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Introduction <br />The following report presents the results of a hydrogeologic evaluation regarding a proposed dry <br />mine gravel quarry operation to be operated by Varra Companies (Varra) near Platteville, <br />Colorado. Varra identifies the proposed mine as Pit 122. The evaluation consisted of reviewing <br />available hydrogeologic data and inputting those data into a numerical groundwater flow model. <br />The model was then used to estimate the effects of dewatering operations on the surrounding <br />groundwater hydrology. This report was prepared as part of an OMLR 112 permit application. The <br />site location is depicted on Figure 1. <br />Background Information <br />The proposed gravel quarry is located in the NW1/4, S33, T3N, R67W of the 6th Principal <br />Meridian. The surrounding land use consists of agricultural, rural residential, commercial and <br />open -cut gravel quarry operations. The proposed mine area occupies an estimated 102 acres <br />and the anticipated average pit depth will be 39 feet below grade. <br />Information provided by current mining operations data and water resource evaluation reports <br />document the local and regional hydrogeology. In September 2008, 22 soil borings were drilled <br />from ground surface to bedrock to determine the potential aggregate mass within the proposed <br />mine boundary (Terracon 2008). Bedrock elevations were also obtained from studies by Colton <br />and Finch, 1974. The depth to bedrock within the proposed mine boundary varied between 13 <br />and 55 feet below ground surface. In general the site consists of three to eight feet of silty sand <br />to sandy clay underlain by sand and gravel with occasional clay and poorly graded sand lenses. <br />The hydraulic conductivity of the sand and coarse gravel deposits is on the order of 125 feet per <br />day (Schneider, 1983) which is consistent with published values and pump test evaluations <br />conducted by the author in similar geologic settings. The average effective porosity of the local <br />sand and gravel deposits is estimated at 0.27. The natural hydraulic gradient as documented by <br />past water resource investigation reports is on the order of 0.002 feet per foot, with the average <br />depth to water estimated at six feet below ground surface. The natural groundwater flow <br />direction is to the northwest within the model and mine area. Seasonal water table fluctuations of