Loading...
HomeMy WebLinkAboutNC0003425_Rox_Appendix G_20191231Corrective Action Plan Update December 2019 Roxboro Steam Electric Plant SynTerra APPENDIX G UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT FOR ROXBORO STEAM ELECTRIC PLANT, SEMORA, NORTH CAROLINA DECEMBER, 2019 PREPARED FOR DUKE ENERGY PROGRESS DUKE ENERGY PROGRESS, LLC INVESTIGATORS LAWRENCE C. MURDOCH, PH.D. - FRx, INC. BONG YU, PH.D. - SYNTERRA CORPORATION REGINA GRAZIANO, M.S. - SYNTERRA CORPORATION RONALD W. FALTA, PH.D. - FALTA ENVIRONMENTAL LLC Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina EXECUTIVE SUMMARY This groundwater flow and transport model report provides basic model development information and simulations of basin closure designs as well as results of corrective action simulations for the Roxboro Steam Electric Plant (Roxboro, Site, Plant). Duke Energy Progress, LLC (Duke Energy) owns and operates the Plant, located at 1700 Dunnaway Road in Semora, Person County, North Carolina. Operations at the Roxboro Plant began in the 1960s, and capacity was added through the 1980s. Currently, four coal-fired units are operated. Coal combustion residuals (CCRs) have historically been managed at on -Site ash basins: the East Ash Basin (EAB) and the West Ash Basin (WAB). Inorganic compounds from wastewater and ash within the basins have leached into the groundwater, and have then been transported by groundwater flow to areas downgradient of the ash basins. Numerical simulations of groundwater flow and transport have been calibrated to April 2019 conditions and used to evaluate different closure scenarios being considered for the ash basins. The predictive simulations presented herein are not intended to represent a final detailed closure design. These simulations use conceptual designs that are subject to change as the closure plans are finalized. The simulations are intended to show the key characteristics of groundwater flow and mobile constituent transport that are expected to result from the closure actions. This model report is intended to provide basic model development information and simulations of conceptual basin closure designs and provide preliminary assessment of the potential groundwater corrective action plan (CAP) to achieve compliance with North Carolina Administrative Code, Title 15A, Subchapter 02L, Groundwater Classification and Standards (02L). The model simulations were developed using flow and transport models MODFLOW and MT3DMS. Boron was the primary constituent of interest (COI) selected to estimate the time to achieve compliance because it is commonly associated with ash but is rare in natural settings, as supported by the North Carolina Department of Environmental Quality (NCDEQ) approved background wells at Roxboro. Boron is unreactive and highly mobile; therefore, it is a good indicator of the maximum extent of plumes originating in coal ash. The mobile constituents sulfate and total dissolved solids (TDS) were also modeled because they are conservative COIs that also migrate in groundwater out of the ash basins to form discernable plumes at Roxboro. The less mobile, more reactive constituents (i.e. arsenic, selenium, chromium) will follow the same flow path as boron; however, these constituents generally are not present at concentrations greater than 02L beyond the compliance boundary or do not have discernable plumes. Therefore, these constituents were evaluated using a geochemical Page ES-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina model. Geochemical modeling was conducted and the accompanying report is separate from this flow and transport report. Refinements that have improved the accuracy and resolution of details in the Roxboro model since previous report versions (SynTerra, 2015b, 2016, 2018) include: 1. Reduced sizes of grid blocks to improve resolution 2. Lowered model bottom elevation to improve resolution at depth 3. Expanded dataset used for model calibration to include hydraulic heads and COI concentrations through April 2019 4. Included data from recently installed deep bedrock wells and wells downgradient of the East Ash Basin to improve model calibration 5. Considered data from pumping tests performed in each ash basin in refinement to the coal ash hydraulic conductivity 6. Revised model grid and coverages based on more recent designs of the closure scenarios (closure -by -excavation and closure -in -place) developed by Wood Environment & Infrastructure Solutions, Inc. (Wood) For COIs evaluated in this report (boron, sulfate, and TDS), simulation results indicate that concentrations greater than the 02L standard are present in groundwater at or beyond the compliance boundary to the north and northeast of the EAB and north of WAB under April 2019 conditions. The presence of COI concentrations above regulatory criteria related to the WAB is associated with the abandoned sluice line corridor just north of the WAB. This source is independent of the WAB and is in the process of being removed with decommissioning of the sluice line piping. The model simulations include additional CCR source areas other than the EAB and WAB, which contribute to the ash basin COI plumes or plumes independent of the ash basins. The additional CCR source areas in the vicinity of the EAB include: 1. The unlined portion of the industrial landfill that extends beyond the engineered liner phases 1- 6 (referred to as the "Halo" area). This area is adjacent to the EAB, so it is included as a CAMA ash source 2. Dry Fly Ash (DFA) silos, transport, and handling area (hereafter referred to as the DFAHA) 3. Gypsum storage area (GSA) including underlying dry fly ash structural fill Page ES-2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Source areas that contribute to groundwater independently of the EAB (considered non- CAMA ash sources) include the GSA and the DFAHA. Their roles as independent COI sources are simulated in this report. The distribution of boron in the saprolite, transition zone, and bedrock flow zones outside of the ash basins resulted from hydrologic and mass loading conditions during operation of the ash basins and contribution of sources independent of the ash basins. These conditions will change during the interim period of ash basin decanting and activities related to construction of either the closure -in -place or closure -by -excavation scenarios. The termination of ash sluicing to the WAB and decanting of ponded water in the WAB by year 2020 will lower the hydraulic head in the WAB, thereby reducing the flow of water containing COIs. The simulated hydraulic head drop in the WAB is greater than that in the EAB. The calibrated model was adjusted to represent conditions that would occur during two closure scenarios described in closure designs provided by Wood. The closure -by - excavation scenario removes ash from the WAB and part of the EAB, and the closure -in - place scenario includes regrading the ash for positive surface drainage and installation of an engineered cap system. Boron plumes are predicted to recede. However, the model indicates three areas where boron concentrations greater than the 02L standard occur beyond the compliance boundary in both closure scenarios. These areas occur along the compliance boundary to the north and northeast of the EAB (Figure ES-1). Concentrations of COIs in groundwater from the WAB source material are predicted to remain less than applicable standards beyond the compliance boundary. Six reference locations (EAB: a, b, c and d and WAB: e and, f) are identified (Figure ES-1) to illustrate the temporal change of maximum boron concentrations in all layers in response to different closure scenarios (Figure ES-2). At each reference location, trends of boron concentration in the closure -in -place scenario are similar to trends in the closure -by -excavation scenario. Boron plumes reach maximum extents at the time of closure or several decades after closure (generally between approximately 2020 and 2100) without additional corrective action. Boron concentration in the simulations then decreases to less than 02L standards at most locations. An exception is at EAB location a (Figure ES-1) where boron concentration remains at approximately 800 µg/L because of the non-CAMA ash sources that remain in place throughout the simulations. The revised simulations presented in this report confirm earlier findings that there is no exposure pathway from the groundwater flow through the ash basins to water supply Page ES-3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina wells in the general vicinity of the ash basins. Domestic and public water supply wells are outside, or upgradient of, the groundwater flow system containing the ash basins. Domestic and public water supply wells are not affected by constituents released from the ash basins or by the different closure scenarios. The selected corrective action uses 50 extraction wells and 27 clean -water infiltration wells to maintain hydraulic control, an active groundwater remediation technique that is readily available and widely accepted in the environmental industry. Simulations with the selected corrective action demonstrate that the 32 extraction wells to the north and northeast of EAB can achieve 02L compliance for COIs from the EAB CAMA sources after approximately 9 years of operation with either closure scenario (upper panel of Figure ES-3). Simulations with the same corrective action demonstrate that the row of 18 extraction wells and 27 clean -water infiltration wells adjacent to the Intake Canal creates a hydraulic barrier that limits COI migration from non-CAMA sources downgradient of the EAB toward the Intake Canal. Concentrations less than 02L can be achieved for COIs downgradient from non-CAMA sources in the same timeframe under either closure scenario (bottom panel of Figure ES-3). The simulations indicate that boron, sulfate, and TDS in groundwater would be in compliance with 02L standards for the EAB and the downgradient additional source areas after approximately 9 years of operation for either the closure -by -excavation scenario or the closure -in -place scenario with the groundwater corrective action modeled. Page ES-4 APPROXIMATELY 20 YEARS I, APPROXIMATELY 20 YEARS POST -CLOSURE -BY -EXCAVATION, POST -CLOSURE -IN -PLACE ■a. ■b. ■c. d ■a. ■b. ■C. d. ■e. ■e. ■f. ■f. APPROXIMATELY 170 YEARS APPROXIMATELY 170 YEARS POST -CLOSURE -BY -EXCAVATION POST -CLOSURE -IN -PLACE ■a. ■b. ■c. d ■a. ■b. ■c. d. ■e. ■e. ■f. ■f. 3e 3 LEGEND GRAPHIC SCALE ■ REFERENCE LOCATION DUKE 1,soo 0 1,600 3,200 ENERGY BORON 700 - 4,000 Ng/L (IN FEET) BORON > 4,000 Ng/L PROGRESS ASH BASIN WASTE BOUNDARY DRAWN BY: R. YU DATE: 11/111/2019 ASH BASIN COMPLIANCE BOUNDARY REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY APPROVED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL COMPLIANCE BOUNDARY s MTena J�/1 11 PROJECT MANAGER: C. EADY INDUSTRIAL LANDFILL WITH PROPOSED LANDFILL EXPANSION www.synterracorp.com NOTES: ALL BOUNDARIES ARE APPROXIMATE. FIGURE ES-1 COMPARISON OF SIMULATED MAXIMUM BORON CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR CONCENTRATIONS IN ALL NON -ASH LAYERS AFTER CLOSURE 2024FOR EASTASHBASIN AND 2027FOR WESTASHBASIN- CLOSURE -BY- UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. REPORT AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER ROXBORO STEAM ELECTRIC PLANT 11, 2017.AERIAL WAS COLLECTED ON JUNE 13, 2016. SEMORA, NORTH CAROLINA DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). EAB Location ct 2,000 1,800 1,600 :1,400 1,200 m 1,000 u 800 c° 600 0 400 O m 200 0 Q0 � Q0 Lo � Ol O N M �t c N N N N N Year EAB Location c 2,000 1,800 -1,600 1,400 1,200 m '1,000 u 800 u 600 o 400 m° 200 0 0) 0 r4 r 0) O N M r4 r4 c-I N N N N N Year WAB Location e 9,000 8,000 b 7,000 c 6,000 L 5,000 v 4,000 io 3,000 0 2,000 L m° 1,000 0 Q0 � Q0 Q0 � Ol O N M c N N N N N Year EAB Location b 2,000 1,800 i ---D- Closure -by -excavation 1,600 Closure -in -place 1,400 ;1,200 o I 2L Stcl = 700 ug/L , m 1,000 0 800 u 600 c 0 400 O ca 200 0 to to to Q0 Q0 Q0 N M 'T c N N N N N Year EAB Location d 6,000 5,000 W 3 c 4,000 m 3,000 v io 2,000 c 0 1,000 O m 0 � � Q0 Q0 � m c O N N N N M N N Year WAB Location f 40,000 35,000 ---D- Closure-by -excav ation noo Closure -in -place 30,000 25,000 2L Stcl = 700 ug/L 4000 ug/L 20,000 0 15,000 U 0 10,000 O ca 5,000 0 Q0 � c N N N N rn fV V N Year Reference locations shown in Fig. ES-1 FIGURE ES-2 40) DUKE DRAWN BY: R. YU DATE: 11/18/2019 SUMMARY OF SIMULATED MAXIMUM BORON REVISED BY: W. PRATER DATE: 12/12/2019 CONCENTRATIONS IN ALL NON -ASH LAYERS AS PROGRESS CHECKED BY: K. LAWING DATE: 12/12/2019 FUNCTIONS OF TIME FOR THE TWO CLOSURE APPROVED BY: K. LAWING DATE: 12/12/2019 SCENARIOS PROJECT MANAGER: C. EADY UPDATED GROUNDWATER FLOW AND ' TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT �mTerra `'�" ' www.s nterracor com y p SEMORA, NORTH CAROLINA CLOSURE -BY -EXCAVATION WITHOUT NON-CAMA CCR SOURCES ICLOSURE-IN-PLACE WITHOUT NON-CAMA CCR SOURCES EAST ASH BASIN CLOSURE -BY -EXCAVATION WITH NON-CAMA CCR SOURCES Imo. .o. s +" �i rats► o h + `' ` ol AA-"' ;4 a. 4 r` ERSTAS Alaw- LEGEND iP EXTRACTION WELLS ♦ CLEAN WATER INFILTRATION WELLS ■ REFERENCE LOCATION ANON-CAMA CCR SOURCE ZONES BORON > 4,000 Ng/L BORON 700 - 4,000 Ng/L ASH BASIN WASTE BOUNDARY - • ASH BASIN COMPLIANCE BOUNDARY - • SOLID WASTE LANDFILL COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. NON-CAMA CCR SOURCES INCLUDE THE GYPSUM STORAGE AREA, DRY FLYASH SILOS, TRANSPORT, AND HANDLING AREATO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). a. _ T EAST ASH BASIN CLOSURE -IN -PLACE WITH NON-CAMA CCR SOURCES +.v ..� �v a. •�`� c. +^. -� - ` EAST ASH BASIN I DUKE t GRAPHICSCALE G 400 $oo ENERGY400 (IN FEET) PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LQWING DATE: 12/19/2019 synTerm PROJECT MANAGER: C. EADY www.synterracorp.com FIGURE ES-3 COMPARISON OF SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION IN THE NORTHERN AREA OF THE EAB UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE OF CONTENTS SECTION PAGE ExecutiveSummary.............................................................................................................. ES-1 1.0 Introduction..................................................................................................................1-1 1.1 General Setting and Background........................................................................1-1 1.2 Objectives................................................................................................................1-2 2.0 Conceptual Model........................................................................................................2-1 2.1 Aquifer System Framework.................................................................................2-1 2.2 Groundwater Flow System.................................................................................. 2-2 2.3 Hydrologic Boundaries......................................................................................... 2-6 2.4 Hydraulic Boundaries...........................................................................................2-6 2.5 Sources and Sinks.................................................................................................. 2-6 2.6 Water Budget......................................................................................................... 2-7 2.7 Modeled Constituents of Interest........................................................................ 2-8 2.8 Constituent Transport........................................................................................... 2-9 3.0 Computer Model..........................................................................................................3-1 3.1 Model Selection......................................................................................................3-1 3.2 Model Description.................................................................................................3-1 4.0 Groundwater Flow and Transport Model Construction ...................................... 4-1 4.1 Model Domain and Grid...................................................................................... 4-1 4.2 Hydraulic Parameters........................................................................................... 4-3 4.3 Flow Model Boundary Conditions.....................................................................4-4 4.4 Flow Model Sources and Sinks............................................................................ 4-5 4.5 Flow Model Calibration Targets......................................................................... 4-8 4.6 Transport Model Parameters............................................................................... 4-8 4.7 Transport Model Boundary Conditions...........................................................4-11 4.8 Transport Model Sources and Sinks................................................................. 4-11 4.9 Transport Model Calibration Targets...............................................................4-13 5.0 Model Calibration to April 2019 Conditions..........................................................5-1 5.1 Flow Model Calibration........................................................................................ 5-1 5.2 Flow Model Sensitivity Analysis......................................................................... 5-5 5.3 Historical Transport Model Calibration............................................................. 5-6 5.4 Transport Model Sensitivity Analysis.............................................................. 5-11 Page Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE OF CONTENTS (CONTINUED) 6.0 Predictive Simulations of Closure Scenarios......................................................... 6-1 6.1 Interim Period with Ash Basin Ponded Water Decanted (Approximate Year 2020-2024 or 2020-2037)........................................................................................ 6-2 6.2 Closure -by -Excavation Scenario.......................................................................... 6-3 6.3 Closure -by -Excavation Scenario with Corrective Action ................................ 6-6 6.4 Closure -in -Place Scenario..................................................................................... 6-9 6.5 Closure -in -Place Scenario with Corrective Action ......................................... 6-12 6.6 Conclusions.......................................................................................................... 6-12 7.0 References......................................................................................................................7-1 LIST OF TABLES Table 5-1 Observed, computed, and residual heads for the calibrated flow model Table 5-2 Calibrated hydraulic conductivity parameters Table 5-3 Water balance on the ash basin groundwater flow system for April 2019 conditions Table 54 Flow model sensitivity analysis Table 5-5a Boron, sulfate, and TDS source concentrations in the ash basins used in historical transport model Table 5-5b Boron, sulfate, and TDS source concentrations outside the ash basins used in historical transport model Table 5-6a Observed and computed boron concentrations (µg/L) in monitoring wells Table 5-6b Observed and computed sulfate concentrations (mg/L) in monitoring wells Table 5-6c Observed and computed TDS concentrations (mg/L) in monitoring wells Table 5-7 Transport model sensitivity to the boron Kd values Table 6-1 Water balance on the ash basin groundwater flow system for July 2020 when WAB is expected to be decanted Table 6-2 East Ash Basin area active remediation approach well summary Page ii Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina LIST OF FIGURES Figure ES-1 Comparison of simulated maximum boron concentrations in all non - ash layers after closure Figure ES-2 Summary of simulated maximum boron concentrations in all non -ash layers as functions of time for the two closure scenarios Figure ES-3 Comparison of simulated maximum boron concentrations in all non - ash layers after 9 years of active groundwater remediation in the northern area of the EAB Figure 1-1 USGS location map Figure 4-1 Numerical model domain Figure 4-2 Fence diagram of the 3D hydrostratigraphic model used to construct the model grid Figure 4-3 Computational grid used in the model with 5x vertical exaggeration Figure 4-4 Hydraulic conductivity estimated from slug tests performed in coal ash at 14 sites in North Carolina Figure 4-5 Hydraulic conductivity estimated from slug tests performed in saprolite at 10 Piedmont sites in North Carolina Figure 4-6 Hydraulic conductivity estimated from slug tests performed in the transition zone at 10 Piedmont sites in North Carolina Figure 4-7 Hydraulic conductivity estimated from slug tests performed in the bedrock at 10 Piedmont sites in North Carolina Figure 4-8 Distribution of model recharge zones Figure 4-9 Model surface water features Figure 4-10 Water supply wells in model area Figure 5-1a Model hydraulic conductivity zones in ash layer 1 Figure 5-1b Model hydraulic conductivity zones in ash layer 2 Figure 5-1c Model hydraulic conductivity zones in ash layer 3 Figure 5-1d Model hydraulic conductivity zones in ash layer 4 Figure 5-1e Model hydraulic conductivity zones in ash layer 5 Figure 5-1f Model hydraulic conductivity zones in ash layer 6 Figure 5-1g Model hydraulic conductivity zones in ash layer 7 Figure 5-1h Model hydraulic conductivity zones in ash layer 8 Figure 5-1i Model hydraulic conductivity zones in saprolite layers 9 and 10 Figure 5-1j Model hydraulic conductivity zones in saprolite layer 11 Figure 5-1k Model hydraulic conductivity zones in transition zone layers 12 and 13 Figure 5-11 Model hydraulic conductivity zones in upper fractured rock layer 14 Figure 5-1m Model hydraulic conductivity zones in upper fractured rock layer 15 Figure 5-1n Model hydraulic conductivity zones in upper fractured rock layer 16 Page iii Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina LIST OF FIGURES (CONTINUED) Figure 5-10 Model hydraulic conductivity zones in lower fractured rock layer 17 Figure 5-1p Model hydraulic conductivity zones in lower fractured rock layer 18 Figure 5-1q Model hydraulic conductivity zones in upper bedrock layer 19 Figure 5-1r Model hydraulic conductivity zones in upper bedrock layer 20 Figure 5-1s Model hydraulic conductivity zones in lower bedrock layer 21 Figure 5-1t Model hydraulic conductivity zones in lower bedrock layer 22 Figure 5-1u Model hydraulic conductivity zones in lower bedrock layer 23 Figure 5-1v Model hydraulic conductivity zones in lower bedrock layer 24 Figure 5-1w Model hydraulic conductivity zones in lower bedrock layer 25 Figure 5-2 Cross-section through ash basin dams showing hydraulic conductivity (colors) and hydraulic heads (lines) Figure 5-3 Comparison of observed and computed heads from the calibrated steady state flow model Figure 5-4 Simulated April 2019 hydraulic heads in upper fractured bedrock flow zone Figure 5-5 Simulated April 2019 local ash basin groundwater flow system in upper fractured bedrock Figure 5-6a East Ash Basin and West Ash Basin source zones for historical transport model Figure 5-6b Source zones adjacent to and downgradient of the EAB and WAB for historical transport model Figure 5-7 Simulated April 2019 boron concentrations in all non -ash layers with CAMA and non-CAMA CCR sources Figure 5-8 Simulated April 2019 sulfate concentrations in all non -ash layers with CAMA and non-CAMA CCR sources Figure 5-9 Simulated April 2019 TDS concentrations in all non -ash layers with CAMA and non-CAMA CCR sources Figure 6-1 Simulated hydraulic heads in upper fractured bedrock in July 2020 Figure 6-2 Simulated local ash basin groundwater flow system in upper fractured bedrock in July 2020 Figure 6-3a Simulated maximum boron concentrations in all non -ash modeling layers with CAMA and non-CAMA CCR sources when EAB closure - in -place is completed Figure 6-3b Simulated maximum boron concentrations in all non -ash modeling layers with CAMA and non-CAMA CCR sources when WAB closure - in -place is completed Page iv Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina LIST OF FIGURES (CONTINUED) Figure 6-3c Simulated maximum boron concentrations in all non -ash modeling layers with CAMA and non-CAMA CCR sources when closure -by - excavation is completed Figure 6-4 Closure -by -excavation design used in simulations (from Wood, 2019c and 2019d) Figure 6-5 Model setup for closure -by -excavation scenario Figure 6-6 Simulated local ash basin groundwater flow system in upper fractured bedrock after closure -by -excavation Figure 6-7a Simulated maximum boron concentrations in all non -ash layers with CAMA and non-CAMA CCR sources approximately 20 years after closure -by -excavation Figure 6-7b Simulated maximum boron concentrations in all non -ash layers with CAMA and non-CAMA CCR sources approximately 70 years after closure -by -excavation Figure 6-7c Simulated maximum boron concentrations in all non -ash layers with CAMA and non-CAMA CCR sources approximately 120 years after closure -by -excavation Figure 6-7d Simulated maximum boron concentrations in all non -ash layers with CAMA and non-CAMA CCR sources approximately 170 years after closure -by -excavation Figure 6-8 Reference locations for time series datasets Figure 6-9a Summary of maximum boron concentrations as functions of time and stratigraphic layer at EAB reference locations a and b for the closure - by -excavation scenario Figure 6-9b Summary of maximum boron concentrations as functions of time and stratigraphic layer at EAB reference locations c and d for the closure - by -excavation scenario Figure 6-9c Summary of maximum boron concentrations as functions of time and stratigraphic layer at WAB reference locations e and f for the closure - by -excavation scenario Figure 6-10 Simulated hydraulic heads in the upper fractured bedrock zone for the closure -by -excavation scenario with active groundwater remediation Figure 6-11 Simulated April 2019 maximum boron concentrations in all non -ash layers downgradient of the East Ash Basin Figure 6-12a Simulated maximum boron concentrations in all non -ash layers for the closure -by -excavation scenario after 9 years of active groundwater remediation Page v Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina LIST OF FIGURES (CONTINUED) Figure 6-12b Simulated maximum boron concentrations in all non -ash layers for the closure -by -excavation scenario after 30 years of active groundwater remediation Figure 6-12c Simulated maximum boron concentrations in all non -ash layers for the closure -by -excavation scenario after 80 years of active groundwater remediation Figure 6-12d Simulated maximum boron concentrations in all non -ash layers for the closure -by -excavation scenario after 130 years of active groundwater remediation Figure 6-12e Simulated maximum boron concentrations in all non -ash layers for the closure -by -excavation scenario after 180 years of active groundwater remediation Figure 6-13 Simulated maximum sulfate concentrations in all non -ash layers for the closure -by -excavation scenario after 9 years of active groundwater remediation Figure 6-14 Simulated maximum TDS concentrations in all non -ash layers for the closure -by -excavation scenario after 9 years of active groundwater remediation Figure 6-15 Closure -in -place design used in simulations (from Wood, 2019a and 2019b) Figure 6-16 Model setup for closure -in -place scenario Figure 6-17 Simulated local ash basin groundwater flow system in upper fractured bedrock after closure -in -place Figure 6-18a Simulated maximum boron concentrations in all non -ash model layers with CAMA and non-CAMA CCR sources approximately 20 years after closure -in -place Figure 6-18b Simulated maximum boron concentrations in all non -ash model layers with CAMA and non-CAMA CCR sources approximately 70 years after closure -in -place Figure 6-18c Simulated maximum boron concentrations in all non -ash model layers with CAMA and non-CAMA CCR sources approximately 120 years after closure -in -place Figure 6-18d Simulated maximum boron concentrations in all non -ash model layers with CAMA and non-CAMA CCR sources approximately 170 years after closure -in -place Page vi Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina LIST OF FIGURES (CONTINUED) Figure 6-19a Summary of maximum boron concentrations as functions of time and stratigraphic layer at EAB reference locations a and b for the closure -in - place scenario Figure 6-19b Summary of maximum boron concentrations as functions of time and stratigraphic layer at EAB reference locations c and d for the closure -in - place scenario Figure 6-19c Summary of maximum boron concentrations as functions of time and stratigraphic layer at WAB reference locations e and f for the closure - in -place scenario Figure 6-20 Simulated hydraulic heads in upper fractured bedrock zone for the closure -in -place scenario with active groundwater remediation Figure 6-21a Simulated maximum boron concentrations in all non -ash layers for the closure -in -place scenario after 9 years of active groundwater remediation Figure 6-21b Simulated maximum boron concentrations in all non -ash layers for the closure -in -place scenario after 30 years of active groundwater remediation Figure 6-21c Simulated maximum boron concentrations in all non -ash layers for the closure -in -place scenario after 80 years of active groundwater remediation Figure 6-21d Simulated maximum boron concentrations in all non -ash layers for the closure -in -place scenario after 130 years of active groundwater remediation Figure 6-21e Simulated maximum boron concentrations in all non -ash layers for the closure -in -place scenario after 180 years of active groundwater remediation Figure 6-22 Simulated maximum sulfate concentrations in all non -ash layers for the closure -in -place scenario after 9 years of active groundwater remediation Figure 6-23 Simulated maximum TDS concentrations in all non -ash layers for the closure -in -place scenario after 9 years of active groundwater remediation Page vii Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 1.0 INTRODUCTION This groundwater flow and transport model report provides basic model development information and simulations of basin closure designs as well as results of corrective action simulations for the Roxboro Steam Electric Plant (Roxboro, Site, Plant). Duke Energy Progress, LLC (Duke Energy) owns and operates the Plant, located at 1700 Dunnaway Road in Semora, Person County, North Carolina. Operations at the Roxboro plant began in the 1960s, and capacity was added through the 1980s. Currently, four coal-fired units are operated. Coal combustion residuals (CCRs) have historically been managed at the on -Site ash basins: the East Ash Basin (EAB) and the West Ash Basin (WAB). The EAB is approximately a half -mile southeast of the Plant, and the WAB is approximately a half -mile southwest of the Plant. 1.1 General Setting and Background The Roxboro Plant is built next to Hyco Reservoir, which provides water for Plant operations and also serves as the local hydrogeologic discharge point (Figure 1-1). The ash basins were created by building dams on north/northwestward-flowing streams that discharged into Hyco Reservoir. The dams created impoundments that were used to store ash. The EAB, the first basin to be constructed, started receiving ash in the mid- 1960s. Construction of the WAB followed, and active use of the WAB began in the early 1970s (Figure 1-1). An unlined industrial landfill was constructed on top of a portion of the EAB in the late 1980s. In 2002, the construction of landfill phases with engineered liner systems began at Roxboro. Operation of the lined landfill phases began in 2004 and continues presently. Dry fly ash was placed in the unlined portion of the industrial landfill, which is above the water table in the EAB. To allow development of the overlying industrial landfill, an earthen separator dike was constructed in the eastern portion of the EAB, which formed a barrier separating the EAB from a portion of the former basin and created the EAB extension impoundment area (Figure 1-1). For the WAB, the main dam was raised 13 feet and a series of dikes (Dikes #1 through #4) and a discharge canal were constructed in 1986. The rock filter dike (Dike #1), constructed of rock fill with a sand filter blanket, was installed near the southern end of the WAB, which isolated the southern end of the WAB and created the WAB extension impoundment area (Figure 1-1). The Roxboro Plant is situated in the eastern Piedmont Physiographic Province, which is underlain by weathered saprolite derived from fractured metamorphic and igneous rocks (Trapp and Horn, 1997). Topography consists of rounded hills and rolling ridges cut by small streams and drainages. Elevations in the vicinity of the Plant range from 410 feet (NVAD 88) during full pool at Hyco Reservoir to 570 feet southeast of the Plant. Page 1-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina The area is underlain with volcanic and sedimentary rocks that have been metamorphosed, intruded by coarse -grained granitic rocks, and subjected to regional structural deformation. The bedrock is fractured and weathered at shallow depths. The upper 10 feet to 30 feet consists of friable, greatly weathered saprolite. The degree of weathering decreases with depth, with a transition zone of up to 30 feet between the greatly weathered saprolite and the underlying fractured rock (SynTerra, 2015). Groundwater within the Site area exists under unconfined, or water table, conditions within the saprolite, transition zone, and in fractures and joints of the underlying bedrock. The shallow water table and bedrock water -bearing zones are interconnected. The saprolite, where the saturated thickness is sufficient, acts as a reservoir for supplying groundwater to the fractures and joints in the bedrock. Shallow groundwater generally flows from local recharge zones in topographically high areas, such as ridges, toward groundwater discharge zones, such as stream valleys. The groundwater flow and transport model for the Roxboro site has been under development since 2015. The development process began with a steady-state groundwater flow model and a transient model of constituent transport that were calibrated to field observations resulting from an extensive assessment effort in early and mid-2015. The first set of simulations were completed in November 2015 (SynTerra, 2015b) and were revised in February 2016 (SynTerra, 2016) and in November 2018 (SynTerra, 2018). 1.2 Objectives The purpose of this study is to update the groundwater flow and constituent transport model of the Site that was previously developed (SynTerra, 2018). Updates include that the bottom elevation of the model has been lowered 100 feet and model grids have been revised to include two more layers. Since 2018, additional assessment activities — including the installation of deep bedrock groundwater monitoring wells associated with both ash basins, installation of additional wells near the Dry Fly Ash (DFA) silos, transport, and handling area (DFAHA), performance of groundwater pumping tests in both ash basins, and multiple groundwater sampling events — have resulted in a significant increase in the data describing hydraulic property and constituent distribution. These additional data have further improved the predictive capability and have increased confidence in the model results. To take advantage of this potential, the model was recalibrated using data from both the new and existing groundwater wells through April 2019. The study consists of three main activities: developing a calibrated steady-state flow model of April 2019 conditions; developing a historical transient model of boron, Page 1-2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina sulfate, and total dissolved solids (TDS) transport that is calibrated to April 2019 conditions; and performing predictive simulations of the possible closure scenarios and remediation actions at the Site. The predictive simulations include consideration of a closure -in -place design that involves capping both the WAB and EAB with a low - permeability engineered cover system, and a closure -by -excavation design that involves excavating the coal ash materials in the WAB and part of EAB, placing the materials in a proposed lined landfill that is an expansion of the existing industrial landfill, and capping both existing and proposed landfills with a low -permeability engineered cover system. Additional corrective action measures that accelerate groundwater remediation are also considered. The predictive simulations provided herein are not intended to represent a final detailed closure or remediation design. These simulations use conceptual designs that are subject to change as the closure and remediation plans are finalized. The simulations are intended to show the key characteristics of groundwater flow and mobile constituent transport that are expected to result from the closure actions and groundwater remediation actions. Page 1-3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 2.0 CONCEPTUAL MODEL The site conceptual model for the Roxboro Plant is primarily based on the Comprehensive Site Assessment Report (SynTerra, 2015a), Corrective Action Plan Part 1 (SynTerra, 2015b), Corrective Action Plan Part 2 (SynTerra, 2016a), Comprehensive Site Assessment Supplement 1 (SynTerra, 2016b), and Comprehensive Site Assessment Update (SynTerra, 2017) and the Corrective Action Plan (CAP) Update (SynTerra, 2019). The reports contain extensive detail and data related to most aspects of the conceptual site model. 2.1 Aquifer System Framework The aquifer system at the Site is unconfined and includes three distinct hydrostratigraphic zones to distinguish the interconnected groundwater system: the shallow (surficial) flow zone, deep (transition) flow zone, and the bedrock flow zone (Legrand, 1988). The saprolite/transition zone consists of partially to thoroughly weathered rock that ranges in thickness from 10 feet to 30 feet at the Site (SynTerra, 2015a). The saprolite/transition zone is underlain by fractured metamorphic rock. The degree of fracturing is spatially variable and generally decreases downward. Vertical and horizontal fracture zones can cause localized zones of high permeability within the rock (Legrand, 1988; Miller, 1990). The permeability of the rock intersected by many of the bedrock wells is moderate, and it is inferred that the fracture density and hydraulic conductivity decrease downward (Legrand, 1988). The saprolite/transition zone is saturated at places close to Site surface water features, including National Pollutant Discharge Elimination System (NPDES)-regulated wastewater ponds and the Intake Canal, where groundwater is discharging, but it is unsaturated in most upland areas. The water table occurs in the fractured bedrock in most upland areas. Ash is saturated within most portions of the ash basins and forms a continuous hydrologic system with the underlying saturated geologic material (typically transition zone and upper bedrock). The ash material fills three alluvial valleys [one valley for the WAB and two valleys for the EAB (eastern and western lobes)] with maximum thicknesses of approximately 80 feet in both basins. Hydraulic conductivity values were determined in the field using slug tests and pumping tests. The hydraulic conductivity of the ash was measured by conducting 17 slug tests at seven wells completed in the ash. Hydraulic conductivity spanned four orders of magnitude, from 0.09 feet- per day (ft/d) to 300 ft/d, with a geometric mean of approximately 2 ft/d. Two pumping tests were conducted in ash in the ash basins, one Page 2-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina using the ABMW-1 well cluster in the WAB and the other using the ABMW-7 well cluster in the EAB. Hydraulic conductivity, based on the analytical solution for the pumping tests, ranges from 0.06 ft/d to 8 ft/d. A numerical forward model used to interpret the pumping tests indicates the ash consists of multiple layers with horizontal hydraulic conductivity that ranges from 0.07 ft/d to 15 ft/d and vertical hydraulic conductivity that ranges from 0.06 ft/d to 2 ft/d (SynTerra, 2019a and 2019e). The hydraulic conductivity of the saprolite was measured by conducting a total of seven slug tests at four wells completed in the saprolite. The hydraulic conductivity of the saprolite ranges from 0.02 ft/d to 700 ft/d with a geometric mean of 0.5 ft/d (SynTerra, 2019). The small sample size occurred because saprolite is saturated in only a few locations adjacent to the NPDES-regulated wastewater ponds and areas associated with the Intake Canal. The hydraulic conductivity of the transition zone was measured by conducting 27 slug tests at 16 wells, and the results ranged from 0.004 ft/d to 800 ft/d with a geometric mean of 0.5 ft/d (SynTerra, 2019). The mean values and the range of hydraulic conductivity estimated from slug tests using wells completed in saprolite are similar to values from tests conducted using wells in the transition zone. The hydraulic conductivity of the fractured bedrock was estimated by conducting 76 slug tests at 52 wells completed in the bedrock. The hydraulic conductivity ranges from 0.002 ft/d to 200 ft/d, with a geometric mean of 0.66 ft/d. The 25th percentile is 0.05 ft/d, the 50th percentile is 0.9 ft/d, and the 75th is 4.5 ft/d. It is inferred that the low end of the range characterizes the lower bedrock. The high values were measured at wells that intersect connected fractures zones in the shallow rock. The hydraulic conductivity of the deep bedrock was measured by conducting 36 slug tests at 10 wells completed at depths of 156 feet to 415 feet below ground surface. The estimated hydraulic conductivity ranges from 0.03 ft/d to 13 ft/d, with a geometric mean of 1.7 ft/d. The high values likely occur where wells intersect fracture zones. This is consistent with the results of geophysical logging (GEL Solutions, 2019), which indicates that most of the deep wells intersect one to several fractures that are permeable enough to contribute to the groundwater flow system 2.2 Groundwater Flow System The groundwater system is recharged by infiltration in the upland areas. The average value of recharge was estimated from the map of recharge in North Carolina by Haven (2003) and from analyzing stream hydrographs. A shapefile of the recharge map by Haven (2003) was enlarged and features of the Site were superimposed. Colors on the recharge map were compared to map legend colors because quantitative data from the Page 2-2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina file were unavailable. This comparison indicated that recharge was in the range of 6-10 inches per year in the watershed draining into the ash basins. The stream flow in Hyco Creek was obtained from measurements recorded at the gauging station USGS 02077200 near Leasburg, NC. The gauging station, located in Caswell County, approximately 10 miles southwest of the Site, measures flow from a watershed covering approximately 45.9 square miles to the south. Hyco Creek flows into Hyco Reservoir, which borders the Site. The stream flow analysis was conducted using 11 years of data starting in January 2002. The hydrograph was analyzed by separating stormflow and baseflow from the hydrograph using the method described by the Institute of Hydrology (1980). This method of hydrograph separation is widely used by the United States Geological Survey (USGS) and others. The separated hydrograph was analyzed using methods described by Mau and Winter (1997) and Rutledge and Mesko (1996) to estimate the recharge required to produce the observed baseflow. Recharge was estimated on a monthly basis and then averaged over the time period of the dataset. The analysis resulted in an estimate of recharge that ranges from 3 to 7 inches per year, depending on how the recharge is assumed to occur between baseflow turning points. Recharge estimated using the hydrograph from Hyco Creek was generally less than that shown on the map by Haven (2003), although the ranges from the two methods overlap. Both of these methods of estimating recharge have advantages and disadvantages, so it was assumed that the recharge to the upland areas was the average of the end members of the two methods, 0.0018 ft/d (approximately 7.9 inches per year). Further, it was assumed that recharge was negligible in the vicinity of the Plant, the lined phases of the industrial landfill, the lined flue gas desulfurization (FGD) ponds at the WAB, the lined gypsum storage area (GSA), and the low -permeability dams. Recharge greater than the regional average was assumed on the unvegetated ash basins. Specific values assumed for the recharge are provided later in Section 4.4. The EAB was originally developed in 1964 with the construction of an earthen dam, approximately 50 feet in height with a crest width of 15 feet, which impounded two creeks and created two lobes (eastern and western) within the basin. CCRs were deposited in the EAB by hydraulic sluicing operations in 1966. In 1973, the East Ash Basin dam was raised 20 feet to its present configuration. By 1983, hydraulic sluicing to the EAB was discontinued with the majority of the eastern lobe filled by the late 1980s. In 1986, the Roxboro facility was converted to dry fly ash handling, resulting in the construction of the industrial landfill (Permit 7302), which was constructed partially in the waste boundary of the EAB. To allow development of the overlying industrial Page 2-3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina landfill, an earthen separator dike was constructed in the eastern portion of the EAB, which formed a barrier separating the EAB from a portion of the former basin creating the EAB extension impoundment area. The original landfill was unlined with subsequent synthetic lined phases constructed over the unlined area beginning around 2002, and the landfill was in operation by 2004. The western lobe of the EAB was partly filled with ash and water in 1990. Presently, the western lobe is unvegetated and filled with ash to an elevation of approximately 470 feet, whereas the landfill on the eastern lobe rises to approximately 530 feet. The elevation of the top of the dam at the EAB is approximately 475 feet. A topographic map from the USGS Geospatial Database, shown in the CSA reports, indicates the ground surface elevation was between 390 and 400 feet below the dam in the EAB. The WAB was created in 1973 with the construction of an earthen dam (main dam) in the Sargents Creek stream channel. The main dam is an earth fill embankment with a central earth core constructed between two cofferdams over a prepared rock foundation with a central core keyway excavated 10 feet into rock. In 1986, the main dam was raised 13 feet and a series of dikes (Dikes #1 through 34) and a discharge canal were constructed. A rock filter dike (Dike #1), constructed of rock fill with a sand filter blanket, was installed in the southern end of the WAB to enhance settling and retention time. The rock filter dike isolated the southern end of the WAB and created the WAB extension impoundment area. The distance measured within the basin from the main dam to the rock filter dike is approximately 4,700 feet in length. Water and ash were hydraulically sluiced to the WAB at the northeast end of the basin near the Plant, with water flow to the south. Sluicing operations to the WAB ceased in December 2018 with the conversion to dry ash handling operations and disposal to the industrial landfill or as beneficial reuse. A series of lined lagoons (FGD ponds) were constructed on top of the northwestern corner of the WAB and are used to settle wastewater and solids formed during the desulfurization of flue gas. Surface water runoff and process wastewater, including landfill leachate, from the EAB are managed via an internal collection system with conveyance to the Lined Retention Basin (LRB) for low volume wastewater treatment. Treated water is discharged to the NPDES-permitted heated water discharge pond with discharge through NPDES Outfall 003. Surface water runoff related to the WAB flows to the south to the rock filter dike with discharge to the western discharge canal, positioned along the western side of the ash basin, which discharges to the heated water discharge pond, which ultimately flows into Hyco Reservoir through NPDES Outfall 003 (Figure 1-1). Page 24 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina The surface of the WAB slopes gently to the southeast, where the elevation is approximately 465 feet. The ground surface elevation was between 390 feet and 410 feet along Sargents Creek prior to construction of the WAB dam. The recharge in the ash basins is expected to be variable, ranging from essentially zero on the lined portions of the landfill and the FGD ponds, to values equal to the regional average on the exposed ash. Average water level elevations in four wells completed within ash of the EAB were very consistent, ranging from 467 feet to 469 feet during baseline measurements. Three wells are completed in ash of WAB with water level elevation from 463 feet to 464 feet during baseline measurement. The stage of the WAB impoundment area southeast of the WAB is approximately 445 feet. The stage of the EAB impoundment area east of the industrial landfill is approximately 465 feet. Hydraulic heads were measured below the ash basins in nine locations. The heads in the underlying bedrock are similar, to slightly lower than, the heads in the basins at most places, indicating that the ash and underlying bedrock are part of a continuous hydrologic system. Wells ABMW-3, ABMW-3BR, and ABMW-3BRL in the WAB, and ABMW-5 and ABMW-51) in EAB, are exceptions, where the head in deepest bedrock well is nearly 40 feet lower than head in the ash basin well. This large head difference indicates a discontinuity in the hydrologic system. It appears that the deep bedrock system is separated locally from the shallow hydrologic system by zones of low hydraulic conductivity. Moreover, we infer that permeable zones in the deep bedrock are hydraulically connected to zones outside of the ash basin where the hydraulic head is lower than in the ash basin. The hydraulic head in the ash basins is bordered regionally by heads of 500 feet or higher in upland areas, and by heads of approximately 410 feet at Hyco Reservoir (full pool is 410 feet). On a more local scale, the hydraulic head between the ash basins and along a topographic ridge that trends toward the eastern lobe of the EAB is higher than within the ash basins themselves. The head is lower than the ash basins in the eastern discharge canal that drains north from the EAB extension impoundment on the east side and the western discharge canal on the west side of the WAB. The distribution of observed hydraulic head indicates a general pattern of groundwater flow that differs between the two lobes of the EAB and the WAB. It is inferred from the head measurements, that groundwater flow into the eastern lobe of the EAB is from uplands to the south and east, and flows north toward the Intake Canal and northeast to the eastern discharge canal draining the extension impoundment to the east. Page 2-5 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Groundwater is inferred to flow into the western lobe of the EAB from the west, south, and east. Groundwater flow from the western lobe is inferred to occur to the north toward the NPDES-permitted wastewater ponds. The distribution of observed hydraulic head indicates that groundwater flows into the WAB from upland areas located to the southeast. It is inferred from the head distribution that groundwater flows from the WAB to the north through and around the dam, as well as to the western discharge canal to the west of the WAB. It is also inferred that flow occurs from the WAB ponded water through and beneath the filter dike in the south central end of the WAB because of the head within the ponded water. 2.3 Hydrologic Boundaries The major discharging locations for the shallow water system serve as hydrologic boundaries to the shallow groundwater system. These include NPDES-permitted wastewater ponds and the Intake Canal. 2.4 Hydraulic Boundaries The shallow groundwater system does not appear to contain impermeable barriers or boundaries in the study area, but it does include hydraulic boundaries between zones of different hydraulic conductivity. The degree of fracturing, and thus the hydraulic conductivity, is expected to decrease with depth in metamorphic rock. This will result in blocks of unfractured rock where the hydraulic conductivity is quite low to negligible. However, isolated fractures might occur that result in large local hydraulic conductivities, and the locations of these fractures is difficult to predict or to comprehensively map. It was assumed that the rock was impermeable below the depth of the bottom modeled layer, and a no -flow boundary was used to represent this condition. 2.5 Sources and Sinks Recharge is the major source of water in the uplands and ash basins. Most of the groundwater discharges to streams and lakes, as previously discussed. Groundwater discharges into the ash basins and flows as pore water through the ash basins, which act as both a source of, and sink for, groundwater. Ponded water occurs in the WAB, and shallow water conditions in the EAB, primarily from groundwater discharge and surface water runoff, are noted. Some surface water may infiltrate to recharge groundwater flowing under the dams at the northern ends of the ash basins. Approximately 63 water supply wells in the vicinity of the Roxboro Plant (SynTerra, 2014) have been identified and included as sinks in the groundwater model. Screen elevations and pumping rates from most of these wells are unknown. Woodland Page 2-6 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Elementary School has two wells to the southwest of the Plant; one of the wells is currently used for water supply. The model assumes both are active because the second may become active in the future, and this is more conservative when considering potential receptors. Woodland Elementary School wells are the only public supply wells in the area. Another water supply well is used by a building materials manufacturing plant that makes drywall located to the northeast of the Roxboro Plant across from the Intake Canal. The remaining water supply wells are assumed to be domestic wells that supply water to single-family residences, largely in the upland areas southwest and southeast of the Plant. Water from some domestic water supply wells was sampled by the North Carolina Department of Environmental Quality (NCDEQ) and used for chemical analysis. These data were consistent with ambient groundwater composition with no evidence of effects from ash basins. The wells are situated in distinct drainage basins/slope-aquifer systems separate and/or upgradient relative to groundwater flow from the Plant area and the ash basins. Measurement data on the discharge rate from the water supply wells was unavailable, so an average discharge rate was used in the model. The average daily water use in North Carolina is 60 gallons to 70 gallons per person (Treece et al. 1990); therefore, a well providing water for a family of four people would be pumped at approximately 280 gallons per day. Residential sanitary waste water is disposed of through septic systems in the vicinity of the Roxboro site, which causes much of the water that is pumped from the aquifer to infiltrate into the vadose zone through septic drain fields. Radcliffe et al. (2006) studied septic drain fields in the southeast and found that 91 percent of the water used by a household was discharged to the septic drain field. This corresponds to a consumptive use of 9 percent. This is consistent with the data presented by Treece et al. (1990), who conclude that consumptive use is less than 6 percent. Daniels et al. (1997) developed a groundwater model of the Indian Creek watershed in North Carolina, which used the analysis of Treece et al. (1990) to characterize pumping and septic return rates. Septic systems were considered a source of water in the model. 2.6 Water Budget The long-term average rate of water inflow to the study area is equal to the rate of water outflow from the study area. Water enters the groundwater system through recharge, typically derived from rain water infiltration but also including septic return, and leaves by discharge of surface water and water supply wells. The magnitude of components of the water budget are difficult to constrain using field data at the Site, but Page 2-7 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina water budget details are derived from the groundwater model and will be provided in Sections 5.0 and 6.0. 2.7 Modeled Constituents of Interest This report will focus on modeling conservative constituents of interest (COIs) boron, sulfate, and total dissolved solids (TDS). The EAB and WAB are NPDES-permitted wastewater treatment systems. Water within the ash basins is not groundwater; therefore, comparison with 02L standards/Interim Maximum Allowable Concentrations (IMAC)/background values is for general comparative purposes only. In ash pore water samples collected from wells, antimony, boron, chromium (total and hexavalent), cobalt, iron, manganese, molybdenum, pH, selenium, strontium, sulfate, TDS, total uranium, and vanadium were detected in the ash pore water at concentrations greater than 02L standards or IMAC values. These compounds were identified in the CSA Update (SynTerra, 2017) as COIs at Roxboro. Many COIs identified are naturally occurring and present at background locations not affected by the ash basin operations. Naturally occurring compounds include antimony, chromium (total and hexavalent), cobalt, iron, manganese, TDS, and vanadium. These constituents are commonly detected in groundwater in the Piedmont province of North Carolina. Background analytical results are used to compare detected constituent concentration ranges from the source area relative to native conditions. Statistically derived background values for the Site have been calculated (SynTerra, 2019b) and used for screening of assessment data collected in areas of potential migration of COIs from a source area. COIs have been grouped by geochemical behavior and mobility. Boron, sulfate, and TDS are considered conservative constituents since they are relatively mobile in groundwater. At Roxboro, the distribution of conservative COIs (boron, sulfate, and TDS) represents the area of maximum COI distribution at or beyond the compliance boundary and the conservative COIs are the focus of corrective action. Geochemical model simulations support that these constituents would be transported conservatively (Kd values <1 mL/g) as soluble species under most conditions (SynTerra, 2019c). The spatial occurrence of these COIs with a discernable plume in the direction of groundwater flow downgradient from source areas supports this conclusion. Of these conservative constituents, boron is generally the most prevalent in affected groundwater and ash pore water at concentrations greater than 02L (700 µg/L). Additionally, the background value for boron (50 µg/L) at Roxboro is consistent with the laboratory reporting limit. This provides some assurance that detectable concentrations of boron, occurring in a discernable plume in the direction of Page 2-8 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina groundwater flow, represent migration from a source area. For these reasons, boron has served as a primary indicator of the maximum extent of constituents with a source in ash. Sulfate and TDS are not as common as boron but are similarly present in concentrations greater than 02L within ash pore water and affected downgradient areas at Roxboro. Sulfate and TDS are also present in concentrations greater than 02L within discernable plumes at additional downgradient source areas, the GSA and the DFAHA. 2.8 Constituent Transport The COIs that are present in the wastewater and coal ash leach into the ash pore water. As water infiltrates through the bottom of the basins or dams, pore water containing COIs can enter the groundwater system. Once in the groundwater system, the COIs are transported by advection and dispersion, subject to retardation through adsorption to solids. During transport, dilution occurs within the groundwater system. As the COIs reach surface water, they are removed from the groundwater system and enter the surface water system, where in general, they are greatly diluted. Page 2-9 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 3.0 COMPUTER MODEL 3.1 Model Selection The numerical groundwater flow model was developed using MODFLOW (McDonald and Harbaugh, 1988), a three-dimensional (3D) finite difference groundwater model created by the United States Geological Survey (USGS). The chemical transport model is the Modular 3-D Transport Multi -Species (MT3DMS) model (Zheng and Wang, 1999). MODFLOW and MT3DMS, widely used in industry and government, are considered to be industry standards. The models were assembled using the Aquaveo GMS 10.3 graphical user interface (httl2://www.aquaveo.com/). 3.2 Model Description MODFLOW uses Darcy's law and the conservation of mass to derive water balance equations for each finite difference cell. MODFLOW considers 3D transient groundwater flow in confined and unconfined heterogeneous systems, and it can include dynamic interaction with pumping wells, recharge, evapotranspiration, rivers, streams, springs, lakes, and swamps. This study uses the MODFLOW-NWT version (Niswonger, et al., 2011). The NWT version of MODFLOW provides improved numerical stability and accuracy for modeling problems with variable water tables. The improved capability is helpful in the present work where the position of the water table in the ash basin can fluctuate depending on the conditions under which the basin is operated and on the closure action activities. MT3DMS uses the groundwater flow field from MODFLOW to simulate 3D advection and dispersion of the dissolved COIs, including the effects of retardation due to COI adsorption to the soil matrix. Page 3-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 4.0 GROUNDWATER FLOW AND TRANSPORT MODEL CONSTRUCTION The flow and transport model of the Site was built through a series of steps. • Step 1: Build a 3D model of the site hydrostratigraphy based on field data. • Step 2: Determine the model domain and construction of the numerical grid. • Step 3: Populate the numerical grid with flow parameters. • Step 4: Calibrate the steady-state flow model with adjustments of the numerical grid. • Step 5: Develop a transient model of historical flow to provide time -dependent constituent transport development. • Step 6: Recalibrate to ensure the flow model matched the observed heads and the transient model reproduced the observed plumes. The current model is a revised version of a model initially developed in 2015 and updated in subsequent years. The process of revising the model involved using the model updated in 2018 as a starting point and following an iterative process of adjusting parameters until the model adequately predicted the observed heads and concentrations. 4.1 Model Domain and Grid The initial steps in the model grid generation process were the determination of the model domain and the construction of a 3D hydrostratigraphic model. The model has dimensions of approximately 4 miles by 3 miles, and with the long dimension trending N30E (Figure 4-1). This trend is parallel to the axis of Hyco Reservoir. The northwest corner of this region was underlain by Hyco Reservoir, and the model was set as inactive to the west of the approximate center of the lake. Portions of the model that were set as inactive are excluded from the numerical simulation. This configuration was selected so that most of the northwest and southwest sides of the model were bounded by Hyco Reservoir. The distance to the southeast and northeast boundaries of the model were made large relative to the area of interest in order to minimize the influence of outer model boundary conditions. The ground surface of the model was interpolated from USGS NED n37w0791/3 arc -sec 20131 degree IMG dataset obtained from http://viewer.nationalmal2.gov/viewer/. The elevations for the top of the ash basin were modified using more recent surveying data from the WSP USA Aerial Topographic Survey from May, 2015. Page 4-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina The hydrostratigraphic model consists of seven units: the EAB and WAB, saprolite, transition zone, upper fractured rock, lower fractured rock, upper bedrock, and lower bedrock. The hydrostratigraphic model was developed using "solids" in GMS (Figure 4-2). Four solids were created and then subdivided after the computational mesh was developed. The solids include: ash, saprolite/transition zone, fractured rock, and unfractured rock. The ash solid includes the EAB and WAB hydrostratigraphic units. The saprolite/transition zone solid includes the saprolite and transition zone units. The lower contact between the ash basin and the underlying saprolite was assumed to be the ground surface prior to construction of the ash basins. An electronic file describing this surface was created by digitizing a preconstruction topographic map. The digitized points were interpolated to create a continuous surface representing the preconstruction ground surface, and this was used as the contact between the ash and the underlying saprolite. The lateral extent of the ash was determined from aerial photographs and maps in the CSA report (SynTerra, 2015). The saprolite and transition zone were combined into the same solids model. The contact between the transition zone and underlying bedrock was determined by interpolating data measured in borings from the CSA report and historical data. This produced an isopach map of the thickness of the weathered zone (saprolite and partially weathered rock in the transition zone). The interpolated isopach surface was subtracted from the ground surface to create the contact used in the model. The methodology outlined above for creating a geologic model was done so the interpolated contacts would approximately follow the ground surface between boreholes, which are consistent with the expectations based on the hydrogeology of the Piedmont region (e.g. LeGrand, 1988; Miller, 1990). The fractured rock is approximately 100 feet thick, based on general field observations and data from boring logs interpretation. The fractured rock solid was subdivided into the upper fractured rock unit and lower fractured rock unit in the model. The unfractured rock solid was subdivided into the upper bedrock and lower bedrock units. The numerical model grid consists of 25 layers representing the hydrostratigraphic units. The model grid was set up to conform to the contacts from the solids. The model grid layers correspond to the solids as follows: Page 4-2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Hydrostratigraphic Layer Grid Layer Ash 1-8 Saprolite 9-11 Transition zone 12-13 Upper fractured rock 14-16 Lower fractured rock 17-18 Upper bedrock 19-20 Lower bedrock 21-25 The numerical grid consists of rectangular blocks arranged in columns, rows and layers. There are 270 columns, 233 rows, and 25 layers (Figure 4-3). The maximum width of the columns and rows is 100 feet. The size of the grid blocks is approximately 50 feet inside and near the ash basins. The horizontal dimension of some of the grid blocks is as small as 15 feet in the vicinity of the dams. Grid layers 1-8 were set as inactive outside of the region of the ash basin as determined from aerial photos and the CSA report (SynTerra, 2015a). Grid layers 9-25 were set as inactive in the northwest corner of the model that represented region on the far side of Hyco Reservoir. 4.2 Hydraulic Parameters The horizontal hydraulic conductivity and the horizontal to vertical hydraulic conductivity anisotropy ratio (anisotropy) are the main hydraulic parameters in the model. The distribution of these parameters is based primarily on the model hydrostratigraphy, with some additional vertical variation. Most of the hydraulic parameter distributions in the model were uniform throughout a model layer. Initial estimates of parameters were based on literature values; results of slug, core and pumping tests; and simulations performed using a preliminary flow model. The hydraulic parameter values were adjusted during the flow model calibration process described further in Section 5.0 to provide a best fit to observed water levels in observation wells. The hydraulic conductivity of coal ash measured at 14 sites in North Carolina ranges over 4 orders of magnitude, with a geometric mean value of approximately 1.8 ft/d (Figure 4-4 through Figure 4-7). Ash hydraulic conductivity values estimated by interpreting slug test data at Roxboro range from 0.09 ft/d to 300 ft/d. Two pumping tests were performed in ash material within the ash basins at Roxboro to help refine the value of this parameter. One test was performed in the EAB and another in the WAB. Hydraulic conductivity based on analytical and numerical solutions ranges from 0.06 Page 4-3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina ft/d to 15 ft/d. Pumping tests were conducted in the ash basins at five other Duke sites. Those pumping tests were analyzed using parameter estimation methods with analytical solutions and with Site -specific numerical models. The results are summarized in Figure 4-4 (SynTerra, 2019a and 2019e). The hydraulic conductivities from hundreds of slug tests performed in saprolite wells at 10 Piedmont sites range over 4 orders of magnitude and have a geometric mean value of 0.9 ft/d (Figure 4-5). Slug tests performed at wells completed in saprolite at Roxboro indicate that hydraulic conductivity ranges from 0.02 ft/d to 700 ft/d. Transition zone hydraulic conductivities from hundreds of slug tests at 10 Piedmont sites range over 5 orders of magnitude, with a geometric mean value of 0.9 ft/d (Figure 4-6). The measured values at Roxboro range from 0.004 ft/d to 800 ft/d. Fractured bedrock hydraulic conductivities from hundreds of slug tests at 10 Piedmont sites in North Carolina (Figure 4-7) range over more than 6 orders of magnitude, with a geometric mean value of 0.3 ft/d. The measured values at Roxboro for shallow fractured rock range from 0.002 ft/d to 200 ft/d. The measured hydraulic conductivity values for lower fracture rock and competent bedrock at Roxboro range from 0.03 ft/d to 10 ft/d. Similar to the hydraulic conductivity obtained from all sites, data from slug tests and pumping tests conducted at the Roxboro span over a large range, indicating that hydraulic conductivity varies spatially due to heterogeneities. The hydraulic conductivity geometric mean values at Roxboro are similar to that of all sites. 4.3 Flow Model Boundary Conditions The flow model outer boundary conditions are different for the different aquifer units. The outer lateral boundary conditions for the saprolite are almost entirely constant head, with small areas of no -flow locally. Boundaries on the west and northern parts of the model include parts of Hyco Reservoir. The head in the upper layer of the model was set to the stage of the lake. The boundaries on the south and east sides of the model are independent of a definitive hydrologic feature. A constant head boundary condition with the head set 3 feet above the top of the saprolite layer was used along these boundaries. This boundary condition forces the water table to be in the top of the saprolite along the south and east boundaries, which is a reasonable approximation of the observed and expected conditions. The constant head boundary condition extends along the upland areas, but it is terminated within a few hundred feet of the locations of streams or lakes. This is Page 4-4 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina because streams or lakes that intersect the boundary are defined by their own boundary conditions (as either constant head or drain -type boundaries). This creates short intervals of no -flow conditions between streams or lakes and the uplands in the saprolite. The constant head boundary condition was assigned to layers 9-16, which is where most of the flow occurs. The underlying layers were set to no -flow. The model boundary on the west and north sides of the model was set to constant head where it cuts across Hyco Reservoir or related water bodies. The boundary condition outlined above was used along the western and northern boundaries where the model cut across upland areas. 4.4 Flow Model Sources and Sinks The flow model sources and sinks on the interior of the model consist of recharge, lakes, wetlands, streams, and groundwater pumping. Recharge is a key hydrologic parameter in the model (Figure 4-8). As described in Section 2.2, the recharge rate for upland areas of the Roxboro was assumed to be 0.0018 ft/d (7.9 inches per year). The recharge rate was set to zero in the regions around the lakes that serve as groundwater discharge zones. The recharge rate in the Roxboro Plant was set to 0.0001 ft/d, due to the large areas of roof and pavement. The recharge rate for the gypsum storage area, the lined area of the industrial landfill in and around the EAB, and the area of the lined FGD ponds on the WAB was set to 0.00001 ft/d (Figure 4-8). Recharge on the dams was set to equal to or lower than 0.0001 ft/d because of the low permeability of these features. Recharge on the exposed ash was assumed to be the same as ambient conditions (0.0018 ft/d). Recharge was omitted from the southern end of the WAB where standing water is present and from the southern extension impoundment (Figure 4-8). Recharge to the exposed portions of the unlined area of the industrial landfill of the EAB was set to be the same as ambient conditions (0.0018 ft/d). A portion of the unlined landfill area was recently covered with an engineered cover system, and as a result, the recharge rate for that area was set to close to zero. Figure 4-8 shows the distribution of recharge zones in the model. Recharge was not adjusted much during the initial model calibration process, but it is included in the sensitivity analysis. The reason for not including recharge as a calibration parameter is that for steady-state unconfined flow, the hydraulic heads are determined primarily by the ratio of recharge to hydraulic conductivity, so the two parameters are not independent. In situations where the groundwater discharges to a flow measuring Page 4-5 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina point (for example, a gauged stream in a watershed), the flow measurement can be used to calibrate the recharge value, allowing both the recharge rate and the hydraulic conductivity to be simultaneously calibrated. However, no streams were gauged at Roxboro, so recharge was fixed. Recharge was adjusted slightly during the model revision. The revision included reducing the recharge on the exposed ash in WAB and EAB, which allowed the heads at ash basin monitoring wells to be adequately explained at ash basin monitoring wells using average ash properties. Lakes and other water bodies were represented as general head boundary set to their stage (Figure 4-9). This includes Hyco Reservoir and NPDES-regulated wastewater ponds within the Plant that were assumed to be at the same stage as Hyco Reservoir. The full pool stage of Hydro Reservoir is 410 feet, but the lake stage was less than full pool when the calibration water levels were made; therefore, 408 feet was used for the stage in the model. The upper two layers of the model used to represent Hyco Reservoir are approximately 20 feet thick. This is consistent with the bathymetry of the lake. However, the distribution of the lake bathymetry was unavailable. Therefore, the lake depth was assumed to be uniform. The stages of NPDES-regulated wastewater ponds were determined from Light Detection and Ranging (LiDAR) data. Streams were represented as Type 3 boundary conditions, called "drains" in MODFLOW (Figure 4-9). The elevation of the streams is set to the ground surface elevation determined from the LiDAR to account for small amounts of incision observed in the field. The drain conductance was set to 100 ft2/day, a relatively large value that will cause negligible head loss, and was not adjusted during calibration. The ash basins were represented by simulating the observed standing water as general head boundary and applying recharge based on estimates from the land cover. This approach treats the ash basins in the same way as other hydrogeologic components in the model, and it was selected as the best approach to characterize April 2019 conditions. However, the hydrologic conditions of the ash basins in the past differ from April 2019 conditions. The ash basins appear as open water bodies in an aerial photograph from 1977. The stage of the water in the ash basins appears to be similar to water levels observed in wells during recent years. Channels through the ash basins were represented as general head, even though streams elsewhere in the model were treated as drains. This was done to allow water to flow into or out of the channels as water flows through the ash basins. Streams were Page 4-6 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina represented as drains because it was assumed that they gain only water from groundwater. The hydraulic history of the ash basins was represented by assuming present conditions with a few exceptions to reasonably approximate the conditions in the basins since they were built. One exception is the distribution of recharge on the basins, which was adjusted to approximate changes resulting from construction. The starting recharge was assumed to be equal to the ambient recharge everywhere in the WAB and EAB. The construction of the lined FGD ponds in the WAB in 2004 was assumed to decrease the recharge to negligible values. In addition, the installation of a liner on and adjacent to a portion of the unlined landfill in 2014 was assumed to reduce the recharge to negligible values at those locations (Figure 4-8). Little information about the public and private wells in the model area is available, other than their locations, which are shown on Figure 4-10 (data from SynTerra, 2015a). Most of the wells are probably open boreholes in the upper 100 feet of bedrock. However, it is common for drillers in the Piedmont to extend wells to depths of several hundred feet in an effort to intersect permeable fractures and create more productive wells or for increased storage capacity. As a result, the depth of the wells probably ranges from 150 feet to 600 feet. The wells are assumed to be screened in grid layer 16 in the model. The pumping rates from the wells were unknown; therefore, it was assumed that the wells were pumped at 280 gallons per day, which is an average water use for a family of four in North Carolina (Treece et al. 1990; North Carolina Water Use,1987, and 1995). Septic return was assumed to be 94 percent of the pumping rate, based on Treece et al. (1990), Daniels et al. (1997) and Radcliffe et al. (2006). The septic return was injected into layer 11 (saprolite) in the model. The wells used for water supply at Woodland Elementary School and at the building materials manufacturing plant were assumed to be pumped at a steady rate of 500 ft3/day. Approximately 280 students and staff are at the Woodland School, according to their website (http://woodland.person.kl2.nc.us/cros/One.aspx?portalId=23434&pageld=222558). The website was accessed in 2016, but it is no longer available. It was assumed that approximately 20 percent of daily water consumption occurred at the school, and the daily water consumption was estimated using the data outlined above of 70 gallons per day (280 gallons per day for a family of four, or 37.4 ft3/d). No data about the building Page 4-7 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina materials manufacturing plant well was available, and a pumping rate of 500 W/d was assumed. 4.5 Flow Model Calibration Targets The steady state flow model calibration targets were average water level measurements from 173 groundwater monitoring wells obtained through April 2019. For comparison, the previous flow model was calibrated with data from 127 wells obtained through November 2017. In general, wells with an ABMW designation are screened in ash, wells with an S designation are screened in the saprolite, and wells with a D designation are screened in the transition zone. Those with a BR designation are screened in the upper fractured rock, and those with a BRL designation are screened in the lower fractured rock or bedrock, with an additional L indicating greater depth. The water levels used for calibration were determined by taking the average value for head data. Water levels are expected to vary on an annual period due to seasonal changes in recharge. These fluctuations in water level are not simulated because the flow model is steady state. The average water level values are the best available estimates of the steady state hydraulic heads, so they were used for calibration. This approach differs from previous calibrations of the model where the most recent water level measurements were used. Water -level data have been recorded quarterly (seasonal) for up to 17 years. Most records span more than one year, so seasonal fluctuations are accommodated by averaging the head values. 4.6 Transport Model Parameters The transient transport model uses a sequence of steady state MODFLOW simulations to provide the time -dependent groundwater velocity field. The transient transport simulation was initiated January 1966 and continued through April 2019. Operations at the Roxboro Plant began in 1966, and the EAB was the first basin to receive ash. The history of the EAB is complex and included the construction of the separator dike in the upstream end of the eastern lobe; creation of an industrial landfill; and development of a lined landfill. However, it is reasonable that the hydraulic head remained similar from the time the basin was filled with water until present day. The implication is that that the pore water exchanged between the ash basins and the natural underlying geological materials under April 2019 conditions is approximately the same as it was during sluicing operations. The flow model assumes that the ash basins fill with water quickly and the heads are maintained at the same level as April 2019 conditions. Page 4-8 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina The key transport model parameters (besides the groundwater flow field) are the boron, sulfate, and TDS source concentrations in the ash basin, and the boron, sulfate, and TDS soil -water distribution coefficients (Kd). Secondary parameters are the effective porosity and the longitudinal, transverse, and vertical dispersivity. The source concentrations were estimated from recently measured ash pore water concentrations in monitoring wells. Source concentrations of the boron, sulfate, and TDS are held constant at the specified levels in the ash layers during historical transport simulations but are allowed to vary in time during the predictive simulations that follow. The numerical treatment of adsorption in the model requires special consideration because part of the system is a porous media (the ash, saprolite, and transition zone) with a relatively high porosity, whereas the bedrock is a fractured media with very low matrix porosity and permeability. As a result, transport in the fractured bedrock occurs almost entirely through the fractures. The MODFLOW and MT3DMS flow and transport models simulate fractured bedrock as an equivalent porous media. With this approach, an effective hydraulic conductivity is assigned to the fractured rock zones so that it produces the correct Darcy flux (volume of water flowing per area of rock per time) for a given hydraulic gradient. However, because the water flows almost entirely through the fractures, this approach requires that a small effective porosity value (0.05 or less) be used for the transport calculations to compute a realistic pore velocity. The velocity of a COI, Vc, is affected by both the porosity, 0, and the retardation factor, R, as: V, _ V (la) OR where the retardation factor is computed internally in the MT3DMS code using a conventional approach: R=1+PbKd (lb) and V is the volumetric flux (Darcy velocity), pb is the bulk density and Kd is the soil - water distribution coefficient assuming linear equilibrium sorption. The retardation factor for COI in fractured rock is expected to be in the same range as R for porous media. However, it is apparent from (1b) that R can become large if 0 is reduced and Kd is held constant. This increase in R is unrealistic, and is the reason why a small Kd value is assigned to the bedrock, where the effective porosity is due to the fractures, and is low. This reduction of Kd is justified on physical grounds because COIs in fractured rock interact with only a small fraction of the total volume in a grid block, whereas COIs in porous media are assumed to interact with the entire volume. The Kd values Page 4-9 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina for COIs in the bedrock layers of the model were reduced by scaling them to the bedrock porosity. This causes the retardation factor in the fractured rock to be similar to R in the saprolite and transition zone. Ash leaching tests were performed on two samples from the EAB and three samples from the WAB using USEPA (LEAF) Method 1316. The leaching data were analyzed to develop Kd values for boron and sulfate in the coal ash. Kd of boron in ash in laboratory data ranges from 0.1 mL/g to 0.5 mL/g with a geometric mean value of 0.24 mL/g. Kd of sulfate in ash in laboratory data ranges from 0.1 mL/g to 0.2 mL/g with a geometric mean value of 0.11 mL/g. Linear sorption Kd values for boron were measured in the laboratory using samples from the coal ash and native aquifer materials obtained from the Site (Langley and Oza, 2015). In general, the measured Kd values are highly variable, and the variability within a given material type was larger than the variability between different materials. The values of Kd used in the model are based on initial estimates of Kd measured in the laboratory, which were then adjusted to improve the match with field data. A boron Kd value of 0.4 mL/g and a sulfate Kd of 0.2 mL/g are used for ash in the model. These values are within the range of the leaching test results. No leaching test was performed for TDS, and it was assumed that Kd in the ash for TDS is the same as that for sulfate (0.2 mL/g). The modeling approach for the predictive simulations of future boron transport allows the COI concentration in the ash to vary with time in response to flushing by groundwater. Using a Kd value derived from ash leaching tests ensures that the model response of the COIs in the ash to groundwater flushing is realistic. The Kd values for the COIs outside of the ash basin were treated as calibration parameters. Boron Kd value was determined to be 0.6 mL/g for saprolite and the transition zone and 0.02 mL/g for fractured rock and bedrock. For sulfate and TDS, Ka was assumed to be 0.2 mL/g for saprolite and the transition zone and 0.02 mL/g for fractured rock and bedrock. Additional heterogeneity in Kd was included during COI calibration, which will be described in Section 5.3. It was assumed the effective porosity was generally uniform within a grid layer and decreases with depth based on the hydrogeologic conceptual model. Page 4-10 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Layer Effective Porosity 1-8 0.3 9-11 0.2 12-13 0.2 14-16 0.05 17-20 0.01 21-25 0.001 Additional heterogeneity for porosity was included during COI calibration, which will be described in Section 5.3. The longitudinal dispersivity was assigned a value of 20 feet, and the transverse dispersivity and the vertical dispersivity were set to 2 feet. The dry bulk density of the porous media was assumed to be 1.6 g/mL. Dispersivity and bulk density were poorly constrained by the available field data, so the assumed values were fixed during the calibration process. 4.7 Transport Model Boundary Conditions The transport model boundary conditions are no flow on the exterior edges of the model except where constant head boundaries exist, where they are specified a fixed concentration of zero. As water containing dissolved constituents enters these zones, the dissolved mass is removed from the model. The infiltrating rainwater is assumed to lack COIs in most locations, and it enters from the upper active layer of the model. The initial condition for the transport model is zero concentration of COIs in groundwater in 1966. No background concentrations are considered. The concentrations in the EAB are assumed to be at the observed concentrations at the start of the simulation. The concentrations in the WAB are zero at the start of the simulation, and they increase to the observed concentrations in 1974 when the ash basin was created. 4.8 Transport Model Sources and Sinks The wastewater and ash in the ash basins are the main sources of COIs in the model. The sources are simulated by holding the constituent concentrations constant in cells located inside the ash basins. This allows infiltrating water to carry dissolved constituents from the ash into the groundwater system. With the MODFLOW/MT3DMS modeling approach, it is critical that the source zone is placed in cells that contain water (not "dry cells"). Some of the cells in the ash basin were dry, so the specified concentration condition was placed in all eight layers representing the ash. Page 4-11 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Chemical analyses from seven wells were used to characterize the distribution of boron, sulfate, and TDS concentrations within the ash basins. The concentration observed in the wells was assumed to represent the concentration in the vicinity of the well throughout the simulation. This resulted in a patch -like distribution of concentration within the ash basins. During the model revision, the concentrations of COIs in the ash was subdivided into additional patches. This was necessary to explain the variation of concentrations observed in the wells installed along the periphery of the basins. The existence of the boron source material outside the waste boundary is inferred based on calibrating the model to observed concentrations, and it is consistent with the known occurrence of the unlined portion of the industrial landfill and landfill base grade structural fill around the periphery of the EAB, in an area called the "Halo" area. Soil and rock affected by COIs in the ash basin can serve as a secondary source of the COIs at the Site. This potential is fully accounted for in the model by continuously tracking the COI concentrations in time in the saprolite, transition zone, and bedrock materials throughout the model. The historical transport model simulates the migration of COIs through the soil and bedrock from the ash basin, and these results are used as the starting concentrations for the predictive simulations. Therefore, even if all of the coal ash is excavated, the transport model predicts soil beneath the ash will have an ongoing effect on groundwater. Additional characterizations were performed in 2019, targeting the gypsum storage area and the DFA silos, transport, and handling area (GSA/DFAHA). This includes reviewing historical topography and engineering drawings to estimate the extent of structural fill composed of dry fly ash, installing additional monitoring wells near the silo area and DFA haul road, surveying of water elevations and COI concentrations in the "unnamed pond" north of EAB and all NPDES-regulated wastewater ponds adjacent to the Intake Canal, and making field measurements to assess the flow rates and COI concentrations in the eastern discharge canal. COI -containing materials in the GSA/DFAHA are included in the model as non-CAMA ash sources. The recharge rate at the lined gypsum storage area was assumed to be low (0.00001 ft/d) to account for a liner beneath the gypsum storage area. Even though the DFAHA are covered by concrete and asphalt pavement, the recharge rate was assumed to be the same as ambient recharge (0.0018 ft/d) to account for the water used in dust suppression that would infiltrate into the ground through cracks in the pavement. The transport model sinks are the constant head lakes and streams. As groundwater enters these features, it is removed along with any dissolved constituent mass. Page 4-12 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 4.9 Transport Model Calibration Targets The transport model calibration targets are boron, sulfate, and TDS concentrations measured in 152 monitoring wells through April 2019. Page 4-13 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 5.0 MODEL CALIBRATION TO APRIL 2019 CONDITIONS 5.1 Flow Model Calibration The flow model was calibrated in stages starting with a model that assumed homogeneous conditions in most hydrostratigraphic layers. In general, calibration was done by seeking the simplest configuration of parameters that matched the observed hydrogeologic conditions and the assumed or observed geologic conditions. The layer properties are nearly homogeneous in many locations through the model domain. Several heterogeneities were assumed to improve the fit between the simulated and observed heads and concentrations. The calibration was initiated using the geologic model to define the geometry of hydrogeologic units. Initial values of hydraulic conductivity for the hydrostratigraphic units were based on optimal values identified during the most recent revision of the model in 2018. Those values were then adjusted to reduce the residuals (difference between the predicted and observed hydraulic heads). Heterogeneities The original model had less precise head predictions at several wells. To further reduce the head residuals, zones of relatively low hydraulic conductivity were inferred near wells where the hydraulic head was underestimated. Including zones with lower hydraulic conductivity increased the simulated head, and the hydraulic conductivities of these zones were decreased until either the head was increased sufficiently or a lower limit of hydraulic conductivity was reached (Figures 5-la-w). Zones of low hydraulic conductivity is likely to occur where clay content is relatively high, or, in some cases, might be caused by human activity (such as the construction of a dam that may compress the soil and reduce the conductivity in the dam footprint). For wells where the hydraulic head was overestimated, zones of relatively high permeability that extend toward a nearby stream or lake were inferred. Including zones with this geometry near the wells reduced the simulated head, and the hydraulic conductivity of each zone was increased until either the head was reduced sufficiently to match the observation, or an upper limit of hydraulic conductivity was reached (Figures 5-la-w). Flat -lying zones of interconnected fractures several hundred feet or more across were described in crystalline rock at the USGS Mirror Lake research site (e.g. Tiedeman et al. 2001), and similar fracture zones have been recognized at other fractured rock sites, which could explain this type of heterogeneity. It was assumed that some fracture zones are roughly flat -lying and equally dimensional, and some are steep -dipping and elongated. Page 5-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Ten (10) deep bedrock wells installed in 2019 provided additional information on the hydraulic conductivity and fracture geometry in bedrock at the Site (SynTerra, 2019f). Depths of these wells range from 163 feet to 415 feet in the WAB and from 156 feet to 403 feet in the EAB. Geophysical methods were used to locate and characterize fractures capable of contributing to the groundwater flow field. Conductive fracture zones down at depth in the deep bedrock zones were observed, which justify the occurrence of fractured zones in the bedrock. Moderate downward head gradient was observed at the MW-205 well cluster in the WAB, whereas up to 33 feet of downward head gradients were observed in the CW-1 well cluster and CCR-108BR well cluster, indicating potential downward groundwater flow from shallow zone to deep bedrock. The heads in the lower wells in these clusters appear to reasonably match the water level elevation in the adjacent eastern discharge canal or western discharge canal, suggesting that zones of connected fractures may occur between the deep wells and the surface water. Heterogeneities to represent these deep fracture zones are included in model layers 19-24 (Figures 5-1q-w). Ash Basin Dams The model grid was refined to improve the representation of the ash basin dams. This includes identifying a low -permeability zone that represents a cutoff on the upstream faces of each dam, and a high -permeability zone that represents an internal drain (Figure 5-2). These features and the dimensions of the dams are consistent with available drawings. The locations and hydraulic conductivities of the zones composing the dams were adjusted locally during calibration to match the hydraulic heads in the vicinity of the dams. Flow Balance and Residuals The final calibrated flow model has the following flow balance for the entire flow model: Volume Balance in Steady State Model in ft3/d Feature Input Output General Head 85,940 -238,267 Recharge 444,252 0 Wells 0 -3,094 Septic field 1,971 0 Drains (streams) 0 -290,802 Total 532,163 -532,163 Notes: 1. Cubic feet per day = ft3/d Page 5-2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina The difference between the input and output is less than 0.01 W/d, which is an error of less than 10-5. This is consistent with the constraint that inflow is equal to outflow at steady state. The major input to the model is from recharge with a lesser amount from general head boundaries. The general head boundaries creating input to the model are where groundwater is flowing into the model from the general head boundaries. The output is divided between groundwater discharging to general head boundaries and drains. A major general head boundary is Hyco Reservoir, and the drains represent streams. Less than 1 percent of the water input is removed by domestic wells. The volume of water supplied by septic fields is slightly less than the water removed by the domestic wells. The revised calibrated flow model has a mean head residual of -0.11 feet and a root mean squared head residual of 2.80 feet. The total span of historical average head ranges over 121 feet, from 410 feet to 531 feet. Using this range to normalize the residual gives a normalized root mean square error of 0.023 (2.3 percent). A comparison of the observed and simulated water levels is listed in Table 5-1, and the observed and simulated levels are cross -plotted in Figure 5-3. Table 5-2 lists the best -fit average hydraulic parameters from the calibration effort. 171 residuals between predicted and observed heads are less than 6 feet and two residuals are between 6 feet and 12 feet (Figure 5-4). The water table is near the ground surface in the ash basins and in the transition zone and upper fractured rock in much of the uplands. Hydraulic Conductivity The hydraulic conductivity of the ash used in the model is 6 ft/d for both ash basins (Table 5-2), which is based on the hydraulic conductivity values from slug tests and pumping tests (Figure 4-4) and adjusted within the estimated range to match the field observed water elevation data. The highest calibrated hydraulic conductivity occurs in the ash and it progressively decreases with depth. The calibrated hydraulic conductivity of the saprolite and transition zones is 1 ft/d. The hydraulic conductivity of the upper fracture rock is 0.3 ft/d, and it decreases to 0.01 ft/d, 0.005 ft/d, and 0.003 ft/d with depth in the lower fractured and competent bedrock zones. The calibrated values of hydraulic conductivity are consistent with values from the slug tests conducted at the Site (SynTerra, 2017). The deep bedrock wells installed in 2019 provide information on hydraulic conductivity, ranging from 0.03 ft/d to 13.2 ft/d with a geometric mean value of 1.75 ft/d (SynTerra, 2019f). These relatively high conductivity values might not represent the prevalent hydraulic conductivity in deep bedrock, because most of these wells were screened at the depths where major fractures were encountered and the slug tests would be biased. The hydraulic conductivity values used Page 5-3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina in the model for lower fractured rock and competent bedrock are much lower than the slug test results, at equal to or less than 0.01 ft/d based on calibration. Hydraulic Head Distribution The computed heads in the upper fracture rock (layer 15) show a high hydraulic head at the south end of both ash basins and a regional low hydraulic head at Hyco Reservoir (Figure 5-4). Ridges of high hydraulic head separate the two lobes of the EAB and western lobe of the EAB from the WAB. Potential Receptor Wells and the Ambient Groundwater Flow System The effect of pumping wells on the distribution of hydraulic head is manifested by a curved hydraulic head contour in the vicinity of the Woodland Elementary School wells on Semora Road along the west side of the simulated area, and a curved hydraulic head contour in the vicinity of the well at the building materials manufacturing plant on the north side of the simulated area (Figure 5-4). This affect is minimal at both the school wells and building materials manufacturing plant well and extends out less than a few hundred feet. These wells are assumed to be pumping at rates higher than the domestic supply wells. Approximately 54 of the domestic water supply wells are located along Dunnaway Road, McGhees Mill Road, and Semora Road, all of which lie along or near groundwater divides. Eight water supply wells are located on Concord Church Road, which trends roughly east -west and is upgradient from the WAB. The water supply wells are located along groundwater divides (topographical ridges) and upgradient of the groundwater flow systems containing the ash basins. Groundwater flows past the water supply wells toward the ash basins, according to the model results. Water flowing past the Concord Church Road wells discharges to Sargents Creek, which flows to the WAB (Figure 5-4). Groundwater flowing past the Dunnaway Road wells discharges to a stream upgradient from the western lobe of the EAB and groundwater flowing past the McGhees Mill Road wells discharges to the extension impoundment on the east side of the EAB (Figure 5-4). Wells along Semora Road, including the school wells, are on the groundwater divide or outside of the flow system containing the ash basins. Water Balance The EAB and WAB are each located within a single watershed. They are separated by a groundwater divide and topographical ridge represented by Dunnaway Road. The water budget analysis identified an approximate local groundwater flow system for each ash basin. This definition implies that groundwater outside the system cannot Page 54 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina enter the local ash basin flow system, but groundwater can leave the system by flowing through or beneath the dam impounding the basin. The local flow system for the WAB is assumed to be bounded by a groundwater divide that extends from one end of the main dam and wraps around the watershed, crosses the filter dam, and then wraps around at the other end of the dam (Figure 5-5). Zones were defined within GMS and the Zone Budget tool in MODFLOW was used to determine components of the water balance. The results were edited slightly to be consistent with the definition of the flow system (Table 5-3). Groundwater flows predominantly into the WAB on the east side of the basin. Groundwater flows out though the main dam to the north, through the dikes along the west sides of the ash basin into the western discharge canal, and through the filter dike on the south side of the WAB (Figure 5-5). The watershed area contributing flow toward the basin is estimated at approximately 352 acres, resulting in about 103 gallons per minute (gpm) of groundwater flow from recharge. Under pre -decanting conditions, water discharge from the groundwater system to ponded water within the ash basin is approximately 35 gpm. Water discharge from the groundwater system by streams outside the ash basin is approximately 18 gpm. Groundwater that discharges through and under the main dam is estimated to be 14 gpm. Groundwater that flows through and under the filter dam is estimated to be 8 gpm. The flow pattern associated with the EAB is variable, but in general groundwater flows into the EAB from the south and northeast and it leaves by flowing out to the northwest to NPDES-permitted wastewater ponds or southeast to EAB extension impoundment area. The watershed area contributing flow toward the basin is estimated at approximately 313 acres, resulting in about 88 gpm of groundwater flow from recharge. Water discharge from the groundwater system by wetlands and shallow saturated conditions upgradient of the main dam is approximately 26 gpm. Water discharge from the groundwater system by streams and seeps inside the ash basin is approximately 10 gpm. Water discharge from the groundwater system by streams outside the ash basin is approximately 32 gpm. Groundwater that flows through and under the main dam is estimated to be 20 gpm. Groundwater that flows through and under the separator dike is estimated to be 5 gpm. 5.2 Flow Model Sensitivity Analysis A parameter sensitivity analysis was performed on the calibrated model by systematically increasing and decreasing the hydraulic conductivity and regional recharge by factors of either 2 or 0.5 from their calibrated values. Table 5-4 summarizes the results of the analysis, expressed in terms of the normalized root mean square error Page 5-5 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina (NRMSE) for each simulation. The NRMSE is calculated by taking the square root of the mean of the squared residuals between the predicted and observed values and dividing by the maximum difference in observed hydraulic head. The NRMSE for the calibrated flow model is 0.0231. The flow model showed the highest degree of sensitivity to the regional recharge and to the hydraulic conductivities of the transition zone and the upper fractured rock stratigraphic units. The saprolite was largely unsaturated, therefore most of the groundwater flow is through the transition zone and upper fractured rock. The NRMSE was only weakly sensitive to the hydraulic conductivities of the ash and the deeper rock. 5.3 Historical Transport Model Calibration The transient flow model used for transport consisted of a sequence of five steady-state flow fields: • The period when the EAB was in operation (1966-1973) • The period when both the EAB and WAB were present and receiving recharge (1974-2004) • The period (2004-2008) when the recharge in the gypsum storage area was reduced after the geosynthetic clay liner (GCL) was placed over the underlying dry fly ash structural fill • The period (2008-2014) when the recharge was reduced in areas of the industrial landfill and lined FGD pond areas • The period (2014-present) when recharge was reduced south of the eastern lobe of the EAB due to the additional phases of the industrial landfill It is important to point out that the period when the ash basins were open water early in operational history is represented in the model by pre -decanting conditions, where only small parts of the basin is open water and the remainder is ash. This is justified since the hydraulic heads in the ash basins are very uniform (vary by less than 3 feet). This is less than the uncertainty in the stage of the ash basins when open water was present. As a result, the interactions between the groundwater system and the ash basins filled with water would be similar to the interactions when the basins contained ash. The effective porosity was assumed to decrease with depth to be consistent with the Site conceptual model. Porosity was modified at four locations where fractures were observed in bedrock, including areas near the CCR-108 well cluster, the CCR-205 well Page 5-6 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina cluster, the CCR-208 well cluster, and a few zones next to the DFA silos, transport, and handling area. An effective porosity of 0.0001 to 0.001 was used to represent fractures in rock in these locations. The COI Ka values were assumed to decrease with depth to maintain a retardation factor that is consistent with values at shallow depths, as described in Section 4.6. Additional heterogeneity in Ka was included to achieve better COI calibration. Zones with localized Ka adjustment include the vicinities of the CCR-108 well cluster, the CCR-205 well cluster, the CCR-207 well cluster, the CCR-208 well cluster, the MW-1 well cluster, the vicinity of the WAB dam, and a few locations in the vicinity of the DFA silos, transport, and handling area. Boron, sulfate, and TDS concentrations in wells in the ash basin were used to set boundary conditions in the model, as shown in Figures 5-6a-b and Tables 5-5a-b. Evaluation of the flow system during the calibration process indicated that several of the observed occurrences of boron, sulfate, and TDS could not be explained using sources solely from the ash basins. It was inferred that CCR materials present in the sluice line corridor, an area to the north of WAB, the unlined portions of the industrial landfill, the structural fill underlying gypsum storage area, and the DFA silos, transport, and handling area must be acting as additional sources. The locations of these additional sources were added during calibration (Figures 5-6a-b and Tables 5-5a-b). The transport simulation was compared with chemical analysis for boron, sulfate, and TDS on samples from 152 wells. The simulated concentrations reasonably match most of the observed concentrations (Table 5-6). Many of the observation wells where boron, sulfate, and TDS were detected are in areas where the predicted concentration gradients are steep (beneath or adjacent to the ash basin, for example), therefore, small changes in location similar to the dimension of a grid block result in significant changes in concentration. This is one factor that explains the differences between predicted and observed concentrations. Boron concentrations greater than the 02L standard (700 µg/L) occur below and adjacent to the ash basins, according to the simulations (Figure 5-7). Six reference locations showing the boron concentration greater than 02L are: a) northwest of the EAB next to the DFA silos, transport, and handling area b) north of the EAB adjacent to the "unnamed pond" c) northeast of the EAB near the CW-1/MW-1BR well cluster Page 5-7 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina d) northeast to east of the EAB, next to the CCR-108/MW-108 well cluster and the eastern discharge canal e) northwest of the WAB near the CCR-205/MW-205 well cluster f) west of the WAB near the CCR-208/MW-208 well cluster Simulations predict boron concentrations greater than 02L occur beyond the compliance boundary north of EAB at locations a, b, and c (Figure 5-7). One of the plumes migrates from the ash basin to the northwest side of EAB (location a), and merged with a plume associated with additional sources at the DFA silos, transport, and handling area. This area is hence referred to as the "commingling zone." The additional sources are located outside of EAB to the west of the gypsum storage area (Figure 5-6c) and are referred to as the "non-CAMA sources" to be distinguished from the source materials within the ash basins. Boron from the ash basin also migrates in water beneath the dam and discharges to Plant NPDES-permitted wastewater ponds at the base of the dam, although concentrations greater than 02L are mostly contained within the compliance boundary. The plume associated with the additional sources at the DFAHA and the GSA migrates to the north toward the Intake Canal. Plumes of boron concentrations greater than 02L occur at location b, adjacent to a standing water feature commonly referred to as the "unnamed pond." Simulations suggest that the plume to the southeast is related to ash material sources in the EAB, and the one to the northwest is related to additional sources to the north of EAB (Figure 5-6c), although recent data are inconclusive on the exact extent of each plume. The additional sources in this case are non-CAMA sources associated with the DFA structural fill beneath the gypsum storage area. The distribution of DFA structural fill is inferred based on historical topographic maps, construction records, and calibration analyses using observed concentrations in monitoring wells. Simulations of these sources predict two plumes underneath the west and northeast sides of the gypsum storage area, which migrate to the north toward the Intake Canal (Figure 5-7). The groundwater flow direction is to the south along the northeast edge of the EAB (Figure 5-5). This occurs because recharge outside of the lined portion of the industrial landfill creates an east -west trending ridge in the hydraulic head distribution along the northern edge of the landfill. Boron apparently occurs in unlined DFA structural fill material placed around the periphery of the industrial landfill, as referred to as the "Halo" area, during historical operations, and some of this material occurs to the north of the divide created by the groundwater ridge. Northward groundwater flow on the north side of the groundwater ridge creates the plumes that extend across the Page 5-8 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina compliance boundary at location c (Figure 5-7). The compliance boundary at this location curves inward and forms a "v" shape. As a result, boron beyond the compliance boundary is predicted to re-enter the compliance boundary on the downgradient side after migrating for approximately 100 feet. Boron concentrations greater than 02L at location d (Figure 5-7) also appear to be associated with the "Halo" area. The plume migrates downward following the flow direction and occurs in deep bedrock, up to 400 feet below ground surface, as evidenced by data from deep bedrock wells (CCR-108/MW-108 well cluster). The groundwater is predicted to discharge into the eastern discharge canal which is within the compliance boundary. The eastern discharge canal acts as a sink (groundwater to surface water discharge zone) for the boron plume in the simulation; hence, concentrations greater than 02L would not migrate to the compliance boundary on the east side of the eastern discharge canal. The only location where boron concentrations greater than 02L occur beyond the WAB compliance boundary occurs at the sluice line corridor (Figure 5-7). COI -affected groundwater has been observed at a transition/bedrock flow zone monitoring well cluster (CW-5, MW-5D, MW-5BR), located within the sluice line corridor. The model predicts boron concentrations greater than 02L in this area based on data collected for MW-5D in November 2018, which were the most updated data at the time of calibration. All CCRs have been handled dry at Roxboro since December 2018, when sluicing to the WAB ceased and segments of piping were decommissioned. Additional data has become available after the model refinement and indicates that COIs have decreased to less than 02L with the exception of sulfate and TDS at MW-5D (SynTerra, 2019d). Concentrations of sulfate and TDS are decreasing, based on groundwater analytical results (SynTerra, 2019d), and they are predicted to decrease to less than the respective 02L standard in a couple of decades. Because the sluice line corridor is considered a separate source from the WAB and is anticipated to be remediated separately after decommission of the sluice lines, this area is not subject to the remedial evaluation in this report. Inside the WAB, a zone of boron concentration greater than 02L occurs along the western and northern sides of the basin according to the simulation (locations e and f, Figure 5-7). This plume does not extend to beyond the compliance boundary according to the simulations, because the groundwater flows out of the ash basin and discharges to the heated water discharge pond and the western discharge canal (part of the Plant's NPDES treatment system), which is approximate to the waste boundary and results in a Page 5-9 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina large decrease in boron concentrations. Groundwater also discharges to the western discharge canal, with lesser flows beneath the primary dam. There is no evidence in the simulations that boron is transported to any of the water supply wells at concentrations greater than 02L. This includes the school wells and the building materials manufacturing plant. The school wells are more than a half -mile from the WAB, and there is a groundwater divide between the wells and the ash basin. Boron along the western side of the WAB discharges after a short flowpath to the western discharge canal. The groundwater flow direction and significant distance to the WAB both indicate that boron transport is not affected by the school wells. Boron concentrations in proximity to the building materials manufacturing plant well to the north of the GSA are predicted to be less than 02L. The model predicts the occurrence of boron that originates in the non-CAMA sources and discharges to the Intake Canal (Figure 5-7). The building materials manufacturing plant well is approximately 800 feet from the edge of the boron 02L plume which discharges to the Intake Canal. The pumping rate of the building materials manufacturing plant well and the permeability distribution in the vicinity of the well are poorly constrained, which causes uncertainty in the simulations of boron transport in the vicinity of the well. As a result, while the simulation results indicate that the building material plant well is unaffected by boron transport, the uncertainty in this result is greater than at the other wells. The revised model includes the assumption that boron occurs in sediments in the EAB and WAB areas identified as extension impoundments upstream of the main portions of the EAB and WAB. The simulations show that groundwater flows toward and discharges into the extension impoundment areas. Pumping of domestic water supply wells is insufficient to alter this flow direction. As a result, boron concentrations greater than 02L are assumed to occur within the EAB and WAB extension impoundment area and have no effect on the quality of water pumped from domestic water supply wells in the general vicinity. The extents of sulfate and TDS plumes with concentrations greater than 02L are similar or less than the boron plume greater than 02L at most of the reference locations (Figure 5-8 and Figure 5-9). For example, at location c, sulfate concentrations greater than the 02L (250 mg/L) extended beyond the compliance boundary for several tens of feet, whereas TDS concentrations greater than the 02L (500 mg/L) stay within the compliance boundary. Sulfate and TDS plumes appear to be slightly larger than the boron plume beneath or downgradient of the gypsum storage area and the DFA silos, transport, and Page 5-10 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina handling area (Figure 5-8 and Figure 5-9). This is likely related to the greater sulfate and TDS levels associated with the non-CAMA sources. 5.4 Transport Model Sensitivity Analysis A parameter sensitivity analysis was conducted to evaluate the boron transport model sensitivity to Kd, which is considered a key parameter affecting transport. Kd is assumed to be uniform across each grid layer and to vary with depth, with additional heterogeneities to match observed data, as described in Section 4.6. The sensitivity analysis was performed on the calibrated transport model by systematically increasing and decreasing the initial boron Kd values for each layer by a factor of 5 from their calibrated values (Table 5-7). The model was then run for the revised Kd values, and the NRMSE was calculated and compared to the NRMSE for the calibrated model. The calibrated transport model simulates concentrations that reasonably match most of the observed concentrations (Table 5-7) with an overall NRMSE of 3.55 percent. Reducing Kd by multiplying by a factor of one -fifth increases NRMSE to 3.83 percent, whereas increasing Kd by five times increases NRMSE to 4.38 percent (Table 5-7). This indicates that the value of Kd used in the model is near an optimal value. It also suggests that the average difference between simulated and observed concentrations is only moderately affected by changes in Kd. Page 5-11 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 6.0 PREDICTIVE SIMULATIONS OF CLOSURE SCENARIOS Following calibration to April 2019 conditions, the model was used to predict future constituent distribution. This process involved a sequence of two simulations: 1. Interim conditions 2. Closure action The simulation of interim conditions involves accounting for transport from the present to the time when the closure action is complete. This will occur over the next several years and involves lowering the water level without disturbing sediment, or decanting the ash basin ponded water especially in the WAB. The second step involves simulating transport processes after closure for several centuries or longer. There are two simulated closure scenarios: one is the closure -by -excavation scenario in which all of the ash in the WAB and part of the ash in the EAB is excavated and placed in an expanded part of the existing EAB industrial landfill, the other is the closure -in - place scenario in which both the WAB and EAB are capped with a low -permeability cover system. Predictive simulations have also been performed for groundwater remediation scenarios that consider each closure design with corrective action that achieves 02L compliance after approximately 9 years of operation. The remediation design uses a combination of clean water infiltration and groundwater extraction to remediate the plume for the COIs modeled. A remediation design scenario that included only groundwater extraction wells related to the GSA/DFAHA area is not considered in this report since preliminary modeling demonstrated much longer time frames to achieve 02L compliance (180 years). The distribution of recharge, locations of drains, and distributions of material were modified to represent the different closure actions. For example, the recharge was modified from recharge flux shown in Figure 4-8. The hydraulic head distribution was recalculated, and the transport was simulated for each case. The closure design changed the hydraulic head inside and outside of the ash basins as the engineered designs interacted with the hydrogeologic conditions. This interaction altered the groundwater flow and the transport of dissolved constituents. Ka values were unchanged. The most significant change compared to the simulations of April 2019 conditions is that the concentrations in the ash basin were allowed to vary with time. Page 6-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 6.1 Interim Period with Ash Basin Ponded Water Decanted (Approximate Year 2020-2024 or 2020-2037) Interim periods from present day to the completion of closure construction were simulated to determine the initial conditions for the closure simulations. Passive decanting of the WAB ponded water began mid -December 2018, initiated by the cessation of sluicing. Completion of decanting is expected by July 2020, contingent on approval of the revised NPDES permit. Simulations began by extending the simulation of April 2019 conditions to July 2020. The COI distributions simulated in July 2020 were then used as initial conditions for the interim scenario. The simulations assume that the ponded water in the south region of the WAB is reduced to a head level of 445 feet along the upgradient side of the filter dike. This head level is the same as the level of the extension impoundment on the south side of the filter dike. It is assumed that the open water features in the WAB and saturated areas of the EAB are allowed to drain. Long-standing open water features in the WAB that were maintained by sluicing were represented as general head features in the model for pre -decanting conditions. These features were switched to drains in the interim period model (Figure 6-1). The ambient recharge rate of 0.0018 ft/d was assumed to occur over the basins, and the concentration of COIs in the recharge was assumed to be zero. Water balance analysis for the WAB shows that total recharge to the watershed is approximately 129 gpm. Approximately 82 gpm of groundwater discharges to the drainage features inside the West Ash Basin, and 17 gpm discharge to drains outside of the ash basin. Approximately 13 gpm of groundwater discharges through and under the main dam, and 2 gpm discharges through and under the filter dam (Figure 6-2 and Table 6-1). Water balance analysis for the EAB shows that total recharge to the watershed is approximately 86 gpm. Approximately 38 gpm of groundwater discharges to the drainage features inside the East Ash Basin, and 32 gpm discharge to drains outside of the ash basin. Approximately 18 gpm of groundwater discharges through and under the main dam, and 8 gpm discharges through and under the separator dike. Results from the Interim Scenario Simulation Hydraulic head distributions during the interim period in the upper fractured bedrock (Figure 6-1) are similar to head distributions prior to decanting the ash basins (Figure 5-4). During the interim period, hydraulic heads within the WAB were reduced and the hydraulic gradients between the primary ash basin and the southern extension of the WAB decreased (Figure 6-1 and Figure 5-4). During the interim period, both the EAB Page 6-2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina and WAB are hydraulically down -gradient from all domestic and public water supply wells in the region (Figure 6-2). The final site closure activities will start after decanting the WAB ponded water and will continue for several years. It is expected that the closure -by -excavation construction can be completed in 17 years (approximately year 2037) for both basins, and the closure -in -place construction can be completed in 4.4 years (approximately year 2024) in the EAB and 6.6 years (approximately 2027) in the WAB. The results of the simulations show that the distribution of boron at concentrations greater than 02L varies slightly when the different closure scenario construction is completed; however, there is negligible change in status of boron concentration distribution at the compliance boundary (Figures 6-3a-c). The boron concentrations at the six reference locations (Figure 5-7) are largely unchanged during the interim period. The predictive simulations of sulfate and TDS during the decanting period also show similar distribution and negligible changes between the closure scenarios. 6.2 Closure -by -Excavation Scenario The closure -by -excavation design for both basins is based on engineering drawings provided by Wood Environment & Infrastructure Solutions, Inc. (Wood) as shown in Figure 6-4 (Wood, 2019c and 2019d) including personal communication with the Wood design team. The scenario involves removal of all the ash in the WAB and ash from the northwest portion of the EAB and placing the excavated material in a proposed lined landfill expansion of the existing industrial landfill in the EAB. The WAB main dam and the filter dike are breached to so the heated water discharge pond extends into the excavated area. The FGD ponds are decommissioned and removed. The sediment and residual ash material in the WAB extension impoundment is dredged. After the filter dike is breached, the extension impoundment becomes part of the heated water discharge pond. Ash in the area upgradient of the EAB dam is excavated and soil is regraded to form the north stormwater basin. The base water level is expected to be approximately 457 feet, controlled by a 10-foot diameter culvert under Dunnaway Road having an inlet invert elevation of approximately 457 feet. The existing industrial landfill (both lined and unlined portions) is capped by a low -permeability cover system. The proposed landfill expansion would be constructed with a base liner system and a lower permeability cap. The sediment and residual ash material in the EAB extension impoundment will be dredged and placed in the landfill expansion. Page 6-3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Model Setup The ash layers in the WAB and the breached section of the dams are given high hydraulic conductivities and zero COI concentrations, so they act neither as a source of COIs, nor as a component of the hydrogeologic flow system. It is assumed that the ground surface in the WAB is restored to the original topographic surface prior to construction of the ash basin. This implies that streams may form in the newly exposed drainages, and regions where the topographic surface is below the level of the heated water discharge pond will be inundated. These conditions were simulated by including drain boundary conditions along the newly formed topographic drainages, and by including regions of fixed hydraulic head in areas where the elevation of the original topographic surface is below 410 feet (Figure 6-5). Water from the "drains" might have to be collected, treated and discharged per NPDES permit requirements. For the EAB, the proposed north stormwater basin is represented by a general head boundary set to the base water elevation of 457 feet. Drains are put in to represent the swales formed on the regraded topographic surface that drains water into the north stormwater basin. An underdrain system is simulated beneath the proposed landfill expansion in the EAB. This is necessary to maintain water levels below the base of the landfill. The drain elevation is set to 10 feet beneath the proposed landfill expansion subgrade. Recharge on the excavated area is assumed to be 0.0018 ft/d, the same as the ambient recharge rate on natural surfaces in the watershed. The recharge flux over the existing industrial landfill and the landfill expansion is 10-7 ft/d based on estimates of cover performance conducted by Wood (2019d). The simulations use results from the interim scenario at year 2037 for initial conditions. The simulation was started in 2037, and the model was run for 1,000 years. Results were saved every few years early in the simulation, and the interval between the saved results increased with time. This causes the temporal resolution to be finer at an earlier time than later in the simulation when changes are expected to small. Spatial Distribution of Hydraulic Head The hydraulic head changes markedly when the closure -by -excavation scenario is implemented compared to hydraulic head during the initial or interim periods. The head change is particularly significant in the WAB where the base level of the heads is lowered by decanting and removal of ash. The hydraulic head contours in WAB wrap around the newly formed impoundment and drainage system (Figure 6-6). Page 64 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Hydraulic heads in the EAB change at places where the proposed north stormwater basin is installed and where the landfill expansion occurs. The head in the western lobe of the EAB increased at several places compared to the initial period, primarily at the proposed landfill expansion where ash is excavated and topographic surface is regraded (Figure 6-6). Lowering the hydraulic head for the basins causes the inferred direction of groundwater flow to change. This is particularly significant along the western side of the WAB where groundwater flow is predicted to be westward toward the western discharge canal during pre -decanting conditions. Groundwater reverses direction and flows eastward to the former perennial stream as a result of the change in the drainage pattern during the closure -by -excavation scenario. The water table is below most of the western discharge canal, so the canal is expected to be dry except at the northwestern corner of the WAB near the heated water discharge pond. Spatial Distribution of COIs After Site Closure The simulated boron concentrations for all non -ash layers approximately 20, 70, 120, and 170 years after closure are shown in Figures 6-7a-d. The extent of boron plume with concentrations greater than 02L recedes with time at most locations, except for the areas impacted by non-CAMA ash sources. This causes the boron plume greater than 02L in the commingling zone between the DFA silos, transport, and handling area and EAB (location a) and the zone next to the north unnamed pond (location b) to persist (Figures 6-7b-d). Boron concentrations greater than the 02L standard also occur beyond the compliance boundary near location c in after approximately 170 years after closure. However, the maximum extent is only approximately 100 feet from the compliance boundary, and because the compliance boundary curves inward to form a "v" shape, the boron concentration greater than the 02L is expected to extend slightly across the compliance boundary before flowing back into the compliance boundary area associated with the eastern discharge canal (Figure 6-7d). The migration of sulfate and TDS follows the same extent as boron. The extent of sulfate and TDS plumes with concentration greater than 02L recedes with time, except for locations a and b, which are associated non-CAMA sources that remain after basin closure (not shown). Time Series for Closure -by -Excavation Scenario Six reference locations were identified to summarize transient concentrations in the vicinity of each ash basin compliance boundary (Figure 6-8). Four locations in the EAB are either where boron concentrations are greater than the 02L standard beyond the compliance boundary in the April 2019 simulation (locations a, b, c) or where boron Page 6-5 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina reaches the eastern discharge canal (location d). Location a is in the commingling zone between ash basin and DFAHA. Locations c and d are near two well clusters that include newly installed deep bedrock wells. Boron concentrations in groundwater greater than 02L associated with the WAB remain within the compliance boundary, except in the separate sluice line corridor source area, which is omitted from the CAP evaluation (see Section 5.3). Reference locations e and f are located along the western discharge canal and are near the newly installed deep bedrock wells in the WAB. Location e is along the northwest corner, whereas location f is along the western side of the WAB. The concentration time series start at the beginning of the simulations in 1966 and end in approximately year 2500. The time series were plotted for the maximum concentration in all layers and for individual model stratigraphic layers, as indicated in the legend of Figures 6-9a-b. The plots for individual layers provide additional information on vertical boron distribution. Boron concentrations greater than the 02L standard are noted during operation of the ash basins at all locations. The general shapes of the time series are similar except for location a. For the other five locations, the boron concentrations start at zero, increase with time to a maximum value between approximately year 2020 and 2100, and then decrease and return to near -zero concentrations (Figure 6-9b). The maximum boron concentration at reference location a persists after approximately year 2100 at concentrations greater than 800 µg/L. This is largely a result of the non-CAMA ash associated with the DFAHA that continues to act as boron sources. Reference location f shows the greatest boron concentration in the WAB , where the concentrations in saprolite, transition zone, and fractured bedrock are greater than 35,000 µg/L in approximately year 2020 (Figure 6-9a). Reference location d shows the greatest concentration in the EAB, where maximum concentrations are greater than 5,000 µg/L in approximately year 2070 (Figure 6-9c). Boron concentrations greater than 02L primarily occur in saprolite, transition zone, and fractured rock for locations a and b, but the effects occur at much deeper depths at the other four locations, as illustrated by increased concentrations in the bedrock layers (Figures 6-9a-c). 6.3 Closure -by -Excavation Scenario with Corrective Action A groundwater corrective action plan to achieve boron, sulfate, and TDS compliance with the respective 02L standards in approximately 9 years after system Page 6-6 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina implementation has been simulated in combination with the closure -by -excavation scenario (Figure 6-10). The simulated design assumes the remedial system outside of the ash basin will be completed in July 2020, and therefore the simulation uses predicted COI distributions from July 2020 as initial conditions. The simulated flow field for July 2020 condition is used for the transport simulation until the completion of the closure -by -excavation scenario, which is assumed to occur in 2037. After that, the remediation system is included in the closure -by -excavation model and another flow field is created and used to run the remaining transport simulation. The corrective action occurs primarily north and northeast of the EAB, and between the non-CAMA sources and the Intake Canal (Figure 6-10). The groundwater remediation systems target areas where COI concentrations are greater than the 02L, including the commingling zone next to DFAHA (location a), the zone next to the north unnamed pond (location b), and the zone to the northeast of the EAB near the deep bedrock wells (locations c and d). COI concentrations greater than 02L next to the Intake Canal are associated with the non-CAMA sources. These sources are not included in ash basin closure, so the sources are assumed to remain unchanged in the model. The remedial approach is to create a hydraulic barrier to prevent COIs from migrating from the vicinity of the GSA and the DFAHA to the downgradient Intake Canal. This is accomplished using a line of extraction and clean water infiltration wells parallel to the Intake Canal (Figure 6-10). Recent monitoring data supported by transport modelling demonstrate no COI concentrations greater than the 02L standard migrating beyond the compliance boundary in the WAB, with the exception of the sluice line corridor area as previously discussed in Section 5.3. The groundwater remediation system proposed consists of 50 groundwater extraction wells pumping at a total extraction rate of 71 gpm and 27 clean water infiltration wells with a total flow rate of 76 gpm (Table 6-2). The extraction wells are simulated using vertical arrays of drain points in MODFLOW. The drain bottom elevations are set to the center of the grid block containing the drain. This simulates a condition where the water is being pumped out of the well casing to maintain a water level near the bottom of the well. The drain conductance values are estimated by considering radial flow to a well, following Anderson and Woessner (1992). For a horizontal hydraulic conductivity of K, a well radius of rW, and horizontal and vertical grid spacing of Ax and Az, the drain conductance for a grid block is computed as: Page 6-7 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina C = k 2zKAz In 0.208Ax r w where & is the well efficiency, which accounts for well skin effects. A well efficiency of & = 0.5 was used for pumping wells. Infiltration wells are treated similarly, using the general head boundary condition in MODFLOW, with a conductance calculated the same way, but with & = 0.25 to account for clogging of the screen and filter pack during infiltration. Hydraulic heads in the infiltration wells were set to 20 feet above the ground surface, which could be maintained without risk of formation damage. The simulations indicate that clusters of extraction wells create cones of depression marked by closed head contours, whereas the line of extraction and infiltration wells creates a variable head pattern as shown in Figure 6-10. The analysis was conducted using two parallel scenarios, one where non-CAMA sources are absent and another where they are left in place (Figures 6-11 through 6-14). Omitting non-CAMA sources from the simulation shows the COI concentrations greater than the 02L standard caused by sources associated with the ash basin. The other scenario shows COI concentrations resulting from all known sources at the Site. Results from the simulations show that the 32 extraction wells to the north and northeast of EAB can achieve boron 02L compliance at most locations along the EAB compliance boundary after 9 years of operation (Figures 6-12a-e). An exception occurs in an area beneath the Unit 3 cooling tower pond, where a small patch of boron concentration greater than the 02L extends less than 100 feet beyond the compliance boundary on the western side of the upper panel of Figure 6-12a. Groundwater beneath the Unit 3 cooling tower pond discharges to an NPDES-regulated wastewater basin. Plumes of boron concentrations greater than 02L are predicted to reach the Intake Canal at three locations under April 2019 conditions when the non-CAMA source are included (Figure 6-11). One of these plumes is downgradient from the commingled zone, another is downgradient from the north unnamed pond, and another extends northward from the eastern end of the GSA. The plumes resulting from the non-CAMA sources are apparent by comparing the upper plots in Figures 6-11 and 6-12a-e, where non-CAMA sources are omitted, to the lower plots where all the sources are included. The three plumes are truncated at the line of extraction and infiltration wells parallel to the Intake Canal after 9 years of active groundwater remediation. Two small vestiges of Page 6-8 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina the plumes are predicted to occur under the Intake Canal after 9 years of remediation, but they are removed soon thereafter (Figures 6-12a-b). And boron concentrations remain in compliance under the Intake Canal since then (Figures 6-12c-e). The simulations demonstrate that a hydraulic barrier created by the 18 extraction wells and 27 clean water infiltration wells could effectively mitigate boron concentration greater than standards to the Intake Canal. The concentrations in the area under the GSA are predicted to expand over time until they reach equilibrium because the model assumes continuous non-CAMA sources. The remediation system is capturing the concentrations downgradient but no other source control measures are assumed. Results from the simulations indicate that sulfate and TDS concentrations in groundwater would also be in compliance with 02L standards for the EAB after 9 years of remediation system operation (Figures 6-13 and 6-14). 6.4 Closure -in -Place Scenario Simulations for the closure -in -place scenario use results from the interim scenario at year 2024 for initial conditions. The boundary conditions, recharge, and geometry were adjusted to represent the closure -in -place scenario. The design of the model is based on the closure -in -place scenarios outlined in Figure 6-15 (Wood, 2019a and 2019b). The design for the closure -in -place scenario includes removing the FGD ponds in the WAB and regrading ash based on the final cover grade plan. The surface of the ash basin will be graded to include swales for stormwater, and drains will be included beneath the swales to intercept ash basin pore water. Proposed concrete flume breach structures will be put in both the main dam and the filter dike. The sediment and residual ash in the WAB extension impoundment will be dredged. The existing industrial landfill in the EAB remains in the closure -in -place design. Ash in the western lobe of EAB will be regraded to form a swale that slopes from the southeast to the northwest. The main dam will be breached and culverts will be included to allow discharge along an outlet channel into the heated water discharge canal that flows into the heated water discharge pond. The existing industrial landfill (both lined and unlined portions) will be capped with a low -permeability cover system. The sediment and residual ash in the EAB extension impoundment will be dredged and disposed in the industrial landfill. Page 6-9 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina Model Setup The closure -in -place scenario was simulated by assuming ash is graded to drain along a path similar to the underlying topography, and the graded surface is capped with a low -permeability cover that limits infiltration. The capped area includes the existing extent of ash. The industrial landfill in the EAB will be left in place, and the cap will be extended to cover the unlined portion of the industrial landfill around the periphery of the EAB (Figure 6-16). It is assumed that the recharge flux over the covered area is 10-7 ft/d based on estimates of cover performance conducted by Wood (2019b). Drains will be used to lower the hydraulic head beneath the cover (Figure 6-16). The drains are positioned 5 feet below the grade of the cap. Drains are included in the WAB and in the western lobe of the EAB, but not in the central and eastern side of the EAB beneath the existing industrial landfill (Figure 6-16). Water from the drains are assumed to be collected, treated, and discharged as required by the NPDES permit. The actual drains in the ash material are represented by boundary conditions called "drains" in MODFLOW. The use of "drain" boundary conditions assumed the actual drains had idealized behavior. For example, a "drain" boundary condition allows water to flow from ash into the drain, but it prevents water from flowing from a drain into ash. The analysis ignores head losses that might occur due to localized pore clogging in the drain, or due to flow along the drain. These assumptions are consistent with a goal of evaluating transport characteristics during the closure -in -place scenario, but additional calculations beyond those shown here will be needed to fully evaluate the hydraulic performance of drains in the ash. The transport model was set up using the flow field from the steady state flow model. The distribution of boron concentrations in November 2024 (when closure -in -place construction is expected to be completed on EAB) from the interim simulation was used as the initial concentration conditions. The simulation was run for 1,000 years and results were saved every few years early in the simulation and the interval between the saved results increased with time. Spatial Distribution of Hydraulic Head The hydraulic head distribution from the closure -in -place simulation is controlled by the drains beneath the cap. In general, the heads beneath the cap are equal to, or below the level of the drains. The hydraulic head in the capped area (Figure 6-17) was compared to the level of the cap in the design and the results indicate that the heads are below the cap. The hydraulic heads below the cap are lower than the heads under the April 2019 conditions, although the general pattern of the head distribution and the directions of groundwater flow are similar (Figure 6-17). The flow direction is Page 6-10 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina predicted to change in a few locations, but the effect of these changes on the boron transport is minor. Spatial Distribution of COIs After Site Closure The simulated boron concentrations for all non -ash layers approximately 20, 70, 120, and 170 years after closure are shown in Figures 6-18a-d. The simulations indicate that the extent of boron plume decreases with time, but concentrations greater than 02L at and beyond the compliance boundary persist at locations a, b, and c (Figures 6-18a-d). Plume migration in the closure -in -place simulation is similar to that in the closure -by - excavation scenario (Figures 6-7a-d and 6-18a-d). Boron concentrations greater than 02L persist at locations a and b because the non-CAMA sources are assumed to remain in place after Site closure. At location c, concentration greater than the 02L migrates to outside the compliance boundary but re-enters the compliance boundary after traveling for approximately 100 ft, due to the geometry of the compliance boundary at that location (Figures 6-18a-d). The distribution of sulfate and TDS follows the same extent as boron. The extent of sulfate and TDS concentration greater than 02L recedes with time, except at locations a and b, which are associated with non-CAMA sources that are assumed will remain after basin closure (not shown). Time Series for Closure -in -Place Scenario Boron concentrations greater than the 02L standard occur during operation of the ash basins at each of the reference locations used for time series (Figures 6-19a-c). The general shapes of the time series are similar to those in the closure -by -excavation scenario (Figures 6-9a-c). At the five locations other than location a, the boron concentrations start at zero, increase with time to a maximum value between approximately year 2020 and 2100, and then decrease and return to near -zero concentrations. At reference location a, the boron concentration persists at levels greater than 800 µg/L because non-CAMA sources are assumed to remain active throughout the simulated period. Reference location f shows the highest concentration in the WAB, where maximum concentrations are greater than 35,000 µg/L in approximately year 2020. Reference location d shows the highest concentration in the EAB, where maximum concentrations are greater than 5,000 µg/L in approximately year 2080. Boron concentrations greater than 02L at locations c, d, e appear to extend deeper than the other three reference locations (Figures 6-19a-c). Page 6-11 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 6.5 Closure -in -Place Scenario with Corrective Action The corrective action design consisting of 50 extraction and 27 clean water infiltration wells described in Section 6.3 was simulated with the closure -in -place scenario. The hydraulic heads in the closure -in -place with remediation wells simulation are a few feet higher in the vicinity of the EAB than they are in the closure -by -excavation simulation, but the difference is small and elsewhere the heads in the two scenarios are virtually identical (e.g., compare the head contours in Figure 6-10 to those in Figure 6-20). The boron concentration contours for the two scenarios are also virtually indistinguishable (e.g., Figures 6-12 and 6-21). Simulations of the distributions of sulfate (Figure 6-22) and TDS (Figure 6-23) for the closure -in -place scenario with remediation wells are also essentially identical to the results for the closure -by -excavation scenario with remediation wells (compare to Figures 6-13 and 6-14). The results show that the same corrective action system used to bring COI concentrations into compliance by year 2029 for the closure -by -excavation scenario would also bring COIs into compliance for the closure -in -place scenario. 6.6 Conclusions The following conclusions are based on the results of the updated groundwater flow and transport simulations: A groundwater flow and transport model was developed based on a hydrogeologic conceptual model typical of the Piedmont physiographic province, and this model was calibrated using hydraulic heads and chemical analyses from more than 100 monitoring wells associated with the ash basins. Water supply wells used for water supply to homes, a school, and a business in the vicinity of Roxboro were also included in the model. • The NRMSE between predicted and observed heads is less than 3 percent, which is within an acceptable range. The NRMSE between predicted and observed boron concentrations is also small, less than 4 percent, indicating that the model provides a reasonable representation of conditions at Roxboro. The calibrated model was adjusted to represent conditions that would occur during the closure -by -excavation and closure -in -place closure scenarios. Predicted future boron concentrations at and beyond the compliance boundary are essentially identical for both closure scenarios. • The simulations indicate that there are no exposure pathways between the groundwater flow through the ash basins and the water supply wells in the vicinity. Domestic and public water supply wells are located upgradient or in Page 6-12 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina different watersheds from the ash basins and are not affected by constituents associated with from the ash basins or by the different closure scenarios. • Under both closure scenarios, COI distribution associated with the WAB remains within the compliance boundary for April 2019 and future timeframes. • Under both closure scenarios, boron concentrations greater than the 02L standard occur at or beyond the EAB compliance boundary for more than 200 years without groundwater corrective action. • With corrective action, the predictive simulations suggest that 02L compliance can be achieved within approximately 9 years of operation for the EAB. Results for closure -by -excavation scenario are the same as those for closure -in -place scenario. • Simulations indicate that sulfate and TDS distributions are similar to boron distributions under the closure -by -excavation and closure -in -place scenarios, and that 02L compliance is achieved within approximately 9 years of operation. • The performance of the two closure scenarios is controlled by COIs that have already migrated outside of the EAB. Both scenarios effectively limit transport of additional COIs toward the compliance boundaries. That is why the results of the simulations of the closure -by -excavation scenario are similar to the results for the closure -by -excavation scenario. • New field data are unlikely to change the conclusion that closure -by -excavation and closure -in -place actions result in similar boron, sulfate, and TDS transport at the compliance boundary. Page 6-13 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 7.0 REFERENCES Anderson, M.P., and W.W. Woessner, 1992, Applied Groundwater Modeling, Simulation of Flow and Advective Transport, Academic Press, Inc., New York NY, 381p. Daniel, C.C., Douglas G. Smith, and Jo Leslie Eimers, 1997, Hydrogeology and Simulation of Ground -Water Flow in the Thick Regolith-Fractured Crystalline Rock Aquifer System of Indian Creek Basin, North Carolina, USGS Water -Supply 2341. Gel Solutions, 2019, Geophysical Logging Report, ABMW-7 BRL, MW-01 BRL, MW-108 BRL, MW-108 BRLL, MW-205 BRL, MW-205 BRLL, MW-205 BRLLL, MW-208 BRL, MW-208 BRLL, MW-208 BRLLL Roxboro Steam Electric Plant, Semora, North Carolina, April 18, 2019 HDR and SynTerra, 2017. Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities. HDR Engineering, Inc. and SynTerra Corporation. Haven, W. T. 2003. Introduction to the North Carolina Groundwater Recharge Map. Groundwater Circular Number 19. North Carolina Department of Environment and Natural Resources. Division of Water Quality, 8 p. Langley, W.G., S. Oza, 2015, Sorption Evaluation of the. Roxboro Steam Electric Plant. Charlotte Department of Civil and Environmental Engineering, report prepared for SynTerra. Legrand, H. 1988. Piedmont and Blue Ridge. Back, W., J. Rosenshein, and P. Seaber, eds. 1988. Hydrogeology: The Geology of North America 0-2: The Decade of North American Geology. Boulder, Colorado: Geological Society of America. Geological Society of America. P. 201-208. Maupin, M., Joan F. Kenny, Susan S. Hutson, John K. Lovelace, Nancy L. Barber, and Kristin S. Linsey. 2014. Estimated Use of Water in the United States in 2010, USGS Circular 1405. McDonald, M.G. and A.W. Harbaugh, 1988, A Modular Three -Dimensional Finite - Difference Ground -Water Flow Model, U.S. Geological Survey Techniques of Water Resources Investigations, book 6, 586 p. Page 7-1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 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 Water Supply and Use, in "National Water Summary 1987 - Hydrologic Events and Water Supply and Use". USGS Water -Supply Paper 2350, p. 393-400. North Carolina; Estimated Water Use in North Carolina, 1995, USGS Fact Sheet FS-087- 97 Radcliffe, D.E., L.T. West, L.A. Morris, and T. C. Rasmussen. 2006. Onsite Wastewater and Land Application Systems: Consumptive Use and Water Quality, University of Georgia. SynTerra, 2014, L.V. Roxboro Steam Electric Plant, Semora, NC, Water Supply Well Survey Report of Findings, September 30, 2014. SynTerra, 2015a, Comprehensive Site Assessment Report, Roxboro Steam Electric Plant, Semora, NC. September 2, 2015. SynTerra, 2015b, Corrective Action Plan Part 1. Roxboro Steam Electric Plant, Semora, NC, 2015 SynTerra, 2016a, Corrective Action Plan, Part 2. Roxboro Steam Electric Plant, Semora, NC, February 29, 2016. SynTerra, 2016b, Comprehensive Site Assessment, Supplement 1 - Roxboro Steam Electric Plant, 2016 SynTerra, 2017, Comprehensive Site Assessment Update - Roxboro Steam Electric Plant, Semora, NC, October 31, 2017 SynTerra, 2018, Preliminary Updated Groundwater Flow and Transport Modeling Report for Roxboro Steam Electric Plant, Semora, NC. November 2018, Revised March 2019. SynTerra, 2019a, Ash Basin Pumping Test Report for Roxboro Steam Electric Plant - Duke Energy Progress, LLC. January 2019. SynTerra, 2019b, Updated Background Threshold Values for Constituent Concentrations in Groundwater, December, 2019 Page 7-2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina SynTerra, 2019c, Analysis of Geochemical Phenomena Controlling Mobility of Ions from the Coal Ash Basin at the Roxboro Steam Electric Plant. December, 2019 SynTerra, 2019d, Corrective Action Plan Update. Roxboro Steam Electric Plant, Semora, NC, December 2019. SynTerra, 2019e, Pumping Test Numerical Simulation Report for Roxboro Steam Electric Plant, Semora, NC. To be submitted. SynTerra, 2019f, Fractured Bedrock Evaluation, Roxboro Steam Electric Plant, December, 2019 Tiedeman, C.R. and P.A. Hseih. 2001. Assessing an Open Hole Aquifer Test in Fractured Crystalline Rock. Ground Water, v. 39, n.1, p 68-78. Trapp, H. and M.A. Horn. 1997. Ground Water Atlas of the U.S. North Carolina and vicinity (HA 730-L). USGS. httl2://12ubs.usgs.gov/ha/ha730/ch 1/L-text4.html. Treece, M.W, Jr., Bales, J.D., and Moreau, D.H., 1990, North Carolina water supply and use, in National water summary 1987 Hydrologic events and water supply and use: U.S. Geological Survey Water -Supply Paper 2350, p. 393-400. US EPA, 2015, httl2://www.el2a.gov/watersense/12ubs/indoor.html accessed 8/26/15. Watermark Numerical Computing, 2004, PEST Model -Independent Parameter Estimation User Manual: 5th Edition. Wood, 2019a, Roxboro West Ash Basin Closure Project, Roxboro Steam Electric Plant, Person County, North Carolina. Closure -in -place Grades - West Ash Basin, February 13, 2019 Wood, 2019b, Roxboro East Ash Basin Closure Project, Roxboro Steam Electric Plant, Person County, North Carolina. East Ash Basin Closure -in -place Grades, February 15, 2019 Wood, 2019c, Roxboro West Ash Basin Closure Plan, Roxboro Steam Station, Person County, North Carolina, June 26, 2019 Wood, 2019d. Roxboro Steam Station, Conceptual Landfill Expansion for CAMA Ash Basin Closure. June 26, 2019 Page 7-3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina 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. Page 74 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina FIGURES 0 WE BUILDING MATERIALS MANUFACTURING PLANT (APPROXIMATE GYPSUM STORAGE AREA Or L C � -1_ HDISHEATED HARGE WATER POND HYCO — �r 1 �1 fil WESTERN DISCHARGE WESTASH BASIN DISCHARGE CANAL U �\ � FILTER DIKE WOODLAND 9 57 O ELEMENTARY �� o SCHOOL ., c- ' C J ROXBORO PLANT PARCEL LINE 1 NOTES , ALL BOUNDARIES ARE APPROXIMATE. DUKE ENERGY PROPERTY LINES ARE REPRESENTED BASED ON DUKE o ENERGY'S INTERPRETATION OF HISTORICAL DOCUMENTED PROPERTY / BOUNDARIES AND CURRENT PERSON COUNTY GIS. l 2016 USGS TOPOGRAPHIC MAP, OLIVE HILL QUADRANGLE, OBTAINED FROM THE USGS STORE AT https://store. usgs.gov/map-locator 4DUKE PERSON COUNTY\ ENERGY MNSTONSALEM PROGRESS 101 CHARLOTTE synTerra W W W.synterraC EASTASH BASIN ♦' EASTERN LOBE 1 w EASTERNHISTORICAL DEPOSITION AREA ASH BASIN WASTE BOUNDARY EASTERN DISCHARGE CAN. EAB EXTENSION Z� IMPOUNDMENT AREA \\S C1 RAI k YE EPAR�yA�T�O�R \D^IK�J` INDUSTRIAL LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY /sso /\ �CURRENT 500'ASHBASIN' O COMPLIANCE BOUNDARY 1/1 aw WOM � � WAB EXTENSION IMPOUNDMENT AREA Kq L O . r\ WATER SUPPLY WELLS u FIGURE 1-1 USGS LOCATION MAP UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA DRAWN BY: J. KIRTZ DATE: 06/11/2019 GRAPHIC SCALE REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 0 500 1,000 2000,3,000 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY (IN FEET) 1 si A� 000I xI LEGEND 1-1 Q!!I WATER SUPPLY WELLS - EFFLUENT DISCHARGE CANAL _DAMS AND DIKES FLOW AND TRANSPORT MODEL BOUNDARY ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY - - SOLID WASTE LANDFILL COMPLIANCE BOUNDARY DUKE ENERGY PROGRESS ROXBORO PLANT BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. THE MODEL BOUNDARY WAS SETATA DISTANCE FROM THE ASH BASINS SUCH THATTHE BOUNDARY CONDITIONS DID NOT ARTIFICIALLY AFFECT THE RESULTS NEAR THE ASH BASINS. DUKE ENERGY PROPERTY LINES ARE REPRESENTED BASED ON DUKE ENERGY'S INTERPRETATION OF HISTORICAL DOCUMENTED PROPERTY BOUNDARIES AND CURRENT PERSON COUNTY GIS. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 DUKE ENERGY PROGRESS ■ GRAPHIC SCALE 1,600 0 1,600 3,200 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: W. PRATER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 4-1 NUMERICAL MODEL DOMAIN UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA 000I xI LEGEND 1-1 Q!!I WATER SUPPLY WELLS - EFFLUENT DISCHARGE CANAL _DAMS AND DIKES FLOW AND TRANSPORT MODEL BOUNDARY ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY - - SOLID WASTE LANDFILL COMPLIANCE BOUNDARY DUKE ENERGY PROGRESS ROXBORO PLANT BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. THE MODEL BOUNDARY WAS SETATA DISTANCE FROM THE ASH BASINS SUCH THATTHE BOUNDARY CONDITIONS DID NOT ARTIFICIALLY AFFECT THE RESULTS NEAR THE ASH BASINS. DUKE ENERGY PROPERTY LINES ARE REPRESENTED BASED ON DUKE ENERGY'S INTERPRETATION OF HISTORICAL DOCUMENTED PROPERTY BOUNDARIES AND CURRENT PERSON COUNTY GIS. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 DUKE ENERGY PROGRESS ■ GRAPHIC SCALE 1,600 0 1,600 3,200 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: W. PRATER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 4-1 NUMERICAL MODEL DOMAIN UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA 0 w CDO w w o O O z J U W 0 aw0z aQ �a0Jz O C17 p C0 O vWW= W O H O J (D L) Q W � LL 20 IMFLU - 1 �O"Co LL 0 OOF-DCw �2 co a�x Q O 0 w W Ur W W LL F- 1 Q a 000(D N N N N LI) N N N N � O N N N W W W W H H H H Q Q Q Q Comm E O U 2- 0 Q f6 0�CDZw N LU�g" N L w } d Y Y Q a }00❑� m ❑ 0 LU > U ZO U �LOwa0 N r � W 2 d()� Z ❑ ❑ U Q d LLJ U w Y 00 � H U 0 of 0 Z uJ � 2 d d ❑ V �n W acan �Dm YWw W Qwo V^ `y j§ƒ z / \ k\/LUo 4-?/ ?. \)k ■ w $� m E \ - E 0 e a § ®- O ■ ■ o 2 \ \ §)\ w z IL ® @ / § / / \ % Cl) « w $ o •§ 0 X � 0\ E 0 §§ 7 7 5// 2 co j g R o k § = / > O « O & ® 0 e? U§-j Z < / � (L « �■2b2 f22��� wa - a -� ■w@2w■ ® « 0 p R 0«_�«2 LLIE@Qw LU/w0A �w22 /2%%m k0k� 0 w ®� U o v a LU F- a a � 4-1 � 2222 � @@@@ LI) jeee Comm Commcl E O / c< LU $ O j/® b e-4 § / §..w=< »j=C, �E§\\ 42e±� p )jƒii . =±o<= O 00 Q N O 0 Fice LU e DL $ �w± AlI|Iq eq OJd @AIle|n n 14 Z_ 0 ~ W v, +� cu in � O w OQ � +J an � Z 0 c : N W J Z a O J E O Co W v O co U O H = x Q Q ?p�aZ J_ 0 4 ♦ J Z a J O 2ZQZQRW �n t— O W LU LL H U O WaCo-iP rl d'WHZWw C9QOQ�0 ELEMOLU O LU 0 0 a�� o W W W >FQmC0 �Q�x UWa0 � H z W 0 J � ZOO O 0a0 U 0 CO J H � Q 0 o a 5 4-1 Y 0000 N N N N LO N N N O N N N O W W W W H H H H Q Q Q Q ❑ ❑ ❑ ❑ E O U } cl a O 0� (D z W o Lu�gb N w d Y } Y Q l� Q }00C,� O mo00W� ow>c) O �U°, O �w=ate O 00 QO lqt fV O oc)aa rl O O O O O wice� uj �J ~ Aliligegoad anileinuan� u V^ r `y z �—„cu H WZO a-J dA J W 0 _� 0 0 N O W E v LO o v (ajz a=w x �� Q o co 0 H Q O 4 ♦ t9 ? W (L O O Jco WaQn Cl) r O 2Coz- Z��U leLLO~w= WQ2aJF- O OHDaW0 O 0 EL— z rl o0w C�LLy� LU w o 0 LU w 0 2 p Z >0Qm UN00 �zz� oo� z0 Ocow L) z (9 ^ LU J ~ F- LU IL rl O rn rn rn rn 0 0 0 (D N N N N LO N N N N O �2 OW W W W Q Q Q Q Comm E O O cl (6 O Q ofcDzLU N oLu Zgb N w }�Y}z O O }ma }mom m000w� O ow>c� O 00 l0 (V O O �`�C)�� 0OfC)aa r-I O O O O O 61) AliligegOad anileinwn: �Z o OL V^� `4 2 .7 Q) JU LU 0 � {7 CL S§)) 0 � ■ LL 0 _ >- o a 2 j § 0 o -0 (D E 0 @ « w § \77D RUo LU -Z < �w¥0 LU E- M 2 R « O < « qZk -jZ co 0L U �■L��� p 4LL@R p w0Ra-i� ■w22w■ 0<2 z �9o�w CO22C� LU0■00 @ >k�\w vvk0 22§■ \�k � vLo �F� a_ 4-1 � 5. O @@@@ \\\\ 0 LULU// < < < < Come E S j O ±o/) \ j\�\ O O ®%/»/ §..w=< »j=C, O mac§/\ \$§iW )jƒii O 00 Q N O O =±o<= LUl� LU e $ Ailllq eq OJd @A|le|n w n � C w } . �� 1966 - 2004 C 2007 - 2014 ® E! fib ®mill I im LEGEND RECHARGE RATE - 0.0005 ft/d - 0.001 ft/d - 0.002 ft/d 0.003 ft/d 0.004 ft/d —FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM GOGGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). 2014 - 2020 DUKE ENERGY PROGRESS WIN GRAPHIC SCALE 2,000 0 2,000 4,000 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 4-8 DISTRIBUTION OF MODEL RECHARGE ZONES UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA EASTASH BASIN 1l �7 DUKE t GRAPHIC SCALE 1,800 0 1,800 3,600 LEGEND ENERGY (IN FEET) PROGRESS DRAINS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: W. PRATER DATE: 12/12/2019 GENERAL HEAD BOUNDARY FEATURES 1p CHECKED BY, K.LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 — ASH BASIN WASTE BOUNDARY synTena PROJECT MANAGER: C. EADY www.synterracorp.com NOTES: ALL BOUNDARIES ARE APPROXIMATE. (] FIGURE 4-9 STREAMSARE INCLUDED IN THE MODELAS DRAINS. LAKES, PONDS, CHANNELS,AND MODEL SURFACE WATER FEATURES WATER IN THE ASH BASIN ARE INCLUDED IN THE MODELAS GENERAL HEAD BOUNDARY FEATURES. UPDATED GROUNDWATER FLOW AND TRANSPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. MODELING REPORT DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200 (NAD83). SEMORA, NORTH CAROLINA s. L EASTASH „�••�' BASIN J.I .c yy � ?� ' 1 11000 B S •9 t '-woe r 9 rm m LEGEND GRAPHIC SCALE DUKE ie WATER SUPPLY WELLS tENERGY 1,500 0 1,500 3,600 ASH BASIN WASTE BOUNDARY (IN FEET) ASH BASIN COMPLIANCE BOUNDARY PROGRESS DRAWN BY: R.YU DATE: 1111s/2019 SOLID WASTE LANDFILL BOUNDARY REVISED BY: B. ELLIOTT DATE: 12/19/2019 SOLID WASTE LANDFILL COMPLIANCE BOUNDARY CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY DUKE ENERGY PROGRESS ROXBORO PLANT BOUNDARY : G CAWING DATE: 12/19/2019 FLOW AND TRANSPORT MODEL BOUNDARY smTena PROJECT MANAGER C EADY ALL BOUNDARIES ARE APPROXIMATE. FIGURE -10 DUKE ENERGY PROPERTY LINES ARE REPRESENTED BASED ON DUKE ENERGY'S WATER SUPPLY WELLS IN MODEL AREA INTERPRETATION OF HISTORICAL DOCUMENTED PROPERTY BOUNDARIES AND CURRENT PERSON COUNTY GIS. UPDATED GROUNDWATER FLOW AND TRANSPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS MODELING REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200 (NAD83). SEMORA, NORTH CAROLINA 16 I ff LEGEND r HYDRAULIC CONDUCTIVITY DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 %' �0.005-0.01 ft/d 1.0-2.0 ft/d ENERGY - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 -0.1 ft/d - 5.0 - 10.0 ft/d PROGRESS 0.1 -0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 - 1.0 ft/d CHECKED BY: K. LAWING DATE: 12/12/2019 1p APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTerm IPROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1a ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 1 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA 16 I ff LEGEND r HYDRAULIC CONDUCTIVITY DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 %' �0.005-0.01 ft/d 1.0-2.0 ft/d ENERGY - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 -0.1 ft/d - 5.0 - 10.0 ft/d PROGRESS 0.1 -0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 - 1.0 ft/d CHECKED BY: K. LAWING DATE: 12/12/2019 1p APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTerm IPROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1b ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 2 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA ff 16 1 �. LEGEND r HYDRAULIC CONDUCTIVITY DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 �0.005-0.01 ft/d 1.0-2.0 ft/d tENERGY - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 -0.1 ft/d - 5.0 - 10.0 ft/d PROGRESS 0.1 -0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 - 1.0 ft/d 1p CHECKED BY: K. LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTerm IPROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1c ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 3 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA ff 16 1 �. LEGEND r HYDRAULIC CONDUCTIVITY DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 �0.005-0.01 ft/d 1.0-2.0 ft/d tENERGY - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 —0.1 ft/d - 5.0 — 10.0 ft/d PROGRESS 0.1 —0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 — 1.0 ft/d 1p CHECKED BY: K. LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTerm IPROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1d ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 4 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA ff 16 1 �. LEGEND r HYDRAULIC CONDUCTIVITY DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 �0.005-0.01 ft/d 1.0-2.0 ft/d tENERGY - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 -0.1 ft/d - 5.0 - 10.0 ft/d PROGRESS 0.1 -0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 - 1.0 ft/d 1p CHECKED BY: K. LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTerm IPROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1e ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 5 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA c ff 16 1 LEGEND r HYDRAULIC CONDUCTIVITY DUKE %'ENERGY 1GRAPHICSCALE ,800 0 1,800 3,600 �0.005-0.01 ft/d 1.0-2.0 ft/d - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 -0.1 ft/d - 5.0 - 10.0 ft/d PROGRESS 0.1 -0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 - 1.0 ft/d 1p CHECKED BY: K. LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTerm IPROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1f ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 6 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA ff 1-. r. t \ 1Y _ •9 -" t Mo 16 LEGEND r HYDRAULIC CONDUCTIVITY DUKE GRAPHICSCALE 1,800 0 1,800 31600 M0.005-0.01 ft/d 1.0-2.0 ft/d tENERGY - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 —0.1 ft/d - 5.0 — 10.0 ft/d PROGRESS 0.1 —0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 — 1.0 ft/d jp CHECKED BY: K. LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTena PROJECT MANAGER: C. EADY www.svnterracorp.com NOTES: ALL BOUNDARIES ARE APPROXIMATE. FIGURE 5-7"Q ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPV IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAVERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 7 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA ff 1-. r. t \ 1Y _ •9 -" t Mo 16 LEGEND r HYDRAULIC CONDUCTIVITY DUKE %'ENERGY GRAPHICSCALE 1,800 0 1,800 31600 M0.005-0.01 ft/d 1.0-2.0 ft/d - 0.01— 0.05 ft/d 2.0 — 5.0 ft/d (IN FEET) - 0.05 —0.1 ft/d - 5.0 — 10.0 ft/d PROGRESS 0.1 —0.5 ft/d - 10.0+ ft/d DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 0.5 — 1.0 ft/d jp CHECKED BY: K. LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTerm PROJECT MANAGER: C. EADY www.svnterracorp.com NOTES: FIGURE 5-1h ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN ASH LAYER 8 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA ff B 1 'A a"�4 ' a m LEGEND t HYDRAULIC CONDUCTIVITY %'DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 �0.005-0.01 ft/d 1.0-2.0 ft/d ENERGY - 0.01-0.05 ft/d - 2.0 — 5.0 ft/d NFEET) - 0.05 —0.1 ft d / - 5.0+ ft/d PROGRESS DRAWN BY: R. YU DATE: 11/18/2019 0.1 -0.5 ft/d REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 - 0.5 - 1.0 ft/d � CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTena IPROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1i ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND MODEL HYDRAULIC CONDUCTIVITY ZONES HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN IN SAPROLITE LAYERS 9 AND 10 TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA B 1 9 \- - --� - - -ft m LEGEND t HYDRAULIC CONDUCTIVITY %'DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 -0.005-0.01 ft/d 1.0-2.0 ft/d ENERGY - 0.01-0.05 ft/d - 2.0 - 5.0 ft/d NFEET) DRAWN BY: R. YU DATE: 11/18/2019 0.05 —0.1 ft d / � 5.0+ ft/d PROGRESS 0.1-0.5 ft/d REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 - 0.5 -1.0 ft/d � CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTena PROJECT MANAGER: C. EADY www.s nterracor .com -ter' ' NOTES: ALL BOUNDARIES ARE APPROXIMATE. FIGURE 5-1, ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPV IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES MODEL HYDRAULIC CONDUCTIVITY ZONES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAVERS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS IN SAPROLITE LAYER 11 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA _ S Y � � I r Ir . . . . . . . . .'y tR I y `1 - t of � + `� �i LEGEND t HYDRAULIC CONDUCTIVITY DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 -0.005-0.01 ft/d 1.0-2.0 ft/d ENERGY (IN FEET) = 0.01-0.05 ft/d = 2.0 — 5.0 ft/d -0.05 —0.1 ft d PROGRESS / - 5.0+ ft/d � DRAWN BY: R. YU DATE: 11/18/2019 0.1 -0.5 ft/d REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 - 0.5 - 1.0 ft/d APPROVED BY: K. LAWING DATE: 12/20/2019 FLOWAND TRANSPORT MODEL BOUNDARY WnTena PROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-1k ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN TRANSITION ZONE LAYERS 12 AND 13 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA 9 1 'JA Air- 00 4 a m LEGEND t HYDRAULIC CONDUCTIVITY %'DUKE 1GRAPHICSCALE ,800 0 1,800 3,600 �0.005-0.01 ft/d 1.0-2.0 ft/d ENERGY - 0.01-0.05 ft/d - 2.0 - 5.0 ft/d NFEET) - 0.05 —0.1 ft d / - 5.0+ ft/d PROGRESS DRAWN BY: R. YU DATE: 11/18/2019 0.1 -0.5 ft/d REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 - 0.5 - 1.0 ft/d � CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 FLOWAND TRANSPORT MODEL BOUNDARY WnTena PROJECT MANAGER: C. EADY www.synterracorp.com NOTES: FIGURE 5-11 ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND MODEL HYDRAULIC CONDUCTIVITY ZONES HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN IN UPPER FRACTURED ROCK LAYER 14 TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA 9 1 )A .4 a •9 m LEGEND t HYDRAULIC CONDUCTIVITY DUKE tENERGY 1GRAPHICSCALE ,800 0 1,800 3,600 0.005-0.01 ft/d 1.0-z.0 ft/d - 0.01-0.05 ft/d - 2.0 — 5.0 ft/d NFEET) DRAWN BY: R. YU DATE: 11/18/2019 - 0.05 —0.1 ft d / - 5.0+ ft/d PROGRESS 0.1 -0.5 ft/d REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 - 0.5 - 1.0 ft/d � CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 FLOWAND TRANSPORT MODEL BOUNDARY synTena I PROJECT MANAGER: C. EADY www.s nterracor .com NOTES: FIGURE 5-1m ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND MODEL HYDRAULIC CONDUCTIVITY ZONES HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN IN UPPER FRACTURED ROCK LAYER 15 TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA 1 r 000000000, !R` !+ \ Via.Y4Air- ; LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY It DUKE ENERGY PROGRESS GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1n ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN UPPER FRACTURED ROCK LAYER 16 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY It DUKE ENERGY PROGRESS 9 m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-10 ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN LOWER FRACTURED ROCK LAYER 17 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY It DUKE ENERGY PROGRESS 9 m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1p ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPV IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN LOWER FRACTURED ROCK LAYER 18 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAVERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA r- LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY f^ ItDUKE ENERGY PROGRESS 9 , -QV rl m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1q ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPV IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN UPPER BEDROCK LAYER 19 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAVERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA r- LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY f^ ItDUKE ENERGY PROGRESS 9 , -QV rl m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1r ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN UPPER BEDROCK LAYER 20 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA n r- LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY ItDUKE ENERGY PROGRESS 9 , -QV rl m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1s ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN LOWER BEDROCK LAYER 21 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA n r- LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY ItDUKE ENERGY PROGRESS 9 , -QV rl m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1t ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN LOWER BEDROCK LAYER 22 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA r- LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY f^ ItDUKE ENERGY PROGRESS 9 , -QV rl m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1u ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN LOWER BEDROCK LAYER 23 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA r- LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY f^ ItDUKE ENERGY PROGRESS 9 , -QV rl m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1v ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN LOWER BEDROCK LAYER 24 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA r- LEGEND HYDRAULIC CONDUCTIVITY =0.005-0.01 ft/d 1.0-2.0 ft/d = 0.01-0.05 ft/d - 2.0 — 5.0 ft/d -0.05-0.1 ft/d -5.0+ ft/d 0.1-0.5 ft/d - 0.5 — 1.0 ft/d FLOWAND TRANSPORT MODEL BOUNDARY f^ ItDUKE ENERGY PROGRESS 9 , -QV rl m GRAPHIC SCALE 1,800 0 1,800 3,600 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-1w ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC CONDUCTIVITY ZONES ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICALANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES IN LOWER BEDROCK LAYER 25 AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR MODEL LAYERS ARE LISTED IN TABLE 5-2. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS REPORT COLLECTED ON FEBRUARY 6, 2017. DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM RIPS 3200(NAD83). SEMORA, NORTH CAROLINA WAB, column 100 Hydraulic Conductivity (ft/d) 0.005-0.01 0.05-0.1 �0.01-0.05 0.1-0.5 0 5C1 100 15C 1 1 1 I vll i i i i i i i 0.5 - 1.0 2.0 - 5.0 1.0 - 2.0 5.0 + Blue arrows indicate the generalized groundwater flow direction. DUKE FIGURE 5-2 ENERGY® DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: W. PRATER DATE: 12/12/20,9 CROSS-SECTION THROUGH ASH BASIN DAMS PROGRESS CHECKED BY: K. LAWING DATE: 12/12/2019 SHOWING HYDRAULIC CONDUCTIVITY (COLORS) APPROVED BY: K. LAWING DATE: 12/12/2019 AND HYDRAULIC HEADS (LINES) PROJECT MANAGER: C. EADY UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT synTerra www.synterracorp.com SEMORA, NORTH CAROLINA o 0 F- .� 0 w a = M N ~ w `6 Uo O 0 Z LLL J J w �D0 0 2 w02Z WDO-1z awZVO w w 0 V M Q V O W 0 Z W~ � pQ20 a wWLUpwz H w LL C0 O 4 mWWOw 0 Q m C0 0mp0 0o of 0 O t y � � IL a 4 0 ~ Q 4 0 U a. a O a 000(D N N N N LI) N N N N � O O It W W W W H H H H Comm E O 0 U Q O Q ofCDzw N a� O Lu v �ggL w ON }�Y}z 0 00 0 O Ln Ln 0 M ..�m< }p}p00C,� zLL,LU �Ow $ ea a e nwi ���) p 4 p l S >UJa-0 �w==& v � W ice uj :) Z O W a `y 0 470 % • • 440 d� •' EAST ASH • �, • BASIN • • • 490 • • _STAS BA SIN • I- 0 �90 S00 LEGEND ERROR BAR RESIDUALS <6 ft AT EACH MONITORING WELL 6-12 ft • MONITORING WELLS -HYDRAULIC HEAD (FEET) -ASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY OEM ��'lll I � DUKE GRAPHIC SCALE t 750 0 750 1,500 ENERGY(IN FEET) PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 5-4 ALL BOUNDARIES ARE APPROXIMATE. SIMULATED APRIL 2019 HYDRAULIC HEADS IN CONTOUR INTERVAL IS 10 FEET, HEAD IS SHOWN FOR MODEL LAYER 15. RESIDUALSARE EOUALTO PREDICTED HEAD -OBSERVED HEAD. UPPER FRACTURED BEDROCK FLOW ZONE BLACK ERROR BARS SHOW THE HEAD STANDARD DEVIATION OF 6 FEET UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. REPORT AERIAL WAS COLLECTED ON JUNE 13,2016. ROXBORO STEAM ELECTRIC PLANT DRAWING HAS BEEN SET COORDINATE SYSTEM FPSI300(NADJ3AND NAVD3)TH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA \11R V o 430 430 430 Rio k�0 420 ��O ❑ Nag /.�QO ' v 480 a EASTASH \ BASIN .a Ng0 57jO o 490 490 � o �0 WES 1 B S'So 1 ` 1 TASH AS/ ® SOp 5po 480 460 �^ o 450 Sop y LEGEND 'FLOW WITHIN LOCAL SYSTEM FLOW OUTSIDE LOCAL SYSTEM GROUNDWATER LEAVING LOCAL SYSTEM Ie WATER SUPPLY WELLS DRAINS — LOCALASH BASIN GROUNDWATER FLOW SYSTEM HYDRAULIC HEAD SASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY Rj Soo � 1 10 2 DUKE GRAPHIC SCALE t 750 0 750 1,500 ENERGY(IN FEET) PROGRESS DRAWN BY: R.YU REVISED BY: B. ELLIOTT DATE: 11/18/2019 DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 5-5 ALL BOUNDARIES AREAPPROXIMATE.ARROWSINDICATE INFERRED FLOW DIRECTION ONLY, MA NOT MAGNITUDE.ITUDE.SIMULATED APRIL 2019 LOCAL ASH BASIN GROUNDWATER FLOW CONTOUR INTERVAL IS 10 FEET, HEADS ARE SHOWN IN MODEL LAYER 15 PRIOR TO DECANTING. SYSTEM IN UPPER FRACTURED BEDROCK STREAMS ARE INCLUDED IN THE MODELAS DRAINS. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. REPORT AERIAL WAS COLLECTED ON JUNE 13,2016. ROXBORO STEAM ELECTRIC PLANT D WING HAS BEEN SET COORDINATE SYSTEM FPSITH A 300(NADJECTION OF 3AND NAVD3)TH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA LEGEND QCOI SOURCE ZONES ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY SO UNDARI ES AREA PPROXIMATE. REFER TO TABLE 5-5a FOR DESCRIPTIONS AND MODEL INPUT CONCENTRATIONS FOR BORON, SULFATE, AND TDS. AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13. 2016. DRAWING HAS BEEN SET WITHA PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). DUKE GRAPHIC SCALE t Rio o Rio 1,420 ENERGY (IN FEET) PROGRESS DRAWN BY: R.YU REVISED BY: R. KIEKHAEFER DATE: 1111812019 DATE: 12/19/2019 1�� CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 5-6a EAST ASH BASIN AND WEST ASH BASIN SOURCE ZONES FOR HISTORICAL TRANSPORT MODEL UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT BORON SOURCE ZONES BORON, SULFATE, AND TDS SOURCE ZONES ft '30 29 27 31 28 23 32 18 24 19 25 20 21 26 33 22 �. 1 2 3 5 6 7 4 WEST ASH 8 9 BASIN 10 11 , SULFATE AND TDS SOURCE ZONES ' EAST ASH BASIN ` 4 35 17 16 ':� 36 P 3837 15 14 WE 4, LEGEND DUKE GRAPHIC SCALE 360 0 360 720 ®LANDFILL HALO AREA ENERGY (IN FEET) QGYPSUM STO RAG E AREA (G SA) PROGRESS DRAWN BY: R.YU DATE 11/18/2019 QDFA SILOS, TRANSPORT, AND HANDLING AREA (DFAHA) REVISED BY: R. KIEKHAEFER DATE: 12/12/2019 CHECKED BY: K. LAWING DATE: 12/12/2019 _WAB SLUICE LINE CORRIDOR APPROVED BY: K. LAWING DATE: 12/12/2019 Y PROJECT MANAGER:C. EADY ®POTENTIAL SOURCES OUTSIDE OF WAB syr, e www.synterracorp.com ASH BASIN WASTE BOUNDARY —ASH BASIN COMPLIANCE BOUNDARY FIGURE 5-6b SOLID WASTE LANDFILL BOUNDARY SOURCE ZONES ADJACENT TO AND SOLID WASTE LANDFILL COMPLIANCE BOUNDARY DOWNGRADIENT OF THE EAB AND WAB FOR NOTES: HISTORICAL TRANSPORT MODEL ALL BOUNDARIES ARE APPROXIMATE UPDATED GROUNDWATER FLOW AND REFER TO TABLE 5-5b FOR DESCRIPTIONSAND MODEL INPUT CONCENTRATIONS FOR BORON, SULFATE, AND TDS TRANSPORT MODELING REPORT AERIAL IBPHOTOGRAPHYOBTAINEDFROMGOOGLEEARTHPROONOCTOBER11,2017.AERIALWASCOLLECTEDONJUNE 0 13, ROXBORO STEAM ELECTRIC PLANT DAWNG HAS BEEN SETWITHA PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 SENORA, NORTH CAROLINA LEGEND DUKE GRAPHIC SCALE 710 0 710 1,420 REFERENCE LOCATION ENERGY BORON 700 -4,000 Ng/L (IN FEET) PROGRESS BORON > 4,000 Ng/L DRAWN BY: R. YU DATE: 11/18/2019 —ASH BASIN WASTE BOUNDARY REVISED BY.' B. ELLIOTT DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY APPROVED BY: K. CAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARYTe PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY yn www.synterracorp.com NOTES: FIGURE 5-7 ALL BOUNDARIES ARE APPROXIMATE. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB AND SIMULATED APRIL 2019 BORON CONCENTRATIONS IN ALL NON -ASH THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. /�/� /� /� WITH ^AMA AND NON-/�^AMA CCR SOURCES LAYERS BORON CONCENTRATIONS ASSOCIATED WITH SEDIMENTS IN THE WAB AND EAB EXTENSION IMPOUNDMENT AREAS ARE NOT SHOWN. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. REPORT AERIAL WAS COLLECTED ON JUNE 13,2016. ROXBORO STEAM ELECTRIC PLANT D WING HAS BEEN SET WITH A OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FPS300(NAD3). SEMORA, NORTH CAROLINA i EAST ASH BASIN LEGEND REFERENCE LOCATION SULFATE > 250 mg/L -ASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY DUKE GRAPHIC SCALE 710 0 710 1,420 ENERGY(IN FEET) PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: B. ELLIOTT DATE: 12/19/2019 1 � CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 5-8 ALL BOUNDARIES ARE APPROXIMATE. SIMULATED APRIL 2019 SULFATE CONCENTRATIONS IN ALL NON- NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB AND /� /� /�/� /� THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. ASH LAYERS WITH LAMA AND NON —LAMA CCR SOURCES AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL WAS COLLECTED ON JUNE 13, 2016. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE REPORT COORDINATE SYSTEM FIPS3200(NADa3). ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA EAST ASH BASIN ■f WEST AS BASIN . , ya 9 4 % a t 1 e LEGEND %' DUKE GRAPHIC SCALE 710 0 710 1,420 ■ REFERENCE LOCATION ENERGY (IN FEET) TDS > 500 mg/L PROGRESS ASH BASIN WASTE BOUNDARY DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: B. ELLIOTT DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY APPROVED BY: K. CAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY n MT�ry� J�/ G www.synterracorp.com NOTES: FIGURE 5-9 ALL BOUNDARIES ARE APPROXIMATE. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB AND SIMULATED APRIL 2019 TDS CONCENTRATIONS IN ALL NON -ASH THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. /� /� /�/� /� LAYERS WITH LAMA AND NON —LAMA CCR SOURCES AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE REPORT COORDINATE SYSTEM FIPS3200(NADa3). ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA 420 Ado O Yj g20 O 46o O"s 0 o Ado a ® w s O EA ASH. , 0 ASIN d 490 1 r � WEST SH,,' ®490 ♦ _ ti; , F' vYa ♦ V 4%� ♦ � 4Jry r. S00 460 O LEGEND DUKE GRAPHIC SCALE 710 0 710 1.420 -DRAINS ENERGY PONDED WATER AREAS THAT WERE DECANTED (IN FEET) —HYDRAULIC HEAD 10' INTERVAL PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 -ASH BASIN WASTE BOUNDARY REVISED BY.' B. ELLIOTT DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY — YPROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY synTe www.synterracorp.com NOTES: ALL BOUNDARIES ARE APPROXIMATE. FIGURE 6-1 WAB IS EXPECTED TO BE DECANTED BY JULY 2020. SIMULATED HYDRAULIC HEADS IN UPPER FRACTURED BEDROCK IN CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN AFTER DECANTING OF WAB FOR JULY 2020 MODEL LAYER 15. STREAMS ARE INCLUDED IN THE MODELAS DRAINS. LAKES, PONDS, CHANNELS AND UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING PONDED WATER IN THE ASH BASIN ARE INCLUDED IN MODEL AS GENERAL HEAD ZONES. REPORT /� /� AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. ROXB ORO STEAM ELECTRIC PLANT AERIAL WAS COLLECTED ON JUNE 13, 2016. DRAWINGHASBEEN SET WI TH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83AND NAVD88). 420 420 420 O � O430 43p 430 ♦ o g �0 420 420 AZ � 430 L - o CO 5 O O ti 5 ♦ � � � 80 4g0 ,+, � • rn "o,d Ng0 CAO TAS Soo �0 BASIN s�o p'� 430 _ Y ' �_ . 440 . ♦' 00, + 47 9 .,T 90 GV^ 6 ? � '� •"' < 540 o & _J,490 490 p lk ' S20 530 O S�0 S00 A h 61 n �60 460 460 <n y`� 450 4S 0 gJp � 530 rn 04�' 0 480 �, 490 g) 0 500 LEGEND —' FLOW WITHIN LOCAL SYSTEM in —' FLOW OUTSIDE LOCAL SYSTEM Q cP0 t�h0 GROUNDWATER LEAVING LOCAL SYSTEM Ie WATER SUPPLY WELLS — LOCALASH BASIN GROUNDWATER FLOW SYSTEM ('DUKE GRAPHICSCALE 710 0 710 1,420 —HYDRAULIC HEAD (FEET) ENERGY —DRAINS (IN FEET) QPONDED WATER AREAS THAT WERE DECANTED PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 —ASH BASIN WASTE BOUNDARY REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY APPROVED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY A ,,,,,,�� PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY sy 1 www.s nterracor .com NOTES: ALL BOUNDARIES ARE APPROXIMATE. ARROWS INDICATE INFERRED FLOW DIRECTION ONLY, NOT FIGURE 6-2 MAGNITUDE. SIMULATED LOCAL ASH BASIN GROUNDWATER FLOW SYSTEM IN WAB IS EXPECTED TO BE DECANTED BY JULY 2020. UPPER FRACTURED BEDROCK IN JULY 2020 CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN AFTER DECANTING OF WAB IN MODEL LAYER 15. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT N ARE INCLUDED IN MODELASAND PONDED WATER NHEAMS ARE E THE DRAINS. ENERAL HEAD ZON ZONES. TTASH BASI ROXBORO STEAM ELECTRIC PLANT AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. SEMORA, NORTH CAROLINA DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83AND NAVD88). LEGEND DUKE GRAPHIC SCALE 710 0 710 1,420 REFERENCE LOCATION tnENERGY BORON 700 - 4,000 Ng/L (IN FEET) BORON > 4,000 Ng/L PROGRESS DRAWN BY: R. YU DATE: 11/18/2019 -ASH BASIN WASTE BOUNDARY REVISED BY.' B. ELLIOTT DATE: 12/12/2019 ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: K. LAWING DATE: 12/12/2019 �lp APPROVED BY: K. LAWING DATE: 12/12/2019 SOLID WASTE LANDFILL BOUNDARY PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY synTena www.synterracorp.com NOTES: FIGURE 6-3a ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH EASTASH BASIN CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR zoza. LAYERS WITH CAMA AND NON-CAMA CCR SOURCES WHEN EAB NON-CAMACCRSOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OF EAB AND CLOSURE -IN -PLACE IS COMPLETED THE DECOMMISSIONED SLUICE LINE CORRIDOR TDTHE NORTH DFWAB. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL PHOWASTO RAPHY LLECTEOONJU E FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. ROXBORO STEAM ELECTRIC PLANT DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83). 1 '. ... a b. ■ EAST ASH BASIN '' rf ■4.; N' ♦ �+.♦ LEGEND ■ REFERENCE LOCATION BORON 700 -4,000 Ng/L BORON > 4,000 Ng/L —ASH BASIN WASTE BOUNDARY - ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY - SOLID WASTE LANDFILL COMPLIANCE BOUNDARY BOUNDARIES ARE APPROXIMATE. IT ASH BASIN CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR -CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB AND DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. IAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. IAL WAS COLLECTED ON JUNE 13, 2016. WING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE RDINATE SYSTEM RIPS 3200 (NAD83). t' DUKE ENERGY PROGRESS R. n GRAPHIC SCALE 710 0 710 1,420 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: B. ELLIOTT DATE: 12/12/2019 CHECKED BY: K. LAWING DATE: 12/12/2019 APPROVED BY: K. LAWING DATE: 12/12/2019 PROJECT MANAGER: C. EADY FIGURE 6-3b SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS WITH CAMA AND NON-CAMA CCR SOURCES WHEN WAB CLOSURE -IN -PLACE IS COMPLETED UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA a. ■ y EASTASH BASIN ■ e - r LEGEND 710 0 710 1,420 tn DUKE GRAPHIC SCALE ■ REFERENCE LOCATION ENERGY BORON 700 -4,000 Ng/L (IN FEET) PROGRESS BORON > 4,000 Ng/L DRAWN BY: R. YU DATE: 11/18/2019 -ASH BASIN WASTE BOUNDARY REVISED BY: B.ELLIOTT DATE: 12/12/2019 CHECKED BY: K. LAWING DATE: 12/12/2019 J�lp - - ASH BASIN COMPLIANCE BOUNDARY APPROVED BY: K. CAWING DATE: 12/12/2019 SOLID WASTE LANDFILL BOUNDARY PROJECT MANAGER: C. EADY — - SOLID WASTE LANDFILL COMPLIANCE BOUNDARY-` .I I G www.synterracorp.com NOTES: FIGURE 6-3c ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EABA MODEL LAYERS WITH CAMAAND NON-CAMA CCR SOURCES WHEN THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. CLOSURE -BY -EXCAVATION IS COMPLETED AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200(NAD83). SEMORA, NORTH CAROLINA ROX C901 039010 Y o� �E:— `� �,;�a� Nam_ aJ• L%1 ram.! q l O 111 ���- �lyr�ly I Ir�.��•�_ • Q .�, Q � � pIJKf � �ROX C90i039 010 0� 006 — B aw— - _,Y+J I\��✓ ROMORO STEAM SA70N n l 'A04rR.,y ` �NOFILE IXPANSION FINAL COVER PLRN NDT FOR C907.ROX 020 006 B DUKE DRAWN BY:DATE: 11/1/209 FIGURE 6-4 CLOSURE -BY -EXCAVATION DESIGN USED IN ENERGY® REVISED BY:: W.. PRATER DATE: 12/122/201,9 PROGRESS CHECKED BY: K. CAWING DATE: 12/12/2019 SIMULATIONS (FROM WOOD, 2019C AND 2019d). APPROVED BY: K. LAWING DATE: 12/12/2019 PROJECT MANAGER: C. EADY UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT WnTerra SEMORA, NORTH CAROLINA www.synterracorp.com F r' r 9ri EAST ASH BASIN R i•w4 t . s Y.y ti44 `¢ 7 �. WEST BASIN 110, a' P . l 5 trl.ii^Tv.n.. ,:vr# Y 6 �i�j�'l.'�F.F, • ' ry tl f': �1.YIY.�O Y4���'+.5 -- ���,f•. ��•f, �>r CRY. �r ..,+�y.��r .w,q; LEGEND DRAINS i DEEP MIXING WALL PONDED WATER ASH BASIN WASTE BOUNDARY - -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY INDUSTRIAL LANDFILL WITH PROPOSED LANDFILL EXPANSION It DUKE ENERGY PROGRESS r 4 �(y Y(4 p y # r, • -4 5 , is z a ` 1 � 1 hyyy��e 0 � a rr— GRAPHIC SCALE 710 0 710 1,420 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: B. ELLIOTT DATE: 12/10/2019 CHECKED BY: K. LAWING DATE: 12/10/2019 APPROVED BY: K. LAWING DATE: 12/10/2019 PROJECT MANAGER: C. EADY ALL BOUNDARIES ARE APPROXIMATE. FIGURE V—C STREAMS ARE INCLUDED IN THE MODELAS DRAINS. PONDEDWATERINTHEWAB MODEL SETUP FOR CLOSURE —BY —EXCAVATION SCENARIO REPSURROUNDINTHEPGUS ED WATER IMPOUNDMENT REPRESENIGN. RINGS AIN STREAM UPDATED GROUNDWATER FLOW AND TRANSPORT SURROUNDING THE WAS IMPOUNDMENT REPRESENTS SPRINGS AND STREAMS THAT MAY FORM IN THE EXCAVATED AREA. THE PONDED WATER IN THE EAB IS THE PROPOSED STORMWATERBASIN. THE DRAIN ACROSS THE SOUTH PART OF THELANDFILL MODELING REPORT REPRESENTS AN UNER-LINER DRAIN TO CONTROL THE GROUNDWATER LEVEL. AERIALPHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. ROXBORO STEAM ELECTRIC PLANT AERIAL WAS COLLECTED ON JUNE 13, 2016. DRAWING HAS BEEN SET WI TH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83). sr�o4 a 00 430 430 430 v 470 A20 ti� o ( 41p 420 � v d 470 410 20 e e }, 1 440 � 14704 � � ♦•,` a 420 0 �3o A 13 0 4Sp ASO 4g0 srSO r� 470 i EASTASH BASIN 480 0 S40 LEGEND 'FLOW WITHIN LOCAL SYSTEM o h t� _'FLOWOUTSIDELOCALSYSTEM 7�tw -3110- GROUNDWATER LEAVING LOCAL SYSTEM h Ie DOMESTIC WELLS �O LOCALASH BASIN GROUNDWATER FLOW SYSTEM w, O —HYDRAULIC HEAD (FEET) -DRAINS �' DUKE 720 GRAPHIC SCALE 0 720 1,440 PONDED WATER ENERGY � DEEP MIXING WALL (IN FEET) PROGRESS -ASH BASIN WASTE BOUNDARY DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: K. LAWING DATE: 12/20/2019 SOLID WASTE LANDFILL BOUNDARY APPROVED BY: K. LAWING DATE: 12/20/2019 SOLID WASTE LANDFILL COMPLIANCE BOUNDARY ^ ,„,�^ PROJECT MANAGER: C. EADY INDUSTRIAL LANDFILL WITH PROPOSED LANDFILL EXPANSION W ' C www.synterracorp.com NOTES: FIGURE 6-6 ALL BOUNDARIES AREAPPROXIMATE.ARROWSINDICATE INFERRED FLOW DIRECTION ONLY, MA NOT MAGNITUDE.ITUDE. SIMULATED LOCAL ASH BASIN GROUNDWATER FLOW SYSTEM IN CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN AFTER DECANTING OF WAB IN MODEL LAYER 15. UPPER FRACTURED BEDROCK AFTER CLOSURE -BY -EXCAVATION STREAMS ARE INCLUDED IN THE MODEL AS DRAI INS. LAKES, PONDS, CHANNELS AND UPDATED GROUNDWATER FLOW AND TRANSPORT PONDED WATER IN THE ASH BASIN ARE INCLUDED IN MODEL AS GENERAL HEAD ZONES. MODELING REPORT AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. /� ROXB ORO STEAM ELECTRIC PLANT DRAWINGHASBEEN SET WI TH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83AND NAVD88). iiL3, 1 LEGEND REFERENCE LOCATION DUKE tn BORON 7 Ng/L ENERGY BORON > 4,000 00 pg/ Ng/L 4, PROGRESS -ASH BASIN WASTE BOUNDARY r ASH BASIN COMPLIANCE BOUNDARY �� SOLID WASTE LANDFILL BOUNDARY r SOLID WASTE LANDFILL COMPLIANCE BOUNDARY r INDUSTRIAL LANDFILL WITH PROPOSED LANDFILL EXPANSION synTerra GRAPHIC SCALE 710 0 710 1,420 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: D. WHATLEY DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY NOTES: FIGURE 6-7a ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. LAYERS WITH CAMA AND NON-CAMA CCR SOURCES NON-CAMA CCR SOURCESINCLUDE THE GSA/DFAHASOURCES TOTHE NORTH OF APPROXIMATELY 20 YEARS AFTER CLOSURE -BY -EXCAVATION EAB AND THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. ROXBORO STEAM ELECTRIC PLANT DRAWINGHASBEEN SET WI TH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83). a, I e 1 » f. ■ y 4 » O { 1 n � ■b. a. `. ®° d. 0 EASTASH BASIN ;.. WEST AS BASIN "z LEGEND ■ REFERENCE LOCATION BORON 700 -4,000 Ng/L BORON > 4,000 Ng/L —ASH BASIN WASTE BOUNDARY - ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY - SOLID WASTE LANDFILL COMPLIANCE BOUNDARY r INDUSTRIAL LANDFILL WITH PROPOSED LANDFILL EXPANSION � r , y tDUKE ' ENERGY PROGRESS GRAPHIC SCALE 710 0 710 1,420 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: D. WHATLEY DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY NOTES: FIGURE 6-7b ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALLNON-ASH CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR2037. LAYERS WITH CAMA AND NON -LAMA CCR SOURCES NON -CA THE DECOMMISSIONED LUDE EDSLUIHELINEC RRIDHA OURCES TO THE RTOTHENORTHORTH OF FWAB. APPROXIMATELY 70 YEARS AFTER CLOSURE -BY -EXCAVATION EAB AND THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL WAS COLLECTED ON JUNE 13,2016. ROXBORO STEAM ELECTRIC PLANT CWITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FPS300(NAD3).SEMORA, NORTH CAROLINA LEGEND DUKE GRAPHICSCALE 710 0 710 1,420 REFERENCE LOCATION tnENERGY BORON 700 - 4,000 Ng/L (IN FEET) BORON > 4,000 Ng/L PROGRESS DRAWN BY: R. YU DATE: 11/18/2019 ASH BASIN WASTE BOUNDARY REVISED BY: D. WHATLEY DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY 4 1p CHECKED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY synTena www.synterracorp.com NOTES: FIGURE 6-7c ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED INYEAR237. LAYERS WITH CAMAAND NON-CAMA CCR SOURCES NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB AND THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. APPROXIMATELY 120 YEARS AFTER CLOSURE -BY -EXCAVATION AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL WAS COLLECTED ON JUNE 13,2016. ROXBORO STEAM ELECTRIC PLANT D WING HAS BEEN SET COORDINATE SYSTEM FPSI300(NADJ3).TION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA LEGEND REFERENCE LOCATION DUKE tn GRAPHIC SCALE 710 0 710 1,420 BORON 700 -4,000 Ng/L ENERGY BORON > 4,000 Ng/L (IN FEET) PROGRESS —ASH BASIN WASTE BOUNDARY DRAWN BY: R.YU DATE:11/18/2019 ASH BASIN COMPLIANCE BOUNDARY REVISED BY: D. WHATLEY DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY APPROVED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL COMPLIANCE BOUNDARYTe PROJECT MANAGER: C. EADY + INDUSTRIAL LANDFILL WITH PROPOSED LANDFILL EXPANSION syn NOTES: FIGURE 6-7d ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE-BY-EXCAVATI ON SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. LAYERS WITH CAMAAND NON-CAMA CCR SOURCES NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB APPROXIMATELY 170 YEARS AFTER CLOSURE -BY -EXCAVATION AND THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL WAS COLLECTED ON JUNE 13,2016. ROXBORO STEAM ELECTRIC PLANT D WING HAS BEEN SET COORDINATE SYSTEM FPSI300(NADJ3).TION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA LEGEND � GRAPHIC SCALE DUKE 710 0 710 1,420 REFERENCE LOCATION EFFLUENT DISCHARGE CANAL tnENERGY N FEET) SASH BASIN WASTE BOUNDARY PROGRESS ASH BASIN COMPLIANCE BOUNDARY DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: D. WHATLEY DATE: 12/10/2019 SOLID WASTE LANDFILL BOUNDARY �lp CHECKED BY: K. LAWING DATE: 12/10/2019 SOLID WASTE LANDFILL COMPLIANCE BOUNDARY APPROVED BY: K. LAWING DATE: 12/10/2019 PROJECT MANAGER: C. EADY INDUSTRIAL LANDFILL WITH PROPOSED LANDFILL EXPANSION synTena www.synterracorp.com NOTES: FIGURE 6-8 ALL BOUNDARIES ARE APPROXIMATE. REFERENCE LOCATIONS FOR TIME SERIES DATASETS AERIAL PHOWASTO RAPHY LLECTEOONJU E FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. UPDATED GROUNDWATER FLOW AND TRANSPORT DRAW ING HAS BEEN SET IJTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FPS300(NAD3). MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA EAB Location a 1,400 1,200 3 1,000 0 800 c a� U 0 600 U 0 400 L 0 m 200 0 1,400 Saprolite, depth = 7 ft. Transition Zone, depth = 22 ft. Fractured rock, depth = 54 ft. Fractured rock, depth = 114 ft. Bedrock, depth = 256 ft. Bedrock, depth = 370 ft. Bedrock, depth = 439 ft. EAB-1 Max. all layer — — 2L Std = 700 ug/L — — — — Ar 0 0 k.0 lD Cr) 0 r -I N 1,200 as 3 c 1,000 0 800 c a� U C 600 U C 0 400 0 m 200 0 0 a) r -I 0 0 N 0 0 0 0 lD lD lD lD rl N M It N N N N Year EAB Location b Saprolite, depth = 6 ft. Transition Zone, depth = 17 ft. Fractured rock, depth = 4 ft. Fractured rock, depth = 95 ft. Bedrock, depth = 254 ft. Bedrock, depth = 380 ft. _ _ _ Bedrock, depth = 453 ft. EAB-2 Max. all layer 2L Std = 700 ug/L 0 0 0 0 lD lD lD QO r -I N M 't N N N N Year Reference locations shown in Fig. 6-8 FIGURE 6-9a 40)DUKE DRAWN BY: R. YU DATE: 11/18/2019 SUMMARY OF MAXIMUM BORON CONCENTRATIONS ENERGY® REVISED BY: W. PRATER DATE: 12/12/2019 AS FUNCTIONS OF TIME AND STRATIGRAPHIC LAYER PROGRESS CHECKED BY: K. LAWING DATE: 12/12/2019 AT EAB REFERENCE LOCATIONS a AND b FOR THE APPROVED BY: K. LAWING DATE: 12/12/2019 CLOSURE -BY -EXCAVATION SCENARIO PROJECT MANAGER: C. EADY UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT WnTerra www.synterracorp.com SEMORA, NORTH CAROLINA EAB Location c 2,000 Saprolite, depth = 7 ft. Aomb 1,800 Transition Zone, depth = 20 ft. 3 1,600 Fractured rock, depth = 51 ft. 0 1,400 Fractured rock, depth = 109 ft. a 1,200 Bedrock, depth = 278 ft. L Bedrock, depth = 412 ft. 1,000 c Bedrock, depth = 488 ft. u 800 EAB-3 Max. all layer 0 600 — — 2L Std = 700 ug/L MY 400 Im 200 0 � QO �D OfV N N (V N Year EAB Location d . m 5,000 O 0 4,000 3,000 U c O u 2,000 c O L O °a 1,000 ,Z: Saprolite, depth =6 ft. Transition Zone, depth = 17 ft. Fractured rock, depth = 44 ft. Fractured rock, depth = 96 ft. Bedrock, depth = 257 ft. Bedrock, depth = 386 ft. Bedrock, depth = 459 ft. EAB-4 Max. all layer 2L Std = 700 ug/L � QO QO QO QO Ql O r-i (V M c-I fV [V (V (V [V DUKE ENERGY® PROGRESS 14' synTerra Year Reference locations shown in Fig. 6-8. FIGURE 6-9b DRAWN BY: R. YU DATE: 11/18/2019 SUMMARY OF MAXIMUM BORON CONCENTRATIONS REVISED BY: W. PRATER DATE: 12/12/20,9 AS FUNCTIONS OF TIME AND STRATIGRAPHIC LAYER CHECKED BY: K. LAWING DATE: 12/12/2019 AT EAB REFERENCE LOCATIONS c AND d FOR THE APPROVED BY: K. LAWING DATE: 12/12/2019 CLOSURE -BY -EXCAVATION SCENARIO PROJECT MANAGER: C. EADY UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT www.synterracorp.com SEMORA, NORTH CAROLINA WAB Location e J 9,000 Saprolite, depth = 10 ft. 3 8,000 Transition Zone, depth = 29 ft. c 0 7,000 Fractured rock, depth = 56 ft. m ; 6,000 Fractured rock, depth = 104 ft. 5,000 Bedrock, depth = 237 ft. 0 Bedrock, depth = 346 ft. 4,000 0 i Bedrock, depth = 412 ft. I0 3,000 WAB-1 Max. all layer 2,000 — — 2L Std = 700 ug/L 1,000 0 0 Q 0 QO 0 0 0 0 QO �O t.D � OfV N N N N Year WAB Location f 40,000 Saprolite, depth = 7 ft. 35,000 Transition Zone, depth = 22 ft. 30,000 Fractured rock, depth = 51 ft. 0 25,000 Fractured rock, depth = 104 ft. L Bedrock, depth = 254 ft. a) c 20,000 Bedrock, depth = 375 ft. 0 u 15,000 Bedrock, depth = 446 ft. c p 10,000 WAB-2 Max. all layer °a — — 2L Std = 700 ug/L 5,000 � � � LD QD a) O r-I N M lcl* r-I N N N N N Year Reference locations shown in Fig. 6-8 FIGURE 6-9c 40)DUKE DRAWN BY: R. YU DATE: 11/18/2019 SUMMARY OF MAXIMUM BORON CONCENTRATIONS ENERGY® REVISED BY: W. PRATER DATE: 12/12/2019 AS FUNCTIONS OF TIME AND STRATIGRAPHIC LAYER PROGRESS CHECKED BY: K. LAWING DATE: 12/12/2019 AT WAB REFERENCE LOCATIONS a AND f FOR THE APPROVED BY: K. LAWING DATE: 12/12/2019 PROJECT MANAGER: C. EADY CLOSURE -BY -EXCAVATION SCENARIO UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT www.synterracorp.com WnTerra SEMORA, NORTH CAROLINA i r b 460 EAST ASH BASIN • ri,' 480 470 LEGEND %' DUKE GRAPHIC SCALE 340 0 340 680 Ge EXTRACTION WELLS ENERGY CLEAN WATER INFILTRATION WELLS (IN FEET) PROGRESS -HYDRAULIC HEAD (FEET) DRAWN BY: R. YU DATE: 11/18/2019 -ASH BASIN WASTE BOUNDARY REVISED BY: R. KIEKHAEFER DATE: 12120/2019 ASH BASIN COMPLIANCE BOUNDARY �lp CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 SOLID WASTE LANDFILL BOUNDARY — Y�� PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY Wn www.synterracorp.com NOTES: FIGURE 6-10 ALL BOUNDARIES ARE APPROXIMATE. SIMULATED HYDRAULIC HEADS IN THE UPPER FRACTURED BEDROCK CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN AFTER CLOSURE -BY -EXCAVATION FOR ZONE FOR THE CLOSURE -BY -EXCAVATION SCENARIO WITH ACTIVE MODEL LAYER 1s. GROUNDWATER REMEDIATION THE REMEDIATION SYSTEM SFiowN WAS DESIGNED FOR ozL COMPLIANCE By 2029. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT TEDONFEBRUAPHOTOGRAPHY BTAINE1 FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED COLLECTED ON FEBRUARV 6, 2017. ROXBORO STEAM ELECTRIC PLANT DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83AND NAVD88). IMULATED WITHOUT NON-CAMA CCR SOURCES EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOUR EAST ASH BASIN LEGEND ■ REFERENCE LOCATION ANON—CAMA CCR SOURCE ZONES BORON 700 — 4,000 fag/L BORON > 4,000 fag/L ASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY ALL BOUNDARIES ARE APPROXIMATE. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 ■d. ■d'�► `o DUKE GRAPHIC SCALE t 340 0 340 680 RGY IN FEET) PROGRESS DRAWN BY: D. WHATLEY DATE: 11/18/2019 REVISED BY: W. PRATER DATE: 12/20/2019 J�lp CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 SynTerra PROJECT MANAGER: C. EADY www_svnterra rnrn.rnm FIGURE 6-11 SIMULATED APRIL 2019 MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS DOWNGRADIENT OF THE EAST ASH BASIN UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA IMULATED WITHOUT NON-CAMA CCR SOURCES r d. EAST ASH BASIN -;A I �4 S SIMULATED WITH NON-CAMA CCR SOURCES - ��,._�;.. lie 7� �� 4»• � � 1 EAST ASH BASIN LEGEND ii� EXTRACTION WELLS CLEAN WATER INFILTRATION WELLS ■ REFERENCE LOCATION =NON-CAMA CCR SOURCE ZONES BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L —ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY -SOLID WASTE LANDFILL COMPLIANCE BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). It DUKE ENERGY PROGRESS 11161p synTena GRAPHIC SCALE 340 0 340 680 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 6-12a SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA SIMULATED WITHOUT NON-CAMA CCR SOURCES - r � r .r e t d. EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES ♦ I 00 � 1 .ter • _ � � � � . � � � . . �C. EAST ASH BASIN ; � r � LEGEND t DUKE ORAP"'C SCALE 340 0 340 680 EXTRACTION WELLS ENERGY (IN FEET) CLEAN WATER INFILTRATION WELLS PROGRESS DRAWN BY: R. YU DATE: 11/18/2019 ■ REFERENCE LOCATION REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 ANON-CAMA CCR SOURCE ZONES APPROVED BY: K. LAWING DATE: 12/19/2019 BORON 700 -4,000 fag/L WWnTerm PROJECT MANAGER: C. EADY BORON > 4,000 fag/L www.synterracorp.com ASH BASIN WASTE BOUNDARY FIGURE 6-12b ASH BASIN COMPLIANCE BOUNDARY SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE SOLID WASTE LANDFILL BOUNDARY CLOSURE -BY -EXCAVATION SCENARIO AFTER 30 YEARS SOLID WASTE LANDFILL COMPLIANCE BOUNDARY OF ACTIVE GROUNDWATER REMEDIATION NOTES: UPDATED GROUNDWATER FLOW AND TRANSPORT ALL BOUNDARIES ARE APPROXIMATE_ MODELING REPORT CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. ROXBORO STEAM ELECTRIC PLANT NON-CAMA CCR SOURCES INCLUDE THE GSAIDFAHASOURCES TOTHE NORTH OFEAB. SEMORA, NORTH CAROLINA AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2919. AERIAL WAS COLLECTED ON FEBRUARY 6, 2917. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM HPS 3299 (NAD83L. IMULATED WITHOUT NON-CAMA CCR SOURCES r ♦ r if _ . 14%C. f EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES 1 AST ASH BASIN LEGEND EXTRACTION WELLS CLEAN WATER INFILTRATION WELLS ■ REFERENCE LOCATION ANON—CAMACCR SOURCE ZONES BORON 700 — 4,000 fag/L BORON > 4,000 fag/L ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 201 DRAWING HAS BEEN SET WITHA PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). E It DUKE ENERGY PROGRESS 1161p synTena ■d. ■ d.W V GRAPHIC SCALE 340 0 340 680 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER:C. EADY FIGURE 6-12c SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 80 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA SIMULATED WITHOUT NON—CAMA CCR SOURCES `all r ♦ r r EAST ASH BASIN ■ SIMULATED WITH NON—CAMA CCR SOURCES �..� oo RAW d. F .. *IV EAST ASH BASIN , LEGEND %' DUKE GRAPHIC SCALE 340 0 340 680 EXTRACTION WELLS ENERGY (IN FEET) CLEAN WATER INFILTRATION WELLS PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 ■ REFERENCE LOCATION 1p REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 QNON-CAMA CCR SOURCE ZONES APPROVED BY: K. LAWING DATE: 12/19/2019 BORON 700 - 4,000 l synTena PROJECT MANAGER: C. EADY BORON > 4,000 l www.synterracorp.com ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY FIGURE 6-12d SOLID WASTE LANDFILL BOUNDARY SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL SOLID WASTE LANDFILL COMPLIANCE BOUNDARY NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION NOTES: SCENARIO AFTER 130 YEARS OF ACTIVE GROUNDWATER REMEDIATION ALL BOUNDARIES ARE APPROXIMATE. A A A TRANSPORT CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED INYEAR 2037. UPDATED GROUNDWATER FLOW AND TR" -NSPORT NON-CAMACCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. MODELING REPORT AERIAL PHOTOGRAPHY OBTAINED FROM ES RI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FE BRUARY 6, ROXBORO STEAM ELECTRIC PLANT 2017. SEMORA, NORTH CAROLINA DRAWING HAS BEEN SET WITHA PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (Ni SIMULATED WITHOUT NON-CAMA CCR SOURCES ` r r d. EAST ASH BASIN ■ • SIMULATED WITH NON-CAMA CCR SOURCES r 00, , ,� s s� ■d EAST ASH BASIN ; LEGEND EXTRACTION WELLS CLEAN WATER INFILTRATION WELLS ■ REFERENCE LOCATION ANON-CAMA CCR SOURCE ZONES BORON 700 - 4,000 fag/L BORON > 4,000 fag/L ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 NAD83). GRAPHIC SCALE t DUKE N ENERGY 340 0 340 680 IN FEET) PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 J�lp REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 WnTena PROJECT MANAGER: C. EADY www.synterracorp.com FIGURE 6-12e SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 180 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA millimiliNk— ""I A Is SIMULATED WITHOUT NON-CAMA CCR SOURCES L. 'r o .,. .a 47�d. EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES xe __A: simmmmliil-% 4 - EAST ASH BASIN LEGEND DUKE tENERGY GRAPHIC SCALE 340 0 340 Ego EXTRACTION WELLS (IN FEET) PROGRESS CLEAN WATER INFILTRATION WELLS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 ■ REFERENCE LOCATION CHECKED BY: K. LAWING DATE: 12/19/2019 ANON-CAMACCR SOURCE ZONES APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER'C. EADY SULFATE > 250 mg/L synTena www.synterracorp.com ASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY FIGURE 6-13 SOLID WASTE LANDFILL BOUNDARY SIMULATED MAXIMUM SULFATE CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE SOLID WASTE LANDFILL COMPLIANCE BOUNDARY CLOSURE -BY -EXCAVATION SCENARIO AFTER 9 YEARS OF NOTES: ACTIVE GROUNDWATER REMEDIATION ALL BOUNDARIES ARE APPROXIMATE UPDATED GROUNDWATER FLOW AND TRANSPORT CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2031. MODELING E I I N G REPORT L IIOSTEAM NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OFEAB. +D /L/� ROXBOR�YO STELA��IM17ELECTRIC PLANT AERIAL PHOTOGRAPHY OBTAINEDFROM ESRI ON DECEMBER4,2619. AERIAL WAS COLLECTED ON FEBRUARY6, 2017. SENORA, NORTH CAROLINA DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINASTATE PLANE COORDINATE SYSTEM FIPS 3266 (NAD63). SIMULATED WITHOUT NON-CAMA CCR SOURCES r ' EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES ® 1 Alp ,. -`r'- Ali a, c. EAST ASH BASIN LEGEND EXTRACTION WELLS CLEAN WATER INFILTRATION WELLS ■ REFERENCE LOCATION ANON-CAMA CCR SOURCE ZONES TDS > 500 mg/L ASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY - SOLID WASTE LANDFILL COMPLIANCE BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2031. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FPS 3200 (NAD133). DUKEGRAPHIC SCALE It EEN RGY 340 G 340 Ego (IN FEET) PROGRESS DRAWN BY: R.YU DATE: 11/111/2019 1�lp REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 WnTena PROJECT MANAGER C. EADY www.synterracorp.com FIGURE 6-14 SIMULATED MAXIMUM TDS CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA DUKE ENERGY® PROGRESS 14-7 synTerra 1 - 1� aomam�� NensR��ur��a.�LT FNPl��LCCWERGR,V]ES -NIEST ASH B45N _ ROX_C901.008.011 moo. aim � v ROX C999.'ZI-011 FIGURE 6-15 DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: W. PRATER DATE: 12/12/2019 CLOSURE -IN -PLACE DESIGN USED IN CHECKED BY: K. LAWING DATE: 12/12/2019 SIMULATIONS (FROM WOOD, 2019a AND 2019b). APPROVED BY: K. LAWING DATE: 12/12/2019 UPDATED GROUNDWATER FLOW AND PROJECT MANAGER: C. EADY TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT SEMORA, NORTH CAROLINA www.synterracorp.com C /420 420 ❑ q,p 4g0 410 410 4�0 sty, `r 420 J' �p q p 430 430 430. o 2p 440 I, 1 hoo 0 410 420 420 a ` o q) O "�� p 10 Im 410 1, ,a° 1 490 1 po 0 480 q9p a N � I 5 • I qgp Spp 440 j q80 i� e i� J LEGEND —'FLOW WITHIN LOCAL SYSTEM —'FLOW OUTSIDE LOCAL SYSTEM GROUNDWATER LEAVING LOCAL SYSTEM ij� WATER SUPPLY WELLS — LOCALASH BASIN GROUNDWATER FLOW SYSTEM —DRAINS —HEAD (FEET) _AREAS CLOSED WITH AN ENGINEERED CAP SYSTEM —ASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY BOUNDARIES ARE APPROXIMATE. ARROWS INDICATE INFERRED FLOW DIRECTION ONLY MAGNITUDE. TOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN AFTER DECANTING OF WAB IN MODEL =R 15. EAMS ARE INCLUDED IN THE MODELAS DRAINS. LAKES, PONDS, CHANNELS AND DIED WATER IN THE ASH BASIN ARE INCLUDED IN MODEL AS GENERAL HEAD ZONES. IAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. IAL WAS COLLECTED ON JUNE 13. 2016. orN\ >I-//" j 53p y4o ❑� 490 490 �� � 540 O 490 � � / —T m — M / No h 540 Sep C 460 qS0 450 DUKE GRAPHIC SCALE t 700 0 700 1,400 ENERGY(IN FEET) PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/20/2019 1�� CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 PROJECT MANAGER: C. EADY FIGURE 6-17 SIMULATED LOCAL ASH BASIN GROUNDWATER FLOW SYSTEM IN UPPER FRACTURED BEDROCK AFTER CLOSURE -IN -PLACE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA WING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE RDINATE SYSTEM RIPS 3200 (NAD83AND NAVD88). ,. a. `. ■ ,.. b. c1 d. 0 ■ d � EASTASH ° BASIN +lfd ■f WEST ASHY' BASINP • ♦ - ". a 1 f _ R T ,• LEGEND DUKE GRAPHIC SCALE 710 0 710 1,420 ■ REFERENCE LOCATION ENERGY BORON 700 -4,000 Ng/L (IN FEET) PROGRESS BORON > 4,000 Ng/L DRAWN BY: R. YU DATE: 11/18/2019 —ASH BASIN WASTE BOUNDARY REVISED BY: D. WHATLEY DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY APPROVED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY PROJECT PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARYna syn FIGURE 6-18a ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE- IN -PLACE ESTIMATED TOSTASHBASIN. ECOMPLETED INYEAR 2024FOR EAST ASH BASIN AND 2027 FOR WEST ASH BASIN. ND2027FORW MODEL LAYERS WITH CAMA AND NON-CAMA CCR SOURCES NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB APPROXIMATELY 20 YEARS AFTER CLOSURE -IN -PLACE AND THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL WAS COLLECTED ON JUNE I3,2016. ROXBORO STEAM ELECTRIC PLANT OF NORTH CAROLINA STATE PLANE CCOORDINATE SEMORA, NORTH CAROLINA SYSTEM FPSI300(NADJ3).TION "' $ . ■ f WEST BA S a. ■ - - b. 6.- ■ d. 0 EAST ASH BASIN LEGEND DUKE GRAPHIC SCALE 710 0 710 1,420 ■ REFERENCE LOCATION ENERGY BORON 700 -4,000 Ng/L (IN FEET) PROGRESS BORON > 4,000 Ng/L DRAWN BY: R. YU DATE: 11/18/2019 ASH BASIN WASTE BOUNDARY REVISED BY: D. WHATLEY DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY APPROVED BY: K. CAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY-` .I I G www.synterracorp.com NOTES: FIGURE 6-18b ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024FOR EAST ASH BASIN AND 2027 FOR WEST ASH BASIN. MODEL LAYERS WITH CAMA AND NON-CAMA CCR SOURCES NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB APPROXIMATELY 70 YEARS AFTER CLOSURE -IN -PLACE AND THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OFWAB. UPDATED GROUNDWATER FLOW AND TR/�ANSPORT MODELING REPORT AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. ROXBORO STEAM ELECTRIC PLANT DRAWINGHASBEEN SET WI TH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83). d ■ 1 EAST ASH - BASIN �P s P j♦ � f ■t. WEST A BAST e y 'a LEGEND DUKE tn GRAPHIC SCALE 710 0 710 1,420 ■ REFERENCE LOCATION ENERGY BORON 700 -4,000 Ng/L (IN FEET) PROGRESS BORON > 4,000 Ng/L DRAWN BY: R. YU DATE: 11/18/2019 ASH BASIN WASTE BOUNDARY REVISED BY: D. WHATLEY DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 - ASH BASIN COMPLIANCE BOUNDARY APPROVED BY: K. LAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY PROJECT MANAGER: C. EADY - SOLID WASTE LANDFILL COMPLIANCE BOUNDARY -`I I G NOTES: FIGURE 6-18c ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024FOR MODEL LAYERS WITH CAMA AND NON-CAMA CCR SOURCES EAST ASH BASIN AND 2027 FOR WEST ASH BASIN. NON-CAMA CCR SOURCESINCLUDE THE GSA/DFAHASOURCES TOTHE NORTH OF APPROXIMATELY 120 YEARS AFTER CLOSURE -IN -PLACE EAB AND THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OF WAB. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, ROXBORO STEAM ELECTRIC PLANT 2017. AERIAL WAS COLLECTED ON JUNE 13, 2016. DRAWINGHASBEEN SET WI TH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83). �P9V m P 101 I BASIN e. b n m ^ a � n . . ■f WEST A BASIN.:, ..., a.: s i LEGEND DUKE GRAPHIC SCALE 710 0 710 1,420 ■ REFERENCE LOCATION ENERGY BORON 700 -4,000 Ng/L (IN FEET) PROGRESS BORON > 4,000 Ng/L DRAWN BY: R. YU DATE: 11/18/2019 -ASH BASIN WASTE BOUNDARY REVISED BY: D. WHATLEY DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 ASH BASIN COMPLIANCE BOUNDARY APPROVED BY: K. CAWING DATE: 12/19/2019 SOLID WASTE LANDFILL BOUNDARY PROJECT MANAGER: C. EADY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY-` .I I G www.synterracorp.com NOTES: FIGURE 6-18d ALL BOUNDARIES ARE APPROXIMATE. SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED INYEAR2024FOREAST ASH BASINAND 2027 FOR WESTASH BASIN. MODEL LAYERS WITH CAMA AND NON-CAMA CCR SOURCES NON-CAMACCRSOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEABAND APPROXIMATELY 170 YEARS AFTER CLOSURE -IN -PLACE THE DECOMMISSIONED SLUICE LINE CORRIDOR TO THE NORTH OFWAB. AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL WAS COLLECTED ON JUNE 13, 2016. DRAWINGHASBEEN SET WI TH A PROJECTION OF NORTH CAROLINA STATE PLANE REPORT ROXBORO STEAM ELECTRIC PLANT COORDINATE SYSTEM FIPS 3200 (NAD83). EAB Location a 1,400 J 1,200 0 1,000 z; L_ 800 a� 0 600 U 0 L 400 O ca 0 Saprolite, depth = 7 ft. Transition Zone, depth = 22 ft. rock, depth = 54 ft. Fractured rock, depth = 114 ft. Bedrock, depth = 256 ft. Bedrock, depth = 370 ft. Bedrock, depth = 439 ft. EAB-1 Max. all layer — — 2L Std = 700 ug/L IFractured 0 0 0 QO I�D 0 Ol 0 r-I c-I f V N • MAI �I Year EAB Location b 0 0 0 QD I�D 0 (V M It (V [V N Saprolite, depth = 6 ft. Transition Zone, depth = 17 ft. Fractured rock, depth = 4 ft. Fractured rock, depth = 95 ft. Bedrock, depth = 254 ft. Bedrock, depth = 380 ft. Bedrock, depth = 453 ft. EAB-2 Max. all layer 2L Std = 700 ug/L 0 k.DrH N M 't (V N (V (V Year Reference locations shown in Fig. 6-8. FIGURE 6-19a 40)DUKE DRAWN BY: R. YU DATE: 11/18/2019 SUMMARY OF MAXIMUM BORON CONCENTRATIONS ENERGY® REVISED BY: W. PRATER DATE: 12/12/2019 AS FUNCTIONS OF TIME AND STRATIGRAPHIC LAYER PROGRESS CHECKED BY: K. LAWING DATE: 12/12/2019 AT EAB REFERENCE LOCATIONS a AND b FOR THE APPROVED BY: K. LAWING DATE: 12/12/2019 CLOSURE -IN -PLACE SCENARIO PROJECT MANAGER: C. EADY UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT WnTerra www.synterracorp.com SEMORA, NORTH CAROLINA J aA c 0 L c a� U i 0 U 0 L 0 ca J tko 3 c 0 L c a� U i 0 U C 0 L 0 ca EAB Location c 2,000 1,800 Saprolite, depth = 7 ft. Transition Zone, depth = 20 ft. 1,600 Fractured rock, depth = 51 ft. 1,400 Fractured rock, depth = 109 ft. 1,200 Bedrock, depth = 278 ft. 1,000 Bedrock, depth = 412 ft. 800 Bedrock, depth = 488 ft. EAB-3 Max. all layer 600 — — 2L Std = 700 ug/L 400 200 0 QO � � � � � rs! (V N N N Year EAB Location d 6,000 Saprolite, depth =6 ft. 5,000 Aft.Transition Zone, depth = 17 ft. Fractured rock, depth = 44 ft. 4,000 Fractured rock, depth = 96 ft. Bedrock, depth = 257 ft. 3,000 Bedrock, depth = 386 ft. Bedrock, depth = 459 ft. 2,000 EAB-4 Max. all layer — — 2L Std = 700 ug/L 1,000 0 0 0 0 0 0 0 Ql r-I O fV r-I N (V (V M (V 't (V Year Reference locations shown in Fig. 6-8 FIGURE 6-19b 40)DUKE DRAWN BY: R. YU DATE: 11/18/2019 SUMMARY OF MAXIMUM BORON CONCENTRATIONS ENERGY® REVISED BY: W. PRATER DATE: 12/12/2019 AS FUNCTIONS OF TIME AND STRATIGRAPHIC LAYER PROGRESS CHECKED BY: K. LAWING DATE: 12/12/2019 AT EAB REFERENCE LOCATIONS c AND d FOR THE APPROVED BY: K. LAWING DATE: 12/12/2019 PROJECT MANAGER: C. EADY CLOSURE -IN -PLACE SCENARIO UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRICAL PLANT www.synterracorp.com WnTerra SEMORA, NORTH CAROLINA WAB Location e 4,500 4,000 J 3 3,500 c 0 3,000 2,500 a� c 2,000 0 U c 1,500 0 L 1,000 I0 500 0 � LO LO � QO LO r-I 0rV N N N N Year WAB Location f 40,000 35,000 wo 3 30,000 0 25,000 Q) 20,000 c 0 U 15,000 c 0 0 10,000 m 5,000 0 � Q � QO LO � � rn rl o N N N N m � Ln � N N N N Year Reference locations shown in Fig. 6-8. FIGURE 6-19c DUKE ENERGY® DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: W. PRATER DATE: 12/12/2019 SUMMARY OF MAXIMUM BORON CONCENTRATIONS AS FUNCTIONS OF TIME AND STRATIGRAPHIC LAYER PROGRESS CHECKED BY: K. LAWING DATE: 12/12/2019 AT WAB REFERENCE LOCATIONS a AND f FOR THE APPROVED BY: K. LAWING DATE: 12/12/2019 PROJECT MANAGER: C. EADY CLOSURE -IN -PLACE SCENARIO UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT WnTerra ROXBORO STEAM ELECTRICAL PLANT SEMORA, NORTH CAROLINA www.synterracorp.com Saprolite, depth = 10 ft. Transition Zone, depth = 29 ft. Fractured rock, depth = 56 ft. Fractured rock, depth = 104 ft. Bedrock, depth = 237 ft. Bedrock, depth = 346 ft. Bedrock, depth = 412 ft. WAB-1 Max. all layer — — 2L Std = 700 ug/L � Saprolite, depth = 7 ft. Transition Zone, depth = 22 ft. Fractured rock, depth = 51 ft. Fractured rock, depth = 104 ft. Bedrock, depth = 254 ft. Bedrock, depth = 375 ft. Bedrock, depth = 446 ft. WAB-2 Max. all layer — — 2L Std = 700 ug/L T ' . 460 - 450 440 11. �.;�• -- �'' _ Alp i ` �. QO J y (o y , tip f. A n _ Asp � 1 ro ■ 00 CD a 0 2 14 ASH -}Y 500 ASIN 490 A6p • ,4, IL r Alp - LEGEND DUKE GRAPHIC SCALE ' 340 0 340 680 It EXTRACTION WELLS ENERGY ♦ CLEAN WATER INFILTRATION WELLS (IN FEET) -HYDRAULIC HEAD (FEET) PROGRESS DRAWN BY: R. YU DATE: 11/18/2019 -ASH BASIN WASTE BOUNDARY REVISED BY: D. WHATLEY DATE: 12/20/2019 y ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: K. LAWING DATE: 12/20/2019 APPROVED BY: K. LAWING DATE: 12/20/2019 SOLID WASTE LANDFILL BOUNDARYTerm PROJECT MANAGER: C. EADY y SOLID WASTE LANDFILL COMPLIANCE BOUNDARY www.synterracorp.com NOTES: FIGURE 6-20 ALL BOUNDARIES ARE APPROXIMATE. SIMULATED HYDRAULIC HEADS IN UPPER FRACTURED BEDROCK ZONE CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN AFTER CLOSURE -IN -PLACE FOR MODEL FOR THE CLOSURE -IN -PLACE SCENARIO WITH ACTIVE LAYER 15. GROUNDWATER REMEDIATION THE REMEDIATION SYSTEM SFiowN WAS DESIGNED FOR ozL COMPLIANCE By 2029. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT TEDONFEBRUAPHOTOGRAPHY BTAINE1 FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARV 6, 2017. COLLECTED ROXBORO STEAM ELECTRIC PLANT DRAW I NG HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE SEMORA, NORTH CAROLINA COORDINATE SYSTEM RIPS 3200 (NAD83AND NAVD88). IMULATED WITHOUT NON-CAMA CCR SOURCES E x ■ EAST ASH BASIAL SIMULATED WITH NON-CAMA CCR SOURCES sue#'„♦` , _- ♦U ' ♦, EAST ASH BA LEGEND �M EXTRACTION WELLS ♦ CLEAN WATER INFILTRATION WELLS ■ REFERENCE LOCATION =NON-CAMA CCR SOURCE ZONES BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L -ASH BASIN WASTE BOUNDARY • ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY • SOLID WASTE LANDFILL COMPLIANCE BOUNDARY ALL BOUNDARIES ARE APPROXIMATE. CLOSURE -IN- LACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024 FOR EAST ASH BASIN AND 2027 FOR WESTASH BASIN. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 J r f? DUKE GRAPHIC SCALE 340 0 340 680 ENERGY(IN FEET) PROGRESS DRAWN BY: R.YU REVISED BY: R. KIEKHAEFER DATE: 11/18/2019 DATE: 12/19/2019 1�� CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 6-21a SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA IMULATED WITHOUT NON-CAMA CCR SOURCES r �q b. C. ■ d. EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES i . . _ T ' , 1 • a ®2 d. ■ EAST ASH BASIN LEGEND %� DUKE GRAPHIC SCALE 340 0 340 680 iP EXTRACTION WELLS ENERGY N FEET) ♦ CLEAN WATER INFILTRATION WELLS ■ REFERENCE LOCATION PROGRESS DRAWN BY: R. YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 QNOWCAMA CCR SOURCE ZONES CHECKED BY: K. LAWING DATE: 12/19/2019 BORON 700 -4,000 Ng/L APPROVED BY: K. LAWING DATE: 12/19/2019 BORON > 4,000 Ng/L s MIem PROJECT MANAGER: C. EADY -ASH BASIN WASTE BOUNDARY J�/1 1 1 1G www.synterracorp.com ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY FIGURE 6-21 b SOLID WASTE LANDFILL COMPLIANCE BOUNDARY SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO NOTFS: AFTER 30 YEARS OF ACTIVE GROUNDWATER REMEDIATION ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024 FOR EAST ASH BASIN AND 2027 FOR MODELING REPORT WESTASH BASIN. ROXBORO STEAM ELECTRIC PLANT NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB. SEMORA, NORTH CAROLINA AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 IMULATED WITHOUT NON-CAMA CCR SOURCES r � � f s EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES EAST ASH BA LEGEND iP EXTRACTION WELLS ♦ CLEAN WATER INFILTRATION WELLS REFERENCE LOCATION Q■NOWCAMA CCR SOURCE ZONES BORON 700 -4,000 Ng/L BORON > 4,000 Ng/L -ASH BASIN WASTE BOUNDARY ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY BOUNDARIES ARE APPROXIMATE. SURE -IN- LACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024 FOR EAST ASH BASIN AND 2027 FOR ITASH BASIN. -CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. IAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4. 2019. AERIAL WAS COLLECTED ON FEBRUARY 6. DUKE ENERGY PROGRESS ■ d GRAPHIC SCALE 340 0 340 680 (IN FEET) DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 6-21c SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO AFTER 80 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA WING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 IMULATED WITHOUT NON-CAMA CCR SOURCES r � � f, oo ■ EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES �A v - _ - b. C. ■ EAST ASH BASIN LEGEND %' DUKE 340 GRAPHIC SCALE 0 340 680 EXTRACTION WELLS ENERGY ♦ CLEAN WATER INFILTRATION WELLS (IN FEET) REFERENCE LOCATION PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 Q■NOWCAMA CCR SOURCE ZONES CHECKED BY: K. LAWING DATE: 12/19/2019 BORON 700 -4,000 Ng/L APPROVED BY: K. LAWING DATE: 12/19/2019 BORON > 4,000 Ng/L A MIe1 1PROJECT MANAGER: C. EADY -ASH BASIN WASTE BOUNDARY J�/1 1 m G www.synterracorp.com ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY FIGURE 6-21 d SOLID WASTE LANDFILL COMPLIANCE BOUNDARY SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO NOTFS: AFTER 130 YEARS OF ACTIVE GROUNDWATER REMEDIATION ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024 FOR EAST ASH BASIN AND 2027 FOR MODELING REPORT WESTASH BASIN. ROXBORO STEAM ELECTRIC PLANT NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB. SEMORA, NORTH CAROLINA AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 IMULATED WITHOUT NON-CAMA CCR SOURCES ♦ ' , r � � +:�.It f tic . i^' _ =a'(•_1'i' � 5L �O• ■� EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES . . 01' v - •1 , a C. I Kiolm -06 ■ d. EAST ASH BASIN LEGEND ' DUKE 340 GRAPHIC SCALE 0 340 680 iP EXTRACTION WELLS ENERGY CLEAN WATER INFILTRATION WELLS (IN FEET) ■ REFERENCE LOCATION PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 QNOWCAMA CCR SOURCE ZONES CHECKED BY: K. LAWING DATE: 12/19/2019 BORON 700 -4,000 Ng/L APPROVED BY: K. LAWING DATE: 12/19/2019 BORON > 4,000 Ng/L A MIem PROJECT MANAGER: C. EADY -ASH BASIN WASTE BOUNDARY J�/1 1 1 1G www.synterracorp.com ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY FIGURE 6-21 e SOLID WASTE LANDFILL COMPLIANCE BOUNDARY SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO 10TE9: AFTER 180 YEARS OF ACTIVE GROUNDWATER REMEDIATION LL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT :LOSURE-IN-PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024 FOR EAST ASH BASIN AND 2027 FOR MODELING REPORT VESTASH BASIN. ROXBORO STEAM ELECTRIC PLANT ION-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB. SEMORA, NORTH CAROLINA ERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 017. IRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 IMULATED WITHOUT NON-CAMA CCR SOURCES r � � -, ♦' 'lA r EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES i F 7 10 LEGEND 40 C EAST ASH BASIN iP EXTRACTION WELLS ♦ CLEAN WATER INFILTRATION WELLS REFERENCE LOCATION Q■NOWCAMA CCR SOURCE ZONES SULFATE > 250 mg/L -ASH BASIN WASTE BOUNDARY -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY SOLID WASTE LANDFILL COMPLIANCE BOUNDARY ALL BOUNDARIES ARE APPROXIMATE. CLOSURE -IN- LACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024 FOR EAST ASH BASIN AND 2027 FOR WESTASH BASIN. NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). DUKE GRAPHIC SCALE t 340 0 340 680 ENERGY(IN FEET) PROGRESS DRAWN BY: R.YU REVISED BY: R. KIEKHAEFER DATE: 11/18/2019 DATE: 12/19/2019 1�� CHECKED BY: K. LAWING DATE: 12/19/2019 APPROVED BY: K. LAWING DATE: 12/19/2019 PROJECT MANAGER: C. EADY FIGURE 6-22 SIMULATED MAXIMUM SULFATE CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA IMULATED WITHOUT NON-CAMA CCR SOURCES M b C. d. ■ EAST ASH BASIN - r SIMULATED WITH NON-CAMA CCR SOURCES A a N, ■d. EAST ASH BASIN LEGEND %n DUKE GRAPHIC SCALE 340 0 340 680 iP EXTRACTION WELLS ENERGY (IN FEET) ♦ CLEAN WATER INFILTRATION WELLS PROGRESS DRAWN BY: R.YU DATE: 11/18/2019 ■ NON-CAMA CCR SOURCE ZONES REFERENCE LOCATION �lp REVISED BY: R. KIEKHAEFER DATE: 12/19/2019 CHECKED BY: K. LAWING DATE: 12/19/2019 A APPROVED BY: K. LAWING DATE: 12/19/2019 TDS > 500 mg/L��11 PROJECT MANAGER: C. EADY m -ASH BASIN WASTE BOUNDARY 1 www.s nterracor .com - -ASH BASIN COMPLIANCE BOUNDARY SOLID WASTE LANDFILL BOUNDARY FIGURE 6-23 SOLID WASTE LANDFILL COMPLIANCE BOUNDARY SIMULATED MAXIMUM TDS CONCENTRATIONS IN ALL NON - ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO NOTES: AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT CLOSURE -IN -PLACE SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2024 FOR EAST ASH BASIN AND 2027 FOR MODELING REPORT WESTASH BASIN. ROXBORO STEAM ELECTRIC PLANT NON-CAMA CCR SOURCES INCLUDE THE GSA/DFAHASOURCES TO THE NORTH OFEAB. SEMORA, NORTH CAROLINA AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLES Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-1 OBSERVED, COMPUTED, AND RESIDUAL HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head (ft) Computed Head (ft) Residual Head (ft) ABM W-1 463.84 462.54 1.31 ABM W-1 BR 462.96 462.42 0.54 ABMW-2 463.04 465.35 -2.31 ABMW-2BR 463.07 465.36 -2.29 ABMW-3 464.55 460.45 4.09 ABMW-3BR 448.07 451.40 -3.34 ABMW-3BRL 427.71 427.68 0.03 ABM W-4 468.50 470.45 -1.95 ABMW-4BR 468.45 470.04 -1.60 ABMW-5 467.51 462.75 4.76 ABMW-5D 434.74 440.44 -5.70 ABMW-6 468.66 468.92 -0.26 ABMW-6BR 468.84 468.80 0.04 ABMW-7 466.93 469.99 -3.05 ABMW-7BR 464.09 467.18 -3.09 ABMW-7BRL 457.44 460.55 -3.11 BG-1 495.46 495.57 -0.11 BG-1BR 495.33 495.52 -0.19 BG-1BRL 482.62 487.13 -4.52 BG-1BRLR 483.79 488.02 -4.23 BG-1D 496.81 495.78 1.03 BG-2BR 486.69 488.31 -1.62 CCR-100BR 471.24 469.72 1.52 CCR-100D 472.19 470.00 2.19 CCR-101 BR 443.11 441.16 1.94 CCR-101 D 445.77 441.06 4.71 CCR-102BR 412.31 416.01 -3.69 CCR-103BR 418.42 416.87 1.55 CCR-104BR 458.47 457.35 1.12 CCR-105BR 480.74 473.97 6.77 CCR-106BR 486.51 485.97 0.53 CCR-107BR 486.66 1 488.97 -2.32 Page 1 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-1 OBSERVED, COMPUTED, AND RESIDUAL HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head (ft) Computed Head (ft) Residual Head (ft) CCR-108BR 489.39 493.50 -4.11 CCR-109BR 474.62 470.75 3.86 CCR-110BR 470.63 473.14 -2.50 CCR-111BR 498.77 497.87 0.90 CCR-112BR-BG 531.23 534.28 -3.05 CCR-113BR 411.05 410.80 0.25 CCR-113D 412.31 410.98 1.33 CCR-200BR 459.05 463.04 -4.00 CCR-201 BR 458.67 463.85 -5.18 CCR-202BR 425.77 427.84 -2.07 CCR-202D 432.05 428.13 3.92 CCR-203BR 412.43 413.25 -0.81 CCR-203D 411.56 413.29 -1.73 CCR-203S 409.94 413.59 -3.66 CCR-204BR 413.61 414.92 -1.32 CCR-205BR 436.12 433.94 2.18 CCR-206BR 455.91 452.58 3.33 CCR-206S 454.09 453.31 0.78 CCR-207 BR 447.98 449.94 -1.96 CCR-207S 450.08 450.19 -0.11 CCR-208BR 450.43 449.41 1.02 CCR-208S 450.43 449.23 1.20 CCR-209BR 457.74 455.07 2.67 CCR-209S 456.85 455.30 1.55 CCR-210BR 452.05 451.04 1.01 CCR-210S 452.64 451.24 1.40 CCR-211 BR 455.58 454.90 0.67 CCR-211S 458.74 455.15 3.59 CCR-212BR 463.33 463.29 0.04 CCR-213BR 467.52 466.74 0.79 CCR-214BR 461.66 464.30 -2.64 CCR-215BR 466.17 467.21 -1.04 Page 2 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-1 OBSERVED, COMPUTED, AND RESIDUAL HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head (ft) Computed Head (ft) Residual Head (ft) CCR-216BR 469.46 468.09 1.37 CCR-217BR 461.61 464.82 -3.21 CCR-218BR 455.05 451.65 3.40 CCR-219BR-BG 469.96 474.16 -4.20 CCR-219D-BG 468.69 473.68 -4.99 CW-1 485.34 477.73 7.61 CW-2 411.07 409.78 1.30 CW-2D 411.01 409.92 1.09 CW-3 446.87 446.11 0.76 CW-3D 449.11 446.70 2.41 CW-4 450.95 447.91 3.04 CW-5 449.37 446.53 2.84 GMW-1A 412.22 416.01 -3.80 GMW-2 419.26 417.19 2.06 GMW-6 455.53 456.42 -0.90 GMW-7 470.38 471.89 -1.51 GMW-8 481.50 485.13 -3.63 GMW-8R 485.47 484.86 0.61 GMW-9 513.23 508.82 4.41 GMW-10 463.62 463.74 -0.12 GMW-11 475.18 472.65 2.53 GPMW-1BR 414.44 417.80 -3.36 GPMW-1D 417.50 420.72 -3.22 GPMW-1S 419.12 422.47 -3.35 GPMW-2BR 412.15 416.20 -4.06 GPMW-2D 412.78 416.43 -3.65 GPMW-3BR 413.76 416.61 -2.85 GPMW-3D 420.76 415.90 4.86 MW-1 410.49 411.22 -0.72 MW-1BR 478.03 476.62 1.41 MW-2 410.23 413.74 -3.51 MW-2BR 478.59 476.93 1.66 Page 3 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-1 OBSERVED, COMPUTED, AND RESIDUAL HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head (ft) Computed Head (ft) Residual Head (ft) MW-3BR 427.21 424.70 2.52 M W-4BR 456.11 452.68 3.43 MW-4BRL 460.45 455.29 5.16 MW-5BR 431.12 431.12 0.00 MW-5D 449.05 445.90 3.15 MW-6BR 410.17 414.59 -4.42 MW-6D 411.39 414.81 -3.42 MW-7BR 463.93 460.10 3.83 MW-8BR 442.23 445.14 -2.91 MW-9BR 417.19 421.14 -3.94 MW-10BR 513.09 509.62 3.47 M W-11 BR 462.50 460.26 2.24 MW-11D 461.35 459.92 1.43 MW-12BR 451.10 448.20 2.89 M W-13 BR 513.44 510.74 2.70 MW-14BR 465.12 469.40 -4.27 MW-14D 466.99 469.72 -2.73 MW-15BR 499.45 496.22 3.23 MW-15D 500.67 496.35 4.32 M W-16 BR 490.16 488.06 2.10 MW-17BR 497.30 499.77 -2.47 MW-18BR 486.60 484.02 2.58 MW-18D 486.94 485.67 1.27 MW-19BRL 526.19 527.08 -0.89 MW-21BRL 481.40 484.23 -2.83 M W-21 BRLR 481.08 484.01 -2.93 MW-22BR 454.28 455.77 -1.50 MW-22BRL 458.50 453.85 4.65 MW-22D 455.80 455.61 0.19 MW-23BRR 512.50 508.18 4.32 MW-24BR 486.61 486.86 -0.25 MW-25BR 494.11 498.11 -3.99 Page 4 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-1 OBSERVED, COMPUTED, AND RESIDUAL HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head (ft) Computed Head (ft) Residual Head (ft) MW-26BR 483.92 483.68 0.24 MW-27BR 451.59 454.94 -3.35 MW-28BR 417.74 421.66 -3.92 MW-29BR 458.98 460.50 -1.52 MW-30BR 459.82 458.35 1.46 MW-31BR 466.37 469.32 -2.95 MW-32BR 471.10 469.21 1.89 MW-33BR 457.22 460.15 -2.93 PZ-12 471.80 469.31 2.49 PZ-14 456.56 455.28 1.28 ABMW-7BRLL 460.86 460.98 -0.12 HWMW-1 BR 418.88 415.61 3.27 MW-1BRL 452.12 448.61 3.51 M W-108 BRL 482.00 482.64 -0.64 M W-108 BRLL 458.85 463.64 -4.79 MW-205BRL 432.48 435.39 -2.90 MW-205BRLL 432.36 435.91 -3.55 MW-205BRLLL 430.02 433.73 -3.71 MW-208BRL 457.25 453.67 3.58 MW-208BRLL 457.35 456.79 0.56 MW-208BRLLL 457.15 458.28 -1.13 MW-34BR 420.52 424.17 -3.65 MW-34D 421.13 423.89 -2.75 MW-35BR 437.58 438.92 -1.34 MW-35D 441.47 439.19 2.28 MW-35S 443.92 439.40 4.52 MW-36BR 440.45 443.92 -3.46 MW-36D 441.69 443.26 -1.57 M W-37 BR 446.20 447.98 -1.78 MW-37D 449.17 448.70 0.48 MW-37S 449.66 449.43 0.24 MW-39BR 454.11 457.03 -2.92 Page 5 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-1 OBSERVED, COMPUTED, AND RESIDUAL HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head (ft) Computed Head (ft) Residual Head (ft) MW-39D 486.19 483.26 2.92 ABMW-1 OWAL-15 463.96 462.65 1.32 ABMW-1 OWAM-15 464.25 462.69 1.55 ABMW-1 OWAM-30 464.26 462.54 1.72 ABMW-1 OWAU-15 464.29 462.57 1.72 ABMW-1 OWAU-30 464.32 462.72 1.60 ABMW-1APW 463.39 462.77 0.62 ABMW-7 OWAL-15 467.08 470.06 -2.98 ABMW-7 OWAM-15R 469.45 470.09 -0.64 ABMW-7 OWAM-30 469.50 470.09 -0.59 ABMW-7 OWAU-15 470.32 470.08 0.25 ABMW-7 OWAU-30 470.35 470.05 0.30 ABMW-7APW 469.52 470.15 -0.63 Prepared by: RY Checked by: KTL Notes ft - feet in NAVD 88 (North American Vertical Datum of 1988) Page 6 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC CONDUCTIVITY PARAMETERS Unit Grid Layer Kn (ft/d) Kn/Kv Ash 1-8 6 10 Saprolite 9-11 1 1 Transition zone 12-13 1 1 Upper fractured rock 14-16 0.3 1 Lower fractured rock 17-18 0.01 1 Upper bedrock 19-20 0.005 1 Bedrock 21-25 0.003 1 Prepared by: RY Checked by: KTL Notes: Kh - horizontal hydraulic conductivity ft/d - feet per day Kh/K� - horizontal hydraulic conductivity divided by vertical hydraulic conductivity Page 7 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-3 WATER BALANCE ON THE ASH BASIN GROUNDWATER FLOW SYSTEM FOR APRIL 2019 CONDITIONS West Ash Basin Water Balance Components Flow In (9Pm) Flow Out (9Pm) Direct recharge to the ash basin 38 Direct recharge to the watershed outside of the ash basin 65 Pond, sluicing channel, wetland in the ash basin 35 Drainage inside the ash basin 0 Drainage outside of the ash basin 18 Flow through and under the main dam 14 Flow through and under the filter dike 8 Others 28 East Ash Basin Water Balance Components Flow In (9Pm) Flow Out (9Pm) Direct recharge to the ash basin 27 Direct recharge to the watershed outside of the ash basin 61 Pond, sluicing channel, wetland in the ash basin 26 Drainage inside the ash basin 11 Drainage outside of the ash basin 32 Flow through and under the main dam 20 Flow through and under the separator dike 5 Others j 6 Prepared by: RY Checked by: KTL Notes: gpm - gallon per minute Others - groundwater flow in/out of the ash basin flow system that are not included in the above categories Page 8 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-4 FLOW MODEL SENSITIVITY ANALYSIS Parameter 0.5x Calibrated Calibrated 2x Calibrated Kh in ash (6 ft/d) 2.36% 2.31% 2.31% Kh in saprolite (1 ft/d) 2.39% 2.31% 2.46% Kh in transition zone (1 ft/d) 2.47% 2.31% 2.61% Kh in upper fractured rock (0.3 ft/d) 3.40% 2.31% 3.63% Kh in lower fractured rock (0.01 ft/d) 2.34% 2.31% 2.31% Kh in upper bedrock (0.005 ft/d) 2.33% 2.31% 2.35% Kh in bedrock (0.003 ft/d) 2.33% 2.31% 2.33% Regional recharge (0.0018 ft/d) 5.29% 2.31% 6.84% Prepared by: RY Checked by: KTL Notes: Parameters are multiplied by 0.5 or 2 and the NRMSE is calculated. Results are expressed as normalized root mean square error (NRMSE) of the simulated and observed heads. Kh — horizontal hydraulic conductivity ft/d — feet per day Page 9 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-5a BORON, SULFATE, AND TDS SOURCE CONCENTRATIONS IN THE ASH BASINS USED IN HISTORICAL TRANSPORT MODEL Source Zone ID Boron (pg/L) Sulfate (m9/L) TDS (m9/L) 1 23000 2000 2200 2 200 800 1200 3 2000 500 800 4 2500 200 500 5 800 1000 1400 6 200 1500 3000 7 5000 550 800 8 8000 2000 1400 9 1600 100 400 10 45000 2200 3800 11 4000 390 2500 12 4500 800 1200 13 25000 1400 2400 14 400 480 600 15 3000 140 700 16 49 80 400 17 10 100 1000 18 10000 250 410 19 700 0 200 20 1200 14 200 21 50 3000 3000 22 2320 100 260 23 500 100 200 24 5000 100 200 25 284 1500 1000 26 4000 200 410 27 10000 20 9000 28 12800 200 410 29 80000 2500 8000 Page 10 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-5a BORON, SULFATE, AND TDS SOURCE CONCENTRATIONS IN THE ASH BASINS USED IN HISTORICAL TRANSPORT MODEL Source Zone ID Boron (Ng/L) Sulfate (mg/L) TDS (mg/L) 30 1000 20 200 31 1500 700 1400 32 5000 20 200 33 0 20 400 34 80000 2000 18000 35 70000 1000 4000 36 1000 10 200 37 20000 1000 2000 38 4000 400 3000 39 10000 100 800 40 12000 200 3000 41 3000 100 600 WEI 1000 0 0 EEI 1000 0 0 Prepared by: RY Checked by: KTL Notes: Location of each source zone is identified in Figure 5-6a. Source concentrations in WAB (zones 18-41) are set to zero for model period before 1974. WEI is WAB extension impoundment and EEI is EAB extension impoundment. It is assumed that CCR material is present in the impoundment sediment. Sediment will be dredged after ash basin closure. pg/L - micrograms per liter mg/L - milligrams per liter Page 11 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-5b BORON, SULFATE, AND TDS SOURCE CONCENTRATIONS OUTSIDE THE ASH BASINS USED IN HISTORICAL TRANSPORT MODEL Source Zone ID Boron (pg/L) Sulfate (m9/L) TDS (m9/L) 1 3000 500 1000 2 7000 2000 2000 3 1000 150 500 4 2000 600 1200 5 2000 2000 5000 6 3000 600 1200 7 5000 600 600 8 3000 600 1200 9 2000 600 1200 10 25000 2000 3000 11 1000 1000 1500 12 16000 1000 2500 13 4000 1000 2500 14 1000 200 3000 15 4000 600 1500 16 2500 400 1500 17 2500 400 1500 18 2000 1500 2200 19 800 800 2200 20 1800 2500 0 21 1000 300 1200 22 10000 700 2500 23 200 1000 1500 24 12000 11000 1500 Page 12 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-5b BORON, SULFATE, AND TDS SOURCE CONCENTRATIONS OUTSIDE THE ASH BASINS USED IN HISTORICAL TRANSPORT MODEL Source Zone ID Boron (Ng/L) Sulfate (mg/L) TDS (mg/L) 25 200 700 1200 26 2000 1000 1800 27 500 1500 1200 28 500 800 1200 29 1000 2000 3000 30 6000 4000 5000 31 500 3000 3000 32 2700 - - 33 3000 - - 34 0 - - 35 - 200 200 36 - 800 1200 37 - 3000 4000 38 - 3500 6500 Prepared by: RY Checked by: KTL Notes: Location of each source zone is identified in Figure 5-6b. COI concentrations in source zones downgradient of EAB (18-31) are set to zero for model period before 2007. COI concentrations in source zones outside of WAB (32-38) are set to zero for model period before 1974. pg/L - micrograms per liter mg/L - milligrams per liter Page 13 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6a OBSERVED AND COMPUTED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Name Observed Boron (Ng/L) Computed Boron (Ng/L) ABMW-1 12800 12800 ABMW-1BR 558 282 ABMW-2 4870 2112 ABMW-2BR 0 0 ABMW-3 289 284 ABMW-3BR 2770 2778 ABMW-3BRL 20 136 ABMW-4 45000 45000 ABMW-4BR 0 66 ABMW-5 24800 25000 ABMW-5D 2980 1778 ABMW-6 2980 3000 ABMW-6BR 0 537 ABMW-7BR 1550 1492 ABMW-7BRL 157 733 BG-1 0 0 BG-1BR 0 0 BG-1BRLR 23 0 BG-1D 0 0 BG-2BR 0 0 CCR-100BR 0 0 CCR-100D 19 0 CCR-101BR 0 13 CCR-101D 0 16 CCR-102BR 0 13 CCR-103BR 3970 4418 CCR-104BR 7700 6375 CCR-105BR 613 415 CCR-106BR 1700 2068 CCR-107BR 2750 1944 CCR-108BR 11000 16724 CCR-109BR 1840 1 1130 Page 14 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6a OBSERVED AND COMPUTED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Name Observed Boron (Ng/L) Computed Boron (Ng/L) CCR-110BR 16600 14691 CCR-111BR 6500 5152 CCR-112BR-BG 0 0 CCR-113BR 0 0 CCR-113D 0 0 CCR-200BR 0 2 CCR-201 BR 21 19 CCR-202BR 2270 1882 CCR-202D 2480 1652 CCR-203BR 751 792 CCR-203D 505 436 CCR-203S 0 130 CCR-204BR 7630 3695 CCR-205BR 7620 6538 CCR-206BR 12100 16948 CCR-206S 19500 12537 CCR-207BR 22600 21489 CCR-207S 8830 15331 CCR-208BR 49800 36089 CCR-208S 36200 40204 CCR-209BR 4340 6719 CCR-209S 3770 5089 CCR-210BR 2490 1004 CCR-210S 909 974 CCR-211 BR 1580 2063 CCR-211S 2660 2516 CCR-212BR 0 86 CCR-213BR 0 31 CCR-214BR 0 8 CCR-215BR 0 0 CCR-216BR 0 0 CCR-217BR 0 182 Page 15 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6a OBSERVED AND COMPUTED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Name Observed Boron (Ng/L) Computed Boron (Ng/L) CCR-218BR 0 141 CW-1 0 449 CW-2 0 186 CW-2D 0 362 CW-3 0 0 CW-3D 0 0 CW-4 0 17 CW-5 211 553 GMW-1A 116 23 GMW-2 5950 4222 GMW-6 2720 6144 GMW-7 2490 2254 GMW-8 3910 2811 GMW-SR 3420 3163 GMW-9 0 18 GMW-10 150 519 GMW-11 1960 1012 GPMW-1BR 1600 1799 GPMW-1D 1240 1887 GPMW-1S 2180 1895 GPMW-2BR 2570 1629 GPMW-2D 0 389 GPMW-3BR 221 5 GPMW-3D 1300 1283 MW-1BR 1930 1424 MW-2 3340 3638 MW-2BR 0 0 MW-3BR 2860 2989 MW-4BR 17 14 MW-5BR 52 123 MW-5D 709 777 MW-6BR 0 0 Page 16 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6a OBSERVED AND COMPUTED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Name Observed Boron (Ng/L) Computed Boron (Ng/L) MW-6D 0 0 MW-7BR 0 0 MW-8BR 0 0 MW-9BR 0 0 MW-10BR 0 0 MW-11BR 0 1 MW-11D 0 1 MW-12BR 0 10 MW-13BR 0 0 MW-14BR 0 0 MW-15BR 0 0 MW-15D 0 0 MW-16BR 0 0 MW-17BR 0 0 MW-18BR 0 0 MW-18D 0 0 MW-19BRL 0 0 MW-20BRL 0 0 MW-21BRLR 72 253 MW-22BR 887 775 MW-22BRL 83 10 MW-22D 641 829 MW-23BRR 0 0 MW-24BR 35 0 MW-25BR 23 0 MW-26BR 0 0 MW-27BR 0 75 MW-28BR 52 0 MW-29BR 0 0 MW-30BR 28 0 MW-31BR 0 0 MW-32BR 29 0 Page 17 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6a OBSERVED AND COMPUTED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Name Observed Boron (pg/L) Computed Boron (pg/L) MW-33BR 0 0 ABMW-7BRLL 137 72 HWMW-1 BR 34 544 MW-1BRL 23 426 MW-108BRL 22700 22427 MW-108BRLL 4700 6501 MW-205BRL 5990 3109 MW-205BRLL 8240 7897 MW-205BRLLL 18900 15008 MW-208BRL 865 1330 MW-208BRLL 1400 3169 MW-208BRLLL 1570 1972 MW-34BR 800 955 MW-34D 521 737 MW-35BR 1460 4245 MW-35D 7880 4854 MW-35S 7820 5817 MW-36BR 1070 1657 MW-36D 1230 1092 MW-37BR 4200 1759 MW-37D 499 467 MW-37S 410 428 MW-39BR 0 0 MW-39D 0 0 Notes Data collected through April 2019. pg/L - micrograms per liter Prepared by: RY Checked by: KTL Page 18 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6b OBSERVED AND COMPUTED SULFATE CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Name Observed Sulfate (mg/L) Computed Sulfate (mg/L) ABMW-1 200 200 ABMW-1BR 19 50 ABMW-2 37 79 ABMW-2BR 91 0 ABMW-3 1500 1500 ABMW-3BR 2800 2935 ABMW-3BRL 490 387 ABMW-4 2200 2200 ABMW-4BR 20 162 ABMW-5 1400 1400 ABMW-5D 16 14 ABMW-6 140 140 ABMW-6BR 60 58 ABMW-7BR 110 299 ABMW-7BRL 250 617 BG-1 18 0 BG-1BR 17 0 BG-1BRLR 79 0 BG-1D 14 0 BG-2BR 36 0 CCR-100BR 28 0 CCR-100D 22 0 CCR-101BR 19 64 CCR-101D 2.3 51 CCR-102BR 390 84 CCR-103BR 630 953 CCR-104BR 1100 1481 CCR-105BR 290 311 CCR-106BR 450 421 CCR-107BR 270 358 CCR-108BR 1200 1492 CCR-109BR 700 883 CCR-110BR 1100 945 CCR-111BR 920 585 CCR-112BR-BG 19 0 CCR-113BR 140 0 Page 19 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6b OBSERVED AND COMPUTED SULFATE CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Name Observed Sulfate (mg/L) Computed Sulfate (mg/L) CCR-113D 130 0 CCR-200BR 45 2 CCR-201 BR 3500 3025 CCR-202BR 1800 1931 CCR-202D 1900 1503 CCR-203BR 490 401 CCR-203D 340 229 CCR-203S 7.9 81 CCR-204BR 320 396 CCR-205BR 150 184 CCR-206BR 230 286 CCR-206S 330 210 CCR-207BR 480 296 CCR-207S 190 198 CCR-208BR 1100 1006 CCR-208S 990 972 CCR-209BR 27 202 CCR-209S 29 147 CCR-210BR 6.4 15 CCR-210S 8.1 10 CCR-211 BR 40 8 CCR-211S 44 10 CCR-212BR 40 1 CCR-213BR 52 1 CCR-214BR 47 0 CCR-215BR 33 0 CCR-216BR 40 0 CCR-217BR 47 0 CCR-218BR 45 0 CW-1 99 77 CW-2 71 106 CW-2D 130 157 CW-3 37 0 CW-3D 38 0 CW-4 38 0 CW-5 120 405 Page 20 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6b OBSERVED AND COMPUTED SULFATE CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Name Observed Sulfate (mg/L) Computed Sulfate (mg/L) GMW-1A 85 73 GMW-2 850 913 GMW-6 800 1516 GMW-7 243 363 GMW-8 480 431 GMW-SR 400 481 GMW-9 13 5 GMW-10 65 89 GMW-11 352 346 GPMW-1BR 1100 1348 GPMW-1D 1100 1416 GPMW-1S 1200 1421 GPMW-2BR 1200 1637 GPMW-2D 680 692 GPMW-3BR 440 4 GPMW-3D 1300 1082 MW-1BR 140 227 MW-2 180 377 MW-2BR 48 0 MW-3BR 1400 2133 MW-4BR 32 0 MW-5BR 210 61 MW-5D 480 363 MW-6BR 14 4 MW-6D 35 7 MW-7BR 26 0 MW-8BR 27 0 MW-9BR 24 0 MW-10BR 39 0 MW-11BR 43 11 MW-11D 39 16 MW-12BR 39 0 MW-13BR 33 0 MW-14BR 13 0 MW-15BR 33 0 MW-15D 29 0 Page 21 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6b OBSERVED AND COMPUTED SULFATE CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Name Observed Sulfate (mg/L) Computed Sulfate (mg/L) MW-16BR 22 0 MW-17BR 37 0 MW-18BR 15 0 MW-18D 32 0 MW-19BRL 23 0 MW-20BRL 13 0 MW-21BRLR 140 42 MW-22BR 660 462 MW-22BRL 120 4 MW-22D 620 576 MW-23BRR 15 0 MW-24BR 61 0 MW-25BR 100 0 MW-26BR 69 0 MW-27BR 280 21 MW-28BR 73 0 MW-29BR 12 0 MW-30BR 64 0 MW-31BR 34 0 MW-32BR 370 0 MW-33BR 27 0 ABMW-7BRLL 90 102 HWMW-1BR 140 642 MW-1BRL 99 84 MW-108BRL 1900 1844 MW-108BRLL 400 652 MW-205BRL 99 80 MW-205BRLL 240 170 MW-205BRLLL 500 293 MW-208BRL 150 32 M W-208 BRLL 110 34 MW-208BRLLL 310 11 MW-34BR 480 634 MW-34D 690 681 MW-35BR 240 1135 MW-35D 700 1083 Page 22 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6b OBSERVED AND COMPUTED SULFATE CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Name Observed Sulfate (mg/L) Computed Sulfate (mg/L) MW-35S 640 672 MW-36BR 940 419 MW-36D 1300 1287 MW-37BR 490 424 MW-37D 630 183 MW-37S 550 131 MW-39BR 30 0 MW-39D 25 0 Notes: Data collected through April 2019. mg/L - milligrams per liter Prepared by: RY Checked by: KTL Page 23 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6c OBSERVED AND COMPUTED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well name Observed TDS (mg/L) Computed TDS (mg/L) ABMW-1 370 410 ABMW-1BR 320 95 ABMW-2 230 185 ABMW-2BR 410 0 ABMW-3 1000 1000 ABMW-3BR 3400 3914 ABMW-3BRL 840 516 ABMW-4 3800 3800 ABMW-4BR 230 275 ABMW-5 2300 2400 ABMW-5D 240 123 ABMW-6 700 700 ABMW-6BR 320 345 ABMW-7BR 420 713 ABMW-7BRL 530 1230 BG-1 310 0 BG-1BR 310 0 BG-1BRLR 460 0 BG-1D 310 0 BG-2BR 310 0 CCR-100BR 420 0 CCR-100D 430 0 CCR-101BR 440 566 CCR-101D 350 402 CCR-102BR 830 785 CCR-103BR 1200 992 CCR-104BR 1900 1555 CCR-105BR 620 762 CCR-106BR 1000 831 CCR-107BR 520 581 CCR-108BR 2000 2342 CCR-109BR 1300 1324 CCR-110BR 1800 2299 CCR-111BR 1800 1461 CCR-112BR-BG 200 0 CCR-113BR 480 0 Page 24 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6c OBSERVED AND COMPUTED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well name Observed TDS (mg/L) Computed TDS (mg/L) CCR-113 D 440 0 CCR-200BR 390 2 CCR-201 BR 5500 5599 CCR-202BR 2700 2601 CCR-202D 3000 1999 CCR-203BR 910 937 CCR-203D 790 693 CCR-203S 660 470 CCR-204BR 3000 2804 CCR-205BR 2600 1382 CCR-206BR 3200 3530 CCR-206S 1300 3030 CCR-207BR 4300 1682 CCR-207S 1000 1222 CCR-208BR 6100 4713 CCR-208S 3800 4383 CCR-209BR 720 922 CCR-209S 800 634 CCR-210BR 410 205 CCR-210S 350 195 CCR-211 BR 320 83 CCR-211S 410 102 CCR-212BR 280 4 CCR-213BR 720 8 CCR-214BR 410 3 CCR-215BR 400 0 CCR-216BR 460 0 CCR-217BR 340 106 CCR-218BR 330 51 CW-1 420 85 11 CW-2 430 158 CW-2D 390 233 CW-3 220 0 CW-3D 330 0 CW-4 320 4 CW-5 370 608 Page 25 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6c OBSERVED AND COMPUTED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well name Observed TDS (mg/L) Computed TDS (mg/L) GMW-1A 380 569 GMW-2 1500 963 GMW-6 1200 1615 GMW-7 900 1356 GMW-8 1400 1275 GMW-SR 1300 1272 GMW-9 170 12 GMW-10 230 276 GMW-11 752 724 GPMW-1BR 1700 2016 GPMW-1D 1700 2080 GPMW-1S 1700 2085 GPMW-2BR 2000 2242 GPMW-2D 1100 986 GPMW-3BR 720 5 GPMW-3D 1800 1382 MW-1BR 660 242 MW-2 2100 2731 MW-2BR 470 0 MW-3BR 2300 2628 MW-4BR 260 6 MW-5BR 520 91 MW-5D 660 544 MW-6BR 220 5 MW-6D 230 10 MW-7BR 180 0 MW-8BR 370 0 MW-9BR 230 0 MW-10BR 350 0 MW-11BR 350 111 MW-11D 320 154 MW-12BR 420 2 MW-13BR 390 0 MW-14BR 340 0 MW-15BR 330 0 MW-15D 380 0 Page 26 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6c OBSERVED AND COMPUTED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well name Observed TDS (mg/L) Computed TDS (mg/L) MW-16BR 260 0 MW-17BR 400 0 MW-18BR 440 0 MW-18D 420 0 MW-19BRL 470 0 MW-20BRL 300 0 MW-21BRLR 580 108 MW-22BR 950 834 MW-22BRL 560 10 MW-22D 1100 1026 MW-23BRR 280 0 MW-24BR 300 0 MW-25BR 560 0 MW-26BR 510 0 MW-27BR 630 39 MW-28BR 410 0 MW-29BR 300 0 MW-30BR 510 0 MW-31BR 400 0 MW-32BR 690 0 MW-33BR 1500 0 ABMW-7BRLL 400 204 HWMW-1BR 490 871 MW-1BRL 620 97 MW-108BRL 3030 2777 MW-108BRLL 927 983 MW-205BRL 1500 627 MW-205BRLL 2000 1450 MW-205BRLLL 4700 2531 MW-208BRL 720 119 MW-208BRLL 990 152 MW-208BRLLL 820 50 MW-34BR 1000 1558 MW-34D 1200 1809 MW-35BR 630 1235 MW-35D 1400 1397 Page 27 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-6c OBSERVED AND COMPUTED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well name Observed TDS (mg/L) Computed TDS (mg/L) MW-35S 1400 1569 MW-36BR 210 594 MW-36D 100 371 MW-37BR 200 621 MW-37D 110 319 MW-37S 1000 228 MW-39BR 310 0 MW-39D 200 0 Notes: Data collected through April 2019. mg/L - milligrams per liter Prepared by: RY Checked by: KTL Page 28 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-7 TRANSPORT MODEL SENSITIVITY TO THE BORON Kd VALUES Well Boron /L Boron model calibrated Model, low Ka Model, high Ka NRMSE 3.55% 3.83% 4.38% ABMW-1 12800 12800 12800 12800 ABMW-1BR 558 282 537 19 ABMW-2 4870 2112 3025 798 ABMW-2BR 0 0 0 0 ABM W-3 289 284 284 284 ABMW-3BR 2770 2778 2899 2247 ABMW-3BRL 20 136 496 6 ABMW-4 45000 45000 45000 45000 ABMW-4BR 0 66 589 0 ABMW-5 24800 25000 25000 25000 ABMW-5D 2980 1778 1779 1658 ABMW-6 2980 3000 3000 3000 ABMW-6BR 0 537 1325 16 ABMW-7BR 1550 1492 1812 155 ABMW-7BRL 157 733 1202 12 BG-1 0 0 0 0 BG-1BR 0 0 0 0 BG-1BRLR 23 0 0 0 BG-1D 0 0 0 0 BG-2BR 0 0 0 0 CCR-100BR 0 0 0 0 CCR-100D 19 0 0 0 CCR-101BR 0 13 14 1 CCR-101D 0 16 16 2 CCR-102BR 0 13 14 6 CCR-103BR 3970 4418 4689 2364 CCR-104BR 7700 6375 6571 5240 CCR-105BR 613 415 402 175 CCR-106BR 1700 2068 2113 650 CCR-107BR 2750 1944 1973 577 CCR-108BR 11000 16724 16733 14857 CCR-109BR 1840 1130 1309 349 CCR-110BR 16600 14691 14691 14237 CCR-111BR 6500 5152 5184 4414 CCR-112BR-BG 0 0 0 0 CCR-113BR 0 0 0 0 CCR-113D 0 0 0 0 Page 29 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-7 TRANSPORT MODEL SENSITIVITY TO THE BORON Kd VALUES Well Boron /L Boron model calibrated Model, low Ka Model, high Ka NRMSE 3.55% 3.83% 4.38% CCR-200BR 0 2 13 0 CCR-201 BR 21 19 21 6 CCR-202BR 2270 1882 1944 1335 CCR-202D 2480 1652 1709 938 CCR-203BR 751 792 834 559 CCR-203D 505 436 460 265 CCR-203S 0 130 137 70 CCR-204BR 7630 3695 3785 2667 CCR-205BR 7620 6538 6541 6530 CCR-206BR 12100 16948 16969 16891 CCR-206S 19500 12537 12541 12520 CCR-207BR 22600 21489 27930 8688 CCR-207S 8830 15331 17938 9104 CCR-208BR 49800 36089 36585 34932 CCR-208S 36200 40204 40788 38219 CCR-209BR 4340 6719 6892 1960 CCR-209S 3770 5089 4924 801 CCR-210BR 2490 1004 1212 693 CCR-210S 909 974 1000 936 CCR-211BR 1580 2063 2082 1459 CCR-211S 2660 2516 2534 1872 CCR-212BR 0 86 109 37 CCR-213BR 0 31 59 3 CCR-214BR 0 8 23 0 CCR-215BR 0 0 0 0 CCR-216BR 0 0 0 0 CCR-217BR 0 182 439 7 CCR-218BR 0 141 202 22 CW-1 0 449 470 97 CW-2 0 186 336 9 CW-2D 0 362 463 98 CW-3 0 0 0 0 CW-3D 0 0 0 0 CW-4 0 17 32 3 CW-5 211 553 570 349 GMW-1A 116 23 24 14 GMW-2 5950 4222 4437 1937 Page 30 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-7 TRANSPORT MODEL SENSITIVITY TO THE BORON Kd VALUES Well Boron /L Boron model calibrated Model, low Ka Model, high Ka NRMSE 3.55% 3.83% 4.38% GMW-6 2720 6144 6218 5636 GMW-7 2490 2254 2295 1782 GMW-8 3910 2811 2930 2112 GMW-8R 3420 3163 3286 2332 GMW-9 0 18 18 14 GMW-10 150 519 563 206 GMW-11 1960 1012 1005 619 GPMW-1BR 1600 1799 1812 1745 GPMW-1D 1240 1887 1889 1874 GPMW-1S 2180 1895 1895 1879 GPMW-2BR 2570 1629 2148 133 GPMW-2D 0 389 552 54 GPMW-3BR 221 5 286 0 GPMW-3D 1300 1283 1692 808 MW-1BR 1930 1424 1450 434 MW-2 3340 3638 3743 1933 MW-2BR 0 0 0 0 MW-3BR 2860 2989 3061 2619 MW-4BR 17 14 27 2 MW-5BR 52 123 129 78 MW-5D 709 777 789 612 MW-6BR 0 0 1 0 MW-6D 0 0 2 0 MW-7BR 0 0 0 0 MW-8BR 0 0 0 0 MW-9BR 0 0 0 0 MW-10BR 0 0 0 0 MW-11BR 0 1 1 0 MW-11D 0 1 2 0 MW-12BR 0 10 12 5 MW-13BR 0 0 0 0 MW-14BR 0 0 0 0 MW-15BR 0 0 0 0 MW-15D 0 0 0 0 MW-16BR 0 0 0 0 MW-17BR 0 0 0 0 MW-18BR 0 0 0 0 Page 31 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-7 TRANSPORT MODEL SENSITIVITY TO THE BORON Kd VALUES Well Boron /L Boron model calibrated Model, low Ka Model, high Ka NRMSE 3.55% 3.83% 4.38% MW-18D 0 0 0 0 MW-19BRL 0 0 0 0 MW-20BRL 0 0 0 0 MW-21BRLR 72 253 604 7 MW-22BR 887 775 813 652 MW-22BRL 83 10 284 0 MW-22D 641 829 857 733 MW-23BRR 0 0 0 0 MW-24BR 35 0 0 0 MW-25BR 23 0 0 0 MW-26BR 0 0 0 0 MW-27BR 0 75 133 1 MW-28BR 52 0 0 0 MW-29BR 0 0 0 0 MW-30BR 28 0 0 0 MW-31BR 0 0 0 0 MW-32BR 29 0 0 0 MW-33BR 0 0 0 0 ABMW-7BRLL 137 72 357 0 HWMW-1BR 34 544 1086 38 MW-1BRL 23 426 1412 13 MW-108BRL 22700 22427 22564 18881 MW-108BRLL 4700 6501 9337 1315 MW-205BRL 5990 3109 3115 3103 MW-205BRLL 8240 7897 7911 7886 MW-205BRLLL 18900 15008 15668 14810 MW-208BRL 865 1330 1364 1294 MW-208BRLL 1400 3169 3328 3040 MW-208BRLLL 1570 1972 2101 1883 MW-34BR 800 955 1086 650 MW-34D 521 737 816 576 MW-35BR 1460 4245 4853 2235 MW-35D 7880 4854 4958 4232 MW-35S 7820 5817 5842 5507 MW-36BR 1070 1657 1719 1476 MW-36D 1230 1092 1113 1027 MW-37BR 4200 1759 1811 1588 Page 32 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 5-7 TRANSPORT MODEL SENSITIVITY TO THE BORON Kd VALUES Well Boron /L Boron model calibrated Model, low Kd Model, high Kd NRMSE 3.55% 3.83% 4.38% MW-37D 499 467 523 359 MW-37S 410 428 468 280 MW-39BR 0 0 0 0 MW-39D 0 0 0 0 Prepared by: RY Checked by: KTL Notes: Boron concentrations are shown for the calibrated model, and for models where the Kd is increased by a factor of 5 and decreased by a factor of 1/5. Kd - soil -water distribution coefficients pg/L - micrograms per liter Page 33 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 6-1 WATER BALANCE ON THE ASH BASIN GROUNDWATER FLOW SYSTEM FOR JULY 2020 WHEN WAB IS EXPECTED TO BE DECANTED West Ash Basin Water Balance Components Flow In (9Pm) Flow Out (9Pm) Direct recharge to the ash basin 56 Direct recharge to the watershed outside of the ash basin 73 Pond, sluicing channel, wetland in the ash basin Drainage inside the ash basin 82 Drainage outside of the ash basin 17 Flow through and under the main dam 13 Flow through and under the filter dike 2 Others 15 East Ash Basin Water Balance Components Flow In (9Pm) Flow Out (9Pm) Direct recharge to the ash basin 26 Direct recharge to the watershed outside of the ash basin 60 Pond, sluicing channel, wetland in the ash basin Drainage inside the ash basin 38 Drainage outside of the ash basin 32 Flow through and under the main dam 18 Flow through and under the separator dike 5 Others 6 Prepared by: RY Checked by: KTL Notes Others - groundwater flows in/out of the watershed that are not accounted in the above categories gpm - gallon per minute Page 34 Updated Groundwater Flow And Transport Modeling Report December 2019 Roxboro Steam Electric Plant, Semora, North Carolina TABLE 6-2 EAST ASH BASIN AREA ACTIVE REMEDIATION APPROACH WELL SUMMARY Number of Extraction Formation Total Depth Wells (feet bgs) 18 Transition zone and 190 Bedrock 18 Bedrock 190 14 Bedrock 250 Number of Clean Water Formation Total Depth Infiltration Wells (feet bgs) 27 Saprolite, Transition 180 zone, Bedrock Prepared by: RY Checked by: KTL Notes: The 50 extraction wells have an average flow rate of 1.4 gpm. The extraction wells are pumped so that the water levels are near the bottom of the wells. The 27 clean water infiltration wells have an average flow rate of 2.8 gpm and the heads of the infiltration wells are maintained at 20 feet above the ground surface. bgs - below ground surface Page 35