NC0004961_Notification of Proposed Pumping_20150622

1' DUKEHarry K.Sideris
ENERGY® Senior Vice President
Environmental,Health&Safety
526 S.Church Street
Mail Code:EC3XP
Charlotte,NC 28202
[phone]
June 22, 2015
Mr. Jeffrey Poupart, Section Chief RECEIVEDIDENRIDWR
NC Division of Water Resources
1617 Mail Service Center JUN 2 6 2015
Raleigh, NC 27699-1617 Water Quality
Permitting Section
Subject: Riverbend Steam Plant—Retired
Notification of proposed pumping activity
NC0004961
Gaston County
Dear Mr. Poupart,
As discussed during the meeting between Division of Water Resources staff and Duke Energy
(Duke) staff on June 3, 2015, this letter is intended to provide details as to the necessary
pumping operations at the subject facility.
Riverbend Steam Station (Riverbend), has three registered dams (GASTO-097, -098, -099).
Potential failure mode analyses (PFMA) has been performed on all three dams. As the water
level continues to drop, a number of logistical concerns with the access walkway and platform,
as well as the riser structure of the secondary basin itself have become apparent.
Engineering analysis has already started to evaluate the structural stability of the riser from the
secondary basin to Mountain Island Lake under seismic and high wind loads as the water level in
the basin continues to decrease. Additionally, as the pond level decreases, the access walkway (a
floating gangway) is becoming steeper, requiring additional engineering analysis to design a
modified access staircase and walkway to maintain OSHA compliance.
Riverbend is also moving towards ash basin closure and demolishing the plant infrastructure
within the next few years. Part of this work includes the dewatering plans, for which pumping
basin water through the riser structure adds additional engineering concerns and associated risks.
It is currently proposed as part of the dewatering plan, to have the pump outlet pipes positioned
over the riser wall and attached inside the riser structure. During the implementation of these
activities there is increased risk of damaging the riser structure and ultimately damaging the
outlet pipe.
The activities listed above have risks associated with them to potentially impact the riser
structure or outlet pipe during the implementation process due to additional loads on the riser
structure and increased flows through the outlet pipe in the case of dewatering. Duke believes
the best alternative to mitigate these risks is to properly abandon the outfall pipe and riser
structure from the secondary basin to Mountain Island lake. This will mitigate risks associated

Mr. Jeff Poupart
Riverbend pumping approval request
June 22, 2015
with safety of the riser and/or pipe. This activity will also require the use of pumps to continue
the removal of water from the basin.
Duke proposes to stage portable pumps onsite to remove water as necessary. Specifically, the
pumps would move water over the crest of the dam with an outlet to the same location where the
outfall pipe originally discharged down the concrete flume to the existing NPDES outfall. All
required sampling and reporting of water removed from the basin would continue as part of this
activity. Engineered plans would be created to assure the pipe is grouted and abandoned
properly, as well as any work that would be required to properly abandon the riser structure. A
full engineering analysis for the pumps required would be completed, as well as a pump
operating plan and safety contingency plan, to assure safe operation.
Duke hereby requests confirmation with this proposal to use pumps to remove water from the
basin at Riverbend. Duke understands that all permit conditions related to monitoring and
compliance would be in place and that no contravention of instream water quality standards
would be allowed as a result of this activity. Duke believes that this would be the safest
alternative, removing additional loads on the riser and pipe that could occur during
implementation and construction related activities.
Given the company's statutory requirement to close these treatment basins within an aggressive
timeframe while maintaining a safe, reliable source of electricity for our customers, we request
your confirmation of this proposal so that further progress can be made towards the statutory
requirements. If you have any questions regarding this letter,please contact Mr. Shannon
Langley at [phone] or [e-mail].
Sincerely,
H. . Sideris
Senior Vice President
Environmental, Health& Safety
cc: Mike Parker DWR Mooresville Regional office
Tina Woodward—EC 13
Shannon Langley—NCRH 14th floor