2009-09-21_PERMIT FILE - C1980007 (2)

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Mountain Coal Company, L.L.C. Exhibit 51 West Elk Mine ~ Lower Refuse Pile • •, Table 9 -SedimentControl Ditch Design', 100.YearStorm ' Ditch triangular shaped, 2 feet deep, 3H:1 V slopes = Average riprap size. Thickness of riprap average of one foot. ' Exhibit 66 refers to these ditches as D'_R-I for the north ditch, D2R-IA for the west ditch, D2R-2 for the southwest ditch. D?R-3 for the east ditch and D2R-4 for the south ditch. The south ditch will be constructed when the pile reaches the maximum height along the south edge. ' As calculated by Manning s equation and is represen[ativeof the velocity with such shallow flows K large diameter riprap. Phase Location 100-year,24-hour Peak Velocity Normal RiprapSize= Discharge(cfs) (fps) Depth(ft) (inches) North' 6.9 4.3 0.74 Unlined Easr' 4.6 4.~ 0.68 Unlined South' 2.8 4.7 0.45 Unlined II North 9.0 4.7 0.80 Unlined East 4.6 4.~ O.S8 Unlined South 2.8 4.7 0.45 Unlined I11 North 8.5 4.6 0.78 Unlined East 5.3 ~.8 0.» Unlined Southwest' 3.4 ~.? 0.46 Unlined West 5.3 5.5 0.~7 Unlined lV North 25.53 10.8 1.~9 Shotcrete East 22.18 34.1 1.07 Shotcrete Wes[ 2.13 5.7 0.93 Unlined Southwest 2.22 253.6' 0.57 I5.0 South 2.71 3.8 I.10 Unlined Subsoil Pile (Phase [ -III) West 0.59 1.5 '036 Unlined North 0.59 5.2 0.19 Unlined East 1.18 4.3 0.27 Unlined Topsoil Pile (Phase I -III) Upper West 2.65 4.9 0.42 Unlined Lower West 2.65 5.1 0.41 Unlined East 2.65 5.0 0.42 Unlined South 2.65 2.3 0.62 Unlined The sedimentation basin storage vs. volume curve for MB-6 is shown in Figure LWP-014 in Appendix L. The current sedimentation basin (MB-2R) embankment has a top elevation of approximately6l'_0 feet with a pond bottom elevation of approximately 6100 feet. A 48-inch CMP drop spillwa}• pipe structure is located a[ elevation 61 17.7 feet with a 8-inch drain valve located approximatelyat elevation 6103 feet. ?']