NC0004987_Application_20200904 (2)

f f DUKE Marshall Steam Station
►e 8320 East NC Hwy 150
ENERGYe Terrell, NC 28682
828.478.7700
April 29, 2020
Ms. Julie Grzyb
North Carolina Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Electronic Mailing
Subject: NPDES Wastewater Permit Modification Request
Duke Energy Carolinas, LLC.
Marshall Steam Station
NPDES Permit #: NC0004987
Catawba County
Dear Ms. Grzyb,
Duke Energy Carolinas, LLC (Duke) requests a modification to the NPDES permit
NC0004987 for Outfall 002 in order to support the closure and remediation activities
associated with the ash basin. It is projected that the 1 million gallons per day (MGD)
daily maximum flow restriction at Outfall 002 during dewatering of the ash basin will
need to be increased to 3 MGD. This increase in flow accounts for flows from
dewatering, rainfall run-off and extracted groundwater from remediation activities.
The details of upcoming closure and remediation activities that warrant the need to
increase flow restriction from 1 MGD to 3 MGD for Outfall 002 are attached. In the
future the Lined Retention Basin (LRB) (NPDES Outfall 005) will receive flows from a
larger landfill footprint, but this is not expected to result in a significant pollutant loading
to the LRB.
A check in the amount of $1,030 is being mailed separately to your office due changes
in processing associated with the coronavirus. If you have questions, please contact
Robert Wylie at [phone] or Robert.Wylie @ duke-energy.com.
!Vrel,
Rick Roper
General Manager III
Marshall Steam Station
cc: Wes Bell (Electronic Mailing)
Attachment: Ash Basin Closure and Remediation Activities

Attachment
Marshall Steam Station
Ash Basin Closure and Remediation Activities
Page 1 of 2

Ash Basin Closure and Remediation Activities
Decanting of the ash basin is currently in progress. In the second half of 2020 the
decanting phase of the ash basin closure project is anticipated to 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.
An evaluation of projected concentrations determined that only two metal parameters were
to be above the calculated allowable limits without treatment. These two parameters were
arsenic (from ash basin pore water) and mercury (from CAP wells). Therefore, a WWTS is
being implemented to remove these two parameters to concentration levels below the
calculated allowable limits.
The ash basin closure project will also result in the need to build a larger landfill footprint.
The leachate from the larger footprint is planned to be sent to a retention basin which will
then pump the leachate to the wastewater Lined Retention Basin that discharge under the
NPDES permitted outfall 005. This outfall was permitted based on an estimated flow of 5
MGD. The actual flow has been historically less than 5 MGD. It is estimated that the flow
from the additional leachate flow will not change the previously projected long-term average
flow or loading of significance.
The flow schematic has been updated as follows to reflect the upcoming changes that are
requested with this permit modification request.
Page 2 of 2

Marshall Steam Station Water Schematic
NPDES Permit #NC0004987
ID Fan Control House
Non -contact Cooling Catawba County
Water Internal Outfall W3 Permit Modification Request
0.2MGD
Intake Screen April 2020
Backwash
Once -through Cooling Water
Outfall 001 _ Lake
1093 MGD Norman
Domestic Wastewater Sanitary POTW
Ash Sluice Submerged Flight Conveyor
Evap. 1.7 MGD
Lake
Norman Water Supply Groundwater
Flue Gas Desulfurization (FGD)
Wastewater
Treatment Outfall 002 �
Lake
Wet Scrubber wastewater from Lake Norman Extraction Wells
System 3.0 MGD
Norman
FGD a
Wastewter Treatment System Internal Outfall 006
(Phys/Chem & Bio)
0.8 MGD
Heat Exchanger Cooling Water 1.15 MGD
Storm water
Air Preheater Water, Precipitator & Boiler Wash Waters,
Misc. Cleaning Wastewaters
Fly Ash Silo Sump
II
Ash Basin
Dewatering
Misc. Equipment Cooling 0.53 MGD 0.04
MGD
Raw water Stormwater
Treatment
`----------
Boiler and Turbine Yard Drain Sumps -----------
1'9
Outfalls 002A and 0028 ;
Yard Sump Overflows ---------
Lake
Sumps {2 flows to lA)
�
Norman
Norman
MGD
(no flow expected) i
Retention Basin Overflow
Alternate 2.43
(no flow expected)
Coal Pile --------- _ _ _
Route MGD
Stormwater Holding Basin MGD Retention Basin
----------------------------�
Outfall 005
Lake
5 MGD
Norman
I Landfill Leachate 0.04 MGD