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

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Mr. Mark Johnson May 31, 2018 Page 5 Dry Unit Moist Unit Saturated Unit Weight(pco Weight(pco Weight(pco Cohesion C'psf Friction Angle�'° NA 112 115 0 0 STABILITY ANALYSES RESULTS The stability analyses assumed the mining will be per the mine plan. The plan includes dry mining in the northwest and northeast cells as water levels will be controlled by the slurry wall. The southwest cell will be dewatered by a series of trenches constructed below the mining level leading to a pump resulting in dewatered conditions at the mined slopes. The perimeter mine slopes will be no steeper than 0.5:1 horizontal to vertical. For conservatism, Civil Resources modeled the weaker overburden material as 5 feet thick effectively lowering the height of the stronger sand and gravel. The most critical sections (listed in Table 1 below) were analyzed. These critical sections were based on one or a combination of the following factors: 1)structure proximity, height of the mine highwall, and/or higher groundwater. Setbacks listed in Table 1 (below) indicate the setback from the structure to the mining limits. The setback distance can be increased as needed to address other restrictions. The factor of safety shown below is the minimum factor of safety of the conditions listed above. TABLE 1 - SLOPE STABILITY RESULTS AND SETBACKS Section Location Critical Structure Static Factor of Seismic Factor of DRMS Draft FOS Structure Setback From Safety at Safety at Structure Requirement Mine Limit ft Structure (0.091g horizontal Static/Seismic West side of Overhead 1 Southwest Cell Powerline 47 1.6 1.3 1.5/1.3 United Overhead 3 West side of Power Line 78 1.7 1.3 Northwest Cell 1.5/1.3 United 4 South side of Gas Line 52 1.6 1.3 1.5/1.3 Northwest Cell KM/A 6 North side of the Power Line 85 1.7 1.3 1.5/1.3 Northwest Cell United Southeast Side Lupton 7 of Northeast Bottom 96 2.0 1.4 1.5/1.3 Cell Ditch 8 North side of Water Line 82 1.6 1.3 1.5/1.3 Northeast Cell CWCWD Notes: KMA=Kerr-McGee/An ad arko CWCWD=Central Weld County Water District CONCLUSIONS Stability analyses were performed on the most critical sections listed above. Other structures will be safer due to increased distance from the mine highwall, shorter highwalls, and/or more favorable groundwater conditions. Based on the Factors of Safety listed in the table above,the mine will not be a hazard to neighboring structures provided the structure and slurry wall offsets, as well as the perimeter mine slopes, follow the mine plan. LIMITATIONS Our review is based on regional geologic mapping, present mining plans, and in part borehole data by Civil Resources and Cesare, Inc. Civil Resources is not responsible for work by others. Stability analyses were performed using typical