Laserfiche WebLink
Since the discharges from 109 and 115 must be adjusted during periods of low flow, they will not exceed the <br />lowest flow rate determined by the Mine Discharge <br />.addition, discharges will cease when the conductivity a <br />converted to sulfate). <br />Yampa River (Below Diversion near Hayden) <br />Calculator and the Fish Creek Borehole Calculator. ]n <br />t Site 30] exceeds 740 umhos/cm (95% of standard when <br />As would be expected at this downstream location on the Yampa River, streamflow increases only nominally (less <br />than 0.1 percent) and concentrations for all mine periods were not affecting Yampa River constituent levels, except <br />for specific conductance and sulfate concentration during the initial mine period (that is, 1984 through 1991 water <br />years). These increases were approximately 1 umhvs,~cm for specific conductance and 1 mg/L for sulfate <br />concentration. Model prediction results for streamf]ow, dissolved solids concentration and sulfate concentration <br />for each of the 4 mining periods are summarized in Exhibit 32, Quantity and Qualiq• Modeling Analyses of <br />Surface-Water Resources of [he Trout Creek Basin. <br />A comparison of predicted increases in concen7ations due to the 32-year time span of mine related impacts <br />downstream on the Pampa River (USGS Station 09244410) was given for dissolved solids and for sulfate (Exhibit <br />32. Quantity and Quality Modeling Analyses of Surface-Water Resources of the Trout Creek Basin). The original <br />modeling indicated that the differences would be barely dtscetnible. The year-by-year, as well as the time trend of <br />decreasing incremental differences in average baseline versus mine impacted concentrations, is apparent from <br />these tabular comparisons. New modeling indicates that with the increased salt loading of the discharges some <br />impacts can be observed in the modeling. <br />]n the modeling developed for TR-32 (June, 1999) the maximum load to the }'ampa River from the underground <br />mine discharges is 22 tons per day (8300 tons/year). The anticipated dissolved solids loads contributed to the <br />stream system from mine flows will impact average ambient conditions in lower Trout Creek (about 70 tons/day) <br />~nd to a lesser degree, the Yampa River (approximately 250 tons/day). On an annual basis, these averaged <br />ambient dissolved solids loads would reflect over 25,400 tons/year for lower Trout Creek and about 89,600 <br />tons/year for the Yampa River near Hayden. The impact will be to increase the dissolved solids loading in lower <br />Trout Creek 3 ]% and to the Yampa River by 9%. Similar increases in the sulfate levels will also occur. <br />Stream Standards Comaarisons <br />The State of Colorado stream standards applicable for the study area consist of: <br />• Segment 13a: Trout Creek and tributaries excluding Segments 136 and 13c not within a National <br />Forest <br />Segment 13b: Foide] Creek and al] tributaries, Fish Creeks and Middle Creeks and all tributaries from <br />County Road 27 to confluence with Trout Creek <br />Segment ]3c: Trout Creek from headgate of Spruce Hill Ditch to confluence with Fish Creek and <br />Tributaries to Trout Creek for County Road 27 to County Road 179 <br />Segment 2: Yampa River, mainstem <br />The segments have the similar water quality standards, except that segment 13a includes drinking water standards, <br />Segment 13b does not include drinking water standards and Segment ]3c includes drinking water standards from <br />June through February. The effect of these segment standards is that the sulfate standard is not applicable to the <br />mine discharge impacted reaches of Foidel, Fish and Middle Creeks year-round and to the portion of Trout Creek <br />between Middle Creek and Fish Creek from March through May. The relevant stream segments are shown on <br />Exhibit 50, Figure E50-4). <br />~J <br />TR99-32 2.05-157 APPdtOAf~;~ r~7 ~ ° ~~~~ ]/3/00 <br />