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COLOWYO COAL COMPANY <br />OOSA -STOKER SIDING <br />SEDIMENTATION POND SUMMARY <br /> <br /> <br /> ORIGINAL 1996 1998 2002 DIFFERENCE <br /> CONFIGURATION STUDY STUDY DIFFERENCE STUDY 1998702002 <br />ATERSHED AREA (acres): <br />Disturbed 5.9 7.0 1,1 0.0 <br />Postmining Topsoiled and Seeded 0.0 0.0 0.0 14.5 14.5 <br />Postmining Undisturbetl 6.0 6.0 0,0 0.0 -6.0 <br />1-2 Year Recamaton 0.0 0.0 0.0 0.0 0.0 <br />3+Year Reclamation 0.0 0.0 0.0 0.0 0.0 <br />Total Area 11.9 13.0 1,1 14.5 1.5 <br />POND PARAMETERS: <br />Bottom Elevation 6321.8 6321.8 6321.8 0.0 6321.8 0.0 <br />Principal Spillway Invert Elevation 6329.6 6329.6 6329.6 0,0 6329.6 0.0 <br />Emergenq Spilhvay Invert Elevation 6332.0 6332.0 6332.0 0.0 6332.0 0,0 <br />Top of Embankment 6621.2 6334.0 6334.0 0.0 6334.0 0,0 <br />Storage Volume Below Emergency Spillway (acft) 3.14 3.14 3.24 0.10 3.2 0.0 <br />Storage Volume Below Principal Spillway (ao-ft) 1.78 1.78 1.87 0.09 1.9 0,0 <br />Principal Spillway Parameters: <br />Type Drop Inlet Drop Inlet Perf. Riser Perf. Riser <br />Riser Diameter (in) 12.0 12,0 12.0 0.0 12.0 0.0 <br />Riser Height {ft) 5.7 5.7 5.7 0.0 5.7 0.0 <br />Banel Diameter (in) 12.0 12,0 12.0 0.0 12.0 0.0 <br />Elevation of Pertoration(s) (ft) N/A N/A 6325.0 6325.0 <br />Size of Perforation(s) (in) N/A N/A 4.0 4.0 <br />Number of Perforations N/A N/A 1 1.0 <br />Emergency Spillway Parameters: <br />type 7rapezoida( Trapezoidal Trapezoidal Trapezoidal <br />Diameter (in) NIA N/A N/A N/A <br />Bottom Witlth (ft) 5.0 5.0 5.0 0.0 5.0 0.0 <br />Length (R) 23.0 23.0 40.0 17.0 40.0 0.0 <br />Side Slopes'z'H:iV (ft) 2.0 2.0 2.0 0.0 2.0 0.0 <br />HYDROLOGICRiYDRAULIC PARAMETERS: <br />Base Flow Rates (cfs) 3.0 0.0 -3.0 0.00 0.0 <br />70-Year, 24-HOUr Storm Event: <br />Precipitation (in) 1.8 1.8 0.0 1.8 0.0 <br />RunoR Volume (ao-R) 0.5 0.6 0.1 0.9 0.3 <br />Principal Spillway Peak Discharge (cts) 4.2 0.5 -3.7 0.6 0.1 <br />Emergency Spillway Peak Discharge (cFs) 0.0 0.0 0.0 0.0 0.0 <br />Peak Surface Water Stage Elevation (R) 6330.9 6326.4 -4.5 6326.9 0.5 <br />25-Near, 24-Hour Storm Event: <br />Precipitation (in) 2.3 2.3 0.0 2.3 0.0 <br />Runoff Volume (ac-R) 0.8 0.8 0.1 1.3 0.5 <br />Prinupal Spilhvay Peak Discharge (cts) 4,5 0.6 -3.9 0.7 0.1 <br />Emergency Spillway Peak Discharge (cfs) 0.0 0.0 0.0 0.0 0.0 <br />Peak Surface Water Stage Elevation (ft) 6331.0 6327.0 4.0 6327.9 0.9 <br />Pond Freeboard (R) 3,0 7.0 4.0 6.1 -0.9 <br />SEDIMENT LOADING PARAMETERS: <br />Storm Predicted Peak Settlable Concentration (ml/l) 0.00 0.00 0.0 0.00 0.0 <br />Predicted Annual Sediment Loading (ac-ft) 0.02 0.02 0.00 0.01 0.0 <br />Available Sediment Storage Volume (aoR) 0.21 0.21 0.00 0.20 0.0 <br />Maximum Sediment Storage Elevation (ft) 6323.9 6323.9 6323.9 0.0 6323.9 0.0 <br />Predicted Number of Slorage Years 108 10.5 0.0 28.4 77.9 <br />• <br />