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Home My WebLink About2020-04-16 Duke Energy Roxboro CAP Update Addendum_20200416DUKE ENERGY® April 16, 2020 Ms. Sheila Holman Assistant Secretary for Environment North Carolina Department of Environmental Quality 1611 Mail Service Center Raleigh, North Carolina 27699-1611 Paul Draovitch Senior Vice President Environmental, Health & Safety 526 S. Church Street Mail Code: EC3XP Charlotte, NC 28202 (980) 373-0408 Subject: Corrective Action Plan Update Addendum Demonstration of 02L Compliance for the East Ash Basin by December 31, 2029 Roxboro Steam Electric Plant Person County, North Carolina Dear Ms. Holman: The attached memorandum prepared by SynTerra Corporation on behalf of Duke Energy, includes revisions to the Roxboro Steam Electric Plant (Roxboro) corrective action strategies presented in Appendix G, "Updated Groundwater Flow and Transport Modeling Report," of the Roxboro Corrective Action Plan (CAP) Update (SynTerra, 2019) submitted to the Department on December 30, 2019. The compliance boundary showing a buffer of 500-feet from waste and wastewater boundaries was utilized in the CAP for flow and transport modeling and design of a corrective action system able to remediate groundwater constituents of interest (COls) attributable to the East Ash Basin (EAB) to concentrations less than the North Carolina Administrative Code (NCAC), Title 15A, Subchapter 02L, Groundwater Classification and Standards (02L) standard by December 31, 2029. A Consent Order (CO) that specifies obligations related to the closure of coal ash impoundments and groundwater corrective action at six Duke Energy coal combustion sites in North Carolina, including Roxboro was signed on February 5, 2020. The CO requires COls attributable to the Roxboro ash basins be remediated to concentrations less than the 02L standard by December 31, 2029 at or beyond the Geographic Limitation. The Geographic Limitation is defined in the CO as 500 feet from the ash basin waste boundary, at the property boundary, or the boundary of a water body, whichever is closer. The boundary for flow and transport modeling and design of the corrective action system for the EAB was revised such that the eastern discharge canal 500-foot buffer is no longer used for future 02L compliance. Modeling with the Geographical Limitation boundary indicated the need for nine additional extraction wells northwest of the EAB to remediate groundwater constituents of interest (COls) attributable to the EAB to concentrations less than the 02L standard by December 31, 2029. Ms. Sheila Holman April 13, 2020 Corrective Action Plan Update Addendum Roxboro Steam Electric Plant Page 2 Corrective action modeling for this Roxboro CAP Update addendum assumes that groundwater remediation activities will begin in 2021 and compliance will be achieved by December 31, 2029. This submittal is only being sent electronically. Please contact Kimberlee Witt at (336) 215- 4576 or Kimberlee.witt@duke-energy.com if you have any questions or need additional information. Sincerely, Paul Draovitch Senior Vice President Environmental, Health & Safety Enclosure: Corrective Action Plan Addendum - Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 (SynTerra Corporation, April 13, 2020) [910 NCDEQ - Rick Bolich NCDEQ - Steve Lanter NCDEQ - Eric Smith NCDEQ - Eric Rice NCDEQ - Ted Campbell (MODFLOW Data Files) NCDEQ - Elizabeth Werner (MODFLOW Data Files) 410 synTerra TECHNICAL MEMORANDUM Date: April 13, 2020 File: 1026.600.12 To: Scott Davies (Duke Energy) Kimberly Witt (Duke Energy) From: Rong Yu, Ph.D. (SynTerra) R Y Johnathan Ebenhack (SynTerra) Craig D. Eady, LG (SynTerra) Subject: Corrective Action Plan Addendum - Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 SynTerra prepared this technical memorandum for Duke Energy to demonstrate that groundwater constituents of interest (COIs) associated with the East Ash Basin (EAB) at the Roxboro Steam Electric Plant (Roxboro, Site) can be remediated beyond the ash basin Geographic Limitation to concentrations less than North Carolina Administrative Code (NCAC), Title 15A, Subchapter 02L, Groundwater Classification and Standards (02L) by December 31, 2029. This memorandum includes revisions to the corrective action strategies presented in Appendix G, "Updated Groundwater Flow and Transport Modeling Report," of the Roxboro Corrective Action Plan (CAP) Update (SynTerra, 2019). Background Duke Energy, the North Carolina Department of Environmental Quality (NCDEQ), and 11 community groups entered into a Settlement Agreement (SA) on December 31, 2019. A Consent Order (CO) to address the SA was finalized on February 5, 2020. The CO specifies obligations related to the closure of coal ash impoundments at six Duke Energy coal combustion sites in North Carolina, including the Roxboro site in Semora, Person County. The CO further describes obligations related to groundwater corrective action plans that apply to those six sites. A specified obligation at Roxboro is that COIs attributable to the ash basins be remediated at or beyond the Geographic Limitation to concentrations less than the 02L standard by December 31, 2029. The Geographic Limitation is defined in the CO as 500 feet from the ash basin waste boundary, at the property boundary, or the boundary of a water body, whichever is closer. The compliance boundary used in the flow and transport report (Appendix G) and presented in the CAP Update submitted to the NCDEQ on December 31, 2019 included a 500-foot buffer zone for the EAB eastern discharge canal based on Duke Energy's legal interpretation of the compliance boundary in this area. Under the CO, the compliance boundary was replaced with a Geographic Limitation, which was based on a 500-foot Page 1 Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 April 13, 2020 Roxboro Steam Electric Plant distance from the ash basin waste boundary. Figure 1 attached provides a comparison of the compliance boundary presented in the CAP Update and the Geographic Limitation stipulated by the CO. The revised corrective action approach presented in this memorandum assumes a Geographic Limitation consistent with the CO and does not include a 500-foot buffer around the EAB discharge canal. The corrective action demonstration follows the same format as Appendix G in the CAP Update and is consistent with the methodology used to evaluate remedial options. Corrective action modeling for this demonstration assumes that remediation activities will begin in February 2021 and compliance will be achieved by December 31, 2029. Revised Corrective Action Plan Design A revised groundwater corrective action approach to achieve compliance with the respective 02L standards for boron, sulfate, and total dissolved solids (TDS) by approximately December 31, 2029, has been simulated based on the new Geographic Limitation. The simulation uses COI distributions estimated for February 2021 as initial conditions. The revised corrective action occurs northeast of the EAB (Figure 2). The corrective action methodology for the EAB includes groundwater extraction methods to capture COI that have migrated from CAMA-regulated sources (i.e., EAB) beyond the Geographic Limitation. The CAP Update also included designs to create a hydraulic barrier to prevent the migration of COIs from sources not regulated by CAMA (Figure 3). The design for this area is not affected by the new Geographic Limitation for the EAB. The revised CAP design includes up to nine additional vertical groundwater extraction wells at the northeast corner of the EAB resulting from the Geographic Limitation change (Figure 2). The actual number and location of extraction wells installed may be adjusted based on field data collected in the area during the pilot testing phase. The proposed vertical extraction wells will have depths that range from approximately 470 feet below ground surface (bgs) to 510 feet bgs. The extraction wells will target COIs that might be present in the deeper bedrock fractures in that area. The revised combined groundwater remediation system for CAMA-regulated and sources not regulated by CAMA consists of up to 59 groundwater extraction wells and 27 clean water infiltration wells. The extraction wells are modelled at an average extraction rate of 1.7 gallons per minute (gpm) and the clean water infiltration wells are modelled with an average flow rate of 2.8 gpm (Table 1 and Figure 2). As discussed in Appendix G, the extraction wells are simulated using vertical arrays of drain points in Page 2 Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 April 13, 2020 Roxboro Steam Electric Plant MODFLOW. The drain bottom elevations are set to the center of each grid block containing the drain. This simulates a condition where the groundwater is being pumped out of the well casing to maintain a water level near the bottom of the well. The drain conductance values are estimated by considering radial flow to a well, based on 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 ( C ) for a grid block is computed as: C = E,,, 21-rKAz In 0.208Ax r W where EW is the well efficiency, which accounts for well skin effects. A well efficiency of Ew = 0.5 was used for the extraction wells. Results The simulations indicate that the cluster of up to nine additional extraction wells create a cone of depression marked by closed head contours to address COIs at or beyond the Geographic Limitation as shown in Figure 3. The analysis was conducted using two parallel scenarios, one where sources not regulated by CAMA are absent and another where those sources are left in place (Figure 4a). One scenario omits sources not regulated by CAMA from the simulation and shows the COI concentrations greater than the 02L standard associated with the EAB. The other scenario shows COI concentrations resulting from additional, downgradient sources at the Site. Results from the simulations show that the 41 extraction wells associated with the CAMA-regulated EAB, including up to nine new wells, can achieve 02L compliance along the EAB Geographic Limitation by December 31, 2029 (Figure 4b). Detailed Cost Estimate A detailed cost estimate for nine additional extraction wells is provided in the attached table (Table 1) as part of Appendix K of the CAP Update. The cost estimate is based on capital costs for design and implementation, the O&M cost, and monitoring costs, including well redevelopment and replacement on an annual basis. The design costs include work plans, design documents and reports necessary for implementation of the alternative. Implementation costs include procurement and construction. O&M costs are based on annual routine labor, materials and equipment to effectively conduct Page 3 Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 April 13, 2020 Roxboro Steam Electric Plant monitoring, routine annual and 5-year reporting, as applicable, and routine and non - routine maintenance costs. Conclusion The following conclusions are based on the results of the revised corrective action simulations: • The revised corrective action approach is capable of reducing modeled COI concentrations related to the EAB to less than 02L at the Geographic Limitation by December 31, 2029. • The proposed starting date of remediation activities is conceptual at this time. The fully operational date depends on permitting and construction schedules. References SynTerra (2019). Corrective Action Plan (CAP) Update, Roxboro Steam Electric Plant, 1700 Dunnaway Road, Semora, North Carolina. Anderson, M.P., & Woessner, W.W. (1992). Applied Groundwater Modeling, Simulation of Flow and Advective Transport. (p. 381). New York City, NY: Academic Press, Inc. Page 4 Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 April 13, 2020 Roxboro Steam Electric Plant FIGURES *. OfiJ11Y�' a LEGEND �' DUKE 340 GRAPHIC SCALE 0 340 680 � ENERGY (IN FEET) ASH BASIN WASTE BOUNDARY PROGRESS DRAWN Br. R.YU DATE: 02/04/2020 ASH BASIN COMPLIANCE BOUNDARY DEPICTED IN CAP REVISED BY: R.YU DATE: 04/03/2020 UPDATE REPORT (SYNTERRA, 2019) CHECKED BY: C. EADY DATE: 04/03/2020 10 APPROVED BY: C. EADY DATE: 04/03/2020 GEOGRAPHIC LIMITATION PROJECT MANAGER: C. EADY — EFFLUENT DISCHARGE CANAL synTerra www.synterracorp.com NOTES: FIGURE 1 ALL BOUNDARIES ARE APPROXIMATE. COMPARISON BETWEEN COMPLIANCE BOUNDARY AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS AND GEOGRAPHIC LIMITATION COLLECTED ONFEBRUARY6,2017. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT CDRAWING HAS BEEN SET OORDINATE SYSTEM RIPS NORTH CAROLINA STATE PLANE STEM FPS3200(NAD 3AND NAVD8 TECHNICAL MEMORANDUM ROXBORO STEAM ELECTRIC PLANT e GRAPHIC SCALE F- 'ti 100 0 100 200 %' DUKE GRAPHIC SCALE 340 0 340 680 LEGEND EXTRACTION WELLS ENERGY (IN FEET) NINE (9)ADDITIONAL EXTRACTION WELLS PROGRESS DRAWN BY: R.YU DATE:02/04/2020 CLEAN WATER INFILTRATION WELLS REVISED BY: R. YU DATE: 04/11/2020 CHECKED BY. C. EADY DATE: 04/11/2020 '41� ASH BASIN WASTE BOUNDARY APPROVED BY: C. EADY DATE: 04/11/2020 PROJECT MANAGER: C. EADY - — GEOGRAPHIC LIMITATION synTerra www.synterracorp.com NOTES: FIGURE 2 ALL BOUNDARIES ARE APPROXIMATE. ACTIVE GROUNDWATER REMEDIATION SYSTEM THE REMEDIATION SYSTEM SHOWN WAS DESIGNED FOR 02L COMPLIANCE BY 2029. NORTHEAST AREA OF THE EAST ASH BASIN AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT COLLECTED ONFEBRUARY6,2017. TECHNICAL MEMORANDUM DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200(NAD83 AND NAVD88). �/ ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA 420 o g2o 420 420 �10 �10 420 410 ra•-.. �� 4�0 O r 4y0 . • 460 0 • p10 : A3� T v I 'A 0 4g0 Lo A60 v ■ EAST ASH M 490 48p �• BASIN • 410 i D 390 �w g . 480 Q 490 v v v a m boo 00 500 ✓ °� 1 , � . O A6'O O rj. �� S � • � 00 GRAPHIC SCALE y �� 100 0 100 200 460 LEGEND t DUKE GRAPHIC SCALE 340 0 340 680 EXTRACTION WELLS ENERGY (IN FEET) O NINE (9)ADDITIONAL EXTRACTION WELLS PROGRESS DRAWN BY: R.YU DATE: 02/04/2020 ♦ CLEAN WATER INFILTRATION WELLS 111,1 REVISED BY: R.YU DATE: 04/11/2020 HYDRAULIC HEAD FEET CHECKED BY: C. EADY DATE: 04/11/2020 (FEET) APPROVED BY: C. EADY DATE: 04/11/2020 ASH BASIN WASTE BOUNDARY WnTerra PROJECT MANAGER: C. EADY GEOGRAPHIC LIMITATION www.synterracorp.com NOTES: FIGURE 3 ALL BOUNDARIES ARE APPROXIMATE. SIMULATED HYDRAULIC HEADS IN UPPER FRACTURED BEDROCK ZONE CONTOUR INTERVAL IS IO FEET. HEADS ARE SHOWN AFTER CLOSURE -IN -PLACE FOR MODEL LAVER 16. WITH ACTIVE GROUNDWATER REMEDIATION THE REMEDIATION SYSTEM SHOWN WAS DESIGNED FOR 02L COMPLIANCE BY 2029. UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4,2019. AERIAL WAS TECHNICAL MEMORANDUM COLLECTED ONFEBRUARY6,2017. ROXBORO STEAM ELECTRIC PLANT COORDINATEDRAWING HAS BEEN SET SYIC8)THCAROLINASTATE PLANE SYSTEM RIPS 3200(NAD 3ANDNAVD8SEMORA, NORTH CAROLINA IMULATED WITHOUT NON-CAMA CCR SOURCES I^ JJJrJJJ JA t � EASTASH BASIN MSIMULATED WITH NON-CAMA CCR SOURCES Pq[ r EAST ASH BASIN LEGEND ■ REFERENCE LOCATION NON-CAMA CCR SOURCE ZONES NOT SUBJECT TO THE 12/31/2029 02L COMPLIANCE DEADLINE. THESE AREAS WILL OBE ADDRESSED BY THE PLANNED REMEDIATION SYSTEM IN THE GYPSUM STORAGE AREAAND FUTURE EXCAVATION BORON 700 - 4,000 Ng/L BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY GEOGRAPHIC LIMITATION ALL BOUNDARIES ARE APPROXIMATE. NON-CAMACCR SOURCES INCLUDE THE GSAIDFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FI PS 3200 (NAD83). �.�.�C. 1_ DUKE tn GRAPHIC SCALE 340 0 340 680 ENERGY (IN FEET) PROGRESS DRAWN BY: R.YU REVISED BY: R. YU DATE: 02/04/2020 DATE: 03/30/2020 1�� CHECKED BY: C. EADY DATE: 03/30/2020 APPROVED BY: C. EADY DATE: 03/30/2020 PROJECT MANAGER: C. EADY FIGURE 4a SIMULATED APRIL 2019 MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS DOWNGRADIENT OF THE EAST ASH BASIN UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT TECHNICAL MEMORANDUM ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA IMULATED WITHOUT NON-CAMA CCR SOURCES EAST ASH BASIN SIMULATED WITH NON-CAMA CCR SOURCES ♦ } �'11-001 a• EAST ASH BASIN LEGEND EXTRACTION WELLS 0 NINE (9) ADDITIONAL EXTRACTION WELLS ♦ CLEAN WATER INFILTRATION WELLS IN REFERENCE LOCATION NON-CAMA CCR SOURCE ZONES NOT SUBJECT TO THE 12/31/2029 02L COMPLIANCE DEADLINE. THESE AREAS WILL BE ADDRESSED BY THE PLANNED REMEDIATION SYSTEM IN THE GYPSUM STORAGE AREAAND FUTURE EXCAVATION BORON 700 - 4,000 Ng/L M BORON > 4,000 Ng/L ASH BASIN WASTE BOUNDARY -GEOGRAPHIC LIMITATION ALL BOUNDARIES ARE APPROXIMATE. CLOSURE -BY -EXCAVATION SCENARIO IS ESTIMATED TO BE COMPLETED IN YEAR 2037. NON-CAMACCR SOURCES INCLUDE THE GSA/DFAHA SOURCES TO THE NORTH OF EAB. AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON FEBRUARY 6, 2017. DRAWING HAS BEEN SET WITH PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FI PS 3200 (NAD83). „c. 4DUKE ' EN RGY PROGRESS d. z d. A GRAPHIC SCALE 340 0 340 680 (IN FEET) DRAWN BY: R. YU DATE: 02/04/2020 REVISED BY: R. YU DATE: 04/11/2020 CHECKED BY: C. EADY DATE: 04/11/2020 APPROVED BY: C. EADY DATE: 04/11/2020 PROJECT MANAGER: C. EADY FIGURE 4b SIMULATED MAXIMUM BORON CONCENTRATIONS IN ALL NON -ASH LAYERS DOWNGRADIENT OF THE EAST ASH BASIN AFTER APPROXIMATELY 9 YEARS OF ACTIVE GROUNDWATER REMEDIATION UPDATED GROUNDWATER FLOW AND TRANSPORT MODELING REPORT TECHNICAL MEMORANDUM ROXBORO STEAM ELECTRIC PLANT SEMORA, NORTH CAROLINA Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 April 13, 2020 Roxboro Steam Electric Plant TABLES Demonstration of 02L Compliance for the Roxboro East Ash Basin by December 31, 2029 April 13, 2020 Roxboro Steam Electric Plant TABLE 1 EAST ASH BASIN/GSA/DFAHA AREA ACTIVE REMEDIATION APPROACH WELL SUMMARY Number of Location Formation Total Depth Extraction Wells (feet bgs) 18 GSA/DFAHA Transition zone and 180 Bedrock 17 NW EAB/ Bedrock 200 GSA/DFAHA 15 N EAB Bedrock 260 9 NE EAB Bedrock 500 Number of Clean Total Depth Water Infiltration Location Formation (feet bgs) Wells Saprolite, 27 GSA/DFAHA Transition zone, 180 Bedrock Prepared by: RY Checked by: CDE Notes: GSA - Gypsum Storage Area DFAHA - Dry Fly Ash Silos, Transport and Handling Area GPM - Gallon per minute BGS - Below ground surface The 59 extraction wells have an average modeled flow rate of 1.7 gpm. The 18 extraction wells next to the Intake Canal are pumped so that the water levels are at 400 ft elevation, which is approximately 10 ft below the water level in the Intake Canal. The remaining 41 extraction wells are pumped so that the water levels are near the bottom of the wells. The 27 clean water infiltration wells have an average flow rate of 2.8 gpm and the heads of the infiltration wells are maintained at 20 feet above the ground surface. Appendix K revised on April 3, 2020 Table 1: Summary of Capital and Annual Costs for the Nine Additional Extraction Wells Source Area 1 - EAB/Industrial Landfill/LCID Alternative 2 - Groundwater Extraction with 2L at EAB Geographic Limitation by 12/31/2029 Roxboro Steam Electric Plant Semora, North Carolina Capital Costs TASK # TASK UNIT QUANTITY RATE COST 1.0 Design/Engineering/Site Preparation Pre -Design Field Planning LUMP SUM 1 $136,000 $136,000 Design Document/Work Plan LUMP SUM 1 $298,000 $298,000 Permitting LUMP SUM 1 $33,000 $33,000 $467,000 2.0 11VIonitoring Well Installation Monitoring Well Installation EACH 0 $0 $0 $0 3.0 Remediation Wells Installation Extraction Well Installation EACH 9 $141,556 $i 274,000 Well Development EACH 9 $14,222 $128,000 Conveyance Piping and Electrical LUMP SUM 1 $417,000 $417,000 $1,819,000 4.0 Project Management Project Management (10 % Capital Cost) LUMP SUM 1 $229,000 $229,000 229,000 Total Capital Cost $2,515,000 Operations, Maintenance & Monitoring Costs TASK # TASK UNIT QUANTITY RATE COST 1.0 Operations and Maintenance Remediation Wells Operations and Maintenance LUMP SUM 1 $344,000 $344,000 344,000 2.0 Groundwater Sampling Groundwater Sampling Event EACH 0 $0 $3.0 0 0 !Wellaintenance Annual Well Maintenance and Replacement EACH 1 $91,000 $91,000 91,000 4.0 Reporting Annual Reporting EACH 1 $90,000 $90,002 Five -Year Review Report EACH 0.2 $88,000 $18,000 108,000 5.0 1 Project Management Project Management (10 % Annual Cost) LUMP SUM 1 $54,000 $54,000 $54,000 Total Annual Cost $597,000 Present Worth Analysis Year(s) Cost Type Total Cost Discount Factor Present Value 0 Capital Costs $2,515,000 1.000 $2,515,000 1-9 Annual Costs $597,000 6.108 $3,646,000 10-12 1 Post -Remedy Monitoring $218,000 1.755 $383,000 13 lWell Abandonment Costs $36,000 0.530 $19,000 Total Life Cycle Cost $6,563,000 Note: 1. Life cycle represents net present value of expenditures with capital costs incurred in Year 0, annual costs incurred thereafter, and well abandonment in the last year. Discount Rate of 5 assumed. 2. Costs presented herein represent a best estimate at this time. Actual costs may change based on a variety of factors during implementation. Page 1 of 2