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~. trace constituents vary greatly with the rates of flow and evaporation, and the locality of sampling. Common elements observed are: calcium, • bicarbonate, sulfate, nitrate-nitrogen, total iron, and total manganese. In general, surface water upstream from current mining activities is alkaline, moderately saline and high in calcium carbonate hardness. Sulfate concentrations appear to increase both as flow increases in small drainages and immediately downstream from disturbed area drainages. Sulfate concentrations exceed the recommended drinking water standard of 250 mg/1 upstream of mining-related disturbance on Foidel Creek, and standards are regularly exceeded downstream on Middle Creek and on Fish Creek. (TABLE 2). Levels of sulfate on lower Trout Creek and along the Yampa River are below the standard. Sulfates in the 1000-1500 mg/1 range frequently have laxative effects, but concentrations as low as 200-500 mg/1 may effect some individuals (USEPA, 1976). As waters from Foidel and Fish Creek are used predominately for irrigation, future uses are unlikely to be limited by elevated sulfate levels. Total suspended solids levels increase with increased flow in all drainages (TABLE 3). Average concentrations in the Yampa and its tributaries all substantially exceed the NPDES discharge limitation for coal mines of 35 mg/1 average with 70 mg/1 once during a thirty day period. TSS levels only meet those criteria during low flows. The mines will have no deleterious Impact on TSS levels as all drainage from disturbed areas must pass through sedimentation ponds and discharge must meet the existing NPDES stream limitation. • Salt concentrations are measured by both electrical conductivity (EC) and total dissolved solids (TDS) (TABLES 4 and 5). In natural, undisturbed drainages, salt concentrations have an inverse relationship with flow; as flow increases salt levels decrease and vice-versa. In small drainages disturbed by mining, TDS levels increase downstream (TABLE 5). Additionally, in areas in which spoils aquifers have matured, TDS levels in adjacent surface waters may be substantially influenced by peak spoils discharge. TDS levels from backfilled spoils surrounding the Foidel Creek underground mine range from 2500 mg/1 to 4200 mg/1 and large quantities of this water can rapidly deteriorate adjacent surface waters when adequate dilution is unavailable. As the time lag between peak surface runoff and peak spoils discharge is several weeks, the surface waters surrounding the mine are most vulnerable to high salt concentrations in the period immediately following peak discharge, as well as during low flow periods in later summer. It has been found that spoils springs will come to predominate spring flow in areas where surface mining has occurred. One 1300 acre block in Eckman Park has two large springs which each have flows ranging from 50 gpm to 1200 gpm. A 1450 acre area in western Eckman Park has at least nine large springs with flows ranging from less than 1 gpm to 250 gpm. • _} 7_ ~ ..