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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 factor; 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 loading equivalent to an HS 20 highway load was applied adjacent to each area to <br />simulate heary equipment loading that could be present at that location for maintenance or <br />construction activities. <br />There are existing oil and gas wells located in the areas where mining will occur. A surface use <br />agreement with the Kerr-McGee Rocky Mountain Company (KMRMC) has been obtained for <br />the wells, transmission lines, and production areas located on the west boundary of the property <br />and in the northeast comer of the property. The setbacks from these wells, transmission lines, <br />and production areas that are specified in this agreement will be maintained throughout the <br />course of the mining activity. A surface use agreement with the KP Kaufman Company (KPK) is <br />currently being negotiated but has not yet been finalized for the well and transmission line <br />located approximately in the center of the property. The slope stability for the mining slope <br />around the KPK well and adjacent to the transmission line has been analyzed in Case 3 below. <br />NCCI will maintain the larger of the setbacks from these structures as specified in either the <br />draft surface use agreement or from the slope stability analysis results. <br />For this project, five (5) cases were identified as critical during the mining operation: <br />Case 1 -Existing Sand Hill Reservoir discharge channel to the south. The mining <br />operation is adjacent to the Sand Hill Reservoir discharge channel in this area. The <br />proposed setback for mining is 70 feet from the top of the north bank of the channel. The <br />mining depth was assumed to be 37 feet in this area based on bore log information in <br />the Terracon report and liner investigation. The mining side slope in this location will be <br />near vertical for the bottom half of the slope and 0.5h:1 v for the top half of the slope. <br />Case 2 -Existing Little Dry Creek to the west. The mining operation is adjacent to <br />Little Dry Creek in this area. The proposed setback for mining is 55 feet from the top of <br />the east bank of the creek. The mining depth was assumed to be 29 feet in this area <br />based on bore log information in the Terracon report and liner investigation. The mining <br />side slope in this location will be near vertical for the bottom half of the slope and 0.5h:1v <br />for the top half of the slope. <br />Case 3 -Existing KPK Oil\Gas well and transmission line. The mining operation <br />surrounds a KPK oil\gas well and is adjacent to the well's transmission line in this area. <br />The proposed setback for mining is 60 feet around the well and 60 feet adjacent to the <br />transmission line. The mining depth was assumed to be 37 feet in this area based on <br />bore log information in the Terracon report and liner investigation. The mining side slope <br />in this location will be near vertical for the bottom half of the slope and 0.5h:1v for the top <br />half of the slope. <br />NCCI Pif #1 <br />Slope Stability Analysis <br />Page 2 <br />