Loading...
HomeMy WebLinkAboutBelews Creek Executive Summary CSADuke Energy Carolinas, LLC I Comprehensive Site Assessment Report FN Creek Steam Station Ash Basin EXECUTIVE SUMMARY Executive Summary — Belews Creek Steam Station On August 20, 2014, the North Carolina General Assembly passed Session Law 2014-122, the Coal Ash Management Act of 2014 (CAMA). Section 130A-309.211 of the act 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 than 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 Carolinas, LLC (Duke Energy) submitted a Work Plan to NCDENR on December 30, 2014 for characterization of the Belews Creek Steam Station (BCSS) ash basin and assessment of soil, groundwater, and surface water potentially impacted by the ash basin system. The Work Plan was subsequently conditionally approved by the NCDENR in correspondence dated March 13, 2015. This CSA report was prepared to comply with 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 no later than 90 days after submittal of this CSA unless an extension is requested and granted by NCDENR. 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 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 March 13, 2015; and • Subsequent meetings and correspondence between Duke Energy and NCDENR. For this CSA, the source area is defined as the ash basin, the closed Pine Hall Road Ash Landfill, and the chemical pond located within the southern portion of the 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 analytical results for source characterization samples were compared to North Carolina Groundwater Quality Standards, as specified in 15A NCAC 2L.0202 (21- Standards), or Interim Maximum Allowable Concentrations (IMACs), and other regulatory screening levels for the purpose of identifying constituents of interest (COls) that may be associated with potential impacts to soil, groundwater, and surface water from the source area. The IMACs were issued in 2010, 2011, and 2012; however, Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY 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. Some COls are present in background and upgradient monitoring wells and may be naturally occurring, and thus require careful examination to determine whether their presence downgradient of the source area is naturally occurring or a result of ash handling and storage. In addition to evaluating the distribution of constituents across the BCSS 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. The assessment consisted of the following activities: • Completion of ash, soil and rock borings and installation of monitoring wells to facilitate collection and analysis of chemical, physical, and hydrogeological parameters of subsurface materials, and groundwater encountered within and beyond the ash basin waste, closed ash landfill and associated compliance boundaries; • Collection and analysis of solid phase (e.g., soil, rock and ash) and liquid phase (e.g., groundwater, ash basin porewater, ash basin surface water, seep, and surface water) samples; • Evaluation of testing data to supplement the initial Site Conceptual Model (SCM) presented in the Work Plan; • Revision to the Receptor Survey previously completed in 2014; and • 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 soil or groundwater impacts at the site. Upgradient, background monitoring wells contain naturally occurring constituents at concentrations that exceeded their respective 2L Standards or IMACs. This information is used to evaluate whether concentrations in groundwater downgradient of the ash basin are also naturally occurring or are influenced by migration of constituents from the ash basin. Naturally occurring constituents reported in background groundwater samples at concentrations greater than 2L Standards or IMACs include antimony, iron, manganese, pH and vanadium. The U.S. Environmental Protection Agency (USEPA) has identified select constituents as leading indicators for detecting groundwater contamination from coal combustion residuals (CCR) units. Boron, TDS and chloride are leading indicator among these detection monitoring constituents, are expected to be highly mobile in the groundwater environment, and therefore can be used to represent the general extent of groundwater impacted by the ash basin at the site. At the BCSS site, the horizontal and vertical migration of boron, and also elevated total dissolved solids (TDS) that are associated ES -2 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY with source constituents (primarily chloride), best represents the impacted groundwater flow and potential transport system. • Boron exceedances at the site are present within the ash basin compliance boundary in the shallow and deep flow layers beneath the ash basin dam and the area immediately downgradient of the dam. There were no exceedances within the deep or bedrock flow layers beneath the ash basin itself. Vertical migration of boron is generally impeded by the underlying bedrock. • TDS exceedances primarily in conjunction with elevated boron and chloride at the site are present in the shallow and deep flow layers beneath the ash basin dam and the area immediately downgradient of the dam within the ash basin compliance boundary. There is also evidence of constituent migration in the deep flow layer immediately west of the ash basin dam and Middleton Loop Road beyond the ash basin compliance boundary. • Groundwater in the shallow and deep flow layers beneath the ash basin predominantly flows north and northwest toward the Dan River as demonstrated by the migration of the above -referenced constituents. There are no water supply wells located between the source areas and the Dan River. • Figure ES -1 depicts the horizontal extent of 2L Standard exceedances for boron in the shallow and deep groundwater flow layers at the site. There were no boron exceedances in the bedrock flow layer. In addition, TDS exceedances above its 2L Standard in association with elevated boron and chloride levels in the shallow and deep groundwater flow layers are also shown on Figure ES -1 • Seeps S-2 and S-4 are located to the west of Middleton Loop Road and the ash basin dam on Duke Energy property. Sample results at these seeps reported elevated levels of TDS and chloride above background concentrations but less than their 2L Standards. This indicates groundwater flow through the northwestern rim of the ash basin toward the Dan River. The seeps may represent preferential flow paths. This flow direction is away from the direction of the nearest public or private water supply wells. • Seep S-6 is located downgradient from the small dike built to retain the ash basin where Pine Hall Road crosses over the original ash basin discharge tower outlet pipe. Boron in excess of its 2L Standard was identified in the sample collected at this location, although this is believed to be a localized measurement and a result of preferential seepage path between the seep and the upstream ash basin and surface water. Duke Energy is in the process of re -grouting the original discharge tower and outlet pipe with cementitious grout to avoid any potential inadvertent discharges to Belews Lake. • Soil sample test results do not provide evidence of soil contamination beneath the ash basin. Although some constituent levels were measured above 2L Standards in soil samples beneath the basin, generally levels appeared to be similar to constituent levels measured from background well soil samples. A soil sample obtained from a boring at the base of the ash basin dam (SB -3) had a cobalt concentration above the background cobalt concentrations at the site and above concentrations of cobalt observed within ash samples from within the ash basin. ES -3 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY ESA Source Information Duke Energy owns and operates the BCSS located in Stokes County, North Carolina. BCSS began operation in 1974 as a coal-fired generating station and currently operates two coal-fired units. Coal ash residue and other liquid discharges from the BCSS coal combustion process have historically been disposed of in the ash basin system located across Pine Hall Road, northwest of the station. The BCSS ash basin consists of a single cell impounded by an earthen dike located on the north end of the ash basin. The ash basin system was constructed from 1970 to 1972 and is located approximately 3,200 feet northwest of the station. The area contained within the ash basin waste boundary is approximately 283 acres. The ash basin is operated as an integral part of the station's wastewater treatment system, which receives permitted flows from the ash removal system, BCSS powerhouse and yard holding sumps, chemical holding pond, coal yard sumps, stormwater, landfill leachate, and treated flue gas desulfurization (FGD) wastewater. Inflows to the ash basin are generally stable due to the base load nature of station operations. Inflows from the station are discharged into the southeast portion of the ash basin. There is one permitted closed ash landfill located adjacent to and southwest of the ash basin. The Pine Hall Road Ash Landfill is permitted by the NCDENR Division of Waste Management (DWM) under Permit No. 85-03. The landfill is located upgradient to the ash basin and is just north of the Pine Hall Road topographic divide. The ash landfill was constructed prior to the requirement for lining industrial landfills and was closed with a hybrid cover system. The larger area of fill has an engineered closure system consisting of a geomembrane cover system capped with soil and vegetation, whereas the flat lower areas were closed with soil and vegetation cover system. An ash structural fill comprised of compacted fly ash was constructed southeast of the ash basin under the structural fill rules found in 15A NCAC 13B .1700. After completion, and engineered cover system consisting of a geomembrane cover system capped with soil and vegetation was installed over the ash structural fill. The ash structural fill is located south of the Pine Hall Road topographic divide and therefore groundwater flow beneath the fill should be predominantly away from the ash basin. There are no groundwater monitoring requirements or compliance boundary associated with the ash structural fill. A chemical pond is located within the southernmost portion of the ash basin and was formed by constructing an earthen dike across a cove within the ash basin. Permitted boiler cleaning solutions and other fluids associated with station operation and maintenance were pumped to the chemical pond for storage and treatment prior to discharge to the ash basin. The chemical pond was removed from inflow service in 2010. ES -4 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY 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 have not been required. ES.3 Receptor Information Properties located within a 0.5 mile radius of the BCSS ash basin compliance boundary generally consists of undeveloped land, rural residential properties and Belews Lake. 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 to be considered in the groundwater transport modeling and human health risk assessment. 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 BCSS ash basin compliance boundary requesting information on the presence of water supply wells and well usage for the properties. The CSA receptor survey activities included contacting and/or reviewing state and local agencies/records to identify public and private water supply sources, identify surface water features, confirm the location of wells, and/or identify any wellhead protection areas located within a 0.5 -mile radius of the BCSS ash basin compliance boundary. The receptor survey activities have identified one public water supply well and 50 private water supply wells in use within the 0.5 -mile radius of the ash basin compliance boundary. No wellhead protection areas were identified within a 0.5 -mile radius of the ash basin compliance boundary. Several surface water bodies that flow from the topographic divide along Middleton Loop Road toward the Dan River were identified within a 0.5 -mile radius of the ash basin. ESA Sampling / Investigation Results ES.4.1 Background Findings As part of the CSA, Duke Energy installed eight additional background monitoring wells (three shallow, three deep, and two bedrock) to compliment the two existing background monitoring wells. The background well locations were selected based on existing knowledge of the site to maximize physical separation from the ash basin and are located in areas believed to not be impacted by ash to provide sufficient background soil and groundwater quality data. Analyses of groundwater samples collected from the eight newly installed background wells and two existing ash basin compliance background wells indicated that the following naturally occurring constituents exceeded 2L Standards or IMACs in background locations: antimony, iron, manganese, and vanadium. The results for all other constituents were reported below 2L Standards or IMACs. The range of concentrations reported in the new background wells is presented below. ES -5 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY Table ES -1. Concentrations Reported in New Background Wells Constituent of Interest Groundwater 2L Standard or IMAC /L Background Well Range of Concentrations /L Antimony 1 * 0.16J pg/L to 1.5 pg/L Arsenic 10 0.2J pg/L to 1.9 pg/L Beryllium 4* 0.17J pg/L to 0.33 pg/L Boron 700 37J pg/L to 50U pg/L Cadmium 2 0.052J pg/L to 0.41 pg/L Chloride 250,000 1,200 pg/L to 9,700 pg/L Chromium 10 0.77J pg/L to 4.8 pg/L Cobalt 1* 0.19J pg/L to 0.9 pg/L Iron 300 50U pg/L to 1,900 pg/L Manganese 50 2.7J pg/L to 93 pg/L pH 6.5-8.5 5.8 SU to 9.0 SU Selenium 20 0.24J pg/L to 1.1 pg/L Sulfate 250,000 920J pg/L to 23,400 pg/L Thallium 0.2* 0.024J pg/L to 0.1 U pg/L TDS 500,00 41,000 pg/L to 173,000 pg/L Vanadium 0.3* 0.31J pg/L to 7.4 pg/L Notes 1. pg/L = micrograms per liter 2. SU = Standard Units 3. J = Estimated concentration 4. U = Not detected 5. * denotes an IMAC ES.4.2 Source Characterization Source characterization was performed through the completion of soil and rock 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 physical and chemical properties evaluated as part of the characterization have been used to better understand impacts to soil and groundwater from the source area and will also be utilized as part of groundwater model development in the CAP. Review of laboratory analytical results of ash samples collected from the ash basin identified eight COls, which include arsenic, boron, cobalt, iron, manganese, selenium and vanadium. COls identified in ash porewater samples include antimony, arsenic, boron, chloride, cobalt, iron, manganese, selenium, sulfate, thallium, TDS and vanadium. COls identified in ash basin surface water samples include antimony, arsenic, boron, chloride, iron, lead, manganese, thallium, TDS, and vanadium. COls identified in ash basin seep samples include boron, chloride, cobalt, manganese, sulfate, thallium, TDS, and vanadium. ES -6 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY SPLP (Synthetic Precipitation Leaching Procedure) testing was conducted to evaluate the leaching potential of constituents from ash. Although SPLP analytical results are being compared to the 2L Standards and IMACs, these leaching results do not represent groundwater samples. The results of SPLP analyses indicated that the following constituents exceeded their 2L Standards: antimony, arsenic, chromium, cobalt, manganese, selenium, thallium, and vanadium. However, many factors influence the transport of these constituents and any potential impacts to groundwater over time will be investigated through modeling as part of the CAP. ES.4.3 Nature and Extent of Contamination Soil and groundwater beneath the ash basin and groundwater downgradient of the ash basin have been impacted by the ash basin at the BCSS site as described below. ES.4.3.1 Soil Reported concentrations of soil samples were compared to background concentrations in addition to the North Carolina Industrial Health and Protection of Groundwater Preliminary Soil Remediation Goals (PSRGs) to delineate the extent of contamination. Soil sample test results do not provide evidence of soil contamination beneath the ash basin. Although some constituent levels were measured above 2L Standards in soil samples beneath the basin, in general levels appeared to be similar to constituent levels measured from background well soil samples. A soil sample obtained from a boring at the base of the ash basin dam (SB -3) had a cobalt concentration above the background cobalt concentrations at the site and above concentrations of cobalt observed within ash samples from within the ash basin. In general, constituent concentrations of, cobalt, iron, manganese, selenium and vanadium were higher in soil compared to ash. The exceedances of PSRGs for cobalt iron, manganese, selenium and vanadium in soil may be reflective of the naturally occurring concentrations of these constituents. ES.4.3.2 Groundwater The approximate horizontal extent of groundwater impacts is projected to be beneath the ash basin and downgradient to the north and northwest of the ash basin dam and Middleton Loop Road. There is evidence of source related constituents migrating beyond the ash basin compliance boundary west of Middleton Loop Road in the area northwest of the operating ash basin discharge tower. The approximate vertical extent of groundwater impacts is generally limited to the shallow and deep flow layers, as shown by the rarity of exceedances within the bedrock flow layer, and vertical migration of COls is impeded by the underlying bedrock. Constituents with concentrations that exceeded 2L Standards or IMACs at the site that are likely due to naturally occurring concentrations include antimony, iron, manganese, pH and vanadium. Concentrations of several COls exceeded their respective 2L Standards or IMACs in groundwater at the site and appear to be caused by the source, including arsenic, beryllium, ES -7 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY boron, cadmium, chloride, chromium, cobalt, thallium and TDS. Details of the nature and extent of contamination for each source -related COI identified in groundwater is described below. • Arsenic exceedances of the 2L Standard were limited to the shallow flow layer in the vicinity of the ash basin dam. • Beryllium exceedances of the IMAC in the shallow flow layer were limited to downgradient of and northwest of the ash basin dam and west of the dam . One exceedance occurred within the deep flow layer downgradient from the ash basin dam. • Boron concentrations exceeding the 2L Standard were limited to the vicinity of the ash basin dam within the shallow and deep flow layers • Cadmium exceeded the 2L Standard at a single location within the deep flow layer downgradient of the ash basin dam. • Chloride concentrations excceded the 2L Standard in the vicinity of the ash basin dam within the shallow and deep flow layers. • Chromium concentrations exceeded the 2L Standard in the vicinity of the ash basin dam and to the west of the dam within the shallow flow layer. Only one well was reported to exceed the chromium 2L Standard within the deep flow layer northeast and upgradient of the original ash basin discharge structure. • Cobalt concentrations exceeded the IMAC within the shallow and deep flow layers in the vicinity of the ash basin dam and to the west and south of the ash basin. There were no cobalt exceedences reported within the bedrock flow layer. • Thallium concentrations exceeded the IMAC within the shallow and deep flow layers in the vicinity of the ash basin dam, and in isolated areas on the western and eastern extents of the ash basin • TDS concentrations exceeded the 2L Standard within the shallow and deep flow layers in the vicinity of the ash basin dam and west of the ash basin dam. • Seeps S-2 and S-4 are located on Duke Energy property west of Middleton Loop Road and the ash basin dam, and sampling reported elevated levels of TDS and chloride above background concentrations but less than their 2L Standards at these locations. This indicates groundwater flow and migration at the northwestern rim of the ash basin toward the Dan River. This flow direction is away from the direction of the nearest public or private water supply wells. ES.4.4 Maximum Contaminant Concentrations The maximum contaminant concentrations in groundwater are mainly located in shallow monitoring wells installed within the ash basin dam or downgradient of the dam. Maximum contaminant concentrations occurring in deep wells are primarily located in the vicinity of the ash basin dam. Maximum contaminant concentrations in ash porewater samples are primarily located at the western most boring in ash and a boring which is located near the discharge point of the sluice lines. ES -8 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY Maximum contaminant concentrations in seep water primarily occurred in seeps located downgradient of the ash basin dam. Most maximum contaminant concentrations in ash basin surface water occurred near the ash basin discharge structure at the northwest corner of the ash basin. The maximum contaminant concentrations for COls in groundwater, ash porewater, ash basin surface water, and seep water samples collected during the CSA are listed below. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY Table ES -2. Maximum Constituent of Interest Concentrations Notes: 1. N/A indicates that a constituent was not detected. 2. J indicates an estimated concentration. 3. J+ indicates an estimated concentration, biased high. 4. J- indicates an estimated concentration, biased low. ES -10 Maximum Contaminant Concentrations (pg/L) COI Seep Water or Groundwater Ash Porewater Effluent Water as Ash Basin Surface Water noted Aluminum 9,600 11,300 N/A 77.9 (AB -1S) AB-4SL SW-AB2 Antimony 8.1 15.2 1.2 1.3 AB -2S AB-8SL 003 SW-AB2 Arsenic 79.1 146 16.9 10.4 MW -103S (AB-8SL) (S-7 SW-AB4 Barium 490 330 300 160 GWA-11 S AB-5SL S-10 SW-AB4 Beryllium 6.6 0.64 2.2 0.111 GWA-11 S AB -7S TF -3 SW-AB2 Boron 13,200 21,900J 15,700 16,300J+ AB -3S) (AB -4S) (003) (SW-AB2) Cadmium 3.8 1.2 2 0.12 MW -103D AB-4SL TF -3 SW-AB2 Chloride 541,000 783,000 501,000 492,000 AB-21D AB-4S 003 SW-AB2 Chromium 50.7 8.5 11.5 7.5 (GWA-17S) (AB -4S S-3 SW-AB8 Cobalt 413 243 268 0.72 MW -102S AB -7S HD -21 SW-AB2 Copper 38.6 3.6 5.6 2.1 AB-41D AB-4SL S-5 SW-AB2 Iron 92,200 77,800J- N/A 1,420 MW -103S AB -7S SW-AB7 Lead 2.8 2 1.5 0.72 GWA-9S AB-4SL S-6 SW-AB2 Manganese 21,300 9,200 27,000J- 330 MW -102S AB -7S HD -21 SW-AB7 Mercury 0.47 0.088J+ 0.154 0.00159 GWA-10S AB-8SL HD -26 SW-AB2 Molybdenum 38.3 3,560 23.2 23.7 GWA-5BR AB-4SL 003 SW-AB2 Nickel 47.9 91.6 46.7 4.1 MW -103D AB -7S HD -21 SW-AB2 Selenium 10.6 38.4 11.2 6.7 GWA-10S AB-4SL TF -1 SW-AB2 Sodium 35,900 14,300 37,100 14,400 MW -102S AB -7S S-9 SW-AB5 Sulfate 132,000 439,000 475,000 123,000 AB -3S AB -7S S-9 SW-AB1 TDS 1,430,000 2,880,000 14,000,000 1,930,000 AB -3S AB-5SL 003 SW-AB2 Thallium 3.6 1.4 1.2 1.4 MW -103D AB -7S 003 SW-AB1 Vanadium 47.2 867 6.4 9.2 AB -2S AB-4SL 003 SW-AB2 Zinc 48 130 63 15.9J MW -102S AB -7S S-9 SW-AB2 Notes: 1. N/A indicates that a constituent was not detected. 2. J indicates an estimated concentration. 3. J+ indicates an estimated concentration, biased high. 4. J- indicates an estimated concentration, biased low. ES -10 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY ES.4.5 Regional Geology and Hydrogeology The BCSS site is within the Milton terrane, one of a number of tectonostratigraphic terranes that have been defined in the southern and central Appalachians. It is bounded on the northwest by the Dan River Basin and Sauratown Mountains Anitclinorium and on the southeast by the Carolina terrane of the larger Carolina superterrane. The Milton terrane is characterized by strongly foliated gneisses and schists, commonly with distinct compositional layering and felsic composition; quartzite, calc-silicate gneiss, and marble are minor units. The available evidence suggest that the rocks of the Milton terrane are mainly Precambrian in age and were metamorphosed and deformed during the early to late Paleozoic. The majority of the rocks in the belt are metamorphosed to the sillimanite and kyanite grade of amphibolite metamorphism. The groundwater system in the Piedmont region in most cases is comprised of two interconnected layers, or two -medium system: 1) residual soil/saprolite and weathered fractured 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. ES.4.6 Site Geology and Hydrogeology The BCSS site and its associated ash basin system is located in the Milton terrane. Rock units mapped in the vicinity of the site include alluvium, terrace deposits, sedimentary rocks of the Dan River Basin, a diabase dike, and felsic gneisses and schists with interlayered hornblende gneiss and schist. The alluvium consists of unconsolidated sand, silt, and clay with occasional subhedral to well-rounded pebbles and cobles. The terrace deposits consist of unconsolidated sand, silt, and clay with pebbles and cobles of quartz. In places, the terrace deposits are comprised of large angular quartz fragments in a red matrix of sand, silt, and clay. The diabase occurs in a long, relatively thin dike. The rocks of the Milton terrane in the area include interlayered augen gneiss, quartz -feldspar gneiss, flaser gneiss, "button" mica schist, and with interlayers of hornblende gneiss and schist. Based on the site investigation, the groundwater system in the natural materials (alluvium, soil, soil/saprolite, and bedrock) at the BCSS site is consistent with the regolith -fractured rock system ES -11 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report FN Creek Steam Station Ash Basin EXECUTIVE SUMMARY and is generally an unconfined, connected aquifer system without confining layers. The groundwater system at the BCSS 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. Groundwater flow and transport at the BCSS site are assumed to follow the local slope aquifer system. Under natural conditions, the general direction of groundwater flow can be approximated from the surface topography. Topographic divides are located to the south and east of the ash basin approximately along Pine Hall Road. A topographic divide exists to the west of the ash basin along Middleton Loop Road. Another topographic divide exists north of the ash basin along a ridgeline that extends from the east dike abutment toward the northeast. These topographic divides generally function as groundwater divides although groundwater flow across topographic divides may be possible based on driving head conditions from the ash basin and the existence of preferential flow paths within the shallow and/or deep flow layers. Seeps S-2 and S-4 appear to be evidence of groundwater flow northwesterly across the topographic divide of Middleton Loop Road based upon elevated concentrations of source constituents. The predominant direction of groundwater flows north and northwest toward the Dan River. ES.4.7 Existing Groundwater Monitoring Data Duke Energy implemented voluntary monitoring around the BCSS ash basin from November 2007 until January 2012. During this period, the voluntary groundwater monitoring wells were sampled twice per year and the analytical results were submitted to NCDENR DWR. No routine groundwater samples are currently being collected from the voluntary wells. Groundwater monitoring as required by the BCSS NPDES Permit NC0024406 began in January 2011. NPDES Permit Condition A (10), dated October 12, 2012, refers to a Sampling Plan approved by the Division which 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. Compliance groundwater monitoring wells were sampled as part of this CSA to supplement the expanded groundwater assessment, assess background groundwater quality and calculate statistical analyses of background groundwater chemical concentrations. One or more groundwater quality standards (21- Standards) have been exceeded in groundwater samples collected at one or more wells, including the background wells (exceedance for pH). Exceedances have occurred for chromium, iron, manganese, pH, and thallium. Concentrations of several COls were reported above 2L Standards or IMACs in groundwater samples collected from compliance and voluntary monitoring wells located downgradient of the source area, including chromium, iron, manganese, pH and thallium. Sample results from upgradient and background compliance wells are consistent with previous results. Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY ES 4.8 Existing Surface Water Monitoring Data Ongoing monitoring of the Dan River for NPDES surface water quality indicates that the ash basin has not resulted in increased constituent concentrations above the North Carolina Surface Water Quality Standards (213 Standards) downstream of the BCSS ash basin discharge for permitted constituents. ES.4.9 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 in which they occur. 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. The screening level risk assessment reviewed NCDENR water well testing results from private water supply wells located near BCSS. According to NCDENR's August 20, 2015 online summary of well testing near coal ash ponds, seven off-site private water supply wells and one public water supply well were sampled and analyzed for COls as part of the NCDENR well testing program. In summary, the Department of Health and Human Services (DHHS) recommended that five wells sampled should not be utilized for drinking water due to the presence of one or more constituents above screening levels defined by DHHS, including iron, vanadium and chromium. These constituents are naturally occurring in groundwater in the region surrounding the BCSS site. There are no water supply wells located between the source areas and the Dan River. ES.4.9 Development of Conceptual Site Model In the initial site conceptual hydrogeologic model presented in the Work Plan dated December 30, 2014, the geological and hydrogeological features influencing the movement, chemical, and ES -13 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY physical characteristics of contaminants were related to the Piedmont hydrogeologic system present at the site. A hydrogeological site conceptual model was developed from data generated during previous assessments, existing groundwater monitoring data, and CSA activities. The ash basin discharges porewater to the subsurface beneath the basin. Groundwater in the vicinity of the ash basin flows to the west and north toward the Dan River. Horizontal migration of groundwater at the site is generally controlled by topographic divides along Pine Hall Road to the south and east of the ash basin and along Middleton Loop Road to the west of the ash basin. These topographic divides generally function as groundwater divides, although groundwater flow across topographic divides may be possible based on hydraulic head conditions from the ash basin and the existence of preferential flow paths within the shallow and/or deep flow layers. The conceptual site model will continue to be refined following evaluation of the completed groundwater model in the CAP and additional information obtained in subsequent data collection activities. ES.4.10 Identification of Data Gaps Through completion of the CSA activities and evaluation of data collected, data gaps have been identified that should be evaluated further to refine the site conceptual model. The data gaps have been separated into two groups: 1) data gaps resulting from temporal constraints and 2) data gaps resulting from evaluation of data collected during the CSA. Temporal data gaps consist of evaluation of petrographic analysis of rock data. Data gaps resulting from evaluation of the data collected during the CSA activities consists of: • The installation of additional groundwater monitoring wells and additional data assessment to fully delineate the horizontal extent of concentrations in impacted groundwater west and downgradient of the ash basin dam and Middleton Loop road. The location of additional groundwater monitoring wells will be developed prior to the submittal of the CAP. Installation would most efficiently be implemented during the CCR monitoring well program phase of work. • Sampling of wells and other locations that were dry during the initial sampling event • The collection of sediment samples, if present, at seep locations S-1 through S-11 to better understand source related constituent impacts. • CSA seep location S-9 exhibited 2L Standard or IMAC exceedances for boron, cobalt, sulfate, and TDS that are associated with the adjacent ash structural fill and not the ash basin given the proximity of the seep to the structural fill. It is anticipated that three to four additional downgradient monitoring wells are needed around the perimeter of the fill to better delineate the groundwater flow and source related constituents towards Belews Lake. The location of the additional wells would occur in parallel to the second round CSA sampling event, and installation should occur concurrent with the implementation of the CCR monitoring program. ES -14 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY ES.5 Conclusions The CSA identified the horizontal and vertical extent of groundwater contamination at the BCSS ash basin, with the exception of data gaps noted, and found it is generally limited to within the ash basin compliance boundary, with the exception of the area impacted west of the ash basin dam and Middleton Loop Road. The source and cause of impacts from boron, and TDS that is associated with elevated levels of chloride, as shown on Figure ES -1, is the coal ash contained in the ash basin. The cause of contamination shown on this figure is leaching of constituents from the coal ash into the underlying soil and groundwater. However, some groundwater, surface water and soil standards were also exceeded due to naturally occurring elements found in the subsurface, including antimony, cobalt, iron, manganese, pH and vanadium. The CSA found no imminent hazards to public health and safety; therefore, no actions to mitigate imminent hazards are required. However, corrective action at the site is required to address soil and groundwater contamination. Proposed corrective action will be outlined in the Corrective Action Plan to be submitted in accordance with CAMA. Soil sample test results do not provide evidence of soil contamination beneath the ash basin. Although some constituent levels were measured above 2L Standards in soil samples beneath the basin, in general levels appeared to be similar to constituent levels measured from background well soil samples. In general, with the exception of the single sample of cobalt concentration above background at the toe of the ash dam, constituent concentrations of barium, cobalt, iron, manganese, selenium and vanadium were higher in soil compared to ash, and are considered to represent naturally occurring background conditions. The CSA found that several COls exceed their respective 2L Standards or IMACs in groundwater samples collected from the assessment. These constituents include antimony, arsenic, beryllium, boron, cadmium, chloride, chromium, cobalt, iron, manganese, pH, thallium, TDS, and vanadium. Exceedances for antimony, iron, manganese, pH and vanadium were also observed at background monitoring well locations. Elevated concentrations above background for EPA CCR detection monitoring constituents boron and chloride occur in limited areas in the vicinity of the ash basin dam and to the west of the ash basin and Middleton Loop Road, which indicates impacts from the ash basin. The approximate vertical extent of groundwater impacts is generally limited to the shallow and deep flow layers, as shown by the rarity of exceedances within the bedrock flow layer, and vertical migration of COls is impeded by the underlying bedrock. Significant factors affecting contaminant transport are those 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, 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 ES -15 Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report Belews Creek Steam Station Ash Basin FN EXECUTIVE SUMMARY the respective soil/rock matrix. The data indicates that geologic conditions present beneath the ash basin impede the vertical migration of contaminants. The CSA found that the direction of mobile contaminant transport is to the north toward the Dan River and not towards off-site receptors. The human health and ecological screening -level risk assessments did not specifically identify the presence of health or environmental risks; however, the results indicate that constituents in environmental media could be of concern and further investigation by a site-specific risk assessment may be warranted. No imminent hazards to human health and the environment were identified during the screening -level risk assessments. In accordance with CAMA, Duke Energy is required to implement closure and remediation of the BCSS ash basin no later than August 1, 2029 (or sooner if classified as intermediate or high risk). Closure for the BCSS ash basin was not defined in CAMA. Based on the findings of this CSA report, groundwater contamination is present beneath and downgradient of the ash basin. Duke Energy will pursue corrective action under 15A NCAC 02L .0106. The approaches to corrective action under rule .0106(k) or (1) will be evaluated along with other remedies depending on the results of groundwater modeling and evaluation of the site's suitability to use monitored natural attenuation or other industry- accepted methodologies. ES -16