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Home My WebLink AboutMarshall- SOIL BTV MEMO_FINAL_20170905TECHNICAL MEMORANDUM Date: September 5, 2017 File: 1026.18 To: Tyler Hardin (Duke Energy) Cc: Kathy Webb (SynTerra) From: Todd Plating (SynTerra) Subject: Background Threshold Values for Soil Marshall Steam Station — Terrell, NC An updated background soil dataset was provided to the North Carolina Department of Environmental Quality (NCDEQ) for Marshall Steam Station (Marshall) on May 26, 2017. Additionally, the revised Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities (statistical methods document) (HDR Engineering, Inc. and SynTerra Corporation, May 2017) was provided to NCDEQ. On July 7, 2017, NCDEQ provided a response letter (Zimmerman to Draovitch, July 7, 2017) for each Duke Energy coal ash facility that identified soil and groundwater data appropriate for inclusion in the statistical analysis to determine background threshold values (BTVs) for both media. As outlined in the NCDEQ July 7, 2017 letter, Duke Energy is required to provide BTVs for both media within 60 days from receipt of the NCDEQ letter for facilities submitting Comprehensive Site Assessments (CSAs) later than October 31, 2017. BTVs for groundwater are provided under separate cover. Updated background soil datasets provided to NCDEQ on May 26, 2017 incorporated comments provided in a letter by NCDEQ (Zimmerman to Draovitch, April 28, 2017). NCDEQ requested that Duke Energy collect a minimum of 10, rather than the previously planned eight, valid background samples prior to the determination of BTVs for each constituent. For soil datasets with less than 10 valid samples available for BTV determination, no formal upper tolerance limit (UTL) statistics could be run and the provisional BTV (PBTVs) for a constituent was computed to be either: 0 The highest value, or y If the highest value is above an order of magnitude greater than the geometric mean of all values, then the highest value should be considered an outlier and removed from further use and the PBTV is computed to be the second highest value. Soil samples meeting the following criteria are considered valid for use in statistical determinations of BTVs: ty Sample was collected from a location that is not impacted by coal combustion residuals or coal associated materials; P:\Duke Energy Carolinas\ Statistics_CAMA \Background Determinations for NCDEQ July 7 2017\BTV TECH MEMO \ Marshall \ Soil \ Marshall- SOIL BTV MEMO_FINAL.docx Background Threshold Values- Soil September 5, 2017 Marshall Steam Station Page 2 of 3 y Sample was collected from a depth not less than 0.5 feet below ground surface; y Sample was collected from a location that is not impacted by other potential anthropogenic sources of constituents; and `7 Sample is collected from the unsaturated zone, greater than one foot (ft) above the seasonal high water table elevation. Additional site -specific requirements related to the Marshall background soil dataset as outlined in the July 7, 2017 NCDEQ letter have been incorporated into the soil background dataset. This technical memorandum summarizes the revised background soil datasets and statistically determined BTVs. Statistical determinations of BTVs were performed in accordance with the revised Statistical Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash Facilities (statistical methods document) (HDR Engineering, Inc. and SynTerra Corporation, May 2017). SOIL BACKGROUND DATA Soil samples were collected from soil borings conducted at Marshall during the 2015 Comprehensive Site Assessment (CSA). Background soil sample locations are presented in Figure 1. The background dataset provided to NCDEQ on May 26, 2017 included pooled soil samples collected from multiple depth intervals. Only samples collected from background locations at depth intervals greater than one foot above the seasonal high water table were included in the dataset. The background soil dataset has been further revised from the May 26, 2017 submittal based on input from NCDEQ in the July 7, 2017 letter. NCDEQ determined the following samples are not appropriate for use in determining BTVs: 0 GWA-1BR — sample collected within the waste boundary of the ash basin and coal pile, and ii MW-14BR — sample collected downgradient of the ash basin and unlined Phase I Landfill. After these samples were removed from the dataset, the remaining background soil dataset was re -screened for outliers prior to statistical determinations. A revised background soil dataset identifying valid samples and statistical outliers are presented as Table 1. Currently, the background dataset contains eight valid samples, below the minimum requirement of 10 samples to use formal statistics to derive BTVs. The background soil dataset for these constituents included laboratory reporting limits above the NCDEQ IHSB Preliminary Soil Remediation Goals (PSRG) Protection of Groundwater standards (dated October 2016). NCDEQ requires that the analytical practical quantitation limit (PQL) for antimony, selenium, and thallium be less than the PSRG Protection of Groundwater for the data to be valid for calculating BTVs. P:\Duke Energy Carolinas\ Statistics_CAMA \Background Determinations for NCDEQ July 7 2017\BTV TECH MEMO \ Marshall \ Soil \ Marshall- SOIL BTV MEMO_FINAL.docx Background Threshold Values- Soil September 5, 2017 Marshall Steam Station Page 3 of 3 PBTVs for all constitients were determined to be either the maximum value, or, if the maximum value was above an order of magnitude greater than the geometric mean of all values, the second highest value. Antimony and thallium datasets currently have zero valid samples, therefore PBTVs are not presented at this time. PBTVs for constituents in site soil are provided in Table 2. Additional soil samples were collected on August 16, 2017 to satisfy the minimum number of soil samples and for analysis of antimony and thallium by a method whereby the PQL is below the PSRG Protection of Groundwater values. Once planned additional samples are included in the dataset, the dataset will be screened for outliers and BTVs computed. Analysis of additional background soil samples is not complete at this time. Boring logs for recently collected samples are included as an Attachment. Analytical data for subsequent collection of background soil samples will be submitted to the NCDEQ Regional Office if received and processed in sufficient time for review prior to the preparation of the updated CSA report. LIST OF FIGURES: Figure 1 Background Soil Sample Location Map LIST OF TABLES: Table 1 Unsaturated Background Soil Data Summary Table 2 Background Threshold Values for Soil ATTACHMENT Boring Logs BGSB-GWA2 BGSB-GWA4 BGSB-GWA6 P:\Duke Energy Carolinas\ Statistics_CAMA \Background Determinations for NCDEQ July 7 2017\BTV TECH MEMO \ Marshall \ Soil \ Marshall- SOIL BTV MEMO_FINAL.docx Background Threshold Values- Soil September 5, 2017 Marshall Steam Station FIGURE P: \ Duke Energy Carolinas \ Statistics_CAMA \ Background Determinations for NCDEQ July 7 2017 \BTV TECH MEMO \ Marshall \ Soil \ Marshall- SOIL BTV MEMO_FINAL.docx GWA�4D GWA-5D BG-3D k iIIII k - ` 3•",Flaw J All a , ,r , e t •-1, ,F. 1 ^ 4 . 7 j JM' ! r T. LEGEND � �, �� •`' 4 -y�_,�� , :«�'••9. -- � •�`�� '� �' �# - O ADDITIONAL BACKGROUND SOIL r SAMPLE LOCATION r• k' r'`'rw, :' r . �. y `'�"� �' . EXISTING BACKGROUND SOIL SAMPLE i �' ® LOCATION -ACCEPTED BY NCDEQ d M tR , t ,. WASTE BOUNDARY ' �.;_ w`ra ti,. z J,y: , - r < ;, T _ — • — • •^ LANDFILL COMPLIANCE BOUNDARY COMPLIANCE BOUNDARY • �, ",,, ` `�Y, �4+��_ +; �� DUKE POWER MARSHALL STEAM :�.:'�` �'y •r e+ +� , . `I� STATION BOUNDARY NOTES: ✓err 4 ` f 2014 AERIAL ORTHOPHOTOGRAPHY OBTAINED FROM USDA NRCS GEOSPATIAL DATA GATEWAY 3 (https://gdg.sc.egov.usda.gov/GDGOrder.aspx). iz DRAWING HAS BEEN SET WITH A PROJECTION OF f NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83/2011). ORAPHIcsc o0 1,200 FIGURE 1 IN FEET BACKGROUND SOIL GR RIVERLE, SO STREET, SUITE 220 CAROLINA SAMPLE LOCATION GREENVI LLE, SOUTH CAROLINA 29601 f ! - PHONE 864-421-9999 '��.W. n rr or . om MARSHALL STEAM STATION tr ` . synTerra DROJECTM MANAGER: DATE:08/18/2017 TERRELL NORTH CAROLINA � l PROJECT MANAGER: T. PLATING i_ � ..,. ✓� }.* iL. .,�, �� CHECKED ^BY: ^BoWILKERc'.i c....•.. .. ....... ..... ..•..a 4. i Background Threshold Values- Soil September 5, 2017 Marshall Steam Station TABLES P: \ Duke Energy Carolinas \ Statistics_CAMA \ Background Determinations for NCDEQ July 7 2017 \BTV TECH MEMO \ Marshall \ Soil \ Marshall- SOIL BTV MEMO_FINAL.docx TABLE 1 BACKGROUND UNSATURATED SOIL DATA SUMMARY MARSHALL STEAM STATION DUKE ENERGY CAROLINAS, LLC, TERRELL, NC Analytical Parameter pH Aluminum Antimony Arsenic Barium Beryllium Boron Cadmium Calcium Chloride Chromium Cobalt Copper Iron Lead Magnesium Manganese Mercury Molybdenum Nickel itrate N) (asReporting Potassium Selenium Sodium Strontium Sulfate Thallium Vanadium Zinc Units S.U. mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg PSRG Protection of Groundwater NE NE 0.9 5.8 580 63 45 3 NE NE 360000 0.9 700 150 270 NE 65 1 NE 130 NE NE 2.1 NE NE NE 0.28 6 1200 Sample ID Sample Collection Date Analytical Results BG-3D (1-2) 6/9/2015 6.1 j 34100 --- 8.4 649 1.3 --- <0.69 1660 <278 420 27.4 50.2 37600 11.1 29200 243 0.05 <2.9 233; 27.8 7470 6.7 <286 243 <278 --- 81.9 59.2 BG-3D (10-12) 6/9/2015 7.5 j 29600 --- <5.7 1030 0.34 --- <0.63 19309 <262 406 28 29.8 34300 3.2 36700 412 <0.0085 <2.6 1 267 26.2 25500 3.7 j <204 209 <262 --- 83.3 72.4 GWA-2DA (3-5) 3/13/2017 4.7 j 27500 --- 1 j 159 2.2 <6.6 <0.17 369 <63.1 10.8 22.6 30.2 38900 13.2 8300 361 0.0074 j <0.66 11.1 6.3 8210 0.92 j <330 3.1 <91.4 --- 97 46.2 GWA-2DA (8-10) 3/13/2017 4.8 j 38400 --- 1.2 j 270 2.9 <7.2 <0.16 267 <59.7 16 16.7 83.2 33400 10.1 16100 734 <0.0072 j <0.72 14.3 6 12900 1.2 j <360 6 <79 --- 112 71.5 GWA-4D (52-53) 5/19/2015 6.2 j 18900 j+ --- --- 345 + 1.8 j- --- <0.72 j 1160 <293 15 23.2 j- 215 j- 42300 j- 3.7 j- 11100 j- 810 j- <0.0098 <3 j 7.1 j- 29.3 9920 --- <299 16.5 <293 j --- 128 j- 70.1 j- GWA-5D (27.5-29.0) 7/1/2015 5.8 j- 23000 --- --- 490 2.6 <19.7 <0.94 260 <384 3.1 8.3 7.3 31500 9.3 11100 509 <0.013 <3.9 4.5 38.4 14000 --- <394 60.7 <384 j --- 67.7 101 GWA-14S (3-5) 3/9/2017 5.2j 18900 --- 1.6 94.4 1.7 <6.4 <0.16 71.3 <56.1 2.4 4 2.6 18300 13.5 5200 334 0.026 <0.64 2.7 5.6 6250 1.1j <322 1.5 56.1j --- 34 30.8 GWA-14S (8-10) 3/9/2017 5.1j 33600 --- 3.8 45.1 1.3 <7.8 <0.19 246 <63.1 23.2 2 8.3 46500 25 2960 219 0.087 <0.4 11.5 6.3 2720 1.4j <390 2.3 56.Sj --- 72.2 23.3 Prepared by: LWD Checked by: TDP Notes: 54 - Indicates value omitted from dataset. Indicates parameter not measured or analyzed. - Indicates data removed /identified as an outlier. PSRG Protection of Groundwater - NCDEQ IHSB Preliminary Soil Remediation Soil Remediation Goals Table - October 2016 mg/kg - milligrams per kilogram < - Not detected above reporting limit j+ - Estimated concentration j- - Estimated concentration; biased low j - Estimated concentration NE - Not established S.U. - Standard Units P:\Duke Energy Carolinas\Statistics_CAMA\Background Determinations for NCDEQ July 7 2017\BTV TECH MEMO\Marshall\Soil\Tables\Table 1 - Marshall Soils.xlsx Page 1 of 1 TABLE 2 BACKGROUND THRESHOLD VALUES FOR SOIL MARSHALL STEAM STATION DUKE ENERGY CAROLINAS, LLC, TERRELL, NC Parameter Reporting Unit PSRG Protection of Groundwater BTVt pH* S.U. NE 4.7 - 7.5 Aluminum mg/kg NE 38,400 Antimony mg/kg 0.9 NA Arsenic mg/kg 5.8 8.4 Barium mg/kg 580 1,030 Beryllium mg/kg 63 2.9 Boron mg/kg 45 19.7 Cadmium mg/kg 3 0.94 Calcium mg/kg NE 1,660 Chloride mg/kg NE 384 Chromium mg/kg 360,000 23.2 Cobalt mg/kg 0.9 28 Copper mg/kg 700 215 Iron mg/kg 150 46,500 Lead mg/kg 270 25 Magnesium mg/kg NE 36,700 Manganese mg/kg 65 810 Mercury mg/kg 1 0.087 Molybdenum mg/kg NE 3.9 Nickel mg/kg 130 14.3 Nitrate (as N) mg/kg NE 38.4 Potassium mg/kg NE 25,500 Selenium mg/kg 2.1 6.7 Sodium mg/kg NE 394 Strontium mg/kg NE 60.7 Sulfate mg/kg NE 384 Thallium mg/kg 0.28 NA Vanadium mg/kg 6 128 Zinc mg/kg 1 1,200 1 101 Prepared by: LWD Checked by: THE Notes• * - Upper and lower limits determined for parameter t - Indicates value is provisional; dataset contains less than 10 valid samples mg/kg - milligrams per kilogram NA - Not applicable; dataset contains zero valid samples NE - Not Established S.U. - Standard Unit P:\Duke Energy Carolinas\Statistics_CAMA\Background Determinations for NCDEQ July 7 2017\BTV TECH MEMO\Marshall\Soil\Tables\ TABLE 2 - Marshall Soil BTVs.xlsx Page 1 of 1 Background Threshold Values- Soil September 5, 2017 Marshall Steam Station ATTACHMENTS P: \ Duke Energy Carolinas \ Statistics_CAMA \ Background Determinations for NCDEQ July 7 2017 \BTV TECH MEMO \ Marshall \ Soil \ Marshall- SOIL BTV MEMO_FINAL.docx PROJECT: Marshall Steam Station WELL / BORING NO: BGSB-GWA2 PROJECT NO: 1026.18 STARTED: 8/16/17 COMPLETED: 8/16/17 DRILLING COMPANY: Geologic Exploration NORTHING: 679247.451537 EASTING: 1414105.50997 DRILLING METHOD: Direct -Push ELEVATION NM ft M.P. ELEV: NM ft BOREHOLE DIAMETER: 2.5" IN WATER: NA ft TOC TOTAL DEPTH: 20.0 ft BGS NOTES: Dry Hole. LOGGED BY: B. Wilker CHECKED BY: T. Plating w p U = (D Q O C� p DESCRIPTION W a 2 < O^ U �v c z OJ p m0 _ p E d a WELL CONSTRUCTION ML Dark brown (7.5YR 3/3), non -cohesive silt w/ organics. Micaceous in part. Dry. ELI CL ML Reddish -orange (2.5YR 4/8), micaceous, cohesive, clayey silt. Sandy in part w/ occasional mottling. Occasional coarse weathered rock fragments throughout. Dry. 5 SP Poorly graded coarse to fine tan (10YR 8/2) sand w/ large CL ML tz fragments. Mottled. Dry Reddish -orange (2.5YR 4/8) micaceous clayey silt, as above. Mottled in part. Dry. CL ML Dark brown (7.5YR 3/4), orange, pink mottled clayey silt. Saprolite. Relict structure present. Non -cohesive. Dry. 10 CL ML Same as above. Reddish -brown (5YR 4/4) clayey silt (saprolite). Mottled in part. Less visible relict structure than above. Non -cohesive. Increasing moisture content @ roughly 14' bgs. 15 CL ML Same as above. Relict structure present 18-20' bgs. Occ qtz frags/sandy inclusions --19' bgs w/ pinkish coloring. Slightly moist, saturation not apparent. 20 25 30 35 CLIENT: Duke Energy Carolinas, LLC SynTerra 148 River Street, Suite 220 PROJECT LOCATION: Terrell, NC Phone: 864-421- s)mTerra Fax 864 679 371199 PAGE 1 OF 1 0 c� m a J F N Q V Q P H N H Z 0 PROJECT: Marshall Steam Station WELL / BORING NO: BGSB-GWPA PROJECT NO: 1026.18 STARTED: 8/16/17 COMPLETED: 8/16/17 DRILLING COMPANY: Geologic Exploration NORTHING: 686083,208635 EASTING: 1416993.72588 DRILLING METHOD: Direct -Push ELEVATION NM ft M.P. ELEV: NM ft BOREHOLE DIAMETER: 2.5" IN WATER: NA ft TOC TOTAL DEPTH: 20.0 ft BGS NOTES: Dry Hole. LOGGED BY: B. Wilker CHECKED BY: T. Plating w p U = (D Q O C� p DESCRIPTION w a 2 < O^ w �v c z OJ p m0 _ p E d a WELL CONSTRUCTION NX CL ML Brick red -orange (2.5YR 4/8) silty clay. Tight, cohesive, occasional mica. Dry. 5 XX CL ML Same as above. 2-3" layer of gravel -sized rk frags @ 5.75' & 7' bgs. Tight, cohesive, dry. Increasing mica content w/ depth. SM Sharp contact @ 8' bgs w/ light orange (5YR 6/8) of sandy silt. Saprolite. Red/white/black mottling w/ relict structure. 10 Micaceous. Tight, dry. SM Same as above. 5YR 6/8 of sandy silt (saprolite). Micaceous, mottled. Dry. 15 SM Same as above. 5YR 6/8 of sandy silt (saprolite). Occasional brick -red clay lenses (2" lense @ -15' bgs). 20 SPG SM Reddish gray (5YR 5/2) fine to coarse, poorly -sorted sand w/ ravel -sized qtz fra s. Silty in part. Sa rolite, as above. 25 30 35 CLIENT: Duke Energy Carolinas, LLC SynTerra 148 River Street, Suite 220 PROJECT LOCATION: Terrell, NC Phone: 864-421- s)mTerra Fax 864 679 371199 PAGE 1 OF 1 PROJECT: Marshall Steam Station WELL / BORING NO: BGSB-GWA6 PROJECT NO: 1026.18 STARTED: 8/16/17 COMPLETED: 8/16/17 DRILLING COMPANY: Geologic Exploration NORTHING: 686780.132398 EASTING: 1411768.32668 DRILLING METHOD: Direct -Push ELEVATION NM ft M.P. ELEV: NM ft BOREHOLE DIAMETER: 2.5" IN WATER: NA ft TOC TOTAL DEPTH: 20.0 ft BGS NOTES: Dry Hole. LOGGED BY: B. Wilker CHECKED BY: T. Plating w p U = (D Q O W C� p DESCRIPTION W a 2 < O^ U �v c z OJ p m0 _ p E d a WELL CONSTRUCTION ML Light brown 7.5YR 5/3 tight silt. No organics. Dry. , / i CL ML Reddish -orange (2.5YR 4/6) clayey silt. Vf sand in part. Cohesive, tight. Micaceous in part. Coarse sand 4-5' bgs. Dry. 5 CL ML Reddish -brown (2.5YR 4/4), cohesive, tight clayey silt. Dry. Micaceous, mottled w/ some relict structure @ 9-10' bgs of sandy silt(saprolite). Some coarse -grained sand in part. 10 CL ML Light tannish brown (7.5YR 6/3) mottling w/ reddish -orange (2.5YR 4/6) clayey silt. Vf-f sand in part. Micaceous. Dry. MH Reddish -light brown (7.5YR 5/4), tight silt. Minor relict structure present. Black mottling —13' bgs. Dr . 15 Sp SM Sharp contact —14' bgs w/ light greyish white (10YR 9.5/1) of silty sand. Fre qtz frags (m to coarse, some gravel). Loose, non -cohesive. Dry. 20 25 30 35 CLIENT: Duke Energy Carolinas, LLC SynTerra 148 River Street, Suite 220 PROJECT LOCATION: Terrell, NC Phone: 864-421- s)mTerra Fax 864 679 371199 PAGE 1 OF 1