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Home My WebLink AboutNC0080853_Plan of Action_20200130AECOM AECOM January 30, 2020 1600 Perimeter Park Drive, Suite 400 Morrisville, North Carolina 27560 919-461-1100 phone 919461-1415 fax NCDEQ / Division of Water Resources RECEIVED NPDES Permitting FEB 03 2020 1617 Mail Service Center Raleigh, North Carolina 27699-1617 NGDEOIDWRINPDES Subject: Corrective Action Plan Update Salem Business Park Remediation Site #NC0080853 Nokia of America Corporation 3370 Lexington Road, Winston-Salem, Forsyth County, North Carolina Dear Mr. Coco: On behalf of Nokia of America Corporation (Nokia), AECOM Technical Services of North Carolina Inc. (AECOM) is submitting the following Corrective Action Plan Update to fulfill the requirements of Condition A.(2.) of National Pollutant Discharge Elimination System (NPDES) Permit #NC0080853 for the groundwater treatment system located at the former Nokia facility, now known as the Salem Business Park Remediation Site, in Winston-Salem, Forsyth County, North Carolina. Background A groundwater treatment system operates at the Site to remediate groundwater impacted with volatile organic compounds (VOCs). The primary treatment unit is a shallow -tray air stripper. As part of the NPDES permit monitoring requirements, effluent samples are collected from a flume (FE-151) located approximately 100 feet downstream of the air stripper. Between 2015 and 2018, the tetrachloroethene (PCE) concentration in effluent samples collected from flume FE-151 ranged from <0.5 micrograms per liter (pg/L) to 5.6 pg/L, with an average concentration of approximately 2.5 pg/L ± 1.8 pg/L. These concentrations have been consistently below the historical permit limit of 17 Ng/L. On August 29, 2018, Nokia received notification from the North Carolina Division of Water Resources (DWR) that the facility would receive a new NPDES permit that would include a concentration limit of 6.1 pg/L for PCE at the permitted effluent sample point (FE-151). While the concentrations of PCE at the permitted effluent sample point have not historically exceeded the new limit, the average factor of safety will be reduced from nearly ten -fold to approximately three- fold. Based on the substantial change in permit -required treatment, Nokia requested a compliance schedule for meeting the new discharge concentration limit. The compliance schedule was included as Condition A.(2.) of the NPDES permit that became effective on February 1, 2019. The new PCE discharge limit also became effective on February 1, 2019, along with a requirement to increase the frequency of PCE sampling from FE-151 from quarterly to monthly. The compliance schedule provides an additional two years (February 2021) for Nokia to achieve compliance with the new PCE limit. AECOM submitted a Corrective Action Plan (CAP) on behalf of Nokia to NCDEQ DWR on August 1, 2019, outlining proactive corrective action activities implemented prior to the CAP submittal, along with proposed additional corrective actions to ensure permit compliance by February 2021 (AECOM, 2019). 14 AECOM 2 Completed Corrective Action Activities In May 2019, Nokia proactively began corrective action activities to improve air stripper performance and ensure consistent compliance with the new PCE discharge limit. Between April 2019 and June 2019, AECOM conducted multiple tests and compliance activities, including instrumentation upgrades, air -to -water ratio optimization, and increased sample QA/QC. These activities are detailed in the CAP submitted on August 1, 2019 (AECOM, 2019). The following additional corrective actions were conducted between July 2019 and January 2020. Continued Evaluation of Sample QA/QC To evaluate laboratory analytical precision and the reproducibility of PCE concentration results at low concentrations (<6 pg/L), duplicate samples were collected from flume FE-151 during the monthly events between April and December 2019. The average difference between parent and duplicate samples during the nine months of evaluation was approximately 0.1 pg/L. These results provide confidence that variability in laboratory measurements is unlikely to result in a "false positive" type of permit exceedance. As a result, AECOM will discontinue laboratory QA/QC evaluation beginning January 2020. Air -to -Water Ratio Testing with Normal Influent Concentrations Air -to -water ratio testing was initially conducted in May 2019 to evaluate if the air stripper operating conditions could be adjusted to maximize PCE removal. Five operational set points were evaluated at an average influent concentration of 780 pg/L, and downstream concentrations were reduced below the laboratory reporting limit (1 pg/L) at all five set points. Although the test demonstrated that adequate removal could be achieved, an optimum air -to -water ratio was not identified. Treatment Testing with Artificially High Influent Concentrations In December 2019, AECOM evaluated air stripper treatment performance at higher than normal influent concentrations by extracting groundwater exclusively from the two extraction wells with the highest PCE concentrations (EW-16 and EW-17). Two sets of influent and effluent samples were collected. Influent PCE concentrations were 2,470 and 3,020 pg/L and resulting effluent PCE concentrations were 3.4 and 3.4 pg/L. This testing demonstrated that adequate treatment could be achieved when influent concentrations are more than two times the normal influent concentrations. Air to Water Ratio Testing with Artificially High Influent Concentrations Because air to water ratio testing conducted on normal influent concentrations did not identify an optimum air -to -water ratio, AECOM repeated the air -to -water ratio test in January 2020 using influent derived from extraction wells EW-16 and EW-17. During the half -day test, the concentration of PCE immediately downstream of the air stripper was between 5.6 and 6.3 pg/L while influent concentrations varied between approximately 906 and 2,080 pg/L. A correlation between air -to -water ratio and PCE removal efficiency was not identified. Conclusions The primary conclusion from the testing conducted in May 2019, December 2019 and January 2020 is that a relationship among the air stripper operational parameters has not been identified to predictably optimize PCE removal. Despite the lack of an apparent optimization model, all samples collected under normal operating conditions indicated that adequate treatment was achieved. Adequate treatment under artificially high influent concentrations was demonstrated in several, but not all of the samples collected. No additional corrective action activities are currently ti y� AECOM 3 5 planned. Nokia will continue to conduct permit -required sampling and monitor air stripper performance as part of routine operation and maintenance activities. If you have any questions or require additional information, please contact Erin Stewart at 919-461-1323. Sincerely, AECOM 4 John Moran, E.I. Staff Engineer Christo her Brownfield, P.E. Project Engineer cc: NCDEQ / Division of Water Resources - WSRO References Erin Stewart, P.G. Project Manager AECOM, 2019. Corrective Action Plan, Salem Business Park Remediation Site #NC0080853. Former North Carolina Works, Lexington Road Plant, Winston-Salem, NC. August 2019.