NCS000546_Contingency Pumping Request Letter_20160108

DUKE
ENERGY,
January, 8 2016
Mr. Jeffrey Poupart
North Carolina Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Mr. Bradley Bennett
North Carolina Division of Energy, Mineral and Land Resources
1612 Mall Service Center
Raleigh, NC 27699-1612
Subject: Allen Steam Station
Contingency Pumping Plans for Alternate Spillway Projects
NPDES Permits NC0004979 and NCS000546
Gaston County
Dear Messrs. Poupart and Bennett,
Harry K. Sideris
Senior Vice President
Environmental, Health & Safety
526 S. Church Street
Mail Code: ECUP
Charlotte, NC 28202
[phone]
This letter sets out our understanding of the conditions required by NCDEQ in connection with
Duke Energy's contingency plan for pumping and diverting wastewater and stormwater during
construction of alternate spillways for the active and retired ash basins at Allen Steam Station.
The conditions were originally set out in emails from Sergei Chernikov (12 and 24 November
2015) and Mike Randall (12 November 2015). Based on those emails, we understand that, if
these conditions are met, NCDEQ has no objection to Duke Energy's implementation of the
contingency plan, as described below.
The spillway projects at Allen Steam Station are designed to address problems with riser
structures in the retired and active ash basins and to repair signs of aging in the outfall pipes of
the retired and active ash basins. Both riser structures will be abandoned, and alternate
spillways will be installed. In the course of installing the alternate spillways in both of these ash
basins, water levels will be lowered to provide safe and practical access to the work area and to
provide sufficient freeboard during critical work activities. Because of the unpredictability of plant
operations and precipitation, it is not possible to project with certainty that freeboard will be
sufficient for periods of critical work activities. Duke Energy has developed a contingency plan
for pumping and diverting wastewater and stormwater if it becomes necessary to remove water
from the basin to maintain freeboard. The contingency plan was previously submitted to
NCDEQ for approval on 27 October 2015.
The details of the contingency plans for each ash basin are as follows:
Active Ash Basin — Any excess wastewater not normally discharged through outfall 002
during drawdown will be pumped from the active ash basin to the stormwater discharge
channel of the retired ash basin, which will then discharge from stormwater outfall
SW015. Pumping will be needed for an estimated 1-2 weeks. Running a pipe overland to
place adjacent to NPDES outfall 002 (which would enable discharge at the outfall) is

Allen Steam Station NPDES Permits NC0004979 and NCS000546
January 8, 2016
Page 2 of 3
impractical because the pipe would have to cross the road and therefore block access to
the work area.
Retired Ash Basin — The inflow of stormwater, which normally flows into the riser
structure and out stormwater outfall SW015, will be pumped into cell 3 of the active ash
basin. The pumping will be sustained for an estimated 2-3 weeks. Running a pipe
overland to place adjacent to SW015 is impractical due to the railroad lines that run in
between the riser structure and the outfall.
The contingency plan will be implemented in accordance with the conditions provided by
NCDEQ. Our understanding of the conditions is as follows:
Condition 1: During the pumping, the facility shall conduct weekly monitoring for the
following parameters: total arsenic, total selenium, total mercury (method 1631 E)_ total
chromium, total lead, total cadmium, total copper, total zinc, and total dissolved solids
(TDS).
Duke's Response: We understand that the weekly monitoring applies only when
pumping wastewater from the active ash basin to the stormwater drainage channel of
the retired ash basin. The weekly monitoring is in addition to that already required by
NC0004979. Wastewater samples will be collected at a safe location, and the results will
be reported according to the terms of NC0004979. Stormwater that is pumped from the
retired ash basin to cell 3 of the active ash basin does not require monitoring since
NC0004979 allows stormwater runoff as an input to the active ash basin.
Condition 2: All other terms and conditions of the existing permit shall be met.
Duke's Response: We understand that any other terms and conditions of either permit
apply during this work effort. During measurable rainfall events. outfall SW015 may not
discharge because of pumping or construction activities. If necessary, this activity will be
recorded on a stormwater discharge monitoring report
Condition 3: The water quality standards in the receiving stream shall not be
contravened.
Duke's Response: Both permits are designed to not allow contravention of water quality
standards if permit conditions are met. The volume of discharges made during
implementation of the contingency plan will not exceed the volume anticipated by the
permits. Duke does not foresee this contingency plan for potential temporary re route of
water to pose any threat of contravention of applicable water quality standards.
Comment 4: The facility shall continuously monitor TSS concentration and the
dewatering pump shall be shutoff automatically when the limits are exceeded. The
pumping is allowed to continue if interruption might result in a dam failure or damage.
Duke's Response: TSS will be monitored at regular intervals and pumping ceased if an
identified set point is exceeded.

Allen Steam Station NPDES Permits NC0004979 and NCS000546
January 8, 2016
Page 3 of 3
Should you have any questions regarding this letter or require additional information, please
contact Ross Hartfield at 980-373-6583 or at [e-mail].
Sincerely,
6P
Harry K. Sideris
Senior Vice President,
Environmental, Health and Safety
NCDEQ cc: Sergei Chernikov, Mike Randall, Zahid Khan, Corey Basinger
Duke cc: Ross Hartfield, Jeremy Pruett, Richard Baker, Jim Wells, Randy Gantt, Thomas
Doering, Scott Harris