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Home My WebLink AboutNC0001422_Final CAP Report 11-02-2015_201511034CIP synTerra CORRECTIVE ACTION PLAN PART I Site Name and Location: L.V. Sutton Energy Complex 801 Sutton Steam Plant Road Wilmington, North Carolina 28401 Groundwater Incident No.: Not Assigned NPDES Permit No.: NC0001422 Date of Report: November 2, 2015 Permittee and Current Duke Energy Progress, LLC Property Owner: 410 South Wilmington Street Raleigh, North Carolina 27601 (704)382-3853 Consultant Information: SynTerra 148 River Street Greenville, South Carolina (864) 421-9999 Latitude and Longitude of Facility: N 34.283296 / W-77.985860�,�.�a"""'""'� -AL °r y '.� 2453 Perry Waldrep, Nl' '(5'�453 Senior Proje t Manager Kath b ,A ' Prjje Dor pcto�` T Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page ES-1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx L.V. SUTTON ENERGY COMPLEX EXECUTIVE SUMMARY North Carolina General Assembly Session Law 2014-122, the Coal Ash Management Act (CAMA) of 2014, requires the owner of a coal combustion residuals surface impoundment to submit a Groundwater Assessment Plan (GAP) to the North Carolina Department of Environmental Quality (NCDEQ,, formerly known as the Department of Environment and Natural Resources) no later than December 31, 2014 and a Groundwater Assessment Report [herein referred to as a Comprehensive Site Assessment (CSA)] no later than 180 days after approval of the GAP. No later than 90 days from submission of the assessment report, or a time frame otherwise approved by NCDEQ not to exceed 180 days from submission of the assessment report, a proposed Groundwater Corrective Action Plan (CAP) is to be submitted. The CAP shall include, at a minimum, all of the following: a. A description of all exceedances of the groundwater quality standards, including any exceedances that the owner asserts are the result of natural background conditions. b. A description of the methods for restoring groundwater in conformance with the requirements of Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code and a detailed explanation of the reasons for selecting these methods. c. Specific plans, including engineering details, for restoring groundwater quality. d. A schedule for implementation of the CAP. e. A monitoring plan for evaluating the effectiveness of the proposed corrective action and detecting movement of any contaminant plumes. Duke Energy requested a 90 day extension for submittal of the final Groundwater Corrective Action Plan. The request was based on discussions with NCDEQ that the CAP would be provided in two parts, with the first part submitted on the original due date and the second part submitted 90 days later. The CAP Part 1 reports (submitted 90 days after the CSA reports) are to include: Background information, A brief summary of the CSA findings, A brief description of site geology and hydrogeology, A summary of the previously completed receptor survey, Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page ES-2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx A description of 2L and 2B exceedances, Proposed site-specific groundwater background concentrations, A detailed description of the site conceptual model, and Groundwater flow and transport modeling. Part 2 will include the remainder of the CAP requirements including: Risk assessment, Alternative methods for achieving restoration, Conceptual plans for recommended corrective actions, Implementation schedule, and Plans for future monitoring and reporting. This CAP Part 1 has been prepared for the Duke Energy Progress, LLC (Duke Energy) L.V. Sutton Energy Complex. The CAP Part 1 provides additional evaluation of the CSA data reported on August 5, 2015. NC CAMA has required Duke Energy to fully excavate the ash basins and FADA (former ash disposal area), with the material landfilled, safely recycled or reused in a lined structural fill (https://www.duke- nergy.com/pdfs/SafeBasinClosureUpdate_Sutton.pdf., accessed on July 28, 2015). The basin and FADA excavation will be the primary source control measure. A Groundwater Mitigation and Monitoring Plan, which includes the installation of 12 extraction wells along the eastern Site boundary, was submitted in July, as required by NCDEQ. The results of the groundwater modeling to evaluate the effects of the ash removal and the implementation of the groundwater extraction plan, on groundwater are provided herein. This CAP Part 1 also provides a description of all exceedances of the groundwater quality standards, including any exceedances that the owner asserts are the result of natural background conditions. ES-1. Introduction Duke Energy Progress, LLC (Duke Energy) owns and operates the L.V. Sutton Energy Complex (Site) located on approximately 3,300 acres near Wilmington, North Carolina. The Site is located along the east bank of the Cape Fear River northwest of Wilmington and west of US Highway 421. The Site started operations in 1954 with three coal-fired boilers that primarily used bituminous coal as fuel to produce steam to generate electricity. Ash generated from coal combustion is stored in ash management areas including the FADA, the 1971 and 1984 ash basins. The 1984 basin has a clay liner. The Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page ES-3 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Site ceased burning coal in November 2013 and switched to natural gas for electricity generation, thus the facility no longer generates coal ash. The Site lies within the Coastal Plain Physiographic Province and is underlain by the sands of the surficial aquifer and the deeper, fine sands, silts and clays of the Pee Dee formation. There is no confining unit present at the Site; due to its lower hydraulic conductivity, the upper Pee Dee contact serves as an aquitard to vertical groundwater flow. Constituents from the ash, primarily boron are present mainly within the lower surficial aquifer. Groundwater flow is radial from the 1971 ash basin; beyond the basin the primary flow directions are east, southeast and west. The cooling pond borders the 1971 and 1984 ash basins to the west, with the Cape Fear River beyond. Public and private water wells are located adjacent to the Site to the east, including 2 active Cape Fear Public Utility supply wells. Plans to discontinue the use of these water supply wells are underway and Duke has taken proactive steps to replace these water supply wells with a new municipal water line extension. Completion of the replacement well field water system is anticipated by December 2015. ES-2. Site Conceptual Model The hydrogeologic site conceptual model (SCM) is based on the configuration of the ash basins relative to Site features including canals, ponds, rivers and production wells (Figures ES-1). The Site is underlain by surficial sands to a depth of approximately 50 feet below ground surface (bgs), which is underlain by fine sands, silts and clays of the Pee Dee formation (Figure ES-2, ES-3). The contrasting permeability between the surficial and Pee Dee formation is a significant part of in this model. The 1971 ash basin was constructed by excavation below the ground water table to a depth of approximately 40 feet below grade and the surficial aquifer was substantially replaced by the ash in this area. The ash stack is approximately 40 feet above Site grade, and therefore the ash is approximately 80 feet thick, with over half of that below the water table. The FADA is a low-lying area containing 10 to 12 feet of ash, most of it below the water table which occurs at two to three feet bgs in that area. Groundwater flow from the 1971 ash basin area is radial. Groundwater flow in the FADA is to the south/southwest. The discharge canal to the south and the cooling pond to the west control groundwater elevation in the surficial aquifer to the west and south of the 1971 ash basin and to the north and west of the FADA. Small sand hills located in the northeast portion of the Site create a localized groundwater divide extending roughly north and south. Surficial groundwater also flows radially from this area. The Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page ES-4 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx operation of offsite production wells to the east appears to locally affect flow within the surficial zone. The surficial aquifer has larger hydraulic conductivity values than does the underlying Pee Dee Formation, resulting in preferential lateral flow. This is reflected in the data indicating the majority of constituent 2L exceedances occur within this zone. This lateral flow, especially in the lower surficial aquifer, is affected by the presence of surface water bodies and by the operation of production wells located along the eastern property boundary. There is an upward vertical gradient between the upper and lower surficial aquifer wells in most locations and a downward vertical gradient between the surficial and Pee Dee formation in most locations. Because of the lower hydraulic conductivities, the flux of water is greater in the shallow formations (above the Pee Dee). Groundwater to surface water interaction at the Site consists primarily of surficial aquifer discharge into process waters within the discharge and intake canals and the cooling pond. In the northern portion of the Site, shallow groundwater discharges to the Cape Fear River, however this area is outside of the zones affected by 2L exceedances. ES-3. Extent of 2L and 2B Exceedances The CSA indicated concentrations of arsenic, barium, boron, iron, manganese, pH thallium, vanadium, and total dissolved solids above 2L or IMAC were present in groundwater samples collected in ash pore water and groundwater beyond the ash basins. Concentrations of cobalt and selenium in excess of the 2L or IMAC were detected in groundwater only. The majority of the 2L or IMAC exceedances and the highest concentrations were detected in the lower surficial zone. Within the upper surficial zone, the extent of constituents exceeding 2L or IMAC detected in ash pore water did not extend beyond the ash basin or FADA with the exception of boron, manganese, pH and vanadium and, with the exception of vanadium, these exceedances appear to extend to or just beyond the compliance boundary. Vanadium above 2L extends to AW-03B at the eastern Site boundary. Within the lower surficial aquifer, 2L or IMAC exceedances extend north of the 1984 ash basin to MW-27C, to the northeast to AW-2C, offsite to the east beyond SMW-1C and to the southeast to MW-28C. Boron is the primary constituent exceeding 2L in these areas. Selenium above IMAC extends northward to MW-27C. Exceedances in the FADA are generally limited to the FADA or short distances to the east, south or west. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page ES-5 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Background concentrations for soil, surface water and surficial zone groundwater have been measured by the CSA. In some instances these background concentrations exceed 2L or IMAC. Exceedances within the Pee Dee formation are limited but include boron, which is likely attributed to ocean salt water intrusion. Additional background wells are planned to determine if 2L exceedances within the Pee Dee can be attributed to the ash basins or are naturally-occurring. Surface water exceedances of 2B or background concentrations were detected in the samples from the Cape Fear River for aluminum. Exceedances of 2B or background were detected in surface water samples from the cooling pond for copper. Since both the background and detected concentrations of aluminum were significantly higher than those detected in Site ash pore water, ground water or cooling pond surface samples, the aluminum exceedance is not attributed to the Site ash basins. Similarly, copper was not detected in the ash pore water or Site groundwater with the exception of low concentrations in two wells. Further evaluation of the source and a risk assessment of the area are anticipated in the CAP Part 2. ES-4. Groundwater Modeling Groundwater modeling was conducted to evaluate the effects of various potential closure options on groundwater and surface water quality. Modeling components included groundwater fate and transport, geochemistry and supporting studies. The constituents included in the fate and transport model were selected based on significant concentrations in ash pore water greater than likely background levels and whether there was a discernible plume of the constituent extending downgradient from the ash basin. Constituents selected for modeling at the Site were arsenic, boron, and vanadium. The transport model closely matched observed concentrations and was used to predict contaminant distributions for the next 5, 15, 30 years based on three scenarios; existing conditions, capping ash in place, and removal of ash. The model for the existing conditions scenario indicated the 2L and IMAC extent area would not increase over time. The results of the model indicated that capping ash in place and removal of ash would reduce the extent of boron exceedances within the upper surficial aquifer by the year 2020. Capping ash in place and removal of ash scenarios simulate a reduction of boron within the lower surficial aquifer after a period of 45 years. Vanadium and arsenic show little migration within all three scenarios. # # # # ") ") ") ") ")") ") ") ") U S-421 P R J -I -1 4 0 S R-2 16 9 S R -2 7 7 9 SR-1394 S R -2 1 4 5 P R J -I -1 4 0 FORMER ASHDISPOSAL AREA 1984 ASHBASIN(LINED) NEW ASHBASIN AREA(LINED) 1971 ASHBASIN COOLINGPOND COOLINGPOND COOLINGPOND COOLINGPOND CAPE FEARRIVER DRAINAGECHANNEL COOLINGPOND FIGURE ES-1SITE CONCEPTUAL MODEL - PLAN VIEWL.V. SUTTON ENERGY COMPLEX ± P:\D uke E nergy P rogress.1026\00 GIS B AS E DATA \Sutton\Map_Docs\D raft_CA P\Figure E S-1 - Executive Summary Figure.mxd L. V. SUTTON ENERGY COMPLEX801 SUTTON STEAM PLANT RDWILMINGTON, NORTH CAROLINA 148 RIVER STREET, SUITE 220GREENVILLE, SC 29601864-421-9999www.synterracorp.com GRAPHIC SCALE 500 0 500 1,000 1,500 2,000 (IN FEET) PROJECT MANAGER: P. WALDREP DRAWN BY: B. YOUNG DATE: 10/19/2015 DATE: 10/19/2015 CHECKED BY: C. SUTTELL NOTES:1 FROM DRINKING WATER WELL AND RECEPTOR STUDY (APPENDIX B). 2 BORON EXHIBITS THE GREATEST THREE-DIMENSIONAL EXTENT OF MIGRATIONFROM THE L.V. SUTTON ENERGY COMPLEX ASH BASIN. THE NORTH CAROLINA 2L(NC2L) FOR BORON IS 700 (µg/L). 3 APRIL 17, 2014 AERIAL ORTHOPHOTOGRAPHY OBTAINED FROM WSP. 4 2012 AERIAL ORTHOPHOTOGRAPHY OBTAINED FROM THE NC CENTER FORGEOGRAPHIC INFORMATION AND ANALYSIS. (http://services.nconemap.gov/) 5 PARCEL BOUNDARY WAS OBTAINED FROM THE NC CENTER FOR GEOGRAPHICINFORMATION AND ANALYSIS. (http://services.nconemap.gov/) 6 DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATEPLANE COORDINATE SYSTEM FIPS 3200 (NAD83/2011). LEGENDWATER SUPPLY WELLS1 WATER SUPPLY WELL IN INVENTORY (APPROXIMATE) WOOTEN PRODUCTION WELL (APPROXIMATE) #CFPUA PRODUCTION WELL LOCATION (APPROXIMATE) EDR REPORTED WELL LOCATION (APPROXIMATE) INVISTA PRODUCTION WELL (APPROXIMATE) ")DUKE ENERGY PROGRESSS PRODUCTION WELL(APPROXIMATE) AREA OF CONCENTRATIONS IN GROUNDWATER ABOVE NC2L GROUNDWATER FLOW DIRECTION (SHALLOW ASH BASIN BOUNDARY ASH BASIN COMPLIANCE BOUNDARY HALF-MILE OFFSET FROM COMPLIANCE BOUNDARY DUKE ENERGY PROGRESS SUTTON PLANT SITE BOUNDARY 1 1 / 0 1 / 2 0 1 5 2 : 4 4 P M P : \ D u k e E n e r g y P r o g r e s s . 1 0 2 6 \ 1 0 8 . S u t t o n A s h B a s i n G W A s s e s s m e n t P l a n \ 1 6 . C o r r e c t i v e A c t i o n P l a n \ F i g u r e s \ D E S U T T O N C A R C O N C E P X - S E C T I O N . d w g 1 4 8 R I V E R S T R E E T , S U I T E 2 2 0 G R E E N V I L L E , S O U T H C A R O L I N A 2 9 6 0 1 P H O N E 8 6 4 - 4 2 1 - 9 9 9 9 w w w . s y n t e r r a c o r p . c o m P R O J E C T M A N A G E R : L A Y O U T : D R A W N B Y : P . W A L D R E P D A T E : J O H N C H A S T A I N F I G U R E E S - 2 ( C U R R E N T C O N D I T I O N S ) 1 0 / 2 9 / 2 0 1 5 1 9 7 1 A S H B A S I N ( S O U R C E ) A S H COOLIN G P O N D L A K E S U T T O N R D S A N D H I L L S W I T H P O S S I B L E R E C H A R G E Z O N E S PROPERTY LINE A S H P O R E W A T E R S A N D Q U A R R Y P O N D CAPE FEAR RIVER MANMADE BERM FORTHE COOLING POND W S W O O T E N P R O P E R T Y D U K E E N E R G Y P R O G R E S S S U T T O N E N E R G Y C O M P L E X P R O D U C T I O N W E L L S F I G U R E E S - 2 C U R R E N T C O N D I T I O N S C R O S S - S E C T I O N C O N C E P T U A L S I T E M O D E L L . V . S U T T O N E N E R G Y C O M P L E X W I L M I N G T O N , N O R T H C A R O L I N A N O T T O S C A L E PEE DEE AQ U I F E R SEA WATER FRESH WATER P E E D E E A Q U I F E R S E A W A T E R F R E S H W A T E R PEE DEE AQ U I F E R P E E D E E A Q U I F E R A R E A O F C O N C E N T R A T I O N S I N G R O U N D W A T E R A B O V E N C 2 L S T A N D A R D LEGENDINFERRED OR MEASUREDAPPROXIMATE WATER TABLE ASHGROUNDWATER ABOVE NC 2L STANDAR D FOR BORONGROUNDWATER BELOW NC 2L STANDA R D FOR BORONINFERRED OR MEASUREDAPPROXIMATE ASH PORE WATER TABLE ASH PORE WATERLITHOLOGIC CONTACT C O O L I N G P O N D N E W L A N D F I L L PROPERTY LINE S A N D Q U A R R Y P O N D CAPE FEAR RIVER MANMADE BERM FORTHE COOLING POND W S W O O T E N P R O P E R T Y D U K E E N E R G Y P R O G R E S S S U T T O N E N E R G Y C O M P L E X P R O D U C T I O N W E L L S 1 1 / 0 1 / 2 0 1 5 2 : 4 6 P M P : \ D u k e E n e r g y P r o g r e s s . 1 0 2 6 \ 1 0 8 . S u t t o n A s h B a s i n G W A s s e s s m e n t P l a n \ 1 6 . C o r r e c t i v e A c t i o n P l a n \ F i g u r e s \ D E S U T T O N C A R C O N C E P X - S E C T I O N . d w g 1 4 8 R I V E R S T R E E T , S U I T E 2 2 0 G R E E N V I L L E , S O U T H C A R O L I N A 2 9 6 0 1 P H O N E 8 6 4 - 4 2 1 - 9 9 9 9 w w w . s y n t e r r a c o r p . c o m P R O J E C T M A N A G E R : L A Y O U T : D R A W N B Y : P . W A L D R E P D A T E : J O H N C H A S T A I N F I G U R E E S - 3 ( S O U R C E R E M O V A L ) 1 0 / 2 9 / 2 0 1 5 F I G U R E E S - 3 S O U R C E R E M O V A L C R O S S - S E C T I O N C O N C E P T U A L S I T E M O D E L L . V . S U T T O N E N E R G Y C O M P L E X W I L M I N G T O N , N O R T H C A R O L I N A N O T T O S C A L E PROPOSED RECOVERY WELL LEGENDINFERRED OR MEASUREDAPPROXIMATE WATER TABLE GROUNDWATER ABOVE NC 2L STANDAR D FOR BORONGROUNDWATER BELOW NC 2L STANDA R D FOR BORONLITHOLOGIC CONTACT PEE DEE AQ U I F E R SEA WATER FRESH WATER P E E D E E A Q U I F E R S E A W A T E R F R E S H W A T E R PEE DEE AQ U I F E R P E E D E E A Q U I F E R A N T I C I P A T E D O R P O T E N T I A L A R E A O F C O N C E N T R A T I O N S I N G R O U N D W A T E R A B O V E N C 2 L S T A N D A R D F O R M E R A S H B A S I N ( S O U R C E R E M O V E D ) A S H PROPOSED LAKE SUTTON RD L A N D F I L L L I N E R Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page i P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx TABLE OF CONTENTS SECTION PAGE L.V. SUTTON ENERGY COMPLEX EXECUTIVE SUMMARY .................................. ES-1 ES-1. Introduction .......................................................................................................... ES-2 ES-2. Site Conceptual Model ........................................................................................ ES-3 ES-3. Extent of 2L and 2B Exceedances ....................................................................... ES-4 ES-4. Groundwater Modeling ...................................................................................... ES-5 1.0 INTRODUCTION ......................................................................................................... 1-1 1.1 Site History and Overview .................................................................................... 1-1 1.2 Purpose of Corrective Action Plan ....................................................................... 1-2 1.3 Regulatory Background ......................................................................................... 1-2 1.3.1 T15A NCAC 2L 0106 – Corrective Action Requirements ........................ 1-2 1.3.2 Coal Ash Management Act Requirements ................................................ 1-3 1.3.3 Regulatory Standards for Site Media ......................................................... 1-5 1.3.4 NCDEQ Requirements ................................................................................. 1-6 1.3.5 NORR Requirements .................................................................................... 1-6 1.4 Summary of CSA Findings .................................................................................... 1-6 1.5 Site Description ....................................................................................................... 1-9 1.6 Site Geology ........................................................................................................... 1-10 1.7 Site Hydrogeology ................................................................................................ 1-10 1.8 Site Hydrology ...................................................................................................... 1-11 1.9 Receptor Survey .................................................................................................... 1-11 1.9.1 Surrounding Land Use ............................................................................... 1-12 1.9.2 Availability of Public Water Supply ......................................................... 1-12 1.9.3 Drinking Water Supply Well Survey Findings ....................................... 1-12 1.9.4 Potential Human Receptors ....................................................................... 1-13 1.9.5 Potential Ecological Receptors ................................................................... 1-13 2.0 BACKGROUND CONCENTRATIONS AND EXTENT OF EXCEEDANCES 2-1 2.1 Provisional Background Concentrations ............................................................. 2-1 2.1.1 Provisional Background Soil Concentrations ............................................ 2-3 2.1.2 Provisional Background Groundwater Concentrations .......................... 2-3 2.1.2.1 Provisional Background Concentration – Upper Surficial Aquifer2-4 2.1.2.2 Provisional Background Groundwater Concentration – Lower Surficial Aquifer .................................................................................... 2-5 Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page ii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 2.1.2.3 Duke Energy Background Private Well Sampling ........................... 2-7 2.1.3 Provisional Background Surface Water Concentrations ......................... 2-8 2.1.4 Provisional Background Sediment Concentrations.................................. 2-9 2.2 Exceedances ............................................................................................................. 2-9 2.2.1 Soil ................................................................................................................... 2-9 2.2.1.1 1971 Ash Basin ....................................................................................... 2-9 2.2.1.2 FADA ...................................................................................................... 2-9 2.2.2 Groundwater ................................................................................................ 2-10 2.2.2.1 1971 Ash Basin ..................................................................................... 2-10 2.2.2.2 Former Ash Disposal Area (FADA) ................................................. 2-12 2.2.3 Surface Water ............................................................................................... 2-13 2.2.4 Sediment ....................................................................................................... 2-13 2.3 Initial and Interim Response Actions ................................................................. 2-14 2.3.1 Source Control ............................................................................................. 2-14 2.3.2 Groundwater Response Actions ............................................................... 2-14 3.0 SITE CONCEPTUAL MODEL ................................................................................... 3-1 3.1 Site Hydrogeologic Conditions ............................................................................. 3-1 3.1.1 Hydrostratigraphic Units ............................................................................. 3-1 3.1.2 Hydrostratigraphic Unit Properties ............................................................ 3-2 3.1.3 Potentiometric Surface – Intermediate/Lower Surficial and Deep (Pee Dee) Flow Layers ........................................................................................... 3-3 3.1.4 Horizontal Hydraulic Gradients ................................................................. 3-3 3.1.5 Vertical Hydraulic Gradients ....................................................................... 3-4 3.2 Site Geochemical Conditions ................................................................................. 3-4 3.2.1 Constituent Sources ...................................................................................... 3-4 3.2.2 Constituent Transport in Groundwater ..................................................... 3-5 3.2.3 Constituent Distribution in Groundwater ................................................. 3-5 3.3 Mineralogical Characteristics ................................................................................ 3-7 3.4 Geochemical Characteristics .................................................................................. 3-7 3.4.1 Cations/Anions .............................................................................................. 3-7 3.4.2 Redox Potential .............................................................................................. 3-8 3.4.3 Solute Speciation ........................................................................................... 3-8 3.4.4 Kd (Sorption) Testing and Analysis ............................................................. 3-9 Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page iii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 3.5 Correlation of Hydrogeologic and Geochemical Conditions to constituent Distribution .............................................................................................................. 3-9 3.6 Facilitated (Colloidal) Transport ......................................................................... 3-11 3.7 Time Versus Boron Concentration Diagrams ................................................... 3-12 4.0 MODELING ................................................................................................................... 4-1 4.1 Sorption Model ........................................................................................................ 4-1 4.2 Geochemical Modeling .......................................................................................... 4-3 4.3 Numerical Fate and Transport Model ................................................................. 4-5 4.4 Flow and Transport Models .................................................................................. 4-6 4.4.1 Flow Model..................................................................................................... 4-6 4.4.2 Transport Model ............................................................................................ 4-7 4.5 Model Results .......................................................................................................... 4-8 4.5.1 Existing Conditions ....................................................................................... 4-8 4.5.2 Capping Ash Basins ...................................................................................... 4-9 4.5.3 Removal of Ash .............................................................................................. 4-9 4.6 Groundwater and Surface Water Interactions .................................................. 4-11 5.0 CORRECTIVE ACTION PLAN PART 2 .................................................................. 5-1 6.0 REFERENCES ................................................................................................................ 6-1 Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page iv P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx LIST OF FIGURES Executive Summary Figure ES-1 Site Conceptual Model - Plan View Figure ES-2 Current Conditions - Cross-Section Conceptual Site Model Figure ES-3 Source Removal - Cross-Section Conceptual Site Model 1.0 Introduction Figure 1-1 Site Location Map Figure 1-2 Site Layout Map Figure 1-3 Drinking Water Well and Receptor Survey 2.0 Extent of 2L and 2B Exceedances Figure 2-1 Areas of Exceedances of Comparative Values in Soil Figure 2-2 Areas of Exceedances of Comparative Values in Groundwater Figure 2-3 Areas of Exceedances of Comparative Values in Surface Water 3.0 Site Conceptual Model Figure 3-1 Potentiometric Surface- Upper Surficial Zone, June 1, 2015 Figure 3-2 Potentiometric Surface- Lower Surficial Zone, June 1, 2015 Figure 3-3 Potentiometric Surface- Pee Dee Aquifer, June 1, 2015 Figure 3-4 Potential Gradient Between Hydrostratigraphic Units Figure 3-5 Isoconcentration Maps - Eh In Upper Surficial Zone Figure 3-6 Isoconcentration Maps - pH In Upper Surficial Zone Figure 3-7 Isoconcentration Maps - DO In Upper Surficial Zone Figure 3-8 Isoconcentration Maps - Eh In Lower Surficial Zone Figure 3-9 Isoconcentration Maps - pH In Lower Surficial Zone Figure 3-10 Isoconcentration Maps - DO In Lower Surficial Zone Figure 3-11 Isoconcentration Maps - Eh In Upper Pee Dee Zone Figure 3-12 Isoconcentration Maps - pH In Upper Pee Dee Zone Figure 3-13 Isoconcentration Maps - DO In Upper Pee Dee Zone Figure 3-14 Time vs. Boron Concentration Graphs 4.0 Modeling Figure 4-1 Computed vs Observed Values Figure 4-2 Proposed Ash Basin Closures and New Landfill Model Scenario Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page v P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx LIST OF TABLES 1.0 Introduction Table 1-1 Groundwater Analytical Results 2.0 Extent of 2L and 2B Exceedances Table 2-1 Provisional Soil Background Concentrations Table 2-2 Provisional Background Groundwater Concentration - Upper Surficial Table 2-3 Historical Background Compliance Statistics - Lower Surficial Unit Table 2-4 Provisional Background Groundwater Concentration - Lower Surficial Table 2-5 Provisional Background Surface Water Concentrations Table 2-6 Soil Exceedances Table 2-7 Surficial Upper Exceedances Table 2-8 Surficial Lower Exceedances Table 2-9 Pee Dee Upper Exceedances Table 2-10 Pee Dee Lower Exceedances Table 2-11 Surface Water Exceedances Table 2-12 Sediment Exceedances 3.0 Site Conceptual Model Table 3-1 Vertical Hydraulic Conductivity of Undisturbed Soil Samples Table 3-2 Hydraulic Conductivity Table 3-3 Local Groundwater Gradients and Flow Velocities Table 3-4 Vertical Groundwater Gradients Table 3-5 Groundwater Analytical Results - 0.45 vs 0.1 Micron Filtration (September 22/23, 2015) Table 3-6 Ratio of Maximum:Minimum Kd Values from Batch Results 4.0 Modeling Table 4-1 Summary of Kd Values from Batch and Column Studies Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page vi P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx LIST OF APPENDICES Appendix A Duke Energy Background Private Well Data Appendix B Laboratory Reports – September 2015 Appendix C Soil Sorption Report Appendix D Geochemical Modeling Report Appendix E Groundwater Modeling Report Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page vii P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx LIST OF ACRONYMS ASTM American Society for Testing and Materials bgs below ground surface CAMA Coal Ash Management Act CAP Correction Action Plan CCR Coal Combustion Residuals CEM Conceptual Exposure Model CFPUA Cape Fear Public Utility Authority CSA Comprehensive Site Assessment DEP Duke Energy Progress, LLC DWR Division of Water Resources ESV Ecological Screening Value FADA Former Ash Disposal Area GAP Groundwater Assessment Plan IMAC Interim Maximum Allowable Concentration MSL Mean Sea Level MW Monitoring Well NC CAMA North Carolina Coal Ash Management Act NCDENR North Carolina Department of Environment and Natural Resources NCDEQ North Carolina Department of Environmental Quality NORR Notice of Regulatory Requirements NPDES National Pollution Discharge Elimination System PSRGs Preliminary Soil Remediation Goals PZ Piezometer SCM Site Conceptual Model Site L.V. Sutton Energy Complex SLERA Screening Level Ecological Risk Assessment SPLP Synthetic Precipitation Leaching Procedure SW Surface Water 2B NCDENR/DWR Title 15, Subchapter 2B. Surface Water and Wetland Standards 2L NCDENR/DWR Title 15, Subchapter 2L. Groundwater Quality Standards TDS Total Dissolved Solids USEPA United States Environmental Protection Agency USGS United States Geological Survey Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 1.0 INTRODUCTION Duke Energy Progress, LLC (Duke Energy) owns and operates the L.V. Sutton Energy Complex (Site) located on approximately 3,300 acres near Wilmington, North Carolina. The Site is located along the east bank of the Cape Fear River northwest of Wilmington and west of US Highway 421. The Site location is shown on Figure 1-1. The Site formerly operated coal-fired boilers that primarily used bituminous coal as fuel to produce steam to generate electricity and currently contains on-site ash storage areas from the former coal combustion. The North Carolina Coal Ash Management Act (NC CAMA) directs owners of coal combustion residuals (CCR) surface impoundments to conduct groundwater monitoring, assessment, and remedial activities, if necessary. A Comprehensive Site Assessment Report (CSA) dated August 5, 2015, has been completed for the Site. The CSA was conducted to collect information necessary to understand the ash basins as a source of potential impact, the vertical and horizontal extent of potential impact, identify potential receptors and screen for potential risks to receptors. NC CAMA requires the preparation of a Corrective Action Plan (CAP) for each regulated facility within 270 days of approval of the assessment work plan (90 days within submittal of the CSA Report). Duke Energy and the North Carolina Department of Environment Quality (NCDEQ) mutually agreed to a two part CAP submittal, with Part 1 being submitted within the original due date and Part 2 being submitted 90 days thereafter. Based on the findings of the CSA report and the requirements of CAMA, this CAP Part 1 presents a synopsis of the CSA and provides further understanding of groundwater exceedances identified. The CAP Part 1 also presents results of groundwater flow, groundwater-surface water interaction, and fate and transport modeling, which will support a risk assessment, an evaluation of potential remedial alternatives and the recommended remedial approach to be provided in the CAP Part 2. 1.1 Site History and Overview The Site started operations in 1954 with three coal-fired boilers that primarily used bituminous coal as fuel to produce steam to generate electricity. Ash generated from coal combustion was originally stored on-site in the 'former ash disposal area (FADA)', also known as the ‘lay of land area’, then in the 1971 ash basin (old ash basin), and finally the 1984 ash basin (new ash basin) (Figure 1.2). These ash storage areas are referred to as the ash management area. The Site ceased burning coal in November 2013 and switched to natural gas for electricity generation at the Site, thus the facility no longer generates coal ash. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 1.2 Purpose of Corrective Action Plan The final CAP (Parts 1 and 2) are designed to describe means to restore groundwater quality to the level of the standards, or as closely thereto as is economically and technologically feasible in accordance with T15A NCAC 02L .0106. Exceedances of numerical values contained in Subchapter 2L and Appendix 1 Subchapter 02L (IMACs) at or beyond the compliance boundary will be the basis for corrective action with the exception of parameters for which naturally occurring background concentrations are greater than the standards. The purpose of the CAP Part 1 is to clarify what constituent concentrations the owner asserts are background at this time, herein referred to as provisional background. The CAP Part 1 also provides the modeling data to understand groundwater flow direction, simulations of the ash basin removal and effects on groundwater. 1.3 Regulatory Background Discharges from the cooling pond and the ash basins are permitted by NCDEQ under the National Pollution Discharge Elimination System (NPDES) Permit NC0001422. The permitted discharge is to the Cape Fear River which abuts the Site to the west. Duke Energy has performed groundwater monitoring under the NPDES permit since 1990. The current groundwater compliance monitor wells required for the NPDES permit are sampled three times a year and the analytical results are submitted to the DEQ. Groundwater compliance monitoring is performed in addition to the normal NPDES monitoring of the discharge flows. In a Notice of Regulatory Requirements (NORR) dated August 13, 2014, DEQ 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 groundwater constituent concentrations detected above 2L groundwater quality standards at the compliance boundary. 1.3.1 T15A NCAC 2L 0106 – Corrective Action Requirements Groundwater corrective action is addressed in T15A NCAC 2L.0106. “…where groundwater quality has been degraded, the goal of any required corrective action shall be restoration to the level of the standards, or as closely thereto as is economically and technologically feasible.” The specific requirements are as follows: (f) Corrective action required following discovery of the unauthorized release of a contaminant to the surface or subsurface of the land, and prior to or concurrent with Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-3 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx the assessment required in Paragraphs (c) and (d) of this Rule, shall include, but is not limited to: (1) Prevention of fire, explosion or the spread of noxious fumes; (2) Abatement, containment or control of the migration of contaminants; (3) Removal, or treatment and control of any primary pollution source such as buried waste, waste stockpiles or surficial accumulations of free products; (4) Removal, treatment or control of secondary pollution sources which would be potential continuing sources of pollutants to the groundwaters such as contaminated soils and non-aqueous phase liquids. Contaminated soils which threaten the quality of groundwaters must be treated, contained or disposed of in accordance with applicable rules. The treatment or disposal of contaminated soils shall be conducted in a manner that will not result in a violation of standards or North Carolina Hazardous Waste Management rules. The rule additionally delineates the following requirements for CAPs: (h) Corrective action plans for restoration of groundwater quality, submitted pursuant to Paragraphs (c) and (d) of this Rule shall include: (1) A description of the proposed corrective action and reasons for its selection. (2) Specific plans, including engineering details where applicable, for restoring groundwater quality. (3) A schedule for the implementation and operation of the proposed plan. (4) A monitoring plan for evaluating the effectiveness of the proposed corrective action and the movement of the contaminant plume. 1.3.2 Coal Ash Management Act Requirements CAMA 2014 – General Assembly of North Carolina Senate Bill 729 Ratified Bill (Session 2013) (SB 729) revised North Carolina General Statute 130A-309.209(a) has additional requirements regarding corrective action at the Site. In regards to this CAP, Section §130A-309.209 of the CAMA ruling specifies groundwater assessment and corrective actions, drinking water supply well Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-4 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx surveys and provisions of alternate water supply, and reporting requirements as follows: (b) Corrective Action for the Restoration of Groundwater Quality. - The owner of a coal combustion residuals surface impoundment shall implement corrective action for the restoration of groundwater quality as provided in this subsection. The requirements for corrective action for the restoration of groundwater quality set out in the subsection are in addition to any other corrective action for the restoration of groundwater quality requirements applicable to the owners of coal combustion residuals surface impoundments. (1) No later than 90 days from submission of the Groundwater Assessment Report required by subsection (a) of this section, or a time frame otherwise approved by the Department not to exceed 180 days from submission of the Groundwater Assessment Report, the owner of the coal combustion residuals surface impoundment shall submit a proposed Groundwater Corrective Action Plan to the Department for its review and approval. The Groundwater Corrective Action Plan shall provide restoration of groundwater in conformance with the requirements of Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code. The Groundwater Corrective Action Plan shall include, at a minimum, all of the following: a. A description of all exceedances of the groundwater quality standards, including any exceedances that the owner asserts are the result of natural background conditions. b. A description of the methods for restoring groundwater in conformance with requirements of Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code and a detailed explanation of the reasons for selecting these methods. c. Specific plans, including engineering details, for restoring groundwater quality. d. A schedule for implementation of the Plan. e. A monitoring plan for evaluating effectiveness of the proposed corrective action and detecting movement of any contaminant plumes. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-5 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx f. Any other information related to groundwater assessment required by the Department. (2) The Department shall approve the Groundwater Corrective Action Plan if it determines that the Plan complies with the requirements of this subsection and will be sufficient to protect public health, safety, and welfare; the environment; and natural resources. (3) No later than 30 days from the approval of the Groundwater Corrective Action Plan, the owner shall begin implementation of the Plan in accordance with the Plan’s schedule. 1.3.3 Regulatory Standards for Site Media Groundwater samples are compared to North Carolina Groundwater Quality Standards found in the North Carolina Administrative Code Title 15A, Subchapter 2L.0202 (2L or 2L Standards) or the Interim Maximum Allowable Concentrations (IMAC) established by NCDEQ pursuant to 15A NCAC 02L.0202(c). The IMACs were issued in 2010, 2011, and 2012, however NCDEQ has not established a 2L for these constituents as described in 15A NCAC 02L.0202(c). For this reason, IMACs noted are for reference only. Surface water sample analytical results are compared to the appropriate North Carolina Surface Water and Wetland Standards found in the North Carolina Administrative Code Title 15A, Subchapter 02B.0200 (2B or 2B standards) established by NCDEQ and USEPA National Recommended Water Quality Criteria. The most conservative of the two values (ecological and human health) was relied upon in the comparison tables included herein to focus evaluation of constituents in surface water for additional evaluation in the risk assessment and corrective action evaluation process. Compositional (total) soil sample analytical results were compared to NCDEQ Preliminary Soil Remediation Goals (PSRGs) ‘new format’ tables for industrial, residential and groundwater exposures (updated March 2015). Sediment sample analytical results were compared to USEPA Region 4 Ecological Screening Values (ESVs). Analytical results of soil samples analyzed using the synthetic precipitation leaching procedure (SPLP) were compared to groundwater criteria including the 2L and IMAC. The SPLP results provide some indication as to the likelihood that Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-6 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx certain constituents may or may not leach from soil to groundwater at a given location. 1.3.4 NCDEQ Requirements NCDEQ issued site specific requirements for the site in letters dated November 4, 2014 and February 6, 2015. Specific NCDEQ requirements attached to the February letter were modified after issuance of the letter and were finalized on July 7, 2015. 1.3.5 NORR Requirements The NORR required Duke Energy to comply with 15A NCAC 02L .0106(g), DWR’s Groundwater Modeling Policy, May 31, 2007, and various site specific requirements. 1.4 Summary of CSA Findings The CSA focused on evaluation of constituents associated with CCR, such as metals and other inorganics. NCDEQ prescribed the list of monitoring parameters to be measured at the Site. Following receipt of the data, parameters were evaluated to assess those most relevant for the Site. These parameters were determined by examining data from monitoring wells installed in ash and groundwater, and then by comparing these results to 2L or IMAC. Previously collected data from NPDES compliance monitoring and assessments, including; Preliminary Site Investigation Data Report-Addendum No. 1, Conceptual Closure Plan, L.V. Sutton Plant and Data Interpretation and Analysis Report, Conceptual Closure Plan, L.V. Sutton Plant, (GeoSyntec Consultants, July 214) were incorporated into this evaluation. When water is present below the ash surface and above the base of the basin, it is referred to as ash pore water. If a constituent concentration exceeded the North Carolina Groundwater Quality Standards in ash pore water wells, as specified in the 2L Standards or the IMACs, it is recognized as having the potential to migrate into groundwater and cause a groundwater exceedance. The geochemical dynamics associated with the ash basin influence on groundwater is also a mechanism that may mobilize naturally occurring metals to leach from soil to groundwater. Some constituents are also present in background monitoring wells and thus require careful examination to determine whether their presence on the downgradient side of the basins is from natural or other sources (e.g., rock and soil, off-site influence) or the ash basins. This assessment of naturally occurring background concentrations will be further evaluated as part of the CAP process, but is also understood to be an ongoing effort as more data becomes available for the site. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-7 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx The CSA determined that coal ash accumulated in the ash basins and FADA are sources of groundwater impact (Table 1-1). The cause of impact is leaching of constituents from the coal ash into the ash pore water and its migration to underlying groundwater. The CSA indicated concentrations of arsenic, barium, boron, iron, manganese, thallium, vanadium, and total dissolved solids (TDS) in excess of North Carolina Administrative Code (NCAC) Title 15A Chapter 02L.0202 groundwater quality standards (2L) or the Interim Maximum Allowable Concentration (IMAC) were detected in groundwater samples collected in ash pore water wells. These constituents were identified as constituents. Concentrations of cobalt and selenium in excess of the 2L or IMAC were detected in groundwater samples collected at compliance monitor wells. The area of selenium to the north of the 1984 basin is being further assessed to facilitate preparation of the CAP Part 2. Based on scientific evaluation of historical and new groundwater assessment data presented in the CSA, the following conclusions were drawn: Recent groundwater assessment results are consistent with previous results from historical and routine compliance boundary monitoring well data. Background monitoring wells contain naturally occurring constituents at concentrations greater than 2L or former IMAC. This information is used to evaluate whether concentrations in groundwater downgradient of the basins are naturally occurring, from another source or influenced by migration of constituents from an ash basin. As examples, iron, manganese, cobalt and vanadium are present in the background monitor well samples at concentrations at or above their applicable 2L or IMAC. Regional groundwater flow is to the west toward the Cape Fear River, to the east toward the Northeast Cape Fear River or to the south toward the convergence of the two rivers. In the vicinity of the 1971 and 1984 ash basins, groundwater flows radially. A groundwater divide is located northeast of the ash basins and groundwater north of the basins flow west toward the cooling pond. Groundwater east and south of the basins flows east, southeast and south. In the FADA, groundwater flows to the southwest. Data indicate the water quality of the Cape Fear River has not been impacted by the ash basins. Aluminum was detected above 2B in a surface water sample collected from the river, however, both the background and detected concentrations of aluminum were significantly higher than those detected in a sample from ash pore water, ground water or cooling pond surface samples. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-8 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Sediment sample data indicate only barium exceeds the regulatory criteria or background concentrations. Based on Site conditions, it does not appear that sediment data collected from the Cape Fear river is reflective of impact from Site groundwater discharge. Migration of constituents, primarily boron, above the 2L, has occurred in the lower surficial aquifer at a depth of approximately 25 to 50 feet below ground surface. Concentrations of boron in the ash pore water and groundwater adjacent to the 1971 ash basin are higher than elsewhere on the Site. Also, boron concentrations are not observed in surficial aquifer background wells and concentrations decrease downgradient of the basins; thus, boron serves as a good indicator of the maximum extent of ash constituent migration. However, boron has also been detected in deeper Pee Dee formation wells at the site. This is likely a result of saltwater intrusion (boron is the 10th most prevalent constituent in sea water). Regional groundwater data supports this. Boron is detectable above the 2L in offsite monitoring wells downgradient and east of the basins. The horizontal extent of the boron concentrations in the surficial aquifer above the 2L has been defined. Boron concentrations greater than 2L do not extend southeast to the public water supply wells located beyond the property boundary southeast of the basins. The approximate extent of horizontal migration of boron is shown on Figure ES-1. The flow paths for constituents indicate a preference for lateral migration, rather than vertical migration, as a result of contrasting hydraulic conductivities between the surficial and Pee Dee formations. A clay confining unit was not observed in the monitoring wells or soil borings within the study area. While no confining unit is present above the Pee Dee Formation, the lower permeability of the Pee Dee Formation reduces vertical migration of constituents. The CSA characterizes the horizontal and vertical extent of constituents and groundwater gradients which now facilitate development of the Site Conceptual Model (SCM) (i.e., the groundwater flow and constituent migration model). This then facilitates development of the CAP. The horizontal extent of boron in the lower surficial aquifer at levels exceeding the 2L has extended beyond the site boundary to the east. Mitigating actions to address this horizontal extent are already initiated. o An interim corrective action plan has been prepared and submitted to NCDEQ. The interim plan proposes 12 groundwater extraction wells Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-9 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx along the eastern property line to intercept the groundwater in the area of boron migration. o Data indicate boron concentrations in nearby water supply wells are less than the 2L. o The approximate extent of horizontal migration of boron in the surficial aquifer is shown on Figure ES-1. 1.5 Site Description The Site consists of approximately 3,300 acres and is developed with the power plant structures, the ash basins, cooling pond and associated canals. The plant structures are located primarily in the south central portion of the Site with the ash basins north of these structures. Plant water production wells are located along the entrance road on the east side of the Site (Figure 1-2). The northern and southern portions of the Site are primarily undeveloped areas containing small sand hills, pine woods and brush. The Site utilizes an approximate 1,100-acre cooling pond, referred to as Lake Sutton, located adjacent to the Cape Fear River. A boat ramp and parking lot are located at the north end of the lake; this feature is accessed by way of Sutton Lake Road, which extends across the Site from NC Hwy 421 to Lake Sutton. The Plant, cooling pond (Lake Sutton) and ash management area are located on the east side of the Cape Fear River. The ash management area is located adjacent to the cooling pond, north of the Plant, as shown on Figure 1-2. The ash management area consists of three locations (Duke Energy, October 31, 2014): The FADA, also known as the lay of land area is located south of the ash basins, on the south side of the canal. It is believed that ash may have been placed in this area between approximately 1954 and 1972. The 1971 ash basin (old ash basin) is an unlined ash basin built in approximately 1971. The basin contains fly ash, bottom ash, boiler slag, storm water, ash sluice water, coal pile runoff, and low volume wastewater. An ash basin with a 12-inch thick clay liner was built in approximately 1984 (new ash basin), located toward the northern portion of the ash management area, and was operated from 1984 to 2013. The basin contains fly ash, bottom ash, boiler slag, storm water, ash sluice water, coal pile runoff, and low volume wastewater. The Site is surrounded by commercial, industrial, mining (sand quarry), residential and forest land. The quarry property and a plant located north of the quarry operate Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-10 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx production wells on land adjacent to the Site. No future change in use of the surrounding land is currently anticipated. 1.6 Site Geology No consolidated rock outcrops are present at the Site. Undeveloped areas consist of small sand hills, low-growth vegetation and pine woods or cleared electric transmission line corridors. The Site subsurface consists of sands of the surficial aquifer which extend to approximately 50 feet bgs. The upper 20 feet or so of this unit consists of well-sorted, light-colored sand, loose to moderately dense with little shell or organics. The lower 30 feet consists primarily of poorly-sorted sands with discontinuous layers of coarse sand and fine gravel. Thin laminae of silts and clays also occur randomly in the lower portion of this unit. Wood remnants were also encountered in places near the contact with the lower Pee Dee Formation. The surficial sands lie uncomfortably over the Pee Dee Formation. The contact between the surficial and the Pee Dee Formation is sharp and distinct due to the dark grey-green color of the fine sands and silts of the Pee Dee. Trace amounts of large shell and sandstone were also occasionally observed at this contact. The Pee Dee Formation extends to the deepest horizon explored (150 feet bgs) during the assessment. The upper portion of the Pee Dee consists of dark gray or medium to dark green fine sands and silt with clay lenses and laminae. Below 75 feet, thin layers of sandstone were encountered; however these were not continuous across the Site. The Pee Dee becomes finer with depth and often is a very dense, low-plasticity clayey silt. 1.7 Site Hydrogeology The surficial unconfined aquifer is the first major hydrostratigraphic unit at the Site. The upper portion of the surficial aquifer is relatively uniform in structure and grain size, primarily consisting of well sorted sands; while the lower portion varies greatly in grain size, with poorly-sorted sands interbedded with numerous coarse-grained layers containing fine gravel and occasionally with thin silt laminae. The upper portion grades into the lower portion between 15 and 25 feet bgs. The Pee Dee Formation directly underlies the surficial zone at the Site. In areas south of the Site a confining unit is reported to be present between the surficial zone and the Pee Dee Formation; this confining unit was not found to be present at the Site. The contact between the Pee Dee Formation and the overlying surficial unit is sharp and sediments of the Pee Dee greatly contrast with the overlying surficial unit. The Pee Dee consists of Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-11 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx dark gray-green, fine-grained, silty, clayey sands or clayey sandy silts with occasionally clay lenses. The first occurrence of groundwater at the Site is in the surficial aquifer at depths ranging from 3 to 17 feet bls. Groundwater flow direction in the upper and lower portions of the surficial aquifer beneath the ash basins flows radially from the central sand hills portion of the Site, indicating this is likely a local recharge area. Generally, groundwater flows east, southeast and south from the Site. Water level data from the Pee Dee formation indicates groundwater flow to the east and south. The presence of high capacity industrial and public water supply pumping wells near the Site complicates the determination of groundwater flow. 1.8 Site Hydrology The Site is located on a peninsula defined by the Cape Fear River, adjacent to the west and the Northeast Cape Fear River, located approximately one mile to the east. Based on regional topography and drainage features, groundwater flow within this peninsula would be either to the west or east to one of the two rivers or to the south where the rivers converge. The water table at the Site is typically located at depths of approximately 3 to 17 feet bgs, depending on antecedent precipitation and topography. The surficial aquifer groundwater flow regime of the Site is hydraulically bounded on the west by the cooling pond and the Cape Fear River which flows south. The Northeast Cape Fear River is approximately one mile east of the Site and regional groundwater flow is anticipated to be south in the areas between the two rivers. Groundwater gradients in the surficial aquifer are affected by manmade features (plant area, cooling pond), the ash basin, Site production wells and off-site public supply wells, production wells for the Invista plant, and production wells for the ST Wooten facility and Site geology. 1.9 Receptor Survey Surveys to identify potential receptors for groundwater including public and private water supply wells (including irrigation wells and unused or abandoned wells) and surface water features within a 0.5-mile radius of the Site compliance boundary have been reported to NCDEQ and were included in the CSA. The surveys included results of a review of publicly available data from NCDEQ Department of Environmental Health, NC OneMap GeoSpatial Portal, DWR Source Water Assessment Program online database, county geographic information system, Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-12 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Environmental Data Resources, LLC records review, the United States Geological Survey National Hydrography Dataset, as well as a vehicular survey along public roads located within 0.5 mile radius of the compliance boundary. 1.9.1 Surrounding Land Use Properties located within a 0.5 mile radius of the Site ash management area compliance boundary are located in New Hanover County, North Carolina, with the exception of an undeveloped portion of land on the west side of the Cape Fear River in Brunswick County. The properties are primarily used for commercial and industrial purposes. There are no residential properties located within the 0.5 mile radius of the compliance boundary. The Site is surrounded by commercial, industrial, mining (sand quarry), residential and forest land. The quarry property and a plant located north of the quarry operate production wells on land adjacent to the Site. 1.9.2 Availability of Public Water Supply Public water is not available for the Site and adjacent properties with the exception of the residences in the Flemington community located southeast of the Site. The Flemington community is supplied with public water by the four Cape Fear Public Utility Authority wells. 1.9.3 Drinking Water Supply Well Survey Findings The well surveys indicated that no wellhead protection areas or surface water bodies used for drinking water are located within a 0.5 mile radius of the compliance boundary. The Site cooling pond (Lake Sutton) and the Cape Fear River are located adjacent to the Site to the west, however, these surface water bodies are not used as drinking water sources. Approximately 32 possible private water supply wells were observed, were reported, or were assumed to be located within the survey area, within 0.5 mile of the compliance boundary (Figure 1-7). This includes eight on-site wells used for Site operations. Some of the private water wells, located on the adjacent Wooten property, are located within the zone of constituent exceedances. These wells are currently used to provide water to the sand quarry facility. Four public supply wells identified adjacent to or near the southeastern boundary of Site: NHC-SW 1(abandoned) 1,100 feet east of property line Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-13 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx NHC-SW 2(not in use) adjacent, east of property line NHC-SW 3 650 feet east of property line NHC-SW 4 800 feet east of property line Public water supply wells NHC-SW3 and NHC-SW4 are routinely monitored for the Site constituents. 1.9.4 Potential Human Receptors A screening level human health risk assessment was performed as a component of the CSA Report (SynTerra, 2015). Preliminary human health conceptual exposure models were prepared as part of the screening level risk assessment. Each model identified the exposure media for human receptors. Human health exposure media includes potentially impacted groundwater, soil, surface water and sediments. The exposure routes associated with the potentially complete exposure pathways evaluated for the site include ingestion, inhalation and dermal contact of environmental media. Potential human receptors under the current use scenario include recreational users along with industrial workers. Potential human receptors under a hypothetical future use scenario include residents, recreational users and industrial workers. The conceptual exposure model will continue to be refined consistent with risk assessment protocol, in the CAP Part 2. 1.9.5 Potential Ecological Receptors The L. V. Sutton site is located in the Mid-Atlantic Floodplains and Low Terraces ecoregion of North Carolina, a continuation of the Southeastern Floodplains and Low Terraces ecoregion (Griffith, et al., 2002). Wetland delineation was conducted in 2015 by AMEC Foster Wheeler, which identified 15 wetland areas and two jurisdictional tributary segments based on current wetland and stream criteria established by the US Army Corps of Engineers and NC Division of Water Resources. A screening level ecological risk assessment (SLERA) was conducted, which involved investigation of areas on site with potential for exposure to ecological receptors (e.g., surface water, seeps, sediment, and soil). Samples were collected and analyzed for the purposes of characterization and comparison to established water, soil, and sediment quality criteria as published by the US EPA and/or NCDEQ. These parameters, when comparing upgradient (i.e., provisional background) locations to downgradient locations, aid in determination of areas of potential concern for ecological receptors, such as: aquatic receptors (e.g., fish, Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 1-14 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx benthic invertebrates, aquatic plants), semi-aquatic receptors (e.g., amphibians, piscivorous birds, piscivorous mammals), terrestrial receptors (e.g., insects, small and large mammals, passerine birds, raptors), and soil organisms (e.g., plants, soil invertebrates, soil microbes). Results of the SLERA, analyzed in the context of background data, indicate that many constituents that exceed screening criteria occur at naturally elevated levels in the area. There are, however, some constituents in various media that are found at greater concentrations in source areas than in background or other receiving areas, such as: copper, manganese, vanadium, and zinc. These have the potential to pose risk to ecological receptors, potentially including those listed on the threatened and endangered list for New Hanover County, such as various terrestrial mammals and birds, and semi-aquatic and aquatic invertebrates and amphibians in their respective media (e.g., soil, sediment, and surface water). These potential risks will be addressed further as part of the risk assessment in the CAP Part 2. Additional details regarding the screening-level risk assessment can be found in the L. V. Sutton CSA report (SynTerra 2015). Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 2.0 BACKGROUND CONCENTRATIONS AND EXTENT OF EXCEEDANCES In accordance with CAMA, the CAP provides a description of all exceedances of groundwater quality standards, including any exceedances that Duke Energy asserts are the result of natural background concentrations. Background concentrations are considered provisional values and will be updated as more data becomes available and with input from NCDEQ. This section establishes provisional background concentrations for the media of interest (soil, groundwater, surface water and sediment). Using provisional background data, the extent of potential ash basin influence can be better understood. Sample results are then compared to regulatory criteria and background concentrations in order to make risk assessment evaluations and ultimately determine areas and media where corrective action evaluation is appropriate. During the CSA, source areas were defined as the ash basins. Source characterization was conducted to identify physical and chemical properties of ash, ash basin pore water, and ash basin seeps (leachate). Analytical results for source characterization samples were compared to 2L or IMAC values, and other regulatory screening levels for the purpose of identifying constituents that may be associated with potential impacts to soil, groundwater, and surface water from the source areas. Numerous constituents are naturally occurring and present in background media and thus require examination to determine whether the concentrations downgradient of the source areas are naturally occurring or a result of influence from the source areas. 2.1 Provisional Background Concentrations Provisional background concentrations are initially used to identify areas of potential source area influence. This is intended to expand on the analysis provided in the CSA. Site-specific background locations were identified for each media (soil, sediment, surface water, and groundwater). Background locations were selected for each media based on topographic maps, groundwater elevation maps, Site Conceptual Model (discussed further in Section 3), historical analytical results, results of the fate and transport model (discussed in Section 4) and input from NCDEQ. Per 15A NCAC .0106(k), any person required to implement a CAP may propose alternate background concentrations based on site-specific conditions. Parameters with reported values in excess of a standard or criteria and located downgradient of a source area were selected for evaluation against provisional background concentration. In addition, background concentrations for constituents which provide an indication of Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx ash basin influence but do not have established criteria, such as strontium and specific conductance in groundwater, have also been evaluated as a basis for comparison to determine horizontal and vertical extent of migration. The compliance boundary background groundwater data at Sutton provides a sufficient database to develop statistically significate values for shallow groundwater. For the other media and groundwater flow zones, provisional background concentrations will be developed based upon analysis of the current CSA data. Additional background data will also be developed and used for further evaluation in the CAP Part 2. For the Pee Dee formation in particular, additional background wells are planned to develop provisional background data for the CAP Part 2. As part of the CAP Part 2, a risk assessment will be conducted to identify areas where corrective action evaluations may be needed. This is done by identifying media locations affected by source areas having a concentration in excess of the appropriate standard or criteria, or the provisional background value, whichever is greater. Where limited background data is currently available, the highest observed background value for each parameter in each media will be considered the potential provisional background value unless the data appears to be an outlier or otherwise unrepresentative. The existing Sutton database indicates that some parameters have background concentrations similar to or greater than measured values in areas potentially affected by the former ash basins. Where sufficient data exists, statistical analysis was conducted to further evaluate observed background concentrations for each media. For the Site, this includes background groundwater data from the compliance monitoring wells screened within the lower surficial aquifer. Where provisional background concentrations are greater than regulatory criteria such as 2L, 2B, or NCPSRG values, provisional background values will be the basis for establishing areas for risk assessment and corrective action evaluations. The soil background concentrations will primarily be used to determine if naturally occurring metals concentrations in soil may leach and produce groundwater concentrations greater than 2L or IMAC. The data also provide an indication of whether naturally occurring soil concentrations are greater than risk-based human consumption concentrations. However, for the purpose of the groundwater corrective action plan, the soil to groundwater leaching concentration is of primary interest. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-3 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 2.1.1 Provisional Background Soil Concentrations Soils collected during installation of background monitoring wells were used to develop provisional soil background concentrations. These locations are: AW-08 (40’-42’ bgs) and MW-37 (4’-6’ & 43’-45’ bgs) (Figure 2-1). Table 2-1 Provisional Soil Background Concentrations Analytical Parameter North Carolina Preliminary Soil Remediation Goals Range of Observed Concentrations Provisional Background Concentration** Industrial Health Residential Health Protection of Groundwater Antimony 94 6.2 0.9 ND ND Arsenic 3 0.67 5.8 ND ND Barium 44,000 3,000 580 0.62 - 6 6 Boron 46,000 3,200 45 4.5 4.5 Cobalt 70 4.6 0.9 ND ND Iron 100,000 11,000 150 31.5 - 1,300 1,300 Manganese 5,200 360 65 0.41 - 6.3 6.3 Nickel 4,400 300 130 0.33 - 0.94 0.94 Selenium 1,200 78 2.1 ND ND Thallium 2.4 0.16 0.28 ND ND Vanadium 1,200 78 6 1.1 - 3.8 3.8 Notes: Created by: EMB Checked by: KDB Soil PSRG – Inactive Hazardous Sites Branch Preliminary Soil Remediation Goals (PSRGs) September 2015 All concentrations reported in milligrams per kilogram ND – Not detected ** Provisional background concentration is equal to the maximum background concentration taken from locations AW-08 and MW-37 Shading indicates comparative value to be used in risk assessment and corrective action evaluation if necessary 2.1.2 Provisional Background Groundwater Concentrations Monitoring wells considered in developing the provisional background groundwater concentrations include existing NPDES compliance boundary wells, wells installed during previous groundwater investigations, and wells recently installed as part of the CSA (Figure 2-2). Discussion of each monitoring well and justification for inclusion in the background data set is included in the CSA (August, 2015). Background wells for each hydrostratigraphic zone are: Upper Surficial: MW-37B, Lower Surficial: MW-4B, MW-5C (compliance wells), MW-37C Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-4 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx The groundwater data collected from these background wells are summarized in Tables 2-2 and 2-4 below. Please note, the analytes on these tables differ from one another because different sets of constituents were detected in the upper and lower surficial zones. Currently there are no background data for the Pee Dee zones. Monitor wells are anticipated to be installed in the upper (75 feet bgs), intermediate (D zone) and lower (E zone) Pee Dee at the MW-5 and MW-37 locations to collect background data for these zones prior to the CAP Part 2. PZ-6D will also be monitored to collect additional Pee Dee background data. 2.1.2.1 Provisional Background Concentration – Upper Surficial Aquifer The data set for the upper surficial aquifer is currently limited to two sampling events of MW-37B. Provisional background concentrations for the upper surficial based on these two sampling events summarized on Table 2-2. Table 2-2 Provisional Upper Surficial Background Concentrations Analytical Parameter NCAC 2L Standard Range of Observed Concentrations Provisional Background Concentration pH (S. U.) 6.5 - 8.5 4.3 - 4.5 4.3 - 4.5 Antimony 1* ND ND Arsenic 10 ND ND Barium 700 8 - 10 10 Boron 700 ND ND Cobalt 1* ND ND Iron 300 31 - 687 687 Lead 15 ND ND Manganese 50 7 - 38 38 Nitrate (as N) 10,000 96 - 102 102 Selenium 20 ND ND Thallium 0.2* ND ND Total Dissolved Solids 500 ND ND Vanadium 0.3* ND ND Notes: Prepared By: EMB Checked By: KDB S.U. = Standard Unit Shading indicates comparative value to be used in risk assessment and corrective action evaluation if necessary Units reported in µg/L unless otherwise stated * Interim Maximum Allowable Concentrations (IMACs) of the 15A NCAC 02L Standard, Appendix 1, April 2013. ** Provisional background concentrations correspond with the maximum concentrations in background well MW-37B (2 sampling events) Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-5 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 2.1.2.2 Provisional Background Groundwater Concentration – Lower Surficial Aquifer Provisional background concentrations in the lower surficial aquifer were determined using historical data from compliance background wells MW- 4B and MW-5C, as well as recent data collected from MW-37C. The historical data set from the compliance wells was evaluated to exclude sample events associated with levels of pH or turbidity that may misrepresent background conditions. Table 2-3, presented in the Tables attachment, displays the analytical data used to evaluate background concentrations and highlights the sample results that have been excluded. Monitoring wells MW-4B and MW-5C were installed prior to 2015. Samples have been collected from these wells for arsenic, chloride, iron, selenium and TDS since 1990 and for the current compliance analyte list since 2006. Both MW-4B and MW-5C are currently used as background wells for NPDES monitoring and are screened in the lower surficial zone. The following method was used to determine a statistically derived prediction limit for surficial groundwater at the Site. Background groundwater data are evaluated using inter-well prediction limits (parametric, nonparametric, and Poisson) to develop site specific prediction limits to represent provisional background concentrations. Based on recommendations from ASTM D6312-98 guidance and USEPA 2007, non-detected values were replaced with half of the detection limit for the parametric and Poisson prediction limit procedures, and the detection limit for the nonparametric prediction limit procedure. Confidence levels were set at 99 percent for the parametric and Poisson prediction interval. Confidence levels for the nonparametric prediction limit are given by n/(n+k) were n is the number of background samples and k is the number of comparisons. The false positive rate is given by 1- [n/(n+k)]. The number of comparisons is defined by the number of recent sample dates multiplied by the number of compliance wells (background wells). Prior to conducting the inter-well statistical analysis, the data set was “screened” and “treated.” The Shapiro-Wilks goodness-of-fit test was used to evaluate the statistical distribution of data sets because they contain less than 50 measurements. Each data set was initially tested to determine whether the distribution is normal. If a data set fails the test of normality, Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-6 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx the natural logarithms of the data are taken and the procedure is repeated. If the transformed data passes, the data set is designated as lognormal. If a log transformed data set fails the test of normality, the data set is designated as non-normal. The parametric prediction limit was used to analyze data that were normally or log normally distributed with less than or equal to 50 percent non-detects (ASTM D6312-98, Section 6.1.1). The nonparametric prediction interval test was performed on normal and lognormal data sets with greater than 50 percent non-detects and for data sets with non-normal distributions with fewer than 90 percent non-detects (ASTM D6312-98, Section 6.1.1). The nonparametric prediction limit compares each individual down gradient concentration for the selected dates to the maximum concentration in background samples. The Poisson prediction limit statistic was utilized to evaluate data with greater than 90 percent non-detects (ASTM D6312-98, Section 6.1.1). A summary of the inter-well statistics is included in Table 2-3. The inter- well prediction limit (parametric) is greater than the 2L Standard and is the background concentration for the following analytes: pH – 4.5 – 8.5 Standard Units (SU) Antimony – 13.7 µg/L Cadmium – 3.9 µg/L Chloride – 267,000 µg/L Cobalt – 2.99 µg/L Iron – 5,900 µg/L Manganese – 828 µg/L Thallium – 3.82 µg/L Vanadium – 1.22 µg/L Provisional background concentrations for the lower surficial zone are summarized in Table 2-4. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-7 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Table 2-4 Provisional Lower Surficial Background Concentrations Analytical Parameter NCAC 2L Standard Range of Observed Concentrations Provisional Background Concentration pH (S.U.) 6.5 - 8.5 4.5- 8.0 4.5 - 8.5 Antimony 1* 0.140 - 1.08 13.7 Arsenic 10 0.28 - 9.8 6.8 Barium 700 0.47 - 80. 95 Boron 700 9.70 - 928 45.0 Cadmium 2 ND - 0.10 3.9 Chloride 250,000 3,200 - 295,000 267,000 Chromium 10 0.61 - 3.0 4.6 Cobalt 1* 0.640 - 2.99 2.99 Copper 1000 1.30 - 27.6 20 Iron 300 11 - 9,700 5,900 Lead 15 0.12 - 3.2 5.7 Manganese 50 6.34 - 602 828 Nitrate (as N) 10,000 30 - 50 250 Selenium 20 1.0 - 17 11 Sulfate 250,000 6,900 - 74,000 53,200 Thallium 0.2* ND - 0.180 3.82 Total Dissolved Solids 500,000 8,000 - 760,000 499,000 Vanadium 0.3* 0.514 - 1.22 1.22 Notes: Created by: TDP Checked By: CJS Provisional background concentration equals parametric prediction concentration from historical background compliance wells MW-04B, MW-05C and MW-37C * Interim Maximum Allowable Concentrations (IMACs) of the 15A NCAC 02L Standard, Appendix 1, April 2013. Units reported in µg/L unless otherwise stated Shading indicates comparative value to be used in risk assessment and corrective action evaluation if necessary S.U. = Standard Unit 2.1.2.3 Duke Energy Background Private Well Sampling Duke Energy conducted a study of private wells located between two and ten miles from the Site. The goal of this study was to provide a locally relevant data set beyond potential influence of the ash basins in order to determine levels of constituents observed naturally near the site. Ranges of observed concentrations from this study are generally consistent with the provisional background concentrations provided in this CAP Part 1. The Site provisional background data were generally higher than the average constituent concentrations in the private well data, with the notable exceptions of boron (260 µg/L) and strontium (267 µg/L). Detailed Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-8 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx information as to well construction details and depths were not available. The private background well study data serves as a good basis for comparison of background concentrations. The private well data are presented in Appendix A. 2.1.3 Provisional Background Surface Water Concentrations A background surface water sample was collected upstream from the ash basins along the Cape Fear River. The upstream Cape Fear River sample (SW-CFUP) serves as a background sample for both the 1971 and 1984 ash basins and the FADA (Figure 2-3). It should be noted that the Invista NPDES outfall (and other NPDES outfalls upgradient in the watershed) will create anthropogenic background influence. Provisional surface water background concentrations for the parameters manganese and zinc were determined as described above and summarized on Table 2-5. Only one background sample on the Cape Fear River is available to date; additional sample events will be used to further define surface water background concentrations for the CAP Part 2. Provisional background concentrations for manganese and zinc (dissolved) are greater than applicable regulatory values. Table 2-5 Provisional Surface Water Background Concentrations Analytical Parameter Surface Water Criteria NCAC 2B / EPA NRWQC Provisional Background Concentration Human Health Ecological pH 5 - 9 6.5-9 6.56 Aluminum 8,000 87 496 Antimony 640 NE ND Iron NE NE 1,390 Manganese 100 NE 118 Mercury (ng/L) NE 0.012 3.87 Thallium 0.47 NE ND Vanadium NE NE 2.44 Zinc (dissolved) 5 36 86 Notes: Created by: TDP Checked By: CJS All provisional background concentrations are based on SW-CFUP All values reported in µg/L unless otherwise stated NE = Not Established ND = Not Detected Shading indicates comparative value to be used in risk assessment and corrective action evaluation if necessary Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-9 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 2.1.4 Provisional Background Sediment Concentrations A background sediment sample was collected upstream from the ash basins along the Cape Fear River. The upstream Cape Fear River sample (SW-CFUP) serves as a background sample for both the 1971 and 1984 ash basins and the FADA (Figure 2-3). No constituents were detected greater than screening values in the upgradient sediment sample, therefore provisional background concentrations are not currently anticipated for the risk assessment and further evaluations. 2.2 Exceedances Soil, sediment, surface water and groundwater results from samples collected downgradient of the ash basins were used to evaluate the distribution of constituents and assess the areas of potential influence. A risk assessment to be conducted as part of the CAP Part 2 will be used to further assess potential areas for corrective action evaluation. 2.2.1 Soil The following describes the observed exceedances in downgradient area soils compared to provisional background and regulatory screening levels for groundwater. Table 2-6 compares soil sample analytical results to regulatory criteria and background values. Sample locations are shown on Figure 2-1. 2.2.1.1 1971 Ash Basin Soil samples collected from beneath the ash in the 1971 ash basin contain iron above PSRGs, protective of groundwater. The sample collected beneath the ash (82-84 feet bgs) is from the base of the surficial aquifer (the depth being greater due to the height of the ash stack) and had an iron concentration of 6,500 mg/kg. This concentration is greater than background and most other soils samples collected outside the basin and within the lower surficial zone. The deep sample collected beneath the 1971 ash basin (96-98 feet) is from the Pee Dee zone and had a concentration of 6,050 mg/kg, which is comparable to other iron concentrations detected in the Pee Dee zones. As previously stated, background concentrations have not been established for the Pee Dee zone and therefore it is unclear if the detected iron concentrations within this zone beneath the ash basin and elsewhere at the Site are naturally-occurring or attributable to the ash basin. 2.2.1.2 FADA Shallow soil samples (10-12 feet bgs) collected from beneath the ash in FADA did not contain metals that exceed PSRGs. Iron and arsenic Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-10 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx exceeded the PSRG in the deep soil sample (53-55 feet bgs) collected beneath the FADA. Arsenic and iron exceed the PSRG at three locations outside of the ash basins and off-site; AW-02, AW-06 and AW-07. Iron also exceeds PSRG at SMW-06 and manganese exceeds the PSRG at AW-07. None of these exceedances are in surficial soils or above the water table. Areas identified where soil exceeds background concentrations and PSRGs in the vicinity of the basins are illustrated conceptually on Figure 2-3. 2.2.2 Groundwater Where groundwater data indicate constituent(s) exceed an applicable regulatory value or the provisional background concentration, the area is interpreted to be influenced by the presence of the source areas. The general area is illustrated conceptually on Figure 2.1. 2.2.2.1 1971 Ash Basin Arsenic, boron, pH, TDS and vanadium were detected in the 1971 basin ash pore water at concentrations above 2L, IMAC and/or provisional background concentrations. Groundwater beneath the 1971 ash basin contains iron, manganese, pH and vanadium above 2L, IMAC and provisional background values. Strontium, which is commonly associated with coal ash, was also detected at elevated concentrations (6,280 µg/L) in the 1971 basin ash pore water. While strontium does not have a 2L or IMAC, its occurrence is a potential indicator of influence of the ash basin to downgradient groundwater. Hexavalent chromium was also detected in the 1971 basin ash pore water. Hexavalent chromium does not have a 2L or IMAC; however concentrations exceeding the EPA tap water standard of .035 µg/L were detected in ash pore water and in groundwater of selected wells. A background concentration for hexavalent chromium has not yet been established for the Site. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-11 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Within the upper surficial aquifer, the following constituents extend beyond the 1971 ash basin at concentrations greater than 2L, IMAC and/or provisional background (Table 2-7): Boron – Extends southeast to MW-19 pH – To the east and southeast of the compliance boundary Vanadium – To the eastern property boundary near AW-3B. Strontium – North to MW-27B and east to MW-31B Hexavalent chromium concentrations above the EPA Tap Water Standard were detected in upper surficial wells MW-23 and MW-24, located at the eastern compliance boundary, and AW-9B, located southeast of the compliance boundary. Hexavalent chromium was detected in other upper surficial wells at concentrations ranging from 0.013 µg/L to 0.024 µg/L. The low boron and strontium levels detected at AW-09 indicate the hexavalent chromium concentration at this location may not be influenced by the ash basins. Within the lower surficial aquifer, boron extends eastward beyond the property boundary (Table 2-8). The perimeter of the area where concentrations are greater than the 2L is defined by offsite wells SMW-4, SMW-5, SMW-6, SMW-2 and AW-5. Arsenic above 2L extends from the 1971 ash basin to MW-19 to the southeast. TDS and pH above the standards also extend eastward from the 1971 ash basin to the eastern property line. Vanadium extends eastward beyond the property line in the direction of SMW-01 and northeast in the direction of SMW-03. The occurrence of elevated concentrations of strontium appears to parallel that of boron; with the strontium concentrations being at least half or more of that of boron. Iron and manganese above 2L and background also extends from the 1971 ash basin eastward to offsite wells, however the concentrations of these constituents are an order of magnitude greater along the eastern property boundary and at offsite wells indicating other factors contribute to these elevated concentrations of these constituents. The strontium data indicate the occurrence of iron and manganese at north of AW-03 (AW-1, AW-02) and northeast offsite (SMW-04) are not related to the ash basin. Hexavalent chromium was detected in select lower surficial aquifer wells above the tap water standard at concentrations ranging from 0.19 µg/L to Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-12 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 0.046 µg/L (AW-09C). The occurrence of hexavalent chromium ranged from the ash basin to offsite well SMW-06D within the lower surficial aquifer. Several constituents were not detected in ash pore water or in groundwater beneath the 1971 ash basin but were detected downgradient in the surficial zone at concentrations greater than background and provisional background. These constituents include: Cobalt – North and east extending approximately to the eastern Site boundary Thallium – Isolated areas at or near compliance boundary to the east and southeast Selenium – Two wells immediately north of the 1984 ash basin. The data set for the Pee Dee zone is limited and background levels have not yet been established. Iron, manganese, pH, boron, TDS and vanadium, which were detected above 2L or IMAC in the Pee Dee beneath the 1971 ash basin, were also detected above 2L or IMAC in some wells east and northeast of the 1971 ash basin (Tables 2-9 and 2-10). Elevated levels of strontium were generally not present at the locations where exceedances of boron were detected within the Pee Dee formation. Concentrations of strontium did increase in the lower Pee Dee, however not at the same ratio to boron as in the surficial zone. Strontium is also a common constituent of salt water. The lack of consistent correlation between strontium and boron occurrence within the Pee Dee further indicates salt water intrusion in this zone. Additional background data for the Pee Dee will be collected and presented in the CAP Part 2, including additional hexavalent chromium data to better assess the source and extent. The information will be evaluated in the CAP Part 2. 2.2.2.2 Former Ash Disposal Area (FADA) Arsenic, barium, and iron were detected in the ash pore water at concentrations above 2L, IMAC and provisional background in the FADA ash pore water. The groundwater beneath the FADA contained arsenic above 2L, IMAC and/or provisional background. Arsenic, iron, manganese and vanadium were detected above 2L, IMAC and/or provisional background in the upper surficial zone and manganese was detected above provisional background in the lower surficial zone in Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-13 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx wells immediately east and south of the FADA. Cobalt was also detected above IMAC and provisional background in the lower surficial zone east and southeast of the FADA. No Pee Dee groundwater data was obtained in the area of the FADA. The FADA is bounded to the north by the Site discharge canal and to the west by Lake Sutton and the Site intake canal followed by the Cape Fear River. Exceedances detected in this area are hydrologically bounded. 2.2.3 Surface Water Where surface water data indicate that a constituent exceeds an applicable regulatory value and the provisional background concentration, the risk assessment will be used to further evaluate the area. The Cape Fear River flows north to south along the west side of the plant’s cooling pond, also referred to as Sutton Lake. The cooling pond is located to the west of the ash basins. These features and the NPDES outfall locations are shown on Figure 1-2. Seven surface water samples were collected during the CSA. Four samples, (SW- 004, SW-8A, SW-6A, and SW-1C), were collected from the cooling pond and three surface water samples (SW-CFUP, SW-CFP, and SW-CF001) were collected from the Cape Fear River (Figure 1-2). The SW-CFUP is a background sample located upgradient of the Site. Exceedances of 2B standards or criteria and provisional background concentrations were detected in the surface water sample (SW-CFP) from the Cape Fear River for aluminum (Table 2-10). Exceedances of 2B or background were detected in surface water samples from the cooling pond for copper and vanadium. Since both the background and detected concentrations of aluminum were significantly higher than those detected in the ash pore water, ground water or cooling pond surface samples, the aluminum exceedance does not appear to be attributed to the Site ash basins. Similarly, copper was not detected in the ash pore water or Site groundwater with the exception of low concentrations in two wells. The cooling pond is a wastewater treatment unit. 2.2.4 Sediment Where sediment data indicate that a constituent exceeds the greater of an applicable regulatory value or a site-specific provisional background concentration, the risk assessment will further evaluate the area. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 2-14 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Seven sediment samples were collected during the CSA. Four samples, (SW-004, SW-8A, SW-6A, and SW-1C), were collected from the cooling pond and three sediment samples (SW-CFUP, SW-CFP, and SW-CF001) were collected from the Cape Fear River (Figure 1-2). The SW-CFUP is a background sample located upgradient of the Site. The EPA Freshwater Sediment standard and/or provisional background concentrations were exceeded for barium in the sediment samples collected at SW-06A and SW-08A and Cape Fear River sample SW-CFP for barium (Table 2- 12). No other constituents exceeded the screening level in the sediment samples. The Cape Fear River sample location is located downgradient from an NPDES outfall for a nearby offsite industrial facility. Additionally, the ash basins are separated from the river by the cooling pond which is constructed with a concrete liner around the perimeter. Based on these factors, the sediment data likely do not reflect impact to the river bank sediment from Site groundwater flow. The risk assessment will include the sediment sample data collected from the cooling pond as it also has public access for fishing. 2.3 Initial and Interim Response Actions 2.3.1 Source Control Duke Energy is required to fully excavate the ash basins in accordance with CAMA requirements; with the material safely recycled or reused in a lined structural fill or disposed in a lined landfill. 2.3.2 Groundwater Response Actions Based on the results of CSA activities, impacted groundwater has migrated beyond the Duke Energy eastern property boundary. To address this, a Groundwater Mitigation and Monitoring Plan was submitted to NCDEQ in July 2015 to address offsite migration of constituents of concern, primarily boron. Twelve extraction wells are proposed along the eastern site boundary to intercept groundwater in the surficial aquifer. Additionally, plans to discontinue the use of the nearby municipal water supply wells are underway and Duke has taken proactive steps to replace these water supply wells with a new municiple water line extension. Completion of the replacement well field water system is anticipated by December 2015. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 3.0 SITE CONCEPTUAL MODEL The site conceptual model (SCM) is an interpretation of processes and characteristics associated with hydrogeologic conditions and constituent interactions at the Site. The purpose of this SCM is to evaluate areal distribution of constituents with regard to site- specific geological/ hydrogeological and geochemical properties at the Site. The SCM was developed utilizing data and analysis from the CSA and fate and transport modeling, and based on discussions between Duke Energy and NCDEQ. 3.1 Site Hydrogeologic Conditions Site hydrogeologic conditions were evaluated through the installation and sampling of groundwater monitoring wells, in-situ and laboratory soil tests, and surface water sampling. The wells were screened within the upper and lower portions of the surficial aquifer and the upper and lower portions of the Pee Dee aquifer. Additional information obtained during slug testing was also utilized to evaluate site conditions. The site conceptual model (SCM) is heavily influenced by the configuration of the ash basins relative to Site features including canals, ponds, rivers and production wells (Figure ES-1). The contrasting permeability between the surficial and Pee Dee formation is a significant part of in this model. 3.1.1 Hydrostratigraphic Units The following materials were encountered during the groundwater assessment site exploration and are consistent with material descriptions from previous site exploration studies: Ash (A) – Ash was encountered in borings advanced within the 1971 and the FADA. The 1971 ash basin was constructed by excavation below the water table to a depth of approximately 40 feet below grade. All but the lower two feet of the surficial sands were removed by this excavation; therefore the ash in the 1971 basin sits just above the contact between the surficial and Pee Dee formations. The ash is approximately 80 feet depp with over half of that saturated. Infiltration of surface water causes some mounding in this basin, resulting in radial groundwater flow away from the mounded area. The discharge canal to the south and the cooling pond to the west control groundwater elevation in the surficial aquifer to the west and south of the 1971 ash basin. Ash within the FADA is approximately 5 to 10 feet thick in a low-lying area and conforms with the surrounding Site grade. The FADA ash becomes saturated at approximately three feet bgs. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Fill (F) – Fill material are generally present in the 1971 and 1984 ash basin berms and extend from surface grade to a height of approximately 20 feet. No borings were conducted within the fill areas. Surficial deposits – The surficial aquifer consists of well sorted to poorly sorted (SW/SP) sands which vary from fine to coarse grained with some fine gravel. The upper zone is primarily a well-sorted, medium-fine grained sand while the lower portion tends to be poorly sorted, with larger grain sizes and occasional layers of coarse sand/fine gravel. The surficial sand deposits extend to an approximate depth of 50 feet bgs. Pee Dee formation – The Pee Dee Formation extends to the deepest horizon explored (150 feet bgs) during the assessment. The upper portion of the Pee Dee consists of dark gray or medium to dark green fine sands and silt with clay lenses and laminae. Below 75 feet, thin layers of sandstone were encountered; however these were not continuous across the Site. The Pee Dee becomes finer with depth and often is a very dense, low-plasticity clayey silt. Based on the site investigation conducted as part of the CSA, the groundwater system in the natural materials (sands, silts, gravel) at the site is an unconfined, connected aquifer system without confining layers. The groundwater system is divided into three layers, referred to in this report as the upper surficial aquifer flow layer, the lower surficial flow layer and the Pee Dee formation flow layer to distinguish flow layers within the connected aquifer system. Hydrostratigraphic units are shown on cross sections presented in the CSA report (SynTerra 2015). 3.1.2 Hydrostratigraphic Unit Properties The material properties required for the groundwater flow and transport model are total porosity, effective porosity, specific yield, and specific storage. These properties were developed from laboratory testing for ash and aquifer sediments and are presented in the CSA report (SynTerra 2015). Specific yield/effective porosity was determined for a number of samples of the ash, upper and lower surficial aquifer and Pee Dee aquifer sands and silts to provide an average and range of expected values (Table 3-1). These properties were obtained through in-situ permeability testing (falling head, constant head, and packer testing where appropriate); slug tests in completed monitoring wells; and laboratory testing of undisturbed samples Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-3 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx (Table 3-2). Results from these tests were utilized in the development of the groundwater flow and fate and transport model further discussed in Section 4. 3.1.3 Potentiometric Surface – Intermediate/Lower Surficial and Deep (Pee Dee) Flow Layers Monitor wells designations at the Site are based on depth, with “A” meaning a shallow well in the upper 15 feet, and subsequently deeper wells designated, “B”(25 feet), “C” (45 feet) within the Surficial Aquifer and “D” (100 feet) and “E” (150 feet) within the lower Pee Dee. Constituents have not been detected at concentrations greater than 2L or IMAC in the shallow (A zone) portion of the aquifer, therefore the CSA and the CAP will focus on the B, C, D and E zones. The construction of the 1971 ash basin removed the majority of the surficial aquifer and was replaced by ash to a depth of approximately 40 feet bgs. The Site is located on a peninsula defined by the Cape Fear River, adjacent to the west and the Northeast Cape Fear River, located approximately one mile to the east. Based on regional topography and drainage features, groundwater flow within this peninsula would be either to the west or east to one of the two rivers or to the south where the rivers converge. At the Site, groundwater in both the intermediate and lower surficial aquifer zones flows radially from the 1971 and 1984 ash basins (Figure 3-1, 3-2). Along the eastern edge of the cooling pond, groundwater flows to the west. On the east side of the 1971 basin, groundwater flows to the east, southeast and south. In the area of the FADA, groundwater flows to the southwest. A groundwater divide or ridge is located northeast of the ash basin which roughly corresponds to the presence of small sand hills in that area. A zone of slightly depressed water levels is centered around the Site production wells and the CFPUA wells in the southeast portion of the Site. Groundwater flow within the Pee Dee flows radially from the central portion of the Site (Figure 3-3), based on the limited data set for this zone. 3.1.4 Horizontal Hydraulic Gradients Horizontal hydraulic gradients were derived for the intermediate (B) surficial flow zone by calculating the difference in hydraulic heads over the length of the flow path between two wells with similar well construction (e.g., both wells having 15-foot screens within the same water–bearing unit). Applying this equation to wells installed during the CSA yields a horizontal hydraulic gradient range of 0.00009 foot per foot (ft./ft.) to 0.001 ft./ft. (Table 3-3). Due to the very Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-4 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx slight difference in vertical gradients among the flow zones at the Site, horizontal hydraulic gradients were not calculated for the C, D and E flow zones. 3.1.5 Vertical Hydraulic Gradients Vertical hydraulic gradient was calculated by taking the difference in groundwater elevation in a deep and shallow well pair over the difference in total well depth of the deep and shallow well pair (Table 3-4). A negative value indicates upward flow and a positive value indicates downward flow (Figure 3- 4). Thirty well pair locations, each consisting of an intermediate and lower surficial zone or surficial and Pee Dee flow zone groundwater monitoring well, were used to calculate vertical hydraulic gradient across the site. Based on review of the results, vertical gradient of groundwater between the surficial flow zone and Pee Dee flow zone is generally downward; ranging from 1.904E-02 foot/foot to 7.172E-04 foot/foot. The vertical gradient between the intermediate and lower surficial varied between upward and downward. However, the gradients were very low and were either upward or downward within the surficial zone with no apparent pattern, indicating the groundwater flow within the surficial zones is primarily horizontal. 3.2 Site Geochemical Conditions The geochemical SCM is described below. As the SCM evolves, the numerical models are changed to reflect new information. The geochemical SCM will be updated as additional data and information associated with constituents, site conditions, or processes are developed. The geochemical SCM is the description of the transport and attenuation factors that affect the mobility of constituents at the site and the long-term capacity of the site for attenuation and stability of immobilized constituents. 3.2.1 Constituent Sources Constituent sources at the Site consist of the 1971 and 1984 ash basins and the FADA. The 1984 basin is underlain by a 12-inch clay liner while the 1971 basin and FADA are unlined. The FADA is located in a low-lying area and much of the ash in this area is saturated with groundwater. The ash basins are inactive; process water has not been added to the ash since 2012. Approximately half of the 1971 basin ash is located below the water table and is therefore, also saturated. The ash storage areas generate leachate as a result of infiltration of precipitation and well as contact with groundwater. Additionally, it has been identified that ash management practices alter the concentration range of constituents in ash leachate, and that certain groups of constituents are more prevalent fly ash, bottom ash and vary over time (EPRI, 2015). Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-5 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx The location of ash, precipitation, and process water in contact with ash is the most significant control on geochemical conditions. Constituents would not be present in groundwater or soils at levels above background without ash-to-water contact. Once leached by precipitation or process water, constituents enter the soil-to-water-to-aquifer system and their concentration and location are controlled by the principles of constituent transport in groundwater. Water-to- aquifer-to-soil interaction is also responsible for the natural occurrence of constituents in background water quality locations. 3.2.2 Constituent Transport in Groundwater The most significant factor affecting inorganic constituent transport in groundwater is retardation, followed by advection, then dispersion, then diffusion. The last three factors can switch order depending upon site specific conditions. Unlike many low molecular weight organic constituents, which can have very low retardation factors, most metals, including those associated with coal ash, experience some retardation. Even a constituent like boron, which has a low distribution coefficient, can easily have a retardation factor of 5 to 10, meaning that the velocity of boron is 0.1 to 0.2 times slower than groundwater. The interaction between the constituent and the soil or aquifer media (retardation) are affected by chemical and mineralogical characteristics of the soil, geochemical conditions present in the aquifer media, and the chemical characteristics of the constituent. The CSA data collected at the Site indicates that geologic conditions present beneath the ash basin system impede the vertical migration of constituents. The CSA report found that the direction of mobile constituent transport is generally in an easterly/southeasterly direction. (SynTerra 2015). 3.2.3 Constituent Distribution in Groundwater The spatial distribution for each constituent detected in groundwater samples collected at the Site is detailed below. Iron - Iron is present in some background wells and in wells across the Site; however the highest detected concentrations were in the FADA ash pore water well (24,700 µg/L). Outside of the basin, iron is present in most wells within the intermediate and lower surficial zones. The highest iron concentration was detected in off-site well SMW-2B (28,800 µg/L). The occurrence of high concentrations of iron is greater in the lower surficial aquifer. Concentrations of iron are lower in the Pee Dee Formation wells. Wells in both the intermediate and lower surficial zones Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-6 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx in the area of the quarry northeast of the Site contained some of the highest concentrations of iron at the Site. Manganese - The occurrence of detected concentrations of manganese over the 2L closely matches that of iron. Cobalt – Cobalt was not detected in the ash pore water wells but was detected in the background wells and several surficial aquifer wells, specifically along the eastern Site boundary and off-site wells, where the highest concentrations were detected. Cobalt was also detected in MW- 15D, near the FADA. Based on these data, it is not clear that the occurrence of cobalt is related to the ash basins. Boron – Boron was detected in the 1971 ash pore water well but not in the FADA ash pore water well. Boron was not detected in background wells. Boron is the most mobile of the metals analyzed, with lateral migration apparently more prevalent than vertical movement. Figure 3-11 shows concentration of boron in compliance wells over time. Elevated boron concentrations were also detected in the Pee Dee Formation wells. However, the occurrence of boron in the lower Pee Dee wells (AW-5E, AW-6E and MW-23E) is closely aligned with concentrations of chloride over 2L. Chloride does not exceed 2L in any other well and its occurrence at that depth, as well as that of boron and other metals may be attributed to salt water intrusion. The detected boron concentration in Site Pee Dee Formation wells is comparable to data available for a well in Myrtle Beach, South Carolina. Arsenic – The occurrence of arsenic is limited vertically and horizontally relative to the ash basins and is present above 2L in only the ash pore water wells and two surficial aquifer wells near the ash basins. Vanadium was detected in the ash pore water wells and in wells across the Site in both the surficial and Pee Dee at concentrations exceeding IMAC. Vanadium was detected in upgradient well AW-8B and background well MW-37B/C. The highest concentration detected, 39.6 µg/L, in MW-20 between the FADA and the cooling pond intake canal, is greater than other areas. Selenium – Selenium was detected in two wells during the CSA; well MW-27B located north of the 1984 ash basin and AW-6D, a perimeter well screened in the upper Pee Dee. Additional sampling was performed in September 2015 in this area to determine if the selenium detected in MW- Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-7 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 27B was related to the ash basins. GWPZ-01A, GWPZ-01B and MW- 36B/C were sampled as part of the 0.1 micron filtration sampling event. Selenium was detected in MW-36B above 2L. These data indicate that the occurrence of selenium in the groundwater in this area is related to the ash basin; additional wells are currently being planned in order to further delineate selenium in this area. Thallium was found to be above IMAC in four wells, however only one well exceeded provisional background. It is not clear that it has migrated from the ash basin as it was not detected in the ash pore water wells and only appears in a limited number of wells at relatively low concentrations. The detected concentrations of thallium are below provisional background in the lower surficial wells (MW-22C and MW-23C) and 0.458 µg/L in upper surficial well MW-19, southeast of the ash basin. Cobalt, iron, manganese, and vanadium may be naturally occurring and were detected in background wells above 2L Standards or IMACs. Based on review of available data, these constituents were observed across the site and correlation to ash management areas is inconclusive. 3.3 Mineralogical Characteristics Soil and rock mineralogy and chemical analyses completed to date are sufficient to support evaluation of geochemical conditions. Soil mineralogy and chemistry results through July 31, 2015 were presented in the CSA report (SynTerra 2015). The dominant minerals in surficial zone soils at the Site are quartz, feldspar and illite, while the Pee Dee zone consisted of predominantly of quartz, illite, calcite, kaolinite and muscovite. The major oxides in the soils are SiO2 (64.92% - 97.96%), Al2O3 (1.27% - 7.39%), and Fe2O3 (1.17% - 4.77%). Soil formation typically results in the loss of common soluble cations and the accumulation of quartz and clay. Feldspars are hydrolyzed to clays. Soil chemistry results do not show marked deviation from normal crustal abundances at the Site. 3.4 Geochemical Characteristics 3.4.1 Cations/Anions Classification of the geochemical composition of groundwater aids in aquifer characterization and SCM development. Piper diagrams can be used to graphically depict geochemistry of groundwater samples collected at a particular site. For Sutton, distributions of major cations and anions in ash pore water and Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-8 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx the surficial and Pee Dee monitor wells plotted on Piper diagrams provide an indication of the characteristics of each zone. Ash pore water is dominated by calcium, magnesium, and carbonate. The sulfate content of the ash pore water is lower than would be anticipated. Ion ratios vary substantially in the surficial zone across the Site, but are generally higher in calcium and magnesium, with the exception of AW-01B in the northeast portion of the Site and SMW-4C off-site to the east. Major ion ratios in samples from the Pee Dee are dominated by sulfate, chlorides, sodium and potassium with outlier ABMW-1D, which is in the upper Pee Dee, beneath the 1971 ash basin having a higher calcium and magnesium content and lower sodium and potassium. 3.4.2 Redox Potential Determination of the reduction/oxidation (redox) potential of groundwater is an important component of groundwater assessments, and helps to understand the mobility, degradation, and solubility of constituents. The Eh, pH and dissolved oxygen measurements for the hydrostratigraphic units at the Site are presented in Figures 3-5 through 3-13. At the Site, anoxic/mixed is the predominant redox category and ferrous iron/ferrous sulfate are the predominant redox processes (Figure 3-5). 3.4.3 Solute Speciation For compliance purposes, inorganic solute concentrations are expressed most often as concentration of the chemical element. In nature, those elements each form a large range of inorganic species. These species can be present due to a change in valance state (oxidation-reduction state of the element) as in the case with ferrous (Fe(II)) and ferric (Fe(III)) iron. The species can also reflect formation of a compound, such that Fe(II)+2 and Fe(OH)2 (aq) are two species formed from the total amount of iron available. Speciation is important for understanding the fate and transport of constituents as species react differently. Select wells were sampled for chemical speciation analyses of arsenic (III), arsenic (V), chromium (VI), iron (II), iron (III), manganese (II), manganese (IV), selenium (IV), and selenium (VI). Speciation analysis revealed that observed anoxic/mixed redox conditions are reflected in the speciation of redox-sensitive species. Reduced As(III), Fe(II), and Mn(II) were the dominant species for each sample containing these metals. This is significant in that As(III) tends to react less with aquifer media than As(V); oxidation of arsenic would improve sorption and attenuation of arsenic. The Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-9 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx presence of reduced species constituents at significant concentrations indicates that consideration of speciation is necessary in evaluation of corrective measures. 3.4.4 Kd (Sorption) Testing and Analysis Laboratory determination of Kd was performed on site-specific samples of soil. Solid samples were batch equilibrated and/or tested in flow through columns to measure the adsorption of constituents at varying concentrations. These multiple data points for each constituent and sample were evaluated to determine if the observed data can be fit to an adsorption isotherm. If fitting was supported, a Kd was calculated. Tests were conducted in duplicate or triplicate to evaluate error. There were nine batch tests and eight column tests conducted on Site samples. See Section 4 for a more detailed discussion of Kd test results. Table 3-6 Ratio of Maximum/Minimum Kd from Batch Results* Constituent Minimum Kd Maximum Kd Max. Kd/Min. Kd Arsenic 4.6 501 109 Boron X X X Barium 3.9 206 53 Cobalt 2 740 370 Selenium 1.4 107 76 Vanadium 1.9 538 283 *UNCC, 2015 Prepared by: DGN Checked by: PBW Units reported in liters per kilogram (L/kg) The ratio of the maximum Kd value to the minimum is a measure of the spread in Kd data. This indicates that the maximum/minimum ratio can be used as a subjective indicator of the potential for constituents to have a Kd that is variable across geomedia, or variable across the site. 3.5 Correlation of Hydrogeologic and Geochemical Conditions to constituent Distribution The site is located in a low flat area, with elevations that range from sea level (the Cape Fear River) to about 25 feet above mean sea level (MSL) on the top of some sand dunes. The water table is relatively flat, and is generally located near the ground surface, with standing water found in some low areas. The ash basin recharge and recharge in general is the major source of water to the shallow groundwater system. Most of this Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-10 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx water discharges to the hydrologic boundaries described above, with a relatively small amount recharging the underlying Pee Dee aquifer. Lateral flow predominates within the lower surficial aquifer, which has considerably higher hydraulic conductivity than the underlying Pee Dee formation. Much of the exceedances at the Site occur within this zone. Vertical gradients at the Site are very low within the Surficial unit as well as between the Surficial and Pee Dee zones. The constituents that are present in the coal ash dissolve into the ash pore water. As water infiltrates through the basins, water containing constituents can enter the groundwater system through the bottom of the ash basins. Once in the groundwater system, the constituents are transported by advection and dispersion, subject to retardation due to adsorption to solids. If the constituents reach a hydrologic boundary or water sink, they are removed from the groundwater system, and they enter the surface water system, where in general, they are greatly diluted. At this site, boron is the primary constituent that is migrating from the ash basins. Three constituents, boron, arsenic and vanadium, were selected for the Fate and Transport modeling discussed in Section 4. These three constituents were selected because: Each were present in the source area (ash pore water) Each were present in detectable concentrations downgradient of the source area and their migration and attenuation could be modeled. Based on their geochemical characteristics, arsenic is expected to migrate short distances from the ash basin, while boron and vanadium are expected to be migrate further. Boron particularly is soluble and mobile as it attenuates primarily by physical processes and exhibits little sorption affinity. Of these constituents, boron is the most prevalent in groundwater at the Site. Boron is present at relatively high concentrations in the 1971 ash basin, and a boron plume extends to wells east of the ash basins. Boron migration appears to occur mainly in the lower part of the surficial aquifer. The modeled Kd values calculated from the minimum and maximum pH and/or EH values, as well as, the averaged Kd values from UNCC’s experimental analysis are presented in Appendix D (Powell, 2015). Except for borate, experimental data are generally captured by the minimum and maximum model predicted Kd values. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-11 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Increasing pH increases sorption. Sorption and partitioning are highly dependent on pH. Therefore, generally low pH conditions will favor higher aqueous concentrations of cationic constituents (e.g. Ba+2, Cr+3, Co2+, Fe 2/Fe+3) whereas higher aqueous concentrations of anionic species (e.g. AsO4-3, SeO3-2, H2VO4-2, H2BO3-) will be expected in higher pH pore waters. Areas with high pH at the Site, the ash basins and at the eastern property boundary (MW-12) correlate with the occurrence of elevated boron in the lower surficial zone. Conversely, areas with low Eh outside of the ash basin appear to correlate with naturally-occurring iron at AW-03C and SMW-04C. Assuming 100% sorption of the summation of the total moles of all constituents, less than 1% of the total available sorption sites was occupied. Therefore it appears the aquifer solids have sufficient sorption capacity for high concentrations of all constituents though the actual sorbed concentrations will vary based on the sorption affinity (i. e. distribution coefficient) of individual constituents. This sorption capacity is reflected in the groundwater modeling report scenario for no action, which indicates the boron plume does not expand over time. Refinement of this SCM, as it pertains to groundwater fate and transport modeling, is discussed in Section 4.3. Furthermore, the SCM will continue to evolve as additional data becomes available during supplemental Site investigation activities. 3.6 Facilitated (Colloidal) Transport Facilitated transport is a phenomenon whereby a constituent may be transported in groundwater more rapidly than expected based on idealized Darcian flow and equilibrium sorptive interactions. One example of facilitated transport is constituent sorption to colloids, which may be small solid phase particles or macromolecules, and resulting transport in the aqueous phase (Huling, 1989). CSA and associated groundwater sampling activities to date have included sampling and analysis for total and dissolved metals. The dissolved fraction was determined by analysis of a sample volume passed through a filter with 0.45 micron pore size. In order to determine whether colloidal transport may be a significant factor in constituent migration, additional groundwater samples were collected from representative monitoring wells in September 2015 and passed through both a 0.45 micron filter and a 0.10 micron filter. Analytical results for this event are summarized on Table 3-5 and the laboratory reports are presented in Appendix B. Review of the results indicates that arsenic, barium, boron, cobalt, iron, manganese, molybdenum, nickel, strontium and thallium occur as soluble ions as evidenced by a near 100% pass through the 0.1 micron filter. Aluminum, antimony, selenium, Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 3-12 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx vanadium and zinc showed some removal by filtration, generally less than 10%. Based on results of the 0.45 micron and the 0.10 micron filtrates and consideration of CCR constituents which exceed 2L at the site, colloidal transport does not appear to be a significant factor in constituent migration. 3.7 Time Versus Boron Concentration Diagrams Time versus concentration diagrams for boron in were reviewed for compliance wells for both the active basin and inactive basins (Figures 3-14). General trends are evident in the compliance wells at the compliance boundary as well as those located at the eastern Site boundary. Compliance wells located at the compliance boundary (MW- 27B, MW-23B/C, MW-24B/C, and MW-23B/C) north and east of the 1971 ash basin have decreased in boron concentrations over the past one to two years. This could be related to the end of sluicing operations in 2013. Conversely, the boron concentrations in wells located at the eastern boundary (MW-12 and MW-31C) have remained fairly consistent during that time. The decrease noted in the compliance boundary wells may be an indicator that, given that no additional ash is being deposited to the ash basins, over time overall boron concentrations will naturally attenuate to asymptotic levels across the Site. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 4.0 MODELING A modeling program was conducted to evaluate the impact of various potential closure options on groundwater and surface water quality. Modeling components included groundwater fate and transport, geochemistry and supporting studies. Stand-alone reports from each principal or organization are included in appendices and are summarized in this portion of the CAP. The modeling work, and associated analysis, included the following: (1) Determination of the ability of on-site soil to sorb dissolved constituents derived by the leaching of ash. The degree of sorption is measured by the distribution coefficient, and was determined by conducting batch and column studies on numerous soil samples collected in key hydrostratigraphic units. The distribution coefficient is a key factor in the numerical flow and transport model and had to be developed before modeling could proceed. (2) Assessment of various retardation processes (processes that lessen the dissolved concentration and reduce the velocity of constituent movement) to determine which are most likely occurring and the likelihood that the process will continue after site closure. (3) Development of numeric fate and transport model to predict the configuration of groundwater flow once a closure plan has been implemented. After the flow model was calibrated, a groundwater quality model was developed to predict groundwater quality conditions once closure is implemented. (4) Development of a model to predict constituent concentrations in major receiving surface water bodies in the area of the site. (5) Models associated with the evaluation of Monitored Natural Attenuation (MNA). 4.1 Sorption Model An important aspect of determining the movement of metals in groundwater is have knowledge the ability of the soil to retain a portion of the dissolved constituent on the soils surface. Generally, the retention is either through sorption or precipitation. Sorption occurs when the dissolved constituent comes in contact with a soil particle and is retained by the particle until it is released and adheres to the adjacent particle. In order to quantify this variable the amount of a constituent dissolved in water and the amount of a constituent adhering to soil must be known. These measurements are often Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx made in a laboratory setting. These studies result in the calculation of the distribution coefficient - Kd. SynTerra retained University of North Carolina at Charlotte to determine site specific distribution coefficients (Kd) for the primary hydrostratigraphic units. UNCCs final report is included as Appendix C. Nine soil samples were collected for testing. One portion of a sample was placed in large-mouth bottles for batch analysis, and a second portion of the sample was packed into columns for testing. A synthetic solution of groundwater was prepared for the batch and column procedures. Test procedures followed USEPA protocol where available. Results from the studies are presented on Table 4-3. Table 4-1 summaries the Kd values from batch and column testing. Table 4-1 Summary of Kd Values from Batch and Column Studies Batch Study Sample Site and Depth Arsenic Boron Barium Cobalt Selenium Vanadium SW-3C 10-12 Trial - 1 78.8 * 20.0 28.3 7.2 14.7 Trial - 2 76.2 * 16.1 24.4 6.9 14.1 SW-3C 41-43 Trial - 1 117.9 * 2.0 66.4 Trial - 2 236.2 * 3.9 107.3 226.9 SW-3C 48-53 Trial - 1 394 * 8.4 * 58.2 302.2 Trial - 2 501.1 * 8.2 * 81.8 538.4 ABMW-1D 38-48 Trial - 1 4.6 1.7 512.7 2.3 * Trial - 2 6.3 42.1 543.7 2.0 * ABMW-1D 83-88 Trial - 1 63.8 * * 736.6 10.8 58.8 Trial - 2 59.2 * * 740.0 10.6 66.7 ABMW-2D 0-8 Trial - 1 30.5 * 263.9 7.6 17.4 Trial - 2 31.1 * * 313.7 7.6 17.3 ABMW-2D 10-12 Trial - 1 8.7 * 11.0 1.9 Trial - 2 * 8.0 10.7 1.4 2.2 ABMW-2D 53-60 Trial - 1 35.3 * 406.0 8.9 45.9 Trial - 2 31.5 * 26.9 436.0 7.8 40.1 MW-23E 145-147 Trial - 1 32.4 * 165.2 660.8 13.3 49.5 Trial - 2 31.9 * 206.2 717.3 13.1 49.0 Geometric Mean 47.7 1.7 22.0 140.9 10.2 36.8 Median 35.3 1.7 18.1 406.0 8.4 47.5 Lower Quartile (exclusive) 30.8 * 8.2 24.4 7.0 15.4 Corrective Action Plan Part 1 November 2015 L.V. 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Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Table 4-1 Continued Column Sample Site and Depth Arsenic Boron Barium Cobalt Selenium Vanadium SW-3C 10-12 160 150 20 250 40 90 SW-3C 41-43 Trail - A 275 - 125 225 150 200 SW-3C 41-43 Trail - B 200 60 110 175 125 150 SW-3C 41-43 Trail - C 325 70 175 225 125 250 ABMW-1B 38-48 500 40 175 120 200 1300 ABMW-1B 83-88 300 55 1050 1000 60 300 ABMW-2D 0-8 185 40 35 525 25 90 ABMW-2D 10-12 375 - 300 450 150 200 ABMW-2D 53-60 240 30 1100 - 75 275 MW-23E 145-147 350 - - - 150 450 Geometric Mean 275 56 167 298 93 238 Median 288 55 175 238 125 225 20th Percentile 188 36 35 164 44 102 Notes: *- No Blank = No Data Units reported in liters per kilogram (L/kg) The samples from SW-03C, ABMW-02D (10’-12’), ABMW-02D (53’-60’) are logged as SW/SP (sand) [surficial unit], whereas the other samples are logged as SP, SM to ML (silty sand to silt) or ash, which has the consistency of silt (SM) [Pee Dee unit]. As indicated by the data, the finer grained soils have greater values of Kd. 4.2 Geochemical Modeling A geochemical model was developed by Dr. Brian Powell as part of the CAP to characterize the current geochemical conditions in and around the Sutton ash basins. The geochemical model was used to provide an analysis of corrective action alternatives, including Tiers II and III of the MNA analysis (Section 6 CAP Part 2). The model simulates the actual chemical reactions between the groundwater, CCR, and other porous media (i.e., constructed and natural subsurface). The key conclusions of the geochemical model are: modeled Kd values generally align with those determined experimentally by Langley et al. (2015) and those used in the fate and transport model, there is a low probability of the aquifers to reach their capacity to sorb or otherwise attenuate the constituents of interest, and pH and oxidation/reduction potential (Eh) have a fundamental influence on the extent of partitioning in pore water at the Sutton site. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-4 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx The conclusions were determined through the development of this model in four steps that together depict potential mechanisms and geochemical processes at work: Eh-pH diagrams showing potential stable chemical phases of the aqueous electrochemical system, calibrated to encompass conditions at the site. Correlation analysis where observations from groundwater measurements are plotted and interpreted, to identify important features of the geochemical system. Sorption model where the aqueous speciation and surface complexations are modeled using the USGS geochemical modeling program PHREEQC. Attenuation calculations where the potential capacity of aquifer solids to sequester constituents of interest were estimated. The Eh-pH diagrams and correlation analysis of field data indicated important details about the potential mobility of constituents at the site including the following: Dissolved oxygen is the dominant redox buffer in these systems. Aluminum and Iron concentrations decrease with increasing pH. Arsenic concentrations appear to remain relatively constant. Sorption of As(III) and As(V) will decrease with increasing pH. Ba, Zn, Co, and Pb present largely as divalent cations whose sorption increases with increasing pH. In all cases, the sorption increases with increasing pH. Aqueous boron concentrations remain relatively constant around 1000 ppb above pH 5; below pH 5, sorption of the neutrally charged H3BO3 or anionic H2BO3- complexes likely reduces the aqueous concentration. The sorption model was designed to evaluate ion sorption to HFO using a diffuse double layer model developed by Dzomback and Morel, 1990. Sorption model simulations include Site specific Eh and pH values and assumption made in the Langley et al. (2015) site report. Modeled Kd values calculated from the minimum and maximum pH and/or Eh values, as well as, the averaged Kd values from the Langley et al. (2015) experimental analysis are presented in Appendix B (Powell, 2015). Except for borate, experimental data are generally captured by the minimum and maximum model predicted Kd values. It is important to note that there are many factors that play a role in the sorption/ desorption of constituents with porous media that were not directly addressed in this model. Incorporating additional functions into a geochemical model does not necessarily translate to an increased confidence in the results. Both mineralogy Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-5 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx and organic carbon are known to affect Kd values in a variety of ways, but were not directly addressed in this model. Organic carbon influence on sorption is highly variable, and given the heterogeneity at the Site, incorporating organic carbon into the model would not add meaningful confidence to the predictive results. The mineralogical data at the Site indicated minute quantities of transition metal minerals that would influence the Kd values, and was addressed in this model by using Eh as a proxy for reducing conditions to account for the potential for reduced forms of minerals with influence, such as sulfides. The attenuation capacity was calculated to determine the affinity of the aquifer materials to retain constituents in the solid phase. Calculations were performed using Site specific data derived from the fate and transport model, the Langley et al. (2015) report, and the NC2L groundwater standard concentrations. Results indicated that HFO sorption sites could sorb all available constituents of interest and would not reach capacity until approximately 400 times the NC2L standards. It is important to note that the calculation assumes 100% sorption, which will not be the case for all constituents, and that while the data reveals it is unlikely that the capacity of the aquifer solids would be exceeded, the results can vary based on the Kd for each constituent and specific geochemical conditions. 4.3 Numerical Fate and Transport Model The purpose of this study is to predict the groundwater flow and constituent transport that will occur as a result of different possible corrective actions at the site. The study consists of three activities: Development of a calibrated steady-state flow model of current conditions, Development of a historical transient model of constituent transport that is calibrated to current conditions, and Predictive simulations of the different corrective action options. Three major elements for the development of the groundwater flow and transport model are summarized below: The site conceptual model for the groundwater model was based on the model presented in the CSA. No significant changes had to be made in the SCM in order to calibrate the flow and transport model. The numerical flow model was developed using MODFLOW and the transport model was developed using MT3DMS. MODFLOW is based on Darcy’s law and MT3DMS uses the groundwater flow field from MODFLOW to simulate 3D Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-6 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx advection and dispersion of the dissolved COIs including the effects of retardation due to COI adsorption to the soil matrix. Key transport model parameters are the constituent source concentration in the ash basin and the distribution coefficients (Kd) calculated by Langley et al., 2015). Source concentrations were taken from ash pore water concentrations obtained from the field and were applied throughout the ash basin as specific concentrations. It was also decided to take the conservative approach and to initially use a low Kd value for each constituent in the model, even though the Kd values are highly variable throughout the site. The initial value used in calibration was the minimum measured value from Langley et al., 2015. Once calibrated, a uniform Kd value is used throughout the model for each modelled constituent. The following excerpts were taken from the the Groundwater Flow and Transport Modeling Report for Sutton Energy Complex (Falta, et. al., 2015). Figure and Table references are retained from the original document and included in Appendix E. 4.4 Flow and Transport Models The flow and transport model for this site was built through a series of steps. The first step was to build a 3D model of the site hydrostratigraphy based on field data. The next step was determination of the model domain and construction of the numerical grid. The numerical grid was then populated with flow parameters which were adjusted during the steady-state flow model calibration process. Once the flow model was calibrated, the flow parameters were used to develop a transient model of the historical flow patterns at the site. The historical flow model was then used to provide the time-dependent flow field for the constituent transport simulations. 4.4.1 Flow Model The steady state flow model calibration targets used 87 water level measurements made in observations wells in June, 2015. The correlation between observed and calculated head measurements for current conditions is shown in Figure 4-1. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-7 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Figure 4-1 Comparison of observed and computed heads from the calibrated steady state flow model. A parameter sensitivity analysis was performed on the calibrated model by systematically increasing and decreasing the main parameters by 50% of their calibrated value. Table 2 shows the results of the analysis, expressed in terms of the normalized root means square error (NRMSE) for each simulation, compared to the calibrated NRMSE of 6.89%. 4.4.2 Transport Model The transient flow model uses a simplified approximation of this complex history that simulates the basin as having a constant footprint over time, equal to its shape since 1981. The basin infiltration rate during sluicing is not known, but it was estimated by taking the results of the calibrated steady state flow model (Section 5.1) and adjusting the infiltration rate to better match the boron transport. The final basin recharge rates used during sluicing in the transient flow model range from 40 to 90 inches per year. These rates are much smaller than the rate of water inflow to the basins with the sluiced ash. The transient flow field was modeled as three successive steady state flow fields; one corresponding to the high infiltration rate in the 1971 basin during ash sluicing from 1971 to 1984, one corresponding to the higher infiltration rate in the 1984 basin during Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-8 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx ash sluicing from 1984 to 2013, and one corresponding to the current basin infiltration rates from 2013 to 2015. The transport model calibration targets are COI concentrations measured in 71 monitoring wells in June, 2015 (SynTerra, 2015). The constituents modeled were selected based on significant concentrations in ash pore water greater than likely background levels and whether there was a discernible plume of the constituent extending downgradient from the ash basin. The major focus of the concentration matching effort was devoted to boron, arsenic, and vanadium in and around the ash basin. Boron was chosen as a tracer for the ash basin for three main reasons: 1) boron is always present in coal ash; 2) there is typically a low background of boron concentrations; 3) boron is the most mobile constituent. The correlation between observed and calculated boron concentration measurements for current conditions are shown in (Table 4). 4.5 Model Results Once the flow model was calibrated and the transport model closely matched observed concentrations, the model was used to predict contaminant distributions for the next 5, 15, 30 years. The dates for those simulations are referred to in the model report as 2020, 2030, and 2045 respectively. The three scenarios modeled for the CAP: Existing Conditions Removal of Ash Capping Ash Basin 4.5.1 Existing Conditions This method relies on natural attenuation processes to reduce the contaminant concentrations over time. In this scenario, the ash basins are left in place without modification and the assumption is made that current recharge and contaminant loading rates from the ash to the underlying formations are held constant. At the Sutton Plant, this means that the conditions present on site since the end of coal burning in 2013 would be carried forward in time. Figures 24 through 41 display the results of the Existing Conditions (referred to as Monitored Natural Attenuation in Falta, et al., 2015 report) for the years 2020, 2030, and 2045 respectively. The boron plume appears to be stable to slowly shrinking during this time period (compare Figures 25, 31, and 37). Although water is still infiltrating the basins at a relatively high rate in this simulation, the rate is greatly reduced from the Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-9 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx historical active ash sluicing period. The combination of reduced boron loading to the groundwater, combined with radial flow and dilution of the outer edges of the plume by infiltrating rainwater serve to gradually stabilize and shrink the plume, although it still extends beyond the property line in 2045. 4.5.2 Capping Ash Basins This simulation assumes that the FADA and 1971 and 1984 ash basins are covered with an impermeable cap that prevents water from infiltrating into the groundwater system. This model is identical to the existing conditions simulation, except that the recharge rate in the FADA and ash basins has been set to zero. Figures 61 through 66 show the simulated boron, concentrations in model layers 4 and 7 at five, fifteen, and thirty years (arsenic and vanadium are not shown because the simulation shows little migration over the 30 year period). The simulated boron plume in 2020 (Figures 61 and 62) is similar to the existing conditions scenario, but by 2030, the capping simulation shows that the boron plume is shrinking (Figures 63 and 64). By the end of the simulation in 2045, the boron plume has receded to the approximate basin and FADA boundaries (Figures 65 and 66). The reduction of the boron plume over time in this case is due in part to the reduced discharge of boron to the groundwater system, and in part to the change in the groundwater flow field. The ash basin capping would eliminate the introduction of boron from infiltrating rainwater, although some boron would enter the system from the coal ash located below the water table in the 1971 basin. The water table mound shifts eastward due to the reduction of infiltration in the basins, causing groundwater in and around the basins to flow westward, towards the cooling pond. 4.5.3 Removal of Ash This simulation uses a preliminary design for ash removal from the FADA and ash basins, with construction of a lined and capped ash landfill east of the current basins (Figure 4-2). Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-10 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Figure 4-2 Map showing proposed ash basin closure and new landfill for the removal of ash model scenario. The ash removal plan involves all ash to be removed from the FADA, and Lake Sutton is allowed to fill that excavation. Ash is removed from the 1984 basin, and that area is graded so that it gently slopes towards Lake Sutton. Ash is removed from the 1971 basin, and the excavation extends nearly to the PeeDee formation in the zone where deep ash is located. The majority of the 1971 basin excavation is then connected to Lake Sutton by breaching the dike on the southwest side of the basin. The removal of ash model assumes that site geometry changes rapidly so that the new design is largely in effect by June, 2017, when the simulation begins. The Lake Sutton constant head zone is enlarged to include the FADA and most of the 1971 ash basin. The concentrations in this the constant head zone are maintained at zero. The deep excavation in the 1971 basin is given a very high conductivity, and is also maintained at New onsite lined landfill North storm water pond South storm water pond All ash is removed. Lake Sutton fills the excavation in 1971 basin and FADA Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 4-11 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx zero concentrations. The remaining 1971 and 1984 ash basin areas are given the background recharge rate of 12 inches per year. The new landfill area is given a recharge rate of zero. All water supply pumping rates are assumed to remain constant at the rates used in last step of the transport flow model. Figures 43 through 60 display the simulates for boron, arsenic, and vanadium for layers 4 and 7. In 2020, the simulation shows relatively small changes to the concentration profiles, except for the zone where the deep ash was removed from the 1971 basin. The deeper boron in the surficial aquifer (Figure 44) shows some movement away from the two stormwater basins. The simulated boron concentrations in the deeper part of the surficial aquifer appear to recede back towards the property line by 2030 (Figure 50). This is due to the combined effect of the source removal, reduced infiltration in the former ash basin areas, zero infiltration below the new landfill, and the high infiltration rates in the two stormwater basins. Relatively little effect is seen on the simulated arsenic or vanadium plumes except for the area that was excavated. By 2045, the simulation shows a much smaller boron plume (Figures 55 and 56) while the simulated arsenic and vanadium plumes show little additional movement. 4.6 Groundwater and Surface Water Interactions For Sutton, the groundwater to the west of the ash basin and FADA flows to the cooling pond, which is part of the facilities wastewater treatment system. The surface water data reflect no apparent impact from the historical ash basin outfall discharges. The anticipated effects of groundwater flow to the cooling pond would be negligible compared to the historical wastewater. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 5-1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 5.0 CORRECTIVE ACTION PLAN PART 2 A risk assessment, an evaluation of potential remedial alternatives and the recommended remedial approach will be provided in the CAP Part 2. Information presented in this CAP Part 1 provides a summary of possible closure activities. The Sutton CSA shows that boron is the key constituent for determining impacts on groundwater quality. Monitoring results show that in the eastern portions of the site, groundwater is flowing to the east and that the beginnings of a boron plume is migrating past the property line. Provisional background values have been established for key parameters. Constituents in groundwater whose background concentrations exceed 2L or IMAC include antimony, chloride, cobalt, iron, manganese, TDS and vanadium. Cobalt was not detected in the ash pore water and the background concentrations indicate it is not a useful indicator of constituent migration from the ash basins. The extent of groundwater affected by releases from the Sutton Plant has been defined and a tentative plan for addressing groundwater exceedances has been developed. The plan includes the following elements. 1) Duke Energy is progressing with activities to excavate ash from the Site ash basins, with placement split between an onsite landfill and the Brickhaven clay pits. Under this alternative, portions of the excavated area will become a part of the cooling pond. 2) Twelve groundwater extraction wells will be installed on the east side of the current basin. Groundwater flow models show that the extractions wells will prevent the migration of impacted groundwater. A groundwater quality monitoring plan will be developed to monitor the effectiveness of the extraction well system. 3) The concepts embodied in monitored natural attenuation (MNA) will be applied to the western half of the current basins and all of the FADA. Groundwater flow under this portion of the plant site is to the west discharging into the cooling pond. A groundwater and surface water quality sampling plan will be developed to track the concentration of key constituents against projections in the fate and transport model and in the geochemical model. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 5-2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx Analytical data summarized in this CAP Part 1 make it clear that the chemistry of groundwater, surface water, and soil varies with the localized environment from which the sample was collected. However, a geochemical model has been developed to analyze the chemistry of the surficial soil environment. The model identifies the likely attenuation reactions occurring in the subsurface environment and calculations based on the model indicate that the reservoir of attenuation potential remains extensive. These findings support the plan described above. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 6-1 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx 6.0 REFERENCES ASTM D6312-98: Standard Guide for Developing Appropriate Statistical Approaches for Groundwater Detection Monitoring Programs. 2012. David A. Dzombak, Francois M.M. Morel, Surface Complexation Modeling, Hydrous Ferric Oxide, 1990 Electrical Power Research Institute (EPRI), Monitored Natural Attenuation for Inorganic Constituents in Coal Combustion Residuals. August 2015 Griffith, G.E., Omernik, J.M., Comstock, J.A., Schafale, M.P., McNab, W.H., Lenat, D.R., MacPherson, T.F., Glover, J.B., and Shelburne, V.B. 2002. Ecoregions of North Carolina and South Carolina, (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,500,000). Falta, R. W., Brames, S. E., Graziano, R., Murdoch, L.C. Groundwater Flow and Transport Modeling Report for L.V. Sutton Energy Complex. 2015. Geosyntec Consultants. (DRAFT) Preliminary Site Investigation Data Report-Addendum No. 1, Conceptual Closure Plan, L.V. Sutton Plant, Project Number GC5592. July 2014. Geosyntec Consultants. (DRAFT) Data Interpretation and Analysis Report, Conceptual Closure Plan, L.V. Sutton Plant, Project Number GC5592. July 2014. Langley, W.G., Daniels, J., Oza, S., Sorption Evaluation Sutton Power Plant. UNC Charlotte, NC. 2015. NCDENR. Classifications and Water Quality Standards Applicable to the Groundwaters of North Carolina. North Carolina Administrative Code Title 15A, Subchapter 02L. 2013. NCDENR. North Carolina Administrative Code Title 15A, Subchapter 02B. Classifications and Water Quality Standards Applicable to the Surface Waters of North Carolina. 2013. NCDENR. North Carolina Administrative Code Title 15A, Subchapter 02L. Classifications and Water Quality Standards Applicable to the Groundwaters of North Carolina. 2013. Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 6-2 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx NCDENR. Classifications and Water Quality Standards Applicable to the Surface Waters of North Carolina (Pending EPA Approval of 2007-2014 Triennial Review). North Carolina Administrative Code Title 15A, Subchapter 02B. 2015. Niswonger, R.G.,S. Panday, and I. Motomu, 2011, MODFLOW-NWT, A Newton formulation for MODFLOW-2005, U.S. Geological Survey Techniques and Methods 6-A37, 44-. North Carolina Department of Natural Resources and Community Development. Geologic Map of North Carolina. 1985. Powell, B., Analysis of Geochemical Phenomena Controlling Mobility of Ions from Coal Ash Basins at the Duke Energy Sutton Energy Complex. Pendleton, SC. 2015. SynTerra. Comprehensive Site Assessment Report. August 5, 2015 USEPA. Risk Assessment Guidance for Superfund Volume I , Human Health Evaluation Manual, (Part A). EPA / 540 / 1-89/002; 1989. USEPA. Guidelines for Ecological Risk Assessment. 1998. USEPA. Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units - Final Report to Congress, v. 1. Office of Air Quality, Planning and Standards. Research Triangle Park, NC 27711, EPA-453/R-98-004a; 1998. USEPA. Report to Congress Wastes from the Combustion of Fossil Fuels, Methods, Findings, and Recommendations, v. 2. 1998. USEPA. Region 4 Ecological Risk Assessment Bulletins—Supplement to RAGS. 2001 USEPA. Monitored Natural Attenuation of Inorganic Contaminants in Ground Water – Volume 1, Technical Basis for Assessment, EPA/600/R-07/139. October 2007. USEPA. National Recommended Water Quality Criteria. 2009. USEPA. Ecological Soil Screening Levels; 2015. USEPA. Region 4 Recommended Ecological Screening Values – Soil. http://www.epa.gov/region4/superfund/images/allprogrammedia/pdfs/tsstableso ilvalues.pdf.2015 Corrective Action Plan Part 1 November 2015 L.V. Sutton Energy Complex SynTerra Page 6-3 P:\Duke Energy Progress.1026\108. Sutton Ash Basin GW Assessment Plan\16.Corrective Action Plan\FINAL CAP REPORT\Final LV Sutton CAP Report 11-02-2015.docx USEPA, Scott G. Huling, Superfund Ground Water Issue, Facilitated Transport, EPA / 540 / 4-89/003; 1989. Zheng, C. and P.P. Wang, 1999, MT3DMS: A Modular Three-Dimensional Multi- Species Model for Simulation of Advection, Dispersion and Chemical Reactions of Contaminants in Groundwater Systems: Documentation and User’s Guide, SERDP-99-1, U.S. Army Engineer Research and Development Center, Vicksburg, MS.