NCS000548_Tier II Notification_20230728

�' Duke Energy
DUKE Marshall Steam Station
ENERGY 8320 East NC Highway 150
Terrell, NC 28682
CAROLINAS
July 24, 2023
Mr. Zahid Khan, Regional Engineer
NC DEQ DEMLR—Mooresville Regional Office
610 East Center Avenue, Suite 301
Mooresville,North Carolina 28115
RE: Duke Energy Carolinas LLC, Marshall Steam Station
Industrial Stormwater NPDES Permit No. NCS000548
Catawba County,North Carolina
Dear Mr. Khan,
Please accept this letter(and electronic submittal) as the written two week notification as
required by Part D, Condition D-6, Table 9, regarding the industrial stormwater system serving
the Marshall Steam Station.
On June 19, 2023, quarterly stormwater samples were collected at the referenced facility and
analyzed in accordance with NCS000548. Analytical results for this monitoring event were
received by Duke Energy on July 19, 2023. Upon review of the results, it was observed that the
benchmark for low level Mercury was exceeded at stormwater outfall SW003. The benchmark
for Mercury is 12 nanograms per liter (ng/L) and the analytical result is 12.8 ng/L. This is the
second consecutive exceedance for this outfall and qualifies this outfall into Tier 11 status. Duke
Energy will document this exceedance and our response/actions within our S WPPP per Part D,
Condition D-6. We will also increase our monitoring frequency of all parameters to monthly
(qualitative and quantitative) and document within our SWPPP the other obligations addressed in
Table 3.
A subsequent stormwater system inspection has been completed at the outfall on July 19, 2023,
and mitigative measures emplaced following the Tier I exceedance in December 2022 appear to
be maintained and in good working order. Additional measures are currently under evaluation
for this outfall.
If any questions or if further discussions are needed, please do not hesitate to contact Scott La
Sala, Environmental Field Support Professional at Marshall Steam Station (828-478-7820, or
[e-mail]
Sincerely,
Jeffrey FlanCo'
General Manager III
Marshall Steam Station
cc:J. Scott La Sala,Carolinas West Field Support
Don Safrit,Carolinas Permitting&Compliance
www.duke-energy.com