NC0038377_Mod coverletter signed-2021_20211215

ROY COOPER
Governor
JOHN NICHOLSON
Interim Secretary
S. DANIEL SMITH NORTH CAROLINA
Director Environmental Quality
December 10, 2021
Ms. Jessica Bednarcik, Senior Vice President
Environmental, Health and Safety
Duke Energy Carolinas, LLC
Mail Code EC13K
P.O. Box 1006
Charlotte, North Carolina 28201-1006
Subject: Final NPDES Major
Modification
Permit NC0038377
Mayo Steam Electric Generating Plant
Person County
Facility Class I
Dear Ms. Bednarcik:
The Division of Water Resources is forwarding herewith the Final Major Modification for Mayo
Steam Electric Generating Plant. This modification is issued pursuant to the requirements of
North Carolina General Statute 143-215.1 and the Memorandum of Agreement between North
Carolina and the U.S. Environmental Protection Agency dated October 15, 2007 (or as
subsequently amended).
The Final Major Modification contains no significant changes from your Draft Major
Modification.
The Final Major Modification maintains the following significant changes contained
in the Draft Major Modification:
1. Landfill leachate from the CCR landfill was added as a contributing flow to the lined
retention basin.
2. The flow limit for Outfall 002 was increased from 2.0 MGD to 3.0 MGD to accommodate
large storm events. The limit was changed from the Daily Maximum to the Monthly
Average to be consistent with other Duke permits.
3. Ammonia conversion maintenance drainage was added as a contributing flow to the lined
retention basin.
4. The sampling frequency for the domestic package plant (internal Outfall 011) was changed
from Weekly to Quarterly to be consistent with other Duke permits.
NORTH CAROHNA
Department of Environmental Quality
North Carolina Department of Environmental Quality I Division of Water Resources
512 North Salisbury Street 11617 Mail Service Center I Raleigh, North Carolina 27699-1617
919.707.9000

5. Industrial storm water from the CCR landfill was added as a contributing flow to the lined
retention basin.
6. The Water Quality Based Effluent Limits for Total Arsenic, Total Chlorides, Total Fluoride,
Total Barium, and Total Antimony were added to the permit (Outfall 002A — lined retention
basin) based on the results of RPA.
If any parts, measurement frequencies, or sampling requirements contained in this permit are
unacceptable to you, you have the right to an adjudicatory hearing upon written request within thirty
(30) days following receipt of this letter. This request must be in the form of a written petition,
conforming to Chapter 150B of the North Carolina General Statutes, and filed with the office of
Administrative Hearings, 6714 Mail Service Center, Raleigh, North Carolina 27699-6714. Unless such
a demand is made, this permit shall be final and binding.
Please note that this permit is not transferable except after notice to the Division. The Division may
require modification or revocation and reissuance of the permit. This permit does not affect the legal
requirements to obtain other permits which may be required by the Division of Water Resources or
any other Federal, State, or Local governmental regulations.
If you have any questions or need additional information, please contact Sergei Chernikov, telephone
number [phone] or email: [e-mail].
cc: Central Files
NPDES Files
Raleigh Regional Office/Water Quality
WSS/Aquatic Toxicology Unit (e-copy)
EPA Region IV (e-copy)
Sincerely,
DocuSigned by:
8FB19B649DD2478...
for S. Daniel Smith, Director
Division of Water Resources
GD_E
NORTH CAROLINA
Opparhn¢nf of Environmental Duality
North Carolina Department of Environmental Quality I Division of Water Resources
512 North Salisbury Street 11617 Mail Service Center I Raleigh, North Carolina 27699-1617
919.707.9000