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Introduction <br />The following report presents the results of a slope stability analysis for a proposed <br />open cut gravel extraction operations at the Varra Hentzelman pit operations near <br />Longmont, Colorado. This analysis was performed at the request of Varra Companies. <br />Background Information <br />The proposed Heintzelman gravel quarry occupies the east half of the east half of section <br />32, Township 3 North, Range 67 West of the 6t' Principal Meridian. The surrounding land <br />use consists of agricultural, rural residential, commercial and open-cut gravel quarry <br />operations. The proposed mine area occupies an estimated 133 acres. The water table at <br />the site is located in unconsolidated alluvial deposits associated with the Saint Wain <br />Creek. Soil conditions generally consist of varying thicknesses of top soil underlain by <br />sand and gravel deposits, which in turn are underlain by Pierre Shale. Over the entire area <br />the average saturated thickness of the sand and gravel deposits (prior to mining) is <br />estimated at 45 feet. It is our understanding that the sand and gravel will be dewatered <br />during aggregate extraction. <br />Overview of Stability Analyses <br />The assumptions used in the bank stability analysis include the following: <br />The static depth to groundwater is between 6 and 7 feet below grade and the <br />water table will intersect the pit bank approximately ten feet above the shale <br />(seepage face). <br />The maximum bank height is 50 feet. <br />A cohesion of 0 is assumed for all unconsolidated deposits. <br />? A cohesion of 700 psf is assumed for underlying shale deposits. <br />? The internal friction angles of the overlying soil and sand and gravel deposits are <br />28 and 49 degrees, respectively. <br />+ The analysis does not account for load surcharges. <br />? During extraction activities the pit bank is sloped at 1.25:1.