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-. ~ i ~ III IIIIIIIIIIIIIIII <br />999 <br />DATE: February 8, 1995 <br />TO: Berhan Keffelew <br />FROM: Allen Sorenson <br /><i <br />\ ~\ <br />~'. ~ <br />RE: Pumping of the Leak Collection Sump, Cripple Creek & Victor <br />Gold Co., Cresson Pad, Permit No. M-80-244 <br />In order to limit the rate of seepage from the pad to the environment, the <br />operator is required to minimize the amount of head allowed to develop on <br />the leach pad composite liner system. Head minimization on the composite <br />liner in the area of the pad above the lower anchor trench is intrinsic <br />to the operation of a valley leach type pad, and is verified at the <br />Cresson pad by the required vibrating wire piezometers. Head minimization <br />in the pregnant solution storage area is accomplished by dewaterinq of the <br />leak collection gravels through pumping out of the leak collection sump. <br />The leak collection sump provides a limited storage capacity. The <br />capacity available in the sump in order for the hydrostatic head on the <br />composite liner to be maintained at less than 2 feet is calculated below: <br />Known: The plan dimensions of the sump are 30' x 100' <br />Assume: The porosity of the leak collection gravel is .25 (conservative <br />for graded gravel). <br />Sump Capacity = 30' x 100' x (2')(.25) = 1500 cu. ft. <br />= 11,220 gallons <br />.. Any discrete leak collection pumping episode that <br />exceeds 11,220 gallons is an indication that <br />excessive head (greater than 2 feet) is being applied <br />to the composite liner that comprises the floor of <br />the sump. Inflows to the sump (as will be <br />demonstrated below) during pumping should be minimal <br />(on the order of K gal./sec.) and can be disregarded. <br />If inflows during pumping become significant, it is <br />an indication of a large leak in the upper <br />geomembrane. <br />