NC0004961_Permit Modification_20080317

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140 :
NCDENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Michael F. Easley, Governor
March 17, 2008
Mr. Ron Lewis
Duke Energy Corporation
EC13K/P.O. Box 1006
Charlotte, NC 28201-1006
William G. Ross, Jr., Secretary
Coleen H. Sullins, Director
Subject: Modification of NPDES Permit NC0004961
Riverbend Steam Plant
Gaston County
Dear Mr. Lewis:
The Division has reviewed and approved your minor modification request regarding the sampling
location for downstream temperature data. This permit modification changes the wording regarding the
downstream sampling location A. 1. of the permit. No other changes to the permit have been made.
Please find enclosed the revised effluent page, which should be inserted into your permit. The old page
may then be discarded. All other terms and conditions contained in the original permit remain unchanged
and in full effect. This permit modification is issued under the requirements of North Carolina General
Statutes 143-215.1 and the Memorandum of Agreement between North Carolina and the U.S.
Environmental Protection Agency.
If any parts, measurement frequencies or sampling requirements contained in this permit modification
are unacceptable to you, you have the right to an adjudicatory hearing upon written request within thirty
(30) days following receipt of this letter. This request must be a written petition conforming to Chapter 150B
of the North Carolina General Statutes, filed with the Office of Administrative Hearings (6714 Mail Service
Center, Raleigh, North Carolina 27699-6714). Unless such demand is made, this decision shall be final and
binding.
If you have any questions concerning this permit modification, please contact Charles Weaver of the
NPDES Unit at [phone], extension 511.
Sincerely,
oleen H. Sullins
cc: Central Files
Mooresville Regional Office / Corey Basinger
NPDES-Unit
1617 Mad Service Center, Raleigh, North Carolina 27699-1617
512 N. Salisbury St., Raleigh, North Carolina 27604
Phone [phone]/ FAX [phone]/www ncwaterquality org
An Equal Opportunity/Affirmative Action Employer - 50% Recycled/10% Post Consumer Paper
NorthCarolina
,Naturally

Permit NC0004961 �*
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A. (1.) EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS [001]
During the period beginning on the effective date of this permit and lasting until expiration, the Permittee is
authorized to discharge once -through cooling water and intake screen backwash from outfall 001 Such
discharges shall be limited and monitored by the Permittee as specified below:
PARAMETER
LIMITS
MONITORING REQUIREMENTS
Monthly Daily
Average Maximum
Measurement Sample Type Sample Location'
Frequency
Flow
Daily
Pump Logs
Influent or Effluent
em erature of
95 0 350C
Dad
Grab
Effluent
em erature �F z
r
89 6 32-C
Dad
Grab
Downstream
em erature °F 3
Dail
Grab
Effluent
Notes•
1. Downstream sampling point downstream at Mountain Island Lake If samples are collected below the water
surface, the Permittee will record the sample depth on the DMR form
2. The ambient temperature shall not exceed 89 60F (32 OOC) and is defined as the daily average downstream
water temperature When the Riverbend Station effluent temperature is recorded below 89.60F (32.00C), as
a daily average, then monitoring and reporting of the downstream water temperature is not required In
cases where the Permittee experiences equipment problems and is unable to obtain daily temperatures from
the existing temperature monitoring system, the temperature monitoring must be reestablished within five
working days.
3 This temperature requirement is in effect when only units with a shared control system are
operating.
1. If the daily average intake temperature is below 36 5OF (2.50C), the daily average effluent temperature
shall not exceed 50 OOF (100C), and
2. If the daily average intake temperature ranges from 36 50F (2.50C) to 55 OOF (12 80C), the daily average
effluent temperature shall not exceed two times the intake temperature (OF) minus 23
The Regional Administrator has determined pursuant to Section 316(a) of the Act that the
thermal component of the discharge assures the protection and propagation of a balanced,
indigenous population of shellfish, fish, and wildlife in and on the receiving body of water.
Chlorination of the once through condenser cooling water, discharged through outfall 001, is
not allowed under this permit. Should Duke Power wish to chlorinate its condenser cooling
water, a permit modification must be requested and received prior to commencing
chlorination.
There shall be no discharge of floating solids or visible foam in other than trace amounts.
3

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Duke CORPORATE EHS SERVICES
its
, �`��Energy® Duke Energy Corporation
526 South Church St
February 25, 2008 Charlotte, NC 28202
Mailing Address
EC13K / PO Box 1006
Charlotte, NC 28201-1006
Mr. Sergei Chernikov
North Carolina Department of Environment
and Natural Resources
Division of Water Quality
NPDES Unit
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
Subject: Duke Energy Carolinas, LLC
Riverbend Steam Station #NC0004961 — Gaston County
Drought Related Mitigation Request
Dear Mr. Chernikov:
As a follow-up to our meeting to discuss potential drought mitigation options on January
29, 2008, three copies of the following minor modification request to relocate the
downstream temperature monitoring location for Riverbend Steam Station (RSS) to a
monitoring site more representative of the water temperature profile of Mt. Island Lake
are enclosed for your review The downstream temperature monitor is presently located
in the tailrace of Mt Island Hydro. Fewer releases of water from Mt. Island Lake and
above normal ambient temperatures due to solar radiation related to drought conditions in
2007 contributed to the daily average water temperature in the tailrace water exceeding
32 degrees C on occasion. Operation of RSS was suspended on these days and a water
temperature comparison study between the forebay and tailrace of Mt. Island Hydro was
initiated in late August 2007 (see Figure 1). Based on results, Duke Energy proposes to
relocate the Riverbend downstream compliance temperature monitoring point at a depth
of 9 in below the water surface by attaching the temperature system monitoring probe to
the anchor line of an existing warning buoy near the forebay of Mt. Island Hydro
Your assistance to expedite review and approval of this drought related concern is greatly
appreciated. Should you have questions regarding this request, please call (704)-607-
8755 or email me [e-mail].
Sincerely,
Ron Lewis
Water Management
Attachment
DENR - WATER OUALITY
POINT SOURCE BRANCH
www duke -energy com

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Figure 1. The water temperature recorded in the forebay and tailrace of Mt. Island Hydro from 27 August to 1 October 2007.