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Mr. Chris Oestreich <br /> May12,2023 <br /> Page 4 <br /> Soil-Bentonite Slurry Well <br /> The proposed slurry wall will consist of a mix of the overburden,alluvial sand,and imported bentonite. The resulting mix <br /> will produce a non-Newtonian fluid with some shear strength characteristics based on a reduced friction angle of the <br /> overlying overburden. Based on engineering judgment,we modeled the slurry wall as follows: <br /> Unit Weight Friction Angle 0'° <br /> (pco Cohesion C psf <br /> 110 0 0 <br /> STABILITYANALYSES RESULTS <br /> The stability analyses assumed the mining will be per the mine plan. The plan includes dry mining in the mine cell as the <br /> water level in these cells are controlled by slurry walls. Exterior mine slopes in the slurry wall lined cells will not exceed <br /> 3h:1 v. <br /> Setbacks listed in Table 1 (below)indicate the setback from the structure to the mining limits. <br /> The factor of safety shown below is the minimum factor of safety of the conditions listed above. <br /> TABLE 1 -SLOPE STABILITY RESULTS AND SETBACKS <br /> Section Location Critical Structure Static Factor Seismic Factor of DRMS Draft FOS <br /> Structure Setback From of Safety at Safety at Structure Requirement <br /> Mine Limit(ft) Structure (0.072g Static/Seismic <br /> horizontal <br /> 1 Mine Cell with Plumb Ditch 40 1.98 1.54 1.5/1.3 <br /> slurry wall(20', <br /> 3h:1 v <br /> 1 Mine Cell with Plumb Ditch 40 1.89 1.50 1.5/1.3 <br /> slung wall(20', <br /> 3h:1v)and <br /> 1,200 psf <br /> surcharge <br /> CONCLUSIONS <br /> The Plumb Ditch is the nearest structure to the mine and is stable based on the Factors of Safety listed in the table <br /> above. The Plumb Ditch section analyzed was under conservative conditions. All other structures in the area are <br /> located at or at greater the 40-feet from the mine limit. Factors of Safety on other neighboring structures will be greater <br /> than those summarized in the Table above. <br />