NCS000548_SW Exceedance_20240401

Duke Energy
Marshall Steam Station
8320 East NC Highway 150
Terrell,NC 28682
CAROLINAS
March 27, 2024
Mr. Jerry Eplin, Regional Engineer
NC DEQ DEMLR—Mooresville Regional Office
610 East Center Avenue, Suite 301 y 1
Mooresville,North Carolina 28115 C,t10:
c l ,1 Url'3i Cite
RE: Duke Energy Carolinas LLC, Marshall Steam Station
Industrial Stormwater NPDES Permit No. NCS000548
Catawba County,North Carolina
Dear Mr. Eplin,
Please accept this letter(and electronic submittal) as the written two week notification as
required by Part D, Condition D-7, Table 10, regarding the industrial stormwater system serving
the Marshall Steam Station.
On February 27, 2024, 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 March 18, 2024. 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 34 ng/L. This Mercury
exceedance is the fourth(4th)to be reported for this 5-year permit period for this outfall and
qualifies this outfall into Tier III status. Pursuant to Part D, Condition D-7(c) of the referenced
permit, Duke Energy will prepare a written Action Plan that will be submitted to the Agency on
or before April 17, 2024. Additionally, Duke will document this exceedance and our
response/actions within our SWPPP and continue monthly monitoring.
A subsequent stormwater system inspection has been completed at the outfall on March 19,
2024, and mitigative measures emplaced following the Tier I exceedance in December 2022
appear to be maintained and in good working order. Additionally, scheduled quarterly
inspections and cleaning of the stormwater system is also being maintained at the site and outfall.
Additional assessment and housekeeping measures are currently under consideration for the
drainage area of SW003.
Please contact Scott La Sala, Environmental Field Support Professional at Marshall Steam
Station(828-478-7820, or joseph.lasala_,duke-ener•y.com) if you have any questions regarding
this notification submittal.
Sincerely,
Jeffrey Flan an
General Manager III
Marshall Steam Station
cc:J.Scott La Sala,Carolinas West Field Support
Don Safrit,Carolinas Permitting&Compliance
www.duke-energy.corn

Duke Energy
Marshall Steam Station
8320 East NC Highway 150
Terrell, NC 28682
CA i_' INAS
March 27, 2024
Mr. Jerry Eplin, Regional Engineer
NC DEQ DEMLR—Mooresville Regional Office
610 East Center Avenue, Suite 301 L k
Mooresville,North Carolina 28115 t"'s
,nee
RE: Duke Energy Carolinas LLC, Marshall Steam Station
Industrial Stouiiwater NPDES Permit No. NCS000548
Catawba County,North Carolina
Dear Mr. Eplin,
Please accept this letter(and electronic submittal) as the written two week notification as
required by Part D, Condition D-5, Table 8, regarding the industrial stormwater system serving
the Marshall Steam Station.
On February 27, 2024, 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 March 18, 2024. Upon review of the results, it was observed that the
benchmark for low level Mercury was exceeded at stormwater outfall SW002. The benchmark
for Mercury is 12 nanograms per liter(ng/L) and the analytical result is 24 ng/L. This
exceedance marks the first (1st)to be reported since June 2021 for this outfall and qualifies this
outfall into Tier I status. Pursuant to Part D, Condition D-5 of the referenced permit, Duke
Energy will document this exceedance and our response/actions within our SWPPP and continue
quarterly monitoring of this outfall.
A subsequent stormwater system inspection has been completed at the outfall on March 19,
2024, and associated BMPs in place appear to be maintained and in good working order.
Scheduled quarterly inspections and cleaning of the stormwater system is also being maintained
at the site and outfall.
Please contact Scott La Sala, Environmental Field Support Professional at Marshall Steam
Station(828-478-7820, or [e-mail]) if you have any questions regarding
this notification submittal.
Sincerely,
Jeffrey Flan an
General Manager III
Marshall Steam Station
cc:J.Scott La Sala,Carolinas West Field Support
Don Safrit,Carolinas Permitting&Compliance
www.duke-energy.com