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1 ' <br />I <br />COLOWYO COAL COMPANY <br />002A -WORK AREA <br />SEDIMENTATION POND SUMMARY <br /> ORIGINAL 1996 1998 2002 DIFFERENCE <br /> CONFIGURATION STUDY STUDY DIFFERENCE STUDY 1998 T02002 <br />WATERSHED AREA (acres): <br />Disturbed 59.2 59.2 0.0 0.0 <br />Postmining Topsoiled and Seeded 0.0 0.0 0.0 108.3 108.3 <br />Postmining Undisturbed 16.4 16.4 0.0 13.2 -3.2 <br />1-2 Year Reclamation 11.6 11.6 0.0 0.0 -11.6 <br />3+ Vear Reclamation 48.7 48.7 0.0 0.0 X8.7 <br />Total Area 135.9 135.9 0.0 121.4 -14.5 <br />POND PARAMETERS: <br />Bottom Elevation 7148.5 7148.5 7149.0 0.5 7146.0 -3.0 <br />Principal Spilhvay Invert Elevation 7155.8 7155.8 7155.8 0.0 7155.8 0.0 <br />Emergenry SDillway Invert Elevation 7158.0 7158.0 7158.0 0.0 7158.0 0.0 <br />Top of Embankment 7160.0 7160.0 7160.0 0.0 7160.0 0.0 <br />Stomge Volume Below Emergency Spillway (ao-ft) 19.57 19.57 19.27 -0.30 23.2 4.0 <br />Stomge Volume Below Principal Spillway (ao-ft) 13.09 13.09 13.00 -0.09 17.0 4.0 <br />Principal Spillway Pammeters: <br />Type Drop Inlet Drop Inlet Pert. Riser Pert. Riser <br />Riser Diameter (in) 12.0 12.0 12.0 0.0 12.0 0.0 <br />Riser Height (ft) 5.1 5.1 5.1 0.0 5.1 0.0 <br />Barrel Diameter (in) 12.0 12.0 12.0 0.0 12.0 0.0 <br />Elevation of Pertoration(s) (ft) N/A N/A 7154.0 7154.0 <br />Size of Pertoretion(s) (in) WA N/A 4.0 4.0 <br />Numberof Pertoroticns WA N/A 3 3.0 <br />Emergency Spillway Parameters: <br />Type Trapezoidal Trapezoidal Trapezoidal Trapezoidal <br />Diameter (in) N/A WA WA WA <br />Bottom Width (ft) 15.0 15.0 15.0 0.0 15.0 0.0 <br />Length (fl) 140.0 40.0 140.0 100.0 140.0 0.0 <br />Side Slopes'z'H:1V (ft) 2.0 3.0 1.5 -1.5 1.5 0.0 <br />HYDROLOGIC/HYDRAULIC PARAMETERS: <br />Base Flow Rates (cfs) 3.00 0.03 -2.97 0.00 0.0 <br />10-Year, 24-HOUr Storm Eveni: <br />Precipitation (in) ~ 1.8 1.8 0.0 1.8 0.0 <br />Runoff Volume (ao-ft) 4.7 5.2 0.5 5.2 0.0 <br />Principal Spillway Peak Discharge (cfs) 4.7 2.1 -2.6 1.4 -0.8 <br />Emergenq SDillway Peak Discharge (cfs) 0.0 0.0 0.0 0.0 0.0 <br />Peak Sudace Water Stage Elevation (ft) 7157.4 7155.4 -2.0 7155.2 -0.2 <br />25-Vear, 24-Hour Storm Event <br />Precipitation (in) 2.3 2.3 0.0 2.3 0.0 <br />Runoff Volume (ao-ft) 7.0 7.6 0.6 8.5 0.9 <br />Principal Spillway Peak Discharge (cfs) 5.6 3.2 -2.5 1.9 -1.3 <br />Emergenry Spillway Peak Discharge (cfs) 0.0 0.0 0.0 0.0 0.0 <br />Peak Surface Water Stage Elevation (ft) 7158.0 7156.0 -2.0 7156.0 0.0 <br />Pond Freebeartl (ft) 2.0 4.0 2.0 4.0 0.0 <br />SEDIMENT LOADING PARAMETERS: <br />Storm Predicted Peak Sealable Concentration (ml/0 0.00 0.00 0.0 0.00 0.0 <br />Predicted Annual Sediment Loading (ao-ft) 0.50 0.48 -0.02 0.12 -0.4 <br />Available Sediment Storage Volume (ao-ft) 1.63 1.54 -0.09 4.86 3.3 <br />Maximum Sediment Stomge Elevaton (ft) 7150.7 7150.7 7150.7 0.0 7150.7 0.0 <br />Predicted Number of Story a Years 3.3 3.2 -0.1 40.2 37.0 <br /> <br /> <br />