2013-12-17_PERMIT FILE - C1992081 (13)

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.843 1.09 • 0 = .623 (watershed area) x (annual precip.-10) where: the watershed area 66.8 mil the annual precipitation = 15.9 inches The 10-year, 7-day high flow D is 148 cfs. The USGS could not derive a regression equation for the 10-year, 7-day low floe because of large mean standard errors of the measurements. The November baseflow value for Station Ill, which is directly opposite the l oadout, was used for the 10-year, 7-day low floe value in this analysis. The low flow 0 using the November bas eflow measurement is 0.14 cfs (see gain/toss study section in Tab 7). A value for the coal leachate volume uas calculated as follows. The surface area covered by coal storage stockpiles uas digitized from a topographic map and determined to be 2 137,000 f[ The greatest non-winter monthly precipitation, based on Hayden Station records, is 1.5 inc hes. A maximum monthl y coal leachate volume that could be generated is 2 3 0.125 ft x 137,000 ft , or 17,125 f[ . Converting this volume to gallons yieltls 128,095 gallons per month. The precipitation is as likely to occur one day as the next, thus a daily leachate volume was calculated by dividing the monthly total by 30. This yieltls a • coal leachate value of 4,270 gallons per day. The folloui ng equations presented by Ferreira (1984) were utilized to catcul ate increases in TDS and chemical load in tons/day as a result of mixing [he daily coal leachate ui [h 10-year, 7-day high and low floes in Dry Creek. L= 0 x L x 0.0027 uh ere: L = the chemical load for either Dry Creek or the coal feat hate in tons/day D = leachate or stream floe in cfs C = [he TDS concentration of the leachate or stream flow in mg/t and: OSC = DSL Oxf where: DSC = resultant TDS concentration for [he mixture in mg/l DSL the sum of the TDS load for the contaminant source and the receiving source expressed as tons/day and calcul aced by [he equation L = 0 x C x 0.0027 5 Revised 04/18/94 IK-v(