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IV - DESIGN ANALYSIS AND CRITERIA <br />The proposed mining slopes were analyzed using the XSTABL v5 computer program. XSTABL <br />was designed to analyze the slope stability of earth embankments subjected to several critical <br />situations that may occur during the life of the embankment. Static and pseudo-static conditions <br />were analyzed in each case. <br />Pseudo-static peak acceleration factors were taken from USGS information for the western <br />United States. The 2% probability of exceedance in 50 years (the most conservative) was used. <br />Surface loads equivalent to an HS 20 highway load or an 80,000 pound railroad load were <br />applied adjacent to each area, when applicable, to simulate heavy equipment loading that could <br />be present at that location. <br />For this project, seven cases were identified as critical during the mining operation: <br />Case A - Existing Prowers County Road HH.5, existing underground telephone <br />line, and existing underground gas line to the south. The mining operation is <br />adjacent to numerous man made structures in this area. The proposed setback for <br />mining is 65 feet from the proposed permit boundary, and 75 feet from the edge of the <br />existing County Road HH.5. The mining depth was assumed to be 44 feet in this area <br />based on bore log information in the JAC report. The mining side slope in this location <br />will vertical. <br />Case B - Omitted <br />Case C - Potential Future Multi-use GP Rail Spur. Note that the rail spur will be <br />owned by GP and therefore does not fall under DRMS's setback requirements. <br />This case has been analyzed to assure GP that the mining slope/setback will <br />provide adequate protection for the potential future multi-use rail spur. The mining <br />operation is adjacent to a potential future multi-use rail spur in this area. The proposed <br />setback for mining is 80 feet from the future rail spur. The mining depth was assumed to <br />be 67 feet in this area based on bore log information in the JAC report. The mining side <br />slope in this location will 2h:ly. <br />Case D - Existing parcel reserved for future highway infrastructure to the west. <br />The mining operation is adjacent to an existing parcel reserved for future highway <br />infrastructure in this area. The proposed setback for mining is 95 feet from the parcel. <br />The mining depth was assumed to be 71 feet in this area based on bore log information <br />in the JAC report. The mining side slope in this location will be vertical. <br />Case E - Existing irrigation ditch to the south. The mining operation is adjacent to an <br />existing irrigation ditch in this area. The proposed setback for mining is 85 feet from the <br />closest irrigation ditch bank. The mining depth was assumed to be 63 feet in this area <br />based on bore log information in the JAC report. The mining side slope in this location <br />will be vertical. <br />West Farm Gravel Pit <br />Slope Stability Analysis <br />Page 2