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Case 7 — Well Head on East Side of Southeast Pit. The mining operation is <br /> adjacent to a well head on the east. The proposed setback for mining is 150 feet <br /> from the well head. The mining depth was assumed to be 28 feet. <br /> The cross-sections located in Appendix B show the estimated phreatic surface <br /> associated with each case as well as the geometry used in the mining. <br /> METHODOLOGY <br /> The mining embankment configuration shown in the computer analysis represents the <br /> estimated conditions for this site. If mining conditions differ from the estimated <br /> conditions, the slope stability will need to be re-evaluated on a case by case basis. The <br /> Bishop Method was used in the computer analysis for determining safety factors. The <br /> procedure searches for circular shear failures and automatically searches for the lowest <br /> safety factor. 2,000 separate failure surfaces were analyzed for each case. The required <br /> minimum safety factors are based on the current standards used by the Colorado State <br /> Engineer's Office (SEO) in evaluating embankment dams, and industry accepted <br /> standards for the evaluation of temporary structures during construction. <br /> SLOPE STABILITY RESULTS <br /> The SEO requires minimum safety factors of 1.3 for static condition analyses and 1.0 for <br /> pseudo-static (earthquake loading) condition analyses for Class I (high hazard) <br /> embankment dams. This design criteria was used to establish the desired minimum <br /> safety factors for this project and should be considered as highly conservative for <br /> evaluating alluvial mining slopes. The calculated factors of safety are within the design <br /> criteria specified for this project and can be considered indicators of the mining slope <br /> performance under the various conditions. The slopes were analyzed using full and <br /> empty reservoir conditions. The results of the static condition and pseudo-static <br /> condition slope stability analyses are summarized in Table 2 and Table 3 on the <br /> following pages. <br /> Lupton Meadows Sand and Gravel <br /> r J&T Consultli Inc. Lupton Meadows Sand and Gravel Mine <br /> � ' g, Slope Stability Analysis <br /> Page 3 <br />