2008-11-26_PERMIT FILE - M2008080 (7)

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geotechnical reports. The mining side slopes in this location will be 3h:1v to 10 feet below the expected water surface, and 2h:1 v from that point down to the pit bottom. A horizontal bench will be located in the slope 3 feet above the expected water surface to facilitate the construction of the slurry wall. Case 6 - Existing oil/gas wells and tank battery to the southeast. The mining operation is adjacent to existing oil/gas wells and an existing tank battery in this area. The proposed setback for mining is 150 feet from the existing oil/gas wells and existing tank battery. The mining depth was assumed to be 80 feet in this area. Bore log information in the geotechnical reports shows the depth of the gravel to be greater than 80 feet in this area, however mining will terminate at a depth of 80 feet to maintain the stability of the mining slope. The mining side slopes in this location will be 3h:1v to 10 feet below the expected water surface, and 2h:1v from that point down to the pit bottom. Case 7 - Existing Plumb Ditch, south branch, to the north. The mining operation is adjacent to an existing ditch in this area. The proposed setback for mining is 25 feet from the proposed permit boundary/existing ditch bank. The mining depth was assumed to be 80 feet in this area. Bore log information in the geotechnical reports shows the depth of the gravel to be greater than 80 feet in this area, however mining will terminate at a depth of 80 feet to maintain the stability of the mining slope. The mining side slopes in this location will be 3h:1v to 10 feet below the expected water surface, and 2h:1v from that point down to the pit bottom. The cross-sections located in Appendix B show the proposed mining slope geometry, estimated phreatic surface, location of the man made structures relative to the mining slope, and location of the most critical slope failure surface for each case. V - METHODOLOGY The mining embankment configuration shown in the computer analysis represents the estimated conditions for this site. If mining conditions differ from the estimated conditions, the slope stability will need to be re-evaluated on a case by case basis. The Bishop Method was used in the computer analysis for determining safety factors. The procedure searches for circular shear failures and automatically searches for the lowest safety factor. 2,000 separate failure surfaces were analyzed for each case. The required minimum safety factors are based on the current standards used by the Colorado State Engineer's Office (SEO) in evaluating embankment dams, and industry accepted standards for the evaluation of temporary structures during construction. Journey Ventures, LLC - Kersey Gravel Pit Slope Stability Analysis Page 3