NC0004961_Ash Basin Capacity Verification_20030102

ie
DDuke
Power,
A Duke Energy Company
December 30, 2002
Mr. David Goodrich
North Carolina Department of Environment
and Natural Resources
Division of Water Quality
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
Subject: Riverbend Steam Station
Gaston County
NPDES Permit # NC0004961
Ash Basin Capacity Verification
Dear Mr. Goodrich:
Duke Power Company
Fossil and Hydro Generation Department
PO Box 1006
Charlotte, NC 28201-1006
0
JAN �' 2 200 I JI
3Ily
With reference to the subject NPDES permit, Special Condition A (8) requires that the ash
basin be evaluated and a report submitted to your office that ensures adequate volume
exists to contain solids, rainfall runoff and the maximum dry weather flow. The attached
calculations indicate that the ash basin is projected to have sufficient available capacity
through the year 2005. Thus, adequate volume exists for the term of the present NPDES
permit (February 28, 2005). The next update will be coordinated with submittal of the
NPDES permit renewal application.
If you have questions or need additional information please contact me at [phone].
Sincerely,
Ronald E. Lewis, Scientist
Environmental, Health and Safety
Fossil -Hydro Carolinas
cc: Rex Gleason, NCDENR - Mooresville Regional Office

Duke Power Company
Riverbend Steam Station — Ash Basin Forecasting
2002 Wet Weather Detention Volume Calculation
Determination of Wet Weather Detention Volume: Wet Weather Detention Volume is
the sum of the runoff accumulated in the ash basin which results from a 10 -yr 24 -hr
storm (assuming 100% runoff) plus the maximum 24 -hr dry weather waste stream which
discharges to the Ash Basin (refer to NPDES Permit NC0004961)
Estimate Runoff to the Ash Basin from a 10 -yr 24 -hr storm:
1. Natural Drainage Area of Ash Basin =
Station Yard Drainage Area Pumped to Ash
Basin =
Total =
2. Precipitation from 10 -yr 24 -hr storm =
3. Total Stormwater Runoff to Ash Basin =
(Assuming 100% runoff)
98.7 Acres
21 8 Acres
120 5 Acres
5.0 Inches
50.21 Acre-feet
Estimated Maximum 24 -hr Dry Weather Waste Stream Discharging to Ash Basin -
1. Maximum recorded Ash Basin Discharge = 10,660,000 Gallons/day
2. Increase maximum daily discharge by 10% for
conservatism and convert units to acre-feet = 1 35.98 Acre-feet
III. Wet Weather Detention Volume:
Sum of Parts I.
and II. =
86.19 Acre-feet

Duke Power Company
Riverbend Steam Station — Ash Basin Forecasting
2002 Wet Weather Detention Volume Calculation
IV. Estimated Quantity of Solids (Ash) to be discharged to Ash Basin through December
31, 2005 Note NPDES Permit expiration date is 2/28/05.
Time Period
Actual or
Estimated Coal
Consumption
1000's tons
% Ash
Estimated
Ash
Production
(1000's
tons)
Estimated
Ash
Production
(Ac -ft
6/1/1995-
12/31/1995
238.4
815%
1991
16.62
1996
7245
917%
6643
55.46
1997
6843
897%
61 38
5124
1998
633.2
9.89%
62.62
5227
1999
6171
9.92%
6122
5111
2000
9886
984%
9725
81 18
2001
9057
1179%
10678
8914
1/1/2002-
/1/2002-
10/31/2002
10/31/2002
649 9
1187%
77.14
6439
1/1/2002-
11/1/2002-
12/31/2002
12/31/2002
130
1180%
15.34
12.81
2003
1386
11.80%
163.58
13655
2004
1451
1230%
178.50
149.01
2005
1344
1230% 1
16528
13798
Total
8409 12
1
910.15
75979
* Calculation assumes an in-place ash density of 55 lbs per cubic foot.

Duke Power Company
Riverbend Steam Station — Ash Basin Forecasting
2002 Wet Weather Detention Volume Calculation
V. Estimated Total Storage Volume Required through 2002•
Wet Weather Detention Volume = 86.2 Acre-feet
Estimated Solids to Ash Basin = 759.8 Acre-feet
2000 Ash Removal Project (354,450 tons) _ -295.9 Acre-feet
Total = 550.1 Acre-feet
VI Results.
Available Storage based on basin survey dated 6/1/1995:
Primary Cell 303.7 Acre-feet
Secondary
Cell 378.3 Acre-feet
Total= 682.0 Acre -
Required Storage Volume:
Through 12/31/2005 =
550.1 Acre-feet
Based on these calculations, there is sufficient capacity in the ash basin to provide
the retention volume specified in the permit through the year 2005.