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<br />The bedrock is mantled on hillslopes by quaternary colluvial <br />deposits, especially at the base of scarp slopes. Alluvial <br />deposits are present in the lower reaches of Foidel Creek and at <br />the confluence of Foidel and Middle Creeks. Alluvial deposits <br />are also present along Fish Creek, Middle Creek and Trout Creek. <br />Alluvial valley floors have been identified within and downstream <br />of the proposed permit area on Fish Creek, downstream from the <br />proposed permit area on Foidel Creek and Middle Creek, on Trout <br />Creek from its confluence with Middle Creek downstream to the <br />Yampa River, and on upper Middle Creek above the permit area. <br />The stratigraphy and geologic structure within the Twentymile <br />Park Synclinal Basin control the ground water flow in the basin. <br />The three regional bedrock aquifers that are present within the <br />basin are the Trout Creek sandstone, the Twentymile sandstone, <br />and the Wadge coal-overburden aquifer. All three aquifers <br />exhibit artesian heads in the central part of the Twentymile Park <br />Basin. The water quality in all three aquifers is moderately <br />poor but is potable and is used for mining, irrigation and <br />domestic purposes. <br />The alluvium of Trout Creek and its tributaries are important <br />sources of ground water. The alluvial bodies are used as water <br />supplies, provide sub-irrigation to vegetation, and supply base <br />flow to the streams. The alluvial bodies are recharged by both <br />the streams and the bedrock aquifers. <br />Ground water flow in the aquifers moves downdip toward the center <br />of the basin, controlled by the geologic structure. Faults may <br />have higher hydraulic conductivities and may allow vertical flow <br />to occur between aquifers which are displaced. Pump tests <br />performed near faults indicate that fault zones act as barriers <br />to horizontal ground water flow. <br />Aquifer recharge occurs along the edges of the Twentymile Park <br />Basin where the rocks outcrop. Recharge is primarily by direct <br />infiltration where the aquifers are exposed while secondary <br />recharge is provided by deep percolation of water through <br />overlying strata. <br />The folding and faulting of the geologic strata within the <br />Twentymile Park Synclinal Basin affects the direction of flow <br />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 <br />strata into the Twentymile Park Basin. Faults in the area <br />produce localized fracture zones within the rock strata. These <br />zones of increased hydraulic conductivity may increase the <br />potential for vertical movement of ground water within the rock <br />strata. However, to-date underground experience in the Foidel <br />7 <br />