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Mr. Mark Johnson <br /> January 24, 2020 <br /> Page 6 <br /> STABILITY ANALYSES RESULTS <br /> The stability analyses assumed the mining will be per the mine plan. The plan includes dewatering with a series of <br /> perimeter drains in Cells 1 and 2b and perimeter highwalls of 2 horizontal to 1 vertical. Dry mining will occur in cells 2a <br /> and 3 as the water level in these cells will be controlled by slurry walls. The perimeter mine slopes of cells 2a and will be <br /> no steeper than 3H:1 V. <br /> Setbacks listed in Table 1 (below) indicate the setback from the structure to the mining limits. The setback distance can <br /> be increased as needed to address other restrictions such as weaker than anticipated soils, deeper mining, or <br /> unanticipated groundwater. <br /> The factor of safety shown below in Table 1 is the minimum factor of safety of the conditions listed above. <br /> TABLE 1 -SLOPE STABILITY RESULTS AND SETBACKS <br /> Cell Section Critical Structure Static Factor of Seismic Factor of DRMS Draft FOS <br /> Structure Setback From Safety at Safety at Structure Requirement <br /> Mine Limit ft Structure 0.096 horizontal Static/Quake <br /> Cell D Last 31 2.1 1.5 1.511.3 <br /> Chance <br /> Ditch <br /> Cell F Fence 25 2.1 1.5 1.511.3 <br /> Cell 1 G Rural Ditch 17 1.6 1.3 1.511.3 <br /> Cell 2a B Gravel 45 2.6 1.7 1.511.3 <br /> Road <br /> Cell 2a E Fence 47 2.8 1.8 1.511.3 <br /> Cell2b A Fence 20 1.8 1.4 1.511.3 <br /> Cell C Drainage 45 2.7 1.8 1.511.3 <br /> Channel <br /> Pond A H Gas Line 31 2.1 1.5 1.511.3 <br /> Pond A I Rural Ditch 74 3.2 1.8 1.511.3 <br /> CONCLUSIONS <br /> Based on the Factors of Safety listed in the table above,the mine will not be a hazard to neighboring structures provided <br /> the structure and slurry wall offsets, as well as the perimeter mine slopes,follow the mine plan. <br /> LIMITATIONS <br /> Our review is based on regional geologic mapping, present mining plans, and in part borehole data by Civil Resources <br /> and others. Stability analyses were performed using typical strength parameters for the various strata in the critical <br /> sections. Should the mining plans change or subsurface conditions vary from those portrayed in this letter,we should be <br /> contacted in order to re-evaluate the potential affects on permanent man-made structures. Stability analyses were run at <br /> the structure in question and were not run on failure surfaces closer to the highwall. Note also that surcharge loads due <br /> to temporary material stockpiles and overburden berms were not considered in the analysis. <br /> Please call with any questions or comments. <br /> Sincerely, <br />