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Yampa River Sediment Load. In addition to yield, water quality also varies seasonally. Total <br />suspended sediment loads are at a maximum during peak flows associated with spring runoff. <br />Steele et al. (1979) reports that up to 90 percent of the annual sediment load of the Yampa River <br />at the Maybell Station is discharged during the period of snowmelt runoff. Total suspended <br />sediment loads increase with increased discharges (flows) in the rivers. Dissolved solids loads <br />show an inverse relationship with stream discharges. <br />Runoff Water Quality. High quality snowmelt runoff contains fairly low levels of total <br />dissolved solids (TDS). Therefore, concentrations of TDS decrease during peak flow periods. In <br />the summer, when ground water discharge makes up a larger percentage of the flow in the rivers, <br />TDS values increase. The Colorado Water Conservation Board (1969) reports that intermittent <br />(and ephemeral) drainages at lower elevations contribute most of the dissolved and suspended <br />solids that leave the basin. <br />Water Quality in Yampa and Williams Fork Rivers. The dominant cations in the Yampa and <br />Williams Fork Rivers are calcium, sodium, and magnesium. Dominant anions are bicarbonate <br />and sulfate with minor chloride. The concentration of total dissolved solids (TDS) averages <br />around 270 mg/1 in the Yampa River immediately below its confluence with the Williams Fork <br />River. The Williams Fork increases the Yampa River's TDS concentration by less than 20 mg /1. <br />The concentration in the Williams Fork averages around 300 mg/l. <br />Use of Yampa River Water. Water within the Yampa River Basin is consumed through the <br />irrigation of croplands, municipal water supplies, stock watering, cooling water for power plants, <br />evapotranspiration by riparian vegetation and phreatophytes, and transbasin diversions. <br />Irrigation of cropland constitutes the largest of these uses. Surface water consumed within the <br />Yampa River drainage basin in 1976 totaled approximately 445,000 acre -feet. Of that, 399,000 <br />acre -feet were used for irrigating croplands and hay meadows or for watering livestock. Other <br />uses included 5,478 acre -feet for industrial purposes, 2,555 acre -feet for municipal water <br />supplies, and 8,283 acre -feet for other unspecified uses (Steele et al., 1979). Industrial <br />consumption has since increased by a total of 18,720 acre -feet per year due to use by the Craig <br />generating station. <br />Irrigation Use of Surface Water. Water for agricultural irrigation is generally obtained by <br />simple stream diversion structures and networks of ditches for flooding grasslands and meadows <br />during summer months. The short growing season precludes growing of warm weather crops <br />such as corn. In the Williams Fork River, an even higher proportion of the water used is for <br />irrigation of grasslands and hay fields. <br />Aquifer Stratigraphy. Within the general vicinity of the Williams Fork Mines, ground water <br />exists in both bedrock and alluvial aquifers. Significant bedrock aquifers are (listed in ascending <br />stratigraphic order) the Trout Creek, Middle, Twentymile, and White Sandstones. The Middle, <br />Twentymile and White Sandstones are in the Williams Fork Formation; the Trout Creek <br />Sandstone is the uppermost member of the underlying Iles Formation. The main alluvial <br />aquifers in the area are associated with the Yampa and Williams Fork Rivers. The alluvial <br />aquifers probably contribute to baseflow of the rivers during dry periods. Coal seams, <br />discontinuous sandstones, and siltstones and smaller alluvial bodies in the area of the mine are <br />also water- bearing, but contain insufficient quantities of water to be considered significant <br />aquifers. <br />Williams Fork Mines 7 Permit Renewal 06 <br />C- 1981 -044 December 8, 2014 <br />