NC0004987_Modification_20210105

DUKEMarshall Steam Station
N4r- (� 8320 East NC Highway 50
ENERGY, Terrell, NC 28682
January 5, 2021
Sergei Chernikov, PhD
North Carolina Department of Environmental Quality
Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617 RECEIVED
Subject: Marshall Steam station JAN 1 2 2021
NPDES Permit NC0004987
NPDES permit modification request NCDEQ/DWR/NpDES
Dear Dr. Chernikov:
Duke Energy requests that NPDES permit # NC0004987 be modified to incorporate
recently modified steam electric Federal Effluent Guidelines (40 CFR Part 423).
It is requested that purge water from the bottom ash handling system be permitted as a
contributing wastewater source to outfall 005. Purge water from the bottom ash
submerged flight conveyer (SFC) handling system will primarily be directed to be used
for FGD makeup water when available but, as allowed in the modified rule in
accordance with 40 CFR 423.13(k)(2)(i)(A), this purge water may be released to the
lined retention basin for treatment and then discharged through outfall 005 as needed to
maintain water system chemistry and/or water balance. In accordance with the updated
federal effluent guideline rule, a 30-day rolling average SFC purge water flow volume of
0.098 MGD is requested to be added to the permit based on a calculated bottom ash
system volume of 0.983 million gallons. Duke Energy requests that this be added as a
special condition.
Additionally, Duke Energy requests for internal outfall 006 that the amended
concentration limits for FGD wastewater found in the modified rule be incorporated into
the permit. Those limits are as follows with changes from current permit limits
highlighted:
Pollutant Existing monthly average/daily Modified Rule monthly
max average/daily max
Arsenic 8 ug/1 and 11/ug/I 8 ug/I and 18
Mercu 356 ng/I and 788 ng/I 34 ng/I and 103 n /1
Selenium 12 us/I and 23 us/1 19 ug/I and 70 u /I
Nitrate/Nitrite 4.4 m•/I and 17 m•/I 3 mg/I and 4 mg/I 1

Dr. Sergei Chernikov
North Carolina Department of Environmental Quality
Division of Water Resources
January 5, 2021
Duke Energy request the pH limits at internal outfall 006 be removed. The pH of the
wastewater is adjusted as needed later in the treatment process and prior to
discharging from the final outfall 005. This change is consistent with other Duke Energy
permits where pH was removed from internal outfalls. Internal outfall 006 is subject to
the Federal Effluent Guidelines 40 CFR 423 and these guidelines do not include pH.
Attached is a check for $1,030 in order to process this modification request. If you have
questions, please contact Robert Wylie at [phone] or Robert.Wylie@duke-
energy.com.
Sincerely,
Rick Roper, General Manager III
Marshall Steam Station
cc: .Robert Wylie via email
Scott La Sala
Shannon Langley — via email