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<br />-32- <br />Date: 8/10/81, 1400 Ca, mg/1: 132 <br />pH: 7.4 Na, mg/1: 36 <br />E.C., umho/cm: 1060 Mg,mg/1: 65 <br />TDS, mg/1: 820 K, mg/1: 4 <br />TSS, mg/l: 12 SOq, mg/1: 350 <br />Total Fe, mg/1: 0.6 C1, mg/1: 9 <br />Total Mn, mg/1: 0.2 C03, mg/1: 0 <br />NOg-N, mg/1: 0.1 NC03, mg/1: 342 <br />Hardn ess, mg/1: 597 SAR: 0.9 <br /> <br />By estimating the rates of discharge from the mine workings and the <br />spoils well, the projected concentration of solute in Foidel Creek was <br />computed using the OSM Stream Water Quality - Continuous Source Program <br />(Selected Hand-Held Calculator Codes for the Evaluation of the Cumulative <br />Hydrologic Impacts of Mining, Office of Surface Mining, 1981). Two <br />scenarios were considered by the applicant; a nominal case with average <br />predicted discharge rates and high flow in the stream, and a worst case <br />with maximum predicted discharge rates and low flow in the stream. <br />Foidel Creek is an intermittent stream with peak flow rates of <br />approximately 25 cfs and a base flaw of 0 cfs; average stream gradient is <br />0.0045 ft. /f t., average channel width is 10 feet and roughness <br />coefficient is 0.035. <br />The nominal case used average values of effluent discharge; 200 gpm <br />(almost 0.5 cfs) from the underground mine and 15 gpm from the wash-bay <br />well. Flow in Foidel Creek was 25 cfs plus U.5 cfs from pump age. The <br />contribution of TDS one mile downstream was computed to be approximately <br />20 mg/1. <br />The worst case used maximum values of effluent discharge; 650 gpm (1.5 <br />cfs) from the underyround mine and lU0 gpm from the wash-bay well. Flow <br />in Foidel Creek was 0 cfs plus 1.5 cfs from mine pumpage. The <br />contribution of TDS one mile downstream was computed to be approximately <br />1,100 mg/1. The analysis was carried downstream into the lower reach of <br />Trout Creek; the contribution of TDS after the confluence with Trout <br />Creek was computed to be approximately 145 mg/1. The concentration of <br />TDS in Trout Creek during low flow periods is approximately 200 mg/l; the <br />baseline concentration plus contribution of TDS from the Foidel Creek <br />Mine will be approximately 350 mg/1. Both the baseline concentrations <br />and the affected concentrations are considered to be good Quality water. <br />This analysis shows that when large amounts (relative to the amount <br />discharged from the spoils well) of water from the underground workings <br />are discharged to the surface along with the water from the wash-bay <br />well, the high TDS concentrations in the spoils water (3,200 mg/1) would <br />be diluted to acceptable levels. However, if the amounts of water <br />discharged from the underground workings are less than the projected <br />amounts (this would certainly be the case in the first years of <br />operation), then the discharge from the spoils well wwould have a much <br />