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_19_ <br />The predictive equation used throughout the worst case prediction is presented <br />below: <br />EQUATION 1 <br />Q~ ~U + Qj ~j = Cd <br />(McWhorter, 1980) <br />u = upstream site <br />i = inflow site <br />d = downstream prediction <br />Q = quantity <br />C = concentration <br />The worst case chemistry of the mine water is therefore projected as 1690 mg/1 <br />of TDS.- <br />The operation plan calls for this water to be pumped and stored in pond SP-2, <br />which also contains runoff from the surface facilities. Water from the pond <br />is proposed for use in the mine and at the surface facilities for dust <br />suppression. A worst case prediction of outflow from the pond is made on an <br />assumption that no dilution from fresh water runoff occurs and reuse of the <br />mine pumpage does not occur, allowing the mine water to reach a level in the <br />pond where the water has to be released to Harvey Gap. <br />The low flow surface water condition is used to predict worst case. These low <br />flow conditions occur during periods of non-irrigation from October 15 to <br />April 15, when the Grass Valley Reservoir outlets are closed to store water <br />for the irrigation season. Base flow occurs due to seepage through the <br />reservoir embankment. The base flow is 0.5 cfs (based on communcation with <br />Silt Water Conservancy District) at an average TDS of 755 mg/l. <br />This base flow is impacted by outflow from pond SP-1 draining the proposed <br />refuse disposal site. The applicant has projected a worst case TDS level of <br />1910 mg/1 seeping through the refuse site. The base flow is merged with the <br />maximum orifice flow of pond SP-1 of 0.1 cfs at 1910 mg/1 TDS. Using <br />Equation 1, this results in: <br />Base flow Harvey Gap + Outflow from Refuse Pond <br />= 948 mg/1 TDS at 0.6 cfs. <br />This flow is merged with the orifice flow from pond SP-2 holding mine water. <br />This results in: <br />