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HomeMy WebLinkAboutNC0004987_MSS_Appendix G_20191231Corrective Action Plan Update December 2019 Marshall Steam Station APPENDIX G SynTerra UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT FOR MARSHALL STEAM STATION TERRELL, NORTH CAROLINA DECEMBER 2019 PREPARED FOR DUKE ENERGY,: CAROLINAS DUKE ENERGY CAROLINAS,, LLC INVESTIGATORS RONALD W. FALTA, PH. D. - FALTA ENVIRONMENTAL LLC REGINA GRAZIANO, M.S. - SYNTERRA CORPORATION YOEL GEBRAI, M.S. - SYNTERRA CORPORATION JOHNATHAN EBENHACK, M.S. - SYNTERRA CORPORATION LAWRENCE C. MURDOCH, PH.D. - FRx, INC. BONG YU, PH. D. - SYNTERRA CORPORATION Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, 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 Marshall Steam Station (MSS, Marshall, Site, Station). Duke Energy Carolinas, LLC (Duke Energy) owns and operates the MSS located in Terrell, Catawba County, North Carolina. Operation of MSS began in 1965. Four coal-fired units currently are in operation there. Operation of the first two units began in 1965 and 1966 with a capacity of 350 megawatts (MW) each. Operation of the second two units began in 1969 and 1970 with a capacity of 648 MW each. The current electricity - generating capacity is 2,090 MW. Wastewater and coal combustion residuals (CCRs) have historically been managed in the Site's ash basin, on -Site landfills, and as structural fills. Inorganic compounds in the wastewater and ash have dissolved and have migrated in groundwater downgradient of the ash basin. Numerical simulations of groundwater flow and transport have been calibrated to pre - decanted conditions and used to evaluate different scenarios being considered as options for closure of the ash basin and remediation of the groundwater. The predictive simulations presented herein are not intended to represent a final detailed closure or groundwater 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 of the ash basin and groundwater remediation. It should be noted that, for groundwater modeling purposes, a reasonable assumption was made about initiation dates for each of the closure and groundwater remediation options. The assumed dates were based on information that is currently evolving and might vary from dates provided in contemporary documents. The potential variance in closure dates presented in the groundwater model is inconsequential to the results of the model. This modeling report is intended to provide basic model development information and simulations of conceptual basin closure and groundwater remediation designs. The model simulations were developed using flow and transport models MODFLOW and MT3DMS. Boron was the constituent of interest (COI) selected to estimate the time to achieve compliance because it is mobile in groundwater and tends to have the largest extent of migration. Total dissolved solids (TDS) was also modeled because it is a conservative COI also migrating in groundwater out of the ash basin. Strontium is included in the model simulations also. Strontium is a more geochemically controlled constituent with relatively greater background values in the Piedmont geologic region. Page ES-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina These characteristics make it difficult to calibrate the model to observed strontium concentrations. Other less mobile, more geochemically controlled constituents (i.e. arsenic, selenium, and chromium) will follow the same flow path as that of boron, but to a lesser extent. The less mobile, geochemically controlled constituents do not have discernable plumes and are modeled separately using a geochemical model. This report describes refinements that have improved the accuracy and resolution of details in the model of the Marshall site since previous versions (HDR, 2016; SynTerra 2018b). The model includes recent revisions to the designs of the closure scenarios developed by AECOM. The model includes data from new deep wells located along the dam. The grid has been refined in some areas to improve the model calibration results. A comprehensive dataset (through the first quarter of 2019) of hydraulic heads and boron concentrations was used to recalibrate the model. The model also considers groundwater corrective action. Results of the simulations indicate that boron concentrations in groundwater greater than the 02L standard— in North Carolina Administrative Code, Title 15A, Subchapter 02L, Groundwater Classification and Standards (02L) — are present southeast of the ash basin. The presence of boron beyond the compliance boundary and beneath Lake Norman is predicted, although there are no data available to verify the predicted concentrations beneath Lake Norman. Boron concentrations greater than the 02L standard are also present north of the dam. Dropping the hydraulic head in the ash basin by decanting and subsequent closure will reduce the driving force for further migration of boron, but will not have a significant effect on the pre -decanting boron distribution in locations where there are boron concentrations greater than 02L. After ash basin decanting, hydraulic gradients become gradual near the ash basin dam, and are largely controlled by the nearby Lake Norman. Proposed groundwater corrective action, however, can reverse the gradients and recover boron that has migrated beyond the 02L compliance boundary. The simulations include an evaluation of two ash basin closure scenarios, one that involves closure -by -excavation and another that involves a final cover system closure - in -place design. Additional predictive simulations of the two closure scenarios with remediation that achieves 02L compliance approximately nine years after of operation are also considered. The remediation design modeled in these scenarios uses both extraction and clean water infiltration to achieve compliance. Modeling results suggest that extraction alone might not achieve compliance in a reasonable timeframe due to the limited effect that extraction systems have on COIs present in the unsaturated zone. Page ES-2 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina The results of the closure simulations for the closure -by -excavation design and final cover system closure -in -place (in the absence of groundwater remediation) design are summarized by the distributions of the maximum boron concentration 14 years after closure (closure -in -place), 3 years before closure (closure -by -excavation), 164 years after closure (closure -in -place), and 147 years after closure (closure -by -excavation) (Figure ES-1) and by the time series of boron concentrations at two representative locations downgradient of the ash basin (Figure ES-1 and Figure ES-2). These predictive simulation results show the boron distribution several decades after closure in addition to a long-term prediction over a century after closure. Results of the simulations show the extent of where the boron concentration in groundwater is greater than the 02L standard. For both closure scenarios, the boron plume is present beyond the compliance boundary 3 years prior to closure for the closure -by -excavation scenario and 14 years post -closure for the closure -in -place scenario (Figure ES-1). The boron plume remains present in concentrations greater than the 02L standard beyond the compliance boundary 147 years post -closure for the closure -by -excavation scenario and 164 years post -closure for the closure -in -place scenario (Figure ES-1). The maximum boron concentration comparisons indicate the closure scenarios have a similar degree of effectiveness in reducing plume migration beyond the compliance boundary for the excavation and closure -in -place system designs (Figure ES-1 and ES-2). The time needed to achieve compliance with the 02L standard at the compliance boundary is more than 200 years for both the closure -by - excavation design and the closure -in -place design without additional groundwater corrective action. Two reference locations downgradient of the ash basin are used to evaluate changes in boron concentrations over time for the two closure designs in the absence of groundwater remediation (Figure ES-1 and ES-2). The boron concentrations are decreasing with time for both closure scenarios. The time to reach compliance is predicted to be more than 200 years for both closure scenarios although the closure -by - excavation design is predicted to reach compliance decades earlier at Point 1. At Point 2, boron is decreasing with time at a similar rate for both closure scenarios. The time to reach compliance will be considerably more than 200 years for both scenarios and there is a marginal difference between the two time series curves The effect of active remediation on each of the closure scenarios is presented in Figure ES-3. The considered remediation design consists of 66 extraction wells pumping at a total extraction rate of 652 gallons per minute (gpm) and 24 clean water infiltration wells infiltrating clean water at a combined rate of 285 gpm. The results show a Page ES-3 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina significant reduction in the time to reach compliance for both scenarios to within 9 years from the start of remediation. There is only a slight difference between the performance of the closure -by -excavation design and the closure -in -place design. Data from recent ash pore water and saprolite pumping tests and new deep bedrock wells near the ash basin dam were included in this revision of the model. Analyses of the numerical and analytical pumping tests indicate that the average hydraulic conductivity of the ash ranges from 0.3 feet per day (ft/d) to 4.5 ft/d in the vicinity of the pumping test wells. It was assumed that this general distribution is representative of the hydraulic conductivity of the ash and an averaged value of 2 ft/d was used throughout the basin. Six new deep bedrock wells (AB-1BRLLL, AB-213R, AB-10BRL, AL-1BRL, AL-2BRLLL, MW-14BRL) were drilled and are included in this model to reduce the uncertainty in model predictions in the deep bedrock. Four wells (AB-2BR, AB-10BRL, AL-1BRL, and MW-14BRL) were drilled to a total depth of 300 feet and two wells (AB-1BRLLL and AL-2BRLLL) to a total depth of 500 feet. AL-1BRL and MW-14BRL are near the Phase I Landfill and AB-10BRL and AL-2BRLLL are in or near the Phase II Landfill. AB-2BR and AB-1BRLLL were installed on the dam. The boron concentration was at or less than the detection limit in each of these deep bedrock wells. The model is calibrated to replicate the sampled boron concentrations at these wells. The model simulations indicate that there are no exposure pathways associated with the groundwater flow through the ash basin and the water supply wells used for water supply in the vicinity of the Marshall site. Water supply wells are outside, or upgradient of the groundwater flow system that contains the ash basin. Groundwater migration of constituents from the ash basin does not affect water supply wells under pre -decanted conditions or pre -closure conditions, or in the future under the different closure scenarios simulated. Page ES-4 CLOSURE -BY -EXCAVATION 3 YEARS PRIOR TO CLOSURE i CLOSURE -IN -PLACE 14 YEARS POST -CLOSURE � � 1•� t ,• a r ' t 8 i ' I i a � I CLOSURE -BY -EXCAVATION 147 YEARS POST -CLOSURE i CLOSURE -IN -PLACE 164 YEARS POST -CLOSURE' ILK t' � I i ♦ ��' ' 1goi #1 LEGEND `� DUKE GRAPHIC SCALE 1,250 0 1,250 2,500 ■ REFERENCE LOCATIONS ENERGY BORON 700 - 4,000 Ng/L CAROLINAS (IN FEET) BORON > 4,000 /L Ng DRAWN BY: Y.DATE: 1/1/2019 REVISED BY: R.. KIEKH KIEKHAEFER DATE: 122/188/2019 — - — - PROPOSED LANDFILL EXPANSION �� CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 ASH BASIN WASTE BOUNDARY PROJECT MANAGER: B. WILKER LANDFILL BOUNDARY synTer www.s nterracor .com FIGURE ES-1 - - ASH BASIN COMPLIANCE BOUNDARY - LANDFILL COMPLIANCE BOUNDARY COMPARISON OF SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR BOTH NOTES: CLOSURE SCENARIOS ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS COLLECTED MODELING REPORT ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH A COORDINATE SYSTEM F PS3 00 ( AD 3)TION OF NORTH CAROLINA STATE PLANE TERRELL, NORTH CAROLINA Point 1, Maximum boron concentration in all layers 3500 3000 tio 2500 c 0 4- 2000 r. d V u 1500 c 0 L m 1000 500 2125 The two reference locations are shown in Fig. ES-1. Year 0 '- 2025 2500 2000 J 0 41 1500 41 V O 1000 O O m 500 0 t` 2025 Closure -in -Place Closure -by -Excavation 02L std = 700 µg/L 2225 Point 2, Maximum boron concentration in all layers 2125 Closure -in -Place Closure -by -Excavation 02L std = 700 L µg/ 2225 The two reference locations are shown in Fig. ES-1. Year J DUKE ENERGY v,-Ni DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 FIGURE ES-2 SUMMARY OF MAXIMUM BORON CONCENTRATION IN ALL LAYERS AS FUNCTIONS a APPROVED BY: B. WILKER DATE: 12/12/2019 OF TIME FOR THE TWO CLOSURE SCENARIOS PROJECT MANAGER: B. WILKER UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION www.synterracorp.com synTerra TERRELL, NORTH CAROLINA CLOSURE -BY -EXCAVATION AFTER 9 YEARS I CLOSURE -IN -PLACE AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION OF ACTIVE GROUNDWATER REMEDIATION ilk r t� a ey .1 1. yiI �s CLOSURE -BY -EXCAVATION AFTER 179 YEARS I CLOSURE -IN -PLACE AFTER 179 YEARS OF ACTIVE GROUNDWATER REMEDIATION OF ACTIVE GROUNDWATER REMEDIATION -�.00' .Y. i A`4v LEGEND / DUKE 1250 GRAPHIC SCALE O50 2,500 CLEAN WATER INFILTRATION WELL ENERGY EXTRACTION WELL (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L CHECKED BY: E. WEBSTER DATE: 12/18/2019 — - — -PROPOSED LANDFILL EXPANSION � APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER ASH BASIN WASTE BOUNDARY synTel 1 Q www.s nterracor .com LANDFILL BOUNDARY FIGURE ES-3 - - - - ASH BASIN COMPLIANCE BOUNDARY COMPARISON OF SIMULATED MAXIMUM BORON LANDFILL COMPLIANCE BOUNDARY CONCENTRATIONS IN ALL NON -ASH LAYERS FOR BOTH CLOSURE SCENARIOS WITH ACTIVE REMEDIATION NOTES: ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER4, 2019. AERIAL WAS COLLECTED MODELING REPORT ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH 3PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM F PS3200 (NAD8 TERRELL, NORTH CAROLINA Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, 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................................................................................................................1-4 2.0 Conceptual Model........................................................................................................2-1 2.1 Aquifer System Framework.................................................................................2-1 2.2 Groundwater Flow System.................................................................................. 2-1 2.3 Hydrologic Boundaries......................................................................................... 2-2 2.4 Hydraulic Boundaries........................................................................................... 2-2 2.5 Sources and Sinks.................................................................................................. 2-2 2.6 Water Budget......................................................................................................... 2-3 2.7 Modeled Constituents of Interest........................................................................ 2-3 2.8 Constituent Transport........................................................................................... 2-3 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............................................................................4-4 4.5 Flow Model Calibration Targets.........................................................................4-6 4.6 Transport Model Parameters............................................................................... 4-6 4.7 Transport Model Boundary Conditions.............................................................4-9 4.8 Transport Model Sources and Sinks................................................................... 4-9 4.9 Transport Model Calibration Targets...............................................................4-10 5.0 Model Calibration To Pre -decanted Conditions....................................................5-1 5.1 Flow Model Calibration........................................................................................ 5-1 5.2 Flow Model Sensitivity Analysis......................................................................... 5-4 5.3 Historical Transport Model Calibration............................................................. 5-4 5.4 Transport Model Sensitivity Analysis................................................................ 5-7 Page i Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE OF CONTENTS (CONTINUED) SECTION PAGE 6.0 Predictive Simulations Of Closure Scenarios........................................................ 6-1 6.1 Interim Models with Ash Basin Decanted (2021-2036 or 2021-2053) ............. 6-1 6.2 Closure -in -place with Monitored Natural Attenuation ................................... 6-2 6.3 Closure -in -place with Active Remediation........................................................ 6-4 6.4 Closure -by -Excavation with Monitored Natural Attenuation ....................... 6-5 6.5 Closure -by -Excavation with Active Remediation............................................ 6-7 6.6 Conclusions Drawn from the Predictive Simulations ...................................... 6-8 7.0 References......................................................................................................................7-1 Page ii Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina LIST OF FIGURES Figure ES-1 Comparison of simulated maximum boron concentrations (µg/L) in all non -ash layers for both closure scenarios Figure ES-2 Summary of maximum boron concentrations as functions of time for both closure scenarios Figure ES-3 Comparison of simulated maximum boron concentrations in all non -ash layers for both closure scenarios with active remediation Figure 1-1 USGS location map, Marshall Steam Station, Terrell, NC Figure 4-1 Numerical model domain Figure 4-2 Fence diagram of the 3D hydrostratigraphic model Figure 4-3 Computational grid used in the model Figure 4-4 Hydraulic conductivity estimated from slug tests performed in ash at 14 sites in North Carolina Figure 4-5 Hydraulic conductivity estimated using slug tests performed in saprolite at 10 Piedmont sites in North Carolina Figure 4-6 Hydraulic conductivity estimated using slug tests performed in the transition zone at 10 Piedmont sites in North Carolina Figure 4-7 Hydraulic conductivity estimated using slug tests performed in fractured rock at 10 Piedmont sites in North Carolina Figure 4-8 Distribution of model recharge zones Figure 4-9 Model surface water features outside of the ash basin area Figure 4-10 Model surface water features in the ash basin area Figure 4-11 Water supply wells in the model area Figure 5-1 Model hydraulic conductivity zones in ash layer 2 Figure 5-2 Model hydraulic conductivity zones in saprolite layer 5 Figure 5-3 Model hydraulic conductivity zones in saprolite layer 6 Figure 5-4 Model hydraulic conductivity zones in saprolite layer 7 Figure 5-5 Model hydraulic conductivity zones in saprolite layer 8 Figure 5-6 Model hydraulic conductivity zones in transition zone layer 9 Page iii Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina LIST OF FIGURES (CONTINUED) Figure 5-7 Model hydraulic conductivity zones in upper fractured bedrock layer 10 Figure 5-8 Model hydraulic conductivity zones in upper fractured bedrock layer 11 Figure 5-9 Model hydraulic conductivity zones in upper fractured bedrock layer 12 Figure 5-10 Model hydraulic conductivity zones in upper fractured bedrock layer 13 Figure 5-11 Model hydraulic conductivity zones in fractured bedrock model layers 14-16 Figure 5-12 Model hydraulic conductivity zones in deep bedrock model layers 17-21 Figure 5-13 Comparison of observed and computed heads from the calibrated steady state flow model Figure 5-14 Simulated heads in the transition zone layer 9 Figure 5-15 Simulated heads in the upper fractured bedrock layer 10 Figure 5-16 Simulated heads prior to decanting with calibration targets in the upper fractured bedrock layer Figure 5-17 Groundwater divide and flow directions under pre -decanted conditions at the MSS Figure 5-18 COI ash basin source zones Figure 5-19 COI landfill source zones Figure 5-20 Simulated maximum boron concentrations (µg/L) in all non -ash layers prior to decanting Figure 5-21 Simulated maximum TDS concentrations (mg/L) in all non -ash layers prior to decanting Figure 5-22 Simulated maximum strontium concentrations (µg/L) in all non -ash layers prior to decanting Figure 6-1 Simulated hydraulic heads in the transition zone after decanting Page iv Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina LIST OF FIGURES (CONTINUED) Figure 6-2 Simulated maximum boron concentrations in all non -ash layers after decanting Figure 6-3 Closure -in -place closure design used in simulations Figure 6-4 Drains used in the closure -in -place design Figure 6-5 Simulated hydraulic heads for the closure -in -place scenario Figure 6-6 a,b,c,d Simulated maximum boron concentrations in all non -ash layers 14 years post -closure (a), 64 years post -closure (b), 114 years post - closure (c), 164 years post -closure (d) for the closure -in -place scenario Figure 6-7 a,b Simulated maximum strontium and TDS concentrations in all non ash layers 14 years post -closure for the closure -in -place scenario Figure 6-8 Simulated hydraulic heads in the transition zone with active groundwater remediation for the closure -in -place scenario Figure 6-9 a,b,c,d Simulated boron concentrations in all non -ash layers after 9 years of active remediation (a), 29 years of active remediation (b), 79 years of active remediation (c), 129 years of active remediation (d), and 179 years of active remediation (e) for the closure -in -place scenario with active groundwater remediation Figure 6-10 a,b Simulated maximum strontium and TDS concentrations in all non - ash layers for the closure -in -place scenario after 9 years of active groundwater remediation Figure 6-11 Closure -by -excavation design used in simulations (from AECOM, 2019) Figure 6-12 Drain network used in closure -by -excavation simulations Figure 6-13 Simulated hydraulic heads in the transition zone after closure -by - excavation Figure 6-14 a,b,c,d Simulated maximum boron concentrations in all non -ash layers in 3 years prior to closure (a), 47 years post -closure (b), 97 years post - closure (c), 147 years post -closure (d) for the closure -by -excavation scenario Page v Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina LIST OF FIGURES (CONTINUED) Figure 6-15 a,b Simulated maximum strontium and TDS concentrations in all non - ash layer 3 years prior to closure for the closure -by -excavation scenario Figure 6-16 Simulated hydraulic heads in the transition zone with active groundwater remediation for the closure -by -excavation scenario Figure 6-17 a,b,c,d Simulated maximum boron concentrations in all non -ash layers after 9 years of active remediation (a), 29 years of active remediation (b), 79 years of active remediation (c), 129 years of active remediation (d), 179 years of active remediation (e) for the closure -by -excavation scenario with active groundwater remediation Figure 6-18 a,b Simulated maximum strontium and TDS concentrations in all non - ash layer after 9 years of active remediation for the closure -by - excavation scenario with active remediation Page vi Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina LIST OF TABLES Table 5-1 Comparison of observed and computed heads for the calibrated flow model Table 5-2 Calibrated hydraulic parameters Table 5-3 Water balance on the groundwater flow system for pre -decanted conditions Table 5-4 Flow model sensitivity analysis Table 5-5a-c Ash basin boron, TDS, and strontium source concentrations used in historical transport model Table 5-6a-c Landfill boron, TDS, and strontium source concentrations used in historical transport model Table 5-7a-c Observed and computed boron, strontium, and TDS in monitoring wells Table 5-8 Transport model sensitivity to the boron Ka values Table 6-1 Water balance on the groundwater flow system for decanted conditions Table 6-2 Groundwater clean infiltration and extraction well information Page vii Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, 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 Marshall Steam Station (MSS, Marshall, Station, or Site). Duke Energy Carolinas, LLC (Duke Energy) owns and operates the MSS located in Terrell, Catawba County, North Carolina (Figure 1-1). MSS is a four -unit coal-fired electricity - generating plant with a combined capacity of 2,090 megawatts (MW). Commercial operations at Marshall Steam Station began in 1965 with Unit 1 (350 MW) followed by operation of Unit 2 (350 MW) beginning in 1966. Operation of Unit 3 (648 MW) began in 1969, and operation of Unit 4 (648 MW) began in 1970. Cooling water for MSS is provided by Lake Norman. Coal combustion residuals (CCRs), composed primarily of fly ash and bottom ash, have historically been managed in the Site ash basin, which was constructed in 1965, immediately north of the plant. The ash basin is located east of a topographic divide along Sherrills Ford Road and south of a topographic divide along Island Point Road. Dry ash has been stored in other areas at the Site, including the unlined Dry Ash Landfill Phase I and Phase II (Permit No. 1804-INDUS-1983), the lined Flue Gas Desulfurization (FGD) Landfill (Permit No. 1809-INDUS-), and the double -lined Industrial Landfill No. 1 (Permit No. 1812-INDUS-2008). Ash was used as structural fill in the Photovoltaic (PV) Structural Fill (State Permit No. CCB0031), the road next to and within the ash basin leading up to the PV Structural Fill (State Permit No. CCB0030), and beneath parts of the Industrial Landfill No. 1 (State Permit No. CCB0072). Inorganic compounds in the ash have dissolved and have been transported in groundwater in the vicinity of the ash basin. Numerical simulations of groundwater flow and transport have been calibrated to pre - decanted conditions and used to evaluate different scenarios being considered as scenarios for closure of the ash basin and remediation of the groundwater. The methods and results of those simulations are described in this report. 1.1 General Setting and Background The Site is located in the Piedmont region of North Carolina. The topography in the area is hilly with elevations ranging from a high of about 910 feet' near the intersection of Sherrills Ford Road and Island Point Road to a low of about 756 feet at Lake Norman. Lake Norman, which serves as the cooling lake for the Station, has a full pool elevation of 760 feet, but the actual water level fluctuates between about 752 feet and 760 feet. Sherrills Ford Road and Island Point Road are located along topographic ridges that act as groundwater divides west and north of the ash basin and landfills. The topography 1 The datum for all elevation information presented in the report is NAVD88. Page 1-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina slopes downward and southeast toward Lake Norman. The ash basin dam is located immediately adjacent to Lake Norman. The water level of the ponded ash basin water has typically been maintained at an elevation of 789 feet. The ponded ash basin water is currently being decanted and this activity is expected to be completed by March 2021. Coal combustion residuals (CCR) were historically sluiced to the ash basin. The ash basin consists of a single cell that was formed by damming the former Holdsclaw Creek near where the creek historically entered the Catawba River. The basin has a dendritic shape with coves of deposited ash. Approximately 394 acres are within the ash basin waste boundary. All coal ash from the MSS was sluiced to the ash basin from 1965 until 1984. Since 1984, fly ash has mainly been disposed of in the Site ash landfills. Sluicing of bottom ash to the ash basin has recently been discontinued. Wastewater from the ash basin is discharged to Lake Norman by National Pollutant Discharge Elimination System (NPDES) permitted Outfall 002 (NC0004987). Two unlined ash landfills, the Phase I Dry Ash Landfill and the Phase II Dry Ash Landfill, are located near and partially within the ash basin. The Phase I Dry Ash Landfill contains about 522,000 tons of fly ash, which was placed from 1984 to 1986. The Phase I Dry Ash Landfill is located just east of the ash basin, near the ash basin dam and Lake Norman. The Phase II Dry Ash Landfill contains about 4,877,280 tons of fly ash and is located in the northeast part of the ash basin. The Phase II Dry Ash Landfill received fly ash starting in 1986 and was completed in 1999. The Phase II Dry Ash Landfill was built over part of the existing ash basin in the northeast part of the basin. These landfills were closed with a soil cover system. The PV Structural Fill, consisting of compacted fly ash, was constructed between 2000 and 2013 in the northwestern part of the ash basin. This PV Structural Fill was built over part of the existing ash basin. This fill was closed with a soil cover system. The Industrial Landfill No. 1 is located adjacent to the northern part of the ash basin, south of Island Point Road. This landfill has a three -component liner with leak detection and leachate collection. Stormwater and leachate from the landfill are collected and piped to the Lined Retention Basin (LRB). The subsurface at the Site is composed of three primary flow zones. The shallow zone is residual soil consisting primarily of saprolite, which forms when bedrock is weathered in place. Below the saprolite zone is a transition zone consisting of less weathered and highly fractured bedrock. Bedrock, present below the transition zone, generally is fractured with decreased fracturing with depth. Typically, the saprolite is partially saturated and the water table fluctuates within it. Water movement is generally preferential through the weathered and fractured bedrock of the transition Page 1-2 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina zone (i.e., enhanced permeability zone). Groundwater within the Site area exists under unconfined, or water table, conditions within the saprolite and 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 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 and Lake Norman. The groundwater flow and transport model for the 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 site assessment in early and mid-2015. The first set of simulations was completed in March 2016 (HDR, 2016). The present model domain has been greatly expanded compared to the 2016 model, and the number of model layers has been doubled. The earlier model was calibrated to hydraulic heads and COI concentrations measured in 2015. Since that time, significant Site activities have taken place including the installation of many additional monitoring wells. The current model has been accordingly revised with respect to the 2015 model. These additional data have further improved the predictive capability and reduced uncertainty in the model results. To take advantage of this potential, the model was recalibrated using data from both the new and existing groundwater wells. The following data sources were used during calibration of the revised groundwater flow and transport model: • Average Site -wide water levels measured in Coal Ash Management Act (CAMA)/CCR/compliance groundwater monitoring wells through the first quarter of 2019. • Groundwater quality data obtained from CAMA/CCR/compliance sampling events conducted in the first quarter of 2019 • Hydrogeologic data described in the Comprehensive Site Assessment (CSA) reports completed in 2015 (HDR, 2015) and 2018 (SynTerra, 2018a) • Ash basin pumping tests in ash and saprolite • Deep bedrock wells • Surface water elevations provided by Duke Energy • Water supply well information provided by Duke Energy Page 1-3 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina This study consists of three main activities: developing a calibrated steady-state flow model of pre -decanted conditions, developing a historical transient model of COI transport that is calibrated to pre -decanted conditions, and performing predictive simulations of the possible closure and groundwater remediation actions at the Site. The predictive simulations include consideration of two different closure scenarios: closure -in -place and closure -by -excavation. In both of the closure scenarios ash is excavated from the Phase I Dry Ash Landfill. In the closure -in -place scenario, a low permeability final cover system is built over the ash in the ash basin, the Phase II Dry Ash Landfill, and the PV Structural Fill. In the excavation scenario ash is excavated from the ash basin, and a final cover system is built over the Phase II Dry Ash Landfill, and the PV Structural Fill. 1.2 Objectives The overall objectives of the groundwater flow and transport modeling are to predict the performance of the two closure scenarios and groundwater remediation designs, and to guide decisions during the selection of closure and groundwater remediation actions. The flow and transport models have been undergoing a process of continuous improvement and refinement by including new field data. The continuous improvement process is designed to increase the accuracy and reliability of the performance predictions. This report describes the results of the most recent refinement of the flow and transport models. These models were developed in early and mid-2019 using data through the first quarter of 2019. The predictive simulations shown in this report are not intended to represent a final detailed closure or groundwater 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 and remediation actions. The predictive simulations in this report are an evaluation of the closure scenario designs and assumptions as of September 2019. Closure designs might have been refined since then, due in part to results from the simulations. The predictive simulations in this report characterize the most recent closure design available when the model was developed, but the design process is ongoing and some aspects of the simulations might differ from the most current closure design. Page 1-4 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina 2.0 CONCEPTUAL MODEL The conceptual site model for the Marshall site is based primarily on the 2015 Comprehensive Site Assessment report (HDR, 2015) and the 2018 Comprehensive Site Assessment Update (2018 CSA) for the MSS (SynTerra, 2018c) and the Corrective Action Plan (CAP) Update (SynTerra, 2019). These reports contain extensive detail and data related to most aspects of the conceptual site model that are used here. Data collected since the 2018 CSA submittal is also included in the model. 2.1 Aquifer System Framework The aquifer system at the Site consists of an unconfined aquifer. Depending on the local topography and hydrogeology, the water table surface might exist in the saprolite, the transition zone, or the fractured bedrock. At some isolated locations along streambeds, the upper unit (saprolite) is absent. At other locations, the upper unit might be unsaturated, with the water table located in deeper units (transition zone and fractured bedrock). The hydraulic conductivity at the Site has been measured in a series of slug tests in the different units. Twenty-seven (27) slug tests were performed in the coal ash, with measured conductivities ranging from 0.007 ft/d to 199 ft/d. Thirty-eight (38) slug tests performed in saprolite wells yielded hydraulic conductivities ranging from 0.004 ft/d to 137 ft/d. Seventy (70) slug tests performed in transition zone wells yielded results ranging from 0.001 ft/d to 35 ft/d. Twenty-six (26) slug tests conducted in bedrock wells indicate hydraulic conductivity values ranging from 0.07 ft/d to 38 ft/d. The range of observed conductivity in the saprolite, transition zone, and bedrock highlights the large degree of heterogeneity in the system. 2.2 Groundwater Flow System The unconfined groundwater system at the Site is dominated by flow due to recharge that falls within a watershed roughly defined by Sherrills Ford Road to the west, Island Point Road to the north, and by a ridge to the east of the ash basin. Within this area, groundwater flows toward the ash basin, and then toward Lake Norman, or a nearby small creek, where it ultimately discharges. The ponded ash basin water was maintained at an elevation of about 789 feet prior to decanting, which is about 33 feet above the typical water elevation in the adjacent Lake Norman. The higher hydraulic head in the ponded ash basin water caused some groundwater flow through the small ridge to the east of the ash basin near the dam. Groundwater flowing through this ridge discharges to the small stream and cove of Lake Norman east of the ash basin. Page 2-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina The groundwater system is recharged from infiltrating precipitation, and from water that infiltrates from the ponded ash basin water. The average value of recharge in the vicinity of the MSS was estimated at 8 inches per year (in/yr). The North Carolina map of recharge by Haven (2003) does not show values for Catawba County, but the average value in nearby counties is consistent with this estimate. A reduced rate of recharge (1 inch per year) was assumed for the power plant, and an infiltration rate of zero was assumed for the constructed wetland areas (which have an underlying geomembrane) and the lined Industrial and FGD landfills. There are three public supply wells and 80 private water wells that have been identified within a half -mile of the ash basin compliance boundary (SynTerra, 2018a). Most of these wells are located west of the Site, along Sherrills Ford Road, and south of the Site, along NC Highway 150. A few wells are located at residences along Island Point Road, north of the Site. Pumping rates for the private wells were not available, and completion depths were available for only about 20 of the wells. 2.3 Hydrologic Boundaries The major discharging locations for the shallow water system serve as hydrologic boundaries to the shallow groundwater system. Lake Norman is the major hydrologic boundary in the area. 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 are 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 Groundwater flow from areal recharge (rainfall infiltration) and flow out of the ponded ash basin water are sources of water to the groundwater system. Groundwater in the model domain discharges to Lake Norman, and to small streams and drainages. These small streams and drainages are located primarily outside of the ash basin around the periphery of the model. The water supply wells within the model area remove only a small amount of water from the overall hydrologic system. Page 2-2 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina 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 from recharge and the ponded ash basin water. Water leaves the system through discharge to Lake Norman and several small creeks, and through private wells. 2.7 Modeled Constituents of Interest Antimony, arsenic, barium, beryllium, boron, cadmium, chromium (hexavalent and total), cobalt, iron, manganese, molybdenum, selenium, strontium, sulfate, TDS, thallium, and vanadium have been identified as constituents of interest (COIs) for groundwater at the Site (SynTerra, 2017). Three COIs that are present beyond the compliance boundary were selected for modeling. The COIs selected consist of boron, TDS, and strontium. Of those three constituents, boron is the most prevalent in groundwater. Boron is present at significant concentrations in the ash basin and near and beneath the Phase I and Phase II Dry Ash Landfills, and the PV Structural Fill. A small boron plume extends to monitoring wells south and east of the ash basin near the ash basin dam. Boron is found in monitoring wells screened in the saprolite, the transition zone, and the bedrock. Boron concentrations in background monitoring wells are less than the .0202 Groundwater Quality Standard - in North Carolina Administrative Code (NCAC), Title 15A, Subchapter 02L, Groundwater Classification Standards (02L) - and are generally less than the laboratory detection limit. TDS is not as prevalent as boron, but it is present greater than the 02L standard in the vicinity of the ash basin and is included in the modeling of the Site. Attenuation for these conservative COIs primarily occurs through physical means (i.e., dispersion and dilution). Strontium transport is also simulated, however since it is a more geochemically controlled constituent and can have fairly high background concentrations in the Piedmont, emphasis was primarily placed on the more conservative COIs during the calibration. This report will focus primarily on boron because it is the dominant mobile constituent but includes results for TDS and strontium. 2.8 Constituent Transport The COIs that are present in the coal ash dissolve into the ash pore water. As water infiltrates through the ash, water containing COIs can enter the groundwater system. Once in the groundwater system, the COIs are transported by advection and dispersion, subject to retardation due to adsorption to solids. If the COIs reach a hydrologic boundary or water sink, they are removed from the groundwater system, and they enter the surface water system, where in general, they are greatly diluted. At this Site, Page 2-3 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina boron and TDS are the primary constituents considered that are migrating from the ash basin. The less mobile, more geochemically controlled constituents (i.e., arsenic, selenium, and chromium) will follow the same flow path as that of boron, but to a lesser extent. Of the less mobile, more geochemically controlled constituents, the only one considered in this report is strontium, while others do not have discernable plumes and are modeled separately using a geochemical model. Page 2-4 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, 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 (31)) 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 are widely used in industry and government, and are considered to be industry standards. The models were assembled using the Aquaveo GMS 10.4 graphical user interface (http://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. Several versions of MODFLOW have been developed since its inception. 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. That 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 activities. Some of the Site's flow models were challenging to run due to the topography and layers that become unsaturated in the model. It was found that using the NWT solver options "MODERATE" with the xMD matrix solver could overcome these difficulties. 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 on the soil and rock matrix. Page 3-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, 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 construct the numerical grid. • Step 3: Populate the numerical grid with flow parameters. • Step 4: Conduct calibration round 1, which includes adjustment of the numerical grid. • Step 5: Develop a transient model of constituent transport development. • Step 6: Conduct calibration round 2 to ensure the flow model matches the observed heads and the transient model reproduces the observed plumes. 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 about 3 miles by 3 miles and uses a north -south orientation (Figure 4-1). The model is generally bounded to the east by Lake Norman, which also forms part of the northern and southern boundary. To the west, the model boundary is more than a half -mile from the ash basin, and it is separated from the ash basin by a major topographic ridge that runs along Sherrills Ford Road, and by creek drainages located west of Sherrills Ford Road. The northern boundary is located beyond the topographic ridge that runs along Island Point Road, and it extends either to Lake Norman, or to a location beyond a creek drainage that runs into Lake Norman. The southern boundary is nearly a mile from the ash basin, and it extends to Lake Norman on both the eastern and the extreme western sides. The distance to the boundary from the ash basin is large enough to prevent boundary conditions from artificially affecting the results near the basin. The ground surface of the model was developed by HDR and was interpolated from the North Carolina Floodplain Mapping Program's 2010 Light Detection and Ranging (LiDAR) elevation data. These data were supplemented by on -Site surveys conducted by Duke Energy in 2014. The elevations used for the top of the ash surface in the ash basin were modified from the topographic and bathymetric data to provide a model surface that can accommodate planned regrading of ash for the closure -in -place closure scenario. For pre -decanted conditions simulations, the portions of the ash basin that Page 4-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina have ponded water above the ash are given a large hydraulic conductivity to represent the open -water conditions. The hydrostratigraphic model (called a solids model in GMS) consists of five units: ash, saprolite, transition zone, upper fractured bedrock, and deeper bedrock. The contact elevations between these units were determined from boring logs from previous studies by HDR (2016). The contact elevations were estimated by HDR for locations where well logs were not available by extrapolation of the borehole data using the Leapfrog Hydro geologic modeling tool. This program was used by HDR to develop surfaces defining the top of the saprolite, transition zone, and bedrock. While the contacts between the upper units (ash, saprolite, transition zone, bedrock) are well defined, the division of the bedrock into an upper fractured zone, a mid -depth bedrock zone and deeper bedrock was subjective. For the purposes of model construction, the upper fractured mid -depth zones are both 150 feet thick. The deeper bedrock extends another 250 feet below the mid -depth zone for a total bedrock thickness of 550 feet in the model. The upper -level and mid -level bedrock zones in the model were given a heterogeneous hydraulic conductivity distribution to represent more and less fractured zones. Figure 4-2 shows a fence diagram of the 3D hydrostratigraphic unit viewed from the southeast, with a vertical exaggeration of 4x. The light grey material corresponds to the ash in the basin, the yellow material is the saprolite, the tan material is the transition zone, the orange material is the upper fractured part of the bedrock, and the dark grey material is the deep bedrock. The numerical model grid is shown in Figure 4-3. The grid is discretized in the vertical direction using the solids model (Figure 4-2) to define the numerical model layers. The top 4 model layers represent the ash basin, including the dam that forms the basin, the Phase II Dry Ash Landfill, and the PV Structural Fill. Model layers 5-8 represent the saprolite except in the Phase I Dry Ash Landfill area, where model layer 5 represents ash. Model layer 9 represents the transition zone. Model layers 10-13 represent the upper fractured part of the bedrock, while model layers 14-16 represent mid -depth parts of the fractured bedrock. The deep bedrock (which may also be fractured) is represented by model layers 17-21. The model varies in thickness from about 630 feet to 720 feet. The discretization in the horizontal direction is variable with smaller grid cells in and around the ash basin area. The minimum horizontal grid spacing in the finely divided areas is about 30 feet, while the maximum grid spacing near the outer edges of the model is about 200 feet. The grid contains a total of 1,036,874 active cells in 21 layers. Page 4-2 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina 4.2 Hydraulic Parameters The horizontal hydraulic conductivity and the horizontal -to -vertical hydraulic conductivity anisotropy ratio are the main hydraulic parameters in the model. The distribution of these parameters is based primarily on the model hydrostratigraphy, with additional horizontal and vertical variation. Most of the hydraulic parameter distributions in the model were heterogeneous across a model layer. The geometries and parameter values of the heterogeneous distributions were determined during the flow and transport model calibration process. Initial estimates of parameters were based on experience at other Piedmont sites in North Carolina, literature values, results of slug and core tests, and simulations performed using a preliminary flow model. The hydraulic parameter values were adjusted during the flow model calibration process described in Section 5.0 to provide a best fit to observed water levels in observation wells and were further refined during calibration of the transport model. Slug test data from hundreds of wells at the Duke Energy coal ash basin sites in North Carolina are shown in Figures 4-4 through 4-7. The hydraulic conductivity of coal ash measured at 14 sites in North Carolina ranges over about 4 orders of magnitude, with a geometric mean of approximately 1.8 ft/d (Figure 4-4). Ash hydraulic conductivity values measured in slug tests at Marshall ranged from 0.001 ft/d to 199 ft/d. The pre -decanted conditions flow model is not very sensitive to the ash conductivity, but the predicted heads in the closure -in -place simulations are more sensitive to the ash hydraulic conductivity. Four pumping tests were conducted within the ash basin including the underlying saprolite in June 2018 to help refine the value of these unit specific parameters. Numerical and analytical hydraulic conductivity estimates that range from 0.3 ft/day to 4.5 ft/day were obtained from these solutions, which are plotted in Figure 4-4 (SynTerra 2019a; SynTerra 2019b). An average hydraulic conductivity of approximately 2 ft/d was used in the model. The hydraulic conductivities from hundreds of slug tests performed in saprolite wells at 10 Duke Energy sites within the Piedmont are shown in Figure 4-5. These also range over 4 or more orders of magnitude, and have a geometric mean value of 0.9 ft/d. Saprolite slug tests performed at Marshall ranged from 0.004 ft/d to 137 ft/d. Transition zone hydraulic conductivities from hundreds of slug tests at 10 Duke Energy sites located in the Piedmont are shown in Figure 4-6. These range over 5 orders of magnitude, with a geometric mean of 0.9 ft/d. The measured values at Marshall range from 0.001 ft/d to 35 ft/d. Page 4-3 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina Fractured bedrock hydraulic conductivities from hundreds of slug tests at 10 Duke Energy sites within the Piedmont in North Carolina (Figure 4-7) range over 6 orders of magnitude, with a geometric mean value of 0.3 ft/d. It is possible that this geometric mean value is larger than the true average value for deep bedrock for three reasons. First, the bedrock wells at these sites are almost all screened in the uppermost few tens of feet of the bedrock, which is expected to be more highly fractured than deeper bedrock zones. Second, the wells are typically screened in zones with visible flowing fractures, rather than in zones with intact unfractured rock. Finally, wells that do not produce water are not slug tested. These factors might bias the slug test data to higher values than might be representative of the deeper bedrock as a whole. At Marshall, the measured values from slug tests in shallow bedrock ranged from 0.07 ft/d to 38 ft/d. 4.3 Flow Model Boundary Conditions Lake Norman forms a hydraulic boundary east of the ash basin. The lake is treated as a high conductance general head boundary in the uppermost active model layer with an elevation of 756 feet. The lake wraps around the northeastern and southeastern parts of the model. The western model boundary does not align with any clearly defined hydraulic features. This boundary is located more than a half -mile from the ash basin, and there is a major topographic ridge between the model boundary and the basin along with two deep creek drainages located west of the ridge. Most of the western boundary is treated as a low conductance general head boundary with the head set to an elevation of 15 feet below the top of the saprolite, except in stream valleys, where a no flow boundary is used perpendicular to the streams. The flow in these valleys is dominated by flow toward the streams, which are modeled as drains. The southwestern boundary is treated as a no -flow boundary as it crosses stream valleys approximately perpendicular to the streams, which are treated as drains in the model. This boundary is also almost a mile away from the ash basin. Model boundaries were set at appropriate distances from the study area to ensure that boundary effects did not affect the simulation results in the vicinity of the ash basins. 4.4 Flow Model Sources and Sinks The flow model sources and sinks consist of Lake Norman, the ponded ash basin water, recharge, wells, streams, ponds and wet areas that are assumed to directly drain into the ponded ash basin water. Recharge is a significant hydrologic parameter in the model, and the distribution of recharge zones in the model is shown in Figure 4-8. As described in Section 2.2, the recharge rate for the MSS site was estimated to be 8 in/yr. The recharge rate for the MSS Plant was set to 1 in/yr due to the large areas of roof and pavement. The ponded ash Page 4-4 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina basin water and other ponds in the model are treated as high conductance general head boundaries. The recharge rate was set to 0 in/yr in the constructed wetlands areas. The recharge rate through the lined FGD and Industrial landfill covers was set to 0 in/yr. Lake Norman, the ponded ash basin water, and several smaller ponds were treated as specified general head zones in the model (Figures 4-9 and 4-10). With this condition, the hydraulic head is specified, along with a conductance. For large values of conductance, this condition acts like a specified head boundary condition. The general head condition was used here because the GMS software can perform external water balance calculations with the general head boundary condition that it cannot perform with the specified head condition. Lake Norman is maintained at an elevation of 756 feet and the ponded ash basin water is maintained at an elevation of 789 feet. The many creeks exert a significant local control on the hydrology in the model. These features are shown as green lines in Figure 4-9. The position of these creeks was determined mainly from the topographic map (Figure 1-1), supplemented by a Site visit during which each drainage feature near the ash basin was inspected. The elevation of locations along the creeks were determined from the surface LiDAR elevations, and those elevations were assumed to be 2 feet below the ground surface. The creeks were simulated using the DRAIN feature in MODFLOW with a high conductance value (100 ft2/d/ft). The outer "fingers" of the ash basin contains several areas of standing water, along with the main sluicing channel. Most of these surface water features were treated as general head boundaries (Figure 4-10). With this condition, the water bodies may add or remove water from the groundwater system, depending on the hydraulic heads in the groundwater flow system. Two marshy areas in the ash basin near the Phase II Dry Ash Landfill were simulated as drains. Figure 4-11 shows the location of public and private water supply wells in the model area. There are three public supply wells in the model domain. One well is located at the plant and is operated by Duke Energy. This well is open from an elevation of 727 feet to 214 feet and it pumps at an average rate of 20,000 gallons per day. A second public supply well is operated by the Boathouse Restaurant on NC Highway 151, across the lake from the plant. This well is open from an elevation of 716 feet to 520 feet, and it was assumed to pump 3,000 gallons per day. A third public supply well is located at The Old Country Church, on NC Highway 150. This well is screened from an elevation of 722 feet to 702 feet and was assumed to pump 280 gallons per day on average. This pumping rate is similar to that of a household and was selected based on the Page 4-5 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina assumption that the church is mainly occupied on Sunday mornings but is vacant during most of the remainder of the week. There are 80 private wells inside the model boundary, five of which are known to be abandoned. Where depth data were available, the private wells were open over the known depths. In most cases, the well depths were unknown, and the wells were assumed to be open in the upper part of the bedrock in model layer 10. The pumping rates from the wells were unknown, and the model assumed a pumping rate of 280 gallons per day, which is an average water use for a family of four (Treece et al. 1990; USGS, 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 simulated as a specified flux into layer 6 (saprolite) in the model. 4.5 Flow Model Calibration Targets The steady state flow model calibration targets were water level measurements made in 220 observation wells through the first quarter of 2019. The water level data for wells with multiple measurements were averaged to account for seasonal variations. Results from all wells sampled were included in the calibration. The wells included those screened in each of the hydrostratigraphic units and many sets of nested wells. 4.6 Transport Model Parameters The transport model uses a sequence of steady-state MODFLOW simulations to provide the time -dependent groundwater velocity field. The MODFLOW simulation started January 1965, and it continued through February 2019. The transient flow field is approximated as a series of flow fields that correspond with conditions at different times as the Industrial and FGD landfills were constructed. The transient flow field was modeled as four successive steady state flow fields; one corresponding with the Site conditions before the Industrial and FGD landfills were constructed, one corresponding with conditions after the eastern cell of the Industrial landfill was completed, one after the FGD landfill was completed, and one after the western cell of the Industrial landfill was completed. These steps all represent minor changes to the groundwater flow field, and they are simulated by adjusting the recharge rate at the landfills from the background value of 8 in/yr to 0 in/yr once the landfills were completed. Neither of these landfills is considered to be a source of COIs at the Site. The key transport model parameters are the constituent source concentrations in the ash, and the constituent soil -water distribution coefficient (Ka). Other parameters are the longitudinal, transverse, and vertical dispersivity, and the effective porosity. The constituent source concentrations in the ash basin, Phase I and II Dry Ash Landfills, and the PV Structural Fill were initially estimated from the ash pore water concentrations Page 4-6 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina and from concentrations in nearby wells. During the transport model calibration process, the basin and other source areas were subdivided, and different concentrations were assigned to different zones at different times. The timing of constituent sources appearing in the Phase I and II Dry Ash Landfills and the PV Structural Fill locations correspond to the time when they became active (The Phase I Dry Ash Landfill became active in 1984, Phase II Dry Ash Landfill became active in 1986, and the PV Structural Fill became active in 2000). The ash basin source zones become active when the model starts (1965). In areas where landfills or structural fill was built over the ash basin, the ash basin areas were activated first (in 1965), followed by the landfill or structural fill at the appropriate time. Once they are activated, source concentrations of the constituent are held constant at the specified levels in the ash layers during the historical transport simulation, but they are allowed to vary in time during the predictive simulations that follow. Changes in concentration within the source zones during the predictive simulations are controlled by flow in these regions and the chemical transport parameters (i.e. Kd values). The numerical treatment of adsorption in the model requires special consideration because part of the system is a porous media (ash, saprolite, and transition zone) with a relatively high porosity, whereas the bedrock is a fractured medium 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 used here simulated the 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 per area of media 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 as with other sites. The velocity of a COI, Vc, is affected by both the porosity, 0, and the retardation factor, R, as: v, =OR (1a) where the COI retardation factor is computed internally in the MT3DMS code using a conventional approach: R=1+PbK d 0 (1b) Page 4-7 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina and V is the volumetric flux (Darcy velocity), pb is the bulk density and Ka is the distribution coefficient assuming linear equilibrium sorption. The retardation factor for boron 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 Ka is held constant. This is unrealistic, and it is the reason why a small Ka value is assigned to the bedrock, where the effective porosity is due to the fractures, and is low. This reduction of Ka 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 Ka for COIs in the bedrock layers of the model was reduced by scaling it 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 five samples from the Marshall ash basin using USEPA (LEAF) Method 1316. The leaching data were analyzed to develop a Ka (partition coefficient) value for boron in the coal ash. The average of those test values was 0.77 mL/g. The modeling approach for the predictive simulations of future boron transport allows the boron concentration in the ash to vary with time in response to water infiltrating and flowing through the ash, dissolving boron, and flowing out of the source areas. Using the Ka value that is derived from ash leaching tests ensures that the model response of the boron in the ash to water flowing through the source areas is realistic. The Ka value for the boron outside of the ash basin was treated as a calibration parameter. Boron is expected to be mobile, and to have a low Ka value. The calibrated Ka values for the saprolite and transition zone layers were 0.5 mL/g. In the fractured bedrock, a much lower value was used as described above of 0.02 mL/g. These values were derived by adjusting the Ka value to better match groundwater boron concentrations in observation wells. The Ka values used for TDS in the model were 0.15 mL/g in the ash, 0.1 mL/g in the saprolite and transition zone, and 0.01 mL/g in the bedrock. The Ka values used for strontium in the model were 0.15 mL/g in the ash, 0.1 mL/g in the saprolite and transition zone, and 0.02 mL/g in the bedrock. The longitudinal dispersivity was assigned a value of 20 feet, the transverse dispersivity was set to 2 feet, and the vertical dispersivity was set to 0.2 feet. The dispersivities are model parameters that are used to describe the diffusion -like spreading of plumes that occurs in addition to transport with the bulk groundwater flow. Dispersivity values are both model -dependent and scale -dependent. The longitudinal dispersivity is typically Page 4-8 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina found to be between 1/200 and 1/10 of the constituent plume travel distance. Transverse and vertical dispersivities are typically on the order of 1/10 and 1/100 of the longitudinal value, respectively. The dispersivities used in this study are consistent with these literature values. The transport model is not very sensitive to the dispersivities within a reasonable range of values. The effective porosity was set to a value of 0.3 in the unconsolidated layers, and to 0.01 in all the bedrock layers. The soil dry bulk density was set to 1.6 g/mL. 4.7 Transport Model Boundary Conditions The transport model boundary conditions are specified as no -flow on the exterior edges of the model except where general head boundaries exist. With a general head condition, water can flow into or out of the model, depending on the head in each gridblock relative to the specified head. If water flows into the model, the concentration of COIs in the incoming water are set to 0 µg/L. Water that flows out of the model removes associated COIs based on their concentration. All of the general head water bodies (lakes, river, and ponds) are treated in this manner. The infiltrating precipitation is assumed to be clean, and enters from the top of the model. The ponded ash basin water is handled differently because it is considered a source of boron in the model. In the ponded ash basin water, the water level is maintained using a constant general head hydraulic boundary, and the boron concentration is specified in model cells below the water surface. The water entering the model from the general head boundary does not contain boron, but as it infiltrates through the ash layers it equilibrates with the specified boron concentrations in those layers. The initial condition for the historical transport model assumes a boron concentration of 0 µg/L throughout the Site in 1965. No background concentrations are considered. 4.8 Transport Model Sources and Sinks The ash basin, Phase I and II Dry Ash Landfills, and the PV Structural Fill are the source of boron in the model. During the historical transport simulation, these sources are simulated by holding the boron concentration constant in cells located inside the ash in these zones, which simulates a continuous replenishing of source material in these zones. The boron concentrations from the historical transport simulation form the initial condition for the predictive simulations of future transport at the Site. The predictive simulations do not hold the boron concentrations constant in the ash source zones because no additional source material is being added to the ash source zones, and this mobile constituent can wash out of the ash over time. The boron Kd value used for the ash was measured in ash leaching tests using ash from the Site to ensure that the simulated boron leaching rate is realistic. Page 4-9 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina COIs in soil and rock at the Site can continue to serve as a source to groundwater. This potential is fully accounted for in the model by continuously tracking the COI concentrations in time in the saprolite, transition zone, and rock materials throughout the model. The historical transport model simulates the migration of boron through the soil and rock from the ash basin, and these results are used as the starting concentrations for the predictive simulations. Therefore, even if all the coal ash is excavated, the transport model predicts ongoing effects on groundwater from the soil beneath the ash. The transport model sinks are the general head or drain conditions used to simulate the lake, ponds, and creeks. As groundwater enters these features, it is removed along with any dissolved COI mass. Similarly, if water containing COIs were to encounter a pumping well, the COIs would be removed with the water. 4.9 Transport Model Calibration Targets The transport model calibration targets are boron concentrations measured in 182 monitoring wells in the first quarter of 2019. All sampled wells are included in the calibration. New wells and data that have been collected since that time were not included in the updated model calibration process. Fall 2019 data from newly installed wells suggest the model predictions are conservative; the model over -predicts the actual groundwater concentrations in some isolated areas. Page 4-10 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina 5.0 MODEL CALIBRATION TO PRE -DECANTED CONDITIONS 5.1 Flow Model Calibration The flow model was calibrated in stages starting with a relatively simple layered model. All calibration was done by manual adjustments of parameters, simultaneously matching the recent water levels measured in all observation wells (Table 5-1). Additional flow model calibration was required to also match the pre -decanted boron distribution. The primary calibration parameters are the three-dimensional distribution of hydraulic conductivity. Each model layer has been subdivided into hydraulic conductivity zones. These model conductivity zones are shown in Figures 5-1 through 5-12, and the calibrated hydraulic conductivity values assigned to each zone in each layer are listed in Table 5-2. Starting at the top, in layers 1-4, the layers represent both the coal ash and the ash basin dam. It was important to calibrate the conductivity of the dam fill material in these layers separately (Figure 5-1) in order to match the head values in wells located in and near the dam. The dam fill material has a calibrated conductivity of 0.03 ft/d. In the pre -decanted steady-state flow model, a high hydraulic conductivity (100 ft/d) was applied to the ponded ash basin water to represent open water (Figure 5-1). The hydraulic conductivity of the ash was assumed to be 2.0 ft/d. The pre -decanted conditions flow model is relatively insensitive to the ash conductivity because the water levels around the ash basin are largely controlled by the ponded ash basin water and other surface water bodies. The value of 2.0 ft/d that was used is close to the median of more than 200 slug tests performed at 14 coal ash basin sites in North Carolina shown in Figure 4-4, and it falls within the range of values measured at Marshall. The selected model ash hydraulic conductivity of 2 ft/d is also consistent with numerical and analytical pumping test analyses (SynTerra 2019a and 2019b). Although the pre - decanted conditions model is not sensitive to this parameter, the predictive closure -in - place simulation is more sensitive to the ash conductivity. The calibrated background hydraulic conductivity for the saprolite (layers 5-8) was 1.0 ft/d, which is equal to the median value for slug tests performed in saprolite at 10 coal ash basin sites in the Piedmont of North Carolina, and near the median for slug tests performed at Marshall (Figure 4-5). This material is heterogeneous and zones of both higher and lower conductivity were required to match the hydraulic heads and boron transport in and around the ash basin (Figure 5-2, 5-3, 5-4, 5-5 and Table 5-2). The range of saprolite conductivity in the model is 0.02 ft/d to 10.0 ft/d, which falls within the range of values measured in slug tests in the 10 Piedmont Sites shown in Figure 4-5. Page 5-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina The calibrated background conductivity for the transition zone (layer 9) was 1.5 ft/d. This value falls near the average value for slug tests performed in the transition zone at 10 Duke Energy sites located in the Piedmont of North Carolina (Figure 4-6). The transition zone is heterogeneous, with values ranging from 0.008 ft/d to 8.0 ft/d (Figure 5-6 and Table 5-2). The low conductivity zones are mainly located in areas where there are topographic ridges or hills. The lower conductivity values are required in order to match the higher hydraulic heads observed in wells in these locations. The upper bedrock zone in the model includes layers 10-13, and it is 150 feet thick. It was necessary to adjust model conductivity values separately in each of these layers in order to match the observed hydraulic heads and boron concentrations in observation wells. The background conductivity value used in the model of 0.7 ft/d is close to the median of values measured from slug tests at 10 Duke Energy sites located in the Piedmont of North Carolina, and in slug tests performed at Marshall (Figure 4-7). The upper bedrock conductivity ranges from 0.003 ft/d to 10 ft/d in the model (Figures 5-7 to 5-10 and Table 5-2). The low values were used to better match high hydraulic heads that are observed in wells located on ridges and other topographically high areas. Higher conductivity values were needed in places to match the lower observed hydraulic heads, and in some cases, to match the observed boron transport. A fairly complicated three-dimensional pattern of conductivity was required beneath the Phase II Dry Ash Landfill to match the heads in shallow and bedrock wells in this area (Figure 5-7, 5-8, 5-9). The wells AL-41) and AL-4BR screened beneath the landfill have average heads of about 811 feet, while the deeper AL-4BRL has a head of only 798 feet. Matching these heads is accomplished by placing a low permeability zone above AL- 4BRL and connecting a highly permeable fracture zone to AL-4BRL (Figure 5-9). This combination also provides a good match with the boron data in this area. The mid -depth bedrock includes model layers 14-16 (Figure 5-11 and Table 5-2) and is 150 feet thick. The background value of 0.1 ft/d is somewhat lower than the shallower bedrock value. It is expected that the degree of fracturing, and hence the average conductivity should decrease with depth. The conductivity of these layers range from 0.005 to 12.0. The high conductivity value is located around well AL-02BRLL, beneath the Phase II Dry Ash Landfill. This well is about 350 feet deep, and it is screened at an elevation of about 570 feet. This deep well intersects a productive fracture zone that consistently indicates high boron concentrations (>10,000 µg/L). The high conductivity zone in layers 13-15 was used to represent a highly fractured zone in this location, and it was needed to reproduce the high observed boron concentrations in this well. A deeper Page 5-2 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina well (AL-02BRLLL) was installed at a depth of about 500 feet at this location in 2019. Boron was not detected at this depth. The deep bedrock layer extends over the bottom 250 feet (layers 17-21) of the model and was assigned a uniform value of 0.01 ft/d (Figure 5-12) with the exception of one zone in part of the ash basin with a hydraulic conductivity of 0.005 ft/d. This was done to reduce the downward gradient in that area in order to improve the boron calibration in AB-6BRL. The flow model calibration is relatively insensitive to this value, but the model conductivity is high enough to allow some water flow in the deep bedrock. The combination of the low rock porosity (0.01) and the high mobility of boron results in some deeper predicted migration of boron in parts of the model. Hydraulic and boron concentration data from the deep bedrock wells were used to refine estimates of the bedrock hydraulic conductivity distribution. The final calibrated flow model has a mean head residual of -0.58 feet, a root mean squared error (RMSE) of 2.86 feet, and a normalized root mean square error (NRMSE) of 2.51 percent. The range of heads at the site is about 114 feet with a maximum of 871.83 feet and a minimum of 756.85 feet. 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 5-13. The best -fit hydraulic parameters from the calibration effort are listed in Table 5-2. The computed heads in the transition zone (model layer 9) are shown in Figure 5-14. The simulated heads in the first fractured bedrock model layer (model layer 10) are shown in Figure 5-15. These are similar to the shallower heads. The calibration wells are also shown in this figure (many of the nested wells plot on top of each other). The green and yellow bars in Figure 5-16 indicate the magnitude of model error at each well. The green color indicates that the difference is less than 5 feet and the yellow color indicates a difference of 5 feet to 10 feet. The majority of the wells have a model error of less than 5 feet. The groundwater flow divide around the ash basin is shown in Figure 5-17 as the red line. This divide wraps around the west, north, and east part of the ash basin area. Inside of this divide, groundwater flows toward the ash basin and Lake Norman (blue arrows), while outside of the divide, groundwater flows away from the ash basin. The approximate water balance in the ash basin watershed is summarized in Table 5-3. The size of the watershed that contributes to groundwater flow toward the ash basin depends on the locations of the groundwater divides that can change over time (e.g., ash basin is excavated or capped) and vary with depth. Under pre -decanted conditions, the Page 5-3 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina watershed area contributing flow toward the basin is estimated at approximately 1327 acres. Removing the areas that are capped landfills, constructed wetlands, and the ponded ash basin water; the remaining area is approximately 1161 acres, resulting in approximately 482 gallons per minute (gpm) of groundwater flow from recharge. Water leakage from the ponded ash basin water to the groundwater system is calculated to be 80 gpm. Flow removed from the groundwater system by streams and ditches is approximately 75 gpm and flow removed from the groundwater system by finger lakes and canals is approximately 270 gpm. To complete the water balance, it is estimated that approximately 217 gpm discharges to Lake Norman when the ponded ash basin water elevation is at 789 feet. Subject to uncertainty, the estimate is related to the subsurface hydraulic conductivity distribution. 5.2 Flow Model Sensitivity Analysis A parameter sensitivity analysis was performed by systematically increasing the main parameters by 100% and decreasing the main parameters by 50% of their calibrated values (Table 5-4). Only the main background hydraulic conductivity values and recharge rate were varied in this study. The model is very sensitive to the recharge rate, and is moderately sensitive to the saprolite, and transition zone conductivities. The model is strongly sensitive to the conductivity of the upper 150 feet of bedrock (the upper bedrock layers 10-13), and it is moderately sensitive to the mid -depth bedrock conductivity. The model is slightly sensitive to the ash conductivity and increasing the ash conductivity reduced the error. The model is not very sensitive to the conductivity of the deeper bedrock. 5.3 Historical Transport Model Calibration The transient flow field was modeled as four successive steady state flow fields; one corresponding to the Site conditions before the Industrial and FGD landfills were constructed, one corresponding to conditions after the eastern cell of the Industrial landfill was completed, one after the FGD landfill was completed, and one after the western cell of the Industrial landfill was completed. These steps all represent small changes to the groundwater flow field, and they are simulated by adjusting the recharge rate from the background value of 8 in/yr to 0 in/yr once the landfills were built. Neither of these landfills are considered to be a source of COIs at the Site because they are lined landfills with negligible infiltration contributing boron concentrations to the groundwater. The boron distribution in and around the ash basin is extremely complex. Dissolved boron concentrations in some locations at the Site are as high as 50,000 µg/L and 100,000 µg/L. At other nearby locations, the boron concentration can be much less, < 700 ug/L. Page 5-4 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina Boron is found as deep as 250 feet below the original ground surface at well AL- 02BRLL. Reproducing this complex pattern of COI distribution required the use of many different specified COI source concentration zones (Figures 5-18 and Tables 5- 5a,b,c). The ash basin was subdivided into 33 different zones with specified boron, strontium, and TDS concentrations (Figure 5-18 and Tables 5-5a,b,c). These sources are activated at the start of the simulation, in 1965. At some locations the COI concentration was not specified in all four of the ash layers; this was done to improve the calibration with transition zone and shallow bedrock wells in those areas. At two locations, the Phase II Dry Ash Landfill and the PV Structural Fill, ash was later placed on top of part of the ash basin. Monitoring wells in these locations sometimes indicate greater boron concentrations than in surrounding wells, and this is reflected in the specified source concentrations. The remaining parts of the Dry Ash Landfills Phase I and Phase II and PV Structural Fill were described using seven specified concentration zones (Figure 5-19 and Tables 5- 6a,b,c). These COI source zones were activated when the respective landfill or structural fill became active. The calibrated Kd values for the boron was 0.5 in the saprolite and transition zone materials, and 0.02 in the bedrock. The effective porosity was set to 0.3 in the unconsolidated layers and reduced to 0.01 in the bedrock layers. Table 5-7 compares measured (first quarter, 2019) and simulated pre -decanted conditions boron concentrations. The simulated maximum boron concentrations in all non -ash flow layers are shown in Figure 5-20. The model predicts boron transport above the 02L standard beyond the current compliance boundary from the ash basin and Phase I Dry Ash Landfill to the south and east near the ash basin dam. This boron migration appears to occur mainly in the saprolite, transition zone, and shallow bedrock, but transport in the mid -depth bedrock is also predicted. Well cluster AB-01 is located near the north eastern toe of the ash basin dam. This set of nested wells includes four bedrock wells that extend as deep as 500 feet below ground surface. The calibrated model gives a good match with the observed boron concentrations in these wells: • 2902 µg/L in well AB-1S (observed value of 2390 µg/L) • 1388 µg/L in well AB-11) (observed value of 1180 µg/L) Page 5-5 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina • 2325 µg/L in well AB-1BR (observed value of 3430 µg/L) • 2035 µg/L in well AB-1BRL (observed value of 2730 µg/L) • 1814 µg/L in well AB-1BRLL (observed value of 2320 µg/L) • 115 µg/L in well AB-1BRLLL (observed value of 63 µg/L) The model also predicts deep boron transport beneath the Phase II Dry Ash Landfill, and it shows significant boron concentrations in some of the deep bedrock wells at this location: • 16760 µg/L in well AL-2S (observed value of 12900 µg/L) • 6995 µg/L in well AL-2D (observed value of 12300 µg/L) • 4941 µg/L in well AL-2BR (observed value of 4820 µg/L) • 5293 µg/L in well AL-2BRL (observed value of 2130 µg/L) • 6771 µg/L in well AL-2BRLL (observed value of 10600 µg/L) • 28 µg/L in well AL-2BRLLL (observed value of <50 µg/L ) The simulation shows boron concentrations greater than the 02L standard to the east of the northern portion of the dam in bedrock beneath monitoring wells MW-10S and MW-10D. Boron concentrations are non -detect in groundwater samples from these wells and this is reproduced by the model. A deeper bedrock well is not available to confirm the predicted boron transport in the bedrock at this location. The results for the strontium and TDS calibrations are shown in Figures 5-21 and 5-22 and Tables 5-7b and 5.7c. The strontium and TDS plumes are not as prevalent boron. However, TDS is present in concentrations greater than 02L beyond the compliance boundary, and the strontium and TDS plumes are predicted to be present beyond the dam and beneath Lake Norman. However, the strike of bedrock fracture orientations measured along the shoreline at AB-1BRLLL and AB-2BR were strongly preferential parallel to the shoreline. This suggests the hydraulic conductivity is higher parallel to the shoreline and lower perpendicular to the shoreline. Therefore, it is possible that the plume actually does not (and would not) extend as far offshore beneath the lake as the current simulations indicate. Overall, the simulated COI concentrations appear to reasonably match the observed concentrations in most areas, and the model -simulated boundary where the concentration is greater than the 02L standard is similar to the observed locations. The normalized root mean square error (NRMSE) of the predicted boron values is 1.77 Page 5-6 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina percent and it is 3.6 percent for the predicted TDS values. For strontium, the NRMSE is 10.8 percent which is higher than for boron and TDS. Strontium can have higher natural background values in the Piedmont and it is also a more reactive COI, which made the calibration more challenging. The simulation results are generally consistent with the monitoring well data that show no effects on water supply wells from the ash basin, structural fill, or landfills. 5.4 Transport Model Sensitivity Analysis A parameter sensitivity analysis was conducted to evaluate the effects of Kd on the NRMSE. Kd is assumed to be uniform across each grid layer and to vary with depth, as described in Section 4.6. The sensitivity analysis was performed on the calibrated transport model by systematically increasing and decreasing boron Kd values by a factor of 5 from their calibrated values (0.5 mL/g in the saprolite and transition zone, and 0.02 mL/g in the bedrock). The model was then run using the adjusted Kd values, and the NRMSE was calculated and compared to the NRMSE for the calibrated model. The calibrated transport model simulates boron concentrations with NRMSE values of 1.77 percent for boron (Table 5-8). Decreasing the boron Kd by multiplying by a factor of one -fifth increases the NRMSE to 4.55 percent and increasing the boron Kd by 5 times increases the NRMSE to 7.76 percent (Table 5-8). The simulation results are seen to be sensitive to the Kd value range tested here. The sensitivity analysis results indicate that the Kd values used for boron are near optimal values. In terms of the boron plume behavior, the low Kd simulation over -predicts the extent of boron migration, while the high Kd simulation under -predicts the extent of boron migration. Page 5-7 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina 6.0 PREDICTIVE SIMULATIONS OF CLOSURE SCENARIOS The simulated February 2019 boron distribution was used as the initial condition in closure simulations of future flow and transport at the Site. There are two main simulated scenarios: one in which the ash in the ash basin and a final cover system is installed over the Phase II Dry Ash Landfill and the PV Structural Fill and one in which a final cover system is installed over the ash basin, Phase II Dry Ash Landfill, and the PV Structural Fill. The Phase I Dry Ash Landfill is excavated in both closure scenarios. The decanting (draining of free-standing water) of the ponded ash basin water, which began in 2019, is expected to be completed by March 2021. Ponded ash basin water decanting will have an effect on the groundwater flow field, because the ponded water level will be lowered by about 17 feet, removing free-standing water. After the ponded ash basin water decanting, the final Site closure activities will start and will continue for several years. The closure -in -place is expected to take 15 years to complete, while excavation is expected to take about 32.4 years to complete. The predictive simulations are run in two steps. The first step is a simulation that starts in 2021 and uses the groundwater flow field after the ponded ash basin water is decanted. The starting boron distribution for this simulation is the simulated February 2019 concentration distribution. This simulation step continues for a period of 15 years (for closure -in -place) or 32.4 years (for closure -by -excavation) ending in either 2036 or 2053. The second step assumes that construction activities have been completed and uses the closure -in -place or closure -by -excavation design flow field for transport simulations. These simulations start in 2036 or 2053 and continue for nearly 200 years after closure. 6.1 Interim Models with Ash Basin Decanted (2021-2036 or 2021- 2053) This simulation represents an interim period after the pond is decanted, but before closure action construction is completed. Decanting of the pond is simulated by removing the specified head zone that represents the pond in the pre -decanted conditions flow simulation and replacing it with a small specified general head area at an elevation of 772 feet, which is 17 feet below the pre -decanted ash basin free water surface. The specified head area is located in the deepest part of the pre -decanted ponded ash basin water (Figure 6-1). Several small ponds in the southern part of the ash basin, and the sluice channel were converted from a general head boundary condition to a drain condition. Recharge at a rate of 8 in/yr is added to the ash basin, and boron initial conditions come from the historical transport simulation. Boron Page 6-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina concentrations in the ash are no longer held constant, and the boron can leach from the ash according to its Ka value (which was derived from ash leaching tests). Boron present in the underlying soil and rock is mobile and moves in response to the groundwater flow with adsorption occurring according to the soil or rock Ka value. The surface drains in the southern part of the ash basin remain in this simulation. Figure 6- 1 shows the simulated steady-state hydraulic heads after the pond is decanted. Figure 6-2 shows the simulated boron distribution in the transition zone in 2036 with the ash basin decanted prior to closure -in -place and excavation. The area subject to infiltration from rainfall is increased due to the decanting of the ash basin with an acreage of 1243. The total groundwater recharge applied to the watershed is 516 gpm. Groundwater drainage inside the ash basin after decanting is predicted to be approximately 300 gpm. Outside of the ash basin, groundwater is drained at a rate of 66 gpm. The inferred groundwater discharge flow rate to Lake Norman is approximately 150 gpm; a reduction of 67 gpm when compared to the estimated discharge to Lake Norman under pre -decanting conditions. These results are summarized in Table 6-1. 6.2 Closure -in -place with Monitored Natural Attenuation The closure -in -place simulations begin with the COI distributions from the decanted basin simulations described above. The ash basin cover design used in the model is based on a closure plan design developed by AECOM (2019) (Figure 6-3). After the ponded ash basin water is decanted, this draft design calls for the ash to be regraded inside the basin to form a gentle slope from north to south toward the dam. Shallow swales are built that approximately trace the original surface water drainage patterns in the basin footprint, with ditches at the center of each swale. The cover system consists of an impermeable geomembrane, covered with 2 feet of soil and a grass surface. The surface drainage ditches follow the centers of the final cover swales and converge to a single channel that discharges into Lake Norman just north of the existing dam. An underdrain system to collect ash pore water below the cap is proposed. The current conceptual design for this subsurface drainage system calls for the installation of drains 5 feet below the elevation of the cover system in a network that corresponds to the cover surface water drainage system. The drain network that was used in the closure - in -place simulation to simulate this underdrain system is shown in Figure 6-4. Drain elevations between these nodes were interpolated along the arcs. The drains are simulated using the MODFLOW DRAIN feature, using a relatively high conductance of 10.0 ft2/d/ft. Groundwater flow into these drains is removed from the model. If the closure -in -place design is selected, the discharge from the drainage system might have to be collected, treated and discharged per the NPDES permit for a period of time. Page 6-2 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina The closure -in -place design is simulated by removing all of the original ash basin surface water features and replacing them with this underdrain network. The ash properties are adjusted to reflect regrading of the ash in the area near the dam (a conductivity of 2 ft/d), and the recharge rate through the cover is set to 0.00054 in/yr. This value is based on landfill cover simulations performed using the Hydrologic Evaluation of Landfill Performance program (HELP) by AECOM. The plans call for excavation of the Phase I Dry Ash Landfill, and three of the northern ash basin fingers near the Phase II Dry Ash Landfill (these three fingers are being removed to install the temporary storm water ponds for storm water being rerouted around the PV Structural Fill). The Phase II Dry Ash Landfill and the PV Structural Fill are capped in this simulation. The recharge rate through the cover of these fills is set to 0.00054 in/yr. The COI initial conditions for this simulation come from the dewatered ponded ash basin water simulation in the year 2036. The boron concentrations in the ash are variable in time, and the Ka value in the ash was set to a value measured in ash leaching tests performed with ash from the basin (0.77 mL/g). The calibrated Kd values for strontium and TDS are both set to 0.15 mL/g. The steady-state hydraulic heads in the transition zone are shown in Figure 6-5. The groundwater flow field changes slightly from pre -decanted conditions, and it continues to be dominated by strong groundwater divides to the west, north, and east, with flow toward Lake Norman. The simulation predicts that the size of the watershed would remain relatively unchanged with an area of approximately 1327 acres. The area subject to infiltration from rainfall is reduced to an acreage of 809 due to capping of the ash basin. The total estimated groundwater recharge is 336 gpm. Groundwater drainage inside the ash basin after decanting is predicted to be approximately 158 gpm. Outside of the ash basin, groundwater drains at a rate of 43 gpm. The estimated groundwater discharge flow rate to Lake Norman is 135 gpm; a reduction of 15 gpm when compared with the estimated discharge to Lake Norman under post -decanting conditions. The simulated maximum boron concentrations in all non -ash model layers is shown for 14 years post -closure (Figures 6-6a), 64 years post -closure (Figures 6-6b), 114 years post -closure (Figures 6-6c), and 164 years post -closure (Figures 6-6d) for the closure -in - place simulation. The closure -in -place simulation suggests that in the absence of corrective action, boron might be present at concentrations greater than the 02L standard beyond the current compliance boundary near Lake Norman for several hundred years. COI concentrations shown in groundwater beneath Lake Norman do not represent surface water concentrations in Lake Norman. The dissolved boron Page 6-3 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina concentration in groundwater that is beyond the current or potential compliance boundary never exceeds the USEPA tap water standard of 4,000 µg/L. The strontium and TDS concentration distributions 14 years post -closure are plotted in Figures 6-7a and6-7b. TDS is predicted to be present beyond the compliance boundary and at greater concentrations than the USEPA secondary standard of 500 mg/L 14 years post -closure. Strontium is also predicted to be present beyond the compliance boundary at concentrations greater than 1,500 µg/L, although no drinking water limits are defined for strontium. Both TDS and strontium are predicted to be present along the dam, in the transition zone and bedrock beneath Lake Norman. These simulations show that water supply wells in the area are not affected by the COIs modeled at any time in the future. 6.3 Closure -in -place with Active Remediation The closure -in -place scenario with corrective action such that 02L compliance is achieved 9 years after operation is simulated in two steps. The first step begins once decanting has been completed and a flow field is calculated for the proposed remediation design. The resulting flow field is then used for the transport simulation until 02L compliance is achieved. Once the closure -in -place construction is completed in approximately 15 years post -decanting, a second simulation continues with a flow field that reflects both the closure -in -place closure system and the groundwater remediation closure system. The corrective action occurs primarily north of the dam and along the dam at the Site (Figure 6-8). The remedial system considered consists of sixty-six (66) extraction wells pumping at a total extraction rate of 652 gpm (Table 6-2). Twenty-four (24) infiltration wells are considered to introduce a total of 285 gpm of clean water to the system. The sixty-six extraction wells have water levels maintained at depths about 125 to 150 ft below the ground surface in the wells. This is necessary to reverse the groundwater gradient and capture the groundwater with concentrations greater than 02L beneath Lake Norman. The well depths range from 126 feet to 257 feet below ground surface. All of the extraction wells pump from the bedrock layers in the model. Twenty-five of the extraction wells pump from the bedrock alone while the remaining forty-one (41) wells also extract from the saprolite and the transition zone. Although there is no boron detected along the southern part of the dam, other COIs including strontium and TDS are present as well. Eight extraction wells are included along the southern portion of the dam to capture the additional COIs. These eight extraction wells are screened in the upper bedrock in the model and generate enough drawdown to capture COIs in the shallower flow zone. All of the infiltration wells are screened only in the saprolite. The Page 6-4 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina heads in the infiltration wells are maintained at two feet below ground surface and primarily flush COIs out of the saprolite east of the compliance boundary. The extraction wells are simulated using a vertical series of MODFLOW DRAIN points. The DRAIN bottom elevations are set to the center of the gridblock containing the drain. This simulates a condition where the water is being pumped out of the well casing to maintain the specified water level near the bottom of the well. The DRAIN conductance values are estimated by considering radial flow to a well, which follows the Anderson and Woessner (1992) approach. 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 gridblock is computed as: C= 2zKAz In 0.208Ax rW The conductance value is reduced by 50 percent to account for well skin effects. Infiltration wells are treated similarly, using the General Head Boundary (GHB) condition in MODFLOW, with a conductance calculated the same way, but with a reduction of 75 percent to account for well clogging. The infiltration heads have been set to 2 feet below the ground surface. The computed heads for the design during the decanted period are shown in Figure 6-8. The remediation system achieves 02L compliance within 9 years of operation (Figures 6-9a). Figure 6-9b through 6-9e show the maximum boron distribution in all non -ash layers at 50-year intervals starting 29 years after operation. The remediation system achieves 02L compliance for boron within nine years of operation (Figure 6-9a), and compliance is maintained through nearly 179 years after the beginning of operations. The additional COIs considered, TDS, and strontium are shown in Figures 6-10a and Figure 6-10b, and are predicted to achieve compliance after 9 years of operation also. 6.4 Closure -by -Excavation with Monitored Natural Attenuation This simulation begins in 32.4 years after ash basin decanting using the COI distributions from the decanted pond simulation described in Section 6.2. Excavation is simulated by setting the COI concentrations in the ash layers in the ash basin and Phase I Dry Ash Landfill to zero. The concentrations of boron in the remaining affected soil underneath the ash basin are set to the values from the decanted pond simulation. The ash layers are given a very high hydraulic conductivity (they are now excavated), and the previous ash basin surface water features are removed. Recharge occurs in the ash Page 6-5 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina basin footprint at the background level of 8 in/yr. The Phase II Dry Ash Landfill and the PV Structural Fill are capped in this simulation, and the recharge is set to 0.00054 inches per year. Ash is currently present in the ash basin below the elevation of Lake Norman. After the ash is excavated from the basin, a storm water pond will be present in the excavated area in the southern part of the ash basin. An engineering drawing of the proposed design is shown in Figure 6-11 and this excavated storm water pond is shown in blue in Figure 6-12. A small stream network is added to the ash basin, following the original drainages along the top of the saprolite surface, and draining toward the excavated storm water pond (Figure 6-12). This drain network (green) simulates the springs and streams that will form in the basin. The storm water pond is treated as a general head boundary with a high conductance and a head set to 765 feet, which is a few feet higher than the elevation of Lake Norman. The steady-state hydraulic heads in the transition zone are shown in Figure 6-13. The groundwater now flows toward the excavated storm water pond, where it discharges. Dissolved COIs that discharge into the storm water pond from groundwater are likely to be diluted in the pond by surface water runoff. If this excavation scenario is selected, the discharge from the springs and streams might have to be collected, treated, and discharged per the NPDES permit for a period of time. The size of the watershed increases to approximately 1394 acres after excavation. The area of the watershed subject to recharge from precipitation is reduced to 1101 acres after subtracting the areas of constructed wetlands and landfills. The recharge to the watershed is now 420 gpm, with 112 gpm of recharge to the basin and 308 gpm of recharge outside of the basin. Groundwater discharge inside the excavated basin to the excavated storm water pond and streams is 284 gpm. Drainage outside of the basin to streams and ditches is estimated to be 20 gpm. The estimated groundwater discharge to Lake Norman is reduced to 116 gpm, which is 19 gpm less than the estimated closure - in -place system discharge to Lake Norman. The simulated maximum boron concentrations in any non -ash layer are shown for 3 years pre -closure (Figure 6-14a), 47 years post -closure (Figure 6-14b), 97 years post - closure (Figure 6-14c), and 147 years post -closure (Figure 6-14d) for the excavation case. The figures show the proposed new landfill to accommodate the excavated ash outlined in black. This simulation suggests that in the absence of any further corrective action, boron might continue to be greater than the 02L standard in groundwater beyond the current compliance boundary near Lake Norman for several hundred years. Due to the Page 6-6 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina low hydraulic gradients under the lake, simulated boron concentrations are persistent under Lake Norman in the transition zone and bedrock throughout the future projections. COI concentrations shown in groundwater beneath Lake Norman do not represent surface water concentrations in Lake Norman. The boron concentration in groundwater that is beyond the current or potential compliance boundary never exceeds the USEPA tap water standard of 4,000 µg/L. The strontium and TDS distributions 3 years before closure of the ash basin are shown in Figures 6-15a and 6-15b. TDS is predicted to be present beyond the compliance boundary and at concentrations greater than the USEPA secondary standard of 500 mg/L in 2050. Strontium is predicted to be present beyond the compliance boundary at concentrations greater than 1500 µg/L, although no drinking water standards are defined for strontium. Both TDS and strontium are predicted to be present along the dam, in the transition zone and bedrock beneath Lake Norman. These simulations show that water supply wells in the area are not affected by the COIs modeled at any time in the future. The simulated transport in the closure -in -place scenario differs from the closure -by - excavation case because groundwater containing boron and other COIs is not intercepted by the excavated storm water pond. Over time, plumes of dissolved boron that originate upgradient in the ash basin, Phase II Dry Ash Landfill, and to a lesser extent, the PV Structural Fill are predicted to migrate to the southeast toward Lake Norman. As in the excavation simulation, the simulated boron concentrations are persistent under Lake Norman in the transition zone and bedrock throughout the future projections due to the low hydraulic gradients under the lake. 6.5 Closure -by -Excavation with Active Remediation The active remediation strategy described in Section 6.3 is applied to the closure -by - excavation scenario. During the period prior to the completion of ash basin closure for the closure -by -excavation scenario the simulation uses a flow field that representative of the decanted ponded ash basin water with the groundwater remediation system. Post -closure, the simulation continues with a flow field that includes the excavated ash basin along with the groundwater remediation system. Similar to the closure -in -place scenario, the corrective action occurs primarily north of the dam and along the dam at the Site. Sixty-six (66) extraction wells pump at a total extraction rate of 652 gpm. Twenty-four (24) infiltration wells are considered and introduce a total of 285 gpm of clean water to the system. Again, although there is no boron detected along the southern part of the dam, other COIs including strontium and TDS are present and the eight southernmost extraction wells along the dam are Page 6-7 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina included to capture the groundwater with dissolved COIs beneath Lake Norman. These additional wells also prevent additional groundwater containing COIs from migrating to Lake Norman. The heads in the infiltration wells are maintained at two feet below ground surface for this scenario. The computed heads following completion of excavation are shown in Figure 6-16 and the well information in Table 6-2 summarizes the design for this scenario as well. The boron distribution in Figures 6-17a through 6-17e show the boron plume at various times for all non -ash layers. The boron plume reaches compliance 9 years after the beginning of the operation of the remedial design and compliance is maintained through the year 2200. The evolution of the plumes are similar to what is displayed in Figures 6-9a through 6-9e for the closure -in -place scenario. The effect the remediation design considered has on TDS and strontium is also significant and Figures 6-18a through 6-18b show that compliance is achieved within 9 years of operation for those COIs also. 6.6 Conclusions Drawn from the Predictive Simulations The following conclusions are based on the results of the groundwater flow and transport simulations: • Water supply wells and domestic wells in the area are not affected by boron currently or at any time in the future for any of the scenarios. • Predicted future boron concentrations at and beyond the current compliance boundary vary for the closure -in -place and closure -by -excavation simulations. In both cases a lesser concentration (but greater than 02L) plume of boron is predicted to continue to migrate south and east toward Lake Norman. • In the absence of remedial measures associated with corrective action, boron is predicted to be greater than the 2L standard at the current compliance boundary near Lake Norman for hundreds of years. • A groundwater remediation system consisting of 66 extraction wells and 24 infiltration wells is simulated and is able to achieve 02L compliance within 9 year of operation for both the closure -in -place and the closure -by -excavation designs. • Simulations indicate that strontium and TDS distributions respond in a way that is similar to boron, and these constituents are effectively controlled by the simulated remediation approach. Page 6-8 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina • New field data are not likely to change the conclusion that excavation and the closure -in -place closure designs result in similar transport of boron, strontium, and TDS at the current compliance boundary. Page 6-9 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina 7.0 REFERENCES AECOM, 2019, Duke Energy Marshall Steam Station 2019 Closure Plan Updates - (Draft 60%)) Ash Basin Closure. Anderson, M.P., and W.W. Woessner, 1992, A112lied 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. 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. HDR, 2015a Comprehensive Site Assessment Marshall Steam Station Ash Basin - September 8, 2015. Terrell, NC. HDR, 2015b, Corrective Action Plan Part 1 Marshall Steam Station Ash Basin- December 7, 2015. Terrell, NC. HDR, 2016, Corrective Action Plan Part 2 Marshall Steam Station Ash Basin - March 3, 2016. Terrell, NC 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. 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-. 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, 2017, 2017 Comprehensive Site Assessment Update, October 31, 2017. Page 7-1 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina SynTerra, 2018a, 2018 Comprehensive Site Assessment Update, January 31, 2018. SynTerra, 2018b, Preliminary Updated Groundwater Flow and Transport Modeling Report for Marshall Steam Station, Terrell, NC. November 2018. SynTerra, 2019a, Ash Basin Pumping Test Report for Marshall, January 2019. SynTerra, 2019b, Pumping Test Numerical Simulation Report for Marshall SynTerra, 2019c, Corrective Action Plan Update Marshall Creek Steam Station - Duke Energy Carolinas, LLC - Terrell, North Carolina. December 2019. 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. USGS, 1987. 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. USGS, 1995. North Carolina; Estimated Water Use in North Carolina, 1995. USGS Fact Sheet FS-087-97. 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 7-2 Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina FIGURES CLOSURE -BY -EXCAVATION 3 YEARS PRIOR TO CLOSURE i CLOSURE -IN -PLACE 14 YEARS POST -CLOSURE � � 1•� t ,• a r ' t 8 i ' I i a � I CLOSURE -BY -EXCAVATION 147 YEARS POST -CLOSURE i CLOSURE -IN -PLACE 164 YEARS POST -CLOSURE' ILK t' � I i ♦ ��' ' 1goi #1 LEGEND `� DUKE GRAPHIC SCALE 1,250 0 1,250 2,500 ■ REFERENCE LOCATIONS ENERGY BORON 700 - 4,000 Ng/L CAROLINAS (IN FEET) BORON > 4,000 /L Ng DRAWN BY: Y.DATE: 1/1/2019 REVISED BY: R.. KIEKH KIEKHAEFER DATE: 122/188/2019 — - — - PROPOSED LANDFILL EXPANSION �� CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 ASH BASIN WASTE BOUNDARY PROJECT MANAGER: B. WILKER LANDFILL BOUNDARY synTer www.s nterracor .com FIGURE ES-1 - - ASH BASIN COMPLIANCE BOUNDARY - LANDFILL COMPLIANCE BOUNDARY COMPARISON OF SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR BOTH NOTES: CLOSURE SCENARIOS ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS COLLECTED MODELING REPORT ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH A COORDINATE SYSTEM F PS3 00 ( AD 3)TION OF NORTH CAROLINA STATE PLANE TERRELL, NORTH CAROLINA Point 1, Maximum boron concentration in all layers 3500 3000 tio 2500 c 0 4- 2000 r. d V u 1500 c 0 L m 1000 500 2125 The two reference locations are shown in Fig. ES-1. Year 0 '- 2025 2500 2000 J 0 41 1500 41 V O 1000 O O m 500 0 t` 2025 Closure -in -Place Closure -by -Excavation 02L std = 700 µg/L 2225 Point 2, Maximum boron concentration in all layers 2125 Closure -in -Place Closure -by -Excavation 02L std = 700 L µg/ 2225 The two reference locations are shown in Fig. ES-1. Year J DUKE ENERGY v,-Ni DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 FIGURE ES-2 SUMMARY OF MAXIMUM BORON CONCENTRATION IN ALL LAYERS AS FUNCTIONS a APPROVED BY: B. WILKER DATE: 12/12/2019 OF TIME FOR THE TWO CLOSURE SCENARIOS PROJECT MANAGER: B. WILKER UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION www.synterracorp.com synTerra TERRELL, NORTH CAROLINA CLOSURE -BY -EXCAVATION AFTER 9 YEARS I CLOSURE -IN -PLACE AFTER 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION OF ACTIVE GROUNDWATER REMEDIATION ilk r t� a ey .1 1. yiI �s CLOSURE -BY -EXCAVATION AFTER 179 YEARS I CLOSURE -IN -PLACE AFTER 179 YEARS OF ACTIVE GROUNDWATER REMEDIATION OF ACTIVE GROUNDWATER REMEDIATION -�.00' .Y. i A`4v LEGEND / DUKE 1250 GRAPHIC SCALE O50 2,500 CLEAN WATER INFILTRATION WELL ENERGY EXTRACTION WELL (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L CHECKED BY: E. WEBSTER DATE: 12/18/2019 — - — -PROPOSED LANDFILL EXPANSION � APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER ASH BASIN WASTE BOUNDARY synTel 1 Q www.s nterracor .com LANDFILL BOUNDARY FIGURE ES-3 - - - - ASH BASIN COMPLIANCE BOUNDARY COMPARISON OF SIMULATED MAXIMUM BORON LANDFILL COMPLIANCE BOUNDARY CONCENTRATIONS IN ALL NON -ASH LAYERS FOR BOTH CLOSURE SCENARIOS WITH ACTIVE REMEDIATION NOTES: ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER4, 2019. AERIAL WAS COLLECTED MODELING REPORT ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH 3PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM F PS3200 (NAD8 TERRELL, NORTH CAROLINA Ilk �i�� � �f!t�7lla/IuA`1%o7 ������� •�/Jl!\11\, /•_� ■�_I /.i���� t 1 13)" \ 1 • _ __�'/'�' : • • �. ter.\�w� I�liar alei 1 ' • I ' `_ ( NORMAN Q • e • • . �`�` ._� 1_ � Q \\ •'��k7 /' Arm J � �� /./�/l�� NORTH QUADRANGLE, OBTAINED FROM THE USGS STORE AT https://store.usgs.gov/map-locator. ' ,w.. FIGURE 1-1 COUNT `ar .. -.LOCATION.. ..-MODELING CAR•ENE .. - ASHEVILLE CHARLOTTE- MARSHALL STEAM STATION 019 .. ,. GRAPHIC SCALE _•• _ _ (IN FEET) APPROVED BY: B. WILKER DATE: ,. B.WILKER ...PROJECTIVIANAGER: I FILL L :. I %6 ` - J% 10001. ACCESS STRUCTURAL .AD I ��PKKyQ- �yF • �`` PP s T � �P 0 Po � i LEGEND ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY STRUCTURAL FILL BOUNDARY - - ASH BASIN COMPLIANCE BOUNDARY - - - LANDFILL COMPLIANCE BOUNDARY DUKE ENERGY CAROLINAS MARSHALL PLANT SITE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: PROPERTY BOUNDARY PROVIDED BY DUKE ENERGY CAROLINAS. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). ALE DUKE 1,100 G0 APHIC S 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 4-1 NUMERICAL MODEL DOMAIN UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA Feet l DUKE ENERGY CARG *p synTerra DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 APPROVED BY: B. WILKER DATE: 12/12/2019 PROJECT MANAGER: B. WILKER www.synterracorp.com FIGURE 4-2 FENCE DIAGRAM OF THE 3D HYDROSTRATIGRAPHIC MODEL USED TO CONSTRUCT THE MODEL GRID UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA DUKE DRAWN BY: Y. GEBRAI DATE: 11/11/2019 FIGURE 4-3 ,& `W' ENERGY CARD REVISED BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 APPROVED BY: B. WICKER DATE: 12/12/2019 PROJECT MANAGER: B. WICKER COMPUTATIONAL GRID USED IN THE MODEL WITH 2X VERTICAL EXAGGERATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION *p synTerra TERRELL, NORTH CAROLINA www.synterracorp.com 1 I[.>F:j M 0.4 0.2 0 4- 0.001 0.01 0.1 K ft/d 1 10 100 • All Sites ■ Marshall slug test Marshall pumping test analytical solution 0 Marshall pumping test numerical solution • Model Number Analytical and numerical solutions for a coal ash pumping test at Marshall are included and show agreement with the slug test values. DUKE ENERGY CARD DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 APPROVED BY: B. WICKER DATE: 12/12/2019 PROJECT MANAGER: B. WICKER 1 FIGURE 4-4 HYDRAULIC CONDUCTIVITY MEASURED IN SLUG TESTS PERFORMED IN COAL ASH AT 14 SITES IN NORTH CAROLINA UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT 1MARSHALL STEAM STATION 1 5)/rlTerf d TERRELL, NORTH CAROLINA www.synterracorp.com 1 111 � 0.6 O a O 0.4 E 3 U M 0.001 0.01 0.1 1 10 100 K ft/d • All Piedmont Sites ♦ Marshall ♦ Model Number DUKE ENERGY CARO DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 APPROVED BY: B. WICKER DATE: 12/12/2019 PROJECT MANAGER: B. WICKER FIGURE 4-5 HYDRAULIC CONDUCTIVITY MEASURED IN SLUG TESTS PERFORMED IN SAPROLITE AT 10 PIEDMONT SITES IN NORTH CAROLINA UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION 1 S)/rlTerf d TERRELL, NORTH CAROLINA www.synterracorp.com 1 1: M 0.6 O a a� M 75 0.4 E 3 V 101M M 0.0001 0.001 0.01 0.1 1 10 100 K ft/d • All Piedmont Sites ♦ Marshall ♦ Model Number DUKE ENERGY CARD DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 APPROVED BY: B. WICKER DATE: 12/12/2019 PROJECT MANAGER: B. WICKER FIGURE 4-6 HYDRAULIC CONDUCTIVITY MEASURED IN SLUG TESTS PERFORMED IN THE TRANSITION ZONE AT 10 PIEDMONT SITES IN NORTH CAROLINA UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION 1 synTerra TERRELL, NORTH CAROLINA www.synterracorp.com 0.6 O a a� 0.4 E 3 U 0.2 0 0.0001 .If� DUKE %- ' ENERGY t, synTerra 60 • • All Piedmont Sites ♦ Marshall ♦ Model Number 0.001 0.01 0.1 1 10 100 K ft/d Each model value corresponds to main background values in the model layer intervals used for calibration. DRAWN BY: Y. GEBRAI DATE: 11/11/2019 FIGURE 4-7 REVISED BY: W. PRATER DATE: 12/12/2019 HYDRAULIC CONDUCTIVITY MEASURED IN SLUG TESTS PERFORMED IN THE CHECKED BY: E. WEBSTER DATE: 12/12/2019 BEDROCK AT 10 PIEDMONT SITES IN NORTH CAROLINA APPROVED BY: B. WICKER DATE: 12/12/2019 PROJECT MANAGER: B. WICKER UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA www.synterracorp.com INDUSTRIAL LANDFILL #1 INDUSTRIAL AREA LEGEND Q RECHARGE ZONES FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/13/2019 CHECKED BY: E. WEBSTER DATE: 12/13/2019 APPROVED BY: B. WILKER DATE: 12/13/2019 PROJECT MANAGER: B. WILKER FIGURE 4-8 DISTRIBUTION OF MODEL RECHARGE ZONES UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA C. ALE DUKE 1,100 G0 APHIC S 1,100 2,200 ENERGY (IN FEET) LEGEND DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/17/2019 CHECKED BY: E. WEBSTER DATE: 12/17/2019 DRAINS APPROVED BY: B. WILKER DATE: 12/17/2019 ROJECT MANAGER: B. WILKER CONSTANT HEAD ZONES WnTerm p www.s nterracor .com Q FLOW AND TRANSPORT MODEL BOUNDARY FIGURE 4-9 NOTES: MODEL SURFACE WATER FEATURES ALL BOUNDARIES ARE APPROXIMATE. OUTSIDE OF ASH BASIN AREA STREAMS ARE INCLUDED IN THE MODEL AS DRAINS. CONSTANT HEAD ZONES ARE PRESENT IN UPDATED GROUNDWATER FLOW AND TRANSPORT THE UPPERMOST ACTIVE MODEL LAYER. MODELING REPORT AERIALOBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED PHOTOGRAPHY0118 MARSHALL STEAM STATION ON F DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE TERRELL, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83). P± LEGEND k 4 'pal, ,J —1 DRAINS GENERAL HEAD BOUNDARIES Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. GENERAL HEAD BOUNDARIES HAVE A SPECIFIED ELEVATION AND A LARGE CONDUCTANCE. DRAINS ARE SET TO THE APPROXIMATE GROUND OR WATER SURFACE ELEVATION. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). Grg E3 40 ALE DUKE 1,100 G0 APHIC S 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/14/2019 CHECKED BY: E. WEBSTER DATE: 12/14/2019 APPROVED BY: B. WILKER DATE: 12/14/2019 s)mTena P=2��B.WIUKER s nterracor .com FIGURE 4-10 MODEL SURFACE WATER FEATURES IN ASH BASIN AREA UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA I � fib',, „A6 . . �•• LEGEND iP WATER SUPPLY WELL ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. PROPERTY BOUNDARY LINE PROVIDED BY DUKE ENERGY CAROLINAS. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11111/21119 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 4-11 WATER SUPPLY WELLS IN MODEL AREA IN ASH BASIN AREA UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 1 W LEGEND HYDRAULIC CONDUCTIVITY (FEET/DAY) Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). #5, 100.0 #2, 2.0 #1, 0.03 DUKE 1,100 G0 APHIC SCALE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 5-1 MODEL HYDRAULIC CONDUCTIVITY ZONES IN ASH LAYER 2 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #23, 0.3 #32, 3.0 #4, 1.0 #3, 1.0 #26, 0.01 #21, 0.05 " /` LEGEND HYDRAULIC CONDUCTIVITY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). / #11, 1.0 R •' 7 AE /., DUKE 1,100 GORAPHIC S 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/13/2019 CHECKED BY: E. WEBSTER DATE: 12/13/2019 APPROVED BY: B. WILKER DATE: 12/13/2019 PROJECT MANAGER: B. WILKER FIGURE 5-2 MODEL HYDRAULIC CONDUCTIVITY ZONES IN SAPROLITE LAYER 5 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 28, 3.0 #16, 0.2 #11, 0.05 #24, 10.0 #25, 0.1 ,V ##5, 3.0 7, 5.0 #31, 0.01 #26, 0.1 #22, 0.02 #4, 0.5 #13, 0.1 #30, 0.3 #21, 0.05 #19, 0.03 LEGEND HYDRAULIC CONDUCTIVITY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). #2, 0.1 #9, 1.0 #8, 2.0 #12, 0.5 #18, 0.05 R '' 7 AE /., DUKE 1,100 GORAPHIC S 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/13/2019 CHECKED BY: E. WEBSTER DATE: 12/13/2019 APPROVED BY: B. WILKER DATE: 12/13/2019 PROJECT MANAGER: B. WILKER FIGURE 5-3 MODEL HYDRAULIC CONDUCTIVITY ZONES IN SAPROLITE LAYER 6 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA oi28,3.0l #16, 0.2#11,0.05 #17, 0.1 #24, 8.0 �� ` #7, 5.0 #5, 3.0 #6, 1.0 8.0 #14, 0.1 � L #31, 0.01 #30, 0.3 LEGEND HYDRAULIC CONDUCTIVITY #26, 0.1 Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). ALE DUKE 1,100 G0 APHIC S 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/13/2019 CHECKED BY: E. WEBSTER DATE: 12/13/2019 APPROVED BY: B. WILKER DATE: 12/13/2019 PROJECT MANAGER: B. WILKER FIGURE 5-4 MODEL HYDRAULIC CONDUCTIVITY ZONES IN SAPROLITE LAYER 7 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #34, 0.02 5, 3.0 \ #24, 0.2 #17, 0.05 #20, 15.0 #16, 0.1 #10, 5.0 #9, 1.0 #31, 10.0 #32, 0.05 #13, 1.0 #12, 0.2 #29, 0.02 #22, 8.0 #7, 0.2 y #21, 0.2 #11, 1.0 #2, 0.1 #33, 0.1 #19, 0.2 #38, 0.01 #25, A A, LEGEND HYDRAULIC CONDUCTIVITY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). ALE DUKE 1,100 G0 APHIC S 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/13/2019 CHECKED BY: E. WEBSTER DATE: 12/13/2019 APPROVED BY: B. WILKER DATE: 12/13/2019 PROJECT MANAGER: B. WILKER FIGURE 5-5 MODEL HYDRAULIC CONDUCTIVITY ZONES IN SAPROLITE LAYER 8 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #28, 0.05 #11, 0.05 #13, 0.1 #10, 5.0 #5, 0.1 #9, 4.0 #25, 8 1 #8, 0.5 #7, 0.5 #32, 0.02 #4, 0.1 #3, 0.0! #2, 0.05 #24, 0.02 #31, 0.02 #26, 0.5 #20, 0.1 #15, 1.5 #21, 0.008 LEGEND HYDRAULIC CONDUCTIVITY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). /., DUKE 1,100 GORAPHIC S AE 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/13/2019 CHECKED BY: E. WEBSTER DATE: 12/13/2019 APPROVED BY: B. WILKER DATE: 12/13/2019 PROJECT MANAGER: B. WILKER FIGURE 5-6 MODEL HYDRAULIC CONDUCTIVITY ZONES IN TRANSITION ZONE LAYER 9 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #29, 0.005 #17, 8.0 #19, 0.03 #32, 0.01 #15, 3.0 #12, 0.01 #28, 2.0 #27, 4.0 #10, 0.1 #8, 4.0 #26, 0.4 #18, 10.0 #5, 0.1 #31, 0.05 #25, 0.05 #6, 0.4 #9, 0.2 #4, 0.02 #7, 0.02 #11, 0.05 #13, 0.2 #24, 0.03 LEGEND HYDRAULIC CONDUCTIVITY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). /., DUKE 1,100 GORAPHIC S AE 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/14/2019 CHECKED BY: E. WEBSTER DATE: 12/14/2019 APPROVED BY: B. WILKER DATE: 12/14/2019 PROJECT MANAGER: B. WILKER FIGURE 5-7 MODEL HYDRAULIC CONDUCTIVITY ZONES IN UPPER FRACTURED BEDROCK LAYER 10 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA I I I A #25, 0.01 #24, 0.01 #11, 0.01 0.003 49, 0.1 #15, 0.1 J #8, 0.0? #12, 0.3 20, 0.01 #21, 0.005 #18, 0.05 LEGEND HYDRAULIC CONDUCTIVITY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). /., DUKE 1,100 GORAPHIC S AE 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/14/2019 CHECKED BY: E. WEBSTER DATE: 12/14/2019 APPROVED BY: B. WILKER DATE: 12/14/2019 PROJECT MANAGER: B. WILKER FIGURE 5-8 MODEL HYDRAULIC CONDUCTIVITY ZONES IN UPPER FRACTURED BEDROCK LAYER 11 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #21, 0.01 #12, 0.1 #13, 10.0 #14, 0.005 #10, 0.1 #20, 2.0 #8, 0.01 1 #5 0 005 #17, 0.01 #15, 0.05 LEGEND HYDRAULIC CONDUCTIVITY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). #6, 0.02 #3, 1.0 #2, 0.1 #4, 0.05 #7, 0.1 /., DUKE 1,100 GORAPHIC S AE 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/21119 REVISED BY: R. KIEKHAEFER DATE: 12/14/2019 CHECKED BY: E. WEBSTER DATE: 12/14/2019 APPROVED BY: B. WILKER DATE: 12/14/2019 PROJECT MANAGER: B. WILKER FIGURE 5-9 MODEL HYDRAULIC CONDUCTIVITY ZONES IN UPPER FRACTURED BEDROCK LAYER 12 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #19, 0.01 #12, 0.005 #10, 7.0 #8, 0.01 E#15, 0.01 #11, 0.2 #16, 0.01 LEGEND HYDRAULIC CONDUCTIVITY FLOW AND TRANSPORT MODEL BOUNDARY #5, 0.005 #3, 0.1 #4, 0.05 #13, 0.05 NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). R •' 7 AE /., DUKE 1,100 GORAPHIC S 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/14/2019 CHECKED BY: E. WEBSTER DATE: 12/14/2019 APPROVED BY: B. WILKER DATE: 12/14/2019 PROJECT MANAGER: B. WILKER FIGURE 5-10 MODEL HYDRAULIC CONDUCTIVITY ZONES IN UPPER FRACTURED BEDROCK LAYER 13 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #5, 0.005 L LEGEND HYDRAULIC CONDUCTIVITY r=- FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). #2, 0.02 ALE DUKE 1,100 G0 APHIC S 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/14/2019 CHECKED BY: E. WEBSTER DATE: 12/14/2019 APPROVED BY: B. WILKER DATE: 12/14/2019 PROJECT MANAGER: B. WILKER FIGURE 5-11 MODEL HYDRAULIC CONDUCTIVITY ZONES IN MID -DEPTH BEDROCK LAYERS 14-16 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA #1, 0.005 LEGEND HYDRAULIC CONDUCTIVITY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ZONES SHOWN WERE USED TO DEFINE HORIZONTAL HYDRAULIC CONDUCTIVITY AND HORIZONTAL TO VERTICAL ANISOTROPY IN THE MODEL. HYDRAULIC CONDUCTIVITY VALUES AND RATIOS OF HORIZONTAL TO VERTICAL ANISOTROPY FOR NUMBERED POLYGONS ARE LISTED IN TABLE 5-2. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). ALE DUKE 1,100 G0 APHIC S 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/14/2019 CHECKED BY: E. WEBSTER DATE: 12/14/2019 APPROVED BY: B. WILKER DATE: 12/14/2019 PROJECT MANAGER: B. WILKER FIGURE 5-12 MODEL HYDRAULIC CONDUCTIVITY ZONES IN DEEP BEDROCK LAYERS 17-21 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 840 N 820 2 co 800 E U ►E:f4] rk-111 Computed vs. Observed Values Head 760 780 800 820 840 860 Observed Heads (ft) Plotted line indicates a ratio of 1:1. .�� DUKE DRAWN BY: Y. GEBRAI DATE: 11/11/2019 FIGURE 5-13 ENERGY BY: W. PRATER DATE: 12/12/2019 CHECKED BY: E. WEBSTER DATE: 12/12/2019 CHECKED APPROVED BY: B. WICKER DATE: 12/12/2019 PROJECT MANAGER: B. WICKER COMPARISON OF OBSERVED AND COMPUTED HEADS FROM THE CALIBRATED STEADY STATE FLOW MODEL UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION tip SyrlTerl d TERRELL, NORTH CAROLINA www.synterracorp.com ro p o 0 \-• 0, 0a o Wo 0 0o so 0 5 c �� LEGEND HYDRAULIC HEAD (FEET) ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN PRIOR TO DECANTING. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88). r b � � a,)) 11 Aso /., GRAPHIC SCALE DUKE 1,100 O 00 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 WnTerm p ROJECT MANAGER: B. WILKER www.synterracorD.com FIGURE 5-14 SIMULATED HYDRAULIC HEADS IN TRANSITION ZONE LAYER 9 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 0 LEGEND HYDRAULIC HEAD (FEET) ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN PRIOR TO DECANTING. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83 AND NAVD88). �Y wM /., GRAPHIC SCALE DUKE 1,100 O 00 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 WnTena PROJECT MANAGER: B. WILKER www.synterracorD.com FIGURE 5-15 SIMULATED HYDRAULIC HEADS IN UPPER FRACTURED BEDROCK LAYER 10 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 87p O 10 00 a� a60 ❑ 160 �o 0 0 I I t- 0 0 • • 0 soo LEGEND ERROR BAR RESIDUALS <5 ft AT EACH MONITORING WELL 5-10 ft MONITORING WELLS HYDRAULIC HEAD (FEET) ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY ALL BOUNDARIES ARE APPROXIMATE. CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN PRIOR TO DECANTING FOR MODEL LAYER 10. RESIDUALS ARE SHOWN AT EACH OBSERVATION POINTAND ARE EQUAL TO PREDICTED HEAD - OBSERVED HEAD. THE SIZE OF THE COLOR BAR FOR THE RESIDUAL INDICATES THE VALUE OF THE RESIDUAL. THE ERROR BAR SYMBOL INDICATES THE SIZE FOR A RESIDUAL OF 5 FEET. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83 AND NAVD88). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 5-16 SIMULATED HYDRAULIC HEADS PRIOR TO DECANTING IN UPPER FRACTURED BEDROCK FLOW ZONE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA '% o o \ I ! \ 79O pp p f LEGEND .' GROUNDWATER FLOW DIRECTION ��- GROUNDWATER DIVIDE HYDRAULIC HEAD (FEET) -- ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. ARROWS INDICATE INFERRED DIRECTION ONLY, NOT MAGNITUDE. CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN PRIOR TO DECANTING FOR MODEL LAYER 10. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83 AND NAVD88). /., DUKE ' ENERGY GRAPHIC SCALE 1,100 0 1,100 2,200 (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 5-17 GROUNDWATER DIVIDE AND FLOW DIRECTIONS UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA i #25 .N �11 -aft , 'k I l LEGEND DUKE AE 1,100 GORAPHICS 1,100 2,200 COI SOURCE ZONES ENERGY (IN FEET) ASH BASIN WASTE BOUNDARY DRAWN BY: Y. GEBRAI DATE: 11/11/2019 LANDFILL BOUNDARY REVISED Br. R.KIEKHAEFER DATE: 12/18/2019 ' ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 LANDFILL COMPLIANCE BOUNDARY �/�'� e PROJECT MANAGER: B. WILKER Q FLOW AND TRANSPORT MODEL BOUNDARY "i " www.s nterracor .com NOTES: FIGURE 5-18 COI ASH BASIN SOURCE ZONES BOUNDARIES ARE ATE. FOR HISTORICAL TRANSPORT MODEL NU TO NUMBER LABELS CORRESPOND TO CONCENTRATION DATA IN TABLE 5-5 a-c. CORRESPOND UPDATED GROUNDWATER FLOW AND TRANSPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. MODELING REPORT DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE MARSHALL STEAM STATION COORDINATE SYSTEM FIPS 3200 (NAD83). TERRELL, NORTH CAROLINA �-_ s ��►i'a; . 7 - 5 LEGEND Q COI SOURCE ZONES ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. NUMBER LABELS CORRESPOND TO CONCENTRATION DATA IN TABLE 5-6 a-c. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). I r" •� GRAPHIC SCALE DUKE 1,100 O 00 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11111/21119 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 WnTerm PROJECT MANAGER: B. WILKER www.synterracorD.com FIGURE 5-19 COI LANDFILL SOURCE ZONES FOR HISTORICAL TRANSPORT MODEL UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA i� LEGEND BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11'11/21119 REVISED BY: B.T DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 WnTerm PROJECT MANAGER: B. WILKER www.synterracorD.com FIGURE 5-20 SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS PRIOR TO DECANTING UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA I !T •4 � a � � r w I• 3 LEGEND DUKE AE 1,100 GORAPHICS 1,100 2,200 TDS > 500 mg/L ENERGY (IN FEET) ASH BASIN WASTE BOUNDARY DRAWN BY: Y. GEBRAI DATE: 11/11/2019 LANDFILL BOUNDARY REVISED BY. R. KIEKHAEFER DATE: 12/18/2019 ' ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 LANDFILL COMPLIANCE BOUNDARY �/�" '�e PROJECT MANAGER: B. WILKER FLOW AND TRANSPORT MODEL BOUNDARY "i www.s nterracor .com NOTES: FIGURE 5-21 SIMULATED MAXIMUM TDS CONCENTRATIONS IN ALL NON - ALL BOUNDARIES ARE APPROXIMATE. ASH LAYERS PRIOR TO DECANTING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8,2018. UPDATED GROUNDWATER FLOW AND TRANSPORT DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE MODELING REPORT COORDINATE SYSTEM FIPS 3200 (NAD83). MARSHALL STEAM STATION TERRELL, NORTH CAROLINA t LEGEND DUKE AE 1,100 GORAPHICS 1,100 2,200 STRONTIUM > 1,500 Ng/L ENERGY (IN FEET) ASH BASIN WASTE BOUNDARY DRAWN BY: Y. GEBRAI DATE: 11/11/2019 LANDFILL BOUNDARY REVISED BY. R. KIEKHAEFER DATE: 12/18/2019 ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 LANDFILL COMPLIANCE BOUNDARY �/�'� ROJECT MANAGER: B. WILKER FLOW AND TRANSPORT MODEL BOUNDARY "i " e pwww.s nterracor .com NOTES: FIGURE 5-22 SIMULATED MAXIMUM STRONTIUM CONCENTRATIONS IN ALL BOUNDARIES ARE APPROXIMATE. ALL NON -ASH LAYERS PRIOR TO DECANTING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8,2018. UPDATED GROUNDWATER FLOW AND TRANSPORT DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE MODELING REPORT COORDINATE SYSTEM FIPS 3200 (NAD83). MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 8,0 0 86 ro �g0 800 $0 I k • L /"'� 830 80 LEGEND Q DRAINS GENERAL HEAD BOUNDARIES HYDRAULIC HEAD (FEET) ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY A*' + { ^gyp I 760 fl 4 790 � 800 760 f 820 DUKE GRAPHIC SCALE 1,100 O 00 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER NOTES: FIGURE 6-1 ALL BOUNDARIES ARE APPROXIMATE. SIMULATED HYDRAULIC HEADS IN TRANSITION ZONE AFTER CONTOUR INTERVAL IS 10 FEET. HYDRAULIC HEADS ARE SHOWN FOR MODEL LAYER 9. DECANTING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS COLLECTED UPDATED GROUNDWATER FLOW AND TRANSPORT ON FEBRUARY 8, 20DRAWING HAS BEEN SET 18. MODELING REPORT COORDINATE SYSTEM FIPSI3 00 ( AD 3TH A CAND NAVD8TION OF 8RTH CAROLINA STATE PLANE MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 1� r�+ i, AO' a �__. _ v��_. '•r 1 of . � ! r LEGEND BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 WnTerm PROJECT MANAGER: B. WILKER www.svnterracorD.com FIGURE 6-2 SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS AFTER DECANTING UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA E "�� �i-,•yY-1 �,. ��y 5�"=t • �•%' _..•'�,1 �.�—. .e,e.ew.wre m�.ramww*� �.'� � iui n•ni. ry ;•INS; ,'„i..,x +!'�rI(_ ..�. r.a ewA if�EFh ed+4wr ee„nrxr t[owa,e�,•w•tt _� - �__ _ r f • - 'h•' •- 14'� wcam.enx.ase.r h'or.�eaenrtvaafn � � Syr, l '•- .•'' ... _ MiF l W�-0s v NOTE � ' -•. wv.>«a... r o...«ris .,cr.. �, ese. rc. nse '7 "ter h �_� s:� _ -i '�`..'^ rr�l � .�.� '• a �• �i- �rri� � a; 'iJ; ;.�•. �� :`� r>dumnaae.�ss.� *=n,.',o'°'�„� s�,�...�oE,.,�� �r " �� y - ,,;' �s��r,,..�..���E9.�,��sE��,,.�.ro�.a,c.� eun, � �� �ll REFERENCES � .e .�'. lY^ �Y ��?� I _, - •1 +i_(::.-6 ,. HC� r Illy •; 1` ._ _: xescer..s..�.am ea. c.,....cr�wer�s 4 � ^� orn \.' -u. rs ea.�s neEoerwr.ea �^� � F� � '.,.�,s rasp / j x x 1�= y y. ��ly ?'F - _=• - _ �:4 n.-mn ro rsen re,e+r ree.rrrt..�s�,e�cea -' __ `�' R' ••�� ( 7 SCONCE-- IJNDRN TA E�—DEIL IT Y se.e A.- DRAFT •ram__ ri _ ins •• �.-.RH,;. '. r. lir. � :o CONCEPTUAL UNDERDRAIN SYSTEM �ERl�Fr 1.1 .1 •. \� v. acn ISSUED ll R NEVI EW L= mcic,ui MAR- v. Xxx-1205 5E JUKE DRAWN BY: Y. GEBRAI DATE: 11/11/2019 FIGURE 6-3 ENERGY REVISED BY: W. PRATER DATE: 12/12/2019 CLOSURE -IN -PLACE DESIGN USED IN SIMULATIONS (FROM AECOM, 2019) CARD CHECKED BY: E. WEBSTER DATE: 12/12/2019 UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT APPROVED BY: B. WILKER DATE: 12/12/2019 MARSHALL STEAM STATION PROJECT MANAGER: B. WILKER 1 TERRELL, NORTH CAROLINA synTerra www.synterracorp.com r .t N _t I _ a LEGEND CALE DUKE 1,100 GQAPHICS1,10 2,200 PROPOSED ASH BASIN UNDERDRAINS ENERGY ASH BASIN WASTE BOUNDARY (IN FEET) LANDFILL BOUNDARY DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/18/2019 - - ASH BASIN COMPLIANCE BOUNDARY CHECKED BY: E. WEBSTER DATE: 12/18/2019 LANDFILL COMPLIANCE BOUNDARY APPROVED BY: B. WILKER DATE: 12/18/2019 synTeYl'd PROJECT MANAGER: B. WILKER Q FLOW AND TRANSPORT MODEL BOUNDARY www.synterracori).com NOTES: FIGURE 6-4 ALL BOUNDARIES ARE APPROXIMATE. DRAINS USED IN THE CLOSURE -IN -PLACE DESIGN PROPOSED ASH BASIN UNDERDRAINS HAVE ELEVATIONS SET TO FEET BELOW THE GROUND UPDATED GROUNDWATER FLOW AND TRANSPORT SURFACE. MODELING REPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE TERRELL, NORTH CAROLINA COORDINATE SYSTEM FIPS 3200 (NAD83). 8�0 60 0 O �o � O � $q0 $30 �O O o O M Mp � M LEGEND HYDRAULIC HEAD (FEET) PROPOSED ASH BASIN UNDERDRAINS ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CONTOUR INTERVAL IS 10 FEET. HYDRAULIC HEADS ARE SHOWN FOR LAYER 9. PROPOSED ASH BASIN UNDERDRAINS (GREEN LINES) HAVE ELEVATIONS SET TO 5 FEET BELOW THE GROUND SURFACE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83 AND NAVD88). I 7 ro � M 11 0 /., DUKE 1,100 GORAPHIC S AE 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/17/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/17/2019 APPROVED BY: B. WILKER DATE: 12/17/2019 PROJECT MANAGER: B. WILKER FIGURE 6-5 SIMULATED HYDRAULIC HEADS FOR THE CLOSURE -IN - PLACE SCENARIO UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA ai ti ! —�� r• � 11"r akI1T 111� ..�, •. 1 LEGEND DUKE 1,100 GORAPHIC S AE 1,100 2,200 BORON 700 - 4,000 Ng/L ENERGY N FEET, BORON > 4,000 Ng/L DRAWN BY: Y. GEBRAI DATE: 11/11/2019 ASH BASIN WASTE BOUNDARY REVISED BY. B.ELLIOTT DATE: 12/18/2019 LANDFILL BOUNDARY CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 — - — - ASH BASIN COMPLIANCE BOUNDARY PROJECT MANAGER: B. WILKER LANDFILL COMPLIANCE BOUNDARY WnTena www.s nterracor .com FLOW AND TRANSPORT MODEL BOUNDARY FIGURE 6-6a SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NOW NOTES: ASH LAYERS FOR CLOSURE -IN -PLACE SCENARIO ALL BOUNDARIES ARE APPROXIMATE. 14 YEARS POST —CLOSURE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. REPORT DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE MARSHALL STEAM STATION COORDINATE SYSTEM FIPS 3200 (NAD86). TERRELL, NORTH CAROLINA r i -44 .. •. AE LEGEND DUKE 1,100 GORAPHIC S 1,100 2,200 BORON 700 - 4,000 Ng/L ENERGY N FEET, BORON > 4,000 Ng/L DRAWN BY: Y. GEBRAI DATE: 11/11/2019 ASH BASIN WASTE BOUNDARY REVISED BY: B. ELLIOTT DATE: 12/18/2019 LANDFILL BOUNDARY CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 - — - ASH BASIN COMPLIANCE BOUNDARY �/�'�e PROJECT MANAGER: B. WILKER LANDFILL COMPLIANCE BOUNDARY "i " www.svnterracorD.com Q FLOW AND TRANSPORT MODEL BOUNDARY FIGURE 6-6b SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON - NOTES: ASH LAYERS FOR CLOSURE -IN -PLACE SCENARIO ALL BOUNDARIES ARE APPROXIMATE. 64 YEARS POST -CLOSURE AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIALWAS COLLECTED UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING ON FEBRUARY 8, 2018. REPORT DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE MARSHALL STEAM STATION COORDINATE SYSTEM FIPS 3200 (NAD83). TERRELL, NORTH CAROLINA LEGEND BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). �> GRAPHIC SCALE DUKE 1,100 O 00 2,200 ENERGY N FEET, CAROLINAS DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.s nterracor .COM FIGURE 6-6c SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR CLOSURE -IN -PLACE SCENARIO 114 YEARS POST -CLOSURE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA f LEGEND BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). i �> DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY CAROLINAS (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11111/21119 REVISED BY: B.T DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.svnterracorn.com FIGURE 6-6d SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR CLOSURE -IN -PLACE SCENARIO 164 YEARS POST -CLOSURE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND STRONTIUM > 1,500 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). DUKE f> ENERGY GRAPHIC SCALE 1,100 O 00 2,200 CAROLINAS N FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER synTerra www cvntarrArnrn rnm FIGURE 6-7a SIMULATED MAXIMUM STRONTIUM CONCENTRATIONS IN ALL NON -ASH LAYERS FOR CLOSURE -IN -PLACE SCENARIO 14 YEARS POST -CLOSURE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND TDS > 500 mg/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). f> DUKE 4 ENERGY® AE 1,100 GORAPHIC S 1,100 2,200 CAROLINAS N FEET DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER wwwsvnterracorn .com FIGURE 6-7b SIMULATED MAXIMUM TDS CONCENTRATIONS IN ALL NON - ASH LAYERS FOR CLOSURE -IN -PLACE SCENARIO 14 YEARS POST -CLOSURE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 810 911 g60 1 850 97 n zg of ro 4/1 LEGEND EXTRACTION WELL CLEAN WATER INFILTRATION WELL HYDRAULIC HEAD (FEET) ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN IN MODEL LAYER 9 WITH REMEDIATION SYSTEM FOR THE CLOSURE -IN -PLACE SCENARIO. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88). N I iU DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY CAROLINAS (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11111/21119 REVISED BY: B.T DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.synterracorp.com FIGURE 6-8 SIMULATED HYDRAULIC HEADS IN TRANSITION ZONE WITH ACTIVE GROUNDWATER REMEDIATION CLOSURE -IN -PLACE SCENARIO UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY. CAROLINAS (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.svnterracorn.com FIGURE 6-9a 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 MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 0,4 .- IAPRIWA^ ""a* - A` ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). -Mow -'-A lw AE cf' DUKE 1,100 GORAPHIC S 1,100 2,200 ENERGY CAROLINAS (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY:B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E..WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 smTerra PROJECT MANAGER: B. WILKER www.svnterracorD.COM FIGURE 6-9b SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO AFTER 29 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). /., DUKE 1,100 GORAPHIC S AE 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.T DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-9c SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO AFTER 79 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). ('AL DUKE 1,100 GORAPHIC S 1,100 2,200 ENERGY CAROLINAS (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11111/21119 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-9d SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO AFTER 129 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA ate- . f ,y. LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). AE cf' DUKE 1,100 GORAPHIC S 1,100 2,200 ENERGY CAROLINAS (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY:B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E..WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.svnterracorD.COM FIGURE 6-9e SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -IN -PLACE SCENARIO AFTER 179 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL STRONTIUM > 1,500 Ng/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. STRONTIUM CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIRS 3200 (NAD83). (>AE DUKE 1,100 GRAPHIC S 1,100 2,200 I ENERGY- CAROLINAS (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/21119 REVISED BY: B.T DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.svnterracorD.COM FIGURE 6-10a SIMULATED MAXIMUM STRONTIUM 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 MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL TDS > 500 mg/L ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. TDS CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). L l �' DUKE I ENERGY CAROLINAS 147 synTerra GRAPHIC SCALE 1,100 0 1,100 2,200 (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-10b SIMULATED MAXIMUM TDS 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 MARSHALL STEAM STATION TERRELL, NORTH CAROLINA A LEGIEND {� +4K - .. , 3{' lt�s■ ae�aunr earn # �w.*�...-..-.-- {y �, NOTES ��.l , `� REFERENCES R�..e�a FW�L �fihplljG PLAb! _ _ -_. _ _ '*� 1 -4Ti'�IaLIXMY i i•:• FC11.M�rT GYgIY .ea���.. va tswmrel �ev����F DUKE ItS DUKE ENERGY CAROLINAS DRAWN BY: Y. GEBRAI REVISED BY: W. PRATER CHECKED BY: E. WEBSTER DATE: 11/11/2019 DATE: 12/12/2019 DATE: 12/12/2019 APPROVED BY: B. WILKER PROJECT MANAGER: B. WILKER DATE: 12/12/2019 www.synterracorp.com WnTerra FIGURE 6-11 CLOSURE -BY -EXCAVATION DESIGN USED IN SIMULATIONS (FROM AECOM, 2019) UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA r LEGEND DRAIN NETWORK EXCAVATED STORMWATER AREA - - - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. STREAMS AND SPRINGS THAT FORM ARE INCLUDED AS A DRAIN NETWORK. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-12 DRAIN NETWORK USED IN THE CLOSURE -BY -EXCAVATION SIMULATIONS UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA 8� T/ 0 0 0 t co 0 LEGEND DRAIN NETWORK EXCAVATED STORMWATER AREA - - PROPOSED LANDFILL EXPANSION HYDRAULIC HEAD (FEET) ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CONTOUR INTERVAL IS 10 FEET. HYDRAULIC HEADS ARE SHOWN FOR MODEL LAYER 9. STREAMS AND SPRINGS THAT FORM ARE INCLUDED AS A DRAIN NETWORK. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83 AND NAVD88). 6p O DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-13 SIMULATED HYDRAULIC HEADS IN THE TRANSITION ZONE AFTER CLOSURE -BY -EXCAVATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTena PROJECT MANAGER: B. WILKER www.sVnterracorp.com FIGURE 6-14a SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON - ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO 3 YEARS PRIOR TO CLOSURE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA I mar3 I ram: u Am 0, LEGEND DUKE 1,100 GORAPHIC S AE 1,100 2,200 BORON 700 - 4,000 Ng/L ENERGY (IN FEET) BORON > 4,000 Ng/L DRAWN BY: Y. GEBRAI DATE: 11/11/2019 — - — -PROPOSED LANDFILL EXPANSION REVISED BY: B. ELLIOTT DATE: 12/18/2019 — — — — — ASH BASIN WASTE BOUNDARY CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 LANDFILL BOUNDARY PROJECT MANAGER: B. WILKER — - — - ASH BASIN COMPLIANCE BOUNDARY WnTena www.sVnterracorl).com LANDFILL COMPLIANCE BOUNDARY FIGURE 6-14b Q FLOW AND TRANSPORT MODEL BOUNDARY SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON - ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO NOTES: 47 YEARS POST -CLOSURE ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED REPORT ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH 3PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM F PS3200 (NAD8 TERRELL, NORTH CAROLINA l !T� + a e LEGEND BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11,11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-14c SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON - ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO 97 YEARS POST -CLOSURE UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA r i I - f 'ma`s • f � I ow LEGEND DUKE 1,100 GRAPHIC SCALE O00 2,200 BORON 700 - 4,000 Ng/L ENERGY BORON > 4,000 Ng/L (IN FEET) - -PROPOSED LANDFILL EXPANSION DRAWN BY: Y. GEBRAI DAE:11,11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 ASH BASIN WASTE BOUNDARY CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 LANDFILL BOUNDARY APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER - — - ASH BASIN COMPLIANCE BOUNDARY www.s nterracor .com LANDFILL COMPLIANCE BOUNDARY FIGURE 6-14d Q FLOW AND TRANSPORT MODEL BOUNDARY SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON - ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO NOTES: 147 YEARS POST -CLOSURE ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED REPORT ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH A OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM F PS3200 (NAD8TERRELL, NORTH CAROLINA LEGEND DUKE AE 1,100 GORAPHIC S 1,100 2,200 ENERGY STRONTIUM > 1,500 Ng/L w FEET) — - PROPOSED LANDFILL EXPANSION DRAWN BY: Y. GEBRAI DAE:11/11/2019 BASIN WASTE BOUNDARY DATE: 12/18/2019 REVISEASH CHECKDBY:B..WEBT CHECKED BY: E. WEBSTER DATE: 12/18/2019 LANDFILL BOUNDARY APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER - — - ASH BASIN COMPLIANCE BOUNDARY synTena www.s nterracor .com LANDFILL COMPLIANCE BOUNDARY FIGURE 6-15a FLOW AND TRANSPORT MODEL BOUNDARY SIMULATED MAXIMUM STRONTIUM CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION NOTES: SCENARIO 3 YEARS PRIOR TO CLOSURE ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED REPORT ON FEBRUARY 8, 2018. MARSHALL STEAM STATION DRAWING HAS BEEN SET WITH A OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM F PS3200 (NAD8 TERRELL, NORTH CAROLINA A 10 v A i 1 T w �1 Y -km LEGEND GRAPHIC SCALE �V' 1,100 0 1,10o z,zoo TDS > 500 mg/L N RGY CAROLINAS (IN FEET) — - — - PROPOSED LANDFILL EXPANSION DRAWN BY: Y. GEBRAI DATE: 11/11/2019 ASH BASIN WASTE BOUNDARY REVISED BY: B. ELLIOTT DATE: 12/18/2019 LANDFILL BOUNDARY CHECKED BY. E.WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 — - — - ASH BASIN COMPLIANCE BOUNDARY synTerra PROJECT MANAGER: B. WILKER LANDFILL COMPLIANCE BOUNDARY www.s nterracor .com FLOW AND TRANSPORT MODEL BOUNDARY FIGURE 6-15b SIMULATED MAXIMUM TDS CONCENTRATIONS IN ALL NON - NOTES: ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO 3 YEARS PRIOR TO CLOSURE ALL BOUNDARIES ARE APPROXIMATE. UPDATED GROUNDWATER FLOW AND TRANSPORT AERIALPHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FG2018. MODELING REPORT DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE MARSHALL STEAM STATION COORDINATE SYSTEM FIPS 3200 (NAD83). TERRELL, NORTH CAROLINA �o� n LEGEND CLEAN WATER INFILTRATION WELL EXTRACTION WELL HYDRAULIC HEAD (FEET) — - — - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. CONTOUR INTERVAL IS 10 FEET. HEADS ARE SHOWN IN MODEL LAYER 9 WITH REMEDIATION SYSTEM FOR CLOSURE BY EXCAVATION SCENARIO DURING INTERIM PERIOD. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88). 4 1 ':f •� *A fir•.. . r /., DUKE 1,100 GORAPHIC S AE 1,100 2,200 ' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.svnterracorp.com FIGURE 6-16 SIMULATED HYDRAULIC HEADS IN TRANSITION ZONE WITH ACTIVE GROUNDWATER REMEDIATION CLOSURE -BY -EXCAVATION SCENARIO UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION !- .VMW LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). e r.. M ('AL DUKE 1,100 GORAPHIC S 1,100 2,200 ENERGY N FEET) CAROLINAS DRAWN BY: Y. GEBRAI DATE: 11111/21119 REVISED BY: R. KIEKHAEFER DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTena PROJECT MANAGER: B. WILKER www.s7terracorp.com FIGURE 6-17a 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 MARSHALL STEAM STATION TERRELL, NORTH CAROLINA ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIRS 3200 (NAD83). AE f DUKE 1,100 GORAPHIC S 1,100 2,200 ENERGY IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-17b SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 29 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIRS 3200 (NAD83). J DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-17c SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 79 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 synTerra PROJECT MANAGER: B. WILKER www.s7nterracorp.com FIGURE 6-17d SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 129 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. BORON CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIRS 3200 (NAD83). !- - f DUKE 1,100 GORAPHIC S AE 1,100 2,200 ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-17e SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS FOR THE CLOSURE -BY -EXCAVATION SCENARIO AFTER 179 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT MARSHALL STEAM STATION TERRELL, NORTH CAROLINA LEGEND INJECTION WELL EXTRACTION WELL STRONTIUM > 1,500 Ng/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - — - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. STRONTIUM CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). mm DUKE 1,100 GORAPHIC S AE 1,100 2,200 %,' ENERGY (IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B.ELLIOTT DATE: 12/18/2019 CHECKED BY: E.. WEB WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 WnTerm PROJECT MANAGER: B. WILKER www.synterracorp.com FIGURE 6-18a SIMULATED MAXIMUM STRONTIUM 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 MARSHALL STEAM STATION TERRELL, NORTH CAROLINA I LEGEND ♦ CLEAN WATER INFILTRATION WELL EXTRACTION WELL TDS > 500 mg/L - - PROPOSED LANDFILL EXPANSION ASH BASIN WASTE BOUNDARY LANDFILL BOUNDARY - - - ASH BASIN COMPLIANCE BOUNDARY LANDFILL COMPLIANCE BOUNDARY Q FLOW AND TRANSPORT MODEL BOUNDARY NOTES: ALL BOUNDARIES ARE APPROXIMATE. TDS CONCENTRATIONS SHOWN WITH ACTIVE REMEDIATION SYSTEM. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 8, 2018. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83). �AAE DUKE 1,100 GORAPHIC S 1,100 2,200 %, ' ENERGY IN FEET) DRAWN BY: Y. GEBRAI DATE: 11/11/2019 REVISED BY: B. ELLIOTT DATE: 12/18/2019 CHECKED BY: E. WEBSTER DATE: 12/18/2019 APPROVED BY: B. WILKER DATE: 12/18/2019 PROJECT MANAGER: B. WILKER FIGURE 6-18b 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 MARSHALL STEAM STATION TERRELL, NORTH CAROLINA Updated Groundwater Flow and Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLES Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-1 COMPARISON OF OBSERVED AND COMPUTED HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head Computed Head Residual Head AB-10D 790.48 791.03 -0.56 AB-10BR 790.96 791.11 -0.15 AB-10BRL 796.12 791.31 4.81 AB-10S 791.59 790.62 0.97 AB-10SL 790.73 790.90 -0.16 AB-11D 796.23 796.95 -0.72 AB-11S 795.13 796.56 -1.43 AB-12BR 794.41 791.95 2.46 AB-12D 791.58 791.92 -0.34 AB-12S 790.55 791.99 -1.44 AB-12SL 790.69 791.89 -1.20 AB-13 D 798.41 804.30 -5.89 AB-13S 799.19 801.79 -2.60 AB-14D 811.60 817.51 -5.90 AB-14DU 814.80 818.77 -3.97 AB-14S 811.07 819.07 -7.99 AB-15BR 806.87 807.89 -1.02 AB-15D 803.71 808.01 -4.30 AB-15S 805.51 808.41 -2.90 AB-15SL 801.44 807.91 -6.48 AB-16D 815.82 815.41 0.41 AB-16DU 817.31 815.54 1.77 AB-16S 816.18 815.39 0.79 AB-17D 820.00 823.33 -3.33 AB-17S 819.32 824.82 -5.49 AB-18D 818.39 819.95 -1.56 AB-18DU 818.39 820.25 -1.86 AB-18S 818.32 819.90 -1.58 AB-1BRL 774.78 773.47 1.31 AB-1BRLL 776.23 773.08 3.15 AB-1BRLLL 777.18 771.41 5.77 AB-1BR 773.85 773.80 0.05 AB-1D 770.71 773.29 -2.57 AB-1S 767.97 772.35 -4.38 AB-20D 826.63 831.58 -4.95 AB-20S 828.56 831.76 -3.20 AB-21 D 793.11 794.19 -1.08 AB-21S 791.72 794.40 -2.68 AB-2D 767.52 762.53 4.99 AB-2S 761.51 761.52 -0.01 AB-3D 796.21 794.05 2.16 AB-3S 796.69 795.69 1.00 AB-4D 794.25 797.17 -2.92 AB-4S 798.21 797.65 0.55 AB-4SL 797.50 797.36 0.14 Page 1 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-1 COMPARISON OF OBSERVED AND COMPUTED HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head Computed Head Residual Head AB-5BR 798.11 802.83 -4.72 AB-5D 798.65 802.84 -4.19 AB-5DU 796.93 802.99 -6.06 AB-5S 798.90 803.24 -4.34 AB-6BRL 819.27 820.33 -1.06 AB-6BR 817.69 820.03 -2.34 AB-6BRA 820.24 820.38 -0.14 AB-6D 819.97 820.23 -0.26 AB-6S 821.76 820.80 0.96 AB-7D 815.46 817.79 -2.32 AB-7DU 819.14 818.69 0.44 AB-7S 816.82 818.41 -1.59 AB-8D 792.42 795.41 -2.99 AB-8DU 793.69 795.34 -1.65 AB-8S 792.06 794.80 -2.73 AB-9BR 790.58 790.38 0.20 AB-9D 789.90 790.42 -0.52 AB-9S 790.64 790.34 0.30 AL-1BR 777.33 777.35 -0.02 AL-1BRL 780.25 777.88 2.36 AL-1D 774.50 777.48 -2.98 AL-1S 779.60 777.67 1.94 AL-2BRLLL 799.02 798.32 0.70 AL-2BRLL 798.05 798.28 -0.23 AL-2BRL 799.06 798.17 0.89 AL-2BR 802.27 797.99 4.28 AL-2D 800.48 797.98 2.50 AL-2S 799.13 798.41 0.72 AL-3BR 804.05 805.79 -1.74 AL-3D 804.68 805.84 -1.16 AL-3S 804.89 806.13 -1.24 AL-4BR 809.43 802.17 7.25 AL-4BRL 797.69 802.78 -5.09 AL-4D 811.15 802.25 8.90 BG-1BR Second 799.68 804.61 -4.94 BG-1D 805.43 805.71 -0.28 BG-1S 808.59 806.52 2.07 BG-2BR 808.50 810.87 -2.37 BG-2S 810.01 812.46 -2.45 BG-3BR 832.31 830.24 2.07 BG-3D 836.46 831.64 4.82 BG-3S 834.98 832.76 2.21 CCR-11 D 787.80 786.37 1.42 CCR-11S 787.72 787.97 -0.25 CCR-12D 788.43 788.76 -0.33 Page 2 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-1 COMPARISON OF OBSERVED AND COMPUTED HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head Computed Head Residual Head CCR-12S 788.45 788.89 -0.44 CCR-13 D 787.40 786.67 0.73 CCR-13S 787.56 786.88 0.67 CCR-14D 787.64 787.11 0.53 CCR-14S 787.54 787.15 0.39 CCR-15D 794.47 792.22 2.25 CCR-15S 794.42 792.27 2.15 CCR-16D 798.35 802.44 -4.10 CCR-16S 808.34 804.93 3.41 CCR-1D 796.60 797.33 -0.73 CCR-is 798.34 797.71 0.62 CCR-2D 794.58 792.31 2.27 CCR-2S 794.56 792.95 1.60 CCR-3D 759.42 759.75 -0.32 CCR-3S 758.79 759.42 -0.63 CCR-4D 761.80 759.98 1.81 CCR-4S 760.73 759.75 0.98 CCR-5D 762.64 759.40 3.24 CCR-5S 761.69 759.10 2.59 CCR-9DA 770.63 773.11 -2.48 CCR-9S 767.20 775.24 -8.04 CP-1S 792.50 788.28 4.22 CP-1 D 792.23 788.04 4.19 CP-2S 800.51 799.79 0.72 CP-2D 800.44 799.12 1.32 CP-3S 796.54 797.56 -1.02 CP-3D 797.16 792.71 4.45 GP-1S 802.12 802.47 -0.35 GP-1D 802.16 801.80 0.36 GP-2S 805.31 804.44 0.86 GP-2D 805.11 803.10 2.00 GP-3S 804.55 805.00 -0.45 GP-3D 805.20 800.26 4.93 PVSF-1S 827.48 830.62 -3.14 PVSF-1D 827.23 829.90 -2.68 PVSF-1BR 826.44 829.63 -3.19 PVSF-2S 821.84 826.28 -4.44 PVSF-2D 821.74 826.32 -4.58 PVSF-2BR 821.45 826.34 -4.89 PVSF-3S 821.31 826.01 -4.70 PVSF-3D 824.09 826.69 -2.60 PVSF-3BR 821.47 826.82 -5.36 GWA-10D 767.92 765.60 2.32 GWA-10S 765.21 764.34 0.87 GWA-11BR 764.04 766.06 -2.02 Page 3 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-1 COMPARISON OF OBSERVED AND COMPUTED HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head Computed Head Residual Head GWA-11D 764.19 765.95 -1.77 GWA-11S 766.39 766.17 0.22 GWA-12BR 859.32 861.13 -1.82 GWA-12D 859.98 861.20 -1.23 GWA-12S 871.83 873.05 -1.22 GWA-13D 860.44 864.69 -4.25 GWA-13DA 863.11 864.58 -1.47 GWA-13S 866.20 866.63 -0.43 GWA-14D 868.97 865.22 3.76 GWA-14S 868.92 866.38 2.54 GWA-15D 758.27 759.18 -0.91 GWA-15S 757.84 759.01 -1.17 GWA-1BR 764.62 764.18 0.44 GWA-1D 762.30 764.24 -1.94 GWA-1S 762.61 764.34 -1.72 GWA-2DA 802.21 801.79 0.42 GWA-2D 803.19 802.08 1.11 GWA-2S 802.60 804.75 -2.15 GWA-3D 833.38 834.74 -1.36 GWA-3S 830.71 834.76 -4.06 GWA-4D 843.27 841.54 1.73 GWA-5D 811.13 813.97 -2.84 GWA-5S 812.58 815.75 -3.17 GWA-6D 802.89 803.06 -0.17 GWA-6S 803.05 803.12 -0.07 GWA-7D 802.32 798.05 4.27 GWA-7S 799.87 799.79 0.07 GWA-8D 817.32 815.74 1.58 GWA-8S 818.31 819.63 -1.32 GWA-9BR 846.50 845.57 0.93 ILF-1S 828.10 825.58 2.51 ILF-1D 827.14 825.80 1.33 ILF-1BR 822.67 826.10 -3.43 ILF-2S 837.43 840.87 -3.44 ILF-2D 838.51 840.90 -2.39 LRB-01S 800.56 805.12 -4.56 LRB-02S 803.42 805.88 -2.45 MS-10 834.11 833.53 0.58 MS-11 826.28 825.63 0.65 MS-12 813.41 814.51 -1.10 MS-13 811.86 813.13 -1.28 MS-14 807.73 807.38 0.35 MS-15 820.33 815.00 5.33 MS-16 811.88 815.35 -3.47 MS-8 827.10 827.82 -0.72 Page 4 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-1 COMPARISON OF OBSERVED AND COMPUTED HEADS FOR THE CALIBRATED FLOW MODEL Well Observed Head Computed Head Residual Head MS-9 825.70 823.08 2.62 MW-1 772.97 777.87 -4.90 MW-10D 756.85 758.84 -1.99 MW-10S 756.91 759.51 -2.60 M W-11 D 840.79 845.60 -4.81 MW-11S 840.67 846.61 -5.94 MW-12D 857.52 859.81 -2.30 MW-12S 858.74 860.99 -2.24 MW-13D 844.03 844.89 -0.86 MW-13S 842.83 844.91 -2.08 MW-14BR 774.62 775.57 -0.95 MW-14BRL 783.49 777.80 5.69 MW-14D 773.57 775.34 -1.77 MW-14S 774.03 775.46 -1.42 MW-2 791.23 792.08 -0.85 MW-3 805.11 805.74 -0.63 MW-4 828.77 831.48 -2.71 MW-4D 828.08 829.85 -1.77 MW-5 797.31 797.78 -0.47 MW-6D 772.72 768.20 4.52 M W-6S 770.21 768.27 1.94 MW-7 813.24 813.71 -0.47 MW-7D 769.87 766.17 3.70 MW-7S 762.48 765.80 -3.32 MW-8D 760.39 759.04 1.35 MW-8S 758.46 758.87 -0.41 MW-9D 759.38 758.18 1.20 MW-9S 761.36 757.18 4.18 MW-PZ1 817.07 818.08 -1.01 MW-PZ10 821.08 820.86 0.22 MW-PZ2 818.89 817.75 1.14 MW-PZ3 809.54 811.37 -1.84 MW-PZ4 810.12 811.79 -1.67 M W-PZ5 808.55 809.52 -0.97 MW-PZ6 808.93 809.58 -0.65 MW-PZ7 803.44 805.49 -2.05 MW-PZ9 806.15 806.69 -0.54 OB-1 Ash Basin 802.79 806.77 -3.98 OB-1 (Dry Ash Landfill 780.50 782.58 -2.08 OB-2 (MW-6) 809.83 805.50 4.34 Notes: Ft - feet Ft. NAVD 88 - North American Vertical Datum of 1988 Prepared by: YG Checked by: WG Page 5 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC PARAMETERS Hydrostratigraphic Unit Model Layers Spatial Zones (number corresponds to Figures 5-1 through 5-7) Horizontal Hydraulic Conductivity, ft/d Anisotropy ratio, Kh:Kv Ash Basin, Landfills, Structural Fill 1-4 #2, 6, 10, 11 coal ash 2.0 10 Ash Basin (pond) 1-4 #5 pond 100 1 Ash Basin Dam 1-4 #1 ash basin dam 0.03 5 Sa rolite 5 #37 sa rolite main model 1.0 1 5 #1 0.1 1 5 #2 0.1 1 5 #3 1 1 5 #4 1 1 5 #5 0.5 1 5 #6 3 1 5 #7 1 1 5 #8 4 1 5 #9 5 1 5 #10 2 1 5 #11 1 1 5 #12 0.1 1 5 #13 0.5 1 5 # 14 0.05 1 5 #15 0.5 1 5 #16 0.1 1 5 #17 3 1 5 #18 10 1 5 #19 0.2 1 5 #20 0.1 1 5 #21 0.05 1 5 #22 0.03 1 5 #23 0.3 1 5 #24 0.05 1 5 #25 1 1 5 #26 0.01 1 5 #27 3 1 5 #28 10 1 5 #29 0.1 1 5 #30 0.2 1 5 #31 0.02 1 5 #32 3 1 5 #33 0.3 1 5 #34 0.3 1 5 #35 0.01 1 5 #36 0.1 1 6 #33 1 1 Page 6 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC PARAMETERS Hydrostratigraphic Unit Model Layers Spatial Zones (number corresponds to Figures 5-1 through 5-7) Horizontal Hydraulic Conductivity, ft/d Anisotropy ratio, Kh:Kv 6 #1 0.1 1 6 #2 0.1 1 6 #3 0.1 1 6 #4 0.5 1 6 #5 3 1 6 #6 1 1 6 #7 5 1 6 #8 2 1 6 #9 1 1 6 #10 0.1 1 6 #11 0.05 1 6 #12 0.5 1 6 #13 0.1 1 6 # 14 0.05 1 6 #15 10 1 6 #16 0.2 1 6 #17 0.1 1 6 # 18 0.05 1 6 #19 0.03 1 6 #20 0.3 1 6 #21 0.05 1 6 #22 0.02 1 6 #23 3 1 6 #24 10 1 6 #25 0.1 1 6 #26 0.1 1 6 #27 0.02 1 6 #28 3 1 6 #29 0.3 1 6 #30 0.3 1 6 #31 0.01 1 6 #32 0.1 1 7 #33 1 1 7 #1 0.1 1 7 #2 1 1 7 #3 0.1 1 7 #4 0.1 1 7 #5 3 1 7 #6 1 1 7 #7 5 1 7 #8 3 1 7 #9 2 1 7 #10 0.1 1 Page 7 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC PARAMETERS Hydrostratigraphic Unit Model Layers Spatial Zones (number corresponds to Figures 5-1 through 5-7) Horizontal Hydraulic Conductivity, ft/d Anisotropy ratio, Kh:Kv 7 #11 0.05 1 7 #12 0.5 1 7 #13 0.2 1 7 # 14 0.1 1 7 #15 8 1 7 #16 0.2 1 7 #17 0.1 1 7 #18 0.1 1 7 # 19 0.03 1 7 #20 0.3 1 7 #21 0.05 1 7 #22 0.05 1 7 #23 3 1 7 # 24 8 1 7 #25 0.05 1 7 #26 0.1 1 7 #27 0.02 1 7 #28 3 1 7 #29 0.3 1 7 #30 0.3 1 7 #31 0.01 1 7 #32 0.1 1 8 #40 1 1 8 #1 0.1 1 8 #2 0.1 1 8 #3 0.1 1 8 #4 2 1 8 #5 1 1 8 #6 0.5 1 8 #7 0.2 1 8 #8 0.5 1 8 #9 1 1 8 #10 5 1 8 #11 1 1 8 #12 0.2 1 8 #13 1 1 8 # 14 2 1 8 #15 1 1 8 #16 0.1 1 8 # 17 0.05 1 8 #18 0.5 1 8 #19 0.2 1 8 #20 15 1 Page 8 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC PARAMETERS Hydrostratigraphic Unit Model Layers Spatial Zones (number corresponds to Figures 5-1 through 5-7) Horizontal Hydraulic Conductivity, ft/d Anisotropy ratio, Kh:Kv 8 #21 0.2 1 8 #22 8 1 8 #23 0.2 1 8 #24 0.2 1 8 #25 0.1 1 8 #26 0.03 1 8 #27 0.3 1 8 #28 0.05 1 8 #29 0.02 1 8 #30 3 1 8 #31 10 1 8 #32 0.05 1 8 #33 0.1 1 8 #34 0.02 1 8 #35 3 1 8 #36 0.3 1 8 #37 0.3 1 8 #38 0.01 1 8 #39 0.1 1 Transition Zone 9 #33 main model 1.5 1 9 #1 0.1 1 9 #2 0.05 1 9 #3 0.05 1 9 #4 0.1 1 9 #5 0.1 1 9 #6 0.01 1 9 #7 0.5 1 9 #8 0.5 1 9 #9 4 1 9 #10 5 1 9 #11 0.05 1 9 #12 0.01 1 9 #13 0.1 1 9 # 14 1 1 9 #15 1.5 1 9 #16 0.5 1 9 #17 0.2 1 9 #18 0.1 1 9 #19 0.1 1 9 #20 0.1 1 9 #21 0.008 1 9 #22 1.5 1 9 #23 1 1 Page 9 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC PARAMETERS Hydrostratigraphic Unit Model Layers Spatial Zones (number corresponds to Figures 5-1 through 5-7) Horizontal Hydraulic Conductivity, ft/d Anisotropy ratio, Kh:Kv 9 #24 0.02 1 9 #25 8 1 9 #26 0.5 1 9 #27 1 1 9 #28 0.05 1 9 #29 1 1 9 #30 1.5 1 9 #31 0.02 1 9 #32 0.02 1 Bedrock (Upper) 10 #33 main model 0.7 1 10 #1 0.05 1 10 #2 0.02 1 10 #3 0.1 1 10 #4 0.02 1 10 #5 0.1 1 10 #6 0.4 1 10 #7 0.02 1 10 #8 4.0 1 10 #9 0.2 1 10 #10 0.1 1 10 #11 0.05 1 10 #12 0.01 1 10 #13 0.2 1 10 # 14 0.7 1 10 #15 3.0 1 10 #16 0.1 1 10 #17 8.0 1 10 #18 10.0 1 10 # 19 0.01 1 10 #20 0.3 1 10 #21 0.3 1 10 #22 8.0 1 10 #23 0.5 1 10 #24 0.03 1 10 #25 0.05 1 10 #26 0.4 1 10 #27 4.0 1 10 #28 2.0 1 10 #29 0.005 1 10 #30 0.2 1 10 #31 0.05 1 10 #32 0.01 1 11 #26 main model 0.7 1 Page 10 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC PARAMETERS Hydrostratigraphic Unit Model Layers Spatial Zones (number corresponds to Figures 5-1 through 5-7) Horizontal Hydraulic Conductivity, ft/d Anisotropy ratio, Kh:Kv 11 #1 0.1 1 11 #2 0.02 1 it #3 1.0 1 11 #4 0.05 1 11 #5 0.003 1 11 #6 0.05 1 11 #7 0.1 1 11 #8 0.02 1 11 #9 0.02 1 11 #10 0.1 1 11 #11 0.01 1 11 #12 0.3 1 11 #13 0.1 1 11 #14 0.1 1 11 #15 0.1 1 11 #16 5.0 1 11 #17 0.005 1 11 #18 0.05 1 11 #19 0.4 1 11 #20 0.01 1 11 #21 0.005 1 11 #22 4.0 1 11 #23 2.0 1 11 #24 0.01 1 11 #25 0.01 1 12 #23 main model 0.7 1 12 # 1 0.02 1 12 #2 0.1 1 12 #3 1.0 1 12 #4 0.05 1 12 #5 0.005 1 12 #6 0.02 1 12 #7 0.1 1 12 #8 0.01 1 12 #9 0.3 1 12 #10 0.1 1 12 #11 0.1 1 12 #12 0.1 1 12 #13 10.0 1 12 #14 0.005 1 12 #15 0.05 1 12 # 16 0.4 1 12 #17 0.01 1 Page 11 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-2 CALIBRATED HYDRAULIC PARAMETERS Hydrostratigraphic Unit Model Layers Spatial Zones (number corresponds to Figures 5-1 through 5-7) Horizontal Hydraulic Conductivity, ft/d Anisotropy ratio, Kh:Kv 12 #18 0.01 1 12 # 19 4.0 1 12 #20 2.0 1 12 #21 0.01 1 12 #22 0.01 1 13 #21 main model 0.7 1 13 #1 0.02 1 13 #2 0.1 1 13 #3 0.1 1 13 #4 0.05 1 13 #5 0.005 1 13 #6 0.02 1 13 #7 0.1 1 13 #8 0.01 1 13 #9 0.3 1 13 #10 7.0 1 13 #11 0.2 1 13 #12 0.005 1 13 #13 0.05 1 13 # 14 0.4 1 13 #15 0.01 1 13 #16 0.01 1 13 #17 4.0 1 13 #18 2.0 1 13 #19 0.01 1 13 #20 0.01 1 Bedrock (mid -depth) 14-16 #8 main model 0.1 1 14-16 #1 0.01 1 14-16 #2 0.02 1 14-16 #3 0.02 1 14-16 #4 12 1 14-16 #5 0.005 1 14-16 #6 0.01 1 14-16 #7 0.01 1 Bedrock lower 17-21 #2 main model 0.01 1 17-21 #1 0.005 1 Notes: Ft/d - feet per day Kh - horizontal hydraulic conductivity K - vertical hydraulic conductivity Prepared by: YG Checked by: WG Page 12 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-3 WATER BALANCE ON THE GROUNDWATER FLOW SYSTEM FOR PRE -DECANTED CONDITIONS Water balance components Flow in (9Pm) Flow out (9Pm) Direct recharge to the ash basin 136 Direct recharge to watershed outside of ash basin 346 Ash basin ponds 80 Drainage outside of the ash basin 345 Flow through and under the dam 217 Notes: Gpm - gallons per minute Prepared by: YG Checked by: WG Page 13 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-4 FLOW MODEL SENSITIVITY ANALYSIS Parameter Decrease by 1/2 Calibrated Increase by 2 Recharge (8 in/yr) 6.35% 2.51% 10.39% Ash Kh (2.0 ft/d) 2.79% 2.51% 2.35% Saprolite Kh (1.0 ft/d) 2.80% 2.51% 2.59% TZ Kh (1.5 ft/d) 2.59% 2.51% 2.47% Upper Bedrock Kh (0.7 ft/d) 3.58% 2.51% 3.07% Mid -depth Bedrock Kh (0.2 ft/d) 2.59% 2.51% 2.43% Lower Bedrock Kh (0.01 ft/d) 2.54% 2.51% 2.52% Prepared by: YG Checked by: WG Notes: The normalized root mean square error (NRMSE) in the calculated heads is shown In/yr - inches per year Ft/d - feet per day Page 14 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-5A ASH BASIN BORON SOURCE CONCENTRATIONS (Ng/L) USED IN HISTORICAL TRANSPORT MODEL Concentration Zone # Boron Concentration Model Layers 1 4,000 1-5 2 5,000 1-5 5 500 1-3 6 500 1-3 7 3,500 1-4 8 100 1-4 9 20,000 1-4 10 (Now Phase II Landfill) 5,000 (1965 - 1986) 1-4 10,000 (1986 - 2019) 1-4 11 400 1-5 12 1,500 1-2 13 5,500 1-2 14 100 1-4 15 97,000 1-4 16 100 1-4 17 1,500 1-4 18 3,000 1-2 20 3,000 1-2 21 100 1-3 22 1,000 1-4 23 1,500 1-3 24 2,500 2-3 25 (Now PV Structural Fill 28,000 1-3 26 900 1-3 27 12,000 1-4 28 1,500 1-4 29 1,200 1-2 30 3,000 1-3 31 5,000 1-5 32 (Now PV Structural Fill 5,000 (1965-2000) 1-4 20,000 (2000-2019) 1-4 33 (Now PV Structural Fill) 5,000 (1965-2000) 1-3 70,000 (2000-2019) 1-3 Notes: pg/L - micrograms per liter Prepared by: YG Checked by: WG Page 15 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-5B ASH BASIN STRONTIUM SOURCE CONCENTRATIONS (Ng/L) USED IN HISTORICAL TRANSPORT MODEL Concentration Zone # Boron Concentration Model Layers 1 0 1-5 2 0 1-5 5 2,000 1-3 6 2,000 1-3 7 2,500 1-4 8 100 1-4 9 9,000 1-4 10 (Now Phase II Landfill) 500 (1965 - 1986) 1-4 5,000 (1986 - 2019) 1-4 11 1,000 1-5 12 2,000 1-2 13 2,000 1-2 14 100 1-4 15 12,000 1-4 16 100 1-4 17 1,000 1-4 18 3,000 1-2 20 2,000 1-2 21 3,000 1-3 22 1,000 1-4 23 3,000 1-3 24 1,500 1-3 25 Now PV Structural Fill 3,500 1-3 26 6,000 1-3 27 6,000 1-4 28 3,000 1-4 29 1,000 1-2 30 2,000 1-3 31 11,000 1-5 32 Now PV Structural Fill 500 1965-2000 1-4 5,000 2000-2019 1-4 33 Now PV Structural Fill 100 (1965-2000) 1-3 500(2000-2019) 1-3 Notes: pg/L - micrograms per liter Prepared by: YG Checked by: WG Page 16 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-5C ASH BASIN TDS SOURCE CONCENTRATIONS (mg/L) USED IN HISTORICAL TRANSPORT MODEL Concentration Zone # TDS Concentration Model Layers 1 0 1-5 2 100 1-5 5 1,000 1-3 6 600 1-3 7 1,000 1-4 8 100 1-4 9 2,000 1-4 10 (Now Phase II Landfill) 1,000 (1965 - 1986) 1-4 2,000 (1986 - 2019) 1-4 11 300 1-5 12 500 1-2 13 3,000 1-2 14 100 1-4 15 9,000 1-4 16 250 1-4 17 500 1-4 18 6,000 1-2 20 500 1-2 21 300 1-3 22 500 1-4 23 1,000 1-3 24 450 2-3 25 Now PV Structural Fill 2,000 1-3 26 500 1-3 27 3,500 1-4 28 500 1-4 29 600 1-2 30 400 1-3 31 800 1-5 32 Now PV Structural Fill 500 1965-2000 1-4 1000 2000-2019 1-4 33 Now PV Structural Fill 500 (1965-2000) 1-3 5,000 (2000-2019) 1-3 Notes: mg/L - milligrams per liter Prepared by: YG Checked by: WG Page 17 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-6A ASH LANDFILL AND STRUCTURAL FILL BORON SOURCE CONCENTRATIONS (Ng/L) USED IN HISTORICAL TRANSPORT MODEL Phase 1 Phase Phase II Phase II Phase Phase PV Date LF (#1) 1 LF LF (#4) LF (#5) II LF II LF Structural (#2) (#6) (#7) Fill (#8) 1965-1984 0 0 0 0 0 0 0 1984-1986 3,500 4,500 0 0 0 0 0 1986-2000 3,500 4,500 50,000 77,000 77,000 1,000 0 2000-2019 3,500 4,500 50,000 77,000 77,000L 1,000 20,000 Prepared by: YG Checked by: WG Notes: pg/L - micrograms per liter TABLE 5-6B ASH LANDFILL AND STRUCTURAL FILL STRONTIUM SOURCE CONCENTRATIONS (Ng/L) USED IN HISTORICAL TRANSPORT MODEL Phase 1 Phase Phase II Phase II Phase Phase PV Date LF (#1) 1 LF LF (#4) LF (#5) II LF II LF Structural #2 #6 #7 Fill #8 1965-1984 0 0 0 0 0 0 0 1984-1986 2,000 5,000 0 0 0 0 0 1986-2000 2,000 5,000 11,000 15,000 7,000 100 0 2000-2019 2,000 5,000 11,000 15,000 7,000 100 200 Prepared by: YG Checked by: WG Notes: pg/L - micrograms per liter TABLE 5-6C ASH LANDFILL AND STRUCTURAL FILL TDS SOURCE CONCENTRATIONS (mg/L) USED IN HISTORICAL TRANSPORT MODEL Phase 1 Phase Phase II Phase II Phase Phase PV Date LF (#1) 1 LF LF (#4) LF (#5) II LF II LF Structural (#2) (#6) (#7) Fill (#8) 1965-1984 0 0 0 0 0 0 0 1984-1986 400 600 0 0 0 0 0 1986-2000 400 600 3,000 5,000 2,000 0 0 2000-2019 400 600 3,000 5,000 2,000 0 5,000 Notes mg/L - milligrams per liter Prepared by: YG Checked by: WG Page 18 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7A COMPARISON OF OBSERVED AND SIMULATED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Boron (Ng/L) Computed Boron (Ng/L) AB-10BR 228 313 AB-10BRL 0 -4 AB-10D 1420 1739 AB-10S 25100 20000 AB-10SL 11600 20000 AB-11D 0 86 AB-11S 0 57 AB-12BR 0 29 AB-12D 928 85 AB-12S 97300 97000 AB-12SL 4430 2463 AB-13D 0 530 AB-13S 958 900 AB-14D 502 562 AB-14DU 130 747 AB-14S 1300 1200 AB-15BR 0 993 AB-15D 36 1577 AB-15S 2980 2500 AB-15SL 214 1641 AB-16D 0 10 AB-16DU 0 24 AB-16S 132 67 AB-17D 0 187 AB-17S 22500 28000 AB-18D 0 147 AB-18DU 0 1436 AB-18S 2120 2457 AB-1BR 3430 2325 AB-1BRL 2730 2035 AB-1BRLL 2320 1814 AB-1 BRLLL 63 115 AB-1D 1180 1388 AB-1S 2390 2902 AB-20D 47 288 AB-20S 75800 70000 AB-21D 26 410 AB-21S 5770 3380 AB-2BR 0 9 AB-2D 270 112 AB-2S 0 23 AB-3D 170 121 AB-3S 1520 1500 AB-4D 350 35 Page 19 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7A COMPARISON OF OBSERVED AND SIMULATED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Boron (Ng/L) Computed Boron (Ng/L) AB-4S 226 400 AB-4SL 588 271 AB-5BR 0 2 AB-5 D 29 2 AB-5DU 44 73 AB-5S 2750 3000 AB-6BR 0 633 AB-6BRA 244 779 AB-6BRL 0 262 AB-6D 5220 1651 AB-6S 3000 5000 AB-7D 0 -9 AB-7DU 236 -66 AB-7S 11300 11688 AB-8D 0 10 AB-8DU 111 71 AB-8S 1280 1000 AB-9BR 0 48 AB-9D 0 76 AB-9S 33 980 AL-1 BR 663 1146 AL-1 BRL 0 4 AL-1 D 3260 2429 AL-1S 2640 3174 AL-2BR 4820 4941 AL-2BRL 2130 5293 AL-2BRLL 10600 6771 AL-2BRLLL 0 28 AL-2D 12300 6995 AL-2S 12900 16760 AL-3BR 1170 1183 AL-3D 5640 3026 AL-3S 63900 77000 AL-4BR 9420 15373 AL-4BRL 29 141 AL-4D 22100 15373 BG-1BR Second 0 0 BG-1D 0 0 BG-1S 32 0 BG-2BR 0 0 BG-2S 0 0 BG-3BR 0 0 BG-3D 0 0 BG-3S 0 0 Page 20 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7A COMPARISON OF OBSERVED AND SIMULATED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Boron (Ng/L) Computed Boron (Ng/L) CCR-11D 3380 2694 CCR-11S 4620 3500 CCR-12D 12 17 CCR-12S 3630 3500 CCR-13D 322 794 CCR-13S 1810 1105 CCR-14D 2280 1530 CCR-14S 3500 4500 CCR-15D 3 9 CCR-15S 7 1 CCR-16D 4 1 CCR-16S 12 2 CCR-1D 7 98 CCR-1S 25 98 CCR-2D 155 272 CCR-2S 121 732 CCR-3 D 7 41 CCR-3S 14 1 CCR-4D 27 130 CCR-4S 323 78 CCR-5D 10 8 CCR-5S 182 89 CCR-9DA 29 595 CCR-9S 3710 2397 GWA-10D 0 7 GWA-10S 98 26 GWA-11BR 0 -19 GWA-11D 1070 1400 GWA-11S 2610 2310 GWA-12BR 0 0 GWA-12D 0 0 GWA-12S 0 0 GWA-13DA 0 0 GWA-13S 28 0 GWA-14D 0 0 GWA-14S 0 0 GWA-15D 70 277 GWA-15S 1720 1869 GWA-1BR 0 68 GWA-1D 0 27 GWA-1S 0 0 GWA-2D 0 0 GWA-2 DA 0 0 GWA-2S 0 0 Page 21 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7A COMPARISON OF OBSERVED AND SIMULATED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Boron (Ng/L) Computed Boron (Ng/L) GWA-3D 0 0 GWA-3S 0 0 GWA-4D 0 0 GWA-5D 0 0 GWA-5S 0 0 GWA-6D 0 0 GWA-6S 0 0 GWA-7D 0 0 GWA-7S 0 0 GWA-8D 0 0 GWA-8S 0 0 GWA-9BR 0 0 MS-10 0 0 MS-11 0 0 MS-12 0 0 MS-13 0 0 MS-14 0 0 MS-15 0 0 MS-16 0 0 MS-8 0 0 MS-9 0 0 MW-1 197 1711 MW-10D 0 18 MW-10S 6 -1 MW-11D 0 0 MW-11S 0 0 MW-12D 0 0 MW-12S 0 0 MW-13D 0 0 MW-13S 0 0 MW-14BR 131 311 MW-14BRL 0 0 MW-14D 2020 1125 MW-14S 2480 2064 MW-2 3110 2895 MW-3 0 101 MW-4 0 0 MW-4D 0 0 MW-5 0 219 MW-6D 194 205 MW-6S 265 79 MW-7 0 -98 MW-7D 401 1619 MW-7S 3470 2453 Page 22 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7A COMPARISON OF OBSERVED AND SIMULATED BORON CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Boron (pg/L) Computed Boron (pg/L) MW-8D 267 200 MW-8S 213 329 MW-9D 485 92 MW-9S 28 197 OB-1 Ash Basin 0 0 OB-1 (Dry Ash Landfill 2980 3148 Notes: pg/L - micrograms per liter Prepared by: YG Checked by: WG Page 23 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7B COMPARISON OF OBSERVED AND SIMULATED STRONTIUM CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Strontium (Ng/L) Computed Strontium (Ng/L) AB-10BR 4080 171 AB-10BRL 3700 -2 AB-10D 2900 886 AB-10S 7200 9000 AB-10SL 6330 9000 AB-11D 1140 76 AB-11S 38 58 AB-12BR 0 13 AB-12D 9910 30 AB-12S 6400 12000 AB-12SL 4070 416 AB-13 D 682 324 AB-13S 3310 6000 AB-14D 552 812 AB-14DU 351 936 AB-14S 1760 1000 AB-15BR 1060 1012 AB-15D 674 1464 AB-15S 4600 1500 AB-15SL 742 1443 AB-16D 433 276 AB-16DU 817 853 AB-16S 315 2032 AB-17D 106 72 AB-17S 2000 3500 AB-18D 186 471 AB-18DU 133 1613 AB-18S 2720 1880 AB-1BR 2420 1930 AB-1BRL 2040 1915 AB-1 BRLL 1840 1814 AB-1BRLLL 1100 180 AB-1D 2440 1484 AB-1S 627 1217 AB-20D 503 44 AB-20S 0 500 AB-21D 690 602 AB-21S 1720 1329 AB-02BR 1200 140 AB-2D 608 1224 AB-2S 15 168 AB-3D 1310 1160 AB-3S 1530 2000 AB-4D 243 373 Page 24 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7B COMPARISON OF OBSERVED AND SIMULATED STRONTIUM CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Strontium (Ng/L) Computed Strontium (Ng/L) AB-4S 644 1000 AB-4SL 797 868 AB-5BR 3570 102 AB-5D 1810 82 AB-5DU 1460 622 AB-5S 4810 3000 AB-6BR 4340 2495 AB-6BRA 3060 2710 AB-6BRL 6420 1046 AB-6D 4430 5041 AB-6S 2810 11000 AB-7D 425 -28 AB-7DU 1090 -7 AB-7S 6420 5907 AB-8D 2220 15 AB-8DU 1590 77 AB-8S 1650 1000 AB-9BR 280 84 AB-9D 243 138 AB-9S 65 832 AL-1BR 3000 928 AL-1 BRL 1440 7 AL-1D 4860 1491 AL-1S 1800 1893 AL-2BR 3860 4669 AL-2BRL 4280 2784 AL-2BRLL 3990 3079 AL-2BRLLL 973 14 AL-2D 11100 6903 AL-2S 5580 7768 AL-3BR 1600 531 AL-3D 3140 2687 AL-3S 14900 15000 AL-4BR 3350 3531 AL-4BRL 1190 89 AL-4D 4730 3531 BG-1BR Second 178 0 BG-1D 686 0 BG-1S 108 0 BG-2BR 220 0 BG-2S 182 0 BG-3BR 168 0 BG-3D 143 0 BG-3S 115 0 Page 25 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7B COMPARISON OF OBSERVED AND SIMULATED STRONTIUM CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Strontium (Ng/L) Computed Strontium (Ng/L) CCR-9DA 750 11 CCR-9S 111 1 GWA-10 D 1840 9 GWA-10S 839 38 GWA-11BR 553 -13 GWA-11D 1710 1268 GWA-11S 970 1753 GWA-12BR 178 0 GWA-12D 285 0 GWA-12S 10 0 GWA-13DA 112 0 GWA-13S 9 0 GWA-14D 79 0 GWA-14S 17 0 GWA-15D 1120 753 GWA-15S 1760 1584 GWA-1BR 299 193 GWA-1D 867 110 GWA-1S 33 2 GWA-2D 600 0 GWA-2DA 931 0 GWA-2S 68 0 GWA-3D 69 0 GWA-3S 41 0 GWA-4D 131 0 GWA-4S 38 0 GWA-5D 83 0 GWA-5S 68 0 GWA-6D 220 0 GWA-6S 58 0 GWA-7D 195 0 GWA-7S 196 0 GWA-8D 169 0 GWA-8S 240 0 GWA-9BR 55 0 MS-10 16 0 MS-11 91 0 MS-12 33 0 MS-13 404 0 MS-14 398 0 MS-15 492 0 MS-16 310 0 MS-8 100 0 MS-9 190 0 Page 26 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7B COMPARISON OF OBSERVED AND SIMULATED STRONTIUM CONCENTRATIONS (Ng/L) IN MONITORING WELLS Well Observed Strontium (pg/L) Computed Strontium (pg/L) MW-1 3010 1795 MW-10D 96 15 MW-10S 4 0 MW-11D 96 0 MW-11S 90 0 MW-12D 156 0 MW-12S 14 0 MW-13D 66 0 MW-13S 59 0 MW-14BR 740 545 MW-14BRL 289 1 MW-14D 2170 2387 MW-14S 2420 3696 MW-2 1580 3230 MW-3 72 121 M W-4 102 0 MW-4D 210 0 MW-5 160 261 MW-6D 1980 74 MW-6S 11 4 MW-7 83 226 MW-7D 1440 2034 MW-7S 356 1764 MW-8D 1670 1059 MW-8S 1590 1102 MW-9D 1130 885 MW-9S 1090 1056 OB-1 Ash Basin 18 3 OB-1 (Dry Ash Landfill) 3320 1964 Notes: pg/L - micrograms per liter Prepared by: YG Checked by: WG Page 27 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7C COMPARISON OF OBSERVED AND SIMULATED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Observed TDS (mg/L) Computed TDS (mg/L) AB-10BR 335 405 AB-10BRL 358 4 AB-10D 338 661 AB-10S 1870 2000 AB-10SL 1320 2000 AB-11D 103 68 AB-11S 36 58 AB-12BR 426 13 AB-12D 622 26 AB-12S 7980 9000 AB-12SL 424 313 AB-13D 218 142 AB-13S 455 500 AB-14D 167 481 AB-14DU 126 559 AB-14S 379 600 AB-15BR 300 247 AB-15D 284 335 AB-15S 558 450 AB-15SL 254 411 AB-16D 226 32 AB-16DU 220 86 AB-16S 237 204 AB-17D 84 45 AB-17S 1130 2000 AB-18D 102 97 AB-18DU 125 323 AB-18S 374 376 AB-1BR 418 767 AB-1BRL 1350 765 AB-1 BRLL 704 741 AB-1 BRLLL 349 191 AB-1 D 574 633 AB-1S 452 511 AB-20D 148 320 AB-20S 4660 5000 AB-21D 208 902 AB-21S 1580 1994 AB-2BR 300 120 AB-2D 385 673 AB-2S 43 84 AB-3D 305 463 Page 28 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7C COMPARISON OF OBSERVED AND SIMULATED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Observed TDS (mg/L) Computed TDS (mg/L) AB-3S 666 500 AB-4D 147 347 AB-4S 163 300 AB-4SL 144 263 AB-5BR 640 245 AB-5D 241 200 AB-5DU 241 1245 AB-5S 5540 6000 AB-6BR 421 244 AB-6BRA 347 243 AB-6BRL 573 128 AB-6D 345 369 AB-6S 557 800 AB-7D 112 -16 AB-7DU 188 -4 AB-7S 2500 3446 AB-8D 278 5 AB-8DU 256 38 AB-8S 387 500 AB-9BR 191 31 AB-9D 152 50 AB-9S 69 245 AL-1BR 418 346 AL-1BRL 482 23 AL-1D 561 340 AL-1S 345 378 AL-2BR 603 1763 AL-2BRL 710 1316 AL-2BRLL 1040 1205 AL-2BRLLL 374 13 AL-2D 1590 2157 AL-2S 2410 2122 AL-3BR 568 177 AL-3D 888 1105 AL-3S 4600 5000 AL-4BR 444 1050 AL-4BRL 322 70 AL-4D 1160 1050 BG-1BR Second 145 0 BG-1D 135 0 BG-1S 86 0 BG-2BR 150 0 BG-2S 119 0 BG-3BR 179 0 Page 29 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7C COMPARISON OF OBSERVED AND SIMULATED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Observed TDS (mg/L) Computed TDS (mg/L) BG-3D 186 0 BG-3S 121 0 CCR-11D 570 312 CCR-11S 114 400 CCR-12D 135 20 CCR-12S 438 400 CCR-13D 405 338 CCR-13S 736 240 CCR-14D 511 208 CCR-14S 374 600 CCR-15D 121 24 CCR-15S 42 3 CCR-16D 148 2 CCR-16S 96 3 CCR-1 D 164 250 CCR-1S 90 245 CCR-2D 74 314 CCR-2S 61 375 CCR-3D 239 142 CCR-3S 45 8 CCR-4D 202 328 CCR-4S 332 317 CCR-5D 241 170 CCR-5S 281 350 CCR-9DA 288 39 CCR-9S 526 28 GWA-10D 452 2 GWA-10S 687 5 GWA-11BR 204 9 GWA-11D 269 270 GWA-11S 522 353 GWA-12BR 113 0 GWA-12D 150 0 GWA-12S 42 0 GWA-13DA 149 0 GWA-13S 83 0 GWA-14D 90 0 GWA-14S 31 0 GWA-15D 353 173 GWA-15S 474 321 GWA-1BR 176 196 GWA-1D 440 115 GWA-1S 60 3 GWA-2D 425 0 Page 30 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7C COMPARISON OF OBSERVED AND SIMULATED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Observed TDS (mg/L) Computed TDS (mg/L) GWA-2DA 448 0 GWA-2S 203 0 GWA-3D 96 0 GWA-3S 66 0 GWA-4D 181 0 GWA-5D 73 0 GWA-5S 77 0 GWA-6D 99 0 GWA-6S 59 0 GWA-7D 45 0 GWA-7S 123 0 GWA-8D 83 0 GWA-8S 90 0 GWA-9BR 103 0 MS-10 35 0 MS-11 47 0 MS-12 25 0 MS-13 40 0 MS-14 48 0 MS-15 94 0 MS-16 80 0 MS-8 46 0 MS-9 46 0 MW-1 400 364 MW-10D 75 14 MW-10S 25 0 MW-11D 68 0 MW-11S 48 0 MW-12D 81 0 MW-12S 25 1 MW-13D 90 0 MW-13S 92 0 MW-14BR 0 88 MW-14BRL 211 2 MW-14D 433 290 M W-14S 594 445 MW-2 292 870 MW-3 68 86 MW-4 65 0 MW-4D 84 0 MW-5 75 123 MW-6D 437 16 MW-6S 61 4 MW-7 63 45 Page 31 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-7C COMPARISON OF OBSERVED AND SIMULATED TDS CONCENTRATIONS (mg/L) IN MONITORING WELLS Well Observed TDS (mg/L) Computed TDS (mg/L) MW-7D 508 858 MW-7S 500 704 MW-8D 371 490 MW-8S 457 350 MW-9D 357 508 M W-9S 449 501 OB-1 Ash Basin 25 0 OB-1 (Dry Ash Landfill) 579 393 Notes• mg/L - milligrams per liter Prepared by: YG Checked by: WG Page 32 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-8 TRANSPORT MODEL SENSITIVITY TO Kd VALUES Well Boron (Ng/L) Boron model calibrated Model, low Kd Model, high Ka NRMSE 1.77% 4.55% 7.76% AB-10BR 228 313 5678 9 AB-10BRL 0 -4 299 0 AB-10D 1420 1739 7961 811 AB-10S 25100 20000 20000 20000 AB-10SL 11600 20000 20000 20000 AB-11D 0 86 368 1 AB-11S 0 57 57 52 AB-12BR 0 29 160 0 AB-12D 928 85 302 0 AB-12S 97300 97000 97000 97000 AB-12SL 4430 2463 3366 364 AB-13D 0 530 1430 47 AB-13S 958 900 900 900 AB-14D 502 562 1906 15 AB-14DU 130 747 1291 85 AB-14S 1300 1200 1200 1200 AB-15BR 0 993 2023 183 AB-15D 36 1577 2375 344 AB-15S 2980 2500 2500 2500 AB-15SL 214 1641 2381 330 AB-16D 0 10 80 1 AB-16DU 0 24 38 3 AB-16S 132 67 72 36 AB-17D 0 187 671 0 AB-17S 22500 28000 28000 28000 AB-18D 0 147 733 1 AB-18DU 0 1436 2419 133 AB-18S 2120 2457 2819 1568 AB-1BR 3430 2325 2763 510 AB-1BRL 2730 2035 2769 310 AB-1BRLL 2320 1814 2711 150 AB-1BRLLL 63 115 1285 0 AB-1D 1180 1388 2393 18 AB-1S 2390 2902 2911 1736 AB-20D 47 288 3814 0 AB-20S 75800 70000 70000 70000 AB-21D 26 410 1653 5 AB-21S 5770 3380 3655 1227 AB-2BR 0 112 359 0 AB-2D 270 0 42 0 AB-2S 0 23 926 0 AB-3D 170 121 1500 0 AB-3S 1520 1500 313 1500 AB-4D 350 35 400 0 Page 33 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-8 TRANSPORT MODEL SENSITIVITY TO Kd VALUES Well Boron (Ng/L) Boron model calibrated Model, low Kd Model, high Ka NRMSE 1.77% 4.55% 7.76% AB-4S 226 400 349 400 AB-4SL 588 271 138 117 AB-5BR 50 2 114 0 AB-5D 29 2 616 0 AB-5DU 44 73 3000 1 AB-5S 2750 3000 1906 3000 AB-6BR 0 633 1757 74 AB-6BRA 244 779 1175 102 AB-6BRL 0 262 2307 11 AB-6D 5220 1651 5000 595 A13-6S 3000 5000 -54 5000 A13-7D 0 -9 -14 0 A13-7DU 236 -66 11814 -3 A13-7S 11300 11688 31 8945 AB-8D 0 10 77 3 AB-8DU 111 71 1000 32 AB-8S 1280 1000 182 1000 AB-9BR 0 48 287 26 AB-9D 0 76 1222 52 AB-9S 33 980 1821 418 AL-1BR 663 1146 293 174 AL-1BRL 0 4 2536 0 AL -ID 3260 2429 3301 1715 AL-1S 2640 3174 28860 734 AL-2BR 4820 4941 21610 11 AL-2BRL 2130 5293 16952 7 AL-2BRLL 10600 6771 250 80 AL-2BRLLL 0 28 34116 0 AL-2D 12300 6995 35351 73 AL-2S 12900 16760 2197 2399 AL-3BR 1170 1183 14730 72 AL-3D 5640 3026 77000 14 AL-3S 63900 77000 35569 77000 AL-4BR 9420 15373 2494 917 AL-4BRL 29 141 35569 0 AL-4D 22100 15373 0 917 BG-1BR (Second) 0 0 0 0 BG-1D 0 0 0 0 BG-1S 32 0 0 0 BG-2BR 0 0 0 0 BG-2S 0 0 0 0 BG-3BR 0 0 0 0 BG-3D 0 0 0 0 BG-3S 0 0 2708 0 Page 34 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-8 TRANSPORT MODEL SENSITIVITY TO Kd VALUES Well Boron (Ng/L) Boron model calibrated Model, low Kd Model, high Ka NRMSE 1.77% 4.55% 7.76% CCR-11D 3380 2694 3500 2264 CCR-11S 4620 3500 206 3500 CCR-12D 12 17 3500 0 CCR-12S 3630 3500 1524 3500 CCR-13D 322 794 1602 103 CCR-13S 1810 1105 1611 229 CCR-14D 2280 1530 4500 1072 CCR-14S 3500 4500 30 4500 CCR-15D 3 9 4 0 CCR-15S 7 1 9 0 CCR-16D 4 1 4 0 CCR-16S 12 2 100 1 CCR-1 D 7 98 98 60 CCR-1S 25 98 521 98 CCR-2D 155 272 856 4 CCR-2S 121 732 133 237 CCR-3D 7 41 7 0 CCR-3S 14 1 776 0 CCR-4D 27 130 203 0 CCR-4S 323 78 109 1 CCR-5D 10 8 176 0 CCR-5S 182 89 2115 0 CCR-9DA 29 595 3468 5 CCR-9S 3710 2397 20 716 GWA-10D 0 7 37 0 GWA-10S 98 26 346 0 GWA-11BR 0 -19 2455 -1 GWA-11D 1070 1400 3089 45 GWA-11S 2610 2310 0 337 GWA-12BR 0 0 0 0 GWA-12D 0 0 0 0 GWA-12S 0 0 0 0 GWA-13DA 0 0 0 0 GWA-13S 28 0 0 0 GWA-14D 0 0 0 0 GWA-14S 0 0 1597 0 GWA-15D 70 277 2815 0 GWA-15S 1720 1869 170 105 GWA-1BR 0 68 97 0 GWA-1 D 0 27 2 0 GWA-1S 0 0 0 0 GWA-2D 0 0 0 0 GWA-2DA 0 0 0 0 GWA-2S 0 0 0 0 Page 35 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-8 TRANSPORT MODEL SENSITIVITY TO Kd VALUES Well Boron (Ng/L) Boron model calibrated Model, low Kd Model, high Ka NRMSE 1.77% 4.55% 7.76% GWA-3D 0 0 0 0 GWA-3S 0 0 0 0 GWA-4D 0 0 0 0 GWA-5D 0 0 0 0 GWA-5S 0 0 0 0 GWA-6D 79 0 0 0 GWA-6S 55 0 0 0 GWA-7D 0 0 0 0 GWA-7S 0 0 0 0 GWA-8D 0 0 0 0 GWA-8S 0 0 0 0 GWA-9BR 0 0 0 0 MS-10 0 0 0 0 MS-11 0 0 0 0 MS-12 0 0 0 0 MS-13 0 0 0 0 MS-14 0 0 0 0 MS-15 0 0 0 0 MS-16 0 0 0 0 MS-8 0 0 0 0 MS-9 0 0 3186 0 MW-1 197 1711 422 132 MW-10D 50 18 -2 0 MW-10S 6 -1 0 0 MW-11D 0 0 0 0 MW-11S 0 0 0 0 MW-12D 0 0 4 0 MW-12S 0 0 0 0 MW-13D 0 0 0 0 MW-13S 0 0 696 0 MW-14BR 131 311 41 2 MW-14BRL 0 0 2214 0 MW-14D 2020 1125 3374 28 MW-14S 2480 2064 12831 129 M W-2 3110 2895 208 138 M W-3 0 101 0 9 MW-4 0 0 0 0 MW-4D 0 0 616 0 MW-5 0 219 211 13 MW-6D 194 205 162 115 M W-6S 265 79 2417 1 MW-7 0 -98 3080 -434 M W-7D 401 1619 2466 9 MW-7S 3470 2453 923 1392 Page 36 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 5-8 TRANSPORT MODEL SENSITIVITY TO Kd VALUES Well Boron (Ng/L) Boron model calibrated Model, low Kd Model, high Kd NRMSE 1.77% 4.55% 7.76% MW-8D 267 200 385 0 MW-8S 213 329 311 9 MW-9D 485 92 267 0 MW-9S 28 197 1 1 OB-1 Ash Basin 0 0 3442 0 OB-1 (Dry Ash Landfill 2980 3148 196 1352 11 Prepared by: YG Checked by: WG Notes: The calibrated model has a normalized root mean square error (NRMSE) of 10.2%. Boron concentrations are shown for the calibrated model, and for models where the Kd is increased by a factor of 5 (high Kd) and decreased by a factor of 5 (low Kd). pg/L - micrograms per liter Page 37 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 6-1 WATER BALANCE ON THE GROUNDWATER FLOW SYSTEM FOR POST -DECANTING CONDITIONS Flow in Flow out Water balance components (9pm) (9Pm) Direct recharge to the ash basin 170 Direct recharge to watershed outside of ash 346 basin Ash basin ponds 16 Drainage outside of the ash basin pond 350 Flow through and under the dam 150 Notes: Gpm - gallons per minute Prepared by: YG Checked by: WG Page 38 Updated Groundwater Flow And Transport Modeling Report December 2019 Marshall Steam Station, Terrell, North Carolina TABLE 6-2 GROUNDWATER CLEAN INFILTRATION AND EXTRACTION WELL INFORMATION Number of Extraction Wells Formation Total Depth (ft bgs) 0 Saprolite/TRZ <100 32 Bedrock 100-150 19 Bedrock 150-200 15 Bedrock 200-250 Number of Clean Water Infiltration Wells Formation Total Depth (ft bgs) 0 Saprolite <20 1 Saprolite 20-40 10 Saprolite 40-60 13 Saprolite 60-80 Prepared by: YG Checked by: WG Notes: The 66 extraction wells have an average flow rate of 10 gpm. The extraction wells are pumped so that the water levels are near the bottom of the wells. The 24 clean water infiltration wells have an average flow rate of 11.5 gpm and the heads of the infiltration wells are maintained a 2 ft below ground surface. Ft - feet Bgs - below ground surface Page 39