PERMFILE47451

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 51 Lower Refuse Pile
• Media Type: D
• Archive: Yes

Mountain Coal Company, L.L.C. Exhibit 51
West Elk Mine Lower Refuse Pile
The 10-year, 24-hour storm peak discharge for each phase and the calculated maximum runoff is shown in
• Table 10. Also shown on this table is the amount of water diverted into the sedimentation basin from
underdrainsand seeps.
Table 10 - 10-Year, 24-Hour Peak Discharge and Maximum Ruuoff
Phase Peak
Discharge
(cfs) Total Storm
RunoR(ft') Total RunoRfrom
Uoderdrains(ft') Total Design
Runotf(ftr)
I 3.7 9,369 NA 9.369
11 4.4 11 ~64 NA 11,264
111 SS 14,106 770' 14,876
fV 10.96 40,946.3 4?60= 43,206'
V' 4;260'
' Assumes 4 gpm flow for?4 hours from rock drains.
= Assumes 4 gpm flow from rock drains and'_0 gpm flow from seep collector drains fora 24 hour period.
Refer to Exhibit 66
' From LRP only
•~ The sedimentation basin is required to handle the precipitation and sediment from a 10-year, 24-hour storm
without discharge, but has been constructed to accommodate a 100-year, 24-hour storm event. The
sediment yield was determined using the Universal Soil Loss Equation. The sediment soil loss equation is
as follows:
A=RxKxLSxCP,where
• A -sediment loss in tons per acre
• R -rainfall factor
• K - soil erodibility
• LS - lengh slope factor
• CP -control practice factor
The factors for the equation were obtained from Soil Erosion by Kirkby & Morgan, 1980, the original lower
refuse permit, and the projected slopes as shown on the various phase diagrams. The sediment yield for
Phases I-1 V, the sediment yield for vegetated areas, the sediment yield for unvegeta[ed slopes. the expected
maximum sediment level for each phase. the 3-year sediment level for each phase, the maximum sediment
level allowed for adequate storage for the 10-year, 24-hour storm without discharge, and the maximum
water elevation obtained for each phase is shown on Table I I . For all phases, sediment will not be allowed
to be ereater than the maximum allowable sediment level. The water or sediment level will not remain
above the maximum sediment elevation shown on Table 1 I for an extended period of time because a
discharge from a 10-year, 24-hour storm event may occur. (Phase V sediment yield is presented in Section
6.3 '. l )
• Sediment level and water level will be monitored by MCC. The information will be periodically reviewed
-- during the various phases to verify the original design assumptions.
~8