NC0003468_Annual Report_20181220

�•� DUKE Dan River Combined Cycle
ENERGY. Duke Energy Carolinas
900 South Edgewood Road
Eden, NC 27288
December 20,2018
Mr. Sergei Chernikov,PhD RECEfVED/DENR/DWR
State of North Carolina DEC 3 2018
Department of Environmental Quality
Division of Water Resources Resources
Complex NPDES Permitting Unit WaterPermirtRg oSunces
ction
1617 Mail Service Center
Raleigh,NC 27699-1617
Subject: Duke Energy Carolinas,LLC
Dan River Combined Cycle Station—NPDES Permit#NC0003468
Ash Basin Working Capacity—Annual Report
Dear Mr. Sergei:
As required by Special Condition A(13)in the Dan River Combined Cycle NPDES permit,attached is the Annual
Report—Ash Basin Working Capacity,which summarizes the actual free water volume of the Ash Ponds and the
physical measurements of the dimensions of the free water volume for your review and file.
Should you have any questions regarding this submittal or require additional information,please contact Joyce
Dishmon at 336-623-0238 or email [e-mail].
I 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 true, accurate, and complete. I am aware that there are significant penalties
for submitting false information, including the possibility of fines and imprisonment for knowing violations
Sincerely,
•
Michael Lanning
GM II—Regulated Stations
Dan River Combined Cycle
Attachment
Cc: Sherri Knight—WSRO,450 West Hanes Mill Road,Suite 300,Winston-Salem,NC 27105
Joyce Dishmon/Filenet,Sr Env Specialist
Dana Newcomb,Lead EHS Field Support

wood.
Memo
To: Joyce Dishmon, Henry Taylor
From: Cedric Ruhl, PE; Shuang Gao, EIT
Date: December 19, 2018
Ref: Dan River Primary and Secondary Ash Basins
Re: Free Water Storage Volume
Duke Energy Carolinas, LLC (Duke) has requested that Wood provide an estimate of the Dan
River Primary and Secondary Ash Basin working capacity to assist with the National Pollutant
Discharge Elimination System (NPDES) permit renewal process.
Estimate Required Free Water Volume
The NPDES permit requires that the Primary and Secondary Ash Basins each have a free water
volume (FWV) capacity to store stormwater runoff and 24 hours of plant discharge water. For
the purposes of this memo the stormwater runoff volume was assumed to consist of runoff from
the 10-year, 24-hour design storm assuming 100 percent of rainfall is converted to runoff(i.e. a
curve number of 100). The Dan River Station no longer sluices material to the Primary or
Secondary Ash Basins; therefore, the plant discharge water volume is 0.
The drainage area to the Primary Ash Basin is the footprint of the Primary Ash Basin itself. The
drainage area to the Secondary Ash Basin is the footprint of the Secondary Ash Basin and a
small portion of overland flow between railroad tracks and the northwestern edge of the ash
basin. The Drainage Area of Primary and Secondary Ash Basin is shown in Figure 1.
The required free water volume was calculated as shown in the following table:
Table 1-Required Free Water Volume
Stormwater Runoff Volume
24-Hour Plant Total Required
Total
Tributary 10-Year,24-Hour Discharge Water Free Water
Basin Stormwater
Drainage Area Rainfall Depth Volume Volume
Runoff Volume
(acres) (in) (acre-feet) (acre-feet) (acre-feet)
Primary Ash Basin 27.42 5.10 11.65 0 11.65
Secondary Ash Basin 19.67 5.10 8.36 0 8.36
Wood Environment&Infrastructure Inc.
4795 Meadow Wood Lane,Ste. Registered in North Carolina
310E Engineering License No.F-1253
Chantilly,Virginia 20151 Geology License No.C-247
703-488-3700
woodplc.com

Dan River Primary and Secondary Ash Basins Free Water Storage Volume
Wood Project No. 7810170870 12/19/2018
Estimate Available Water Storage Volume
The Primary and Secondary Ash Basins are in the process of being decommissioned in
accordance with state Dam Safety and Erosion Control permits. Stage-storage relationships for
the Primary and Secondary Ash Basins were developed as part of Dam Safety permitting and
are provided in the following tables:
Table 2A-Stage-Storage Relationship for Primary Ash Basin
Elevation Surface Area Incremental Cumulative Storage
(ft) (acres) Storage Volume Volume
(acre-feet) (acre-feet)
510 26.12 0.00 0.00
512 26.55 52.67 52.67
514 26.98 53.53 106.20
516 27.41 54.39 160.59
518 27.85 55.26 215.85
520 28.29 56.13 271.98
522 28.73 57.01 328.99
524 29.17 57.89 386.89
525 29.39 29.28 416.17
Table 2B-Stage-Storage Relationship for Secondary Ash Basin
Incremental Cumulative Storage
Elevation Surface Area
(ft) (acres) Storage Volume Volume
(acre-feet) (acre-feet)
515 7.07 0.00 0.00
516 7.47 7.27 7.27
517 7.87 7.67 14.94
518 8.14 8.01 22.95
519 8.34 8.24 31.19
520 8.52 8.43 39.62
521 8.68 8.60 48.22
522 8.85 8.77 56.98
523 9.15 9.00 65.98
524 9.81 9.48 75.46
525 11.60 10.71 86.17
526 12.24 11.92 98.09
527 12.50 12.37 110.46
528 13.04 12.77 123.23
528.52 13.38 6.87 130.09
529 13.69 6.50 136.59
The Primary and Secondary Ash Basins are hydraulically connected via a weir internal to the
ash basins; therefore, the maximum storage elevation in the Primary Ash Basin (525 feet)
controls storage for the Secondary Ash Basin as well.
2

I �I
Dan River Primary and Secondary Ash Basins Free Water Storage Volume
Wood Project No. 7810170870 12/19/2018
Compare Required Free Water Volume to Available Water Storage Volume
The required free water volume was compared to the available water storage volume as shown
in the following table:
Table 3-Summary of Required vs.Available Storage Volume
Total Required
Available Storage Available Storage
Free Water
Basin Volume Volume>Total
Volume
(acre-feet) Required FWV?
(acre-feet)
Primary Ash Basin _ 11.65 416.17 yes
Secondary Ash Basin 8.36 86.17 yes
Conclusion
The Primary and Secondary Ash Basins meet or exceed the required free water volume
requirements. CCR material will be excavated from the Primary and Secondary Ash Basins
during closure of these units which will result in an increase in available storage volume.
Attachments
Figure 1 — Drainage Area and Flow Path (Primary and Secondary Ash Basin)

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•.ry••0•t. M1 14 wood DRAINAGE AREA AND FLOW PATH _
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(PRIMARY AND SECONDARY ASH BASIN)
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