NC0004987_Fact Sheet_20200904

DEQ/DWR
FACT SHEET FOR NPDES PERMIT DEVELOPMENT/Major Modification
NPDES No. NC0004987
Facility Information
Applicant/FacilityName:
Duke Energy — Marshall Steam Station
Applicant Address:
Water Management, Duke Energy, P.O. Box 1006, Charlotte, NC
28201
Facility Address:
8320 E. NC Highway 150, Terrell, NC 28682
Permitted Flow
Not Limited
Type of Waste:
99.9% Industrial, 0.1% Domestic
Facility/Permit Status:
Major Modification
County:
Catawba
Miscellaneous
Receiving Stream:
Lake Norman
Regional Office:
Mooresville
Stream Classification:
WS-IV & B CA
USGS Topo
Quad:
Lake Norman North
303 d Listed?:
No
Permit Writer:
Ser ei Chernikov, Ph.D.
Subbasin:
03-08-32
Date:
June 8, 2020
Drainage Area (mi2):
NA
Summer 7Q10 cfs
Release 60 cfs
Winter 7Q10 cfs :
NA
1Q10 cfs :
IWC % :
23
SUMMARY
This permit is being modified to increase flow limit for Dewatermg Phase from 1.0 MGD to 3.0 MGD
for Outfall 002.
Decanting of the ash basin is currently in progress. In the second half of 2020 the decanting phase of
the ash basin closure project will move into dewatering. The input from rainfall run-off and
dewatering activities will account for approximately 2 million gallons per day (MGD) to Outfall 002. A
pilot study for the groundwater remediation system associated with the Corrective Action Plan (CAP)
Update, submitted to NCDEQ on December 31, 2019, plans to begin in the first half of 2021 with the
full system being implemented shortly after. The full-scale remediation project will be extracting and
discharging an estimated 1 MGD of groundwater to Outfall 002. Infiltration wells are also included in
the remediation system, for which water will be pumped from Lake Norman, treated, then allowed to
infiltrate into groundwater to increase remediation system effectiveness. The infiltration wells will
increase aquifer productivity and flush out constituents from the unsaturated zone. Groundwater will
then be pumped from the aquifer through the extraction wells and sent to a Waste Water Treatment
System (WWTS) prior to discharging from Outfall 002. Therefore, the maximum daily discharge from
Outfall 002 is projected to be 3 MGD during the future ash basin closure activities.
A new WWTS is being built to treat wastewater generated from the dewatering activities. It will consist
of a high rate clarifier followed by filtration when needed. Ahead of the clarification, the wastewater
will be chemically treated to assist in metal precipitation and settleability. These chemicals may include,
organo-sulfide, hydrogen peroxide, sodium hydroxide, a coagulant and a polymer for a flocculant.
Sodium Bisulfite may be used to ensure there is no excess of oxidant leaving the treatment system.
There will be a final pH adjustment step in which sulfuric acid or sodium hydroxide is used to ensure

the pH is within the limits. The sludge generated by the clarifier and filter backwash is planned to be
sent back into the ash basin for removal by the excavation contractor.
A new Reasonable Potential Analysis was conducted for Outfall 002 based on the 3.0 MGD flow
limit. The Analysis indicated that the Arsenic limits shall be reduced. Hence, the new Arsenic
limits have been incorporated into the permit.
All the remaining terms and conditions of the permit remain unchanged.
PROPOSED SCHEDULE
Draft Permit to Public Notice: June 30, 2020 (est.)
Permit Scheduled to Issue: August 31, 2020 (est.)
STATE CONTACT
If you have any questions on any of the above information or on the attached permit, please contact
Sergei Chernikov at [phone] or [e-mail].
NPDES Permit NC 0004987
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