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TETRA TECH Updated Tucson South Proposed Gravel Mine Slope Stability Analysis <br /> N <br /> November 8 2019 <br /> Section E—Gas Well West of the Proposed West Pit Boundary <br /> Section E (static analysis Figures E-1; seismic analysis Figures E-2) evaluated the proposed setback for an <br /> existing gas well to the west of the proposed West Pit boundary. A mud lens is modeled based on previous <br /> studies in the area'. The aggregate layer is noticeably thinner in this area. The weight of a tank in the area is <br /> simulated by a 3,000 psf load. The proposed slurry wall is modeled 15 feet from the edge of a gravel apron for the <br /> well. The water table on the west side of the slurry wall was modeled at approximately seven feet below ground <br /> surface. The water table was not modeled above the mud lens on the east side of the slurry wall since the pit is <br /> assumed to be dewatered. The gravel apron was the critical location in the model. <br /> Section F—Power Poles to the West of the Proposed West Pit Boundary <br /> Section F (static analysis Figures F-1; seismic analysis Figures F-2) evaluated the proposed setback for the <br /> power poles to the west of the proposed West Pit boundary. The closest power pole to the proposed mine <br /> boundary was modeled. A mud lens was present and modeled based on previous studies in the area'. The <br /> proposed slurry wall is modeled. The overburden is assumed to be approximately constant in thickness. The <br /> existing grade at the location would prevent the cutting of a mine slope, only a reclamation slope was considered <br /> for this cross section. <br /> Section G— Brighton Ditch <br /> Section G (static analysis Figures G-1; seismic analysis Figures G-2) evaluated the proposed setback for the <br /> Brighton Ditch to the west of the proposed West Pit boundary. The section of the ditch closest to the proposed <br /> mine boundary was modeled. The proposed slurry wall is modeled 15 feet inside of the affected land boundary. <br /> The overburden is assumed to be approximately constant in thickness. The existing grade at the location would <br /> prevent the cutting of a mine slope, only a reclamation slope was considered for this cross section. A mud lens is <br /> not modeled based on previous studies in the area'. The setback presented is measured from the affected land <br /> boundary. <br /> Section H —Highway 7 from North Cell (East) <br /> Section H (static analysis Figures H-1; seismic analysis Figures H-2) evaluated the proposed setback for Highway <br /> 7 to the south of the proposed East pit boundary. A mud lens is not modeled based on previous studies in the <br /> area'. The proposed slurry wall is modeled. A 500 psf load was modeled to simulate traffic on Highway 7. A <br /> power pole adjacent to Highway 7 is used as the critical structure for the setback. Right-of-way requirements may <br /> increase the required offset for this section. <br /> Section I— Highway 7 from South Cell <br /> Section I (static analysis Figures 1-1; seismic analysis Figures 1-2) evaluated the proposed setback for Highway 7 <br /> and a power line to the north of the proposed South pit boundary. A mud lens was present and modeled based on <br /> previous studies in the area7.A slurry wall will not be constructed around the cell and is not modeled. A steady <br /> state phreatic surface was modeled along the top of the mud seam, and daylights along the cut slope to model <br /> open pit dewatering. A 2H:1V mine slope was modeled to increase yield from the pit, the reclamation slope <br /> remained at 3H:1V. A 500 psf load was modeled to simulate traffic on the Highway 7. A 200 psf load was <br /> modeled to simulate the weight of a screening berm on the north side of the South Cell. <br /> Section J— Brighton Return Ditch <br /> Section J (static analysis Figures J-1; seismic analysis Figures J-2) evaluated the proposed setback for the <br /> Brighton Return Ditch to the southwest of the proposed South pit boundary. A mud lens was present and modeled <br /> based on previous studies in the area'. A slurry wall will not be constructed around the cell and is not modeled. A <br /> steady state phreatic surface was modeled along the top of the mud seam, and daylights along the cut slope to <br /> model open pit dewatering. A 2H:1V mine slope was modeled to increase yield from the pit, the reclamation slope <br /> remained at 3H:1 V. In order to comply with regulatory stability requirements, without increasing mine setback <br /> limits, the phreatic surface must be dewatered as to not seep down the face of the mine slope. The ditch was <br /> modeled with approximately five feet of water. <br /> Section K—Gravel Road and Waterline <br /> Section K(static analysis Figures K-1; seismic analysis Figures K-2) evaluated the proposed setback for a <br /> building and gravel road and waterline to the west of the proposed South pit boundary. A mud lens was present <br /> and modeled based on previous studies in the area7.A slurry wall will not be constructed around the cell and is not <br /> modeled. A steady state phreatic surface was modeled along the top of the mud seam, and daylights along the <br /> cut slope to model open pit dewatering. A 2H:1V mine slope was modeled to increase yield from the pit, the <br /> reclamation slope remained at 3H:1V. The waterline adjacent to the gravel road is the critical structure. A 3000 <br /> TETRA TECH <br />