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HomeMy WebLinkAboutNC0038377_GW Assessment WP_20141001Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra TABLE OF CONTENTS SECTION PAGE Executive Summary 1.0 Introduction ......................................................................................................................1 2.0 Site History and Source Characterization ...................................................................3 2.1 Plant Description .........................................................................................................3 2.2 Ash Basin ......................................................................................................................3 2.3 Groundwater Monitoring System ............................................................................3 3.0 Receptor Information ......................................................................................................5 4.0 Regional Geology and Hydrogeology .........................................................................7 5.0 Site Geology and Hydrogeology ...................................................................................8 6.0 Groundwater Monitoring Results ................................................................................9 6.1 Groundwater Analytical Results ..............................................................................9 6.2 Preliminary Statistical Evaluation Results ..............................................................9 7.0 Assessment Work Plan..................................................................................................11 7.1 Anticipated Ash Basin Boring Locations ...............................................................11 7.2 Anticipated Soil Boring Locations ..........................................................................12 7.2.1 Inside Ash Basin ..................................................................................................12 7.2.2 Outside Ash Basin ...............................................................................................12 7.3 Anticipated Sediment and Surface Water Locations ...........................................13 7.4 Anticipated Groundwater Monitoring Wells .......................................................13 7.4.1 General Construction, Development, Aquifer Testing ..................................13 7.4.2 Background Wells ...............................................................................................15 7.4.3 Ash Basin Area ....................................................................................................15 7.4.4 Downgradient Assessment Areas ....................................................................15 7.4.5 Groundwater Sampling .....................................................................................16 7.5 Influence of Pumping Wells on Groundwater System ........................................16 7.6 Site Conceptual Model .............................................................................................17 7.7 Development of Groundwater Computer Model ................................................17 8.0 Implementation Schedule and Report Submittal ....................................................18 9.0 References ........................................................................................................................20 Page i P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra List of Figures Figure 1 - Site Location Map Figure 2 - Site Layout Figure 3 - Geology Map Figure 4 - Anticipated Sample Locations List of Tables Table 1 - Summary of Concentration Ranges for Constituents Detected Greater than 2L Standards Table 2 - Groundwater Assessment Parameter List Table 3 - Assessment Sampling Plan List of Appendices Appendix A - NCDENR Letter of August 13, 2014 Page ii P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra EXECUTIVE SUMMARY Duke Energy Progress, Inc. (Duke Energy), owns and operates the Mayo Steam Electric Plant (Mayo Plant), located near Roxboro, in Person County, North Carolina. The coal ash residue from the coal combustion process has been placed in the plant’s ash basin, which is 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) #NC003837. In a letter dated August 13, 2014, the DWR requested that Duke Energy prepare a Groundwater Assessment Plan to identify the source and cause of contamination, any imminent hazards to public health and safety and actions taken to mitigate them, all receptors and significant exposure pathways. In addition, the plan should determine the horizontal and vertical extent of soil and groundwater contamination and all significant factors affecting contaminant transport and the geological and hydrogeological features influencing the movement, chemical, and physical character of the contaminants. The following assessment plan anticipates: • Implementation of a receptor survey to identify public and private water supply wells (including irrigation wells and unused or abandoned wells), surface water features, and wellhead protection areas (if present) within a 0.5 mile radius of the Mayo Plant waste compliance boundary; • Installation of borings within the ash basin and former 1981 landfill permit #73-B for chemical and geotechnical analysis of residuals and in-place soils; • Installation of background soil borings; • Installation of monitoring wells and piezometers; • Collection and analysis of groundwater samples from existing site wells and newly installed monitoring wells; • Statistical evaluation of groundwater analytical data; and • Development of a groundwater model to evaluate the long term fate and transport of constituents of concern in groundwater associated with the ash basin. The information obtained through this Work Plan will be utilized to prepare a comprehensive site assessment (CSA) report in accordance with the Notice of Regulatory Requirements (NORR). In addition to the components listed above, a P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra human health and ecological risk assessment will be conducted. This assessment will include the preparation of a conceptual site model illustrating potential pathways from the source to possible receptors. During the CSA process if additional investigations are required, NCDENR will be notified. P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 1.0 INTRODUCTION Duke Energy Progress, Inc. (Duke Energy), owns and operates the Mayo Steam Electric Plant (Mayo Plant), located near Roxboro, in Person County, North Carolina (Figure 1). The Plant is a single unit, coal-fired electricity-generating facility. Coal combustion residues (CCR) have historically been managed in the Plant’s on-site ash basin. 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 Pollution Discharge Elimination System (NPDES). Dry ash has been hauled and disposed in the lined dry flyash (DFA) landfill located at the nearby Roxboro Steam Electric Plant (near Semora, NC). It is anticipated that beginning in Fall 2014, CCR from the Plant will be managed in a newly constructed on-site landfill. Groundwater monitoring has been performed in accordance with the conditions of NPDES Permit #NC0038377 beginning in December 2010. A monitoring network of 10 compliance wells is employed. Elevated concentrations greater than the North Carolina Administrative Code (NCAC) Title 15A Chapter 02L (g) groundwater quality standards (2L Standards) for iron (seven wells, including background wells), manganese (nine wells, including background wells), total dissolved solids (TDS; two wells), and boron (one well, CW-2) have been detected. The compliance boundary for the Mayo ash basin is defined in accordance with NCAC Title 15A Chapter 02L.0107(a) (T15 A NCAC 02L .0107(a)) as being established at either 500 feet from the waste boundary or at the property boundary, whichever is closest. Monitoring wells CW-1, CW-1D, CW-2, CW- 2D, CW-3, CW-4, CW-5, and CW-6 are located at or near the compliance boundary. Wells BG-1 and BG-2 are located southwest, upgradient, of the ash basin and are considered background wells. In a Notice of Regulatory Requirements (NORR) letter dated August 13, 2014, the DWR of the NCDENR requested that Duke Energy prepare a Groundwater Assessment Plan to conduct a Comprehensive Site Assessment (CSA) in accordance with 15A NCAC 02L .0106(g) to address elevated groundwater concentrations greater than 2L Standards at the compliance boundary. A summary of the concentrations is provided in Table 1 and a copy of the DWR letter is provided in Appendix A. SynTerra has prepared this Groundwater Assessment Plan on behalf of Duke Energy to fulfill the DWR letter request and to satisfy the requirements of NC Senate Bill 729 as ratified August 2014. Specifically, this document describes the plans to meet the requirements of 15A NCAC 02L .0106(g) including; Page 1 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra • Identify the source and cause of contamination; • Identify any imminent hazards to public health and safety and actions taken to mitigate them in accordance to 15A NCAC 02L .0106(f); • Identify receptors and significant exposure pathways; • Determine the horizontal and vertical extent of soil and groundwater contamination and significant factors affecting contaminant transport; and • Determine geological and hydrogeological features influencing the movement, chemical, and physical character of the contaminants. The information obtained through this Work Plan will be utilized to prepare a comprehensive site assessment (CSA) report in accordance with the requirements of the NORR. In addition to the components listed above, a human health and ecological risk assessment will be conducted. This assessment will include the preparation of a conceptual site model illustrating potential pathways from the source to possible receptors. During the CSA process if additional investigations are required, NCDENR will be notified. Page 2 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 2.0 SITE HISTORY AND SOURCE CHARACTERIZATION 2.1 Plant Description The Mayo Plant is a coal-fired electricity-generating facility located in Person County, North Carolina, near the city of Roxboro. The location of the plant is shown on Figure 1. The Mayo Plant became fully operational in June 1983. The plant is located on Boston Road (US Highway 501) north of Roxboro. The northern plant property line extends to the North Carolina/Virginia state line. The overall topography of the Plant generally slopes toward the east (Mayo Reservoir) and northeast (Crutchfield Branch). 2.2 Ash Basin The Mayo Plant ash basin is approximately 153 acres in size with an earthen dike. Ash generated from the plant’s coal combustion is contained in the ash basin. The Mayo Plant NPDES permit (NC0038377) authorizes two discharges to Mayo Lake. Outfall 001 discharges cooling tower water and circulating water system discharge water. Outfall 002 is comprised of a number of streams including internal outfall 008 (cooling tower blowdown), internal outfall 009 (FGD blowdown), ash transport water, coal pile runoff, and other sources including water from wastewater treatment processes. Stormwater outfalls are also authorized for the Mayo Plant. 2.3 Groundwater Monitoring System Ten wells comprise the compliance monitoring well network for the Mayo Plant, two background wells and eight downgradient wells. The locations of the compliance monitoring wells, the waste boundary, and the compliance boundary are shown on an aerial image, Figure 2, and on a geologic map, Figure 3. Monitoring wells BG-1 and BG-2 represent background groundwater quality upgradient (southwest) of the ash basin. The compliance boundary wells on the east side of the ash basin are well pair CW-1/CW-1D. Monitoring well CW-5 is the compliance boundary well for the west side of the ash basin. Monitoring wells CW- 2/CW-2D, CW-3, CW-4, and CW-6 are downgradient compliance boundary wells to the north and northeast of the ash basin. In accordance with the current NPDES permit, the monitoring wells are sampled three times per year in April, July, and November. The analytical results for the compliance monitoring program are compared to the 2L Standards or site-specific background concentrations. A summary of the NPDES monitoring requirements is provided below. Page 3 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra It is proposed that monitoring for aluminum be discontinued. Aluminum is a very common, naturally-occurring element in soil and rocks of the area. A preliminary statistical evaluation indicates that aluminum concentrations in downgradient compliance monitoring wells are not statistically significant increases (SSIs) over the background well data set for the most recent sampling event. Further, aluminum is not consistently monitored across the entirety of Duke Energy facilities, and there is no 2L Standard for aluminum. NPDES Groundwater Monitoring Requirements Well Nomenclature Parameter Description Frequency Monitoring Wells BG-1, BG-2, CW-1, CW-1D, CW-2, CW-2D, CW-3, CW-4, CW-5, CW-6 Aluminum Chloride Mercury TDS April, July, and November Antimony Chromium Nickel Thallium Arsenic Copper Nitrate Water Level Barium Iron pH Zinc Boron Lead Selenium Cadmium Manganese Sulfate Page 4 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 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, SynTerra is in the process of conducting a receptor survey to identify water supply wells, public water supplies, surface water bodies, and wellhead protection areas (if present) within a 0.5 mile radius of the Mayo Plant compliance boundary. The compliance boundary for groundwater quality, in relation to the ash basins, is defined in accordance with 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 receptors include 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 Lee Plant compliance boundary. The survey consists of a review of publicly available data from NCDENR Department of Environmental Health (DEH), Virginia Department of Environmental Quality, NC OneMap GeoSpatial Portal, DWR Source Water Assessment Program (SWAP) online Page 5 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra database, Person County GIS, Environmental Data Resources, Inc. (EDR) Records Review, the USGS National Hydrography Dataset (NHD), as well as a vehicular survey along public roads located within 0.5 mile radius of the compliance boundary. Two primary surface water features are present within the 0.5 mile radius of the compliance boundary. Mayo Lake, located to the east of the Plant, is a 2,800-acre lake formed in 1977. Crutchfield Branch is a prominent fluvial surface water drainage feature on the Plant. Crutchfield Branch originates near the base of the ash basin and flows towards the north/northeast, crossing into Virginia, and eventually merging with Mayo Creek. Additional receptor information will be collected as part of the anticipated assessment to comply with the CSA guidelines (NCDENR August 2014). Page 6 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 4.0 REGIONAL GEOLOGY AND HYDROGEOLOGY The Mayo Plant is situated in the eastern Piedmont Region of north-central North Carolina. The Piedmont is characterized by well-rounded hills and rolling ridges cut by small streams and drainages. Elevations in the area of the Mayo Plant range between 570 feet above mean sea level (msl) near the Plant entrance along Boston Road to 360 feet msl in the Crutchfield Branch stream area on the north side of the Plant. Geologically, the Plant is located at the contact between two regional zones of metamorphosed intrusive rocks: the Carolina Slate Belt (now referred to as Carolina Terrane) on the east and the Charlotte Belt (or Charlotte Terrane) to the west (Figure 3). The majority of the Mayo Plant, including the largest portion of the ash basin and Mayo Lake are situated in the Carolina Terrane (USGS, 2007). The characteristics and genesis of the rocks within these regional metamorphic belts have been the subject of intense study to describe the geology in tectonic, structural, and/or litho-stratigraphic terms (Hibbard, et. al., 2001). Rocks of Charlotte Terrane are characterized by strongly foliated felsic mica gneiss and schist and metamorphosed intrusive rocks. Carolina Terrane rocks in the vicinity of the Plant are typically felsic meta-volcanics and meta-argillites. This is consistent with the description of the geologic nature of the area according to the Geologic Map of North Carolina (1985). The Geologic Map of North Carolina describes the felsic meta-volcanic rock as metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; interbedded with mafic and intermediate volcanic rock, meta-argillite and meta- mudstone. The felsic mica gneiss of the Charlotte Terrane is described as being interlayered with biotite and hornblende schist. These general observations are consistent with site-specific observations from well logs for the Mayo Plant, which document the bedrock of the northwestern portion of the compliance boundary as intermediate meta-volcanic rock and the bedrock of the remainder of the site as felsic meta-volcanics or meta-argillites. Rocks of the region, except where exposed in road cuts, stream channels, and steep hillsides, are covered with unconsolidated material formed from the in-situ chemical and physical breakdown of the bedrock. This unconsolidated material is referred to as saprolite or residuum. Direct observations at the Mayo Plant confirm the presence of residuum, developed above the bedrock, which is generally 10 to 30 feet thick. The residuum extends from the ground surface (soil zones) downward, transitioning through a zone comprised of unconsolidated silt and sand, downward through a transition zone of partially weathered rock in a silt/sand matrix, down to the contact with competent bedrock. Page 7 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 5.0 SITE GEOLOGY AND HYDROGEOLOGY Based on previous activities at the site, subsurface lithology beneath the Plant area is comprised of tan, brown to orange sandy silt and fine to coarse sands grading into partially weathered rock and then competent bedrock. The first occurrence of groundwater tends to be within the partially weathered rock or competent bedrock at depths ranging from nine to 20 feet below land surface (bls) along the downgradient compliance boundary and greater than 30 feet bls upgradient of the ash basin. The layout of the compliance boundary wells relative to the mapped geologic units is shown on Figure 3. Groundwater within the area exists under unconfined, also known as water table, conditions within the residuum and/or saprolite zones and in the fractures and joints of the underlying bedrock. The water table and bedrock aquifers are interconnected. The residuum acts as a reservoir for water supply to the fractures and joints in the underlying bedrock. Shallow groundwater generally flows from local recharge zones in topographically high areas, such as ridges, toward groundwater discharge zones, such as stream valleys. Ridge and topographic high areas may serve as groundwater recharge zones. Groundwater flow patterns in recharge areas tend to develop a somewhat radial pattern from the center of the recharge area outward toward the discharge areas and are expected to mimic surface topography. The closest surface water discharge for the plant is to the north-northeast at Crutchfield Branch and, for the eastern portions of the property, to the east and Mayo Lake. Routine water level measurements and corresponding elevations from the compliance monitoring well network indicate that groundwater flows from upland areas (southwestern portion of the property) towards the northeast and Crutchfield Branch. The approximate groundwater gradient for July 2014 data was 135 feet (vertical change) over 5,500 feet (horizontal distance) or 24.5 feet/1,000 feet as measured from upgradient background well BG-2 to downgradient well CW-2. Groundwater elevation data collected from the two well pairs indicate the vertical gradient tends to be downward or neutral between the transition zone and upper bedrock. Page 8 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 6.0 GROUNDWATER MONITORING RESULTS 6.1 Groundwater Analytical Results July 2014 was the twelfth compliance monitoring event conducted in accordance with the NPDES Permit. The routine analytical data indicates that boron, iron, manganese, total dissolved solids (TDS) and pH tend to have concentrations greater than 2L Standards. Boron tends to be detected near or greater than the 2L Standard in compliance boundary well CW-2. Iron tends to be detected greater than the 2L Standard in background wells BG-1 and BG-2 and compliance boundary wells CW-5 and CW-6. Manganese tends to be detected greater than the 2L Standard in background well BG-2 and in compliance boundary wells CW-2, CW-2D, CW-5, and CW-6. TDS tends to be similar to or greater than the 2L Standard in compliance boundary wells CW-3 and CW-6. In general, the groundwater pH tends to be slightly less than or within the 2L Standard range. The concentration ranges for the constituents which are greater than the 2L Standards are provided in Table 1. Antimony, barium, cadmium, chromium, lead, and thallium have each been detected in at least one background or compliance boundary well at concentrations greater than the 2L Standard. However, these constituents have not been detected at elevated concentration with regularity and are believed to be related to sample turbidity or represent data outliers. 6.2 Preliminary Statistical Evaluation Results As a preliminary evaluation tool, statistical analysis was conducted on the groundwater analytical data collected between December 2010 and July 2014. The statistical analysis was conducted in accordance with US EPA, Statistical Training Course for Ground Water Monitoring Data Analysis, EPA530-R-93-003, 1992 and US EPA’s Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities; Unified Guidance EPA 530/R-09-007, March 2009. An inter-well prediction interval statistical analysis was utilized to evaluate the groundwater data. The inter-well prediction interval statistical evaluation involves comparing background well data to the results for the most recent sample date from compliance boundary wells. Monitoring wells BG-1 and BG-2 are the upgradient background wells. Monitoring wells CW-1, CW-1D, CW-2, CW-2D, CW-3, CW-4, CW- 5, and CW-6 are considered downgradient compliance boundary wells. Statistical analysis was performed on the inorganic constituents with detectable concentrations for the most recent routine sampling event (July 2014). Page 9 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra The statistical analysis indicated statistically significant increases (SSIs) over background concentrations for the following: • CW-1 nitrate (however, the concentration is consistently much less than the 2L Standard); • CW-2 boron and sulfate (Concentrations for both constituents are consistently less than the 2L Standard); • CW-2D boron and sulfate (Concentrations for both constituents are consistently less than the 2L Standard); • CW-3 chloride and sulfate (Concentrations for both constituents are consistently much less than the 2L Standard); • CW-4 sulfate (however, the concentration is consistently much less than the 2L Standard); and • CW-6 chloride (which is consistently less than the 2L Standard), manganese (which is consistently greater than the 2L Standard), and sulfate (which is consistently less than the 2L Standard). It is noteworthy that the current data for CW-5 indicates no SSIs over background concentrations. Based upon topography and available water levels, CW-5 appears to be located upgradient of the influence of the ash basin. A more robust statistical analysis will be completed as part of the CSA using data from additional background wells. Page 10 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 7.0 ASSESSMENT WORK PLAN The scope of work discussed in this plan is designed to meet the requirements of 15A NCAC 02L .0106(g) which are: • Identify the source and cause of contamination; • Identify any imminent hazards to public health and safety and actions taken to mitigate them in accordance to 15A NCAC 02L .0106(f); • Identify all receptors and significant exposure pathways; • Determine the horizontal and vertical extent of soil and groundwater contamination and all significant factors affecting contaminant transport; and • Determine geological and hydrogeological features influencing the movement, chemical, and physical character of the contaminants. The following sections generally describe anticipated assessment activities to fill data gaps associated with the source, vertical and horizontal extent, in soil and groundwater, for the constituents that are greater than the 2L Standards. The assessment may need to be iterative with possible additional assessment activities prior to the preparation of the CSA. Groundwater sample collected will generally be analyzed for the constituents listed in Table 2. The following activities are anticipated at this time. 7.1 Anticipated Ash Basin Boring Locations Borings are anticipated within the ash basin to determine the thickness of ash as well as to determine the current residual saturation. Seven borings are anticipated in the ash basin near the locations shown on Figure 4. The borings may be conducted using Direct Push Technology (DPT) or Roto-Sonic drilling (or other drilling methods), which is a core drilling method that employs simultaneous high frequency vibration and low speed rotational motion along with downward pressure to advance a recovery core barrel. The core barrel is generally advanced at continuous intervals of 5 to 10 feet. The ash/soil core is then brought to the surface and vibrated from the barrel into a plastic sleeve for visual classification, sample collection, and optional storage in wooden core boxes. The Roto-Sonic cores will be extended to approximately 20 feet below the bottom of the ash (if possible) to allow for characterization of the underlying native soil, partially weathered rock or competent bedrock. Page 11 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra Ash samples will be collected for laboratory analysis of total metals and SPLP metals plus various geotechnical parameters. To characterize the variation in ash composition, two samples, a shallow and a deep, are anticipated at each location, if the ash thickness is less than 20 feet. If the thickness is greater than 20 feet, three samples (shallow, intermediate, and deep), may be collected. A summary of the boring details is provided in Table 3. The depths at which the samples are collected will be noted on sample IDs. 7.2 Anticipated Soil Boring Locations 7.2.1 Inside Ash Basin As discussed above, Roto-Sonic drilling (or similar technology) may be used to conduct borings within the ash basin. These borings are anticipated to extend to a depth of approximately 20 feet below the ash (if possible) to characterize the native material below the ash basin. Soil samples are anticipated at each of the boring locations immediately below the ash and at the bottom of the borings to provide information on the vertical distribution of metals beneath the basin. The soil samples will be analyzed for total metals, SPLP metals, and geotechnical parameters (such as plasticity index, grain-size w/ hydrometer, pH, and organic carbon content). A summary of the anticipated boring details is provided in Table 3. Following soil sample collection, the borings will be abandoned by filling with a bentonite-grout mixture. 7.2.2 Outside Ash Basin To characterize the vertical and horizontal extent of metals in soil or partially weathered rock beyond the ash basin, background soil borings are anticipated at the locations shown on Figure 4. Hollow stem auger drilling (or similar technology) will be conducted along with Standard Penetration Test (SPT) to complete the soil borings. Hollow stem auger methods use continuous flight augers with a bit on the bottom that drives cuttings to the surface during the drilling process. SPTs are generally performed at five-foot intervals in the borings. Soil samples are obtained with a standard 1.4-inch ID/2-inch outside diameter (OD) split-tube sampler. In conjunction with the SPTs, split-spoon soil samples can be examined for visual soil classification and laboratory testing. Page 12 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra Along with split-spoon samples, relatively undisturbed samples are anticipated for potential laboratory testing. Samples may be collected using a Shelby Tube sampler to obtain the undisturbed samples per ASTM D1587 (2008). Shallow and deep soil samples are anticipated at each boring location if possible. The shallow soil samples would be collected from the 1-2 foot interval and the deep soil samples would be collected from immediately above the water table to provide information on the vertical distribution of metals beyond the ash basin and to be used as comparison with those soil samples collected below the ash basin. The collected soil samples would be analyzed for total metals, SPLP metals, and geotechnical parameters (Table 3). If the water table occurs below the depth of competent bedrock, a soil sample near the depth of auger refusal may be collected as the ‘deep’ soil sample. Following collection of the soil samples, the borings will be abandoned by filling with a bentonite-grout mixture. 7.3 Anticipated Sediment and Surface Water Locations Surface water and sediment samples are not anticipated at this time. Data associated with recent seep sampling will be used to infer preferential pathways and migration from groundwater to surface water in various areas of the plant. Seep data analysis may be used to guide the collection of additional sediment or surface water data in the future. 7.4 Anticipated Groundwater Monitoring Wells A number of monitoring wells, piezometers and former plant production wells are present at the site. These existing wells will be supplemented with additional wells to complete the CSA. 7.4.1 General Construction, Development, Aquifer Testing Monitoring wells and piezometers will be constructed by North Carolina- licensed well drillers. Drilling equipment will be decontaminated prior to use at each location using a high pressure steam cleaner. Monitoring wells will be constructed of 2-inch ID, National Sanitation Foundation (NSF) grade polyvinyl chloride (PVC) (ASTM 2012a,b) schedule 40 flush-joint threaded casing and 0.010-inch machine-slotted screen. Monitoring wells will be installed as nested Type II wells at each location. A shallow well will be installed with the top of the well screen approximately 5 feet below the water table if possible. Based upon available drilling logs, the Page 13 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra residuum appears dry while drilling. Observable water tends to occur within the partially weathered rock (transition zone) and within competent bedrock. The deeper well will be installed to a depth of the first observed water bearing zone below the shallow screened interval, likely in competent bedrock. This will provide information on the vertical distribution of aquifer characteristics (chemistry and aquifer parameters) as well was determining the vertical hydraulic gradient. For nested Type II wells, the well screen intervals will typically be a 10 foot length for the shallow well and a 5 foot length for the deeper well. The deeper of the nested wells will be installed first. The annular space between the borehole wall and the well screens will be filled with clean, well-rounded, washed, high grade No. 2 silica sand. The sand pack will be placed to approximately 2 feet above the top of the slotted screen, and then a pelletized bentonite seal will be placed above the filter pack to just below the elevation of the anticipated bottom of the shallow well. The sand pack for the shallow well will then be placed to approximately 2 feet above the slotted screen. At a minimum, a 2-foot pelletized bentonite seal will be placed above the filter pack of the shallow screen. The remainder of the annular space will be filled with a neat cement grout from the top of the upper bentonite seal to near ground surface. The monitoring wells will be completed with either steel above ground protective casings with locking caps or steel flush-mount manholes with locking expansion caps, and well tags. The protective covers will be secured and completed in a concrete collar and 2-foot square concrete pad. Following installation, the monitoring wells will be developed in order to remove drill fluids, clay, silt, sand, and other fines which may have been introduced into the formation or sand pack during drilling and well installation, and to establish communication of the well with the aquifer. Well development will be performed using a portable submersible pump, which will be repeatedly moved up and down the well screen interval until the water obtained is relatively clear. Development will be continued by sustained pumping until monitoring parameters (e.g., conductivity, pH, temperature) are generally stabilized; estimated quantities of drilling fluids, if used, are removed; and, turbidity decreases to acceptable levels. After the wells have been developed, hydraulic conductivity tests (rising head slug tests) will be conducted on each of the wells. The slug tests will be performed in general accordance with ASTM D4044-96 Standard Test Method Page 14 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra (Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining Hydraulic Properties of Aquifers and NCDENR Performance and Analysis of Aquifer Slug Test and Pumping Test Policy, dated May 31, 2007. The data obtained during the slug tests will be reduced and analyzed using AQTESOLV™ for Windows, version 4.5, software to determine the hydraulic conductivity of the soils in the vicinity of wells. 7.4.2 Background Wells Existing background wells BG-1 and BG-2 are positioned to provide representative data for comparison with background groundwater conditions. Additional background well data will be useful to broaden the range of potential background groundwater concentrations. Therefore, two additional background well pairs (BG-3/BG-3D and BG-4/BG-4D) are anticipated along the southern side of the property as shown on Figure 4. A summary of the boring details is provided in Table 3. 7.4.3 Ash Basin Area To provide residual ash saturation and the depth to groundwater information, three piezometer pairs are anticipated within the ash basin as shown on Figure 4. A shallow piezometer, screened at the base of the ash, will be used to monitor residual saturation. A deeper piezometer, screened approximately 10 to 20 feet below the basin, will be used to monitor the aquifer below the basin. 7.4.4 Downgradient Assessment Areas A preliminary review of site data and existing monitoring well locations indicate that horizontal and vertical coverage around the compliance boundary is mostly adequate to complete a CSA of the Mayo Plant with the following exceptions. Near the northwest corner of the property, a bedrock well will be installed adjacent to compliance boundary well CW-5 to monitor groundwater conditions in the shallow bedrock at this location. In addition, a sentinel well pair will also be installed near the intersection of Hwy 501 and Mayo Lake Road to confirm the direction of groundwater flow is toward the northeast as would be expected based upon topography. A well pair will be installed on the west side of Boston Road, due west of the ash basin to monitor groundwater conditions at this location. A well pair will be installed downgradient of existing compliance well pair CW- 2/2D to monitor downgradient groundwater quality along Crutchfield Branch. Page 15 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra Toward the northeast, a well near the compliance boundary on the east side of the former 1981 landfill (Permit #73-B) and two well pairs further toward the northeast are anticipated to provide potentiometric data to refine the groundwater flow regime and water quality in the area. To the east, an additional well pair is anticipated to the northeast of the plant. The approximate locations of the additional monitoring well pairs are shown on Figure 4. A summary of the boring details is provided in Table 3. 7.4.5 Groundwater Sampling It is anticipated that groundwater samples will be collected using a low-flow sampling technique consistent with compliance monitoring well sampling protocol. The groundwater samples will be analyzed for the parameters listed in Table 2. Total and dissolved metals analysis will be conducted. In addition to the groundwater samples collected from the new monitoring wells, it is anticipated that groundwater samples will be collected from one or more of the existing site monitoring wells, as well as from the existing site water supply wells, if possible. A summary of the anticipated groundwater samples is included in Table 3. During groundwater sampling activities, water level measurements will be made at the existing site monitoring wells, piezometers, and new wells. The data will be used to generate water table and potentiometric maps of the transition zone and upper bedrock aquifer. 7.5 Influence of Pumping Wells on Groundwater System There are three former plant water supply wells located on the southern side of the property near the entrance road. The wells are no longer in use. Preliminary information indicates 21 potential water supply wells may be located within a 0.5 mile radius of the compliance boundary. The wells are believed to be located greater than 0.25 miles from the ash basin and in topographically upgradient positions. It is anticipated that due to the distance from the ash basin and likely limited withdrawal rates, the use of the off-site wells should not substantially affect the groundwater flow system near the ash basin. The anticipated new well pairs near the southern side of the property and near the northwest corner of the property will be used to confirm this assumption. Additional information on the potential off-site water supply wells will also be collected as part of the assessment. Page 16 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 7.6 Site Conceptual Model Using existing hydrogeological site data along with data that will be generated during the CSA activities, a Site Conceptual Model (SCM) will be prepared. The SCM will be prepared in accordance with Evaluating Metals in Groundwater at DWR Permitted Facilities (July 2012) and the NCDENR memorandum, Hydrogeologic Investigation and Reporting Policy (May 31, 2007). The SCM will define the groundwater flow systems at the site, horizontally and vertically, and provide a better understanding of the fate and transport of constituents of concern in groundwater. This information will be used to develop a groundwater computer model for Mayo Plant. Figure 4 shows the proposed locations for geologic cross sections anticipated for the SCM. 7.7 Development of Groundwater Computer Model Data from existing and new monitoring wells will be used to develop a groundwater computer model of the system. The groundwater modeling will be conducted in accordance with the requirements of the May 31, 2007 NCDENR memorandum, Groundwater Modeling Policy. At this time, it is anticipated that a numerical groundwater flow model will be developed using the MODFLOW finite difference model that was developed by the USGS and is one of the most widely accepted and widely used groundwater flow models. The MODFLOW model will be created as a multi-layer flow model to better determine the vertical flow component of the aquifer system which will allow for more accurate fate and transport modeling. Once the model is created, it will be calibrated to site conditions by modifying model inputs, such as hydraulic conductivity, within established limits based on actual site data, until a reasonable match between the model and actual site conditions is accomplished. After the MODFLOW model is calibrated, the modeled flow data will be imported into MT3D or RT3D and a fate and transport model will be created. MT3D and RT3D are three-dimensional numerical solute fate and transport model, which will be used to predict the short and long-term movement of the constituents of interest in groundwater at the site and under the various predictive scenarios discussed above. Due to the data requirements of the computer modelling, the computer model will be completed after the majority of the groundwater assessment activities. The results of the groundwater modelling are anticipated as an appendix to the CSA Report. Page 17 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 8.0 IMPLEMENTATION SCHEDULE AND REPORT SUBMITTAL Implementation will take place immediately following approval of this Groundwater Assessment Plan by DWR. The anticipated schedule of activities and project completion following plan approval is provided below. • 10 days to begin field activities upon approval of plan (Including, but not limited to, notification of public utility locate services, road access clearing, container requests from laboratories for the soil and groundwater samples, assemble information on existing site wells and piezometers in addition to compliance boundary well information) • 60 days to complete field activities • Complete drilling activities • Conduct slug tests • Survey soil borings, wells, and other assessment locations • Collect groundwater and other assessment samples • Collect site-wide water levels • Setup groundwater computer model • 30 days after completion of field activities receive analytical data • 60 days after receipt of analytical data evaluate results, conduct statistical evaluation, prepare summary tables, develop CSM, and calibrate computer model. • 20 days to complete Assessment Report, per NC Senate Bill 729, August 2014. • 90 days (up to 180 days) to complete computer modeling and Corrective Action Plan. • Conduct additional work as may be required to complete the CSA. • 90 days to complete CSA preparation, review, and submittal, in accordance with NCDENR guidance (August 2014). Project Assumptions Include: • No more than one iterative assessment step will be required; • No off-site assessment or access agreements are anticipated; Page 18 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra • DEP will make a diligent effort to collect all receptor information in accordance with NCDENR guidance (August 2014); however, it is anticipated that all such information may not be available; • If off-site water supply wells sampling is deemed necessary, NCDENR staff may be requested to assist with access; • No special permitting is anticipated; • Data may not reflect all seasonal or extreme hydrologic conditions; • During the CSA process, if additional investigations are required NCDENR, will be notified; and • In addition to the components listed above, a human health and ecological risk assessment will be conducted. Page 19 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx Groundwater Assessment Work Plan September 2014 Mayo Steam Electric Plant SynTerra 9.0 REFERENCES ASTM, D4044-96 Standard Test Method (Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining Hydraulic Properties of Aquifers. Dicken, Connie L., Suzanne W. Nicholson, John D. Horton, Michael P. Foose, and Julia A.L. Mueller, December 2007, Preliminary integrated geologic map databases for the United States – Alabama, Florida, Georgia, Mississippi, North Carolina, and South Carolina, Version 1.1: United States Geological Survey, USGS Open File Report 2005-1323, < http://pubs.usgs.gov/of/2005/1323>. Hibbard, James P., Edward F. Stoddard, Donald T. Secor, and Allen J. Dennis, 2002, The Carolina Zone: overview of Neoproterozoic to Early Paleozoic peri-Gondwanan terranes along the eastern Flank of the southern Appalachians: Earth Science Reviews, v. 57. North Carolina Geological Survey, 1985, Geologic map of North Carolina: North Carolina Geological Survey, General Geologic Map , scale 1:500000. North Carolina Department of Environment and Natural Resources, May 31, 2007, Groundwater Modeling Policy. North Carolina Department of Environment and Natural Resources, May 31, 2007, Hydrogeologic Investigation and Reporting Policy. North Carolina Department of Environment and Natural Resources, May 31, 2007, Performance and Analysis of Aquifer Slug Tests and Pumping Test Policy. Page 20 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Mayo GW Assessment Plan.docx FIGURES P:\Progress Energy.1026\10. NC Sites\01. Seep And NPDES Permit Assistance\MAYO\dwg\Groundwater Assessment Plan Figures\DUKE MAYO-GW Assessment Figures.dwg PROJECT MANAGER: LAYOUT: DRAWN BY: KATHY WEBB DATE:S. ARLEDGE FIG 1 (USGS SITE LOCATION) 2014-09-25 FIGURE 1 SITE LOCATION MAP MAYO STEAM ELECTRIC PLANT 10600 BOSTON RD ROXBORO, NORTH CAROLINA CLUSTER SPRINGS, VA QUADRANGLE 2000 GRAPHIC SCALE 1000 IN FEET 10000CONTOUR INTERVAL: MAP DATE: 10ft 1987 148 RIVER STREET, SUITE 220 GREENVILLE, SOUTH CAROLINA PHONE 864-421-9999 www.synterracorp.com SOURCE: USGS TOPOGRAPHIC MAP OBTAINED FROM THE NRCS GEOSPATIAL DATA GATEWAY AT http://datagateway.nrcs.usda.gov/ MAYO LAKE POWER PLANT PERSON COUNTY RALEIGH WILMINGTON GREENVILLE GREENSBORO CHARLOTTE FAYETTEVILLE PROPERTY BOUNDARY 500' COMPLIANCE BOUNDARY WASTE BOUNDARY 6000 600 1200GRAPHIC SCALEIN FEETFIG 2 (SITE LAYOUT)2014-09-25J. WYLIES. ARLEDGEPROJECT MANAGER:LAYOUT NAME:DRAWN BY:CHECKED BY:K. WEBBDATE:DATE:FIGURE 2SITE LAYOUTwww.synterracorp.com148 River Street, Suite 220Greenville, South Carolina 29601864-421-9999LEGEND2014-09-25500 ft COMPLIANCE BOUNDARYDUKE ENERGY PROGRESS MAYO PLANTWASTE BOUNDARYMAYO STEAM ELECTRIC PLANT10600 BOSTON RDROXBORO, NORTH CAROLINABACKGROUND MONITORING WELL (SURVEYED)COMPLIANCE MONITORING WELL (SURVEYED)CW-1BG-1SOURCES:1. 2010 AERIAL PHOTOGRAPH OF PERSON COUNTY,NORTH CAROLINA OBTAINED FROM THE NRCSGEOSPATIAL DATA GATEWAY AThttp://datagateway.nrcs.usda.gov/2. 2012 AERIAL PHOTOGRAPH OF HALIFAX COUNTY,VIRGINIA WAS OBTAINED FROM NRCS GEOSPATIALDATA GATEWAY AT http://datagateway.nrcs.usda.gov/3. 2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSPFLOWN ON APRIL 17, 2014.4. DRAWING HAS BEEN SET WITH A PROJECTION OFNORTH CAROLINA STATE PLANE COORDINATE SYSTEMFIPS 3200 (NAD 83).NORTH CAROLINA-VIRGINIA STATE LINE (APPROXIMATE)BOSTON RD(US HWY 501)MAYO LAKE RDMAYO LAKE RDOLD US 501 MULLINS LNLOUISIANA PACIFICCORPORATION10475 BOSTON RD(TIED INTO THE CITY OFROXBORO WATER LINE)RT HESTER RDRAILROADRAILROADRAILROADRAILROAD HUELL M A T T H E W S HWY (U S H W Y 5 0 1 )PERSON COUNTYHALIFAX COUNTY1 9 8 1 L A N D F I L L P E R M I T N O . 7 3 - BPOWERPLANTBOSTON RD(US HWY 501)RAILROAD WOODY LOOPCRUTCHFIELDBRANCHMAYO CREEKMAYO RESERVOIRMAYOCREEKCRUTCHFIELDBRANCHEDR 1FORMER US HWY 501RAW WATERINTAKESTRUCTUREBG-1BG-2CW-1CW-1DCW-2CW-6CW-2DCW-3CW-4CW-5ACTIVE ASH BASIN CZfg CZbg CZfg CZfg PzZg CZfv CZfv CZfv CZfv CZve MAYO RESERVOIR MAYO CREEK CRUTCHFIELD BRANCH CZfg BOWES BRANCH PzZg 148 RIVER STREET, SUITE 220 GREENVILLE, SOUTH CAROLINA 29601 PHONE 864-421-9999 www.synterracorp.com PROJECT MANAGER: LAYOUT: DRAWN BY: KATHY WEBB DATE:S. ARLEDGE FIG 3 (GEOLOGY MAP) 2014-09-25 FIGURE 3 GEOLOGY MAP DUKE ENERGY PROGRESS MAYO STEAM ELECTRIC PLANT 10600 BOSTON RD ROXBORO, NORTH CAROLINA DISCLAIMER The information on this map was derived from digital databases at the NC Department of Transportation Website. Care was taken in the creation of this map. SYNTERRA cannot accept any responsibility for errors, omissions, or positional accuracy. There are no warranties, expressed or implied, including the warranty of merchantability or fitness for a particular purpose, accompanying this product. However, notification of any errors will be appreciated. CZbg LEGEND - UNIT NAME CZg METAMORPHOSED GRANITIC ROCK (EASTERN SLATE BELT) CZfg FELSIC MICA GNEISS (CHARLOTTE AND MILTON BELTS) PzZg METAMORPHOSED GABBRO AND DIORITE (EASTERN SLATE BELT) BIOTITE GNEISS AND SCHIST (INNER PIEDMONT) GEOLOGY SOURCE NOTE: GEOLOGY SHAPEFILES OBTAINED FROM THE USGS Preliminary integrated geologic map databases for the United States - Alabama, Florida, Georgia, Mississippi, North Carolina, and South Carolina, DATED 2007 AT http://pubs.usgs.gov/of/2005/1323/ CZfv FELSIC METAVOLCANIC ROCK (EASTERN SLATE BELT) CZv METAVOLCANIC ROCK (CHARLOTTE AND MILTON BELTS) CZve METAVOLCANIC-EPICLASTIC ROCK (EASTERN SLATE BELT) CW-1 CW-6 CW-5 BG-1 BG-2 CW-4 CW-3 CW-2 MAYO STEAM ELECTRIC PLANT 10600 BOSTON RD PERSON COUNTY NEAR ROXBORO, NC 1500 0 1500 3000 GRAPHIC SCALE IN FEET 500 ft COMPLIANCE BOUNDARY DUKE ENERGY PROGRESS MAYO PLANT WASTE BOUNDARY CW-3 COMPLIANCE MONITORING WELL LEGEND 4804806000 600 1200GRAPHIC SCALEIN FEETFIG 4 (CROSS SECTIONS)(11X17)2014-09-25J. WYLIES. ARLEDGEPROJECT MANAGER:LAYOUT NAME:DRAWN BY:CHECKED BY:K. WEBBDATE:DATE:FIGURE 4ANTICIPATED SAMPLELOCATIONSwww.synterracorp.com148 River Street, Suite 220Greenville, South Carolina 29601864-421-9999LEGENDBACKGROUND MONITORING WELL (SURVEYED)COMPLIANCE MONITORING WELL (SURVEYED)2014-09-25500 ft COMPLIANCE BOUNDARYDUKE ENERGY PROGRESS MAYO PLANTWASTE BOUNDARYCW-1EDR 1EDR REPORTED SUPPLY WELL (APPROXIMATE)PARCEL LINE (PERSON CO GIS)FLOW DIRECTIONBG-1DUKE ENERGY PROGRESS PRODUCTIONWELL - NOT IN SERVICE (APPROXIMATE)DEP 1MAYO STEAM ELECTRIC PLANT10600 BOSTON RDROXBORO, NORTH CAROLINAAW-3ANTICIPATED MONITORING WELL LOCATIONANTICIPATED SOIL BORING LOCATIONANTICIPATED ASH/SOIL BORING LOCATIONANTICIPATED GEOLOGIC CROSS SECTION2007 LiDAR CONTOUR MAJOR420SOURCES:1. 2010 AERIAL PHOTOGRAPH OF PERSON COUNTY, NORTHCAROLINA OBTAINED FROM THE NRCS GEOSPATIAL DATAGATEWAY AT http://datagateway.nrcs.usda.gov/2. 2012 AERIAL PHOTOGRAPH OF HALIFAX COUNTY, VIRGINIAWAS OBTAINED FROM NRCS GEOSPATIAL DATA GATEWAYAT http://datagateway.nrcs.usda.gov/3. 2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSPFLOWN ON APRIL 17, 2014.4. WELL SURVEY INFORMATION, PROPERTY LINE, LANDFILLLIMITS AND BOUNDARIES ARE FROM ARCGIS FILESPROVIDED BY S&ME AND PROGRESS ENERGY.5. PARCEL BOUNDARIES WERE OBTAINED FROM PERSONCOUNTY (NC) GIS DATA AT http://gis.personcounty.net6. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTHCAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200(NAD 83).7. 10ft CONTOUR INTERVALS FROM NCDOT LiDAR DATED 2007https://connect.ncdot.gov/resources/gis/pages/cont-elev_v2.aspx8. VIRGINIA 10ft CONTOUR INTERVALS FROM USGSTOPOGRAPHIC MAP OBTAINED FROM THE NRCSGEOSPATIAL DATA GATEWAY AThttp://datagateway.nrcs.usda.gov/NOTE:1. CONTOUR LINES ARE USED FOR REPRESENTATIVEPURPOSES ONLY AND ARE NOT TO BE USED FOR DESIGNOR CONSTRUCTION PURPOSES.BG-1BG-2CW-1CW-1DCW-2CW-6CW-2DCW-3CW-4NORTH CAROLINA-VIRGINIA STATE LINE (APPROXIMATE)BOSTON RD(US HWY 501)MAYO LAKE RDMAYO LAKE RDOLD US 501 MULLINS LNLOUISIANA PACIFICCORPORATION10475 BOSTON RDRT HESTER RDRAILROADRAILROADRAILROADRAILROAD RAILROAD HUELL M A T T H E W S HWY (U S H W Y 5 0 1 )PERSON COUNTYHALIFAX COUNTY1 9 8 1 L A N D F I L L P E R M I T N O . 7 3 - BACTIVE ASH BASINPOWERPLANTBOSTON RD(US HWY 501)RAILROAD WOODY LOOPCRUTCHFIELDBRANCHMAYO CREEKMAYO RESERVOIRMAYOCREEKCRUTCHFIELDBRANCHEDR 1DEP 1DEP 3DEP 2FORMER US HWY 501RAW WATERINTAKESTRUCTURECW-5BG-3BG-3DBG-4BG-4DAW-3DAW-3AW-2DAW-2CW-7AW-1DAW-1CW-5DCW-7DCW-6CW-6DAW-4DAW-4MONITORING WELLS / PIEZOMETERS / SOILBORINGS (APPROXIMATE)MW-2MW-2PZ-1PZ-1APZ-2PZ-2APZ-3PZ-3APZ-4PZ-4AMW-4GENERALIZED GROUNDWATER FLOWDIRECTION•SUPPORTED BY GROUNDWATER ELEVATION DATAPOINTS OR TOPOGRAPHIC DATA TABLES TABLE 1SUMMARY OF CONCENTRATION RANGES FOR CONSTITUENTS DETECTED GREATER THAN 2L STANDARDSMAYO STEAM ELECTRIC PLANT DUKE ENERGY PROGRESS, INC., ROXBORO, NORTH CAROLINAPARAMETER ANTIMONY BARIUM BORON CADMIUM CHROMIUM IRON LEAD MANGANESE THALLIUM TDS pH2L STANDARD (eff. 4/1/2013)1700 70021030015500.2500 6.5 - 8.5Units (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l)(ug/l) (mg/l) SUBG-1 Background 0.13 - 4.2 90 - 1040 <2L<2L 4.7 - 40.1 261 - 65700 2.3 - 33.1 8.9 - 2270 <0.1 - 0.35 <2L 5.2 - 7.0BG-2 Background<2L <2L <2L<2L 5.9 - 10.2 152 - 2660 <2L 27 - 248 <2L<2L 6.3 - 6.6CW-1CB<2L <2L <2L 0.082 - 2.19 <2L<2L<2L 7 - 104<2L<2L 5.6 - 6.7CW-1DCB<2L <2L <2L<2L <5 - 11 <2L<2L 5 - 422<2L<2L <2LCW-2CB<2L <2L 351 - 785 <2L<2L<2L<2L 11.4 - 535 <2L<2L 5.0 - 6.1CW-2DCB<2L <2L <2L<2L<2L 48 - 522 <2L 33.5 - 270 <2L<2L 6.1 - 6.8CW-3CB<2L <2L <2L<2L<2L 21 - 908 <2L 12.1 - 481 <2L 421 - 520 6.3 - 6.7CW-4CB<2L <2L <2L<2L<2L 28 - 784 <2L<2L<2L<2L 5.8 - 6.4CW-5CB<2L <2L <2L<2L<2L 98.9 - 1080 <2L 387 - 706 <0.1 - 0.361 <2L 6.4 - 7.0CW-6CB<2L <2L <2L<2L<2L 1220 - 1870 <2L 1090 - 1440 <2L 417 - 550 6.5 - 7.1Notes:Prepared by: RBI Checked by: MCMCB - Compliance Boundary< 2L - Constituent has not been detected above the 2L Standard or beyond range for pHShown concentration ranges only include concentrations detected above the laboratory's reporting limit.Well IDWell Location Relative to Compliance BoundaryConcentration RangePage 1 of 1P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Tables\Table 1 Summary Concentration Ranges Mayo.xlsx TABLE 2 GROUNDWATER ASSESSMENT PARAMETER LIST MAYO STEAM ELECTRIC PLANT DUKE ENERGY PROGRESS, INC., ROXBORO, NORTH CAROLINA PARAMETER UNITS FIELD EQUIPMENT/ LAB METHOD pH SU YSI Professional Plus or YSI 556 MPS Specific Conductivity S/cm YSI Professional Plus or YSI 556 MPS Temperature CYSI Professional Plus or YSI 556 MPS ORP mV YSI Professional Plus or YSI 556 MPS Dissolved Oxygen mg/L YSI Professional Plus or YSI 556 MPS Turbidity NTU Hach 2100Q Antimony g/L EPA 200.8 Arsenic g/L EPA 200.8 Barium mg/L EPA 200.7 Boron mg/L EPA 200.7 Cadmium g/L EPA 200.8 Chromium g/L EPA 200.8 Copper mg/L EPA 200.7 Iron mg/L EPA 200.7 Lead g/L EPA 200.8 Manganese mg/L EPA 200.7 Mercury g/L EPA 245.1 Molydbenum g/L EPA 200.8 Nickel g/L EPA 200.8 Selenium g/L EPA 200.8 Thallium (low level)g/L EPA 200.8 Zinc mg/L EPA 200.7 Nitrate as Nitrogen mg-N/L EPA 300.0 Ferrous Iron mg/L (Field Test Kit) Sulfate mg/L EPA 300.0 Sulfide mg/L SM 4500 Sd Methane mg/L RSK 175 Chloride mg/L EPA 300.0 Calcium mg/L EPA 200.7 Magnesium mg/L EPA 200.7 Sodium mg/L EPA 200.7 Potassium mg/L EPA 200.7 Bromide mg/L EPA 300.1 Total Organic Carbon mg/l EPA 5310 Alkalinity (as CaCO3)mg/L SM 2320B Total Dissolved Solids mg/L SM 2540C Prepared by: RBI Checked by: JAW Notes: SU - Standard Units mg/L - milligrams per liter S/cm - microsiemens per centimeter NTU - Nephelometric Turbidity Units C - degrees Celsius g/L - micrograms per liter mV - millivolts mg-N/L - milligrams nitrate (as nitrogen) per liter Field Parameters Lab Parameters - Inorganics (Total & Dissolved) Lab Parameters - Anions/Cations Page 1 of 1 P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Tables\Table 2 Assessment Parameter List Mayo.xlsx TABLE 3 ASSESSMENT SAMPLING PLAN MAYO STEAM ELECTRIC PLANT DUKE ENERGY PROGRESS, INC., ROXBORO, NORTH CAROLINA ASH MANAGEMENT AREA BORING / WELL ID ESTIMATED BORING DEPTH (ft bgs) ESTIMATED NO. OF SAMPLES SAMPLE MEDIA SAMPLE DEPTHS/INTERVALS/ TARGET ZONES LAB ANALYSIS PURPOSE/NOTES AB-1 (and piezometer pair location) 40 5 Ash Ash Ash Soil Soil Water 1-2' Mid Depth Above ash/soil contact 2' Below ash/soil contact Bottom of boring Total metals + SPLP Total metals + SPLP Total metals + SPLP Total metals + Geotech Total metals + Geotech Water Level Refine ash thickness, determine residual saturation of ash, characterize ash chemistry and leachability, characterize soil chemistry beneath ash, geologic cross section, groundwater modeling AB-2 40 5 Ash Ash Ash Soil Soil 1-2' Mid Depth Above ash/soil contact 2' Below ash/soil contact Bottom of boring Total metals + SPLP Total metals + SPLP Total metals + SPLP Total metals + Geotech Total metals + Geotech Refine ash thickness, determine residual saturation of ash, characterize ash chemistry and leachability, characterize soil chemistry beneath ash, geologic cross section, groundwater modeling AB-3 (and piezometer pair location) 40 5 Ash Ash Ash Soil Soil Water 1-2' Mid Depth Above ash/soil contact 2' Below ash/soil contact Bottom of boring Total metals + SPLP Total metals + SPLP Total metals + SPLP Total metals + Geotech Total metals + Geotech Water Level Refine ash thickness, determine residual saturation of ash, characterize ash chemistry and leachability, characterize soil chemistry beneath ash, geologic cross section, groundwater modeling AB-4 40 5 Ash Ash Soil Soil 1-2' Mid Depth Above ash/soil contact 2' Below ash/soil contact Bottom of boring Total metals + SPLP Total metals + SPLP Total metals + SPLP Total metals + Geotech Total metals + Geotech Water Level Refine ash thickness, determing residual saturation of ash, characterize ash chemistry and leachability, characterize soil chemistry beneath ash, geologic cross section, groundwater modeling AB-5 (and piezometer pair location) 40 5 Ash Ash Ash Soil Soil Water 1-2' Mid Depth Above ash/soil contact 2' Below ash/soil contact Bottom of boring Total metals + SPLP Total metals + SPLP Total metals + SPLP Total metals + Geotech Total metals + Geotech Water Level Refine ash thickness, determing residual saturation of ash, characterize ash chemistry and leachability, characterize soil chemistry beneath ash, geologic cross section, groundwater modeling AB-6 40 5 Ash Ash Ash Soil Soil 1-2' Mid Depth Above ash/soil contact 2' Below ash/soil contact Bottom of boring Total metals + SPLP Total metals + SPLP Total metals + SPLP Total metals + Geotech Total metals + Geotech Water Level Refine ash thickness, determing residual saturation of ash, characterize ash chemistry and leachability, characterize soil chemistry beneath ash, geologic cross section, groundwater modeling AB-7 40 5 Ash Ash Ash Soil Soil 1-2' Mid Depth Above ash/soil contact 2' Below ash/soil contact Bottom of boring Total metals + SPLP Total metals + SPLP Total metals + SPLP Total metals + Geotech Total metals + Geotech Refine ash thickness, determing residual saturation of ash, characterize ash chemistry and leachability, characterize soil chemistry beneath ash, geologic cross section, groundwater modeling SB-5 40 2 Waste Soil TBD Total metals + SPLP Define waste thickness, characterize waste chemistry and leachability, characterize soil chemistry beneath landfill, groundwater modeling SB-6 40 2 Waste Soil TBD Total metals + SPLP Define waste thickness, characterize waste chemistry and leachability, characterize soil chemistry beneath landfill, groundwater modeling SB-1 30 2 Soil Soil 1-2' Just above the water table Total metals + Geotech Total metals + Geotech Background soil quality in felsic gneiss and groundwater modeling data SB-2 30 2 Soil Soil 1-2' Just above the water table Total metals + Geotech Total metals + Geotech Background soil quality near geologic contact and groundwater modeling data SB-3 3 2 Soil Soil 1-2' Just above the water table Total metals + Geotech Total metals + Geotech Background soil quality near geologic contact and groundwater modeling data SB-4 30 2 Soil Soil 1-2' Just above the water table Total metals + Geotech Total metals + Geotech Background soil quality in meta volcanic rock and groundwater modeling data BG-3/BG-3D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Background water quality Groundwater modeling Sentinel wells BG-4/BG-4D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Background water quality Groundwater modeling Sentinel wells CW-5D 60 3 Soil Soil Water Just above the water table Within lower screen interval Bedrock Total metals Total metals Table 2 List Groundwater flow direction Groundwater modeling CW-7/CW-7D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Groundwater flow direction Groundwater modeling AW-1/AW-1D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Background water quality Groundwater modeling Sentinel wells AW-2/AW-2D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Groundwater modeling Groundwater flow direction Horizontal and vertical extent AW-3/AW-3D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Groundwater flow direction Groundwater modeling Background water quality AW-4/AW-4D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Groundwater modeling Background water quality Sentinel wells AW-5/AW-5D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Groundwater modeling Groundwater flow direction Horizontal and vertical extent AW-6/AW-6D 30 50 4 Soil Soil Water Water Just above the water table Within lower screen interval Transition zone Bedrock Total metals Total metals Table 2 List Table 2 List Groundwater modeling Groundwater flow direction Horizontal and vertical extent Site Production Wells DEP 1,2 &3 unknown 3 Water Screened interval Table 2 List Confirm no influence in lower bedrock fractures, groundwater modeling Existing Monitoring Wells TBD Variable TBD Water Well Screen Interval (variable)Table 2 List Groundwater modeling and statistical evaluation Notes: SPLP (Synthetic Preciptation Leaching Procedure) Metals - As, B, Ba, Cd, Cr, Cu, Fe, Hg, Mn,Mo, Ni, Pb, Sb, Se, Tl, and Zn. Total Metals - As, B, Ba, Cd, Cr, Cu, Fe, Hg, Mn,Mo, Ni, Pb, Sb, Se, Tl, and Zn. Geotech - Geotechnical parameters include moisture content, particle size distribution, Atterberg limits, specific gravity, and permeability. Prepared by: KWW Checked by: HJF Ash Basin Background Soil Permitted Landfill New Monitoring Wells P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Tables\Table 3‐Assessment Sampling Plan.xlsx Page 1 of  1 APPENDIX A NCDENR LETTER OF AUGUST 13, 2014