NC0004774_Other_20200311

%> DUKE
ENERGY,
March 11, 2020
Division of Water Resources
WQ Permitting Section - NPDES
Attn: Sergei Chernikov
1617 Mail Service Center
Raleigh, NC 27699-1617
Division of Water Resources
Attn.: Corey Basinger
Mooresville Regional Office
610 East Center Avenue, Suite 301
Mooresville, NC 28115
ELECTRONIC SUBMITTAL
Subject: Buck Combined Cycle Station
NPDES Permit NC0004774
Start -Up of Wastewater Retention Basin
Buck Combined Cycle Station
1385 Dukeville Rd.
Salisbury, NC 28146
With reference to paragraph C. (9) of the subject permit, this letter provides notification
to you that the start-up of the new wastewater retention basin (WWRB) is currently
scheduled for March 25, 2020. Attachment 1 provides a description of the WWRB.
Attachment 2 provides a water flow schematic diagram that shows where the new
treatment basin is located within the station's wastewater processes. During station
operation this system will primarily receive wastewater from the site wastewater sump
system. If the water chemistry of the cooling tower blowdown system is in specification,
and no additional treatment is needed, then the system has the option to send the
blowdown directly to outfall 001A by way of the wastewater sump, as it currently does.
During outages cleanout material from the cooling tower basin and the clarifier is
planned to be sent to the WWRB.
If you have any questions, please contact Robert Wylie at [phone] or
[e-mail].
Sincerely,
Kris Eisenrieth, General Manager II
Buck Combined Cycle
Attachments
cc: Roberto Scheller

Attachment 1
New Wastewater Retention Basin Description
NPDES Permit NC0004774

New Wastewater Retention Basin Description
NPDES Permit NC0004774
Duke Energy (Duke) is building a new wastewater retention basin at the Buck Combined Cycle Station located
on Dukeville Road in Rowan County, North Carolina. The wastewater retention basin is intended to hold and
treat wastewater from the combined cycle wastewater sump, cooling tower blowdown, clarifier
cleaning/draining and the future ash beneficiation facility. Normal operation is to route the water currently
going directly to outfall 001A to the new wastewater retention basin for additional treatment or if it is
determined that no additional treatment is warranted the water could be sent from the sump directly to
Outfa 11001A.
The new wastewater retention basin provides Buck Combined Cycle Station the option to close the outlet
structure and treat the wastewater if the plant has a known process upset and the flow into the basin has
qualities that would exceed the permit limits for outfall 001A. The plant could then continue to route water
into the basin or bypass the basin straight to the NPDES outfall if the quality of that water meets the
requirements of the NPDES permit.
The final basin design has a maximum berm height of 24 feet with a maximum of storage volume of 47.6 acre-
feet. The basin capacity is 7.4 mgals. The basin will have a 20 foot wide emergency spillway on the southwest
corner to prevent berm overtopping. The basin is to be lined to prevent infiltration of wastewater into the
ground. The final basin design includes a 60 mil HDPE liner with a protective geotextile below and above the
HDPE liner. This liner is covered with 18 inches of stone.
The basin flow path is designed to maximize retention time and increase settling efficiency. The final basin
design includes three floating baffles with alternating flow openings. The basin is also designed to adjust pH if
needed with caustic or acid to ensure compliance with the NPDES permit limits of>_ 6.0 and <_ 9.0 standard
units.
A description for the inputs to the new wastewater retention basin are as follows:
Combined Cycle Wastewater Sump: The flow rate from the combined cycle wastewater sump varies
depending on the number of pumps running in parallel. The wastewater sump has three pumps, but rarely
does more than one pump is run. The average daily flow (ADF) from the wastewater sump is approximately
350 gpm. The average daily flow rate includes the pump cycling on and off. The maximum flow rate while one
pump is running is approximately 660 gpm.
Cooling Tower Blowdown Cleaning: The estimated volume of water that is drained from the cooling tower
blowdown basin when it is cleaned is 1.5 mgal. The cooling tower blowdown is cleaned once every four years.
Clarifier Cleaning and Draining: The estimated volume of water that is drained from the clarifier when it is
cleaned is 1 mgal. The clarifier is cleaned once a year.
Future Flows from Ash Beneficiation Facility: The flow rate from the future ash beneficiation facility was
estimated to be 100 gpm. It is designated as internal outfall 008.

Attachment 2
Buck Combined Cycle Station
Water Flow Schematic Diagram
101901 OTARM011411I1I1LftLI

Wastewater Source Flows
1.) 0.58 MGD / 400 gpm
Cooling Tower
Blowdown
2.) 0.007 MGD / 5 gpm
O/W Separator
3.) 0.014 MGD / 10 gpm
OF Backwash
4.) 0.022 MGD / 18 gpm
RO Reject
Yadkin
�Softener
Potable Septic
Water Users Systems
To Clarifier
I Intake I
Evaporation
& Drift
Chiller
Cooling
Service Water
Users
Buck Combined Cycle Station
NPDES Wastewater Flow Schematic 0 Combined Cycle
Evaporation & Drift
� Blowdown
Main Cooling
Tower De -Chlorination
� 1
Condenser J
Wastewater
Oil/Water Sump
Separator 2
Oil Off -site
F3 HHRSG
Blowdown
Service Water/
Clarifier Filter Clearwell Firewater
Storage Tanks
Sludge Filter Press Solids Off -site Disposal
Thickener
Clarifier
Maintenance Solids Off -site Disposal
Drain
4
Ultra Filter Reverse Ion Demin
Osmosi Exchange Storage
Emergency
Firewater
Floor Drain
Turbine
Offline
Cooling
Tower
Cleanout
Wastewater ) Yadkin River
Retention Basin �'—'—►/ Outfall OOlA
Beneficiation Clarifier
Facility Cleanout
Heat Recovery Vent &
Steam Generators Drain
Condenser
Hotwell
_� Turbine Evaporation
Online Wash
Turbin�Wash
Wate> Off -site Disposal