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SEDIMENT POND SIZING CALCULATIONS <br />Phase One Refuse Disposal For The Northern No. 1 (FF Seam) Coal Mine <br />Rainfall Information <br />Storm Precipitation Runoff* <br />(inches) (inches) <br />10 yr 24 hr 1.90 1.0 <br />25 pr 24 hr 2.26 1.3 <br />100 yr 24 hr 2.77 1.8 <br />* From Figure 10.1 (1 of 2) page 10.21 of Hydrolo~v Section 4 of SCS National <br />Engineering Handbook. Assumes CN = 90. This is very conservative and should <br />substantially overestimate the runoff volume. <br />Runoff Volume From 10 yr 24 hr Storm Event <br />VRO = 11.0 inches) 1 ft (18 acres) <br />12 in <br />= 1.5 acre ft <br />Sediment Storage Volume <br />It is assumed that the entire azea is disturbed and 0.1 acre-ft per acre <br />has been allowed. This is a very conservative assumption and should yield well in <br />excess of the required three yeazs of sediment storage. <br />vSS = (0.1) (18) <br />= 1.8 <br />