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• The theoretical value of 489 mg/L (TDS) compares closely with the 433 mglL (TDS) that was actually measured at <br />Site 69, which is downstream from the confluence. <br />The salt balance analysis for Foidel Creek was based on data from discharge monitoring reports for water years <br />1990, 1991, 1992, and 1993. Data used in the salt balance included discharge rate, total dissolved solids (TDS) <br />concentration, and specific conductance. Specific conductance was used to estimate total dissolved solids based <br />on the following relationship: <br />TDS = (0.75) x (specific conductance) <br />The salt loads for each discharge point were computed as follows: <br />Salt Load (tons/day) = TDS(mg/I) x Discharge Rate (cfs) x 0.0026948 <br />The salt load for Foidel Creek was calculated by adding the average monthly Flows and salt loads from ponds A, B, <br />D, E, F, G, and T to the average monthly flow and salt load on Foidel Creek upstream of all discharge points at <br />station 14. The estimated average TDS concentration downstream of the discharge points on Foidel Creek were <br />determined by the following calculation: <br />Monthly Avg. Conc. ~mg l !~ .Summation of Monthly Avg. Salt Louds (tons /day) <br />Summation of Flows (cfs) x 0.0026948 <br />The salt load analysis for Foidel Creek shows that discharge from sediment ponds will increase the salt load of this <br />• creek. During low flow periods (June through September) flow in Foidel Creek occurs because of discharge from <br />sediment ponds impounding water from mine surface runoff and spoil springs. Average TDS of discharge from <br />sediment ponds for the low flow period is 2499 mg/I. Background TDS for Foidel Creek (Station 14) is 525 mg/I. <br />Flow at Station 14 occurs only during spring runoff and in response to storm events. The average predicted total <br />dissolved solids concentration for Foidel Creek calculated using data from all months is 2392 mg/I with a mean <br />salt load of 9.90 tons per day. <br />The potential recharge to the Twentymile Sandstone by Foidel Creek has been estimated for periods of low Flow <br />when total dissolved solid concentrations are highest. The water in Foidel Creek has an average width of 5.0 feet <br />and an average depth of 0.5 feet. The creek crosses two areas of outcrop for the Twentymile Sandstone. One <br />outcrop Itas been estimated at 300 feet in length and the other at approximately 4,488 feet in length. The area of <br />sandstone that could be in contact with the creek is 1,500 square feet for the first outcrop and 22,440 square feet <br />for the second outcrop. <br />The Hydraulic conductivity of the Twentymile Sandstone has been measured at 0.17 fUday to 0.28 fUday. <br />Theoretical recharge to the sandstone is estimated as follows: <br />Q = KIA <br />with Q = recharge <br />K = hydraulic conductivity <br />I = Bead (depth of water), and <br />A = area. <br />• <br />M R 97- I S4 2.06-24 13/09/97 <br />