NC0004774_Application_20191217

DUKE
�. ENERGY
August 15, 2019
North Carolina Division of Water Resources
NPDES Complex Permit Branch
Attn: Julie Grzyb
1617 Mail Service Center
Raleigh, NC 27699-1617
Subject: Duke Energy Carolinas, LLC
Buck Combined Cycle
Permit Modification Request
NC0004774
Rowan County
Dear Ms. Grzyb.
Duke Energy
Buck Combined Cycle
1385 Dukeville Road
Salisbury, NC 28146
Duke Energy respectfully requests a permit modification to the Buck Combined Cycle
Wastewater permit NC0004774, Part I., Section A.(3.) Outfall 001 A - CTCC Operations,
specifically, the temperature parameter referencing Footnote 3. A check in the amount of
$1,080 is included for the fee associated with this request.
Footnote 3 and the associated temperature parameter are remnants from the coal-fired steam
station, now demolished. We request that the terms found in footnote 3 for outfall(s) 001A and
006 be removed from the permit as they are not applicable to the operation of the combined
cycle unit.
Basis of request
Footnote 3 originates from an EPA nomograph from 1976 as the basis for the restrictions to
protect aquatic life from cold shock due to the thermal load from the retired Buck Fossil Steam
Station. This was first approved by North Carolina DENR in 1993. Additional delta T thermal
limits, as noted in Footnote 3, are based on the EPA nomograph (USEPA 1976) and intended to
protect warm water fish from cold shock in the event of a winter season plant shut -down event.
Historically, fossil steam stations could operate units separately, thus varying discharge flow
and heat load to the receiving stream. If all units functioned either on one control unit or as
autonomous units, this configuration could have impacts on the receiving stream if all units were
shutdown at once versus scaled over time. Basically, if all steam units were online, withdrawing
water, heating it, and then discharging the heated effluent, losing all units at once would cause a
shock to the receiving stream and the aquatic life surrounding the discharge point. The thermal
rise calculation paired with the control unit designation seeks to regulate the potential thermal
shock of losing one or multiple operating units.
Combined cycle plants discharge significantly less heated effluent, i.e. approximately 0.6 MGD
compared to 170+ MGD, than the demolished steam station, and have cooling towers that help
regulate the effluent discharge temperature.

Buck Combined Cycle
NC0004774
Page 2
Additionally, the permit Fact Sheet makes note of the insignificance of this parameter with
respect to the CTCC versus the demolished steam station: (excerpt from p.22 of NPDES Fact
Sheet)
Temperature. This condition includes the same 35°C effluent limit and temperature rise limits as before and,
in paragraphs below the limits table, other provisions of the thermal variance.
With retirement of the BSS coal-fired units, heated discharges are less than I% of past flows and thermal
loads. It is not clear that a variance or mixing zone is needed any longer. Duke Energy has requested
continuation of its 316(a) temperature variance for this permit cycle so that it can evaluate the need. A
special condition in Section C of the permit provides that, if Duke Energy plans to request continuation of the
variance in the next cycle, it must perform a thermal mixing study to justify the variance and determine the
extent of the thermal mixing zone.
A thermal mixing study is scheduled for 2019. Due to higher than average flows in the Yadkin
River, the study is delayed until flows resemble 7Q10 conditions.
If you have any questions, please contact Elizabeth Glenn at [phone].
1 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, trite, accurate, and complete. 1 am aware that there are significant penalties
for submitting false information, including the possibility of fines and imprisonment for knowing violations.
Yours truly,
Kristopher C. Eisenrieth,
General Manager II
Buck Combined Cycle
NC DEQ Raleigh — 7018 0680 00018853 7495 / 9590 9402 3915 8060 3625 28
NC DEQ Mooresville — 7018 0680 00018853 7488 / 9590 9402 3857 80601485 01
Cc: Roberto Scheller NCDEQ DWR - 610 E. Center Ave. Suite 301 Mooresville, NC 28115

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