2018-07-10_PERMIT FILE - M2018037 (4)

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Mr. Mark Johnson May 31, 2018 Page 3 • Grasshopper Well Head (East of NW Cell, Kerr-McGee/Anadarko) • Inouye 11-31A Well Head (East of NE Cell, Kerr-McGee/Anadarko) • Vynckier Donald Gu B NO2 Well Head (East of NE Cell, Kerr-McGee/Anadarko) • Inouye 15-31A Well Head (East of NE Cell, Kerr-McGee/Anadarko) • Fiber Optic in WCR 14.5 ROW(North Boundary, Century Link) • Lupton Bottom Ditch (Between NW& NE Cell) • Fort Lupton Waste Water Pond (South Boundary) STABILITY ANALYSES Recently, Division of Reclamation and Mining Safety(DRMS) staff drafted a policy regarding stability analyses of neighboring structures. The draft summarizes adequate factors of safety(FOS)for non-critical and critical structures. The structures around the Inouye mine are, for the most part, considered critical structures. Discussions the author of the memo, Mr. Tim Cazier, indicate the FOS will be adopted by the MLRB. The FOS are for both static and seismic (from an earthquake)stability analyses. For generalized strength assumptions and critical structures, an FOS of 1.5 is considered sufficient for static conditions and an FOS of 1.3 is considered suitable for seismic conditions. The stability of structures within 200 feet of the proposed mining limits was evaluated at six sections under anticipated loading conditions around the perimeter of the site as discussed below. The computer program XSTABL was used for the analysis. The method for selecting the critical failure surface for each analyzed loading condition is the following. The Modified Bishop's Method of Analysis is used to find the critical failure surface by randomly searching with 20 termination points and 20 initiation points (400 failure circles)with 7 foot line segments over a broad range of the slope surface and at the structure in question. This procedure is repeated over different initiation and termination locations until the most critical factor of safety failure surface is identified. The range is narrowed and 20 initiation points and 20 termination points (400 failure circles) with 7 foot line segments for the final run of 400 circles to determine the lowest factor of safety. Therefore, prior to submitting the final stability run, at least 800 failure surfaces were analyzed to determine the lowest factor of safety. Both static stability under anticipated mining conditions and seismic stability under peak ground acceleration loads were performed. Seismic loading was obtained from the U.S.G.S. Unified Hazard Tool. Review of the Hazard Tool indicated a maximum horizontal acceleration of 0.091g with a return period of 2,475 years for the site. The six cross section locations were selected and analyzed as described below. All of the cross sections were modeled with a nearly vertical high wall of 0.5:1 (horizontal:vertical) at the mine limit. The locations are shown on the attached Figures. ► Section 1: This section is on the west side of the southwest cell and considers the point where the tallest mine high wall (deepest bedrock) in this cell is closest to a critical structure (the overhead power line). The power line is approximately 47 feet from the mine limit. This is also an area where an off-site pond is nearby and the groundwater table will be more elevated. ► Section 3: This section is on the west side of the northwest cell and considers the point where the tallest highwall on the west side of this cell comes closest to the United power line. The power line is approximately 78 feet from mine high wall. ► Section 4: This section is on the south side of the northwest cell and considers the point where the Kerr- McGee/Anadarko gas line is closest to the mine. The gas line is approximately 52 feet from the mine high wall. ► Section 6: This section is on the north side of the northwest cell and considers the point with the tallest high wall in this cell is closest to the United power line on the south side of WCR 14.5. The power line is approximately 85 feet from mine high wall.