FA-8008_42237_CA_O_20220705_Status Update Email

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:Tuesday, July 5, 2022 9:02:00 PM
Attachments:image001.pngF1_Remediation Activities_20220629_v6.pdf
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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 last update in January, 2022. DukeEnergy and ERM have conducted the following activities associated with release Incident 42237since January 2022: Groundwater dewatering/water treatment system design, permitting, and installation (Feb-April). The groundwater dewatering portion of the system consists of 29 extraction wells. The water treatment portion of the system consists of a settling tank, bag filters, sandfilters, granular activated carbon filters, a silt bag, and rip-rap splash pad.One soil sample (SW-02) previously collected from the USTs excavation near thePowerhouse had a benzo(a)pyrene concentration exceeding the Industrial/Commercialmaximum soil contaminant concentration (MSCC). As discussed with you on March 21,2022, to address this residual impact, remaining native soils in the SW-02 area wereexcavated to 8.5 ft below ground surface (bgs) on April 5, 2022, and the excavatedmaterial was properly disposed (see attached Figure 1). NCDEQ DWR approved the Dewatering and Discharge Plan on April 7, 2022. Theapproved plan included conditions for sampling (quarterly), notification, and reporting.Duke Energy started the groundwater dewatering/water treatment system on April 21,2022.The system has run continuously since start up with the exception of minordowntime for maintenance.NCDEQ DWR conducted a site visit to inspect the groundwaterdewatering/treatment system on May 3, 2022 and found no discrepancies.As of June 30, 2022, since startup 3,176,758 gallons of groundwater have beenextracted and discharged. The water table elevation in the construction area hasbeen lowered approximately 30’-35’ 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 occurredapproximately every two weeks starting April 22, 2022.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 or
regulatory reporting limits for all sampling events.In consideration of the influent/effluent sampling data, Duke has requested that theNCDEQ DWR approve modification of the Dewatering and Discharge Plan toreduce the components of the water treatment system. NCDEQ DWR approval ofthis request is pending following additional sampling of the system with therequested reduced treatment.Excavation for the fish passage construction resumed June 1 -3, 2022 but was temporarilysuspended on June 6, 2022 due to Support of Excavation (SOE) Wall constructionactivities. The attached recent aerial photo illustrates the current excavation footprint ofthe Blewett Falls Development Project.SOE Wall and associated tiebacks installation activities began on June 9, 2022, areongoing, and should be complete once the excavation target depth is reached.Excavation activities are scheduled to resume July 7, 2022 and are expected to continueuntil September 1, 2022. As referenced above, the overall excavation for the fish passage construction activities is currentlyon-going. A portion of the original proposed remedial excavation area is included within thislarger excavation. Upon substantial completion of the fish passage construction (or sooner ifpractical) replacement monitoring wells will be installed within the USTs release area andsubsequently sampled. As discussed in a conference call on March 21, 2022, ERM will prepare a report for submittal tothe NCDEQ documenting the USTs removal, soil sampling, and soil analytical data following thesubstantial completion of fish passage construction excavation activities. A subsequent reportwill be prepared and submitted to the NCDEQ at a later date documenting the replacementmonitoring 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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SW-01 SW-02
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SB-01
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Legend
5 feet bgs Excavation Area
8 feet bgs Excavation Area
8.5 feet bgs Excavation Area
10 feet bgs Excavation Area
12 feet bgs Excavation Area
Building Foundation Buttress
Limits of Proposed Excavation
Location of Removed UST
&<D
Impacted Area Excavated in Conjunction with the Fish Passage Project
Abandoned Monitoring Wells
&) ERM Soil Boring
k Confirmation Soil Sample
\\opsbdcfile01\Data\Boston\Team\DMMV\Clients_A_E\Duke\BlewettFalls_NC\MXD\202109_USTSampling\F1_ProposedSAP_v4.mxd, REVISED: 06/29/2022, SCALE: 1:240 when printed at 11x17ERMEnvironmental Resources Managementwww.erm.com
Figure 1: Remediation Activities Location MapDuke Energy Progress - Blewett Falls Hydroelectric Station Development Project2593 Power Plant Rd
Anson County, Lilesville, NC
0 10 20
Feet
1 inch = 20 feet
¯DRAWN BY: Allison.GuzmanSource: Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c) OpenStreetMap contributors, and the GIS User Community Coordinate System: NAD 1983 StatePlane North Carolina FIPS 3200 Feet
NotesBased on analytical results, SW-02 area was over-excavated to 8.5 feet bgs on April 5, 2022 as indicated on figure.