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Ground water flow in [he aquifers moves downdip toward the center of the basin, controlled <br />by the geologic structure. Faults may have higher hydraulic conductivities and may allow <br />vertical flow to occur between aquifers which are displaced. Pump tests performed neaz faults <br />indicate that fault zones act as barriers to horizontal ground water flow. <br />Aquifer recharge occurs along the edges of the Twentymile Park Basin where the rocks <br />outcrop. Recharge is primarily by direct infiltration where the aquifers are exposed while <br />secondary rechazge is provided by deep percolation of water through overlying strata. <br />The folding and faulting of the geologic strata within the Twentymile Park Synclinal Basin <br />affects the direction of flow within the rock aquifers. In the permit and adjacent areas, the <br />ground water flow in the bedrock aquifers is down the dip of the strata into the Twentymile <br />Pazk Basin. Faults in the area produce localized fracture zones within the rock strata. These <br />zones of increased hydraulic conductivity may increase the potential for vertical movement of <br />ground water within the rock strata. However, to-date underground experience in the Foidel <br />Creek mine has shown that ground water movement along the faults is minimal. <br />The Twentymile Sandstone is separated from the Wadge coal-overburden aquifer by up to 700 <br />feet of very low permeability shale within [he permit and adjacent areas. The underlying <br />250-foot shale and the overlying shales and siltstones of the upper Williams Fork Formation <br />and the Lewis Shale Formations confine the Twentymile Sandstone aquifer, allowing artesian <br />conditions to develop. To the northeast, the Twentymile Sandstone recharges the alluvial <br />aquifer and provides base flow to the tributaries of Trout Creek down gradient of the <br />proposed permit azea. Salts in the Twentymile Sandstone waters are predominantly sodium <br />bicazbonate and result in TDS levels of 150 mg/l. This aquifer is occasionally used for <br />domestic needs. Spoil springs have developed in many old pit areas and aze added to the <br />water monitoring program as they are identified. <br />The climate of the permit area is classified as semi-arid, with significant elevationally related <br />variations in temperature and precipitation. Average annual precipitation within the permit <br />area would be somewhere between the 15.45 inch average for Hayden and the 24 inch <br />average for Steamboat Springs, with precipitation increasing with elevation. <br />Two broadly classified soil complexes exist within the proposed permit area. These aze typic <br />Paleoborolls - Borollic Camborthids and Argic Cryoborolls - Cryic Paleoborolls. The former <br />complex consists primazily of clayey, well drained soils developing in place from soft shales. <br />These soils are used for cropland, pastureland and rangeland, with native vegetation consisting <br />primarily of big sagebrush and mountain shrub communities. These soils occur primarily in <br />the Mine 2 area, and lower slopes of Mine 1 and Eckman Park. The latter complex consists <br />of moderately deep to deep, well drained loamy soils formed from sandstone and shale on <br />mountain sides and ridges. These soils are used almost exclusively as rangeland and wildlife <br />habitat, supporting native vegetation communities including mountain shrub, big sagebrush <br />and aspen. These soils occur predominately within Eckman Pazk. <br />8 <br />