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HomeMy WebLinkAboutNC0001422_FINAL Sutton CSA Report 08-05-2015_201508056uRE ENERGY Auyust 4, 2015 Mr. Donald R. van der vaarff, Secretary North Carolina Department of Environment and Natural Resuurces i eui l9lail Service Center Raleigh, North Carolina 2/ba9-1bul Subject: uuMPREHENSIVE SITE ASSESSMENT REPORT Duke Eneryy E.v. Suttun Eneryy Gumplex Wilmington; New Hanover County, North Carolina NPDES Permit IQu. NCu001422 Dear Mr. van der Vaart: Rariy R. saeris Senior Vice -President Environmental, I9ealtR & Sarety 526 Suuth Church Street: Mail Code EC3XP Charlotte, ivortrl Larolina 25zuz 704-382-4303 In accordance With the %F111 Carolina Department ut Environment and Natural Resources Division of Water Resources' February 6, 2015 letter (Cnditibnal Approval of 1�rcrvizica Grou-ndwaafCrASS&Swi i"T WurK Man), DuRe Eneryy hereby submits the Comprehensive Site Assessment (GSA) Report for the L.V. Sutton E, iv, yy Cumplcx. As inaivatea 6eluw, DuRe Eneryy is alsu pruvidiny the USA Report to additional NGDENR Central Office personnel, the NGDENR Wilmington Regional Office, a, id the Cual ASH Manayement Gummissiun. We consider develupment ana submittal ut tHis GSA Repurt to satisty the directives of your Gunditional Approval letter as well as the requirements of Suction i 3uA-3u9.2ua(a)(4) ana Section 13uA-3ua.2u9(d) ut the Cual ASH Manayement Act of 2014. It yuu Have uumments and/or questions, please direct them to me at 704-382-4303 or Ed Sullivan, Manager of Waste & Groundwater Pruyrdms, at 98u-3t3-3ily. Sincerely Rarry R. Sideris Senior Vice -President Environmental, Realth & Safety Enclosure: Comprehensive Site Assessment Repurt, L.V. Sutton Eneryy Complex cc. Stanley (Jay) Zimmerman, Director, Division of Water Resources, Central office Steven Canter; Hydrogeologist, Water Quality Reyiunal upertiuns Section, Central cmice Turn Reeaer, Assistant Secretary Tor Environment NGDENR Wilmington Regional Office Uual Ash Manayement Commission 4cll synTerra COMPREHENSIVE SITE ASSESSMENT REPORT 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: LX Sutton Energy Complex 801 Sutton Steam Plant Road Wilmington, North Carolina 28401 Not Assigned NC0001422 August 5, 2015 Duke Energy Progress, Inc. 526 South Church St Charlotte, NC 28202 (980) 373-3719 SynTerra 148 River Street Greenville, South Carolina (864) 421-9999 N 34.283296 / W-77.985860 / Perry Wrep a for Project eager Webb, NC PG 1328 Project Director INNOVATE 148 River Street, Suite 220 Greenville, SC 29601 (864)421-9999 Fax (864)421-9909 www.synterracorp.com DIVISION OF WATER RESOURCES Certification for the Submittal of a Comprehensive Site Assessment Responsible Party and/or Permittee: Duke Energy Progress, Inc. Contact Person: Harry Sideris Address: 526 South Church Street City: Charlotte State: NC Zip Code: 28202 Site Name: L.V. Sutton Energy Complex Address: 801 Sutton Steam Plant Road City: Wilmington State: NC Zip Code: 28401 Groundwater Incident Number (applicable): NA/ Coal Ash Management Act CSA I, Kathy Webb, a Professional Engineer/Professional Geologist (circle one) for SynTerra Corporation (firm or company of employment) do hereby certify that the information indicated below is enclosed as part of the required Comprehensive Site Assessment (CSA) and that to the best of my knowledge the data, assessments, conclusions, recommendations and other associated materials are correct, complete and accurate. (Each i m must be initialed by the certifying licensed professional) 1. The source of the coal combustion residuals (contamination) has been identified. A list of all potential sources of the coal combustion residuals (contamination) is attached. 2. Imminent hazards to public health and safety have been evaluated. 3. Potential receptors and significant exposure pathways have been identified 4. Geological and hydrogeological features influencing the movement of groundwater have been identified. The chemical and physical character of the contaminants have been identified. 5. The CSA sufficiently characterizes the cause, significance and extent of groundwater and soil contamination associated with the regulated coal ash management areas such that a groundwater Corrective Action Plan can be developed. If any of the above statements have been altered or items not initialed, provide a detailed explanation. Failure to initial any item or to provide written justification for the lack thereof will result in immediate return of the CSA to the responsible party. (Please Alix Seal and Signature) SIA w OGI °+sr. W P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\DWR CSA Certification Page.docx Page 1 of 2 Item 1. The CSA was specifically designed to assess the coal ash management areas of the facility. Sufficient information is available to prepare the groundwater corrective action plan for the ash management areas of the facility. Data limitations are discussed in Section 14 of the CSA report. Continued groundwater monitoring at the site is planned. Item 2. Imminent hazards to human health and the environment have been evaluated. The NCDENR data associated with nearby water supply wells is provided herein and is being evaluated. In the meantime, plans are underway to replace the nearby public water supply system and to install an interim groundwater corrective action plan. Item 5. The groundwater assessment plan for the CSA as approved by NCDENR was specifically developed to assess the coal ash management areas of the facility for the purposes of developing a corrective action plan for groundwater. Other areas of possible contamination on the property were not evaluated. P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\DWR CSA Certification Page.docx Page 2 of 2 Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-i P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx L.V. SUTTON ENERGY COMPLEX EXECUTIVE SUMMARY The North Carolina Coal Ash Management Act (CAMA) requires the preparation of a Comprehensive Site Assessment (CSA) Report for each regulated facility within 180 days of approval of the Work Plan. This report addresses Duke Energy’s L.V. Sutton Energy Complex (Site). The Work Plan for the Site was approved on February 6, 2015. The purpose of this assessment is to identify the source and cause of exceedances of regulatory standards, potential hazards to public health and safety, receptors and exposure pathways. NC Department of Environment and Natural Resources (NCDENR) prescribed the list of monitoring parameters to be measured at the Site. Once the sampling portion of the CSA was complete, data were examined to pick those parameters that were most relevant to the Site. These parameters were determined by examining data from monitoring wells installed in ash, and then by comparing these results to 2L or the former Interim Maximum Allowable Concentrations (IMACs). Appendix #1 of 15A NCAC Subchapter 02L Classifications and Water Quality Standards Applicable to The Groundwaters of North Carolina, lists IMACs. The IMACs were issued in 2010 and 2011, however NCDENR has not established a 2L standard for these constituents as described in 15A NCAC 02L.0202(c). For this reason, IMACs noted in this report are for reference only. Parameters detected in ash pore water samples at values greater than 2L or IMAC, were designated as a ‘Constituent of Interest’ (COI). Some COIs (e.g., iron and manganese) are also present in background monitoring wells and thus require careful examination to determine whether their presence on the downgradient side of a basin is from natural sources (e.g., rock and soil) or the ash basin. This assessment addresses the horizontal and vertical extent of COIs in soil and groundwater, significant factors affecting groundwater flow conditions, and the geological and hydrogeological features influencing the movement, chemical, and physical character of COIs. Data presented in this assessment report is the basis for the Corrective Action Plan (CAP) required within 270 days of the approved Work Plan to identify alternative strategies to address groundwater impacts at the site. The Corrective Action Plan, as required by CAMA, will include groundwater model results of the anticipated ash removal to assess the effects on groundwater. A Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-ii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx groundwater monitoring plan will be provided to assess changes in groundwater conditions over time. In accordance with CAMA Section 3(b), Duke Energy will fully excavate the ash basins at the Site, with the material to be safely recycled or reused in a lined structural fill or disposed in a lined landfill. Additionally, a Groundwater Mitigation and Monitoring Plan was submitted to NCDENR in July 2015 which proposed a groundwater extraction system as an interim corrective action to address the migration of COIs. Based on the evaluation of both historical and recently obtained CSA data, the following conclusions are provided: Recent groundwater assessment results are consistent with previous results from historical and routine compliance boundary monitoring well data. Background monitoring wells contain naturally occurring COIs at concentrations greater than 2L or former IMAC. This information is used to evaluate whether concentrations in groundwater downgradient of the basins are naturally occurring, from another source or influenced by migration of constituents from an ash basin. As examples, iron, manganese, cobalt and vanadium are present in the background monitor well samples at concentrations at or above their applicable 2L or IMAC. Regional groundwater flow is to the west toward the Cape Fear River, to the east toward the Northeast Cape Fear River or to the south toward the convergence of the two rivers. In the vicinity of the 1971 and 1984 ash basins, groundwater flows radially. A groundwater divide is located northeast of the ash basins and groundwater north of the basins flow west toward the cooling pond. Groundwater east and south of the basins flows east, southeast and south. In the Former Ash Disposal Area (FADA), groundwater flows to the southwest. Data indicate the water quality of the Cape Fear River has not been impacted by the ash basins. Migration of COIs, primarily boron, above the 2L, has occurred in the lower surficial aquifer at a depth of approximately 25 to 50 feet below ground surface. Concentrations of boron in the ash pore water and groundwater adjacent to the 1971 ash basin are higher than elsewhere on the Site. Also, boron concentrations are not observed in surficial aquifer background wells and concentrations Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-iii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx decrease downgradient of the basins; thus, boron serves as a good indicator of the maximum extent of ash constituent migration. However, boron has also been detected in deeper Pee Dee formation wells at the site. This is likely a result of saltwater intrusion (boron is the 10th most prevalent constituent in sea water). Regional groundwater data supports this. Boron is detectable above the 2L in offsite monitoring wells downgradient and east of the basins. The horizontal extent of the boron concentrations above the 2L has been defined. Boron concentrations greater than 2L do not extend southeast to the public water supply wells located beyond the property boundary southeast of the basins. The approximate extent of horizontal migration of boron is shown on Figure ES-1. The flow paths for COIs indicate a preference for lateral migration, rather than vertical migration, as a result of contrasting hydraulic conductivities between the surficial and Pee Dee formations. A clay confining unit was not observed in the monitoring wells or soil borings within the study area. While no confining unit is present above the Pee Dee Formation, the lower permeability of the Pee Dee Formation reduces vertical migration of COIs. The CSA characterizes the horizontal and vertical extent of COIs and groundwater gradients which now facilitate development of the Site Conceptual Model (SCM) (i.e., the groundwater flow and constituent migration model). This then facilitates development of a CAP due within 90 days of submittal of this CSA report. The horizontal extent of boron in the lower surficial aquifer at levels exceeding the 2L has extended beyond the site boundary to the east. Mitigating actions to address this horizontal extent are already initiated. o An interim corrective action plan has been prepared and submitted to NCDENR. The interim plan proposes 12 groundwater extraction wells along the downgradient property line to intercept the groundwater in the area of boron migration. o Data indicate boron concentrations in nearby water supply wells are less than the 2L. o The approximate extent of horizontal migration of boron in the surficial aquifer is shown on Figure ES-1. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-iv P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Brief summaries of portions of the Comprehensive Site Assessment report are presented in the following sections. ES.1 Source Information Mineralogical, physical, and chemical properties of the Site ash basins have been characterized for use in the hydrogeological SCM. The ash management area consists of three locations; the FADA, the 1971 ash basin and the 1984 ash basin. The FADA, which contains a depth of ash less than 15 feet, is located in a low-lying area and was developed near original ground surface. The 1971 ash basin was excavated to a depth of approximately 40 feet below ground surface (bgs) and contains approximately 80 vertical feet of ash at its deepest point. The 1984 ash basin was constructed near original ground surface and contains a clay liner. Groundwater within the 1971 and 1984 basins is mounded and hydraulically upgradient of the surrounding land surface to the northeast, east and southeast and the normal pool elevation of the cooling pond located to the west. Seepage of water from within the 1971 and 1984 ash basins to groundwater under the basins migrates in a radial pattern. ES.2 Initial Abatement and Emergency Response Duke Energy is currently planning to fully excavate the ash basins in accordance with CAMA requirements; with the material safely recycled or reused in a lined structural fill or disposed in a lined landfill. A Groundwater Mitigation and Monitoring Plan was submitted to NCDENR in July 2015 to address offsite migration of constituents of concern, primarily boron. Twelve extraction wells are proposed along the eastern site boundary to intercept groundwater in the surficial aquifer. Plans to discontinue the use of the nearby municipal water supply wells are underway and Duke has taken proactive steps to replace these water supply wells with a new water line extension. Completion of the replacement well field water system is anticipated by December 2015. ES.3 Receptor Information Land use surrounding the Site includes commercial, industrial, mining (sand quarry), residential, and forest land. The Site is located on a small peninsula formed by the Cape Fear River bordering the Site to the west and the Northeast Cape Fear River located approximately one mile to the east. The two rivers converge in the City of Wilmington south of the Site. Well inventories of public and private wells have been compiled. Nearby property owners have been contacted regarding private wells and a number of water supply wells have been sampled at the direction of NCDENR. Inventories of public and private water supply wells have been updated as part of this assessment. The Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-v P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx groundwater model being developed for the Site will provide additional information on the likelihood of private and public wells being impacted by the Site. ES.3-1 Public Water Supply Wells Four Cape Fear Public Utility Authority (CFPUA) municipal water supply wells are located near the southeastern property boundary of the site. Two of these wells are not in use. Analyses on samples collected routinely from the wells indicate concentrations of manganese slightly above the 2L. Data indicate these exceedances are not related to the ash basins. The CFPUA wells are approximately 50 feet deep within the surficial sand aquifer. These two wells will be eliminated once the new water line is completed in December 2015. After which, all four wells will be properly abandoned. ES.3-2 Private Water Supply Wells Inventories of other smaller public and private water supply wells have been compiled. NCDENR contacted nearby property owners regarding water supply wells and managed the sampling of the wells in accordance with CAMA. Water supply wells are located within 0.5 mile of the site, including on-site wells used for plant operations and wells for commercial and industrial developments. Some of the wells are production wells that might also be used as a source of drinking water as there are no public water lines to these facilities. While some of these wells are potentially located downgradient to the site, and 2L or IMAC were exceeded in some samples for iron, manganese, cobalt and vanadium, these constituents are common to groundwater in the region and their occurrence cannot be conclusively attributed to the ash basins. Where industrial water supply wells are located in the area mapped with boron 2L exceedances based upon monitoring well data, the water supply well sample data provided by NCDENR indicate the boron concentrations are not greater than the 2L for the production well samples. ES.3-3 Human and Ecological Receptors Consumption of groundwater, recreational use of affected surface water (particularly ‘Lake Sutton’ located west of the ash basins, built as the plant cooling pond but open to the public for fishing) and consumption of fish and game potentially affected by these waters are the primary potential exposure pathways for humans in the vicinity of the ash basins. The ecological exposure medium includes potentially impacted soil, surface water and sediments at the site. Groundwater does not present a complete Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-vi P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx exposure pathway to ecological receptors. Potentially complete pathways evaluated for the Site include incidental ingestion of soil or sediment, and ingestion of prey or plants. The Cape Fear River Basin supports over 95 species of commercial and recreational fish, including 42 rare aquatic species. The Cape Fear shiner (Notropis mekistocholas), a federally endangered fish species, is known only to inhabit this river basin. The shortnose sturgeon (Acipenser brevirostrum), red- cockaded woodpecker (Leuconotopicus borealis), Saint Francis’ satyr (Neonympha mitchellii francisci), and the West Indian manatee (Trichechus manatus) (in estuarine areas) are also known species in the Cape Fear River and are federally listed as endangered. The American alligator (Alligator mississippiensis) and the loggerhead turtle (Caretta caretta) are federally listed as threatened. ES.4 Sampling / Investigation Results ES.4-1 Nature and Extent of Contamination Arsenic, barium, boron, cobalt, iron, manganese, selenium, thallium, vanadium and total dissolved solids (TDS) have been identified as site specific COIs based on concentrations in excess of the 2L or IMAC in the saturated ash (pore) water or groundwater. Iron, manganese and vanadium were detected in the ash pore water, however these are naturally-occurring metals common to regional groundwater and their occurrence at the Site cannot be wholly attributed to the ash basins. Cobalt and thallium were not detected in ash pore water samples, therefore the concentrations in groundwater appear to be naturally occurring. Selenium occurs in groundwater in an isolated area north of the ash basins; however it was not detected in the 1971 ash basin pore water. Groundwater data immediately north of the 1984 ash basin can be collected to determine if it is the source of the selenium in this area of the Site. Historical groundwater monitoring has shown that values for iron and occasionally manganese can be greater than the 2L in background wells. Site specific historical data are not available for vanadium. However, iron, manganese and vanadium are known to be commonly occurring in background shallow groundwater in the coastal plain region of North Carolina. Manganese and cobalt were detected in background wells MW-37B/C and MW-5C and iron and vanadium were detected in MW-37B/C at concentrations greater than 2L or IMAC. Arsenic in groundwater at concentrations greater than the 2L is limited to an area southeast of the 1971 ash basin and below the FADA. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-vii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Boron is detectable above the 2L in offsite monitor wells directly east and downgradient of the basins. The horizontal extent of the boron concentrations above the 2L has been defined. Boron concentrations greater than the 2L do not extend southeast to the public water supply wells located beyond the property boundary. The horizontal extent of boron in groundwater greater than the 2L is shown on Figure ES-1. Field observations indicate that the Pee Dee formation is not associated with a clay-confining layer at the site; however the low permeability of the Pee Dee formation, based on hydraulic conductivity values, contrasts with that of the overlying surficial sands and acts as an aquitard to downward vertical flow. ES.4-2 Maximum Contaminant Concentrations For the COIs identified on the basis of basin ash pore water concentrations, boron, iron, manganese and vanadium are the most prevalent in groundwater. Iron, manganese and vanadium were also detected in background wells and the occurrence of these metals can also be attributed to regional groundwater quality. Of these, boron is the only COI that is not typical of surficial aquifer background conditions and attributed to the ash basins in the surficial aquifer wells. The highest concentration of boron in groundwater was detected in MW-23C, a compliance boundary well screened in the lower surficial aquifer and located 500 feet east of the 1971 ash basin. The boron concentration in MW-23C was 3,060µg/l in March 2015 and 2,050µg/l in June 2015. The highest concentration of arsenic in groundwater occurs beneath the FADA. Higher concentrations were detected in the 1971 ash basin pore water well, which is screened below the water table but is not considered groundwater. The CSA data indicate that arsenic migration in groundwater is limited to the FADA waste boundary and an area just southeast of the 1971 ash basin (MW-21C). The highest concentration of iron in groundwater was detected in a sample from SMW-2B, an offsite monitoring well screened in the upper surficial aquifer and located approximately 800 feet east of the site property boundary. The iron concentration at this location is interpreted to be unrelated to the ash basins based on the distribution of iron concentrations across the site. Similar high iron concentrations were also detected in other offsite monitor wells and wells located along the eastern site boundary or upgradient to the ash basins; suggesting the iron is naturally-occurring or related to an offsite source. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-viii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The highest concentration of manganese in groundwater was also detected in a sample from an offsite well, SMW-3C, screened in the lower surficial aquifer and located approximately 900 feet east of the site property boundary. The distribution of manganese is similar to that of iron and is also considered to be unrelated to the ash basins. The highest concentrations of TDS in groundwater were detected in the Pee Dee Formation wells and in surficial wells located along the eastern property boundary. The highest concentration of vanadium in groundwater was 39.6 µg/l detected in a sample collected from MW-20, a well screened in the upper surficial aquifer located southwest and downgradient of the FADA. Cobalt was not detected in the ash pore water and as such its occurrence in several wells at the site is not considered related to the ash basins. The highest concentration of cobalt in groundwater, 93.1µg/l, was detected in SMW-2C; an offsite well which is screened in the lower surficial aquifer and located east of the site property boundary. Selenium was not detected in the ash pore water and is only detected in two wells. Additional data associated with the 1984 basin is needed to rule it out as a possible source of the selenium. Exceedances of 2B concentrations were detected in the surface water samples for aluminum, copper, iron and zinc. Aluminum and copper exceedances were detected in samples collected from the cooling pond. Aluminum was detected above the 2B concentration in samples collected from the Cape Fear River at locations upgradient, adjacent and downgradient to the ash basins, while zinc was detected above the 2B concentration in upgradient samples. ES.4-3 Source Characterization Ash within the basins and the FADA are the source of COIs in groundwater, primarily boron. Ash disposal in the FADA ended in 1971 and sluicing of ash to the 1971 and 1984 basins was discontinued in 2013. The ash within the FADA is less than 15 feet thick and groundwater in the FADA is approximately three feet bgs. The underlying soils in the FADA consist of the medium-fine grained sands of the surficial aquifer. The ash in the 1971 basin is approximately 80 feet thick. The 1971 ash basin area appears to have been excavated below grade to a depth of approximately 40 feet and all but the lower couple of feet of the surficial sands were removed prior to Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-ix P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx placement of the ash. The Pee Dee Formation underlies the remnant surficial aquifer sands below the ash basin. The water level recorded in the 1971 basin was approximately 34 feet bgs and therefore ash below this depth is saturated. When the 1971 ash basin was operational, the discharge was routed to the cooling pond. The cooling pond outfall to the Cape Fear River is regulated under a NPDES permit. The 1971 ash basin continues to receive rainwater and storm water runoff from the plant, which infiltrates into the subsurface of the ash basin. No runoff or discharge occurs from the ash basin. The 1984 ash basin was constructed with a 12-inch thick clay liner. Therefore, drilling into or through the clay liner to collect similar data for the 1984 basin was not conducted. ES.4-4 Receptor Survey A receptor survey was conducted in accordance with CAMA during 2014 and has been updated herein with additional available information. Public water supply wells in New Hanover County draw water from the surficial aquifer. The closest public water supply wells are two active wells located to the southeast of the ash basins and the property line. These wells are routinely sampled. No COIs are detected above the 2L in the public supply wells with the exception of manganese. Based on data obtained during the assessment, the occurrence of manganese in the area of the public supply wells cannot be conclusively attributable to the ash basins. Other water supply wells identified within ½ mile of the compliance boundary are located east and southeast of the site. During 2015, NCDENR managed the sampling of water supply wells in the area. Only iron, manganese, cobalt, and vanadium were reported at concentrations greater than 2L or IMAC. Based on data obtained during the assessment, the occurrence of iron, manganese and cobalt in the wells cannot be directly attributed to the ash basins. Vanadium is also a naturally-occurring element in groundwater and assessment data does not definitively indicate a connection between the detection of vanadium in the supply wells and the ash basins. Boron results for the water supply wells sampled at the direction of NCDENR were reported to be less than the 2L. Constituents of potential concern (COPCs) for human and ecological receptors identified using screening level risk assessment methodology include aluminum, antimony, arsenic, barium, beryllium, boron, cadmium, sulfide, TDS, chromium, Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-x P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx copper, iron, lead, manganese, molybdenum, selenium, thallium, vanadium, and zinc. This list is longer than the list of site COIs due to the conservative approach of comparing analytical results to published reference values in the risk assessment screening process. Additional risk evaluation will be provided as part of the CAP. ES.4-5 Regional Geology and Hydrogeology The Site lies within the Coastal Plain Physiographic Province. The Coastal Plain comprises a wedge shaped sequence of stratified marine and non-marine sedimentary material deposited on crystalline basement. In the eastern part of the North Carolina Coastal Plain, groundwater is obtained from the surficial, Castle Hayne, and Pee Dee aquifers, although the Castle Hayne is not present in the area of the Site. The Coastal Plain groundwater system consists of aquifers comprised of permeable sands, gravels, and limestone separated by confining units of less permeable material. ES.4-6 Site Geology and Hydrogeology Soils exposed at the surface in the Site area are relatively recent Coastal Plain sediments. Sediments of the surficial aquifer are underlain unconformably by the unconfined Pee Dee Formation at approximately 50 feet below land surface. No confining unit was found between the surficial aquifer and the Pee Dee Formation at the site. However, data indicate lower hydraulic conductivities in the Pee Dee formation than in the overlying surficial aquifer, indicating the Pee Dee acts as an aquitard to vertical migration. The site is located on a peninsula of land defined by the Cape Fear River, adjacent to the west and the Northeast Cape Fear River, located approximately one mile to the east. Based on regional topography and drainage features, groundwater flow within this peninsula would be either west or east to one of the two rivers or to the south where the rivers converge. At the site, the current interpretation of groundwater flow indicates that in close proximity to the 1971 and 1984 ash basins, groundwater flows radially; toward the west along the edge of the cooling pond and to the east, southeast and south on the east side of the 1971 ash basin. In the FADA, groundwater flow is to the southwest. A groundwater divide or ridge is located northeast of the ash basins. Areas where shallow water levels appear to be influenced by operating water wells occur near the plant production wells, which are used for industrial purposes, the CFPUA (public water supply) wells, located southeast of the site, and the Wooten plant production wells, located directly to the east of the ash basins. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-xi P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Depth to the water table is approximately 7 to 18 feet below land surface. The potential influence of on-site production wells, off-site municipal and industrial production wells is being evaluated with the groundwater flow model to be presented with the CAP. The model results will be used to further assess the groundwater flow directions at the site. As the model is being prepared, additional groundwater and surface water elevation data may be collected. ES.4-7 Existing Groundwater Monitoring Data The compliance monitoring data indicate that iron has been consistently detected at concentrations greater than the 2L for background well MW-4B, while manganese has been detected at a concentration greater than 2L intermittently. Manganese is consistently detected at a concentration greater than the 2L at the southern compliance well MW-7C. Manganese is typically the only constituent detected at a concentration greater than the 2L at background well MW-5C, to the north of the basins. Manganese and selenium are consistently detected at concentrations greater than the 2L at the northern compliance boundary well MW-27B. Boron, iron, and manganese have been detected at concentrations greater than the 2L in eastern compliance wells MW-19, MW-21C, MW-22B, MW-23C and MW-24C. ES.4-8 Development of Site Conceptual Model A hydrogeological site conceptual model was developed from data generated during previous assessments, existing groundwater monitoring data, and 2015 groundwater assessment activities. In general, the ash basin pore water seeps directly into the porous sands of the surficial aquifer underneath the unlined 1971 ash basin and the FADA. It is anticipated that some migration may occur from the lined basin, however to a lesser extent. The contrast of permeabilities across the surficial/Pee Dee contact reduces downward vertical groundwater flow. The highest concentrations of COIs are detected in the lower surficial aquifer at a depth of approximately 45 feet, above the surficial/Pee Dee contact. The horizontal extent of boron in the surficial groundwater flow zone greater than 2L is shown on ES-1. ES.5 Identification of Data Gaps The horizontal and vertical extent of COIs have been sufficiently determined for soil and groundwater. Source area and groundwater characterization data will be used to support preparation of flow and transport groundwater modeling for the site. The site Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ES-xii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx conceptual model provided herein will also support the modeling and the preparation of the CAP. There are no data gaps that will be limiting factors in the execution of the groundwater model or development of the CAP. However, the following additional information would be useful: 1. Determination of background COI concentrations for deep (Pee Dee formation) groundwater. 2. Evaluation of potential offsite sources or natural conditions related to the concentrations of iron and manganese. 3. Further evaluation of the 1984 basin as a potential source of the selenium in the groundwater north of the ash basin. ES.6 Conclusions Duke Energy plans to excavate the ash basins at the Site in accordance with CAMA requirements. The impact of the ash excavation on long term groundwater quality will be evaluated as part of the groundwater flow and transport modeling to be provided in the Corrective Action Plan. Data indicate groundwater has been impacted by the seepage of ash pore water from the unlined 1971 ash basin and FADA. The lined ash basin may also contribute to this impact, but to a lesser extent. Detectable boron concentrations have migrated offsite to the east. However, the 2015 data collected by NCDENR indicate the boron concentrations in the public and private water supply wells sampled are less than 2L. The extent of the boron concentrations greater than 2L in the surficial aquifer has been defined. The anticipated horizontal and vertical extent of potential migration will be further evaluated by the groundwater modeling to be provided in the CAP. A Groundwater Mitigation and Monitoring Plan has been submitted to protect water supply wells located east of the site. The plan includes the installation of 12 groundwater extraction wells along the eastern property boundary. Groundwater modeling to be provided in the CAP will also evaluate this action combined with removal of the ash from the basins. A plan for future groundwater monitoring is presented in Section 16 of this report. The Corrective Action Plan, based on the data presented in this report and subsequent groundwater modeling, will be submitted within 90 days of this report. # # # # ") ") ") ") ")") ") ") ") U S-421 S R-2 1 6 9 P R J -I -1 4 0 SR-1394 S R -2 7 7 9 S R -2 1 4 5 P R J -I -1 4 0 FORMER ASHDISPOSAL AREA 1984 ASHBASIN(LINED) NEW ASHBASIN AREA(LINED) 1971 ASHBASIN COOLINGPOND COOLINGPOND COOLINGPOND COOLINGPOND CAPE FEARRIVER DRAINAGECHANNEL COOLINGPOND COOLING PONDCOOLING POND FIGURE ES-1SITE CONCEPTUAL MODEL - PLAN VIEWL.V. SUTTON ENERGY COMPLEX ± WATER SUPPLY WELLS1 WATER SUPPLY WELL IN INVENTORY (APPROXIMATE) WOOTEN PRODUCTION WELL (APPROXIMATE) #CFPUA PRODUCTION WELL LOCATION (APPROXIMATE) EDR REPORTED WELL LOCATION (APPROXIMATE) INVISTA PRODUCTION WELL (APPROXIMATE) ")DUKE ENERGY PROGRESSS PRODUCTION WELL (APPROXIMATE) P:\D uke Energy Progress.1026\00 GIS BASE DATA\Sutton\Map_Docs\Draft_CSA_v07152015\Sutton - Figure ES-1 - Executive Summary Figure.mxd L. V. SUTTON ENERGY COMPLEX801 SUTTON STEAM PLANT RDWILMINGTON, NORTH CAROLINA 148 RIVER STREET, SUITE 220GREENVILLE, SC 29601864-421-9999www.synterracorp.com GRAPHIC SCALE 500 0 500 1,000 1,500 2,000 (IN FEET) PROJECT MANAGER: J. MAHAN DRAWN BY: J. MEADOWS DATE: 07/31/2015 DATE: 07/31/2015 CHECKED BY: K. WEBB NOTES:1 FROM DRINKING WATER WELL AND RECEPTOR STUDY (NOVEMBER 2014). 2 BORON EXHIBITS THE GREATEST THREE-DIMENSIONAL EXTENT OFMIGRATION FROM THE L.V. SUTTON ENERGY COMPLEX ASH BASIN. THE NORTHCAROLINA 2L (NC2L) FOR BORON IS 700 μg/L. 3 APRIL 17, 2014 AERIAL ORTHOPHOTOGRAPHY OBTAINED FROM WSP. 4 2012 AERIAL ORTHOPHOTOGRAPHY OBTAINED FROM THE NC CENTER FORGEOGRAPHIC INFORMATION AND ANALYSIS. (http://services.nconemap.gov/) 5 PARCEL BOUNDARY WAS OBTAINED FROM THE NC CENTER FORGEOGRAPHIC INFORMATION AND ANALYSIS. (http://services.nconemap.gov/) 6 DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATEPLANE COORDINATE SYSTEM FIPS 3200 (NAD83/2011). AREA OF CONCENTRATIONS IN GROUNDWATER ABOVE NC2L 2 GROUNDWATER FLOW DIRECTION (SHALLOW AQUIFER) ASH BASIN BOUNDARY ASH BASIN COMPLIANCE BOUNDARY HAL F-MILE OFFSET FROM COMPLIANCE BOUNDARY DUKE ENERGY PROGRESS SUTTON PLANT SITE BOUNDARY LEGEND Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra i P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx TABLE OF CONTENTS SECTION PAGE L.V. Sutton Energy Complex Executive Summary ................................................................ i ES.1 Source Information ........................................................................................................ iv ES.2 Initial Abatement and Emergency Response ........................................................... iv ES.3 Receptor Information .................................................................................................... iv ES.3-1 Public Water Supply Wells ................................................................................. v ES.3-2 Private Water Supply Wells ............................................................................... v ES.3-3 Human and Ecological Receptors ...................................................................... v ES.4 Sampling / Investigation Results ................................................................................ vi ES.4-1 Nature and Extent of Contamination ............................................................... vi ES.4-2 Maximum Contaminant Concentrations ........................................................ vii ES.4-3 Source Characterization ................................................................................... viii ES.4-4 Receptor Survey .................................................................................................. ix ES.4-5 Regional Geology and Hydrogeology .............................................................. x ES.4-6 Site Geology and Hydrogeology ....................................................................... x ES.4-7 Existing Groundwater Monitoring Data ......................................................... xi ES.4-8 Development of Site Conceptual Model .......................................................... xi ES.5 Identification of Data Gaps ......................................................................................... xi ES.6 Conclusions .................................................................................................................... xii 1.0 Introduction ..................................................................................................................... 1 1.1 Purpose of Comprehensive Site Assessment ......................................................... 2 1.2 Regulatory Background ............................................................................................ 2 NCDENR Requirements ..................................................................................... 2 1.2.1 NORR Requirements ........................................................................................... 2 1.2.2 Coal Ash Management Act Requirements ....................................................... 2 1.2.3 1.3 NCDENR-Duke Energy Correspondence .............................................................. 3 1.4 Approach to Comprehensive Site Assessment ...................................................... 4 NORR Guidance ................................................................................................... 4 1.4.1 USEPA Monitored Natural Attenuation Tiered Approach ........................... 4 1.4.2 ASTM Conceptual Site Model ............................................................................ 5 1.4.3 1.5 Technical Objectives .................................................................................................. 5 2.0 Site History and Description ........................................................................................ 6 Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 2.1 Site Location, Acreage, and Ownership ................................................................. 6 2.2 Plant Description ........................................................................................................ 6 2.3 General Site Description ........................................................................................... 7 2.4 Adjacent Property, Zoning, and Surrounding Land Uses ................................... 7 2.5 Adjacent Surface Water Bodies and Classifications .............................................. 7 2.6 Meteorological Setting ............................................................................................... 7 2.7 Hydrologic Setting ..................................................................................................... 8 2.8 Permitted Activities and Permitted Waste ............................................................. 8 2.9 History of NPDES and Surface Water Monitoring ............................................... 8 2.10 Assessment Activities or Previous Site Investigations ......................................... 9 2.11 Corrective Actions ................................................................................................... 12 3.0 Source Characteristics .................................................................................................. 13 3.1 Coal Combustion and Ash Handling System ...................................................... 13 3.2 Physical Properties of Ash ...................................................................................... 13 3.3 Chemical Properties of Ash .................................................................................... 13 3.4 Description of Ash Basins and Other Ash Storage Areas .................................. 15 4.0 Receptor Information ................................................................................................... 17 4.1 Summary of Receptor Survey Activities............................................................... 17 4.2 Summary of Receptor Survey Findings ................................................................ 18 Public Water Supply Wells ............................................................................... 18 4.2.1 Private Water Supply Wells ............................................................................. 19 4.2.2 5.0 Regional Geology and Hydrogeology ...................................................................... 20 5.1 Regional Geology ..................................................................................................... 20 5.2 Regional Hydrogeology .......................................................................................... 20 6.0 Site Geology and Hydrogeology ................................................................................ 22 6.1 Site Geology .............................................................................................................. 25 Soil Classification ............................................................................................... 25 6.1.1 Rock Lithology ................................................................................................... 26 6.1.2 Structural Geology ............................................................................................. 26 6.1.3 Soil and Rock Mineralogy and Chemistry ..................................................... 26 6.1.4 6.2 Site Hydrogeology ................................................................................................... 26 Groundwater Flow Direction ........................................................................... 27 6.2.1 Hydraulic Gradients .......................................................................................... 28 6.2.2 Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Hydraulic Conductivity .................................................................................... 28 6.2.3 Groundwater Velocity ....................................................................................... 28 6.2.4 Effects of Geologic/Hydrogeologic Characteristics on Contaminants ....... 29 6.2.5 6.3 Hydrogeologic Site Conceptual Model ...................................................................... 29 6.4 Geochemical Site Conceptual Model .................................................................... 30 Iron ....................................................................................................................... 30 6.4.1 Vanadium ............................................................................................................ 30 6.4.2 Manganese .......................................................................................................... 31 6.4.3 Boron .................................................................................................................... 31 6.4.4 Arsenic ................................................................................................................. 33 6.4.5 Cobalt ................................................................................................................... 33 6.4.6 6.5 Electrochemical Charge Balance ............................................................................ 33 6.6 Equilibrium ............................................................................................................... 34 7.0 Source Characterization ............................................................................................... 36 7.1 Identification and Description of Sources ............................................................ 36 Coal Combustion and Ash Handling System ................................................ 36 7.1.1 Description of Ash Basins ................................................................................. 36 7.1.2 7.2 Characterization of Sources .................................................................................... 37 Physical Properties of Ash ................................................................................ 37 7.2.1 Chemical Properties of Ash .............................................................................. 38 7.2.2 Chemistry of Ash Pore Water .......................................................................... 39 7.2.3 Hydrology of the Ash Basins ........................................................................... 39 7.2.4 7.3 Piezometers and Seeps ............................................................................................ 40 7.4 Constituents of Interest ........................................................................................... 41 8.0 Soil and Rock Characterization .................................................................................. 42 8.1 Background Soil ....................................................................................................... 43 Soils beneath the Ash Basin .............................................................................. 43 8.1.1 Site Soils ............................................................................................................... 44 8.1.2 Surficial Soils....................................................................................................... 44 8.1.3 8.2 Comparison of Results to Applicable Levels ....................................................... 45 9.0 Sediment and Surface Water Characterization ....................................................... 46 9.1 Comparison of Exceedances to 2B Standards ...................................................... 46 9.2 Discussion of Results for Constituents Without Established 2B ....................... 47 Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 10.0 Groundwater Characterization ................................................................................... 48 10.1 Background Groundwater Conditions ................................................................. 48 10.2 Discussion of Redox Conditions ............................................................................ 48 10.3 Regional Groundwater Data for Constituents of Potential Concern................ 49 10.4 Groundwater Analytical Results ........................................................................... 49 10.5 Comparison of Results to 2L Standards ............................................................... 53 11.0 Hydrogeological Investigation ................................................................................... 55 11.1 Hydrostratigraphic Layer Development .............................................................. 55 11.2 Hydrostratigraphic Layer Properties .................................................................... 55 Confining Unit .............................................................................................. 55 11.2.1 In-Situ Tests ................................................................................................... 56 11.2.2 Slug Tests ....................................................................................................... 56 11.2.3 Porosity .......................................................................................................... 56 11.2.4 11.3 Groundwater Flow Direction ................................................................................. 56 11.4 Hydraulic Gradient .................................................................................................. 57 11.5 Groundwater Velocity ............................................................................................. 57 11.6 Contaminant Velocity .............................................................................................. 57 11.7 Characterization of COI Distribution .................................................................... 57 11.8 Groundwater / Surface Water Interaction ............................................................ 57 12.0 Screening-Level Risk Assessment ............................................................................. 58 12.1 Human Health Screening........................................................................................ 58 Introduction ................................................................................................... 58 12.1.1 Conceptual Exposure Model ....................................................................... 58 12.1.2 12.1.2.1 Current/Future Recreational Fisherman .............................................. 60 12.1.2.2 Current/Future Recreational Swimmer ................................................ 60 12.1.2.3 Current/Future Recreational Hunter .................................................... 60 12.1.2.4 Current/Future Industrial Worker ........................................................ 60 12.1.2.5 Future Resident ........................................................................................ 60 Risk-Based Screening Levels ....................................................................... 60 12.1.3 Site Specific Risk Based Remediation Standards ..................................... 78 12.1.4 12.2 Ecological Screening ................................................................................................ 78 Introduction ........................................................................................................ 78 12.2.1 Ecological Setting ............................................................................................... 78 12.2.2 Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 12.2.2.1 Facility Site Summary ............................................................................. 78 12.2.2.2 Regional Ecological Setting .................................................................... 78 12.2.2.3 Description of Ecoregion and Expected Habitats ............................... 79 12.2.2.4 Watershed in which the Site is Located ............................................... 79 12.2.2.5 Average Rainfall ...................................................................................... 79 12.2.2.6 Average Temperature ............................................................................. 79 12.2.2.7 Length of Growing Season ..................................................................... 79 12.2.2.8 Threatened and Endangered Species that use Habitats in the Ecoregion ................................................................................................................... 79 12.2.2.9 Site-Specific Ecological Setting .............................................................. 79 12.2.2.10 On-site and Off-site Land Use ............................................................. 79 12.2.2.11 Habitats within the Site Boundary ...................................................... 80 12.2.2.12 Description of Man-made Units that May Act as Habitat ............... 80 12.2.2.13 Site Layout and Topography ............................................................... 80 12.2.2.14 Surface Water Runoff Pathways ......................................................... 81 12.2.2.15 Soil Types................................................................................................ 81 12.2.2.16 Species Normally Expected to Use Site under Relatively Unaffected Conditions ................................................................................................................. 81 12.2.2.17 Species of Special Concern ................................................................... 81 12.2.2.18 Nearby Critical and/or Sensitive Habitats ......................................... 81 Fate and Transport Mechanisms ...................................................................... 81 12.2.3 Preliminary Exposure Estimate and Risk Calculation.................................. 83 12.2.4 Comparison to Ecological Screening Levels .................................................. 83 12.2.5 12.3 Uncertainty and Data Gaps .................................................................................... 90 12.4 Scientific/Management Decision Point ................................................................. 90 12.5 Risk Assessment Summary..................................................................................... 91 13.0 Groundwater Modeling ............................................................................................... 92 13.1 Groundwater Modeling to be Performed in CAP ............................................... 92 13.2 Description of Kd Term Development.................................................................. 93 13.3 Description of Flow Transects ................................................................................ 93 13.4 Other Model Inputs ................................................................................................. 94 14.0 Data Gaps – Site Conceptual Model Uncertainties ................................................ 95 14.1 Data Gaps .................................................................................................................. 95 Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 14.2 Site Heterogeneities ................................................................................................. 95 14.3 Impact of Data Gaps and Site Heterogeneities .................................................... 96 15.0 Planned Sampling for CSA Supplement ................................................................. 97 16.0 Interim Groundwater Monitoring Plan .................................................................... 98 16.1 Sampling Frequency ................................................................................................ 98 16.2 Constituent and Parameter List ............................................................................. 98 16.3 Proposed Sampling Locations ................................................................................ 98 16.4 Proposed Background Wells .................................................................................. 98 17.0 Discussion ...................................................................................................................... 99 17.1 Maximum COI Concentrations .............................................................................. 99 17.2 Summary of Completed and Ongoing Work ..................................................... 100 17.3 Contaminant Migration and Potentially Affected Receptors .......................... 100 18.0 Conclusions and Recommendations ....................................................................... 101 18.1 Source and Cause of Contamination ................................................................... 101 18.2 Imminent Hazards to Public Health and Safety and Actions Taken to Mitigate Them ........................................................................................................................ 101 18.3 Receptors and Significant Exposure Pathways ................................................. 101 18.4 Horizontal and Vertical Extent of Soil and Groundwater Contamination .... 102 18.5 Geological and Hydrogeological Features influencing the Movement, Chemical, and Physical Character of the Contaminants .............................................. 104 18.6 Proposed Continued Monitoring......................................................................... 104 18.7 Preliminary Evaluation of Corrective Action Alternatives.............................. 104 19.0 References ..................................................................................................................... 106 Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra vii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF FIGURES Executive Summary Figure ES-1 Site Conceptual Model - Plan View 1.0 Introduction Figure 1-1 Site Location Map Figure 1-2 Site Layout Map 2.0 Site History and Description Figure 2-1 1949 Aerial Photograph Figure 2-2 1981 Aerial Photograph Figure 2-3 Historical USGS Topographic Map 3.0 Source Characteristics Figure 3-1 Known Sample of Ash for Comparison Figure 3-2 Elemental Composition for Bottom Ash, Fly Ash, Shale, and Volcanic Ash Figure 3-3 Coal Ash TCLP Leachate Concentration Ranges Compared to Regulatory Limits Figure 3-4 Trace Element Concentration Ranges in Ash Compared to EPA Residential Soil Screening Levels 6.0 Site Geology and Hydrogeology Figure 6-1 Geologic Cross-Section A-A' Figure 6-2 Geologic Cross-Section B-B' and C-C' Figure 6-3 Geologic Cross-Section A-A' North End with Photographs Figure 6-4 Geologic Cross-Section A-A' South End with Photographs Figure 6-5 Geologic Cross-Section C-C' with Photographs Figure 6-6 Potentiometric Surface - Upper Surficial Aquifer, June 1, 2015 Figure 6-7 Potentiometric Surface - Lower Surficial Aquifer, June 1, 2015 Figure 6-8 Potentiometric Surface - Pee Dee Aquifer, June 1, 2015 Figure 6-9 Cross Section - Site Conceptual Model Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra viii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF FIGURES 8.0 Soil and Rock Characterization Figure 8-1 Geologic Cross-Section A-A' with COI Analytical Results Figure 8-2 Geologic Cross-Sections B-B' and C-C' with COI Analytical Results Figure 8-3 Site Map with Soil Exceedances 10.0 Groundwater Characterization Figure 10-1 Site Layout with 2L Exceedances - Upper Surficial Aquifer Figure 10-2 Site Layout with 2L Exceedances - Lower Surficial Aquifer Figure 10-3 Site Layout with 2L Exceedances - Upper Pee Dee Wells Figure 10-4 Site Layout with 2L Exceedances - Lower Pee Dee Wells Figure 10-5 June 2015 Isoconcentration Map - Arsenic in Upper Surficial Wells Figure 10-6 June 2015 Isoconcentration Map - Barium in Upper Surficial Wells Figure 10-7 June 2015 Isoconcentration Map - Boron in Upper Surficial Wells Figure 10-8 June 2015 Isoconcentration Map - Cobalt in Upper Surficial Wells Figure 10-9 June 2015 Isoconcentration Map - Iron in Upper Surficial Wells Figure 10-10 June 2015 Isoconcentration Map - Manganese in Upper Surficial Wells Figure 10-11 June 2015 Isoconcentration Map - pH in Upper Surficial Wells Figure 10-12 June 2015 Isoconcentration Map - Thallium in Upper Surficial Wells Figure 10-13 June 2015 Isoconcentration Map - Total Dissolved Solids in Upper Surficial Wells Figure 10-14 June 2015 Isoconcentration Map - Vanadium in Upper Surficial Wells Figure 10-15 June 2015 Isoconcentration Map - Arsenic in Lower Surficial Wells Figure 10-16 June 2015 Isoconcentration Map - Barium in Lower Surficial Wells Figure 10-17 June 2015 Isoconcentration Map - Boron in Lower Surficial Wells Figure 10-18 June 2015 Isoconcentration Map - Cobalt in Lower Surficial Wells Figure 10-19 June 2015 Isoconcentration Map - Iron in Lower Surficial Wells Figure 10-20 June 2015 Isoconcentration Map - Manganese in Lower Surficial Wells Figure 10-21 June 2015 Isoconcentration Map - pH in Lower Surficial Wells Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra ix P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF FIGURES 10.0 Groundwater Characterization (Continued) Figure 10-22 June 2015 Isoconcentration Map - Thallium in Lower Surficial Wells Figure 10-23 June 2015 Isoconcentration Map - Total Dissolved Solids in Lower Surficial Wells Figure 10-24 June 2015 Isoconcentration Map - Vanadium in Lower Surficial Wells Figure 10-25 June 2015 Isoconcentration Map - Arsenic in Upper Pee Dee Wells Figure 10-26 June 2015 Isoconcentration Map - Barium in Upper Pee Dee Wells Figure 10-27 June 2015 Isoconcentration Map - Boron in Upper Pee Dee Wells Figure 10-28 June 2015 Isoconcentration Map - Cobalt in Upper Pee Dee Wells Figure 10-29 June 2015 Isoconcentration Map - Iron in Upper Pee Dee Wells Figure 10-30 June 2015 Isoconcentration Map - Manganese in Upper Pee Dee Wells Figure 10-31 June 2015 Isoconcentration Map - pH in Upper Pee Dee Wells Figure 10-32 June 2015 Isoconcentration Map - Thallium in Upper Pee Dee Wells Figure 10-33 June 2015 Isoconcentration Map - Total Dissolved Solids in Upper Pee Dee Wells Figure 10-34 June 2015 Isoconcentration Map - Vanadium in Upper Pee Dee Wells Figure 10-35 June 2015 Isoconcentration Map - Arsenic in Lower Pee Dee Wells Figure 10-36 June 2015 Isoconcentration Map - Barium in Lower Pee Dee Wells Figure 10-37 June 2015 Isoconcentration Map - Boron in Lower Pee Dee Wells Figure 10-38 June 2015 Isoconcentration Map - Cobalt in Lower Pee Dee Wells Figure 10-39 June 2015 Isoconcentration Map - Iron in Lower Pee Dee Wells Figure 10-40 June 2015 Isoconcentration Map - Manganese in Lower Pee Dee Wells Figure 10-41 June 2015 Isoconcentration Map - pH in Lower Pee Dee Wells Figure 10-42 June 2015 Isoconcentration Map - Thallium in Lower Pee Dee Wells Figure 10-43 June 2015 Isoconcentration Map - Total Dissolved Solids in Lower Pee Dee Wells Figure 10-44 June 2015 Isoconcentration Map - Vanadium in Lower Pee Dee Wells Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra x P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF FIGURES 10.0 Groundwater Characterization (Continued) Figure 10-45 CCR Rule Detection Monitoring Constituent Map - Upper Surficial Aquifer Figure 10-46 CCR Rule Detection Monitoring Constituent Map - Lower Surficial Aquifer Figure 10-47 CCR Rule Detection Monitoring Constituent Map - Upper Pee Dee Wells Figure 10-48 CCR Rule Detection Monitoring Constituent Map - Lower Pee Dee Wells Figure 10-49 CCR Rule Assessment Monitoring Constituent Map - Upper Surficial Aquifer Figure 10-50 CCR Rule Assessment Monitoring Constituent Map - Lower Surficial Aquifer Figure 10-51 CCR Rule Assessment Monitoring Constituent Map - Upper Pee Dee Wells Figure 10-52 CCR Rule Assessment Monitoring Constituent Map - Lower Pee Dee Wells Figure 10-53 Ash Pore Water Piper Diagrams Figure 10-54 Pee Dee Water Piper Diagrams Figure 10-55 Surficial Aquifer (Shallow) Piper Diagrams Figure 10-56 Surficial Aquifer (Intermediate) Piper Diagrams Figure 10-57 Surficial Aquifer (Deep) Piper Diagrams Figure 10-58 Surface Water Piper Diagram Figure 10-59 Compliance Well Box and Whisker Plots - Arsenic, Barium, Boron Figure 10-60 Compliance Well Box and Whisker Plots - Chloride, Iron, Manganese Figure 10-61 Compliance Well Box and Whisker Plots - Nitrate, Selenium, Sulfate Figure 10-62 Compliance Well Box and Whisker Plots - TDS, Thallium, Zinc Figure 10-63 Compliance Well Box and Whisker Plots - Dissolved Oxygen, pH, Turbidity Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra xi P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF FIGURES 11.0 Hydrogeological Investigation Figure 11-1 Geologic Cross-Sections with Boron and Arsenic Figure 11-2 Geologic Cross-Sections with Iron and Cobalt Figure 11-3 Geologic Cross-Sections with Manganese and Vanadium Figure 11-4 Geologic Cross-Sections with Thallium 12.0 Screening-Level Risk Assessment Figure 12-1 Conceptual Exposure Model - Human Health Figure 12-2 COPC Locations Flagged - Groundwater - Ash Pore Water - Human Health Figure 12-3 COPC Locations Flagged - Groundwater - Upper Surficial Aquifer - Human Health Figure 12-4 COPC Locations Flagged - Groundwater - Lower Surficial Aquifer - Human Health Figure 12-5 COPC Locations Flagged - Groundwater - Upper Pee Dee Aquifer - Human Health Figure 12-6 COPC Locations Flagged - Groundwater - Lower Pee Dee Aquifer - Human Health Figure 12-7 COPC Locations Flagged - Soils (0-2 feet) - Human Health Figure 12-8 COPC Locations Flagged - Sediment - Human Health Figure 12-9 COPC Locations Flagged - Surface Water - Human Health Figure 12-10 Conceptual Exposure Model - Ecological CEM Figure 12-11 COPC Locations Flagged - Soils (0-2 feet) - Ecological Figure 12-13 COPC Locations Flagged - Sediment - Ecological Figure 12-12 COPC Locations Flagged - Surface Water - Ecological 16.0 Interim Groundwater Monitoring Plan Figure 16-1 Proposed Groundwater Monitoring Locations Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra xii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF TABLES 2.0 Site History and Description Table 2-1 NPDES Groundwater Monitoring Requirements Table 2-2 Compliance Well 15 NCAC 2L Exceedances 3.0 Source Characteristics Table 3-1 Ash, Rock, and Soil Composition 6.0 Site Geology and Hydrogeology Table 6-1 Exploration and Sampling Plan Table 6-2 Soil, Sediment, and Ash COIs and Analytical Methods Table 6-3 Ash Pore Water, Groundwater, and Surface Water COIs Analytical Methods Table 6-4 Well Construction Data Table 6-5 Water Level Measurements - June 2015 Table 6-6 Local Groundwater Gradients and Flow Velocities Table 6-7 In-Situ Hydraulic Conductivity Test Results Table 6-8 Vertical Hydraulic Conductivity of Undisturbed Soil Samples 7.0 Source Characterization Table 7-1 Physical Properties of Ash Table 7-2 Mineralogy of Ash Table 7-3 Chemical Properties of Ash Table 7-4 Leaching Properties of Ash Table 7-5 Whole Rock Metal Oxide Analysis of Ash Table 7-6 Whole Rock Elemental Analysis of Ash Table 7-7 Ash Pore Water Analytical Results Table 7-8 2015 15 NCAC 2L Exceedances in Ash Pore Water Table 7-9 Valence Speciation of Ash Pore Water 8.0 Soil and Rock Characterization Table 8-1 Physical Properties of Soil Table 8-2 Mineralogy of Soils Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Table 8-3 Chemical Properties of Soil Table 8-4 Leaching Properties of Soil Table 8-5 Whole Rock Metal Oxide Analysis of Soil Table 8-6 Whole Rock Elemental Analysis of Soil 9.0 Sediment, Seep, and Surface Water Characterization Table 9-1 Sediment Analytical Results Table 9-2 Surface Water Analytical Results Table 9-3 15 NCAC 2B Exceedances in Surface Water 10.0 Groundwater Characterization Table 10-1 Groundwater Analytical Results Table 10-2 15 NCAC 2L Exceedances in Groundwater Table 10-3 Valence Speciation of Groundwater Table 10-4 Radiological Analytical Results Table 10-5 Cations-Anions Balance 12.0 Screening-Level Risk Assessment Table 12-1 Risk Screening Table: Coal Ash Pore Water Data Table 12-2 Coal Ash COPC Determination Table 12-3 Risk Screening Table: Surficial Aquifer Background Groundwater Data Table 12-4 Risk Screening Table: Surficial Aquifer Downgradient Groundwater Data Table 12-5 Risk Screening Table: Pee Dee Formation Groundwater Data Table 12-6 Soils (0-2) Analytical Results with Screening Criteria - Residential and Industrial Soils - Human Health Table 12-7 Sediment Analytical Results with Screening Criteria - Residential and Industrial Soils - Human Health Table 12-8 Surface Water Analytical Results with Screening Criteria - EPA Recommended Water Quality Criteria and NCAC 2B Standards - Human Health Table 12-9 Matrix for Determination of Constituents of Potential Concern - Human Health Table 12-10 Threatened & Endangered Species in New Hanover County Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra xiv P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Table 12-11 Surface Water Analytical Results with Screening Criteria - NCAC 2B and EPA Recommended Water Quality Criteria for Aquatic Life (Acute and Chronic) - Ecological Table 12-12 Soils (0-2) Analytical Results - EPA Ecological Soil Screening Levels and EPA Region 4 Recommended Ecological Screening Values for Soil Table 12-13 Sediment Analytical Results with Screening Criteria - EPA Region 4 Soil Screening Levels and EPA Region 4 Recommended Ecological Screening Values - Ecological Table 12-14 Matrix for Determination of Constituents of Potential Concern - Ecological 16.0 Interim Groundwater Monitoring Plan Table 16-1 Recommended Groundwater Monitoring Parameters Table 16-2 Recommended Groundwater Monitoring Locations Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF APPENDICES Appendix A Regulatory Correspondence NCDENR to DEP, 7/7/2015 NCDENR to DEP, 6/9/2015 NCDENR CSA Guideline Adjustment, Final Addendum 1, June 2015 NCDENR to DEP, 5/22/2015 NCDENR to DEP, 2/6/2015 NCDENR to DEP, 11/4/2014 NCDENR to DEP, 8/13/2014 NCDENR Hydrogeologic Investigation and Reporting Policy Appendix B Water Well and Receptor Survey Table B-1 NCDENR 2015 Water Well Data Table B-2 NCDENR Water Supply Well Tracking Information Table B-3 Public and Private Water Supply Wells (0.5 Mile Radius) Table B-4 Parcel Ownership Information Figure B-1 Receptor Vicinity Map NCDENR 2015 Water Well Sample Laboratory Results and Chain of Custody Forms (CD) Appendix C Methodology SynTerra Field Procedures Appendix D Quality Control Data Table D-1 Rinse Blank Analyses for Soils Table D-2 Rinse Blank Analyses for Groundwater -TOTAL Table D-3 Rinse Blank Analyses for Groundwater -DISSOLVED Appendix E 2015 Groundwater Assessment Documentation Boring Logs and Well Construction Diagrams Driller Well Construction Records Historical Boring Logs and Well Construction Diagrams Appendix F Soils Test Data Whole Rock Metal Oxides, Whole Rock Elemental Analysis, X-ray Diffraction Grain Size Distribution and Specific Gravity Moisture Content Vertical Hydraulic Conductivity Comprehensive Site Assessment Report August 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF APPENDICES Appendix G In-Situ Hydraulic Conductivity Measurements Slug Test Results Appendix H Statistical Analysis of Compliance Well Groundwater Results Table 1 Summary of Percent Nondetects, Treatment Type, and Data Distribution - March 2015 Table 2 Summary of Interwell Prediction Limit Results – March 2015 Figure H-1 Time versus Concentration - Comparison Between Compliance & Background Wells - Barium Figure H-2 Time versus Concentration - Comparison Between Compliance & Background - Boron Figure H-3 Time versus Concentration - Comparison Between Compliance & Background - Chloride Figure H-4 Time versus Concentration - Comparison Between Compliance & Background - Iron Figure H-5 Time versus Concentration - Comparison Between Compliance & Background - Manganese Figure H-6 Time versus Concentration - Comparison Between Compliance & Background - Sulfate Figure H-7 Time versus Concentration - Comparison Between Compliance & Background - TDS Figure H-8 Time versus Concentration and ORP MW-4B, MW-22B, MW-23B Figure H-9 Time versus Concentration and ORP MW-24B, MW-27B, MW-28B Figure H-10 Time versus Concentration and ORP MW-5C, MW-7C, MW-21C Figure H-11 Time versus Concentration and ORP MW-22C, MW-23C, MW-24C Figure H-12 Time versus Concentration and ORP-MW-28C, MW-31C Figure H-13 Time versus Concentration and ORP-MW-11, MW-12, MW 19 Appendix I Screening Level Risk Assessment Ecological Assessment Checklist Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra xvii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF ATTACHMENTS Attachment 1 Historical Geosyntec Reports Attachment 2 Topographic, Underground Utility Maps, and EDR Reports (CD) Attachment 3 Drinking Water and Receptor Survey Reports (CD) Attachment 4 Comprehensive Analytical Results Table (CD) Attachment 5 Laboratory Reports - Chemical Analyses (CD) Attachment 6 Photographs (CD) Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra xviii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF ACRONYMS AMSL above mean sea level ARAR Applicable or Relevant and Appropriate Requirements ASTM American Society for Testing and Materials BBL BW Blasland, Bouck and Lee Background Well bgs below ground surface CAMA Coal Ash Management Act CCR Coal Combustion Residuals CEM Conceptual Exposure Model CFPUA COI Cape Fear Public Utility Authority Constituents of Interest COPC Constituents of Potential Concern CPT CSA Cone Penetrometer Test Comprehensive Site Assessment CUB DEP Confining Unit Boring Duke Energy Progress, Inc. DO Dissolved Oxygen DPT Direct Push Technology DWR Division of Water Resources EDXRF Energy Dispersive X-ray Diffraction ESV Ecological Screening Value FADA GAP Former Ash Disposal Area Groundwater Assessment Plan GIS Geographic Information System HHRA Human Health Risk Assessment HQ IMAC Hazard Quotient Interim Maximum Allowable Concentration MCL Maximum Contaminant Level MSL Mean Sea Level MW Monitoring Well NCDENR North Carolina Department of Environment and Natural Resources NOAA National Oceanic and Atmospheric Administration Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra xix P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx LIST OF ACRONYMS NORR Notice of Regulatory Requirements NPDES National Pollution Discharge Elimination System NTU Nepthalic Turbidity Unit NURE ORP National Uranium Resource Evaluation Oxidation-Reduction Potential OW Observation Well PVC Polyvinylchloride PZ Piezometer RSL USEPA Regional Screening Level SCM Site Site Conceptual Model L.V. Sutton Energy Complex SLERA Screening Level Ecological Risk Assessment SPLP Synthetic Precipitation Leaching Procedure SW Surface Water 2B NCDENR/DWR Title 15, Subchapter 2B. Surface Water and Wetland Standards 2L NCDENR/DWR Title 15, Subchapter 2L. Groundwater Quality Standards TDS Total Dissolved Solids TOC Total Organic Carbon USACE US Army Corps of Engineers USEPA United States Environmental Protection Agency USGS United States Geological Survey Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 1.0 INTRODUCTION Duke Energy Progress, Inc. (Duke Energy) owns and operates the L.V. Sutton Energy Complex (Site) located on approximately 3,300 acres near Wilmington, North Carolina. The Site is located along the east bank of the Cape Fear River northwest of Wilmington and west of US Highway 421. The Site location is shown on Figure 1-1. The Site started operations in 1954 with three coal-fired boilers that primarily used bituminous coal as fuel to produce steam to generate electricity. Ash generated from coal combustion was originally stored on-site in the 'former ash disposal area (FADA)', also known as the ‘lay of land area’ , then in the 1971 ash basin (old ash basin), and finally the 1984 ash basin (new ash basin) (Figure 1-2). These ash storage areas are referred to as the ash management area. The Site ceased burning coal in November 2013 and switched to natural gas for electricity generation, thus the facility no longer generates coal ash. Discharges from the cooling pond and the ash basins are permitted by the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Resources (DWR) under the National Pollution Discharge Elimination System (NPDES) Permit NC0001422. Duke Energy has performed groundwater monitoring under the NPDES permit since 1990. The current groundwater compliance monitor wells required for the NPDES permit are sampled three times a year and the analytical results are submitted to the DWR. Groundwater compliance monitoring is performed in addition to the normal NPDES monitoring of the discharge flows. Concentrations of arsenic, barium, boron, iron, manganese, thallium, vanadium, and total dissolved solids (TDS) in excess of North Carolina Administrative Code (NCAC) Title 15A Chapter 02L.0202 groundwater quality standards (2L) or the Interim Maximum Allowable Concentration (IMAC) have been measured in groundwater samples collected in ash pore water wells. These constituents are considered constituents of interest (COI) for this assessment. Concentrations of cobalt and selenium in excess of the 2L or IMAC have been measured in groundwater samples collected at compliance monitor wells. Since cobalt and selenium were not detected in the ash pore wells, they are not considered COIs. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 1.1 Purpose of Comprehensive Site Assessment The Comprehensive Site Assessment (CSA) was conducted to collect information necessary to understand the ash basin as a source of potential impact, the vertical and horizontal extent of COIs, identify potential receptors of constituents, evaluate risks to receptors, and ultimately develop a Corrective Action Plan (CAP). A Site Conceptual Model (SCM) and associated physical properties and chemical data are to be used as the basis for a groundwater flow model and an associated COI fate and transport model for the ash basin. Some of the COIs are present in upgradient groundwater and these will be discussed later in this document. The subsequent CAP for the Site is to be based on the results of risk assessments and groundwater models. 1.2 Regulatory Background In a Notice of Regulatory Requirements (NORR) dated August 13, 2014, DWR requested that Duke Energy prepare a Groundwater Assessment Plan to conduct a CSA in accordance with 15A NCAC 02L .0106(g) to address groundwater constituent concentrations detected above 2L groundwater quality standards at the compliance boundary. NCDENR Requirements 1.2.1 NCDENR issued site specific requirements for the Site in letters dated November 4, 2014 and February 6, 2015. Specific NCDENR requirements for the CSA attached to the February letter were modified after issuance of the letter and were finalized in June 2015. NORR Requirements 1.2.2 The NORR required Duke Energy to comply with 15A NCAC 02L .0106(g), DWR’s Groundwater Modeling Policy, May 31, 2007, and various site specific requirements. Coal Ash Management Act Requirements 1.2.3 In addition, the Coal Ash Management Act (CAMA) 2014 – General Assembly of North Carolina Senate Bill 729 Ratified Bill (Session 2013) (SB 729) revised North Carolina General Statute 130A-309.209(a) require the following: (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. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 3 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx (1) No later than December 31, 2014, the owner of a coal combustion residuals surface impoundment shall submit a proposed Groundwater Assessment Plan for the impoundment to the Department for its review and approval. The Groundwater Assessment Plan shall, at a minimum, provide for all of the following: a. A description of all receptors and significant exposure pathways. b. An assessment of the horizontal and vertical extent of soil and groundwater contamination for all contaminants confirmed to be present in groundwater in exceedance of groundwater quality standards. c. A description of all significant factors affecting movement and transport of contaminants. d. A description of the geological and hydrogeological features influencing the chemical and physical character of the contaminants. e. A schedule for continued 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 On behalf of Duke Energy, SynTerra submitted to NCDENR a proposed Groundwater Assessment Plan (GAP) for the Site dated September 2014. Subsequently, NCDENR issued a comment letter dated November 4, 2014 containing both general comments applicable to the Duke Energy ash basin facilities and site-specific comments for the Site (Appendix A). In response to these comments, SynTerra prepared and submitted a revised Groundwater Assessment Work Plan (Revision 1) on December 30, 2014, for performing the groundwater assessment as prescribed in the NORR and SB 729, and to address the NCDENR review of the Work Plan dated November 4, 2014 and Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 4 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx subsequent meetings among Duke Energy, SynTerra, and NCDENR. Conditional approval of the Work Plan was dated February 6, 2015 (Appendix A). 1.4 Approach to Comprehensive Site Assessment The approach to the CSA was developed to meet NCDENR’s requirements. NORR Guidance 1.4.1 This CSA was conducted in accordance with the conditionally approved Work Plan to meet the requirements of 15A NCAC 02L .0106(g). This rule requires: (g) The Site assessment conducted pursuant to the requirements of Paragraph (c) of this Rule, shall include: (1) The source and cause of contamination; (2) Any imminent hazards to public health and safety and actions taken to mitigate them in accordance with Paragraph (f) of this Rule; (3) All receptors and significant exposure pathways; (4) The horizontal and vertical extent of soil and groundwater contamination and all significant factors affecting contaminant transport; and (5) Geological and hydrogeological features influencing the movement, chemical, and physical character of the contaminants. USEPA Monitored Natural Attenuation Tiered Approach 1.4.2 The assessment data is also compiled in a manner to be consistent with “Monitored Natural Attenuation of Inorganic Contaminants in Groundwater” (EPA/600/R-07/139). The tiered analysis approach discussed in this guidance document is designed to align site characterization tasks to reduce uncertainty in remedy selection. The tiered assessment data collection includes information to: 1. Evaluate active contaminant removal from ground water and dissolved plume stability, 2. Evaluate the mechanisms and rates of attenuation, 3. Evaluate the long-term capacity for attenuation and stability of immobilized contaminants, and 4. Evaluate anticipated performance monitoring needs to support the selected remedy. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 5 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx This assessment information will be used to develop a CAP for the Site. The CAP will provide a demonstration of these in support of the recommended Site remedy. ASTM Conceptual Site Model 1.4.3 The American Society for Testing and Materials (ASTM) E1689-95(2014) generally describes the major components of conceptual site models, including an outline for developing models. To the extent possible, this guidance was incorporated into preparation of the SCM. 1.5 Technical Objectives The rationale for borings and wells installed and sampled during the assessment fall into one of the following categories: Determine the range of background groundwater quality from pertinent geologic settings (horizontal and vertical) across a broader area of the Site and a greater distance from the ash basins. Evaluate groundwater quality from pertinent geologic settings (horizontal and vertical extent of coal ash leachate constituents) at a greater distance down gradient of the ash basins than previously available. Establish perimeter (horizontal and vertical) boundary conditions for a groundwater modeling. Provide source area information including pore water chemistry, physical and hydraulic properties, coal ash thickness and residual saturation within the ash basins. Address soil chemistry data gaps in the vicinity of the ash basins & FADA (horizontal and vertical extent of coal ash leachate constituents in soil) and a comparison to background concentrations. Determine potential routes of exposure and receptors. The following report presents the information obtained from the field investigation to address the requirements of 15A NCAC 02L .0106(g), the conditional approval letter, and CSA guidance document (revised June 2015). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 6 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 2.0 SITE HISTORY AND DESCRIPTION An overview of the Site setting and operations is presented in the following sections. 2.1 Site Location, Acreage, and Ownership The Site is a former coal-fired electrical power generation facility located on approximately 3,300 acres near the City of Wilmington in New Hanover County (Figure 1-1). Duke Energy Progress, Inc. owns the Site. Records available from Environmental Data Resources, Inc. (Attachment 2) do not contain any information prior to construction of the Site. 2.2 Plant Description The Site started operations in 1954 and consisted of three coal-fired boilers that primarily used bituminous coal as fuel to produce steam. Ash generated from coal combustion was first stored on-site in the FADA; beginning in 1971 ash was stored in the ‘old ash basin’ and then in 1984 the ‘new ash basin’ (Figure 1-2). These ash storage areas are referred to as the ash management area. The Plant, cooling pond (Lake Sutton) and ash management area are located on the east side of the Cape Fear River. The ash management area is located adjacent to the cooling pond, north of the Plant, as shown on Figure 1-2. The ash management area consists of three locations (Duke Energy, October 31, 2014): The FADA, also known as the lay of land area is located south of the ash basins, on the south side of the canal. It is believed that ash may have been placed in this area between approximately 1954 and 1972. The 1971 ash basin (old ash basin) is an unlined ash basin built in approximately 1971. The basin contains fly ash, bottom ash, boiler slag, storm water, ash sluice water, coal pile runoff, and low volume wastewater. An ash basin with a 12-inch thick clay liner was built in approximately 1984 (new ash basin), located toward the northern portion of the ash management area, and was operated from 1984 to 2013. The basin contains fly ash, bottom ash, boiler slag, storm water, ash sluice water, coal pile runoff, and low volume wastewater. During coal sluicing operations, water was discharged from the 1971 and 1984 ash basins to the cooling pond under the NPDES permit. Historical aerial photographs of the Site from 1949 and 1981 are presented as Figures 2-1 and 2-2. The 1971 and 1984 ash basins are impounded by an earthen dike. A USGS topographic map (composite from 1944 – 1954 maps) of the Site indicates that the property was undeveloped rural land at Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 7 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx that time (Figure 2-3). According to Duke Energy (Duke Energy, October 31, 2014) the old and new ash basins contain approximately 6,320,000 tons of ash and the FADA area contains approximately 840,000 tons of ash. No other types of waste other than NPDES permitted waste are believed to have been placed in the basins or FADA. Coal ash, a potential source of impact at the Site, is no longer generated at the Site. Duke Energy will fully excavate the ash basins with the material to be safely recycled or reused in a lined structural fill or place in a lined landfill as required by CAMA. 2.3 General Site Description The Site consists of approximately 3,300 acres and is developed with the power plant structures, the ash basins, cooling pond and associated canals. The plant structures are located primarily in the south central portion of the Site with the ash basins north of these structures. Plant water production wells are located along the entrance road on the east side of the Site (Figure 1-2). The northern and southern portions of the Site are primarily undeveloped areas containing small sand hills, pine woods and brush. The Site utilizes an approximate 1,100-acre cooling pond, referred to as Lake Sutton, located adjacent to the Cape Fear River. A boat ramp and parking lot are located at the north end of the lake; this feature is accessed by way of Sutton Lake Road, which extends across the Site from NC Hwy 421 to Lake Sutton. 2.4 Adjacent Property, Zoning, and Surrounding Land Uses The Site is surrounded by commercial, industrial, mining (sand quarry), residential and forest land. The quarry property and a plant located north of the quarry operate production wells on land adjacent to the Site. No future change in use of the surrounding land is currently anticipated. 2.5 Adjacent Surface Water Bodies and Classifications The Cape Fear River, borders the Site immediately to the west. The Cape Fear River flows south toward the town of Wilmington and is tidally influenced. NCDENR classifies the Cape Fear River as “C;Sw” (Aquatic Life, Secondary Recreation, Fresh/Swamp water). 2.6 Meteorological Setting The Site lies within the southeastern United States coastal plain climate zone that exhibits a humid subtropical climate type (NOAA, 2013). The high rainfall amounts and substantial seasonal temperature variations in this region promote rapid weathering of surficial geologic formations. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 8 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 2.7 Hydrologic Setting Topography fluctuates from approximately 45 feet above mean sea level (MSL) at the top of the 1971 ash basin to the water level along the Cape Fear River shoreline along the west and southwest Site boundaries. Outside of the ash basin, natural topography varies from 30 MSL among the small isolated sand hills in undeveloped portions of the Site, to 10 feet MSL in the Site area and the FADA to the southeast. The Site plant, cooling pond, and ash basins are located on the east side of the Cape Fear River, which flows south and is tidally influenced. 2.8 Permitted Activities and Permitted Waste The ash management areas, operated under NPDES Permit NC0001422, are located along the east side of the cooling pond (north of the plant, shown with a 500 foot compliance boundary on Figure 1-2). The permit authorizes the discharge of cooling pond blowdown, recirculation cooling water, non-contact cooling water and treated wastewater from Internal Outfalls 002, 003 and 004 via Outfall 001 from the cooling pond to the Cape Fear River. The cooling pond outfall discharges to the Cape Fear River via permitted Outfall 001. Internal outfalls 005 and 006 are discussed below. 2.9 History of NPDES and Surface Water Monitoring The NPDES program regulates wastewater discharges to surface waters to ensure that surface water quality standards are maintained. The Site operates under NPDES Permit NC0001422 (effective January 1, 2012) which authorizes discharge of cooling pond blowdown, recirculated cooling water, noncontact cooling water, and treated wastewater from internal Outfalls 002, 003, and 004 (via external Outfall 001); coal pile runoff, low volume wastes, ash sluice water (including wastewater generated from the Rotomix system), and storm water runoff (Outfall 002); chemical metal cleaning waste (Outfall 003); and ash sluice water (including wastewater generated from the Rotomix system), coal pile runoff, low volume wastes, and storm water runoff (Outfall 004). With the operation of the natural gas fired combined cycle generation facility, the Site also discharges from internal Outfall 005 (ultrafilter water treatment system filter backwash, Closed Cooling Water Cooler blowdown, Reverse Osmosis/ Electrodeionization system reject wastewater, and other Low Volume wastewater) to the Cooling Pond. The Site also discharges from internal Outfall 006 (Low Volume wastewater including the Heat Recovery Steam Generator blowdown and auxiliary boiler blowdown). NPDES permits require renewal every 5 years. In addition to surface water monitoring, the NPDES permit requires groundwater monitoring. For purposes of this monitoring, the applicable groundwater reference is the Groundwater Quality Standard 2L or former Interim Maximum Allowable Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 9 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Concentration (IMAC)) referenced in 15A NCAC 02L.0202. Appendix #1 of 15A NCAC Subchapter 02L Classifications and Water Quality Standards Applicable to The Groundwaters of North Carolina, lists IMACs. The IMACs were issued in 2010 and 2011, however NCDENR has not established a 2L standard for these constituents as described in 15A NCAC 02L.0202(c). For this reason, IMACs noted in this report are for reference only. The current groundwater monitoring plan for the Site includes the sampling of 17 wells. Two additional wells have been added to the routine sampling on a voluntary basis since November 2013. The sampling plan for the groundwater monitoring is presented in Table 2-1. Duke Energy has performed groundwater monitoring under the NPDES permit since 1990. The current compliance groundwater monitor wells required for the NPDES permit are sampled three times a year and the analytical results are submitted to the DWR. The compliance groundwater monitoring is performed in addition to the normal NPDES monitoring of the discharge flows. 2.10 Assessment Activities or Previous Site Investigations In addition to the required groundwater monitoring associated with permit activities, additional sampling activities have been conducted at the Site since the late 1980s. Due to the number of previous activities conducted at Site, only the most recent are discussed here, with the exception of the FADA. Existing monitor wells were installed by Blasland, Bouck & Lee (2004-2005), Catlin Engineers and Scientists (2011), and SynTerra (2013). Existing piezometers were installed by Golder Associates (2008). Monitoring wells were also installed in 1984, 1986, and 1990, but either well logs were not available for these wells or well logs did not specify the entity who installed the wells. In 2003, Carolina Power and Light signed an Administrative Order with the NC Superfund Section Inactive Hazardous Sites Branch to voluntarily remediate the FADA under the Registered Environmental Consultant Program (effective December 30, 2003). Subsequent investigations included a Phase I Remedial Investigation completed by Blasland, Bouck, & Lee, Inc. (BBL) in September 2004, and a Phase II Remedial Investigation completed by BBL in May 2006, a Remedial Action Plan completed by BBL in March 2006 and a Remedial Action Plan Addendum completed by BBL in February 2007. In August 2007, Progress Energy submitted a letter to NCDENR, Division of Water Management, terminating the Administrative Agreement for the Site. The Administrative Agreement termination was accepted and the FADA ash storage Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 10 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx area transferred from the Responsible Party Voluntary Remedial Action category to the Sites Priority List category of the Inactive Hazardous Sites Inventory. Catlin Engineers and Scientists (Catlin) conducted Phase I groundwater assessment activities and selected suitable locations for placement of monitor wells for a Phase II Work Plan (January 15, 2010). These assessments addressed a broader area of the Site than did the previous Phase I/Phase II assessments completed by BBL. Sampling of seven existing wells/piezometers was also included in the Phase I assessment scope of work. The results from the Phase I assessment did not detect arsenic, selenium, or sulfate at concentrations greater than the 2L Standard in any of the groundwater samples collected. Boron, iron, and manganese were detected at concentrations greater than the 2L Standard at one or more of the monitor wells and piezometers. However, as reported in the Phase I report (February 11, 2011), shallow groundwater (“A” zone wells/piezometers) was generally not impacted by COIs. Based on the results of the Phase I report, a Phase II Work Plan was prepared and submitted to NCDENR for approval. The Work Plan proposed targeting intermediate and deeper zones and also included a telescoping well (MW-28T) to investigate the potential presence of a confining clay and to collect a discrete deeper well sample. Further, the Phase II Work Plan included two (2) temporary leachate characterization collection points within the ash basin to obtain field scale data on ash basin leachate composition. The Phase II work consisted of installing 13 new monitor wells, two temporary leachate collection points, and soil samples from each monitoring well boring for laboratory analysis, groundwater gauging, slug testing, and two groundwater sampling events. The results from the Phase II work indicated that arsenic was not detected above 2L in any of the new wells. Boron was detected above the 2L in 8 of the 18 Phase II monitor wells sampled, primarily in the deeper wells. Iron was detected above 2L in 10 of the 18 Phase II sampled monitor wells. Manganese was detected in all the Phase II groundwater samples above 2L with the exception of samples collected from wells MW-16 and MW-28T. Only two monitor wells (MW-24B and MW-27B, September/October 2011 and January 2012 sampling events) indicated selenium concentrations greater than 2L. Duke has continued with ongoing compliance well monitoring and reporting of results to NCDENR. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 11 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx As part of Duke Energy’s ongoing plans to address closure options for the ash basin at the Site, Geosyntec Consultants (Geosyntec) conducted assessment activities to develop a conceptual closure plan for the Site ash management area. The assessment activities included both hydrogeologic and environmental assessment activities and geotechnical investigations of subsurface conditions within the ash management area. The environmental activities included: Installation of eight groundwater piezometers (four shallow and four intermediate-depth) near the toe of the basin dikes. Installation of two pore water piezometers within the ash basins. Installation of three intermediate- depth and four deep groundwater monitor wells outside of the ash basins to evaluate water levels and potential impacts to groundwater in the surficial aquifer at the Site; Four staff gauges were installed at certain surface water locations to facilitate monitoring of surface water elevations; Soil samples from background locations, from ash within the basins, from native soil below the ash in the basins, and from monitoring well borings located around the ash basins were collected and analyzed for COIs; Groundwater and ash pore water samples were collected and analyzed for select chemical constituents from the newly installed and certain non- compliance monitor wells and piezometers located throughout the Site; and Aquifer performance testing was conducted within one ash piezometer to obtain an estimate of the hydraulic conductivity within the ash basins, and five groundwater monitor wells were monitored with pressure transducers to evaluate water level fluctuations. The activities associated with the geotechnical investigation included; Completion of 11 soil test borings (six through the perimeter dikes, three within the ash basins and two within an area evaluated for a potential on- site landfill); 14 Cone Penetration Test (CPT) soundings (including six seismic CPT) soundings) and six direct push borings (DP); Pore water dissipation tests were performed at nine selected CPT and seismic CPT locations; Two piezometers were installed, one within the 1971 basin and one within the 1984 ash basin; and Standard geotechnical laboratory tests were performed on collected soil and ash field samples. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 12 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx No seeps have been identified at the Site. However, NCDENR and Duke Energy collected split samples from the intake canal of the cooling pond and the discharge canal to the cooling pond on March 10, 2014. The samples were analyzed for select anions, metals, and TDS. 2.11 Corrective Actions A Groundwater Mitigation and Monitoring Plan (Plan) was submitted to NCDENR on July 9th, 2015, as required by the NORR dated June 9, 2015 in response to results of receptor sampling and analyses. The Plan includes the installation of groundwater extraction wells along the eastern Site boundary. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 13 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 3.0 SOURCE CHARACTERISTICS The following overview of coal ash was prepared by HDR, Incorporated and supplied for this report. 3.1 Coal Combustion and Ash Handling System Coal ash is produced from the combustion of coal. The coal is dried, pulverized, and conveyed to the burner area of a boiler. The smaller particles produced by coal combustion, referred to as fly ash, are carried upward in the flue gas and are captured by an air pollution control device, such as an electrostatic precipitator. The larger particles of ash that fall to the bottom of the boiler are referred to as bottom ash or boiler slag. 3.2 Physical Properties of Ash Coal ash consists of fly ash and bottom ash produced from the combustion of coal. The physical and chemical properties of coal ash are determined by reactions that occur during the combustion of the coal and subsequent cooling of the flue gas. 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 or boiler slag. 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 38 to 0.05 mm. In general, bottom ash has a grain size distribution similar to that of fine gravel to medium sand (EPRI 1995). Specific gravities of fly ash range from 2.1 to 2.9. The specific gravities of bottom ash typically range from 2.3 to 3.0. The permeability of fly ash and bottom ash vary based on material density, but would be within the range of a soil with a similar gradation and density (EPRI 1995). Permeability and other physical properties of the ash found in the RBSS ash basin are presented later in this report. 3.3 Chemical Properties of Ash 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 Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 14 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 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). Duke Energy has typically burned bituminous coal from Appalachian sources. The majority of fly ash particles are glassy spheres mainly composed of amorphous or glassy aluminosilicates, crystalline matter, and carbon. Figure 3-1 presents a photograph of ash collected from the ash basin at Duke Energy's Cliffside Steam Station showing a mix of fly ash and bottom ash at 10 µm and 20 µm magnifications. The glassy spheres can be observed in the photograph. The glassy spheres are generally immune to dissolution. During the later stages of the combustion process and as the combustion gases are cooling after exiting the boiler, molecules from the combustion process condense on the surface of the glassy spheres. These surface condensates consist of soluble salts (e.g., calcium (Ca+2), sulfate (SO-2), 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, calcium. Oxides of magnesium, potassium, titanium and sulfur comprise approximately 4 percent by weight (EPRI 1995). Trace elemental composition typically is approximately 1 percent by weight and may include arsenic, antimony, barium, boron, cadmium, chromium, copper, manganese, mercury, nickel, lead, selenium, silver, thallium, zinc, and other elements. For comparison, Figure 3-2 shows the elemental composition of fly ash and bottom ash compared with typical values for shale and volcanic ash. Table 3-1 shows the bulk composition of fly ash and bottom ash compared with typical values for soil and rock. In addition to these constituents, fly ash may contain unburned carbon. Bituminous coal ash typically yields slightly acidic to alkaline solutions (pH 5 to 10) on contact with water. The geochemical factors controlling the reactions associated with leaching of ash are complex. Factors such as the chemical speciation of the constituent, solution pH, Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 15 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx solution-to-solid ratio, and other factors control the chemical concentration of the resultant solution. Constituents that are held on the glassy surfaces of fly ash such as boron, arsenic, and selenium may initially leach more readily than other constituents. As noted in Table 3-1, aluminum, silicon, calcium, and iron represent the larger fractions of fly ash by weight. Calcium and iron may limit the release of arsenic by forming calcium-arsenic precipitates. Formation of iron hydroxide compounds may also sequester arsenic and retard or prevent release of arsenic to the environment. Similar processes and reactions may affect other constituents of concern; however, certain constituents such as boron and sulfate will likely remain highly mobile. In addition to the variability that might be seen in the mineralogical composition of the ash, based on different coal types, different age of ash in the basin, etc., it is anticipated that the chemical environment of the ash basin varies over time, distance, and depth. EPRI (2010) reports that 64 samples of coal combustion products (including fly ash, bottom ash, and flue gas desulfurization residue) from 50 different power plants were subjected to USEPA Method 1311 Toxicity Characteristic Leaching Procedure (TCLP) leaching and no TCLP result exceeded the TCLP hazardous waste limit. Figure 3-3 provides the results of that testing. 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 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 3-4 also 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 range of concentrations for chromium in bottom ash and the trace element concentrations for the remaining constituents were below their respective RSLs. 3.4 Description of Ash Basins and Other Ash Storage Areas The ash management area consists of three locations; the FADA, the 1971 ash basin and the 184 ash basin. The FADA appears to have been a low-lying area that was filled with ash. The thickness of the ash encountered at AB-2 extended from the ground surface to a depth of approximately 8 feet thick. Groundwater was measured at approximately 3 feet bls at ABMW-2. The 1971 ash basin area appears to have been excavated below grade to a depth of approximately 40 feet. Samples collected from AB-1 indicate surficial sand was Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 16 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx removed, except for approximately two feet at the bottom prior to placement of the ash. The ash is approximately 79 feet deep, as measured from the top of the ash, at AB-1 and the top of the ash basin is approximately 40 feet above Site grade. The water level in ABMW-1 was measured at approximately 34 feet bls. There is a small area of standing water in the northwest portion of the 1971 ash basin. The excavated sand may have been used locally in the construction of the basin or canal berms. Both the FADA and the 1971 ash basins are unlined. The 1984 basin appears to have been constructed above grade and is lined with a 12- inch clay layer. The northern portion of this basin contains standing water. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 17 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 4.0 RECEPTOR INFORMATION The Site is located northwest of Wilmington on the west side of Highway 421. The topography at the Site is relatively gentle, generally sloping downward toward the Cape Fear River to the west and south. The Site is bounded to the west by the Cape Fear River, to the north by undeveloped land, to the east by a sand quarry and light industrial use properties. Residential properties are located southeast of the southeastern property boundary. Properties located within a 0.5 mile radius of the Site ash management area compliance boundary are located in New Hanover County, North Carolina, with the exception of an undeveloped portion of land on the west side of the Cape Fear River in Brunswick County. The properties are primarily used for commercial and industrial purposes. There are no residential properties located within the 0.5 mile radius of the compliance boundary. The ash basins are impounded by earthen dikes. The ash basin system was an integral part of the plant’s wastewater treatment system which received inflows from the ash removal system, plant yard drain sump, and storm water flows. Locations of subsurface utilities in the plant area to 1,500 feet beyond the basin boundary are exhaustive and difficult to complete and map with certainty. Due to the isolation of the ash basin from the plant area, subsurface utilities are not expected to be major contaminant flow pathways. Identification of piping near and around the ash basin was conducted by Stantec in 2014 and utilities around the Site property were also included on a 2014 topographic map by WSP (Attachment 2) to meet this NCDENR requirement. 4.1 Summary of Receptor Survey Activities Surveys to identify potential receptors for groundwater including public and private water supply wells (including irrigation wells and unused or abandoned wells) and surface water features within a 0.5-mile radius of the Site compliance boundary have been reported to NCDENR (SynTerra, Drinking Water Well and Receptor Survey, September 2014, and Supplement to Drinking Water Well and Receptor Survey, November 2014). These reports are included in Attachment 3. The first report included results of a review of publicly available data from NCDENR Department of Environmental Health, NC OneMap GeoSpatial Portal, DWR Source Water Assessment Program online database, the Cape Fear Public Utility Authority (CFPUA), county geographic information system, Environmental Data Resources, Inc. records review, the United Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 18 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx States Geological Survey National Hydrography Dataset, as well as a vehicular survey along public roads located within 0.5 mile radius of the compliance boundary. The first report indicated that no wellhead protection areas or surface water bodies are located within a 0.5 mile radius of the compliance boundary (Appendix B). The Site cooling pond (Lake Sutton) and the Cape Fear River are located adjacent to the Site to the west, however, these surface water bodies are not used as drinking water sources. Approximately 32 possible private water supply wells were observed, were reported, or were assumed to be located within the survey area, within 0.5 mile of the compliance boundary. This includes eight on-site wells used for Site operations. The second report supplemented the initial report with information obtained from questionnaires sent to owners of property within the 0.5 mile radius of the compliance boundary. The report included a sufficiently scaled map showing the ash basin location, the facility property boundary, the waste and compliance boundaries, all monitor wells, and the approximate location of identified water supply wells. A table presented available information about identified wells including the owner's name, address of well location with parcel number, construction and usage data, and the approximate distance from the compliance boundary. The questionnaires were designed to collect information regarding whether a water well or spring is present on the property, its use, and whether the property is serviced by a municipal water supply. If a well is present, the property owner was asked to provide information regarding the well location and construction information. The results from the previous survey and the questionnaires indicated approximately 34 wells might be located within or in close proximity to the survey area (reported wells, observed wells, and possible wells), including the eight on-site production wells at the Site. 4.2 Summary of Receptor Survey Findings Aquifers beneath the Site, including the surficial aquifer, are used for water supply in the Site vicinity. The Site is likely a recharge area for these aquifers. Public Water Supply Wells 4.2.1 Four Cape Fear Public Utility Authority public supply wells were identified adjacent to or near the southeastern boundary of Site: NHC-SW 1(abandoned) 1,100 feet east of property line NHC-SW 2(not in use) adjacent, east of property line Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 19 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx NHC-SW 3 650 feet east of property line NHC-SW 4 800 feet east of property line Public water supply wells NHC-SW3 and NHC-SW4 are routinely monitored for Site COIs. Private Water Supply Wells 4.2.2 Surveys to identify potential receptors including public and private water supply wells (including irrigation wells and unused or abandoned wells) and surface water features within a 0.5-mile radius of the Site compliance boundary have been reported to NCDENR (SynTerra, Drinking Water Well and Receptor Survey, September 2014, and Supplement to Drinking Water Well and Receptor Survey, November 2014). The first report included results of a review of publicly available data from NCDENR Department of Environmental Health, NC OneMap GeoSpatial Portal, DWR Source Water Assessment Program online database, county geographic information system, Environmental Data Resources, Inc. records review, the United States Geological Survey National Hydrography Dataset, as well as a vehicular survey along public roads located within 0.5 mile radius of the compliance boundary. During 2015, NCDENR managed the sampling of water supply wells within or near the survey area. The data are provided in Appendix B. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 20 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY According to the Geologic Map of North Carolina, published by the North Carolina Department of Natural Resources and Community Development (1985), the Site lies within the Coastal Plain Physiographic Province. The following section provides a regional understanding of the hydrogeology of the Coastal Plain area and may not represent actual conditions at the Site. The North Carolina Coastal Plain is approximately 90 to 150 miles wide from the Atlantic Ocean westward to its boundary with the Piedmont province. Two natural subdivisions of the Coastal Plain were described by Stuckey (1965): the Tidewater region and the Inner Coastal Plain. The Site is located within the Tidewater region, which consists of the coastal area where large streams and many of their tributaries are affected by ocean tides (Winner, Jr. and Coble, 1989). The Site is located on the east side of the Cape Fear River within the alluvial plain between the coastal dunes and the interior uplands (NUS Corporation, 1989). 5.1 Regional Geology The Coastal Plain comprises a wedge shaped sequence of stratified marine and non- marine sedimentary rocks deposited on crystalline basement. The sedimentary sequences range in age from recent to lower Cretaceous (Narkunas, 1980). The surficial sands are underlain by the Pee Dee Formation in the Site area. In the Wilmington area, the Pee Dee confining unit has an average thickness of 10 feet. The Pee Dee Formation contains fine to medium grained sand interbedded with gray to black marine clay and silt. Sand beds are commonly gray or greenish gray and contain varying amounts of glauconite. Thin beds of consolidated calcareous sandstone and impure limestone are interlayered with the sands in some places. The Pee Dee Formation contains a confining unit at the top in areas south of the Site; however the Pee Dee confining unit below the surficial sands was not encountered at the Site. 5.2 Regional Hydrogeology In the eastern part of the North Carolina Coastal Plain, groundwater is obtained from the surficial, Castle Hayne, and Pee Dee Formations. The Coastal Plain groundwater system consists of aquifers comprised of permeable sands, gravels, and limestone separated by confining units of less permeable material. According to Winner, Jr. and Coble (1989), the surficial aquifer consists primarily of fine sands, clays, shells, peat beds, and scattered deposits of coarse-grained material in the form of relic beach ridges and floodplain alluvium. The areal extent of the surficial Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 21 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx aquifer in the Coastal Plain is approximately 25,000 square miles with an average thickness of 35 feet. The average estimated hydraulic conductivity is 29 feet per day (Winner, Jr. and Coble, 1989). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 22 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 6.0 SITE GEOLOGY AND HYDROGEOLOGY Two sedimentary geologic units (Coastal Plain surficial deposits and the Pee Dee Formation) have been encountered in exploratory borings installed at the Site (Figure 1- 2). The surficial deposits extend to approximately 50 feet below ground surface (bgs) and consist of medium-fine to coarse grained sands with laterally inconsistent beds of coarse sand and fine gravel in the lower 30 feet. The Pee Dee Formation lies unconformably below the surficial sands and consists of fine sands and silts with occasional clay lenses. The Site investigation conducted in accordance with the GAP (Section 3.2) included installation of soil borings, groundwater monitor wells, borings in and through the 1971 ash basin and FADA, and installation of an additional well to sample ash pore water (Table 6-1 [revision of Table 9 from the GAP]). Physical and chemical properties of soil samples collected from the borings and wells and sediment samples collected from ditches and streams were determined (Table 6-2). Chemical analyses of a broad list of potential constituents of concern were conducted on samples of groundwater and surface water from the cooling pond and the Cape Fear River (Table 6-3). Ten monitoring well pairs were installed on-site north, east and southeast of the ash basins; six monitoring well pairs were installed on off-site properties east of the Site and two monitoring well pairs (ABMW-1S/D and ABMW -2S/D) were installed within the 1971 ash basin and the FADA. These wells were installed in accordance with GAP Sections 7.1.2 and 7.1.3 (Table 6-1, Table 6-4, Appendices C and E). Based on preliminary data, seven additional deep wells were added off-site (SMW-6D) and on- site at AW-2D, AW-5D/E, AW-6E and MW-23E. Ten soil borings, designated confining unit borings (CUBs), were performed in the southeastern and southern portions of the Site. The borings extended through the surficial deposits to the underlying Pee Dee Formation in an attempt to locate the Pee Dee confining unit. The confining unit is not present at the Site within the area of this assessment. The primary technical objectives for the new well locations was to establish perimeter boundary conditions for the groundwater modeling that will be used to develop the CAP for the Site and to develop additional background data on groundwater quality. These well installations were selected to anchor strategically positioned flow path transects to facilitate model analysis (Figure 1-2). Flow from the 1971 ash basin to potential receptor areas is to the east and southeast. No potential receptors were Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 23 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx identified to the west. Three transects were selected for the Site to illustrate flow path conditions in the vicinity of the ash basins. Section A-A’ provides the best illustration of the ash basins source area and FADA (basin dams, canals and ash) in relation to the upland area to the north and receptor area to the southeast. Sections B-B’ and C-C’ illustrate conditions from the Cape Fear River eastward through the Site property. Specific objectives for each location follow: To refine the horizontal and vertical extent of metals in the aquifer, five additional well pairs (AW-1B/C through AW-5B/C) were installed along the property line east of the ash management area. The wells were installed as well pairs to also provide vertical information on aquifer chemistry and vertical gradients. Additional deep wells AW-2D, AW-5D/E and AW-6E were added to provide further vertical delineation at those locations. Well pair AW-6B/D and monitor well AW-7D were installed adjacent to previously existing wells MW-12 and MW-31C, downgradient from the ash management area. These wells were installed to provide information on the vertical distribution of constituents of concern at these locations. A proposed monitor well, AW-7B, was originally proposed but not installed when it was determined that MW-31B was appropriately constructed to monitor the targeted flow zone. To further define water quality beyond the compliance boundary to the north, monitor wells AW-8B/C were installed north of well MW-27B. MW-9B/C were installed south of the MW-7 well cluster to address groundwater conditions beyond the compliance boundary southeast of the 1971 ash basin and FADA. Monitor well pair MW-37B/C were installed to address background groundwater conditions further south of MW-4B. In addition to assessment well clusters AW-1 through AW-9, sentinel well clusters (SMW-1B/C through SMW-6B/C/D) were installed to monitor groundwater conditions between nearby receptors and the property boundary for the Site. The GAP designated monitor wells according to depth, with “A” meaning a shallow well in the upper 15 feet, and subsequently deeper wells designated, “B”(25 feet), “C” (45 feet) or “D” (100 feet). The “E” (150 feet) designation was added when deeper wells were required based on preliminary assessment data. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 24 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Based on historical Site data, COIs typically have not been detected at concentrations greater than 2L or IMAC in the shallow (water table) portion of the aquifer. Therefore, no shallow wells (“A” designation) were installed. Shallow intermediate wells (“B” designation) were installed at a depth of approximately 20 to 25 feet within the middle section of the surficial aquifer. Deep intermediate monitor wells (“C” designation) were installed in the lower surficial aquifer at a depth of 40 to 45 feet bgs. The GAP proposed deep wells to be installed on top of a confining unit at the base of the surficial aquifer, at an estimated depth 75 feet bgs. However, a confining unit was not encountered and the top of the Pee Dee was established to be at approximately 50 feet bgs. Therefore deep wells designated as “D” wells were installed within the Pee Dee formation at a depth of approximately 100 feet bgs. Additional, deeper, wells designated as “E” wells, were installed to a depth of 150 feet bgs at AW-5, AW-6 and MW-23 (Figure 1-2). Each of the wells were installed as a single cased monitoring well, with the exception of ABMW-2D in the FADA, which is cased through the ash to depth of 14 feet bgs. The well casings consist of two-inch diameter PVC schedule 40 flush-joint threaded casing and pre-packed screens. The well screen intervals are 5 or 10 feet long for each of the monitor wells. The annular space between the borehole wall and the pre-packed well screens for each of the wells was filled with clean, well-rounded, washed, high grade 20/40 mesh silica sand. The sand pack was placed to at least 2 feet above the top of the pre-packed screen, and then at least two feet of pelletized bentonite was placed as a seal above the filter pack. The remainder of the annular space was filled with a neat cement grout from the top of the upper bentonite seal to near ground surface. Monitor wells were completed with either steel above ground protective casings or steel flush-mounted casings with locking caps and well tags. The protective covers were secured and completed in a concrete collar and 2-foot square concrete pad. The hydraulic conductivity of each well was tested by the instantaneous change in head or “slug” test method in accordance with GAP Section 7.1.4 (Appendix C). Drinking water purchased from New Hanover County was used for drilling fluid. A sample of the “source water” was analyzed for the full set of GAP parameters (Attachment 5). No exceedances of 2L were detected in the purchased drinking water with the exception of iron. GAP COIs antimony, arsenic, boron, barium, cobalt, manganese, and vanadium were undetected in the sample. Iron was detected at 963 micrograms per liter (µg/L). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 25 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 6.1 Site Geology No consolidated rock outcrops are present at the Site. Areas in the Site and associated impoundments have been constructed by mass grading resulting in disturbed or possibly imported geologic materials. Undisturbed areas consist of small sand hills, low-growth vegetation and pine woods or electric transmission line corridors. The Site subsurface consists of sands of the surficial aquifer which extend to approximately 50 feet bgs. The upper 20 feet or so of this unit consists of well-sorted, light-colored sand, loose to moderately dense with little shell or organics. The lower 30 feet consists primarily of poorly-sorted sands with discontinuous layers of coarse sand and fine gravel. Thin laminae of silts and clays also occur randomly in the lower portion of this unit. Wood remnants were also encountered in places near the contact with the lower Pee Dee Formation. The surficial sands lie unconformably over the Pee Dee Formation. The contact between the surficial and the Pee Dee Formation is sharp and distinct due to the dark grey-green color of the fine sands and silts of the Pee Dee. Trace amounts of large shell and sandstone were also occasionally observed at this contact. The Pee Dee Formation extends to the deepest horizon explored (150 feet bgs) during the assessment. The upper portion of the Pee Dee consists of dark gray or medium to dark green fine sands and silt with clay lenses and laminae. Below 75 feet, thin layers of sandstone were encountered; however these were not continuous across the Site. The Pee Dee becomes finer with depth and often is a very dense, low-plasticity clayey silt. Geologic cross-sections A-A’, B-B’, and C-C’ are presented in Figures 6-1 and 6-2. Photographs of sonic drill core from monitor wells and several of the soil borings are displayed on the geologic cross-sections to illustrate Site geology (Figures 6-3, 6-4, and 6-5). The full set of photographs is included as Attachment 6. Soil Classification 6.1.1 The surficial aquifer consists of well sorted to poorly sorted (SW/SP) sands which vary from fine to coarse grained with some fine gravel. The upper zone is primarily a well-sorted, medium-fine grained sand while the lower portion tends to be poorly sorted, with larger grain sizes and occasional layers of coarse sand/fine gravel. Oxide staining (reddish-yellow and orange), were common near the base of the lower surficial unit. The upper zone typically contains more fines and fine-grained sand than the lower zone based on samples from AW-8C and AW-9C. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 26 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The contrast in grain size across the surficial/Pee Dee contact is illustrated by comparing the grain size analyses of two samples from SMW-2C collected above and below the contact. Above the contact the sample consists of approximately 78% medium to coarse grained sand. The soil below the contact contained over 70% fine sand, silt or clay-sized particles. Pee Dee sediments at the Site are light to dark green and dark gray silty fine sands and clayey silts with occasional clay lenses and thin sandstone layers. The sediments in the upper Pee Dee contain fewer fines; as exemplified by the grain size analyses on samples collected from AW-7D at a depth of 99 feet and from AW-5E and MW-23E at a depth of greater than 140 feet contained over 40% silts or clays whereas samples from the upper Pee Dee at AW-7D at a depth of 49 feet contained less than 8% fines. Turbidity in samples collected from these lower zones are higher due to the fines content. Grain size analyses, moisture content and other physical soil test results are presented in Appendix F. Rock Lithology 6.1.2 There are no rocks within the CSA area. Structural Geology 6.1.3 Due to the unconsolidated nature of the subsurface, structural geology does not appear to be a factor in the SCM for the Site. Soil and Rock Mineralogy and Chemistry 6.1.4 Mineralogy and chemistry of the soils encountered are presented in Section 8. 6.2 Site Hydrogeology The surficial unconfined aquifer is the first major hydrostratigraphic unit at the Site. As discussed in Section 6.1, the upper portion of the surficial aquifer is more uniform in structure and grain size, primarily consisting of well sorted sands. The lower portion varies greatly in grain size, with poorly-sorted sands interbedded with numerous coarse-grained layers containing fine gravel and occasionally with thin silt laminae. The upper portion grades into the lower portion between 15 and 25 feet bgs. The Pee Dee Formation directly underlies the surficial zone at the Site. In areas south of the Site a confining unit is reported to be present between the surficial zone and the Pee Dee Formation; this confining unit was not found to be present at the Site. As described in Section 6.1, the contact between the Pee Dee Formation and the overlying surficial unit is sharp and with greatly contrasting soil types. It is anticipated that the less permeable sediments of the Pee Dee would impede vertical groundwater flow and flow within the coarse-grained layers would be significantly higher. This is discussed further in Section 6.2.3 Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 27 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The first occurrence of groundwater at the Site is in the surficial aquifer at depths ranging from 3 to 17 feet bls. Groundwater elevations in June 2015 (Table 6-5) indicate the groundwater flow direction in the upper and lower portions of the surficial aquifer beneath the ash basins flows radially from the central sand hills portion of the Site, indicating this is likely a local recharge area. Generally, groundwater flows east, southeast and south from the Site. Water level data from the Pee Dee formation indicates groundwater flow to the east and south. The presence of high capacity industrial and public water supply pumping wells near the Site complicates the determination of groundwater flow. This will be clarified upon completion of the groundwater flow model. Groundwater Flow Direction 6.2.1 Potentiometric surface maps for the upper surficial, lower surficial, and Pee Dee aquifers are presented as Figures 6-6, 6-7, and 6-8, respectively. The initial zone of saturation is comprised of pore water within the ash basins and shallow sediment. Groundwater gradients in the surficial aquifer are affected by manmade features (plant area, cooling pond), the ash basin, Site production wells and off-site public supply wells, production wells for the Invista plant, and production wells for the ST Wooten facility and Site geology. If the proposed extraction wells are installed along the eastern property line these will also affect groundwater flow direction in the surficial and Pee Dee formations. Additionally, when the CFPUA wells adjacent to the Site to the east, are removed, alteration of groundwater flow is anticipated in that area. The water table at the Site is typically located at depths of approximately 3 to 18 feet bgs, depending on antecedent precipitation and topography. The surficial aquifer groundwater flow regime of the Site is hydraulically bounded on the west by the cooling pond and the Cape Fear River which flows south. The Northeast Cape Fear River is approximately one mile east of the Site and regional groundwater flow is anticipated to be south in the areas between the two rivers. The Site is located on a peninsula defined by the Cape Fear River, adjacent to the west and the Northeast Cape Fear River, located approximately one mile to the east. Based on regional topography and drainage features, groundwater flow within this peninsula would be either to the west or east to one of the two rivers or to the south where the rivers converge. At the Site, groundwater flows radially from the 1971 and 1984 ash basins. Along the eastern edge of the cooling pond, groundwater flows to the west. On the east side of the 1971 basin, groundwater flows to the east, southeast and south. In the area of the FADA, groundwater flows to the southwest. A groundwater divide or ridge is located Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 28 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx northeast of the ash basin which roughly corresponds to the presence of small sand hills in that area. A zone of slightly depressed water levels is centered around the Site production wells and the CFPUA wells in the southeast portion of the Site. The potential influence from the off-site municipal and industrial production wells (and the potential extraction wells) will be factored into the groundwater flow model being prepared for the CAP. As the model is being prepared additional groundwater and surface water elevation monitoring data may be collected. Hydraulic Gradients 6.2.2 Horizontal hydraulic gradients were calculated using data collected from surface water and monitoring well locations on June 1st, 2015 (Table 6-6 and Figure 6-6, 6-7, and 6-8). The gradients ranged from 0.00009 foot per foot (ft./ft.) to 0.001 ft./ft. Hydraulic Conductivity 6.2.3 Slug tests were conducted at each newly-installed CSA groundwater monitoring wells and were analyzed for hydraulic conductivity in accordance with GAP Section 7.1.4 (Table 6-7, Appendix G). Infiltration tests using Guelph permeameters were deemed unnecessary by the groundwater model developer since the slug test data is available. Hydraulic conductivity of upper surficial aquifer wells range from 1.64 x 10-5 to 7.00 x 10-2 cm/sec. Wells screened in the lower surficial aquifer range from 1.74 x 10-3 cm/sec to 6.14 x 10-2 cm/sec. Wells screened in the upper Pee Dee Formation have a geometric mean value of 1.3 x 10-5 cm/sec and wells in the lower Pee Dee have a mean value of 2.72 x 10-7 cm/sec. Vertical hydraulic conductivity results for undisturbed samples from the upper Pee Dee fine sands and clayey silts are relatively low (6.7 x 10-4 cm/sec to 1.5 x 10-7 cm/sec, Table 6-8). The higher conductivity values in the Pee Dee were recorded for samples near the contact with the surficial, which has fewer fines than the soils deeper in the formation. These data indicate that lateral groundwater flow will predominate over downward vertical flow at the Site. Accordingly, lateral migration of COIs would be expected relative to vertical migration. Groundwater Velocity 6.2.4 Groundwater velocities calculated for the four flow paths described in Section 6.2.2. range from 0.185 to 8.55 feet per year. Slug tests that were conducted in Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 29 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx wells screened below the ash basin were analyzed for hydraulic conductivity and were used to calculate the flow velocity. Flow rates from the ash basins to surrounding areas are the highest due to the hydraulic gradient from the basins to the surrounding areas. Effects of Geologic/Hydrogeologic Characteristics on 6.2.5 Contaminants The retardation factor of subsurface soils will be determined by Kd analyses, the results of which are pending. These results will be incorporated in the preparation of the CAP. 6.3 Hydrogeologic Site Conceptual Model The hydrogeologic site conceptual model (SCM) is based on the configuration of the ash basins relative to Site features including canals, ponds, rivers and production wells (Figure 6-9). The contrasting permeability between the surficial and Pee Dee formation is a significant part of in this model. The 1971 ash basin was excavated below the water table to a depth of approximately 40 feet below grade. All but the lower two feet of the surficial sands were removed by this excavation; therefore the ash in the 1971 basin sits just above the contact between the surficial and Pee Dee formations. The ash is approximately 80 feet with over half of that saturated. Infiltration of surface water causes some mounding in this basin, resulting in radial groundwater flow away from the mounded area. The discharge canal to the south and the cooling pond to the west control groundwater elevation in the surficial aquifer to the west and south of the 1971 ash basin. Small sand hills located in the northeast portion of the Site create a localized groundwater divide extending roughly north and south. Surficial groundwater also flows radially from this area. The surficial aquifer has larger hydraulic conductivity values than does the underlying Pee Dee Formation, resulting in preferential lateral flow. This lateral flow, especially in the lower surficial aquifer, is affected by the presence of surface water bodies and by the operation of production wells located along the eastern Site property boundary. There is a downward vertical gradient between the upper and lower surficial aquifer wells in most locations and a downward vertical gradient between the surficial and Pee Dee formations. Although because of the lower hydraulic conductivities, the flux of water is greater in the shallow formations (above the Pee Dee). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 30 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 6.4 Geochemical Site Conceptual Model This section contains geochemical information on the COIs for the Site groundwater assessment. This information provides a necessary context for the data collected to characterize the ash basin source area and potential receptors. Data from published sources address the relative abundance of each COI in the rocks at the earth surface (“crust”), the occurrence of the elements in coal, the leaching characteristics of ash, and fate and transport of COIs that might be released to the environment. Based on exceedances of 2L or IMAC in samples of ash pore water and groundwater, iron, vanadium, manganese, boron, barium, arsenic, cobalt and antimony (listed in order of prevalence) are addressed in the following paragraphs. Iron 6.4.1 Iron has been detected in samples above the 2L in most monitor wells across the property, including background wells. Iron is estimated to be the fourth most abundant element in the Earth’s crust at approximately five weight percent (Parker, 1967, Table 18 and Figure 3). Oxygen (46.60 weight percent), silicon (27.72 weight percent), and aluminum (8.13 weight percent) occur in higher concentrations. Iron occurs in divalent (ferrous, Fe+2), trivalent (ferric, Fe+3), hexavalent (Fe+6), and Fe-2 oxidation states. Iron is a common mineral forming element, occurring primarily in mafic (dark colored) minerals including micas, pyrite (iron disulfide), and hematite (iron oxide), as well as in reddish colored clay minerals. Clay minerals and pyrite are common impurities in coal. Under combustion conditions in a coal-fired boiler, clay minerals would be dehydrated to mullite or gibbsite, possibly liberating iron, and pyrite would oxidize to hematite or magnesioferrite. Research summarized by Izquierdo and Querol (2012) indicates that iron leaching from coal ash is on the order of one percent of the total iron present due to the low pH required to solubilize iron minerals. Despite the low apparent mobilization percentage, iron can be one of the COIs detected in the highest concentrations in ash pore water. Ferric iron is soluble at pH less than 2 at typical surface conditions (25°C and 1 atmosphere total pressure, Schmitt, 1962). For this reason, dissolved iron in surficial waters is typically oxidized to the trivalent state resulting in formation of ferric iron oxide flocculation that exhibits a characteristic reddish tint. Vanadium 6.4.2 Analysis for vanadium in groundwater samples from the Site was initiated with the 2015 groundwater assessment. Exceedances of the former IMAC of 0.0003 Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 31 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx mg/L were detected in samples from each of the ash pore well locations; and in many samples from each of the depth horizons sampled. Vanadium is estimated to be the 22nd most abundant element in the crust (0.011 weight percent, Parker, 1967). Vanadium occurs in four oxidation states (V+5, V+4, V+3, and V+2). It is a common trace element in both clay minerals and plant material. The National Uranium Resource Evaluation (NURE) program was initiated by the Atomic Energy Commission in 1973 with a primary goal of identifying uranium resources in the United States (http://pubs.usgs.gov/of/1997/ofr-97- 0492/, accessed on June 8, 2015). The Hydrogeochemical and Stream Sediment Reconnaissance program (initiated in 1975) was one component of NURE. Planned systematic sampling of the entire United States began in 1976 under the responsibility of four Department of Energy national laboratories. Samples were collected from 5,178 wells across North Carolina. Of these, the concentration of vanadium was equal to or higher that the former IMAC of 0.0003 mg/L in 1,388 well samples (27 percent). Manganese 6.4.3 Manganese was detected above 2L in more samples at the Site than any other metal except iron. The majority of the 2L exceedances occur in the surficial aquifer; with 2L exceedances in the Pee Dee limited to wells below or adjacent to the ash basins with the exception of AW-2D and PZ-10 in the northern portion of the Site. Manganese is estimated to be the 12th most abundant element in the crust (0.100 weight percent, Parker, 1967). Manganese exhibits geochemical properties similar to iron with Mn+7, Mn+6, Mn+4, Mn+3, Mn+2, and Mn-1 oxidation states. Manganese substitutes for iron in many minerals. Similar to iron, manganese leaching from coal ash is limited to less than 10 percent of the total manganese present due to the low pH required to solubilize manganese minerals (Izquierdo and Querol, 2012). Despite the low apparent mobilization percentage, manganese can be detected in relatively high concentrations in ash pore water. Boron 6.4.4 High concentrations of boron (over 5 times 2L) were detected in the ash pore water sample from the 1971 ash basin and were also detected in several wells screened in the lower surficial aquifer and the Pee Dee. Boron is a trace element in the crust, with estimated concentrations ranging from as little as 1 mg/kg in mafic igneous rocks to hundreds of milligrams per kilogram in clay rich rocks (Parker, 1967, Table 19). It occurs only in the trivalent form (B+3). Boron is concentrated in sedimentary rocks like those that underlie Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 32 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx the Site (Urey, 1953). This observation indicates that a mechanism exists to concentrate boron in minerals since the oceans could dissolve all of the boron estimated to be present in the crust (Fleet, 1965). Fleet presents both biogenic and mineralogical processes to account for the preferential concentration of boron in the crust. Boron is a micronutrient (Goldberg, 1997) that is concentrated in plant tissue, including the plants from which coal formed. Because boron is associated with the carbon (fuel) in coal, it tends to volatilize during combustion and subsequently condense onto fly ash as a soluble borate salt (Dudas, 1981). Boron leaches readily (up to 50 percent of total present) and rapidly from fly ash (Cox et al., 1978). Boron is considered a marker COI for coal because boron impact is rarely associated with other types of industrial activities. Boron is the primary component of very few minerals. Tourmaline, a rare gem mineral, forms under high temperature and pressure (Hurlbut, 1971). The remaining common boron minerals, including borax that was mined for laundry detergent in Death Valley, form from the evaporation of seawater in deposits known as evaporites. For this reason, boron mobilized into the environment will remain in solution until incorporation into plant tissue or adsorption by a mineral. Boron is commonly occurs in salt water and has been detected in wells within the Pee Dee Formation in the region of the Site. A well located in Myrtle Beach South Carolina and screened from 95 - 105 feet within the Pee Dee formation was reported to contain a concentration of 1,600 µg/L of boron. (Ground-Water Quality Data From the Southeastern Coastal Plain, Mississippi, Alabama, Georgia, South Carolina, and North Carolina, Roger W. Lee, U. S. Geological Survey, Open File Report 84-237, 1984). Fleet describes sorption of boron by clays as a two-step process. Boron in solution is likely to be in the form of the borate ion (B(OH)4 −. The initial sorption occurs onto a charged surface. Observations that boron does not tend to desorb from clays indicates that it migrates rapidly into the crystal structure, most likely in substitution for aluminum. Goldberg et al. (1996) determined that boron sorption sites on clays appear to be specific to boron. For this reason, there is no need to correct for competition for sorption sites by other anions in transport models. Goldberg (1997) lists aluminum and iron oxides, magnesium hydroxide, clay minerals, calcium carbonate (limestone), and organic matter as important sorption surfaces in soils. Boron sorption on oxides is diminished by competition from numerous anions. Boron solubility in groundwater is controlled by Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 33 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx adsorption reactions rather than by mineral solubility. Goldberg concludes that chemical models can effectively replicate boron adsorption data over changing conditions of boron concentration, pH, and ionic strength (p. 43). Arsenic 6.4.5 Arsenic was detected in the ash pore water well samples and a few wells in the lower surficial and Pee Dee Formation below or near the ash basins. Arsenic is a trace element in the crust, with estimated concentrations ranging from less than 1 mg/kg in mafic igneous rocks to 13 mg/kg in clay rich rocks (Parker, 1967, Table 19). It occurs in multiple valence states (As+5, As+3, and As-3). Arsenic in coal occurs primarily in pyrite (iron sulfide, with arsenic replacing iron in the crystal structure) (Finkelman, 1995). Arsenic condenses on fly ash as arsenate (As+5) (Goodarzi et al., 2008). Leaching tests on ash indicate that trace quantities up to 50 percent of the arsenic present can be leached. In addition to the solubility of the source, the concentration of calcium and presence of oxides appear to limit the mobility of arsenic (Izquierdo and Querol, 2012). Cobalt 6.4.6 Cobalt was detected above IMAC in several upper surficial aquifer wells and most lower surficial aquifer wells but not in any of the Pee Dee Formation wells. Cobalt is a base metal that exhibit geochemical properties similar to iron and manganese. Each occurs as a divalent and trivalent ion. Cobalt can occur as Co-1. In terms of distribution in the crust, cobalt exhibits a strong affinity for mafic igneous and volcanic rocks and deep-sea clays (Parker, 1967, Table 19). Cobalt occurs in clay minerals and substitutes into the pyrite crystal structure. There is also evidence that it is organically bound in coal (Finkelman, 1995). Izquierdo and Querol (2012) report limited leaching of cobalt from coal, attributing this observation to incorporation into iron oxide minerals. 6.5 Electrochemical Charge Balance Constituents dissolved in solution exhibit either positive (called cations, such as Fe+2) or negative (anions, such as HCO3-) charges because they are not chemically bound in a solid. Comparison of the concentration of major cations and anions in a solution such as a groundwater sample can be used for two purposes. First, charge balance within a small tolerance (five to ten percent) provides an indication that all of the major constituents have been identified. Second, lack of charge balance in a well characterized sample can be an indication of disequilibrium. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 34 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Electrochemical charge balance is calculated by converting concentrations of major cations (calcium, potassium, sodium, magnesium, iron, and manganese) and major anions (chloride, bicarbonate + carbonate, sulfate + sulfide, and nitrate + nitrite) to molar equivalents, summing the total of each, and comparing the results as a percentage off equality. Groundwater that is in equilibrium with the soil or rock that surrounds it should exhibit equal concentrations of cations and anions (refer to Section 6.4.5). Lack of charge balance can be an indication that other chemical constituents are “major” cations or anions. Lack of charge balance can also be an indication of disequilibrium. The chemical weathering that occurs as rainwater infiltrates into the ground everywhere in the southeastern United States is the result of chemical disequilibrium. If the rainwater were in equilibrium with soil and rock, weathering would not occur. Similarly, discharge of contaminants from a source can cause disequilibrium in affected groundwater as reactions initiated by the introduced contaminants proceed. Groundwater samples collected for the CSA were analyzed for a large suite of cations and anions. It is unlikely that anions, in particular, have not been fully characterized. Deviations in solution chemistry indicated by charge balance calculations are evaluated in this report to identify a cause. 6.6 Equilibrium The conditions under which chemical reactions such as the binding of dissolved arsenic into an iron oxide can be determined by experiments conducted under highly controlled, or equilibrium, conditions (Nash, 1971, p. 101-107). These experimental data yield powerful predictive capabilities regarding the results of chemical reactions so long as the assumption of equilibrium can be made. Equilibrium is attained over time when the entropy (S, defined as the chemical capacity for change) of the reaction reaches a maximum for the conditions (e.g., temperature, pressure, concentration, etc.) under which the reaction is occurring. Equilibrium calculations do not address the time required for entropy to reach a maximum (Denbigh, 1971, p.40-42). In general, conditions at the surface of the earth are not conducive to driving reactions to the maximum level of entropy, or equilibrium. It is for this reason that chemists use reactors to create conditions of elevated temperature and pressure to convert a mixture of chemicals into a product in a short period of time. For these reasons, use of equilibrium equations to predict the results of chemical reactions in an ash basin or in the shallow subsurface of the earth is at best an approximation. These equations are a proper and appropriate starting point to predict the chemical reactions that will occur over time as ash sluice water accumulates in a Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 35 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx basin, becomes ash pore water, and subsequently migrates from the basin. However, because the assumption that equilibrium will be attained cannot be supported, the predictions in this report and subsequent documents based on such calculations are approximations and must be critically evaluated with professional judgment. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 36 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 7.0 SOURCE CHARACTERIZATION The groundwater assessment was focused on the ash basins and FADA at the Site as potential sources of groundwater impact, as described in the following sections. Methods used to characterize the source materials are described in Appendix C. 7.1 Identification and Description of Sources Coal is formed from plant material that accumulated in settings comparable to modern day swamps. Coalification is the process by which plant material is converted to coal by elevated heat and pressure that result from burial beneath overlying soil and rock. Varying amounts of inorganic sediment such as sand, silt, and clay are deposited in swamps with the dead plant material. Additional inorganic impurities such as pyrite likely formed from interstitial liquids as the plant material was converted to coal. The chemical character of coals evolves in a regular manner with increasing depths of burial and passage of time. Depth ranges up to 2,000 meters (6,560 feet) BGS and temperature ranges of 70° to 80°C (158° to 176°C) are accepted as the conditions under which coals form (Kisch, 1969, p. 407-425; Turner, 1981, p. 303-305). Coal Combustion and Ash Handling System 7.1.1 Coal was pulverized prior to combustion in the boilers. Bottom ash is comprised primarily of the inorganic impurities in coal that did not burn in the boiler. The grain size or specific gravity of this material prevents entrainment in the flue gas. Fly ash is fine material that was removed from the flue gas stream by electrostatic precipitators at the Site. Electrostatic precipitators went into service at the Site between 1972 and 1975 for the three coal-fired units. Ash was conveyed hydraulically from the plant boilers to the FADA area first and then to the ash basins. During operation, ash laden sluice water flowed by gravity to a pump pit for conveyance by pipe to the ash basin. Hydraulic placement of ash was accomplished by moving the influent pipe to different locations within the basins. Ash particles settled in the basin while the water was impounded. Description of Ash Basins 7.1.2 The FADA appears to have been a low-lying area that was filled with ash. The thickness of the ash encountered at AB-2 extended from the ground surface to a depth of approximately 8 feet thick. Groundwater was measured at approximately 3 feet bgs at ABMW-2. The 1971 ash basin area appears to have been excavated below grade to a depth of approximately 40 feet. Samples collected from AB-1 indicate surficial sand was removed, except for approximately two feet at the bottom prior to placement Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 37 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx of the ash. The ash is approximately 79 feet deep, as measured from the top of the ash, at AB-1 and the top of the ash basin is approximately 40 feet above Site grade. The water level in ABMW-1 was measured at approximately 34 feet bgs. There was a small area of standing water in the northwest portion of the 1971 ash basin during this assessment (2015). The excavated sand may have been used locally in the construction of the basin or canal berms. Both the FADA and the 1971 ash basins are unlined. The 1984 basin appears to have been constructed above grade and is lined with a 12-inch clay layer. The northern portion of this basin contains standing water as of this assessment (2015). The ash basin embankments are well vegetated. Soil has been used to construct the perimeter levees. According to Duke Energy (October 31, 2014) the 1971 and 1984 ash basins contain approximately 6,320,000 tons of ash and the FADA area contains approximately 840,000 tons of ash. No other ash storage facilities have been identified on the Site property. 7.2 Characterization of Sources Prior characterization of the ash basin was supplemented by two borings and installation of two monitor wells during the current assessment. The borings were installed using sonic drilling methods with continuous sample recovery (Appendix C). Each boring penetrated the bottom of the ash. Two ash samples from AB-1 and one from AB-2 and two soil samples were collected from each boring for physical and chemical testing in accordance with GAP Section 7.1.1. Only one ash sample was collected from AB-2 due to the thin section of ash at this location. The contact between ash and underlying soils was distinct in both borings. Physical intrusion of ash into the underlying soils appears limited. Physical Properties of Ash 7.2.1 Physical properties (grain size, specific gravity, and moisture content) and mineralogy determinations were performed on samples from the ash basin. Physical properties were measured using ASTM methods and mineralogy was determined by X-ray diffraction (Appendix C). With the exception of the sample from AB-2, the ash is fine grained (primarily silt with some clay size particles) and exhibits a lower specific gravity than soils which typically range from 2.2 to 2.5 (Table 7-1). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 38 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Mineralogy was determined for ash samples from AB-1 at 3’-5’ bgs & 43’-45’ bgs (Table 7-2). The samples tested were predominately quartz (43.1 & 42.3 percent). The AB-1, 3’-5’ sample contained 23.3 percent calcium, while the AB-1, 43’ -45’ sample contained 34.6 percent aluminum. The AB-2 ash sample from the FADA was found to contain 70.3 percent quartz. The ash samples also contained hematite (Fe2O3) which is presumed to have formed in the boiler from minerals that contained reduced iron (such as pyrite). Chemical Properties of Ash 7.2.2 Three samples of ash, two from the 1971 basin and one from the FADA were analyzed for total metals and total organic carbon (TOC). In addition one ash sample from each the 1971 ash basin and the FADA and submitted for metals susceptible to leaching by the USEPA Synthetic Precipitation Leaching Procedure (SPLP, Appendix C). The 1971 ash basin ash samples were found to contain iron, mercury, and selenium above the USEPA Mid-Atlantic Risk Assessment Regional Screening Levels – Protective of Groundwater (Table 7-3). Manganese was detected in both samples at concentrations well below screening levels, 24.2 mg/kg and 35.2 mg/kg. Boron was detected at estimated concentrations of 8.7 mg/kg and 7.2 mg/kg. Residual carbon (measured as TOC) in the samples ranged from 7,130 to 145,000 mg/kg. The FADA ash sample contained barium, beryllium, copper, iron, lead, mercury and selenium above the groundwater screening level as well as aluminum, cobalt and vanadium in excess of the residential health screening level. Boron was detected at an estimated concentration of 21.9 mg/kg. Residual carbon (measured as TOC) was detected at 91,000 mg/kg. All of the 25 metals analyzed for except beryllium, cadmium, chloride, nitrate, cobalt, iron, lead, thallium and vanadium in the 1971 ash basin sample and cadmium, chloride, nitrate and mercury in the FADA ash sample were detected in the SPLP leachate. No metals were detected in the 1971 ash basin leachate sample that exceeded 2L or IMAC. Antimony, arsenic, cobalt, iron and vanadium were detected in the FADA leachate sample at concentrations exceeding the 2L or IMAC (Table 7-4). Three ash samples were tested by Energy Dispersive X-Ray Fluorescence for metal oxides (Table 7-5) and a suite of elements (Table 7-6). The sample from the FADA and the shallow sample from the 1971 ash basin were comprised Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 39 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx primarily of silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3), while the lower ash sample from the 1971 basin was comprised of silicon dioxide, aluminum oxide and iron oxide. Chemistry of Ash Pore Water 7.2.3 Two samples of ash pore water collected from ABMW-01S (1971 ash basin) and ABMW-2S (FADA) were analyzed for the expanded list of COIs (Table 6-3). Arsenic, manganese, and vanadium were detected in ash pore water samples from both the 1971 basin and the FADA above the corresponding 2L or IMAC (Table 7-8). Boron was also detected in the 1971 basin sample above 2L while barium and iron were detected above the 2L in the FADA ash pore water. Molybdenum, a metal for which a 2L Standard has not been assigned, was detected in samples from both basins at a concentrations ranging from .005 to 0.190 mg/L. Elevated concentrations of calcium, magnesium, sodium, bicarbonate and chloride were also detected in the samples of ash pore water (Table 7-7). Sorption characteristics (Kd) for arsenic, barium, boron, cobalt, iron, manganese, selenium and vanadium are being determined for the ash. Results of these analyses are pending and will be submitted in the CAP. Sorption factors are being determined for these metals for the following reasons: Arsenic, barium, boron, iron, manganese, and vanadium were detected above the 2L or IMAC in ash basin pore water Cobalt and selenium were detected above the 2L or IMAC in a sample from one or more of the monitor wells. The valence state, or chemical speciation, of arsenic, chromium, iron, manganese, and selenium were determined for pore water from ABMW-1S and ABMW-2S (Table 7-9). Hydrology of the Ash Basins 7.2.4 Depth to water in the 1971 ash basin was measured at approximately 34 feet bgs at an elevation of 11.16 above mean sea level (AMSL). The vadose zone in the ash basin is comprised almost wholly of ash. The maximum thickness of the ash is approximately 80 feet; therefore approximately 46 feet of ash are saturated. The underlying natural ground surface consists of approximately one to two feet of surficial sands underlain by fine sands and silts of the Pee Dee formation. The water level in AMBW-1D, screened within the Pee Dee formation, is 10.55 AMSL, Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 40 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx indicating a slight downward vertical gradient in the 1971 ash basin. The downward head loss is 0.71 ft. over a distance of 46 feet, yielding a downward vertical gradient of 0.0154 ft./ft. The top of the 1971 ash basin stack stands approximately 20 feet above adjacent land grade; indicating the ash basin likely serves as a recharge area to the surficial aquifer. Groundwater measurements indicate the adjacent sand hills east of the basin are also acting as a recharge area. No water level data was collected within the clay-lined 1984 basin; however standing water is present on the north side of this basin. The depth to water in the FADA is approximately two to three feet bgs at an elevation of 7.42 feet AMSL. The ash thickness at ABMW-1S is approximately eight feet; therefore at least five feet of the ash is saturated in the FADA. Due to the low-lying ground in the FADA, this area can become flooded during periods of heavy rain and the entire ash thickness would be saturated. The natural soil beneath the ash in the FADA consists of surficial sands to a depth of approximately 46 feet bgs. The ash-soil contact was observed to be saturated and loose; indicating some perching of groundwater in the ash on the natural ground surface below. The water level in the deep FADA well, ABMW-2D, was measured at two to three feet bgs at an elevation of 7.39 AMSL, indicating a downward vertical gradient in this area. The drainage canal for the Site process water extends along the southern boundary of the 1971 ash basin and likely intersects shallow groundwater and controls the elevation at which groundwater flows from the 1971 ash basin to the south (Figure 1-2). Also, the cooling pond located adjacent to the 1971 ash basin to the west likely also serves as a recharge to the surficial aquifer and effects flow in the zone from the ash basin. The horizontal hydraulic conductivity of the ash in the screened interval of ABMW-01 (1971 ash basin) was determined to be 1.5 x 10-4 cm/sec while the hydraulic conductivity of the screened interval of ABMW-2S (FADA) was determined to be 8.17 x 10-4 cm/sec (Appendix G). These values will be used as an input to the Site groundwater model. 7.3 Piezometers and Seeps No seeps were identified at the Site and no data from piezometers were collected relative to the ash basins. Ash pore water infiltrates into the surficial aquifer below the unlined ash basin. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 41 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 7.4 Constituents of Interest COIs identified in conjunction with the Site ash basins include arsenic, boron, barium, cobalt, iron, manganese, TDS, pH and vanadium. The ash pore water samples collected from the pore water wells (Table 7-7) exceed the 2L or IMAC for these COIs with the exception of cobalt. Three of the samples fell within the pH range of 6.5 to 8.5, while one sample (ABMW-1S) exhibited a pH of 8.97during the second sampling event. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 42 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 8.0 SOIL AND ROCK CHARACTERIZATION Soil borings were performed at each of the 16 new well locations to collect soil samples from the unsaturated zone and the zone of saturation in areas outside of the ash basins. These samples were analyzed for total metals, TOC, and leaching characteristics. A total of 38 groundwater monitor wells were installed at 16 locations outside the ash basins. Two or more wells were constructed at each location (with the exception of AW-7, where a previously existing well served the purpose of the proposed well); screened in the upper and lower surficial aquifer. At selected locations, an additional one or two more wells were installed; within the upper and/or lower portion of the Pee Dee Formation. The wells were installed to provide groundwater samples from the following saturated zones: Shallow intermediate zone Lower surficial aquifer Upper portion of the Pee Dee Formation Lower portion of the Pee Dee Formation Samples from these locations were analyzed to determine mineralogy, physical, and chemical properties (Appendix F). Rinse blanks from sample collection equipment were collected. Rinse blanks for most soil samples were collected by pouring deionized water through the sonic drill bit. COIs detected in these samples indicate that rust that collects on the bit overnight was rinsed into the sample bottle. Although iron, cobalt and vanadium were detected in several of the equipment blanks associated with the soil, the overall quality of the sample data is not impacted. With the exception of iron, the constituents found in the blank samples were either not detected in the associated soil and groundwater samples or were detected at concentrations significantly higher than that found in the blanks. Iron is commonplace in soils and groundwater at the Site and its detection in the equipment blank samples is not considered to impact the overall quality of the sample data (Appendix D). Geologic cross-sections illustrating groundwater COI concentrations are presented as Figures 8-1 and 8-2. Further discussion of groundwater sample results are presented in Section 10 of this document. A map showing soil concentrations above applicable comparison levels is presented in Figure 8-3. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 43 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 8.1 Background Soil Soil samples collected from background locations are discussed in conjunction with soils from the remainder of the Site in the following section. Shallow soils at background locations AW-08 and MW-37 are similar to the surficial aquifer sands in monitor wells outside of the basin. Soils were tested in accordance with Work Plan Section 7.1.1. Physical property testing of soil samples indicates that Site soils are predominately sand (Table 8-1), with the exception of the silts identified in the lower Pee Dee formation. Mineralogical determinations indicate that feldspar, calcite and clay minerals (kaolinite and illite) accompany quartz in soil samples from the Site (Table 8-2). Dolomite was detected in one sample. Soils beneath the Ash Basin 8.1.1 The contact between the ash and underlying soils in the ash basin borings was visually distinct. There was no visible evidence of substantial migration of ash into underlying soils or mixing of ash with those soils. Comparison of chemical analytical data for soils beneath the ash basin with the chemistry of the ash as revealed in both total (Table 7-3) and leaching data (Table 7-4) yields the following observations: Aluminum, arsenic, barium, cobalt and selenium concentrations in the ash are significantly higher than in the underlying soils, indicating that these metals are relatively immobile. Iron occurs in soils beneath the basin at concentrations significantly higher than that at background and other soils outside the basin, indicating that the ash could be a source of iron. Vanadium concentrations in ash and soil are comparable (although soils beneath the basin are consistently lower than ash), and leaching data indicate that vanadium is relatively immobile. Arsenic leaching results indicate that it should exhibit relatively high mobility, but the presence of low levels of arsenic in soils beneath the basin indicate moderate mobility. Boron concentrations in ash and soils across the Site are below PSRG; however, boron is present in many groundwater samples downgradient Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 44 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx of the ash basins but not in background locations. These data indicate that if the ash were the source of the boron, the leaching process is near completion and that boron in solution in groundwater samples does not precipitate or adsorb at appreciable levels in soil. SPLP data on ash samples indicate concentrations below 2L. Site Soils 8.1.2 With the exception of the soil samples collected from the ash basin borings, all soil samples collected during the assessment were collected from near the Site perimeter, with the exception of AW-8, which is located north of the compliance boundary for the ash basins. COIs detected above a Regional Screening Level (RSL) in the soil samples include arsenic, iron manganese, vanadium, cobalt and boron. However, boron and cobalt exceeded the RSL in only one sample from the Pee Dee formation and manganese was detected in only two soil samples from the Pee Dee formation. Vanadium was found in concentrations above the RSL in only three samples; all collected from the Pee Dee formation. Iron was the only COI to exceed RSL in samples collected from the surficial aquifer and was detected in most samples with the notable exception of upgradient location AW-08 and background location MW-37. Iron was also detected in most Pee Dee samples. Metal oxide analysis of soil samples (Tables 8-3, 8-4, 8-5, and 8-6 and Figure 8-1) indicate that oxides of silicon (74 to 100 percent) and aluminum (1.3 to 5.4 percent) are the predominate chemicals present. Trace metal oxides (potential COIs) detected in appreciable concentrations include iron (0.2 to 2.8 percent), and manganese (non-detect to .02 percent). All of the metals analyzed in SPLP leaching tests, with the exception of arsenic and mercury were detected in leachate, or had estimated quantities, from one or more soil sample. Review of these results indicates that aluminum, barium, boron, iron, sodium and vanadium would be mobilized from natural soils at the Site in the highest concentrations. Surficial Soils 8.1.3 Soil samples from the surface to two feet bgs were collected at 14 locations. Iron was the only COI detected above a soil screening level. These results are discussed in greater detail in Section 12.2.5. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 45 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 8.2 Comparison of Results to Applicable Levels Qualitative evaluation of the soil chemistry data suggest that, with the potential exception of iron concentrations, soils beneath the ash basins, at AW-8 and at the perimeter of the Site have not been greatly affected by the ash basins. While there are numerous detections in soils of COIs above the RSL, other than iron, these exceedances are detected only in the Pee Dee formation and only at three locations, AW-6, AW-7 and SMW-6. Given the distance of these boring locations from the ash basins and the lack of detection in soils of these COIs at other locations along flow transects, it is questionable whether these exceedances can be attributed to operation of the ash basin. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 46 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 9.0 SEDIMENT AND SURFACE WATER CHARACTERIZATION Sediment and surface water samples were collected from seven locations beyond the perimeter of the ash basin. To provide information on surface water quality in the cooling pond and Cape Fear River, with respect to the ash management area, seven surface water samples were collected. Four samples, (SW-004, SW-8A, SW-6A, and SW-1C), were collected from the cooling pond at the locations shown on Figure 1-2. Three surface water samples (SW-CFUP, SW-CFP, and SW-CF001) were collected from the Cape Fear River (Figure 1-2). These samples were collected during an outgoing tide. SW-CFUP is considered an upgradient sample. SW-CPF was collected from the makeup pump to the cooling pond, which is routinely sampled as part of the NPDES permit. SW-CF001 was collected downgradient of NPDES Outfall 001. Sediment samples were collected from the bed surface at each of the surface water sample locations (Figure 1-2). The SW-CFUP location is considered a background sediment sample. The sediment samples were analyzed for total inorganics, using the same constituents list proposed for the soil and ash samples and pH, cation exchange capacity, particle size distribution, percent solids, percent organic matter, and redox potential. Residential soil screening levels were exceeded in the sediment samples collected at SW-CF001 and SW-CFP for iron, manganese and cobalt (Table 9-1). Iron was detected at the highest concentrations; 11,700 mg/kg at SW-CR001 and 10,900 mg/kg at SW-CFP. Detected concentrations of manganese were 226 mg/kg at SW-CF001 and 414 mg/kg at SW-CFP. Cobalt was estimated at a concentration of 7.6 mg/kg in SW-CFP. An estimated concentration of 4.6 mg/kg of arsenic was reported for SW-06A from the cooling pond perimeter. Since these concentrations are often naturally- occurring and their concentrations cannot be quantified within laboratory quality control limits, no conclusion can be drawn related to these data. No other COIs were detected above industrial or residential screening levels. 9.1 Comparison of Exceedances to 2B Standards Exceedances of 2B concentrations were detected in the surface water samples for aluminum, copper, and zinc. Aluminum and copper exceedances were detected at SW- 01C (cooling pond) and the SW-04 (cooling pond) sample exceeded the 2B concentration for copper. The SW-CF001 (NPDES Outfall to river), SW-CFP (river sample) and the SW-CFUP (upgradient river sample) samples exceeded the 2B concentration for Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 47 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx aluminum. The SW-CFUP also exceeded the 2B concentration for zinc. The SW-06A and SW-08A samples exceeded the 2B concentration for copper. 9.2 Discussion of Results for Constituents Without Established 2B COIs for which a 2B concentration has not been established include boron, iron, manganese, TDS, and vanadium (Table 9-3). Boron was detected at concentrations ranging from 196 to 204 µg/L in the water samples collected from the cooling pond. Boron was not detected in water samples collected from the Cape Fear River. Iron was detected at a concentrations ranging from 49 µg/L to 127 µg/L in the cooling pond samples and at concentrations ranging from 1,310 to 1,830 µg/L in the Cape Fear River samples. Manganese was detected at a concentration of 7 µg/L in SW-01C from the cooling pond and at concentrations ranging from 42 to 96 µg/L in samples collected from the Cape Fear River. TDS was detected in a range of 89 to 150 µg/L in all surface water samples. Vanadium was detected in all surface water samples at concentrations ranging from 1.25 to 1.76 µg/L in the river samples and 3.04 to 3.87 µg/L in the cooling pond samples. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 48 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 10.0 GROUNDWATER CHARACTERIZATION Groundwater samples from the 42 new monitor wells and 29 existing monitor wells were analyzed for the GAP COIs (Table 10-1). In addition, 28 wells, including previously existing wells and new wells, were sampled for speciation of selected COIs. A Comprehensive Analytical Results table is presented in Attachment 4. 10.1 Background Groundwater Conditions MW-5C, located approximately 3,000 feet north of the ash basins, is considered the background location for groundwater in the northern portion of the Site. MW-5C is screened in the lower surficial aquifer. Concentrations of cobalt (1.62 µg/L) and manganese (441 µg/L) were detected in MW-5C during compliance well sampling in June, 2015. No other constituents exceeded 2L or IMAC in the MW-5C sample. MW-4B has historically been used as a background well for the southern portion of the Site. During the CSA, MW-37B/C were installed as an additional background wells in the southern portion of the Site. Iron and manganese were detected at concentrations exceeding 2L in MW-4B. Cobalt, iron and manganese were also detected above 2L or IMAC in MW-37B and MW-37C and vanadium was detected above IMAC in MW-37C. 10.2 Discussion of Redox Conditions Soil staining in the saturated zone which would indicate oxidizing conditions is present in some portions of the lower the surficial aquifer. Reddish-orange layers of medium to coarse sands were observed in the lower surficial aquifer in AW-9D, CUB-03 and CUB- 06 in the southeast portion of the Site and SMW-1C, SMW-4C, SMW-5C and SMW-6D, east of the central portion of the Site. The Pee Dee Formation exhibited evidence of reducing conditions that include gray color and strongly negative ORP readings in groundwater. Strongly negative ORP readings, as well as the presence of wood in quantities ranging from trace to a 2-foot layer (AW-3C) are evidence of reducing conditions in some areas of the lower portion of the surficial aquifer. Valence speciation determinations were performed on groundwater samples from monitor wells installed in 2015, compliance wells, and select existing wells along flow transects outward from the ash basin (Table 10-3). General observations follow: As+3 was the dominant species detected for each sample containing arsenic. The sample from ABMW-2D, beneath the FADA, which contained the highest concentration of total arsenic, was found to contain 119 µg/L of As+3 versus 7.71 µg/L of As+5. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 49 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Hexavalent chromium was detected at concentrations comparable (same order of magnitude) to the proposed California drinking water standard of 0.01 µg/L. Reduced iron was the dominant species in each sample with the exception of AW-06D in the Pee Dee Formation and SMW-03B in the surficial aquifer. Mn+3 was the dominant species where manganese was detected with the exception of the wells screened in the lower Pee Dee. 10.3 Regional Groundwater Data for Constituents of Potential Concern Iron, manganese, cobalt and vanadium are detected across the Site, including at the background locations. It is anticipated that site specific background levels will be calculated for these metals after eight sets of groundwater data are available. NURE data on vanadium were discussed in Section 6.3.2 of this report. These data have not been analyzed in detail, but they make it clear that vanadium is common in North Carolina groundwater. As previously referenced in Section 4.4.4, regional groundwater data indicate boron concentrations in the Pee Dee Formation can be elevated. A well in Myrtle Beach which is screened within the Pee Dee was found to contain 1,600 µg/L boron, likely due to salt water intrusion, given the depth of the sample and the proximity to the coast. 10.4 Groundwater Analytical Results Iron, boron and manganese were detected at the highest concentrations in the largest number of wells across the Site. Cobalt and vanadium were also detected at concentrations exceeding IMAC in a high number of wells, but at lower concentrations. Figures 10-1 through 10-4 illustrate groundwater sample concentrations greater than 2L or IMAC in wells installed within the upper surficial, lower surficial, Upper Pee Dee and Lower Pee Dee aquifers, respectively. Geologic cross sections illustrating COI analytical results are presented on Figure 8-1 and 8-2. Iron is present in some background wells and in wells across the Site; however the highest detected concentrations were in the FADA ash pore water well (29,200 µg/L). Outside of the basin, the highest iron concentration was detected in off-site well SMW- 2B (28,800 µg/L). Elevated concentrations are present at most locations adjacent to, and downgradient of the ash basins however, it is unclear that the high concentrations in the off-site wells east of the Site are related to the ash basins, based on their distribution and occurrence. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 50 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The occurrence of high concentrations of iron is greater in the lower surficial aquifer. Concentrations of iron are lower in the Pee Dee Formation wells. The occurrence of detected concentrations of manganese over the 2L closely matches that of iron. Cobalt was not detected in the ash pore water wells but was detected in the background wells and several surficial aquifer wells, specifically along the eastern Site boundary and off-site wells, where the highest concentrations were detected. Cobalt was only detected in MW-15D, near the FADA. Based on these data, it is not clear that the occurrence of cobalt is related to the ash basins. Cobalt has an IMAC of 1 ug/L. Boron was detected in the 1971 ash pore water well but not in the FADA ash pore water well. Boron was not detected in background wells. Boron is the most mobile of the metals of concern (refer to Section 6.3.3), with lateral migration apparently more prevalent than vertical movement. Elevated boron concentrations were also detected in the Pee Dee Formation wells. However, the occurrence of boron in the lower Pee Dee wells (AW-5E, AW-6E and MW-23E) is closely aligned with concentrations of chloride over 2L. Chloride does not exceed 2L in any other well and its occurrence at that depth, as well as that of boron and other metals may be attributed to salt water intrusion. The detected boron concentration in Site Pee Dee Formation wells is comparable the previously reference well in Myrtle Beach, South Carolina. Arsenic has migrated limited distances vertically and horizontally from the ash basins and is present above 2L in only the ash pore water wells and two surficial aquifer wells near the ash basins. Vanadium was detected in the ash pore water wells and in wells across the Site in both the surficial and Pee Dee aquifers at concentrations exceeding IMAC. Vanadium was detected in upgradient well AW-8B and background well MW-37B/C. The highest concentration detected, 39.6 µg/L, in MW-20 between the FADA and the cooling pond intake canal, is greater than other areas. Selenium was detected in only two wells; well MW-27B located north of the 1984 ash basin and AW-6D, a perimeter well screened in the upper Pee Dee. Thallium was found to be above IMAC in four wells. It is not clear that it has migrated from the ash basin as it was not detected in the ash pore water wells and only appears in a limited number of wells at relatively low concentrations. The detected concentrations of thallium are 0.506 µg/L or lower and the exceedances are limited to an area southeast of the old ash basin (MW-7C, MW-19, MW-22 and MW-23). Isoconcentration maps illustrate the distribution of COIs in the upper surficial aquifer, (Figures 10-5 through 10-14), the lower surficial aquifer (Figures 10-15 through 10-24), Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 51 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx wells screened in the Upper Pee Dee Formation (Figures 10-24 through 10-34) and wells screened in the Lower Pee Dee Formation (Figure 10-35 through 10-44). Samples from the upgradient wells AW-08B/C, the two ash pore wells ABMW-1S and ABMW-2S, and the two monitor wells beneath the ash basins (ABMW-1D and ABMW- 2D) were analyzed for isotopes of uranium and radium (Attachment 5). Uranium-238 (U238) was detected in the both samples from the 1971 ash basin, ABMW-1S and ABMW- 1D. Uranium was not detected in the upgradient wells or the FADA wells. Radium226 was detected in all samples except upgradient sample AW-8C and radium228 was detected in both wells beneath the ash basins (ABMW-1D and ABMW-2D). The highest concentration of Ra226 was 1.65 picoCuries per liter (pCi/L) in the upgradient well sample AW-8B, comparable to the 1.62 pCi/L in the sample from beneath the 1971 ash basin. Ra228 was detected at 2 pCi/L in ABMW-1D and 1.6 pCi/L in ABMW-2D. Maps of groundwater analytical results related to detection monitoring constituents and inorganic parameters as identified in the USEPA April 2015 Final Ruling 40 CFR Parts 257 and 261 (CCR Rule), including boron, calcium, chloride, conductivity, pH, sulfate, and total dissolved solids are included as Figures 10-45 through 10-48. Maps of groundwater analytical results related to assessment monitoring constituents as identified in the USEPA April 2015 Final Ruling 40 CFR Parts 257 and 261, including aluminum, antimony, arsenic, barium, beryllium, cadmium, chromium, copper, iron, lead, manganese, mercury, molybdenum, selenium, sulfate, sulfide, thallium, and vanadium are included as Figures 10-49 through 10-52. All the CCR rule constituents were not monitored as part of the CSA and therefore maps for all CCR constituents are not provided. Distributions of major cations and anions in ash pore water and the surficial and Pee Dee monitor wells plotted on Piper diagrams provide an indication of the characteristics of each zone. Ash pore water is dominated by calcium, magnesium, and carbonate. The sulfate content of the ash pore water is lower than would be anticipated (Figure 10-53). Ion ratios vary substantially in the surficial zone across the Site, but are generally higher in calcium and magnesium, with AW-01B in the northeast portion of the Site and SMW-4C off-site to the east being clear outliers (Figure 10-56). Major ion ratios in samples from the Pee Dee are dominated by sulfate, chlorides, sodium and potassium with outlier ABMW-1D, which is in the upper Pee Dee, beneath the 1971 ash basin having a higher calcium and magnesium content and lower sodium and potassium (Figures 10-53 and 10-58). Variations of constituent concentrations through time are illustrated in Appendix H. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 52 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Interwell prediction limits (parametric, nonparametric, and Poisson) were used to compare background well data to the results for the most recent sample data from compliance wells. Based on recommendations from ASTM (2012) guidance and USEPA (2007), nondetected values were replaced with half of the detection limit for the parametric and Poisson prediction limit procedures, and the detection limit for the nonparametric prediction limit procedure. Confidence levels were set at 99 percent for the parametric and Poisson prediction interval. Confidence levels for the nonparametric prediction limit are given by n/(n+k) were n is the number of background samples and k is the number of comparisons. The false positive rate is given by 1-[n/(n+k)]. The number of comparisons is defined by the number of recent sample dates multiplied by the number of compliance wells (background wells). Prior to conducting the interwell statistical analysis, the data set was “screened” and “treated.” The Shapiro-Wilks goodness-of-fit test was used to evaluate the statistical distribution of data sets because they contain less than 50 measurements. Each data set was initially tested to determine whether the distribution is normal. If a data set fails the test of normality, the natural logarithms of the data are taken and the procedure is repeated. If the transformed data passes, the data set is designated as lognormal. If a log transformed data set fails the test of normality, the data set is designated as non- normal. The parametric prediction limit was used to analyze data that were normally or log normally distributed with less than or equal to 50 percent nondetects (ASTM D6312-98, Section 6.1.1). The nonparametric prediction interval test was performed on normal and lognormal data sets with greater than 50 percent nondetects and for data sets with non-normal distributions with fewer than 90 percent nondetects (ASTM D6312-98, Section 6.1.1). The nonparametric prediction limit compares each individual downgradient concentration for the selected dates to the maximum concentration in background samples. The Poisson prediction limit statistic was utilized to evaluate data with greater than 90 percent nondetects (ASTM D6312-98, Section 6.1.1). Rinse blanks from sample collection equipment were collected as summarized in Appendix C. Although various constituents were detected at low level concentrations in several of the equipment blanks associated with the groundwater samples as well as a number of the filter blanks, the overall quality of the sample data is not impacted. The constituents found in the blank samples were either not detected in the associated soil and groundwater samples or were detected at concentrations significantly higher than that Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 53 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx found in the blanks. The single exception being iron, commonplace across the Site and its detection in equipment blanks is not considered to significantly impact the data. Rinse blanks from the pumps and filters used to collect groundwater samples yielded negligible detections of COIs (Appendix D). 10.5 Comparison of Results to 2L Standards Twelve metals were detected in groundwater samples above 2L or IMAC; antimony, arsenic, barium, boron, chromium, cobalt, iron, lead, manganese, selenium, thallium, and vanadium (Table 10-2). Of the twelve metals exceeding 2L or IMAC, cobalt, and manganese were detected in background wells MW-5C and MW-37B/C and iron was detected in background wells MW-37B/C. Vanadium was detected above IMAC in background well MW-37C. Only arsenic, barium, boron, iron, manganese and vanadium were detected above 2L or IMAC in the ash pore water. Lead was detected at a concentration of 16 µg/L in one well, AW-01B, located approximately 3,600 feet northeast of the 1971 ash basin in the first sampling event but was below detection limits for all other wells in both the first and second sampling events. Lead was not detected in AW-01B during the second sampling event. The turbidity during the first sampling event at AW-01B was 249 Nepthalic Turbidity Units (NTUs) but was 9.87 during the second sampling event. Based on these data, the detection of lead in AW-01B during the first sampling event is an anomaly related to turbidity and therefore lead is not considered a COI at this Site. Chloride was detected above 2L in the three deep Pee Dee Formation wells at concentrations ranging from 490 to 540 mg/L. These concentrations are twice those detected in the upper Pee Dee Formation wells and much greater than those detected in the surficial aquifer wells and ash pore water wells. It is likely that the exceedance of chloride in the lower Pee Dee wells represents salt water intrusion and is not representative of Site conditions; chloride is not considered a COI. Additionally, the detected concentrations of boron in the lower Pee Dee wells are significantly greater than those detected in upper Pee Dee and surficial wells at the same locations. These data may indicate that the detected concentrations of boron in the lower Pee Dee wells may also be representative of salt water conditions. Regional groundwater data supports this. A well located in Myrtle Beach South Carolina and screened from 95-105 feet within the Pee Dee formation was reported to contain a concentration of 1,600 µg/L of boron. (Ground-Water Quality Data From the Southeastern Coastal Plain, Mississippi, Alabama, Georgia, South Carolina, and North Carolina, Roger W. Lee, U. S. Geological Survey, Open File Report 84-237, 1984). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 54 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Selenium was detected in only two wells; well MW-27B located north of the 1984 ash basin and AW-6D, a perimeter well screened in the upper Pee Dee. The detected concentrations were slightly above 2L in each instance. The selenium detection in AW- 6D is an anomaly in that the laboratory reported a dissolved concentration above 2L but a total concentration below detection limits. Additionally, AW-6D was sampled three times and the selenium concentration was reported below the detection limit in two of the three samples. Based on these data, the occurrence of selenium in these wells appears to be unrelated to the ash basins and is therefore not currently considered a COI. However, since MW-27B has historically contained selenium concentrations above 2L and it may be influenced by radial flow from the adjacent 1984 ash basin. Since no data is available for the 1984 ash pore water, it cannot be conclusively eliminated as a source of selenium detected in MW-27B. Collection of additional data for selenium has been identified as a data gap that does not compromise the preparation of the CAP. Total dissolved solids (TDS) exceeded 2L in the 1971 ash basin pore water well, in the upper surficial aquifer well AW-01B, in the lower surficial well MW-31C and in Pee Dee Formation wells AW-2D, AW-5E, AW-6D/E, AW-9D, MW-23E and SMW-6D. TDS is considered a COI based on these data. Levels of pH outside the 2L range were measured in most of the Site wells. The ash pore water well, ABMW-1S and several of the Pee Dee wells had pH levels above 8.5 while most surficial wells had pH levels below 6.5. Exceedances of 2L or IMAC for iron, cobalt, manganese, and vanadium are most common across the Site (Figures 8-1, 8-2, 10-1, 10-2, 10-3, and 10-4). Each is naturally occurring and common in shallow wells in this hydrogeologic setting. In most cases for iron comparison of total concentrations to a corresponding “dissolved” (filtered) concentration indicates that iron is associated with solids. Site specific background concentrations need to be calculated for these COIs. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 55 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 11.0 HYDROGEOLOGICAL INVESTIGATION Results of the hydrological investigation summarized in this section are the primary components of the SCM. 11.1 Hydrostratigraphic Layer Development The surficial aquifer and the Pee Dee Formation are the two distinct hydrostratigraphic layers discussed in this assessment report. These aquifers are each composed of Coastal Plain sediments. The saturated portion of the ash basins are superimposed on the surficial aquifer. The 1971 ash basin area was excavated to a depth of approximately 40 feet bgs, effectively replacing the upper and lower surficial aquifer in this location. Given the difference in ash and surficial soil hydraulic conductivities, it is likely the ash serves as an interruption to flow within the surficial aquifer. The FADA ash thickness extends to only eight feet bgs but is saturated at three feet bgs and is considered part of the upper surficial aquifer flow zone. Published data had indicated that the surficial aquifer, was of an average thickness of 35 feet, and was underlain by the Castle Hayne confining unit, with an average thickness of 20 feet. The Castle Hayne aquifer was reported to have an average thickness of 60 feet in the northern Wilmington area. Additionally, the Pee Dee confining unit was reported to underlie the Castle Hayne aquifer and have an average thickness of 10 feet and mark the upper limit of the Pee Dee Formation. Previous studies by Catlin Engineers (2010) and Geosyntec (2014) (Attachment 1) did not confirm the presence of the Castle Hayne aquifer or the confining unit of the Pee Dee formation. Eight borings performed for this assessment extended to a depth of 100 feet bgs and three extended to a depth of 150 feet bgs. Neither the Castle Hayne confining unit/aquifer nor the Pee Dee confining unit were encountered. Additionally, 10 soil borings were extended to the top of the Pee Dee formation in the southeastern portion of the Site in an effort to identify a confining unit. No confining unit was identified during this assessment. The surficial aquifer lies unconformably over the fine sands and silts of the upper Pee Dee formation at the Site. 11.2 Hydrostratigraphic Layer Properties Groundwater analytical results from the assessment plotted on the geologic cross- sections illustrate the properties of these layers (Figures 11-1 through 11-4). Confining Unit 11.2.1 Previous reports and published data indicated that a confining unit was present in the upper portion of the Pee Dee Formation. No confining unit was identified at the Site during this assessment. In addition to monitor well borings that Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 56 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx extended into the Pee Dee formation, 10 soil borings, designated Confining Unit Borings (CUB) were installed in the southeastern and southern portions of the Site for the purpose of locating the confining unit. These borings generally encountered the same conditions as the monitor well borings; a sharp contact between the lower surficial aquifer and the Pee Dee Formation with the poorly sorted sands of the surficial directly overlying the dark gray/green fine sands and silts of the Pee Dee. In-Situ Tests 11.2.2 No in-situ tests were conducted except for slug tests. Slug Tests 11.2.3 Slug testing is described in Section 6.2.3 and summarized in Table 6-7. Slug testing indicates mean hydraulic conductivity values of 3.69 x 10-4 cm/sec within the ash basin and 5.13 x 10-2 cm/sec within the surficial aquifer. Hydraulic conductivity values were considerably lower in the upper Pee Dee wells (2.75 x 10-5 cm/sec) and lower still in the lower Pee Dee wells (4.56 x 10-7 cm/sec). Porosity 11.2.4 No porosity tests were performed due to the inability to collect undisturbed samples of the loose sands of the surficial aquifer; however a porosity value of 25-50 percent was used based on published dated (Fetter, Applied Hydrogeology, Fourth Edition). The porosity values for the upper Pee Dee were determined to be 41.4 – 42.5 percent in the upper portion (45 – 50 ft. bgs) of the Pee Dee and 30.1 percent in a lower portion (99 ft. bgs). 11.3 Groundwater Flow Direction Measurements in groundwater wells indicate overall flow is to the east and south (Figures 6-6 through 6-8). Groundwater at the Site flows radially from the ash basin and sand hills in the central portion of the Site. The cooling pond, which has a level approximately 10 feet above the adjacent Cape Fear River, provides additional head to the surficial aquifer. The current interpretation of groundwater flow indicates a groundwater divide or ridge east of the ash basin. Groundwater appears to flow in all directions from this ridge but primarily to the east, west and south. The 1971 basin appears to act as somewhat of a groundwater sink. This area was excavated to a depth of approximately 40 feet bgs prior to placement of the ash. The original topography of the Site suggests that natural groundwater flow in the ash management areas would have been to the west and southwest toward a former creek and the river beyond. Groundwater to the east and south of the groundwater divides flows east and south. The highest groundwater Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 57 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx elevation at the Site was recorded in MW-5C to the north and the lowest was recorded in MW-37B to the south; indicating a regional north to south flow direction. The potential interferences from the off-site municipal, industrial production wells (and the potential extraction wells) and Site production wells will be considered in the groundwater flow model is being prepared for the CAP. As the model is being prepared additional groundwater and surface water elevation monitoring may be conducted. 11.4 Hydraulic Gradient The horizontal hydraulic gradient from the ash basin to surrounding areas ranges from 0.000091 to 0.001 foot per foot (Table 6-8). 11.5 Groundwater Velocity Groundwater velocities calculated for the four flow paths described in Section 6.2.2. range from 0.185 to 8.55 feet per year. Slug tests that were conducted in wells screened below the ash basin were analyzed for hydraulic conductivity and were used to calculate the flow velocity. Flow rates from the ash basins to surrounding areas are the highest due to the hydraulic gradient from the elevated basins to the surrounding areas. 11.6 Contaminant Velocity Site specific sorption coefficients are being determined by the UNCC laboratory. While not included in this report, site specific sorption coefficients will be available for incorporation into the groundwater modeling that will be performed for the CAP. COIs are expected to migrate at rates lower than groundwater velocity. Boron is likely an exception to this generalization. 11.7 Characterization of COI Distribution Distributions of COIs from the ash basin to the surrounding area are illustrated on the primary flow transect (Section B-B’). Horizontal distribution is generally to the east/southeast. 11.8 Groundwater / Surface Water Interaction Due to the shallow groundwater table and the porous nature of the surficial aquifer sediments, interaction between the cooling pond and canals is expected to be rapid with these surface water bodies loading the underlying surficial aquifer. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 58 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 12.0 SCREENING-LEVEL RISK ASSESSMENT Potential risks to human health and the environment have been assessed in accordance with applicable federal and state guidance, as described in Section 8 of the Proposed Groundwater Assessment Work Plan to support the groundwater assessment and inform corrective action decisions, (SynTerra December 2014). Screening level human health and ecological risk assessments have been performed to serve as the foundation for evaluating potential risks to human and ecological receptors at the Site. NCDENR has managed sample collection from nearby private water supply wells. Data from these samples are contained in Appendix B. Preliminary constituents of potential concern (COPCs) have been identified based on evaluations performed in accordance with NCDENR recommendations regarding coal ash constituents. Both screening level risk assessments compare maximum constituent concentrations to appropriate risk-based screening values as a preliminary step in evaluating the potential for unacceptable risks to potential receptors. The screening-level risk assessment is not designed to characterize the horizontal and/or vertical extent of potential impact, but rather to identify coal ash related constituents that exceed published human and/or ecological health screening criteria and warrant further consideration with respect to corrective action. 12.1 Human Health Screening Introduction 12.1.1 This screening level human health risk assessment (HHRA) has been prepared in accordance with Section 8 of the Proposed Groundwater Assessment Work Plan (SynTerra 2014) and USEPA guidance for human health risk assessment, including the USEPA Region 4 2014 Draft Final Human Health Risk Assessment Supplemental Guidance, as applicable. Conceptual Exposure Model 12.1.2 Consistent with standard risk assessment practice for developing conceptual models, separate Conceptual Exposure Models (CEMs) were developed for on- site human health evaluations. Figure 12-1 has been prepared illustrating potential exposure pathways from the source area to possible human receptors. The information in the CEM has been used in conjunction with the analytical data collected as part of the CSA. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 59 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The human health CEM is based on characterization of primary and secondary sources and corresponding release mechanism from the sources. COPCs are identified for environmental media affected by primary and secondary sources as well as their potential routs of migration and transport to potentially exposed on-site populations (receptors). Figure 12-1 identifies the source and release mechanisms for the Site along with exposure medium and route. Potential receptors at the Site are identified, with consideration of current land use scenarios. The individual components of the human health CEM are further described in the following sections. Primary Constituent Source The primary source of Site related constituents in groundwater is historical coal ash management conducted in the FADA, 1971 Ash Basin, and the 1984 Ash Basin. Groundwater, soil, surface water and sediment in the vicinity of these sources that contain Site related constituents serve as an exposure medium. Primary Release and Transport Mechanisms Consistent with focus of this assessment on migration of ash basin constituents into water, the primary potential constituent release and transport pathways at the Site are as follows: Desorption of coal ash constituents to coal ash pore water; Infiltration of coal ash pore water to underlying groundwater; Discharge of coal ash pore water to the cooling pond (Lake Sutton) followed by discharge to the Cape Fear River via the NPDES permitted outfall. Secondary Release Mechanisms The secondary potential constituent release and transport pathways at the Site are as follows: Transport of coal ash constituents in groundwater to sediments and Transport of coal ash constituents in sediments to surface water. Exposure Medium, Pathways and Exposure Routes The exposure medium includes potentially impacted groundwater, soil, surface water and sediments. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 60 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The exposure routes associated with the potentially completed exposure pathways evaluated for the Site include ingestion, inhalation and dermal contact of environmental media. 12.1.2.1 Current/Future Recreational Fisherman The potential exists for current and/or future fisherman on Lake Sutton to be exposed to COPCs at the Site. This exposure scenario is considered in the risk screening. 12.1.2.2 Current/Future Recreational Swimmer The potential exists for current and/or future swimmer in Lake Sutton to be exposed to COPCs at the Site. This exposure scenario is considered in the risk screening. 12.1.2.3 Current/Future Recreational Hunter The potential exists for current and/or future hunter to be exposed to COPCs at the Site. This exposure scenario is considered in the risk screening. 12.1.2.4 Current/Future Industrial Worker The potential exists for current and/or future industrial workers to be exposed to COPCs at the Site. This exposure scenario is considered in the risk screening. 12.1.2.5 Future Resident The potential exists for future residents to be exposed to COPCs at the Site. This exposure scenario is considered in the risk screening. Risk-Based Screening Levels 12.1.3 The human health risk assessment includes an initial comparison of constituent concentrations in various media to risk-based screening levels. A comparison of constituent concentrations in various media to the following risk-based screening levels is presented in the following sections. The screening criteria include chemical-specific screening levels based on concentrations that are Applicable or Relevant and Appropriate Requirements (ARARs) [e.g., Safe Drinking Water Act maximum contaminant levels (MCLs)] and concentrations resulting from risk - based calculations that set concentration limits using carcinogenic or systemic toxicity values under specific exposure conditions. These include: Coal Ash Constituents – Regional screening level (RSLs) for soil protective of groundwater and human health under residential-use Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 61 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx scenarios and industrial-use scenarios (USEPA Regional Screening Levels (RSLs) rev., June 26, 2015). Coal Ash Pore Water - NCDENR Title 15A, Subchapter 2L. Groundwater - NCDENR Title 15A, Subchapter 2L Standards, Interim Maximum Allowable Concentrations (IMACs; 15A NCAC 02L.0202), and USEPA Screening Level for Hexavalent Chromium in Residential Tap Water (USEPA Regional Screening Levels (RSLs) rev., June 26, 2015). Soil and Sediments - USEPA Residential and Industrial Soil Regional Screening Levels (RSLs) Target Cancer Risk 1x10-6/Target Hazard Quotient of 0.1 (USEPA Regional Screening Levels (RSLs) rev., June 26, 2015). Surface Water - North Carolina Surface Water Standards (Subchapter 2B) and USEPA National Recommended Water Quality Criteria for Human Health for the consumption of water and organisms (NCDENR, http://portal.ncdenr.org/web/wq/ps/csu/swstandards, Triennial Review; USEPA National Recommended Water Quality Criteria; 2004). Soil, sediment and groundwater will be compared to background data from available local, regional and national background sediment, soil and ground water data, as available. Coal Ash and Coal Ash Pore Water Coal ash and water retained within the FADA and ash basins are the sources of constituents addressed by this risk screening process. Constituents impacting groundwater from other onsite sources, offsite sources, or naturally occurring sources, may be acknowledged, but are beyond the scope of this risk screening process. Consequently, COPCs going forward will be attributable only to the coal ash. Coal Ash Coal ash COPCs are, by definition, constituents of coal ash. Three ash samples were collected from two borings installed within the Site ash basins. The coal ash samples were analyzed for 28 inorganic constituents and total organic carbon (TOC). Coal ash analytical results are summarized in Table 7-3 and compared with constituent soil regional screening levels (RSLs) derived for the protection of groundwater as well as the protection of human health under residential-use and industrial-use scenarios. Constituents that have at least one soil screening criteria and were detected at concentrations below all applicable RSLs, or were not detected and their analytical method detection limits where below their Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 62 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx respective RSLs, may not be considered a coal ash COPC. Coal ash constituents that may not be coal ash COPCs are listed below: Antimony Molybdenum Boron Nickel Cadmium Strontium Total Chromium Thallium Manganese Zinc Conversely, the following coal ash constituents are retained as preliminary coal ash COPCs for the reasons indicated (Table 7-3): Coal Ash Constituent Concentrations Greater Than One Or More Soil RSLs Coal Ash Constituents That Have No Soil RSLs Aluminum Arsenic Beryllium Cobalt Copper Iron Lead Mercury Selenium Vanadium Calcium Chloride Magnesium Nitrate (as N) Potassium Sodium Sulfate TDS Coal Ash Pore Water Coal ash pore water is precipitation that has infiltrated through the coal ash and is retained within an ash basin. Coal ash pore water above the ash/soil interface results in saturated conditions within disposed ash. Desorption of coal ash constituents into precipitation that has infiltrated into the coal ash is expected to be greatest wherever the coal ash is under saturated conditions for extended periods of time. The coal ash pore water and solubilized inorganic constituents will eventually infiltrate into the underlying groundwater. Consequently, coal ash pore water can potentially impact groundwater quality when solubilized inorganic constituents are present at concentrations above 2L or IMAC. Conversely, solubilized inorganic constituents present in ash pore water at concentrations below 2L or IMAC do not pose unacceptable risk to the quality of underlying groundwater. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 63 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx A total of five coal ash pore water samples were collected from two monitoring wells screened within the coal ash. Ash pore water samples were analyzed for 28 inorganic constituents. Analytical results of ash pore water analyses are presented in Table 12-1 along with constituent 2L or IMAC, where applicable. The coal ash pore water samples and constituents that exceeded a 2L or IMAC are identified in Figure 12-2. An ash pore water constituent that has a 2L or IMAC and is detected at a concentration below its 2L or IMAC, or was not detected and its analytical method detection limit is below its 2L or IMAC, is not a coal ash COPC because it do not pose an unacceptable risk to the quality of underlying groundwater. Site coal ash constituents that meet these conditions are listed below: Antimony Mercury Beryllium Nickel Cadmium Nitrate (as N) Chloride Selenium Total Chromium Sulfate Cobalt Thallium Copper Zinc Lead Conversely, a coal ash constituent that exceeds its groundwater screening criteria or has an analytical method detection limit greater than its groundwater screening criteria, or has no groundwater screening criteria may adversely affect the quality of underlying groundwater. The following Site coal ash constituents are retained as preliminary coal ash COPCs for the reasons indicated: Coal Ash Constituent Concentrations Greater than 2L or IMAC Coal Ash Constituents that have no 2L or IMAC Arsenic Barium Boron Iron Lead Manganese TDS Vanadium Aluminum Calcium Magnesium Molybdenum Potassium Sodium Strontium Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 64 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Calcium/Magnesium/Potassium/Sodium Calcium, magnesium, potassium, and sodium analyses were conducted for the purpose of characterizing the geochemistry of different aquifers. These constituents are found in abundance in natural groundwater systems and are routinely quantified by geochemists to generate piper diagrams or plots of major cations and anions. Cation and anion data collected has been used to generate piper diagram plots that categorize geochemical characteristics of the coal ash pore water, the surficial aquifer, and the Pee Dee Formation (Section 10). Furthermore, these naturally occurring constituents do not pose unacceptable risks to human health when present in groundwater at moderate concentrations. This is one reason why these constituents have no established numerical limits (e.g., 2L, IMACs, Safe Drinking Water Act MCLs) in groundwater for the protection of human health. Calcium, the most abundant mineral in the body, is found in many foods and is available as an over-the-counter dietary supplement. Likewise, magnesium, potassium and sodium are also present in many common foods and are also available as, or included in, over-the-counter dietary supplements. Although calcium, magnesium, potassium and sodium are coal ash constituents, it is unlikely that they will be significant contributors to potential human health risk posed by coal ash constituents. For these reasons, calcium, magnesium, potassium and sodium will not be considered coal ash COPCs (Table 12-2). Coal Ash COPC Determination Coal ash COPC determinations are summarized in Table 12-2 along with the rationale for the determination. Constituents that are coal ash COPCs will be evaluated as to whether they are groundwater, soil, sediment or surface water COPCs that are potentially attributable to coal ash. Constituents that are not coal ash COPCs will not be evaluated going forward. Groundwater Site groundwater meets the definition of Class GA groundwater (15A NCAC 02L.0201). Consequently, the 15A NCAC 02L.0202 and IMAC groundwater quality values (2L or IMAC) apply. The concentrations of groundwater constituents that have 2L or IMAC are compared to those screening criteria. Groundwater constituents having concentrations below their respective 2L or IMAC in all groundwater samples do not pose an unacceptable risk to human health. Groundwater constituents having concentrations above their respective 2L or IMAC warrant further evaluation. The source of groundwater constituents detected above 2L or IMAC could be naturally occurring conditions (e.g., elevated metals in saturated subsurface matrix), high turbidity groundwater Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 65 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx samples, an offsite contaminant release, the coal ash, or other site related source of groundwater constituents. A constituent that exceed its 2L or IMAC or has no 2L or IMAC and is a coal ash COPC will be a designated groundwater COPC potentially attributable to coal ash. Conversely, a constituent in groundwater that exceeds its 2L or IMAC or has no 2L or IMAC but is not a coal ash COPC will not be a groundwater COPC potentially attributable to coal ash. The following groundwater constituents are not groundwater COPCs potentially attributable to coal ash because they are not coal ash COPCs (Table 12-2): Antimony Beryllium Cadmium Calcium Chloride Total Chromium Cobalt Copper Lead Magnesium Mercury Molybdenum Nickel Nitrate (as N) Potassium Selenium Sodium Strontium Sulfide Thallium Zinc Groundwater wells were sampled in February, March, April, and/or June 2015. The following field parameters were monitored and recorded during sampling: pH (s.u.) Temperature (OC) Specific Conductivity (µS/cm) Water Level (ft. below TOC) Dissolved Oxygen (DO; mg/L) Turbidity (ntu) Oxidation/Reduction Potential In addition, ferrous iron concentration (mg/L) in groundwater was estimated using a colorimetric field screening procedure. Field parameters and analytical results are assimilated on risk assessment screening Tables 12-1, 12-3, 12-4 and, 12-5. In addition, groundwater analytical results are evaluated against the 2L or IMAC, where applicable. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 66 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Background Groundwater There are two water bearing units associated with the Site groundwater assessment; the surficial aquifer and the Pee Dee Formation. There are four groundwater monitor wells (MW-4B, MW-05C, MW-37B, and MW-37C) monitored for background conditions within the surficial aquifer. No background wells have been installed within the Pee Dee Formation. Background wells for the surficial aquifer and the analytical results of background groundwater samples collected in 2015 are provided on Table 12-1. Included in Table 12-1 are statistical metrics (number of samples analyzed, number of detections, average (statistical mean – detections only) constituent concentrations, and maximum constituent concentration and comparisons of constituent concentrations to the respective 2L or IMAC. Background Groundwater – Surficial Aquifer Analytical results of groundwater samples collected in 2015 from the surficial aquifer background wells indicate that the following constituents were detected at concentrations above respective 2L or IMAC: Cobalt Iron Manganese Vanadium Cobalt was detected above the IMAC (1 µg/L) in at least one groundwater sample collected from each of the four background groundwater monitor wells in 2015. The initial groundwater sample collected from MW-37B in March 2015 contained no cobalt above the detection limit (<1 µg/L); however, cobalt was detected at a concentration of 2.52 µg/L during confirmation sampling conducted in June 2015. Similarly, the initial groundwater sample collected from MW-37C in March 2015 contained cobalt a concentration of 2.99 µg/L; however, cobalt was not detected above the detection limit during confirmation sampling conducted in June 2015. This inconsistency of cobalt detections in groundwater samples collected from background monitor wells suggest that further confirmation sampling is warranted. To date, iron concentrations at the four background wells have been inconsistent. Iron was detected above the 2L (300 µg/L) in 4 out of the 9 background groundwater samples collected in 2015. Iron concentrations in both groundwater samples collected from MW-37B (687 µg/L 9,580 µg/L) were above the 2L; however, iron concentrations were 13 µg/L or below in the three groundwater Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 67 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx samples collected from MW-05C. Furthermore, the iron concentration in the MW-37C March 2015 groundwater sample was 9,500 µg/L however the iron concentration in the MW-37C June 2015 groundwater sample was 33 µg/L. Similarly, the iron concentration in the AW-04B February 2015 groundwater sample was 2,600 µg/L however the iron concentration in the AW-04B June 2015 groundwater sample was 41 µg/L. Manganese was detected in all surficial aquifer background samples collected in 2015 with 6 out of 9 samples exceeded the 2L (50 µg/L). Manganese concentrations in two samples collected from MW-05C were in relatively consistent range (441 – 535 µg/L). In contrast, the manganese concentration in the MW-37B March 2015 groundwater sample was 38 µg/L; however, the manganese concentration in the MW-37B June 2015 groundwater sample was 254 µg/L. Similarly, the manganese concentration in the MW-37C March 2015 groundwater sample was 233 µg/L however the manganese concentration in the MW-37C June 2015 groundwater sample was 6 µg/L. Vanadium was detected above the IMAC (0.3 µg/L) only in background well MW-37C. Vanadium concentrations in two samples collected from MW-37C were 1.15 µg/L and 1.22 µg/L. Vanadium was not analyzed in the MW-05C groundwater samples and vanadium concentrations were below the detection limit (0.3 µg/L) in the MW-37B groundwater samples. Speciation analysis was conducted on groundwater samples collected from background well MW-05C (Table 10-3). The concentration of hexavalent chromium Cr(VI) was 0.019 µg/L. The EPA screening level for hexavalent chromium in residential tap water is 0.035 µg/L (USEPA RSLs; rev., June 26, 2015). Downgradient Groundwater – Surficial Aquifer Analytical results of surficial aquifer downgradient groundwater samples collected in 2015 are presented in Table 12-4. The following constituents were detected at concentrations above respective 2L or IMAC or do not have a groundwater screening value protective of human health: Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 68 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Surficial Aquifer COPC Potentially Attributable To Coal Ash Not A Coal Ash COPC(1) Aluminum Arsenic Boron Iron Manganese TDS Vanadium Cobalt Lead Nitrate (as N) Selenium Thallium Note (1): See Table 12-2 Aluminum is a coal ash COPC because it is in coal ash at concentrations greater than soil RSL (Table 7-3) but is not included in the 2L or IMAC. Aluminum was detected in 85 out of 86 downgradient surficial aquifer groundwater samples at concentrations ranging from <5 µg/L to 18,300 µg/L. Aluminum may be eliminated as a surficial aquifer COPC if it can be demonstrated that it is naturally occurring or a site-specific groundwater criteria protective of human health is developed for aluminum. Until then, aluminum is a surficial aquifer COPC potentially attributable to coal ash. Arsenic concentrations were below the detection limit (1 µg/L) in 85 out of 104 surficial aquifer groundwater samples analyzed. Of the 19 samples having quantifiable arsenic concentrations, only 5 of the samples collected from ABMW- 2D, MW-15, and MW-21C had arsenic concentrations above the 2L (10 µg/L). These wells are in close proximity of the FADA or the 1971 ash basin (Figure 2-1) and are screened at similar depth intervals. Arsenic is a surficial aquifer COPC potentially attributable to coal ash. Boron was not detected above the analytical detection limit (<50 µg/L) in seven background samples but is in ash pore water and the surficial aquifer. Boron was detected in 63 out of 104 surficial aquifer groundwater samples collected in 2015. Twenty-one of the 63 surficial aquifer groundwater samples collected from 10 wells contained concentrations of boron above the 2L (700 µg/L). In every instance, these wells were sampled at least twice and boron concentrations were confirmed to be above the 2L with the minimum, average, and maximum boron concentrations being 776 µg/L (SMW-01C), 1,628 µg/L (statistical mean/detections only), and 3,060 µg/L (MW-23C), respectively. Boron in ash pore water collected from ABMW-01S (1971 Ash Basin) ranged between 3,940 – 3,690 µg/L whereas boron in ash pore water collected from ABMW-02S (FADA) Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 69 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx ranged between 222 – 234 µg/L. Boron is a surficial aquifer COPC potentially attributable to coal ash. Surficial aquifer groundwater samples were analyzed for total (CrIII plus CrVI) chromium. Eight out of 104 samples analyzed contained measurable quantities of total chromium at concentrations ranging between 1.01 to 6.94 µg/L. The 2L value for total chromium is 10 µg/L. Speciation analysis was conducted on ash pore water samples ABMW-01S and ABMW-02S (Table 7-9). The concentration of hexavalent chromium Cr(VI) in ash pore water samples ABMW-01S (0.025 µg/L) and ABMW-02S (0.026 µg/L) were less than the EPA screening level for hexavalent chromium in residential tap water (0.035 µg/L; USEPA Generic Screening Tables, June 26, 2015). Consequently, there is no evidence to date that suggests that the concentration of hexavalent chromium in coal ash pore water is greater than the EPA screening value for tap water. However, speciation analysis was conducted on 17 samples collected from 17 surficial aquifer downgradient groundwater monitor wells (Table 10-3). The concentration of hexavalent chromium Cr(VI) exceeded the EPA screening level for hexavalent chromium in residential tap water (0.035 µg/L; USEPA Generic Screening Tables, June 26, 2015) in samples collected from the following wells: Well ID Cr(VI) Concentration AW-09B 0.038 µg/L AW-09C 0.046 µg/L MW-23B 0.051 µg/L Consequently, hexavalent chromium is a surficial aquifer COPC; however, hexavalent chromium is not a coal ash COPC. Therefore, hexavalent chromium is not a surficial aquifer COPC potentially attributable to coal ash. Iron is a COPC for coal ash pore water as well as surficial aquifer background and downgradient groundwater. Iron was detected in one coal ash pore water well (ABMW-02S; FADA) and in two surficial aquifer background wells (MW- 37B, MW-37C) at average concentrations of 25,333 µg/L and 4,950 µg/L, respectively. Iron was detected in 97 out of 104 surficial aquifer groundwater samples with 62 of the 97 detections at concentrations above the 2L (300 µg/L). The average concentration of iron in samples that exceeded the 2L is 5,559 µg/L. Confirmation sampling and statistical analyses may be required to determine if Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 70 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx iron leaching from the coal ash is influencing iron concentrations in the surficial aquifer. Manganese, a coal ash pore water COPC, was detected in surficial aquifer background and downgradient groundwater. Manganese was detected above the 2L (50 µg/L) in every coal ash pore water sample and in 5 out of 7 surficial aquifer background groundwater samples with maximum concentrations of 970 µg/L and 535 µg/L, respectively. Manganese was detected above the 2L in 68 out of 104 surficial aquifer downgradient groundwater samples with maximum concentrations of 2,120 µg/L in the AW-03B. Other surficial aquifer downgradient wells having at least one groundwater sample containing manganese concentrations greater than 1,000 µg/L are AW-04C (2,120 µg/L), MW-24C (1,470 µg/L), and MW-31C (1,840 µg/L). Confirmation sampling and statistical analysis may be required to determine whether manganese from coal ash has impacted manganese concentrations in the surficial aquifer. TDS concentrations exceeded the 2L (500 mg/L) in ash pore water well ABMW- 01S (760 µg/L April and 680 µg/L June, 2015) whereas TDS concentrations in groundwater samples collected from surficial aquifer background wells did not exceed 81 µg/L. TDS concentrations exceeded the 2L in 5 surficial aquifer downgradient groundwater samples collected from 3 wells. The only surficial aquifer downgradient well where TDS concentrations consistently exceeded the 2L is MW-31C where concentrations in three groundwater samples ranged between 510 - 540 µg/L. The maximum TDS concentration was detected in well AW-01B (910 µg/L February); however, the June groundwater sample (44 µg/L) collected from well AW-01B did not confirm TDS concentrations above the 2L. Confirmation sampling and statistical analyses may be required to confirm elevated concentrations of TDS at these wells. Vanadium was detected at concentrations above the IMAC (0.3 µg/L) in every coal ash pore water sample (3.58 µg/L average; 8.72 µg/L maximum) whereas vanadium was detected above the IMAC in 2 out of 4 surficial aquifer background groundwater samples (1.15 µg/L average; 1.22 µg/L maximum) and in 33 out of 73 surficial aquifer downgradient groundwater samples (2.04 µg/L average; 39.6 µg/L maximum). This maximum vanadium concentration was detected in a groundwater sample collected from well MW-20 which is located between the FADA, former coal storage area, and the cooling water canal. Confirmation sampling and statistical analysis may be warranted to determine whether vanadium TDS in the surficial aquifer is naturally occurring or from an on-site source. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 71 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Sampling locations in the upper surficial and lower surficial aquifer where constituent concentrations were greater than their screening criteria are identified in Figures 12-3 and 12-4, respectively. Downgradient Groundwater – Pee Dee Formation Analytical results of Pee Dee Formation downgradient groundwater samples collected in 2015 are presented in Table 12-5. The following constituents were detected at concentrations above their respective 2L or IMAC or do not have a groundwater screening value protective of human health: Pee Dee Formation COPC Potentially Attributable To Coal Ash Not A Coal Ash COPC(1) Aluminum Boron Iron Manganese TDS Vanadium Antimony Chloride Total Chromium Cobalt Note (1): See Table 12-2 Antimony and total chromium detected in Pee Dee downgradient groundwater samples above the IMAC (1 µg/L) and 2L (10 µg/L), respectively. Similarly, chloride and cobalt were detected in multiple Pee Dee groundwater samples at concentrations above the 2L (250 mg/L) or IMAC (1 µg/L), respectively. However, antimony, total chromium, chloride, and cobalt are not coal ash COPCs (Table 12-2). Consequently, antimony, total chromium, chloride, and cobalt are not Pee Dee COPCs potentially attributable to coal ash. Speciation analysis was conducted on ash pore water samples ABMW-01S and ABMW-02S (Table 7-9). The concentration of hexavalent chromium Cr(VI) in ash pore water samples ABMW-01S (0.025 µg/L) and ABMW-02S (0.026 µg/L) was less than the EPA screening level for hexavalent chromium in residential tap water (0.035 µg/L; USEPA Generic Screening Tables, June 26, 2015). Consequently, there is no evidence to date that suggests that the concentration of hexavalent chromium in coal ash pore water is greater than the EPA screening value for tap water. However, speciation analysis was conducted on 9 samples collected from 9 Pee Dee downgradient groundwater monitor wells (Table 10-3). The concentration of hexavalent chromium Cr(VI) exceeded its EPA screening level for hexavalent chromium in residential tap water (0.035 µg/L; USEPA Generic Screening Tables, June 26, 2015) in samples from the following wells: Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 72 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Well ID Cr(VI) Concentration AW-06E 0.064 µg/L MW-23E 0.046 µg/L Consequently, hexavalent chromium is a Pee Dee Formation COPC; however, hexavalent chromium is not a coal ash COPC. Therefore, hexavalent chromium is not a Pee Dee COPC potentially attributable to coal ash. Aluminum is a coal ash COPC because it is in coal ash at concentrations greater than soil RSL (Table 7-3) but does not have a 2L or IMAC. Aluminum was detected in 20 out of 24 downgradient Pee Dee groundwater samples at concentrations ranging from <5 µg/L to 96 µg/L. Aluminum may be eliminated as Pee Dee COPC if it can be demonstrated that it is naturally occurring or a site- specific groundwater criteria protective of human health is developed for aluminum. Until then, aluminum is a Pee Dee COPC potentially attributable to coal ash. Boron was detected in every (24 out of 24) Pee Dee Formation groundwater samples collected in 2015. Boron concentrations exceeded the 2L (700 µg/L) in 11 out of the 24 upper and lower Pee Dee Formation groundwater samples with the average and maximum concentrations being 876 µg/L and 2,500 µg/L (MW-23E), respectively. The presence of boron in the Pee Dee Formation may be attributed to salt water intrusion (Sections 10.4 and 10.5); however, boron is a coal ash COPC (Table 12-2) and will therefore be retained as a Pee Dee COPC potentially attributable to coal ash. Iron is a coal ash COPC and was detected in all Pee Dee groundwater samples at concentrations ranging between 48 µg/L to 1,270 µg/L. Iron concentrations in 7 out of 24 Pee Dee samples were greater than 2L (300 µg/L). Consequently, iron is a Pee Dee COPC potentially attributable to coal ash. Manganese is a coal ash COPC and was detected in all Pee Dee groundwater samples at concentrations ranging between 5 µg/L to 940 µg/L. Manganese concentrations in 7 out of 24 Pee Dee samples were greater than the 2L (50 µg/L). Consequently, manganese is a Pee Dee COPC potentially attributable to coal ash. TDS is a coal ash COPC and was detected in all Pee Dee groundwater samples at concentrations ranging between 320 mg/L to 1,500 mg/L. TDS concentrations in 14 out of 24 Pee Dee samples were greater than the 2L (500 µg/L). Consequently, TDS is a Pee Dee COPC potentially attributable to coal ash. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 73 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Vanadium is a coal ash COPC and was detected in 17 out of 24 Pee Dee groundwater samples at concentrations ranging between <0.3 µg/L to 940 µg/L. Vanadium concentrations in 7 out of 24 Pee Dee samples where greater than IMAC (0.3 µg/L). Consequently, vanadium is a Pee Dee COPC potentially attributable to coal ash. COPCs potentially attributable to coal ash that have been retained for the Pee Dee Formation are presented in Table 12-5. Figures 12-5 and 12-6 show sample locations where these COPCs have been identified. Additional refinement of COPCs for site-specific considerations will be included as part of a corrective action plan. Soils and Sediments Soil samples were evaluated separately from sediments in order to appropriately evaluate risk exposure scenarios for potential human receptors. Soils and sediment analytical results were evaluated relative to USEPA soil Regional Screening Levels (RSLs) protective of human health under residential-use and industrial-use scenarios (USEPA Regional Screening Levels (RSLs) rev., June 26, 2015). The following constituents are not soil or sediment COPCs potentially attributable to coal ash because they are not coal ash COPCs (Table 12-2): Antimony Beryllium Cadmium Calcium Chloride Total Chromium Copper Lead Magnesium Mercury Molybdenum Nickel Nitrate (as N) Potassium Selenium Sodium Strontium Sulfate Thallium Zinc In addition, hexavalent chromium was detected in ash pore water samples ABMW-01S (0.025 µg/L) and ABMW-02S (0.26 µg/L) at concentrations below the EPA screening level (0.035 µg/L) for tap water (USEPA Regional Screening Levels (RSLs) rev., June 26, 2015). Consequently, these constituents are not considered soil or sediment COPCs attributable to coal ash and therefore, will not be evaluated further. Inorganic constituents that are coal ash COPCs but have no USEPA RSL values protective of human health for soil are retained as a COPC potentially Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 74 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx attributable to coal ash. These constituents will be retained as COPC potentially attributable to coal ash until it can be demonstrated that constituent concentrations are naturally occurring or a site-specific criteria protective of human health is developed for inorganic constituents that have no soil RSLs protective of human health. Soil and sediment samples are often diluted by the analytical laboratory because the concentrations of some target inorganic constituents (e.g., iron and manganese) are beyond the range of their instrumentation. A consequence of sample dilution is an increase in the analytical method detection limit of constituents that may be present at much lower concentrations. If the analytical method detection limit of a constituent is increased to a concentration that is higher than its screening level, the constituent will be retained as a COPC because it is possible that the constituent concentration may be greater than the screening criteria but less than the elevated analytical method detection limit. The constituent will retain the COPC designation unless it can be demonstrated that its concentration is below the screening criteria. Prior to future sampling events, the analytical laboratory will be provided with the screening criteria for constituents that are retained as COPCs because their analytical method detection limit was greater than their respective risk screening level. The analytical laboratory will be asked to reanalyze samples at lower dilutions when the analytical method detection limits of critical constituents are greater than their respective risk screening level. Soils Surface soil samples were collected from the top two feet of soil borings installed at the Site. Figure 2-1 identifies soil boring locations. Soil sample analytical results are summarized in Table 12-6 and compared relative to USEPA soil industrial-use and residential-use RSLs, as applicable. No constituents were detected above their respective RSL in any of the 14 surficial soil (0 – 2 ft.) samples collected (Table 12-6); however, the analytical method detection limits of antimony, cobalt and thallium were greater than some or all of their respective soil industrial-use and/or residential-use RSLs. Regardless, antimony, cobalt and thallium are not retained as COPCs potentially attributable to coal ash because they are not coal ash COPCs (Table 12-2). Arsenic was not detected in any of the 14 soil samples. However, the analytical method detection limit for arsenic in six soil samples was greater than the soil industrial-use RSL (3 µg/L) and the soil residential-use RSL (0.68 µg/L). Since Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 75 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx arsenic is a coal ash COPC and it is not certain that arsenic concentrations in six soil samples are below the soil industrial-use and residential-use RSLs, arsenic will be retained as a soil COPC potentially attributable to coal ash. Arsenic may be eliminated as a soil COPC potentially attributable to coal ash when supplemental surficial soil sampling is conducted and arsenic concentrations or their analytical method detection limits are below the soil residential RSL (0.68 µg/L). The locations of surficial soil COPCs potentially attributable to coal ash are presented on Figure 12-7. Sediments Sediment samples consist of samples collected at co-located surface water sample locations identified on Figure 2-1. Following is a description of the locations where sediment samples were collected: Water Body Sediment and Surface Water Sample ID Sample Location Description Lake Sutton SW-01C South end of Lake Sutton where cooling channel begins SW-004 East side of Lake Sutton adjacent to coal ash management area and NPDES Outfall SW-004 SW-06A North end of Lake Sutton where cooling channel ends and Lake Sutton begins SW-08A Southwest on Lake Sutton Cape Fear River SW-CFUP Upstream relative to Lake Sutton SW-CFP West of Lake Sutton SW-CF001 Downstream relative to Lake Sutton Evaluation of inorganic COPCs in sediments is based upon USEPA RSLs for soil protective of human health under residential and industrial use scenarios. Constituents that are coal ash COPCs and are detected in sediment samples at concentrations that are greater than their respective industrial and/or residential- use RSL, or their analytical method detection limits are greater than their respective industrial and/or residential-use RSL are considered COPCs potentially attributable to coal ash. In addition, inorganic constituents that are coal ash COPCs and have no USEPA RSL for soil will be retained as a sediment COPC potentially attributable to coal ash. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 76 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Aluminum, barium, boron and vanadium are coal ash COPCs (Table 12-2); however, all of these constituents were detected at concentrations below their respective residential-use and industrial-use RSLs (Table 12-7). Consequently, aluminum, barium, boron and vanadium are not sediment COPCs potentially attributable to coal ash (Table 12-9). Cobalt was detected in sediment sample SW-CFP (7.6 J mg/kg) at a concentration that was greater than the residential-use RSL (2.3 mg/kg). In addition, the analytical method detection limits for all other sediment samples are also greater than the residential-use RSL (Table 12-7); however, cobalt is not a coal ash COPC (Table 12-2). Therefore, cobalt is not a sediment COPC potentially attributable to coal ash (Table 12-9). Arsenic, a coal ash COPC (Table 12-2), was detected in sediment sample SW-06A (4.6 J mg/kg) at an estimated concentration that was slightly more than the industrial-use RSL (3 mg/kg) but was significantly greater than the residential- use RSL (0.68 mg/kg). In addition, the analytical method detection limits for arsenic in all other sediment samples were higher than the residential-use and industrial-use RSLs (Table 12-7). Arsenic is a sediment COPC potentially attributable to coal ash (Table 12-9). Iron and manganese are coal ash COPCs (Table 12-2). They are also sediment COPCs potentially attributable to coal ash because they were both detected at concentrations above their respective residential-use RSLs in Cape Fear River sediment samples SW-CF001 and SW-CFP (Table 12-9). Iron and manganese were detected at concentrations below their respective RSLs in all other sediment samples (Table 12-7). The locations of sediment COPCs potentially attributable to coal ash are presented on Figure 12-8. Surface Water Surface water analytical results were evaluated against the North Carolina surface water standards (Subchapter 2B) and USEPA National Recommended Water Quality Criteria (WQC) protective of human consumption of water and organisms (NCDENR 4/22/15; USEPA 2015). Surface water sample locations are shown on Figure 2-1. The locations of surface water COPCs potentially attributable to coal ash are presented on Figure 12-9. Surface water analytical results are summarized in Table 12-8 where they are compared to their respective 2B concentrations and the EPA National Recommended WQC protective of human health for the consumption of water and organisms (fish). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 77 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx A general description of the locations where surface water samples were collected is presented in the previous section where sediment analytical results are evaluated. Aluminum and thallium were the only constituents detected at concentrations greater than respective USEPA National Recommended WQC protective of human consumption of water and organisms. Surface water 2B concentrations for the protection of human health have not been established for aluminum or thallium (Table 12-8). Aluminum is a coal ash COPC (Table 12-2) and is a surface water COPC potentially attributable to coal ash because the aluminum concentrations in all nine surface water samples were greater than the USEPA National Recommended WQC protective of human consumption of water and organisms (6.5 µg/L). Aluminum concentrations ranged from 34 µg/L to 977 µg/L. Although thallium was detected in surface water samples SW-004 (0.29 µg/L) and SW-06A (0.249 µg/L) at concentrations slightly greater than the USEPA National Recommended WQC protective of human consumption of water and organisms (0.24 µg/L), thallium is not a surface water COPC potentially attributable to coal ash because it is not a coal ash COPC (Table 12-2). Boron, iron and manganese are coal ash COPCs and all were detected in five or more of the nine surface water samples. Total and dissolved boron was detected in five surface water samples at concentrations ranging from 185 µg/L to 211 µg/L. Total iron and total manganese were detected in every surface water sample. Total iron concentrations ranged between 49 µg/L and 1,830 µg/L and total manganese concentrations ranged between 8 µg/L and 121 µg/L. Surface water 2B concentrations for the protection of human health and USEPA National Recommended WQC protective of human consumption of water and organisms have not been established for boron, iron, and manganese (Table 12-8). Consequently, boron, iron and manganese will be retained as a surface water COPC potentially attributable to coal ash until site-specific surface water criteria protective of human health are developed for these compounds. Summary Table 12-9 summarizes human health risk assessment screening level COPCs potentially attributable for each media that are. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 78 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Site Specific Risk Based Remediation Standards 12.1.4 Based on the results of the preliminary comparison to risk-based screening levels, media-specific remediation standards may be warranted in accordance with the Eligibility Requirements and Procedures for Risk-Based Remediation of Industrial Sites Pursuant to NC General Statutes 130A-310.65 to 310.77 as part of a corrective action plan. If warranted, these standards will be calculated per the corrective action plan based on the COPCs defined by the screening level risk assessment. 12.2 Ecological Screening Introduction 12.2.1 This screening level ecological risk assessment (SLERA) has been prepared in accordance with the guidelines for conducting a SLERA for sites under the authority of NCDENR Division of Waste Management. The objective of the SLERA is to evaluate the likelihood that adverse ecological effects may result from exposure to environmental stressors associated with conditions at the site. This scope of work is equivalent to Step 1 - preliminary problem formulation and ecological effects evaluation (USEPA, 1998) and Step 2 – estimation of the level of a constituent exposure to a plant or animal at the site and comparison of the maximum constituent concentrations to Ecological Screening Values. Ecological Setting 12.2.2 12.2.2.1 Facility Site Summary The Site is a former coal-fired electricity-generating facility located at 801 Sutton Steam Plant Road, Wilmington, New Hanover County, North Carolina. The location of the Site is shown on Figure 1-1; the approximate coordinates of the site are: latitude N 34.283296; longitude W -77.985860. The Site utilizes an approximate 1100-acre cooling pond (i.e. Lake Sutton) located adjacent to the Site and bounded by the Cape Fear River to the west and ash basins (partially) to the east. There are three ash management areas: (1) the Former Ash Disposal Area is bordered by the plant, Lake Sutton, and the canal north of the plant; (2) the Old Ash Basin Area is north of the same canal and east of Lake Sutton; (3) the New Ash Basin Area is north of the Old Ash Basin Area and east of Lake Sutton. 12.2.2.2 Regional Ecological Setting The Site is located in the Mid-Atlantic Floodplains and Low Terraces ecoregion of North Carolina, a continuation of the Southeastern Floodplains and Low Terraces ecoregion (Griffith et al. 2002). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 79 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 12.2.2.3 Description of Ecoregion and Expected Habitats This region is characterized by hardwood forests often dominated by oak, green ash, red maple, and hickories, and may contain some deepwater Cypress-gum swamp areas (Griffith et al. 2002). This region also typically includes large, slow rivers with swamps, ponds, oxbow lakes, and alluvial deposits. 12.2.2.4 Watershed in which the Site is Located The Cape Fear River watershed (that falls within six 8-digit catalog units), is the state’s largest, encompassing approximately 9,300 square miles in all or part of 26 counties (NCDENR). 12.2.2.5 Average Rainfall Total annual precipitation in this region is approximately 49 inches (http://www.usclimatedata.com/). 12.2.2.6 Average Temperature The annual average high temperature is 74°F and the annual average low temperature is 54°F (http://www.usclimatedata.com/). 12.2.2.7 Length of Growing Season The growing season in Wilmington, NC is approximately 210 to 242 days (based on two stations) (NCSU 2015). 12.2.2.8 Threatened and Endangered Species that use Habitats in the Ecoregion A list of state and federally threatened and endangered species for New Hanover County is provided in Table 12-10. 12.2.2.9 Site-Specific Ecological Setting A Checklist for Ecological Assessments/Sampling has been completed for this site, and is provided (Appendix I). 12.2.2.10 On-site and Off-site Land Use The Site was commissioned in 1954; this facility included three coal-fired steam units and three combustion turbine units. The coal-fired units were retired in November 2013 while the simple cycle combustion turbines remain in operation. A new gas-fired, combined-cycle 625 megawatt station began operation in November 2013, after the coal-fired units were retired. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 80 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The approximate size of the property is 3,300 acres, and consists primarily of the former coal-fired unit structures, combined-cycle combustion units, various other metal buildings, ash management areas, and a 1,100 acre cooling pond (i.e. Lake Sutton). There is a 137 acre area with two ash basins (e.g. Old Ash Basin Area, and New Ash Basin Area) containing 6,320,000 tons of ash. There is also an area called the “Former Ash Disposal Area” that contains 840,000 tons of ash. The Cape Fear River borders the Site on the west, approaching the Site north of Lake Sutton, flowing south along the west side of the lake, turning east toward the Site (i.e. south of the lake) and then meandering southward away from the Site. The areas adjacent to the Cape Fear River consist mostly of forested/shrub wetlands (http://www.fws.gov/wetlands/data/mapper.HTML). Existing ecological studies publically available for the site were reviewed. In 2014, a wetland delineation of the Site was conducted by AMEC Foster Wheeler, Inc. (AMEC) (Appendix I). The delineation identified 15 wetland areas and two jurisdictional tributary segments based on current wetland and stream criteria established by the United States Army Corps of Engineers (USACE) and North Carolina Division of Water Resources (DWR). 12.2.2.11 Habitats within the Site Boundary There are several potential habitats on the Site, including: mixed pine/hardwood forest, wetlands, lake, and river areas. For a detailed description of habitats, see the Checklist for Ecological Assessments/Sampling in Appendix I. 12.2.2.12 Description of Man-made Units that May Act as Habitat The 1,100 acre Lake Sutton may act as a man-made aquatic habitat. 12.2.2.13 Site Layout and Topography A general site layout can be found in Figure 1-2, and the topography is consistent with the typical parameters of the Southeastern Plains Ecoregion (e.g. relatively flat with areas of moderate to steep terraces leading down to the Cape Fear River. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 81 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 12.2.2.14 Surface Water Runoff Pathways The site has been graded in such as manner as to manage/divert runoff (e.g. stormwater) using features such as swales, ditches, and culverts into nearby water bodies (e.g. Cape Fear River, Lake Sutton). 12.2.2.15 Soil Types The Southeastern Plains Ecoregion is generally composed of alluvium and deposits of sand, silt, and gravel (Griffith et al. 2002). For a detailed description of site lithology, see Section 6.1.1 of this report. 12.2.2.16 Species Normally Expected to Use Site under Relatively Unaffected Conditions Wildlife expected to be in the area of the site would potentially include those listed in Table 12-10, and also other game and non-game wildlife endemic to the Mid-Atlantic Floodplains and Low Terraces ecoregion of North Carolina. 12.2.2.17 Species of Special Concern The Cape Fear River Basin supports over 95 species of commercial and recreational fish, including 42 rare aquatic species. The Cape Fear shiner (Notropis mekistocholas), a federally endangered fish species, is known only to inhabit this river. The shortnose sturgeon (Acipenser brevirostrum), red- cockaded woodpecker (Leuconotopicus borealis), Saint Francis’ satyr (Neonympha mitchellii francisci), and the West Indian manatee (Trichechus manatus) (in estuarine areas) are also known species in the Cape Fear River and are federally listed as endangered. The American alligator (Alligator mississippiensis) and the loggerhead turtle (Caretta caretta) are federally listed as threatened. See Table 12-10 for a full list of Threatened and Endangered Species. 12.2.2.18 Nearby Critical and/or Sensitive Habitats There are 15 wetland areas on-site that are identified in the 2014 wetland delineation and depicted in the USFWS National Wetland Inventory. For a detailed description, see the Checklist for Ecological Assessments/Sampling (Appendix I). Fate and Transport Mechanisms 12.2.3 Fate and transport mechanisms at this Site would include: erosion, storm water runoff, and flow of surface water bodies. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 82 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Conceptual Exposure Model Consistent with standard risk assessment practice for developing conceptual models, separate Conceptual Exposure Models (CEMs) were developed for the human health and ecological risk evaluations. Figure 12-10 has been prepared illustrating potential exposure pathways from the source area to possible ecological receptors. The information in the CEM has been used in conjunction with the analytical data collected as part of the CSA. The ecological CEM is based on characterization of primary and secondary sources and corresponding release mechanism sources, the COPC for each affected environmental medium, and the migration and transport potential of this constituent to potentially exposed populations (receptors). Figure 12-10 identifies the source and release mechanisms for the Site along with exposure medium and route. Potential receptors at the Site are identified, with consideration of current and future potential land use scenarios. The individual components of the ecological CEM are further described in the following sections. Primary Constituent Source The primary known source of site related constituents in groundwater at the Site is from historical activities conducted in the ash basin. The affected soil, surface water, and sediment in the vicinity of the ash pond serve as a secondary source. Release and Transport Mechanisms The potential constituent release and transport pathway at the Site are as follows: Infiltration to groundwater. Secondary Release Mechanisms The secondary potential constituent release and transport pathways at the Site are as follows: Storm water runoff Infiltration/percolation. Exposure Medium, Pathways, and Exposure Routes The exposure medium includes potentially impacted soil, surface water and sediments at the site. Groundwater does not present a complete exposure pathway to ecological receptors. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 83 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx The exposure routes associated with the potentially completed exposure pathways evaluated for the Site include incidental ingestion and ingestion of prey or plants. Completed exposure pathways are the means by which potential receptors come into contact with site-related COPCs. The completed exposure pathways under current and future land use scenarios are identified in Figure 12-10 and include: Terrestrial mammals Aquatic mammals Birds (including waterfowl) Benthic invertebrates Herptiles Fish Insects Aquatic vegetation Algae/moss Woody plants Herbaceous plants Preliminary Exposure Estimate and Risk Calculation 12.2.4 Exposure estimates used in the screening level ecological risk assessment are represented by maximum concentrations of analytes detected in surface water, seep, sediment, and soil samples. Hazard quotients (HQs) are defined as the ratio of exposure estimates to ecological screening values (i.e. HQ = maximum observed analyte concentration: ecological screening value). If exposure estimates exceeded an ecological screening value (i.e. HQ>1), analytes were retained as a COPCs for further consideration. COPCs are identified in the next section. Comparison to Ecological Screening Levels 12.2.5 A comparison of constituent concentrations in various media to the following risk-based screening levels has been made and is presented in Tables 12-11 to 12- 13. These include species-specific screening levels based on constituent concentrations that are Applicable or Relevant and Appropriate Requirements (ARARs), designed for protection of ecological receptors from specific exposure conditions that elicit toxic responses. These screening levels are derived from risk-based calculations that set concentration limits using USEPA and state standards for the following media: Groundwater - Not applicable, as groundwater has no direct pathway to ecological receptors Surface water – 2B Criteria for Aquatic Life (NCDENR 2015a) and/or USEPA National Recommended Water Quality Criteria for Aquatic Life Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 84 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx (USEPA 2009) and/or USEPA Region 4 Surface Water Quality Criteria – Chronic (USEPA 2001) Soil - USEPA Region 4 Recommended Ecological Screening Values for Soil (USEPA 2015b) Sediment – USEPA Region 4 Recommended Ecological Screening Values for Soil (USEPA 2015b) and/or USEPA Region 4 Effects Value – Sediment (USEPA 2001) Soil, sediment and groundwater background sample data from prior investigations are considered, as well as regional and national background data, as available Groundwater Direct exposure pathways of groundwater to ecological receptors are incomplete, and therefore do not pose any appreciable risk. Surface Water Surface water samples were evaluated in order to appropriately evaluate risk exposure scenarios for potential ecological receptors. Surface water samples consist of samples collected from the water column (i.e. below the water/air interface when feasible) at selected sample locations. Figure 1-2 shows the locations of the surface water sample locations at the Site. As detailed Tables 12-11 and 12-14, the following inorganic constituents are excluded from the list of ecological COPCs for surface water because either (a) maximum detected concentrations were less than comparison criteria, or (b) the constituents were not detected in the sample and their detection limit values were less than all comparison criteria (2B Criteria for Aquatic Life and/or USEPA National Recommended Water Quality Criteria for Aquatic Life and/or USEPA Region 4 Surface Water Quality Criteria – Chronic): Antimony Arsenic Boron Chloride Chromium Iron Mercury Nickel Selenium Thallium The following inorganic constituents will be retained as COPCs for further evaluation because their maximum detected concentrations were greater than Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 85 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx comparison criteria (2B Criteria for Aquatic Life and/or USEPA National Recommended Water Quality Criteria for Aquatic Life and/or USEPA Region 4 Surface Water Quality Criteria – Chronic): Aluminum Copper Zinc Total aluminum was detected in six surface water samples at concentrations greater than USEPA National Recommended Water Quality Criteria for Aquatic Life – Chronic (87 µg/L) and USEPA Region 4 Surface Water Quality Criteria – Chronic (87 µg/L). Dissolved copper was detected in five surface water samples at concentrations greater than USEPA Region 4 Surface Water Quality Criteria – Chronic (0.00654 mg/L) and 15A NCAC 2B Criteria for Aquatic Life – Acute and Chronic (0.0036 mg/L and 0.0027 mg/L, respectively). Dissolved zinc was detected in three surface water samples (SW-004, SW-06A, and SW-CFUP DUP) at concentrations greater than all comparison criteria. The result at SW-CFUP DUP may be anomalous, as total zinc in the same location ID was measured at 0.0068 mg/L, which more closely mirrors the SW-CFUP sample results (Table 12-11). Dissolved zinc was detected in one surface water sample (SW-CFUP) at a concentration greater than USEPA Region 4 Surface Water Quality Criteria – Chronic (0.00654 mg/L) and 15A NCAC 2B Criteria for Aquatic Life – Acute and Chronic (0.0036 mg/L). Dissolved zinc was detected in three surface water samples at concentrations greater than 15A NCAC 2B Criteria for Aquatic Life – Acute and Chronic (0.0036 mg/L). The following constituents will be added to the list of COPC uncertainties since they are not subject to published 2B Criteria for Aquatic Life or USEPA National Recommended Water Quality Criteria for Aquatic Life: Barium Cobalt Manganese Methane Molybdenum Nitrite/Nitrate Strontium Sulfate Sulfide Vanadium Calcium, magnesium, potassium, and sodium are omitted from the list of COPCs as they have no applicable criteria, are ubiquitous in nature, and are considered Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 86 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx to be macrominerals with negligible toxicity to ecological receptors. These constituents were quantified as a component of the water characterization process. Soil Soil samples were evaluated separately from sediments in order to appropriately evaluate risk exposure scenarios for potential ecological receptors. Surface soil samples were collected from the top two feet of soil borings conducted at the Site facility. Figure 1-2 shows the locations of the soil borings. The following inorganic constituents (Tables 12-12 and 12-14) are excluded from the list of ecological COPCs for surface soils because their maximum detected concentrations were less than their respective comparison criteria for soils, or (b) the constituents were not detected in the sample and their detection limit values were less than all comparison criteria (USEPA Region 4 Recommended Ecological Screening Values for Soil): Arsenic Barium Beryllium Cadmium Cobalt Copper Lead Manganese Mercury Nickel Zinc The following constituents will be retained as COPCs for further evaluation because their maximum detected concentrations in soil were greater than their respective comparison criteria for soils (USEPA Region 4 Recommended Ecological Screening Values for Soil): Aluminum Chromium Iron Vanadium Aluminum was detected in ten of 14 samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (50 mg/kg). Chromium was detected in six of 14 samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (0.4 mg/kg). Iron was detected in eight of 14 soil samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (200 mg/kg). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 87 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Vanadium was detected in five of 14 samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (2 mg/kg). Antimony, boron, molybdenum, selenium, thallium, and vanadium will be added to the list of COPC uncertainties due to lack of quantifiable analytical results. Antimony had several results that were less than the detection limit, which was greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (3.5 mg/kg). Boron was detected at less than the detection limits in all samples, which were greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (0.5 mg/kg). Molybdenum had four results less than detection limit values, which were greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (2 mg/kg). Selenium was detected at less than the detection limits in all samples, which were greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (0.81 mg/kg). Thallium had ten results less than detection limit values, which were greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (1 mg/kg). Vanadium, while having five instances of exceeding USEPA Region 4 Recommended Ecological Screening Values for Soil (2 mg/kg), also had six instances of the detection limit being greater than this criterion. The following constituents will be added to the list of COPC uncertainties since they are not subject to published USEPA Region 4 Recommended Ecological Screening Values for Soil: Calcium Nitrate Strontium Sulfate Calcium, magnesium, potassium, and sodium are omitted from the list of COPCs as they have no applicable criteria, are ubiquitous in nature, and are considered to be macrominerals with negligible toxicity to ecological receptors. These constituents were quantified as a component of the soil characterization process. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 88 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Sediment Sediment samples were collected at co-located surface water locations identified on Figure 1-2. As summarized on Tables 12-13 and 12-14, the following inorganic constituents are excluded from the list of ecological COPCs for sediment because either (a) their maximum detected concentrations were less than their respective comparison criteria (USEPA Region 4 Recommended Ecological Screening Values for Soil and/or USEPA Region 4 Effects Values for Sediment), or (b) the constituents were not detected in the sample and detection limit values were less than both comparison criteria: Barium Beryllium Cadmium Cobalt Copper Lead Mercury Nickel The following constituents will be retained as COPCs for further evaluation because their maximum detected concentrations in soil were greater than their respective comparison criteria for soils (USEPA Region 4 Recommended Ecological Screening Values for Soil and/or USEPA Region 4 Effects Values for Sediment): Aluminum Boron Chromium Iron Manganese Molybdenum Vanadium Zinc Aluminum was detected in all sediment samples at concentrations exceeding the USEPA Region 4 Recommended Ecological Screening Values for Soil (50 mg/kg). Boron was detected in one sediment sample (SW-06A), which exceeded USEPA Region 4 Recommended Ecological Screening Values for Soil (0.5 mg/kg). This result, however, was below the reporting limit, and therefore estimated. The remainder of samples had detection limits greater than this criterion. Chromium was detected in all sediment samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (0.4 mg/kg). Iron was detected in all sediment samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (200 mg/kg). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 89 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Manganese was detected in four sediment samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (100 mg/kg). Molybdenum was detected in one sediment sample (SW-004) at a concentration greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (2 mg/kg). Two other samples had detection limits greater than this criterion. Vanadium was detected in six sediment samples at concentrations greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (2 mg/kg). The remaining sample had a detection limit greater than this criterion. Zinc was detected in one sediment sample (SW-CFP) at a concentration greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (50 mg/kg). Antimony, arsenic, boron, molybdenum, selenium, thallium, and vanadium will be added to the list of COPC uncertainties due to lack of quantifiable detections. Antimony was not detected in any samples, but detection limits for all sample analyses were greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (3.5 mg/kg) and USEPA Region 4 Effects Values for Sediment (2 mg/kg). Arsenic had detection limits greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (10 mg/kg) and EPA Region 4 Effects Values for Sediment (7.24 mg/kg) in two analyses. Boron had detection limits greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (0.5 mg/kg) in all but one analysis. Molybdenum was not detected in three samples with detection limits greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (2 mg/kg). Selenium was not detected in any samples, all of which had detection limits greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (0.81 mg/kg). Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 90 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Thallium was not detected in any samples, but detection limits for all sample analyses were greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (1 mg/kg). Vanadium was not detected in one sample with a detection limit greater than USEPA Region 4 Recommended Ecological Screening Values for Soil (2 mg/kg). The following constituents will be retained as sediment uncertain COPCs for further evaluation because they do not have a published USEPA Region 4 Recommended Ecological Screening Values for Soil: Calcium Nitrate Strontium Sulfate Table 12-14 summarizes ecological COPCs retained for each medium. Figures 12-11 to 12-13 show sample locations with COPCs. 12.3 Uncertainty and Data Gaps This screening level risk assessment was conducted as part of the groundwater assessment under the primary assumption that sampling locations, sample media, and analytes, as defined in the Work Plan, were sufficient for screening human health and ecological risks at the Site. All proposed samples were collected, and analyses completed as planned; however, due to analytical constraints (e.g., method detection limits and dilution effects during sample preparation for analysis) and/or anomalous results, there are numerous constituents for which (a) detection limits were greater than one or more screening criteria, (b) reported results were greater than detection limits, but less than reporting limits (i.e., estimated), or (c) reported results seemed anomalous (e.g., dissolved metal concentration greater than total metal concentration). This presents the possibility that the actual concentration of a given constituent might exceed one or more screening criteria while not being detected by instrumentation, the result was incorrectly estimated, or some unknown error occurred which interfered with accurate reporting. For this reason, these particular instances have been noted and affected constituents flagged as COIs that require further consideration. The COIs flagged for these reasons include antimony, arsenic, beryllium, boron, cadmium, lead, molybdenum, selenium, sulfide, thallium, and vanadium. 12.4 Scientific/Management Decision Point Based on the results of the human health and ecological screen, media-specific remediation standards will be calculated in accordance with the Eligibility Requirements and Procedures for Risk-Based Remediation of Industrial Sites Pursuant to NC General Statutes 130A-310.65 to 310.77 after additional sample collection. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 91 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 12.5 Risk Assessment Summary The Screening Level Human Health and Ecological Risk Assessments conducted as part of this groundwater assessment resulted in the identification of the following COPCs (in groundwater, surface water, sediment, and/or soil) at the Site: pH, aluminum, antimony, arsenic, barium, boron, chloride, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nitrate (as N), selenium, thallium, TDS, vanadium, and zinc (Tables 12-9 and 12-14). Calcium, magnesium, potassium, and sodium are omitted from the list of COPCs as they have no applicable criteria, are ubiquitous in nature, and are considered to be macrominerals with negligible toxicity to ecological receptors. These constituents were quantified as a component of the water, soil, and sediment characterization processes. To summarize: the potential exists for exposure of the COPCs listed above to human and/or ecological receptors, as identified in the CEMs (Figures 12-1 and 12-10), at levels exceeding those listed in one or more screening criteria. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 92 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 13.0 GROUNDWATER MODELING A brief synopsis of the groundwater modeling effort is included in the following sections. 13.1 Groundwater Modeling to be Performed in CAP The proposed numerical modeling involves development of a groundwater flow model and a chemical transport model. The groundwater modeling will be conducted in accordance with the requirements of the May 31, 2007 NCDENR Memorandum titled Groundwater Modeling Policy. The numerical groundwater flow model will be developed using MODFLOW, a three- dimensional finite difference groundwater model created by the United States Geological Survey (USGS). In MODFLOW, Darcy’s law and the conservation of mass are used to derive balance equations for each finite difference cell. MODFLOW considers three-dimensional transient groundwater flow in confined and unconfined heterogeneous systems, and it can included dynamic interaction with pumping wells, recharge, evapotranspiration, rivers, streams, springs, lakes, and swamps. The numerical model will be used as a quantitative conceptual model of the Site where flow features such as boundary conditions, sources and sinks, material zones, hydrologic parameters, and external stresses will be defined. The boundaries of the flow model will be located far (several miles) away from the Site so that boundary conditions do not dominate the modeled flow regime. The boundary conditions will depend on the type of boundary, but will be either specified head (for surface water boundaries), or no-flow (for groundwater divides). Parts of the boundary may be modeled using a specified or head-dependent flux. The Site model sources and sinks will consist of drains, springs, rivers, swamps and ponds, industrial production wells and water supply wells. Material zones or hydrostratigraphic layers will be defined from previously existing boring logs in addition to the 52 boring logs generated during the 2015 assessment. Recharge, evapotranspiration, and precipitation are representations of external stresses that are used in the model. Recharge will be initially estimated using the average characteristics of the regional hydrogeology. These initial estimates will then be refined during a model calibration process where the model parameters are adjusted to provide a better match with Site field data. To further define heterogeneities, a 2-D scatter point set will be used to define specified hydraulic values within vertical or horizontal zones. Specified hydraulic values will be Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 93 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx given set ranges that reflect field conditions from core measurements, historical slug and pump tests from Geosyntec (2012), and recent slug tests from the 42 wells installed under the GAP. The model will be calibrated in part by adjusting the specified hydraulic value distribution to minimize the residuals between the predicted hydraulic heads and the observed values. Historical hydraulic heads and recent June 2015 measurements from 96 wells will be used as observed values. The chemical transport model will use the Modular 3-D Transport Multi-Species model, which uses the groundwater flow field from MODFLOW to simulate three-dimensional advection and dispersion of the dissolved COCs including the effects of retardation due to COC adsorption to the soil matrix. The COC source terms will consist of initial distributions of the COCs in the subsurface that are estimated from Site boring and observation well data. During the calibration process, these source terms, and to a lesser extent some of the transport parameters will be adjusted to provide a best match with the field COC data. Model limitations will be primarily related to uncertainties in field data. Model confidence will always be higher in areas where a high density of field data can constrain the model. Numerical model errors are easily recognizable and minimized by experienced users. 13.2 Description of Kd Term Development An adaptation of the column method described by Daniels and Das (2014) to develop Kd estimates was used on Site soil samples. Soil samples with measured dry density and maximum particle size of 2 mm were placed in lab-scale columns configured to operate in the up-flow mode. A solution with measured concentrations of the COI was pumped through each column, effluent samples will be collected at regular intervals over time. When constituent breakthroughs are verified, a “clean” solution (no COIs) will be pumped through the columns and effluent samples collected. Samples will be analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS) and ion chromatography (IC). Plots of effluent COI concentration versus cumulative pore volumes exchanged will be analyzed to estimate Kd values and to confirm reversibility of COI sorption. Kd factors for boron, iron, manganese, and vanadium will be utilized in the transport model. 13.3 Description of Flow Transects Groundwater flow from the ash basins to potential receptor areas is to the east and southeast (Figure 6-6 through 6-8). Three transects were selected for the Site to Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 94 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx illustrate flowpath conditions in the vicinity of the ash basin (Figures 1-2). Section A-A’ (Figure 6-1) provides the best illustration of the three ash basin source areas in relation to the undeveloped area to the north, the Site and receptor area to the east. Sections B- B’ and C-C’ (Figure 6-2) illustrate conditions from the cooling pond eastward through the 1971 ash basin area to the Site perimeter. 13.4 Other Model Inputs At a Coastal Plain site such as Site, the stratigraphy of the sedimentary units in the subsurface is the primary component of the model. Key components of the model include the contact between the surficial aquifer and the Pee Dee Formation and the characteristics of the lower surficial aquifer. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 95 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 14.0 DATA GAPS – SITE CONCEPTUAL MODEL UNCERTAINTIES Information to date is sufficient to prepare a SCM and to support preparation of the groundwater model for the Site. Although data gaps remain they are not a limiting factor in developing the SCM or are anticipated to be a limiting factor for completion of the groundwater modeling or development of the CAP. The primary data gaps that have been identified during this assessment is the determination of deep (Pee Dee Formation) background concentrations and the determination of potential off-site sources of COIs. 14.1 Data Gaps Data gaps identified during the assessment include the following: Identification of the background levels of COIs in deep aquifer zones. Insufficient groundwater analytical data to rule out the 1984 ash basin as a source of selenium detected MW-27B. Determination of off-site sources responsible for concentrations of COIs east and northeast of the Site. 14.2 Site Heterogeneities Sedimentary geologic units at the site include the surficial alluvial deposits underlain by sediments of the Pee Dee Formation. Heterogeneities among these units are discussed below. The surficial deposits include an upper zone of relatively homogenous medium-fine sand. The lower surficial contains more heterogeneity of grain size, including zones of coarse sand to fine gravel, and in some cases large pieces of wood. Greater groundwater flow, as evidenced by greater hydraulic conductivity values, is facilitated through this zone. The Pee Dee Formation underlies the surficial deposits unconformably across the Site. Pee Dee sediments are made up of dense fine sands, often silty or clayey. The contact between surficial deposits and the Pee Dee is sharp and distinct. Lateral groundwater flow is enhanced by this heterogeneity. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 96 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 14.3 Impact of Data Gaps and Site Heterogeneities Additional deep wells outside of the ash basin a can provide data on background levels in the lower Pee Dee Formation. Additional monitoring of existing wells will assist in determining if off-site conditions are impacting assessment wells. Pending groundwater modeling and Kd analyses of soil retardation factors will also provide additional data regarding the effects of the Site heterogeneities. These data gaps will not compromise the groundwater modeling or the CAP. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 97 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 15.0 PLANNED SAMPLING FOR CSA SUPPLEMENT The following sample collection is anticipated to supplement the CSA: • Collection of groundwater sample from wells located north of 1984 ash basin (PZ-1A/B and MW-36B/C) and/or installation of additional wells in this area for the purpose of metals analyses. • Speciation sampling of chromium for wells located along the eastern Site boundary. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 98 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 16.0 INTERIM GROUNDWATER MONITORING PLAN The outline for an interim groundwater monitoring plan is contained in this section. 16.1 Sampling Frequency Groundwater samples would continue to be collected three times per year. The schedule followed for the existing compliance sampling has yielded meaningful seasonal data that can assist in the development of the SCM. 16.2 Constituent and Parameter List The proposed list of constituents for analysis is included as Table 16-1. 16.3 Proposed Sampling Locations Proposed groundwater monitor wells to be included in the interim groundwater sampling program are listed in Table 16-2 and illustrated on Figure 16-1. 16.4 Proposed Background Wells Of the monitor wells listed in Table 16-2, wells at locations MW-5B/C and MW-37B/C would be designated background wells. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 99 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 17.0 DISCUSSION All aspects of the GAP were accomplished, with the exception of the infiltration tests that were superseded by in-situ hydraulic conductivity testing. The SCM for the Site entails the following major components: The ash basins and FADA sit atop Coastal Plain sediments north and northwest of the main plant area. Regional groundwater flow is generally south toward the convergence of the Cape Fear and East Cape Fear River. At the Site, groundwater flow is somewhat complex and is affected by topography, the ash basin and cooling pond as well as the operation of nearby production and water supply wells. Groundwater flows in all directions from the ash basin but the salient flow direction is to the east and southeast. The potential interferences from the off-site municipal and industrial production wells (and the potential extraction wells) will be considered in the groundwater flow model is being prepared for the CAP. As the model is being prepared additional groundwater and surface water elevation monitoring points may be collected. Ash pore water in the FADA and 1971 ash basins infiltrate directly into the porous surficial aquifer below. No seeps or surface drains direct ash pore water from the basins. The vertical migration of COIs has been reduced by the lower permeability of the Pee Dee Formation. The COIs are most prevalent in the lower surficial aquifer. Concentrations of COIs related to the ash basins, particularly boron, have migrated off- site to the east. A Groundwater Mitigation and Monitoring Plan, which includes the installation of 12 extraction wells screened in the lower surficial aquifer, has been submitted to address this condition. 17.1 Maximum COI Concentrations COI concentrations above 2L extend beyond the compliance boundary and beyond the eastern Site boundary. The highest concentrations are generally found in the ash pore water or wells near the ash management area. High levels of iron and manganese occur in the northeast portion of the Site and in off-site wells which do not appear to be connected to the Site ash management area. Migration of COIs to surface water is indicated by comparison of well water level data in the FADA and 1971 ash basins to the surface water level of the cooling pond. However, no impact to the surface water is indicated based on laboratory data. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 100 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 17.2 Summary of Completed and Ongoing Work Work anticipated under the GAP was completed. 17.3 Contaminant Migration and Potentially Affected Receptors Potential receptors of COIs exist in off-site private and public water supply wells. Concentrations of boron near 2L have been detected in two private wells. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 101 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 18.0 CONCLUSIONS AND RECOMMENDATIONS The conclusions developed during the CSA are summarized in this section. 18.1 Source and Cause of Contamination Coal ash accumulated in the ash basins and FADA are sources of groundwater impact. The cause of impact is leaching of constituents from the coal ash into the ash pore water and its migration to underlying groundwater 18.2 Imminent Hazards to Public Health and Safety and Actions Taken to Mitigate Them 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). Paragraph (f) provides requirements for corrective action. Potential impact to water supply wells located to the east of the Site is being addressed. Several steps that have been initiated include: A Groundwater Mitigation and Monitoring Plan has been submitted that includes the installation of 12 extraction wells along the eastern Site boundary to intercept groundwater in the surficial aquifer. Plans to discontinue the use of the nearby municipal water supply wells are underway. Completion of the replacement well field water system construction is anticipated by December 2015. Preparations are being made to excavate the ash from the basins, thus removing the source of groundwater impact. 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. A screening level human health risk assessment and screening level ecological risk assessment was performed with the results provided in Section 12. Consumption of groundwater, recreational use of affected surface water, and consumption of fish and game affected by contaminants are the primary exposure pathways for humans in the vicinity of the ash basin. Cape Fear Public Utility Authority water supply wells are located adjacent to the Site on the east side. These wells produce water from the surficial aquifer at a depth of approximately 50 feet bgs. These well are located downgradient of the Site based on data collected in the CSA. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 102 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Thirty-two private water wells were identified within 0.5 miles of the Site compliance boundary during the CSA. Public and private wells that are located near the eastern Site boundary have been surveyed. NCDENR has managed the sampling of water supply wells in the area. No COIs are detected above the 2L in the public supply wells with the exception of manganese. Based on data obtained during the assessment, the occurrence of manganese in the area of the public supply wells cannot be conclusively attributable to the ash basins. In the private wells, only iron, manganese, cobalt, and vanadium were reported at concentrations greater than 2L or IMAC. Based on data obtained during the assessment, the occurrence of iron, manganese and cobalt in the wells cannot be directly attributed to the ash basins. Vanadium is also a naturally-occurring element in groundwater and assessment data does not definitively indicate a connection between the detection of vanadium in the supply wells and the ash basins. Boron results for the water supply wells sampled at the direction of NCDENR were reported to be less than the 2L. The installation of extraction wells and the replacement of the public well supply wells are planned to close potential exposure pathways to these receptors. 18.4 Horizontal and Vertical Extent of Soil and Groundwater Contamination The horizontal extent of COIs in soil and groundwater has been delineated. No surficial soil impact was detected with the exception of iron, which is representative of background concentrations. Groundwater impact is considered to be present where the analytical results were in excess of the site background concentrations and in excess of the 2L or IMAC Standard. Arsenic, barium, boron, iron, manganese, vanadium and total dissolved solids (TDS) have been identified as site specific constituents of interest (COIs) based on concentrations in excess of the 2L Standard or IMAC concentration in ash pore water. Horizontal groundwater impact has been defined by monitor wells on-site to the north and south and off-site to the east. Wells could not be installed west of the ash basins due to the presence of the cooling pond and Cape Fear River, however, surface water data and groundwater elevation data do not indicate the need for further assessment in that direction. Vertical delineation has been defined in the upper portion of the Pee Dee Formation, assuming the chloride concentrations in the lower Pee Dee wells are indicative of salt water intrusion and account for the boron concentrations detected at that level. This Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 103 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx assumption is supported by several lines of evidence based on the data collected. The screen elevations of the Pee Dee wells are approximately 80 to 130 feet below sea level and the Site is located in close proximity to the Atlantic coast. Numerous pumping wells are located in the vicinity of the Site which would help facilitate salt water intrusion. The average chloride concentration in the Pee Dee wells is nearly eight times that of the surficial wells and the specific conductance is nearly four times greater in the Pee Dee wells than in the surficial wells. Additionally, regional groundwater data also indicate naturally-occurring, elevated boron levels in sea water. Constituent transport is dependent on leaching from the coal ash source that results from solubility due to chemical disequilibrium (the dissolved phase is more stable than the solid phase under the conditions at the time). Factors that affect reactions with material along the flow path resulting in removal of the constituents from groundwater control the extent of migration. These factors vary by constituent and vary based on the properties of the soil or aquifer materials along the flow path. Sorption and precipitation are the primary mechanisms that immobilize cations (aluminum, arsenic, boron, cobalt, iron, manganese, thallium, and vanadium). A number of factors specific to constituent and to the site conditions are involved in determining which of these mechanisms occur and how much of the constituent is partitioned out of the groundwater. The results of testing performed to determine the chemical, physical, and mineralogical characteristics of the soil and aquifer materials and the site groundwater were performed during the CSA. Additional testing is being performed to determine the adsorptive capacity of the site soils and aquifer materials to the specific groundwater constituents by development of site specific partition coefficient Kd terms. The Kd testing will provide site specific values for the ability and capacity of site soils to remove constituents from groundwater and will assist in understanding the mechanisms affecting transport at the site. Kd tests and the associated groundwater modeling will also allow for evaluation of the long-term constituent 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. Iron, manganese, and vanadium are commonly detected in shallow groundwater in the coastal plain region of North Carolina. Calculation of proposed site specific background concentrations will occur when a sufficient number of samples to perform statistical analysis have been collected. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 104 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 18.5 Geological and Hydrogeological Features influencing the Movement, Chemical, and Physical Character of the Contaminants The primary feature that influences migration of contaminants is the permeable nature of the surficial aquifer in contrast with the underlying Pee Dee Formation. While no confining unit was discovered at the Site as anticipated in the initial site conceptual model presented in the Work Plan dated December 30, 2014, data collected to date indicate that vertical migration is slowed by the lower permeability of the Pee Dee Formation approximately 50 feet bgs at the Site. The contrast in permeabilities between the surficial unit and the underlying Pee Dee is sufficient to create preferential lateral flow 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 direction of the movement of the constituents confirmed by the CSA is toward the east and south, as anticipated. The rate of groundwater movement varies with the hydraulic conductivity and porosity of the site soil and rock materials and ranges from 0.185 to 8.55 feet per year. Data collected during the CSA, coupled with Kd data to be supplied at a later date, will be used to build groundwater flow and transport models for the site. 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 Interim groundwater monitoring is proposed in Section 16. 18.7 Preliminary Evaluation of Corrective Action Alternatives A Groundwater Mitigation and Monitoring Plan has been submitted that includes the installation of 12 extraction wells along the eastern Site boundary to intercept elevated levels of boron in groundwater from the surficial aquifer. Groundwater modeling will provide an estimate of the degree of residual groundwater impact over time. In the subsequent CAP, Duke Energy will pursue corrective action under 15A NCAC 02L .0106 (k) or (l) depending on the results of the groundwater modeling and the evaluation of site suitability for monitored natural attenuation. Evaluation of monitored natural attenuation would be performed using the approach found in Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 105 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Volumes 1 and 2 (EPA Reference) and potential modeling of interaction between groundwater and surface water. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 106 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx 19.0 REFERENCES ASTM D6312-98: Standard Guide for Developing Appropriate Statistical Approaches for Groundwater Detection Monitoring Programs. 2012. ASTM E1689-95: Standard Guide for Developing Conceptual Site Models for Contaminated Sites. 2014. ASTM D4044-96: Standard Test Method (Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining Hydraulic Properties of Aquifers. Cox, J.A., Lundquist, G.L., Przyjazny, A., and Schmulbach, C.D. Leaching of Boron from Coal Ash. Environmental Science and Technology. 1978: 722-723. Daniel, C.C., III, and Sharpless, N.B. 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 U.S. Geological Survey. 1983: 73. Daniels, John L. and Das, Gautam P. Practical Leachability and Sorption Considerations for Ash Management. Boston, MA: Wentworth Institute of Technology Geo-Congress 2014 Technical Papers: Geo-characterization and Modeling for Sustainability. 2014. Denbigh, K. The Principles of Chemical Equilibrium. 3rd ed. Cambridge, UK: Cambridge University Press. 1971: 494. Dudas, M.J. Long-Term Leachability of Selected Elements from Fly Ash. Environmental Science and Technology. 1981: 840-843. Duke Energy, http://www.duke-energy.com/pdfs/duke-energy-ash-metrics.pdf (Updated Oct. 31, 2014) Electric Power Research Institute. Electric Power Research Institute, Physical and Hydraulic Properties of Fly Ash and Other By-Products from Coal Combustion, Product ID: 101999. February 1993. Electric Power Research Institute. A Field and Laboratory Study of Solute Release from Sluices Fly Ash, Product ID: 104585. December 1994. Electric Power Research Institute. Coal Ash Disposal Manual: 3rd Edition, Product ID: 104137. January 1995. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 107 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Electric Power Research Institute. Comparison of Coal Combustion Products to Other Common Materials: Final Report, Product ID: 1020556. September 2010. Finkelman, R.B, in Swaine, D.J. and Goodzari, eds. Environmental Aspects of Trace Elements in Coal. Kluwer Academic Publishers. 1995: 24-50. Fleet, M. E. L. Preliminary Investigations into the Sorption of boron by Clay Minerals. Clay Minerals. 1965; 6(3): 3-16. Griffith, G.E., Omernik, J.M., Comstock, J.A., Schafale, M.P., McNab, W.H., Lenat, D.R., MacPherson, T.F., Glover, J.B., and Shelburne, V.B. 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). Geosyntec Consultants. (DRAFT) Preliminary Site Investigation Data Report-Addendum No. 1, Conceptual Closure Plan, L.V. Sutton Plant, Project Number GC5592. July 2014. Geosyntec Consultants. (DRAFT) Data Interpretation and Analysis Report, Conceptual Closure Plan, L.V. Sutton Plant, Project Number GC5592. July 2014. Goldberg, S. Reactions of Boron with Soils. Plant and Soil. 1997; 193: 35-48. Goldberg, S., Forster, H. S., Lesch, S. M., and Heick, E. L. Influence of Anion Competition on Boron Adsorption by Clays and Soils. Soil Science. 1996; 161(2): 99-103. Goodzari, F., Huggins, F.E., and Sanei, H. Assessment of Elements, Speciation of As, Cr, Ni and Emitted Hg for a Canadian Power Plant Burning Bituminous Coal. International Journal of Coal Geology. 2008; 74:1-12. Horton, J. W. and Zullo, V. A. The Geology of the Carolinas. Carolina Geological Society Fiftieth Anniversary Volume. 1991:406. Hurlbut, C. S. Dana’s Manual of Mineralogy. 18th ed. New York: John Wiley & Sons, Inc. 1971: 579. Izquierdo, M., and Querol, X. Leaching Behaviour of Elements from Coal Combustion Fly Ash: An Overview. International Journal of Coal Geology. 2012;94: 54-66. Comprehensive Site Assessment Report August 2015 L.V. Sutton Energy Complex SynTerra Page 108 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\1.11 CSA Reporting\Sutton CSA Report 08-05-2015.docx Kisch, H. J. Coal-Rank and Burial-Metamorphic Mineral Facies. Oxford: Pergamon Press. Advances in Organic Geochemistry. 1968; 1969: 407-425. Narkunas, J. Groundwater Evaluation in the Central Coastal Plain of North Carolina. North Carolina Department of Natural Resources and Community Development. 1980:119. Nash, L.K. Chem-Thermo: A Statistical Approach to Classical Thermodynamics. Reading, MA: Addison-Wesley Publishing Company. 1971: 207. NCDENR. Guidelines for Performing Screening Level Ecological Risk Assessments within North Carolina. 2003. NCDENR. Groundwater Modeling Policy Memorandum. May 31, 2007. NCDENR. Classifications and Water Quality Standards Applicable to the Groundwaters of North Carolina. North Carolina Administrative Code Title 15A, Subchapter 02L. 2013. NCDENR. 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Field Exploration Data Report, Progress Energy – Sutton Plant Ash Pond, Lumberton, North Carolina, S&ME Project No. 1054-12-062. June 11, 2012. SynTerra. Drinking Water Well and Receptor Survey for Sutton Power Plant, NPDES Permit# NC0005363. September 2014. SynTerra, Groundwater Monitoring Program Sampling, Analysis, and Reporting Plan for Sutton Power Plant, NPDES Permit# NC0005363. October 2014. SynTerra. Supplement to Drinking Water Well and Receptor Survey - Sutton Power Plant, NPDES Permit# NC0005363. November 2014. SynTerra. Proposed Groundwater Assessment Work Plan for L.V. Sutton Energy Complex, NPDES Permit # NC0005363. December 2014. Turner, Francis J. Metamorphic Petrology. Washington: Hemisphere Publishing Corporation. 1981: 524. USEPA. Risk Assessment Guidance for Superfund Volume I , Human Health Evaluation Manual, (Part A). EPA / 540 / 1-89/002; 1989. USEPA. Guidelines for Ecological Risk Assessment. 1998. Comprehensive Site Assessment Report August 2015 L.V. 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