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Mr.Dan Worden <br /> April 18,2008 <br /> Page 2 <br /> The second soil profile modeled was based on the stratigraphy encountered near TH-1,in the northeast <br /> area of the site. This profile was similar to the first,except that bedrock was located at a depth of 41 <br /> feet and a 5-foot thick the mud lens was located approximately above the bedrock surface. <br /> The stmtigraphy encountered near TH-3 in the northeast area of the site,is typical of a majority of the <br /> pit. The stratigraphy encountered near TH-1 in the northeast area of the site,is a worst case scenario <br /> that is generally localized to the eastern end of the north side of the pit. <br /> DRMS ANALYSIS HIGIHVALL SETBACK TO SLURRY WALL <br /> The Division of Reclamation Mining and Safety(DRMS)requires that the gravel mine highwalls be <br /> modeled as vertical unless it can be demonstrated that the slope angle of the highwall will be controlled <br /> during mining. We understand that these mining highwall slopes were mined or will be mined at 3:1 <br /> (horizontal to vertical). Additionally,since no laboratory data is available for strength parameters the <br /> DRMS requires that the analysis be performed using the parameters for sites where laboratory testing is <br /> absent. These parameters are given below on Table 1: <br /> Table 1: DRMS Model Parameters <br /> Effective Effective Moist Unit Weight Saturated <br /> Soil Type Friction Angle Cohesion Unit Weight <br /> '(degrees) c'(psi) Y.(PO Y,( c <br /> Overburden 28 50 114 126 <br /> Gravel 35 0 130 137 <br /> Mud Lens 28 50 114 126 <br /> Slurry Wall 1 0 110 122 <br /> Weathered Bedrock 14 0 124 134 <br /> Bedrock 28 100 124 134 <br /> The parameters for weathered bedrock are much more conservative than those typically encountered in <br /> the project area and,it is our opinion,that they are not representative of conditions at the site. <br /> Table 2 below summarizes the results of our analysis. The factor of safety required by the DRMS for <br /> temporary mine slopes and reservoir embankments are also provided. Output graphics for each of the <br /> analyses are attached. <br /> Table 2: Hi hwall Setback to Slurryall DRUMS Analysis Results <br /> Setback Calculated Typical Required <br /> Model Distance(feet) Factor°f Factor of Safety <br /> DRMS analysis near TH-3 15 1.83 1.5 <br /> DRMS analysis near TH-1 15 1.67 1.5 <br /> The setback distance in Table 2 is calculated from the mine highwall to the proposed slurry wall. A <br /> setback distance of 25 feet between the property line and the proposed slurry wall was used in our <br />