FA-8008_42237_M_C_20230403_Status Update

From:Mike Hays
To:Currie, Ken
Cc:Gilbert, Christopher; Young, Emily; Parish, Ty C; Blair Burgess
Subject:[External] Duke Energy Blewett Falls_Incident No. 42237_Update
Date:Monday, April 3, 2023 10:18:33 AM
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Hello Ken, On behalf of Duke Energy, I wanted to provide you with an update on the progress of theBlewett Falls Development Project since the submittal of the Initial Abatement Action Reportdated December 23, 2022. Duke Energy and ERM have conducted the following activitiesassociated with release Incident 42237 since December 2022: Excavation of the fish passage footprint and concurrent Support of Excavation (SOE) Wallconstruction is on-going and has reached an approximate elevation of 107’ (surfaceelevation near the powerhouse in the vicinity of the former USTs is approximately 153’). The target depth for the excavation is 100’ elevation. The maximum depth of soil impactrelated to the UST Incident is 135’ elevation. The attached recent aerial photo illustratesthe current excavation footprint of the Blewett Falls Development Project.Excavation activities conducted since late December 2022 have occurred below themaximum depth of soil impact (135’ elevation as identified during the Comprehensive SiteInvestigation) and exhibited no visual or olfactory evidence of petroleum impact. Soilexcavated from January through March was handled as clean soil.Groundwater dewatering for the fish passage construction activities was initiated in April2022.The system has run continuously since start up with the exception of minordowntime for maintenance.NCDEQ DWR has conducted site visits to inspect the groundwater dewateringsystem on May 3, 2022, and July 21, 2022 and found no discrepancies.As of March 29, 2023, since startup 12,133,548 gallons of groundwater have beenextracted and discharged. The water table elevation in the construction area hasbeen lowered approximately 40’-45’ to date and is currently below the zone ofpetroleum impacted soil.Dewatering system influent/effluent sampling for Turbidity, Total Suspended Solids, andTPH DRO in accordance with the dewatering and discharge plan has occurred periodicallystarting April 22, 2022 (influent/effluent sampling bi-weekly until July 2022, followed byeffluent sampling monthly to date).TPH DRO was detected in the influent sample above the laboratory reporting limitin the initial sample collected April 22, 2022.Subsequent sampling events have not detected TPH DRO above laboratoryreporting limits in either the influent or effluent samples.Turbidity and TSS concentrations have been below laboratory reporting limits orregulatory reporting limits for all sampling events.
In consideration of the influent/effluent sampling data, Duke requested that theNCDEQ DWR approve modification of the Dewatering and Discharge Plan toreduce the components of the water treatment system. NCDEQ DWR approved thisrequest in July 2022. As referenced above, the overall excavation for the fish passage construction activities is currentlyon-going and estimated at 95% completion. A portion of the original proposed remedialexcavation area is included within this larger excavation. Upon substantial completion of the fishpassage construction (or sooner if practical) replacement monitoring wells will be installed withinthe USTs release area and subsequently sampled. A subsequent report will be prepared and submitted to the NCDEQ at a later date documentingthe replacement monitoring wells installation and groundwater analytical data. If you have any questions or need further information, please feel free to contact either ChrisGilbert of Duke Energy or myself. Best Regards, Mike

Mike Hays, P.G.
Principal Consultant, Geologist
ERM NC, Inc.
300 West Summit Avenue, Suite 330 | Charlotte, NC 28203
Mobile [phone]
[e-mail] │www.erm.com
The business of sustainability

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