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2.1. Active Mining Slope <br /> The active mining slope is proposed to range from 0.5H:1V to vertical.An analysis of the worst- <br /> case vertical slope resulted in a failure circle with a minimum Factor of Safety (FOS) < 1.5; the <br /> minimum DRMS requirement for slopes near critical structures using general inputs. Further <br /> analysis was conducted to determine the location of the failure slope with a FOS = 1.5. The <br /> resulting slope was approximately 27.8 feet from the crest of the active mining area. As described <br /> above, the minimum setback between the property line and mining is 25 feet, and the nearest <br /> structures are also within 25 feet of mining. Therefore, the current 25-foot setback is not adequate <br /> for containing the slope failure within the property or protecting nearby structures. <br /> 2.2. Final Mining Slope <br /> The active mining slope will be backfilled and graded with overburden to a 2H:1 V slope.An analysis <br /> of these slope conditions resulted in a failure circle with a minimum FOS < 1.5. Further analysis to <br /> determine the FOS = 1.5 failure slope result in a failure circle which extends approximately 6.3 feet <br /> from the mining crest, which is more than 18 feet from the property boundary and any nearby <br /> structures. Therefore, there is no risk to structures or areas outside of the property boundary <br /> resultant of mining during the final mining slope conditions. <br /> 2.3. Reclaimed Slope <br /> The reclaimed slopes are proposed to be 3H:1V, obtained by backfilling and grading the final <br /> mining slope with overburden. An analysis of these slopes resulted in a FOS = 2.03, which is more <br /> than sufficient to meet DRMS standards regarding slope stability. Additionally, this circular failure <br /> scenario was contained entirely on the reclaimed slope face. Therefore, the permanent slope <br /> conditions following mine reclamation pose no risk of failure outside the property or to any nearby <br /> structures. <br /> 3. Conclusion <br /> During the final mining conditions, the FOS = 1.5 failure slope will be contained within the property <br /> and isolated from nearby structures. This is assuming backfilled and graded 2H:1V slopes, as <br /> described in the current permit. This is sufficient to satisfy the DRMS requirements for slope <br /> stability. The permanent reclaimed condition of 3H:1 V backfilled slopes will have a FOS =2.04, <br /> which is also sufficient for DRMS requirements. <br /> The location of the FOS = 1.5 failure slope during the active mining condition is beyond the <br /> minimum 25' setback currently required by the approved permit. The failure slope is approximately <br /> 27.8 feet from the mining crest, while the property boundary and nearest structures are as close as <br /> 25 feet from the mining crest. Lewicki &Associates recommend that the applicant revise their <br /> mining plan and increase the minimum setback from structures and the property boundary to 30 <br /> Wattenberg West Slope <br /> Stability 4 0 Lcwicki&Associates <br /> May 2022 <br />