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Section 780.21 (c) Continued. <br />• The Eckman Park mine plan calls for an initial boxcut at the deepest <br />planned mining level to be followed by strip mining. in incremental <br />stages upslope from the boxcut. Excavation of th.e initial boxcut <br />will expose the overbi•.rden aquifer where it is saturated under a <br />maximum piezometric head of 120 feet. The exposed portico of the <br />overburden aquifer will drain water through the highwalls into the <br />pit. The rate of dewatering through time has been estimated using <br />the methods of Stallman as described by Lohman (1972), pp. 41-43. <br />Stallman's equation for discharge from a confined aquifer in a <br />channel drain with constant drawdown is as follows: <br />Q = 2s ST <br />~~ <br />where: Q = discharge from both sides of the drain per <br />• unit length of drain, 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, unit less. <br />T = transmissivity, in gallons per day per <br />foot. <br />The above equation is a line-sink formula for a channel of infinite <br />extent, and only the discharge from the long sides of the drain are <br />considered. The additional water which will drain i:to the ends of <br />the boxcuts have been estimated by adapting the point-sink, constant <br />drawdown equation of Jacob and Lohman in Lohman (1972), p. 23. <br />Q = 4Yf sT(2.30 log 2.25 Tt) -1 <br />2 <br />r S <br />• <br />780-178 <br />