NC0038377_Interim Date Compliance Submittal_20201027

re DUKE
ti►, ENERGY
October 16, 2020
Mr. Danny Smith, Director
North Carolina Division of Water Resources RECEIVED
1617 Mail Service Center OCT 2 7 1020
Raleigh, NC 27699-1617
NCDEQIDWRINPDES
Subject: Duke Energy Progress, LLC.
Mayo Electric Generating Plant
Special Order by Consent (SOC)
EMC SOC WQ S 18-005
Interim date compliance submittal
Dear Mr. Smith:
In accordance with the NC Environmental Management Commission Special Order by Consent
(SOC), EMC SOC WQ S 18-005, Duke Energy Progress, LLC. hereby submits this notification
related to the completion of decanting of the ash basin in accordance with SOC condition 2.b.2.
The subject SOC requires decanting completion by December 31, 2020. As of the date of this
letter, Duke Energy considers the ash basin to have reached a decanted state.
Specifically, on August 31, 2020, a shift of ash material within the footprint of the Mayo ash
basin occurred. Courtesy notifications of this event were made to DWR staff on September 1,
2020. Prior to the internal shift of CCR material, Mayo's ash basin had been decanted over the
previous few months from EL 479' to EL 451'. After the material shift, an updated detailed
bathymetric survey was performed. The new elevation of CCR material was determined to be
approximately 460' leaving - 4 feet of water above the settled material across the footprint of the
basin. The settled material is almost completely uniform and there is no deep location at which
to set up a pump. These post event reviews of site conditions along with conversations with
Department staff have led to the determination that the basin has reached a decanted state under
the terms of the consent order. For tracking and clarity purposes, Duke Energy will conduct the
required post decanting evaluations and submit the final seep report within 90 days of the date of
this letter.
Duke Energy may conduct minor, periodic maintenance decanting, if needed, to maintain the
basin level prior to transitioning into the dewatering phase of the permit. In accordance with the
NPDES permit, Duke Energy will provide written, 7-day advance notice of the commencement
of dewatering of the basin below the three-foot level or involving the mechanical movement of
ash to facilitate water removal. This is anticipated to commence closer to the time of ash
excavation. Samples of the remaining basin water have been taken to determine the
characteristics of this water after the CCR material shift. If needed, additional treatment will be
employed to assure that any water released as maintenance decanting flows will be similar to the
characteristics of water released to date.

This notice fulfills our reporting obligation found in section 2.) b. of the subject Order. If you
have any questions, please contact Mr. Shannon Langley [phone].
I certify, under penalty of law, that this document and all attachments were
prepared under my direction or supervision in accordance with a system designed
to assure that qualified personnel properly gather and evaluate the information
submitted. Based on my inquiry of the person or persons who manage the system,
or those persons directly responsible for gathering the information, the information
submitted is, to the best of my knowledge and belief true, accurate, and complete.
I am aware that there are significant penalties for submitting false information,
including the possibility of fines and imprisonment for knowing violations.
Sincerely,
Tom Copo ant Manager
Roxboro Steam Electric Plant
cc: Jeff Poupart
NC Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Bob Sledge
NC Division of Water Resources
1617 Mail Services Center
Raleigh, NC 27699-1617
Scott Vinson, Supervisor
Raleigh Regional Office
3800 Barrett Drive
Raleigh, NC 27608
Leanne Wilson
Lori Tollie/FileNet—via email
Shannon Langley—via email