NC0038377_Draft Cover Letter - 2021_20211215

ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
S. DANIEL SMITH
Director
NORTH CAROLINA
Environmental Quality
July 27, 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: Draft NPDES Major Modification
Permit NC0038377
Mayo Steam Electric Generating Plant
Person County
Facility Class I
Dear Ms. Bednarcik:
The Division has received your request for a Major Modification of the subject permit.
Enclosed with this letter is the modified permit. Please review this permit modification carefully to
ensure thorough understanding of the conditions and requirements it contains.
The draft permit modification contains the following significant changes from your current
permit:
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.
5. Industrial stormwater 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.
NORTH CAROLINA
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

Please provide any comments you have regarding the draft permit modification to this
office by August 30, 2021. At this time, the Division is also publishing a notice in the newspapers
of general circulation in Person County, inviting public comment on the Draft Modification.
Following the 30-day comment period, we will review all pertinent comments received and take
appropriate action on the permit modification.
If you have any questions about the NPDES permit process, please contact me at the
following e-mail address: [e-mail], or telephone number: 919-707-3606.
cc: Central Files
NPDES Files
EPA Region IV (e-copy)
Raleigh Regional Office/Water Quality (e-copy)
Raleigh Regional Office/PWS (e-copy)
WSS/Aquatic Toxicology Unit (e-copy)
G=D_E
NORTH CAROIJNA
Department al Environmental Quality
Sincerely,
Sergei Chernikov, Ph.D.
Environmental Engineer III
Industrial NPDES Permitting Unit
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