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<br />i~s.harges into Foidel Creek was evidenced by the no flow periods in the <br />stream during the summer and fall. As mentioned earlier, Foidel is now a <br />perennial stream with its bast flow regime influenced by mine discharges. <br />Peak flows occur in response to snowmelt runoff, from i4arch through June, and <br />high intensity rainfall events. <br />The Yampa and its tributaries are all calcium sulfate dominated waters. <br />Several have equal components of calcium and magnesium. Baseline surface <br />water quality in the Upper Trout Creek drainage is affected by farming, road <br />drainage, and previous mining. Concentrations of major and trace constituents <br />vary greatly with the rates of flow and evaporation, and the locality of <br />sampling. Predominant concentrations of calcium, bicarbonate, sulfate, <br />nitrate-nitrogen, total iron, and total manganese are observed. In general, <br />surface water upstream from current mining activities is alkaline, moderately <br />saline and high in calcium carbonate hardness. <br />Sulfate concentrations appear to increase both as flow increases in small <br />drainages and immediately downstream from disturbed area drainages. Sulfate <br />concentrations exceed the recommended drinking water standard of 250 mg/1 <br />upstream of mining-related disturbance on Foidel Creek, and standards are <br />regularly exceeded downstream on Middle Creek and on Fish Creek. (Table 5). <br />Levels of sulfate on lower Trout Creek and along the Yampa River are below the <br />standard. Sulfates in the 1000-1500 mg/1 range frequently have laxative <br />effects, but concentrations as low as 200-500 mg/1 :'n, effect some individuals <br />(USEPA, 1976). As waters from Foidel and Fish Creek are used predominately <br />for irrigation, future uses are unlikely to be limited by elevated sulfate <br />levels. <br />Total suspended solids levels increase with increased flow in all drainages <br />(Table 5). Average concentrations in the Yampa and its tributaries all <br />substantially exceed the NPDES discharge standard for coal mines of 35 mg/1 <br />average with 70 mg/1 once during a thirty day period. TSS levels only meet <br />that standard during low flows. The mines will have no deleterious impact on <br />TSS levels as all drainage from disturbed areas must pass through <br />sedimentation ponds and discharge must meet the existing NPDES standards. <br />Salt concentrations are measured by both electrical conductivity (EC) and <br />total dissolved solids (TDS) {Tables 6 and 7). In natural, undisturbed <br />drainages, salt concentrations have an inverse relationship with flow; as flow <br />increases salt levels decrease and vice-versa. <br />In small drainages disturbed by mining, TDS levels increase downstream (Table <br />7). Additionally, in areas in which spoils aquifers have matured, TDS levels <br />in adjacent surface waters may be substantially influenced by peak spoils <br />discharge. TDS levels from backfilled spoils surrounding the Foidel Creek <br />underground mine range from 2500 mg/1 to 4200 mg/1 and large quantities of <br />this water can rapidly deteriorate adjacent surface waters when adequate <br />dilution is unavailable. As the time lag between peak surface runoff and peak <br />spoils discharge is several weeks, the surface waters surrounding the mine are <br />most vulnerable to high salt concentrations in the period immediately <br />following peak discharge, as well as during low flow periods in later summer. <br />35 <br />