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• Coal Refuse Pile Surface Area {from General Facilities Map (Map 2.05-M1 (5 of 5)) <br />Flat Areas (top bench and catch benches) - 87,100 ft2 <br />Slope Areas (bench outslopes at 2H:1V) - 155,700 ftz <br />Slope Correction (based on ZH:1 V slope, 0 = 26.56°, correction factor is 1/cos 0) <br />- 1.12 <br />Corrected Slope Area -155,700 x 1.12 = 174,400 ft2 <br />Total Refuse Pile Surface Area - 87,100 + 174,400 = 261,500 ftZ <br />Maximum Infiltration (Using Darcys Equation) <br />Q = Aki <br />where Q is design flow (cfs) <br />A is surface area of refuse pile (ftZ) <br />k is permeability of the refuse (Typical k values for coal refuse <br />range from 10"3 to 10.6 cm/sec. In order to reflect maximum <br />infiltration rates and underdrain flows, a conservative value of <br />• 10.3 cmisec or 3.3 x 10"S fUsec was used) <br />i is flow gradient in fUft (for vertical infiltration i = 1) <br />Q = 261,500 ft 2 x 3.3 x 10_S fUsec x 1 fUft = 8.6 cfs <br />Underdrain Sizing (Using Wilkens and Leps Equation from "Engineering and Design <br />Manual for Disposal of Excess Spoil", TM-2/83 (OSM, 1983)) <br />V - Wmo.s i o.sa <br />v- <br />Where Vv is average water velocity through rockfil] voids (fUsec) <br />W is an empirical constant for rockfill material (1/sec} <br />m is hydraulic mean radius of rock voids (inches) <br />i is hydraulic gradient (from Map 2.05-MI (5 of 5) - (6,250'- <br />6,040'/800' = 0.26 fUft) <br />Values for Wm°.S for various DSO rock sizes aze provided in Table 4.3 and shown <br />on the figure, Wm°'S vs Rock Size, in the "Engineering and Design Manual for <br />Disposal of Excess Spoil", TM-2183 (OSM, 1983) <br />Assuming a DSO of 18 inches, Wm 'S = 50 in/sec or 4.2 ft/sec <br />• V„ = 4.2 ft/sec x (0.26 ft/ft )° Sa = 2.03 fUsec <br />