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4-16 <br />• Alluvial Aquifers <br />The relatively small areal extent and the lithological character <br />of alluvial materials indicate that the alluvial aquifers will <br />not produce significant amounts of water. <br />Since the proposed mine is located above the alluvial fills, <br />no direct disturbance of the alluvial aquifer will result from <br />the actual mining operation. <br />To ascertain ground water conditions in the alluvial aquifer, <br />a total of six baseline monitoring wells were installed in this <br />potential aquifer. <br />Of the six baseline monitoring wells in the alluvium associated <br />with East Salt Creek (Figure 2.3-5), three were dry on December 30, <br />1977. Well No. 3 never realized water sufficient to collect and <br />analyze. Other wells were frequently dry during sample periods. <br />During the other periods, the depth to water level in the monitoring <br />wells where water was present was between 7. and 17 feet below the <br />ground surface. The total depth of alluvial sediments is about 80 <br />feet in the central parts of the valley, of which only about <br />50 to 70 feet is saturated most of the year. <br />The exact quantity of water flowing in the alluvial aquifer <br />underlying East Salt Creek is not known; however, a rough approxi- <br />mation is possible. Sheridan's baseline monitoring wells indicate <br />a hydraulic gradient of about 80 feet per mile. Assuming the <br />transmissivity of the saturated thickness of alluvium (40 feet) <br />• <br />