2018-11-21_REVISION - M2004044 (22)

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1 N TETRA TECH Updated Tucson South Proposed Gravel Mine Slope Stability Analysis November 9, 2018 A total of eight sections were evaluated for the critical structures as follows and as shown in Figure 1. For all sections, the groundwater level on the pit side of the slurry wall was modeled at the base of the pit. Section 1 —Tucson St. Setback from the West Mine Pit Section 1, (static analysis Figure 2, seismic analysis Figure 3) evaluated the proposed setback for Tucson St. from the West Pit boundary. A 500 psf load is applied to the road to represent live traffic loads. A mud lens is present based on previous studies in the areas. No slurry wall is modeled, and the area is assumed to be dewatered by the slurry walls surrounding the property. Section 2—Tucson St. Setback from the East Mine Pit Section 2 (static analysis Figure 4, seismic analysis Figure 5) evaluated the proposed setback for Tucson St. from the East Pit boundary. A 500 psf load is applied to the road to represent live traffic loads. No mud lens is modeled based on previous studies in the areas. No slurry wall is modeled, and the area is assumed to be dewatered by the slurry walls surrounding the property. Section 3—South Platte River Section 3 (static analysis Figure 6, seismic analysis Figure 7) evaluated the proposed setback for the South Platte River from the East Pit boundary. The section where the South Platte River came closest to the proposed mine boundary was modeled. In general, the South Platte River is greater than 200 feet away from the proposed mine boundary. A mud lens is not modeled based on previous studies in the areas. The proposed slurry wall is modeled, and the area is assumed to have a groundwater table approximately three feet below ground surface on the east side of the slurry wall. Offset regulations may dictate the location of the slurry wall and the mine extents. Section 4—Pipeline North of the Proposed Mine Boundary Section 4 (static analysis Figure 8, seismic analysis Figure 9) evaluated the proposed setback for the pipeline north of the proposed East and West Pit boundaries. A mud lens is not modeled based on previous studies in the area6. The proposed slurry wall is modeled. The groundwater table on the north side of the slurry wall was modeled at approximately six feet below ground surface. Section 5—Gas Well West of the Proposed West Pit Boundary Section 5 (static analysis Figure 10, seismic analysis Figure 11) evaluated the proposed setback for the gas well to the west of the proposed West Pit boundary. A mud lens is modeled based on previous studies in the area6. The aggregate layer is noticeably thinner in this area. The weight of the gas well is simulated by a 3,000 psf load. The proposed slurry wall is also modeled. The water table on the west side of the slurry wall was modeled at approximately seven feet below ground surface. Section 6— Power Poles to the West of the Proposed West Pit Boundary Section 6 (static analysis Figure 12, seismic analysis Figure 13) evaluated the proposed setback for the power poles to the west of the proposed West Pit boundary. The closest power pole to the proposed mine boundary was modeled. A mud lens is not modeled based on previous studies in the area6. The proposed slurry wall is modeled. Groundwater on the west side of the slurry wall was modeled to be approximately two to five feet below the ground surface since the Brighton Ditch is also in the vicinity. Section 7—Brighton Ditch Section 7 (static analysis Figure 14, seismic analysis Figure 15) evaluated the proposed setback for the Brighton Ditch to the west of the proposed West Pit boundary. The section of the ditch closest to the proposed mine boundary was modeled. The proposed slurry wall is modeled. Groundwater on the west side of the slurry wall was modeled to be approximately one to three feet below the ground surface.A mud lens is not modeled based on previous studies in the area6. Section 8—Highway 7 Section 8 (static analysis Figure 16, seismic analysis Figure 17) evaluated the proposed setback for Highway 7 to the south of the proposed East and West Pit boundaries. A mud lens is not modeled based on previous studies in the area6. The proposed slurry wall is modeled, and the water table is assumed to be approximately 15.5 feet below ground surface on the south side of the slurry wall. A 500 psf load is modeled to simulate traffic on the highway. 6 Goss, C. (2004, May 25). RE: Material Quantities at Proposed Tucson South Resource; Tetra Tech RMC Job No. 19-3919.019.00. Longmont, CO: Tetra Tech. Page 315