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Home My WebLink AboutNC0004979_Allen Assessment Work Plan_Final_20140925 Allen Steam Station Ash Basin Proposed Groundwater Assessment Work Plan NPDES Permit NC0004979 September 25, 2014 Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin Table of Contents i Table of Contents Executive Summary .............................................................................................................. ES-1 1.0 Introduction .......................................................................................................................... 1 2.0 Site History........................................................................................................................... 2 2.1 Plant Description ...................................................................................................... 2 2.2 Ash Basin Description ............................................................................................... 2 2.3 Regulatory Requirements ......................................................................................... 3 3.0 Receptor Information ............................................................................................................ 5 4.0 Regional Geology and Hydrogeology ................................................................................... 6 5.0 Site Geology and Hydrogeology ........................................................................................... 7 6.0 Groundwater Monitoring Results .......................................................................................... 8 7.0 Assessment Work Plan ........................................................................................................ 9 7.1 Ash and Soil Sampling Plan ...................................................................................... 9 7.1.1 Boring and Sampling Methods ...................................................................... 9 7.1.2 Proposed Soil and Ash Sampling Locations and Depths ..............................10 7.2 Groundwater Sampling Plan ....................................................................................11 7.2.1 Well Installation and Development ...............................................................11 7.2.2 Hydrogeologic Evaluation .............................................................................12 7.2.3 Groundwater Sampling.................................................................................12 7.3 Surface Water Sampling Plan ..................................................................................12 7.3.1 Ash Basin Surface Water Samples ..............................................................12 7.3.2 Seep Samples ..............................................................................................13 7.4 Site Hydrogeologic Conceptual Model .....................................................................13 7.5 Site-Specific Background Concentrations ................................................................13 7.6 Groundwater Model .................................................................................................13 8.0 Proposed Schedule .............................................................................................................15 9.0 References..........................................................................................................................16 Appendix A – Notice of Regulatory Requirements Letter from John E. Skvarla, III, Secretary, State of North Carolina, to Paul Newton, Duke Energy, dated August 13, 2014. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin Table of Contents ii List of Figures 1. Site Location Map 2. Site Layout Map 3. Proposed Well and Sample Locations List of Tables 1. Groundwater Monitoring Requirements 2. Monitoring Well Locations 3. Exceedances of 2L Standards 4. Environmental Exploration and Sampling Plan 5. Soil and Ash Parameters and Analytical Methods 6. Groundwater, Surface Water, and Seep Parameters and Analytical Methods Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin Executive Summary ES-1 Executive Summary Duke Energy Carolinas, LLC (Duke Energy), owns and operates the Allen Steam Station (Allen), located along the Catawba River in Gaston County near the town of Belmont, North Carolina (see Figure 1). Allen began operation in 1957 as a coal-fired generating station and currently operates five coal-fired units. The coal ash residue from Allen’s coal combustion process has historically been disposed in the station’s ash basin located to the south of the station and adjacent to the Catawba River. The discharge from the ash basin is permitted by the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES) Permit NC0004979. On August 13, 2014, NCDENR issued a Notice of Regulatory Requirements (NORR) letter to Duke Energy, pursuant to Title 15A North Carolina Administrative Code Chapter (15A NCAC) 02L.0106. The NORR stipulates that for each coal-fueled plant owned, Duke Energy will conduct a comprehensive site assessment (CSA) that includes a Groundwater Assessment Work Plan (Work Plan) and a receptor survey. In accordance with the requirements of the NORR, HDR is in the process of completing a receptor survey to identify all receptors within a 0.5-mile radius (2,640 feet) of the Allen ash basin compliance boundary. This receptor survey will also address the requirements of the General Assembly of North Carolina Session 2013 Senate Bill 729 Ratified Bill (SB 729). Soil and groundwater sampling will be performed to provide information pertaining to the horizontal and vertical extent of potential soil and groundwater contamination. This will be performed by sampling select existing wells, installing and sampling approximately 32 nested monitoring well pairs (shallow and deep), and collecting soil and ash samples. This work will provide additional information on the chemical and physical characteristics of site soils and ash, as well as the geological and hydrogeological features of the site that influence groundwater flow and direction and potential transport of constituents from the active ash basin and inactive ash basin. Samples of ash basin water will be collected and used to evaluate potential impacts to groundwater and surface water. In addition, seep samples will be collected from locations identified in August 2014 (as part of Duke Energy’s NPDES permit renewal application) to evaluate potential impacts to surface water. The information obtained through implementation of this Work Plan will be utilized to prepare a CSA report in accordance with the requirements of the NORR. If it is determined that additional investigations are required during the review of existing data or data developed from this assessment, Duke Energy and HDR will notify the NCDENR regional office prior to initiating additional sampling or investigations. HDR will also perform an assessment of risks to human health or safety and to the environment. This assessment will include the preparation of a conceptual site model illustrating potential pathways from the source to possible receptors. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 1.0 Introduction 1 1.0 Introduction Duke Energy Carolinas, LLC (Duke Energy), owns and operates the Allen Steam Station (Allen), located along the Catawba River in Gaston County near the town of Belmont, North Carolina (see Figure 1). Allen began operation in 1957 as a coal-fired generating station and currently operates five coal-fired units. The coal ash residue from Allen’s coal combustion process has historically been disposed in the station’s ash basin located to the south of the station and adjacent to the Catawba River. The discharge from the ash basin is permitted by the North Carolina Department of Environment and Natural Resources (NCDENR) Division of Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES) Permit NC0004979. On August 13, 2014, NCDENR issued a Notice of Regulatory Requirements (NORR) letter to Duke Energy, pursuant to Title 15A North Carolina Administrative Code (15A NCAC) Chapter 02L.0106. The NORR stipulates that for each coal-fueled plant owned, Duke Energy will conduct a comprehensive site assessment (CSA) that includes a Groundwater Assessment Work Plan (Work Plan) and a receptor survey. In accordance with the requirements of the NORR, HDR is in the process of completing a receptor survey to identify all receptors within a 0.5-mile radius (2,640 feet) of the Allen ash basin compliance boundary. The NORR letter is included as Appendix A. On behalf of Duke Energy, HDR has prepared this proposed Work Plan for performing the groundwater assessment as prescribed in the NORR. If it is determined that additional investigations are required during the review of existing data or data developed from this assessment, Duke Energy and HDR will notify the NCDENR regional office prior to initiating additional sampling or investigations. HDR will also perform an assessment of risks to human health or safety and to the environment. This assessment will include the preparation of a conceptual site model illustrating potential pathways from the source to possible receptors. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 2.0 Site History 2 2.0 Site History 2.1 Plant Description Allen is a five-unit, coal-fired, electric generating plant with a capacity of 1,140 megawatts located on the west bank of the Catawba River on Lake Wylie, in Belmont, Gaston County, North Carolina. The site is located east of South Point Road (NC 273) and the surrounding area generally consists of residential properties, undeveloped land, and Lake Wylie (Figure 1). The station’s ash basin is situated between the Allen station to the north and surface water divides to the west (along South Point Road) and south (along Reese Wilson Road), which both drop in elevation to the east toward Lake Wylie. The surface water divide along South Point Road likely functions as a groundwater divide. The topography at the site generally slopes downward from that divide toward Lake Wylie. The entire Allen site is approximately 1,009 acres in area. 2.2 Ash Basin Description The station’s ash basin consists of an active ash basin and an inactive ash basin. The active ash basin was commissioned in 1973 and is currently in operation.1 The inactive ash basin is located to the north of the active ash basin and is not in operation. A large portion of the area on top of the inactive ash basin is permitted as an industrial landfill by the NCDENR Division of Waste Management (Permit No. 3612). The area contained within the ash basin waste boundary, which is shown on Figures 2 and 3, is approximately 322 acres in area. There are two earthen dikes impounding the active ash basin; the East Dike, located along the west bank of Lake Wylie, and the North Dike, separating the active and inactive ash basins. The surface area of the active ash basin is approximately 169 acres1 with an operating pond elevation of approximately 633.5 feet. The full pond elevation of Lake Wylie is approximately 568.7 feet. The ash basin is operated as an integral part of the station’s wastewater treatment system, which receives flows from the ash removal system, coal pile runoff, landfill leachate, flue-gas desulfurization (FGD) wastewater, the station yard drain sump, and stormwater flows. Due to variability in station operations and weather, the inflows to the ash basin are highly variable. The inflows from the ash removal system and other plant discharges are discharged through sluice lines to the ash basin. Prior to 2009, all of the fly ash produced was sluiced to the ash basin. Since 2009, fly ash has been dry-handled and is infrequently sluiced to the ash basin. All of the bottom ash produced by the station is sluiced to the ash basin. Effluent from the ash basin is discharged from the discharge tower via a 42-inch-diameter reinforced concrete pipe, to Lake Wylie. The water surface elevation in the ash basin is controlled by the use of stop logs in the discharge tower. 1 Information obtained from Duke Energy Carolinas, LLC CERCLA 104(e) Request for Information to US Environmental Protection Agency, Allen Steam Station, dated March 26, 2009 Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 2.0 Site History 3 2.3 Regulatory Requirements The NPDES program regulates wastewater discharges to surface waters, to ensure that surface water quality standards are maintained. Allen operates under NPDES Permit NC0004979, which authorizes Duke Energy to discharge once-through cooling water (Outfall 001); operate a septic tank and ash pond with pH adjustment and domestic wastewater discharge, stormwater runoff, ash sluice, water treatment system wastewaters, FGD system blowdown, landfill leachate, and miscellaneous cleaning and maintenance wash waters (Outfall 002); coal yard sump overflow (Outfall 002A); power house sump overflow (Outfall 002B); miscellaneous equipment for non-contact cooling and sealing water (Outfall 003); and miscellaneous non- contact cooling water, vehicle washwater, and intake screen backwash (Outfall 004) to the Catawba River in accordance with effluent limitations, monitoring requirements, and other conditions set forth in the permit. Furthermore, the NPDES Permit authorizes Duke Energy to continue operation of the FGD wet scrubber wastewater treatment system discharging to the ash settling basin through internal Outfall 005. The NPDES permitting program requires that permits be renewed every five years. The most recent NPDES permit renewal at Allen became effective on March 1, 2011, and expires May 31, 2015. In addition to surface water monitoring, the NPDES permit requires groundwater monitoring. Groundwater monitoring has been performed in accordance with the permit conditions beginning in March 2011. NPDES Permit Condition A (11), Version 1.1, dated June 15, 2011, lists the groundwater monitoring wells to be sampled, the parameters and constituents to be measured and analyzed, and the requirements for sampling frequency and reporting results. These requirements are provided in Table 1. The compliance boundary for groundwater quality at the Allen ash basin site is defined in accordance with Title 15A NCAC 02L .0107(a) as being established at either 500 feet from the waste boundary or at the property boundary, whichever is closer to the waste. The location of the ash basin compliance monitoring wells, the ash basin waste boundary, and the compliance boundary are shown on Figure 2. The locations for the compliance groundwater monitoring wells were approved by the NCDENR DWR Aquifer Protection Section (APS). All compliance monitoring wells included in Table 2 are sampled three times per year (in March, July, and November). Analytical results are submitted to the DWR before the last day of the month following the date of sampling for all compliance monitoring wells except AB-9S, AB-9D, AB-10S, and AB-10D. The compliance groundwater monitoring system for the Allen ash basin consists of the following monitoring wells: AB-1R, AB-4S, AB-4D, AB-9S, AB-9D, AB-10S, AB-10D, AB-11D, AB-12S, AB-12D, AB-13S, AB-13D, and AB-14D (shown on Figures 2 and 3). All the compliance monitoring wells were installed in 2010. One or more groundwater quality standards (2L Standards) have been exceeded in groundwater samples collected at monitoring wells AB-1R, AB-4S, AB-4D, AB-9S, AB-9D, AB- 10S, AB-10D, AB-11D, AB-12S, AB-12D, AB-13S, AB-13D, and AB-14D. Exceedances have Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 2.0 Site History 4 occurred for boron, iron, manganese, pH, and nickel. Table 3 presents exceedances measured from March 2011, through July 2014. Monitoring wells AB-4S, AB-9S, AB-10S, AB-12S, and AB-13S were installed with 15-foot well screens placed above auger refusal to monitor the shallow aquifer within the saprolite layer. Monitoring wells AB-4D, AB-9D, AB-10D, AB-11D, AB-12D, AB-13D, and AB-14D were installed with either 5-foot or 10-foot well screens placed in the uppermost region of the fractured rock transition zone. Monitoring well AB-1R is located to the northwest of the inactive ash basin and is considered by Duke Energy to represent background water quality at the site. AB-1R was installed with a 20- foot well screen placed above auger refusal to monitor the shallow aquifer within the saprolite layer. With the exception of monitoring wells AB-9S, AB-9D, AB-10S, and AB-10D, the ash basin monitoring wells were installed at or near the compliance boundary. AB-11D is located to the south of the active ash basin. Monitoring wells AB-12S, AB-12D, AB-4S, AB-4D, and AB-13S, AB-13D are generally located to the west of the active ash basin. Monitoring well AB-14D is located to the south of a portion of the inactive ash basin and near the western extent of the property. Monitoring wells AB-9S, AB-9D, AB-10S, and AB-10D are located inside of the compliance boundary downgradient from the inactive and active ash basins (where it was not possible to access the compliance boundary). Monitoring wells AB-9S and AB-9D are located to the southeast of the inactive ash basin and AB-10S and AB-10D are located to the east of the active ash basin. Compliance with 2L Standards (at the compliance boundary) for AB-9S, AB- 9D, AB-10S, and AB-10D is determined by using predictive calculations or a groundwater model. For these four monitoring wells, Duke Energy uses a groundwater model to predict the concentrations at the compliance boundary. The predicted results from the groundwater model and the analytical results for samples collected during the sampling events are to be submitted to the DWR annually. Note that monitoring wells AB-1, AB-2, AB-2D, AB-5, AB-6A, AB-6R, and AB-8 were installed by Duke Energy in 2004 and 2005 as part of a voluntary monitoring system.2 Voluntary monitoring well AB-8 was found damaged and abandoned in 2010. No samples are currently being collected from the voluntary wells. The existing voluntary wells are shown on Figure 3. 2 AB-1 and AB-8 were abandoned in 2010. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 3.0 Receptor Information 5 3.0 Receptor Information The August 13, 2014 NORR states: No later than October 14th, 2014 as authorized pursuant to 15A NCAC 02L .0106(g), the DWR is requesting that Duke perform a receptor survey at each of the subject facilities and submitted to the DWR. The receptor survey is required by 15A NCAC 02L .0106(g) and shall include identification of all receptors within a radius of 2,640 feet (one-half mile) from the established compliance boundary identified in the respective National Pollutant Discharge Elimination System (NPDES) permits. Receptors shall include, but shall not be limited to, public and private water supply wells (including irrigation wells and unused or abandoned wells) and surface water features within one-half mile of the facility compliance boundary. For those facilities for which Duke has already submitted a receptor survey, please update your submittals to ensure they meet the requirements stated in this letter and referenced attachments and submit them with the others. If they do not meet these requirements, you must modify and resubmit the plans. The results of the receptor survey shall be presented on a sufficiently scaled map. The map shall show the coal ash facility location, the facility property boundary, the waste and compliance boundaries, and all monitoring wells listed in the respective NPDES permits. Any identified water supply wells shall be located on the map and shall have the well owner's name and location address listed on a separate table that can be matched to its location on the map. In accordance with the requirements of the NORR, HDR is in the process of completing a receptor survey for Allen to identify all receptors within a 0.5-mile radius (2,640 feet) of the ash basin compliance boundary to be submitted to NCDENR no later than October 1, 2014. This receptor survey will also address the requirements of the General Assembly of North Carolina Session 2013 Senate Bill 729 Ratified Bill (SB 729). The receptors include, but are not limited to, 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 Allen ash basin compliance boundary. The compliance boundary for groundwater quality, in relation to the ash basin, is defined in accordance with Title 15A NCAC 02L .0107(a) as being established at either 500 feet from the waste boundary or at the property boundary, whichever is closer to the source. The receptor survey will include a map showing the coal ash facility location, the facility property boundary, the waste and compliance boundaries, and all monitoring wells listed in the NPDES permit. The identified water supply wells will be located on the map and the well owner's name and location address listed on a separate table that can be matched to its location on the map. During completion of the CSA, HDR will update the receptor information as necessary, in general accordance with the CSA receptor survey requirements. If necessary, an updated receptor survey will be submitted with the CSA report. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 4.0 Regional Geology and Hydrogeology 6 4.0 Regional Geology and Hydrogeology North Carolina is divided into distinct regions by portions of three physiographic provinces: the Atlantic Coastal Plain, Piedmont, and Blue Ridge (Fenneman, 1938). Allen is located in the Charlotte terrane within the Piedmont province. The Piedmont province is bounded to the east and southeast by the Atlantic Coastal Plain and to the west by the escarpment of the Blue Ridge Mountains, covering a distance of 150 to 225 miles (LeGrand, 2004). The topography of the Piedmont region is characterized by low, rounded hills and long, rolling, northeast-southwest trending ridges (Heath, 1984). Stream valley to ridge relief in most areas range from 75 to 200 feet. Along the Coastal Plain boundary, the Piedmont region rises from an elevation of 300 feet above mean sea level, to the base of the Blue Ridge Mountains at an elevation of 1,500 feet (LeGrand, 2004). Charlotte terrane bedrock consists primarily of igneous and metamorphic bedrock. The fractured bedrock is overlain by a mantle of unconsolidated material known as regolith. The regolith includes, where present, the soil zone (a zone of weathered, decomposed bedrock known as saprolite) and, where present, alluvium. Saprolite, the product of chemical and mechanical weathering of the underlying bedrock, is typically composed of clay and coarser granular material up to boulder size and may reflect the texture of the rock from which it was formed. The weathering product of granitic rocks are quartz rich and sandy textured; whereas, rocks poor in quartz and rich in feldspar and other soluble minerals form a more clayey saprolite. The regolith serves as the principal storage reservoir for the underlying bedrock (LeGrand 2004). A transition zone may occur at the base of the regolith between the soil-saprolite and the unweathered bedrock. This transition zone of partially weathered rock is a zone of relatively high permeability compared to the overlying soil-saprolite and the underlying bedrock (LeGrand 2004). Groundwater flow paths in the Piedmont are almost invariably restricted to the zone underlying the topographic slope extending from a topographic divide to an adjacent stream. LeGrand describes this as the local slope aquifer system. Under natural conditions, the general direction of groundwater flow can be approximated from the surface topography (LeGrand 2004). Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation. Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains (LeGrand 2004). Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 5.0 Site Geology and Hydrogeology 7 5.0 Site Geology and Hydrogeology Based on a review of soil boring and monitoring well installation logs provided by Duke Energy, subsurface stratigraphy consists of the following material types: fill, ash, residuum, saprolite, partially weathered rock (PWR), and bedrock. In general, residuum, saprolite, and PWR were encountered on most areas of the site. Bedrock was encountered sporadically at a range of depths across the site. Bedrock was encountered at approximately 10 feet below ground surface (bgs) in areas on the southern extent of the site, approximately 29 feet bgs in areas on the western extent of the site, and as deep as approximately 108 feet bgs in areas on the eastern extent of the site near the Catawba River. In addition, alluvium is expected to be present beneath the southern portion of the active ash basin where, based on historic USGS topographic maps, two streams existed and flowed toward the Catawba River prior to construction of the active ash basin. The general stratigraphic units, in sequence from the ground surface down to boring termination, are defined as follows:  Fill – Fill material generally consisted of re-worked silts and clays that were borrowed from one area of the site and re-distributed to other areas. Fill was used in the construction of dikes and presumably as cover for the ash storage area and as cover for the Retired Ash Basin Ash Landfill.  Ash – Of the logs reviewed, borings were advanced through ash in the area of the Retired Ash Basin Ash Landfill only. Although previous exploration activities, for which Duke Energy provided boring logs, did not evaluate the inactive portions of the retired ash basin, the ash storage areas and the active ash basin, ash is expected to be present in these ash management areas.  Alluvium – Alluvium was not encountered in the boring information provided to HDR. However, alluvium is expected to be present beneath the southern portion of the active ash basin where two streams previously existed and flowed toward the Catawba River prior to construction of the active ash basin. Alluvium is unconsolidated soil and sediment that has been eroded and redeposited by streams and rivers.  Residuum – Residuum is the in-place weathered soil that generally consists of white, yellow, red, brown, gray, or olive sandy clay to silty sand. This unit was encountered in various thicknesses across the site.  Saprolite – Saprolite is soil developed by in-place weathering of rock similar to the bedrock that consists of brown, tan, or green silty sand with trace mica. The primary distinction from residuum is that saprolite typically retains some structure (e.g., mineral banding) from the parent rock. This unit was found in areas across the site and was described as white, yellow, red, or brown silty extremely weathered rock with relict rock structure.  Partially Weathered Rock (PWR) – PWR occurs between the saprolite and bedrock and contains saprolite and rock remnants. This unit was described as white to reddish yellow to olive brown to dark gray with quartz and potassium feldspar fragments.  Bedrock – Bedrock was encountered in borings completed around the western, southern, and eastern extents of the ash basin. Depth to top of bedrock ranged from 10 to 108 feet below ground surface. Bedrock was described as granite, quartzite, and gabbro. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 6.0 Groundwater Monitoring Results 8 6.0 Groundwater Monitoring Results From March 2011 through July 2014, the compliance groundwater monitoring wells at Allen have been sampled a total of 11 times. During this period, these monitoring wells were sampled in:  March 2011  July 2011  November 2011  March 2012  July 2012  November 2012  March 2013  July 2013  November 2013  March 2014  July 2014 With the exception of boron, iron, manganese, pH, and nickel, the results for all monitored parameters and constituents were less than the 2L Standards. Table 3 lists the range of exceedances for boron, iron, manganese, pH, and nickel for the sampling events listed above. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 7.0 Assessment Work Plan 9 7.0 Assessment Work Plan Soil and groundwater sampling will be performed to provide information pertaining to the horizontal and vertical extent of potential soil and groundwater contamination. Based on readily available site background information, and dependent upon accessibility, HDR anticipates collecting soil and/or ash samples from 6 soil boring locations and during installation of approximately 32 nested monitoring well pairs (shallow and deep). Groundwater samples will be collected from the proposed monitoring wells. The proposed well and boring locations are listed in Table 4 and shown on Figure 3. HDR may also resample select existing monitoring wells to supplement groundwater quality data. This work will provide additional information on the chemical and physical characteristics of site soils and ash, as well as the geological and hydrogeological features of the site that influence groundwater flow and direction and potential transport of constituents from the active ash basin and inactive ash basin. Samples of ash basin water will be also be collected and used to evaluate potential impacts to groundwater and surface water. If conditions allow for representative sampling, water samples will be collected from seep sample locations (S-1 through S-9) identified in August 2014 (as part of Duke Energy’s NPDES permit renewal application) to evaluate potential impacts to surface water. A summary of the proposed exploration plan, including estimated sample quantities and depths of soil borings and monitoring wells, is presented in Table 4. If it is determined that additional investigations are required during the review of existing data or data developed from this assessment, Duke Energy and HDR will notify the NCDENR regional office prior to initiating additional sampling or investigations. 7.1 Ash and Soil Sampling Plan 7.1.1 Boring and Sampling Methods Prior to drilling each boring, all down-hole equipment and tools will be cleaned by washing with high pressure hot water. A designated remote cleaning area will be established in the field. Water for cleaning will be obtained from a tap or hydrant (to be designated) at Allen, or supplied by the drilling contractor from an off-site source. Cleaning water will not require collection, treatment, or disposal. Borings will be advanced using hollow stem auger or roller cone drilling techniques to facilitate collection of down-hole data. Standard Penetration Testing (SPT) (ASTM D 1586) and split- spoon sampling will be performed at 2.5-foot to 5-foot increments using an 18-inch split-spoon sampler. The sampler will be decontaminated with a non-phosphate detergent wash between sampling depths. Ash and soil samples will be collected by the Project Scientist/Engineer. Borings will be logged by the Project Scientist/Engineer and ash/soil samples will be observed, visually classified, and photographed in the field for origin, consistency/relative density, color, and soil type in accordance with the Unified Soil Classification System (ASTM D2487/D2488). Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 7.0 Assessment Work Plan 10 Samples will be identified with a unique boring number and approximate collection depth (e.g., AB-21 (20-22’)). Sample containers will be provided by HDR’s contracted laboratory prior to commencement of the on-site investigation. Samples will be delivered to the analytical laboratory in time to extract the samples within their specified hold times (to be provided by the laboratory). HDR will provide the name, phone number, and email address of the laboratory project manager to facilitate sample analysis coordination. Boring locations will be surveyed for horizontal and vertical control upon completion of the field exploration program. 7.1.2 Proposed Soil and Ash Sampling Locations and Depths HDR anticipates collection of soil and ash samples for laboratory analysis at 9 locations within the active ash basin and on the north and east dikes (i.e., from monitoring well borings designated as AB-20 through AB-28), 11 locations within the inactive ash basin and on the east dike (i.e., from monitoring well borings designated as AB-29 through AB-39), and 6 soil boring locations in the ash storage area (designated as SB-1 through SB-6). The borings located within the waste boundary will extend approximately 20 feet below the ash/native soil interface or to refusal, whichever is encountered first. In addition, HDR anticipates collection of soil samples at three background locations (designated as BG-1 through BG-3). Soil samples will not be collected for laboratory analysis during installation of monitoring wells located outside the waste boundary (designated as GWA-1 through GWA-9). No borings will be advanced within the footprint of the double-lined ash landfill located in the east portion of the inactive ash basin. Proposed boring locations are shown on Figure 3. CONSTITUENT SAMPLING AND ANALYSES In general, ash is expected to be encountered in AB-series and SB-series borings. Ash samples will be collected from shallow and deeper vertical intervals to evaluate variations in type (e.g., fly ash or bottom ash) and chemical profile of the ash. In locations where ash thickness is expected to be greater than 30 feet, a third ash sample may be collected from a depth mid-way between the shallow and deeper intervals in a particular boring. Shallow ash samples will be collected from the 4-foot to 5-foot intervals and deeper ash samples will be collected from the 1-foot to 2-foot intervals overlying the ash/native soil interface. The depth of deeper ash samples is expected to vary based on ash thickness at each specific boring location. Ash samples will be analyzed by HDR’s subcontract laboratory for total and leachable inorganic compounds, as presented in Table 5. Soil samples will be collected below the ash/native soil interface and from the terminus of each boring to characterize soil quality beneath the ash management areas. Soil samples will be analyzed by HDR’s subcontract laboratory for total inorganics using the same constituents list proposed for the ash samples. INDEX PROPERTY SAMPLING AND ANALYSES Physical characteristics of ash and soil will be tested both in the field and in the laboratory to provide data for use in groundwater modeling. The location and depth of the index property Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 7.0 Assessment Work Plan 11 samples will be based on site-specific geology and decided upon in the field. Based on HDR’s current understanding of site-specific geology, five hydrostratigraphic units are present on-site. In general, a minimum of five in-situ permeability tests, either falling or constant head tests, will be performed in each of the hydrostratigraphic units. In addition, a minimum of five packer tests will be performed in bedrock. Laboratory testing of soil and ash collected from SPT samples will include tests for grain size (with hydrometer), specific gravity, and porosity (calculation). 7.2 Groundwater Sampling Plan Groundwater samples will be collected from the proposed wells shown on Figure 3. Groundwater quality data may be supplemented through evaluation of historical data or re- sampling of select existing monitoring wells. The purpose and anticipated construction details of the proposed monitoring wells are as follows:  AB-series Wells – One shallow well screened across the water table (15-foot well screen) and one deep well with screen installed in the transition zone (5-foot well screen in weathered rock below auger refusal) will be installed at each location. The AB-series well locations were selected to provide water quality data in, beneath, and adjacent to the ash basin.  GWA-series Wells – One shallow well screened across the water table (15-foot well screen) and one deep well with screen installed in the transition zone (5-foot well screen in weathered rock below auger refusal) will be installed at each location. The GWA- series well locations were selected to provide water quality data beyond the waste boundary for use in groundwater modeling (i.e., to evaluate the horizontal and vertical extent of potentially impacted groundwater around the ash basin).  BG-series Wells – One shallow well screened across the water table (15-foot well screen) and one deep well with screen installed in the transition zone (5-foot well screen in weathered rock below auger refusal) will be installed at each location. The background well locations were selected to provide additional physical separation from possible influence of the ash basin on groundwater. These wells will also be useful in the statistical analysis to determine the site-specific background water quality concentrations (SSBCs). 7.2.1 Well Installation and Development SHALLOW MONITORING WELLS At each monitoring well location specified on Figure 3 with an “S” qualifier in the well name (e.g., AB-21S), a shallow well will be constructed with a 2-inch-diameter, schedule 40 PVC screen and casing. Each of these wells will have a 10-foot to 15-foot well screen (0.010-slot) set to bracket the water table at the time of installation. DEEP MONITORING WELLS At each monitoring well location specified on Figure 3 with a “D” qualifier in the well name (e.g., AB-21D), a double-cased deep well will be constructed with a 6-inch-diameter PVC outer casing Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 7.0 Assessment Work Plan 12 and a 2-inch-diameter PVC inner casing and well screen. The purpose of installing cased wells at the site is to restrict vertical mixing within the shallow and deeper portions of the unconfined aquifer during well installation. Outer well casings (6-inch casing) will be advanced to auger refusal and set approximately 1 foot into PWR. Note that location-specific subsurface geology will dictate actual casing depths on a per-well basis. Air rotary drilling will be used to advance the borehole a minimum of 10 feet into PWR or bedrock with the intent of setting a 5-foot well screen at least 10 feet below the bottom of the outer casing. All newly installed monitoring wells will be developed using appropriate measures (e.g., agitation, surging, pumping, etc.). Water quality parameters (specific conductance, pH, temperature and turbidity) will be measured and recorded during development and should stabilize before development is considered complete. Development will continue until development water is visually clear (target < 50 Nephelometric Turbidity Units (NTU) Turbidity) and sediment free. Following development, sounding the bottom of the well with a water level meter should indicate a “hard” (sediment free) bottom. Development records will be prepared under the direction of the Project Scientist/Engineer and will include development method(s), water volume removed, and field measurements of temperature, pH, conductivity, and turbidity. 7.2.2 Hydrogeologic Evaluation Hydraulic conductivity (slug) tests will be completed in select monitoring wells under the direction of the Project Scientist/Engineer. Slug tests will be performed to meet the requirements of the NCDENR Memorandum titled, “Performance and Analysis of Aquifer Slug Tests and Pumping Tests Policy,” dated May 31, 2007. Water level change during the slug tests will be recorded by a data logger. In addition, approximately 5 to 10 packer tests will be conducted during installation of the Type III wells to facilitate permeability testing of the upper five feet of rock. 7.2.3 Groundwater Sampling Subsequent to monitoring well installation and development, each newly installed well will be sampled using low-flow sampling techniques. During low-flow purging and sampling, groundwater is pumped into a flow-through chamber at flow rates that minimize or stabilize water level drawdown within the well. Indicator parameters are measured over time (usually at 5-minute intervals). When parameters have stabilized within ±0.2 pH units and ±10 percent for temperature, conductivity, and dissolved oxygen (DO), and ±10 millivolts (mV) for oxidation reduction potential (ORP) over three consecutive readings, representative groundwater has been achieved for sampling. Turbidity levels of 10 NTU or less will be targeted prior to sample collection. Groundwater samples will be analyzed by a North Carolina certified laboratory for the constituents included in Table 6. Select constituents may be analyzed for total and dissolved concentrations. 7.3 Surface Water Sampling Plan 7.3.1 Ash Basin Surface Water Samples Surface water samples will be collected from the active ash basin at the approximate open water locations shown on Figure 3 (SW -1 through SW -4). At each location two water samples Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 7.0 Assessment Work Plan 13 will be collected – one sample close to the surface (i.e., 0 to 1 foot from surface) and one sample at the approximate middle depth of the water body. The middle depth sample will vary based on the water level in the water body. In areas where the water body is less than 5 feet deep, one water sample will be collected from the location at the approximate middle depth of the water body. Ash basin surface water samples will be analyzed for the same constituents as groundwater samples (Table 6). Select constituents may be analyzed for total and dissolved concentrations. 7.3.2 Seep Samples Water samples will be collected from the seep sample locations shown on Figure 3 (S-1 through S-9). The seep samples will be collected for laboratory analysis of the constituents listed in Table 6. Select constituents may be analyzed for total and dissolved concentrations. Duke Energy collects surface water samples from Lake Wylie from upstream and downstream locations for their existing NPDES permit requirements. If seep analytical results indicate potential for impacts to Lake Wylie, then surface water quality data collected in Lake Wylie will be reviewed. 7.4 Site Hydrogeologic Conceptual Model The data obtained during the proposed assessment will be supplemented by available reports and data on site geotechnical, geologic, and hydrologic conditions to develop a site hydrogeologic conceptual model (SCM). The NCDENR document, “Hydrogeologic Investigation and Reporting Policy Memorandum,” dated May 31, 2007 (Reference 6), will be used as general guidance. In general, the SCM will utilize site information to characterize the geologic and hydrogeologic characteristics of the area of interest, and, where appropriate, lead directly to the proper construction of a groundwater flow and transport model. 7.5 Site-Specific Background Concentrations Statistical analysis will be performed to determine the SSBCs to assess whether or not exceedances can be attributed to naturally occurring background concentrations or attributed to potential contamination. Specifically, the relationship between exceedances and turbidity will be explored to determine whether or not there is a possible correlation due to naturally occurring conditions and/or well construction. 7.6 Groundwater Model Groundwater flow and chemical constituent fate and transport at the site will be modeled in three dimensions using the MODFLOW -2005 groundwater flow numeric engine and the MT3D transport model with linear isotherm sorption to predict chemical constituent concentrations over time at the compliance boundary. The groundwater model layers will be developed based on hydrogeologic properties and other data obtained during the site investigation and the SCM. The model will include the effects of recharge from precipitation. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 7.0 Assessment Work Plan 14 Site soil samples will be collected and used to develop site-specific distribution coefficient, Kd, terms using batch methods (US EPA Batch-type procedures for estimating soil adsorption of chemicals Technical Resource Document 530/SW-87/006-F). The selection of the initial concentrations and the predictions of the concentrations for constituents with respect to time are to be developed with consideration of the following data:  Site-specific analytical results from leach tests and from total digestion of ash samples taken at varying locations and depths within the ash basin and ash storage piles (if present),  Analytical results from appropriate groundwater monitoring wells or surface water sample locations outside of the ash basin,  Analytical results from monitoring wells installed in the ash basin pore-water (screened in ash), and  Published or other data on sequential leaching tests performed on similar ash. The groundwater modeling will be conducted in general conformance with the requirements of the May 31, 2007, NCDENR Memorandum titled, Groundwater Modeling Policy. The groundwater model and the report on the results of the groundwater modeling will be prepared by Dr. William Langley, P.E., Department of Civil and Environmental Engineering, University of North Carolina at Charlotte. Dr. Langley will perform the work under contract with HDR and the groundwater model report will be included as an attachment to the CSA. The groundwater model will be used, as required, to evaluate options for potential corrective action in the subsequent phase of work. Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 8.0 Proposed Schedule 15 8.0 Proposed Schedule Duke Energy will submit the CSA Report within 180 days of NCDENR approval of this Work Plan. The anticipated schedule for implementation of field work, evaluation of data, and preparation of the Work Plan is presented in the table below. Activity Start Date Duration to Complete Field Exploration Program 10 days following Work Plan approval 75 days Receive Laboratory Data 14 days following end of Exploration Program 15 days Evaluate Lab/Field Data, Develop SCM 5 days following receipt of Lab Data 30 days Prepare and Submit CSA 10 days following Work Plan approval 170 days Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan Allen Steam Station Ash Basin 9.0 References 16 9.0 References 1. Fenneman, Nevin Melancthon. “Physiography of eastern United States.” McGraw-Hill. 1938. 2. Heath, R.C., 1984, “Ground-water regions of the United States.” U.S. Geological Survey Water-Supply Paper 2242, 78 p. 3. LeGrand, Harry E. 2004. “A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina, A Guidance Manual,” North Carolina Department of Environment and Natural Resources Division of Water Quality, Groundwater Section. 4. NCDENR Memorandum “Performance and Analysis of Aquifer Slug Tests and Pumping Tests Policy,” May 31, 2007. 5. NCDENR document, “Hydrogeologic Investigation and Reporting Policy Memorandum,” dated May 31, 2007. 6. US EPA Batch-type procedures for estimating soil adsorption of chemicals Technical Resource Document 530/SW -87/006-F. Figures Tables Table 1 – Groundwater Monitoring Requirements Well Nomenclature Constituents and Parameters Frequency Monitoring Wells: AB-1R, AB-4S, AB-4D, AB-9S*, AB-9D*, AB-10S*, AB-10D*, AB-11D, AB-12S, AB-12D, AB-13S, AB-13D, AB-14D Antimony Chromium Nickel Thallium March, July, November Arsenic Copper Nitrate Water Level Barium Iron pH Zinc Boron Lead Selenium Cadmium Manganese Sulfate Chloride Mercury TDS Note: Monitoring wells marked with * are located inside of the compliance boundary. TABLE 2 – MONITORING WELL LOCATIONS Monitoring Well Locations Monitoring Well At or Near the Compliance Boundary AB-1R, AB-4S, AB-4D, AB-11D, AB-12S, AB-12D, AB-13S, AB-13D, AB-14D Inside of the Compliance Boundary AB-9S, AB-9D, AB-10S, AB-10D TABLE 3 – EXCEEDANCES OF 2L STANDARDS MARCH 2011 – JULY 2014 Parameter Boron Iron Manganese Nickel pH Units µg/L µg/L µg/L µg/L SU 2L Standard 700 300 50 100 6.5 - 8.5 Well ID Range of Exceedances AB -1R No Exceedances 381 No Exceedances No Exceedances 5.9 – 6.2 AB-4S No Exceedances 314 – 555 64 – 285 No Exceedances 5.8 – 6.1 AB -4D No Exceedances No Exceedances No Exceedances No Exceedances 5.8 – 6.3 AB-9S 708 – 740 5,600 – 10,500 9,320 – 10,200 No Exceedances 6.1 – 6.4 AB -9D No Exceedances 356 – 909 95 No Exceedances 6.4 AB -10S No Exceedances 333 - 704 373 - 526 No Exceedances 5.9 – 6.3 AB-10D No Exceedances 307 – 881 53 – 144 No Exceedances 5.9 – 6.4 AB-11D No Exceedances 355 – 844 No Exceedances No Exceedances 5.5 – 6.1 AB -12S No Exceedances 573 53 – 56 No Exceedances 4.7 – 5.2 AB-12D No Exceedances 307 – 823 No Exceedances No Exceedances 6.1 – 6.4 AB -13S No Exceedances 324 – 817 55 – 165 No Exceedances 5.3 – 5.9 AB-13D No Exceedances 391 – 3,100 57 – 240 No Exceedances 5.9 – 6.4 AB-14D No Exceedances 301 – 8,350 52 – 945 104 – 544 5.2 – 6.2 TABLE 4 – ENVIRONMENTAL EXPLORATION AND SAMPLING PLAN ALLEN STEAM STATION Exploration Area Soil Borings Shallow Monitoring Wells Deep Monitoring Wells Surface Water Boring IDs Quantity Estimated Boring Depth (ft bgs) Well IDs Quantity Estimated Well Depth (ft bgs) Screen Length (ft) Well IDs Quantity Estimated Casing Depth (ft bgs) Estimated Well Depth (ft bgs) Screen Length (ft) Quantity of Locations Quantity of Samples Active Ash Basin AB-20 through AB-28 9 70-120 AB-20S through AB-28S 9 15-50 10-15 AB-20D through AB-28D 9 55-105 70-120 5 4 8 Inactive Ash Basin AB-29 through AB-9, SB-1 through SB-6 17 45-110 AB-29S through AB-39S 11 15-60 10-15 AB-29D through AB-39D 11 30-95 45-110 5 N/A N/A Beyond Waste Boundary N/A 0 N/A GWA-1S through GWA-9S 9 20-35 15 GWA-1D through GWA-9D 9 30-75 45-90 5 N/A N/A Background BG-1, BG-2, and BG-3 3 60-120 BG-1S, BG-2S, and BG-3S 3 30-55 15 BG-1D, BG-2D, and BG-3D 3 45-105 60-120 5 N/A N/A Notes: 1. Estimated boring and well depths based on data available at the time of work plan preparation and subject to change based on site -specific conditions in the field. 2. Laboratory analyses of soil, ash, groundwater, and surface water samples will be performed in accordance with the constitu ents and methods identified in Tables 5 and 6. 3. Additionally, soils will be tested in the laboratory to determine grain size (with hydrometer), specific gravity, and perm eability. 4. During drilling operations, downhole testing will be conducted to determine in-situ soil properties such as horizontal and vertical hydraulic conductivity. 5. Actual number of field and laboratory tests will be determined in field by Field Engineer or Geologist in accordance with project specifications. TABLE 5 – SOIL AND ASH PARAMETERS AND ANALYTICAL METHODS INORGANIC COMPOUNDS UNITS METHOD Antimony mg/kg EPA 6020 Arsenic mg/kg EPA 6020 Barium mg/kg EPA 6010 Boron mg/kg EPA 6010 Cadmium mg/kg EPA 6020 Chloride mg/kg SM4500-Cl-E Chromium mg/kg EPA 6010 Copper mg/kg EPA 6010 Iron mg/kg EPA 6010 Lead mg/kg EPA 6020 Manganese mg/kg EPA 6010 Mercury mg/kg EPA Method 7470A/7471 Nickel mg/kg EPA 6010 pH SU EPA 9045 Selenium mg/kg EPA 6020 Thallium (low level) mg/kg EPA 6020 Zinc mg/kg EPA 6010 Notes: 1. Soil samples to be analyzed for Total Inorganics using USEPA Methods 6010/6020 and pH using USEPA Method 9045, as noted above. 2. Ash samples to be analyzed for Total Inorganics using USEPA Methods 6010/6020 and pH using USEPA Method 9045; select ash samples will also be analyzed for leaching potential using SPLP Extraction Method 1312 in conjunction with USEPA Methods 6010/6020. SPLP results to be reported in units of mg/L for comparison to 2L Standards. 1 TABLE 6 – GROUNDWATER, SURFACE WATER, AND SEEP PARAMETERS AND ANALYTICAL METHODS PARAMETER UNITS METHOD FIELD PARAMETERS pH SU Field Water Quality Meter Specific Conductance mmho/cm Field Water Quality Meter Temperature ºC Field Water Quality Meter Dissolved Oxygen mg/L Field Water Quality Meter Oxidation Reduction Potential mV Field Water Quality Meter NPDES CONSTITUENTS Antimony µg/L EPA 200.8 or 6020 Arsenic µg/L EPA 200.8 or 6020 Barium µg/L EPA 200.7 or 6010 Boron µg/L EPA 200.7 or 6010 Cadmium µg/L EPA 200.8 or 6020 Chloride mg/L EPA 300.0 Chromium µg/L EPA 200.7 or 6010 Copper mg/L EPA 200.7 or 6010 Iron µg/L EPA 200.7 or 6010 Lead µg/L EPA 200.8 or 6020 Manganese µg/L EPA 200.7 or 6010 Mercury µg/L EPA 245.1 Nickel µg/L EPA 200.7 or 6010 Nitrate as Nitrogen mg-N/L EPA 300.0 Selenium µg/L EPA 200.8 or 6020 Sulfate mg/L EPA 300.0 Thallium (low level) µg/L EPA 200.8 or 6020 Total Dissolved Solids mg/L EPA 160.1 or SM 2540C Zinc mg/L EPA 200.7 or 6010 ADDITIONAL GROUNDWATER CONSTITUENTS Alkalinity (as CaCO3) mg/L SM2320B Calcium mg/L EPA 200.7 Ferrous Iron mg/L SM4500-Fe Magnesium mg/L EPA 200.7 Potassium mg/L EPA 200.7 Sodium mg/L EPA 200.7 Sulfide mg/L SM4500S-F Total Organic Carbon mg/L SM5310 Note: 1. Select constituents may be analyzed for total and dissolved concentrations. Appendix A Notice of Regulatory Requirements Letter from John E. Skvarla, III, Secretary, State of North Carolina, to Paul Newton, Duke Energy, dated August 13, 2014.