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<br />Introductlon <br />The following report presents the results of a slope stability analysis for the embankment <br />that separates the Cache la Poudre River and Varna Companies (Varre) Durham pit <br />gravel operation. This ar~lysis was pertormed 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 Infomratiorr <br />The Varna gravel quany occupies a portion of the northeast comer of Section Nine and fhe <br />central portion of the north-half of Section 10, Township 5 NoAh, Range 67 west of the 8" <br />Prirxtipal Mertdian. The surrounding land use consists of agricultural, rural residential, <br />commensal and open-art gravel quany operations. The permitted mine area occupies an <br />estimated 230 saes with an approximate 100 saes of the operation dewatered and <br />excavated to bedrock. The water table at the site is located in unconsolidated alluvial <br />deposits assocated with the Cache la Poudre River. Solt conditions generally cor~ist of <br />varying Uridcnesses of top soil underlain by sand and gravel deposits, which in tum 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 28 feet The natural hydraulic <br />gradient as documented by past water resource investigation reports ~ 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 fluctuaflorrs of between one and three feet are common for this area; trovuever, <br />fluctuations of greater than ten feet have been documented during drought conditions <br />(Sctvreider,19fl3). <br />The mine is dewatered by allowing groundwater to fbw from the side wails of the <br />excavation into ditd~res excavated irrto the shale bedrock at the toe Of the exa+vation wails. <br />The ditches are sloped so water drains to the north toward the Cactne la Poudre River. The <br />water is then pumped from the excavation into the rimrer_ A setffing pond is boated west of <br />