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<br />introduction <br />The following report presents the results of a slope stability analysis for the embankment <br />that separates the Cache la Poudre River and Varra Companies (Varra) . Durham pit <br />gravel operation. This analysis was performed as part of the Flood Control Mitigation <br />Plan required by Colorado Division of Minerals and Geology, In association with DMG <br />Permit # M78-056. <br />Background Information <br />The Varra gravel quarry occupies a portion of the northeast comer of Section Nine and the <br />central portion of the north-half of Section 10, Township 5 North, Range 67 west of the e <br />Principal Meridian. The surrounding land use consists of agricultural, rural residential, <br />commercial and open-cut gravel quarry operations. The permitted mine area occupies an <br />estimated 230 acres with an approximate 100 acres of the operation dewatered and <br />excavated to bedrock. The water table at the site is located in unconsolidated alluvial <br />deposits associated with the Cache la Poudre River. Soil conditions generally consist of <br />varying thicknesses of top soil underlain by sand and gravel deposits, which in turn are <br />underlain by Pierre Shale. Over the entire area the average saturated thickness of the <br />sand and gravel deposits (prior to mining) is estimated at 26 feet. The natural hydraulic <br />gradient as documented by past water resource investigation reports is on the order of <br />0.002 feet per foot, with the depth to water varying between 6 and 15 feet below ground <br />surface. The natural groundwater flow direction is to the east - northeast Seasonal water <br />table fluctuations of between one and three feet are common for this area; however, <br />fluctuations of greater than ten feet have been documented during drought conditions <br />(Schneider, 1983). <br />The mine is dewatered by allowing groundwater to flow from the side walls of the <br />excavation into ditches excavated into the shale bedrock at the toe of the excavation walls. <br />The ditches are sloped so water drains to the north toward the Cache la Poudre River. The <br />water is then pumped from the excavation into the river. A settling pond is located west of