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Page 9 of 27 <br /> Flow in the Yampa River depends primarily on mountain snowpack. Flows range from intermittent to <br /> perennial, depending on location and precipitation patterns. The Williams Fork River is a major tributary <br /> of the Yampa River. The Williams Fork drains approximately 350 square miles,or ten percent of the <br /> Yampa River Valley. The Williams Fork fluctuates seasonally like the Yampa,but is more dependent on <br /> snowmelt, and there is less ground water discharge to sustain the flows of the river during low flow <br /> periods. Flows in the Williams Fork in the permit area typically range between 2500 cfs during spring <br /> runoff and less than 100 cfs during low flow. <br /> Water quality also varies seasonally. Total suspended sediment loads are at a maximum during peak <br /> flows associated with spring runoff. Steele et al. (1979)reports that up to 90 percent of the annual <br /> sediment load of the Yampa River at the Maybell Station is discharged during the period of snowmelt <br /> runoff. Total suspended sediment loads increase with increased discharges (flows) in the rivers. The load <br /> of dissolved solids shows an inverse relationship with stream discharges. <br /> High quality snowmelt runoff contains low levels of total dissolved solids (TDS). Therefore, <br /> concentrations of TDS decrease during peak flow periods. In the summer,when ground water discharge <br /> makes up a larger percentage of the flow in the rivers, TDS values increase. The Colorado Water <br /> Conservation Board(1969)reports that intermittent(and ephemeral) drainages at lower elevations <br /> contribute most of the dissolved and suspended solids that leave the basin. <br /> The dominant cations in the Yampa and Williams Fork Rivers are calcium, sodium, and magnesium. <br /> Dominant anions are bicarbonate and sulfate with minor chloride. The concentration of total dissolved <br /> solids(TDS) averages around 270 mg/1 in the Yampa River immediately below its confluence with the <br /> Williams Fork River. The Williams Fork increases the Yampa River's TDS concentration by less than 20 <br /> mg/1. The concentration in the Williams Fork averages around 300 mg/l. <br /> Water within the Yampa River Basin is consumed through the irrigation of croplands,municipal water <br /> supplies, stock watering, cooling water for power plants, evapotranspiration by riparian vegetation and <br /> phreatophytes, and transbasin diversions. Irrigation of cropland constitutes the largest of these uses. <br /> Other uses include industrial purposes,municipal water supplies,and other unspecified uses. <br /> Aquifer Stratigraphy. <br /> Within the general vicinity of the Williams Fork Mines,ground water exists in both bedrock and alluvial <br /> aquifers. Significant bedrock aquifers are (listed in ascending stratigraphic order)the Trout Creek, <br /> Middle, Twentymile, and White Sandstones. The Middle, Twentymile and White Sandstones are in the <br /> Williams Fork Formation;the Trout Creek Sandstone is the uppermost member of the underlying Iles <br /> Formation. The main alluvial aquifers in the area are associated with the Yampa and Williams Fork <br /> Rivers. The alluvial aquifers probably contribute to baseflow of the rivers during dry periods. Coal <br /> seams, 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 aquifers. <br /> Williams Fork Mines Prepared by: R ReiRey M.S. GISP <br /> C1981044 December 2023 <br />