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Home My WebLink AboutNC0004774_CSA Report_20150823Comprehensive Site Assessment Report Buck Steam Station Ash Basin Site Name and Location Groundwater Incident No. NPDES Permit No. Date of Report Permittee and Current Property Owner Consultant Information Latitude and Longitude of Facility Buck Steam Station 1555 Dukeville Road Salisbury, NC 28146 Not Assigned NC0004774 August 23, 2015 Duke Energy Carolinas, LLC 526 South Church St Charlotte, NC 28202-1803 704.382.3853 HDR Engineering, Inc. of the Carolinas 440 South Church St, Suite 900 Charlotte, NC 28202 704.338.6700 350 71' 19" N, 800 37; 69" W This document has been reviewed for accuracy and quality commensurate with the intended application. Thomas M. Yanoschak, P.E. Senior Engineer to DUKE ENERGY ■aaneoar- Malcolm Schaeffer, L.C. Senior Geologist Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY Executive Summary - Buck Steam Station On August 20, 2014, the North Carolina General Assembly passed Session Law 2014-122, the Coal Ash Management Act of 2014 (CAMA). N.C. Gen. Stat. § 130A-309.211 requires the owner of a coal combustion residuals surface impoundment to submit a Groundwater Assessment Plan (Work Plan) to the North Carolina Department of Environment and Natural Resources (NCDENR) no later December 31, 2014 and a Groundwater Assessment Report (herein referred to as a Comprehensive Site Assessment [CSA]) no later than 180 days following approval of the Work Plan. Duke Energy submitted a Work Plan to NCDENR on September 25, 2014 establishing proposed site assessment activities and schedules for the implementation, completion, and submission of a CSA report in accordance with 15A NCAC 02L .0106(g) for the Buck Steam Station (Buck). NCDENR reviewed the Work Plan and provided Duke Energy with initial comments on November 4, 2014. A revised Work Plan was subsequently submitted to NCDENR on December 30, 2014 and NCDENR provided final comments and conditional approval of the revised Work Plan on February 24, 2015. This CSA was prepared to comply with the CAMA and is submitted to NCDENR within the allotted 180-day timeframe. Data generated during the CSA will be used in development of the Corrective Action Plan (CAP), due 90 days after submittal of this CSA. The purpose of this CSA is to characterize the extent of contamination resulting from historical production and storage of coal ash, evaluate the chemical and physical characteristics of the contaminants, investigate the geology and hydrogeology of the Site including factors relating to contaminant transport, and examine risk to potential receptors and exposure pathways. This CSA was prepared in general accordance with requirements outlined in the following statutes, regulations and documents: • Groundwater Classification and Standards, Title 15A North Carolina Administrative Code (NCAC), Subchapter 2L • Coal Ash Management Act of 2014, N.C. Gen. Stat. §§130A-309.200 et. seq., • Notice of Regulatory Requirements (NORR) issued by NCDENR on August 13, 2014, • Conditional Approval of Revised Groundwater Assessment Work Plan issued by NCDENR on February 24, 2015, and • Subsequent meetings and correspondence between Duke Energy and NCDENR. For this CSA, the source area is defined as the ash basin, which consists of the active ash basin and the inactive ash basin. Source characterization was performed to identify physical and chemical properties of ash, ash basin surface water, ash porewater, and ash basin seeps. The ash, ash basin surface water, ash porewater, and seep analytical results were compared to 2L Standards, IMACs, and other regulatory screening levels for the purpose of identifying constituents of interest (COls). These COls are considered to be associated with potential impacts to soil and groundwater from the ash basin. This CSA also identifies constituents that exceeded 2L Standards or IMACs from groundwater sample locations outside the ash basin boundary. For the purposes of this report, these ES-1 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY constituents were also identified as COls. Some COls (e.g., iron and manganese) are present in background and upgradient monitoring wells and thus require careful examination to determine whether their presence downgradient of the ash basin is naturally occurring or a result of ash handling and storage. Descriptions of COls outside the ash basin boundary are identified in Section 10 (Groundwater Characterization) and Section 11 (Hydrogeological Investigation) of this CSA. This inclusive approach to identification of COls will be refined during development of the CAP to focus on those constituents that are attributable to the ash basin. COls were also evaluated in the human health and ecological screening level risk assessment in Section 12.0. In addition to evaluating the distribution of constituents across the Buck site, significant factors affecting constituent transport, and the geological and hydrogeological features influencing the movement and chemical and physical character of the COls were also evaluated. Some Cols (e.g., antimony, cobalt, chromium, iron, manganese and vanadium) are also present in background monitoring wells and thus require careful examination to determine whether their presence downgradient of the ash basin or ash storage areas is naturally occurring or a result of ash handling and storage. The IMACs were issued in 2010, 2011 and 2012; however, NCDENR has not established a 2L Standard for these constituents as described in 15A NCAC 2L.0202(c). For this reason, the IMACs noted in this report are for reference only. In addition to evaluating the distribution of constituents across the Buck site, significant factors affecting constituent transport, the geological and hydrogeological features influencing the movement and the chemical -physical character of the COls were also evaluated. The assessment consisted of the following activities: • Completion of soil and rock borings and installation of groundwater monitoring wells to faciliatate collection and analysis of chemical, physical, and hydrogeological parameters of subsurface materials encountered within and beyond the waste and compliance boundaries. • Evaluation of testing data to supplement the Site Conceptual Model (SCM). • Revision to the Receptor Survey previously completed in 2014. • Completion of a Screening -level Risk Assessment. Based on scientific evaluation of historical and new data obtained during completion of the above -referenced activities, the following conclusions can be drawn: • No imminent hazard to human health or the environment has been identified as a result of groundwater migration from the ash basin or ash storage areas. • Recent groundwater assessment results are generally consistent with previous results from historical and routine compliance boundary monitoring well data although some new COls were identified due to a more robust sampling program. • Upgradient, background monitoring wells contain naturally occurring metals and other constituents at concentrations that exceeded their respective 2L Standards or IMACs. This information is used to evaluate whether concentrations in groundwater ES-2 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin EXECUTIVE SUMMARY downgradient of the basin and ash storage area are also naturally occurring, originate from upgradient sources or might be influenced by migration of constituents from the ash basin and ash storage area. Examples of naturally occuring metals and consituents include antimony, chromium, cobalt, iron, manganese, and vanadium, which were all detected in background groundwater samples at concentrations greater than 2L Standards or IMACs. Groundwater flow is predominately in the north direction toward the Yadkin River and is downgradient from and not towards off -site receptors. However, there also is a component of groundwater flow to the west of Cell 1 and there is localized flow in an area east of the source that requires further evaluation (between Cells 2 and 3). No information gathered as part of this CSA suggests that water supply wells or springs within the 0.5-mile radius of the compliance boundary are impacted by the source, aside from the single permitted well owned by Duke Energy. The U.S. Environmental Protection Agency (USEPA) has identified constituents for groundwater detection monitoring programs that can be used as indicators of groundwater contamination from coal combustion residuals which may be evaluated for statistically significant increases over background with time. Specifically, boron and sulfate would be expected to migrate rapidly and would provide early detection as to whether contaminants were migrating from the ash basin system. The horizontal and vertical migration of boron best represents the groundwater flow and potential transport system at the site. Sulfate, while generally a good indicator, can occasionally occur naturally above its applicable standards and should be used as an indicator with more caution. Sulfate exceedances at well locations outside the waste boundary appear to be unrelated to the ash basin, and may be related to the bedrock geology. This is indicated by the unique geochemistry and lack of boron observed at certain wells exhibiting exceedances of sulfate, as well as the general lack of sulfate exceedances in ash basin porewater. Figure ES-1 indicates the estimated horizontal extent of 2L Standard exceedances for boron in the shallow, deep, and bedrock monitoring layers at the site. The horizontal migration of boron in the flow layers best represent the dominant flow and transport system in the vicinity of the ash basin and ash storage area. Vertical migration of constituents is impeded but not eliminated by underlying bedrock. Boron is highly soluble and was identified by the USEPA as one of the leading indicators for releases of contaminants from ash. Because of these characteristics, boron can be used to represent the general extent of the shallow, deep, and bedrock flow layers impacted by the ash basin and ash storage area. The approximate extent of groundwater impacted with COI exceedances attributable to CCRs, such as boron, is limited to the shallow, deep, and bedrock flow layers beneath the ash basin and ash storage area, and areas immediately downgradient of the ash basin and ash storage area located to the north. Based on available data, it appears groundwater impacted by the ash basin and ash storage area is contained within the Duke Energy property boundary. • There are no indications of boron exceedances of the 2L Standards or IMACs upgradient from the Buck site. ES-3 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY • The assessment identified potential soil and groundwater impacts. The approximate extent of measured constituents is primarily limited to an area within the ash basin compliance boundary and the area north of the compliance boundary to the Yadkin River. There also appears to be a smaller component of groundwater flow west of ash basin Cell 1 (and within the property boundary) resulting in potential movement of constituents beyond the western compliance boundary between Cell 1 and the unnamed tributary to the Yadkin River near the western extent of the Buck site. • NCDENR identified seeps and CSA-identified seeps that contained water were sampled during the CSA field program. The one NCDENR seep that could be sampled (BSWW002 S001) did not exhibit USEPA ash indicator exceedances of the 2L Standards.Samples obtained from CSA-identified seeps S-9 and TERRACOTTA PIPE #1, both located near the base of the Cell 1 dam, were reported above the 2L Standard for boron. • Sediment was sampled at 14 active and dry seep locations. The only USEPA ash related COI that exhibited an exceedance of the North Carolina Industrial Health and Protection of Groundwater Preliminary Soil Remediation Goal (PSRG) was boron which occurred at location TERRACOTTO PIPE #1. • The data included in this CSA are to be used in the development of a Corrective Action Plan, due 90 days after submittal of this CSA. This will include groundwater modeling to evaluate the site's suitability to use monitored natural attenuation (MNA). If not applicable, additional measures such as active remediation by hydraulic capture and treatment, among others, would be evaluated. When properly applied, alternatives such as these can provide effective long term management of sites requiring corrective action. Brief summaries of essential portions of the CSA are presented in the following sections. ESA Source Information Duke Energy owns and formerly operated the Buck station, located on the Yadkin River in Rowan County near the town of Salisbury, North Carolina. Buck began operation in 1926 as a coal-fired generating station. The Buck Combined Cycle Station (BCCS) natural gas facility was constructed at the site and began operating in late 2011. Subsequently, Buck was decommissioned and taken offline in April 2013. The coal ash residue from Buck's coal combustion process was historically disposed of in the station's ash basin system located adjacent to the station and the Yadkin River. The discharge from the ash basin system is permitted by the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES) Permit NC0004774. Since 2006, Duke Energy has implemented voluntary and NPDES permit -required groundwater monitoring at Buck. Twice per year voluntary groundwater monitoring around the Buck ash basin was performed from November 2006 until May 2010, with analytical results submitted to the NCDENR DWR. Compliance groundwater monitoring as required by the NPDES permit ES-4 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin EXECUTIVE SUMMARY began in March 2011. From March 2011 through July 2015, the compliance groundwater monitoring wells at Buck have been sampled three times per year for a total of 14 times. The Buck ash basin system is located near the Yadkin River and comprises three cells designated as Cell 1, Cell 2, and Cell 3, and associated embankments and outlet works. The ash basin is located to the south (Cell 1) and southeast (Cells 2 and 3) of the retired Buck Units through 6 and the BCCS. An area between Cell 1 and Cell 2 has also been utilized for storage of dredged ash from Cell 1 and is referred to as the ash storage area. This unlined storage area is located topographically upgradient and adjacent to the east side of Cell 1. The dry ash storage area was constructed in 2009 by excavating ash within the eastern half of Cell 1 in order to provide additional capacity for sluiced ash and covers approximately 14 acres. All coal ash from Buck was disposed of in the ash basin from approximately 1957 until 2013. Fly ash precipitated from flue gas and bottom ash collected in the bottom of the boilers were sluiced to the ash basin using conveyance water withdrawn from the Yadkin River. The ash basin system is operated as an integral part of the station's wastewater treatment system, which receives permitted and variable discharges from the ash removal system, coal pile runoff, landfill leachate, the station yard drain sump, and site stormwater. ES.2 Initial Abatement and Emergency Response No imminent hazard to human health or the environment has been identified; therefore, initial abatement and emergency response actions are not required. ES.3 Receptor Information Properties located within a 0.5-mile radius of the Buck ash basin compliance boundary generally consist of residential, agricultural, and undeveloped properties located in Rowan County to the west, south, and east of the ash basin. The Yadkin River flows east along the northern boundary. Hunting and game lands are located north of the ash basin system across the Yadkin River in Davidson County. Duke Energy submitted a receptor survey to NCDENR (HDR 2014a) in September 2014, and subsequently submitted to NCDENR a supplement to the receptor survey (HDR 2014b) in November 2014 based on the CSA Guidelines. The update included contacting and/or reviewing the agencies/records to identify public and private water supply sources identified and reviewing questionnaires that were received after the submittal of the November 2014 supplement to the September 2014 receptor survey (i.e. questionnaires received after October 31, 2014). The purpose of the receptor survey was to identify the exposure locations that are critical to be considered in the groundwater transport modeling and human health risk assessment. The CSA receptor survey activities included contacting and/or reviewing the following agencies/records to identify public and private water supply sources, confirm the location of ES-5 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin EXECUTIVE SUMMARY wells, and/or identify any wellhead protection areas located within a 0.5-mile radius of the Buck ash basin compliance boundary: • NCDENR Division of Water Resources (DWR) Public Water Supply Section's (PWSS) most current Public Water Supply Water Sources GIS point data set; • NCDENR DWR Source Water Assessment Program (SWAP) online database for public water supply sources; • Environmental Data Resources (EDR) local/regional water agency records review; • Rowan County Health Department Environmental Health Division; • Davidson County Health Department; • Salisbury -Rowan Utilities Department; and • USGS National Hydrography Dataset. The review of these records identified a total of 166 private water supply wells within a 0.5-mile radius of the Buck ash basin compliance boundary. The Rowan County Health Department had records for 28 of the 166 identified private water supply wells. Ten additional private water supply wells are assumed to exist since well houses could not be visually observed at these residences located within a 0.5-mile radius of the Buck ash basin compliance boundary. Two public water supply wells were identified within a 0.5-mile radius of the Buck ash basin compliance boundary. One water supply well was identified within the Duke Energy property boundary that supplies drinking water to the site.. Several unnamed tributaries of the Yadkin River were identified within a 0.5-mile radius of the ash basin, and several surface water features that flow toward the Yadkin River were identified within a 0.5-mile radius of the Buck ash basin. ESA Sampling / Investigation Results ES.4.1 Background Findings As part of the CSA, Duke Energy installed seven additional nested wells (three shallow, two deep, one upper bedrock, and one bedrock monitoring well) in selected areas of the site upgradient from the ash basin and ash storage area to supplement the existing nested shallow and deep monitoring wells (installed in 2006) by providing additional background soil and groundwater quality data. The COI concentration range in background groundwater samples which exceeded the 2L Standard are provided below. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY Constituent of Interest Groundwater 2L Standard or IMACs (Ng/L) Range of Exceedances Antimony 1 3.8 pg/L to 5.8 Ng/L Chromium 10 0.22J pg/L to 10.3 pg/L Cobalt 1 4 Ng/L to 7.2 pg/L Iron 300 306J Ng/L to 1,900 pg/L Manganese 50 54 pg/L to 850 Ng/L Vanadium 0.3 0.86J pg/L to 26.6 pg/L These COls were found to be present within groundwater monitoring wells at several locations across the site. Their presence within the background wells at concentrations exceeding the 2L or IMAC Standards requires analysis to determine whether downgradient exceedances are due to natural condition or impacts from the ash basin and ash storage area. ES.4.2 Nature and Extent of Contamination Soil and groundwater beneath the ash basin and ash storage area has been impacted by ash handling and storage at the Buck site. Concentrations of several COls appear to exceed their respective 2L Standards or IMACs in groundwater beyond the compliance boundary toward the Yadkin River, although some of these COls also exceed 2L in the background wells. These exceedances appear contained on Duke Energy Property. Samples obtained from on -site seeps also exhibit concentrations of COls exceeding their respective 2L Standards or IMACs. ES.4.2.1 Groundwater - Shallow Flow Layer Within the shallow flow layer (including beneath the ash storage area), there are five Cols identified as in the groundwater in multiple groundwater samples: cobalt, chromium, iron, manganese, and vanadium. All of these COls also appear within one or more of the background well locations at concentrations exceeding the applicable groundwater standard. Almost all of the iron exceedances within the shallow aquifer (12 of 13) occurred within unfiltered samples indicating the source of the iron within the shallow groundwater samples is primarily suspended solids. Six other COls identified in the shallow flow layer are antimony, boron, nickel, selenium, sulfate, and Total Dissolved Solids, but they are in isolated locations. ES.4.2.2 Groundwater - Deep Flow Layer Within the deep flow layer (including beneath the ash basin and ash storage area), there are seven COls identified in the groundwater (D wells): antimony, boron, chromium, cobalt, iron, manganese, and vanadium. Vanadium also appears within three of the deep flow layer background well locations at concentrations exceeding the applicable 2L Standard or IMAC. Almost all of the iron exceedances within the deep flow layer (10 of 12) occurred within unfiltered samples indicating the source of the iron within the deep flow layer groundwater samples is primarily suspended solids. Two other COls identified in the deep flow layer are sulfate and TDS, but they are in isolated locations. ES-7 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY ES.4.2.3 Groundwater — Bedrock Flow Layer Within the bedrock flow layer (including beneath the ash basin), there are four COls identified in the groundwater (BR and BRU wells): antimony, chromium, iron, manganese, and vanadium. None of these COls appear within the bedrock background well location (BG-3BRU) at a concentration exceeding the applicable groundwater standard. All eight of the iron exceedances within the bedrock flow layer occurred within unfiltered samples indicating the source of the iron within the bedrock groundwater samples is primarily suspended solids. Six other COls identified in the bedrock flow layer are barium, boron, cobalt, selenium, sulfate and TDS, but they are in isolated locations. ES.4.2.4 Seep Samples Seep sampling results at the Buck site have identified nine Cols in the seep water: antimony, arsenic, boron, chromium, cobalt, iron, manganese, thallium, and vanadium. Comparing COI concentrations in the seep water to the maximum COI concentrations encountered in groundwater sampled from the background wells indicates nine seep locations (BSWW002 S001, Terracotta Pipe #1, Culvert Discharge, S-1, S-2, S-3, S-5, S-8, and S-9) where at least one seep COI concentration exceeded the maximum background groundwater COI concentration (arsenic, boron, chromium, cobalt, iron, manganese, thallium, and vanadium) . ES.4.2.5 Soil, Rock and Sediment Concentrations Soil samples were obtained from 29 separate locations during CSA drilling activities within the Buck site (including locations beneath the ash basin and ash storage area). Eight Cols were identified in soil samples obtained from these locations: arsenic (5 locations), barium (1 location), boron (4 locations), cobalt (29 locations), iron (29 locations), manganese (29 locations), selenium (5 locations), and vanadium (29 locations). With the exception of barium, all of these COls appear in one or more of the background well locations at concentrations exceeding the most restrictive PSRG standard. The COI concentrations observed in the soil from the various locations within the Buck site generally bracket the concentrations observed in soil samples from the background locations or within reasonable proximity of the bracketed background concentrations. Rock samples (including partially weathered rock [PWR] samples) were obtained from ten separate locations during CSA drilling activities within the Buck site, including locations beneath the ash basin and ash storage area. Five COls were identified in rock samples obtained from these locations: arsenic (1 location), cobalt (8 locations), iron (10 locations), manganese (9 locations), and vanadium (8 locations). With the exception of arsenic, all of these COls appear within the background location where rock was obtained (BG-2) at concentrations exceeding the most restrictive PSRG standard. Sediment samples were obtained from 14 seep locations at the Buck site. Seven COls were identified in the sediment samples: arsenic (4 locations), boron (1 location), cobalt (all locations), iron (all locations), manganese (13 locations), selenium (1 location) and vanadium (all locations). A background sediment location (SW-2) was not obtained due to dry conditions at the time of sampling; therefore a comparison of these results with background conditions is ES-8 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY not possible at this time. Such a comparison may be possible after completion of the second comprehensive sampling event and will be included in the CSA supplement. ES.4.3 Maximum Contaminant Concentrations The maximum contaminant concentrations reported in groundwater, ash porewater, seep water, and ash basin surface water samples collected during the CSA are listed below. Maximum Constituent of Interest (COI) Concentrations COI Background wells Groundwater (Ng/L) Ash Porewater (N9/L) Seep Water (N9/L) Ash Basin Surface Water (Ng/L) Aluminum 160 n/a n/a n/a 13,000 Antimony 5.8 19.3 24.4 1.8 n/a Arsenic 11 14.9 1,350 38.6 71.3 Barium 86 830 720 n/a n/a Boron 49J 3,000 6,500 820 n/a Cadmium 0.025J n/a n/a n/a 0.37 Chromium 10.3 65.4 n/a 32.7 n/a Cobalt 6.8 356 44.7 41.1 23.9 Copper 45.8 n/a n/a n/a 32.4 Iron 1,900 27,900 44,700 34,900 n/a Lead 0.24 n/a n/a n/a 12.7 Manganese 850 4,100 3,900 3,900 n/a Nickel 10.9 107 n/a n/a n/a Selenium 0.39J 30.3 n/a n/a n/a Sulfate 22,700 703,000 n/a n/a n/a TDS 175,000 1,046,000 565,000 n/a n/a Thallium 0.032J 0.24 0.67 n/a 0.45 Vanadium 26.6 67.9 347 132 n/a Zinc 77 n/a n/a n/a 50 J = Estimated Concentration ES.4.4 Source Characterization Source characterization was performed through the completion of borings and installation of groundwater monitoring wells within the footprint of the ash basin cells, ash storage area, associated solid matrix (ash), and aqueous sample (ash porewater),and the collection and analysis of samples. Ash samples were collected for analysis of physical characteristics (e.g., grain size, porosity, etc.) to provide data for evaluation of retention/transport properties within and beneath the ash basin and ash storage area. Ash samples were collected for analysis of chemical characteristics (e.g., total inorganics, leaching potential, etc.). The results of the characterization will be used to refine the CSM and to provide data for use in the CAP. Review of laboratory analytical results of ash samples collected from the ash basin and ash storage area identified eight COls including arsenic, cobalt, barium, boron, cobalt, iron, manganese, selenium, and vanadium. COls identified in ash basin porewater include antimony, arsenic, barium, boron, cobalt, iron, manganese, thallium, and vanadium. COls identified in ash ES-9 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY basin surface water include aluminum, antimony, arsenic, cadmium, cobalt, copper, lead, thallium, and zinc. SPLP (Synthetic Precipitation Leaching Procedure) testing was conducted to evaluate the leaching potential of Cols from ash. Although SPLP analytical results are being compared to the 2L Standards and IMACs, these samples do not represent groundwater samples. The results of SPLP analyses indicated that the following COls exceeded their 2L Standards: antimony, arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium. However, many factors influence the transport of these COls and any potential impacts to groundwater over time will be investigated through modeling as part of the CAP. There are 14 seeps (S-1 through S-10, Culvert Discharge, Wet Area Near Pump House, Terracotta Pipe #1, and Terracotta Pipe #2) located within the Duke Energy property boundary and three seeps (S-1 A, S-1 B, and S-1 C) located outside of the Duke Energy property boundary associated with the ash basin at the Buck site, excluding the "NCDENR seeps." Duke Energy was not able to obtain permission from the property owner to obtain off -site seep samples S-1A, S-1 B, and S-1 C; therefore these seeps were not sampled. Twelve of the 14 on -site seeps were sampled as the remaining seeps (Wet Area Near Pump House and Terracotta Pipe #2) were dry on the day of sampling. Of the seep locations sampled in time for this report, seven COls were reported exceeding the 2L Standards: boron, chromium, cobalt, iron, manganese, thallium, and vanadium. There are six NCDENR seep locations identified at Buck for sampling. Only one seep, BSWWO02 S001, was active on the day of sampling and the rest were dry. Samples collected from BSWWO02 S001 exceeded the 2L or IMAC Standards for the following COls: antimony, arsenic, iron, manganese, and vanadium. ES.4.5 Regional Geology and Hydrogeology The Buck site is within the Charlotte terrane, one of a number of tectonostratigraphic terranes that have been defined in the southern and central Appalachians and is in the western portion of the larger Carolina superterrane (Horton et al. 1989; Hibbard et al. 2002; Hatcher et al. 2007). On the northwest side, the Charlotte terrane is in contact with the Inner Piedmont zone along the Central Piedmont suture along its northwest boundary and is distinguished from the Carolina terrane to the southeast by its higher metamorphic grade and portions of the boundary may be tectonic in origin (Secor et al. 1998; Dennis et al. 2000). The Charlotte terrane is dominated by a complex sequence of plutonic rocks that intrude a suite of meta -igneous rocks (amphibolite metamorphic grade) including mafic gneisses, amphibolites, meta-gabbros, and metavolcanic rocks with lesser amounts of granitic gneiss and ultramafic rocks with minor metasedimentary rocks including phyllite, mica schist, biotite gneiss, with quartzite and marble along its western portion (Butler and Secor 1991; Hibbard et al. 2002). The general structure of the belt is primarily a function of plutonic contacts. The groundwater system in the Piedmont region is described as being comprised of two interconnected layers, or two -medium system: 1) residual soil/saprolite and weathered fractured ES-10 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY rock (regolith) overlying 2) fractured crystalline bedrock. 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 regolith layer serves as the uppermost zone of the unconfined groundwater system and provides an intergranular medium through which the recharge and discharge of water to and from the underlying fractured rock occurs. A transition zone (TZ) of higher hydraulic conductivity at the base of the regolith is present in many areas of the Piedmont (Schaeffer 2014a). Typically, the residual soil/saprolite is partially saturated and the water table fluctuates within it. Water movement is generally preferential through the overlying soil and saprolite and weathered/fractured bedrock of the TZ. 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. ES.4.6 Site Geology and Hydrogeology The Buck site and its associated ash basin and ash storage areas are located in the Charlotte terrane. The Charlotte terrane consists of an igneous complex of Neoproterozoic to Paleozoic ages (Hibbard et al, 2002) that range from felsic to mafic in composition (Butler and Secor 1999). The Charlotte terrane is bordered on the east and southeast by the Carolina terrane and to the west and northwest by the Inner Piedmont (Cat Square and Tugaloo terranes) and the Kings Mountain terrane. The structural contact of the Inner Piedmont and Charlotte terrane is the Central Piedmont Shear Zone. The Buck site is underlain by interbedded felsic, intermediate, and mafic metavolcanic rocks. The felsic metavolcanic rocks are fine- to medium -grained, locally coarse -grained or agglomeritic, rhyolitic to dacitic metatuffs. The intermediate and mafic metavolcanic rocks are fine- to medium -grained, locally coarse -grained or agglomeritic rocks of basaltic, andesitic, and dacitic compositions. They are primarily tuffs and flows and with minor hypabyssal intrusives present. The rocks are metamorphosed to the upper amphibolite grade of metamorphism. Based on the site investigation, the groundwater system in the natural materials (alluvium, soil, soil/saprolite, and bedrock) at Buck is consistent with the Piedmont regolith-fractured rock system and is an unconfined, connected system of three flow layers. In general, groundwater within the shallow, deep (TZ), and bedrock layers flows radially from the ash basins and nouthward toward the Yadkin River. ES.4.7 Existing Groundwater Monitoring Data Twelve monitoring wells were installed by Duke Energy in 2006 as part of a voluntary groundwater monitoring system near the ash basin. Voluntary monitoring wells MW-2S and ES-11 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY MW-2D were abandoned during construction of the Buck Combined Cycle Station. With the exception of MW-6S, MW-6D, MW-3S, and MW-3D, no samples are currently being collected from the voluntary wells, and as a result, they are not included in this CSA. Compliance groundwater monitoring as required by the Buck NPDES Permit NC0004774 began in March 2011 and includes 14 wells. NPDES Permit Condition A (11), Version 1.1, dated June 15, 2011, lists the groundwater monitoring wells to be sampled, the parameters and constituents to be measured and analyzed, and the requirements for sampling frequency and reporting results (provided in Table 2-1). Locations for the compliance groundwater monitoring wells were approved by the NCDENR DWR or it predecessor. One or more groundwater quality standards (2L Standards) have been exceeded in groundwater samples collected from each of the compliance monitoring wells. Exceedances have occurred for boron, chromium, iron, manganese, pH, sulfate, and total dissolved solids (TDS). ES.4.8 Screening -Level Risk Assessment The prescribed goal of the human health and ecological screening level risk assessments is to evaluate the analytical results from the COI sampling and analysis effort and using the various criteria taken from applicable guidance, determine which of the COls may present an unacceptable risk, in what media, and therefore, should be carried through for further evaluation in a baseline human health or ecological risk assessment or other analysis, if required. Constituents of Probable Concern (COPCs) are those COls that have been identified as having possible adverse effects on human or ecological receptors that may have exposure to the COPCs at or near the site. The COPCs serve as the foundation for further evaluation of potential risks to human and ecological receptors. To support the CSA effort and inform corrective action decisions, a screening level evaluation of potential risks to human health and the environment to identify preliminary, media -specific COPCs has been performed in accordance with applicable federal and state guidance, including the Guidelines for Performing Screening Level Ecological Risk Assessments within the North Carolina Division of Waste Management (NCDENR, 2003). The criteria for identifying COPCs vary by the type of receptor (human or ecological) and media, as shown in the comparison of contaminant concentrations in various media to corresponding risk -based screening levels presented in Tables 12-1 through 12-9. COls were not screened out as COPCs based on a comparison to background concentrations, as the NCDENR Division of Waste Management's Screening Level Environmental Risk Assessment guidance (2003) does not allow for screening based on background. Site -specific background concentrations will be considered in the uncertainty section of the baseline ecological risk assessment, if determined to be necessary. This initial screening, does not specifically identify that health or environmental risks are present, rather the results indicate constituents in the environmental media for further investigation by a site -specific risk assessment. It should be noted that the observed levels of ES-12 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin EXECUTIVE SUMMARY certain COls in the naturally occurring background at Buck would also warrant consideration of a BERA. N ES.4.9 Development of Conceptual Site Model The human health and ecological risk assessment conceptual site models, illustrating potential pathways of exposure from source to receptors are provided in this report. In the initial site conceptual hydrogeologic model presented in the Work Plan, the geological and hydrogeological features influencing the movement, chemical, and physical characteristics of contaminants were related to the Piedmont hydrogeologic system at the site. A hydrogeological site conceptual model was developed from data generated during previous assessments, existing groundwater monitoring data, and 2015 groundwater assessment activities. Groundwater flow is predominately in the north direction toward the Yadkin River and is downgradient from and not towards off -site receptors. However, there also is a component of groundwater flow to the west of Cell 1 and there is localized flow in an area east of the source that requires further evaluation (between Cells 2 and 3). ES.4.10 Identification of Data Gaps Through completion of groundwater assessment field activities and evaluation of data collected during those activities, Duke Energy has identified data gaps that will require further evaluation to refine the CSM. The data gaps have been separated into three groups: 1) data gaps resulting from temporal constraints, 2) data gaps resulting from evaluation of data collected during the CSA, and 3) data gaps resulting from other sources. ES.4.10.1 Data Gaps Resulting from Temporal Constraints Data gaps identified in this category are generally present due to insufficient time to collect, analyze, or evaluate data collected during the CSA activities. It is expected that the majority of these data gaps will be remedied in a CSA supplement to be submitted to NCDENR following completion of the second comprehensive groundwater sampling event. • Mineralogical Characterization of Soil and Rock — a total of 16 soil, three TZ, and 9 bedrock samples were submitted to three third -party mineralogical testing laboratories for analysis of soil and rock composition. As of the date of this report, Duke Energy has not received all of the results of this testing; however, results will be provided in the CSA supplement. • Additional Speciation of Monitoring Wells — In order to meet the requirements of the NORR, Duke Energy conducted speciation of groundwater samples for arsenic, chromium, iron, manganese, and selenium from selected wells along inferred groundwater flow transects. Adjustments to the speciation sampling are proposed in Section 15.0, the results of which will be reported in the CSA supplement. • Dry Sampling Locations — Due to dry conditions at the time of the initial sampling event, several proposed surface water and seep sampling locations were dry and could not be sampled. Another attempt to sample these locations will be made during the second Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY comprehensive groundwater sampling event. If successful, the results will be provided in the CSA supplement. These locations include: o Surface water locations SW-1 and SW-2 located along an unnamed tributary to the Yadkin River on the east side of the Buck site. o On -site seeps:. Seeps identified as Wet Area Near Pump House and Terracotta Pipe #2 were dry and could not be sampled. o NCDENR seep locations BS SWO01 AA S001, BS SWO03AA S001, BSSWO01 S001, BSSW074SO01, and BSSW074SO01. ES.4.10.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities • A shallow groundwater monitoring well in the nest of GWA-2BRU and GWA-2BR would assist with the groundwater flow direction determination in this location. Additional monitoring well nests nortwest and southwest of GWA-2BRU/BR would assist in refining groundwater flow direction in this area and provide information regarding constituent concentrations between the Cell 2 Primary Pond and the southern pond associated with the Cell 3 Secondary Pond. • The bedrock background monitoring well BG-1 BR could not be sampled due to insufficient water in the well during the sampling event. A replacement bedrock background well in this location may be warranted if BG-1 BR is not a viable well. Also, a bedrock well installed at the BG-3S/D would provide additional data regarding background bedrock concentrations at the site. • Groundwater samples were not collected from all of the onsite voluntary wells or existing monitoring wells that were installed during the site closure investigation. During subsequent sampling events, groundwater elevations will be measured and groundwater samples will be collected from these wells in conjunction with the newly installed assessment monitoring wells. • The vanadium method reporting limit provided by the analytical laboratory was 1.0 ug/L. The IMAC for vandium is 0.3 ug/L. The vanadium results reported at concentrations less than the laboratory method reporting limit are estimated. During subsequent monitoring events, a laboratory method reporting equal to or less than the IMAC should be utilized. • Review of Non -Ash Contamination Information: Review of information regarding areas of non -ash contamination (i.e., petroleum -contaminated areas) to evaluate potential interference with remedial methods is needed, if applicable. • Obtain soil samples located outside of the ash basin for SPLP analysis to compare results against SPLP analysis of ash. • Perform mineralogy analysis of soil and rock samples in wells where COls are present above 2L or IMAC Standards to determine if constituents occur naturally ES.4.10.3 Data Gaps Resulting from Other Sources • Sampling of Off -Site Seeps — the Work Plan included obtaining a surface water sample (S-1A) and samples at two seep locations (S-1 B and S-1 C) associated with an off -site ES-14 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY pond located near the eastern extent of Duke Energy's property boundary. Duke Energy was not able to obtain permission from the property owner to collect these samples. ES.5 Conclusions The CSA found that the source and cause of impacts (as shown on figure ES-1) for certain parameters in some areas of the site is the coal ash contained in the ash basin and ash storage area. The cause of this contamination, shown on the referenced figure, is leaching of constituents from the coal ash into the underlying soil and groundwater and subsequent transport of the groundwater downgradient from the ash basin. However, some groundwater, surface water and soil standards were also exceeded due to naturally occurring elements found in the subsurface. The CSA found no imminent hazards to public health and safety; therefore, no actions to mitigate imminent hazards are required. However, corrective actions at the Buck site are required to address soil and groundwater contamination shown on Figure ES-1. These will be addressed as part of the CAP. The CSA identified the horizontal and vertical extent of groundwater contamination within the compliance boundary (as shown in figure ES-1), and found that the source and cause of the groundwater exceedances within that boundary is a result of both natural conditions and the coal ash contained in the ash basin and ash storage area. In general, COls exceeding 2L Standards or IMACs on the northern side of the waste boundary are judged to be highly influenced by the source. Some of these exceedances were measured outside the compliance boundary, although within the Duke Energy property boundary. Background monitoring wells contain naturally occurring metals and other constituents at concentrations that exceeded their respective 2L Standards or IMACs. Examples of naturally occurring constituents include antimony, cobalt, iron, manganese, and vanadium. Some of these naturally occurring constituents were also detected in newly installed background monitoring well groundwater samples at concentrations greater than 2L Standards or IMACs. The horizontal and vertical extent of groundwater impacts above 2L Standards or IMACs is shown, with exception of the areas associated with the data gaps identified in Section 14.1 on Figures 10-10 through 10-51. Groundwater contamination is considered to be present where the analytical results were greater than the site background concentrations and in excess of the 2L Standards or IMACs. The assessment found COI groundwater concentrations above background concentrations for antimony, arsenic, barium, boron, chromium, cobalt, iron, manganese, nickel, selenium, thallium, vanadium, sulfate, and TDS. The approximate extent of groundwater contamination is shown on these figures and is generally limited to an area within the ash basin compliance boundary and the area north of the compliance boundary near the Yadkin River (within the Duke Energy property boundary). Exceedances measured south, east, and west of the waste boundary are judged to be predominately related to natural conditions, although some source related exceedances were identified. All source related exceedances are ES-15 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY judged to be within the compliance boundary in these areas; however, some data gaps were identified as discussed in Section 17. The CSA found that the primary direction of flow and mobile contaminant transport is predominately to the north toward the Yadkin River (within the Duke Energy property boundaries) and not towards other off -site receptors. No information gathered as part of this CSA suggests that water supply wells or springs within the 0.5-mile radius of the compliance boundary are impacted by the source. This CSA also identified the horizontal and vertical extent of soil contamination as shown on Figures 8-1 through 8-4. Soil contamination is considered to be present where analytical results for COls were in excess of the maximum site soil background concentrations and in excess of the most restrictive PSRG for each COI. The approximate contaminated soil extent is shown on these figures. The assessment found the soil contaminants in excess of the maximum background soil COI concentrations are arsenic, barium, boron, and iron. Groundwater flow is predominately in the north direction toward the Yadkin River. However, there also is a component of groundwater flow to the west of Cell 1 and there is localized flow in an area east of the source that requires further evaluation (between Cells 2 and 3). Exceedances of COls have been observed in monitoring wells in these areas and near the ash basin west compliance boundary. The exceedances, however, do not include COls identified by the USEPA as indicators of CCR related contamination. Further, the constituents identified with exceedances to the south, east and west of the source have also been identified in the background wells. In accordance with CAMA, Duke Energy is required to implement closure and remediation of the Buck ash basin no later than August 1, 2029. Closure for the Buck ash basin was not defined in CAMA. However, CAMA does require Duke Energy to submit a proposed CAP such that NCDENR can prioritize site closure based on risk classifications. No later than December 31, 2015, NCDENR is to develop proposed classifications for all coal combustion residuals surface impoundments, including active and retired sites, for the purpose of closure and remediation. At which time a schedule for closure and required remediation that is based on the degree of risk to public health, safety and welfare, the environment, and natural resources posed by the impoundments and that gives priority to the closure and required remediation of impoundments that pose the greatest risk (CAMA 2014). The classification for the Buck ash basin will be based upon this CSA and the corrective action plan (CAP) which is to be submitted within 90 days of submittal of the CSA. The risk classifications as described in CAMA include: (1) High -risk impoundments shall be closed as soon as practicable, but no later than December 31, 2019. A proposed closure plan for such impoundments must be submitted as soon as practicable, but no later than December 31, 2016. ES-16 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN EXECUTIVE SUMMARY (2) Intermediate -risk impoundments shall be closed as soon as practicable, but no later than December 31, 2024. A proposed closure plan for such impoundments must be submitted as soon as practicable, but no later than December 31, 2017. (3) Low -risk impoundments shall be closed as soon as practicable, but no later than December 31, 2029. A proposed closure plan for such impoundments must be submitted as soon as practicable, but no later than December 31, 2018. Following NCDENR's risk classification determination, a Closure Plan for the ash basin is to be submitted for NCDENR's approval (CAMA 2014). Based on the findings of this CSA report, the future CAP, NCDENR's risk classification, and the approved Closure Plan, appropriate action will be taken for ash basin closure. In the subsequent CAP, Duke Energy will pursue corrective action under 15A NCAC 02L .0106 (k) or (1) depending on the results of the groundwater modeling and the evaluation of the site's suitability to use MNA. This would potentially require evaluation of MNA using the approach found in Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Volumes 1 and 2 (EPA Reference) and the potential modeling of groundwater surface water interaction. If these approaches are found to not be satisfactory, additional measures such as active remediation by hydraulic capture and treatment, among others, would be evaluated. When properly applied, alternatives such as these can provide effective long term management of sites requiring corrective action. ES-17 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN TABLE OF CONTENTS Table of Contents Section Page No. 1.0 Introduction........................................................................................................................1 1.1 Purpose of Comprehensive Site Assessment................................................................1 1.2 Regulatory Background..................................................................................................2 1.2.1 NCDENR Requirements..........................................................................................2 1.2.2 Notice of Regulatory Requirements........................................................................3 1.2.3 Coal Ash Management Act Requirements..............................................................3 1.3 NCDENR-Duke Energy Correspondence.......................................................................4 1.4 Approach to Comprehensive Site Assessment..............................................................4 1.4.1 NORR Guidance.....................................................................................................5 1.4.2 USEPA Monitored Natural Attenuation Approach...................................................5 1.4.3 ASTM Conceptual Site Model Guidance.................................................................5 1.5 Limitations and Assumptions..........................................................................................6 2.0 Site History and Description...............................................................................................8 2.1 Site Location, Acreage, and Ownership.........................................................................8 2.2 Site Description..............................................................................................................8 2.3 Adjacent Property, Zoning, and Surrounding Land Uses...............................................9 2.4 Adjacent Surface Water Bodies and Classifications.......................................................9 2.5 Meteorological Setting..................................................................................................10 2.6 Hydrologic Setting........................................................................................................10 2.7 Permitted Activities and Permitted Waste....................................................................11 2.8 NPDES and Surface Water Monitoring........................................................................12 2.9 NPDES Flow Diagram..................................................................................................12 2.10 History of Site Groundwater Monitoring........................................................................12 2.10.1 Voluntary Groundwater Monitoring Wells..............................................................13 2.10.2 Compliance Groundwater Monitoring Wells..........................................................13 2.11 Assessment Activities or Previous Site Investigations..................................................14 2.12 Decommissioning Status..............................................................................................14 3.0 Source Characteristics.....................................................................................................16 3.1 Coal Combustion and Ash Handling System................................................................16 3.2 Description of Ash Basins and Ash Storage Area........................................................16 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN TABLE OF CONTENTS 3.2.1 Ash Basin..............................................................................................................17 3.2.2 Ash Storage Area..................................................................................................18 3.2.3 Dams.....................................................................................................................18 3.3 Physical Properties of Ash............................................................................................19 3.4 Chemical Properties of Ash..........................................................................................19 4.0 Receptor Information........................................................................................................22 4.1 Summary of Previous Receptor Survey Activities........................................................22 4.2 Summary of CSA Receptor Survey Activities and Findings.........................................23 4.3 NCDENR Well Water Testing Program........................................................................25 5.0 Regional Geology and Hydrogeology..............................................................................26 5.1 Regional Geology.........................................................................................................26 5.2 Regional Hydrogeology................................................................................................26 6.0 Site Geology and Hydrogeology......................................................................................29 6.1 Site Geology.................................................................................................................29 6.1.1 Soil Classification..................................................................................................29 6.1.2 Rock Lithology.......................................................................................................30 6.1.3 Structural Geology.................................................................................................30 6.1.4 Geologic Mapping.................................................................................................30 6.1.5 Fracture Trace Study.............................................................................................31 6.1.6 Effects of Geologic Structure on Groundwater Flow.............................................32 6.1.7 Soil and Rock Mineralogy and Chemistry.............................................................32 6.2 Site Hydrogeology........................................................................................................33 6.2.1 Groundwater Flow Direction..................................................................................33 6.2.2 Hydraulic Gradient.................................................................................................33 6.2.3 Effects of Geologic/Hydrogeologic Characteristics on Contaminants ...................34 6.2.4 Site Hydrogeologic Conceptual Model..................................................................34 7.0 Source Characterization...................................................................................................36 7.1 Ash Basin.....................................................................................................................37 7.1.1 Ash (Sampling and Chemical Characteristics)......................................................37 7.1.2 Ash Basin Surface Water (Sampling and Chemical Characteristics) ....................38 7.1.3 Ash Porewater (Sampling and Chemical Characteristics).....................................38 7.1.4 Ash Porewater Speciation..................................................................................... 39 7.1.5 Radiological Laboratory Testing............................................................................39 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN TABLE OF CONTENTS 7.2 Ash Storage Area.........................................................................................................39 7.2.1 Ash (Sampling and Chemical Characteristics)......................................................39 7.2.2 Ash Porewater (Sampling and Chemical Characteristics).....................................40 7.3 Seeps...........................................................................................................................40 7.3.1 Review of NCDENR March 2014 Sampling Results.............................................40 7.3.2 CSA Seep Sampling Results.................................................................................41 7.3.3 Comparison of Exceedances to 2B Standards......................................................41 7.3.4 Observed Ranges of 2B Standard COI Concentrations........................................42 7.3.5 Discussion of Results for Constituents without 2B Standards...............................42 7.4 Surface Water Speciation.............................................................................................43 7.5 Leaching Potential of Ash.............................................................................................43 7.6 Constituents of Interest.................................................................................................44 7.6.1 COls in Ash (based on total inorganics analysis, as shown in Table 7-2).............44 7.6.2 COls in Ash Basin Surface Water (based on water quality analysis (totals), as shownin Table 7-4).............................................................................................................44 7.6.3 COls in Ash Porewater (based on water quality analysis (totals), as shown in Table7-5)............................................................................................................................45 7.6.4 COls in Seeps (based on water quality analysis (totals), as shown in Table 7-10) 45 7.6.5 Summary of COls from Source Characterization..................................................46 8.0 Soil and Rock Characterization........................................................................................47 8.1 Background Sample Locations.....................................................................................47 8.2 Analytical Methods and Results...................................................................................47 8.3 Comparison of Soil Results to Applicable Levels.........................................................47 8.4 Comparison of Soil Results to Background..................................................................48 8.4.1 Background Soil....................................................................................................48 8.4.2 Soil Beneath Ash Basin.........................................................................................48 8.4.3 Soil Beneath Ash Storage Area.............................................................................48 8.4.4 Soil Outside the Waste Boundary .........................................................................49 8.5 Comparison of PWR and Bedrock Results to Background...........................................49 8.5.1 Background PWR and Bedrock.............................................................................49 8.5.2 PWR and Bedrock Beneath Ash Basin.................................................................49 8.5.3 PWR and Bedrock Beneath Ash Storage Area.....................................................50 8.5.4 PWR and Bedrock Outside Waste Boundary ........................................................50 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN TABLE OF CONTENTS 9.0 Sediment Characterization...............................................................................................51 9.1 Sediments.....................................................................................................................51 10.0 Groundwater Characterization.........................................................................................52 10.1 Regional Groundwater Data for Constituents of Interest..............................................52 10.1.1 Antimony...............................................................................................................52 10.1.2 Arsenic..................................................................................................................53 10.1.3 Barium...................................................................................................................53 10.1.4 Boron..................................................................................................................... 54 10.1.5 Chromium..............................................................................................................54 10.1.6 Cobalt.................................................................................................................... 55 10.1.7 Iron........................................................................................................................55 10.1.8 Manganese............................................................................................................55 10.1.9 Nickel.....................................................................................................................56 10.1.10 Selenium............................................................................................................57 10.1.11 Sulfate................................................................................................................58 10.1.12 TDS....................................................................................................................58 10.1.13 Thallium.............................................................................................................59 10.1.14 Vanadium...........................................................................................................59 10.1.15 pH......................................................................................................................60 10.2 Background Wells.........................................................................................................60 10.3 Discussion of Redox Conditions...................................................................................62 10.4 Groundwater Analytical Results...................................................................................62 10.4.1 Ash Basin..............................................................................................................64 10.4.2 Ash Storage Area..................................................................................................64 10.4.3 Outside the Waste Boundary................................................................................64 10.5 Comparison of Results to 2L Standards and IMACs....................................................65 10.6 Comparison of Results to Background.........................................................................65 10.6.1 Background Wells MW-6S and MW-6D................................................................65 10.6.2 Newly Installed Background Wells........................................................................66 10.6.3 Regional Groundwater Data..................................................................................66 10.6.4 Groundwater Beneath the Ash Basin....................................................................67 10.6.5 Groundwater Beneath the Ash Storage Area........................................................67 10.6.6 Groundwater Beyond the Waste Boundary...........................................................67 IV Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN TABLE OF CONTENTS 10.7 Cation and Anion Water Quality Data...........................................................................70 10.8 CCR Rule Groundwater Detection and Assessment Monitoring Parameters...............70 11.0 Hydrogeological Investigation..........................................................................................73 11.1 Hydrostratigraphic Layer Development........................................................................73 11.2 Hydrostratigraphic Layer Properties.............................................................................74 11.2.1 Borehole In -Situ Tests...........................................................................................74 11.2.2 Monitoring Well and Observation Well Slug Tests................................................75 11.2.3 Laboratory Permeability Tests...............................................................................76 11.2.4 Hydrostratigraphic Layer Parameters....................................................................76 11.3 Hydraulic Gradients......................................................................................................76 11.4 Groundwater Velocity...................................................................................................77 11.5 Contaminant Velocity....................................................................................................77 11.6 Plume's Physical and Chemical Characterization........................................................77 11.7 Groundwater / Surface Water Interaction.....................................................................80 11.8 Estimated Seasonal High and Seasonal Low Groundwater Elevations — Compliance andVoluntary Wells................................................................................................................81 12.0 Screening -Level Risk Assessment...................................................................................82 12.1 Human Health Screening.............................................................................................82 12.1.1 Introduction............................................................................................................ 82 12.1.2 Conceptual Site Model..........................................................................................83 12.1.3 Human Health Risk -Based Screening Levels.......................................................85 12.1.4 Site -Specific Risk Based Remediation Standards.................................................86 12.1.5 NCDENR Receptor Well Investigation..................................................................86 12.1.6 Human Health Risk Screening Summary ..............................................................86 12.2 Ecological Screening....................................................................................................87 12.2.1 Introduction............................................................................................................ 87 12.2.2 Ecological Setting..................................................................................................87 12.2.3 Fate and Transport Mechanisms...........................................................................92 12.2.4 Comparison to Ecological Screening Levels.........................................................92 12.2.5 Uncertainty and Data Gaps...................................................................................94 12.2.6 Scientific/Management Decision Point.................................................................. 94 12.2.7 Ecological Risk Screening Summary....................................................................95 13.0 Groundwater Modeling.....................................................................................................96 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN TABLE OF CONTENTS 13.1 Fate and Transport Groundwater Modeling..................................................................96 13.2 Batch Geochemical Modeling.......................................................................................97 13.3 Geochemical Site Conceptual Site Model....................................................................97 14.0 Data Gaps — SCM Uncertainties....................................................................................100 14.1 Data Gaps..................................................................................................................100 14.1.1 Data Gaps Resulting from Temporal Constraints................................................100 14.1.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities ....... 100 14.1.3 Data Gaps Resulting from Other Sources...........................................................101 14.2 Site Heterogeneities...................................................................................................101 14.3 Impact of Data Gaps and Site Heterogeneities..........................................................101 15.0 Planned Sampling for CSA Supplement........................................................................102 15.1 Sampling Plan for Inorganic Constituents..................................................................102 15.2 Sampling Plan for Speciation Constituents................................................................102 16.0 Interim Groundwater Monitoring Plan............................................................................103 16.1 Sampling Frequency...................................................................................................103 16.2 Constituent and Parameter List..................................................................................103 16.3 Proposed Interim Sampling Locations........................................................................103 16.4 Proposed Interim Background Wells..........................................................................103 17.0 Discussion......................................................................................................................104 17.1 Summary of Completed and Ongoing Work...............................................................104 17.2 Nature and Extent of Contamination..........................................................................105 17.2.1 Groundwater and Seep Contamination...............................................................105 17.2.2 Soil, Rock, and Sediment Contamination............................................................106 17.3 Maximum Contaminant Concentrations.....................................................................106 17.4 Contaminant Migration and Potentially Affected Receptors.......................................108 18.0 Conclusions....................................................................................................................109 18.1 Source and Cause of Contamination..........................................................................109 18.2 Imminent Hazards to Public Health and Safety and Actions Taken to Mitigate them in Accordance to 15A NCAC 02L .0106(f)................................................................................109 18.3 Receptors and Significant Exposure Pathways..........................................................109 18.4 Horizontal and Vertical Extent of Soil and Groundwater Contamination and Significant Factors Affecting Contaminant Transport..............................................................................109 18.5 Geological and Hydrogeological Features influencing the Movement, Chemical, and Physical Character of the Contaminants...............................................................................111 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN TABLE OF CONTENTS 18.6 Proposed Continued Monitoring.................................................................................112 18.7 Preliminary Evaluation of Corrective Action Alternatives............................................112 19.0 References.....................................................................................................................114 Vii Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF FIGURES List Of Figures (organized by CSA report section) Executive Summary • Figure ES-1: Plan View — General Groundwater Flow Direction, Location of Receptor Wells, Constituent Plume Characterization 1.0 Introduction <No Figures> 2.0 Site History and Description • Figure 2-1: Site Location Map • Figure 2-2: Site Layout Map • Figure 2-3: Pre -Ash Basin USGS Map • Figure 2-4: Site Features Map • Figure 2-5: Site Vicinity Map • Figure 2-6: Buck Steam Station Flow Schematic Diagram • Figure 2-7: Compliance and Voluntary Monitoring Wells 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: Trace Elements in Fly Ash vs Soil (EPRI) • Figure 3-5: Trace Elements in Bottom Ash vs Soil (EPRI) 4.0 Receptor Information • Figure 4-1: USGS Receptor Map • Figure 4-2: Receptor Map - Aerial Base • Figure 4-3: Ash Basin Underground Features • Figure 4-4: Surface Water Bodies • Figure 4-5: Properties Contiguous to the Ash Basin Waste Boundary 5.0 Regional Geology and Hydrogeology • Figure 5-1: Tectonostratigraphic Map of the Southern and Central Appalachians • Figure 5-2: Regional Geologic Map • Figure 5-3: Interconnected, Two -Medium Piedmont Groundwater System • Figure 5-4: Conceptual Variations of the Transition Zone due to Rock Type and Structure • Figure 5-5: Piedmont Slope -Aquifer System Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin LIST OF FIGURES 6.0 Site Geology and Hydrogeology • Figure 6-1: Site Geologic Map • Figure 6-2: Monitoring Well and Sample Locations • Figure 6-3: Topographic Lineaments and Rose Diagram • Figure 6-4: Aerial Photography Lineaments and Rose Diagram • Figure 6-5: Water Table Surface - Shallow Wells (S) (7/6 & 7, 2015) • Figure 6-6: Potentiometric Surface - Deep Wells (D) (7/6 & 7, 2015) • Figure 6-7: Potentiometric Surface - BR - Bedrock Groundwater Elevations (7/6 & 7, 2015) 7.0 Source Characterization Figure 7-1: Source Characterization Sample Location 8.0 Soil and Rock Characterization • Figure 8-1: Soil Analytical Results — Plan View (PSRG Exceedances) • Figure 8-2.1: Cross Section A -A' with Solid Matrix Analytical Results • Figure 8-2.2: Cross Section A -A' with Solid Matrix Analytical Results • Figure 8-3: Cross Section B-B' with Solid Matrix Analytical Results • Figure 8-4: Cross Section C-C' with Solid Matrix Analytical Results 9.0 Surface Water and Sediment Characterization • Figure 9-1: Seep and Surface Water Sample Locations (show NPDES seeps) • Figure 9-2: NCDENR March 2014 Sample Location 10.0 Groundwater Characterization • Figure 10-1: Arsenic Concentrations in Groundwater • Figure 10-2: Iron Concentrations in Groundwater • Figure 10-3: Regional Groundwater Quality - Manganese • Figure 10-4: Regional Groundwater Quality • Figure 10-5: Thallium Distribution in Soil • Figure 10-6: Regional Groundwater Quality - Vanadium • Figure 10-7: Monitoring Well and Sample Locations • Figure 10-8: Typical Well Construction Details • Figure 10-9: Groundwater Analytical Results — Plan View (21- and IMAC Standard Exceedances) • Figure 10-10: Antimony Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-11: Antimony Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-12: Antimony Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-13: Arsenic Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-14: Arsenic Isoconcentration Contour Map — Shallow Aquifer (D Wells) Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin LIST OF FIGURES • Figure 10-15: Arsenic Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-16: Barium Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-17: Barium Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-18: Barium Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-19: Boron Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-20: Boron Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-21: Boron Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-22: Chromium Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-23: Chromium Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-24: Chromium Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-25: Cobalt Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-26: Cobalt Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-27: Cobalt Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-28: Iron Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-29: Iron Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-30: Iron Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-31: Manganese Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-32: Manganese Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-33: Manganese Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-34: Nickel Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-35: Nickel Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-36: Nickel Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-37: Selenium Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-38: Selenium Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-39: Selenium Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-40: Sulfate Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-41: Sulfate Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-42: Sulfate Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-43: Thallium Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-44: Thallium Isoconcentration Contour — Shallow Aquifer (S Wells) • Figure 10-45: Thallium Isoconcentration Contour — Shallow Aquifer (D Wells) • Figure 10-46: Total Dissolved Solids Isoconcentration Contour Map — Shallow Aquifer (S Wells) • Figure 10-47: Total Dissolved Solids Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-48: Total Dissolved Solids Isoconcentration Contour — Deep Aquifer (BR Wells) • Figure 10-49: Vanadium Isoconcentration Contour Map — Shallow Aquifer (S Wells) Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin LIST OF FIGURES • Figure 10-50: Vanadium Isoconcentration Contour Map — Shallow Aquifer (D Wells) • Figure 10-51: Vanadium Isoconcentration Contour Map — Deep Aquifer (BR Wells) • Figure 10-52: Cross Section A -A' with Groundwater Analytical Results • Figure 10-53: Cross Section A -A' with Groundwater Analytical Results • Figure 10-54: Cross Section B-B' with Groundwater Analytical Results • Figure 10-55: Cross Section C-C' with Groundwater Analytical Results • Figure 10-56: Piper Diagram — Ash Basin Porewater and Ash Basin Surface Water and Background Monitoring Wells • Figure 10-57: Piper Diagram — Ash Basin Porewater and Ash Basin Surface Water and Seeps • Figure 10-58: Piper Diagram — Ash Basin Porewater and Ash Basin Surface Water and Downgradient Shallow (S) Monitoring Wells • Figure 10-59: Piper Diagram — Ash Basin Porewater and Ash Basin Surface Water and Downgradient Deep (D) Monitoring Wells • Figure 10-60: Piper Diagram — Ash Basin Porewater and Ash Basin Surface Water and Downgradient Upper Bedrock (BRU) Monitoring Wells • Figure 10-61: Piper Diagram — Ash Basin Porewater and Ash Basin Surface Water and Downgradient Bedrock (BR) Wells • Figure 10-62: Piper Diagram — Background Shallow (S) Monitoring Wells with Downgradient Shallow (S) Monitoring Wells • Figure 10-63: Piper Diagram — Background Deep (D) Monitoring Wells with Downgradient Deep (D) Monitoring Wells • Figure 10-64: Cation/Anion Concentrations (bar chart) — Ash basin porewater • Figure 10-65: Cation/Anion Concentrations (bar chart) — Ash basin surface water • Figure 10-66: Cation/Anion Concentrations (bar chart) — Background wells • Figure 10-67: Cation/Anion Concentrations (bar chart) — Seep wells • Figure 10-68: Cation/Anion Concentrations (bar chart) — Downgradient S (1 of 2) • Figure 10-69: Cation/Anion Concentrations (bar chart) — Downgradient S (2 of 2) • Figure 10-70: Cation/Anion Concentrations (bar chart) — Downgradient D (1 of 2) • Figure 10-71: Cation/Anion Concentrations (bar chart) — Downgradient D (2 of 2) • Figure 10-72: Cation/Anion Concentrations (bar chart) — Downgradient BRU • Figure 10-73: Cation/Anion Concentrations (bar chart) — Downgradient BR • Figure 10-74: Sulfate:Chloride Ratio in Ash basin porewater • Figure 10-75: Sulfate:Chloride Ratio in Ash basin surface water • Figure 10-76: Sulfate:Chloride Ratio in Background well • Figure 10-77: Sulfate:Chloride Ratio in Seep well • Figure 10-78: Sulfate:Chloride Ratio in Downgradient S well (1 of 2) • Figure 10-79: Sulfate:Chloride Ratio in Downgradient S well (2 of 2) • Figure 10-80: Sulfate: Chloride Ratio in Downgradient D well (1 of 2) • Figure 10-81: Sulfate:Chloride Ratio in Downgradient D well (2 of 2) • Figure 10-82: Sulfate:Chloride Ratio in Downgradient BRU well Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF FIGURES • Figure 10-83: Sulfate:Chloride Ratio in Downgradient BR well • Figure 10-84: Stacked Time Series Plot: Boron • Figure 10-85: Stacked Time Series Plot: Chromium • Figure 10-86: Stacked Time Series Plot: Iron • Figure 10-87: Stacked Time Series Plot: Manganese • Figure 10-88: Stacked Time Series Plot: pH • Figure 10-89: Stacked Time Series Plot: Sulfate • Figure 10-90: Stacked Time Series Plot: TDS • Figure 10-91: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6D) vs Deep wells: Boron • Figure 10-92: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6D) vs Deep wells: Chromium • Figure 10-93: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6D) vs Deep wells: Iron • Figure 10-94: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6D) vs Deep wells: Manganese • Figure 10-95: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6D) vs Deep wells: Sulfate • Figure 10-96: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6D) vs Deep wells: pH • Figure 10-97: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6D) vs Deep wells: TDS • Figure 10-98: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6S) vs Shallow wells: Boron • Figure 10-99: Stacked Time Series Plot: Compliance Wells — Background well (MW- 6S) vs Shallow wells: Chromium • Figure 10-100: Stacked Time Series Plot: Compliance Wells — Background well (MW-6S) vs Shallow wells: Iron (tot) • Figure 10-101: Stacked Time Series Plot: Compliance Wells — Background well (MW-6S) vs Shallow wells: Manganese • Figure 10-102: Stacked Time Series Plot: Compliance Wells — Background well (MW-6S) vs Shallow wells: pH • Figure 10-103: Stacked Time Series Plot: Compliance Wells — Background well (MW-6S) vs Shallow wells: Sulfate • Figure 10-104: Stacked Time Series Plot: Compliance Wells — Background well (MW-6S) vs Shallow wells: TDS • Figure 10-105: Stacked Time Series Plot: Boron vs Turbidity: MW — 11 D • Figure 10-106: Stacked Time Series Plot: Chromium vs Turbidity: MW-12S • Figure 10-107: Stacked Time Series Plot: Iron vs Turbidity: MW-6S • Figure 10-108: Stacked Time Series Plot: Iron vs Turbidity: MW-7D • Figure 10-109: Stacked Time Series Plot: Iron vs Turbidity: MW-8S • Figure 10-110: Stacked Time Series Plot: Iron vs Turbidity: MW-8D xii Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin LIST OF FIGURES • Figure 10-111: Stacked Time Series Plot: Iron vs Turbidity: MW-9S • Figure 10-112: Stacked Time Series Plot: Iron vs Turbidity: MW-9D • Figure 10-113: Stacked Time Series Plot: Iron vs Turbidity: MW-10D • Figure 10-114: Stacked Time Series Plot: Iron vs Turbidity: MW-11S • Figure 10-115: Stacked Time Series Plot: Iron vs Turbidity: MW-11 D • Figure 10-116: Stacked Time Series Plot: Iron vs Turbidity: MW-12S • Figure 10-117: Stacked Time Series Plot: Iron vs Turbidity: MW-12D • Figure 10-118: Stacked Time Series Plot: Iron vs Turbidity: MW-13D • Figure 10-119: Stacked Time Series Plot: Manganese vs Turbidity: MW-6S • Figure 10-120: Stacked Time Series Plot: Manganese vs Turbidity: MW-7S • Figure 10-121: Stacked Time Series Plot: Manganese vs Turbidity: MW-7D • Figure 10-122: Stacked Time Series Plot: Manganese vs Turbidity: MW-8S • Figure 10-123: Stacked Time Series Plot: Manganese vs Turbidity: MW-9S • Figure 10-124: Stacked Time Series Plot: Manganese vs Turbidity: MW-10D • Figure 10-125: Stacked Time Series Plot: Manganese vs Turbidity: MW-11 S • Figure 10-126: Stacked Time Series Plot: Manganese vs Turbidity: MW-11 D • Figure 10-127: Stacked Time Series Plot: Manganese vs Turbidity: MW-12S • Figure 10-128: Stacked Time Series Plot: pH vs Turbidity: MW-6S • Figure 10-129: Stacked Time Series Plot: pH vs Turbidity: MW-6D • Figure 10-130: Stacked Time Series Plot: pH vs Turbidity: MW-7S • Figure 10-131: Stacked Time Series Plot: pH vs Turbidity: MW-7D • Figure 10-132: Stacked Time Series Plot: pH vs Turbidity: MW-8S • Figure 10-133: Stacked Time Series Plot: pH vs Turbidity: MW-8D • Figure 10-134: Stacked Time Series Plot: pH vs Turbidity: MW-9S • Figure 10-135: Stacked Time Series Plot: pH vs Turbidity: MW-9D • Figure 10-136: Stacked Time Series Plot: pH vs Turbidity: MW-10D • Figure 10-137: Stacked Time Series Plot: pH vs Turbidity: MW-11 S • Figure 10-138: Stacked Time Series Plot: pH vs Turbidity: MW-11 D • Figure 10-139: Stacked Time Series Plot: pH vs Turbidity: MW-12S • Figure 10-140: Stacked Time Series Plot: pH vs Turbidity: MW-12D • Figure 10-141: Stacked Time Series Plot: pH vs Turbidity: MW-13D • Figure 10-142: Stacked Time Series Plot: TDS vs Turbidity: MW-10D • Figure 10-143: 40 CFR 257 Appendix III Detection Monitoring Constituents Detected in Shallow Wells • Figure 10-144: 40 CFR 257 Appendix III Detection Monitoring Constituents Detected in Deep Wells • Figure 10-145: 40 CFR 257 Appendix III Constituents Detected in Bedrock Wells • Figure 10-146: 40 CFR 257 Appendix IV Assessment Monitoring Constituents Detected in Shallow Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF FIGURES • Figure 10-147: 40 CFR 257 Appendix IV Assessment Monitoring Constituents Detected in Deep Wells • Figure 10-148: 40 CFR 257 Appendix IV Assessment Monitoring Constituents Detected in Bedrock Wells 11.0 HydrogeologicalInvestigation • Figure 11-1: Major Flow Transects 12.0 Screening -Level Risk Assessment • Figure 12-1: Human Health Screening Conceptual Site Model • Figure 12-2: Ecological Conceptual Site Model 13.0 Groundwater Modeling <No Figures> 14.0 Data Gaps — Conceptual Site Model Uncertainties <No Figures> 15.0 Planned Sampling for CSA Supplement <No Figures> 16.0 Interim Groundwater Monitoring Plan <No Figures> 17.0 Discussion <No Figures> 18.0 Conclusions <No Figures> 19.0 References <No Figures> Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF TABLES List Of Tables (organized by CSA report section) Executive Summary <No Tables> 1.0 Introduction • Table 1-1: Comparison of Sampling Data to Federal and State Regulatory Standards 2.0 Site History and Description • Table 2-1: NPDES Groundwater Monitoring Requirements • Table 2-2: Exceedances of 2L Standards at Compliance Wells (March 2011-March 2015) • 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 4.0 Receptor Information • Table 4-1: Public and Private Water Supply Well Information within 0.5-mile Radius of Ash Basin Compliance Boundary • Table 4-2: Property Owner Addresses Contiguous to the Ash Basin Waste Boundary 5.0 Regional Geology and Hydrogeology <No Tables> 6.0 Site Geology and Hydrogeology • Table 6-1: Soil Mineralogy Results • Table 6-2: Soil Chemistry Results, Oxides • Table 6-3: Soil Chemistry Results, Elemental • Table 6-4: Transition Zone Mineralogy • Table 6-5: Oxide Composition of Transitional Zone Samples • Table 6-6: Elemental Composition of Transitional Zone Samples • Table 6-7: Whole Rock Chemistry Results, Oxides.xlsx • Table 6-8: Whole Rock Chemistry Results, Elemental • Table 6-9: Assessment Monitoring Well Construction Information • Table:6-10: Compliance and Voluntary Monitoring Well Construction Information • Table 6-11: Summary of Hydraulic Gradient Calculations XV Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin LIST OF TABLES 7.0 Source Characterization • Table 7-1: Soil and Ash Parameters and Analytical Methods • Table 7-2: Ash Sample Results • Table 7-3: Ash Basin Surface Water, Porewater and Seep Parameters and Analytical Methods • Table 7-4: Ash Basin Surface Water Sample Results • Table 7-5: Ash Basin Porewater Sample Results • Table 7-6: Ash Sample SPLP Results • Table 7-7: Ash Basin Porewater Sample Results - Speciation • Table 7-8; Groundwater Radiological Sample Results • Table 7-9: NCDENR March 2014 Sampling Results • Table 7-10: Seep Sample Results • Table 7-11: Surface Water Sample Results - Speciation 8.0 Soil and Rock Characterization • Table 8-1: Environmental Exploration and Sampling Plan • Table 8-2: Solid and Ash Parameters and Analytical Methods • Table 8-3: Total Inorganic Results — Background Soil • Table 8-4: Total Inorganic Results — Background PWR and Bedrock • Table 8-5: Total Inorganic Results - Soil • Table 8-6: Total Inorganic Results - PWR and Bedrock • Table 8-7: Frequency and Concentration Ranges in Soil for COI Exceedances of North Carolina PSRGs • Table 8-8: Frequency and Concentration Ranges in PWR and Bedrock for COI Exceedances of North Carolina PSRGs • Table 8-9: Range of Constituent Concentrations and Comparison to Range of Reported Background Concentrations — Soil Beneath Ash Basin • Table 8-10: Range of Constituent Concentrations and Comparison to Range of Reported Background Concentrations — Soil Beneath Ash Storage Area • Table 8-11: Range of Constituent Concentrations and Comparison to Range of Reported Background Concentrations — Soil Outside the Waste Boundary • Table 8-12: Range of Constituent Concentrations and Comparison to Range of Reported Background Concentrations — PWR and Bedrock Beneath Ash Basin • Table 8-13: Range of Constituent Concentrations and Comparison to Range of Reported Background Concentrations — PWR and Bedrock Beneath Ash Storage Area • Table 8-14: Range of Constituent Concentrations and Comparison to Range of Reported Background Concentrations — PWR and Bedrock Outside of Waste Boundary 9.0 Surface Water and Sediment Characterization 0 Table 9-1: Total Inorganic Results - Sediment Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin LIST OF TABLES 10.0 Groundwater Characterization • Table 10-1: State and Federal Drinking Water Standards • Table 10-2: Constituents in Private Wells • Table 10-3: Iron and Manganese Concentrations • Table 10-4: Redox Conditions — General Redox Category • Table 10-5: Groundwater Sample Results — Background — Total and Dissolved • Table 10-6: Groundwater Sample Results — Total and Dissolved • Table 10-7: Groundwater Sample Results — Background — Speciation • Table 10-8: Groundwater Sample Results — Speciation • Table 10-9: Range of COI Concentrations in Groundwater Beneath the Ash Basin • Table 10-10: Range of COI Concentrations in Groundwater Beneath the Ash Storage Area • Table 10-11: Range of COI Concentrations in Groundwater Outside the Waste Boundary 11.0 HydrogeologicalInvestigation • Table 11-1: Soil/Material Properties for Ash, Fill, Alluvium, Soil/Saprolite • Table 11-2: Field Permeability Test Results • Table 11-3: Slug Test Permeability Results • Table 11-4: Historic Slug Test Permeability Results • Table 11-5: Laboratory Permeability Test Results • Table 11-6: Historic Laboratory Permeability Test Results • Table 11-7: Total Porosity for Upper Hydrostratigraphic Units (A, F, S, M1, and M2) • Table 11-8: Estimated Effective Porosity/Specific Yield and Specific Storage for Upper Hydrostratigraphic Units (A, F, S, M1, and M2) • Table 11-9: Hydrostratigraphic Layer Properties — Horizontal Hydraulic Conductivity • Table 11-10: Hydrostratigraphic Layer Properties — Vertical Hydraulic Conductivity • Table 11-11: Total Porosity, Secondary (Effective) Porosity/Specific Yield, and Specific Storage for Lower Hydrostratigraphic Units (TZ and BR) • Table 11-12: Groundwater Seepage Velocities • Table 11-13: Hydraulic Gradients — Vertical 12.0 Screening -Level Risk Assessment • Table 12-1: Selection of Human Health COPCs — Groundwater • Table 12-2: Selection of Human Health COPCs — Soil • Table 12-3: Selection of Human Health COPCs — Sediment • Table 12-4: Contaminants of Potential Human Health Concern • Table 12-5: Selection of Ecological COPCs — Soil • Table 12-6: Selection of Ecological COPCs — Sediment • Table 12-7: Contaminants of Potential Ecological Concern Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF TABLES Table 12-8: Threatened and Endangered Species in Rowan County 13.0 Groundwater Modeling <No Tables> 14.0 Data Gaps — Conceptual Site Model Uncertainties <No Tables> 15.0 Planned Sampling for CSA Supplement • Table 15-1: CSA Supplemental Sampling Plan 16.0 Interim Groundwater Montoring Plan • Table 16-1: Recommended Parameters and Constituents • Table 16-2: Sample Locations in Interim Groundwater Monitoring Plan 17.0 Discussion <No Tables> 18.0 Conclusions <No Tables> 19.0 References <No Tables> Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin LIST OF APPENDICES List of Appendices Appendix A: Introduction • NCDENR NORR Letter • Summary of Work Plan Submittals and NCDENR-Duke Energy Correspondence • Revised Groundwater Assessment Work Plan Appendix B: Receptor Information • Updated Receptor Survey Report • NCDENR Well Water Sampling Results • NCDENR Water Supply Well Tracking Spreadsheet • Background Water Supply Well Analytical Results Appendix C: Source Characterization • Drilling Procedures • Drilling and Installation Variances Appendix D: Soil and Rock Characterization • Sampling Procedures • Sampling Variances Appendix E: Field and Sampling Quality Control / Quality Assurance • Field Sampling Quality Assurance/Quality Control Procedures • Data Analysis Quality Assurance/Quality Control Procedures Appendix F: Surface Water, Seep and Sediment Characterization • Sampling Procedures • Sampling Variances Appendix G: Groundwater Characterization • Well Development Procedure • Well Development Forms • Well Abandonment Forms • Sampling Procedures • Sampling Forms • Sampling Variances • Evaluation of Turbidity in Existing Voluntary and Compliance Wells • Evaluation of Need for Off -site Monitoring Wells • Statistical Analysis of Groundwater Results Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF APPENDICES Appendix H: Hydrogeological Investigation • Boring Logs • Well Construction Records • Historical Boring Logs and Well Construction Records • Soil Physical Lab Reports • Mineralogy Lab Reports • Slug Test Procedures • Slug Test Reports • Field Permeability Data • Fetter -Bear Diagrams — Porosity • Estimated Seasonal High Groundwater Elevations Calculation Appendix I: Screening -Level Risk Assessment • Trustee Letters and Responses • Checklist for Ecological Assessments/Sampling Appendix J: Historical Analytical Result Tables Appendix K: Laboratory Reports (Compact Disc) Appendix L: Soil Sample and Rock Core Photographs Appendix M: CSA Certification Form Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF ACRONYMS AND ABBREVIATIONS List of Acronyms and Abbreviations pg/L micrograms per liter 2L Standards 15A NCAC 02L .0202 Groundwater Quality Standards AMEC AMEC Environment & Infrastructure AST Aboveground Storage Tank ASTM American Society for Testing and Materials BG Background bgs Below ground surface BR Bedrock Buck Buck Steam Station CAMA Coal Ash Management Act CAP Corrective Action Plan CCR Coal Combustion Residuals COI Constituent of Interest COPC Contaminant of Potential Concern CSA Comprehensive Site Assessment CSM Conceptual Site Model CY Cubic Yards DEH NCDENR Department of Environmental Health DO Dissolved oxygen DORS Distribution of Residuals Solids DTW Depth to Water Duke Energy Duke Energy Carolinas, LLC DWR NCDENR Division of Water Resources EDR Environmental Data Resources EPD Georgia Environmental Protection Division EPRI Electric Power Research Institute ESH Estimated Seasonal High ESL Estimated Seasonal Low GSCM Geochemical Site conceptual model GIS Geographic Information Systems HFO Hydrous ferric oxide HQ Hazard Quotient IMAC Interim Maximum Allowable Concentration Kd Sorption Coefficient MCL Maximum Contaminant Levels mD millidarcies MDL Method detection limit XXI Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin �� LIST OF ACRONYMS AND ABBREVIATIONS mg/kg Milligrams per kilogram mm milligrams MNA Monitored Natural Attenuation MRL Maximum Reporting Level MW Megawatt N Standard Penetration Testing Values NRCS Natural Resources Conservation Service NCAC North Carolina Administrative Code NCDENR North Carolina Department of Environment and Natural Resources NCDHHS North Carolina Department of Health and Human Services NCNHP North Carolina Natural Heritage Program NCWRC North Carolina Wildlife Resources Commission ng/L Nanograms per liter NHD USGS National Hydrography Dataset NORR Notice of Regulatory Requirements NPDES National Pollutant Discharge Elimination System NTU Nephelometric Turbidity Unit INURE National Uranium Resource Evaluation PL Prediction Limit PMCL Primary Maximum Contaminant Level ppb parts per billion ppm parts per million PSRG Preliminary Soil Remediation Goal PWR Partially Weathered Rock PWSS NCDENR DWR Public Water Supply Section RCRA Resource Conservation and Recovery Act REC Recovery RL Reporting Limit RQD Rock Quality Designation RSL USEPA Regional Screening Level SCM Site Conceptual Model SCS U.S. Department of Agriculture Soil Conservation Service SLERA Screening Level Ecological Risk Assessment SMCL Secondary Maximum Contaminant Level SMDP Scientific/Management Decision Point SPLP Synthetic Precipitation Leaching Procedure SQL Sample Quantitation Limit SWAP NCDENR DWR Source Water Assessment Program TCLP Toxicity Characteristic Leaching Procedure Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN LIST OF ACRONYMS AND ABBREVIATIONS TDS Total Dissolved Solids TZ Transition Zone UNC University of North Carolina UNCC University of North Carolina at Charlotte USCS Unified Soil Classification System USDA U.S. Department of Agriculture USEPA U.S. Environmental Protection Agency USGS U.S. Geological Survey UST Underground Storage Tank Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 1.0 INTRODUCTION 1.0 Introduction Duke Energy Carolinas, LLC (Duke Energy) owns and formerly operated the Buck Steam Station (Buck), located on the Yadkin River in Rowan County near Salisbury, North Carolina. Buck began operation in 1926 as a coal-fired generating station. The Buck Combined Cycle Station (BCCS) natural gas facility was constructed at the site and began operating in late 2011. Subsequently, Buck was decommissioned and taken offline in April 2013. The coal ash residue from Buck's coal combustion process was historically disposed of in the station's ash basin located adjacent to the station and the Yadkin River. The entire site includes Buck, BCCS, the ash basin (which consists of three cells), and an ash storage area. Duke Energy has implemented voluntary and National Pollutant Discharge Elimination System (NPDES) permit -required compliance groundwater monitoring at Buck. Twice per year voluntary groundwater monitoring around the Buck ash basin was performed from November 2006 until May 2010, with analytical results submitted to the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Resources (DWR). Compliance groundwater monitoring, required by the NPDES permit, began in March 2011. From March 2011 through July 2015, the compliance groundwater monitoring wells at Buck have been sampled a total of 14 times as part of three times per year sampling required in the NPDES permit and have been submitted to DWR. Recent monitoring events have indicated exceedances of 15A NCAC 02L .0200 Groundwater Quality Standards (2L Standards) at Buck, prompting NCDENR's requirement for Duke Energy to perform a groundwater assessment at the site and prepare a Comprehensive Site Assessment (CSA) report. The Coal Ash Management Act of 2014 (CAMA), NC Session Law 2014-122, also directed owners of coal combustion residuals (CCR) surface impoundments to conduct groundwater monitoring and assessment and submit a Groundwater Assessment Report. This CSA is submitted to meet the requirements of both NCDENR and CAMA. 1.1 Purpose of Comprehensive Site Assessment The purpose of this CSA is to characterize the extent of contamination resulting from historical production and storage of coal ash, evaluate the chemical and physical characteristics of the contaminants, investigate the geology and hydrogeology of the site including factors relating to contaminant transport, and examine risk to potential receptors and exposure pathways. This CSA was prepared in general accordance with requirements outlined in the following regulations and documents: • Groundwater Classifications and Water Quality Standards, 15A NCAC Subchapter 2L; • Coal Ash Management Act of 2014, N.C. Gen.Stat. §§130A-309.200 et seq.; • Notice of Regulatory Requirements (NORR) issued by NCDENR on August 13, 2014; • Conditional Approval of Revised Groundwater Assessment Work Plan issued by NCDENR on February 24, 2015; and • Subsequent meetings and correspondence between Duke Energy and NCDENR. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 1.0 INTRODUCTION Constituents in groundwater were compared to the 2L Standards or Interim Maximum Allowable Concentrations (IMACs) established by NCDENR pursuant to 15A NCAC 2L.0202(c). The IMACs were issued in 2010, 2011 and 2012; however, NCDENR has not established a 2L Standard for these constituents as described in 15A NCAC 2L.0202(c). For this reason, the IMACs noted in this report are for reference only. This assessment includes evaluation of possible impacts from the ash basins and related ash storage facilities, and consisted of the following activities: • Completion of soil borings, installation of groundwater monitoring wells and collection of seep samples to faciliatate collection and analysis of chemical, physical, and hydrogeological parameters of subsurface materials encountered within and beyond the waste and compliance boundaries; • Evaluation of testing data to supplement the site conceptual model (SCM); • Update of the receptor survey previously completed in 2014; and • Completion of a screening -level risk assessment. For this CSA, the source area is defined as the ash basin and ash storage area. 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 to identify physical and chemical properties of ash, ash basin surface water, ash porewater, and ash basin seeps. The ash, ash basin surface water, ash porewater, and seep analytical results were compared to 2L Standards, IMACs, and other regulatory screening levels for the purpose of identifying constituents of interest (COls). These COls are considered to be associated with potential impacts to soil and groundwater from the ash basin and storage area. In addition, this CSA also identifies constituents that exceeded 2L Standards or IMACs from groundwater sample locations outside the ash basin boundary. For the purposes of this report, these constituents were also identified as COls. It is important to recognize that certain COls (e.g., iron and manganese) may be naturally occurring and may be found in background monitoring wells and thus require careful examination to determine whether their presence near or downgradient of the ash basin or ash storage areas is a naturally occurring condition or a result of ash handling and storage. Occurrences of Cols outside the waste boundary are identified in Sections 10.0 (Groundwater Characterization) and 11.0 (Hydrogeological Investigation) of this CSA. This inclusive approach to identification of Cols will be refined during development of the CAP to focus on those constituents that are attributable to the ash basin. COls were also evaluated in the human health and ecological screening level risk assessment in Section 12.0. 1.2 Regulatory Background 1.2.1 NCDENR Requirements The NCDENR DWR regulates wastewater discharges from coal ash ponds to state waters, streams, and lakes, and requires groundwater monitoring and stormwater management at these facilities. The agency also has regulatory responsibility for facilities that contain fly and bottom Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 1.0 INTRODUCTION ash from coal burning power operations. Duke Energy's coal-fired power facilities are also regulated through federal NPDES wastewater permits. As part of these permits, the facilities must also comply with the state water quality standards and U.S. Environmental Protection Agency (USEPA) water quality criteria. Groundwater monitoring is performed at Duke Energy facilities in accordance with approved monitoring plans and NPDES permits for each site. Included in these monitoring evaluations is a determination if site -specific background concentrations (i.e., naturally occurring constituents in the soil profile and groundwater) for various constituents are contributing to reported concentrations. For each facility, if it is determined that activities on the property are causing noncompliance with NCDENR regulatory requirements, the agency will require the permittee to perform an assessment and to develop and implement a Corrective Action Plan (CAP) in accordance with state regulations. 1.2.2 Notice of Regulatory Requirements On August 13, 2014, NCDENR issued a Notice of Regulatory Requirements (NORR) letter notifying Duke Energy that exceedances of the 2L Standards were reported at 14 coal ash facilities owned and operated by Duke Energy, including Buck. The NORR stipulated that for each ash facility, Duke Energy shall conduct a CSA following submittal of a Groundwater Assessment Work Plan (Work Plan) and receptor survey. In accordance with the NORR requirements, a Work Plan was developed, a receptor survey was performed to identify all receptors within a 0.5-mile radius (2,640 feet) of the Buck ash basin compliance boundary, and a CSA was conducted for each coal ash facility. The NORR letter is included as Appendix A. 1.2.3 Coal Ash Management Act Requirements The Coal Ash Management Act (CAMA) of 2014 (N.C. Gen. Stat. §130A-309.200 et seq.) requires that coal combustion residuals (CCRs) in high priority impoundments be removed and disposed in a landfill, used in a structural fill, or used for beneficial reuse. As a component of implementing this objective, CAMA provides instructions for owners of CCR surface impoundments to perform various groundwater monitoring and assessment activities. Section §1 30A-309.21 1 of CAMA 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 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 1.0 INTRODUCTION 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. e. A schedule for conitnued groundwater monitoring. f. Any other information related to groundwater assessment required by the Department. 2) The Department shall approve the Groundwater Assessment Plan if it determines that the Plan complies with the requirements of this subsection and will be sufficient to protect public health, safety, and welfare; the environment; and natural resources. (3) No later than 10 days from approval of the Groundwater Assessment Plan, the owner shall begin implementation of the Plan. (4) No later than 180 days from approval of the Groundwater Assessment Plan, the owner shall submit a Groundwater Assessment Report to the Department. The Report shall describe all exceedances of groundwater quality standards associated with the impoundment. 1.3 NCDENR-Duke Energy Correspondence In response to both the NORR letter and CAMA requirements, Duke Energy submitted a Work Plan to NCDENR DWR on September 25, 2014 establishing proposed site assessment activities and schedules for the implementation, completion, and submission of a CSA report in accordance with 15A NCAC 02L .0106(g). NCDENR DWR reviewed the Work Plan and provided Duke Energy with initial comments on November 4, 2014. A revised Work Plan was subsequently submitted to NCDENR DWR on December 30, 2014 and NCDENR DWR provided final comments and conditional approval of the revised Work Plan on February 24, 2015. In addition, Duke Energy submitted proposed adjustments to the CSA guideline and requested clarifications regarding groundwater sampling and speciation of selected constituents to NCDENR DWR on May 14 and May 22, 2015. NCDENR DWR provided responses to these proposed revisions and clarifications in June 2015. Copies of relevant correspondence including Work Plan submittals are included in Appendix A. 1.4 Approach to Comprehensive Site Assessment The CSA approach was developed based on the NORR guidelines and CAMA requirements. Development of the SCM is based on several documents including but not limited to USEPA's Monitored Natural Attenuation tiered approach, ASTM 1689-95 (2014) Standard Guide for Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 1.0 INTRODUCTION Developing Site Conceptual Models for Contaminated Sites, and comments received by NCDENR. 1.4.1 NORR Guidance The NORR letter (Appendix A) outlined general guidelines for the CSA report, including guidance from 15A NCAC 02L .0106(g) as described in Section 1.1. The NORR letter also included Guidelines for Comprehensive Site Assessment for those involved in the investigation of contaminated soil and/or groundwater. The components included in the NORR guidelines were used in developing the site Work Plan and this CSA report. 1.4.2 USEPA Monitored Natural Attenuation Approach In accordance with NCDENR requirements and the February 16, 2015 Conditional Approval letter (Appendix A), the elements of the USEPA's Monitored Natural Attenuation (MNA) tiered approach has been utilized as part of the investigation associated with the CSA. This approach is described in its guidance document entitled "Monitored Natural Attenuation of Inorganic Contaminants in Groundwater" (Vols. 1 & 2) (October 2007). MNA may be used as a component to meet corrective action requirements if site conditions meet the requirements associated with use of MNA. The approach involves a detailed analysis of site characteristics controlling and sustaining attenuation to support evaluation and selection of MNA as part of a cleanup action for inorganic contaminant plumes in groundwater (USEPA 2007). The site characterization is conducted in a step -wise manner to facilitate collection of data necessary to progressively evaluate the effectiveness of natural attenuation processes within the site aquifer(s). Four general elements are included in the tiered site analysis approach: • Demonstration of active contaminant removal from groundwater and dissolved plume stability; • Determination of the mechanism and rate of attenuation; • Determination of the long-term capacity for attenuation and stability of immobilized contaminants, before, during, and after any proposed remedial activities; and • Design of performance monitoring program, including defining triggers for assessing the remedial action strategy failure, and establishing a contingency plan. Duke Energy will evaluate the USEPA MNA approach further during preparation of the CAP. 1.4.3 ASTM Conceptual Site Model Guidance ASTM standard guidance document E1689-95 (ASTM 2014) "Standard Guide for Developing Conceptual Site Models for Contaminated Sites" (ASTM 2014)" was used as a general component of this CSA. The guidance document provides direction in developing conceptual site models used for the integration of technical information from multiple sources, selection of sampling locations to establish background concentrations of substances, identification of data needs and guidance of data collection activities, and evaluation of risks to human and environmental health posed by a contaminated site. According to ASTM E1689-95, six basic activities are associated with developing a conceptual site model: Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 1.0 INTRODUCTION • Identification of potential contaminants; • Identification and characterization of the source(s) of contaminants; • Delineation of potential migration pathways through environmental media, such as groundwater, surface water, soils, sediment, biota, and air; • Establishment of background areas of contaminants for each contaminated medium; • Identification and characterization of potential environmental receptors (human and ecological); and • Determination of the limits of the study area or system boundaries. Development of a conceptual site model is typically iterative and the complexity of the model should be consistent with the complexity of the site and available data. Information gained through site investigation activities is used to characterize existing physical, biological, and chemical systems at a site. The conceptual site model describes and integrates processes that determine contaminant releases, contaminant migration, and environmental receptor exposure to contaminants. Development of the model is essential to determine potential exposure routes and identifying possible impacts to human health and the environment (ASTM 2014). The conceptual site 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 effectiveness of remedial actions in reducing the exposure of environmental receptors to contaminants (ASTM 2014). This CSA was conducted in accordance with the conditionally approved Work Plan to meet the NCDENR, NORR, and CAMA regulatory requirements described in Section 1.2, and using the NORR, USEPA, and ASTM approaches described above. This assessment information will be used to develop a CAP, to be submitted separately, for the Buck site that will provide a demonstration of these criteria in support of the recommended site remedy. Data obtained from sampling during this CSA are compared to federal and state regulatory standards shown in Table 1-1. Beginning in Section 7.0, laboratory results are compared to the above -referenced regulatory standards and discussed as either "exceeding" or "not exceeding" those standards. The evaluation of exceedances of these standards forms the basis for determining the need for additional work later in this document 1.5 Limitations and Assumptions Development of this CSA is based on information provided to HDR by both public and private entities including universities, federal, state and local governments, and information and analytical reports generated by Duke Energy. HDR assumes the information in these documents to be accurate and reliable. This information was used to estimate exposure routes and migration pathways in the subsurface. This CSA was developed using a standard of care ordinarily used by engineering practice under the same or similar circumstances, but may include assumptions based on the accuracy and reliability of data from various entities. CAMA Section §1 30A-309.21 1 (a) requires that "No later than 180 days from approval of the Groundwater Assessment Plan, the owner shall submit a Groundwater Assessment Report to Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 1.0 INTRODUCTION the Department". The schedule dictated by CAMA is compressed; therefore, data interpretation is limited and subject to change upon receipt of additional data in subsequent rounds of sampling and additional data collected to resolve data gaps identified in Section 14.0. The additional data will be used to inform the corrective actions identified in the CAP. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 2.0 SITE HISTORY AND DESCRIPTION 2.0 Site History and Description This section provides a description of the Buck site based on relevant historical data and representative information. The purpose of this characterization is to familiarize readers with the site and use the general information as part of the overall ASTM conceptual site model development approach. 2.1 Site Location, Acreage, and Ownership The Buck site is located northwest of Leonard Road on the south bank of the Yadkin River near Spencer, Rowan County, North Carolina (Figure 2-1). The Buck site occupies approximately 640 acres (Figure 2-2), and is owned by Duke Energy. As of the date of this report, site ownership and land use prior to Duke Energy could not be determined from available records. 2.2 Site Description Buck was a six -unit coal-fired electricity generating facility along the Yadkin River. Buck began operation of Units 1 and 2 in 1926 as a coal-fired generating station with a capacity of 256 megawatts (MW). Units 1 and 2 were retired in 1979. Units 3 and 4 at Buck, 113 MW combined, were retired in mid-2011 and Units 5 and 6, 143 MW combined, were retired in April 2013. There are no coal-fired units currently in operation at Buck. Construction of the 620 MW BCCS natural gas facility began in 2008. Commercial operation of the natural gas facility began in late- 2011. Three combustion turbine units formerly operated adjacent to the coal-fired units and were retired in October 2012. Buildings and other structures associated with power production are generally located in the northwestern section of the site. The eastern portion of the site is generally wooded with the exception of the remaining ponded areas of the ash basin. The ash basin system at Buck consists of three cells, associated earthen dikes, discharge structures, and two canals. The cells are designated as Cell 1 Additional Primary Pond (Cell 1), Cell 2 Primary Pond (Cell 2), and Cell 3 Secondary Pond (Cell 3). The ash basin is located to the south (Cell 1) and southeast (Cells 2 and 3) of Buck, with a final NPDES permitted outfall that discharges into the Yadkin River on the northeast side of Buck. A 1953 topographic map depicting the site prior to construction of the ash basin features is provided as Figure 2-3. The original ash basin at Buck began operation in 1957 and was formed by constructing a dam across a tributary of the Yadkin River, and occupied the approximate combined footprint of Cells 2 and 3. The original ash basin was eventually divided into two cells (Cells 2 and 3) in 1977 by construction of a separate divider dam and raising the western portion of the original dam. In 1982, additional storage was created by construction of Cell 1, separate from the other cells, by building a new dam upgradient from Cell 2. An unlined dry ash storage area is located on the eastern side of Cell 1 and contains dewatered ash that was excavated from Cell 1 in 2009 to provide additional volume for sluiced ash. The ash storage area is located with the footprint of and drainage area of Cell 1 and has a soil cover that is vegetated. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 2.0 SITE HISTORY AND DESCRIPTION Topography at the Buck site ranges from an approximate high elevation of 734 feet (NAVD 88) at the communications cell tower near the southwest edge of the property to an approximate low elevation of 620 feet at the Yadkin River on the northern margin of the site, with a total elevation change of approximately 114 feet over an approximate distance of 0.9 miles. Surface water drainage flow generally follows site topography from the south to north across the site except where natural drainage patterns have been modified by the ash basin or other construction features (refer to Section 3.2). A site features map is shown in Figure 2-4. 2.3 Adjacent Property, Zoning, and Surrounding Land Uses Properties located within a 0.5-mile radius of the Buck ash basin compliance boundary generally consist of residential, agricultural, and undeveloped properties located in Rowan County to the west, south, and east of the ash basin. The Yadkin River flows from west to east along the northern boundary. Hunting and game lands are located north of the ash basin across the Yadkin River in Davidson County. Buck is zoned as Industrial (IND) by Rowan County. Properties to the east and south are zoned Rural Agricultural (RA). Properties to the west are zoned as either Rural Agricultural with Agricultural Overlay (RA -AO) or 1-85 Economic Development District (85-ED-2). Figure 2-5 depicts the properties surrounding Buck and zoning designations. 2.4 Adjacent Surface Water Bodies and Classifications Surface water features located at the Buck site are shown in Figure 2-2. The site is located within the Yadkin -Pee Dee River basin about two miles northwest of High Rock Lake. Surface water classifications in North Carolina are promulgated in Title15A NCAC Subchapter 2B. The Yadkin River at Buck has a classification of WS-V. Class WS-V waters are protected as water supply sources which are generally upstream and draining to Class WS-IV waters or waters used by industry to supply their employees with drinking water or as waters formerly used as water supply. These waters are also protected for Class C uses which include secondary recreation, fishing, wildlife, fish consumption, aquatic life including propagation, survival and maintenance of biological integrity, and agriculture. Secondary recreation includes wading, boating, and other uses involving human body contact with water where such activities take place in an infrequent, unorganized, or incidental manner (NCDENR 2015). Three small farm ponds are located on adjacent properties south of the Buck site. The easternmost pond is the source of a stream that drains from south to north across the easternmost portion of the site into the Yadkin River. The western farm ponds both drain from south to north into the southern end of Cell 1. An unnamed stream also exists near the western edge of the Buck site near a transmission line corridor and drains into the Yadkin River. Portions of Cells 1, 2, and 3 of the ash basin also currently contain ponded areas of water. None of these ponds or streams is classified. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 2.0 SITE HISTORY AND DESCRIPTION 2.5 Meteorological Setting In winter, the average temperature in Rowan County is 42°F and the average daily minimum temperature is 31 °F. In summer, the average temperature is 770F and the average daily maximum temperature is 89°F (USDA-NRCS 2004). The total average annual precipitation in Rowan County is 46 inches. Thunderstorms occur approximately 41 days each year (USDA- NRCS 2004). The average relative humidity in midafternoon is approximately 54 percent, with humidity reaching higher levels at night. The prevailing wind is from the southwest, and average wind speed is highest (8.8 miles per hour) in March and April (USDA-NRCS 2004). 2.6 Hydrologic Setting The general direction of groundwater flow can be approximated from the ground surface topography with groundwater discharge to streams and the Yadkin River, and from groundwater elevation measurements. Two unnamed tributaries of the Yadkin River are located along the eastern and western sides of the Buck site. A topographic divide is located approximately along Leonard Road, to the south of the ash basin. The topographic divide likely also functions as a groundwater hydrologic boundary. The Yadkin River is located to the north of Buck. The predominant direction of groundwater flow from the ash basin is in a northerly direction, generally towards the Yadkin River, with localized components of flow toward the unnamed tributaries on the eastern and western sides of the site. Water level data within Cell 1, Cell 2, and Cell 3 were reviewed from the time period between January 1985 and March 2015. During this time period, all three cells were in operation. Cell 1 surface water levels generally exhibited gradual increases as would be expected as the level of ash within the cell increased. Water elevations within Cell 1 remained relatively steady at approximately 693 feet from January 1985 until April 1986 when the water elevation was raised to 694.3 feet. The water elevations within Cell 1 remained between 694 and 695 feet until January 2005 when the elevation was raised to 700.2 feet, and elevations thereafter remained relatively steady between approximately 699 and 700 feet until October 2006. The water elevations were subsequently raised to approximately 701.5 feet in October 2006, 703 feet in January 2007, 704 feet in February 2007, and 705 feet from July 2008 through January 2009. Water elevations varied from approximately 689 to 705 feet from January 2009 through January 2010, which included the time period when ash was being excavated out of the eastern side of Cell 1 and into the ash storage area. Water elevations then remained relatively steady at approximately 705 feet until dropped to approximately 700 feet in October 2013. The last coal- fired units at Buck were retired in April 2013. Since October 2013, the water elevation within Cell 1 has remained relatively constant at approximately 701 feet through March 2015. This last drop in water levels was initiated by Duke Energy to improve access within Cell 1 for the field activities associated with the CSA. There have been no dam construction or modifications for Cell 1 since before January 1985; therefore, the noted changes in water elevations were achieved by removing and adding stop logs. Smaller variations in water elevations could be attributed to variations in the flows from the stations and storm events. Im Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 2.0 SITE HISTORY AND DESCRIPTION Cell 2 and Cell 3 surface water elevations have shown less variability than within Cell 1 between January 1985 and March 2015, which is due to the use of Cell 1 as the primary means of ash storage during this time period. Cell 2 water elevations generally fluctuated between approximately 680 and 683 feet. Cell 3 water elevations generally fluctuated between 673 and 675 feet. These variations are likely attributed to the addition/removal of stop logs, variability in station operations, precipitation, and /or evapotranspiration. The ash basin affects the local groundwater elevations that underlie the ash basin. Water level measurements recorded downgradient of the ash basin cells indicate localized groundwater mounding due to the presence of the ash basin. Water level measurements recorded upgradient (south) of the ash basin cells indicate that groundwater flow is to the north (toward the ash basin). Groundwater recharge in the area 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). Of the average annual precipitation of 42 to 46 inches in the Piedmont area of North Carolina, mean annual recharge ranges from 4.0 to 9.7 inches per year (Daniel 2001). The hydrologic setting is described in greater detail in Section 5.0. 2.7 Permitted Activities and Permitted Waste Duke Energy is authorized to discharge treated wastewater from Buck to receiving waters designated as the Yadkin River in the Yadkin -Pee Dee River Basin in accordance with NPDES Permit NC0004774, which was most recently renewed on January 1, 2012. Any other point source discharge to surface waters of the state is prohibited unless it is an allowable non- stormwater discharge or is covered by another permit, authorization, or approval. The NPDES permit authorizes the following discharges in accordance with effluent limitations, monitoring requirements, and other conditions set forth in the permit: • Once -through non -contact condenser cooling water (CCW) for Buck is discharged to the Yadkin River through Outfall 001; • Make-up water process wastes, boiler cleaning water, stormwater flows from the yard Buck are discharged into the ash basin and then into the Yadkin River through Outfall 002; • Discharges from the BCCS wastewater collection sump (yard and floor drains from the generation equipment areas and auxiliary systems, water treatment building area, fire protection system, sanitary waste system, condenser circulating system, cooling tower blow down) are discharged into the ash basin and then into the Yadkin River through Outfall 002; • Yard sump overflow from Buck is discharged into the Yadkin River through Outfall 002A; • Outfall 003 has been eliminated; • Intake screen backwash from Buck is discharged into the Yadkin River through Outfall 004; and M Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 2.0 SITE HISTORY AND DESCRIPTION • Miscellaneous equipment cooling water from Buck is discharged into the Yadkin River through Outfall 005. Most of the discharges listed above as associated with Buck have been reduced or eliminated as a result of decommissioning Buck. There are no active or inactive permitted solid waste facilities (landfills) at the site. NPDES and Surface Water Monitoring The NPDES program regulates wastewater discharges to surface waters to ensure that surface water quality standards are maintained. The NPDES permitting program requires that permits be renewed every five years. The most recent NPDES permit renewal for Buck was issued on January 1, 2012 and expires on August 31, 2016. The current permit cited above requires surface water monitoring as part of the permit conditions. Surface water samples are required to be collected associated with Outfalls 001, 002, and 002A. The sample locations, parameters, and constituents to be measured and analyzed, and the requirements for sampling frequency and reporting results are outlined in the permit. 2.9 NPDES Flow Diagram The NPDES flow diagram for Buck is provided in Figure 2-6. This diagram shows the current inflows and outflows to the ash basin. The decommissioning of Buck has significantly reduced flows from Buck to the ash basin. Stormwater from the Buck yard drainage sump and runoff from the basin watershed is estimated to result in an average flow of 0.364 million gallons per day (MGD) to the basin. The estimated average sanitary waste flow from Buck to the basin is 0.002 MGD. Other remaining flows from Buck to the ash basin are relatively minor. Current inflows into the ash basin from BCCS include approximately 1.18 MGD from the cooling towers and condenser system, 0.040 MGD from the chiller system, and 0.073 MGD from the plant sumps. There is also a minor flow from the BCCS septic system into the ash basin. The contributing sources to these inflows are depicted on Figure 2-6. Figure 2-6 indicates a total outflow of 4.4 MGD from the ash basin, which includes ash sluice and other flows that are no longer directed to the ash basin since the decommissioning of the Buck. Based on the current outflows described above, the current discharge from the ash basin is approximately 1.66 MGD. 2.10 History of Site Groundwater Monitoring The location of the ash basin voluntary and compliance monitoring wells, the approximate ash basin waste boundary, and the compliance boundary are shown in Figure 2-7. The compliance boundary for groundwater quality at the Buck ash basin site is defined in accordance with Title Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 2.0 SITE HISTORY AND DESCRIPTION 15A NCAC 02L .0107(a) as being established at either 500 feet from the waste boundary or at the property boundary, whichever is closer to the waste. 2.10.1 Voluntary Groundwater Monitoring Wells Monitoring wells MW-1 S, MW-1 D, MW-2S, MW-2D, MW-3S, MW-3D, MW-4S, MW-4D, MW-5S, MW-5D, MW-6S, and MW-6D were installed by Duke Energy in 2006 as part of the voluntary monitoring system for groundwater near the ash basin. The existing voluntary wells are shown on Figure 2-7. Duke Energy performed biannual voluntary groundwater monitoring around the Buck ash basin from November 2006 until May 2010. During this period, twelve voluntary groundwater monitoring wells were sampled biannually and the analytical results were submitted to NCDENR DWR. Voluntary monitoring wells MW-2S and MW-2D were abandoned during construction of BCCS. With the exception of MW-6S, MW-6D, MW-3S, and MW-3D, no samples are currently being collected from the voluntary wells and they are not included in this CSA. 2.10.2 Compliance Groundwater Monitoring Wells Compliance groundwater monitoring, as required by the Buck NPDES Permit NC0004774, includes 14 compliance wells and began in March 2011. NPDES Permit Condition A (11), Version 1.1, dated June 15, 2011, lists the groundwater monitoring wells to be sampled, the parameters and constituents to be measured and analyzed, and the requirements for sampling frequency and reporting results (provided in Table 2-1). Locations for the compliance groundwater monitoring wells were approved by the former NCDENR DWR Aquifer Protection Section. The compliance groundwater monitoring system for the Buck ash basin consists of the following monitoring wells: MW-6S, MW-6D, MW-7S, MW-7D, MW-8S, MW-8D, MW-9S, MW-9D, MW- 10D, MW-11 S, MW-11 D, MW-12S, MW-12D, and MW-13D. Compliance groundwater monitoring wells were installed in December 2010. All compliance monitoring wells are sampled three times per year (in March, July, and November) for constituents listed in Table 2-1... Analytical results are submitted to the NCDENR DWR before the last day of the month following the month of sampling for all compliance monitoring wells. The compliance groundwater monitoring is performed in addition to the current NPDES monitoring of surface water discharges from Buck. From March 2011 through July 2015, the compliance groundwater monitoring wells at Buck have been sampled a total of 14 times. During this period, these monitoring wells were sampled in: • March, July, and November 2011 • March, July, and November 2012 • March, July, and November 2013 • March, July, and November 2014 • March and July 2015 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 2.0 SITE HISTORY AND DESCRIPTION One or more 2L Standards have been exceeded in groundwater samples collected from each of the compliance monitoring wells. Exceedances have occurred at least once in one or more wells for boron, chromium, iron, manganese, pH, sulfate, and total dissolved solids (TDS), although some of the analytes are naturally occurring in the regional geology. Table 2-2 presents exceedances measured from March 2011 through March 2015. Monitoring wells MW-6S, MW-7S, MW-8S, MW-9S, MW-11 S, and MW-12S were installed with 10-foot to 15-foot well screens placed above auger refusal to monitor the shallow aquifer within the saprolite layer. These wells were installed to total depths ranging from 13.8 feet below ground surface (bgs) at MW-9S to 21 feet bgs at MW-8S. Monitoring wells MW-6D, MW-7D, MW-8D, MW-9D, MW-1 OD, MW-11 D, MW-12D, and MW- 13D were installed with 5-foot to 15-foot well screens placed in the uppermost region of the fractured rock transition zone. These wells were installed to total depths ranging from 29.2 feet bgs at MW-9D to 108.5 feet bgs at MW-6D. Monitoring wells MW-6S and MW-6D are located to the southeast of Cell 1 at the compliance boundary and are considered to represent background water quality conditions at the site. The other ash basin compliance monitoring wells were also installed at or near the compliance boundary. 2.11 Assessment Activities or Previous Site Investigations Between 1987 and 2012, several historical onsite investigations have been conducted in response to fuel oil, diesel, and gasoline releases linked to the piping, aboveground storage tanks (ASTs), and underground storage tanks (USTs) associated with operations at Buck. A summary of the historical environmental incidents on -site is provided in Table 2-3. In September 2013, Duke Energy commenced implementation of a geotechnical and environmental field exploration program at Buck in support of development of a conceptual closure plan for the ash basin and ash storage area. The work performed as part of this effort included the installation of 29 borings in and around the Buck ash basin. Monitoring wells were installed within ash, soil, and bedrock for the purpose of environmental sampling and to measure groundwater elevations at the site. Samples of ash pore water, groundwater, ash, soil, and surface water were analyzed. Geotechnical testing was also performed on samples of ash and soil. The results from this field exploration and testing program were summarized in a conceptual design data report for the Buck ash basin closure (HDR 2014c). Pertinent information contained within the data report is included within this CSA report to supplement data obtained from the recent field activities. 2.12 Decommissioning Status Initial decommissioning activities at Buck began in 2013 and involved relocation of remaining coal by truck, relocation of plant equipment, removal of combustion turbine units and coal handling equipment, asbestos removal, and modifications to select gas plant systems. Ongoing decommissioning activities include relocation of electrical equipment and demolition of auxiliary Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 2.0 SITE HISTORY AND DESCRIPTION buildings and structures (scheduled to be completed by the end of 2015), removal of remaining powerhouse equipment and material for salvage and demolition of powerhouse and chimneys (scheduled to begin in 2016), and restoration of the Buck (scheduled to begin in 2017). In conjunction with decommissioning activities and in accordance with CAMA requirements, Duke Energy will permanently close the Buck ash basin. The required date of closure depends on the risk ranking classification assigned to the basin by NCDENR. DENR is required to submit their recommended risk ranking classification to the Coal Ash Commission no later than December 31, 2015. Classification of the Buck ash basin as a high -risk impoundment would require the basin to be excavated and closed as soon as practical, but no later than December 31, 2019, and a proposed closure plan must be submitted to NCDENR no later than December 31, 2016. A high -risk classification would require the basin to be excavated and closed by either converting the impoundment to a lined industrial landfill or by removal of all CCR from Buck and placement within an off -site landfill, structural fill, or other beneficial use allowed by law. Classification of the Buck ash basin as an intermediate -risk impoundment would require the basin to be excavated and closed as soon as practical, but no later than December 31, 2024. A proposed closure plan for such a classification must be submitted to NCDENR as soon as practical, but no later than December 31, 2017. An intermediate -risk classification would require the basin to be excavated and closed by one of the same options listed for high -risk impoundments. Classification of the Buck ash basin as a low -risk impoundment would require the basin to be closed as soon as practical, but no later than December 31, 2029. A proposed closure plan for such a classification must be submitted to NCDENR as soon as practical, but no later than December 31, 2018. A low -risk classification would allow the basin to be closed by one of the same options listed for high -risk impoundments but will also allow closure in -place by construction of a cap system over the CCR designed to minimize infiltration and erosion. The final USEPA CCR rule (U.S. Environmental Protection Agency 2015), however, requires breaching of the impoundment dike and stabilization of the ash within the impoundment if saturated ash is present within the impoundment. Per the requirements of the USEPA CCR Rule, Duke Energy is preparing a Closure Plan that will be required to be posted on an external website by October 2016. The insights gained from this CSA and the associated CAP will inform the closure plan development. 15 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 3.0 SOURCE CHARACTERISTICS 3.0 Source Characteristics This section provides a general description of the Buck coal combustion and ash handling system, a description of the ash basin and ash storage area, and provides a discussion on the general physical and chemical properties of ash. 3.1 Coal Combustion and Ash Handling System Coal ash is produced from the combustion of coal. The coal is dried, pulverized, and conveyed to the burner area of a boiler. The smaller particles produced by coal combustion, referred to as fly ash, are carried upward in the flue gas and are captured by an air pollution control device, such as an electrostatic precipitator. The larger particles of ash that fall to the bottom of the boiler are referred to as bottom ash. Coal ash residue from the coal combustion process was disposed in the Buck ash basin from approximately 1957 until the last coal-fired generating units were retired in April 2013. Fly ash from the electrostatic precipitators was collected in hoppers. Bottom ash and boiler slag was collected in the bottom of the boilers. After collection, both fly ash and bottom ash/boiler slag were sluiced to the ash basin using conveyance water withdrawn from the Yadkin River. The sluice lines originally discharged the water/ash slurry and other flows into the northwest section of Cell 2. After Cell 1 was constructed in 1982, the discharge lines from Buck were redirected into the northeast section of Cell 1. Refer to Figure 2-2 for a depiction of these features. During operation of the coal-fired units, the ash basin received variable inflows from the ash removal system and other permitted discharges. Currently, the ash basin receives variable inflows from the Buck station yard drain sump, stormwater flows, and miscellaneous low volume wastes. The basin also receives variable inflows from the BCCS wastewater collection sump. Duke Energy is in the process of evaluating alternatives for removing these flows from the ash basin to allow total decommissioning of the ash basin system. 3.2 Description of Ash Basins and Ash Storage Area The Buck ash basin system is located near the Yadkin River and comprises three cells designated as Cell 1, Cell 2, and Cell 3 (as previously described in Section 2.2), and associated embankments and outlet works, as shown in Figure 2-2. The ash basin is located to the south (Cell 1) and southeast (Cells 2 and 3) of the retired Buck Units 1 through 6 and the BCCS. An area between Cell 1 and Cell 2 has also been utilized for storage of dredged ash from Cell 1 and is referred to as the ash storage area. Buck historically produced approximately 100,000 tons of ash per year. Note that this quantity is an estimate and actual quantities fluctuated based on generation rates, outages, coal mineralogy, and other factors. The ash basin system will sometimes be referred to collectively as the ash basin or source for convenience in this report. Beyond Cell 1, Cell 2, Cell 3 and the ash storage area adjacent to Cell 1, no other CCR waste storage or disposal areas are known to exist at the Buck site. 16 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 3.0 SOURCE CHARACTERISTICS 3.2.1 Ash Basin The original ash basin at Buck began operation in 1957 and was formed by constructing a dam across a tributary of the Yadkin River with a crest elevation of 680 feet. The footprint of the original ash basin was the approximate current footprint of Cells 2 and 3. As the ash basin capacity diminished over time, the original basin was eventually divided into two ash basins (Cells 2 and 3) by construction of a separate intermediate dike over ash and raising the elevation of the western portion of the earthen dike along the Yadkin River by 10 feet in 1977. In 1982, additional storage was created by construction of Cell 1, separate and upgradient from Cell 2, by building a new dike with a crest elevation of 710 feet. Until Cell 1 was constructed, ash generated from the coal combustion process at Buck was sluiced (via ash discharge lines) into the northwest section of Cell 2. Following construction of Cell 1, discharge of sluiced ash into the ash basin system was rerouted from Cell 2 to the northeast section of Cell 1. All coal ash from Buck was disposed of in the ash basin from approximately 1957 until 2013. Fly ash precipitated from flue gas and bottom ash collected in the bottom of the boilers were sluiced to the ash basin using conveyance water withdrawn from the Yadkin River. The discharge flow from Cell 1 enters Cell 2 via the Cell 1 discharge tower. Flow from Cell 2 enters Cell 3 via the Cell 2 discharge tower. Flow is discharged through NPDES Outfall 002 to the Yadkin River through the Cell 3 discharge tower located at the north end of Cell 3. The Cell 3 concrete discharge tower drains through a 36-inch-diameter corrugated metal pipe. The approximate current basin elevations (obtained June 2015) for the three ash basin cells are: Cell 1 — pond elevation 701 feet; Cell 2 — pond elevation 682 feet; Cell 3 — pond elevation 673 feet. The elevation of the Yadkin River near the site is approximately 620 feet. The ash basin pond elevations are controlled by the use of concrete stop logs in the three discharge towers. The area contained within the waste boundary for Cell 1 encompasses approximately 90 acres. For purposes of delineating the waste boundary, Cells 2 and 3 are considered a single unit, with the area contained within this portion of the waste boundary encompassing approximately 80.7 acres. The ash basin waste boundary is shown on Figure 2-2. The quantity of ash contained within the ash basin was estimated by comparing the digitized pre -basin topographic survey of the site to a topographic and bathymetric survey of the basin, dated November 2013, which was after the last coal-fired generating unit was retired. The estimated in -place quantities of ash are: Cell 1 — 2,366,000 cubic yards (cy), Cell 2 — 1,624,000 cy, and Cell 3 — 227,000 cy. Actual ash quantities may vary from those calculated since soil borrow operations are known to have taken place within the ash basin boundaries prior to the deposition of ash. During operation of the coal-fired units, the ash basin received variable inflows from the ash removal system and other permitted discharges. Currently, the ash basin receives variable inflows from the station yard drain sump, stormwater flows, and BCCS wastewater and no Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 3.0 SOURCE CHARACTERISTICS longer receives sluiced ash. Duke Energy is evaluating alternatives for removing these flows from the ash basin in order to allow total decommissioning of the ash basin system. Cell 3 and the southern portion of Cell 2 continue to serve as treatment units for the ash basin system. Trees and other vegetation have naturally established in the northern portion of Cell 2. The water level within Cell 1 has been lowered such that there is relatively little ponding occurring within the cell. 3.2.2 Ash Storage Area An unlined ash storage area is located topographically upgradient and adjacent to the east side of Cell 1 (Figure 2-2). The dry ash storage area was constructed in 2009 by excavating ash within the eastern half of Cell 1 in order to provide additional capacity for sluiced ash and covers approximately 14 acres. Following the completion of excavation and stockpiling, the dry ash storage area was graded to drain to Cell 1 and a minimum of 18 and 24 inches of soil cover were placed on the top slopes and sideslopes, respectively, and vegetation was established. The estimated in -place quantity of ash stored at this location is 209,000 cy based on a comparison of original site topography and the topographic survey of the site from November 2013. 3.2.3 Dams There are five regulated earthen dams within the Buck ash basin system. These include the Cell 2/Cell 3 main dam located adjacent to the Yadkin River, the Cell 1 dam located south of the BCCS, an intermediate dam that divides Cell 2 and Cell 3, and the small dams associated with the Cell1 and Cell 2 discharge towers. The Cell 2/Cell 3 main dam was constructed in 1956 and was formed by constructing a dam across a tributary of the Yadkin River with a crest elevation of 680 feet and a total height at its deepest point of approximately 60 feet. As the ash basin capacity diminished over time, the original basin was eventually divided into two cells (Cells 2 and 3) by construction of a separate intermediate dike over ash and raising the elevation of the western portion of the earthen dike along the Yadkin River by 10 feet (in 1977). At this same time, the canal for the Cell 2 discharge tower was excavated and the dam associated with the discharge tower was constructed with a base elevation at 670 feet and a crest elevation of 690 feet. In 1979, the intermediate dam dividing Cell 2 and Cell 3 was reinforced by constructing an earthen embankment with a crest elevation of 682 feet over ash on the downstream side of the dam. The embankment has a washed stone blanket drain between the soil and underlying ash. In 1982, additional storage was created by construction of Cell 1 with a crest elevation of 710 feet and a total height at its deepest point of approximately 60 feet. At this same time, the canal for the Cell 1 discharge tower was excavated and the dam associated with the discharge tower was constructed with a base elevation at 685 feet and a crest elevation of 710 feet. im Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 3.0 SOURCE CHARACTERISTICS 3.3 Physical Properties of Ash Ash in the Buck ash basin 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. In general, coal is dried, pulverized, and conveyed to the burner area of a boiler for combustion. As described in Section 3.1, material that forms larger particles of ash and falls to the bottom of the boiler is referred to as bottom ash. Smaller particles of ash, known as fly ash, are carried upward in the flue gas and are captured by an air pollution control device Approximately 70 to 80 percent of the ash produced during coal combustion is fly ash (EPRI 1993). Typically 65 to 90 percent of fly ash has particle sizes that are less than 0.010 millimeter (mm). In general, fly ash has a grain size distribution similar to that of silt. The remaining 20 to 30 percent of ash produced is considered to be bottom ash. Bottom ash consists of angular particles with a porous surface and is normally gray to black in color. Bottom ash particle diameters can vary from approximately 0.05 to 38 millimeters. In general, bottom ash has a grain size distribution similar to that of fine to medium sand (EPRI 1995). Based on published literature not specific to this 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 a similar gradation and density (EPRI 1995). Permeability and other physical properties of the ash found in the Buck ash basin are presented later in this report. 3.4 Chemical Properties of Ash In general, the specific mineralogy of coal ash varies based on many factors including the chemical composition of the coal, which is directly related to the geographic region where the coal was mined, the type of boiler where the combustion occurs (i.e., thermodynamics of the boiler), and air pollution control technologies employed. The overall chemical composition of coal ash resembles that of siliceous rocks from which it was derived, particularly shale. Oxides of silicon, aluminum, iron, and calcium make up more than 90 percent of most siliceous rocks, soils, fly ash, and bottom ash. Other major and minor elements (sulfur, sodium, potassium, magnesium, titanium) make up an additional 8 percent, while trace constituents account for less than 1 percent. The following constituents are considered to be trace elements: arsenic, barium, cadmium, chromium, lead, mercury, selenium, copper, manganese, nickel, lead, vanadium, and zinc (EPRI 2010). According to Duke Energy, the specific coal sources used at Buck were low sulfur coal from central Appalachia, comprised of eastern Kentucky, southern West Virginia, and southwestern Virginia. 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 im Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 3.0 SOURCE CHARACTERISTICS collected from the ash basin at Duke Energy's Cliffside Steam Station, which is similar to Buck ash. The figure shows a mix of fly ash and bottom ash at 10 pm and 20 pm 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; however, consist of soluble salts (e.g. calcium (Ca2+), sulfate (S042-), metals (copper (Cu), zinc (Zn), and other minor elements (e.g. boron (B), selenium (Se), and arsenic (As)) (EPRI 1994). The major elemental composition of fly ash (approximately 95 percent by weight) is composed of mineral oxides of silicon, aluminum, iron, and calcium. Oxides of magnesium, potassium, titanium and sulfur comprise approximately 4 percent by weight (EPRI 1995). Trace elemental composition typically is approximately 1 percent by weight and may include arsenic, antimony, barium, boron, cadmium, chromium, copper, manganese, mercury, nickel, lead, selenium, silver, thallium, zinc, and other elements. For comparison, Figure 3-2 shows the elemental composition of fly ash and bottom ash compared with typical values for shale and volcanic ash. Table 3-1 shows the bulk composition of fly ash and bottom ash compared with typical values for soil and rock. In addition to these constituents, fly ash may contain unburned carbon. Bituminous coal ash typically yields slightly acidic to alkaline solutions with pH levels ranging from approximately 5 to 10 on contact with water. The geochemical factors controlling the reactions associated with leaching of ash are complex. Factors such as the chemical speciation of the constituent, solution pH, solution -to -solid ratio, and other factors control the chemical concentration of the resultant solution. Constituents that are held on the glassy surfaces of fly ash such as boron, arsenic, and selenium may initially leach more readily than other constituents. As noted in Table 3-1, aluminum, silicon, calcium, and iron represent the larger fractions of fly ash and bottom ash by weight. The presence of calcium 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, which is based on different coal types, different age of ash in the basin, and other factors, it is anticipated that the chemical environment of the ash basin varies over time, distance, and depth. EPRI (2010) reports that 64 samples of coal combustion products (including fly ash, bottom ash, and flue gas desulfurization residue) from 50 different power plants were subjected to USEPA Method 1311 Toxicity Characteristic Leaching Procedure (TCLP) (USEPA 2008) leaching and no TCLP result exceeded the TCLP hazardous waste limit. Figure 3-3 provides the results of that testing. The report also presents the trace element concentrations for fly ash and bottom ash compared to USEPA Residential Soil Screening Levels (RSLs) for ingestion and dermal exposure. Figure 3-4 shows the 10th to 90th percentile range for trace element concentrations (mg/kg) in fly ash and the associated USEPA RSLs. The trace element concentrations for 20 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 3.0 SOURCE CHARACTERISTICS arsenic were greater than the RSL for arsenic. The RSLs of the remaining constituents were greater than or within the 10th to 90th percentile range for their trace element concentrations. Figure 3-5 shows similar data for bottom ash. As with fly ash, the trace element concentrations for arsenic in bottom ash were greater than the RSL for arsenic. The RSL for chromium was within the 101h to 90th percentile range of concentrations for chromium in bottom ash. The 10th to 90th percentile range for the remaining constituents were below their respective RSLs. Site -specific ash data is discussed in Section 7.0 of this report. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 4.0 RECEPTOR INFORMATION 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 non -water supply wells and other receptors that were evaluated as part of this CSA effort. The NORR CSA receptor survey guidance requirements include listing and depicting all water supply wells, public or private, including irrigation wells and unused wells (other than those that have been properly abandoned in accordance with 15A NCAC 2C.0113) within a minimum of 1,500 feet of the known extent of contamination. In NCDENR's June 2015 response to Duke Energy's proposed adjustments to the CSA guidelines, NCDENR DWR acknowledged the difficulty with determining the known extent of contamination at this time and stated that they expected all drinking water wells located 2,640 feet (0.5-miles) downgradient from the established compliance boundary to be documented in the CSA reports as specified in the CAMA requirements. The approach to the receptor survey in this CSA includes listing and depicting all water supply wells (public or private, including irrigation wells and unused wells) within a 0.5-mile radius of the ash basin compliance boundary. An additional receptor survey requirement in the NORR CSA guidance is 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. Drawings of underground utilities were not readily available for review; however, underground utilities are typically located at relatively shallow depths below the ground surface. It is assumed that any underground utilities present at the site would not act as potential preferential pathways for contaminant migration through underground utility corridors to these water supply well receptors because the Yadkin River serves as the down -gradient hydrologic divide for groundwater flow from potentially impacted areas. Therefore, the mapping of underground features that would serve as preferential pathways was limited to underground piping and drains located between the ash basin waste boundaries and these surface water features. 4.1 Summary of Previous Receptor Survey Activities Duke Energy submitted a receptor survey to NCDENR (HDR 2014a) in September 2014, and subsequently submitted to NCDENR a supplement to the receptor survey (HDR 2014b) in November 2014. The purpose of the receptor survey was to identify the potential exposure locations that are critical with regard to groundwater transport modeling and human health risk assessment. The supplementary information was obtained from responses to water supply well survey questionnaires mailed to property owners within a 0.5-mile (2,640-foot) radius of the 22 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 4.0 RECEPTOR INFORMATION Buck ash basin compliance boundary requesting information on the presence of water supply wells and well usage. The previous survey activities included contacting and/or reviewing the following agencies/records to identify public and private water supply sources, confirm the location of wells, and/or identify any wellhead protection areas located within a 0.5-mile radius of the Buck ash basin compliance boundary: • NCDENR DWR Public Water Supply Section's (PWSS) most current Public Water Supply Water Sources GIS point data set; • NCDENR DWR Source Water Assessment Program (SWAP) online database for public water supply sources; • Environmental Data Resources (EDR) local/regional water agency records review; • Rowan County Health Department Environmental Health Division; • Davidson County Health Department; • Salisbury -Rowan Utilities Department; and • USGS National Hydrography Dataset. In addition, a field reconnaissance was performed on March 11, 2014 to identify public and private water supply wells (including irrigation wells and unused or abandoned wells) and surface water features located within a 0.5-mile radius of the Buck ash basin compliance boundary. A windshield survey was conducted from public roadways to identify water meters, fire hydrants, valves, and any potential well heads/well houses. Duke Energy site personnel provided information regarding water supply wells located on Duke Energy property. During the week of October 8, 2014, 254 water supply well survey questionnaires were mailed to property owners requesting information on the presence of water supply wells and well usage information for each property. The mailing list was compiled from a query of the parcel addresses included in the Rowan County GIS database utilizing the 0.5-mile offset. Between July 30 and August18, 2015, several of the agencies/records listed above were contacted to provide additional update information. Updated information is provided in Appendix B. 4.2 Summary of CSA Receptor Survey Activities and Findings As part of this CSA report, the previously completed Receptor Survey activities were updated based on the CSA Guidelines. The update included contacting and/or reviewing the agencies/records to identify public and private water supply sources identified in Section 4.1 and reviewing questionnaires that were received after the submittal of the November 2014 supplement to the September 2014 receptor survey (i.e. questionnaires received after October 31, 2014). A summary of the receptor survey findings is provided below. The identified water supply wells are shown in the USGS receptor map in Figure 4-1 and on an aerial photograph on Figure 4-2. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 4.0 RECEPTOR INFORMATION Figure 4-3 presents underground utility features near the ash basin system while Figure 4-4 presents surface water features identified on and surrounding the Buck site, Available property and well information for the identified water supply wells is provided in Table 4-1. Table 4-2 provides names and addresses of property owners contiguous to the ash basin waste boundary which corresponds to the parcels depicted on Figure 4-5. • A total of 166 private water supply wells were identified within a 0.5-mile radius of the Buck ash basin compliance boundary. The Rowan County Health Department had records for 28 of the 166 identified private water supply wells. • Ten additional private water supply wells are assumed at residences located within a 0.5-mile radius of the Buck ash basin compliance boundary based on the absence of municipal water lines. • Two public water supply wells were identified within a 0.5-mile radius of the Buck ash basin compliance boundary. PWS 0180647 is owned by Duke Energy and resides east of the BCCS. • One water supply well (PWS ID: 0180647)) (including irrigation wells and unused or abandoned wells) was identified within the Buck ash basin potential area of interest on Duke Energy property. • One previously identified public water supply well (PWS NC0180630) has been determined to exist outside of the 0.5-mile radius of the Buck compliance boundary and has been removed from Figures 4-1, 4-2, and Table 4-1. The location that was erroneously assigned to this well (Bethel Methodist Church) was determined to no longer be considered to have a public water supply well and therefore is now listed as a location with a reported private water supply well (Well ID 173) on Figure 4-1, Figure 4-2, and Table 4-1. • One previously identified public water supply well (PWS NC0180630) was an error and the property is now listed as having an assumed private water supply well (Well ID 176) on Figure 4-1, Figure 4-2, and Table 4-1. • A new house was identified within the 0.5-mile radius of the Buck ash basin compliance boundary and is now listed as having an assumed private water supply well (Well ID 174) on Figure 4-1, Figure 4-2, and Table 4-1. • No wellhead protection areas were identified within a 0.5-miles radius of the Buck ash basin compliance boundary. • Several unnamed tributaries of the Yadkin River were identified within a 0.5-mile radius of the ash basin. • Several surface water features that flow toward the Yadkin River were identified within a 0-5-mile radius of the Buck ash basin. Based on the returned water supply well questionnaires since October 31, 2014, the following revisions were noted: • Four of the previously reported 86 "field identified" private water supply wells were confirmed to have private water supply wells located on the properties. These wells are Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 4.0 RECEPTOR INFORMATION now identified as "reported" private water supply wells on Figure 4-1, Figure 4-2 and Table 4-1. The Well IDs with revised identifications are 61,124, 152, and 166. One new well has been identified based on information provided in the returned questionnaires. This well is now identified as a "reported" private water supply wells on Figure 4-1, Figure 4-2 and Table 4-1. The new Well ID is 175. Further details of HDR's receptor survey activities and findings are presented in Appendix B 4.3 NCDENR Well Water Testing Program Section § 130A-309.211 (c) of the CAMA requires the owner of a coal combustion residuals surface impoundment to conduct a Drinking Water Supply Well Survey that identifies all drinking water supply wells within 0.5-mile down -gradient from the established compliance boundary of the impoundment and submit the Well Survey to NCDENR. Since the direction of groundwater flow was not fully established at the site, NCDENR required the sampling to include all potential drinking water receptors within 0.5-mile of the compliance boundary in all directions. Between February and July 2015, NCDENR arranged for independent analytical laboratories to collect and analyze water samples obtained from private wells identified during the Well Survey, if the owner agreed to have their well sampled. Appendix B provides tabulated sampling results provided by Duke Energy from NCDENR, a water supply well tracking spreadsheet provided by NCDENR, and well sample results provided by NCDENR for wells outside of the 0.5-mile radius that would be considered to represent background results. 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 and have been excluded. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY 5.0 Regional Geology and Hydrogeology 5.1 Regional Geology North Carolina is divided into three physiographic provinces: the Atlantic Coastal Plain, Piedmont, and Blue Ridge (Fenneman 1938). The Buck site is located in 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 of 150 to 225 miles in the Carolinas (LeGrand 2004). 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 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). The Buck site is within the Charlotte terrane, one of a number of tectonostratigraphic terranes that have been defined in the southern and central Appalachians and is in the western portion of the larger Carolina superterrane (Figure 5-1; Horton et al. 1989; Hibbard et al. 2002; Hatcher et al. 2007). On the northwest side, the Charlotte terrane is in contact with the Inner Piedmont zone along the Central Piedmont suture along its northwest boundary and is distinguished from the Carolina terrane to the southeast by its higher metamorphic grade and portions of the boundary may be tectonic (Secor et al. 1998; Dennis et al. 2000). The Charlotte terrane is dominated by a complex sequence of plutonic rocks that intrude a suite of metaigneous rocks (amphibolite metamorphic grade) including mafic gneisses, amphibolites, metagabbros, and metavolcanic rocks with lesser amounts of granitic gneiss and ultramafic rocks with minor metasedimentary rocks including phyllite, mica schist, biotite gneiss, and quartzite with marble along its western portion (Butler and Secor 1991; Hibbard et al. 2002). The general structure of the belt is primarily a function of plutonic contacts. A geologic map of the area around the Buck site 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 ferro-magnesium minerals form a more clayey saprolite. 5.2 Regional Hydrogeology The groundwater system is described as being comprised of two interconnected layers, or two - medium system: 1) residual soil/saprolite and weathered fractured rock (regolith) overlying 2) fractured crystalline bedrock (Heath 1980; Harried and Daniel 1992; Figure 5-3). The regolith 26 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY 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 regolith layer serves as the uppermost zone of the unconfined groundwater system and provides an intergranular medium through which the recharge and discharge of water from the underlying fractured rock occurs. Within the fractured crystalline bedrock layer, the fractures control both the hydraulic conductivity and storage capacity of the rock mass. A transition zone (TZ) at the base of the regolith has been interpreted to be present in many areas of the Piedmont. Harned and Daniel (1992) describe the TZ as consisting of partially weathered/fractured bedrock and lesser amounts of saprolite that grades into bedrock and they described the zone as "being the most permeable part of the system, even slightly more permeable than the soil zone". Harned and Daniel (1992) suggested the TZ 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 et al. 1964; Nutter and Otton 1969; Harned and Daniel 1992). Schaeffer (2009; 2014a), using a database of 669 horizontal hydraulic conductivity measurements in boreholes at six locations in the Carolina Piedmont, statistically showed that a TZ of higher hydraulic conductivity exists in the Piedmont groundwater system when considered within Harned and Daniel's (1992) two types of bedrock conceptual framework. The TZ is described as being comprised of partially weathered rock, open, steeply dipping fractures, and low angle stress relief fractures, either singly or in various combinations below refusal (auger, roller cone, or casing advancer; Schaeffer 2011; 2014b). The TZ has less advanced weathering relative to the regolith and generally the weathering has not progressed to the development of clay minerals that would decrease the permeability of secondary porosity developed during weathering, (i.e., the new fractures developed during the weathering process, and /or the enhancement of existing fractures). The characteristics of the TZ can vary widely based on the interaction of rock type, degree of weathering, degree of systematic fracturing, presence of stress -relief fracturing, and the general characteristics of the bedrock (foliated/layered, massive, or in between). The TZ is not a continuous layer between the regolith and bedrock; it thins and thickens within short distances and is absent in places (Schaeffer 2011; 2014b). The absence, thinning, and thickening of the TZ is related to the characteristics of the underlying bedrock (Schaeffer 2014b). As previously mentioned, the TZ may vary due to different rock types and associated rock structure. Harned and Daniel (1992) further divided the bedrock into two conceptual models: 1) foliated/layered (metasedimentary and metavolcanic sequences) and 2) massive/plutonic (plutonic and metaplutonic complexes) structures (Figure 5-4). Strongly foliated/layered rocks are thought to have a well -developed TZ due to the breakup and weathering along the foliation 27 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY planes or layering, resulting in numerous rock fragments (Harned and Daniel 1992). More massive 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 and Daniel 1992). Schaeffer (2014a) proved Harned and Daniel's (1992) hypothesis that foliated/layered bedrock would have a better developed TZ than plutonic/massive bedrock. The foliated/layered bedrock TZ has a statistically significant higher hydraulic conductivity than the massive/plutonic bedrock TZ (Schaeffer 2014a). LeGrand's (1988; 1989) conceptual model of the groundwater setting in the Piedmont incorporates Daniel and Harned's (1992) above two -medium system into an entity that is useful for the description of groundwater conditions. That entity is the surface drainage basin that contains a perennial stream (LeGrand 1988). Each basin is similar to adjacent basins and the conditions are generally repetitive from basin to basin. Within a basin, movement of groundwater is generally restricted to the area extending from the drainage divides to a perennial stream (Slope -Aquifer System; Figure 5-5; LeGrand 1988; 1989; 2004). Rarely does groundwater move beneath a perennial stream to another more distant stream or across drainage divides (LeGrand 1989). The crests of the water table underneath topographic drainage divides represent natural groundwater divides within the slope -aquifer system and may limit the area of influence of wells or contaminant plumes located within their boundaries. The concave topographic areas between the topographic divides may be considered as flow compartments that are open-ended down slope. Therefore, the groundwater system is a two medium system generally 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 sedimentary rock. The systems are separated by the TZ portion of the residual soil, saprolite, and weathered rock. 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 aquifers 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 consist of interlocking crystals and primary porosity is very low, generally less than 3 percent. Secondary porosity of crystalline bedrock due to weathering and fractures ranges from 1 to 10 percent (Freeze and Cherry 1979); but, porosity values of 1 to 3 percent are more typical (Daniel and Sharpless 1983). Daniel (1990) reported that the porosity of the regolith ranges from 35 to 55 percent near land surface but decreases with depth as the degree of weathering decreases. 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). 28 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 6.0 SITE GEOLOGY AND HYDROGEOLOGY 6.0 Site Geology and Hydrogeology 6.1 Site Geology The Buck site and its associated ash basin system are located in the Charlotte terrane. The Charlotte terrane consists of an igneous complex of Neoproterozoic to Paleozoic ages (Hibbard et al. 2002) that range from felsic to mafic in composition (Butler and Secor 1999). The Charlotte terrane is bordered on the east and southeast by the Carolina terrane and to the west and northwest by the Inner Piedmont (Cat Square and Tugaloo terranes) and the Kings Mountain terrane. The structural contact of the Inner Piedmont and Charlotte terrane is the Central Piedmont Shear Zone. The Charlotte terrane is dominated by plutonic rocks with some large areas of metavolcanic rocks, but few metasedimentary rocks are present. The oldest rocks in the belt consist of metamorphosed volcanic -plutonic complexes that range in composition from ultramafic to felsic and from coarse -grained plutonic rocks through porphyritic hypabyssal rocks including extrusive volcanic flows and tuffs. Rock types include mafic gneiss, amphibolite, metagabbro, and metavolcanicrocks with lessor amounts of biotite gneiss, granitic gneiss, mica schist, quartzite, and ultramafic rocks. These rocks have been intruded by a complex sequence of plutonic rocks. The plutonic rocks are extensive and compositions include granite, diorite, monzonite, gabbro, norite, and pyroxenite. The Buck site is underlain by a metavolcanic complex ranging in composition from felsic to mafic (Figure 6-1). The installed well and sample locations are shown on Figure 6-2. 6.1.1 Soil Classification The following soils/materials were encountered in the boreholes: • Ash — Ash was encountered in borings advanced within the ash basin and ash storage areas, as well as through dikes. Ash was generally described as gray to dark gray, non - plastic, loose to medium dense, dry to wet, fine to coarse grained. • Fill — Fill material generally consisted of re -worked silts, clays, and sands that were borrowed from one area of the site and re -distributed to other areas. Fill was generally classified as silty sand, clay with sand, clay, and sandy clay on the boring logs. Fill was used in the construction of dikes, and as cover for ash storage area. • Alluvium —Alluvium encountered in borings during the project was classified as clay and sand with clay. In some cases alluvium was logged beneath ash. • Residuum (Residual soils) — Residuum is the in -place weathered soil that consists primarily of silt with sand, clayey sand, sandy clay, clay with gravel, and clayey silts. Residuum varied in thickness and was relatively thin compared to the thickness of saprolite. 29 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 6.0 SITE GEOLOGY AND HYDROGEOLOGY • Saprolite/Weathered Rock — Saprolite is soil developed by in -place weathering of rock that retains remnant bedrock structure. Saprolite consists primarily of medium dense to very dense silty sand, sandy silt, sand, sand with gravel, sand with clay, clay with sand, and clay. Sand particle size ranges from fine to coarse grained. Much of the saprolite is IHIMM-181W19 M Geotechnical property testing was completed for disturbed and undisturbed samples in accordance with American Society for Testing and Materials (ASTM) standards. Forty-one undisturbed ('Shelby Tube') samples were submitted for geotechnical testing. Geotechnical property testing for undisturbed samples comprised Unified Soil Classification System (USCS) classification (ASTM D 2487), natural moisture content (ASTM D 2216), Atterberg Limits (ASTM D 4318), grain size distribution, including sieve analysis and hydrometer (ASTM D 422), total porosity calculated from Specific Gravity (ASTM D 854), and hydraulic conductivity (ASTM D 5084). Two undisturbed samples were unable to receive the full suite of index property tests due to low recovery, wax and gravel mixed in the tube, loose material, or damaged tubes. Thirty- three disturbed ('Split Spoon,' or'Jar') samples received grain size distribution with hydrometer (ASTM D 422), and natural moisture content (ASTM D 2216). The results are presented in Table 11-1. 6.1.2 Rock Lithology The Buck site is underlain by interbedded felsic, intermediate, and mafic metavolcanic rocks. The felsic metavolcanic rocks are fine- to medium -grained, locally coarse -grained or agglomeritic, rhyolitic to dacitic metatuffs. The intermediate and mafic metavolcanic rocks are fine- to medium -grained, locally coarse -grained or agglomeritic rocks of basaltic, andesitic, and dacitic compositions. They are primarily tuffs and flows and with minor hypabyssal intrusives present. The rocks are metamorphosed to upper amphibolite grade of metamorphism. 6.1.3 Structural Geology The major structures in the rock are layering/foliation of the various volcanic units. The rock ranges from non-foliation/massive to intensely foliated with steep dips. Shear zones occur along the contacts of the volcanic units and suggesting shearing along limbs of tight isoclinal folds. Fracture zones occur in the rock core and are generally healed with later greenschist metamorphic minerals, primarily epidote and chlorite. Fractures and joints below refusal in the boreholes exhibit iron and manganese staining that is indicative of water movement. The strike orientation of the fracture zones cannot be determined from examination of the rock core but is likely parallel to the strike of the volcanic units (northeast). Suitable rock/saprolite exposures for determining structural orientations were not located during field reconnaissance near the site. 6.1.4 Geologic Mapping A site visit was conducted in April 2015 to identify (and map if present) outcrops at the site and within a 2-mile radius of the site. No rock outcrops were identified at the Buck site or within a 2- 0 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 6.0 SITE GEOLOGY AND HYDROGEOLOGY mile radius of the site. The geologic map presented in Figure 6-1 is based on mapping by Goldsmith et al. (1988) with the first encountered rock type in the new boreholes shown. 6.1.5 Fracture Trace Study 6.1.5.1 Introduction 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 identify potential fracture locations, and hence potential preferential pathways for infiltration and flow of groundwater near a site, results are not definitive. Lineaments identified as part of fracture trace analysis may or may not correspond to actual locations of fractures exposed at the surface, and if fractures are present, it cannot be determined from fracture trace analysis whether these are open or healed. Healed fractures intruded by diabase are common in the vicinity of the site. Strongly linear features at the earth's surface are commonly formed by weathering along steeply dipping to vertical fractures in bedrock. Morphological features such as narrow, sharp crested ridges, narrow linear valleys, linear escarpments, and linear segments of streams otherwise characterized by dendritic patterns are examples. Linear variations in vegetative cover are also sometimes indicative of the presence of exposed fractures, though in many cases these result from unrelated human activity or other geological considerations (e.g., change in lithology). Straight (as opposed to curvilinear) features are commonly associated with the presence of steeply dipping fractures. Curvilinear features in some cases are associated with 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 oftentimes 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. Substantial surface alteration occurs over an estimated 30 percent of the aerial -photography study area for the Buck site. 6.1.5.2 Methods Available geologic maps for 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. Low -altitude aerial photography provided by Duke Energy (from WSP Global, Inc.) covering approximately 5 square miles, and USGS 1:24000 scale topographic maps covering an area of approximately 38 square miles were examined. Maps examined included portions of the Salisbury, N.C. and Southmont, N.C. USGS 7.5' (1:24,000 scale) topographic quadrangles. Digital copies of the quadrangles were obtained and a Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 6.0 SITE GEOLOGY AND HYDROGEOLOGY 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 6-3. Photography provided for review included 1"=600' scale, 9 x 9 inch black -and -white (grayscale) contact prints dated April 17, 2014. Stereo coverage was complete across the area shown on Figure 6-4. 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. 6.1.5.3 Results Lineaments identified from topographic maps are shown, and lineament trends indicated by a rose diagram, are included on Figure 6-3. Geologic structures, including fractures, are not well preserved in the deeply weathered, saprolitic soil underlying the site and its immediate vicinity. A total of 12 topographic lineaments were identified, with tends predominantly toward the north- northeast. These occur within the metavolcanic unit and likely parallel the layering/foliation of the metavolcanic sequence, a joint set that strikes parallel to the layering/foliation, or shear zones (discussed in Section 6.1.3). Lineaments identified from aerial photography are shown and lineament trends indicated by a rose diagram are included on Figure 6-4. A total of 4 lineaments were identified, all in the form of linear stream courses. One of these was also identified as part of topographic -maps interpretation as noted in the preceding paragraph. Two of the lineaments trend northeast, and the remaining two trend north-northeast. 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. Due to the extensive land alterations results of aerial -photography interpretation were inconclusive. Five lineaments were identified as shown on Figure 6-4. 6.1.6 Effects of Geologic Structure on Groundwater Flow The most important effects of geologic structure on groundwater flow is likely along the contacts of metavolcanic units and the fractures and shears zones noted in the rock core that are parallel to the contacts. 6.1.7 Soil and Rock Mineralogy and Chemistry Soil mineralogy is complete and soil chemistry analyses are incomplete as of the date of this report. Soil and mineralogy and chemistry results through August 17, 2015 are shown in Table 6-1 (mineralogy), Table 6-2 (chemistry, % oxides), and Table 6-3 (chemistry, elemental composition). Completed laboratory analyses of the mineralogy and chemical composition of TZ materials are presented in Tables 6-4 (mineralogy), 6-5 (chemistry, % oxides), and 6-6 (chemistry, elemental). Rock chemistry results are complete and are presented in Table 6-7 32 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 6.0 SITE GEOLOGY AND HYDROGEOLOGY (chemistry, % oxides) and Table 6-8 (chemistry, elemental).The petrographic analysis of nine rock samples (thin -sections) and the remaining soil chemistry analyses will be included in a Buck CSA Supplement. The dominant minerals in the soils are quartz, feldspar (both alkali and plagioclase feldspars), kaolinite, biotite, and amphibole. Other minerals identified include mullite, vermiculite, illite, and illite/smectites. The major oxides in the soils are Si02 (46.25% - 70.47%), A1203 (14.93% - 28.07%), and Fe203 (2.70% - 14.95%). MnO ranges from 0.02% to 0.30%. The dominant minerals in the TZ are quartz, feldpar (both alkali and plagioclase feldspars), biotite, chlorite and amphibolite. The major oxides in the TZ are Si02 (58.27% - 65.72%), AI203 (14.36% - 14.85%), and Fe203 (5.87% - 9.63%). MnO ranges from 0.11 % to 0.16%. The major oxides in the rock samples are Si02 (46.50% - 64.69%), AI203 (11.86% - 19.21 %), and Fe203 (5.62% - 11.62 %). 6.2 Site Hydrogeology 6.2.1 Groundwater Flow Direction Based on the site investigation, the groundwater system in the natural materials (alluvium, soil, soil/saprolite, and bedrock) at the Buck site is consistent with the regolith-fractured rock system and is generally an unconfined, connected aquifer system without confining layers as discussed in Section 5.2. The groundwater system at the Buck site is divided into three layers referred to in this report as the shallow, deep (TZ), and bedrock flow layers, so as to distinguish flow layers within the connected aquifer system. Voluntary, compliance, and groundwater assessment monitoring wells were gauged for depth to water and total well depth during a comprehensive groundwater elevation measurement event on July 6 and 7, 2015. Depth to water measurements were subtracted from surveyed top of well casing elevations to produce groundwater elevations in shallow, deep, and bedrock monitoring wells. Groundwater flow direction was estimated by contouring these groundwater elevations. The location of each well relative to groundwater flow from the ash basin (i.e., whether upgradient or downgradient) is shown for the newly installed groundwater assessment wells in Table 6-9 and for the voluntary and compliance wells in Table 6-10 In general, groundwater within the shallow wells (S), wells in the TZ (D), and wells in fractured bedrock (BR) flow from the ash basins and toward the Yadkin River. Ground water flow for the shallow, TZ, and fractured bedrock flow zones are shown on Figures 6-5, 6-6, and 6-7, respectively. 6.2.2 Hydraulic Gradient Horizontal hydraulic gradients were derived for the shallow aquifer, 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., both wells having 15-foot screens within the same water —bearing unit). The following equation was used to calculate horizontal hydraulic gradient: 33 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 6.0 SITE GEOLOGY AND HYDROGEOLOGY 1= dh / dl where i is the hydraulic gradient; dh is the difference between two hydraulic heads (measured in feet); and dl is the flow path length between the two wells (measured in feet). Applying this equation to wells installed during the CSA activities yields the following average horizontal hydraulic gradients (measured in feet/foot): • S and SL wells: 0.037 ft/ft • D and BRU wells: 0.029 ft/ft • BR wells: 0.027 ft/ft A summary of hydraulic gradient calculations is presented in Table 6-11. 6.2.3 Effects of Geologic/Hydrogeologic Characteristics on Contaminants Migration, retardation, and attenuation of COls 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 13.0. As previously agreed upon with NCDENR, the results of the groundwater model will be presented in the CAP. 6.2.4 Site Hydrogeologic Conceptual Model The hydrogeologic site conceptual model (SCM) is a conceptual interpretation of the processes and characteristics of a site with respect to the groundwater flow and other hydrologic processes at the site. The NCDENR document, "Hydrogeologic Investigation and Reporting Policy Memorandum," dated May 31, 2007 was used as general guidance to developing the model. General components of the SCM consist of developing and describing the following aspects of the site: geologic/soil framework, hydrologic framework, and the hydraulic properties of site materials. More specifically, the SCM describes how these aspects of the site affect the groundwater flow at the site. In addition to these site aspects, the SCM: • Describes the regional and site geology and hydrogeology (Sections 5.0, 5.1, 6.1 and 6.2); • Presents longitudinal and transverse cross -sections showing the hydrostratigraphic layers, (Section 8.2); • Develops the hydrostratigraphic layer properties required for the groundwater model, (Section 11.2); • Presents a groundwater contour map showing the potentiometric surface of the shallow aquifer, (Section 6.2.1); and • Presents information on horizontal (Section 6.2.2) and vertical groundwater gradients (Section 11.3). 34 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 6.0 SITE GEOLOGY AND HYDROGEOLOGY The SCM serves as the basis for developing and understanding the hydrogeologic characteristics of the site and for developing a groundwater flow and transport model. Historic site groundwater elevations and ash basin water elevations were used to develop a historic estimated seasonal high groundwater contour map for the site. A fracture trace analysis was also performed for the site, as well as onsite/near-site geologic mapping, to better understand site geology and to confirm and support the SCM. An updated SCM, based on data obtained during the CSA activities and refined through completion of groundwater modeling, will be presented in the CAP after submittal of this CSA report. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION 7.0 Source Characterization For purposes of this assessment the source area is defined by the ash waste boundary as depicted on Figure 2-2. Buck sources include the ash basin system and ash storage area. Source characterization was performed to identify the physical and chemical properties of the ash in the source area. The source characterization involved developing selected physical properties of ash, identifying the constituents found in ash, measuring concentrations of constituents present in the ash porewater, and performing laboratory analyses to estimate constituent concentrations resulting from the leaching process. The physical and chemical properties developed as part of this characterization will be used to better understand impacts to soil and groundwater from the source area and will also be utilized as part of the groundwater modeling and other evaluations to be performed in the CAP. Buck source characterization was performed through the completion of soil borings, installation of monitoring wells, and associated solid matrix and aqueous sample collection and analysis. Ash samples were collected for analysis of physical characteristics (e.g., grain size, porosity, etc.) to provide data for evaluation of retention/transport properties within and beneath the ash basin and ash storage area. 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. Source characterization procedures and variances are documented in Appendix C. Field parameters are documented in Appendix H. For the purpose of this section of the report, COls are any constituents that exceeded their applicable regulatory standard in the ash, ash basin surface water, and ash porewater. Sample results were compared to the following regulatory standards or criteria for the purpose of identifying COIs: • Ash — NCDENR DWM IHSB Preliminary Industrial Health and/or Protection of Groundwater PSRGs' • Ash basin surface water — 2B Standards • Ash basin porewater — 2L Standard or IMAC These comparisons are useful in understanding potential impacts to soil, groundwater, and surface water. However, the exceedances of standards or criteria identified in this comparison do not necessarily indicate that exceedances of groundwater, surface water, or soil standards are present outside the ash basin. For example, comparison of analytical results for ash samples to cleanup standards for soil can provide insight to the types of constituents and the concentrations present in ash relative to those standards; however, an exceedance of a PSRG value in an ash sample does not necessarily indicate that exceedances are present in the underlying soil. North Carolina Department of Environment and Natural Resources Division of Waste Management Inactive Hazardous Sites Branch Preliminary Soil Remediation Goals March 2015. 36 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION Ash, ash basin surface water, ash porewater, and seep sample locations used for source characterization are shown on Figure 7-1. Ash porewater refers to water samples collected from wells installed within the ash basin and ash storage area and screened in the ash layer and although compared to 2L Standards, porewater is not considered to be groundwater. A summary of constituents and laboratory methods used for analysis of solid matrix samples (soil and ash) are presented in Table 7-1. Laboratory results of total inorganic and anion/cation analyses of ash samples collected from the ash basins and ash storage area are presented in Table 7-2. Laboratory parameters and analytical methods for aqueous matrix (i.e., ash basin surface water, porewater, and seeps) are presented in Table 7-3. Laboratory results of ash basin surface water samples are presented in Table 7-4. Ash basin porewater sample results are presented in Table 7-5. Synthetic Potential Leaching Procedure (SPLP) analyses of ash samples are presented in Table 7-6. As described in the approved Work Plan, both unfiltered and filtered (0.45 um filter) porewater, surface water, and seep samples were collected for analyses of constituents whose results may be biased by the presence of turbidity.2 Unless otherwise noted, concentration results discussed are for the unfiltered samples and represent total concentrations. 7.1 Ash Basin 7.1.1 Ash (Sampling and Chemical Characteristics) Twenty borings (AB-1 D, AB-2S/SL/D/BR, AB-3S/D, AB-4S/SL/BRU/BR, AB-5S/SL/BRU, AB- 6BRU, AB-7S/SL/BRU, and AB-8S/D) were advanced within the ash basin waste boundary to obtain ash samples for chemical analyses. Most of the ash samples were obtained from Deep (D) or Upper Bedrock (BRU) borings, although some samples were obtained from the other borings when there were recovery issues. Eight COls were reported above the North Carolina PSRGs for Industrial Health and/or Protection of Groundwater Standards within the ash basin waste boundary: arsenic, barium, boron, cobalt, iron, manganese, selenium, and vanadium (see Table 7-2). Arsenic exceeded its Industrial Health and Protection of Groundwater PSRGs in all but one of the ash basin ash samples, and the single non-exceedance was below a detection level greater than both PSRGs. Iron and vanadium exceeded their respective Protection of Groundwater PSRGs in all of the ash basin ash samples but did not exceed any of their Industrial Health PSRGs. With the exception of four samples that were below a detection level greater than the Protection of Groundwater PSRG, cobalt exceeded its Protection of Groundwater PSRG in all of the ash basin ash samples but did not exceed its Industrial Health PSRG in any of those samples. Manganese exceeded its Protection of Groundwater PSRG in roughly half of the ash samples collected but did not exceed its Industrial Health PSRG in any of the samples. 2 The USEPA (EPA 2002) recommends that when possible, especially when sampling for contaminants that may be biased by the presence of turbidity, the turbidity reading is desired to stabilize at a value below 10 Nephelometric Turbidity Units (NTUs) 37 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 7.0 SOURCE CHARACTERIZATION Selenium exceeded its Protection of Groundwater PSRG in roughly one quarter of ash basin ash samples but did not exceed its Industrial Health PSRG in any of the samples. Note that all of the selenium exceedances were estimated below laboratory reporting limits. Boron only slightly exceeded its Protection of Groundwater PSRG in one sample from AB-6BRU but did not exceed its Industrial Health PSRG in that sample. Barium only exceeded its Protection of Groundwater PSRG in two samples from AB-2D and AB-7BRU but did not exceed its Industrial Health PSRG in those samples. All other constituents were less their applicable PSRGs for all ash basin ash samples analyzed. 7.1.2 Ash Basin Surface Water (Sampling and Chemical Characteristics) Seven ash basin surface water samples (SW-AB1, SW-AB2, SW-AB3, SW-AB4, SW-AB5, SW- A136, and SW-AB7) were collected from the surface of ponded areas within the ash basin. Sample SW-AB1 was collected within Cell 1. Samples SW-AB2 and SW-AB3 were collected from Cell 2. Samples SW-AB4 through SW-AB7 were collected from Cell 3. Fourteen COIs: aluminum, antimony, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, thallium, vanadium, zinc, and TDS had results exceeding 2B Standards in ash basin surface water within the ash basin system. However, the only constituents that exceeded 2B Standards in dissolved phase samples were arsenic (at all locations except SW-AB1), antimony (SW-AB3), and copper (SW-AB3), indicating that turbidity/suspended solids may have influenced the totals results. All other constituents were below their respective 2B Standards in dissolved phase samples collected at all seven ash basin surface water locations. The ash basin water is compared to the 2B and 2L Standards or IMACs for comparative purposes and is not considered surface water or groundwater. 7.1.3 Ash Porewater (Sampling and Chemical Characteristics) Ash porewater refers to water samples collected from wells installed within the ash basin area that are screened within the ash layer. HDR does not consider porewater results to be representative of groundwater. Ten porewater monitoring wells (AB-2S/SL, AB-3S, AB-4S/SL, AB-5S/SL, AB-7S/SL, and AB-8S) were installed within the ash basin waste boundary and screened within the ash layer. These wells are not considered to be representative of groundwater. Ten COls were reported above 2L Standards or IMACs in ash porewater samples collected from wells within the ash basin waste boundary: antimony, arsenic, barium, boron, cobalt, iron, manganese, thallium, TDS, and vanadium. Ash porewater sample locations are shown on Figure 7-1 and 2L Standard or IMAC exceedances are listed in Table 7-5. Exceedances of the 2L Standard or IMAC for arsenic, manganese and vanadium were observed in nearly all ash porewater samples. Exceedances of the 2L Standard for boron were observed in roughly half of the ash porewater samples in both totals and dissolved analyses. Exceedances of the 2L Standard or IMAC for antimony, cobalt, and iron were observed in the majority of ash porewater samples in totals analyses but in roughly half of ash porewater samples in the dissolved phase (i.e., turbidity/suspended solids appear to have had an effect on certain ash porewater samples). Exceedances of the IMAC for thallium were observed in three ash porewater samples Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION (AB-2S, AB-3S, and A13-8S). An exceedance of the 2L Standard for barium was observed in a single ash porewater sample (AB-2SL), but the dissolved phase result was less than the 2L Standard. A single exceedance of the 2L Standard for TDS was observed in a single ash porewater sample (AB-2S). 7.1.4 Ash Porewater Speciation Speciation is the analysis of the composition of a particular analyte in a system. Speciation is important for understanding the fate and transport of COIs. Ten locations, AB-2S/SL, AB-3S, AB-4S/SL, AB-5S/SL, AB-7S/SL, and AB-8S, were sampled for chemical speciation analyses of arsenic (III), arsenic (V), chromium (III), chromium (VI), iron (II), iron (III), manganese (ll), manganese (IV), selenium (II), selenium (IV), and selenium (VI). Results for chemical speciation of porewater samples are presented in Table 7-7. Further evaluation of chemical speciation results will be included in the CAP. 7.1.5 Radiological Laboratory Testing Dissolved radionuclides from naturally occurring sources (e.g. soil or rock) may exist in water. The USEPA regulates various radionuclides in drinking water. For purposes of this assessment, radium-226, radium-228, uranium-233, uranium-234, uranium-236, and uranium-238 were analyzed. Three locations, BG-1 D, BG-1 S, and MW-3D were sampled for the analytes listed above. Results for radiological laboratory testing of porewater samples are presented in Table 7-8. Further evaluation of radiological laboratory testing results will be included in the CAP. 7.2 Ash Storage Area 7.2.1 Ash (Sampling and Chemical Characteristics) Five borings (AS-1 S/D, AS-2D, and AS-3S/D) were advanced within the ash storage area waste boundary to obtain ash samples for chemical analyses. Six COls were reported above the North Carolina PSRGs for Industrial Health and/or Protection of Groundwater Standards within the ash storage area waste boundary: arsenic, cobalt, iron, manganese, selenium, and vanadium (see Table 7-2). Arsenic exceeded its Industrial Health and Protection of Groundwater PSRGs in all of the ash basin ash samples collected. Cobalt, iron and vanadium exceeded their respective Protection of Groundwater PSRGs in all of the ash basin ash samples but did not exceed any of their Industrial Health PSRGs. Manganese exceeded its Protection of Groundwater PSRG in the majority of the ash samples collected but did not exceed its Industrial Health PSRG in any of the samples. Selenium exceeded its Protection of Groundwater PSRG in only one of the six ash samples analyzed from the ash storage area but did not exceed its Industrial Health PSRG in that sample. All other constituents were less than their applicable PSRGs for all ash storage area samples analyzed. 0 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 7.0 SOURCE CHARACTERIZATION 7.2.2 Ash Porewater (Sampling and Chemical Characteristics) Monitoring wells installed within the ash storage area were constructed with screened intervals set below ash since the water tables encountered at the time of drilling were below the ash/soil interface. Thus, ash porewater within the ash storage area was not evaluated. 7.3 Seeps 7.3.1 Review of NCDENR March 2014 Sampling Results NCDENR performed a water sampling event at Buck in March 2014. This sampling event included only seeps. The locations and analytical results of this sampling event were provided by NCDENR to Duke Energy and are assumed to be accurate. The location of these samples is presented on Figure 7-1. Seep water sample identifiers and their location relative to site features are: • BS SWO01AA S001 (seep near Cell 3 discharge to Yadkin River) • BS SWO03AA S001 (toe of Cell 1 dam) • BS WWO02 S001 (Cell 3 discharge to Yadkin River) • BSSW001 S001 (west of BCCS) • BSSW074SO01 (east of the BSS powerhouse on bank of Yadkin River) • BSSW076SO01(east of the BSS powerhouse on bank of Yadkin River) Four COls exceeded their respective 2B Standards: aluminum, arsenic, selenium, and sulfate. However, it appears that all results were for total inorganic metals and that dissolved analyses were not performed. March 2014 sampling results and measured field parameters were also compared to 2L Standards and IMACs (see Table 7-9). Six COls exceeded their respective 2L standards: arsenic, boron, iron, manganese, sulfate, and TDS. The NCDENR seep water sample results were reviewed prior to site assessment activities and select seep samples with exceedances of the 2B Standards and/or 2L Standards or IMAC were identified to be re -sampled as part of the CSA assessment activities. A discussion of the seep re -sampling results is provided below. 7.3.1.1 Resampling of NCDENR Seeps One of the seeps was resampled in June 2015 as part of this CSA (BS WWO02 S001). The other five seeps were dry during this sampling event and no samples were collected. Samples collected from BS WWO02 S001 exceeded the 2L Standards or IMACs for the following COls: antimony, arsenic, iron, manganese and vanadium (see Table 7-10). Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION 7.3.2 CSA Seep Sampling Results 7.3.2.1 Seeps There are fourteen seeps (S-1 through S-10, Culvert Discharge, Wet Area Near Pump House, Terracota Pipe #1, and Terracota Pipe #2) located within the Duke Energy property boundary and three planned seep and surface water sampling locations (S-1A, S-1 B, and S-1 C) located outside of the Duke Energy property boundary at Buck, excluding the previously described NCDENR seeps. Seeps S-1 through S-4 are associated with an unnamed tributary to the Yadkin River along the eastern property boundary and downgradient of ash basin Cell 3. Seep S-5, Culvert Discharge, and Wet Area Near Pump House are located near the toe of Cell 2 and Cell 3 main dam. Seep S-6 is located between ash basin Cell 2 and the Yadkin River. Seeps Terracota Pipe #1 and Terracota Pipe #2 are located at the base of the main dam northwest of ash basin Cell 1. Seeps S-7 through S-10 are associated with an unnamed tributary to the Yadkin River near the western property boundary and downgradient of ash basin Cell 1. Seep locations are shown on Figure 7-1. Duke Energy was not able to obtain permission from the property owner to obtain off -site seep samples S-1 A, S-1 B, and S-1 C; therefore these samples were not sampled. Seep locations Wet Area Near Pump House and Terracota Pipe #2 were dry during the sampling event. Of the seep locations sampled, ten COls were reported exceeding the 2L Standards or IMACs: antimony, arsenic, boron, chromium, cobalt, iron, lead, manganese, thallium, and vanadium (see Table 7-10). However, it is important to note that the dissolved concentrations of chromium and iron were below their 2L Standards for all of the seep samples. Therefore, the exceedances of these constituents in the totals phase may be due to turbidity/suspended solids. Results for many of the seep samples indicated these same significant differences between the totals and dissolved analyses for many constituents expected to be found above PSRGs in native soils. The USEPA (EPA 2002) recommends that when possible, especially when sampling for contaminants that may be biased by the presence of turbidity, the turbidity reading is desired to stabilize at a value below 10 Nephelometric Turbidity Units (NTUs) 7.3.3 Comparison of Exceedances to 2B Standards Samples of seep surface water obtained from around the perimeter of the ash basin exceeded the 2B Standard for aluminum at each location with the exception of S-10. Aluminum exceedances in the totals phase may be related to turbidity/suspended solids, as the concentration at each location, except S-1, was below the aluminum 2B Standard in the dissolved phase. Arsenic exceeded the 2B Standard at seep location BSWWO02 S001 only. Cadmium exceeded the 2B Standard at seep locations S-2 and S-3. Chromium exceeded the 2B Standard at seep location S-2. Chromium exceedances in the totals phase may be related to turbidity/suspended solids, as the concentration at each location was below the chromium 2B Standard in the dissolved phase. Cobalt exceeded the 2B Standard at seep locations S-1, S-2, S-3, S-5, and S-8 although the 2B Standard was only exceeded in the dissolved phase at S-1, S-5 and S-8. Copper exceeded the 2B Standard at seep locations S-1, S-2, S-3, S-5, S-7, and S-9. Copper exceedances in the totals phase may be related to turbidity/suspended solids, as 41 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 7.0 SOURCE CHARACTERIZATION the concentration at each location was below the copper 213 Standard in the dissolved phase. Lead exceeded the 213 Standard at seep locations BSWWO02 S001, S-1, S-2, S-3, S-5, and S- 9. Lead exceedances in the totals phase may be related to turbidity/suspended solids, as the concentration at each location was below the lead 213 Standard in the dissolved phase. Nickel exceeded the 213 Standard at seep location S-2. Nickel exceedance in the totals phase may be related to turbidity/suspended solids, as the concentration at this location was below the nickel 213 Standard in the dissolved phase. Zinc exceeded the 213 Standard at seep locations S-2, S-3, and S-7. Zinc exceedances in the totals phase may be related to turbidity/suspended solids, as the concentration at each location, except S-7, was below the zinc 213 Standard in the dissolved phase. Constituents which exceeded the 213 Standards in the seep water samples have been identified as seep water COIs. Sulfide was not detected in any of the seep water samples. 7.3.4 Observed Ranges of 2B Standard COI Concentrations 7.3.4.1 Background Surface Water The background surface water location is identified as SW-2. This location was dry during the sampling event, therefore, no observed ranges for background analytical results are available for comparison to surface water samples from other sampling locations. 7.3.4.2 Seeps Seep locations are identified as S-1 and S-10, Culvert Discharge, and Terracotta Pipe #1. Ranges of totals phase concentrations for COls exceeding 213 standards are presented below. • Aluminum 14.8 pg/L to 18,700 pg/L • Arsenic 0.23J pg/L to 50 pg/L • Cadmium <0.08U pg/L to 0.21 pg/L • Chromium 0.3J fag/L to 34.7 pg/L • Cobalt 0.18J pg/L to 1,050 pg/L • Copper 0.27J pg/L to 85 pg/L • Lead <0.1 U pg/L to 21.9 pg/L • Nickel 0.47J pg/L to 21.8 pg/L • Thallium 0.019J pg/L to 1.1 pg/L (single occurrence) • Zinc 5.2J fag/L to 260 pg/L 7.3.5 Discussion of Results for Constituents without 2B Standards Surface water samples were also analyzed for the following constituents that do not have 2B Standards: boron, calcium, iron, manganese, mercury, selenium, and vanadium. Each of these constituents was detected in at least one surface water sample. 7.3.5.1 Background Surface Water The background surface water location is identified as SW-2. This location was dry during the sampling event, therefore, no observed ranges for background analytical results for constituents Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION without 2B Standards are available for comparison to surface water samples from other sampling locations. 7.3.5.2 Seeps Seep locations are identified as S-1 and S-10. Ranges of totals phase concentrations for Cols without 2B Standards are presented below. • Boron 36J fag/L and 820 fag/L • Calcium 6,990 pg/L and 62,800 pg/L • Iron 19.3J pg/L and 34,900 pg/L • Manganese 3J fag/L and 6,300 pg/L • Mercury 0.00174 pg/L and 0.87 pg/L • Selenium 0.21 J pg/L and 10.9 pg/L • Vanadium 1.6 pg/L and 132 pg/L 7.4 Surface Water Speciation Speciation is the analysis of the composition of a particular analyte in a system. Speciation is important for understanding the fate and transport of COls. Ten locations, S-1 A, S-1 B, S-1 C, BS SW001 AA S001, BS SWO03AA S001, BS WWO02 S001, BSSW001 S001, BSSW0745001, BSSW076S001, and BS Outfall 002 were designated to be sampled for chemical speciation analyses of arsenic (III), arsenic (V), chromium (III), chromium (VI), iron (II), iron (III), manganese (II), manganese (IV), selenium (II), selenium (IV), and selenium (VI). Locations S- 1 A, S-1 B, and S-1 C are associated with an off site small pond located southeast of Cell 3. These samples could not be collected since an access agreement could not be negotiated with the property owner. Of the remaining surface water speciation sample locations, only BS WWO02 S001 and BS Outfall 002 could be sampled since the other locations were dry at the time of sampling. Results for surface water speciation are presented in Table 7-11. 7.5 Leaching Potential of Ash In addition to total inorganic testing of ash samples, 8 ash samples collected from borings completed within the ash basin and ash storage area were analyzed for leachable inorganics using SPLP (see Table 7-6). The purpose of the SPLP testing is to evaluate the leaching potential, of COls that may result in impacts to groundwater above the 2L Standards or IMACs. Although SPLP analytical results are being compared to the 2L Standards, these samples do not represent groundwater samples. The results of the SPLP analyses indicated that the following COI exceeded their 2L Standards or IMAC at locations shown in Figure 7-1: antimony, arsenic, chromium, cobalt, iron, manganese, selenium, thallium, and vanadium. Leaching of constituents from ash stored in the ash storage area will likely be different from the leaching that occurs when ash is stored in a saturated condition, as found in the ash basins. The ash in these two different storage environments would experience differences in the time of exposure to the leaching solution, the liquid to solid ratio, and the chemical properties of leaching liquid. This 43 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION would likely lead to differences in the constituents leached in the two differing environments and in the concentrations of the leached constituents. In general the infiltration for the ash storage area will be variable and intermittent, as infiltration is precipitation induced. The infiltration rate is dependent on a number of factors with the primary factors being climate, vegetation, and soil properties. The precipitation and air temperature are the two aspects of climate that most directly affect groundwater infiltration. Vegetation affects the infiltration rate through interception and by means of transpiration. The primary soil properties that affect infiltration are represented by the hydraulic conductivity of the material. For areas where saturated conditions exist, the infiltration and subsequent groundwater recharge would be represented by Darcy's law. However, in the case of an ash basin the recharge flow rate calculation is complicated by the flow through the earthen dike, and through the material underlying the ash basin (saprolite, transition zone, and bedrock). An area where the surface is saturated or where water is present in the ash basin will receive constant infiltration with the rate being controlled by the factors described above. The potential migration of contaminants from the ash basin and ash storage area will occur by the movement of ash leachate into the underlying soil layers and groundwater through infiltration. The infiltration of precipitation for the ash storage area and the infiltration of the ash basin water into the underlying soil material will be modeled in the groundwater model being prepared for the CAP. 7.6 Constituents of Interest Based on evaluation of the ash, ash basin surface water, and ash porewater sampling data, the following COls were identified: 7.6.1 COls in Ash (based on total inorganics analysis, as shown in Table 7-2) • Arsenic • Barium • Boron • Cobalt • Iron • Manganese • Selenium • Vanadium 7.6.2 COls in Ash Basin Surface Water (based on water quality analysis (totals), as shown in Table 7-4) • Aluminum* • Antimony • Arsenic 44 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION • Cadmium* • Chromium* • Cobalt* • Copper • Iron* • Lead* • Manganese* • Thallium* • Vanadium* • Zinc* • TDS Ash basin surface water COls listed with an asterisk (*) above exhibited a significant difference between the totals and dissolved analyses which led to the dissolved concentrations all measured below applicable standards. 7.6.3 COls in Ash Porewater (based on water quality analysis (totals), as shown in Table 7-5) • Antimony • Arsenic • Barium* • Boron • Cobalt • Iron • Manganese • Thallium • TDS • Vanadium Ash porewater COls listed with an asterisk (*) above exhibited a significant difference between the totals and dissolved analyses which led to the dissolved concentrations all measured below applicable standards. 7.6.4 COls in Seeps (based on water quality analysis (totals), as shown in Table 7-10) • Antimony • Arsenic • Boron • Chromium* • Cobalt • Iron • Lead* • Manganese Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 7.0 SOURCE CHARACTERIZATION • Thallium* • Vanadium Ash porewater COls listed with an asterisk (*) above exhibited a significant difference between the totals and dissolved analyses which led to the dissolved concentrations all measured below applicable standards. 7.6.5 Summary of COIs from Source Characterization • Antimony — exceeded relative standards in ash basin surface water, ash porewater, and seeps. • Aluminum — exceeded 2B Standard in apparently turbid ash basin surface water only (i.e., no exceedances in dissolved phase) • Antimony — exceeded relative standards in ash basin surface water, ash porewater, and seeps • Arsenic — exceeded relative standards in ash samples, ash basin surface water, ash porewater, and seeps • Barium — exceeded relative standards in ash samples and ash porewater • Boron — exceeded relative standards in ash samples, ash porewater, and seeps • Cadmium - exceeded 2B Standard in a single, apparently turbid ash basin surface water only (i.e., did not exceed in dissolved phase) • Chromium — exceeded 2B Standard in two apparently turbid seep samples (i.e., no exceedances in dissolved phase) • Cobalt — exceeded relative standards in ash samples, ash basin surface water, ash porewater, and seeps • Copper — exceeded 2B Standard in apparently turbid ash basin surface water only (i.e., no exceedances in dissolved phase) • Iron — exceeded relative standards in ash samples, ash porewater, ash porewater, and seeps • Lead — exceeded 2B Standard in apparently turbid ash basin surface water and one seep sample only (i.e., no exceedances in dissolved phase) • Manganese — exceeded relative standards in ash samples, ash basin surface water, ash porewater, and seeps. • Selenium — exceeded relative standards in ash samples. • TDS — exceeded relative standards in ash basin surface water and ash porewater. • Vanadium — exceeded relative standards in ash samples, ash basin surface water, ash porewater, and seeps. • Zinc — exceeded 2B Standard in apparently turbid ash basin surface (i.e., no exceedances in dissolved phase) 46 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 8.0 SOIL AND ROCK CHARACTERIZATION 8.0 Soil and Rock Characterization The purpose of soil and rock characterization is to characterize the soil and rock on the site for corrective action and compare to applicable cleanup levels. Soil and rock samples were collected and analyzed in general accordance with the procedures and methods described in the Work Plan. Refer to Appendix D for a detailed description of these methods and variances from the sampling plan outlined in the Work Plan, and Appendix E for field and sampling quality control / quality assurance protocol. Soil, PWR, and bedrock samples were collected from background locations, beneath the ash basin ash storage area, and from locations beyond the waste boundary. Table 8-1 summarizes the soil and rock sampling plan utilized for groundwater assessment activities. Variances from the proposed sampling plans are presented in Appendix D. The boring locations are shown on Figure 8-1. 8.1 Background Sample Locations Background (BG) boring locations were identified based on the CSM at the time the Work Plan was submitted. The BG locations (BG-1, BG-2 and BG-3) were chosen in areas assumed not to be impacted by and topographically upgradient of the ash basin and ash storage area. Based on the groundwater contours shown in Figures 6-5 through 6-7, and the CSM, the background locations are considered to be hydrologically upgradient of the ash basin and ash storage area. As a result, the BG boring locations are considered to be representative of background soil conditions at the site. 8.2 Analytical Methods and Results Parameters and laboratory methods used for analysis of solid matrix samples are presented in Table 8-2. Total inorganic results for background soil samples are presented in Table 8-3. Total inorganic results for background PWR and bedrock samples are presented in Table 8-4. Total inorganic results for soil samples are presented in Table 8-5. Total inorganic results for PWR and bedrock samples are presented in Table 8-6. Figure 8-1 depicts the total inorganic results for soil, PWR, and bedrock analysis. Cross - sections presenting the vertical distribution of COls along the transects are depicted on Figures 8-2 through 8-4. 8.3 Comparison of Soil Results to Applicable Levels The soil analytical results are compared to the North Carolina Preliminary Soil Remediation Goals (PSRGs) for Industrial Health and Protection of Groundwater Standards presented in Tables 8-3 through 8-6. Frequency and concentration ranges in soil for COI exceedances of North Carolina PSRGs are presented in Table 8-7. Frequency and concentration ranges in PWR and bedrock for COI exceedances of North Carolina PSRGs are presented in Table 8-8. 47 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 8.0 SOIL AND ROCK CHARACTERIZATION The subsections below provide a summary of COls that exceeded the North Carolina PSRGs in at least one of the samples analyzed. Parameters not listed below were not reported at concentrations exceeding the North Carolina PSRGs in the collected soil samples. Comparison of Soil Results to Background In addition to comparison of results to regulatory criteria, soil sample results have also been compared to background concentrations observed in samples collected from the BG sample locations. Boring locations are shown on Figure 8-1. 8.4.1 Background Soil Background soil locations are identified as BG-1 D, BG-21D, and BG-3BRU. Background soil concentration ranges are listed below for constituents that exceeded the North Carolina PSRGs in at least one soil sampling location at the Buck site. Results with a J qualifier indicate an estimated concentration reported between the laboratory method detection limit and the method reporting limit. Total inorganic results for background soil samples are presented in Table 8-3. • Arsenic <1.7J mg/kg to <8.8U mg/kg • Boron 46.3 mg/kg to 56.3 mg/kg • Cobalt 7.3J mg/kg to 257 mg/kg • Iron 18,400 mg/kg to 68,800 mg/kg • Manganese 238 mg/kg to 3,620 mg/kg • Selenium 4.8J mg/kg to 7.2J mg/kg • Vanadium 70.1 mg/kg to 197 mg/kg 8.4.2 Soil Beneath Ash Basin Soil samples within the ash basin boundary were obtained from AB-1 D, AB-21D, AB-31D, AB- 4BRU, AB-5BRU, AB-6BRU, AB-7BRU, AB-81D, AB-91D, and AB-10D/GTB. The range of constituent concentrations in soils beneath the ash basin, along with a comparison to the range of reported background soil concentrations, is provided in Table 8-9. Constituent concentrations of soils beneath the ash basin tend to be generally similar to background concentrations for all constituents. With the exception of two samples taken beneath ash at AB-81D, barium concentrations beneath the ash basin are similar to background concentrations. 8.4.3 Soil Beneath Ash Storage Area Soil samples beneath the ash storage area were obtained from AS-1 D, AS-21D, and AS-3S. The range of constituent concentrations in soil samples beneath the ash storage area, along with a comparison to the range of reported background soil concentrations, is provided in Table 8-10. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 8.0 SOIL AND ROCK CHARACTERIZATION Constituent concentrations of soils beneath the ash storage area generally tend to be slightly higher than background concentrations for boron and iron. Concentrations for other constituents generally tend to be similar to background soil concentrations. 8.4.4 Soil Outside the Waste Boundary Soil samples outside the waste boundary were obtained from GWA-1 S/D, GWA-2BRU, GWA- 3D, GWA-4D, GWA-5S/BRU, GWA-6BRU, GWA-7D, GWA-8D, GWA-9D, GWA-10D, GWA- 11 D, GWA-12S/BRU, and GWA-22D. The range of constituent concentrations in soils outside the waste boundary, along with a comparison to the range of reported background soil concentrations is provided in Table 8-11. Constituent concentrations for soils outside the waste boundary tend to be similar to background soil concentrations for all constituents. Comparison of PWR and Bedrock Results to Background In addition to comparison of results to regulatory criteria, PWR, and bedrock sample results have also been compared to background concentrations as discussed below. 8.5.1 Background PWR and Bedrock Background PWR and bedrock samples were obtained from BG-1 BR and BG-2D. Background PWR and bedrock sample concentration ranges are listed below for constituents that exceeded the North Carolina PSRGs in at least one PWR or bedrock sampling location at Buck. Results with a J qualifier are estimated concentrations. • Cobalt 6.3J mg/kg to 8.1 mg/kg • Iron 1,170 mg/kg to 12,400 mg/kg • Manganese 178 mg/kg to 235 mg/kg • Vanadium 20.5 mg/kg to 43.2 mg/kg Note that these background PWR and bedrock concentrations are based on three samples obtained from two boring locations. It is therefore difficult to draw conclusions regarding background conditions based on this limited data. 8.5.2 PWR and Bedrock Beneath Ash Basin PWR and bedrock samples beneath the ash basin were obtained from AB-1 D, AB-2D/BR, AB- 3D, AB-413R. AB-5BRU, AB-6BRU, AB-7BRU, AB-8D, and AB-913R. The range of constituent concentrations in PWR and bedrock samples beneath the ash basin, along with a comparison to the range of reported background PWR and bedrock concentrations, are provided in Table 8-12. Constituent concentrations for PWR and bedrock beneath the ash basin tend to be generally similar to background soil concentrations for cobalt, iron, manganese, and vanadium. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 8.0 SOIL AND ROCK CHARACTERIZATION 8.5.3 PWR and Bedrock Beneath Ash Storage Area PWR and bedrock samples beneath the ash storage area were obtained from AS-1 D and AS- 2D. The range of constituent concentrations in PWR and bedrock samples beneath the ash storage area, along with a comparison to the range of reported background PWR and bedrock concentrations, is provided in Table 8-13 Constituent concentrations for PWR and bedrock beneath the ash storage area tend to be higher than background soil concentrations for cobalt, iron, manganese, and vanadium. Note that the maximum concentrations of arsenic, iron and manganese in PWR and bedrock beneath the ash basin were observed in a sample obtained from 83.5 to 84.0 feet below ground surface at AS-21D, which is well below the bottom of ash. Otherwise, arsenic, iron and manganese concentrations were similar to background. 8.5.4 PWR and Bedrock Outside Waste Boundary PWR and bedrock samples outside the waste boundary were obtained from GWA-31D, GWA- 5D, GWA-6D, GWA-91D, and GWA-11 D. The range of constituent concentrations in PWR and bedrock samples outside the waste boundary, along with a comparison to the range of reported background PWR and bedrock concentrations is provided in Table 8-14. Constituent concentrations for PWR and bedrock outside the waste boundary tend to be higher than background PWR and bedrock concentrations for iron, manganese, and vanadium. Concentrations for cobalt tend to be similar to background soil concentrations. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 9.0 SEDIMENT CHARACTERIZATION 9.0 Sediment Characterization The purpose of sediment characterization is to evaluate whether storage of ash has resulted in impacts to surface waters in the vicinity of the ash basin and ash storage area at Buck. The sediment characterization was performed in general accordance with the procedures described in the Work Plan. Sampling methodology and variances from the procedures are summarized in Appendix F. Sediment sample locations are shown on Figure 7-1. 9.1 Sediments Sediment samples were collected coincidentally with each of the seep samples at seep locations S-1 through S-10, BSWW002, Culvert Discharge, Terracotta Pipe #1, and Wet Area Near Pump House. Sediment samples were analyzed for the constituent and parameter list used for soil and rock characterization (see Table 8-2). In the absence of NCDENR sediment criteria, the sediment sample results were compared to North Carolina PSRGs for Protection of Groundwater and Industrial Soil. Exceedances of North Carolina PSRGs are summarized in Table 9-1. Sediment sample locations are shown on Figure 7-1. Seep sediment sample constituents cobalt, iron, and vanadium exceeded the North Carolina PSRGs for Protection of Groundwater in all sediment samples but did not exceed the PSRGs for Industrial Soil for any sample. Arsenic exceeded the PSRG for Protection of Groundwater at sediment sample S-6 and exceeded the PSRG for Industrial Soil at sediment samples BSWWO02 S001, S-6, Culvert Discharge, and Wet Area Near Pump House. Boron exceeded the PSRG for Groundwater Protection at only Terracotta Pipe #1. Manganese exceeded the PSRGs for Protection of Groundwater at each location with the exception of S-10 but did not exceed the PSRGs for Industrial Soil at any location. Selenium exceeded the PSRG for Groundwater Protection at only the Wet Area Near Pump House location. Antimony, cadmium, and thallium were not detected in sediment samples collected at Buck. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION 10.0 Groundwater Characterization The purpose of groundwater characterization is to compare groundwater at the site to 2L Standards or IMACs, and to inform the corrective actions identified in the CAP. Groundwater sampling methods and the rationale for sampling locations were in general accordance with the procedures described in the Work Plan. Refer to Appendix G for a detailed description of these methods. Variances from the proposed well installation locations, methods, quantities, and well designations are presented in Appendix G. 10.1 Regional Groundwater Data for Constituents of Interest Individual sampling events serve to characterize the hydrogeologic and chemical conditions at a particular monitoring location at a particular time. When interpreting the results from a sampling event, a number of factors that affect the sample results should be taken into consideration. Among these are the geologic and hydrogeologic setting, the location of the sample points in the regional groundwater flow system, potential interactions between suspected contaminants and the geological and biological constituents present in the formation (Barcelona 1985). As a result of these factors it may be possible that the analytical results for a given constituent are influenced by naturally occurring conditions as opposed to conditions caused by releases from the ash basin. This section presents an overview of the regional and statewide groundwater conditions for COls found at Buck that have promulgated state or federal standards. The 2L Standards recognize that the concentrations of naturally occurring substances in groundwater may exceed the standard established in .0202(g). Rule .0202(b)(3) states that when this occurs, the Director of the DWR will determine the standard. North Carolina 2L Standards and IMACs are established by NCDENR, whereas primary and secondary Maximum Contaminant Levels (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). Table 10-1 lists COls at the Buck site, along with their associated 2L Standards, IMACs, and federal drinking water standards (MCLs and SMCLs). Regional background information on COls at the Buck site are provided (in alphabetical order) below in Section 10.11 through 10.1.13. In additional, regional background information on pH is also provided in Section 10.1.14 as pH levels can affect the leachability of metal ions in groundwater. 10.1.1 Antimony Antimony is a silvery -white, brittle metal. In nature, antimony combines with other elements to form antimony compounds. Small amounts of antimony are naturally present in rocks, soils, water, and underwater sediments. 52 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION Only a few ores of antimony have been encountered in North Carolina. Antimony has been found in combination with other metals, and is found most commonly in Cabarrus County and other areas of the Carolina Slate Belt (Chapman 2013). In a USGS study of naturally occurring trace minerals in North Carolina, 57 private water supply wells were sampled to obtain trace mineral data. Of the wells sampled, no wells contained antimony above the USEPA primary MCL (Chapman 2013). Antimony is compared to IMAC since no 2L Standard has been established for this constituent by NCDENR. 10.1.2 Arsenic Natural arsenic occurs commonly and comes mainly from the soil. The USEPA estimates that the amount of natural arsenic released into the air as dust from the soil is about equal to the amount of arsenic released by all human activities (EPRI 2008). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at the University of North Carolina (UNC) analyzed private well water samples in North Carolina. These samples were tested by the North Carolina State Laboratory of Public Health from 1998-2010. The Buck site is located in Rowan County, North Carolina near the border of Davidson County. Data collected from 2,341 private wells across Rowan and Davidson counties indicated that 43 samples had arsenic concentrations exceeding the federal drinking water primary MCL, which is the same as the 2L Standard for arsenic (NC DHHS 2010). The summary statistics for both counties are provided in Table 10-2. In a state-wide investigation into arsenic concentrations in private wells, Sanders et al. (2011) found strong geological patterns in arsenic concentrations in groundwater across the state of North Carolina (Figure 10-1). The Buck site is located in an area where concentrations of naturally occurring arsenic in groundwater range from 1.1 - 5.0 pg/L. 10.1.3 Barium Two forms of barium, barium sulfate and barium carbonate, are often found in nature as underground ore deposits. Barium is sometimes found naturally in drinking water and food. However, since certain barium compounds (barium sulfate and barium carbonate) do not mix well with water, the amount of barium found in drinking water is typically small. Barium compounds such as barium acetate, barium chloride, barium hydroxide, barium nitrate, and barium sulfide dissolve more easily in water than barium sulfate and barium carbonate, but because they are not commonly found in nature, they do not usually occur in drinking water unless the water is contaminated by barium compounds that are released from waste sites (EPRI 2008). Barium is naturally released into the air by soils as they erode in wind and rain, and is released into the soil and water by eroding rocks. Barium released into the air by human activities comes mainly from barium mines, metal production facilities, and industrial boilers that burn coal and oil. Anthropogenic sources of barium in soil and water include copper smelters and oil drilling 53 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION waste disposal sites. Industries reporting to the USEPA released 119,646 tons of barium and barium compounds into the environment in 2005 (EPRI 2008). Regional metamorphic greenschist to upper amphibolite facies rocks in the Piedmont's King's Mountain Belt contains deposits of barium sulfate (barite). Barium is especially common as concretions and vein fillings in limestone and dolostone, which are not common geologic rocks in the North Carolina Piedmont; however, at various times in the past century and a half, the Carolinas have been major producers of barite (USEPA 2014). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at UNC analyzed private well water samples in North Carolina. These samples were tested by the North Carolina State Laboratory of Public Health from 1998-2010. Since the Buck site is located near the border of Rowan and Davidson counties, statistics for both are included here. Data collected from 1,042 private wells across Rowan and Davidson counties from 1998- 2010 indicated that no samples had barium concentrations exceeding the primary MCL of 2,000 pg/L (NC DHHS 2010). The summary statistics for both counties are provided in Table 10-2. 10.1.4 Boron 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). Boron is usually present in water at low concentrations. Surface waters typically have concentrations of 0.001 to 5 mg/L, with an average concentration of about 0.1 mg/L. Background boron concentrations in groundwater near power plants were compiled from data presented in EPRI technical reports, and ranged from <0.01 to 0.59 mg/L with a median concentration of 0.07 mg/L (EPRI 2005). 10.1.5 Chromium Chromium is a blue -white metal found naturally only in combination with other substances. It occurs in rocks, soil, plants, and volcanic dust and gases (EPRI 2008) 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 pg/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 2013). In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at UNC analyzed private well water samples in Rowan and Davidson counties. The samples were tested by the North Carolina State Laboratory of Public Health from 1998-2010. 54 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION This study found average chromium concentrations were 5.6 pg/L and 5.3 pg/L in Rowan and Davidson counties, respectively (NC DHHS 2010). Statistics for both counties are included in Table 10-2. 10.1.6 Cobalt The concentration of cobalt in surface and groundwater in the United States is generally low — between 1 and 10 parts of cobalt in 1 billion parts of water (ppb) in populated areas. The concentration may be hundreds or thousands of times higher in areas that are rich in cobalt - containing minerals or in areas near mining or smelting operations. In most drinking water, cobalt levels are less than 1 to 2 ppb (USGS 1973). Cobalt is compared to IMAC since no 2L Standard has been established for this constituent by NCDENR. 10.1.7 Iron Iron is a naturally occurring element that may be present in groundwater from the erosion of natural deposits (NC DHHS 2010). According to Harden (2009), iron commonly exceeds state and federal regulatory standards in North Carolina groundwater. Iron exceedances occurred in over half of the state's 10 geozones. The average concentration of iron detected in North Carolina private well water from sampling conducted in 2010 (NC DHHS 2010) is shown in Figure 10-2. A study by the Superfund Research program at UNC found that only 15 of the 100 counties in North Carolina had average concentrations below the SMCL of 300 pg/L. The average iron concentrations in Rowan and Davidson counties were 125,698 pg/L and 531 pg/L, respectively (Table 10-2). 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 pg/L. The study found the regional variations summarized in Table 10-3. 10.1.8 Manganese 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. Manganese occurs naturally in soils, saprolite, and bedrock and is thus a natural component of groundwater (EPRI 2008). Manganese concentrations tend to cluster by soil system and geozone throughout North Carolina, as shown in Figure 10-3. The Carolina Slate and Milton geozones have the highest proportions of manganese-exceedances, although six other geozones exceeded the state standard as well (Gillespie 2013). Geozones with magmatic -arc rocks and low-grade metamorphic rocks, seen in Figure 10-3, tend to include abundant manganese -bearing mafic minerals likely to contribute manganese for subsurface water cycling (Gillespie 2013). These rock types are distributed throughout North Carolina and contribute to spatial variations of manganese concentrations throughout the state. High manganese concentrations are associated with silty soils, and sedimentary, unconsolidated, or weathered lithologic units. Low 55 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION concentrations are associated with non -weathered igneous bedrock and soils with high hydraulic conductivity (Polizzotto 2014, Gillespie 2013). 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 can then migrate through pre-existing fractures during the movement of groundwater through bedrock. If this aqueous -phase manganese is exposed to higher pH in the groundwater system, it will precipitate out of solution. This results in preferential pathways becoming "coated" in manganese oxides and introduces a concentrated source of manganese into groundwater (Gillespie 2013). Manganese (II) in suspension of silt or clay is commonly oxidized by microorganisms present in soil, leading to the precipitation of manganese minerals (ATSDR 2012). Roughly 40-50% of North Carolina wells have manganese concentrations higher than the state drinking water standard (Gillespie 2013). Concentrations are spatially variable throughout the state, ranging from less than 0.01 mg/L to more than 2 mg/L. This range of values reflects naturally derived concentrations of the constituent and is largely dependent on the bedrock's mineralogy and extent of weathering (Gillespie 2013). In a 2015 study by DENR (Summary of North Carolina Surface Water Quality Standards 2007- 2014) it was found that concentrations vary regionally, however "manganese occurs naturally at significant concentrations in the groundwater of NC," with a statewide average concentration of 102 pg/L. The study found the regional variations summarized in Table 10-3. Using the USGS National Uranium Resource Evaluation (NURE) database, all manganese tests within a 20-mile radius of the Buck site are shown on Figure 10-4. These samples were taken at depths ranging from 7-360 feet bgs, and the manganese concentrations ranged from below detection limits to 439.9 pg/L. Manganese concentrations in the three locations nearest to the Buck site are less than the SMCL and 2L Standard of 50 pg/L. 10.1.9 Nickel Nickel is a hard, lustrous, silvery -white metal that resists corrosion. It occurs in all types of soils, and is frequently in rocks and underwater sediments (EPRI 2008). Nickel combines easily with other metals to form mixtures called alloys. For example, nickel mixed with steel forms stainless steel, a common alloy that resists rust and corrosion. The U.S. nickel coin contains 25% nickel mixed with copper. Nickel and its alloys are also used in batteries, spark plugs, electrical resistance wires, metal jewelry, cookware, and textile dyes (EPRI 2008). While nickel can exist in oxidation states -1 through +4, the only important oxidation state is Ni(II) under normal environmental conditions (EPRI 2008). Sulfide deposits are by far the most important present source of nickel, in regard to both quantity of nickel and number of deposits; however, North Carolina's nickel is frequently found in iron and aluminum -rich soil called laterite (USGS 1973, Horton et al. 1991). Laterite is formed .2 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION by the weathering of iron- and magnesium -rich rocks in humid, tropical to sub -tropical areas. The repeated processes of dissolution and precipitation lead to a uniform dispersal of nickel that is not amenable to concentration by physical means; therefore, these ores are concentrated by chemical means such as leaching (ATSDR 2012). There has been interest in a few small residual nickel laterites in the Blue Ridge Mountains geologic province of southwestern North Carolina. The nickeliferous soils form above alpine peridotites and duniites. In general, the anomalous nickel values (as high as 1 to 3% nickel) consist of garnierite and genthite in small veinlets in lateritic soils and in the upper portion of underlying bedrock. The veinlets themselves run as high as 10% nickel. The largest concentration is found in one million tons of 1 % nickel soils near Webster, North Carolina (Horton et al. 1991). Despite this abundance, there are no nickel mining operations currently in the U.S., as U.S. supplies are imported or recycled (ATSDR 2012). Nickel is a natural constituent of soil and is transported into streams and waterways in runoff either from natural weathering or from disturbed soil. Much of this nickel is associated with particulate matter. Nickel also enters bodies of water through atmospheric deposition (ATSDR 2012). The primary source of nickel in drinking -water is leaching from metals in contact with drinking -water, such as pipes and fittings (WHO 2007). Nickel concentrations in groundwater depend on the soil use, pH, and depth of sampling. Once nickel is in surface and ground water systems, physical and chemical interactions (complexation, precipitation/dissolution, adsorption/desorption, and oxidation/reduction) occur that will determine its fate and that of its constituents (USEPA 2009). Acid rain increases the mobility of nickel in the soil and thus might increase nickel concentrations in groundwater (WHO 2007). 10.1.10 Selenium Selenium is a semi -metallic gray metal that commonly occurs naturally combined with rocks and soil. It is common to find trace amounts of selenium in food, drinking water, and air -borne dust. Over geologic time, selenium has been introduced to the earth's surface and atmosphere through volcanic emissions and igneous extrusions. Weathering and transport partition the element into residual soils, where it is available for plant uptake, or to the aqueous environment, where it may remain dissolved, enter the aquatic food chain, or redeposit within a sedimentary rock such as shale (EPRI 2008). Groundwater containing selenium is typically the result of either natural processes or industrial operations. Naturally, selenium's presence in groundwater is from leaching out of selenium - bearing rocks. It is most common in shale ranging from 0.6 to 103 mg/kg. Anthropogenically, selenium is released as a function of the discharge from petroleum and metal refineries and from ore mining and processing facilities. Ore mining may enhance the natural erosive process by loosening soil, creating concentrations in erodible tailings piles, and exposing selenium containing rock to runoff (Martens 2002, USEPA 2014). 57 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION In a statistical summary of groundwater quality in North Carolina, the Superfund Research Program at UNC analyzed 1,040 private well water samples in Rowan and Davidson counties from 1998-2010. The concentrations ranged from 2.5 to 74.3 pg/L, and one sample exceeded the 50 pg/L primary MCL for selenium. The mean selenium concentration measured in these counties was 2.7 pg/L (NC DHHS 2010). Selenium summary statistics are reported in Table 10- 2. 10.1.11 Sulfate Sulfates are naturally occurring substances that are found in minerals, soil, and rocks. They are present in ambient air, groundwater, plants, and food. The principal commercial use of sulfate is in the chemical industry. Sulfates are discharged into water in industrial wastes and through atmospheric deposition (USEPA 2003). While sulfate has a 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). In the Piedmont and Blue Ridge Aquifers chapter of the USGS Groundwater 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," (USGS 1997). 10.1.12 TDS Groundwater contains a wide variety of dissolved inorganic constituents as a result of chemical and biochemical interactions between the groundwater and the elements in the soil and rock through which it passes. Total Dissolved Solids (TDS) mainly consist of cation and anion particles (e.g., calcium, chlorides, nitrate, phosphorus, iron, sulfur, and others) that can pass through a 2 micron filter (USEPA, 1997). TDS is therefore a measure of the total amount of dissolved ions in the water, but does not identify specific constituents, or explain the nature of ion relationships. TDS concentrations in groundwater can vary over many orders of magnitude and generally range from 0 — 1,000,000 µg/L. The ions listed below are referred to as the major ions as they make up more than 90 percent of the TDS in groundwater. TDS concentrations resulting from these constituents are commonly greater than 5,000 µg/L (Freeze and Cherry, 1979). • Sodium (Na') • Magnesium (Mg2+) • Calcium (Ca2+) • Chloride (CI-) • Bicarbonate (HCO3 ) • Sulfate (SO42-) Minor ions in groundwater include: boron, nitrate, carbonate, potassium, fluoride, strontium, and iron. TDS concentrations resulting from minor ions typically range between 10 — 1,000 µg/L Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION (Freeze and Cherry, 1979). Trace constituents make up an even smaller portion of TDS in groundwater and include: aluminum, antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, lead, manganese, nickel, selenium, thallium, vanadium, and zinc among others. TDS concentrations resulting from trace constituents are typically less than 100 µg/L (Freeze and 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. Because TDS is not considered a hazard to human health, it has no USEPA-defined MCL. The USEPA has established an SMCL for TDS because elevated levels are associated with negative aesthetic effects, such as taste and odor of drinking water. Water containing more than 2,000,000 — 3,000,000 µg/L TDS is generally too salty to drink (the TDS of seawater is approximately 35,000,000 µg/L) (Freeze and Cherry, 1979). 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). 10.1.13 Thallium 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 2008). 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 (Le, substratum) soil horizons was estimated across the United States. The overall thallium concentrations range from <0.1 mg/kg to 8.8 mg/kg. North Carolina concentrations from this study are depicted in Figure 10-5. Thallium is compared to an IMAC since no 2L Standard was established for this constituent by NCDENR. 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 (MRL=1 pg/L) (Donahue 2007). 10.1.14 Vanadium 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. Occurrence of vanadium in groundwater is known to be limited to its soluble oxidation state, V(V). In their study on regional distribution of vanadium in groundwater, Wright et al. (2010) found that high levels of vanadium in groundwater were almost always associated with oxic and alkaline groundwater conditions. Vanadium is compared an IMAC of 0.3 pg/L since no 2L Standard has been established for this constituent by NCDENR. M Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION In a study by the Georgia EPD, 120 sites in the Blue Ridge and Piedmont physiographic regions (regions shared with North Carolina) were sampled and detectible traces of vanadium were found in six samples (with a reporting limit of 10 tag/L). Only two of these samples were in basic pH groundwater while the rest were sampled in more acidic waters (see Figure 10-6). Using the USGS NURE database, all vanadium tests within a 20-mile radius of the Buck site are shown on Figure 10-6. Concentrations in this region range from <0.10 to 42.9 pg/L. 10.1.15 pH The pH scale is used to measure acidity or alkalinity. A pH value of 7 indicates neutral water. A value lower than the USEPA-established SMCL range (<6.5 Standard Units) is associated with 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 2,341 private well water samples for pH in Rowan and Davidson counties. The samples were analyzed by the North Carolina State Laboratory of Public Health from 1998-2010. This study found that 13.74% of wells in Rowan County and 20.25% of wells in Davidson County had a pH result outside of the EPA's SMCL range (NC DHHS 2010). Using the USGS NURE database, pH values within a 20-mile radius of the Buck site generally ranged between 6.01 and 8.0. 10.2 Background Wells Background (BG) monitoring well locations were identified based on the SCM at the time the Work Plan was submitted. The BG locations were selected to be installed in areas of the site that are topographically upgradient and assumed not to be impacted by the ash basin and ash storage area. Based on the groundwater contours (Figures 6-7 through 6-9) and the updated SCM, the BG locations are considered to be hydrologically upgradient of the ash basin and ash storage area. Therefore, the BG monitoring well locations are considered to be representative of background groundwater quality conditions at the Buck site. BG monitoring wells include two existing groundwater monitoring wells MW-6S/D, and seven newly installed groundwater monitoring wells BG-1 S/D/BR, BG-2S/D, and BG-3S/BRU. BG monitoring wells are depicted on Figure 10-7. Well construction details are summarized in Tables 6-8 and 6-9. A generalized well construction diagram for newly installed wells is shown on Figure 10-8. Well installation procedures are documented in Appendix G, along with variances from the Work Plan. Boring logs are provided in Appendix H. BG wells MW-6S/D were installed in 2006 as compliance monitoring wells to evaluate background water quality at the site and are located at the southern extent of the ash basin compliance boundary. MW-6S was installed to a depth of 28 feet bgs and screened from 18 to 28 feet bgs. MW-6D was installed to a depth of 108.5 feet bgs and screened from 103.5 to 108.5 feet bgs. Groundwater flow in the vicinity of MW-6S/D is to the northeast towards the ash 0 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION basins and to the Yadkin River. Historical groundwater data for MW-6S/D dates back to November 2006. The compliance monitoring wells are sampled three times a year (January, May, and September) and 20 sampling events have been conducted to date. This is considered sufficient data to adequately perform statistic analysis of the background concentrations (see Appendix G). Duke Energy recognizes that the NCDENR DWR Director is responsible for establishing site -specific background levels for groundwater as stated in 15A NCAC 02L .0202(a)(3). The concentrations in the statistical report are provided as information to aid in this determination, and for comparative purposes for groundwater at the site. Monitoring well MW-6S had antimony (dissolved fraction) and cobalt reported at concentrations greater than their IMACs. Monitoring well MW-6D had vanadium reported at a concentration exceeding the IMAC. Concentrations of arsenic and boron were less than the laboratory reporting limits for the samples collected from both of these wells. Concentrations of chloride, calcium, and sulfate were reported at concentrations similar to or less than the newly installed background wells. The existing background monitoring well results do not exhibit ash related constituents at elevated levels compared to the porewater sample results and the ash basin water results. The concentrations of constituents associated with coal ash in monitoring wells MW-6S and MW-6D are similar to, or less than, the concentrations reported in the newly installed background wells. Newly installed background monitoring wells BG-1 S/D/BR, BG-2S/D, and BG-3S/BRU were installed to evaluate background water quality in the regolith, TZ, and bedrock. BG-1 S was installed to 30 feet bgs and screened from 15 to 30 feet bgs. BG-1 D was installed to 104 feet bgs and screened from 99 to 104 feet bgs. BG-1 BR was installed to 141 feet bgs and screened from 136 to 141 feet bgs; however, the well had insufficient water in the well at the time of sampling to collect a groundwater sample. BG-2S was installed to 32.10 feet bgs and screened from 17.10 to 32.10 feet bgs. BG-2D was installed to 104 feet bgs and screened from 99 to 104 feet bgs. BG-3S was installed to 40.30 feet bgs and screened from 25.30 to 40.30 feet bgs. BG 3BRU was installed to 75 feet bgs and screened from 70 to 75 feet bgs. Currently, insufficient data is available to qualify BG-1 S/D/BR, BG-2S/D, and BG-3S/BRU as background monitoring wells and provide associated statistical analysis. As data become available, statistical analysis will be performed and determination made as to whether these wells qualify as background monitoring wells. Based on review of available information, the number of background wells located within the property boundary of the site is adequate for monitoring background groundwater quality; however, background monitoring well BG-1 BR may not be a viable bedrock background well due to the lack of water in the well at the time of sampling. A replacement bedrock background well may be necessary if BG-1 BR continues to produce inadequate amounts of water for sample collection. The background wells are located hydrologically upgradient and were strategically placed to maximize physical separation from the ash basin and ash storage area. a Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION 10.3 Discussion of Redox Conditions Determination of the reduction/oxidation (redox) condition of groundwater is an important component of groundwater assessments, and helps to understand the mobility, degradation, and solubility of contaminants. By applying the framework of the Excel Workbook for Identifying Redox Processes in Ground Water (Jurgens, McMahon, Chapelle, and Eberts 2009) to the analytical results in the following sections, the predominant redox process or category was assigned to samples collected during the groundwater assessment. Categories include oxic, suboxic, anoxic, and mixed. Assignment of redox category was based upon concentrations of DO, nitrate as nitrogen, manganese (II), iron (II), sulfate, and sulfide as inputs. Constituent criteria appropriate for inputs to the Excel Workbook, as well as an explanation of the redox assignments, can be found in Tables 1 and 2, respectively, of the USGS Open File Report 2009-1004 (Jurgens, et al. 2009). Redox assignment results are presented in Table 10-4. 10.4 Groundwater Analytical Results A total of 64 groundwater monitoring wells were installed at Buck between March and July 2015 as part of the groundwater assessment program. Groundwater monitoring well locations are shown on Figure 10-7. Monitoring well information is provided in Tables 6-8 and 6-9. Monitoring wells were installed in general accordance with procedures described in the Work Plan and a detailed description is provided in Appendix H. Boring logs and field parameters are also provided in Appendix H. Groundwater sample results are compared to the North Carolina 2L Standards and IMACs. Background groundwater sample field parameters and laboratory analytical results for totals and dissolved constituents are summarized in Table 10-5 and background speciation groundwater laboratory results are summarized in Table 10-7. Groundwater sample field parameters and laboratory results for totals and dissolved constituents are summarized in Table 10-6 and assessment well groundwater speciation laboratory results are summarized in Table 10-8. Groundwater sampling results are depicted on Figure 10-9. Variances from the proposed sampling plans are presented in Appendix G. Field and sampling quality control / quality assurance protocols are provided in Appendix E. Duke Energy conducted speciation of groundwater samples for arsenic, chromium, iron, manganese, and selenium from selected wells along inferred groundwater flow transects. Speciation results for background groundwater and groundwater samples are provided in the above referenced tables and the remaining results will be included in the CSA supplement. Well designations and descriptions for the installed assessment monitoring wells include: • AB - Ash Basin — Monitoring wells installed to provide water quality data in and beneath the ash basins and ash basin dikes. • AS — Ash Storage Area — Monitoring wells installed to provide water quality data beneath the ash storage area. 62 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION • GWA — Groundwater Assessment — Monitoring wells installed outside of the waste boundary for use in groundwater modeling (i.e., to evaluate the horizontal and vertical extent of potentially impacted groundwater outside the waste boundary). • BG — Background — Monitoring wells installed to provide information on background water quality. • S — Shallow - Monitoring wells installed in regolith or ash that were screened to bracket the water table surface at the time of installation. • SL — Shallow Lower - Monitoring wells installed with the bottom of the well screen set above the ash-regolith interface. • D — Deep - Monitoring wells installed with the screened interval within the partially weathered/fractured bedrock transistion zone at the base of the regolith. • BRU — Bedrock Upper - Monitoring wells that were originally proposed to be "D" wells; however, a partially weathered/fractured bedrock transition zone was not encountered in the boring. These wells were screened within the first 15 feet of fresh, competent bedrock encountered below the regolith. • BR — Bedrock - Monitoring wells screened across water -bearing fractures within fresh competent bedrock after continuous coring of at least 50 feet into competent bedrock. Groundwater monitoring wells were developed prior to sampling activities in general accordance with well development procedures detailed in Appendix G. The well development forms are also included in Appendix G. Groundwater samples were collected and analyzed in general accordance with the procedures and methods described in the Work Plan and in Duke Energy's Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater Assessment Program, dated May 22, 2015. Refer to Appendix D for a detailed description of these methods. Appendix D also includes a summary of variances from the well development and sampling plans. Appendix E includes the field and sampling quality control / quality assurance protocols. Groundwater samples were collected from background locations, beneath the ash basin, beneath the ash storage area, and from locations outside the waste boundary. Groundwater samples were also collected from pre-existing voluntary and compliance wells on the site. Field parameters are documented in Appendix H. Groundwater isoconcentration contours with respect to each COI are depicted in Figures 10-10 through 10-51. Cross -sections presenting horizontal and vertical distribution of COls are depicted on Figures 10-52 through 10-55. COI concentrations along the flow transects will be modeled in the CAP. The USEPA recommends that when possible, especially when sampling for constituents that may be biased by the presence of turbidity, that turbidity values in the stabilized well should be less than 10 Nephelometric turbidity units (NTUs) (USEPA 2002). Compliance monitoring wells with analytical results exceeding the 2L Standards have been individually plotted with the associated turbidity values (Figures 10-105 through 10-143). Maximum contaminant concentrations for groundwater can be found in Section 17.3. 63 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 10.0 GROUNDWATER CHARACTERIZATION 10.4.1 Ash Basin 10.4.1.1 Beneath the Ash Basin Waste Boundary A total of 25 groundwater monitoring wells (8 shallow, 4 shallow lower, 3 deep, 7 upper bedrock, and 3 bedrock) were installed beneath the ash basin system. These monitoring wells include AB-1 D, AB-2S/SL/BRU/BR, AB-3S/D, AB-4S/SL/BRU/BR, AB-5S/SL/BRU, AB-6D, AB- 7S/SL/BRU, AB-8S/BRU, AB-9S/BRU/BR, and AB-1 OS/D. These groundwater monitoring wells were installed to evaluate groundwater quality beneath the ash basin. Installed groundwater monitoring wells were developed prior to sampling activities in general accordance with well development procedures detailed in Appendix G. Well development forms are also included in Appendix G. Groundwater monitoring wells were subsequently collected and analyzed in general accordance with the procedures and methods described in the Work Plan and in Duke Energy's Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater Assessment Program, dated May 22, 2015. Any variances from the proposed development and groundwater sampling plans are included in Appendix G. Groundwater samples were collected from background locations (described above), locations upgradient of the ash basin, beneath the ash basin, and downgradient of the ash basin. Groundwater samples were also collected from select existing voluntary and compliance monitoring wells. Parameters and constituent analytical methods for the groundwater samples collected are provided in Table 7-3. Laboratory results for groundwater samples were compared to 2L Standards and IMACs. Background groundwater results are presented in Table 10-5. Groundwater sample results (for total and dissolved constituents and other parameters) for monitoring wells located upgradient of the ash basin (not considered background), beneath the ash basin, and downgradient of the ash basin are presented in Table 10-6. Field parameters collected at the time of sampling are provided in Appendix H. Groundwater analytical results for constituents that exceed 2L Standards or IMACs are depicted on Figure 10-9. Field and sampling quality control / quality assurance protocols are provided in Appendix E. 10.4.2 Ash Storage Area A total of 5 groundwater monitoring wells (2 shallow and 3 deep) were installed within the ash storage area. These monitoring wells include AS-1 S/D, AS-2D, and AS-3S/D. These groundwater monitoring wells were installed to evaluate groundwater quality beneath the ash storage area. 10.4.3 Outside the Waste Boundary A total of 27 groundwater monitoring wells (10 shallow, 8 deep, 5 bedrock upper, and 4 bedrock) were installed outside the waste boundary of the ash basin and ash storage area. These included wells downgradient, side -gradient and upgradient of the ash basin. These monitoring wells include the following: GWA-1 S/D, GWA-2D/BRU, GWA-3S/BRU/BR, GWA- 4S/D, GWA-5S/BRU, GWA-6S/BRU/BR, GWA-7S/D, GWA-8D, GWA-9S/D/BR, GWA-10S/D, GWA-11 S/D, GWA-12S/BRU, and GWA-22D. The groundwater monitoring wells located Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION outside the waste boundary, were installed to evaluate the impact of the ash basin and ash storage area on groundwater quality. A total of 14 existing groundwater monitoring wells, compliance and voluntary, were sampled to supplement groundwater quality data for this groundwater assessment. These borings include the following: MW-3S/D, MW-7S/D, MW-8S/D, MW-9S/D, MW-1OD, MW-11S/D, MW-12S/D, and MW-13D. Time series plots, time history plots, stacked time series plots and correlation plots for existing wells are depicted in Figures 10-84 to 10-142. 10.5 Comparison of Results to 2L Standards and IMACs Groundwater results were compared to their respective 2L Standards or IMACs and exceedances are summarized below. Table 10-6 and Figure 10-9 present the groundwater results with exceedances of 2L Standards or IMACs. 10.6 Comparison of Results to Background 10.6.1 Background Wells MW-6S and MW-6D Background monitoring well MW-6S and MW-6D concentrations were selected for comparison based on the information presented in Section 10.2, the amount of historical data available, and a location hydraulically upgradient of the ash basin and ash storage area. With the exception of antimony, cobalt, iron, manganese, and vanadium, the results for all other constituents have been reported at less than their respective 2L Standard and IMACs at these wells throughout their monitoring history. The background concentration ranges for the constituents that are considered Cols at Buck are provided below. Results with J qualifiers are estimated concentrations less than the laboratory method reporting limit. • Antimony 0.58 pg/L to 3.8 pg/L • Arsenic 0.5U lag/L to 2U lag/L • Barium 23 pg/L to 86 pg/L • Boron 50U pg/L • Chromium 1.1 lag/L to 3.0 pg/L • Cobalt 0.51J lag/L to 4 pg/L • Iron 10 pg/L to 1,270 pg/L • Manganese 15 pg/L to 228 pg/L • Nickel 0.5U pg/L to 8 pg/L • Selenium 0.21J lag/L to 0.5U pg/L • Thallium 0.03J pg/L to 0.2U lag/L • Vanadium 1.3J lag/L to 9 lag/L • Sulfate 140 lag/L to 2,400 lag/L • TDS 21,000 lag/L to 140,000 lag/L Notes: pg/L = micrograms per liter J = Estimated concentration U = Not detected 65 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION 10.6.2 Newly Installed Background Wells Recently installed background monitoring wells are designated BG-1 S/D/BR, BG-2S/D, and BG- 3S/BRU. Newly installed background wells will be compared to the Buck well network in the future after additional analysis. With the exception of antimony (one exceedance), chromium (one exceedance), cobalt (two exceedances), iron (three exceedances), manganese (two exceedances), and vanadium (six exceedances), the results for all other constituents were reported at less than the 2L Standards or IMACs. The background concentration ranges in the newly installed background wells for constituents that are considered COls at Buck are provided below. Concentrations with J qualifiers are estimated concentrations less than the laboratory method reporting limits. • Antimony 0.23J pg/L to 3.8 pg/L • Arsenic 0.26 pg/L to 1 J pg/L • Barium 6.4 pg/L to 55 pg/L • Boron 38J pg/L to 50U pg/L • Chromium 0.42J pg/L to 10.3 pg/L • Cobalt 0.15J pg/L to 7.2 pg/L • Iron 110 pg/L to 1,900 pg/L • Manganese 3.1 J pg/L to 770 pg/L • Nickel 0.84 pg/L to 10.9 pg/L • Selenium 0.27J pg/L to 0.51LI pg/L • Thallium 0.032J pg/L to 0.1 U pg/L • Vanadium 0.86J pg/L to 26.6 pg/L • Sulfate 860J pg/L to 22,700 pg/L • TDS 51,000 pg/L to 175,000 pg/L Notes: pg/L = micrograms per liter J = Estimated concentration U = Not detected 10.6.3 Regional Groundwater Data The details regarding the regional groundwater data are presented in Section 10.1. Average chromium concentrations reported for Rowan and Davidson counties were 5.6 pg/L and 5.3 pg/L, respectively. Average iron concentrations reported for Rowan and Davidson counties were 125,698 pg/L and 531 pg/L, respectively. Selenium concentrations reported in Rowan and Davidson counties ranged from 2.5 pg/L to 74.3 pg/L. Vanadium concentrations reported within a 20 mile radius of Buck ranged from <0.10 pg/L to 42.9 pg/L. The state of North Carolina average for manganese is reported at 102 pg/L. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 10.0 GROUNDWATER CHARACTERIZATION 10.6.4 Groundwater Beneath the Ash Basin Groundwater monitoring locations beneath the ash basin were obtained from AB-1 D, AB- 2D/BR, AB-31D, AB-4D/BR, AB-5BRU, AB-6BRU, AB-7BRU, AB-8, AB-9S/BRU/BR, and AB- 1 OS/D. The range of COI concentrations along with a comparison to the range of reported background groundwater in monitoring wells MW-6S and MW-6D and the regional groundwater data, is provided in Table 10-9. COls in groundwater beneath the ash basin with concentrations higher than background and/or regional concentrations include: arsenic, boron, chromium, cobalt, iron, manganese, and selenium. Antimony, and vanadium concentrations in groundwater beneath the ash basin are within or below the range of background and/or regional concentrations. 10.6.5 Groundwater Beneath the Ash Storage Area Groundwater beneath the ash storage area was obtained from monitoring wells AS-1 S/D, AS- 2D, and AS-3S/D. The range of COI concentrations, along with a comparison to the range of reported background groundwater and the regional groundwater data, is provided in Table 10- 10. COls in groundwater beneath the ash storage area with concentrations higher than background and/or regional concentrations include: boron, chromium, cobalt, iron, manganese, nickel, sulfate, and TDS. Constituents in groundwater beneath the ash storage area with concentrations that are within or below the range of background and/or regional concentrations include: antimony, selenium, thallium and vanadium. 10.6.6 Groundwater Beyond the Waste Boundary Groundwater samples collected from beyond the waste boundary were obtained from MW- 3S/D, MW-7S/D, MW-8S/D, MW-9S/D, MW-10S/D, MW-11 S/D, MW-12S/D, MW-13D, GWA- 1 S/D, GWA-2BRU/BR, GWA-3S/BRU/BR, GWA-4S/D, GWA-5S/BRU, GWA-6S/BRU/BR, GWA-7S/D, GWA-81D, GWA-9S/D/BR, GWA-10S/D, GWA-11 S/D, GWA-12S/BRU and GWA- 22D. The range of COI concentrations, along with a comparison to the range of reported background groundwater and the regional groundwater data, is provided in Table 10-11. To evaluate how COI concentrations varied around and beyond the ash basin waste boundary, analyses of sampling results for several groupings of monitoring wells were compared to background monitoring well constituent concentration ranges. 10.6.6.1 Groundwater South of Ash Basin Cell 1 Groundwater monitoring wells located to the south (or upgradient) of Cell 1 include MW-7S/D, MW-8S/D and GWA-1 S/D. Background well pair MW-6S/D is also located upgradient of and to the south of Cell 1. Groundwater samples from one or more of these wells exceeded the 2L Standards or IMACs for chromium, cobalt, iron, manganese, and/or vanadium. Groundwater samples from the background monitoring wells MW-6S/D exceeded the IMACs for cobalt and vanadium for the CSA sampling, but had no other exceedances. Groundwater COI Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION concentrations for monitoring wells south of Cell 1 were all within or below the background monitoring well concentration ranges. All of these wells are located within the compliance boundary. 10.6.6.2 Groundwater West of Ash Basin Cell 1 Groundwater monitoring wells located to the west of Cell 1 include MW-9S/D, GWA-10S/D, GWA-11 S/D, and GWA-22D. These wells are located between Cell 1 and the stream located to the west of Cell 1 and are located within the compliance boundary. Groundwater samples from one or more of these wells exceeded the 2L Standards or IMACs for chromium, cobalt, iron, manganese, and vanadium. Newly installed background monitoring wells BG-1 S/D and BG- 2S/D are located approximately 2000 feet and topographically upgradient of the southeast end of Cell 1. Samples from these background monitoring wells exceeded the 2L Standards or IMACs for antimony, chromium, cobalt, iron, manganese, and vanadium. Groundwater COI concentrations for wells west of Cell 1 were higher than the background monitoring well concentration ranges for cobalt and vanadium. All other 2L or [MAC exceedance concentrations were similar to or below the background monitoring well concentrations. Additional evaluation related to natural soil/rock mineralogy and chemistry is discussed in Section 14 Data Gaps. 10.6.6.3 Groundwater East of Ash Basin Cells 1, 2, and 3 Groundwater monitoring wells located to the south and east of Cells 2 and 3 are either side - gradient and/or downgradient to groundwater flow direction near Cells 2 and 3, depending on location. It is likely that regional groundwater flow is from the divide along Leonard Road towards Cells 1, 2, and 3, and flow is combined with an element of a local groundwater gradient with flows from Cell 1 to Cell 2 and on to Cell 3. The measured water levels in wells MW-12S/D is slightly higher that the water level measured in the adjacent Cell 2, indicating groundwater flow is towards Ce112. The water measured in MW-13D is slightly higher that the water level measured in the adjacent Cell 3 indicating groundwater flow is towards Cell 3. Groundwater samples results in from these two wells exceeded the 2L Standards or IMAC for iron, manganese, and/or vanadium. Groundwater samples from the background monitoring wells BG- 3S and BG-3BRU also exceeded the 2L Standards or IMAC for these COIs. Wells GWA2BR and GWABRU are located along the compliance boundary near the dike between Cell 2 and Cell 3. The water levels measured in these two wells shows an upward vertical gradient indicating that groundwater in this area is discharging into the ash basin region. These wells had exceedances of 2L standards or IMACs for antimony, barium, chromium, TDS, vanadium, and/or iron. Wells GWA-2BRU/BR and GWA-3S/BRU/BR. GWA-2BRU/BR are located in an area where insufficient data exists to fully evaluate groundwater flow direction (this data gap is discussed further in Section 14.0). Wells GWA-3S, GWA-313R, and GWA-3BRU are located to the east of Cell 3 and are downgradient of Cell 3. These wells are located inside of the compliance boundary on the east side of a small stream. These wells had exceedances of 2L standards or IMACs for cobalt, iron, manganese, and/or vanadium. The iron, cobalt, and vanadium concentrations are in the range of the results from MW-6S/D. m Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION 10.6.6.4 Groundwater North of Ash Basin Cells 1, 2, and 3 Groundwater monitoring wells located to the north of the ash basin are all downgradient of Cells 1, 2, and 3 and generally are located between Cells 1, 2, and 3 and the Yadkin River. These wells include: GWA-9S/D/BR, GWA-81D, GWA-7S/D, MW-10S/D, GWA-12S/BRU, GWA- 6S/BR/BRU, MW-3S/D, GWA-5S/BRU, MW-11 S/D, and GWA-4S/D. Groundwater samples from these wells exceeded the 2L Standards or IMACs for antimony, boron, chromium, cobalt, iron, manganese, sulfate, TDS, and vanadium. The background monitoring wells also exceeded the 2L Standards or IMACs for all of these COls except boron, sulfate, and TDS. Boron exceeded the 2L Standard in MW-11 D and in MW-3S (an estimated concentration); sulfate and TDS exceeded their 2L Standards in GWA-6S/BR/BRU and MW-101D. Groundwater COI concentrations for downgradient wells north of Cells 1, 2, and 3 were higher than the background monitoring well concentration ranges for boron, chromium, cobalt, iron, sulfate, TDS, and vanadium. Source related measured constituent levels above 2L Standards or IMACs were measured outside the compliance boundary. This includes boron which is shown on Figure ES-1. 10.6.6.5 Groundwater within Various Layers Beneath the Site Within the shallow layer (including beneath the ash storage area), there are ten COls identified in the groundwater within the shallow flow layer (S wells not screened within ash): boron, cobalt, chromium, iron, manganese, nickel, sulfate, thallium, TDS and vanadium. Chromium, cobalt, iron, manganese, and vanadium also appear in one or more of the background wells at concentrations exceeding the applicable 2L Standard or IMACs. Most of these measurements occurred beneath or within the source and north of the source, with constituents to the north (above applicable standards and background measurements) being boron, chromium, iron, manganese, sulfate and TDS. Almost all of the iron exceedances in the shallow layer (12 of 13) and chromium exceedances (3 of 3) occurred in unfiltered samples indicating the source of the iron and chromium in the shallow groundwater samples is primarily suspended solids. Six COls identified in the shallow layer (antimony, boron, nickel, selenium, sulfate, and TDS) are in isolated locations. Within the deep flow layer (D wells) (including beneath the ash basin and ash storage area), there are nine COls identified in the groundwater: antimony, boron, chromium, cobalt, iron, manganese, sulfate, TDS, and vanadium. Most of these measurements occurred beneath the source or north of the source, with constituents to the north (above applicable standards and background measurements) being boron, iron, sulfate, TDS, and vanadium. Almost all of the iron exceedances within the deep flow layer (10 of 12) occurred within unfiltered samples indicating the source of the iron within the deep flow layer groundwater samples is primarily suspended solids. Two of the COls identified in the deep flow layer (sulfate and TDS) are in isolated locations. Within the bedrock flow layer (including beneath the ash basin), there are eleven COls in the groundwater within the bedrock flow layer (BR and BRU wells): antimony, barium, boron, chromium, cobalt, iron, manganese, selenium, sulfate, TDS and vanadium. Most of these Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION measurements occurred north of the source, with constituents to the north (above applicable standards and background measurements) being sulfate, TDS, and vanadium. None of these COls appear within the bedrock background well location (BG-3BRU) at a concentration exceeding the applicable groundwater standard, although it is worth noting that there is little background information for deep samples and some of the chemical and mineralogical for rock samples has not been received from the lab for evaluation. All eight of the iron exceedances within the bedrock flow layer occurred within unfiltered samples indicating the source of the iron within the bedrock groundwater samples is primarily suspended solids. Six of the COls identified in the bedrock flow layer (barium, boron, cobalt, selenium, sulfate and TDS) are in isolated locations. No boron was identified in the bedrock flow layer and sulfate levels may be the result of natural conditions. This is discussed further in Section 14 Data Gaps. 10.7 Cation and Anion Water Quality Data Cations and anions are used in hydrogeological investigations to assess naturally occurring ions in groundwater. Cations are positively charged ions whereas anions are negatively charged ions. There are eight ions commonly used to evaluate groundwater. These ions consist of four cations: calcium, magnesium, sodium, and potassium and four anions: chloride, sulfate, carbonate, and bicarbonate. Geochemical makeup of groundwater aids in aquifer characterization. Piper diagrams are used to graphically depict geochemistry of groundwater samples collected at a particular site. Cation and anion concentrations at Buck from groundwater monitoring wells and ash basin groundwater monitoring wells are shown in Figures 10-64 and 10-83. In general, calcium and sulfate are elevated. Piper diagrams were generated for Buck show comparison of geochemistry between ash basin porewater, ash basin water, seeps, upgradient and downgradient groundwater monitoring wells and background groundwater monitoring wells. Ash basin water and ash basin porewater are generally higher in sulfate and chloride percentages compared to the background groundwater monitoring wells. Ash basin water tends to have high percentages of sodium and potassium, while ash basin porewater tends to have a high percentage of calcium. Piper diagrams are shown in Figures 10-56 to 10-63. 10.8 CCR Rule Groundwater Detection and Assessment Monitoring Parameters Appendix III to Part 257 Constituents for Detection Monitoring and Appendix IV to Part 257 Constituents for Assessment Monitoring On April 17, 2015, the USEPA published its final rule "Disposal of Coal Combustion Residuals from Electric Utilities" to regulate the disposal of coal combustion residuals (CCR) as solid waste under subtitle D of the Resource Conservation and Recovery Act (RCRA). Among other requirements, the final rule establishes requirements for a groundwater monitoring program 70 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION consisting of detection monitoring and, if necessary, assessment monitoring and corrective action. USEPA selected constituents to be used in the groundwater detection monitoring program as indicators of groundwater contamination from CCR. USEPA selected constituents for detection monitoring that are present in CCR, would be expected to migrate rapidly, and that would provide early detection as to whether contaminants were migrating from the disposal unit. (80 FIR 74: 21397). As stated in the FIR (80 FIR 74: 21342): These detection monitoring constituents or inorganic indicator parameters are: boron, calcium, chloride, fluoride, pH, sulfate and total dissolved solids (TDS). These inorganic indicator parameters are known to be leading indicators of releases of contaminants associated with CCR and the Agency strongly recommends that State Directors add these constituents to the list of indicator parameters to be monitored during detection monitoring of groundwater if and when a MSWLF decides to accept CCR. (Emphasis added) NCDENR requested that figures be included in the CSA report that depict groundwater analytical results for the constituents in 40 CFR 257, Appendix III detection monitoring and 40 CFR 257, Appendix IV assessment monitoring. Detection monitoring constituents in 40 CFR 257 Appendix III are: • Boron • Calcium • Chloride • Fluoride (this constituent was not analyzed for in the CSA) • pH • Sulfate • TDS The analytical results for the detection monitoring constituents are found on Figures 10-144 to 10-146. Constituents for assessment monitoring listed in 40 CFR 257 Appendix IV include: • Antimony • Arsenic • Barium • Beryllium • Cadmium • Chromium 71 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 10.0 GROUNDWATER CHARACTERIZATION • Cobalt • Fluoride (not analyzed for the CSA) • Lead • Lithium (not analyzed for the CSA) • Mercury • Molybdenum • Selenium • Thallium • Radium 226 and 228 combined The analytical results for the assessment monitoring constituents are found on Figures 10-147 to 10-149. Aluminum, copper, iron, manganese, and sulfide were included in the Appendix IV constituents in the draft rule; USEPA removed these constituents in the final rule. These constituents were removed because they lack MCLs and were not shown to be constituents of concern based on either the risk assessment conducted for the CCR Rule or the damage cases reference in the CCR Rule. Therefore, these constituents are not included on the above referenced figures. In addition, NCDENR requested that vanadium be included on these figures. Figure 10-9 shows vanadium as well as other constituents where they exceeded the relevant regulatory standards. 72 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 11.0 HYDROGEOLOGICAL INVESTIGATION 11.0 Hydrogeological Investigation The purpose of the hydrogeological investigation is to characterize site hydrogeological conditions including groundwater flow direction, hydraulic gradient and conductivity, groundwater and contaminant velocity, and slug test results. The hydrogeological investigation was performed in general accordance with the procedures described in the Work Plan. Refer to Appendix H for a description of these methods. 11.1 Hydrostratigraphic Layer Development The following materials were encountered during the site exploration and are consistent with material descriptions from previous site exploration studies: • Ash — Ash was encountered in borings advanced within the ash basin and ash storage areas, as well as through dikes. Ash was generally described as gray to dark gray, non -plastic, loose to medium dense, dry to wet, fine to coarse -grained. • Fill — Fill material generally consisted of re -worked silts, clays, and sands that were borrowed from one area of the site and re -distributed to other areas. Fill was generally classified as silty sand, clay with sand, clay, and sandy clay on the boring logs. Fill was used in the construction of dikes, and as cover for ash storage area. • Alluvium —Alluvium encountered in borings during the project was classified as clay and sand with clay. In some cases alluvium was logged beneath ash. • Residuum (Residual soils) — Residuum is the in -place weathered soil that consists primarily of silt with sand, clayey sand, sandy clay, clay with gravel, and clayey silts. Residuum varied in thickness and was relatively thin compared to the thickness of saprolite. • Saprolite/Weathered Rock — Saprolite is soil developed by in -place weathering of rock that retains remnant bedrock structure. Saprolite consists primarily of medium dense to very dense silty sand, sandy silt, sand, sand with gravel, sand with clay, clay with sand, and clay. Sand particle size ranges from fine to coarse grained. Much of the saprolite is micaceous. • Partially Weathered/Fractured Rock — Partially weathered (slight to moderate) and/or highly fractured rock encountered below auger refusal. • Bedrock — Sound rock in boreholes, were generally slightly weathered to fresh and relatively unfractured.o Based on the CSA site investigation, the groundwater system is consistent with the regolith- fractured bedrock system discussed in Section 5.2. To define the hydrostratigraphic units, the classification system of Schaeffer (2014a) used to show that the TZ is present in the Piedmont groundwater system (discussed in Section 5-2) was modified to define the hydrostratigraphic layers of the natural groundwater system. The classification system is based on Standard Penetration Testing values (N) and the Recovery (REC) and Rock Quality Designation (RQD) collected during the drilling and logging of the boreholes (Borehole/Well logs in Appendix H). 73 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 11.0 HYDROGEOLOGICAL INVESTIGATION The ash, fill, and alluvial layers are as encountered at the site. The natural system (except alluvium) includes the following layers: • M1 — Soil/Saprolite: N<50 • M2 — Saprolite/Weathered Rock: N>50 or REC<50% • TZ — Transition Zone: REC>50% and RQD<50% • BR — Bedrock: REC>85% and RQD>50%. Rock core runs that fell between the values for TZ and BR (REC<85% and RQD>50% or REC>85% and RQD<50%) were assigned a hydrostratigraphic layer based on a review of the borehole logs, rock core photographs, and geologic judgment. The same review was performed in making the final determination of the thickness of the TZ as it could extend into the next core run that meets the BR criterion because of potential core loss or fractured/jointed rock with indications of water movement (iron/manganese staining). The above layer designations (M1, M2, TZ, and BR) are used on the geologic cross -sections with transect locations shown on Figure 11-1. The ash, fill and alluvial layers are represented by A, F, and S, respectively on the cross -sections and tables. 11.2 Hydrostratigraphic Layer Properties The material properties required for the groundwater flow and transport model, total porosity, effective porosity, specific yield and specific storage for ash, fill, alluvium, and soil/saprolite were developed from laboratory testing (Table 11-1; test data in Appendix H), historic laboratory testing (Table 1-1 in Appendix H), and published data (Domenico and Mifflin 1965). Table 11-1 has a column labeled `Estimated Specific Yield/Effective Porosity' and the values are estimated from the laboratory soil data (grain size analysis) utilizing Fetter -Bear diagrams (worksheets in Appendix H), as described by Johnson (1967) and published data. This technique provides a simple method to estimate specific yield; however, there are limitations to the method that may not provide an accurate determination of the specific yield of a single sample (Robson 1993). Specific yield/effective porosity were determined for a number of samples of the A, F, S, M1, and M2 layers to provide an average and range of expected values. The effective porosity (primarily fracture porosity) and specific storage of the TZ and bedrock were estimated from published data (Sanders 1998; Domenico and Mifflin 1965). Hydraulic conductivity (horizontal and vertical) of all layers, except vertical hydraulic conductivity for the TZ and bedrock (BR), was developed utilizing site historic permeability data in -situ permeability testing (falling head, constant head, and packer testing where appropriate), slug tests in completed monitoring wells, and laboratory testing of undisturbed samples (ash, fill, soil/saprolite: test results in Appendix H) during this investigationo 11.2.1 Borehole In -Situ Tests 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, alluvium, and soil/saprolite. In -situ borehole 74 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 11.0 HYDROGEOLOGICAL INVESTIGATION horizontal permeability tests, either falling or constant head tests as appropriate for field conditions, were performed just below refusal in the first 5 feet of a rock cored borehole (TZ, if present). The flush bottom test involves advancing the borehole through the overburden with a casing advancer until the test interval is reached. The cutting tool is removed from the casing and the casing is filled with water to the top and the drop of the water level in the casing is measured over a time period of 60 minutes. In the open hole test, after the top of the test interval is reached, the cutting tool but not the casing, is advanced an additional number of feet (five feet in the majority of tests) and drop of the water level in the casing is measured over a time period of 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 a period of 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 11-2 and the worksheets are provided in Appendix H. 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 11-2 and the shut-in and packer tests worksheets are provided in Appendix H. 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 (1995) 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. 11.2.2 Monitoring Well and Observation Well Slug Tests Hydraulic conductivity (slug) tests were completed in monitoring wells and observation wells under the direction of the Lead Geologist/Engineer. 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-tests 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. 75 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 11.0 HYDROGEOLOGICAL INVESTIGATION The slug test results are presented in Table 11-3 and the Slug Test Report is provided in Appendix H. Historic slug test data is presented in Table 11-4. 11.2.3 Laboratory Permeability Tests Laboratory permeability tests were conducted on undisturbed samples (Shelby tubes) of ash, fill, soil, and saprolite collected during the field investigation. The tests were performed in accordance with ASTM D 5084 (ASTM 2010). Results of the laboratory permeability tests are presented in Table 11-5 and historic laboratory permeability tests are presented in Table 11-6 11.2.4 Hydrostratigraphic Layer Parameters The soil material parameters for the A (ash), F (fill), S (alluvium), M1 (soil/saprolite), and M2 (saprolite/weathered rock) were developed by grouping the data into their respective hydrostratigraphic unit and calculating the mean, median, and standard deviation of the different parameters. Estimated values for total porosities for the Hydrostratigraphic layers A, F, S, M1, and M2 are presented in Table 11-7. Values for estimated effective porosity/specific yield are presented in Table 11-8. The values for specific storage presented in Table 11-8 are based on published data (Domenico and Mifflin 1965).The hydraulic conductivity parameters were developed by grouping the data into their respective hydrostratigraphic units and calculating the geometric mean, median, and standard deviation of the different parameters. Vertical hydraulic conductivity values are not available for the TZ and BR units, but are unlikely to be equal. As an initial assumption, vertical hydraulic conductivity for these units can be considered to be equal to the horizontal hydraulic conductivity and adjusted as necessary during flow model calibration. Horizontal and vertical hydraulic conductivity parameters are presented Tables 11-9 and 11-10, respectively. The values of secondary (effective) porosity and specific storage for the TZ and BR units are based on published values (Sanders 1998; Domenico and Mifflin 1965) and are presented in Table 11-11. Further development of the above parameters and others required for the flow and contaminant transport model will be provided in the CAP. 11.3 Hydraulic Gradients Horizontal hydraulic gradient is calculated by taking the difference in hydraulic head over the distance between two wells with similar well construction. Section 6.2.2 provides additional details for horizontal hydraulic gradients calculated for the site. Vertical hydraulic gradient was calculated by taking the difference in groundwater elevation in a deep and shallow well pair over the difference in total well depth of the deep and shallow well pair. A positive output indicates upward flow and a negative output indicates downward flow. Thirteen well pair locations, each consisting of a shallow and deep groundwater monitoring well, were used to calculate vertical hydraulic gradient across the site. Based on review of the results, vertical gradient of groundwater is generally downward across the site. Vertical gradient calculations are summarized in Table 11-13. 76 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 11.0 HYDROGEOLOGICAL INVESTIGATION 11.4 Groundwater Velocity Darcy's Law is an equation that describes the flow rate or flux of fluid through a porous media. To calculate the velocity that water moves through a porous medium, the specific discharge, or Darcy flux, is divided by the effective porosity, ne. The result is the average linear velocity or seepage velocity of groundwater between two points. The following equation was used to calculate groundwater velocities through each hydrostratigraphic unit present at the site: v = Ki ne where vis velocity; Kis horizontal hydraulic conductivity; i is horizontal hydraulic gradient; and ne is the effective porosity Seepage velocities for groundwater were calculated using horizontal hydraulic gradients established in Section 6.2.2, horizontal hydraulic conductivity values for each hydrostratigraphic unit established in Table 11-9 and effective porosity values established in Tables 11-8 and 11- 11. Hydrostratigraphic layers are defined in Section 11.1. Average groundwater seepage velocity results are summarized in Table 11-12. The rate of groundwater migration varies with the hydraulic conductivity and porosity of the site soil and rock materials and ranged from 5.3 ft/yr to 91.8 ft/yr in soils, and 4.0E+2 ft/yr to 2.29E+5 ft/yr in rock. 11.5 Contaminant Velocity Contaminant velocity depends on factors such as; the rate of groundwater flow, the effective porosity of the flow layer material, and the soil -water partition coefficient, or Kd term. Site specific Kd terms will be developed using samples collected during the site investigation. The testing to develop the Kd terms is still underway and the results will be presented in the CAP. The groundwater modeling to be performed in the CAP will present the velocities for the modeled contaminants. 11.6 Plume's Physical and Chemical Characterization Plume physical and chemical characterization is detailed below for each constituent detected in porewater and groundwater samples, and is based on the isoconcentration maps (Figures 10- 10 through 10-51 and cross sections (Figures 8-2 through 8-4). These descriptions are based on a single groundwater sampling event described in the approved Work Plan, both unfiltered and filtered (0.45 pm filter) samples were collected for analyses of constituents whose results may be biased by the presence of turbidity.3 Unless otherwise noted, concentration results discussed are for the unfiltered samples and represent total concentrations. 3 The USEPA (EPA 2002) recommends that when possible, especially when sampling for contaminants that may be biased by the presence of turbidity, the turbidity reading is desired to stabilize at a value below 10 Nephelometric Turbidity Units (NTUs) 77 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 11.0 HYDROGEOLOGICAL INVESTIGATION • Antimony concentrations were not reported above the IMAC in monitoring wells screened within the shallow flow layer except at background locations BG-1 S and MW-6S. Antimony concentrations in monitoring wells screened within the deep flow layer exceeded the IMAC within the ash storage area at AS-2D and north of the ash basin compliance boundary at GWA-7D. Antimony concentrations in the bedrock flow layer exceeded the IMAC within ash basin Cells 2 and 3 at AB-4BR, AB-6BRU, AB-7BRU, and AB-9BRU, as well as near the compliance boundary east of Cell 2 at GWA-2BR and GWA-2BRU.Wells within the bedrock flow layer had more exceedances than wells within the deep and shallow flow layer. • Arsenic concentrations were not reported above 2L Standards in monitoring wells screened within the shallow or deep flow layers. Arsenic concentration in monitoring wells screened within the bedrock flow layer exceeded the 2L Standards within ash basin Cell 2 at AB-4BR only. • Barium concentrations were not reported above 2L Standards in monitoring wells screened within the shallow flow layer or deep flow layer. Barium concentrations in monitoring wells screened within the bedrock flow layer exceeded the 2L Standards near the compliance boundary east of ash basin Cell 2 at GWA-2BR only. • Boron concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard beneath the ash storage area at AS-1 S and at voluntary well MW-3S located near the toe of the ash basin Cell 2/3 main dam. Boron concentrations in monitoring wells screened within the deep flow layer exceeded the 2L Standard within ash basin Cell 1 at AB- 1 D and AB-1 OD, and at compliance well MW-11 D located at the toe of the ash basin Cell 2/3 main dam. Boron concentrations in monitoring wells screened within the bedrock flow layer exceeded the 2L Standards at AB-9BRU near the ash basin Cell 2/3 main dam. • Chromium concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard at background well BG-1 S; near the compliance boundary north of ash basin Cell 2 at GWA-6S and GWA-7S; and near the compliance boundary west of ash basin Cell 1 at GWA-11 S. Chromium concentrations in the S wells generally exhibited a significant difference between unfiltered and filtered concentrations, indicating that some exceedances may be related to turbidity. Chromium concentrations in monitoring wells screened within the deep flow layer exceeded the 2L Standard within ash basin Cell 1 at AB- 1 OD, beneath the ash storage area at AS-31D, near the compliance boundary west of ash basin Cell 1 at GWA-11 D, and near the compliance boundary south of Cell 1 at GWA-1 D. Chromium concentrations in monitoring wells screened within the bedrock flow layer exceeded the 2L Standards within ash basin Cells 2/3 at AB-6BRU, AB-7BRU, and AB-9BR; and near the compliance boundary east of Cell 2 at GWA-2BR. Cobalt concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard at all locations, including the background locations, with the exception of GWA-1 S, GWA-1OS, MW-7S, MW-9S, and, MW-12S. Cobalt concentrations in monitoring wells screened within the deep flow layer exceeded the IMAC beneath the ash storage area at AS-2D; near the compliance boundary north of ash basin Cell 1 at GWA-81D, GWA-91D, and GWA-22D; near the compliance boundary south of Cell 1 at MW-7D and MW-8D; and near the compliance boundary north of ash basin Cell 3 at GWA-41D. Cobalt concentrations in monitoring wells screened within the bedrock flow layer exceeded the IMAC within ash basin Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 11.0 HYDROGEOLOGICAL INVESTIGATION Cell 2 at A13-613RU and near the compliance boundary north of Cell 2 at GWA-613RU. Cobalt has more exceedances in the shallow flow layer than in the deep and beadrock flow layer. • Iron concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard at all locations with the exception of BG-2S, MW-6S, MW-9S, MW-12S, AS-1 S, GWA-1 S, and GWA-10S. Iron concentrations in monitoring wells screened within the deep flow layer exceeded the 2L Standard beneath the ash storage area at AS-21D and AS-31D; near the compliance boundary north of ash basin Cell 1 at MW-91D, GWA-81D, and GWA-9D; near the compliance boundary south of Cell 1 at MW-71D and MW-8D; near the compliance boundary north of ash basin Cell 3 at GWA-4D; and near the compliance boundary west of ash basin Cell 2 at GWA-71D. Iron concentrations in monitoring wells screened within the bedrock flow layer exceeded the 2L Standards within ash basin Cell 2 at AB-413RU, AB- 613RU, and AB-9BR; within ash basin Cell 3 at A13-713RU; near the compliance boundary east of Cell 3 at GWA-313RU; near the compliance boundary east of Cell 3 at GWA-2BRU; and near the compliance boundary north of Cell 2 at GWA-513RU and GWA-6BRU. Iron exhibited a significant difference between unfiltered and filtered analyses, indicating that turbidity/suspended solids may be affecting unfiltered iron analyses. • Manganese concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard at all locations with the exception of BG-3S, MW-6S, MW-7S, MW-9S, GWA-1 S, and GWA-10S. Manganese concentrations in monitoring wells screened within the deep flow layer exceeded the 2L Standard beneath the ash storage area at AS-21D; within ash basin Cell 1 at AB-2D; near the compliance boundary south of Cell 1 at MW-7D; near the compliance boundary north of Cell 1 at GWA-81D, GWA-91D, and GWA-22D; and near the compliance boundary north of ash basin Cell 2 at MW-10D. Manganese concentrations in monitoring wells screened within the bedrock flow layer exceeded the 2L Standard within ash basin Cell 2 at AB-613RU; within ash basin Cell 3 at A13-713RU; and north of Cell 2 at GWA-513RU, GWA-6BRU, and GWA-12BRU. Manganese concentrations generally tend to be highest in shallow wells on the northern portion of the site. Manganese generally tends to be higher in S wells than in D/BR wells across the site. • Nickel concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard within the ash storage area at AS-1S. No other excedances of nickel were noted within the deep or bedrock flow layer monitoring wells. • Selenium concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard within the ash storage area at AS-1 S. There were no selenium concentrations exceeding the 2L Standard in monitoring wells screened within the deep flow layer. Selenium concentrations in monitoring wells screened within the bedrock flow layer exceeded the 2L Standards within ash basin Cell 2 at A13-413R. • Sulfate concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard within the ash storage area at AS-1 S and near the compliance boundary north of ash basin Cell 2 at GWA-6S. Sulfate concentrations in monitoring wells screened within the deep flow layer exceeded the 2L Standard near the compliance boundary north of ash basin Cell 2 at MW-10D. Camparing the ionic composition of groundwater samples from GWA-6S and MW-10D to ash porewater samples (see Section 10.7) indicates the groundwater and porewater exhibit different hydrochemical facies which may indicate sulfate exceedances in these wells may not be due to the ash basin. Sulfate concentrations in Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 11.0 HYDROGEOLOGICAL INVESTIGATION monitoring wells screened within the bedrock flow layer exceeded the 2L Standard near the compliance boundary north of ash basin Cell 2 at GWA-6BR and GWA-6BRU and near the compliance boundary east of Cell 2 at GWA-2BR. Comparing the ionic composition of groundwater samples from GWA-6BR, GWA-6BRU, and GWA-2BR to ash porewater samples (see Section 10.7) indicates the groundwater and porewater exhibit different hydrochemical facies which may indicate that the sulfate exceedances in these wells may not be due to the ash basin. • TDS concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard within the ash storage area at AS-1 S and near the compliance boundary north of ash basin Cell 2 at GWA-6S. TDS concentrations in monitoring wells screened within the deep flow layer exceeded the 2L Standard near the compliance boundary north of ash basin Cell 2 at MW-10D. TDS concentrations in monitoring wells screened within the bedrock flow layer exceeded the 2L Standard near the compliance boundary north of ash basin Cell 2 at GWA-6BR and GWA-6BRU, and near the compliance boundary east of Cell 2 at GWA-2BR. Locations of these TDS exceedances match locations where sulfate exceeded its 2L standard. • Thallium concentrations in monitoring wells screened within the shallow flow layer exceeded the 2L Standard within the ash storage area at AS-1 S. There were no thallium concentrations exceeding the 2L Standard in monitoring wells screened within the deep or bedrock flow layers. • Vanadium concentrations exceeded the IMAC in all wells screened within the shallow, deep, and bedrock flow layers with the exception of MW-6S. The relative concentrations of vanadium are generally higher in the deep then in the bedrock wells and shallow wells. 11.7 Groundwater / Surface Water Interaction As discussed in Section 5.2, shallow and deep groundwater flow typically follows the topographic gradient and shallow groundwater generally discharges to nearby surface water bodies (i.e. streams). Groundwater/surface water interaction is evident at the site based on the potentiometric surface maps for the shallow flow layer, and to a lesser extent, for the deep flow layer in Figures 6-5 and 6-7. These figures illustrate a mounding effect where the ponded water within the ash basin is driving groundwater flow towards the Yadkin River and toward the unnamed tributaries to the Yadkin River located near the eastern and western extents of Buck. The ponded areas are areas of recharge to the underlying flow layers as indicated by groundwater elevations near the ponded areas generally correlating with the ponded water elevations. Fluctuations in water level within the Yadkin River will not have a significant effect on groundwater flow at Buck except at locations immediately adjacent to the river. The topographic relief in the area is such that the typically minor fluctuations in river stage are small compared to the elevations of the ash ponds. A survey performed in July 2015 indicated the stage within the Yadkin River was at approximately elevation 620 feet while ponded water elevations within Cells 1, 2, and 3 of the ash basin were approximately 700, 682, and 673 feet, respectively. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 11.0 HYDROGEOLOGICAL INVESTIGATION 11.8 Estimated Seasonal High and Seasonal Low Groundwater Elevations — Compliance and Voluntary Wells Estimated Seasonal Low (ESL) and Estimated Seasonal High (ESH) groundwater elevations were calculated using historical groundwater elevations for select compliance and voluntary wells at the site. The calculated ESL and ESH depth to water (DTW) was performed statistically by multiplying the standard deviation of the historical DTW measurements by a factor of 1.2 then adding to the mean DTW measurement. To obtain the site modification factors for ESL and ESH conditions, the calculated ESL and ESH DTW in the historical site wells were compared to the current groundwater levels on site and the difference was calculated. The difference between ESH and ESL DTW and current conditions was then averaged for the representative site wells to create a modification factor to add to current DTW. Compliance wells MW-8S, MW- 9S, MW-1OD, MW-11S, MW-12S and MW-13D were selected as the most representative shallow wells for natural seasonal fluctuations at the site, as they are located away from the ash basin and are, therefore, less likely to be influenced by the water level in the ash basin system. Appendix H summarizes calculated ESH and ESL groundwater elevations for newly installed groundwater monitoring wells. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 12.0 SCREENING -LEVEL RISK ASSESSMENT 12.0 Screening -Level Risk Assessment The prescribed goal of the human health and ecological screening level risk assessments is to evaluate the analytical results from the COI sampling and analysis effort and using the various criteria taken from applicable guidance, determine which of the COls may present an unacceptable risk, in what media, and therefore, should be carried through for further evaluation in a baseline human health or ecological risk assessment or other analysis, if required. Contaminants of Potential Concern (COPCs) are those COls that have been identified as having possible adverse effects on human or ecological receptors that may have exposure to the COPCs at or near the site. The COPCs serve as the foundation for further evaluation of potential risks to human and ecological receptors. To support the CSA effort and inform corrective action decisions, a screening level evaluation of potential risks to human health and the environment to identify preliminary, media -specific COPCs has been performed in accordance with applicable federal and state guidance, including the Guidelines for Performing Screening Level Ecological Risk Assessments within the North Carolina Division of Waste Management (NCDENR, 2003). The criteria for identifying COPCs vary by the type of receptor (human or ecological) and media, as shown in the comparison of contaminant concentrations in various media to corresponding risk -based screening levels presented in Tables 12-1 through 12-8. In the human health and ecological screening level risk assessments, the maximum concentrations detected for all COls, [or other appropriate data point (i.e., the analytical reporting limit [RL]) in the 2015 sampling and analyses for coal ash detection and assessment monitoring analytes were compared against established and conservative human health and ecological screening toxicity reference values, likely to be protective for even the most sensitive types of receptors. These comparisons are used to determine which COls present a potentially unacceptable risk to human and/or ecological receptors and may warrant further evaluation. Those COls determined to pose a potential for adverse impacts are identified as preliminary COPCs. Other factors that will be considered qualitatively in the evaluation of final COPCs that would be incorporated into a baseline risk assessment include frequency of detection and a comparison to background. Site- and media -specific risk -based remediation standards may be calculated, pending additional sample collection, if and where additional sampling and site -specific standards are deemed necessary. 12.1 Human Health Screening 12.1.1 Introduction This screening level human health risk assessment has been prepared in accordance with applicable NCDENR and USEPA guidance and the approved Work Plan. 82 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 12.0 SCREENING -LEVEL RISK ASSESSMENT 12.1.2 Conceptual Site Model The Conceptual Site Model (CSM) is a dynamic tool for understanding site conditions and potential exposure scenarios for human receptors that may be exposed to site -related contamination. The CSM provides graphical representation of the following: • A source and mechanism of chemical release; • A retention or transport medium for COPCs; • A point of contact between the human receptor and the medium; and • A route of exposure to constituents for the potential human receptor at the contact point. An exposure pathway is considered complete only if all four "source to receptor" components are present. A CSM has been prepared illustrating potential exposure pathways from the source area to possible receptors (see Figure 12-1). The information in the CSM has been used in conjunction with the analytical data collected as part of the CSA to determine COPCs for the site. Potential receptors are defined as human populations that may be subject to contaminant exposure. Both current and future land and water use conditions were considered when determining exposure scenarios. Current and future land use of the Buck site and associated ash basin and ash storage area is expected to remain predominantly industrial while decommissioning of the coal-fired generating station is in progress (HDR 2014d). The BCCS natural gas facility will remain in active use for the foreseeable future. Lands surrounding the site include residential, undeveloped and recreational areas, as well as Yadkin River, which supplies water to various municipalities. The following potential receptors are identified in the CSM: • Current/future on -site construction worker with potential exposure to groundwater in trenches, surface and subsurface soil and surface water; • Current/future on -site outdoor worker with potential exposure to surface soil and surface water; • Current/future adult and child off -site resident with potential exposure to surface soil and groundwater; and • Current/future on -site trespasser with potential exposure to surface soil, surface water and sediment. Other exposure pathways for all potential receptors were evaluated and it was determined that they would not have a significant impact on the risk assessment (e.g., outdoor worker inhalation of inorganics in surface water in open air). Other exposure scenarios will also serve as surrogates that will provide information about the magnitude of these potential risks. The following presents a description of each receptor and potentially complete exposure pathway: 83 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 12.0 SCREENING -LEVEL RISK ASSESSMENT 12.1.2.1 Current/Future Construction Worker It was assumed that construction activities during decommissioning and restoration of Buck could take place on -site and that construction workers would potentially be exposed to COPCs in various media during this timeframe. The potentially complete exposure pathways include incidental ingestion, dermal contact and particulate inhalation exposure to surface and subsurface soil. Construction workers in a trench with contact to groundwater may have inhalation of metal COPCs with inhalation toxicity criteria and incidental ingestion of and dermal contact (over limited parts of the body) with groundwater. Given the presence of the ash basin and ash storage area, dermal contact and incidental ingestion exposure to surface water would also be considered a potentially complete exposure pathway for this receptor. 12.1.2.2 Current/Future Outdoor Worker Outdoor workers are assumed to be involved with non -intrusive activities (e.g., landscapers that will maintain the site). This receptor reflects a longer timeframe and different exposure pathways than that of construction workers. Outdoor workers are assumed to have incidental ingestion, dermal contact and particulate inhalation exposure to surface soil as well as dermal contact and incidental ingestion exposure to surface water (e.g., ash basins). Exposure to COPCs in groundwater is not identified in the CSM because outdoor workers are assumed not to ingest untreated water; any COPCs aerosols or fumes will dissipate in open air, and there is limited opportunity for dermal contact. Construction worker exposure scenarios are considered a conservative surrogate to estimate the potential risk from groundwater to outdoor workers. 12.1.2.3 Current/Future Off -Site Resident (Adult/Child) The potential for off -site residents to be exposed to COPCs in untreated groundwater is included in the CSM, as approximately 170 private water supply wells and springs were identified in Rowan County within a 0.5-mile radius of the ash basin compliance boundary south of the Buck site, as described in Section 4.0 above and the 2014 Drinking Water Supply Well and Receptor Survey and its Supplement (HDR 2014a and b) (Figure 4-1). These exposures will consider all on and off -site monitoring well data, excluding the receptor survey data, which is being handled independent of this risk analysis. Exposure routes are to include ingestion of groundwater (not incidental, but potable use) as well as dermal contact during bathing/showering and inhalation during bathing/showering for those metals in groundwater with available inhalation -based toxicity criteria. Residents are potentially exposed to contaminants in surface soil during non -intrusive outdoor activities (e.g., lawn mowing); the potential exposure pathways include ingestion, dermal and inhalation of soil particulates. The Yadkin River is a public drinking water supply that is treated before consumption (Salisbury - Rowan Utilities, 2015); therefore, residential exposure to COPCs in untreated surface water has not been evaluated. 84 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 12.0 SCREENING -LEVEL RISK ASSESSMENT 12.1.2.4 Current/Future Trespasser (Adolescent/Adult) Trespassers may come into direct contact with or incidentally ingest surface water and sediment while on -site and near the Yadkin River during what is assumed to be predominantly recreational activity. This will occur at different rates depending on the specific activity and setting. The exposure parameters for this scenario will be determined and will incorporate all on - and off -site data for these media. Exposure routes are to include incidental ingestion, dermal contact and particulate inhalation of surface soil, as well as incidental ingestion and dermal contact with surface water and sediment. This receptor reflects greater exposure to surface water, sediment and soil COPCs compared to potential exposures of similar potential receptors (e.g., off -site recreator). 12.1.3 Human Health Risk -Based Screening Levels A comparison of contaminant concentrations in various media to corresponding risk -based screening levels has been made and is presented in Tables 12-1 through 12-5. These include: • Groundwater: USEPA tap water RSLs, NCDENR 2L Standards, and North Carolina interim maximum allow concentration (IMAC) criteria • Soil: USEPA industrial soil Regional Screening Levels (RSLs) at a target cancer risk of 1 E-06 and noncancer Hazard Quotient of 0.1 • Surface water: USEPA National Recommended Water Quality Criteria and NCDENR 2B Standards, considering the surface water classification for local water bodies • Sediment: USEPA residential soil RSLs Table 12-1 presents the Comparison of Groundwater Sample Concentrations to USEPA Tap water Regional Screening Levels, NCDENR 2L Standards and IMAC criteria; Table 12-2, the Comparison of Soil Sample Concentrations to USEPA Residential and Industrial Soil Regional Screening Levels; and Table 12-3, the Comparison of Sediment Sample Concentrations to USEPA Residential Soil Regional Screening Levels. Table 12-4 present a summary of the COls that were detected at concentrations exceeding their relevant human health or other applicable criteria on a media -specific basis, in groundwater, surface water, sediment, and soil. Those COls exceeding relevant screening criteria are identified as COPCs for purposes of this human health risk assessment. • In groundwater, lead, titanium and zinc were eliminated as COPCs. With the exception of sodium, which was retained because no screening value were available for comparison, all other COls exceeded their respective screening value. See Table 12-1 for maximum concentrations detected, the detailed screening results, identification of COPCs and contaminant categories. • Arsenic, cobalt, iron and manganese were detected at concentrations exceeding the industrial soil screening levels and are determined to be COPCs. Sodium was retained 85 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 12.0 SCREENING -LEVEL RISK ASSESSMENT by default, because the RL for this analyte exceeded the screening value. See Table 12- 2 for the soil COI maximum concentrations, COPCs and contaminant category data. Aluminum, arsenic, cobalt, iron, manganese and vanadium are determined to be COPCs based on exceedances of screening values. Antimony and thallium are retained because the RL was used as maximum detected value or the RL exceeded screening values; sodium was retained because no comparison criteria were available. Sediment COPCs and contaminant categories are presented in Table 12-3. COls were not screened out as COPCs based on a comparison to background concentrations, as USEPA recommends all COls exceeding risk -based screening levels be considered in a baseline risk assessment (USEPA 2002). Statistical background concentrations have been developed as Prediction Limits (PLs), calculated for each COI using groundwater data in site background wells. PLs are a calculation of the upper limit of possible future values based on the Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities Unified Guidance (USEPA, March 2009). If concentrations of COI detected exceed the PL, then the groundwater concentrations are assumed to have increased above background levels. Site -specific background concentrations will be considered in the uncertainty section of the baseline risk assessment, if determined to be required. 12.1.4 Site -Specific Risk Based Remediation Standards Based on the results of the comparison to risk -based screening levels, media -specific remediation standards will be calculated in accordance with the Eligibility Requirements and Procedures for Risk -Based Remediation of Industrial Sites Pursuant to North Carolina General Statute 130A-310.65 to 310.77 should additional sample collection and site -specific standards be deemed necessary. 12.1.5 NCDENR Receptor Well Investigation Approximately 90 off -site private water supply wells and one public water supply well were sampled and analyzed for constituents as part of the NCDENR well testing program, as described in Section 4.0. At Buck, vanadium ranged from 1.63--97.86 pg/L in the wells sampled; iron from 323-5720 fag/L; manganese, 80.5-108 pg/L; and zinc from 2090 to 2600 pg/L. Vanadium, iron, lead, manganese and zinc concentrations exceeded applicable drinking water standards. NCDENR recommended that 74 wells not be utilized for drinking water due to presence of vanadium, hexavalent chromium, iron, manganese, sodium, sulfate, and/or cobalt in one or more of these wells. All of the off -site private water supply wells are upgradient of the ash basin. 12.1.6 Human Health Risk Screening Summary A human health CSM was developed to identify potential pathways of exposure from COPC source to receptor populations; including several possible exposure scenarios. Maximum concentrations of COls were compared to media -specific screening levels; COls exceeding screening levels and those having no screening levels or issues with RLs were retained as COPCs, in accordance with guidance. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 12.0 SCREENING -LEVEL RISK ASSESSMENT As a result of the screening, three COls, lead, titanium and zinc were excluded as COPCs in groundwater. Arsenic, cobalt, iron and manganese were retained as COPCs as a result of exceeding their respective screening values; sodium was retained by default due to a lack of screening criteria. Six COls (i.e., aluminum, arsenic, cobalt, iron, manganese and vanadium) are determined to be COPCs based on exceedances of their screening values in sediment. 12.2 Ecological Screening 12.2.1 Introduction This screening -level ecological risk assessment (SLERA) has been prepared in accordance with the Guidelines for Conducting a Screening Level Ecological Risk Assessments within the North Carolina Division of Waste Management (NCDENR, 2003). An ecological CSM has been developed for this site and is provided as Figure 12-2. 12.2.2 Ecological Setting 12.2.2.1 Site Summary Refer to Section 2.0 for a description of the Buck site. 12.2.2.2 Regional Ecological Setting The site is located in the Southern Outer Piedmont eco-region of North Carolina adjacent to Yadkin River; this eco-region is bordered by the Northern Inner Piedmont and Carolina Slate Belt eco-regions (Griffith et al. 2002). 12.2.2.3 Description of the Eco-Region and Expected Habitats The region consists of irregular plains and low to moderate gradient streams with less precipitation and elevation than the Inner Piedmont. The common rock types include gneiss, schist and granite covered by deep saprolite and mostly red, clayey subsoil. Land cover consists of mixed white oak forests, croplands and pastures, as well as pine plantations (Griffith et al. 2002). 12.2.2.4 Watershed in which the Site is Located The site is located in the Yadkin — Pee Dee River Basin watershed. The North Carolina portion of the river basin encompasses approximately 7,200 miles. 12.2.2.5 Average Rainfall The average annual precipitation for Salisbury has been 42.81 inches over the past 30 years. The average for the State of North Carolina is 48.87 inches (Weather DB, 2015). Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 12.0 SCREENING -LEVEL RISK ASSESSMENT 12.2.2.6 Average Temperature The average temperature for Salisbury is 59.55' F. The average winter temperature is 46.60 F. The average spring temperature is 55' F. The average summer temperature is 75.5° F and average fall temperature is 61.10 F (Weather DB, 2015). 12.2.2.7 Length of Growing Season According to the North Carolina State University Cooperative Extension, the average growing season for Rowan County is 201 days, with a standard deviation of 16 days. 12.2.2.8 Threatened and Endangered Species that use Habitats in the Eco-Region A list of threatened and endangered species for Rowan County is provided in Table 12-8. 12.2.2.9 Site -Specific Ecological Setting An ecological checklist and habitat figure has been completed for this site and is provided in Appendix I. The site is located on the Yadkin River (headwater of High Rock Lake) in Rowan County near the town of Salisbury, North Carolina. The June 2015 AMEC Natural Resources Technical Report identified ten potential jurisdictional wetland areas on the site measuring a total of approximately 13.9 acres. No open water areas were identified. There were 11 potential jurisdictional drainage features; nine intermittent and two perennial streams. Portions of the Buck site adjacent to High Rock Lake are within the regulated 100-year flood zone (AMEC, 2015). Requests for information were submitted to several federal and state agencies, in accordance with the North Carolina Guidelines for Performing Screening Level Ecological Risk Assessments (NCDENR, 2003). A copy of the requests and responses are provided in Appendix I and a summary of the information is provided, as follows. North Carolina Department of Cultural Resources In a letter dated June 23, 2015, the North Carolina Department of Cultural Resources indicated that there are "no historic resources which would be affected by the project'. North Carolina Natural Heritage Program In a letter dated June 9, 2015, the North Carolina Natural Heritage Program (NCNHP) provided information obtained from their database, both for the Buck site and within a one -mile radius of the site (see Appendix 1). According to the NCNHP database, High Rock Reservoir Wetlands, a Natural Area, is located within the site. One Managed Area, North Carolina Agricultural Development and Farmland Preservation Trust Fund Easement, is located within the site. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 12.0 SCREENING -LEVEL RISK ASSESSMENT Two Natural Areas, Leonard Road Slopes and Yadkin River/Grants Creek Forests, are within a one -mile radius of the site. Managed Areas, Linwood Game Land and two North Carolina Agriculture Development and Farmland Preservation Trust Fund Easements, are within a one - mile radius of the site. North Carolina Wildlife Resources Commission In a letter dated June 19, 2015, the North Carolina Wildlife Resources Commission reported the following: • The site drains to High Rock Lake in the Yadkin -Pee Dee River basin. • There are records for the federal species of concern and state special concern Eastern small -footed bat (Myotis leibii) and the state threatened Eastern lampmussel (Lampsilis radiata) near the site. In addition, there are historical records for the federal species of concern and state special concern — vulnerable Carolina birdfoot-trefoil (Acmispon helleri) near the site. • Bald eagles nest and forage in the area. • The site is breeding and roosting habitat for migratory waterfowl species including, but not limited to, gadwall, mallard, green -winged teal, ring-necked duck, American black duck, and wood duck. Other species that have been documented in the area, but not necessarily on the site, include: hooded merganser, ruddy duck, canvasback, scaup, bufflehead, and redhead. In addition, the Buck site is nesting habitat for Osprey and there are records for colonial wading bird colonies (great blue heron and great blue heron/great egret) on or adjacent to the site. • The site is used by migratory waterfowl (see species list above). • There is recreational fishing in High Rock Lake. Recreational species include: striped bass, largemouth bass, channel catfish, white crappie, black crappie, bluegill, white bass, and flathead catfish. United States Department of Agriculture, National Forests in North Carolina In an email dated May 28, 2015, it was reported that there are no Designated and Proposed Federal Wilderness and Natural Areas, National Preserves and Forests, or Federal Land Designated for the Protection of Natural Ecosystems with a half -mile of Buck . United States Department of the Interior, National Park Service In an email dated June 3, 2015, the United States Department of the Interior, National Park Service indicated that "the NPS has not identified any resource concerns at this time". 12.2.2.10 On -site and Off -site Land Use On -site land use is approximately 30% heavy industrial, 5% light industrial, 55% undisturbed, and 10% water bodies and cleared areas. Land use within a one -mile radius of the site is 50% undisturbed, 20% residential, 20% agricultural, and 10% waterbodies (including the Yadkin River). m Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 12.0 SCREENING -LEVEL RISK ASSESSMENT 12.2.2.11 Habitats within the Site Boundary Based on HDR's July 8, 2015 site visit, the following habitats are present on the Buck site. • 166 acres of Mixed Hardwoods • 40 acres of Pine Plantation • 37 acres of Bottomland Hardwoods 10 acres of Shrub/Scrub 126 acres of Open Fields • Aquatic features including ash basins, streams, and wetlands For a detailed description of habitats, refer to the Checklist for Ecological Assessments located in Appendix I. 12.2.2.12 Description of Man-made Units that may Act as Habitat A 171-acre ash basin system (i.e., three cells) is present on site and may act as man-made habitat. 12.2.2.13 Site Layout and Topography The natural topography at the Buck site ranges from an approximate high elevation of 740 feet near the southwest edge of the property near Dukeville Road to an approximate low elevation of 620 feet at the interface with the Yadkin River on the northern extent of the site. Topography generally slopes from a south to north direction with an elevation loss of approximately 120 feet over an approximate distance of 1.1 miles. 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 (HDR, 2014). 12.2.2.14Surface Water Runoff Pathways Swales, drainage ditches, and groundwater seeps were observed during HDR's July 8, 2015 site visit. Unnamed drainage features are located near the western and eastern edges of the site and generally flow south to the Yadkin River. 12.2.2.15Soil Types Based on lithological data obtained from soil boring and well installation activities conducted by HDR during ash basin closure assessment activities (HDR, 2014C), subsurface stratigraphy consists of the following material types: fill, ash, residual soil, saprolite, alluvium, PWR, and bedrock. In general, residual soil, saprolite, and PWR were encountered on most areas of the Buck site. Ash was encountered within the ash basin and ash storage area, while alluvium was restricted to areas adjacent to historical drainage features in the northwest portion of ash basin Cell 1 and the northeast portion of Cell 3 (i.e., near the Cell 1 and Cell 3 dams). Bedrock was encountered between 67 feet and 113 feet in several deep borings completed within ash basin Cells 1, 2, and 3 (HDR, 2014). Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 12.0 SCREENING -LEVEL RISK ASSESSMENT During AMEC's review of the National Resource Conservation Service (NRCS) Soil Survey indicated the presence of a number of soil map units, including Cecil sandy loam (CcC), Cecil sandy clay loam (CeB2 and CeC2), Chewacla (ChA), Enon fine sandy loam (EnB and EnC), Hiwassee clay loam (HwB2 and HwC2), Mecklenburg clay loam (MeB2 and McC2), Pacolet sandy loam (PaD), Pacolet sandy clay loam (PcC2), Poindexter-Mocksville complex (PxD), loamy Udorthents (Ud), Vance sandy loam (VaB and VaC), Vance sandy clay loam (VnB2), Wahee loam (WaA), and open water (W) (AMEC, 2015). 12.2.2.16Species Normally Expected to Use Site under Relatively Unaffected Conditions Terrestrial communities occur in both natural and disturbed habitats in the study area; these may support a diversity of wildlife species. Information on the species that would normally be expected to use this and similar sites in the Piedmont eco-region under relatively unaffected conditions was obtained from relevant literature, mainly the Biodiversity of the Southeastern United States, Upland Terrestrial Communities (Wiley and Sons, 1993). Mammal species that may be present include eastern cottontail (Sylvilagus floridanus), gray squirrel (Sciurus carolinensis), various vole, rat and mice species, red (Vulpes vulpes) and gray fox (Urocyon cinereoargenteus), raccoon (Procyon lotor), Virginia opossum (Didelphis virginiana), and white-tailed deer (Odocoileus virginiana). Avian species are the most diverse. Canopy dwellers include the great crested flycatcher (Myiarchus crinitus), Carolina chickadee (Parus carolinensis), tufted titmouse (P. bicolor), white breasted nuthatch (Sitta carolinensis), blue -gray gnatcatcher (Polioptila caerulea), red -eyed vireo (Vireo olivaceus), yellow -throated vireo (V. flavifrons), various warblers and tanagers, and American redstart (Setophaga ruticilla). Subcanopy species include a variety of woodpeckers, eastern pewee (Contopus virens), Acadian flycatcher (Empidonax virescens), American crow (Corvus brachyrhynchos), blue jay (Cyanocitta cristata), and Carolina wren (Thryothorus ludovicianus). Catbirds (Dumetella carolinensis), brown thrashers (Toxostoma rufum), and mockingbirds (Mimus polyglottos) are found along adjacent brushy edges, fields, and thickets. Understory species include wood thrush (Hylocichla mustelina), American robin (Turdus migratorius), white -eyed vireo (Virea griseus), Kentucky warbler (Oporornis formosus), common yellow -throat (Geothlypis trichas), and yellow breasted chat (Icteria virens). Predatory birds include several hawk and owl species, and the turkey vulture (Cathartes aura). Amphibians and reptiles that tend to be associated with the terrestrial -aquatic interface in streams, rivers, and open waters may include certain turtles (e.g., the Striped Mud and Gulf Coast Spiny Softshell turtles); and frogs, snakes, and amphibians such as the Three -lined salamander. For a more detailed description, see Appendix I. Streams of the southeastern piedmont support a range of aquatic benthic macroinvertebrate groups including mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera), water beetles (Coleoptera), dragonflies and damselflies (Odonata), dobsonflies and alderflies 91 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 12.0 SCREENING -LEVEL RISK ASSESSMENT (Megaloptera), true flies (Diptera), worms (Oligochaeta), crayfish (Crustacea), and clams and snails (Molluscs). Streams, rivers, ponds, and reservoirs support populations of game fish that may include redbreast sunfish (Lepomis auritus), bluegill (Lepomis macrochirus), warmouth (Lepomis gulosus), and largemouth bass (Micropterus salmoides). The most widespread non -game fish species are American eel (Anguilla rostrata), eastern silvery minnow (Hybognathus regius), bluehead chub (Nocomis leptocephalus), golden shiner (Notemigonus crysoleucas), spottail shiner (Notropis hudsonius), whitefin shiner (N. niveus), swallowtail shiner (N. procne), creek chub (Semotilus atromaculatus), creek chubsucker (Erimyzon oblongus), silver redhourse (Moxostoma anisurum), yellow bullhead (Ictalurus natalis), flat bullhead (I. platycephalus), margined madtom (Noturus insignis), and tessellated darter (Etheostoma olmstedi). 12.2.2.17 Species of Special Concern For a detailed list of species of special concern that may be present, see Table 12-8. 12.2.2.18 Nearby Critical and/or Sensitive Habitats For a detailed description, see Section III.D of the Ecological Checklist provided in Appendix I. 12.2.3 Fate and Transport Mechanisms Potential fate and transport mechanisms at/near Buck include erosion, seeps, stormwater runoff and flow of surface water bodies. An Ecological CSM (Figure 12-2) has been prepared illustrating potential exposure pathways from the source area to possible ecological receptors. The information in the Ecological CSM has been used in conjunction with the analytical data collected as part of the CSA to develop an understanding of the sources, pathways and media of exposure as well as the receptors potentially impacted by site -related COPCs. 12.2.4 Comparison to Ecological Screening Levels The sampling and analysis program completed as part of the Buck CSA investigation is described earlier in this report. Media of primary concern for ecological receptors, i.e., surface water, sediment and soil have been sampled extensively, in accordance with the NCDENR approved Work Plan. The results of the comparison of COI concentrations in various media to risk -based screening levels are presented in the following tables: • Table 12-5, a Comparison of Soil Sample Concentrations to USEPA Ecological Soil Screening Levels and USEPA Region IV Recommended Ecological Screening Values; • Table 12-6, the Comparison of Sediment Sample Concentrations to USEPA Region IV Recommended Ecological Screening Values; These tables include the COPCs' respective category 1-5 determination (as applicable) and as described in Section 12.1.3 above. 92 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 12.0 SCREENING -LEVEL RISK ASSESSMENT The potential for ecological risk was also estimated by calculating screening hazard quotients (HQ) using the appropriate screening value of each contaminant and comparing that value to the USEPA Region IV Ecological Screening Values. COls having a HQ greater than or equal to 1 are identified as COPCs. Table 12-7 presents a summary of the COls that were detected at concentrations exceeding their relevant ecological screening media -specific or other criteria. Those COls exceeding the relevant criteria are identified as ecological COPCs for purposes of the SLERA. Note that NCDENR SLERA guidance does not allow for exclusion of COls as COPCs based on a comparison to background concentrations. NCDENR guidance requires a determination of which contaminant category the COPCs fall into as a result of the data comparison to screening levels and is also presented in the ecological COPC tables (Tables 12-6 through 12-8). These include: • Category 1 — Contaminants whose maximum detection exceeds the media specific ecological screening value included in the COPC tables. • Category 2 — Contaminants that generated a laboratory SQL that exceeds the USEPA Region IV media -specific ecological screening value for that contaminant. • Category 3 — Contaminants that have no USEPA Region IV ecological screening value, but were detected above the laboratory SQLs. • Category 4 — Contaminants that were not detected above the laboratory SQLs and have no USEPA Region IV ecological screening value. In soil, all COls except cadmium, lead and mercury, were determined to be COPCs. Aluminum, barium, beryllium, boron, total chromium, cobalt, copper, iron, manganese, molybdenum, nickel, selenium, vanadium and zinc were detected at concentrations exceeding their respective ecological soil screening levels. The other COls were retained based on issues regarding their respective RL exceeding the screening values or a lack of criteria for comparison. These have been retained as COPCs by default. See Table 12-5 for detailed information, including the maximum concentrations detected. For several COPCs, the exceedances are greater than one order of magnitude above the screening levels; these include aluminum, boron, total chromium, iron, and vanadium. COPCs identified in sediment based on a comparison of maximum detected concentrations to available criteria include total chromium, copper, nickel and zinc; aluminum, antimony, arsenic, barium, beryllium, boron, cadmium, cobalt, iron, manganese, molybdenum, selenium, sodium, strontium, thallium, and vanadium were retained due to issues related to their RL exceeding the screening value or there being no screening value available. Lead and mercury have been excluded as COPCs. Details on the COPC screening and contaminant category are provided in Table 12-6. 93 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 12.0 SCREENING -LEVEL RISK ASSESSMENT COls were not screened out as COPCs based on a comparison to background concentrations, as NCDENR SLERA guidance does not allow for screening based on background. Site -specific background concentrations, discussed above in Section 12.1.3, will be considered in the uncertainty section of the baseline ecological risk assessment, if determined to be necessary. 12.2.5 Uncertainty and Data Gaps There are uncertainties inherent in any environmental investigation and risk evaluation that involve the natural heterogeneity of the media, nature, and extent of constituents in the environment, due to their individual fate and transport characteristics, and varied, site -specific conditions. These uncertainties are considered in developing the sampling and analysis plan, data quality assurance processes, and understanding of the site. These screening level assessments are designed to be very conservative in identifying potential COPCs that would be carried forward into a baseline human health, and/or ecological risk assessment. They include all on- and off -site analytical data, and use the maximum concentration detected as the comparison point to applicable screening criteria. Also, no COls were eliminated as COPCs based on background levels; this will be evaluated in the baseline risk assessment, if they are required to be performed. These are highly unlikely to be the actual exposure concentrations, given the natural attenuation, dilution, and distances to potential receptors. There is a high level of confidence that any constituent with potential to impact human health or ecological receptors has been identified as a result of these assessments. 12.2.6 Scientific/Management Decision Point If through the HQ analysis it is determined that COls have been detected at maximum concentrations that exceed applicable screening criteria, that is an indication that additional assessment of potential risks is warranted. This does not mean that impacts are in fact, occurring; only that further data collection or evaluation should be considered. This determination is known as the Scientific/Management Decision Point (SMDP) and the conclusion reached must be one of the following: • There is adequate information to conclude that the ecological risks are neglibible; or • Site has inadequate data to complete the risk characterization. Data gaps need to be filled prior to completion of the screening process; or • The information indicates a potential for adverse ecological effects and a more thorough assessment is warranted. Given that several COPCs have been identified as having a HQ of greater than 1 in soil, surface water and sediment, there is adequate information indicating a potential for adverse effects to occur and further assessment may be warranted. The need for further evaluation should be considered in light of the other ongoing or planned environmental impact studies for this site. 94 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 12.0 SCREENING -LEVEL RISK ASSESSMENT 12.2.7 Ecological Risk Screening Summary Cadmium, lead and mercury are the only COls that have been excluded as COPCs in soil; several COPCs exceed their respective screening criteria by one or more orders of magnitude. Fewer COPCs have been identified in sediment and several of those are retained by default for having no criteria or due to RL issues, not due to maximum concentrations actually exceeding screening criteria. Impacts from limited ecological receptor groundwater exposure are minimal and have not been evaluated. For Buck, identification of potential data gaps and overall coordination of further ecological risk assessment efforts, specifically for surface water and sediment impacts, should consider the other activities that are ongoing related to ash basin closure activities to avoid duplication of effort. 95 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 13.0 GROUNDWATER MODELING 13.0 Groundwater Modeling Groundwater modeling will be performed and submitted in the CAP in accordance with NCDENR's Conditional Approval letter. The groundwater modeling will consist of groundwater flow and fate and transport modeling, performed with MODLFOW and MT3DMS, and batch geochemical modeling, performed with PHREEQC. The following section presents an overview of the fate and transport modeling, the batch geochemical modeling and the site geochemical conceptual model. The CAP will also present a discussion of the geochemical properties of the COls and how these properties relate to the retention and mobility of these constituents. 13.1 Fate and Transport Groundwater Modeling A three-dimensional groundwater flow and contaminant fate and transport model (MODFLOW/MT3DMS Model) will be developed for the ash basin site. The objective of the modeling will be to predict the following in support of the CAP: • Predict concentrations of the COls at the compliance boundary or other locations of interest over time, • Estimate the groundwater flow and constituent loading to surface water discharge areas, and • Predict approximate groundwater elevations in the ash for the proposed corrective action The model and model report will be developed in general accordance with the guidelines found in the memorandum Groundwater Modeling Policy, NCDENR DWQ, May 31, 2007. The groundwater model will be developed from the hydrogeologic conceptual model presented in the CSA, from existing wells and boring information provided by Duke Energy, and from information developed during the site investigation. The model will also be supplemented with additional information developed by HDR from other Piedmont sites, as applicable. The site conceptual model (SCM) is a conceptual interpretation of the processes and characteristics of a site with respect to the groundwater flow, boundary conditions, and other hydrologic processes at the site. Although the site is anticipated in general to conform to the LeGrand conceptual groundwater model, due to the configuration of the ash basin and the boundary conditions present at the site, a three-dimensional groundwater model is warranted. The groundwater modeling will be performed under the direction of Dr. William Langley, P.E., Department of Civil and Environmental Engineering, University of North Carolina Charlotte (UNCC). Groundwater flow and constituent fate and transport will be modeled using Visual MODFLOW 2011.1 (flow engine USGS MODFLOW 2005) and MT3DMS. The modeling process, the development of the model, the development of the hydrostratigraphic layers, the model extent (or domain), and the proposed model boundary conditions were Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 13.0 GROUNDWATER MODELING described in Section 7.0 of the work plan. To date, no changes to the proposed model development are warranted based on data collected during the site investigation. The MUDMS model will use site specific Kd values developed from samples collected along the major flow transects. The testing to develop the Kd terms is underway, but is not complete at this time; therefore, the results of that testing will be presented in the CAP. The methods used to develop the Kd terms was presented in Section 7.7.2 of the work plan. 13.2 Batch Geochemical Modeling As described in the work plan, batch geochemical simulations using PHREEQC will be used to estimate sensitivity of the proposed sorption constants used with MT3DMS and to assist in understanding the mechanisms involved in attenuation of selected constituents. Geochemical modeling using PHREEQC can be used to indicate the extent to which a COI is subject to solubility constraints, a variable Kd, or other processes. PHREEQC can also identify postulated solid phases calculation of their respective saturation indices. The specific locations where the batch geochemical modeling will be performed will be determined after the development of the Kd terms and a review of the site data. 13.3 Geochemical Site Conceptual Site Model SCMs are developed to be a representation of what is known or suspected about contamination sources, release mechanisms, transport, and fate of those contaminants.4 An SCM can be a written and/or graphic presentation of site conditions to reflect the current understanding of the site, identify data gaps, and be updated as new information is collected throughout the project. SCMs can be utilized to develop understanding of the different aspects of site conditions, such as a hydrogeologic conceptual site model, to help understand the site hydrogeologic condition affecting groundwater. SCMs can also be used in a risk assessment to understand contaminant migration and pathways to receptors. On June 25, 2015, NCDENR made the following request: Since speciation of groundwater and surface water samples is a critical component of both the site assessments and corrective action, the Division expects a geochemical site conceptual site model (CSM) developed as a subsection in the Comprehensive Site Assessment (CSA) Reports. The geochemical CSM should provide a summary of the geochemical interactions between the solution and solid phases along the groundwater flowpath that impact the mobility of metal constituents. At a minimum, the geochemical CSM will describe the adsorption/desorption and mineral precipitation/dissolution processes that are believed to impact dissolved concentrations along the aquifer flowpaths away from the ash basin sources. The model descriptions should include the data upon which the conceptual model is based and any calculations (such as mineral saturation indices) that are made to develop the site -specific model. 4 EPA MNA Volume 1 97 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 13.0 GROUNDWATER MODELING Metal speciation analyses cover a broad aspect of metals' geochemistry, including solution complexation with other dissolved species and specific association with aquifer solids, such as a metal adsorbed onto HFO or precipitated as a sulfate mineral. A comprehensive speciation analysis that requires a relatively complete groundwater analysis is expected that includes use of an ion speciation computer code (such as PHREEQC) capable of calculating solution complexes, surface complexation onto HFO, and mineral saturation indices. This type of speciation calculation is necessary for the development of a geochemical SCM and understanding metal mobility in an aquifer. In previous correspondence, NCDENR agreed that the proposed geochemical modeling described in the Work Plan, to be performed using PHREEQC, will be included in the CAP. Specifically, the model descriptions and calculations, such as mineral saturation indices, will be provided in the CAP. This approach will allow completion of the testing to develop the site - specific Kd terms and site mineralogy, and will allow the geochemical modeling to be coordinated with the groundwater flow and transport model. Elements of the geochemical site conceptual site model (GSCM) described below will be incorporated into the fate and transport and the geochemical modeling performed for the CAP. The GSCM will be updated as additional data and information associated with contaminants, site conditions, or processes such as migration of contaminants is developed. The GSCM will be useful in understanding the transport and attenuation factors that affect the mobility of contaminants at the site and the long-term capacity of the site for attenuation and stability of immobilized contaminants. The GSCM will describe the geochemical aspects of the site sources that influence contaminant transport. Site sources at Buck consist of the ash basin and ash storage area. These source areas are subject to different processes that generate leachate migrating into the underlying soil layers and into the groundwater. For example, the ash storage area would generate leachate as a result of infiltration of precipitation, while the ash basin would generate leachate based on the pond elevation in the basin. General factors affecting the geochemistry of the site are as follows: Factors Affecting Ash Formation (Primary Source): • Chemical and mineralogical composition of coal • Thermodynamics of coal combustion process Factors Affecting Leaching in the Ash Basins (Primary Source Release Mechanism): • Chemical composition of ash • Mineral phase of ash • Physical characteristics of ash • Inflow of water into/out of basin • Period of time ash has been in basin • Geochemical conditions in ash basin • Precipitation -dissolution reactions • Sorptive properties of materials in ash 98 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 13.0 GROUNDWATER MODELING Factors Affecting Leaching in the Ash Storage Area (Primary Source Release Mechanism): • Chemical composition of ash in storage area • Mineral phase of ash in storage area • Physical characteristics of ash in storage area • Inflow of precipitation in to ash storage area • Period of time ash has been in storage • Geochemical conditions in ash storage area • Precipitation -dissolution reactions • Sorptive properties of materials in ash Factors Affecting Sorption and Precipitation of Constituents onto Soil/Aquifer Materials Beneath Ash (Secondary Source Release Mechanism): • Chemical composition of soil • Physical composition of soil • Rate of infiltration/percolation of porewater • Chemical composition of leachate infiltrating into soil • Sorption capacity of soil • Geochemistry of groundwater flowing beneath unit Factors Affecting Desorption and Dissolution of Constituents From Soil/Aquifer Materials Beneath Ash (Secondary Source Release Mechanism): • Chemical composition of soil • Physical composition of soil • Rate of infiltration/percolation of porewater • Attenuation capacity of soil • Chemical composition of leachate or precipitation infiltrating into soil • Geochemistry of groundwater flowing beneath unit The results of the Kd testing, the results from the site mineralogy testing, and the geochemical modeling developed in the CAP will be used to refine the GSCM. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 14.0 DATA GAPS — CONCEPTUAL SITE MODEL UNCERTAINTIES 14.0 Data Gaps — SCM Uncertainties 14.1 Data Gaps Through completion of groundwater assessment field activities and evaluation of data collected during those activities, Duke Energy has identified data gaps that will require further evaluation to refine the SCM. The data gaps have been separated into three groups: 1) data gaps resulting from temporal constraints, 2) data gaps resulting from evaluation of data collected during the CSA, and 3) data gaps resulting from other sources. 14.1.1 Data Gaps Resulting from Temporal Constraints Data gaps identified in this category are generally present due to insufficient time to collect, analyze, or evaluate data collected during the CSA activities. It is expected that the majority of these data gaps will be remedied in a CSA supplement to be submitted to NCDENR following completion of the second comprehensive groundwater sampling event. • Mineralogical Characterization of Soil and Rock: a total of 16 soil, three TZ, and nine bedrock samples were submitted to three third -party mineralogical testing laboratories for analysis of soil and rock composition. As of the date of this report, Duke Energy has not received all of the results of this testing; however, results should be available for inclusion in the CSA Supplement. This data is important with regard to evaluating some of the COI concentrations measured above 2L Standards or IMACs and above the background well concentrations. These measured constituent concentrations were identified in cross- or downgradient wells north and west of the source. • Dry Sampling Locations: Due to dry conditions at the time of the initial sampling event, several proposed sampling locations could not be sampled. These locations included NCDENR seep locations (BS SWO01AA S001, BS SWO03AA S001, BSSW074SO01, and BSSW074SO01), two other seep locations noted above (Wet Area Near Pump House and Terracotta Pipe #2), and surface water locations along an unnamed tributary to the Yadkin river located on the east side of the Buck site (SW-1 and SW-2). Two groundwater monitoring wells were also dry at the time of sampling (BG-1 BR and AB- 5D). Another attempt to sample these locations will be made and results will be provided in the CSA Supplement. 14.1.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities A shallow groundwater monitoring well in the nest of GWA-2BRU and GWA-2BR would assist with the groundwater flow direction determination at this location. Two additional monitoring well nests, consisting of a shallow and deep well each, located nortwest and southwest of GWA-2BRU/BR would assist in refining groundwater flow direction in this area and provide information regarding constituent concentrations between Cell 2 and the Cell 3 ponds. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 14.0 DATA GAPS — CONCEPTUAL SITE MODEL UNCERTAINTIES • The bedrock background monitoring well BG-1 BR could not be sampled due to insufficient water in the well during the sampling event. A replacement bedrock background well in this location may be warranted if BG-1 BR is not a viable well. • Groundwater samples were not collected from all of the onsite voluntary wells or existing monitoring wells that were installed during the site closure investigation. During subsequent sampling events, groundwater elevations will be measured and groundwater samples will be collected from these wells in conjunction with the newly installed assessment monitoring wells. • Obtain soil samples located outside of the ash basin for SPLP analysis to compare results against SPLP analysis of ash. • Perform minerology analysis of soil and rock samples in wells where COls are present above 2L Standards or IMACs to determine if constituents occur naturally. 14.1.3 Data Gaps Resulting from Other Sources Sampling of Off -Site Seeps: The Work Plan included obtaining a surface water sample (S-1 A) and samples at two seep locations (S-1 B and S-1 C) associated with an off -site pond located near the eastern extent of Duke Energy's property boundary. Duke Energy was not able to obtain permission from the property owner to gather these samples. Permission to obtain these samples should be pursued for future sampling events. 14.2 Site Heterogeneities Heterogeneities, with regard to groundwater flow, were not identified during completion of the CSA. In general, groundwater within the shallow flow layer, TZ material, and fractured bedrock flows toward small streams/drainage features located near the western and eastern extents of Buck or north toward the Yadkin River. Heterogeneities, with regard to COI concentrations, were not identified during completion of this CSA. However, heterogeneities may be identified following completion of the groundwater model for Buck. 14.3 Impact of Data Gaps and Site Heterogeneities Certain data gaps can be addressed with additional groundwater and surface water sampling at existing wells. As discussed in Section 15, the second comprehensive groundwater sampling event is planned for August/September 2015. A plan for interim groundwater sampling between submittal of the CSA and implementation of the anticipated CAP is proposed in Section 16 and will further supplement the existing data. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 15.0 PLANNED SAMPLING FOR CSA SUPPLEMENT 15.0 Planned Sampling for CSA Supplement The specifics of a second comprehensive sampling event at the Buck site are currently under discussion between NCDENR and Duke Energy. The second sampling event will be conducted to: • Supplement data obtained during the initial sampling event; • Evaluate seasonal variation in groundwater results; and • Potentially collect additional samples for chemical speciation of arsenic, chromium, iron, manganese and selenium, although such additional samples are not currently needed for CAP development or further risk assessment. 15.1 Sampling Plan for Inorganic Constituents All samples collected will be analyzed for total inorganic compounds. Samples with exceedances of 2L Standards or IMACs during the initial sampling event will also be analyzed for dissolved -fraction inorganics. The scope of the second event sampling is anticipated to be the following: • Collection of second set of data for all new site assessment wells, seeps and surface water for CSA Work Plan parameters (including total and dissolved metals using 0.45 pm filters); • Locations that were previously dry will be re-evaluated and sampled if sufficient water is present to do so; and • Collection of dissolved metals data using 0.1 pm filters from the flow transect wells selected for geochemical modeling. 15.2 Sampling Plan for Speciation Constituents Duke Energy and NCDENR are currently conducting discussions concerning the specifics of the requirements for sampling associated with speciation. A summary of the proposed sampling program for the second comprehensive sampling event is included on Table 15-1. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 16.0 INTERIM GROUNDWATER MONITORING PLAN 16.0Interim Groundwater Monitoring Plan CAMA requires a schedule for continued / interim groundwater monitoring. In addition, Duke Energy is required to implement closure and remediation of the Buck ash basin, which is not yet defined in CAMA. However, CAMA does require Duke Energy to submit a proposed closure plan such that NCDENR can prioritize site closure based on risk classifications. As such, Duke Energy plans to conduct interim groundwater monitoring at select wells identified in Table 15-1 to bridge the gap between completion of CSA activities and implementation of the proposed CAP. 16.1 Sampling Frequency Interim groundwater sampling is planned to occur two additional times during 2015/early 2016 (timing will be such that the samples are not auto -correlated), then quarterly until the CAP is approved by NCDENR and implemented by Duke Energy. This sampling frequency will allow for evaluation of seasonal fluctuations in COI concentrations, as well as provide additional data for statistical analysis of site -specific background concentrations. 16.2 Constituent and Parameter List The proposed constituents and parameters for analysis remain the same and are presented in Table 7-3 16.3 Proposed Interim Sampling Locations The proposed sampling locations are to remain the same and are shown on Figure 6-2. 16.4 Proposed Interim Background Wells The proposed background wells are BG-1 S/D/BR, BG-2S/D, BG-3S/BRU, and MW-6S/D. Note that outside of this Interim Groundwater Monitoring Plan, background wells are planned to be sampled a total of four times in 2016. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 17.0 DISCUSSION 17.0Discussion 17.1 Summary of Completed and Ongoing Work To date, the following activities have been completed in support of this CSA: • Installation of 64 groundwater monitoring wells within the ash basin and ash storage area, beyond the waste boundary, and in background locations; • Completion of topographic and well/boring location surveys; • Collection of ash samples from borings completed within the waste boundary and analysis for total inorganics, TOC, anions/cations, SPLP, and physical properties; • Collection of soil samples from borings completed within the waste boundary, beyond the waste boundary, and background locations and analysis for total inorganics, TOC, anions/cations, and physical properties; • Collection of PWR and bedrock samples from borings completed within the waste boundary, beyond the waste boundary, and background locations and analysis for total inorganics, TOC, and anions/cations; • Collection of soil samples for analysis of chemistry and mineralogy; • Collection of rock samples for chemical analysis; • Collection of rock samples for petrographic analysis (thin -sections); • Performance of in -situ horizontal (open hole) and vertical (flush bottom) permeability tests; • Completion of packer tests in 6 bedrock borings; • Completion of rising- and falling -head slug tests in 61 newly installed monitoring wells; • Collection of groundwater samples from 78 newly installed, compliance, voluntary, and previously installed monitoring wells, and analysis of samples for total and dissolved inorganics, and anions/cations; • Speciation of groundwater samples for arsenic, chromium, iron, manganese, and selenium in groundwater samples collected from 46 monitoring wells installed along anticipated groundwater flow transects; • Collection of 7 surface water samples, 13 groundwater seep samples, and 14 sediment samples, and analysis for total inorganics and anions/cations; • Speciation of 21 groundwater seep sample for arsenic, chromium, iron, manganese and selenium; • Evaluation of solid and aqueous matrix laboratory data; • Completion of an updated Receptor Survey; and • Completion of fracture trace analysis; and • Preparation of this CSA Report. The following activities are on -going (as described in more detail in Section 14.1.1) and will be provided to NCDENR in the CSA Supplement: Analysis of soil samples for chemistry and mineralogy and rock samples for chemistry and petrography; 104 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 17.0 DISCUSSION • Evaluation of the need for additional groundwater monitoring wells in the vicinity of the GWA-2 monitoring well cluster to better define groundwater flow and the horizontal and vertical extent of COls in the area. • Additional speciation testing, if necessary, to support groundwater modeling activities; and 17.2 Nature and Extent of Contamination Soil and groundwater beneath the ash basin and ash storage area have been impacted by ash handling and storage at Buck as shown on Figure ES-1. Concentrations of several COls exceeded their respective 2L Standards or IMACs in groundwater beyond the compliance boundary as shown on this figure. Samples obtained from on -site seeps also exhibit concentrations of Cols exceeding their respective 2L Standards or IMACs. As noted on Figure 10-9, exceedances of the 2L Standards and IMACs were observed in nearly all monitoring wells across the site, including in monitoring wells located at the outermost extent of the monitoring well system. Many of these COls were also identified in the background wells and are not related to the ash basin or ash storage area. Preliminary review of these exceedances indicates, in most cases, the exceedances observed at the outermost extent of the monitoring well system are related to background water quality, naturally occurring conditions, and/or sampling conditions. However, in areas downgradient of the source, particularly north of the waste boundary, measured COI concentrations exceeded the 2L Standards or IMACs and were higher than concentrations in background wells. Boron was also measured outside of the compliance boundary on the north side of the site. Since measurements of coal ash indicator COls for upgradient and side -gradient wells were similar to, or below the measured ranges or concentrations in the background wells, there does not appear to be coal ash related contamination south, east or west of the compliance boundary. A second round of sampling will be performed at all locations sampled during the CSA. The results from the CSA sampling, the second round of sampling, and the site -specific background concentrations will be used to further define the source of these observed exceedances at the site. The results of this evaluation will be presented in the CSA supplement. 17.2.1 Groundwater and Seep Contamination COls identified in the source and above background and 2L Standards / IMACs were measured in wells predominately downgradient of the sources. Some of these constituent levels were measured in areas east and west of the source; however, most of these measurements were made north of the source. With the flow direction being predominately south to north, with a western component, the source does not appear to be impacting COI concentrations toward off - site receptors immediately south and east of the of the Buck site; however, additional water level information would be beneficial to better characterize the potentiometric surfaces in the region southeast of GWA-2S/BR. Seep sampling results at the Buck site have identified nine Cols in the seep water: antimony, arsenic, boron, chromium, cobalt, iron, manganese, thallium, and vanadium. Comparing COI concentrations in the seep water to the maximum COI concentrations encountered in 105 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 17.0 DISCUSSION groundwater sampled from the background wells indicates seven seep locations (BSWW002 S001, Terracotta Pipe #1, Culvert Discharge, S-2, S-3, S-5, and S-9) where at least one seep COI concentration exceeded the maximum background groundwater COI concentration. Almost all of the iron exceedances within the seep samples (9 of 10) occurred within unfiltered samples indicating the source of the iron within the seep water is primarily suspended solids. Six COls identified in the seep water (antimony, arsenic, boron, chromium, lead and thallium) occur at concentrations exceeding the applicable groundwater standard at only one or two locations each. 17.2.2 Soil, Rock, and Sediment Contamination Soil samples were obtained from 29 separate drilling locations during CSA drilling within the Buck site (including locations beneath the ash basin and ash storage area). For purposes of this discussion, each drilling location is considered to include all borings drilled at the location (i.e., all S, D, and BRU well borings). Within soil samples obtained from these locations, there are eight COls identified in the soil: arsenic (5 locations), barium (1 location), boron (4 locations), cobalt (29 locations), iron (29 locations), manganese (29 locations), selenium (5 locations), and vanadium (29 locations). With the exception of barium, all of these COls appear within one or more of the background well locations at concentrations exceeding the applicable groundwater standard. The COI concentrations observed in the soil from the various locations within the Buck site generally bracket the concentrations observed within soil samples from the background locations or within a reasonable proximity of the bracketed background concentrations. Rock samples (including PWR samples) were obtained from ten separate drilling locations during CSA drilling within the site (including locations beneath the ash basin and ash storage area). For purposes of this discussion, each drilling location is considered to include all borings drilled at the location (i.e., all S, D, and BRU well borings). Within rock samples obtained from these locations, there are five COls identified in rock: arsenic (1 location), cobalt (8 locations), iron (10 locations), manganese (9 locations), and vanadium (8 locations). With the exception of arsenic, all of these Cols appear within the background location where rock was obtained (BG- 2) at concentrations exceeding the applicable groundwater standard. Sediment samples were obtained from 14 seep locations at the Buck site. Within the sediment samples, there are seven COls identified as constituents in sediment: arsenic (4 locations), boron (1 location), cobalt (14 locations), Iron (14 locations), manganese (13 locations), selenium (1 location), and vanadium (14 locations). A background sediment location (SW-2) was not obtained due to dry conditions at the time of sampling; therefore a comparison of these results with background conditions is not possible at this time. Such a comparison may be possible after completion of the second comprehensive sampling event and will be included in the CSA supplement. 17.3 Maximum Contaminant Concentrations The maximum contaminant concentrations reported in groundwater, ash porewater, seep water, and ash basin water samples collected during the CSA are listed below. 106 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 17.0 DISCUSSION Maximum Contaminant Concentrations for COls in groundwater are shown below: • Antimony: 19.3 pg/L (GWA-2BR) • Arsenic: 14.9 pg/L (AB-4BR) • Barium: 830 pg/L (GWA-2BR) • Boron: 3000 pg/L (AS-1 S) • Chromium: 65.4 pg/L (GWA-7S) • Cobalt: 356 pg/L (AS-1 S) • Iron: 27,900 pg/L (AB-9S) • Manganese: pg/L 4,100 ug/L (AS-1S) • Nickel: 107 pg/L (AS-1S) • Selenium: 30.3 pg/L (AB-4BR) • Sulfate: 703,000 pg/L (AS-1S) • Thallium 0.24 pg/L (AS-1 S) • TDS: 1,040,000 pg/L (GWA-6BR) • Vanadium 67.9 pg/L (GWA-11S) Maximum Contaminant Concentrations for COls in porewater are shown below: • Antimony: 24.4 pg/L (AB-2S) • Arsenic: 1,350 pg/L (AB-2SL) • Barium: 720 pg/L (AB-2SL) • Boron: 6,500 pg/L (AB-4SL) • Cobalt: 14.2 pg/L (AB-4S) • Iron: 14,400 pg/L (AB-5SL) • Manganese: 3,900 pg/L (AB-5SL) • Thallium 0.67 pg/L (AB-8S) • TDS: 565,000 pg/L (AB-2S) • Vanadium: 347 pg/L (AB-2S) Maximum Contaminant Concentrations for COls in seep water are shown below: • Antimony: 2 pg/L (BSWW002 S001) • Arsenic: 50 pg/L (BSWW002 S001) • Boron: 1,000 pg/L (Terracotta Pipe #1) • Chromium: 34.7 pg/L (Culvert Discharge) • Cobalt: 1,050 pg/L (Culvert Discharge) • Iron: 34,900 pg/L (S-2) • Lead 21.9 pg/L (Culvert Discharge) • Manganese: 6,300 pg/L (S-1) • Thallium: 1.1 pg/L (Culvert Discharge) • Vanadium: 174 pg/L (Culvert Discharge) 107 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 17.0 DISCUSSION Maximum Contaminant Concentrations for COls in ash basin surface water are shown below: • Aluminum: 13,000 pg/L (SW-AB2) • Antimony: 5.7 fag/L (SW-AB3) • Arsenic: 71.3 fag/L (SW-AB4) • Cadmium: 0.37 fag/L (SW-AB4) • Chromium: 11.3 fag/L (SW-AB4) • Cobalt: 23.9 fag/L (SW-AB2) • Copper: 32.4 fag/L (SW-AB2) • Iron: 35,000 fag/L (SW-AB4) • Lead: 12.7 fag/L (SW-AB2, SW-AB4) • Manganese: 640 fag/L (SW-AB4) • Thallium: 0.45 fag/L (SW-AB2) • Vanadium: 65.8 fag/L (SW-AB4) • Zinc: 50 fag/L (SW-AB4) • TDS: 560,000 fag/L (SW-AB3) 17.4 Contaminant Migration and Potentially Affected Receptors Groundwater at the Buck site generally flows from south to north toward to the Yadkin River with components of flow to the east and west toward unnamed tributaries to the Yadkin River located near the eastern and western extents of the site. A comparison of COls within samples of seep water to the maximum Cols in groundwater samples obtained from background wells indicates eight seep locations where at least one COI exceeded the maximum background groundwater COI concentration. The seep COls that exceeded background groundwater COls include arsenic, boron, chromium, cobalt, iron, lead, manganese, and vanadium. These seeps drain to either the unnamed tributaries to the Yadkin River located near the eastern and western extents of the Buck site or directly to the Yadkin River near the base of the ash basin Cell 2/3 dam. Based on this information, contaminated groundwater is migrating to these surface water features. A comparison of COls within samples of groundwater obtained from monitoring wells installed near the ash basin compliance boundary to the maximum Cols in groundwater samples obtained from background wells indicates 13 well locations where at least one COI exceeded the maximum background COI concentration. For purposes of this discussion, each well location is considered to include all borings drilled at the location (i.e., all S, D, and BRIJ well borings). These well locations include MW-3, MW-10, MW-11, GWA-1, GWA-2, GWA-3, GWA- 4, GWA-5, GWA-6, GWA-7, GWA-9, and GWA-11. Based on this information, groundwater impacted by the ash basin and ash storage area is migrating downgradient beyond the compliance boundary. The human health and ecological CSMs, provided as Figures 12-1 and 12-2 illustrate the potentially affected receptors; these will be reviewed and revised as necessary based on information indicated above. M Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 18.0 CONCLUSIONS 18.0 Conclusions 18.1 Source and Cause of Contamination The CSA found that the source and cause of impacts (as shown on Figure ES-1) for certain parameters in some areas of the site is the coal ash contained in the ash basin and ash storage area. The cause of this contamination, shown in the referenced figure, is leaching of constituents from the coal ash into the underlying soil and groundwater and subsequent transport of the groundwater downgradient from the ash basin. However, some groundwater, surface water and soil standards were also exceeded due to naturally occurring elements found in the subsurface. 18.2 Imminent Hazards to Public Health and Safety and Actions Taken to Mitigate them in Accordance to 15A NCAC 02L .0106(f) 15A NCAC 02L .0106(g)(2) requires the site assessment to identify any imminent hazards to public health and safety and the actions taken to mitigate them in accordance with Paragraph (f) of .0106(g). The CSA found no imminent hazards to public health and safety; therefore, no actions to mitigate imminent hazards are required. However, corrective actions at the Buck site are required to address soil and groundwater contamination shown on Figure ES-1. These will be addressed as part of the CAP. 18.3 Receptors and Significant Exposure Pathways The requirement contained in the NORR and the CAMA concerning receptors was completed with the results provided in Section 4.0. A screening level human health risk assessment and screening level ecological risk assessment was performed with the results provided in Section 12.0. The identified receptors and significant exposure pathways are identified in the human health and ecological CSMs (Figures 12-1 and 12-2). 18.4 Horizontal and Vertical Extent of Soil and Groundwater Contamination and Significant Factors Affecting Contaminant Transport The CSA identified the horizontal and vertical extent of groundwater contamination within the compliance boundary (as shown on Figure ES-1), and found that the source and cause of the groundwater exceedances within that boundary is a result of both natural conditions and the coal ash contained in the ash basin and ash storage area. In general, COls exceeding 2L Standards or IMACs on the northern side of the waste boundary are judged to be highly influenced by the source. Some of these exceedances were measured outside the compliance boundary, although within the Duke Energy property boundary. M Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 18.0 CONCLUSIONS Background monitoring wells contain naturally occurring metals and other constituents at concentrations that exceeded their respective 2L Standards or IMACs. Examples of naturally occurring constituents include antimony, cobalt, iron, manganese, and vanadium. Some of these naturally occurring constituents were also detected in newly installed background monitoring well groundwater samples at concentrations greater than 2L Standards or IMACs. The horizontal and vertical extent of groundwater impacts above 2L Standards or IMACs is shown, with exception of the areas associated with the data gaps identified in Section 14.1 on Figures 10-10 through 10-51. Groundwater contamination is considered to be present where the analytical results were greater than the site background concentrations and in excess of the 2L Standards or IMACs. The assessment found COI groundwater concentrations above background concentrations for antimony, arsenic, barium, boron, chromium, cobalt, iron, manganese, nickel, selenium, thallium, vanadium, sulfate, and TDS. The approximate extent of groundwater contamination is shown on these figures and is generally limited to an area within the ash basin compliance boundary and the area north of the compliance boundary near the Yadkin River (within the Duke Energy property boundary). Exceedances measured south, east, and west of the waste boundary are judged to be predominately related to natural conditions, although some source related exceedances were identified. All source related exceedances are judged to be within the compliance boundary in these areas; however, some data gaps were identified as discussed in Section 17. The CSA found that the primary direction of flow and mobile contaminant transport is predominately to the north toward the Yadkin River and not towards other off -site receptors. No information gathered as part of this CSA suggests that water supply wells or springs within the 0.5-mile radius of the compliance boundary are impacted by the source. This CSA also identified the horizontal and vertical extent of soil contamination as shown on Figures 8-1 through 8-4. Soil contamination is considered to be present where analytical results for COls were in excess of the maximum site soil background concentrations and in excess of the most restrictive PSRG for each COI. The approximate contaminated soil extent is shown on these figures. The assessment found the soil contaminants in excess of the maximum background soil COI concentrations are arsenic, barium, boron, and iron. The significant factors affecting contaminant transport are those factors that determine how the contaminant reacts with the soil/rock matrix, resulting in retention by the soil/rock matrix and removal of the contaminant from groundwater. The interaction between the contaminant and the retention by soils are affected by the chemical and physical characteristics of the soil, the geochemical conditions present in the matrix (if present), the matrix materials, and the chemical characteristics of the contaminant. Migration of each contaminant is related to the groundwater flow direction, the groundwater flow velocity, and the rate at which a particular contaminant reacts with materials in the respective soil/rock matrix. The data indicates that geologic conditions present beneath the ash basin impedes the vertical migration of contaminants. The two primary mechanisms that immobilize metals (iron and manganese) and semi -metals (arsenic, boron, and selenium) and prevent their movement in groundwater are sorption and ON Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 18.0 CONCLUSIONS precipitation (Ref NCDENR). The major attenuation mechanism for sulfate, a non-metal, is sorption (EPRI). In these processes, the contaminant is in effect removed from groundwater and partitions onto the surface of the soil/rock matrix (adsorption) or precipitates into a solid phase, in both cases, removing the contaminant from groundwater. A number of factors specific to the constituent and to site conditions are involved in determining which of these mechanisms occur and how much of the contaminant partitions out of the groundwater. Sections 7.0, 8.0, 9.0, and 10.0 present the results of testing performed to evaluate the chemical, physical, and mineralogical characteristics of the soil and aquifer materials and the site groundwater. As described above, the determination of the mechanism and the amount of the contaminant removed from the groundwater depends on a number of site specific factors. The adsorptive capacity of the site soils and aquifer materials to the specific groundwater contaminants is evaluated by development of site specific partition coefficient Kd terms, as described in Section 13.0. The Kd testing provides site specific values for the ability and capacity of site soils to remove contaminants from groundwater and will assist in understanding the mechanisms affecting contaminant transport at the site. The Kd tests and the associated groundwater modeling also allow for evaluation of the long-term contaminant loading and the capacity of the site soil and aquifer material to attenuate this loading. The results of this testing, the groundwater modeling, and the evaluation of the long term groundwater conditions at the site will be presented in the CAP. 18.5 Geological and Hydrogeological Features influencing the Movement, Chemical, and Physical Character of the Contaminants Groundwater flow is predominately in the north direction toward the Yadkin River. However, there also is a component of groundwater flow to the west of Cell 1 and there is localized flow in an area east of the source that requires further evaluation (between Cells 2 and 3). Exceedances of COls have been observed in monitoring wells in these areas and near the ash basin west compliance boundary. The exceedances, however, do not include COls identified by the USEPA as indicators of CCR related contamination. Further, the constituents identified with exceedances to the south, east and west of the source have also been identified in the background wells. The initial site conceptual hydrogeologic model presented in the Work Plan, dated December 30, 2014, indicated the geological and hydrogeological features influencing the movement, chemical, and physical characteristics of contaminants are related to the Piedmont hydrogeologic system present at the site. The movement of the contaminants is related to the groundwater flow direction, the groundwater flow velocity, and the rate at which a particular contaminant reacts with materials in the aquifer. The rate of groundwater movement varies with the hydraulic conductivity and porosity of the site soil and rock materials and ranged from 5.3 ft/yr to 91.8 ft/yr in soils, and 4.0E-2 ft/yr to 2.29E-5 ft/yr in rock. M Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 18.0 CONCLUSIONS Other factors include redox conditions, the concentration of the solution, the chemical composition of the solution and the contaminant, and the mineralogy of the soil or rock matrix. The influence of these factors as determined by the chemical, physical, hydrologic, and mineralogical characterization of the ash, ash basin porewater, the groundwater, and the site soil and rock will be incorporated into the groundwater modeling discussed in Section 13.0. Geological and hydrogeological features at the site do not influence the physical character of the constituents other than through the process of sorption and precipitation. The Kd term development and the leaching test results, that will be presented in the CAP, will be key to understanding the influences of the site soils and rock on the constituents. The groundwater model will provide information to allow evaluation of the capacity of the site soil and aquifer material to attenuate the loading imposed by the conditions modeled for the proposed corrective action. 18.6 Proposed Continued Monitoring A plan for continued monitoring of select monitoring wells and parameters/constituents is presented in Section 16.0 and will be implemented following approval of this CSA report. 18.7 Preliminary Evaluation of Corrective Action Alternatives In accordance with CAMA, Duke Energy is required to implement closure and remediation of the Buck ash basin no later than August 1, 2029. Closure for the Buck ash basin was not defined in CAMA. However, CAMA does require Duke Energy to submit a proposed CAP such that NCDENR can prioritize site closure based on risk classifications. No later than December 31, 2015, NCDENR is to develop proposed classifications for all coal combustion residuals surface impoundments, including active and retired sites, for the purpose of closure and remediation. At which time a schedule for closure and required remediation that is based on the degree of risk to public health, safety and welfare, the environment, and natural resources posed by the impoundments and that gives priority to the closure and required remediation of impoundments that pose the greatest risk (CAMA 2014). The classification for the Buck ash basin will be based upon this CSA and the corrective action plan (CAP) which is to be submitted within 90 days of submittal of the CSA. The risk classifications as described in CAMA include: (1) High -risk impoundments shall be closed as soon as practicable, but no later than December 31, 2019. A proposed closure plan for such impoundments must be submitted as soon as practicable, but no later than December 31, 2016. (2) Intermediate -risk impoundments shall be closed as soon as practicable, but no later than December 31, 2024. A proposed closure plan for such impoundments must be submitted as soon as practicable, but no later than December 31, 2017. 112 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 18.0 CONCLUSIONS (3) Low -risk impoundments shall be closed as soon as practicable, but no later than December 31, 2029. A proposed closure plan for such impoundments must be submitted as soon as practicable, but no later than December 31, 2018. Following NCDENR's risk classification determination, a Closure Plan for the ash basin is to be submitted for NCDENR's approval (CAMA 2014). Based on the findings of this CSA report, the future CAP, NCDENR's risk classification, and the approved Closure Plan, appropriate action will be taken for ash basin closure. In the subsequent CAP, Duke Energy will pursue corrective action under 15A NCAC 02L .0106 (k) or (1) depending on the results of the groundwater modeling and the evaluation of the site's suitability to use MNA. This would potentially require evaluation of MNA using the approach found in Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Volumes 1 and 2 (EPA Reference) and the potential modeling of groundwater surface water interaction. If these approaches are found to not be satisfactory, additional measures such as active remediation by hydraulic capture and treatment, among others, would be evaluated. When properly applied, alternatives such as these can provide effective long term management of sites requiring corrective action. 113 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 19.0 REFERENCES 19.0 References AMEC. 2015. Natural Resources Technical Report, Buck Steam Station, Salisbury, North Carolina. June 24. American Society of Testing and Materials. 2014. E1689-95, "Developing Conceptual Site Models for Contaminated Sites," ASTM International, West Conshohocken, PA, DOI: 10.1520/E1689. American Society of Testing and Materials. 2010. D2216, "Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass," ASTM International, West Conshohocken, PA, DOI: 10.1520/ D2216-10. American Society of Testing and Materials. 2010. D4318, "Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils," ASTM International, West Conshohocken, PA, DOI: 10.1520/D4318-10. American Society of Testing and Materials. 2010. D854, "Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer," ASTM International, West Conshohocken, PA, DOI: 10.1520/D0854-1. American Society of Testing and Materials. 2010. D5084, "Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter," ASTM International, West Conshohocken, PA, DOI: 10.1520/D5084-1. American Society of Testing and Materials. 2007. D422, "Standard Test Method for Particle - Size Analysis of Soils," ASTM International, West Conshohocken, PA, DOI: 10.1520/D0422-63 R07. American Society of Testing and Materials. 2001. D2487, "Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)," ASTM International, West Conshohocken, PA, DOI: 10.1520/D2487-11. Agency for Toxic Substances and Disease Registry. 2012. Toxicological profile for Manganese. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service. Barcelona, M. J., Gibb, J. P., et al. 1985. Practical Guide for Ground -water Sampling. Illinois State Water Survey. Department of Energy and Natural Resources. Champaign, Illinois. Butler, J. R. and Secor, D. T., Jr. 1991. The Central Piedmont, in, Horton, J. W., Jr. and Zullo, V. A., eds., The Geology of the Carolinas: The University of Tennessee Press, Knoxville, p. 59-78.Butler, J. R. and Secor, D. T., Jr. 1991. The Central Piedmont, in, Horton, J. W., Jr. and Zullo, V. A., eds., The Geology of the Carolinas: The University of Tennessee Press, Knoxville, p. 59-78. 114 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 19.0 REFERENCES Cunningham, W. L. and Daniel III, C. C. 2001. Investigation of ground -water availability and quality in Orange County, North Carolina: U. S. Geological Survey, Water -Resources Investigations Report 00-4286, 59p. Daniel III, C.C. and Sharpless, N. B. 1983. Ground -water supply potential and procedures for well -site selection upper Cape Fear basin, Cape Fear basin study, 1981-1983: North Carolina Department of Natural Resources and Community Development and U.S. Water Resources Council in cooperation with the U.S. Geological Survey, 73 p. Daniels, J. L. and Das, G. P. 2014. Practical Leachability and Sorption Considerations for Ash Management, Geo-Congress 2014 Technical Papers: Geo-characterization and Modeling for Sustainability. Wentworth Institute of technology, Boston, MA. Deer, W. A., R. A. Howie, and J. Zussman. 1966. An Introduction to the Rock -Forming Minerals: John Wiley & Sons Inc., New York, N. Y., 528p. Dennis, A. J, Secor, D. T., and Shervais, J. W. 2000. Faults bounding eclogite-bearing gneisses: Geological Society of America Abstracts with Program, v. 32 (2), p. A-14. Donahue, J. and Kibler, S. 2007. Georgia Department of Natural Resources. Environmental Protection Division. Groundwater Quality in the Piedmont/Blue Ridge Unconfined Aquifer System of Georgia. Atlanta: 2007. Duke Energy. 2007. Certificate of Public Convenience and Necessity for the Buck Combined Cycle Project, 2007 [Online] URL: at http://www.duke-energy.com/pdfs/Buck-Updated- Preliminary-CPCN-Final-06-29-07.pdf Electric Power Research Institute. 2014. Assessment of Radioactive Elements in Coal Combustion Products, 2014 Technical Report 3002003774, Final Report August 2014. Electric Power Research Institute. 2010. Comparison of Coal Combustion Products to Other Common Materials, 1020556, Final Report September 2010. Electric Power Research Institute. 2009. Electric Power Research Institute, Technical Update — Coal Combustion Products — Environmental Issues — Coal Ash: Characteristics, Management and Environmental Issues, EPRI 1019022. September 2009. Electric Power Research Institute. 2008a. Toxics Release Inventory. Chemical Profile: Arsenic. Palo Alto, CA. Electric Power Research Institute. 2008b. Toxics Release Inventory. Chemical Profile: Selenium. Palo Alto, CA. Electric Power Research Institute. 2005. Chemical Constituents in Coal Combustion Product Leachate: Boron, EPRI, Palo Alto, CA: 2005. Technical Report 1005258. Electric Power Research Institute. 1995. Coal Ash Disposal Manual: Third Edition, EPRI TR- 104137, January 1995. 115 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin FN 19.0 REFERENCES Electric Power Research Institute. 2004. Electric Power Research Institute, "Chemical Attenuation Coefficients for Arsenic Species Using Soil Samples Collected from Selected Power Plant Sites: Laboratory Studies", Product ID:1005505, December 2004. Electric Power Research Institute. 1994. "A Field and Laboratory Study of Solute Release from Sluices Fly Ash", EPRI TR-104585, December 1994. Electric Power Research Institute. 1993. Electric Power Research Institute, Physical and Hydraulic Properties of Fly Ash and Other By -Products from Coal Combustion, EPRI TR- 101999. February 1993. Fenneman, N. M. 1938. "Physiography of eastern United States." McGraw-Hill. 1938. Freeze, R. A. and Cherry, J. A. 1979. Ground Water, Englewood Cliffs, NJ, Prentice -Hall, 1979. Gillespie, E. 2013. Characterizing the Sources and Variability of Manganese in Well Water of the North Carolina Piedmont. International Conference on the Biogeochemistry of Trace Elements. Gillispie, E. C., Austin, R., Abraham, J., Wang, S., Bolich, R., Bradley, P., Amoozegar, A., Duckworth, O., Hesterberg, D., and Polizzotto, M. L. 2014. Sources and variability of manganese in well water of the North Carolina Piedmont. Water Resources Research Institute of the University of North Carolina System Annual 2014 Conference, Raleigh, NC, March 2014. Poster Presentation. Griffith, G. E., et al. 2002. Ecoregions of North Carolina and South Carolina, (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,500,000). Harden, S. L., Chapman, M. J., and Harned, D. A. 2009. Characterization of groundwater quality based on regional geologic setting in the Piedmont and Blue Ridge Physiographic Provinces, North Carolina: U.S. Geological Survey Scientific Investigations Report 2009-5149. Harned, D. A. and Daniel III, C. C. 1992. The transition zone between bedrock and regolith: Conduit for contamination?, p. 336-348, in Daniel, C. C., III, White, R. K., and Stone, P. A., eds., Groundwater in the Piedmont: Proceedings of a Conference on Ground Water in the Piedmont of the Eastern United States, October 16-18, 1989, Clemson University, 693p. Hatcher, R. D. Jr., Bream, B. R., and Merschat, A. J. 2007. Tectonic map of the southern and central Appalachians: A tale of three orogens and a complete Wilson cycle, in Hatcher, R. D., Jr, Carlson, M. P., McBride, J. H., and Martinez Catalan, J. R., eds., 4-D Framework of Continental Crust: Geological Society of America Memoir 200, p. 595-632. HDR. 2014a. `Buck Combined Cycle Ash Basin Drinking Water Supply Well and Receptor Survey, NPDES Permit NC0004774." am Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 19.0 REFERENCES HDR. 2014b. "Buck Combined Cycle Ash Basin Supplement to Drinking Water Supply Well and Receptor Survey." HDR. 2014c. "Data Report: Buck Steam Station Ash Basin Closure — Conceptual Design- Draft." HDR. 2014d. Buck Combined Cycle Station — Ash Basin. Proposed Groundwater Assessment Work Plan (Rev. 1), NPDES Permit NC0004774. Heath, R. C. 1984. "Ground -water regions of the United States." U.S. Geological Survey Water - Supply Paper 2242, 78 p. Heath, R. C. 1980. Basic elements of groundwater hydrology with reference to conditions in North Carolina: U.S. Geo-logical Survey Open -File Report 80-44, 86 p. Hibbard, J. P., Stoddard, E. F., Secor, D. T., and Dennis, A. J. 2002. The Carolina Zone: overview of Neoproterozoic to Early Paleozoic peri-Gondwanan terranes along the eastern flank of the southern Appalachians: Earth -Science Reviews 57, p. 299-339. Horton, J. and Zullo, V. 1991. The Geology of the Carolinas. Knoxville: University of Tennessee Press. Horton, J. W., Jr., Drake, A. A., Jr., and Rankin, D. W. 1989. Tectonostratigraphic terranes and their Paleozoic boundaries in the central and southern Appalachians, in, Dallmeyer, R; D., ed., Terranes in the circum-Atlantic Paleozoic orogens: Geological Society of America Special Paper 230, p. 213-245. Jurgens, B. C., McMahon, P. B., Chapelle, F. H., and Eberts, S. M. 2009. An Excel® workbook for identifying redox processes in ground water: U.S. Geological Survey Open -File Report 2009-1004 8 p. Krauskopf, K. B. 1972. Geochemistry of micronutrients: in Micronutrients in Agriculture, J.J. Mortvedt, F.R. Cox, L.M. Shuman, and R.M. Walsh, eds., Soil Science Society of America, Madison, Wisconsin, p. 7-36. LeGrand, H. E. 2004. "A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina, A Guidance Manual," North Carolina Department of Environment and Natural Resources Division of Water Quality, Groundwater Section. LeGrand, H. E. 1989. A conceptual model of ground water settings in the Piedmont region. In Ground Water in the Piedmont, ed. C.C. Daniel III, R.K. White, and P.A. Stone, 693. Proceedings of a Conference on Ground Water in the Piedmont of the Eastern United States, Clemson University, Clemson, South Carolina. Charlotte, NC: U.S. Geological Survey. LeGrand, H. E. 1988. Region 21, Piedmont and Blue Ridge. In Hydrogeology, The Geology of North America, vol. 0-2, ed. W.B. Back, J.S. Rosenshein, and P.R. Seaber, 201-207. Geological Society of America. Boulder CO: Geological Society of America. 117 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report �� Buck Steam Station Ash Basin 19.0 REFERENCES Martens, Dean A. 2002. "Selenium." Encyclopedia of Soil Science. New York: Marcel Dekker, 2002. 840-42. North Carolina Department of Environment and Natural Resources. 2015. Summary of North Carolina Surface Water Quality Standards 2007-2014 North Carolina Department of Environment and Natural Resources. 2015. Surface Water Classifications. [Online] URL: http://portal.ncdenr.org/web/wq/ps/csu/classifications North Carolina Department of Environment and Natural Resources. 2013a. 15A NCAC 2B .0200s. Classifications and Water Quality Standards Applicable to the Surface Waters and Wetlands of North Carolina. NC and EPA Combined Surface Water Quality Standards and Criteria Table. May 15. [Online] URL: http://portal.ncdenr.org/web/wcl/ps/csu/swstandards North Carolina Department of Environment and Natural Resources. 2013b. 15A NCAC 02L. Groundwater Rules. Groundwater Standards Table. April 1. [Online] URL: http://portal.ncdenr.org/web/wq/ps/csu/gwstandards#4 North Carolina Department of Environment and Natural Resources. 2013c. 15A NCAC 02L. Groundwater Rules. Interim Maximum Allowable Concentrations (IMACs) Table. April 1. [Online] URL: http://portal.ncdenr.orq/web/wq/ps/csu/gwstandards#4 North Carolina Department of Environment and Natural Resources. 2015. Division of Mitigation Services, Watershed Planning Documents [Online] URL: http://portal.ncdenr.org/web/eep/rbrps/vadkin North Carolina Department of Environment and Natural Resources. 2012. NPDES Permit for Buck Steam Station. [Online] URL: http://portal.ncdenr.org/c/document library/get file?uuid=03bd562a-088d-47aa-8dcl- ed710ebf4e49&groupld=38364 North Carolina Department of Environment and Natural Resources. 2007. "Performance and Analysis of Aquifer Slug Tests and Pumping Tests Policy," May 31, 2007. North Carolina Department of Environment and Natural Resources.2007. "Hydrogeologic Investigation and Reporting Policy Memorandum," dated May 31, 2007. North Carolina Department of Environment and Natural Resources. 2003. Division of Waste Management - Guidelines for Performing Screening Level Ecological Risk Assessments within North Carolina. North Carolina Department of Environment and Natural Resources, Division of Water Quality. 2013. "Evaluating Metals in Groundwater at DWQ Permitted Facilities: A Technical Assistance Document for DWQ Staff", July 2013. North Carolina Department of Environment and Natural Resources — Division of Water Quality. 2007 North Carolina Water Supply Watersheds, Division of Water Quality. [Online] Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 19.0 REFERENCES URL:httD://Dortal.ncdenr.ora/c/document librarv/aet file?uuid=df304l6f-cd0e-46bd 9ce4-fcc470aa324d&grou pl d=38364 North Carolina Department of Environment and Natural Resources — Division of Water Resources. 2015. NC Surface Water Classifications, NC Classifications Website [Online] URL: http://ncdenr.maps.arcqis.com/apps/webappviewer/index.html?id=6e125ad7628f494694 e259c80dd64265 North Carolina Department of Health and Human Services, Department of Public Health. 2010. "Concentration of Iron Detected in NC Private Well Water, Average 1998-2010 and Average 2010." Well Water & Health. University of North Carolina Superfund Research Program. [Online] URL: http://epi.publichealth.nc.gov/oee/wellwater/ North Carolina Department of Public Health. 2015. Fish Consumption Advisories. Division of Public Health. March 27. [Online] URL: httD://eDi.Dublichealth.nc.aov/oee/fish/advisories.html North Carolina General Assembly. 2014. Senate Bill 729/S.L. 2014-122. Became law without signature September 20, 2014. North Carolina State University, A&T State University, NC Cooperative Extension Resources. [Online] URL http://content.ces.ncsu.edu/average-growing-season-for-selected-north- carolina-locations/ North Carolina Watersheds [Online] URL: http://www.carolana.com/NC/Transportation/nc watersheds.html Nutter, L. J. and Otton, E. G. 1969. Groundwater occurrence in the Maryland Piedmont: Maryland Geological Survey Report of Investigations, No. 10, 42p. Parkhurst, D.L., and Appelo, C.A.J. 2013. Description of input and examples for PHREEQC version 3—A computer program for speciation, batch -reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Techniques and Methods, book 6, chap. A43, 497 p. Polizzotto, M. 2014. Surface and Subsurface Properties Regulating Manganese. Progress Report to the Water Resources Research Institute of the University of North Carolina. Sanders, A.P, K.P. Messier, M. Shehee, K. Rudo, M.L. Serre, R.C. Fry (2011) Arsenic in North Carolina: Public Health Implications, Environment International, Vol. 38 pp. 10-16 Schaeffer, M. F. 2014a. Piedmont groundwater system, Part 1 — The transition zone between regolith and bedrock: Existence: Geological Society of America, Abstracts with Program, April 2014, v. 46, no. 3, p. 26-27. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 19.0 REFERENCES Schaeffer, M. F. 2014b. Piedmont groundwater system, Part 2 — The transition zone between regolith and bedrock: Characteristics: Geological Society of America, Abstracts with Program, April 2014. v. 46, no. 3, p. 27. Schaeffer, M. F. 2011. Carolina Piedmont groundwater system: What does the transition zone look like?: 19th Annual David S. Snipes/Clemson Hydrogeology Symposium, April 7, 2011, p. 43-44. Schaeffer, M. F. 2009. Hydraulic conductivity of Carolina Piedmont soil and bedrock: Is a transition zone present between the regolith and bedrock?: 17th Annual David S. Snipes/Clemson Hydrogeology Symposium, April 2, 2009, p. 32-36. Secor, D. T, Barker, C., Balinsky, M., and Colquhoun, D. 1998. The Carolina terrane in northeastern South Carolina: history of an exotic volcanic arc: South Carolina Geology, v. 40, p. 1-17. Stewart, J. W. 1964. Infiltration and permeability of weathered crystalline rocks, Georgia Nuclear Laboratory, Dawson County, Georgia: United States Geological Survey, Bulletin 1133-D, p. D 1-D57. Stewart, J. W., Callahan, J. T., Carter, R. F, et al. 1964. Geologic and hydrologic investigation at the site of the Georgia Nuclear Laboratory, Dawson County, Georgia: United States Geological Survey Bulletin 1133-F, p. F1-F90. Tang, G., Mayes, M. A., Parker, J. C., and Jardine, P. M. 2010. CXTFIT/Excel—A modular adaptable code for parameter estimation, sensitivity analysis and uncertainty analysis for laboratory or field tracer experiments. Computers & Geosciences, 36(9), 1200-1209. U.S. Department of Agriculture — Natural Resource Conservation Service. 2004.Soil Survey of Rowan County, North Carolina U.S. Environmental Protection Agency. 2015. Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals From Electric Utilities. 40 CFR Parts 257 and 261. Federal Register Vol. 80, No. 74, April 17, 2015. U.S. Environmental Protection Agency. 2015. Regional Screening Levels Generic Tables. January. [Online] URL: http://www.epa.gov/reg3hwmd/risk/human/rb- concentration table/Generic Tables/index.htm U.S. Environmental Protection Agency. 2014. National Recommended Water Quality Criteria. Aquatic and Human Health Criteria Tables. December 3. [Online] URL: http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm US Environmental Protection Agency. 2014. National Primary Drinking Water Regulations US Environmental Protection Agency. 2012. Sulfate in Drinking Water. [Online] URL: http://water.epa.gov/drink/contaminants/unregulated/su[fate.cfm 120 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 19.0 REFERENCES U.S. Environmental Protection Agency. 2008. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods. Document no. SW-846. 3rd Edition. U.S. Environmental Protection Agency. 2007. Monitored Natural Attenuation of Inorganic Contaminants in Ground Water — Volume 1, Technical Basis for Assessment. EPA/600/R-07/139. US Environmental Protection Agency. 2003. Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on Sulfate. U.S. Environmental Protection Agency Region 4. 2001. Ecological Risk Assessment Bulletins -- Supplement to RAGS. Tables 1 - 4. November 30. [Online] URL: http://www.epa.gov/region4/superfu nd/programs/riskassess/ecolbul. html#tbl l U.S. Environmental Protection Agency. 1998. Guidelines for Ecological Risk Assessment. April. [Online] URL http://www2.epa.gov/sites/production/files/2014- 11/documents/eco risk assessment1998.pdf U.S. Environmental Protection Agency. 1998. Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units —Final Report to Congress. Volume 1. Office of Air Quality, Planning and Standards. Research Triangle Park, NC 27711, EPA-453/R- 98-004a. U.S. Environmental Protection Agency. 1998. Report to Congress Wastes from the Combustion of Fossil Fuels, Volume 2 Methods, Findings, and Recommendations. U.S. Environmental Protection Agency. 1997. Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments U.S. Environmental Protection Agency. 1987. Batch -type procedures for estimating soil adsorption of chemicals Technical Resource Document 530/SW-87/006-F. U.S. Fish and Wildlife Service. Endangered and Threatened Species and Species of Concern by County for North Carolina. [Online] URL: http://www.fws.gov/raleigh/species/cntylist/nc counties.html U.S. Fish and Wildlife Service. 2009. Range -wide Indiana Bat Protection and Enhancement Plan Guidelines. [Online] URL: http://www.fws.gov/frankfort/pdf/inbatpepquidelines.pdf. U.S. Geological Survey. 1997. Radioactive elements in coal and fly ash: abundance, forms, and environmental significance. U.S. Geological Survey Fact Sheet FS-163-97. US Geological Survey. 1997. Ground Water Atlas of the United States: Delaware, Maryland, New Jersey, North Carolina, Pennsylvanis, Virginia, West Virginia. Piedmont and Blue Ridge Aquifers. [Online] URL: http://pubs.usgs.gov/ha/ha730/ch I/L-text4.html U.S. Geological Survey. 1973. United States Mineral Resources. United States Government Printing Office. 121 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Buck Steam Station Ash Basin 19.0 REFERENCES U.S. Geological Survey Geological Survey. 1961. A. Ogata and R.B. Banks Professional Paper 411-A "A Solution of Differential Equation of Longitudinal Dispersion in Porous Media". Weather DB. 2015. Salisbury, North Carolina Average Rainfall. [Online] URL: http://rainfall.weatherdb.com/ Weather DB 2015. Eden, North Carolina Average Temperature [Online] URL: http://temperature.weatherdb.com/ Wiley and Sons, 1993. Biodiversity of the Southeastern United States, Upland Terrestrial Communities. World Health Organization. 2007. Nickel in Drinking -water. Background document for development of WHO Guidelines for Drinking -water Quality. htti)://www.who.int/water sanitation health/adwarevision/nickel2ndadd.adf 122