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Mountain Coal Company <br />West Elk Mine <br />Exhibit 51 <br />Lower Refuse Pile <br />TABLE 11. Sedimentation Basin Sediment and Water Yields; 10-Year, 24-Hour Storm <br /> Phase I Phase 11 Phaze III Phase IV <br />Total aces drsturbed (including waste and subsoil 121 13.9 16.6 23.6 ' <br />and topsoil stockpiles) <br />Total aces to be vegetated and reclaimed during 2.4 5.9 8.3 .13.6 ~ <br />the life of the refuse pile <br />Total aces unreclaimed during life of pile 9.7 8.0 8.3 0 <br />Estimated life of pile (years) 1.8 1.1 1.7 5.0 <br />Sediment Yield (ft') from vegetated slopes during 71.0 109.0 233.0 3455.0 <br />life of pile (C=.01) <br />Sediment Yield (ftr) from unreclaimed slopes dur- 28,809 14,520 73,281 N.A. <br />ing life of pile (C=1) <br />Total sediment yield (ft') 28,880 14,629 23514 3455 <br />Final elevation of sediment assuming no cleanout 6108.2 6106.3 6107.5 6104.5 <br />during life of pile (feet) <br />Total storm yield (ft3); 10-year, 24-hour storm event 12,737 14,632 18,267 50,094' <br />Elevation of pool assuming no sediment (feet) 6106.1 6106.3 6106.9 6101 -: <br />Maximum allowed elevation of sediment or water 6107.3 6107.1 6106,6 6103.3: <br />for storage o[ 10.year, 24-hour storm event <br />Required cleanout schedule to maintain sediment -semi-: <br />level below the maximum sediment of water eleva- annually annually annually annually <br />tion <br />Sediment yield (ftr) for cleanout period 16,005 13,299 13,832 ' 6969.6 <br />Sediment elevation at end of cleanout period 6106.5 6106.1 6106.2 `61028 <br />Total yield (fP) for cleanout period sediment yield 28,742 27,931 32,099 :57063 <br />and 10.year, 24-hour storm <br />Elevation of pool assuming total sediment yield for 6108.1 6108.0 6108.6 :6107.65 , <br />cleanout period and 10-year, 24-hour storm <br />Total elevation difference (feet below spillway) 0.9 1.0 0.4 ~i35 ~ <br />between spillway (elevation 6109) and pool for 10. <br />year, 24-hour storm with cleanout period sediment <br />yield <br />27 <br />