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SerFer reservoir Slope Stability Summary <br />A stability analysis was performed for the proposed final reclamation reservoir <br />embankment at the proposed Serfer mine site using the DOS program XSTABL. For the <br />entire embankment, the homogeneous fill was tested using the values representative of <br />the on-site materials. The values were taken from material tests from nearby pit <br />locations. Two typical cross sections were prepared. The first cross section had a <br />reclaimed slope of 3H:1 V and the second typical cross section assumed a ditch located 12 <br />feet from the top of the embankment and just outside of the reclaimed embankment fill <br />area. The cross-section the embankment consisted of three zones: bedrock, undisturbed <br />sand and gravel, and the homogeneous fill. The soil properties used in the analysis are <br />shown in the table below. <br />Soil Moist Density Sat. Density c' (psf) Friction Angle <br />Bedrock 125.0 129.0 2000 30 <br />Homogenous 113.8 119.4 100 25 <br />Fill <br />Native Sand & 110.0 114.0 0 32 <br />Gravel <br />Two scenarios for each cross section were analyzed. The first scenario (1) assumes that <br />the reservoir is full and conditions are static. The second scenario (2) is referred to as a <br />rapid drawdown condition and assumes that the reservoir had to be emptied quickly. The <br />required minimum safety factors are based on the current standards used by the Colorado <br />State Engineer's Office (SEO) in evaluating embankment dams, and industry accepted <br />standards for the evaluation of temporary structures during construction. The SEO <br />requires minimum Factor of Safety (FOS) of 1.5 for static condition analyses and 1.2 for <br />rapid drawdown condition analyses. <br />Conclusions <br />Both scenarios had acceptable factors of safety. The placement of the ditch near the top <br />of the embankment did not impact the stability of the slope. <br />ThP tnhlP hPlow chnwc the minimum values that meet the State Engineers requirements. <br />Scenario Condition Calculated FOS Required FOS <br />1 Steady State 2.06 1.50 <br />1 Rapid Drawdown 2.57 1.20 <br />2 Steady State 2.57 1.50 <br />2 Rapid Drawdown 2.06 1.20 <br />Therefore the slope stability analysis demonstrates the embankment is stable under both <br />scenarios and conditions.