NC0004979_Modification_20201104

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ROY COOPER ��
Governor � ��
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MICHAEL S. REGAN ` , -^--.'"
Secretory ,,` ' `h"'"` '��`.-
S. DANIEL SMITH NORTH CAROLINA
Director Environmental Quality
November 04, 2020
Duke Energy Carolinas LLC
Attn: Rick Roper, GM III
253 Plant Allen Road
Belmont, NC 28012
Subject: Permit Modification
Application No. NC0004979
Plant Allen Steam Station
Gaston County
Dear Applicant:
The Water Quality Permitting Section acknowledges the November 4, 2020 receipt of your permit modification
application and supporting documentation. Your application will be assigned to a permit writer within the Section's NPDES
WW permitting branch. Per G.S. 150B-3 your current permit does not expire until permit decision on the application is
made. Continuation of the current permit is contingent on timely and sufficient application for renewal of the current
permit. The permit writer will contact you if additional information is required to complete your permit renewal. Please
respond in a timely manner to requests for additional information necessary to allow a complete review of the application
and renewal of the permit.
Information regarding the status of your renewal application can be found online using the Department of Environmental
Quality's Environmental Application Tracker at:
https://deq.nc.gov/permits-regulations/permit-guidance/environmental-application-tracker
If you have any additional questions about the permit, please contact the primary reviewer of the application using the
links available within the Application Tracker.
Sincerely,
-...5C ,
Wren Thedford
Administrative Assistant
Water Quality Permitting Section
cc: Central Files w/application
ec: WQPS Laserfiche File w/application
North Carolina gDepartment of
1 Environmental Quality I Divs�on of V:ater Fey��roes
/JD Mooresv3 to Reional Office 614 East CenterAvenue,Suite 301 I Your North Caro,na 28115
- i.:.....e.., 704-&63-1699

sc, DUKE Allen Steam Station
253 Plant Allen Roan
Belmont NC 28012
ENERGY
October 27, 2020
Sergei Chernikov, PhD, Acting Supervisor
Industrial Permitting Branch �` ,C D
NC Division of Water Resources RECE
1617 Mail Service Center
Raleigh, NC 27699-1617 Q C T 2 9 V 2020G
Subject: NPDES permit modification request
NCDEQ/DWRINPDES
Allen Steam Station
NC0004979
Gaston County
Dear Dr. Chernikov,
Duke Energy Carolinas, LLC (Duke Energy) hereby requests modification of the subject NPDES
permit to make the following changes:
1. Incorporate updated provisions and Technology Based Effluent Limits (TBEL) found in
40 CFR Part 423 related to bottom ash discharge and Flue Gas Desulfurization (FGD)
wastewater. The final rule states, "Where permits with the 2015 rule limitations have
already been issued, EPA expects that the final rule requirements will be incorporated
through permit modifications in most cases." Specifically, Duke Energy requests that the
FGD effluent discharge limits be updated in accordance with the terms of the recently
modified rule and that terms related to the discharge of bottom ash transport water be
updated to align with updates to 40 CFR Part 423. The final rule was published in the
Federal Register on October 13, 2020 and will become effective 60 days after
publication. For FGD wastewater, Duke Energy has announced the retirement dates of
the units at the Allen plant as follows: Units 1, 2, 3: 2024 and Units 4, 5: 2028. Based
on the station retirement provision found in the modified steam electric effluent
guidelines rule, Duke Energy request that the limits for the FGD system be set for TSS
and Oil and Grease only. Duke Energy requests that a narrative requirement to properly
operate and maintain the existing FGD wastewater equipment be included in the permit.
Duke Energy will work with the Department to provide the necessary documentation to
confirm the retirement dates and intentions as part of this permit modification request.
Duke Energy will work with the Department as part of this modification request to
provide the necessary information to develop the terms of the permit related to the
discharge of a blowdown stream of water from the submerged flight conveyer bottom ash
handling system under the new steam electric effluent guidelines related to bottom ash.
www.duke-energy.com

2. Duke Energy requests the permit authorize the routing of the flows from the ash basin
dewatering process and/or the groundwater extraction process to the Lined Retention
Basin (LRB) wastewater treatment system and outfall 006 in addition to release from
outfall 002. This will allow for needed flexibility as forthcoming closure decisions are
made and allow for the station to assure closure deadlines are met. Since these flows are
all subject to the same TBEL's, the limits for TSS and Oil and Grease would not need
modification.
3. Duke Energy requests that the flow limit for dewatering at outfall 002 be increased from
1.0 MGD to 3.0 MGD. This will assure timely and effective closure of the basin by
allowing for water to be removed at a greater rate. This will also allow for flexibility in
handling of extracted groundwater by allowing it to be released to either the ash basin
discharge outfall (outfall 002) or the Lined Retention Basin outfall (outfall 006).
4. Duke Energy requests that groundwater extraction clearly be included in the sources of
flow at both the ash basin outfall (outfall 002) and the Lined Retention Basin outfall
(006). Duke Energy is planning a substantial groundwater extraction and infiltration
process as part of remediation and site closure. Characterization of the groundwater
flows has been previously submitted to the Department.
5. Duke Energy requests leachate from the proposed lined CCR landfills to be included in
the sources of flow to the Lined Retention Basin outfall (006). Characterization from
untreated ash basin pore water is enclosed with this request as Attachment 1 to provide
an estimate of the concentrations or various constituents in the untreated wastewater.
Estimated flow volumes for leachate are an average flow of 0.36 MGD with an estimated
peak flow of 0.86 MGD.
6. An updated process flow diagram with the changes noted in this request is enclosed as
Attachment 2.
7. Duke Energy requests the permit move the upstream sampling location to a point
upstream of outfall 006. Currently, the upstream sampling location for the ash basin is
located downstream of the Lined Retention Basin (LRB) outfall.
8. Duke Energy requests the pH limit at internal outfall 005 be removed. The pH of the
wastewater is adjusted as needed later in the treatment process. This change is consistent
with other Duke Energy permits where pH was removed from internal outfalls. Internal
outfall 005 is subject to Federal Effluent Guidelines and these guidelines do not include
pH.
A check in the amount of$1,030 is included with this submittal to cover the required permit
modification fee. Should you have any questions about this request please feel free to contact
Ms. Elizabeth Glenn at [phone].

Sincerely,
Rick Roper
General Manger III
Allen Steam Station
ENCLOSURES
Cc:
Randy Gantt
Shannon Langley
Matt Hanchey
Scott Martin

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Attachment 2
Plant Allen 2020 Water Schematic
Condenser O utfa 11001
/ Cooling ►
Water 649 MGD South Fork River
Sanitary
Waste Landfill r
Outfall 002A
Leachate Intermittent Catawba River-I
(existing) w I
—1 Coal Yard 4 Coal Handling
New Landfills Sump Sumps
Closed Loop
1 Bottom Ash 7- I Atm Leachate 0.36 MGD / Storm —water ► Holding basin
System 1 Storage Basin
I I
1 I Internal ?
1 ,1. O utfa 11005 J
I / FGD 1 FGDWWTS OutfalI002
0.5 MGD Stormwater 3.0 MG D
►
Water I -. Catawba River
/ Treatment I
Atm Ash Silo FGD Wastewater
I I Sump / Stormwater _ Ash Basin M Treatment
Sump - System
l
11 t Seeps
Boiler I Stormwater I ►
I Turbine Room — 11.0 MGD
Catawba River
Sumps .. w .r
Boiler Room 4 Yard Drainage Outfall 006
/ / Retention Basin ►
Sumps I 1 Sump 3.5 MGD Catawba River
_/ Misc Equip Outfall 003 ►
Cooling&Seals 4.5 MG D
1.2 MGD South Fork River
Limestone
Stormwater ► Groundwater Groundwater
Sump Infiltration Wells Extraction Wells
Pow/Powerhouse Outfall 002E ►
um
(Intermittent) Catawba River
/ Intake Screen Outfall 004 ►
Backwash 6.5 MG D
Catawba River
Asiatic Clam/
/ Debris Filter /
Backwash * Flows are average estimates Catawba River
———-P Alternative Flow Path