2009-08-10_PERMIT FILE - C1982056A (5)

Home Browse Search

Since the discharges from 109 and 115 must be adjusted during periods of low flow, they will not exceed the lowest flow rate determined by the Mine Discharge Calculator and the Fish Creek Borehole Calculator or based on compliance considerations under TCC's CDPS discharge permits. Yampa River Below Diversion near Hayden) As would be expected at this downstream location on the Yampa River, streamflow increases only nominally (less than 0.1 percent) and concentrations for all mine periods were not affecting Yampa River constituent levels, except for specific conductance and sulfate concentration during the initial mine period (that is, 1984 through 1991 water years). These increases were approximately 1 umhos/cm for specific conductance and 1 mg/L for sulfat~° concentration. Model prediction results for streamflow, dissolved solids concentration and sulfate concentration fo:r each of the 4 mining periods are summarized in Exhibit 32, Quantity and Quality Modeling Analyses of Surface- Water Resources of the Trout Creek Basin. A comparison of predicted increases in concentrations due to the 32-year time span of mine related impact:> downstream on the Yampa River (USGS Station 09244410) was given for dissolved solids and for sulfate (Exhibit 32, Quantity and Quality Modeling Analyses of Surface-Water Resources of the Trout Creek Basin). The original modeling indicated that the differences would be barely discernible. The year-by-year, as well as the time trend o;f decreasing incremental differences in average baseline versus mine impacted concentrations, is apparent from these; tabular comparisons. New modeling indicates that with the increased salt loading of the discharges some impact;; can be observed in the modeling. In the modeling developed for TR-32 (June, 1999) the maximum load to the Yampa River from the underground mine discharges is 22 tons per day (8300 tons/year). The anticipated dissolved solids loads contributed to the; stream system from mine flows will impact average ambient conditions in lower Trout Creek (about 70 tonslday;- and to a lesser degree, the Yampa River (approximately 250 tons/day). On an annual basis, these averaged ambient dissolved solids loads would reflect over 25,400 tons/year for lower Trout Creek and about 89,600 tons/year for the; Yampa River near Hayden. The impact will be to increase the dissolved solids loading in lower Trout Creek 31 %~ and in the Yampa River by 9%. Similar increases in the sulfate levels will also occur. Stream Standards Comparisons The State of Colorado stream standards applicable for the study area consist of: • Segment 13a: Trout Creek and tributaries excluding Segments 13b and 13c not within a National Forest: • Segment 13b: Foidel Creek and all tributaries, Fish Creeks and Middle Creeks and all tributaries from County Road 27 to confluence with Trout Creek • Segment 13c: Trout Creek from headgate of Spruce Hill Ditch to confluence with Fish Creek and' Tributaries to Trout Creek for County Road 27 to County Road 179 • Segment 2: Yampa River, mainstem The segments have the similar water quality standards, except that segment 13a includes drinking water standards for active water supply uses, Segment 13b does not include drinking water standards and Segment 13c includes drinking water standards from June through February. The effect of these segment standards is that the sulfate standard is not applicable to the mine discharge impacted reaches of Foidel, Fish, Middle and Trout Creeks year- round. The relevant stream segments are shown on Exhibit 50, Figure E50-4). r~ MR08-230 2.05-157 09/05/08