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CNAPTERFIVE Dratt EIS Rerrisions <br />U <br />Pace 3-13: Water Quality <br />Surface water in the Piceance Creek drainage basin is described as mixed bicazbonate in the <br />upper portions of the drainage basin and sodium bicazbonate in the lower potions. Chemical <br />components found in Piceance Creek surface waters aze attributed to the weathering of surficial <br />materials in the area. The principal ionic constituents in Piceance Creek include sodium, <br />calcium, magnesium, bicazbonate, sulfate, chloride, potassium, and fluoride ~ Tobin 1987). <br />Sodium, bicazbonate, and sulfate levels generally decrease during the spring snowmelt runoff <br />because of the increased amount of water, while chloride and fluoride remain essentially <br />constant. Calcium and magnesium concentrations show small decreases, and potassium • <br />increases during the snowmelt. During the irrigation season (July), sodium becomes <br />concentrated, and calcium and magnesium concentrations increase. In later summer and fall, <br />Piceance Creek flow is controlled primarily by groundwater discharges <br />Sediment yield from Piceance Creek is-l~ris variable. The hi¢hest sediment yields occur due <br />to runoff from localized thunderstorms in the later spring and eazly summer ~aa~gthat <br />transport high sediment loads from the intermittent tributaries. Sediment solaces aze the Uinta <br />Formation (sandstones and silts) extending downstream from the town of Rio Blanco and the <br />valley alluvium (USGS 1996). Sparsely covered slopes consist of loose material that is highly <br />erodible. Extreme sediment load for the period of record 1970 to 1997 neaz the confluence with <br />the White River pies varied from a daily minimum of 0.10 ton (June 1978) to a maximum of <br />6,095 tons (May 1983). Exiieme sedunent concentration in the water pies varied from a <br />minimum of 4 mg/l (October 1977) to a maximum of 25,000 mg/I (September 1978) (USGS <br />1997). <br />The USGS has monitored water quality at the three aaeina stations periodically since 1970. <br />Table 3.3-1 (modified)presents a summary of the recorded data for the period December 1985 to <br />September 1998. The complete raw data from the USGS records are provided in Appendix J of <br />the Final EIS. Total dissolved solids ranee from 481 me/1(below the town of Rio Blanco) to <br />3.130 mg/1 (at White River) over the period 1985 to 1998. with a mean of 1,037 me/I. Colorado <br />Ambient Water Oualiri Standards aze provided in Table 3.3-1 (modified) fo:r comparison. The <br />water quality in Piceance Creek eenerally meets all applicable standards, with the exception of <br />5-6 <br />