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lined gravel pits. As mining progresses the bedrock in particular should be evaluated for seepage <br /> potential considering the assumptions made for this design. <br /> BACKGROUND <br /> The site is located near Firestone in Weld County, Colorado, immediately north of Weld County <br /> Road (WCR) 26 and east of WCR 15. The Firestone Resource Mine Site is currently not active <br /> and is in the permit application process. Construction of a compacted soil embankment slope <br /> liner is proposed to be completed inside the mine highwall during mining as slope areas are <br /> exposed and the mining proceeds. <br /> We have based our analysis on preliminary data regarding the typical soil profile at the site on <br /> data provided by the client. <br /> SOIL CONDITIONS <br /> The preliminary data identified approximately 5 feet of overburden soils above the gravel <br /> resource consisting mainly of clays. This overburden was generally underlain by approximately <br /> 26 feet of medium dense to very dense sand and gravel. An intermediate sandy clay to clayey <br /> sand layer mud lens in the sand and gravel was not mentioned in the preliminary data. Because <br /> this mud lens layer was not present, our analysis considered the sand and gravel layer to be <br /> continuous. Beneath the sand and gravel the bedrock in the area is expected to consist of sandy <br /> siltstone or silty sandstone identified on regional mapping as the Fox Hills Sandstone Formation. <br /> Static groundwater was observed to be approximately 7 feet below the ground surface. For the <br /> purposes of our analysis it was assumed to be 7 feet below the ground surface. <br /> STABILITY ANALYSIS <br /> Our stability analysis involved generating a computer model of limit equilibrium analysis using <br /> the Slope/W computer program. Table 1 summarizes the parameters of the soils used in the <br /> model. <br /> Table 1: Model Parameters <br /> Soil type Effective Friction Effective Moist Unit Weight <br /> Angle, (de rees) Cohesion,c'(psj) ,,,(P c <br /> Overburden 27 25 110 <br /> Sand and Gravel 34 0 115 <br /> Bedrock 26 700 126 <br /> Weathered Bedrock 24 0 126 <br /> Slope liner Zone I(core) 26 150 115 <br /> Slope liner Zone 1 B (shell) 30 100 118 <br /> Stability Berm 26 50 122 <br /> These parameters are based on similar soils from other projects in the area and engineering <br /> judgment. Based on comparison with published data (Table 1, Typical Properties of Compacted <br /> Soils, DM-702, Foundations and Earth Structures, Naval Facilities Engineering Command, <br /> - 2 - <br />