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• SENECA II WEST MINE <br />POND 006 PHASE V SUMMARY <br />Runoff Volume 110-year, 24-hour) <br />Peak Discharge 125-year, 24-hour) <br />Sediment Volume 11 year) <br />Outlet Works <br />Principal Spillway :24" CMP Riser with 24" culvert <br />Top of Riser <br />Base of Riser <br />Emergency Spillway: Trapezoidal Channel <br />Bottom Width <br />Side Slopes <br />Invert <br />Peak Water Elevations <br />10-year, 24-hour <br />25-year, 24-hour <br />Top of Embankment <br />Freeboard <br />Sediment Storage {1.5 below principal spillway invert) <br />Years Storage <br />Peak Settleable Concentration 110-year, 24-hour) <br />18.24 ac-ft <br />183.6 cfs- <br />8.48 ac-ft <br />7073.0 ft <br />7065.2 ft <br />15 ft <br />3H:1 V <br />7075.5 ft <br />7075.49 ft <br />7077.4 ft <br />7080.0 ft <br />2.6 ft <br />11.1 ac-ft <br />1.3 years <br />0.01 ml/I <br />The phase V design shows that the principal spillway needs to be raised 1.5 feet to an elevation of <br />• 7073.0. This design also shows that the pre-settling basin is no longer required, and that the Clean <br />Water Diversion no longer exists. SCC is still evaluating if any more coal removal will take place at the <br />bottom of the "B" pit. Therefore, SCC will leave the pre-settling basin in at this time until we decide <br />that we will either mine this area or reclaim it. The basin is still functioning properly by trapping <br />sediment in it, in addition to pond 006, which is the NPDES discharge point. <br />J <br />Revised 4/00 <br />