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Ambient (baseline) streamflow and water-quality conditions were depicted in the calibration module of the digital- <br />• computer model (WATBALC) Exhibit 32, Quantity and Quality Modeling Analyses of Surface-water Resources of <br />the Trout Creek Basin). Both monthly (seasonal) and annual (both year-to-year and period-of-record mean) values <br />were derived by monitoring site (model node), for the period of historical record for all hydrologic (streamflow and <br />water-quality) variables of interest. Hydrologic accountability was achieved by aggregating upstream contributions of <br />flow and water quality and comparing model-analysis results with observed downstream conditions. <br />A regional characterization is given in terms of selected water-quality variables for the Trout Creek Basin and that <br />reach of the Yampa River upstream and downstream from the confluence with Trout Creek. For purposes of <br />contrasting the range of historical hydrological hydrologic conditions, a regional water-quality characterization is <br />given in Exhibit 32, Quantity and Quality Modeling Analyses of Surface-Water Resources of the Trout Creek Basin <br />for mean annual (that is 8-yeaz average) conditions as well as for a dry year (1977 water year) and a wet year (1983 <br />water year) within this 8-year period. these designated years represent, in general, the driest year (1977) and wettest <br />year (1983), respectively, for the 8-year calibration period. In this summary, the water-quality variables selected for <br />an average year comparison of baseline conditions consist of dissolved solids, sulfate, and ion concentrations. <br />Average baseline dissolved-solids concentrations in the Middle Creek sub-basin range aerially from about 380 to 390 <br />mg/I in upper Middle Creek and the headwaters of the Foidel Creek Tributary to nearly 890 mgJl in lower Middle <br />Creek near its confluence with Trout Creek (Exhibit 32, Quantity and Quality Modeling Analyses of Surface-Water <br />Resources of the Trout Creek Basin). [n comparison, average dissolved-solids concentrations are lower in Fish Creek <br />than in Middle Creek and Foidel Creek. Dissolved solids range from an average of 280 to 285 mg/I at the upstream <br />Fish Creek sampling sites to 440 to 460 mg/I in the lower Fish Creek reaches. Trout Crcek upstream from Middle <br />Creek has an estimated average dissolved-solids concentration of nearly 220 mg/1. Due to the relatively higher <br />dissolved-solids concentrations contributed by the downstream tributaries of Middle Creek and Fish Creek, the <br />average dissolved-solids concentrations of Trout Creek are estimated to increase to 380 mg/I below Middle Creek and <br />to increase to nearly 400 mg/1 below the Fish Creek confluence and in Trout Creek near its confluence with the <br />Yampa River. Largely as a consequence of Trout Creek inflows, the mean annual dissolved-solids concentrations of <br />the Yampa River between Milner and Hayden increase in a downstream direction, from about 140 mg/I upstream <br />from the Trout Creek confluence to between 155 and 170 mg/I downstream from Trout Creek. <br />As would be expected, areal pattems in average sulfate concentrations of streams in the Trout Creek stream system <br />and in the Yampa River mirror those observed and described previously for dissolved solids. Mean annual sulfate <br />concentrations in Foidel Creek range from over 240 mg/1 upstream to nearly 790 mg/I below Mine No. 1 and nearly <br />600 mg/l downstream near its confluence with Middle Creek. Middle Creek exhibits its average sulfate <br />concentrations of over 110 mg/I upstream from Foidel Creek to over 400 mg/I downstream from Foidel Creek. <br />Average sulfate concentrations in Fish Creek are substantially lower than in Foidel Creek, ranging from almost 60 <br />mg/I upstream to slightly over 170 mg/I upstream from Middle Creek to almost 160 mg/I below Middle Creek. <br />Sulfate concentrations in the lower reaches of Trout Creek are not appreciably affected by Fish Creek inflows. Due to <br />Trout Creek inflows, sulfate concentrations of the Yampa River increase by about 50 percent (or 12 mg/1), from an <br />average of 24 mg/I upstream from the confluence with Trout Creek to between 34 and 38 mg/I downstream from <br />Trout Creek. <br />Somewhat different patterns in spatial variability are observed in the case of iron concentrations. In general, iron <br />concentrations are relatively greater in Fish Creek than in Foidel Creek and Middle Creek, in contrast to the <br />patterns described previously for dissolved-solids and sulfate concentrations (Exhibit 32, Quantity and Quality <br />Modeling Analyses of Surface Water Resources of the Trout Creek Basin). Iron concentrations generally increase <br />in a downstream direction in cases of Foidel Creek, Fish Creek, and Trout Creek. However, variability is quite low <br />and the impact of Trout Creek inflows on iron concentrations in the Yampa River is negligible. In fact, a <br />substantial loss of iron loads may occur upstream from the Yampa River monitoring site neaz Hayden. Tron <br />concentrations do not show much variability with stream flows; hence, no comparisons are reported for wet or dry <br />year conditions (Exhibit 32, Quantity and Quality Modeling Analyses of Surface Water Resources of the Trout <br />Creek Basin). <br />Permit Renewal No. 3 2.04-36 12/10/98 <br />