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The Williams Fork River is a major tributary to the Yampa River and enters the <br />Yampa River within the permit area of the Eagle Mines. It drains - <br />approximately 350 mil, or 10%, of the Yampa River Valley and shows many of <br />the same characteristics as the Yampa River, except that the Williams Fork is <br />more dependent on snowmelt and there is less ground water discharge to sustain <br />the flows of the river during low flow periods. <br />In addition to yield, water quality also varies seasonally. Total suspended <br />sediment loads are at a maximum during peak flows associated with spring <br />runoff. Steele et al., (1979) reports that up to 90% of the annual sediment _ <br />load of the Yampa River at the Maybell station is discharged during the period <br />of snawmeit runoff. Total suspended sediment Toads increase with increased <br />discharges (flows) in the rivers. Dissolved solids loads show an inverse <br />relationship with stream discharges. High quality snowmelt runoff contains <br />relatively low levels of total dissolved solids (TDS). Therefore, <br />concentrations of TDS decrease during peak flow periods. In the summer, when <br />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 <br />that intermittent (and ephemeral) drainages at lower elevations contribute <br />most of the dissolved and suspended solids that leave the basin. <br />The dominant cations in the Yampa and Williams Fork Rivers include calcium, <br />sodium, and magnesium, while dominant anions are bicarbonate and sulfate with <br />some chloride present. The total dissolved solids (TDS) load in the Yampa <br />River is increased by discharges from the Williams Fork River. In the <br />Williams Fork River the average dissolved solids concentration is 311 mg/1. <br />Dissolved solids concentration of the Yampa River average 264 mg/1 upstream <br />from the confluence with the Williams fork River and 284 mg/1 downstream. <br />Water within the Yampa River Basin is consumed through the irrigation of <br />croplands, municipal water supplies, stock watering, cooling water for power <br />plants, evapotranspiration by riparian vegetation and phreatophytes, and <br />transbasin diversions. Irrigation of cropland constitutes the largest of <br />these uses. Surface water consumed within the Yampa River drainage basin in <br />1976 totaled approximately 445,000 acre-feet. Of that, nearly 399,000 <br />acre-feet were used for irrigating croplands and hay meadows or for watering <br />livestock. Other uses included 5,478 acre-feet for industrial purposes, 2,555 <br />acre-feet for municipal water supplies, and 8,283 acre-feet for other <br />unspecified uses (Steele et al., 1979). Industrial consumption has since <br />increased by a total of 18,720 acre-feet/year due to use by the Craig <br />generating station. <br />Water for agricultural irrigation is generally obtained by simplQ stream <br />diversion structures and networks of ditches for flooding grasslands and <br />meadows during the summer months. The short growing season precludes growing <br />of warm weather crops such as corn, In the Williams Fork River, an even <br />higher proportion of the water used is for irrigation of grasslands and hay <br />fields. , <br />D. Probable Hydrologic Consequences <br />The Eagle No. 5 and No. 6 Mines are located in a hydrologically sensitive <br />area; there are four bedrock aquifers that can potentially be affected by <br />mining together with two stream/alluvial systems. Underground mining creates <br />_28_ <br />