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Mr. Jeff Gregg January 5, 2006 Page 3 STABILITYANALYSES ~~ CIVIL RES~URCES,LLC The stability of the proposed mining limits was evaluated (at six sections at Phases 1 and 2 and two sections at Phase 3) under anticipated and required loading conditions around the perimeter of the site, 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. Modified Bishop's method of analysis is used to find the critical failure surface by randomly searching with 15 termination points and 15 initiation points (225 failure circles) over a broad range of the slope surface. 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 for the final run of 225 circles to determine the lowest factor of safety. The final stability run analyzes the critical surface using the Spencer method by inputting the X and Y coordinates of the circle center and the X; location of the intersection of the circle with the ground surface. The Spencer method is preferred because it is able to satisfy both moment and force equilibrium, but can only analyze one surface at a time. Therefore, prior to submitting the final stability run, at least 600 failure surfaces were analyzed to determine the lowest factor of safety. The eight cross-section locations were selected to analyze minimum setbacks for stability of structures, using appropriate surcharge loads, for the mining limits. Phases 1 and 2 (Sections A through F) are modeled with a 0.5:1 (H:V) highwall and does not include a slurry wall. All mining slopes in Phase 3 are modeled to be no steeper than 3:1 (H:V). Phase 3 was modeled to include asoil-bentonite slurry wall (Sections G and H). The locations are described below and shown on Figure 1. - Section A-A': This section considers the closest distance to WCR 23.75 along the northern margin of Phase 1. A surcharge of 250 psf was included to model the live load on WCR 23.75. - Section B-B': This section considers the existing concrete ditch along the southern portion of Phase 1. A high phreatic surface was included to model the maximum water surface from the ditch. - Section C-C': This section considers a storage building on the Lujan property along the western margin of the site. A surcharge of 1500 psf was included to model the dead load from the building. - Section D-D': This section considers a storage building on the Parker property along the western margin of Phase 2. A surcharge of 1500 psf was included to model the dead load from the building. - Section E-E': This section considers the closest distance to WCR 23.5 and utilities in the road ROW along the western margin of Phase 2. A surcharge of 250 psf was included to model the live load on WCR 23.5. - Section F-F': This section considers the closest distance to WCR 23.5 along the southern margin of Phase 3. A surcharge of 250 psf was included to model the live load on WCR 23.5. - Section G-G': This section considers a storage building on the Kirkpatrick property along the northern margin of Phase 3. A surcharge of 500 psf was included to model the dead load from the building. The proposed slurry wall was modeled at 40 feet and 50 feet from the existing property line. - Section H-H': This section considers the closest distance to the Mountain View Water Users Association waterline, utilities in the road ROW and WCR 23.5 along the western margin of Phase 3. A surcharge of 250 psf was included to model the live load on WCR 23.5. The proposed slurry wall was modeled at 40 feet and 50 feet from the existing property line. The material index and engineering strengths assumed in this slope stability report are discussed below.