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Banks and Gesso Apri13, 2007 Page 3 Analysis I This stability analysis involves modeling the expected excavation with anear-vertical highwall and evaluating the variety of failure surfaces which result in a FOS less than 1.01. The failure surface which extended the furthest behind the highwall with a FOS less than 1.01 daylights approximately 120 ft offset from the highwall crest. The critical failure surface through the point 120 ft offset from the highwall crest is shown in Figure 3. According to [he analysis, failure surfaces which daylight more than 120 ft behind the slope crest have FOS greater than 1.01; failures originating in front of that'point may have FOS less than 1. Therefore, for a highwall mined to anear-vertical slope configuration, the minimum required setback from the highwall to a structure is 120 ft. However, the high tension power lines are assumed to be on deep foundations. Information about the design and construction of the deep foundations is not known. In order to avoid reducing the lateral resistance of the deep foundations, an offset of 200 ft is recommended adjacent to the towers. Aaalvsis 2 The second analysis evaluates the reduced setback which could be realized from mining to a specific slope as an alternative to a vertical highwall. Specifically, the required maximum slope steepness that could be allowed while maintaining a 25 ft setback was evaluated. The slope steepness was varied until a slope which resulted in a FOS greater than 1.01 through a daylight point 25-ft offset from the slope crest was determined. The slope configuration meeting these criteria is a 2.25H:1 V slope. Figure 4 demonstrates the factor of safety for the critical failure surface through the point 25 ft offset from the crest of a 2.25H:1 V slope; failures originating in front of that point may have FOS less than 1. Therefore, io maintain the minimum 25 ft setback between the top of the excavated slope and the adjacent structures, the mine side slopes should be flatter than 2.25H:1 V. Material beneath and behind the 2.25H:1 V slope should not be removed, even temporarily. To avoid reducing the lateral resistance of the deep foundations, an offset of 100 ft is recommended adjacent to the towers. STOCKPILE LOADING A stockpile is proposed on the west side of the property and is expected to be up to 40 ft high, offset a minimum of 60 ft from the overhead utility, buried Fiber optic line, and railroad. The engineering qualities of the in-situ overburden are not known, but the utilities and railroad are expected to be beyond the zone of influence of the increased loading imparted by [he stockpile as long as the minimum 60 ft separation is maintained. LIMITATIONS These analyses were based on limited available information about the site and were performed for the temporary slope condition. Site-specific investigations would better characterize the engineering parameters of the subsurface materials. Site-specific information may reduce the required setback for anear-vertical highwall, or may indicate that slopes steeper than 2.25H: 1 V can be excavated while maintaining a 25 ft setback. Reclamation slope fill has not been considered in these analyses.