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Mining and Water Storage Analysis <br />Raptor Pit 125 <br />Weld County, Colorado <br />Page 1 <br /> <br /> <br />Introduction <br />The following report presents the results of a hydrogeologic evaluation regarding a proposed <br />gravel quarry operation operated by Raptor Materials, LLC (Raptor) near Platteville, Colorado. <br />Raptor identifies the mine as its Pit 125 Operation. The evaluation consisted of reviewing available <br />hydrogeologic data and inputting those data into a numerical groundwater flow model. The <br />model was then used to estimate the effects of dry mining and lining the pits for water storage <br />on the surrounding groundwater hydrology. The site location and mine boundary area are <br />depicted on Figure 1. <br /> <br />Background Information <br />The proposed gravel quarry is located in portions of section 29, Township 3 North, Range 67 <br />West of the 6th principal meridian. The surrounding land use consists of agricultural, rural <br />residential and natural gas and oil gathering operations. The proposed mine occupies an estimated <br />197 acres. The water table at the site is located in unconsolidated alluvial deposits with the depth <br />to water varying between seven and 28 feet below ground surface. Soil conditions generally consist <br />of varying thicknesses of top soil underlain by sand and gravel deposits, which in turn are underlain <br />by claystone and sandstone bedrock. Over the entire area the average saturated thickness of the <br />sand and gravel deposits (prior to mining) is estimated at about 35 feet. It is our understanding that <br />the sand and gravel will be dewatered during aggregate extraction. The site location is presented <br />on Figure 1. The mine permit identifies three tracts for sand and gravel extraction which are <br />depicted on Figure 2. This analysis was predictive for the dry mining (dewatering) and lining of <br />three pits identified as A, B and C and using the pits as surface water storage subsequent to <br />aggregate extraction activities. Garrett Varra of Raptor has indicated that mining will progress <br />from south to north and model simulations were ran accordingly. <br /> <br />The hydraulic conductivity of alluvial deposits can vary greatly; however, for this study a value of <br />200 feet per day was used for gravely sand. The average effective porosity of the local sand and <br />gravel deposits is estimated at 0.27. The natural hydraulic gradient as documented by past water <br />resource investigation reports is on the order of 0.002 feet per foot for the majority of the study <br />area east of the Saint Vrain River. Based on USGS studies the depth to groundwater has been <br />measured at less than two feet to greater than 30 feet across the study area. Seasonal water table <br />fluctuations between one and three feet are common for this area; however, fluctuations of