstream of CSS in the Broad River. Surface water samples were collected from the Broad River during the January/February 2017 sampling event from locations: SW-BR-BG - Located west of the CSS site, representative of background surface water conditions, SW-BRU5-01 - Located northeast and downstream of the Unit 5 inactive ash basin, SW-SBRBG - Located on the Second Broad River and representative of background surface water locations, SW-BRU14-1, SW-BRU14-2, and SW-BRU14-3 - Located adjacent to the Units 1-4 inactive ash basin, SW-BRAB-01 – Located adjacent to the western portion of the ash storage area, and SW-BRAB-02 and SW-BRAB-03 – Located north of and adjacent to the active ash basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The results of the sampling indicated that, generally, at downgradient locations and/or locations adjacent to the ash basins, constituent concentrations, where detected, are consistent with constituent concentrations from background locations. NCDEQ Sample Locations NCDENR collected water samples from locations at CSS during March 2014. Several of these locations were re-sampled during CSA Round 1. Locations are presented on Figure 2-10. Analytical results are provided in Appendix B, Table 3. The locations of these water samples were provided by NCDEQ to Duke Energy and are assumed to be accurate. Water sample identifiers and location relative to site features are: CLFSD063 (between Unit 6 and Unit 5 inactive ash basin) CLFSP051 (Units 1-4 inactive ash basin near Broad River) CLFSP058 (northwest of active ash basin near Broad River) CLFSP059 (north of ash storage area near Broad River) CLFSP061 (west of active ash basin near Suck Creek) CLFTD005 (near S-19 near Broad River) CLFTD004 (near S-2 near Broad River) CLFTD052 (Units 1-4 inactive ash basin near Broad River) CLFSTR065 (north of active ash basin) CLFSTR064 (northeast of active ash basin near Broad River) CLFWW057 (wastewater discharge north of active ash basin) These samples represent areas of seepage, wastewater, or storm water, and the results are not compared with 2B Standards. Comparison of Exceedances to 2B Standards 9.1 Sample locations CCPSW-01, CCPSW-02, and SW-2 are considered background surface water quality locations with regard to the downgradient samples collected from Suck Creek (SW-SC-01, SW-SC-02, SW-SC-03, SW-SC-04, SW-SC-05, SW-SC-06, SW-3, SW- SC-07, and SW-4). Sample locations SW-BRBG, SW-9, and SW-SBRBG are considered background surface water quality locations with regards to the downstream samples collected from the Broad River (SW-BRU5-01, SW-BRU14-01, SW-BRU14-02, SW-BRU14-03, SW-BRAB-01, SW-BRAB-02, and SW-BRAB-03). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 the associated total reportable concentrations are not included in the assessment as they are considered invalid. 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: Suck Creek Samples CCPSW-01: (Suck Creek background sample): Mercury (1/16) CCPSW-02: (Suck Creek background sample): No 2B exceedances (0/16) SW-2 (Suck Creek background sample): No 2B exceedances (0/15) SW-SC-01: No 2B exceedances (0/4) SW-SC-02: No 2B exceedances (0/4) SW-SC-03: No 2B exceedances (0/4) SW-SC-04: No 2B exceedances (0/4) SW-SC-05: No 2B exceedances (0/4) SW-SC-06: No 2B exceedances (0/4) SW-3: No 2B exceedances (0/9) SW-SC-07: No 2B exceedances (0/4) SW-4: pH (2/9) Sample results from Suck Creek indicate that field parameter pH has been reported as being outside the 2B range on two occasions at sample location S-4, located prior to Suck Creek converging with the Broad River. Broad River Samples SW-BRBG (Broad River background sample): No 2B exceedances (0/4) SW-9 (Broad River background sample): Turbidity (1/8), TDS (1/8) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx SW-SBRBG (Broad River background sample): No 2B exceedances (0/4) SW-BRU5-01: No 2B exceedances (0/4) SW-BRU14-01: No 2B exceedances (0/4) SW-BRU14-02: No 2B exceedances (0/4) SW-BRU14-03: No 2B exceedances (0/4) SW-BRAB-01: Dissolved Oxygen (2/4), Turbidity (1/4) SW-BRAB-02: Dissolved Cadmium (2/4), Hardness (2/4) SW-BRAB-03: Dissolved Cadmium (1/4), Hardness (2/4) Sample results from the Broad River indicate that field parameters (turbidity and dissolved oxygen (DO)), TDS, dissolved cadmium and hardness have been reported as being greater than 2B values on one or two occasions, but not consistently. 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. Suck Creek Samples Aluminum was detected in the background sample SW-02 at a concentration greater than the laboratory method reporting limit (MRL) (>100 µg/L). The reported aluminum concentrations in the downgradient sample locations have been within the range of the reported background concentrations. Boron has been detected in the background samples CCPSW-01 and CCPSW-02 at estimated concentrations less than the MRL (<50 µg/L). The reported boron concentrations in the downgradient sample locations have been within the range of the reported background concentrations. Chromium was not detected in the background samples CCPSW-01 and SW-02 at a concentration greater than the MRL (<1 µg/L). The most recent sample from CCPSW-02 had a chromium concentration at 1.05 µg/L. Concentrations of chromium in the downgradient sample locations have been within the range of the reported background concentrations. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Hexavalent chromium concentrations were reported as high as 0.31 µg/L at the background sample location SW-02. Concentrations of hexavalent chromium in eight of the nine downgradient sample locations are reported as being less than the background concentration. Location SW-SC-07, has reported values greater than the background concentration, ranging from 0.15 to 0.89 µg/L. Cobalt was reported in the background sample SW-02 at concentrations of 0.19 µg/L to 0.64 µg/L. Concentrations of cobalt at most downgradient sample locations have been within the range of the reported background concentrations. Samples from SW-SC-02, SW-SC-05, and SW-SC-06 have exceeded the background concentration range for cobalt. Iron concentrations range from 818 µg/L to 2,424 µg/L at the background sample locations. Concentrations of iron in the downgradient sample locations have been within the range of the reported background concentrations. Manganese concentrations range from 31 µg/L to 119 µg/L at the background sample location. Concentrations of manganese at SW-SC-02 have exceeded the background concentration range for manganese. The remaining sample locations have had concentrations reported as being less than the background concentration range. Strontium concentrations range from 18 µg/L to 59.3 µg/L at the background sample location SW-02. All downgradient sample locations have had concentrations reported as being less than the background concentration range. Thallium was not detected at the background sample at a concentration greater than the MRL (<0.1 to <0.2 µg/L). Concentrations of thallium in the downgradient sample locations have been within the range of the reported background concentrations. Vanadium concentrations were reported at 0.33 to 0.88 µg/L at the background sample location SW-02. Concentrations of vanadium at SW-03 and SW-04 have exceeded the background concentration for vanadium. The remaining sample locations have had concentrations reported as being less than the background concentration. Broad River Samples Aluminum was detected in the background sample SW-09 at concentrations ranging from 69.2 µg/L to 1,760 µg/L. The reported aluminum concentrations in the downgradient sample locations have been within the range of the reported background concentrations. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Boron has been detected in the background sample SW-09 at estimated concentrations less than the MRL (<50 µg/L). Concentrations of boron at SW- BRAB-01, SW-BRAB-02, and SW-BRAB-03 have exceeded the MRL (>50 µg/L) and background concentration range for boron. The remaining sample locations have had concentrations reported as being non-detectable. Chromium was detected in the background sample SW-09 at a concentration greater than the MDL (>1 µg/L). Sample locations SW-BRBG and SW-SBRBG have chromium concentrations below the MDL (<1 µg/L). Concentrations of chromium in the downgradient sample locations have been within the range of the reported background concentrations. Hexavalent chromium concentrations were reported as high as 0.12 µg/L at the background sample location SW-09. Concentrations of hexavalent chromium in eight of the nine downgradient sample locations are reported as being less than the background concentration. Locations SW-BRAB-01, SW-BRAB-02, SW- BRAB-03, SW-BRU14-01, and SW-BRU14-02 have reported values as being greater than the background concentration. The reported values range from 0.13 µg/L to 0.76 µg/L. Cobalt was reported in the background sample at concentrations ranging from 0.11 µg/L to 2.1 µg/L. Concentrations of cobalt at SW-BRAB-02 and SW-BRAB-03 have exceeded the background concentration range for cobalt. The remaining downgradient sample locations have been within the range of the reported background concentrations. Iron concentrations range from 225 µg/L to 2,190 µg/L at background sample locations. Concentrations of iron at SW-BRAB-01 have exceeded the background concentration range for iron. The remaining downgradient sample locations have been within the range of the reported background concentrations. Manganese concentrations range from 17.8 µg/L to 160 µg/L at background sample locations. Concentrations of manganese at SW-BRAB-01, SW-BRAB-02, and SW-BRAB-03 have exceeded the background concentration range for manganese. The remaining sample locations have had concentrations reported as being less than the background concentration range. Strontium concentrations range from 18.8 µg/L to 34 µg/L at the background sample locations. Concentrations of strontium at SW-BRAB-01, SW-BRAB-02, and SW-BRAB-03 have exceeded the background concentration range for strontium. The remaining downgradient sample locations have had concentrations reported as being less than the background concentration range. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Thallium was not detected in the background sample at a concentration greater than the MDL (<0.1 to <0.2 µg/L). Concentrations of thallium in SW-BRAB-02 and SW-BRAB-03 have exceeded the background concentration range for thallium. The remaining downgradient sample locations have been within the range of the reported background concentrations. Vanadium concentrations were reported at 0.43 µg/L to 5.5 µg/L at the background sample locations. All downgradient sample locations have been within the range of the reported background concentrations. Discussion of Surface Water Results 9.3 Suck Creek Suck Creek samples CCPSW-1 and CCPSW-2 were collected upstream of S-2 from Suck Creek and downgradient of the CCP Landfill. Surface water samples SW-3 and SW-4 were collected immediately downstream of SW-2 in Suck Creek. Water samples SW- SC-1, SW-SC-2, SW-SC-3, SW-SC-4, SW-SC-5, SW-SC-6, and SW-SC-7 were collected from Suck Creek in between background sample location SW-2 and the confluence with the Broad River to help determine potential routes of exposure and receptors related to the ash basins. The additional surface water samples were collected from Suck Creek and the Broad River near the stream/river bank most likely to be impacted by potentially contaminated groundwater discharge. Eight of nine Suck Creek samples had no 2B exceedances. Sample location SW-4 had two historical reported 2B exceedances of pH. The 2B exceedances of pH were less than the concentrations reported in background samples. Background sample CCPSW-1 had one 2B exceedance of mercury. All other downgradient sample locations had mercury concentrations less than concentrations reported in this background sample. Exceedances of the 2B standards were not reported in any of the surface water samples collected between SW-2 and SW-SC-7. Sample SW-4 is downgradient of the ash storage area; however, the historical sampling results show an inconsistency in pH values at this locations and do not suggest that the reported 2B exceedances in Suck Creek are a result of influence from the ash basin. Sample CCPSW-1 is located south of CSS, upgradient of the CCP landfill and all of the CSS ash basins. Because the historical mercury exceedances of the 2B standard in CCPSW-1 are upgradient of surface water and groundwater flow directions compared to CSS basins and the concentration of mercury is inconsistent compared with other historical and recent samples collected at this location, it is unlikely the exceedances are associated with the landfill or ash basins. Based on the available data for the upgradient and downgradient Suck Creek samples, the CSS ash basin is not the source of 2B exceedances in Suck Creek. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Broad River Water samples SW-BRU5-1, SW-BRU14-1, SW-BRU14-2, SW-BRU14-3, SW-BRAB-1, SW-BRAB-2, and SW-BRAB-3 were collected downstream of background samples SW- BRBG, SW-9, and SW-SBRBG from the Broad River to help determine potential routes of exposure and receptors related to the ash basins. The additional surface water samples were collected from the Broad River near the stream/river bank most likely to be impacted by potentially contaminated groundwater discharge. Four of seven downstream Broad River samples had no 2B exceedances. Sample location SW-4 had two historical reported 2B exceedances of pH. The 2B exceedances of pH were below the concentrations reported in background samples. Background sample CCPSW-1 had one 2B exceedance of mercury. All other downgradient sample locations had mercury concentrations less than concentrations reported in this background sample. Turbidity and TDS are the only 2B exceedances reported in the background (SW-9); and dissolved oxygen, dissolved cadmium and hardness are the only 2B exceedances reported downstream (SW-BRAB-1, SW-BRAB-2, and SW-BRAB-3) in samples collected from the Broad River. The background sample has had exceedances of parameters that are inconsistent with reported values and concentrations downstream. The Broad River background turbidity exceedance had a reported value of 44.9 NTUs and the background TDS exceedances had a reported concentration of 10,000 µg/L. The downstream samples do not have TDS exceedances and the only turbidity exceedance had a reported value of 34.6 NTUs at SW-BRAB-1. Sample SW-BRAB-1 also had two historical exceedances of dissolved oxygen at 0.29 µg/L and 0.20 µg/L. Samples SW- BRAB-2 and SW-BRAB-3 had dissolved cadmium concentrations which ranged from 0.17 µg/L to 0.18 µg/L. Hardness exceeding concentrations from these two locations had a range of 102 mg/L to 121 mg/L. These exceedances are inconsistent at each sample location and are not represented in other downstream locations. Based on the available data for the upstream and downstream Broad River samples, the CSS ash basins and ash storage area are not the source of 2B exceedances in the Broad River. Thallium concentrations were not reported in the Broad River background samples at concentrations greater than the MRL (<0.015 µg/L to <0.1 µg/L). Concentrations of thallium in SW-BRAB-2 and SW-BRAB-3 have exceeded the background concentration range. The remaining downgradient sample locations have been within the range of the reported background concentrations. Concentrations of thallium at SW-BRAB-2 have ranged from 0.48 µg/L to 0.61 µg/L and concentrations at SW-BRAB-3 have ranged from 0.43 µg/L to 0.56 µg/L. The concentrations in the upstream sample (SW-BRAB-2) have 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx been consistently greater than the downstream sample (SW-BRAB-3) during the sampling events. Surface water sample locations SW-BRAB-2 and SW-BRAB-3 are located immediately downstream of the permitted NPDES outfall 002, and downstream of the ash storage area and active ash basin. As shown on Figure 11-31 the extent of groundwater migration from the active ash basin and western portion of the ash storage area with thallium concentrations greater than background and the IMAC extend downgradient and potentially reach the Broad River in the shallow flow layer. Figure 9-1 shows the most recently available groundwater and surface water data for the areas located north of the ash storage area and the active ash basin downstream dam. In the shallow monitoring wells located closest to the bank of the Broad River and reporting from upstream to downstream well locations, thallium is reported at concentrations of <0.01 ug/L at GWA-28S, 0.12 µg/L at GWA-21S, <0.1 µg/L at MW-4D, 0.017 µg/L at MW-20D, and 0.024 µg/L at GWA-22S. The concentrations of thallium generally decrease in a downstream direction (west to east). The two surface water samples (SW-BRAB-2 and SW-BRAB-3) are located between monitoring wells MW-4D and MW-20D. Based on the reported thallium groundwater results in these monitoring wells, impacted groundwater emanating from the ash storage area or the active ash basin does not appear to be the source of the elevated thallium concentrations reported in the Broad River. Permitted NPDES Outfall 002 is located at the toe of the active ash basin downstream dam and upstream of surface water samples SW-BRAB-2 and SW-BRAB-3 generally in the location of monitoring well MW-4D. The ash basin water has been sampled at the former discharge structure of the outfall (SW-7 and active ash pond), and the results are presented on Appendix B, Table 3. Thallium results from this wastewater sample prior to entering the discharge structure has had thallium concentrations reported ranging from 0.49 µg/L to 1.5 µg/L. Based on this information, it is likely that the NPDES permitted outfall (002) is the source of elevated thallium concentrations reported in downstream samples collected from the Broad River. Piper diagrams for surface waters are included as Figure 9-2. A Piper diagram provides 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 9-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx A Piper diagram for surface water samples from Suck Creek and the Broad River are compared with data from background locations upgradient of CSS basins in Suck Creek and the Broad River is presented as Figure 9-2. Observations based on the diagram include: Surface water samples collected from Suck Creek are generally characterized as calcium-sodium-bicarbonate and show higher concentrations of chloride and sulfate compared to background locations. Downgradient surface water sample SW-SC-1 is located west of the southern extension of the active ash basin plots nearest background locations. From there, downstream samples SW-SC-2 through SW-SC-6 plot with higher relative concentrations of major water chemistry ions chloride and sulfate. The water chemistry type of these samples may indicate potential mixing from source water impacted groundwater. See Section 3.3 for piper discussion of ash pore water chemistry. Surface water samples collected from the Broad River are characterized as calcium-chloride-bicarbonate and are consistent with water chemistry results of background locations. Downgradient surface water sample SW-BRAB-3, located east of the active ash basin in the Broad River, plots away from other Broad River locations with higher concentration of chloride, calcium, and sodium. The water chemistry of this sample is similar to the water chemistry results of ash pore water and may be representative of mixing with the permitted NPDES discharge upgradient of this location. See Section 3.3 for Piper discussion of ash pore water chemistry. The water chemistry signature of Suck Creek locations is similar to the background surface water data at the Site, but higher relative concentration of major water ions chloride and sulfate, indicate that Suck Creek locations may have impact from source related water. The water chemistry signature of all Broad River locations, with the exception of location SW-BRAB-3, is similar to the background surface water data at the Site, indicating that these locations reflect natural background conditions. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 10.0 GROUNDWATER SAMPLING RESULTS This section provides a summary of groundwater analytical results for the most recent data available (3Q2017; August 2017) with discussion of historical data results and trends. Comprehensive tables with all media data is provided in Appendix B. A separate table is provided for the CCR monitoring network. 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 is shown on the pertinent maps. The most recently available CCR well data is also posted for completeness. One comprehensive round of CAMA sampling and analysis was conducted prior to, and reported in, the August 2015 CSA. In addition, the following CAMA groundwater sampling and analysis events have been completed: Round 2 - September 2015 (reported in the CAP Part 1) (HDR, 2015b) Round 3 - November 2015 (background wells only, reported in the CSA Supplement 1 as part of the CAP Part 2 report) (HDR, 2016b) Round 4 - December 2015 (background wells only, reported in the CSA Supplement 1 as part of the CAP Part 2) (HDR, 2016b) Round 5 – February, March and April 2016 (reported in the CSA Supplement 2) (HDR, 2016c) Round 6 – June and July 2016 Round 7 – September and October 2016 Round 8 - December 2016 Round 9 - February 2017 Round 10 - May 2017 Round 11 – August 2017 Groundwater sampling methods and the rationale for sampling locations were in general accordance with the procedures described in the Work Plan (HDR, 2014b) and are included in Appendix G. Variances from the proposed well installation locations, methods, quantities, and well designations are presented in Appendix G. Analytical 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx data reports are included in Appendix I. A background summary report for groundwater is included as Appendix H. 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 on the south side of the ash basins and the Site, north of McCraw Road and Duke Power Road (north of the topographic/hydrologic divide generally along McCraw Road/Duke Power Road) were upgradient and/or background. After the background wells were installed and sampled a sufficient number of times, statistical analysis was used to define background conditions for each flow layer. The following monitoring wells have been approved by NCDEQ as background monitoring wells (Zimmerman to Draovitch, July 7, 2017, Appendix A): BG-1S – Shallow CCPMW-1S – Shallow MW-30S – Shallow MW-32S – Shallow GWA-24S – Shallow GWA-25S – Shallow GWA-30S – Shallow BG-1D – Deep (transition zone) MW-24D – Deep (transition zone) MW-32D – Deep (transition zone) GWA-24D – Deep (transition zone) MW-32BR – Bedrock CCPMW-1D - Bedrock 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx MW-24DR – Bedrock GWA-24BR – Bedrock GWA-30BR – Bedrock MW-22BR – Bedrock MW-22DR – Bedrock Nine background (BG) monitoring wells (BG-1S/D/BR, BG-2D, MW-30S/D, and MW- 32S/D/BR) were 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-24D and MW-24DR), and the CCP Landfill background monitoring wells (CCPMW-1S and CCPMW-1D). 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. Elevated pH due to grout contamination negated the use of the data collected from monitoring wells BG-2D, MW-30D and BG-1BR. On October 17, 2017, monitoring well MW-30D was replaced with background monitoring well MW-30DA. On April 5, 2017, monitoring well BG-1BR was replaced with background monitoring well BG- 1BRA. Background Dataset Statistical Analysis 10.1.1 For CAMA evaluation purposes, 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 layers – shallow, deep, and bedrock. Well locations are presented on Figure 2-10. NCDEQ requested that the updated background groundwater dataset exclude data from the background data set due to one or more of the following conditions: 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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. Sample collection occurred less than 60 days after the previous sampling event. Non-detected results are greater than 2L/IMAC. 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) and provided to NCDEQ DWR for review. DWR calculated PBTVs based on the vetted background data in the letter to Duke Energy dated July 7, 2017, using the statistical methods document and provided concurrence/non-concurrence with Duke Energy’s calculated PBTVs for groundwater in an October 11, 2017 letter (Zimmerman to Draovitch, October 11, 2017, Appendix A). The PBTVs for naturally occurring concentrations of inorganic constituents in groundwater approved (initially), revised, and approved by NCDEQ DWR are provided in Table 10-1. The following sections summarize the refined background datasets with the NCDEQ DWR approved PBTVs. Shallow Flow Layer Seven monitoring wells - BG-1S, CCPMW-1S, MW-30S, MW-32S, GWA-24S, GWA-25S, and GWA-30S, are used to monitor background groundwater quality within the shallow flow layer. NCDEQ indicated in the July 7, 2017 letter that those shallow wells were retained for use in determination of PBTVs. The shallow flow layer dataset is presented in Appendix H, Table 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. NCDEQ DWR revised the iron PBTV from 765.3 ug/L to 684 ug/L, and the vanadium PBTV from 1.059 ug/L to 0.8 ug/L. The approved PBTVs for the shallow flow layer are provided in Table 10-1. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Deep Flow Layer Four monitoring wells - BG-1D, MW-24D, MW-32D, and GWA-24D - monitor background groundwater quality within the deep flow layer. NCDEQ indicated in the July 7, 2017 letter that those deep wells were retained for use in determination of PBTVs. The deep flow layer dataset is presented in Appendix H, Table 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 Upper Tolerance Limit (UTL) statistics. NCDEQ DWR revised the cobalt PBTV from 9.041 ug/L to 5.1 ug/L, and the iron PBTV from 559.7 ug/L to 515 ug/L. The PBTVs for the deep flow layer are presented in Table 10-1. Bedrock Flow Layer Seven monitoring wells - MW-32BR, CCPMW-1D, MW-24DR, GWA-24BR, GWA-30BR, MW-22BR, and MW-22DR - monitor background groundwater quality within the bedrock flow layer. NCDEQ indicated in the July 7, 2017 letter that those bedrock wells were retained for use in determination of PBTVs. The bedrock flow layer dataset is presented in Appendix H, Table 1. The background groundwater dataset meets the minimum requirement of 10 samples for all constituents. PBTVs were calculated for constituents monitored within the bedrock flow layer using formal UTL statistics. All of the calculated PBTVs were acceptable to NCDEQ DWR. The PBTVs for the bedrock flow layer are presented in Table 10-1. Summary The calculated groundwater PBTVs were less than their applicable 2L Standards or IMACs for all flow layers with the following exceptions: Cobalt in all flow layers (shallow PBTV of 10.65 µg/L, deep PBTV of 5.1 µg/L, and bedrock PBTV of 1.497 µg/L; IMAC = 1 µg/L) Iron in all flow layers (shallow PBTV of 684 µg/L, deep PBTV of 515 µg/L, and bedrock PBTV of 6,220 µg/L; 2L = 300 µg/L) Manganese in all flow layers (shallow PBTV of 168.8 µg/L, deep PBTV of 78.31 µg/L, bedrock PBTV of 89.4 µg/L; 2L = 50 µg/L) Vanadium in all flow layers (shallow PBTV of 0.8 µg/L, deep PBTV of 1.095 µg/L, and bedrock PBTV 0.37 µg/L; IMAC = 0.3 µg/L) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx pH in all flow layers (shallow PBTV range of 4.4 to 6.1 SU, deep PBTV range of 4.8 to 6.1 SU, bedrock PBTV range of 5.4 to 7.4 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). Cation –anion charge balance calculations are an indicator of data quality. Samples with a charge balance of greater than 10% are not included in the diagrams. Plots of shallow, deep and bedrock groundwater including background locations are shown for the active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin and ash storage area on Figure 10-1 through Figure 10-12. All background monitoring well locations are shown on Figure 2- 10. Background water types at CSS are consistent with findings from a five-year study of groundwater flow and quality conducted at four research stations in the Piedmont and Blue Ridge Physiographic Provinces of North Carolina, located in a similar geologic setting as the Site (Huffman et al., 2006). Samples collected from background wells at CSS generally indicate calcium-sodium-bicarbonate water. Downgradient Groundwater Concentrations 10.2 In order to best reflect current conditions at the site, the third quarter 2017 CAMA groundwater sample results are the focus for data evaluation in this report. Results 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx from prior events are incorporated in data evaluation and summarized as appropriate. The third quarter 2017 data is the primary dataset used for generating isoconcentration maps and graphical representation of data such as Piper diagrams. A data table for the CCR Rule monitoring network is also provided in Appendix B. The following evaluation focuses on CAMA CSA monitoring data. Monitoring wells AB-1S and CLMW-5S are located within the active ash basin downstream dam. AB-2S is located within the active ash basin upstream dam. IB-3 (abandoned) was located within the Units 1-4 inactive ash basin dam. U5-3S (abandoned), U5-3S-A (abandoned), and U5-4S are located in the Unit 5 inactive ash basin main dam, and U5-6S is located in the Unit 5 inactive ash basin saddle dam. These wells are located within the ash basin waste boundary. 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 11-1 through 11-45. 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. Active Ash Basin Arsenic No arsenic exceedances of the 2L standard were reported in the shallow, deep or bedrock flow layers for wells associated with active ash basin. Boron The leading edge of the boron plume in the shallow flow layer is located southwest of the basin and discharges to Suck Creek. The north end of the boron 2L exceedances plume intersects with the western portion of the ash storage area and extends toward the Broad River. In the eastern portion of the ash basin there is one boron exceedance located at the downstream dam at well MW-11S. In the deep flow layer, boron 2L 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx exceedances are limited to the west side of the basin at wells GWA-27D and GWA- 27DA, and the toe of the upstream dam, and north of the western branch of the active ash basin. All locations are within the compliance boundary. In the bedrock flow layer, boron is not reported in any of the wells at a concentration greater than the 2L standard. Boron is reported at a concentration greater than the PBTV at the toe of the upstream dam at GWA-20BR, west of the active ash basin at GWA-27BR and north and northeast of the downstream dam, near the Broad River at GWA-21BR and MW-20DR. The remaining bedrock downgradient well locations did not have boron detected. Chromium The extent of exceedances of chromium is confined to the shallow flow layer, at the downstream dam extending near or beyond the compliance boundary at MW-11S and GWA-22S. No chromium exceedances were reported in the deep or bedrock flow layer for wells associated with active ash basin. Hexavalent Chromium No hexavalent chromium exceedances of the total chromium 2L standard were reported in the shallow, deep or bedrock flow layers for wells associated with active ash basin. Cobalt Cobalt PBTVs for each flow layer are greater than the IMAC and are used as the comparative values to discuss cobalt exceedances. The extent of exceedances of cobalt in the shallow flow layer are all within the compliance boundary and are limited to north of the ash basin downstream dam at well GWA-21S, and southwest of the basin near the upstream dam, and south of the basin. Exceedances in the deep flow layer are all within the compliance boundary and located near the upstream dam along the southern and northern waste boundary, and one location north of the basin. Cobalt exceedances in the bedrock flow layer are reported southeast at GWA-24BR and north at MW-20DR of the ash basin. Iron Iron PBTVs for each flow layer are greater than the 2L and are used as the comparative values to discuss iron exceedances. Exceedances in the shallow flow layer are located near or beyond the compliance boundary at downgradient locations north and northeast at wells GWA-22S, GWA-21S, AB-1S, and CLMW-4, and west of the basin at the upstream dam at wells GWA-20S, MW-8S, and AB-2S. Iron exceedances of the 2L standard in the deep flow layer are located near or beyond the compliance boundary and are located north and northeast of the basin at wells AB-1D, GWA-22BRU, MW-4D and MW-20D, and at the upstream dam. In the bedrock flow layer, iron exceedances are within the waste boundary and near the upstream dam at well GWA-20BR. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Manganese Manganese PBTVs for each flow layer are greater than the 2L and are used as the comparative values to discuss manganese exceedances. Exceedances in the shallow flow layer are all within the compliance boundary and located within the southern portion of the active ash basin at CLMW-6, and at downgradient locations north and northeast of the basin at wells AB-1S, CLMW-4, CLMW-5S, GWA-21S and MW-11S, and west of the basin. Manganese exceedances in the deep flow layer near or beyond the compliance boundary were reported northwest of the active ash basin within the compliance boundary, and west and north of the basin. Manganese exceedances are also reported in the bedrock flow layer beneath the southern portion of active ash basin and near or beyond the compliance boundary at the upstream dam at well GWA-20BR, and north of the active ash basin at wells GWA-21BR, GWA-28BR, and MW-20DR. Strontium The extent of exceedances of strontium in the shallow flow layer is beneath the active ash basin within the waste boundary, at the waste boundary near the upstream dam, and near or beyond the compliance boundary north of the basin near the downstream dam. Exceedances of strontium in the deep flow layer are located northwest of the ash basin at the upstream dam at wells AB-1D, GWA-21BRU, GWA-22BRU, MW-4D, and MW-20D, and near or beyond the compliance boundary to the southwest. Bedrock flow layer exceedances are located near the upstream dam, and near or beyond the compliance boundary north of the downstream dam at wells GWA-21BR and MW- 20DR. Sulfate The extent of exceedances of sulfate is limited to the shallow flow layer, north of the active ash basin within the waste boundary, between the basin and the ash storage area. Sulfate exceedances were not detected in the deep or bedrock flow layers. Thallium The extent of exceedances of thallium in the shallow flow layer is within the compliance boundary to the west, and northwest of the active ash basin within the western ash storage area. Thallium exceedances are detected in the deep flow layer within the waste boundary at well GWA-20D and at the north end of the ash basin near the ash storage area. Thallium exceedances were not reported in the bedrock flow layer. TDS The extent of exceedances of TDS exceedances in the shallow flow layer are located north of the active ash basin within the waste boundary, between the basin and the ash storage area. TDS exceedances were reported in the deep flow layer northwest of the 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx active ash basin near the upstream dam within the compliance boundary. TDS exceedances were not reported in the bedrock flow layer. Vanadium The extent of exceedances of vanadium in the shallow flow layer is located beneath the basin, and north of the basin between the basin and the ash storage area. Vanadium exceedances in the deep flow layer are detected beneath the basin and at the upstream dam within the compliance boundary, and near or beyond the compliance boundary north and northeast of the basin and downstream dam. A vanadium concentration equal to the PBTV in the bedrock flow layer was reported at one well upgradient and east of the active ash basin. A vanadium exceedance was detected within the compliance boundary near the active ash basin downstream dam at well MW-21BR. Total Uranium There are no MCL exceedances of total uranium located in the shallow, deep or bedrock flow layers for wells associated with the active ash basin. Total Radium There are no MCL exceedances of total radium located in the shallow, deep or bedrock flow layers for wells associated with the active ash basin. Units 1-4 Inactive Ash Basin Arsenic Arsenic 2L exceedances in the shallow flow layer are limited one location north of the basin. There are no deep or bedrock flow layer exceedance of arsenic reported in wells associated with Units 1-4 inactive ash basin. Boron Downgradient boron exceedances of 2L in the shallow flow layer are isolated to one location, IB-3S, north of the ash basin at the compliance boundary. In the deep flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Units 1-4 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard upgradient to the basin at well GWA-14D, and downgradient of the basin. In the bedrock flow layer, boron is not reported in the monitoring wells adjacent to or beneath the former Units 1- 4 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard upgradient at wells GWA-13BR and GWA-33BR and beneath the basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Chromium The extent of exceedances of chromium in the shallow flow layer is located upgradient of the Units 1-4 inactive ash basin and at a location near or beyond the waste boundary north of the basin at wells GWA-14S and IB-3S. Chromium exceedances in the deep flow layer are located north of the basin, near and beyond the waste boundary at GWA- 11BRU and IB-3D. Chromium exceedances were not reported in the bedrock flow layer. Hexavalent Chromium No hexavalent chromium exceedances of the 2L standard were reported in the shallow, deep or bedrock flow layers for wells associated with Units 1-4 inactive ash basin. Cobalt Cobalt PBTVs for each flow layer are greater than the IMAC and are used as the comparative values to discuss cobalt exceedances. The extent of exceedances of cobalt in the shallow flow layer is limited to one well location beneath the Units 1-4 inactive ash basin at well IB-2AL. Cobalt exceedances were not reported in the deep or bedrock flow layers. Iron Iron PBTVs for each flow layer are greater than the 2L and are used as the comparative values to discuss iron exceedances. Exceedances in the shallow flow layer are located within the footprint of the ash basin, beyond the northern waste boundary, and upgradient of the waste boundary at well GWA-14S. The extent of iron exceedances in the deep flow layer are located beneath the ash basin at IB-3D and IB-4D, north and northwest, and upgradient of the waste boundary at wells GWA-33D, GWA-44D, and MW-23D. Iron exceedances were not reported in the bedrock flow layer. Manganese Manganese PBTVs for each flow layer are greater than the 2L and are used as the comparative values to discuss manganese exceedances. The extent of exceedances of manganese in the shallow is within the waste boundary, and near or beyond the waste boundary north and upgradient of the waste boundary at wells GWA-14S, GWA-38S, and GWA-33S. Exceedances of the manganese in the deep flow layer are located beneath the ash basin, at the northern waste boundary, and upgradient of the ash basin at wells GWA-33D and MW-23D. Manganese exceedances in the bedrock flow layer are located beneath the ash basin, and northeast of the waste boundary at well GWA- 29BRA, and upgradient of the waste boundary at wells GWA-13BR, GWA-33BR, and GWA-44BR. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Strontium Strontium does not have an established standard; therefore the PBTVs for each flow layer are used as the comparative values to discuss strontium exceedances. The extent of exceedances of strontium in the shallow is within the waste boundary, and near or beyond the waste boundary north, and upgradient of the waste boundary at wells GWA-14S, GWA-38S, and GWA-33S. Exceedances of the strontium in the deep flow layer are located beneath the ash basin, at the northern waste boundary, and upgradient of the ash basin at wells GWA-14D, GWA-33D, GWA-43D, GWA-44D, and MW-23D. Strontium exceedances in the bedrock flow layer are located beneath the ash basin, downgradient at well GWA-29BRA, and upgradient of the waste boundary at wells GWA-13BR, GWA-14BR, GWA-33BR, and GWA-44BR. Sulfate Sulfate exceedances in the shallow flow layer are located within the ash basin and upgradient of the waste boundary at well GWA-44S. In the deep flow layer 2L exceedances are reported upgradient of the waste boundary at wells GWA-44D and MW-23D. There is one sulfate 2L exceedance in the bedrock flow layer upgradient of the waste boundary at GWA-44BR. A separate source may be contributing to the exceedances of sulfate reported at GWA-44BR. Thallium Downgradient thallium exceedances of the IMAC in the shallow flow layer are located at the waste boundary northeast and northwest of the ash basin. There are no thallium exceedances of the IMAC in the deep or bedrock flow layer for wells associated with Units 1-4 inactive ash basin. TDS TDS 2L exceedances in the shallow flow layer are limited to within the footprint of the ash basin and not downgradient. The exceedances reported in the deep flow layer are upgradient of the waste boundary at wells GWA-44D and MW-23D. There is one TDS 2L exceedance in the bedrock flow layer upgradient of the basin at GWA-44BR. Vanadium Vanadium PBTVs for each flow layer are greater than the IMAC and are used as the comparative values to discuss vanadium exceedances. Exceedances in the shallow flow layer are located within the ash basin and north, near or beyond the waste boundary, at wells GWA-11S and CCR-IB-1S, and upgradient at well GWA-14S. Thallium exceedances in the deep flow layer are within the waste boundary and beyond the waste boundary at well CCR-IB-3D. Exceedances in the bedrock flow layer are reported 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-13 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx upgradient of the waste boundary at two isolated locations, GWA-14BR and GWA- 44BR. Total Uranium There are no shallow, deep or bedrock exceedances of total uranium reported in monitoring wells associated with Units 1-4 inactive ash basin Total Radium There are no shallow or deep exceedances of total radium reported in monitoring wells associated with Units 1-4 inactive ash basin. One exceedance in the bedrock flow layer is reported upgradient of the waste boundary at well GWA-44BR. Unit 5 Inactive Ash Basin Arsenic Arsenic exceedances were not reported in the shallow flow layer at the Unit 5 inactive ash basin. The extent of arsenic exceedances in the deep and bedrock flow layers is an isolated location beneath the western portion of the basin within the waste boundary at wells U5-2D and U5-2BR. Boron In the shallow flow layer, boron is not reported in the monitoring wells downgradient of the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron was reported at concentrations greater than the PBTV at wells within the basin, adjacent and downgradient to the basin. Boron in the deep flow layer is reported at a concentration greater than the PBTV and the 2L standard beneath the northern waste boundary, but not downgradient of the basin. In the deep flow layer one 2L exceedance is reported downgradient and north of the ash basin at the waste boundary. Boron is reported at concentrations greater than the PBTV but less than the 2L standard at U5-2D, U5-3D, U5-5D, U5-6D, and U5-7D located beneath the basin and locations either sidegradient or downgradient of the basin. In the bedrock flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV beneath the basin and downgradient of the basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-14 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Chromium Chromium exceedances in the shallow flow layer is limited to an isolated location east of and sidegradient of the Unit 5 inactive ash basin, beyond the waste boundary, at well MW-42S. Chromium exceedances in the deep flow layer were detected within the waste boundary and near or beyond the eastern waste boundary. Chromium exceedances were not reported in the bedrock flow layer. Hexavalent Chromium No hexavalent chromium exceedances of the 2L standard were reported in the shallow, deep or bedrock flow layers for wells associated with Unit 5 inactive ash basin. Cobalt Cobalt PBTVs for each flow layer are greater than the IMAC and are used as the comparative values to discuss cobalt exceedances. Cobalt exceedances were reported in the shallow flow layer within the waste boundary, north, northeast, and southeast of the basin. Exceedances of the deep flow layer PBTV are located within the waste boundary, and to the northeast beyond the waste boundary, and in the southeast at the waste boundary. In the bedrock layer exceedances are beneath the basin within the waste boundary and at the northern waste boundary. Iron Iron PBTVs for each flow layer are greater than the 2L and are used as the comparative values to discuss iron exceedances. Iron exceedances in the shallow flow layer are located within the waste boundary of the ash basin and at downgradient locations northeast and northwest of the ash basin at wells GWA-4S, GWA-35S, GWA-36S, and GWA-37S. Exceedances of the deep flow layer are located in the northeast and northwest beneath the ash basin and beyond the waste boundary at wells GWA-1BRU, GWA-4D, GWA-35D, GWA-36D, and MW-34BRU. One iron exceedance was reported south of and upgradient of the basin, beyond the waste boundary in the bedrock flow layer at well GWA-30BR. Manganese The extent of exceedances of manganese in the shallow flow layer is within the waste boundary, and north and east, near or beyond the waste boundary at wells GWA-2S, GWA-4S, GWA-5S, GWA-35S, GWA-36S, GWA-37S, GWA-45S, and MW-38S. Manganese exceedances in the deep flow layer are located beneath the basin, and north, west, and east of the basin, near or beyond the waste boundary at wells GWA-1BRU, GWA-2BRU, GWA-3D, GWA-4D, GWA-5BRU, GWA-31D, GWA-35D, GWA-36D and MW-38D. Manganese in the bedrock flow layer is detected beneath the basin, and at one location northeast of the ash basin beyond the waste boundary at well MW-38BR. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-15 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Strontium Strontium does not have an established standard; therefore the PBTVs for each flow layer are used as the comparative values to discuss strontium exceedances. The extent of exceedances of strontium in the shallow flow layer are located within the Unit 5 inactive ash basin, and at locations near and beyond the waste boundary east and north of the basin at wells GWA-2S, GWA-35S, GWA-36S, GWA-37S, MW-36S, and MW-38S, including locations sidegradient of the basin at wells GWA-4S, GWA-5S, GWA-45S, MW-42S. Strontium exceedances in the deep flow layer are located beneath the basin and at locations west, north and east of the basin, near and beyond the waste boundary at wells GWA-2BRU, GWA-3D, GWA-4D, GWA-5BRU, GWA-31D, GWA-35D, GWA- 36D, GWA-37D, MW-34BRU, MW-37BRU, MW-38D and MW-40BRU. In the bedrock flow layer strontium exceedances are reported beneath the basin and beyond the waste boundary, northeast of the ash basin at one location, MW-38BR. Sulfate The extent of exceedances of sulfate in the shallow flow layer is within, near, and beyond the waste boundary southeast of the ash basin. Sulfate exceedances are detected east and north of the Unit 5 inactive ash basin, near and beyond the waste boundary in the deep flow layer. An isolated sulfate exceedance is reported in the bedrock flow layer, beyond the waste boundary north of the basin at well MW-38BR. Thallium The exceedances of thallium in the shallow flow layer are located near and beyond the waste boundary, north and east of the Unit 5 inactive ash basin. Thallium in the deep flow layer is detected near or beyond the northern and eastern waste boundaries. A thallium exceedance in the bedrock flow layer is reported at isolated location beneath the western portion of the basin at U5-2BR. TDS The extent of exceedances of TDS in the shallow flow layer is near and beyond the waste boundary, east of the Unit 5 inactive ash basin. TDS exceedances in the deep flow layer are located near and beyond the waste boundary, east and north of the basin. An isolated TDS exceedance in the bedrock flow layer was reported north of ash basin, beyond the waste boundary at well MW-38BR. Vanadium The vanadium PBTVs for each flow layer are greater than the IMAC and are used as the comparative values to discuss vanadium exceedances. The extent of exceedances of vanadium in the shallow flow layer are located within the waste boundary, north of the Unit 5 inactive as basin near or beyond the waste boundary, and northeast of the basin, 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-16 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx near and beyond the waste boundary. Vanadium exceedances in the deep flow layer are located beneath the basin, and southeast, northeast, north and northwest, near and beyond the waste boundary. Exceedances of vanadium in the bedrock flow layer are limited to an isolated area northeast of the basin, near or beyond the waste boundary. Total Uranium There are no shallow, deep or bedrock MCL exceedances of total uranium reported in wells associated with Units 5 inactive ash basin. Total Radium There are no shallow, deep or bedrock MCL exceedances of total radium reported in wells associated with Units 5 inactive ash basin. Ash Storage Area Arsenic No arsenic exceedances of the 2L standard were reported in the shallow, deep or bedrock flow layers for wells associated with the ash storage area. Boron Boron exceedances in the shallow flow layer are located within the waste boundary of the western portion of the ash storage and north of the western portion of the ash storage area at well AS-2S. Boron 2L exceedances in the shallow flow layer are not reported in the eastern portion of the ash storage area with one exception at the southern waste boundary. In the deep flow layer, boron 2L exceedances are limited to monitoring well AS-7D, located beneath the western portion of the ash storage area. Monitoring well AS-2D is downgradient of this location prior to the Broad River and the compliance boundary and the boron concentration is reported at greater than the PBTV and less than the 2L standard. In the bedrock flow layer, boron is not reported in any of the wells at a concentration greater than the 2L standard but is reported at a concentration greater than the PBTV downgradient of the western portion of the ash storage area at AS-2BR. Boron was not detected in the remaining bedrock downgradient wells. Chromium Chromium exceedances are limited to one location within the western ash storage area waste boundary in the shallow flow layer. Chromium exceedances were not detected in the deep or bedrock flow layers associated with the ash storage area. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-17 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Hexavalent Chromium No hexavalent chromium exceedances of the 2L standard were reported in the shallow, deep or bedrock flow layers for wells associated with the ash storage area. Cobalt Cobalt PBTVs for each flow layer are greater than the IMAC and are used as the comparative values to discuss cobalt exceedances. The extent of exceedances of cobalt exceedances in the shallow flow layer is located within the western portion of the ash storage area, and near or beyond the waste boundary but within the compliance boundary at wells AS-2S, CLMW-2 and CLMW-3S. Cobalt exceedances were not detected in the deep flow layer. No cobalt exceedances of the PBTV were reported in the deep flow layer. An isolated exceedance in the bedrock flow layer was reported beyond the waste boundary and within the compliance boundary downgradient of the western portion of the ash storage area at well MW-2DA. Iron No iron exceedances were reported in the shallow, deep or bedrock flow layers for wells associated with the ash storage area. Manganese Manganese PBTVs for each flow layer are greater than the 2L standard and are used as the comparative values to discuss manganese exceedances. Exceedances in the shallow flow layer are limited to within the waste boundary of the ash storage area and at the northern waste boundary at wells AS-2S, CLMW-1, CLMW-2, and CLMW-3S. Manganese exceedances in the deep flow layer are located within the western portion of the waste boundary and near or beyond the waste boundary at well AS-2D. In the bedrock flow layer exceedances are located primarily within the western portion of the ash storage area and northwest of the ash storage area at wells AS-2BR and MW-2DA. Strontium Strontium does not have an established 2L standard; therefore the PBTVs for each flow layer are used as the comparative values to discuss strontium exceedances. The extent of exceedances in the shallow flow layer are located within the waste boundary and downgradient along the west, northwest waste boundary at AS-2S, CLMW-1, CLMW-2 and CLMW-3S. Exceedances of strontium in the deep flow layer are located beneath the western portion of the ash storage area and along the west, northwest waste boundary at AS-2D and CLMW-3D. Exceedances of the strontium PBTV in the bedrock flow layer are located beneath the western portion of the ash storage area and downgradient beyond the waste boundary, northwest of the ash storage area at well AS-2BR. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-18 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Sulfate Sulfate 2L exceedances in the shallow flow layer are within the waste boundary of the western portion of the ash storage area and downgradient along the northwest waste boundary at AS-2S. There are no reported 2L exceedances of sulfate in the deep and bedrock flow layers at the ash storage area. Thallium Thallium IMAC exceedances in the shallow flow layer are limited to within the footprint of the western portion of the ash storage area and downgradient along the northwest waste boundary at AS-2S, CLMW-1, CLMW-2, and CLMW-3S. Thallium exceedances in the deep flow layer are isolated to one location, within the waste boundary, beneath the ash storage area. There are no exceedances of the thallium in the bedrock flow layer at the ash storage area. TDS Exceedances of TDS in the shallow flow layer are limited to within the waste boundary of the western portion of the ash storage area and downgradient along the northwest waste boundary at AS-2S. There are no reported 2L exceedances of TDS in the deep or bedrock flow layers at the ash storage area. Vanadium Vanadium PBTVs for each flow layer are greater than the IMAC and are used as the comparative values to discuss vanadium exceedances. Exceedances in the shallow flow layer are limited to within the footprint of the eastern portion of the ash storage area and not downgradient. There are no reported PBTV exceedances of vanadium in the deep flow layer at the ash storage area. Exceedances in the bedrock flow layer are located beneath the eastern ash storage area northern waste boundary and northwest of the western ash storage area at wells AS-2BR and MW-2DA. Total Uranium There are no shallow, deep or bedrock MCL exceedances of total uranium reported in wells associated with the ash storage area. Total Radium There are no shallow, deep or bedrock MCL exceedances of total radium reported in wells associated with the ash storage area. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-19 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Non-CAMA Related Source Area An additional area of exceedances that appears not to be associated with the identified source areas (active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage area), is located east of Unit 6 and west of Suck Creek. In the shallow flow layer, cobalt, iron, and manganese were reported at concentrations greater than the PBTV and 2L/IMAC at GWA-33S. Strontium was reported at a concentration greater than the PBTV in GWA-44S, MW-23S, GWA-33S, and GWA-43S. Sulfate and TDS 2L exceedances were reported in GWA-44S. In the deep flow layer, to the East of Unit 6 and west of Suck Creek, boron was reported in MW-23D at a concentration (54.1 ug/L) greater than the PBTV of 50 ug/L. Iron and manganese were reported at concentrations greater than PBTV and 2L at GWA-44D, MW-23D, and GWA-33D. Strontium was reported at a concentration greater than the PBTV in GWA-44D, MW-23D, GWA-33D, and GWA-43D. Sulfate and TDS 2L exceedances were reported in GWA-44D and MW-23D. In the bedrock flow layer, boron was reported in GWA-44BR (51.8 ug/L) and GWA-33 BR (79.8 ug/L) greater than the PBTV of 50 ug/L. A cobalt PBTV/IMAC exceedance was reported in GWA-44BR. Manganese was reported greater than the PBTV/2L at GWA- 44BR, MW-23DR, and GWA-33BR. Strontium was reported at a concentration greater than the PBTV at GWA-44BR and GWA-33BR. Sulfate and TDS 2L exceedances were reported in GWA-44BR. Vanadium was reported at a concentration greater than the PBTV and IMA at GWA-44BR. Piper Diagrams (Comparison to Downgradient/ 10.2.1 Separate Flow Regime) An 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 CSS for the active ash basin, Units 1-4 inactive ash basin and Unit 5 inactive ash basin resembles bituminous coal ash leachate water from EPRI’s study, which describes the water as a calcium-sodium-calcium-sulfate (EPRI, 2012). In comparison, CSS ash pore water from AB-4SL and U5-7S have elevated bicarbonate component relative to sulfate and chloride. See Section 3.3 for Piper discussion of ash pore water chemistry. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-20 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Active Ash Basin Shallow downgradient locations characterized by sodium-calcium-chloride to sodium-calcium-sulfate water chemistry type include: GWA-20S, GWA-21S, GWA-22S, GWA-26S, GWA-28S, MW-8S, MW-10S and MW-11S. All of those locations, with the exception of MW-11S had boron concentrations less than 700 µg/L for the most recent sample results available. MW-11S indicates potential mixing between background and impacted water. Upgradient location GWA- 26S and downgradient location GWA-28S contained boron concentrations below the detection limit of 50 µg/L for the most recent sample results available. These locations are characterized as calcium-sodium-bicarbonate type and are consistent with background water chemistry indicating little influence from source areas or a high degree of mixing with background groundwater. Deep groundwater locations characterized by sodium-chloride-bicarbonate to sodium-chloride-calcium water chemistry type include: AB-1D, AB-2D, AB-4D, CCR-12D, CCR-13D, CCR-15D, GWA-20D, GWA-27DA, GWA-47D, MW-10D and MW-20D. Location AB-4D is located beneath the basin but is the only sample with boron concentrations less than the detection limit of 50 µg/L for the most recent sample results available and is characterized as chloride-sodium- bicarbonate. The unique water chemistry signature and the lack of boron detection may indicate groundwater beneath the basin in the deep layer is unimpacted. GWA-27DA is located southeast of the basin and is the only location with boron concentrations greater than 700 µg/L for the most recent sample results available. The water chemistry of this location is similar to ash pore water chemistry indicating potential mixing between background groundwater and impacted groundwater. Bedrock downgradient locations AB-4BR, AB-06BR, BG-1BR, GWA-21BR, GWA- 27BR, GWA-28BR, GWA-48BR, MW-20DR and MW-21BR are characterized as calcium-potassium-bicarbonate type water, consistent with background groundwater in the bedrock flow layer. AB-06BR, BG-1BR, GWA-28BR, GWA- 48BR and MW-21BR had boron concentrations less than the detection limit of 50 µg/L and no locations had boron concentrations greater than 700 µg/L for the most recent sample results available. No bedrock locations are characterized as sodium-calcium-sulfate type water which indicates bedrock groundwater at these locations is unimpacted by source groundwater. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-21 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Units 1-4 Inactive Ash basin Shallow downgradient locations characterized by chloride-calcium-sulfate water chemistry type include: GWA-10S, GWA-11S, GWA-12S, GWA-33S, GWA-38S, GWA-43S, GWA-44S, and MW-23S. Monitoring wells GWA-12S, GWA-33S, GWA-44S, and MW-23S indicated boron concentrations below the detection limit of 50 µg/L for the most recent sample results available. Well GWA-12S, located northeast of the basin, shows water chemistry most similar to background well GWA-30S, located south of the basin, indicating little influence from source at this location. Monitoring wells GWA-10S, GWA-11S, GWA-38S, and GWA-43S contained boron concentrations less than 700 µg/L for the most recent sample results available. The water chemistry of those wells indicates potential mixing between background and impacted water. Deep groundwater locations characterized by calcium-sulfate-bicarbonate water chemistry type include: CCR-IB-1D, CCR-IB-3D, GWA-10D, GWA-14D, GWA- 29D, GWA-33D, GWA-43D, GWA-44D, IB-1D, IB-3D, and MW-23D. Locations CCR-IB-1D, GWA-10D, GWA-29D, GWA-33D, GWA-43D, GWA-44D, and IB-1D indicated boron concentrations below the detection limit of 50 µg/L for the most recent sample results available and shows water chemistry most similar to background well MW-32D, located south of the basin, indicating little influence from source groundwater at these locations. Locations CCR-IB-3D, GWA-14D, IB-3D, and MW-23D contained boron concentrations less than 700 µg/L for the most recent sample results available. The water chemistry of those wells indicates potential mixing between background and impacted water. Bedrock downgradient locations GWA-13BR, GWA-29BRA, GWA-33BR, GWA- 44BR, IB-4BR, and MW-23DR are characterized as calcium-sulfate to calcium- bicarbonate type water. Water chemistry from background bedrock monitoring wells is characterized as calcium bicarbonate with less percent calcium than downgradient and ash pore water wells. GWA-29BRAand MW-23DR had boron concentrations below the detection limit of 50 µg/L and show water chemistry similar to that of background wells indicating bedrock groundwater at these locations is not impacted by source groundwater. GWA-33BR, GWA-44BR, and IB-4BR locations had boron concentrations less than 700 µg/L for the most recent sample results available. Location GWA-44BR shows water chemistry within range of wells screened in ash pore water within Units 1-4 inactive basin indicating bedrock groundwater at this location may be impacted by source groundwater. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-22 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Unit 5 Inactive Ash Basin Shallow downgradient locations characterized by sulfate-calcium-magnesium to sulfate-calcium-bicarbonate water chemistry type include: GWA-2S, GWA-5S, GWA-34S, GWA-35S, GWA-45S, MW-36S, MW-38S, MW-40S, and MW-42S. Monitoring wells GWA-34S, GWA-45S, MW-40S and MW-42S indicated boron concentrations below the detection limit of 50 µg/L for the most recent sample results available. Well GWA-34S, located northwest of the basin, shows water chemistry most similar to background well GWA-30S, located south of the basin, indicating little influence from source northwest of the basin. Monitoring wells GWA-2S, GWA-35S, MW-36S, and MW-38S contained boron concentrations less than 700 µg/L for the most recent sample results available. The water chemistry of these wells are within range of ash pore water results from Unit 5 inactive basin, indicating potential mixing between background and impacted water. Deep groundwater locations characterized by calcium-sulfate-bicarbonate water chemistry type include: BG-2D , GWA-3D, GWA-31D, GWA-34BRU, GWA-35D, GWA-36D, MW-30D, MW-38D, U5-2D, U5-3D, U5-4D, U5-5D, U5-6D, U5-7D, and U5-8D. Locations BG-2D, GWA-34BRU, MW-30D, U5-4D, and U5-8D indicated boron concentrations below the detection limit of 50 µg/L for the most recent sample results available, and show water chemistry similar to background well MW-32D, located south of the basin, indicating there may be little influence from source groundwater at these locations. Locations GWA-3D, GWA-31D, GWA-35D, GWA-36D, MW-38D, U5-2D, U5-3D, U5-5D, U5-6D, and U5-7D contained boron concentrations less than 700 µg/L for the most recent sample results available. The general water chemistry of these wells, except GWA-35D, indicates there maybe be potential mixing between background and impacted water. Bedrock downgradient locations GWA-31BR, GWA-31BRA, MW-38BR, and U5- 2BR are characterized as calcium-sulfate to calcium-bicarbonate type water. Water chemistry from background bedrock monitoring wells is characterized as calcium-sodium-bicarbonate with less percent calcium than downgradient and ash pore water wells. GWA-31BR, GWA-31BRA, and MW-38BR, located east and northeast of the basin, had boron concentrations below the detection limit of 50 µg/L but show water chemistry similar to ash pore water wells. Monitoring well U5-2BR, located in bedrock beneath the basin, had boron concentrations less than 700 µg/L for the most recent sample results available but water chemistry results nearest background well water chemistry. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-23 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Ash Storage Area Shallow downgradient locations characterized by calcium-sulfate to calcium- bicarbonate water chemistry type include: AS-2S, AS-4S, AS-5S, AS-6S, CLMW-2, and CLMW-3D. Monitoring wells AS-4S, AS-5S, and AS-6S indicated boron concentrations below the detection limit of 50 µg/L for the most recent sample results available. These locations have higher percentages of bicarbonate than sulfate and show water chemistry most similar to background well GWA-30S, indicating little influence from source at these locations. Well AS-2S contained boron concentrations greater than 700 µg/L, and wells CLMW-2 and CLMW-3D contained boron concentrations less than 700 µg/L for the most recent sample results available. The water chemistry of these wells indicates potential mixing between background and impacted water. Deep groundwater locations characterized by calcium-sulfate-bicarbonate water chemistry type include: AS-1D, AS-2D, AS-6D, and AS-7D. Monitoring well AS- 6D indicated boron concentrations below the detection limit of 50 µg/L for the most recent sample results available. This location has a higher percentage of bicarbonate than sulfate and shows water chemistry most similar to background well MW-32D, indicating little influence from source at these location. Well AS- 7D contained boron concentrations greater than 700 µg/L, and wells AS-1D and AS-2D contained boron concentrations less than 700 µg/L for the most recent sample results available. The water chemistry of these wells indicates potential mixing between background and impacted water. Bedrock downgradient locations AS-2BR, AS-5BR, AS-6BRA, MW-2DA, and MW-25DR are characterized as calcium-sulfate to calcium-bicarbonate type water. Water chemistry from background bedrock monitoring wells is generally characterized as calcium bicarbonate with a lower percentage of calcium than at downgradient and ash pore water wells. AS-5BR, AS-6BRA, MW-2DA, and MW- 25DR had boron concentrations less than the detection limit of 50 µg/L and show water chemistry similar to background wells. The AS-2BR location had boron concentrations less than 700 µg/L for the most recent sample results available, but shows water chemistry similar to background bedrock groundwater. No bedrock locations are characterized as sodium-calcium-sulfate type water, indicating bedrock groundwater at these locations is not impacted by source groundwater. Piper diagrams for shallow, deep, and bedrock well data from the active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-24 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx area compared with data from background shallow, deep and bedrock monitoring wells are presented as Figure 10-1 to Figure 10-12. 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 which constituents 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, 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 CSS was submitted to NCDEQ on September 5, 2017 (SynTerra, 2017). A list of NCDEQ-approved groundwater PBTVs were provided to Duke Energy on October 11, 2017 (Zimmerman to Draovitch; Appendix A). Revised proposed PBTVs for groundwater are included 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 basins, ash pore water, seeps, soil, and groundwater 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-25 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 public interest associated with drinking water supply wells. As directed by the July 14, 2017 NCDEQ correspondence, a comparative value of 10 µg/L is used for both total and hexavalent chromium. NCDEQ also requested that uranium and radium be included as COIs at each CAMA-related site. Molybdenum and strontium do not have 2L standards, IMACs, or 2B standards established; however, those constituents are considered potential contaminants of concern with regard 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 Sulfate Total dissolved solids (TDS) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-26 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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; however, they are included as part of the current Implementation Monitoring Plan (IMP). In addition, NCDEQ requested that vanadium be included. CSS Groundwater COIs 10.3.4 Exceedances of comparative values, the distribution of constituents in relation to the ash management areas, co-occurrence with CCR indicator constituents such as boron and sulfate, and likely migration directions based on groundwater flow direction are considered in determination of groundwater COIs. 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 CSS: 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-27 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Arsenic Boron Chromium (total) Chromium (hexavalent) Cobalt Iron Manganese pH Strontium Sulfate Thallium TDS Vanadium Total Uranium Total Radium Table 10-2 lists the COIs at CSS 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 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. 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 (14 wells), chromium (one 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 10-28 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx well), cobalt (two wells), iron (15 wells), manganese (four wells), and vanadium (four wells). Concentrations of analyzed constituents exceeded the 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 – 4 wells Barium – 14 wells Calcium – 9 wells Chromium (hexavalent) – 8 wells Chromium (total) – 1 well Copper – 11 wells Magnesium – 10 wells Lead – 4 wells Molybdenum – 1 well Manganese – 2 wells Selenium – 1 well Nickel – 2 wells Sulfate – 1 well Sodium – 6 wells Vanadium – 4 wells TDS – 1 well Zinc – 11 wells All of the private water supply wells are upgradient and the reported exceedances likely reflect natural variations or local groundwater conditions, well construction, and/or maintenance. It is also unknown if the water supply wells are constructed in bedrock (as assumed) or may be bored wells in the shallow (saprolite) or deep (transition zone) flow layers. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 11.0 HYDROGEOLOGICAL INVESTIGATION Results of the hydrological investigation summarized in this section are primary components of the Site Conceptual Model.1 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 data available (August 2017). Plume Physical Characterization 11.1 Boron is the primary CCR-derived constituent in groundwater and is detected at concentrations greater than the 2L standard beneath the active ash basin, the western portion of the ash storage area, the southeastern portion of the Units 1-4 inactive ash, and at limited locations at the Unit 5 inactive ash basin. 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 areas. The groundwater plume is defined as any location (in three-dimensional space) where groundwater quality is impacted by the ash basins or ash storage area. 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 source areas. The comprehensive groundwater data table (Appendix B, Table 1) and an understanding of groundwater flow dynamics and direction (Section 6.3, Figure 6-15 to 6-23) 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, 1 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. The data is posted to Duke Energy’s publicly accessible Internet site as required under the CCR rule. The most recent data available has been considered in this assessment for refinement of constituent distribution. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx potassium, sodium, total organic carbon (TOC), and zinc. Sporadic and low- concentration exceedances of these constituents in the groundwater data do not necessarily demonstrate horizontal or vertical distribution in groundwater that indicates impact from the ash basin. The horizontal extent of the plume in each flow layer is depicted in concentration isopleth maps (Figure 11-1 to 11-45). The maps use groundwater analytical data to spatially and visually define areas where groundwater concentrations are greater than 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. Active Ash Basin Boron is not reported at a concentration greater than the 2L standard in samples taken from the bedrock flow layer. Boron is reported at a concentration greater than the PBTV at GWA-20BR, located at the toe of the upstream dam. Boron is also reported at a concentration greater than the PBTV and less than the 2L standard at GWA-27BR, located west of the active ash basin, approximately halfway between the basin and Suck Creek. Boron is also reported at a concentration greater than the PBTV and less than the 2L standard at GWA-21BR and MW-20DR, located north and northeast of the active ash basin downstream dam, near the Broad River. The remaining bedrock downgradient wells did not have boron detected. In the deep flow layer, boron 2L exceedances are limited to monitoring well GWA- 27DA located on the west side of the active ash basin and monitoring wells GWA-20D and CCR-11D located at the toe of the active ash basin upstream dam. Both of these locations are located within the compliance boundary, and GWA-20D and CCR-11D are also located within the waste boundary. Both of those well locations are upstream of and the groundwater in this area flows towards Suck Creek prior to the compliance boundary. The leading edge of the boron plume in the shallow flow layer west of the ash basin is located southwest of the active ash basin. Groundwater was not encountered at monitoring well GWA-47D above refusal and the boron concentration in GWA-47D is less than the 2L standard. On the west side of the active ash basin, groundwater was not encountered above refusal during drilling activities at the CCR-14 location. The deep well at this location has 2L exceedances, and it is expected that shallow groundwater impacts would exist in the vicinity of this well flowing toward Suck 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Creek. At the upstream dam, the shallow boron groundwater plume terminates near the southern portion of the dam. The north end of the plume for boron 2L exceedances extends on the western side of the active ash basin and intersects with the western portion of the ash storage area. The leading edge of the plume in this location continues under the ash storage area toward the Broad River. In the eastern portion of the ash basin, there is one boron exceedance located at MW-11S at the downstream dam. Monitoring wells CLMW-4 and GWA-22S are downgradient of MW-11S and their concentrations are less than the 2L standard prior to the compliance boundary. As described in Section 6.0, there is no hydrogeologic confining unit at CSS; therefore, under these unconfined conditions, groundwater moves freely across each layer shown in a vertical gradient map (Figure 6-23). Figures 11-46 through 11-60 depict concentration versus distance for COIs in the shallow and deep flow layers from the source along a plume centerline to the north, downgradient of the downstream dam. Concentrations of each COI were measured from sampling in August 2017. The wells show consistent results 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 AB-4BR was used for the bedrock flow layer. At the dam, downgradient of the ash basin, AB-1S was used for the shallow flow layer; AB-1D was used for the deep flow layer. Well GWA-21BR was substituted for the bedrock flow layer as the intermediate point along the distance transect; no bedrock well location exists on the dam. Wells beyond the waste boundary but within the compliance boundary downgradient of the ash basin downstream dam are GWA- 21S for the shallow flow layer and GWA-21BRU for the deep flow layer and MW-20DR is substituted for the bedrock flow layer as the terminal point on the distance transect. While PBTVs could not be distinguished on these graphs because values differ by flow unit, the graphs show constituent concentrations in source areas and downgradient and the graphs aid in understanding plume distribution. Iron, sulfate and radium in the shallow flow layer, and pH, sulfate, and radium in the deep flow layer are the only COIs with net increasing trends. Boron, chromium, manganese, radium, strontium, and TDS all show increasing trends in the bedrock flow layer. The vertical extent of the plume is depicted in the cross-sectional views of the site (Figures 6-2 and 11-61 to 11-75). Cross-section A-A’ is a transect of the ash basin and the plume, along the plume centerline, from south to north including the downstream dam. There are 14 CAMA wells and one CCR well along the centerline. These wells 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx represent background, source area, and downgradient locations relative to the ash basin. Cross-section K-K’ is a transect of the ash basin and the plume, along the plume centerline, from southeast to northwest, including the upstream dam. There are 18 CAMA wells along this transect. These wells are background, source area, and downgradient locations relative to the ash basin. The well screens in the CAMA wells accurately monitor groundwater conditions. 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 active ash basin, extending into the transition zone north of the basin, beneath the upstream dam, and west of the basin. Boron concentrations are less than the 2L standard in the bedrock flow layer. In general, in areas downgradient of the dams, there are upward vertical gradients, as expected, due to the greater upstream heads as indicated by the upward vertical hydraulic gradient conditions encountered at monitoring wells GWA-21BRU to GWA- 21BR located north of the active ash basin downstream dam near the Broad River. Groundwater elevations are not available for the calculation of vertical gradients in the well clusters installed near and along the base of the upstream dam, northwest of the ash basin. A downward gradient exists within the bedrock below the ash basin, to the east and west of the northern portion of the ash basin. Upward hydraulic vertical gradients are observed upgradient, south, and southwest of the active ash basin. The horizontal and vertical extent of the boron plume has been defined at the active ash basin. 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. Units 1-4 Inactive Ash Basin For the bedrock flow layer, boron is not reported as being in the monitoring wells adjacent to or beneath the Units 1-4 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard at GWA-13BR, located upgradient and adjacent to the basin, and at IB- 4BR located beneath the basin. For the deep flow layer, boron is not reported as being in the monitoring wells adjacent to or beneath the Units 1-4 inactive ash basin at concentrations greater than the 2L 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard at GWA-14D, located upgradient and adjacent to the basin, and at CCR-IB- 3D and GWA-11BRU, located downgradient of the basin. For the shallow flow layer, boron was reported at monitoring well IB-3S, formerly located in the crest of the dam of the Units 1-4 inactive ash basin at a concentration greater than the 2L standard. The water in this well drains toward the Broad River. Boron was reported at concentrations greater than the PBTV but less than the 2L standard at wells adjacent to the basin. The leading edge of the boron plume in the shallow flow layer is north of the Units 1-4 inactive ash basin, beyond monitoring well GWA-11S, toward the Broad River. As described in Section 6.0, there is no hydrogeologic confining unit at CSS; therefore, under these unconfined conditions, groundwater moves freely across each layer shown in a vertical gradient map (Figure 6-23). Figures 11-46 through 11-60 show concentration versus distance for COIs in the shallow, deep, and bedrock flow layers from the source along a plume centerline to the northeast, downgradient of the basin. Concentrations of each COI were measured from sampling conducted September 2015 to August 2017. The wells show consistent results for each constituent represented. Within the source area, well IB-4S-SL was used for the shallow flow layer, well IB-4D was used for the deep flow layer and IB-4BR was used for the bedrock flow layer. At the waste boundary, downgradient of the ash basin, IB- 3S was used for the shallow flow layer; IB-3D was used for the deep flow layer. Wells furthest downgradient of the ash basin and nearest the Broad River but within the waste boundary are GWA-29D for the deep flow layer, GWA-29BRA for the bedrock flow layer. No shallow well location exists in the downgradient area. 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 the graphs aid in understanding plume distribution. Boron, chromium, cobalt, manganese, sulfate and thallium in the shallow flow layer show net increasing trends from source area to the waste boundary. No constituents show an increasing trend in the deep flow layer. Constituents pH and strontium show increasing trends in the bedrock flow layer. The vertical extent of the plume is shown in the cross-sectional views of the site (Figures 6-9 and 11-76 to 11-90). Cross-section H-H’ is a transect of the ash basin and the plume, along the plume centerline, from south to north. There are 11 CAMA wells along the centerline. Those wells represent background, source area, and downgradient locations relative to the ash basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The well screens in the CAMA wells accurately monitor groundwater conditions. The vertical extent of the plume does not extend into the transition zone or bedrock beneath or surrounding the Units 1-4 inactive ash basin at concentrations greater than the 2L standard. Groundwater elevations are not available for the calculation of vertical gradients in the deep to bedrock clusters installed near the basin. However, downward gradients are observed northeast and east downgradient of the basin, and upward gradient exists in upgradient areas, northwest and southwest of the basin. The horizontal and vertical extent of the boron plume has been defined at the Units 1-4 inactive ash basin. 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. Unit 5 Inactive Ash Basin In the bedrock flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard at U5-2BR, U5-4BR, and U5-5BR located beneath the basin and downgradient of the basin. For the deep flow layer, boron is not detected downgradient of the Unit 5 inactive ash basin at a concentration greater than the 2L standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard at U5-2D, U5-3D, U5-5D, and U5-7D located beneath the basin, and downgradient of the basin. For the shallow flow layer, boron is not reported as being in the monitoring wells downgradient of the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron was reported at concentrations greater than the PBTV but less than the 2L standard at wells adjacent to the basin and downgradient of the basin. The leading edge of the boron plume in the deep flow layer is north of the Unit 5 inactive ash basin, near the waste boundary. As described in Section 6.0, there is no hydrogeologic confining unit at CSS; therefore, under these unconfined conditions, groundwater moves freely across each layer shown in a vertical gradient map (Figure 6- 12). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Figures 11-46 through 11-60 depict concentration versus distance for COIs in the shallow, deep, and bedrock flow layers from the source along a plume centerline to the northeast, downgradient of the basin. Concentrations of each COI were measured from sampling June 2016 to August 2017. The wells used are consistent for each constituent represented. Within the source area, well U5-7SL was used for the shallow flow layer, well U5-2D was used for the deep flow layer, and U5-2BR was used for the bedrock flow layer. Downgradient, at the ash basin dam, U5-4S was used for the shallow flow layer; U5-4D was used for the deep flow layer. Wells farthest downgradient of the ash basin and nearest the Broad River but within the waste boundary are GWA-2S for the shallow flow layer, GWA-2BRU for the deep flow layer, and GWA-38BR for the bedrock flow layer. No shallow well location exists in the downgradient area. 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 the graphs aid in understanding plume distribution. TDS in the shallow flow layer is the only constituent that shows a net increasing trend from source area to downgradient. Radium, from the source area to downgradient of the basin, is the only constituent with an increasing trend in the deep flow layer. Chromium, pH, sulfate, strontium, and TDS show increasing trends, from source area to downgradient, in the bedrock flow layer. The vertical extent of the plume extent is shown in the cross-sectional views of the site (Figures 6-13 and 11-103 to 11-120). Cross-section L-L’ is a transect of the ash basin and the plume, along the plume centerline, from southeast to northwest. There are 10 CAMA wells along the centerline. Those wells represent background, source area, and downgradient locations relative to the ash basin. The well screens in the CAMA wells accurately monitor groundwater conditions. The vertical extent of the plume does not extend into the bedrock beneath or surrounding the Unit 5 inactive ash basin at concentrations greater than the 2L standard. In the shallow to deep flow layers, a general downward vertical hydraulic gradient exists within the ash basin and at surrounding locations, except at locations MW-37 and MW-38, where an upward gradient is observed. This upward gradient is probably due to the Broad River elevation. In the deep to bedrock flow layers there are greater downward gradients between well pairs. 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). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The horizontal and vertical extent of the boron plume has been defined at the Unit 5 inactive ash basin. 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. Ash Storage Area In the bedrock flow layer, boron is not reported in any of the wells at a concentration greater than the 2L standard. Boron is reported at a concentration greater than the PBTV at AS-2BR, located downgradient of the western portion of the ash storage area. The remaining bedrock downgradient wells did not have boron detected. In the deep flow layer, boron 2L exceedances are limited to monitoring well AS-7D, located beneath the western portion of the ash storage area. Monitoring well AS-2D is downgradient of this location before the Broad River and the compliance boundary and the boron concentration is reported at greater than the PBTV and less than the 2L standard. The leading edge of the boron plume in the shallow flow layer north of the ash storage area is located beyond monitoring well AS-2S, located north of the western portion of the ash storage area near the Broad River. Boron 2L exceedances are not reported as being in the eastern portion of the ash storage area with the exception of at monitoring well CCR-6S. As described in Section 6.0, there is no hydrogeologic confining unit at CSS; therefore, under these unconfined conditions, groundwater moves freely across each layer shown in a vertical gradient map (Figure 6-12). Figures 11-46 through 11-60 depict concentration versus distance for COIs in the shallow, deep and bedrock flow layers from the source along a plume centerline to the northeast, downgradient of the basin. Concentrations of each COI were measured from sampling conducted July 2017 to August 2017. The wells used are consistent for each constituent represented. Within the source area, well CCR-7S was used for the shallow flow layer, well CCR-7D was used for the deep flow layer and AS-6BRA was used for the bedrock flow layer. Outside the waste boundary but within the compliance boundary, no shallow well location exists in the downgradient area, but AS-7D was used for the deep flow layer and MW-2DA was used for the bedrock flow layer. Wells farthest downgradient of the ash basin and nearest the Broad River are AS-2S for the 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx shallow flow layer, AS-2D for the deep flow layer and AS-2BR 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. Arsenic, chromium and cobalt in the shallow flow layer show a net increasing trend from source area to downgradient. Arsenic, cobalt, iron, pH, sulfate, strontium and TDS show an increasing trend in the deep flow layer. Arsenic, boron, pH, sulfate, strontium, TDS, thallium and uranium show increasing trends, from source area to downgradient, in the bedrock flow layer. The well screens in the CAMA wells accurately monitor groundwater condition. The vertical extent of the plume is best represented by groundwater concentrations in bedrock wells beneath and downgradient of the ash basin. Boron is not present in the bedrock flow layer beneath or downgradient of the ash storage area. A downward gradient exists between the shallow and deep flow layers at all locations within and surrounding the basin, except at AS-4 located in the basin. In the deep to bedrock flow layers, the largest downward gradient of the Site exists at AS-5. Groundwater and the plume migrate from the impacted groundwater in the active ash basin to the western portion of the ash storage area. Saturated ash in the vicinity of monitoring well location AS-7 appears to contribute to the concentration of some COIs (e.g., boron). The horizontal and vertical extent of the boron plume has been defined at the ash storage area. 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. Transects planned for use in the geochemical model are slightly different than those shown in cross-section on current figures. Transects used for geochemical modeling are planned to focus on specific areas of interest to optimize geochemical evaluation. Details of the geochemical model are further discussed in Section 13. A description of each planned transect, purpose for the transect, and data inventory for each of the four chosen flow transects for the geochemical model is detailed in subsections to follow. The proposed geochemical flow transects are shown on Figure 11-121. Data inventory associated with the geochemical flow transects is summarized on Table 11-1. An asterisk (*) indicates the well was installed in ash pore water. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Unit 5 Inactive Ash Basin Transect Wells that comprise the Unit 5 inactive ash basin transects for geochemical modeling begin at two different source well locations and converge downgradient as follows: From the west — U5-2S-SLA*/D/BR and GWA-2S/BRU/BR From the east — U5-7S*/SL*/D, CCR-U5-4S/D, and GWA-2S/BRU/BR This flow transect consist of three wells screened within the ash pore water, two within the shallow flow layer, four within the deep flow layer, and two within the bedrock flow layer. Groundwater in the Unit 5 inactive ash basin generally trends north funneling downgradient, toward the wetlands area adjacent to the Broad River. The highest concentrations for most COIs are located at the two source area well clusters, U5-2 and U5-7, with concentrations generally decreasing below the 2L beyond the waste boundary. One notable exception is seen at CCR-U5-4D which has the highest concentration of boron for this source area. Of the 11 wells along the two centerlines of flow for this source area, two wells have zero valid sampling events (GWA-2BR and U5-2S-SLA*) and one well has four valid sampling events (U5-7D). There are 10 wells located perpendicular to the proposed centerlines of flow for the Unit 5 inactive ash basin. Of those 10 wells, two are screened within the shallow flow layer, five within the deep flow layer, and three within the bedrock flow layer. All wells within the surficial and deep flow layers have at least five valid sampling events. Two of the three bedrock wells (U5-5BR and U5-4BRA) have had zero valid sampling events as of August 2017. Active Ash Basin- West Transect The wells that comprise the active ash basin-west transect, beginning upgradient and continuing downgradient along the flow path are as follows: GWA-27DA, CCR-12S/D, AB-2S/D/BRO, and GWA-20S/D/BR. In the active ash basin, groundwater trends down three different fingers of the waste boundary, westward toward Suck Creek, north toward the ash storage area, or northeast toward the ponded portion of the active ash basin. Three geochemical flow transects were chosen for the active ash basin to account for the three primary flow paths associated with this source area. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Along the western waste boundary of the active ash basin, groundwater flow trends westward toward Suck Creek, before ultimately flowing north towards the Broad River. The active ash basin - west transect begins at two sidegradient wells with elevated concentrations of several COIs. Maximum concentrations of boron along this flow path are located at CCR-12S for the shallow flow layer, GWA-27DA for the deep flow layer, and GWA-27BR for the bedrock flow layer. Concentrations of COIs generally decrease at downgradient locations at and below the upstream dam. This flow transect consist of ten wells: three wells screened in the shallow flow layer, four screened within the deep flow layer, and three within the bedrock flow layer. Of these ten wells, four have had less than five valid groundwater sampling events: GWA- 27BR with four valid sampling events, GWA-20BR with two valid sampling events, CCR-12D with one valid sampling event, and AB-2BRO which was recently installed and was not sampled prior to August 2017. Ash Storage Area Transect The wells that comprise the ash storage area transect, beginning at a source wells and continuing downgradient along the flow path are as follows: AB-3S*/SLA*/I/BRUA/BR, CCR-7S/D, AS-1SB/D, AS-7S*/D/BRA, and AS-2S/D/BR. The highest concentration of boron for both the shallow and deep flow layers along the ash storage area transect are at the CCR-7 well cluster, with concentrations generally decreasing downgradient along the flow path. A notable exception to this descreasing trend occurs at the AS-7 well cluster just beneath the ash storage area. Coal ash was observed at variable vertical extents within the overburden at wells along this transect. Beginning at the source well and continuing downgradient the total vertical length of ash in borings along the transect are as follows: approximately 70 feet at AB-3, no ash at CCR-7, 25 feet at AS-1, 40 feet at AS-7, and no ash at AS-2. This heterogeneous nature of the ash storage area can account for minor fluctuations in concentrations along the flow path. The geochemical transect used in the 1-D PHREEQC transport model for the ash storage area transect will begin at the CCR-7 well pair, as it represents an end member location with elevated concentrations of CCR within the shallow and deep flow units. The ash storage area transect consist of three wells screened in ash pore water, four screened within the shallow flow layer, five within the deep flow layer, and three within the bedrock flow layer. Of these 15 wells, five have less than five valid sampling events as of August 2017: AS-2BR with two valid sampling events and AB-3SLA*, AB- 3BRUA, AB-3BR and AS-7BRA with no valid sampling event. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx There are 12 wells perpendicular to the centerline of flow for the ash storage area transect. Of these 12 wells, six are screened within the shallow flow layer, three within the deep flow layer, and three within the bedrock flow layer. All but two wells (AS-5BR and GWA-29BRA) along this transect have at least five valid sampling events. For AS- 5BR, four of the seven total sampling events had pH values greater than 9.0, however, the last three sampling events have revealed no issues with pH. GWA-29BRA, with one valid sampling event, was recently installed and has only been sampled once as of August 2017. Active Ash Basin- East Transect The active ash basin- east transect consists of AB-1S/D/BRO and GWA-21S/BRU/BR. The eastern finger of the active ash basin is ponded, with the downstream dam located parallel to the Broad River in the northeast portion of the active basin. With the source wells upgradient limited by the ponded portion of the active ash basin and only a narrow strip of land available between the toe of the dam and the Broad River, the active ash basin- east transect is made up of six wells at two locations. Of these six wells, two are screened in the shallow flow layer, two within the deep flow layer, and two within the bedrock flow layer. All wells along this flow transect have at least eight valid sampling events to date with the exception of the recently installed bedrock well, AB-1BRO which had not been installed as of August 2017. There are 12 wells perpendicular to the centerline of flow for the active ash basin- east transect. Of these 12 wells, three are screened within the shallow flow layer, five within the deep flow layer, and four within the bedrock flow layer. Four of these wells contain less than five valid sampling events as of August 2017. Plume Chemical Characterization 11.2 Plume chemical characterization is detailed below for each COI. Analytical results are based on the most recent groundwater sampling event for which data are available. The range of detected concentrations is presented with the number of detections for the sampling event. Descriptions of the COIs identified for CSS 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. Arsenic Reported Range: 0.10 µg/L – 3700 µg/L; Number of Detections/Total Samples: 128/147 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-13 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Concentrations in 4 samples exceeded the 2L standard (10 µg/L). Arsenic exceeded the PBTV for the shallow flow layer in AB-3I (screened beneath active ash basin) and downgradient of the ash storage area. Arsenic exceeded the PBTV for the deep flow layer in wells beneath the Unit 5 inactive ash basin. Arsenic exceeded the PBTV for the bedrock flow layer upgradient of the ash storage area, in wells beneath the active ash basin and in wells beneath the Unit 5 inactive ash basin. Some soil concentrations from immediately beneath the active ash basin exceed the PSRG for POG and the PBTV. Arsenic is a trace element in the crust, with estimated concentrations ranging from less than 1 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). Both natural and anthropogenic sources of arsenic can naturally attenuate on aquifer solids. The primary attenuation mechanism for arsenic with aquifer solids are precipitation of metal arsenates or arsenites or precipitation of arsenic sulfides, co-precipitation with common soil/sediment minerals such as iron oxides and iron sulfides, and adsorption to iron oxyhydroxides, iron sulfides, or other mineral surfaces. The long-term stability of arsenic immobilized onto aquifer solids will depend on the groundwater chemistry over time, specifically: pH, redox potential (Eh), and the concentration of other anions competing for sorption sites (EPA, 2007). The 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). Boron Reported Range: 26 µg/L – 15,300 µg/L; Number of Detections/Total Samples: 77/147 Concentrations in 10 samples exceeded the 2L (700 µg/L). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-14 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Boron exceeded the PBTV for the shallow flow layer in AB-3I (screened beneath the active ash basin) and beneath the Unit 5 inactive ash basin. Boron exceeded the PBTV for the deep flow layer in wells beneath the active ash basin, the Unit 5 inactive ash basin and downgradient of the basins. Boron exceeded the PBTV for the bedrock flow layer in wells located beneath the Unit 5 inactive ash basin. Some soil concentrations from immediately beneath the active ash basin exceed the POG PSRG and PBTV. Boron is a trace element in the crust, with estimated concentrations ranging from as little as 1 mg/kg in mafic igneous rocks to hundreds of milligrams per kilogram in clay rich rocks (Parker, 1967). It occurs only in the trivalent form (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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-15 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 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 (Goldberg, Forster, Lesch, & Heick, 1996). 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 (Goldberg, 1997). Boron sorption on oxides is diminished by competition from numerous anions. Boron solubility in groundwater is controlled by adsorption reactions rather than by mineral solubility. Goldberg concludes that chemical models can effectively replicate boron adsorption data over changing conditions of boron concentration, pH, and ionic strength. Chromium Reported Range: 0.11 µg/L – 41.2 µg/L; Number of Detections/Total Samples: 135/147 Concentrations in 5 samples exceeded the 2L (10 µg/L). Chromium concentrations exceeded the PBTV for the shallow flow layer in wells downgradient of the ash basins. Chromium exceeded the PBTV for the deep flow layer in wells beneath the active ash basin and the Unit 5 inactive ash basin. Chromium concentrations exceeded the PBTV for the bedrock flow layer in wells located beneath the Unit 5 inactive ash basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-16 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Soil concentrations from immediately beneath the active ash basin and Unit 5 inactive ash basin exceed the POG PSRG. Few soil concentrations exceeded PBTVs. Chromium is a blue-white metal found naturally occurring in combination with other substances. It occurs in rocks, soils, plants, and volcanic dust and gases (EPRI, 2008a). Background concentrations of chromium in groundwater generally vary according to the media in which they occur. Most chromium concentrations in groundwater are low, averaging less than 1.0 µg/L worldwide. Chromium tends to occur in higher concentrations in felsic igneous rocks (such as granite and metagranite) and ultramafic igneous rocks; however, it is not a major component of the igneous or metamorphic rocks found in the North Carolina Piedmont or the Blue Ridge (Chapman, Cravotta, III, Szabo, & Lindsey, 2013). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at 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 to 2012. The average chromium concentrations were 5.1µg/L and 5.2µg/L in Gaston and Mecklenburg Counties respectively. Hexavalent Chromium Reported Range: 0.011 µg/L – 0.83 µg/L; Number of Detections/Total Samples: 110/147 No samples of hexavalent chromium exceeded the total chromium 2L standard (10 µg/L). Hexavalent chromium concentrations exceeded the PBTV for the shallow flow layer in wells beneath the active ash basin, beneath the Unit 5 inactive ash basin and downgradient of both. Hexavalent chromium exceeded the PBTV for the deep flow layer in wells beneath the active ash basin and the Unit 5 inactive ash basin. Hexavalent chromium concentrations exceeded the PBTV for the bedrock flow layer in wells located beneath the Unit 5 inactive ash basin. Few soil concentrations from immediately beneath the Units 1-4 inactive ash basin, collected before excavation, exceeded the POG PSRG. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-17 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Chromium exists primarily in the +3 and +6 oxidation states under environmental conditions (commonly written as Cr(III) and Cr(VI)). Hexavalent chromium, Cr(VI), is relatively mobile with an acute toxicity, whereas trivalent chromium, Cr(III), has a relatively low toxicity and is considered immobile in the environment. The distribution of chromium species is largely controlled by the pH and redox processes. Cr (VI) is the dominant form of chromium in shallow aquifers where aerobic conditions exist; however, the oxidation of Cr(III) to Cr(VI) is considered poor with dissolved oxygen. In contrast, Cr(III) is readily oxidized to the mobile Cr(VI) in the presence of solid MnO2 (Palmer & Puls, 1994). Thus, where elevated concentrations of manganese oxides exist in the environment, Cr(III) is inclined to oxidize to the more mobile Cr(VI). Alternatively, 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 (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, and manganese 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, Means, Chen, & others, 1995). Iron Reported Range: 13 µg/L – 42,300 µg/L; Number of Detections/Total Samples: 119/147 Concentrations in 71 samples exceeded the 2L (300 µg/L). Iron concentrations exceeded the PBTV for the shallow flow layer in wells screened beneath the active ash basin, the ash storage area and downgradient of both. Iron exceeded the PBTV for the deep flow layer in wells beneath the active ash basin, the Unit 5 inactive ash basin, and downgradient of both locations. Upgradient concentrations also exceeded PBTVs. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-18 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Iron concentrations exceeded the PBTV for the bedrock flow layer in wells located beneath the active ash basin. Some soil concentrations from beneath the active ash basin, ash storage area and Unit 5 inactive ash basin exceeded the POG PSRG and PBTV. Iron is a naturally occurring element that may be present in groundwater from the erosion of natural deposits (NCDHHS, 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 5 percent by weight (Parker, 1967). Only Oxygen (46.60 weight percent), silicon (27.72 weight percent), and aluminum (8.13 weight percent) occur in higher concentrations. Iron occurs in divalent (ferrous, 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. 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 (Izquierdo & Querol, 2012). Despite the low apparent mobilization percentage, iron is often one of the COIs detected in the highest concentrations in ash pore water. The extent to which iron dissolves in water depends on the amount of oxygen present in the water, and to a lesser extent, upon its degree of acidity (Stumm & Morgan, 1996). Fe(III) is the dominant oxidation state at high DO concentrations (greater than 1-2 mg/L). As the DO is depleted, Fe(III) is reduced to the more mobile Fe(II) species; pH values also play an important role in iron speciation and mobility. At low pH values, both Fe(II) and Fe(III) are stable and mobile in solution, as pH increases from ~2-~8 the dissolved concentrations of Fe(III) decreases as Fe(III) forms hydroxide complexes and ultimately precipitating iron bearing mineral phases. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-19 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Manganese Reported Range: 5.70 µg/L – 15,400 µg/L; Number of Detections/Total Samples: 144/147 Concentrations in 100 samples exceeded the 2L (50 µg/L). Manganese concentrations exceeded the PBTV for the shallow flow layer in AB-3I (screened beneath the active ash basin), beneath the ash storage area and downgradient of both. Manganese exceeded the PBTV for the deep flow layer in wells beneath the active ash basin, the Unit 5 inactive ash basin, and downgradient of both locations. Upgradient concentrations also exceeded PBTVs. Manganese concentrations exceeded the PBTV for the bedrock flow layer in wells located beneath the active ash basin. Some soil concentrations from beneath the ash basin, ash storage area, and Unit 5 basin exceed the POG PSRG and 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), (Polizzoto, 2014). Manganese is most readily released to the groundwater through the weathering of mafic or siliceous rocks (Gillespie, 2013). When manganese-bearing minerals in saprolite, such as biotite, are exposed to acidic weathering, the metal can be liberated from the host mineral and released to groundwater. It then migrates through pre-existing fractures during the movement of groundwater through bedrock. If this aqueous-phase manganese is exposed to higher pH in the groundwater system, it will precipitate out of solution. This results in preferential pathways becoming “coated” in manganese oxides and introduces a concentrated source of manganese into groundwater (Gillespie, 2013). Manganese (II) in suspension of silt or clay is commonly oxidized by microorganisms present in soil, leading to the precipitation of manganese minerals (ATSDR, 2012). Roughly 40 percent to 50 percent of North Carolina wells have manganese concentrations higher than the state drinking water standard (Gillespie, 2013). Concentrations are spatially variable throughout the state, ranging from less than 0.01 mg/L to more than 2 mg/L. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-20 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx This range of values reflects naturally derived concentrations of the constituent and is largely dependent on the bedrock’s mineralogy and extent of weathering (Gillespie, 2013). Manganese is estimated to be the 12th most abundant element in the crust (0.100 weight 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. A 2016 study associated with the NC Division of Water Resources and the NC Geological Survey used laboratory, spectroscopic, and geospatial analyses to demonstrate how natural pedogenetic (soil forming) and hydrogeochemical processes couple to export Mn from the near-surface to fractured bedrock aquifers with the Piedmont. The study determined that Mn- oxides accumulate near the water table within the chemically weathering saprolite. Hydrologic gradients provide a driving force for the downward mobility to the fractured-bedrock (Gillespie, 2013). pH Reported Range: 3.7 – 8.9; Number of Detections/Total Samples: 147/147 Concentrations in 107 samples exceeded the 2L (6.5 - 8.5). pH exceeded the PBTV for the shallow flow layer in wells screened beneath the active ash basin, the ash storage area, and beneath the Unit 5 inactive ash basin. pH PBTVs were also exceeded upgradient and downgradient of the basins. pH exceeded the PBTV for the deep flow layer in wells screened beneath the active ash basin, the Unit 5 inactive ash basin and downgradient of both locations. pH concentrations exceeded the PBTV for the bedrock flow layer in wells located beneath the active ash basin, the ash storage area, and the Unit 5 inactive ash basin. Some soil concentrations from beneath the active ash basin, ash storage area and Unit 5 inactive ash basin exceed the POG PSRG and PBTV. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-21 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The pH scale is used to measure acidity or alkalinity. A pH value of 7 S.U. 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, 2013). 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 to 2012. This study found that 16.9 percent of wells in Cleveland County and 20.3 percent of wells in Rutherford County had a pH result outside of the USEPA’s SMCL range. Using the USGS NURE database, all pH tests within a 20-mile radius of CSS are a pH range from 5.1 to 8.7. Strontium Reported Range: 3.2 µg/L – 3,070 µg/L; Number of Detections/Total Samples: 147/147 Concentrations in 86 samples exceeded PBTVs. Strontium exceeded the PBTV for the shallow flow layer in wells screened beneath the active ash basin and ash storage area. PBTV exceedances were also detected in the shallow flow layer upgradient and downgradient of the basins. Strontium exceeded the PBTV for the deep flow layer in wells screened beneath the Unit 5 inactive ash basin, the ash storage area, and downgradient of both. Strontium exceeded the PBTV for the deep flow layer in wells screened beneath the Unit 5 inactive ash basin, the ash storage storage area and downgradient of both. Some soil concentrations from immediately beneath the active ash basin exceed the POG PSRG and PBTV. 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-22 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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: 0.54 µg/L – 561 µg/L; Number of Detections/Total Samples: 132/147 Concentrations in 14 samples exceed the 2L standard (250 mg/L). Sulfate exceeded the PBTV for the shallow flow layer in wells beneath the active ash basin and downgradient of the ash storage area. Upgradient PBTV exceedances were also detected in the shallow flow layer. Sulfate exceeded the PBTV for the deep flow layer in wells beneath the Unit 5 inactive ash basin, the ash storage area, and downgradient of both. Sulfate exceeded the PBTV for the deep flow layer in wells beneath the Unit 5 inactive ash basin, the ash storage area, and downgradient of both. Sulfate is a naturally occurring substance found in minerals, soil, and rocks. It is present in ambient air, groundwater, plants, and food. Primary natural sources of sulfate include atmospheric deposition, sulfate mineral dissolution, and sulfide mineral oxidation. The principal commercial use of sulfate is in the chemical industry. Sulfate is discharged into water in industrial wastes and through atmospheric deposition (USEPA, 2003). Anthropogenic sources include coal mines, power plants, phosphate refineries, and metallurgical refineries. While sulfate has an SMCL, and no enforceable maximum concentration set by the USEPA, ingestion of water with high concentrations of sulfate may be associated with diarrhea, particularly in susceptible populations, such as infants and transients (USEPA, 2012). However, adults generally become accustomed to high sulfate concentrations after a few days. It is estimated that about 3 percent of the public drinking water systems in the United States may have sulfate concentrations of 250 mg/L or greater (Miao, Brusseau, Carroll, & others, 2012). Sulfate is on the list of enforced regulated contaminates that may cause cosmetic effects or aesthetic effects in drinking water (USEPA, 2014). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-23 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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: 0.031 µg/L – 1.9 µg/L; Number of Detections/Total Samples: 74/147 Concentrations in 17 samples exceeded the IMAC (0.2 µg/L). Thallium concentrations exceeded the PBTV for the shallow flow layer in AB-3I (screened beneath the active ash basin), the ash storage area, and downgradient of both. Thallium exceeded the PBTV for the deep flow layer in wells screened beneath the active ash basin. Thallium exceeded the PBTV for the bedrock flow layer in wells located beneath the active ash basin. Few soil concentrations from immediately beneath the active ash basin units POG PSRG. 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 (EPRI, 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. 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). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-24 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx TDS Reported Range: 26 µg/L – 942 µg/L; Number of Detections/Total Samples: 131/147 Concentrations in 12 samples exceed 2L (500 mg/L). TDS concentrations exceeded the PBTV for the shallow flow layer in CLMW-3D (screened beneath the active ash basin), Unit 5 inactive ash basin and downgradient of the ash storage area. TDS concentrations exceeded the PBTV for the deep flow layer in wells screened beneath the Unit 5 inactive ash basin, the ash storage area, and downgradient of both. TDS exceeded the PBTV for the deep flow layer in wells screened beneath the Unit 5 inactive ash basin. Groundwater contains a wide variety of dissolved inorganic constituents as a result of chemical and biochemical interactions between the groundwater and the elements in the soil and rock through which it passes. TDS mainly consist of dissolved cation and anion particles (e.g., calcium, chlorides, nitrate, phosphorus, iron, sulfur, and others) in varying concentrations. TDS is measured by weighing the solid residue left after evaporating a measured volume of sample to dryness (Freeze & Cherry, 1979). 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. The ions listed below are referred to as the major ions as they make up more than 90 percent of the TDS in groundwater. 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 from 10 µg/L to 1,000 µg/L (Freeze & Cherry, 1979). Trace constituents make up an even smaller portion of TDS in groundwater and 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-25 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx include: aluminum, antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, lead, manganese, nickel, selenium, thallium, vanadium, and zinc among others. TDS concentrations resulting from trace constituents are typically less than 100 µg/L (Freeze & Cherry, 1979). In some cases, contributions from anthropogenic sources can cause some of the elements listed as minor or trace constituents to occur as contaminants at concentration levels that are orders of magnitude above the normal ranges indicated above. TDS in water supplies originate from natural sources, sewage, urban, and agricultural run-off, and industrial wastewater. Salts used for road de-icing can also contribute to the TDS loading of water supplies. Concentrations of TDS from natural sources have been found to vary from less than 30 mg/L to as much as 6,000 mg/L. Water containing more than 2,000 – 3,000 mg/L TDS is generally too salty to drink (the TDS of seawater is approximately 35,000 mg/L) (Freeze & Cherry, 1979). Reliable data on possible health effects associated with the ingestion of TDS in drinking water are not available (WHO, 1996). TDS is on the 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, 2014). 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: 0.07 µg/L – 12.2 µg/L; Number of Detections/Total Samples: 101/147 Concentrations in 58 samples exceeded the IMAC value (0.3 µg/L). Vanadium concentrations exceeded the PBTV for the shallow flow layer in AB-3I and CLMW-3D (screened beneath the active ash basin), the ash storage area and the Unit 5 inactive ash basin. Vanadium exceeded the PBTV for the deep flow layer in wells beneath the active ash basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-26 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Vanadium concentrations exceeded the PBTV for the bedrock flow layer in wells located beneath the active ash basin. Some soil concentrations from beneath the active ash basin and Unit 5 inactive ash basin exceed the POG PSRG and 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 (EPRI, 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 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 S. , 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). Total Uranium Reported Range: 0.00061 µg/L – 0.1 µg/L; Number of Detections/Total Samples: 24/51 No IMAC exceedances. No concentrations exceed the PBTVs or IMAC in the shallow, transition or bedrock units. Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is the 51st element in order of abundance in the Earth's crust. Uranium is also the highest-numbered element to be found naturally in significant quantities on Earth and is almost always found combined with other elements. The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat that keeps the outer core 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-27 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx liquid and drives mantle convection, which in turn drives plate tectonics. Uranium is more plentiful than antimony, tin, cadmium, mercury, or silver, and it is about as abundant as arsenic or molybdenum. Uranium is found in hundreds of minerals, including uraninite (the most common uranium ore), carnotite, autunite, uranophane, tobernite, and coffinite. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores. Total Radium Reported Range: 0.38 µg/L – 4.6 µg/L; Number of Detections/Total Samples: 50/50 No IMAC exceedances. No concentrations exceed the PBTVs or IMAC in the shallow, transition or bedrock units. Radium is a naturally occurring radioactive element (or radionuclide) that generally is present at low levels in all soil, water, and rocks. It is derived from the decay of the common and long-lived radioactive elements uranium and thorium. Three commonly occurring isotopes of radium are radium-224, radium- 226, and radium-228 (abbreviated as Ra-224, Ra-226, and Ra-228, respectively). Each radium isotope varies in abundance because each decays at a different rate (known as a “half-life”) to a daughter product or progeny (a different element). Radium-226 is the most abundant radium isotope in the environment, primarily because of its long half-life (about 1622 years). Ra-228 has a half-life of slightly less than 6 years, and Ra-224 has a very short half-life (less than 4 days). [https://water.usgs.gov/nawqa/trace/radium/Ra_FAQ.html] (USGS, 2014). Like all rocks and soils, raw coal contains naturally occurring radionuclides (Table 1 and Figure 5). Average concentrations of uranium and thorium in raw coals are 0.3–2.0 pCi/g 238U and 0.35 pCi/g 232Th, respectively. Concentrations of these radionuclides in raw coal are comparable to those in the earth’s crust (U.S. Geological Survey, 1997). The average amount of uranium and thorium in the earth’s crust is estimated to be 0.76 pCi/g 238U and 1.1 pCi/g 232Th, respectively. As the ash content of the coal increases, the enrichment factor decreases. For bituminous and subbituminous coals with 10–15% ash, Lauer et al. (2015) reported that total radium activities in the ash were 7–10 times greater than in the original feed coal. [EPRI -Radioactivity in Coal Combustion Products - Technical Brief — Coal Combustion Products – Environmental Issues Program 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-28 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The USGS found three geochemical conditions were associated with elevated concentrations of radium in groundwater. These include 1) low levels of dissolved oxygen (dissolved oxygen less than 1 milligram per liter) acidic water (pH less than 6), and water with high concentrations of dissolved solids (especially calcium, barium, magnesium, strontium, potassium, sulfate, or bicarbonate). These water conditions can prevent radium from adsorbing to aquifer sediments and increase its solubility in groundwater. [https://water.usgs.gov/nawqa/trace/radium/Ra_FAQ.html] The somewhat greater frequency of occurrence of radium in anoxic conditions is the most important factor controlling radium in aquifers used for drinking water supply in the United States. The occurrence pattern, whether in the Appalachian crystalline-rock aquifers or in the larger setting of the continental United States, reflects the critical role that sorption processes, specifically to iron (and manganese) oxyhydroxides, play in controlling the concentration of radium in dilute groundwaters. [Naturally Occurring Contaminants in the Piedmont and Blue Ridge Crystalline-Rock Aquifers and Piedmont Early Mesozoic Basin Siliciclastic-Rock Aquifers, Eastern United States, 1994–2008 - Scientific Investigations Report 2013– 5072 U.S. Department of the Interior U.S. Geological Survey] (Chapman, Cravotta, III, Szabo, & Lindsey, 2013). Water treatment by adsorption and water-softening techniques are thought to be effective in reducing radium in untreated drinking water (Watson et al. 1984). Therefore, it is likely that radium in water does not migrate significantly from the area where it is released or generated (EPA 1985a). Limited field data also support the generalization that radium is not mobile in groundwater (Kaufmann et al. 1976; Swanson 1985). [(Agency for Toxic Substances and Disease Registry U.S. Public Health Service, In collaboration with U.S. Environmental Protection Agency, 1990)] Pending Investigations 11.3 Supplemental data collection to support groundwater modeling and long-term monitoring is anticipated to support the CAP process. Additional data requirements identified during the CSA and in discussions with NCDEQ to support the CAP are discussed below. Replacement and Additional Monitoring Wells On May 16, 2017, Ted Campbell with NCDEQ DWR sent an email to Duke Energy outlining additional data needs for the horizontal and vertical assessment at CSS. These well location requests were discussed during a meeting between Duke Energy and 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-29 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx NCDEQ at the NCDEQ Mooresville Regional Office (MRO) on June 30, 2017, and a revised list of monitoring wells for installation was agreed upon. The following monitoring wells were installed: GWA-54S/D/BRO GWA-56S/D AB-2BRO GWA-51D AS-8S/D AB-1BRO MW-11BRO Additional monitoring wells were also installed to replace grout contaminated monitoring wells. These wells include: AB-3SLA (replaces AB-3SL) MW-11DA (replaces MW-11D) MW-30DA (replaces MW-30D) The locations of these monitoring wells are presented on Figure 2-10. The analytical results from these wells were not available in time for interpretation as part of this CSA report. However, the boring logs and well construction records are included in Appendix F. A data summary table with the groundwater results is included as Table 1 in Appendix B. The results of the samples collected from these monitoring wells will be included in the CAP. Additional Surface Water Samples To confirm thallium concentrations reported in surface water samples collected downstream of the permitted NPDES outfall in the Broad River, an additional surface water sampling event was conducted on December 14, 2017. A surface water sample was collected upgradient of the outfall (SW-BRAB-01), and from the two surface water sample locations downgradient of the outfall (SW-BRAB-02 and SW-BRAB-03). One water sample was also collected from the water in the active ash basin (Ponded AB). The results will be compared with groundwater data from nearby wells and reported in the updated CAP. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-30 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Samples to Support Geochemical Modeling Additional metal oxy-hydroxide phases of iron (HFO) and aluminum (HAO) data are anticipated to support geochemical modeling conducted as part of the CAP. Soil and rock samples collected from drilled boreholes along the primary groundwater flow transect are used. The boreholes will be positioned adjacent to existing monitoring wells located along the primary groundwater flow transects. The samples will be located: Background/Upgradient Directly beneath the ash basins and ash storage area Downgradient of the ash basins and ash storage area The samples are anticipated to be collected at vertical intervals that coincide with nearby well screen elevations. Analysis results of collected samples would be used to improve input parameters for the updated geochemical model. Additional HFO samples should be collected for the following locations (Figure 2-10) within the screened interval (*indicates well installed within ash pore water): Unit 5 Inactive Ash Basin Transect U5-7S*, U5-7D, U5-2S-SLA*, U5-2D, U5-2BR, CCR-U5-4S, CCR-U5-4D, GWA-2S, GWA- 2BR Active Ash Basin- West Transect GWA-27DA, GWA-27BR, CCR-12S, CCR-12D, AB-2D, AB-2BRO, GWA-20D, GWA- 20BR Ash Storage Area Transect CCR-7S, CCR-7D, AS-1SB, AS-1D, AS-7S*, AS-7D, AS-7BRA, AS-2D and AS-2BR Active Ash Basin- East Transect AB-1S, AB-1D, AB-1BRO, GWA-21S, GWA-21BRU, and GWA-21BR Additional Well Beneath the Ash Storage Area An additional well screened in the shallow flow zone beneath the ash storage area, where a significant thickness of regolith was not previously screened, may be warranted at the following location and depth intervals: 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 11-31 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx • AS-7 (45-55’ bgs) This well would not likely change assessment results, but would facilitate effectiveness monitoring for the selected corrective action remedy to be evaluated in the upcoming CAP. Pending review of data from recently installed deep bedrock wells, further assessment may be desired to refine vertical extent of groundwater impacts. Sediment Samples from Broad River Sediment samples have not been collected from the Broad River. To confirm sediment concentrations in the Broad River, an additional sediment sampling event is anticipated. The results will be reported in the updated CAP. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 12-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 12.0 RISK ASSESSMENT A baseline human health and ecological risk assessment was performed as a component of CAP Part 2 (HDR, 2016a) and is included in Appendix J of this report. The 2016 risk assessment characterized potential risks to humans and wildlife exposed to coal ash constituents present in environmental media for the purpose in aiding corrective action 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 August 2017) in order to confirm or update risk conclusions (Section 7 of Appendix J) in support of remedial action. Data used in the 2016 risk assessment (Section 3 of Appendix J) included groundwater samples collected from January 2011 through September 2015, surface water samples from February 2010 through October 2015, and AOW water samples from May 2015 through October 2015. AOW soil and sediment samples were collected March 2015 to July 2015. This risk assessment update uses sample data presented in Attachment A of the 2016 risk assessment (Appendix J) along with groundwater and surface water data presented in Appendix B of this report. AOW locations are outside the scope of this risk assessment because AOWs, wastewater, and wastewater conveyances (discharge canals) are evaluated and governed wholly separate in accordance with the NPDES Program administered by NCDEQ DWR. This process is ongoing in a parallel effort to the CSA and subject to change. No new sediment or soil samples, other than for background evaluations, have been collected that are applicable to the 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. Section 2 of Appendix J provides a detailed description of the exposure pathways, exposure routes, and potential receptors considered in the 2016 assessment. The CSMs presented in the 2016 assessment (Figures 2-3 and 2-4 of Appendix J) describe the sources and potential migration pathways through which groundwater beneath the ash basin may have transported coal ash-derived constituents to other environmental media (receiving media) and, in turn, to potential human and ecological receptors. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 12-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 Comparison of new maximum constituent concentrations to the risk assessment human health and ecological screening values Comparison of new maximum constituent concentrations to site-specific 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 and the influence on the 2016 risk assessment conclusions are summarized below by exposure areas (Figure 12-1) at CSS. Human Health Screening Summary 12.1 On-Site Groundwater Groundwater sample locations used in the human health assessment are presented in Figure 12-1. These wells were evaluated because they represent the potential worker exposure area as determined in the 2016 risk assessment. No potential unacceptable risks to humans exposed to groundwater from the site were identified during the 2016 assessment (Section 5 of Appendix J). Groundwater analytical results are included in Appendix B, Table 1 of this report. Groundwater data collected since the 2016 risk assessment were compared to USEPA’s human health regional screening levels (RSLs) and risk-based concentrations (RBCs) from the 2016 risk assessment. Inclusion of new data resulted in maximum concentrations greater than the 2016 assessment for several constituents. The new maximum concentrations were less than their respective RBC for all constituents measured. No evidence of unacceptable risks to receptors from exposure to site groundwater was identified. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 12-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx On-Site Surface Water Surface water samples collected on-site and evaluated as part of this assessment are presented on Figure 2-10. On-site surface water data is included in Appendix B, Table 2 of this report. As detailed in Sections 5 and 7 of Appendix J, the 2016 risk assessment found no evidence of unacceptable risks to humans exposed to on-site surface water. On-site surface water sample locations included in this assessment were SW-3 and SW-4 from Suck Creek and 47 additional surface water samples collected in 2016-2017 from the Broad River and Suck Creek. Samples collected at the locations SW-BRAB-02 and BRAB-03 were not considered in this risk assessment update because of their proximity to an NPDES outfall on the Broad River. As previously stated, wastewater and wastewater conveyances are evaluated and governed wholly separate in accordance with the NPDES Program administered by NCDEQ DWR. Zinc detected in the SW- BRU5-01(1) (22.9 B) sample was also detected in the equipment blank and not considered because of unacceptable data quality. Samples with turbidity greater than 2B of 25 NTUs were also omitted from this evaluation. The current dataset contains samples with detected concentrations of constituents greater than those evaluated in the 2016 risk assessment, which were screened against RSLs and RBCs. None of the maximum concentrations were greater than their respective RBCs. No evidence of unacceptable risks to humans exposed to on-site surface water was identified based on evaluation of the surface water data collected to date. Off-Site Surface Water Off-site surface water samples were not collected from the Broad River for the 2016 risk assessment. Instead, off-site exposures were evaluated using on-site surface water sample data (SW-3 and SW-4) as surrogates for off-site conditions. This conservative approach was taken to provide an upper-bound estimate of potential surface water concentrations. The 2016 risk assessment reported no unacceptable risks to off-site human receptors exposed to surface water. Sample locations used in this assessment for off-site surface are discussed above in the on-site surface water section. To conservatively evaluate recent surface water data, the maximum detected concentrations of constituents in were compared to RBCs. With the exception of cobalt, all maximum detected concentrations of constituents were less than their respective RBCs. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 12-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx To be consistent with the 2016 risk assessment process, cobalt detected in surface water was used to estimate the concentration in fish tissue and evaluate potential risks for recreational and subsistence fishermen. The maximum detected concentrations of cobalt resulted in a hazard index (HI) of 1 under the hypothetical recreational fisher and an HI of 31 under the subsistence fisher exposure scenarios. The mean concentration or 95 percent UCL of cobalt would be less than the RSL of 1 µg/L and would result in an HI less than 1 for the hypothetical recreational fisher. Of the 49 surface water samples, only three samples, from locations SW-SC-06, SW-BRAB-01, and SW-03, had cobalt concentrations greater than the RSL of 1 µg/L. The use of on-site surface water data as a surrogate for off-site exposure conditions, highly conservative assumptions about transfer of constituents from surface water to fish tissue, and assumed fish ingestion rates likely combine to overestimate risks under the fisher exposure scenarios. Ecological Screening Summary 12.2 The 2016 risk assessment included evaluation of potential ecological risks by exposure area (Section 6 of Appendix J). Four exposure areas were established based on available data and included the following: Ecological Exposure Area 1, located northeast (downstream) of Units 1-4 inactive ash basin and the active ash basin along the Broad River Ecological Exposure Area 2, located south of Units 1-4 inactive ash basin and west of the active ash basin along Suck Creek Ecological Exposure Area 3, located south of the active ash basin along Suck Creek Ecological Exposure Area 4, located north of Unit 5 inactive ash basin and west of the steam station along the Broad River The 2016 ecological risk assessment included both surface water and AOW water in the evaluation (Sections 3 and 6 of Appendix J). The assessment resulted in potential “no observed adverse effects level” (NOAEL) based risks to birds (hazard quotient (HQ)=1) and mammals (HQ=6 for muskrat and HQ=8 for meadow vole) exposed to aluminum and birds (HQ=1) exposed to selenium in Exposure Area 1. The evaluation of Exposure Area 2 resulted in multiple receptors with NOAEL based HQs greater than one, ranging from HQ=2 for aluminum (American robin) and barium (great blue heron) to HQ=81 for aluminum (meadow vole). There were also multiple “lowest observed adverse effects level” (LOAEL) based HQs in Exposure Area 2 greater than one for several constituents, ranging from HQ=2 for manganese (great blue heron) and selenium (great blue heron) to HQ=10 for vanadium (great blue heron). The assessment resulted in potential 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 12-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx NOAEL based risks to mammals (HQ=1 for meadow vole) exposed to aluminum in Exposure Area 3. As part of this assessment, Ecological Exposure Areas were re-evaluated based on additional surface water data (Figure 12-2). Results of this evaluation are described below by Exposure Area. Exposure Area 1 – Surface Water Exposure Area 1 encompasses an area along the Broad River from Units 1-4 inactive ash basin to just below the ash storage area and active ash basin. Surface water sample S-4 was included in this area during the 2016 risk assessment. The 2016 assessment resulted in potential ecological risk for birds and mammals exposed to aluminum and birds exposed to selenium in Exposure Area 1 (Sections 6 and 7 of Appendix J). Thirty-five (35) additional surface water samples were collected from the Broad River during 2016-2017. Data for the surface water samples are included in Appendix B, Table 2. Several constituents were detected at concentrations greater than detected concentrations in the single sample (S-4) evaluated in 2016. Of the constituents detected, aluminum, cadmium, iron, and manganese concentrations were greater than the ESVs, with only aluminum exceeding toxicity reference values (TRVs); therefore, no additional risk from these constituents is anticipated. The TRV exceedances are largely driven by aluminum in the sediments. The surface water concentrations used in the assessment have a negligible effect on the ADD and thus do not raise the HQ appreciably. No additional risk from these constituents is anticipated, other than risk reported in the 2016 risk assessment. Potential risk to birds and mammals estimated for Exposure Area 1 are consistent with the 2016 assessment (Section 7 of Appendix J). Exposure Area 2 – Surface Water Exposure Area 2 encompasses an area south of the Units 1-4 inactive ash basin and west of the active ash basin. Surface water sample S-3 was included in this area during the 2016 risk assessment. The 2016 assessment resulted in potential ecological risk for multiple terrestrial and aquatic receptors (great blue heron, muskrat, American robin, and meadow vole) with several COPCs (aluminum, barium, cobalt, copper, manganese, selenium, and vanadium) with LOAEL-based HQs greater than 1. Thirty (30) additional surface water samples were collected within Exposure Area 2 during 2016-2017. Data for the surface water samples are included in Appendix B, Table 2. Three constituents (aluminum, iron, and manganese) were detected in surface 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 12-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx water at concentrations greater than ESVs; however, the concentrations for these constituents were less than the AOW aqueous concentrations used in the 2016 assessment for Exposure Area 2. Therefore, no potential risks from these constituents are anticipated beyond those estimated in the 2016 risk assessment. Potential risks to birds and mammals estimated for Exposure Area 2 are anticipated to remain consistent with the 2016 assessment (Sections 7 and 7 of Appendix J). Exposure Areas 3 and 4 – Surface Water Surface water samples have not been collected in Exposure Areas 3 and 4 since the 2016 risk assessment. Samples evaluated within the two exposure areas were limited to AOW samples. As stated previously, AOW samples were not evaluated as part of this assessment due to being included under the NPDES program. Private Well Receptor Assessment Update 12.3 An independent study was conducted that evaluated 2015 groundwater data. The groundwater data evaluated as part of the study included data that was collected and analyzed by an independent analytical laboratory on behalf of NCDEQ. At the time of the CAP 2 Report, a total of 23 groundwater samples were collected from 21 private water supply wells within close proximity (less than 0.5 miles) of the CSS pre-2017 compliance boundaries. The groundwater analytical data was provided in the 2015 CSA report as an appendix and further summarized as part of the CAP 2 (CAP 2, Section 5.6; Haley & Aldrich, 2015). Details regarding the observations presented in the independent study were presented in the CAP 2 Risk Assessment, which is included as Appendix J of this report. The Haley & Aldrich report concluded that the constituents detected in the private wells sampled by NCDEQ are consistent with background conditions and do not indicate impact from constituents derived from coal ash. NCDEQ continued to collect and analyze samples from water supply wells within a 0.5- mile radius of the CSS ash basin pre-2017 compliance boundaries during 2015 and early 2016. An additional three samples from three private water supply wells were collected by NCDEQ. Duke Energy collected samples from private water supply wells in 2016 and 2017 after the NCDEQ sampling effort. Recent (2016-2017) analytical results from off-site water supply wells indicate that constituent concentrations are less than 2L or less than PBTVs for site groundwater, with the exception of four vanadium detections. Vanadium was detected in samples collected from four private wells at concentrations (0.41 µg/L to 1.1 µg/L) greater than the IMAC (0.3 µg/L) and the bedrock PBTV of 0.37 µg/L but well below the federal tap 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 12-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx water RSL (86 µg/L). Additionally, groundwater flow from the active ash basin is to the north and northwest and the closest private wells are situated to the south, east, and northeast. Based on these observations, there are no indications that potential for risks to off-site residences exposed to groundwater exist. Risk Assessment Update Summary 12.4 An update to the 2016 human health and ecological risk assessment was conducted. There is no evidence of unacceptable risks to humans exposed to groundwater on-site. Limited potential for unacceptable risks to humans was estimated for the hypothetical recreational and subsistence fisher due to the surface water derived estimate of cobalt concentration in fish tissue. Limited potential for unacceptable risks to birds and mammals for Exposure Areas 1 and 2 was consistent with the 2016 assessment. Fisher risks were overestimated in the risk assessment based on conservative exposure model assumptions. This update to the human health and ecological risk assessment supports a risk classification of “low” for groundwater related consideration. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 13-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 13.0 GROUNDWATER MODELING RESULTS The Site-specific groundwater flow and transport models and the Site-specific geochemical models are currently being updated for use in the CAP. Groundwater flow, transport, and geochemical models simulate movement of COIs through the subsurface to support the evaluation and design of remedial options at the Site. The existing data inventory requested in section 4.3 of “Monitored Natural Attenuation For Inorganic Contaminants in Groundwater: Guidance for Developing Corrective Action Plans Pursuant to NCAC 15A.0106(l)” (NCDEQ-DWR, October 2017) is summarized in Table 11-1. The models will provide insights into: 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. 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, extent, and rates of constituent movement at the field scale. 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. Design: Model predictions will be used to help design basin closure and groundwater corrective action strategies in order to achieve compliance with 2L. 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. Information from the geochemical model will provide insight into the complex processes that influence constituent mobility. 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. The updated CAP will further discuss the purpose and scope of both the groundwater and geochemical models. The CAP will detail model development, calibration, assumptions and limitations. The CAP will also include a detailed remedial option evaluation, based on observed conditions and the results of predictive modeling. The 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 13-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 subsections provide a brief summary of modeling efforts completed to date at the CSS and present a description of the updated models to be submitted in the updated CAP. Summary of Flow and Transport Model Results 13.1 CAP Part 1 Model 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 basins at the CSS Site. The initial groundwater model in the CAP Part 1 (HDR, 2015b) included a calibrated steady- state flow model of June 2015 conditions; a calibrated historical transient model of constituent transport to match June 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 (with existing ash configuration) Ash removal (excavation of ash) The initial model presented in the CAP Part 1 used antimony, arsenic, boron, chromium, hexavalent chromium, cobalt, lead, nickel, sulfate, thallium and vanadium as primary modeling constituents. The remedial alternative evaluation simulations in the CAP Part 1 model were run to a total time of 250 years. CAP 1 contains the report describing the development and results from this modeling. CAP Part 2 Model As part of the CAP Part 2 (HDR, 2016a), the model was revised to include barium and beryllium for evaluation. Additionally, the model predictive time period for the CAP Part 2 (HDR, 2016) simulation scenarios was 100 years. The revised model in the CAP Part 2 (HDR, 2016a) included a calibrated steady-state flow model of June 2015 conditions and a calibrated historical transient model of 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 13-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx constituent transport to June 2015 conditions. In addition, CSA data was used to refine the layer assignments, hydraulic conductivity values and recharge rates within the model. A total of approximately 13 private water supply wells were also identified in the CSA and were included in the model. The revised model in the CAP Part 2 (HDR, 2016a) included a calibrated steady state flow model of June 2015 conditions and one potential basin closure scenarios. Appendix B of CAP 2 (HDR, 2016a) contains the report describing the development and results from this modeling. Updated CAP Model The flow and transport model is currently being updated as a part of the updated CAP and will include: development of a calibrated steady-state flow model that includes data available through the fourth quarter of 2017; development of a historical transient model of constituent transport; and predictive simulations of basin closure plus groundwater corrective action scenarios. The updated flow and transport model will consider boron and additional COIs that are negligibly affected by geochemical processes. Predictive remedial scenarios will have simulation times that continue until modeled COIs concentrations are below the 2L Standards, IMAC, or PBTVs at the compliance boundary. The distribution of recharge, locations of drains, and distribution of material will be modified to represent the following different basin closure options in the revised/updated models: Complete Excavation with passive remediation Complete Excavation with active remediation Cap-in-place with passive remediation (MNA) Cap-in-place with active remediation. The results of these simulations will be included as part of the updated CAP submittal. Summary of Geochemical Model Results 13.2 The CSS geochemical model investigates how variations in geochemical parameters affect movement of constituents through the subsurface. The geochemical SCM will be updated as additional data and information associated with Site constituents, conditions, or processes are developed, and will be updated based on discussions and 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 13-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx comments from NCDEQ. The geochemical modeling approach presented in the following subsections 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. CAP Part 2 Geochemical Model The geochemical model presented in the CAP Part 2 (HDR, 2016a) included: Eh-pH (Pourbaix) diagrams showing potential stable chemical phases of the aqueous electrochemical system, calibrated to encompass pH and redox potentials at the Site; Sorption model in which the aqueous and surface speciation of constituents was 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; Attenuation calculations in which the potential capacity of aquifer solids to sequester constituents of interest were estimated. Details on the development and results of the CAP Part 2 geochemical model are found in Appendix C of CAP Part 2 (HDR, 2016a). Updated Geochemical Model Development The geochemical model in the updated CAP will contain refinements based on updated data and on comments and discussions with DEQ. The updated geochemical modeling will use hydraulically significant flow transects to investigate the geochemical controls on groundwater concentrations in and around source areas at the Site (see Figure 11-121) for selected constituents. The model will compare trends in the concentrations of each COI along transects with the model output to verify that the conceptual and qualitative models can predict COI behavior. Then the model will be also 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). 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 13-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The hydraulically significant flow transects that will be used in the geochemical model were described in Section 11.1. These were determined by considering: Associated source areas, Plume movement focusing on the centerline of the area(s) of impact (i.e., the plume(s)), Geologically derived flow zones (geozones), Hydraulic gradients Downgradient receptors, and Available data. The updated geochemical model will develop parameters for each aquifer or geozone by considering the bulk densities, porosities, and hydraulic gradients used in the flow and transport models. Those 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. Those processes will be modeled using: 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 13-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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. Data Inventory To appropriately characterize and model the geochemical behavior of constituents in the subsurface requires a significant amount of data collection and analysis. In addition to hydraulic controls and groundwater data, it is important to properly evaluate the physical and chemical properties of the solid phase aquifer material in contact with groundwater. In preparation for the updated geochemical model to be presented with the CAP, a data inventory was conducted to determine where additional data needs exist (Table 11-1). As part of the data inventory, a Solid Phase-Groundwater Interactions Data Map (Figure 11-121) was completed to indicate where solid and aqueous phase data exist and where additional samples will be collected to address data needs for the updated geochemical model. Data distribution and results of information related to soil/groundwater/COI interaction is presented on Figure 11-121. This data map shows the following: The boron plume within the shallow aquifer (boron is used as a proxy for the general area of impact) The geochemical flow transects The soil water pairs (i.e., where solid phase total metals analysis are available within a screened interval of a well The currently available data and locations for HFO/HAO, Kd (Table 13-1), and hydraulic conductivity (k) values Proposed locations for additional HFO/HAO samples to be used in the updated geochemical model as described in Section 11-3 The requested data inventory is summarized in Table 11-1. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 14.0 SITE ASSESSMENT RESULTS A site conceptual model (SCM) is an interpretation of processes and characteristics associated with hydrogeologic conditions and constituent interactions at the Site. The site assessment results provide the information to evaluate distribution of constituents with regard to site-specific geological/hydrogeological properties. Nature and Extent of Contamination 14.1 The site assessment described in this CSA presents the results of investigations required by CAMA and 2L regulations. Ash sluiced to, and accumulated within, the basins and stored in the ash storage area is determined to be a source of impacts 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 CSS ash basins and ash storage area include arsenic, boron, chromium, hexavalent chromium, cobalt, iron, manganese, pH, strontium, sulfate, thallium, TDS, vanadium, total uranium, and radium. Most recent concentrations of COIs in groundwater, surface waters, and AOWs are provided on Figures 14-83 and 14-84. 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.) as well as physical properties of the subsurface. 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. Most recent concentrations of COIs in CSS solid medium, as well as available geochemical properties of soils, are provided on Figure 14-82. 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, seep, 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx the character and configuration of the ash basin relative to specific Site features such as manmade and natural drainage features, engineered drains, and streams; 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 CSS and were evaluated during the CSA: Ash – The ash pore water unit consists of saturated ash material. Observed ash depths range from a few feet to more than 70 feet in in the active ash basin, 50 feet in the Units 1-4 inactive ash basin, from 9.5 feet to 67 feet in the Unit 5 inactive ash basin, and from 7 feet to 57 feet in the ash storage area. Shallow – The shallow flow layer consists of soil and saprolite materials that overlie the transition zone and bedrock. Alluvial deposits were encountered beneath the Units 1-4 inactive 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; however, 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 CSS. Water-bearing fractures are minimally productive. The CSS active ash basin acts as a bowl-like feature toward which groundwater flows from the basin to the north, west, and northwest. Groundwater primarily flows north toward the Broad River with the western portion of the basin flowing west and northwest toward Suck Creek. Groundwater at the Site flows away from the topographic and hydrologic divide (highest topographic portion of the Site) generally located along McCraw Road (Duke Power Road) to the 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 active ash basin main dam and the NPDES outfall/discharge and to the northwest by the active ash basin upstream dam. 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 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx ash basin. Ponded water is not present in the Unit 5 inactive ash basin or the ash storage area and the Units 1-4 inactive ash basin has been excavated. In summary, there are no substantive differences in water level among wells completed in the different flow layers across the Site (shallow, deep, bedrock), and generally lateral groundwater movement predominates over vertical movement. The vertical gradients are near equilibrium across the Site, with some exceptions of downward and upward gradients, 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 flow 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. Groundwater flow directions and the overall morphology of the potentiometric surface vary very little from the “dry” to “wet” seasons. Water levels do fluctuate up and down with significantly increased or decreased precipitation, but the overall groundwater flow directions do not change due to seasonal changes in precipitation. Horizontal gradients from in the active ash basin range from 0.003 to 0.033 ft./ft. Gradients are lowest compared to other basin areas likely due to the low relief of the basin that has greater area footprint than other basins at the Site. Horizontal gradients crossing Units 1-4 inactive ash basin (0.044 ft./ft.) and Unit 5 inactive ash basin (0.05 ft./ft.) have the greatest gradients. The gradients are influenced by the steep relief in the areas between the ash basin and the Broad River shoreline. Vertical gradients in saprolite and transition zone are near equilibrium, indicating that there is no distinct horizontal confining layer beneath CSS. Generally, downward (recharge) gradients are more prevalent across the Site. Upward gradients are observed upgradient of the active ash basin in shallow to deep and deep to bedrock flow layers and downgradient of the active ash basin, Unit 1-4 inactive ash basin, and Unit 5 inactive ash basin. 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 active ash basin, the western portion of the ash storage area, the north end of the Units 1-4 inactive ash basin, and north of the Unit 5 inactive ash basin. Boron is not detected in background groundwater. Boron, in its most common forms, is soluble in water, and 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- 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx derived plume moving downgradient from the source areas (active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage area). 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. Active Ash Basin In the bedrock flow layer, boron is not reported in any of the wells at a concentration greater than the 2L standard. Boron is reported at a concentration greater than the PBTV at GWA-20BR, located at the toe of the upstream dam. Boron is also reported at a concentration greater than the PBTV and less than the 2L standard at GWA-27BR, located west of the active ash basin, approximately half way between the basin and Suck Creek. Boron is also reported at a concentration greater than the PBTV and less than the 2L standard at GWA-21BR and MW-20DR, located north and northeast of the active ash basin downstream dam, near the Broad River. The remaining bedrock downgradient wells did not have boron detected. In the deep flow layer, boron 2L exceedances are limited to monitoring well GWA-27D, GWA-27DA and CCR-14D located on the west side of the active ash basin, monitoring wells GWA-20D, CCR-9D, and CCR-11D located at the toe of the active ash basin upstream dam, and monitoring wells CCR-6D and CCR-8D north of the active ash basin. These locations are located within the compliance boundary and GWA-20D, CCR-6D, CCR-9D, and CCR-11D are located within the waste boundary. The leading edge of the boron plume in the shallow flow layer west of the ash basin is located beyond monitoring well CCR-16S, located southwest of the active ash basin with boron 2L exceedances. Monitoring well GWA-47D is located northwest of CCR- 16S. Groundwater was not encountered at this well location above refusal and the boron concentration in GWA-47D is less than the 2L standard. The edge of the boron plume is located between CCR-16S and GWA-47D, beyond the waste boundary and within the compliance boundary. On the west side of the active ash basin groundwater was not encountered above refusal during drilling activities at the CCR-14 location. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The deep well at this location has 2L exceedances and it is expected that shallow groundwater impacts would exist in the vicinity of this well flowing toward Suck Creek. At the upstream dam the boron plume is defined by monitoring wells CCR-12S, within the compliance boundary. The shallow groundwater plume terminates between this well and northern locations associated with the ash storage area. The north end of the boron 2L exceedances plume extends on the western side of the active ash basin and intersects with the western portion of the ash storage area. The leading edge of the plume in this location continues under the ash storage area toward the Broad River. In the eastern portion of the ash basin there is one boron exceedance located at MW-11S at the downstream dam. Monitoring wells CLMW-4 and GWA-22S are downgradient of this monitoring well and their concentrations are less than the 2L standard prior to the compliance boundary. Chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are also constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. The extent of chromium exceedances is confined to the shallow layer, beyond the waste boundary but within the compliance boundary, downgradient northeast of the downstream dam at GWA-22S and MW-11S. Chromium was not reported at a concentration greater than the 2L in the deep or bedrock flow layers. The extent of cobalt exceedances in the shallow flow layer are all within the compliance boundary and are limited to north of the ash basin downstream dam at well GWA-21S, southwest of the basin near the upstream dam, and south of the basin. Exceedances of the deep flow layer are all within the compliance boundary and located near the upstream dam along the southern and northern waste boundary, and one location north of the basin. Cobalt exceedances in the bedrock flow layer are reported southeast at GWA-24BR and north at MW-20DR of the ash basin. The extent of exceedances of iron in the shallow and deep flow layers is downgradient northeast, north and west of the basin; all within compliance boundary. In the deep and bedrock flow layers iron is detected at waste boundary on the upstream dam. The extent of iron exceedances in the shallow flow layer is located near or beyond the compliance boundary at downgradient locations north and northeast at AB-1S, CLMW- 4, GWA-22S, and GWA-21S, and west of the basin at the upstream dam at wells GWA- 20S, MW-8S, and AB-2S. Iron exceedances of the 2L standard in the deep flow layer are located near or beyond the compliance boundary and are located north and northeast of the basin at wells AB-1D, GWA-22BRU, MW-4D, and MW-20D, and at the upstream 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx dam. In the bedrock flow layer, iron exceedances are within the waste boundary and near the upstream dam at well GWA-20BR. The extent of exceedances of manganese in the shallow flow layer are all within the compliance boundary and located within the southern portion of the active ash basin at CLMW-6, and at downgradient locations north and northeast of the basin at wells AB- 1S, CLMW-4, CLMW-5S, GWA-21S, and MW-11S, and west of the basin. Manganese exceedances in the deep flow layer near or beyond the compliance boundary were reported northwest of the active ash basin within the compliance boundary at wells CCR-15D, GWA-27D, GWA-27DA, and GWA-47D, west of the basin at wells AB-2D, CCR-12D, GWA-20D, and MW-8D, and north of the basin at wells AB-1D, GWA- 21BRU, MW-10D, and MW-20D. Manganese exceedances are also reported in the bedrock flow layer beneath the southern portion of active ash basin and near or beyond the compliance boundary at the upstream dam at well GWA-20BR, and north of the active ash basin at wells GWA-21BR, GWA-28BR, and MW-20DR. The extent of exceedances of strontium in the shallow flow layer is beneath the active ash basin within the waste boundary, at the waste boundary near the upstream dam, and near or beyond the compliance boundary north of the basin near the downstream dam at wells CLMW-4, GWA-21S, GWA-22S, and MW-11S. Exceedances of strontium in the deep flow layer are located northwest of the ash basin at the upstream dam at wells AB-1D, GWA-21BRU, GWA-22BRU, MW-4D, and MW-20D, and near or beyond the compliance boundary southwest. Bedrock flow layer exceedances are located near the upstream dam at wells GWA-27BR, GWA-20BR, and GWA-33BR, and near or beyond the compliance boundary north of the downstream dam at wells GWA-21BR and MW-20DR. The extent of exceedances of sulfate is limited to the shallow flow layer, north of the active ash basin within the waste boundary, between the basin and the ash storage area. Sulfate exceedances were not detected in the deep or bedrock flow layers. The extent of exceedances of thallium in the shallow flow layer is within the compliance boundary west and northwest of the active ash basin within the western ash storage area. Thallium exceedances are detected in the deep flow layer within the waste boundary at well GWA-20D and at the north end of the ash basin near the ash storage area. Thallium exceedances were not reported in the bedrock flow layer. The extent of exceedances of TDS exceedances in the shallow flow layer are located north of the active ash basin within the waste boundary, between the basin and the ash storage area. TDS exceedances were reported in the deep flow layer northwest of the 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx active ash basin near the upstream dam within the compliance boundary. TDS exceedances were not reported in the bedrock flow layer. The extent of exceedances of vanadium in the shallow flow layer is located beneath the basin, and north of the basin between the basin and the ash storage area at wells CCR- 7S and CCR-9S. Vanadium exceedances in the deep flow layer are detected beneath the basin and at the upstream dam within the compliance boundary at wells CCR-11D, CCR-14D, and CCR-16D, and near or beyond the compliance boundary north and northeast of the basin and downstream dam. A vanadium concentration equal to the PBTV in the bedrock flow layer was reported at one well upgradient and east of the active ash basin. A vanadium exceedance was detected within the compliance boundary near the active ash basin downstream dam at well MW-21BR. The bedrock aquifer is generally the source of water for supply wells in the area. The cobalt concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. The iron, manganese and strontium exceedances appear to be contributed to by the active ash basin; however there are no downgradient water supply wells relative to the active ash basin. As groundwater under the active ash basin flows north toward the downstream dam, and northwest toward the upstream dam, the hydraulic impact of the ash basin dams 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 dams are impacted by COIs. 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 GWA-20BR, GWA-21BR, GWA-27BR and MW-20DR based on data from wells positioned downgradient and sidegradient from the ash basin. Concentrations of boron in the bedrock flow layer are below 2L for all locations. Units 1-4 Inactive Ash Basin In the bedrock flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Units 1-4 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV but less than the 2L standard at GWA-13BR and GWA-33BR located upgradient and adjacent to the basin, and at IB- 4BR located beneath the basin. In the deep flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Units 1-4 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx than the PBTV but less than the 2L standard at GWA-14D, located upgradient and adjacent to the basin, and at locations downgradient of the basin. In the shallow flow layer, boron was reported at monitoring well IB-3S, formerly located in the crest of the dam of the Units 1-4 inactive ash basin at a concentration greater than the 2L standard. The groundwater in this area drains toward the Broad River. Boron was reported at concentrations greater than the PBTV but less than the 2L standard at wells adjacent to the basin. Arsenic, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are also detected in groundwater at concentrations greater than background and 2L/IMAC near or beyond the waste boundary. The extent of arsenic exceedances in the shallow flow layer are limited one location, north of the basin. There are no deep or bedrock flow layer exceedance of arsenic is reported in wells associated with Units 1-4 inactive ash basin. The extent of chromium exceedances in the shallow flow layer is located upgradient of the Units 1-4 inactive ash basin and at a location near or beyond the waste boundary north of the basin at wells GWA-14S and IB-3S. Chromium exceedances in the deep flow layer are located north of the basin, near and beyond the waste boundary at GWA- 11BRU and IB-3D. Chromium exceedances were not reported in the bedrock flow layer. The extent of cobalt exceedances in the shallow flow layer is limited to one well location beneath the Units 1-4 inactive ash basin at well IB-2AL. Cobalt exceedances were not reported in the deep or bedrock flow layers. The extent of iron exceedances in the shallow flow layer is located within the footprint of the ash basin, beyond the northern waste boundary, and upgradient of the waste boundary at well GWA-14S. The extent of iron exceedances in the deep flow layer are located beneath the ash basin at IB-3D and IB-4D, north and northwest, and upgradient of the waste boundary at wells GWA-33D, GWA-44D, and MW-23D. Iron exceedances were not reported in the bedrock flow layer. The extent of exceedances of manganese in the shallow flow layer is within the waste boundary, and north, near or beyond the waste boundary, and upgradient of the waste boundary at wells GWA-14S, GWA-38S, and GWA-33S. Exceedances of manganese in the deep flow layer are located beneath the ash basin, at the northern waste boundary, and upgradient of the ash basin at wells GWA-33D and MW-23D. Manganese exceedances in the bedrock flow layer are located beneath the ash basin, and northeast 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx of the waste boundary at well GWA-29BRA, and upgradient of the waste boundary at wells GWA-13BR, GWA-33BR, and GWA-44BR. The extent of exceedances of strontium in the shallow flow layer is within the waste boundary, and near or beyond the waste boundary north, and upgradient of the waste boundary at wells GWA-14S, GWA-38S, and GWA-33S. Exceedances of the strontium in the deep flow layer are located beneath the ash basin, at the northern waste boundary, and upgradient of the ash basin at wells GWA-14D, GWA-33D, GWA-43D, GWA-44D, and MW-23D. Strontium exceedances in the bedrock flow layer are located beneath the ash basin, downgradient at well GWA-29BRA, and upgradient of the waste boundary at wells GWA-13BR, GWA-14BR, GWA-33BR, and GWA-44BR. The extent of sulfate exceedances in the shallow flow layer is located within the ash basin, and upgradient of the waste boundary at well GWA-44S. In the deep flow layer 2L exceedances are reported upgradient of the waste boundary at wells GWA-44D and MW-23D. There is one sulfate 2L exceedance in the bedrock flow layer upgradient of the waste boundary at GWA-44BR. A separate source may be contributing to the exceedances of sulfate reported at GWA-44BR. The extent of thallium exceedances in the shallow flow layer is located within the waste boundary and at the northeast waste boundary at well GWA-10S and the northeast waste boundary at well IB-3S. There are no thallium exceedances of the IMAC in the deep or bedrock flow layer for wells associated with Units 1-4 inactive ash basin. The extent of TDS exceedances in the shallow flow layer is limited to within the waste boundary of the ash basin and not downgradient. The exceedances reported in the deep flow layer are upgradient of the waste boundary at wells GWA-44D and MW-23D. There is one TDS exceedance in the bedrock flow layer upgradient of the basin at GWA- 44BR. A separate source may be contributing to the exceedances of TDS reported at GWA-44BR. The extent of vanadium exceedances in the shallow flow layer is located within the waste boundary of the ash basin, and north, near or beyond the waste boundary, and upgradient at well GWA-14S. Thallium exceedances in the deep flow layer are within the waste boundary and beyond the waste boundary. Exceedances in the bedrock flow layer are reported upgradient of the waste boundary at two isolated locations, GWA- 14BR and GWA-44BR. The bedrock aquifer is generally the source of water for supply wells in the area. The cobalt and vanadium concentrations reported in bedrock groundwater are likely due to 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx natural geochemical conditions. The manganese and strontium exceedances appear to be contributed to by the Units 1-4 inactive ash basin; however there are no downgradient water supply wells relative to the Units 1-4 inactive ash basin. The sulfate and TDS exceedances south of the Units 1-4 inactive ash basin and east of Unit 6 appear to be contributed to by a separate source from the Units 1-4 inactive ash basin. The surficial and transition zone flow units at CSS— 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 20 – 22 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 but is variable depending on constituent mobility and fracture geometry. IB-4BR, drilled to a depth of 75 feet bgs, contains detected boron concentrations below 2L, but has manganese and strontium detected above the PBTV. Downgradient, GWA-29BRA is drilled to 58 ft bgs and also has manganese and strontium detected above the PBTV but does not have detections of boron. Upgradient of the basin, GWA-44BR is drilled to 99 ft bgs and contains cobalt, manganese, strontium, sulfate, TDS and vanadium above 2L or PBTV. Boron is detected below 2L at this location. Groundwater in the transition zone beneath the basin is impacted. Wells completed in surficial, transition zone, and bedrock proximate to the north and northeast side of the ash basin dam are impacted by COIs. Boron is present in groundwater downgradient of the ash basin on the Site in concentrations that exceed the 2L in the shallow flow layer. In the deep flow layer boron is detected upgradient, within the basin and downgradient of the basin below 2L. In bedrock, boron is detected at GWA-13BR, GWA-33BR, GWA-44BR, and IB-4BR, based on data from wells positioned upgradient and downgradient from the ash basin. Concentrations of boron in the bedrock flow layer are below 2L for all locations. Unit 5 Inactive Ash Basin In the bedrock flow layer, boron is not reported in the monitoring wells adjacent to or beneath the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron is reported at concentrations greater than the PBTV beneath the basin and downgradient of the basin. In the deep flow layer one 2L exceedance is reported downgradient and north of the ash basin at the waste boundary. Boron is reported at concentrations greater than the PBTV but less than the 2L standard at U5-2D, U5-3D, U5-5D, U5-6D, and U5-7D located beneath the basin and sidegradient and downgradient of the basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx In the shallow flow layer, boron is not reported in the monitoring wells downgradient of the Unit 5 inactive ash basin at concentrations greater than the 2L standard. Boron was reported at concentrations greater than the PBTV at wells within the basin, adjacent and downgradient to the basin. Arsenic, chromium, iron, manganese, strontium, sulfate, thallium, TDS, and vanadium are also constituents detected in groundwater at concentrations greater than background and 2L/IMAC near or beyond the waste boundary. Arsenic exceedances were not reported in the shallow flow layer at the Unit 5 inactive ash basin. The extent of arsenic exceedances in the deep and bedrock flow layers is an isolated location beneath the western portion of the basin within the waste boundary at wells U5-2D and U5-2BR. The extent of chromium exceedances in the shallow flow layer is limited to an isolated location east of and sidegradient of the Unit 5 inactive ash basin, beyond the waste boundary, at well MW-42S. Chromium exceedances in the deep flow layer were detected within the waste boundary and near or beyond the eastern waste boundary, including sidegradient locations. Chromium exceedances were not reported in the bedrock flow layer. The extent of cobalt exceedances in the shallow flow layer are within the waste boundary, and near or beyond the waste boundary, north, northeast, and southeast of the basin. Exceedances of the deep flow layer are located within the waste boundary, and to the northeast beyond the waste boundary, and in the southeast at the waste boundary. In the bedrock layer exceedances are beneath the basin within the waste boundary and at the northern waste boundary. The extent of iron exceedances in the shallow flow layer are located within the waste boundary of the ash basin and at downgradient locations northeast and northwest of the ash basin at wells GWA-4S, GWA-35S, GWA-36S, and GWA-37S. Exceedances of the deep flow layer are located in the northeast and northwest beneath the ash basin and beyond the waste boundary at wells GWA-1BRU, GWA-4D, GWA-35D, GWA-36D, and MW-34BRU. One iron exceedance was reported south of and upgradient of the basin, beyond the waste boundary in the bedrock flow layer at well GWA-30BR. The extent of exceedances of manganese in the shallow flow layer is within the waste boundary, and north and east, near or beyond the waste boundary, at wells GWA-2S, GWA-4S, GWA-5S, GWA-35S, GWA-36S, GWA-37S, GWA-45S, and MW-38S. Manganese exceedances in the deep flow layer are located beneath the basin, and north, 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx west, and east of the basin, near or beyond the waste boundary at wells GWA-1BRU, GWA-2BRU, GWA-3D, GWA-4D, GWA-5BRU, GWA-31D, GWA-35D, GWA-36D, and MW-38D. Manganese in the bedrock flow layer is detected beneath the basin, and at one location northeast of the ash basin beyond the waste boundary at well MW-38BR. The extent of exceedances of strontium in the shallow flow layer are located within the Unit 5 inactive ash basin, and at locations near and beyond the waste boundary, east and north of the basin at wells GWA-2S, GWA-35S, GWA-36S, GWA-37S, MW-36S, and MW-38S, including locations sidegradient of the basin at wells GWA-4S, GWA-5S, GWA-45S, MW-42S. Strontium exceedances in the deep flow layer are located beneath the basin and at locations west, north and east of the basin, near and beyond the waste boundary at wells GWA-2BRU, GWA-3D, GWA-4D, GWA-5BRU, GWA-31D, GWA- 35D, GWA-36D, GWA-37D, MW-34BRU, MW-37BRU, MW-38D, and MW-40BRU. In the bedrock flow layer strontium exceedances are reported beneath the basin and beyond the waste boundary, northeast of the ash basin at one location, MW-38BR. The extent of exceedances of sulfate in the shallow flow layer is within, near, and beyond the waste boundary southeast of the ash basin. Sulfate exceedances are detected east and north of the Unit 5 inactive ash basin, near and beyond the waste boundary in the deep flow layer. An isolated sulfate exceedance is reported in the bedrock flow layer, beyond the waste boundary north of the basin at well MW-38BR. The exceedances of thallium in the shallow flow layer are located near and beyond the waste boundary, north and east of the Unit 5 inactive ash basin. Thallium in the deep flow layer is detected near or beyond the northern and eastern waste boundaries. A thallium exceedance was reported at isolated location beneath the western portion of the basin at U5-2BR. The extent of exceedances of TDS in the shallow flow layer is near and beyond the waste boundary, east of the Unit 5 inactive ash basin. TDS exceedances in the deep flow layer are located near and beyond the waste boundary, east and north of the basin. An isolated TDS exceedance in the bedrock flow layer was reported north of ash basin, beyond the waste boundary at well MW-38BR. The extent of exceedances of vanadium in the shallow flow layer are located within the waste boundary, north of the Unit 5 inactive ash basin near or beyond the waste boundary, and northeast of the basin, near and beyond the waste boundary. Vanadium exceedances in the deep flow layer are located beneath the basin, and southeast, northeast, north and northwest, near and beyond the waste boundary. Exceedances of 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-13 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx vanadium in the bedrock flow layer are limited to an isolated area northeast of the basin, near or beyond the waste boundary. The bedrock aquifer is generally the source of water for supply wells in the area. The thallium concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. The arsenic, cobalt, manganese, strontium, sulfate, and TDS exceedances appear to be contributed to by the Unit 5 inactive ash basin; however, there are no downgradient water supply wells relative to the Unit 5 inactive ash basin. The surficial and transition zone flow units at CSS— 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 40 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 but is variable depending on constituent mobility and fracture geometry. U5-2BR drilled to a depth of 105 feet bgs contains arsenic above 2L, however U5-5BR downgradient and drilled to depth of 110 feet bgs, contains no arsenic detected above 2L. U5-2BR also contains cobalt, manganese, strontium and thallium concentrations above PBTV. Downgradient of the basin MW-38BR contains manganese, sulfate, strontium and TDS above 2L or PBTV. The depth of this location is unknown. Groundwater in the transition zone beneath the basin is impacted. 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 south 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 the transition zone. Boron is widely detected below 2L within in the basin and at downgradient locations. In the bedrock boron is detected at only U5-2BR and CCR- U5-5D based on data from wells positioned beneath the basin and downgradient from the ash basin. Boron concentrations reported in the bedrock flow layer are below 2L for all locations. Ash Storage Area In the bedrock flow layer, boron is not reported in any of the wells at a concentration greater than the 2L standard. Boron is reported at a concentration greater than the PBTV at AS-2BR, located downgradient of the western portion of the ash storage area. The remaining bedrock downgradient wells did not have boron detected. In the deep 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-14 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx flow layer, boron 2L exceedances are limited to monitoring well AS-7D, located beneath the western portion of the ash storage area. Monitoring well AS-2D is downgradient of this location prior to the Broad River and the compliance boundary and the boron concentration is reported at greater than the PBTV and less than the 2L standard. The leading edge of the boron plume in the shallow flow layer north of the ash storage area is located beyond monitoring well AS-2S, located north of the western portion of the ash storage area near the Broad River. Boron 2L exceedances are not reported in the eastern portion of the ash storage area with the exception of in one monitoring well. Chromium, cobalt, manganese, strontium, sulfate, thallium, TDS and vanadium are also constituents detected in groundwater at concentrations greater than background and 2L/IMAC near or beyond the waste boundary. The extent of chromium exceedances is limited to one location within the western ash storage area waste boundary in the shallow flow layer. Chromium exceedances were not detected in the deep or bedrock flow layers associated with the ash storage area. The extent of exceedances of cobalt exceedances in the shallow flow layer is located within the western portion of the ash storage area, and near or beyond the waste boundary but within the compliance boundary at wells AS-2S, CLMW-2, and CLMW- 3S. Cobalt exceedances were not detected in the deep flow layer. No cobalt exceedances of the PBTV were reported in the deep flow layer. An isolated exceedance in the bedrock flow layer was reported beyond the waste boundary and within the compliance boundary downgradient of the western portion of the ash storage area at well MW-2DA. The extent of manganese exceedances in the shallow flow layer are limited to within the waste boundary of the ash storage area and at the northern waste boundary at wells As- 2S, CLMW-1, CLMW-2, and CLMW-3S. Manganese exceedances in the deep flow layer are located within the western portion of the waste boundary and near or beyond the waste boundary at well AS-2D. In the bedrock flow layer exceedances are located primarily within the western portion of the ash storage area and northwest of the ash storage area at wells AS-2BR and MW-2DA. The extent of strontium exceedances in the shallow flow layer are located within the waste boundary and downgradient along the west, northwest waste boundary at AS-2S, CLMW-1, CLMW-2, and CLMW-3S. Exceedances of strontium in the deep flow layer are located beneath the western portion of the ash storage area and along the west, northwest waste boundary at AS-2D and CLMW-3D. Exceedances of the strontium PBTV in the bedrock flow layer are located beneath the western portion of the ash 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-15 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx storage area and downgradient beyond the waste boundary, northwest of the ash storage area at well AS-2BR. The extent of sulfate exceedances in the shallow flow layer are within the waste boundary of the western portion of the ash storage area and downgradient along the northwest waste boundary at AS-2S. There are no reported exceedances of sulfate in the deep and bedrock flow layers at the ash storage area. The extent of thallium exceedances in the shallow flow layer are limited to within the footprint of the western portion of the ash storage area and downgradient along the northwest waste boundary at AS-2S, CLMW-1, CLMW-2, and CLMW-3S. Thallium exceedances in the deep flow layer are isolated to one location, within the waste boundary, beneath the ash storage area. There are no exceedances of the thallium in the bedrock flow layer at the ash storage area. The extent of TDS exceedances in the shallow flow layer are limited to within the waste boundary of the western portion of the ash storage area and downgradient along the northwest waste boundary at AS-2S. There are no reported 2L exceedances of TDS in the deep or bedrock flow layers at the ash storage area. The extent of vanadium exceedances in the shallow flow layer are limited to within the footprint of the eastern portion of the ash storage area and not downgradient. There are no reported PBTV exceedances of vanadium in the deep flow layer at the ash storage area. Exceedances in the bedrock flow layer are located beneath the eastern ash storage area northern waste boundary and northwest of the western ash storage area at wells AS-2BR and MW-2DA. The bedrock aquifer is generally the source of water for supply wells in the area. The vanadium concentrations reported in bedrock groundwater are likely due to natural geochemical conditions. The manganese and strontium exceedances appear to be contributed to by the ash storage area; however there are no downgradient water supply wells relative to the ash storage area. The surficial and transition zone flow units at CSS— 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 40 feet of fractured bedrock. The vertical extent of the plume is represented by groundwater concentrations in bedrock wells beneath and downgradient of the ash basins and ash storage area but is variable depending constituent mobility and fracture geometry. AS-2BR, drilled to a depth of 97 feet bgs, 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-16 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx contains boron detected below 2L and manganese and strontium concentrations above the PBTV. However MW-2DA, drilled to 76 feet bgs has the absence of boron but has manganese and strontium detected above the PBTV. AS-5BR, drilled to a depth of 80 ft bgs, does not contain the boron, manganese or strontium concentration observed ad AS- 2BR, however contains vanadium above the PBTV. Groundwater in the transition zone beneath the basin is impacted. 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. Wells completed in surficial, transition zone, and bedrock proximate to the north side of the ash basin, as well as bedrock beneath the basin are impacted by COIs. As groundwater and the plume migrate in the downgradient direction north of the basin, it is likely that a combination of impacted groundwater from the upgradient active ash basin and unimpacted groundwater from upgradient recharge areas to the south contribute to or mitigate 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 the shallow flow layer and beneath the ash basin in the transition zone. In bedrock, boron is detected at only AS- 2BR at a concentration less than 2L. Maximum Constituent Concentrations 14.2 Changes in COI concentrations over time are included as time-series graphs (Figures 14-1 through Figure 14-66). The maximum historical detected COI concentrations in ash pore water, groundwater beneath the ash basins and ash storage area, and groundwater beyond the waste boundaries are included as follows. The 2L standards and IMACs are not applicable to ash pore water results. Active Ash Basin Arsenic – Ash Basin: 4,250 µg/L (AB-04SL); Outside Basin: 26 µg/L (MW-11D) Boron - Ash Basin: 11,300 µg/L (AB-06S); Outside Basin: 1,300 µg/L (GWA-27D) Chromium – Ash Basin: 95.8 µg/L (AB-07BR); Outside Basin: 125 µg/L (GWA- 47D) Chromium (hexavalent) – Ash Basin: 11.8 µg/L (AB-03BRU); Outside Basin: 6.4 µg/L (GWA-26D) Iron – Ash Basin: 25,400 (AB-02D); Outside Basin: 62,200 µg/L (CLMW-04) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-17 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Manganese – Ash Basin: 13,900 (AB-03BRU); Outside Basin: 5,810 µg/L (MW- 08D) pH - Ash Basin: 4.8 (AB-04D) – 12.9 (AB-07BR); Outside Basin: 1.9 (MW-24D) – 10.3 (GWA-20BR) Strontium - Ash Basin: 11,400 µg/L (AB-07BR); Outside Basin: 3,900 µg/L (GWA- 26D) Sulfate – Ash Basin: 1060 mg/L (AB-03S); Outside Basin: 190 mg/L (MW-11D) TDS – Ash Basin: 12,600 mg/L (AB-07BR); Outside Basin: 910 mg/L (GWA-26D) Thallium – Ash Basin: 0.76 mg/L (AB-03S); Outside Basin: 0.48 mg/L (MW-22BR) Total Radium- 10.05 pCi/L (AB-02D); Outside Basin: 9.62 pCi/L (GWA-21BR) Total Uranium – Ash Basin: 0.0712 mg/L (AB-05S); Outside Basin: 0.0017 mg/L (GWA-27BR) Vanadium – Ash Basin: 215 µg/L (AB-04SL): Outside Basin: 24 µg/L (MW-11D) Units 1-4 Inactive Ash Basin Arsenic – Ash Basin: 356 µg/L (IB-04S/SL); Outside Basin: 81.9 µg/L (CCR-IB-03S CAMA) Boron - Ash Basin: 842 µg/L (IB-03S); Outside Basin: 600 µg/L (GWA-10S) Chromium – Ash Basin: 50 µg/L (IB-03D); Outside Basin: 185 µg/L (GWA-29BR) Chromium (hexavalent) – Ash Basin: 3.1 µg/L (IB-03S); Outside Basin: 5.5 µg/L (GWA-29BR) Iron – Ash Basin: 16,400 (IB-04S/SL); Outside Basin: 27,000 µg/L (GWA-29D) Manganese – Ash Basin: 27,400 µg/L (IB-03S); Outside Basin: 3,700 µg/L (GWA- 11S) pH - Ash Basin: 4.6 (IB-03S) – 10.9 (IB-01D); Outside Basin: 4.6 (MW-23S) – 13.2 (GWA-29BR) Strontium - Ash Basin: 2,800 µg/L (IB-04S/SL); Outside Basin: 40,400 µg/L (GWA-29BR) Sulfate – Ash Basin: 550 mg/L (IB-01S); Outside Basin: 520 mg/L (GWA-10S) TDS – Ash Basin: 1,030 mg/L (IB-04S/SL); Outside Basin: 1,940 mg/L (GWA- 29BR) Thallium – Ash Basin: 1.28 mg/L (IB-01S); Outside Basin: 5.6 mg/L (GWA-14S) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-18 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Total Radium- Ash Basin: NA pCi/L; Outside Basin: 40.52 pCi/L (GWA-44BR) Total Uranium – Ash Basin: NA mg/L; Outside Basin: 0.0081 mg/L (GWA-44BR) Vanadium – Ash Basin: 11.6 µg/L (IB-01D): Outside Basin: 154 µg/L (GWA- 44BR) Unit 5 Inactive Ash Basin Arsenic – Ash Basin: 4,680 µg/L (U5-02D); Outside Basin: 37.5 µg/L (GWA-45D) Boron - Ash Basin: 500 µg/L (U5-05D); Outside Basin: 416 µg/L (GWA-03D) Chromium – Ash Basin: 178 µg/L (MW-42D); Outside Basin: 248 µg/L (GWA- 03D) Chromium (hexavalent) – Ash Basin: 16 µg/L (U5-04BR); Outside Basin: 21 µg/L (GWA-31D) Iron – Ash Basin: 133,000 (U5-01S); Outside Basin: 32,900 µg/L (GWA-37S) Manganese – Ash Basin: 11,800 (U5-01S); Outside Basin: 9,150 µg/L (GWA-37S) Strontium - Ash Basin: 5,700 µg/L (U5-04BR); Outside Basin: 714 µg/L (GWA- 36S) Sulfate – Ash Basin: 632 mg/L (U5-05BR); Outside Basin: 585 mg/L (GWA-05S) TDS – Ash Basin: 2,690 mg/L (U5-04BR); Outside Basin: 10,700 mg/L (MW-32S) Thallium – Ash Basin: 1.2 mg/L (U5-06S); Outside Basin: 1.9 mg/L (GWA-04S) Total Radium- Ash Basin: 4.9 pCi/L (U5-05BR); Outside Basin: 6.014 pCi/L (GWA-04D) Total Uranium – Ash Basin: 0.013 mg/L (U5-02S-SLA); Outside Basin: 0.0051 mg/L (GWA-45D) Vanadium – Ash Basin: 207 µg/L (U5-06S); Outside Basin: 179 µg/L (GWA-45D) Ash Storage Area Arsenic – Ash Storage: 368 µg/L (AS-07S); Outside Basin: 11.5 µg/L (AS-02S) Boron - Ash Storage: 1,850 µg/L (CLMW-01); Outside Basin: 1,080 µg/L (AS-02S) Chromium – Ash Storage: 838 µg/L (AS-04S); Outside Basin: 8.8 µg/L (AS-02D) Chromium (hexavalent) – Ash Storage: 25.2 µg/L (AS-07BR); Outside Basin: 2.3 µg/L (AS-02S) Iron – Ash Storage: 42,300 (AS-07S); Outside Basin: 710 µg/L (AS-02S) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-19 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Manganese – Ash Storage: 16,800 (AS-07S); Outside Basin: 13,100 µg/L (AS-02S) pH - Ash Storage: 3.8 (CLMW-03S) – 13.0 (AB-06BR); Outside Basin: 4.1 (AS-02S) – 9.4 (AS-02BR) Strontium - Ash Basin: 11,410 µg/L (AS-07BR); Outside Basin: 434 µg/L (AS-02D) Sulfate – Ash Basin: 686 mg/L (AS-07BR); Outside Basin: 421 mg/L (AS-02S) TDS – Ash Basin: 12,600 mg/L (AS-07BR); Outside Basin: 715 mg/L (AS-02S) Thallium – Ash Storage: 0.67 mg/L (AS-01SB); Outside Basin: 0.57 mg/L (AS-02S) Total Radium- Ash Storage: 1.732 pCi/L (CLMW-01); Outside Basin: 1.229 pCi/L (AS-02D) Total Uranium – Ash Storage: 00.0014 mg/L (AS-07S); Outside Basin: 0.0018 mg/L (AS-02BR) Vanadium – Ash Storage: 39.2 µg/L (AS-04S): Outside Basin: 5.2 µg/L (AS-02D) 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 flow will be greater in the regolith. At the Site, all hydrogeologic zones are saturated; however, west of the active ash basin, between the basin and Suck Creek the first saturated flow layer encountered in several monitoring wells is the deep flow layer. 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. At CSS, 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 CSS 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 fractures of varying orientations, gradients, pressure, and size. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-20 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Gradients measured within the ash basins support the interpretation that ash pore water mixes with shallow/surficial groundwater and migrates downward into the transition zone. Continued vertical migration of groundwater downgradient of the ash basin is also evidenced by detected constituent concentrations. Ash constituents become dissolved in groundwater that flows generally north in response to hydraulic gradients, with potential mixing of source area groundwater and regional groundwater sidegradients 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 and seeps are 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 basins and out of the ash basins is restricted to the local flow regime. Shallow groundwater and surface water flow from the ash basins is into the Broad River, with groundwater and surface water in the central portion of the site flowing toward Suck Creek and on to the Broad River. Boron is present in groundwater beneath the active ash basin and downgradient to the north, extending under the western portion of the ash storage area to the Broad River, and to the northwest to Suck Creek. Boron is also present in the shallow flow layer north of the Units 1-4 inactive ash basin extending to the Broad River, and in the deep flow layer at the Unit 5 inactive ash basin extending toward the Broad River. Trend Analysis Figures 14-67 to 14-81 shows the most recent COI groundwater data available for the monitoring wells. The figures are color-coded to visually depict whether historical 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. Active Ash Basin Figures 14-67 to 14-81 show concentrations of boron, chromium, manganese, iron, sulfate and TDS, in the active ash basin, increasing downgradient north, near the Broad River, and northwest, near Suck Creek. For boron, concentrations are predominantly increasing in monitoring wells screened in the shallow zone and transition zone, downgradient of the ash basin. The only bedrock wells that show increasing trends at 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-21 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx the active ash basin are GWA-21BR and GWA-27BR. Constituents that show both variable temporal and spatial trends are arsenic, hexavalent chromium, cobalt, thallium and vanadium in the active ash basin. Units 1-4 Inactive ash basin Figures 14-67 to 14-81 show concentrations of arsenic, cobalt, manganese, thallium, and vanadium in Units 1-4 inactive ash basin, increasing downgradient north, near the Broad River. For boron, concentrations are predominantly decreasing in monitoring wells screened in the shallow zone and transition zone, downgradient of the ash basin. The only wells that show increasing trends are GWA-14D, GWA-33BR, and GWA-44BR. Constituents that show both variable temporal and spatial trends are total chromium, hexavalent chromium, iron, sulfate, and TDS. Unit 5 Inactive ash basin Figures 14-67 to 14-81 show concentrations of arsenic, boron, cobalt, sulfate, and TDS in Unit 5 inactive ash basin, increasing downgradient north and northeast, near the Broad River. For boron, concentrations are predominately increasing in monitoring wells screened in the shallow zone and transition zone, downgradient of the ash basin. The only bedrock well that shows an increasing trend is U5-2BR. Constituents that show both variable temporal and spatial trends are total chromium, hexavalent chromium, iron, manganese, thallium, and vanadium. Ash Storage Area Figures 14-67 to 14-81 show concentrations of arsenic, boron, total chromium, hexavalent chromium, cobalt, iron and manganese in the ash storage area, increasing downgradient north, near the Broad River. For boron, concentrations are predominantly increasing in monitoring wells screened in the shallow zone and transition zone, downgradient of the ash basin. Constituents that show both variable temporal and spatial trends are sulfate, TDS, thallium, and vanadium. Potentially Affected Receptors Human Health and Ecological A previously completed human health risk assessment concluded no evidence of potential human health risks exist for the CSS Plant. A screening level risk assessment has been completed (Section 12.0). The screening assessment included an evaluation of recent analytical data for their potential to influence the 2016 risk assessment conclusions. There is indication that potential human health risks associated with the ash basins exist. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-22 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The ecological risk assessment reported potential risks to birds and mammals exposed to aluminum in surface water and sediment of Exposure Area 1, as well as potential risks to birds exposed to selenium in Exposure Area 1. Risk estimates for Exposure Area 2 resulted in multiple receptors with LOAEL based risk estimates greater than 1 for several constituents. Additionally, the 2016 risk assessment resulted in potential ecological risk to mammals exposed to aluminum in Exposure Area 3. Risk estimate updates indicate risk within Exposure Areas 1 and 2 are consistent with the 2016 assessment. Surface water samples have not been collected in Exposure Areas 3 and 4 since the 2016 risk assessment. Samples evaluated within the two exposure areas were limited to AOW samples. As stated previously, AOW samples were not evaluated as part of this assessment due to inclusion in the NPDES permitting process. Water Supply Wells Concentrations of analyzed constituents exceeded the respective PBTVs for a number of samples collected from private water supply wells; however, these data should be interpreted with consideration of the items below: There is limited information about the sampled wells available. It is likely the wells were constructed as open-hole bedrock wells. However, it is possible that some of the wells may have been bored and constructed within the shallow (saprolite) or deep (transition zone) flow layers. Groundwater geochemistry in fractured bedrock aquifers can be quite variable. PBTVs were developed using groundwater data from a set of seven bedrock 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 71 private water supply wells. The geologic map of the area indicates varying rock types in the area surrounding the Site. Well construction and well materials may influence analytical results. The updated CAP will address any potential future risk to future groundwater receptors. A numerical capture zone analysis for the CSS 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 6-19 and 6-20, discussed in Section 6.3) private water supply wells are located in upgradient or a 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-23 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx sufficient distance sidegradient to not be impacted by groundwater migration from the ash basins or ash storage area. Boron was not detected in any of the water supply wells sampled sidegradient of the ash basin. Piper diagrams for water supply wells, with available water chemistry data, and background bedrock monitoring wells are compared with ash pore water data and downgradient bedrock monitoring well data from the active ash basin and Unit 5 inactive ash basin and are presented as Figure 4-3 and 4-4. These basins are near the property boundary, and water supply wells are located south and east of the basins. Observations based on the diagrams include: Water supply wells are characterized as calcium-sodium-bicarbonate water type, consistent with samples collected from the background bedrock well at CSS. Water supply well C-1002 (located southeast of the active ash basin) shows higher concentrations of sulfate and chloride relative to bicarbonate, compared to other water supply wells. This water supply well location plots nearby background location MW-32BR, located south of the Unit 5 inactive ash basin, suggesting water chemistry upgradient of the ash basin may be variable. From the active ash basin, downgradient bedrock monitoring wells GWA-21BR and MW-20DR (located north of the ash basin between the basin and the Broad River) plot along with background wells BG-1BR, MW-24DR, and MW-32BR, indicating these downgradient wells are likely representative of unimpacted groundwater within the bedrock flow layer. From the Unit 5 inactive ash basin, downgradient bedrock monitoring wells GWA-31BR and MW-38BR, located northeast and north of the basin, plot with ash pore water locations U5-7S and U5-7SL indicating potential mixing with impacted source area groundwater. Bedrock monitoring well U5-2BR, located in bedrock beneath the southwest extension of the ash basin, plots with background and water supply well water chemistry results. This suggests bedrock groundwater south of the basin is upgradient and unimpacted by source area groundwater, and is consistent with north, northeast groundwater flow direction from the ash basin. See Section 6.3 for groundwater flow direction. The water chemistry signature of the water supply wells with available water chemistry data is similar to the background bedrock well data at the Site, indicating that these 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-24 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx wells reflect natural background conditions and are not impacted by the ash basins or ash storage area. The data does not indicate that offsite private water supply wells have been impacted by the active ash basin, Unit 5 inactive ash basin, the Units 1-4 inactive ash basin or the ash storage area at the CSS site. Surface Waters As shown in Figures 11-1 to 11-45, the extent of groundwater migration from the ash basins and ash storage area at concentrations greater than background and 2L/IMAC extend downgradient of the basins and ash storage area and intersect the Broad River and Suck Creek. Therefore, the surface water data may reflect contributions from groundwater migration from the ash basins and ash storage area. The updated CAP will provide this evaluation. CAP 1 and CAP 2 provided an evaluation of the COI concentrations in surface water due to groundwater discharge from the ash basin. The evaluation was performed by using a mixing model approach. The groundwater fluxes from the fate and transport model were used to represent the groundwater discharge. For each groundwater COI that discharges to surface waters at a concentration exceeding its applicable groundwater quality standard or criteria, the appropriate dilution factor and upstream (background) concentration were applied to calculate the surface water concentration. This concentration was then compared with the applicable water quality standard or criteria to determine surface water quality standard compliance. In Suck Creek, eight of nine surface water samples had no 2B exceedances. Sample location SW-4 had two historical reported 2B exceedances of pH. Sample SW-4 is downgradient of the ash storage area; however, the historical sampling results show an inconsistency in pH values at this location and do not suggest that the reported 2B exceedances in Suck Creek are a result of influence from the ash basin. The 2B exceedances of pH were below the concentrations reported in background samples. Background sample CCPSW-01 had one 2B exceedance of mercury. All other downgradient sample locations had mercury concentrations below concentrations reported in this background sample. Based on the available data for the upgradient and downgradient Suck Creek samples the CSS ash basin is not the source of 2B exceedances in Suck Creek. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 14-25 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx In the Broad River, four of seven downstream Broad River samples had no 2B exceedances. Sample location SW-4 had two historical reported 2B exceedances of pH. The 2B exceedances of pH were below the concentrations reported in background samples. Background sample CCPSW-01 had one 2B exceedance of mercury. All other downgradient sample locations had mercury concentrations below concentrations reported in this background sample. Turbidity and TDS are the only 2B exceedance reported in the background (SW-9); and dissolved oxygen, dissolved cadmium, and hardness are the only 2B exceedances reported downstream (SW-BRAB-01, SW-BRAB- 02, and SW-BRAB-03) in samples collected from the Broad River. The background sample has had exceedances of parameters that are inconsistent with reported values and concentrations downstream. Sample SW-BRAB-01 also had two historical exceedance of dissolved oxygen at 0.29 and 0.20 µg/L. Samples SW-BRAB-02 and SW- BRAB-02 had dissolved cadmium concentrations with a range of 0.17 µg/L to 0.18 µg/L. Hardness exceeding concentrations from these two locations had a range of 102 mg/L to 121 mg/L. These exceedances are inconsistent at each sample location and are not represented in other downstream locations. Based on the available data for the upstream and downstream Broad River samples, the CSS ash basin is not the source of 2B exceedances in the Broad River. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-1 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 15.0 CONCLUSIONS AND RECOMMENDATIONS The assessment described in this CAMA CSA 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 in accordance with the CAMA and 2L. The following conclusions are based on evaluation described in this CAMA CSA report: Ash sluiced to, and accumulated within, the ash basin and stored in the ash storage area is determined to be a source and cause of groundwater impacts at CSS. The updated CSA has determined no unacceptable risks to public health and safety from exposure to groundwater, surface water, or sediment impacts related to the ash basin. The CSS ash basins are currently designated as “Intermediate” risk under CAMA, meaning that closure of the ash basin is required by 2024. A "Low" risk classification and closure via a cap-in-place scenario are considered appropriate as alternative water supplies are being provided in accordance with G.S. 130A-309.213.(d)(1) of House Bill 630. Receptors including water supply wells and surface water bodies were identified and found to be not impacted by the ash basins and generally in compliance with applicable regulatory standards. Significant exposure pathways are understood and constituent concentrations detected in water supply wells are deemed to not be from the ash basin. Impacts to groundwater in all three flow layers have been identified beneath and downgradient of the ash basins and ash storage area at CSS. Supplemental data collection to support groundwater modeling and long-term monitoring is anticipated to support the CAP process. Secondary sources have been identified in soil beneath the ash. Shallow soil impacts are anticipated to be addressed through basin closure and the CAP. Surface water receptors downgradient of the ash basins and ash storage area (e.g. Broad River) demonstrate compliance with 2B standards, with the occasional exception of dissolved cadmium and hardness, TDS and pH, and DO. Localized influence from NPDES permitted outfall is likely contributing to some of these exceptions. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-2 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Additional sediment data collection is anticipated to support the evaluation of potential monitored natural attenuation (MNA) in the area of the groundwater plume discharge to surface water. The collection of additional data to support potential MNA as a groundwater corrective action strategy and additional plume definition is anticipated. A discussion of preliminary corrective action alternatives that may be appropriate to consider during the updated CAP development are presented herein. Overview of Site Conditions at Specific Source Areas 15.1 The horizontal and vertical extent of exceedances has been defined (Figure ES-1). Boron exceedances in the shallow flow layer are primarily located beneath the active ash basin and the western portion of the ash storage area, extending to the Broad River, and in the northern portion of the Units 1-4 inactive ash basin extending to the Broad River. In the deep flow layer, boron exceedances are located beneath the northern portion of the active ash basin, west of the active ash basin, beneath the toe of the active ash basin upstream dam, and beneath the western portion of the ash storage area, all within the compliance boundary. Boron exceedances in the deep flow layer are located north of the Unit 5 inactive ash basin. There are no boron exceedances reported in the bedrock flow layer. During the CSA assessment, an area of exceedances that appears not to be associated with the identified source areas (active ash basin, Units 1-4 inactive ash basin, Unit 5 inactive ash basin, and the ash storage area) is located east of Unit 6 and west of Suck Creek. Details regarding the exceedances reported in this area are included in Section 10.2. In the following discussion of the nature and extent of contamination, exceedances are defined as concentrations greater than the 2L/IMAC, except when the PBTV is greater than the 2L/IMAC, or there is no 2L/IMAC established for the constituent. In these cases, the PBTV is used to determine constituent exceedances. Active Ash Basin Chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS, and vanadium are also constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. The extent of exceedances of chromium is confined to the shallow layer, at the downstream dam extending near or beyond the compliance boundary. Chromium exceedances were not reported in the deep or bedrock flow layers. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-3 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The extent of exceedances of cobalt near or beyond the compliance boundary are limited to north of the ash basin downstream dam in the shallow flow layer and southeast of the basin in the bedrock flow layer. Cobalt exceedances in the bedrock flow layer are reported southeast and north of the ash basin. Cobalt exceedances are also detected near the waste boundary in the shallow and deep flow layers near the upstream dam. The extent of exceedances of iron in the shallow and deep flow layers is downgradient northwest and north of the basin and within or near the waste boundary at the upstream dam. The exceedances of iron reported north of the active ash basin downstream dam are detected near or beyond the compliance boundary. In the bedrock flow layer iron exceedances are reported at two wells within the waste boundary. The extent of exceedances of manganese in the shallow flow layer is at locations beneath the southern end of the basin, at the upstream dam within the compliance boundary. Shallow manganese exceedances near or beyond the compliance boundary were detected north of the active ash basin downstream dam. Manganese exceedances in the deep flow layer were reported northwest of the active ash basin within the compliance boundary and west and north of the active ash basin near or beyond the compliance boundary. Manganese exceedances are also reported in the bedrock flow layer beneath the active ash basin and near or beyond the compliance boundary north of the active ash basin. The extent of exceedances of strontium in the shallow flow layer is beneath the active ash basin within the waste boundary, and near or beyond the compliance boundary north of the basin near the downstream dam. Exceedances of strontium in the deep flow layer are located northwest of the ash basin at the upstream dam and near or beyond the compliance boundary west and north of the active ash basin. Bedrock flow layer exceedances are located near the upstream dam and near or beyond the compliance boundary north of the downstream dam. The extent of exceedances of sulfate is limited to the shallow flow layer, north of the active ash basin within the waste boundary, between the basin and the ash storage area. Sulfate exceedances were not detected in the deep or bedrock flow layers. The extent of exceedances of thallium in the shallow flow layer is within the compliance boundary west and northwest of the active ash basin. Thallium exceedances are detected in the deep flow layer at the north end of the ash basin near the ash storage area. Thallium exceedances were not reported in the bedrock flow layer. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-4 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The extent of exceedances of TDS exceedances in the shallow flow layer are located north of the active ash basin within the waste boundary, between the basin and the ash storage area. TDS exceedances were reported in the deep flow layer northwest of the active ash basin near the upstream dam within the compliance boundary. TDS exceedances were not reported in the bedrock flow layer. The extent of exceedances of vanadium in the shallow flow layer is located beneath the basin and north of the basin between the basin and the ash storage area. Vanadium exceedances in the deep flow layer are detected beneath the basin and at the upstream dam within the compliance boundary, and near or beyond the compliance boundary northeast of the downstream dam. A vanadium concentration equal to the PBTV in the bedrock flow layer was reported at one well upgradient and east of the active ash basin. A vanadium exceedance was detected within the compliance boundary near the active ash basin downstream dam. For soil samples below the ash in the active ash basin, boron, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium had reported values greater than the preliminary soil remediation goals (PSRG) for protection of groundwater (POG). Although some constituent levels were measured greater than the PSRG for POG standards in soil samples beneath the basin, when compared with the Site’s PBTVs, most constituent concentrations are similar to calculated soil background values, with the exception of boron, cobalt, and manganese. Soil sample analytical results indicate shallow impacts to the soil beneath the active ash basin. Units 1-4 Inactive Ash Basin Arsenic, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS and vanadium are also constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. An arsenic exceedance in the shallow flow layer is reported near or beyond the northern waste boundary. Arsenic exceedances were not reported in the deep or bedrock flow layers. The extent of exceedances of chromium in the shallow flow layer is located upgradient of the Units 1-4 inactive ash basin and at a location near or beyond the waste boundary north of the basin. Chromium exceedances in the deep flow layer are located north of the basin, near and beyond the waste boundary. Chromium exceedances were not reported in the bedrock flow layer. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-5 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The extent of exceedances of cobalt in the shallow flow layer is limited to one well location beneath the Units 1-4 inactive ash basin. Cobalt exceedances were not reported in the deep or bedrock flow layers. The extent of iron exceedances in the shallow and deep flow layers are located beneath the Units 1-4 inactive ash basin and near and beyond the northern and eastern waste boundary, and upgradient of the basin. Iron exceedances were not reported in the bedrock flow layer. The extent of exceedances of manganese in the shallow, deep, and bedrock flow layers is north of the Units 1-4 inactive ash basin, near or beyond the waste boundary, and south of the basin at upgradient locations. The extent of exceedances of strontium in the shallow, deep and bedrock flow layers is beneath the Units 1-4 inactive ash basin, north of the basin near and beyond the waste boundary and at upgradient locations south of the basin. The extent of exceedances of sulfate exceedances in the shallow, deep and bedrock flow layers is at upgradient locations south of the ash basin. Sulfate exceedances are not detected beneath or downgradient of the basin. The extent of exceedances of thallium at the Units 1-4 inactive ash basin in the shallow flow layer is located near or beyond the northeast and northwest waste boundary along. Thallium exceedances were not reported in the deep or bedrock flow layers. The extent of exceedances of TDS in the shallow flow layer is located within the Units 1- 4 inactive ash basin waste boundary. The exceedances reported in the deep and bedrock flow layers are upgradient, south of the basin. The extent of exceedances of vanadium in the shallow, deep and bedrock flow layer is downgradient near or beyond the northeast and northwest waste boundaries and at isolated upgradient locations in the shallow and bedrock flow layers. For soil samples below the ash, arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium had reported values greater than the PSRG for POG. Although some constituent levels were measured greater than the PSRG for POG standards in soil samples beneath the basin, when compared with the Site’s PBTVs most constituent concentrations are similar to calculated soil background values, with the exception of arsenic and chromium which had several PBTV exceedances reported. Soil sample 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-6 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx analytical results indicate shallow impacts to the soil beneath the Units 1-4 inactive ash basin. Unit 5 Inactive Ash Basin Arsenic, chromium, cobalt, iron, manganese, strontium, sulfate, thallium, TDS, and vanadium are constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. Arsenic exceedances were not reported in the shallow flow layer at the Unit 5 inactive ash basin. The extent of exceedances of arsenic in the deep and bedrock flow layers is an isolated location beneath the western portion of the basin within the waste boundary. Chromium exceedances in the shallow flow layer is limited to an isolated location east of and sidegradient of the Unit 5 inactive ash basin, beyond the waste boundary. Chromium exceedances in the deep flow layer were detected near or beyond the eastern waste boundary, including one sidegradient location. Chromium exceedances were not reported in the bedrock flow layer. Cobalt exceedances in the shallow and deep flow layers are located near or beyond the waste boundary north of and east of the Unit 5 inactive ash basin as well as an isolated location in the shallow flow layer east of and sidegradient of the basin waste boundary. Cobalt exceedances in the bedrock flow layer are located beneath the basin, and north of the basin, near or beyond the waste boundary. The extent of exceedances of iron in the shallow and deep flow layers is within the Unit 5 inactive ash basin waste boundary and north of the basin, near or beyond the waste boundary. One iron exceedance was reported south of and upgradient of the basin, beyond the waste boundary in the bedrock flow layer. The extent of exceedances of manganese in the shallow flow layer is within the waste boundary, and north and east, near or beyond the waste boundary. Manganese exceedances in the deep flow layer are located beneath the basin, and north, west, and east of the basin, near or beyond the waste boundary. Manganese in the bedrock flow layer is detected beneath the basin, and northeast of the ash basin beyond the waste boundary. The extent of exceedances of strontium in the shallow flow layer are located within the Unit 5 inactive ash basin, and at locations east and north of the basin, near and beyond the waste boundary, including locations sidegradient of the basin. Strontium 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-7 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx exceedances in the deep flow layer are located beneath the basin and at locations west, north and east of the basin, near and beyond the waste boundary. In the bedrock flow layer strontium exceedances are reported beneath the basin and beyond the waste boundary, northeast of the ash basin. The extent of exceedances of sulfate in the shallow flow layer is within, near, and beyond the waste boundary southeast of the ash basin. Sulfate exceedances are detected east and north of the Unit 5 inactive ash basin, near and beyond the waste boundary in the deep flow layer. An isolated sulfate exceedance is reported in the bedrock flow layer, beyond the waste boundary north of the basin. The exceedances of thallium in the shallow flow layer are located near and beyond the waste boundary, north and east of the Unit 5 inactive ash basin. Thallium in the deep flow layer is detected near or beyond the northern and eastern waste boundaries. A thallium exceedance was reported at isolated location beneath the western portion of the basin. The extent of exceedances of TDS in the shallow flow layer is near and beyond the waste boundary, east of the Unit 5 inactive ash basin. TDS exceedances in the deep flow layer are located near and beyond the waste boundary, east and north of the basin. An isolated TDS exceedance was reported north of ash basin, beyond the waste boundary. The extent of exceedances of vanadium in the shallow flow layer are located within the waste boundary, north of the Unit 5 inactive as basin near or beyond the waste boundary, and northeast of the basin, near and beyond the waste boundary. Vanadium exceedances in the deep flow layer are located beneath the basin, and southeast, northeast, north and northwest, near and beyond the waste boundary. Exceedances of vanadium in the bedrock flow layer are limited to an isolated area northeast of the basin, near or beyond the waste boundary. For the one soil sample below the ash, arsenic, chromium, cobalt, iron, manganese, and vanadium had reported values greater than the PSRG for POG. Although some constituent levels were measured greater than the PSRG for POG when compared with the Site’s PBTVs most constituent concentrations are similar to calculated soil background values, with the exception of arsenic. Soil sample analytical results indicate impacts to the soil beneath the Unit 5 inactive ash basin. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-8 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Ash Storage Area Chromium, cobalt, manganese, strontium, sulfate, thallium, TDS, and vanadium are also constituents detected in groundwater at concentrations greater than 2L/IMACs and/or PBTVs. Chromium exceedances are limited to one location within the ash storage area waste boundary in the shallow flow layer. Chromium exceedances were not detected in the deep or bedrock flow layers associated with the ash storage area. The extent of exceedances of cobalt exceedances in the shallow flow layer is located within the western portion of the ash storage area, and beyond the waste boundary within the compliance boundary. Cobalt exceedances were not detected in the deep flow layer. An isolated exceedance in the bedrock flow layer was reported beyond the waste boundary and within the compliance boundary downgradient of the western portion of the ash storage area. The extent of exceedances of manganese in the shallow flow, deep, and bedrock flow layers is near or beyond the compliance boundary, north of the western portion of the ash storage area. The extent of exceedances of strontium in the shallow, deep, and bedrock flow layers is located near or beyond the compliance boundary, downgradient of the western portion of the ash storage area. The extent of exceedances of sulfate in the shallow flow layer near or beyond the compliance boundary are located downgradient of the western portion of the ash storage area. No sulfate exceedances were reported in the deep or bedrock flow layers associated with the ash storage area. The extent of exceedances of thallium in the shallow flow layer is near or beyond the compliance boundary, downgradient of the western portion of the ash storage area. Thallium exceedances were not reported near or beyond the compliance boundary in the deep or bedrock flow layers. The extent of exceedances of TDS in the shallow flow layer is near or beyond the compliance boundary, downgradient of the western portion of the ash storage area. TDS exceedances were not reported near or beyond the compliance boundary in the deep or bedrock flow layers. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-9 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Vanadium exceedances were not reported near or beyond the compliance boundary in the shallow or deep flow layers. An isolated exceedance beyond the waste boundary and within the compliance boundary was reported north of the western portion of the ash storage area. For soil samples below the ash, chromium, iron, and vanadium had reported values greater than the PSRG for POG. Although some constituent levels were measured greater than PSRG for POG in soil samples beneath the ash storage area, when compared with the Site’s PBTVs the concentrations were less than the calculated soil background values. Soil sample analytical results do not indicate impacts to the soil beneath the ash storage area. 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 used to develop an understanding of the different aspects of site conditions, such as a hydrogeologic conceptual site model, and 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 CSS ash basins and ash storage area are located in the eastern and western portions of the Site and receive surface water runoff and groundwater recharge from upland areas south, east and west of the basins. Assessment results indicate the thickness of CCR ranges from a few feet to approximately 70 feet in the active ash basin, 50 feet in the Units 1-4 inactive ash basin (now excavated), 9.5 feet to 67 feet in the Unit 5 inactive ash basin, and from 7 feet to 57 feet in the ash storage area. Assessment findings determined that CCR accumulated in the ash basin is the primary source of impact to groundwater. As previously discussed, residual concentrations of COIs in soil beneath 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-10 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx the active ash basin, Units 1-4 inactive ash basin, and Unit 5 inactive ash basin may also represent a secondary source. The ash basin and ash storage area pore water migrates to the subsurface. Groundwater from the ash basins and ash storage area flows downgradient of the basins and discharges to the Broad River. The western portion of the ash storage area discharges to Suck Creek which flows to the Broad River. Horizontal migration of groundwater at the Site is generally controlled by topographic divide along McCraw Road (Duke Power Road) to the south. This topographic divides generally functions as a groundwater divide. The Broad River to the north of the Site also functions as a groundwater discharge zone to prevent continued migration to the areas north of the Broad River. The horizontal and vertical extent of exceedances has been defined. In groundwater, the maximum COI concentrations occur in the shallow and deep flow layers. The maximum concentrations are beneath and downgradient of the ash basins and ash storage area. 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 beneath and downgradient of the ash basins and ash storage area. The bedrock aquifer is generally the source of water for supply wells in the area. As outlined above, the bedrock aquifer has been impacted by CCR constituent migration from the ash basins; however, there are no downgradient water supply wells from the ash basins or ash storage area. Constituent concentrations in bedrock groundwater directly downgradient of the ash basins are less than 2L with the exception of isolated iron, sulfate, and TDS exceedances. The water chemistry signature of the water supply wells is similar to that of 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. As shown in Figures 11-1 to 11-45, the extent of groundwater migration from the ash basins and ash storage area at concentrations greater than background and 2L extend downgradient of the basins to the Broad River and Suck Creek. The surface water data reflect contributions from the ash basins, however exceedances of the 2B standards are not reported. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-11 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx The ecological risk assessment reported potential risks to birds and mammals exposed to aluminum in surface water and sediment of Exposure Area 1, as well as potential risks to birds exposed to selenium in Exposure Area 1. Risk estimates for Exposure Area 2 resulted in multiple receptors with LOAEL based risk estimates greater than 1 for several constituents. Additionally, the 2016 risk assessment resulted in potential ecological risk to mammals exposed to aluminum in Exposure Area 3. Risk estimate updates indicate risk within Exposure Areas 1 and 2 are consistent with the 2016 assessment. Surface water samples have not been collected in Exposure Areas 3 and 4 since the 2016 risk assessment. Samples evaluated within the two exposure areas were limited to AOW samples. As stated previously, AOW samples were not evaluated as part of this assessment due to inclusion in the NPDES permitting process. The SCM will be further refined after evaluation of the completed groundwater model in the CAP and the collection of additional information. Interim Monitoring Program 15.3 An Effectiveness Monitoring Program (EMP) is required by CAMA §130A-309.209 (b)(1)e. The EMP for CSS will begin once the basin closure and groundwater CAP have been implemented. After CAP approval but before final closure, an Interim Monitoring Plan (IMP) was proposed. The IMP is designed to supplement the compliance monitoring 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. The IMP and EMP are based on the hydrogeologic and engineering characteristics of the Site provided in the CSA and CAP. The CAP, and a proposed EMP, will be submitted at a future date; therefore, this section presents details concerning the IMP only. IMP Implementation 15.3.1 An IMP has been implemented in accordance with NCDEQ correspondence (NCDEQ, December 20, 2017) that provided an approved “Revised Interim Monitoring Plans for 14 Duke Energy Facilities” (Appendix A). This sampling plan has further been modified based on discussions and correspondence with NCDEQ. 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, 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-12 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx North Carolina, June 10, 2015 (Appendix D) conditionally approved by NCDEQ in a June 11, 2015 email with an attachment summarizing their approval conditions. A North Carolina-certified laboratory will analyze samples 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 monitored as part of the IMP are included in Table 15-2. IMP Reporting 15.3.2 Currently, data summary reports comprised of analytical results received during the previous month are submitted to NCDEQ on a monthly basis. In addition, NCDEQ directed that an annual IMP report be submitted by April 30 of the following year of data collection. The reports shall include materials that provide “an integrated, comprehensive interpretation of site conditions and plume status.” The initial report was to be submitted to NCDEQ no later than April 30, 2018; however, the December 20, 2017 correspondence provides that the required date for an annual monitoring report will be extended to a date in 2018 to be determined later. COIs for Monitored Natural Attenuation at Site Specific Source 15.4 Areas 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 were considered in this CSA for the determination of groundwater COIs. Hexavalent chromium, total uranium, and total radium were requested by NCDEQ to be considered COIs for the CSA. Based on these criteria and Site-specific conditions, observations, and findings, the following list of groundwater COIs for CSS have been initially developed: Arsenic Boron 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-13 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Chromium (total) Chromium (hexavalent) Cobalt Iron Manganese pH Strontium Sulfate Thallium TDS Vanadium Total Uranium Total Radium NCDEQ published “Monitored Natural Attenuation for Inorganic Contaminants in Groundwater: Guidance for Developing Corrective Action Plans Pursuant to NCAC 15A .0106 (l) in October 2017” (MNA Guidance). The purpose of the document is to outline NCDEQ DWR expectations and approvable MNA CAP for inorganic constituents. The document states that the requirements of 02L .0106 (l) must be met for each COI and each source area at a facility. A COI is defined in the document as a constituent that occurs above 02L standards/IMACs and background levels at or beyond a compliance boundary, or a constituent that occurs above 02L standards/IMACs and background levels in bedrock within a compliance boundary in an area with vulnerable downgradient receptors. The Units 1-4 inactive ash basin and the Unit 5 inactive ash basin do not have established compliance boundaries; therefore, the COI definition is interpreted to be “a constituent that occurs above 02L standards/IMACs and background levels at or beyond a waste boundary” for these ash basins. Due to the large waste area associated with the active ash basin, and that contaminated groundwater discharge moves toward two different areas and set of receptors, this basin has been divided into two source areas (active ash basin – Suck Creek and active 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-14 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx ash basin – Broad River) for COI determinations and will be assessed as such during the MNA evaluation in the CAP. Based on the criteria outlined in the MNA Guidance the following list of groundwater COIs have been determined for consideration in the CAP: Active Ash Basin – Suck Creek Cobalt Iron Manganese Strontium Active Ash Basin – Broad River Cobalt Iron Manganese Strontium Units 1-4 Inactive Ash Basin Boron Chromium (total) Cobalt Manganese Strontium Sulfate Thallium TDS Vanadium Unit 5 Inactive Ash Basin Arsenic Boron Chromium (total) 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-15 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Cobalt Iron Manganese Strontium Sulfate Thallium TDS Vanadium Ash Storage Area Manganese Strontium Vanadium Preliminary Evaluation of Corrective Action Alternatives 15.5 Closure of the ash basins is required by 2024 under CAMA (Intermediate Risk). Groundwater in the bedrock flow unit, typically used for private drinking water supply wells in the region, is generally not impacted. In locations beneath the ash basin where soil samples could be collected, analytical results indicate shallow impacts of COIs above PBTVs. Site-wide simulation data for the updated model will be extended out for the time period required to achieve compliance with the 2L or IMAC at the compliance boundary. 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 that a source control measure of either capping the ash basins and minimizing infiltration, or excavation, or a combination of the two, will be designed after 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 for the active ash basin, the Unit 5 inactive ash basin, and the ash storage area. The Units 1-4 inactive ash basin has been excavated. The updated CAP will evaluate potential groundwater remedial strategies in addition to closure options. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-16 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx CAP Preparation Process 15.5.1 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 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 updated CAP will include: Corrective action objectives and evaluation criteria Technology assessment Formulation of remedial action alternatives 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-17 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx Analysis, selection, and description of selected remedial action alternatives Conceptual design elements, including identification of predesign 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. COIs in groundwater flow are distributed throughout the shallow flow layer and into the transition zone/deep flow layer and fractured bedrock. The preliminary screening of potential groundwater corrective action follows: Source control by capping in place or excavation, and monitored natural attenuation, will be vital components to the CAP. Groundwater migration barriers. The depth and heterogeneity of the impacted zone must be considered to determine if this technology may be feasible. In-situ chemical immobilization. This technology has been demonstrated to be effective for a number of relevant COIs. Its ability to achieve required boron concentrations will require evaluation. Permeable reactive barrier. Similar to in-situ chemical immobilization, permeable reactive barrier technology can be evaluated for all site COIs. Groundwater extraction. Given Site conditions, preliminary screening of potentially applicable technologies indicates that some form of groundwater extraction could potentially be a viable choice as a key element of groundwater corrective action in combination with source control and 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 flow and transport and geochemical modeling. Summary 15.5.2 This preliminary evaluation of corrective action alternatives is intended to provide insight into the revised CAP preparation process, as outlined in 2L. It is 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 15-18 P:\Duke Energy Carolinas\21. CLIFFSIDE\CSA Update\FINAL Cliffside CSA January 2018.docx 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 constituents. If required, the potentially applicable technologies include several groundwater extraction technologies such as conventional vertical wells, along with angle- drilled and horizontal wells. Migration barriers, in-situ chemical immobilization, and permeable reactive barriers are also identified as potentially applicable to the development of remedial action alternatives. In the event that extracted groundwater may require treatment prior to discharge, several water treatment technologies for the relevant COIs are also identified, 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. 2018 Comprehensive Site Assessment Update January 2018 Cliffside Steam Station SynTerra Page 16-1 P:\Duke Energy Carolinas\21. 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