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Exhibit 7, Item 20, Table 4 <br />COLOWYO COAL COMPANY <br />SEDIMENTATION POND SUMMARY PROPOSED PLAN - SOUTH TAYLOR MINE PLAN <br />Revision Date: 5/31/10 <br />Exh. 7 -20 -7 Revision No.: TR -81 <br />SECTION 28 <br />SECTION 21 <br />WEST TAYLOR <br />WEST TAYLOR <br />POND <br />POND <br />POND <br />POND <br />Original Design <br />TR -81 <br />WATERSHED AREA (acres): <br />Disturbed <br />27.8 <br />33.4 <br />53.6 <br />0.0 <br />Postmining Topsoiled and Seeded <br />24.1 <br />68.5 <br />78.9 <br />0.0 <br />Undisturbed <br />137.8 <br />178.0 <br />182.0 <br />219.6 <br />1 -2 Year Reclamation <br />182.3 <br />255.4 <br />201.8 <br />514.7 <br />3+ Year Reclamation <br />0.0 <br />0.0 <br />94.9 <br />27.5 <br />Total Area Draining to Pond <br />371.96 <br />535.28 <br />611.2 <br />761.8 <br />Excluded <br />39.7 <br />63.5 <br />132.4 <br />0.0 <br />Total Watershed Area <br />411.70 <br />598.77 <br />743.53 <br />761.80 <br />POND PARAMETERS: <br />3.0 <br />Upstream Toe Elevation Original Ground <br />7058.0 <br />6969.0 <br />7456.0 <br />7456.0 <br />Principal Spillway Invert Elevation <br />7071.0 <br />6982.0 <br />7471.0 <br />7471.0 <br />Emergency Spillway Invert Elevation <br />7077.0 <br />6988.0 <br />7476.0 <br />7476.0 <br />Top of Embankment <br />7082.0 <br />6993.0 <br />7481.0 <br />7481.0 <br />Storage Volume Below Emergency Spillway Invert (ac -ft) <br />8.31 <br />14.05 <br />5.64 <br />5.64 <br />Storage Volume Below Principal Spillway Invert (ac -ft) <br />4.62 <br />8.37 <br />2.90 <br />2.90 <br />Storage Volume Below Lowest Spillway Perforation (ac -ft) <br />2.46 <br />5.44 <br />1.77 <br />1.77 <br />Principal Spillway Parameters: <br />Type <br />Perforated Riser <br />Perforated Riser <br />Perforated Riser <br />Perforated Riser <br />Riser Diameter (in) <br />18.0 <br />18.0 <br />18.0 <br />18.0 <br />Riser Height (ft) <br />16.0 <br />18.0 <br />16.0 <br />16.0 <br />Barrel Diameter (in) <br />18.0 <br />18.0 <br />18.0 <br />18.0 <br />Elevation of Lowest Perforation(s) (ft) <br />7066.0 <br />6978.0 <br />7468.0 <br />7468.0 <br />Size of Perforation(s) (in) <br />3.0 <br />3.0 <br />3.0 <br />3.0 <br />Number of Perforations per Elevation <br />2.0 <br />2.0 <br />2.0 <br />2.0 <br />Emergency Spillway Parameters: <br />Type <br />Trapezoidal <br />Trapezoidal <br />Trapezoidal <br />Trapezoidal <br />Diameter (in) <br />N/A <br />N/A <br />N/A <br />N/A <br />Bottom Width (ft) <br />30.0 <br />30.0 <br />30.0 <br />30.0 <br />Crest Length (ft) <br />30.0 <br />30.0 <br />30.0 <br />30.0 <br />Side Slopes'z'H:1V (ft) <br />2.0 <br />2.0 <br />2.0 <br />2.0 <br />HYDROLOGIC /HYDRAULIC PARAMETERS: <br />Base Flow Rates (cfs) <br />0.00 <br />0.00 <br />0.00 <br />0.00 <br />10 -Year, 24 -Hour Storm Event: <br />Precipitation (in) <br />1.80 <br />1.80 <br />1.80 <br />1.80 <br />Runoff Volume (ac -ft) <br />3.51 <br />4.72 <br />5.19 <br />13.67 <br />Principal Spillway Peak Discharge (cfs) <br />1.79 <br />2.09 <br />10.83 <br />18.17 <br />Emergency Spillway Peak Discharge (cfs) <br />0.00 <br />0.00 <br />0.00 <br />0.00 <br />Peak Surface Water Stage Elevation (ft) <br />7070.68 <br />6982.07 <br />7472.63 <br />7475.57 <br />50% of PMP, 6 -Hour Storm Event: <br />Precipitation (in) <br />4.20 <br />4.20 <br />4.20 <br />4.20 <br />Runoff Volume (ac -ft) <br />25.15 <br />39.22 <br />45.51 <br />91.86 <br />Principal Spillway Peak Discharge (cfs) <br />24.07 <br />25.53 <br />25.53 <br />976.05 <br />Emergency Spillway Peak Discharge (cfs) <br />225.19 <br />461.29 <br />770.39 <br />901.09 <br />Peak Surface Water Stage Elevation (ft) <br />7079.24 <br />6990.73 <br />7479.51 <br />7480.28 <br />Pond Freeboard (ft) <br />2.76 <br />2.27 <br />1.49 <br />0.72 <br />SEDIMENT LOADING PARAMETERS (10 -Year, 24 -Hour Event): <br />Storm Predicted Peak Sediment Concentration (mg /I) <br />276,801 <br />499,358 <br />135,418 <br />8,774 <br />Storm Predicted Sediment Supply (tons) <br />736.8 <br />2381.4 <br />527.9 <br />94.5 <br />Storm Predicted Peak Settlable Concentration (ml /1) <br />57.88 <br />183.24 <br />0.0 <br />0.0 <br />Available Sediment Storage Volume (ac -ft) <br />0.29 <br />0.94 <br />0.21 <br />0.21 <br />Revision Date: 5/31/10 <br />Exh. 7 -20 -7 Revision No.: TR -81 <br />