2007-08-10_REVISION - M2001107 (4)

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IV -DESIGN ANALYSIS AND CRITERIA The proposed mining slopes were analyzed using the XSTABL v5 computer program. XSTABL was designed to analyze the slope stability of earth embankments subjected to several critical situations that may occur during the life of the embankment. Static and pseudo-static conditions were analyzed in each case. Pseudo-static peak acceleration factors were taken from USGS information for the western United States. The 2% probability of exceedance in 50 years (the most conservative) was used. Surface loading equivalent to an HS 20 highway load was applied adjacent to each area to simulate heavy equipment loadittg that could be present at that location for maintenance or construction activities. There are existing oil and gas wells located in the areas where mining is proposed. The oil/gas companies that own the wells require that a surface use agreement between the oil/gas company and the mine operator be signed before mining can be done adjacent to their wells. Normally the mining setback from any well that the oil/gas companies require is much larger than slope stability would dictate. Therefore, no slope stability analysis has been done for these areas. For this project, eight cases were identified as critical during the mining operation: Case A -Proposed irrigation pipeline, proposed gas line, existing overhead electric transmission line, WCR 25, and existing building to the east. The mining operation is adjacent to numerous man made structures in this area. The proposed setback for mining is 55 feet from the proposed irrigation pipeline, 75 feet from the WCR 25 right-of--way, and 105 feet from the property line. The mining depth was assumed to be 34 feet in this area based on bore log information in the Terracon report and addendum. The mining side slope in this location will be near vertical for the bottom half of the slope and 0.5h:1v for the top half of the slope. Case B - Proposed irrigation pipeline, proposed gas pipeline, existing underground electric service line, and existing building to the north. The mining operation is adjacent to numerous man made structures in this area. The proposed setback for mining is 55 feet from the proposed irrigation pipeline and 120 feet from the property line. The mining depth was assumed to be 34 feet in this area based on bore log information in the Terracon report and addendum. The mining side slope in this location will be near vertical for the bottom half of the slope and 0.5h:1v for the top half of the slope. Case C -Proposed gas pipeline, two existing gas pipelines to the north. The mining operation is adjacent to numerous man made structures in this area. The proposed setback for mining is 55 feet from the proposed gas pipeline and 100 feet from the property line. The mining depth was assumed to be 31 feet in this area based on bore log information in the Terracon report and addendum. The mining side slope in this location will be near vertical for the bottom half of the slope and 0.5h:1v for the top half of the slope. Rankin PropeRy Gravel Pif Ezpansbn Project Sbpe Stability Analysis Page 2