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Section 780.21(c) Continued. <br />Revised 11/20/80 <br />The foregoing equation is a line-sink formula for a channel drain, <br />which approximates inflow to the pit beepage from the mine floor. <br />The additional water which will drain into the ends of the active <br />pit have been estimated by adapting the point-sink, constant draw- <br />down equation of Jacob and Lohman in Lohman (1972), p. 23. <br />Q = 4 ~ sT 02.30 log 2.25 Ttl -1 <br />r2S J <br />Where: Q = discharge at time = t, in gallons per day. <br />s = drawdown of piezometric head at time zero, <br />constant in feet. <br />t = time since discharge began, in days. <br />S = storage coefficient, unitless. <br />T = transmissivity, in cubic feet per foot per <br />day. <br />r = radius of discharge point, equal to half of <br />the pit width, in feet. <br />The discharge into the active pit for any time after t = 0 can be <br />calculated by adding the result of the first equation to the second <br />equation. Thus, the discharge was assessed by imposing boundary <br />conditions on two sides (the highwall and footwall) and including <br />recharge from below. The dewatering of the coal aquifer was <br />simulated by this method and discharge was found to reach a maximum <br />L~.2~j Cis cr 121e Pr- <br />of 24,200 cubic feet per day d9uring the mining of Pit ll2 in 1983. <br />Average annual discharge rates in gallons per day were calculated <br />using new dimensions for the active pit for each successive year of <br />mining. The calculated dewatering rates for the mine plan in the <br />Kerr ldorth Area are shown in Figure 22, Kerr North Area Mine Dis- <br />charge. <br />780-113 as <br />