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Groundwater <br />The proposed operation is located in the shallow alluvial sands and <br />gravel of the Poudre River. This aquifer consists of clays, silts, <br />sands, and gravel that have been washed downstream from the Poudre <br />headwaters. These deposits are listed by the USGS as Pleistocene <br />and Holocene in age. Probable well yields from an unconsolidated <br />alluvial aquifer in this area are estimated to be less than 500 gpm <br />by the USGS. The depth to the water table is estimated to be less <br />than five feet on this property under average conditions. <br />The property will be mined as a dry mine. This requires dewatering <br />the aquifer at the mine site through the use of dewatering pumps. <br />The proposed dewatering operations will create a cone of depression <br />in the groundwater table which could impact nearby owners of <br />shallow alluvial wells. <br />Figure G-1 shows the location of all permitted and decreed <br />groundwater wells in the area within a 4,000 foot radius of the <br />property. No wells are shown to the north of the Cache La Poudre <br />River. The river will form a hydraulic barrier to any drawdown and <br />thus prevent injury to wells on the north side. <br />A pump test of the alluvial aquifer was done in Section 34 up- <br />gradient of the proposed mining site. This test is shown in the <br />Colorado Groundwater Circular No. 11 published by the Colorado <br />Water Conservation Board in 1965. The results of this test show a <br />yield of 460 gpm. The permeability of the well was measured at <br />3,100 gpd per square foot and the transmissivity was estimated to <br />be 120,000 gpd per foot. The results of this test are considered <br />to be representative of most wells in the area. <br />The area surrounding the mining site is geologically complex. The <br />Laramie-Fox Hills Aquifer ends within a few miles of the site. <br />However, the USGS has identified both the Laramie and Fox Hills <br />' sandstone formations to the north. This would indicate the <br />al]uvial aquifer in this area is underlain with this formation. <br />The Lone Tree terrace deposit also comes in from the north and <br />joins in this vicinity. <br />Existing mining operations in the area have identified a thick clay <br />` layer that separates the alluvial aquifer from these other <br />I` formations. In some locations upstream of this site, there have <br />been reports of a secondary alluvial deposit that underlies the <br />alluvium and the clay seam. This may be a part of the Lone Tree <br />deposit. <br />G-2 <br />