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Case 3a - North Property Line (NORTH 3a). The mining operation is adjacent <br />to a private property and some minor electric utilities for a portion of the north <br />side of the site. The mining depth was assumed to be 85 feet in this area based <br />on bore log information in the geotechnical reports. The proposed interim setback <br />for mining is 120 feet from the final mining limit (247 feet from the property line). <br />Case 4a - Existing Gas Well (WELL 4a). An existing gas well is located in the <br />center of the proposed pit. The mining depth was assumed to be 85 feet in the <br />area based on bore log information in the geotechnical reports. The proposed <br />interim minimum setback for mining is 110 feet from the final mining limit (260 <br />feet from the gas well). <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 interim mining condition. <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 1.25 for static condition analyses and 1.0 <br />for 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 results of the static condition and <br />pseudo-static condition slope stability analyses are presented on the following page in <br />Tables 2 through 5. <br />Broken Arrow Investments, LLC - Derr Pit - M-2008-17 <br />J&T Consulting, Inc. Technical Revision No. 1- Slope Stability Analysis e 3