NC0004987_Dam Repair Activities 2014_20141116

ATA
NCDENR
North Carolina Department of Environment and Natural Resources
Pat McCrory John E. Skvarla, III
Governor Secretary
November 16, 2014
Molly Davis
Municipal and Industrial Permitting Section
US EPA Region 4
61 Forsyth Street
Atlanta, GA 30303-8960
Subject: Requested Concurrence on Duke Energy Dam Repair Activities Duke Energy Marshall
Steam Station NC0004987
Dear Ms. Davis:
The Division of Water Resources (DWR)requests your guidance and concurrence on steps
necessary to conduct identified dam structure repair activities identified by the Division of Energy,
Mineral, and Land Resources(DEMLR) at the Marshall Steam Station covered by DWR permit
NC0004987. Your letter of September 16 and subsequent video conference discussion on October
14 regarding adjustment of water levels in the coal ash ponds indicates that EPA Region IV has
concerns regarding whether any of these activities are authorized under their current permit. In
light of your concerns, Duke Energy is unable to proceed with necessary dam repair activities.
Continued delay of dam repairs endangers both the public and the environment.
Intensive dam inspections were conducted by DEMLR staff following the Dan River coal ash spill
in February 2014. DEMLR staff noted repairs needed on various Duke Energy dams and Duke
Energy subsequently generated the attached spreadsheet indentifying all of Duke Energy's current
repair projects. As a result of these inspections, the Marshall Steam Station received a Notice of
Deficiency on August 11,2014 from the Dam Safety Program of the DEMLR. There are
activities planned at this facility to reduce risk of pipe failure or other potential catastrophic
unauthorized discharge. Generally, the requested work only involves discharging free water from
the ash pond through the existing decant structure to allow necessary access. In this particular case
the decant structure will be repaired which will require first a decrease in the flow through the
structure(will stop logs are installed) and then an increase in flow when activities are concluded
and the stop logs are removed. At no time will the flow rate of the discharged free water exceed
the flow originally considered in the Marshall NPDES permit.
The details of the requested work are provided as an attachment. Please note Scope#1, Part 3,
paragraph C indicates that flow control will be necessary to repair the outfall pipe using the
existing stop logs. For your convenience, the facility's permit can be viewed at
http://portal.ncdenr.org/c/document library/get file?p 1 id=1169848&folderld=1333482&name=
DLFE-28038.pdf
1611 Mail Service Center,Raleigh,North Carolina 27699-1611
Phone:[phone] Internet:www.ncwater.org
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-NPDES permit Condition 15 Ash Settling Basin which requires the permittee to maintain enough
storage for a 10 year-24 hour storm and mandates removal of settled material to ensure capacity.
-NPDES permit Condition 23 Structural Integrity Inspections of the Ash Pond Dam which
requires the permittee to meet the dam safety requirements established in NC Administrative Code
15A 2K.
-Hydraulic Analysis for Marshall Steam Station revised August 5, 2014 submitted as a part of
Scope 3. Page 13 of the Analysis clearly indicates that stop logs were considered when developing
discharge curve for this structure.
-Certificate of Approval for repairs activities issued by Dam Safety on September 18 conditional
on compliance with DWR permit requirements.
-The October 10 project specifications for Scope#1, Part 3,Paragraph C indicates that flow
control will be necessary to repair the outfall pipe using the existing stop logs. This flow control is
necessary to allow grout to set to fix cracks in the outfall pipe. In this instance, localized crack
repair will need to be performed on the"Riser"pipe as well as on the`Barrel"pipe of the decant
structure(spillway). Note: These repairs are required by the DEMLR Dam Safety Program to
ensure the integrity of the spillway section components.
The Division seeks guidance from EPA regarding whether the required lowering and then raising
of the free water level in the ash pond is authorized under the existing NPDES permit or whether a
permit modification is needed. We look forward to your timely response so we can instruct the
permittee how to proceed. If you do have any questions please feel free to contact me at(919)
807-6309, or via e-mail at [e-mail].
Sincerely,
Jeff Poupart
Water Quality Permitting Section Chief
cc: Steve McEvoy, DEMLR
Central Files
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