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Mr.Timm Comer <br /> Manager,Environmental Resources ameo" <br /> Hydro-JexTM Program Review <br /> December 17.2009 <br /> safety Factor <br /> 0.00 <br /> 0.25 <br /> 0.50 <br /> 0.75 <br /> 1.0o <br /> 1.25 <br /> 1. <br /> 1.50 <br /> 75 <br /> 2.00 <br /> 25 <br /> 250 <br /> 2.75 <br /> 3.00 1 <br /> 3.25 <br /> 3.50 <br /> 3.75 <br /> 4.00 <br /> 1.25 <br /> �.50 <br /> 4.75 <br /> 5.00 1.62 <br /> 5.25 <br /> 5.50 <br /> 5.75 <br /> 6.00* <br /> 41500 42OW 42WO 43000 43W 44M _ M <br /> Figure 11 9852 Stability Analysis, 1/2 Pressure <br /> Figures 12 and 13 present the pressure profile and extent of saturation for injection at the 9810 elevation. <br /> For this scenario, the full injection pressure (e.g. just below the overburden pressure) was used. The <br /> stability analysis for this scenario is presented in Figure 14. The results of the stability analysis indicate a <br /> FOS of 1.62, which meets the VLF design criteria for acceptable factor of safety. The results from the <br /> stability analysis indicate that, even though high injection pressures are used, the injection depth is <br /> sufficiently low enough to have no material impact on overall stability. <br /> The results of the hydraulic and stability analysis indicate that VLF stability will not be affected, if the <br /> following guidance is followed: <br /> 1. The injection wells should be located a minimum of 20 feet from the crest of any ore benches. <br /> Only wells that will have deep (+100 feet) injection depths can be located closer than 20 feet from <br /> the bench crest; <br /> 2. Injection pressures in the upper 70 feet should not exceed 1/2 of the overburden pressure. Higher <br /> injection pressures can be used for depths greater than 70 feet, but should not exceed the <br /> overburden pressure; and <br /> 3. Injection pressures should always be closely monitored and controlled to avoid any local <br /> instabilities. <br /> S.iPROJECTS11125E CCV COMB-correspondencelhydro jex letter doe 8 <br />