2008-12-04_PERMIT FILE - C1994082 ‎(6)‎

• Permit No: C1994082
• IBM Index Class Name: Permit File
• Doc Date: 12/4/2008
• Doc Name: Part I Postmine Storage Capacity Addendum ‎(TR37)‎ Pond 011
• Section_Exhibit Name: Tab 13 Attachment 13-4A.1
• Media Type: D
• Archive: No

United States - Volume II - Colorado (Miller, et al., 1973). A standard SCS
Type II storm was utilized for each analysis.
• 10-year, 24-hour event: 1.7 inches
• 25-year, 24-hour event: 2.1 inches
• 100-year, 24-hour event: 2.5 inches
Sedimentology. To determine the sediment loading to the pond, the average
annual "R" method was used. The amount of sediment storage is determined for
a defined length of time and is based on the design storm R, design storm
sediment load, average annual R, and the number cf storage years (Y). R is
the rainfall erosivity factor. The equation for required sediment storage
is.
Required Storage = (Annual R)(# years)(Storm Sediment Load)
Storm R
The TR-37 SEDCAD4 demonstration used an annual R value of 10 versus the 1997
design which used an R value of 30. This updated R value was obtained from
Figure 8A.1, Isolines of R factor for Western U. S., which was taken from
Design Hydrology and Sedimentology for Sma11 Catchments (Haan, et. al.,
1993).
Y
)
P. sensitivity analysis was conducted varying the number of storage years (
to maximize sediment storage capacity and maintain compliance with the
applicable rules and regulations. The number of storage years (Y) was
increased in the Sedimentology sub-routine until the effluent settleable
solids concentration in Pond 011 discharge exceeded the water quality
criterion (0.5 milliliters per liter [ml/1]), or the model indicated there
was less than two (2) foot of storage room in the pond (the elevation
difference between calculated top of sediment storage and principal spillway
invert elevation), as recommended by Warner et al (1998). The SEDCAD4 model
results present the maximum sediment storage while retaining capacity to
store the design storm runoff and maintain compliance with applicable rules
and regulations.
Reclaimed Condition Storage Capacity. Results of the TR-37 SEDCAD4
demonstration show the storm runoff volume for the entire watershed from the
10-year, 24-hour event to be 0.70 acre-feet (ac-ft). The following
summarizes Pond 011 storage capacity for the TR-37 10-year, 24-hour event
SEDCAD4 demonstration.
Principal spillway invert elevation (ft msl) = 7,004.4 ft
Total pond storage capacity (at principal spillway elev.) = 3.2 ac-ft
Storm predicted effluent peak settleable concentration = 0.0 ml/1
Predicted annual sediment loading = <0.01 ac-ft
TR-37 13-4A.1-3 Revised 02/08