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9) Slope heights: highwalls before reclamation: maximum 40 feet bench height. <br /> Reclaimed slopes maximum 90 feet at 1:1 slope. For conservative analysis, 100 foot <br /> height was used. Calculations (see Enclosure 1) were performed using the <br /> Washington Slip Circle method (see References) and confirmed by "hand <br /> verification" using AutoCAD (see References: EMI 1 10-2-1902) and reviewed using <br /> "chart solutions" (EM1 1 10-2-1902, Appendix E). It should be noted that the <br /> geotechnical analysis is of the excavated highwalls, and is therefore very <br /> conservative for the buttressed highwalls with engineered backfill, with or without <br /> georeinforcement. <br /> 10) Post-placement use of site: Commercial/light industrial, with the slopes being <br /> identified as unused/available for wildlife, landscape/buffering zones. Some <br /> potential commercial/industrial use of the lower 20 feet of slopes is possible (for <br /> stacking and as part of storage bins/work areas). <br /> 11)Structures potentially adversely affected by slope failure: See Exhibit L (Revised). <br /> 11)Where there is the potential for off-site impacts due to failure of any geologic structure <br /> or constructed earthen facility, which may be caused by mining or reclamation <br /> activities, the Applicant shall demonstrate through appropriate geotechnical and <br /> stability analyses that off-site areas will be protected with appropriate factors of safety <br /> incorporated into the analysis. The minimum acceptable safety factors will be subject <br /> to approval by the Office, on a case-by-case basis, depending upon the degree of <br /> certainty of soil or rock strength determinations utilized in the stability analysis, <br /> depending upon the consequences associated with a potential failure, and <br /> depending upon the potential for seismic activity at each site. <br /> 1) Factor of safety(Simplified Bishop Method): 3.6. Factor of safety(slip circle method <br /> (Washington) 9.0. Other methods included FS ranging from 3 to 9. <br /> 2) Due to recent and current mining, conditions along the north side of the permit <br /> area have been able to be observed directly, within 20-30 feet of the permit <br /> boundary. Therefore there is a high degree of certainty regarding soil conditions <br /> and it is fairly simple to make good estimates of soil strength, moisture conditions, <br /> and other factors. <br /> 3) Less is known about soil conditions on the east and south sides, as mining has not <br /> been done as extensively. Therefore, it is assumed that conditions are similar to the <br /> north side, but this will need to be verified by frequent observation as mining <br /> proceeds in these areas. However, risks are less significant in these areas. <br /> 4) Based on analysis of general nature of potential impacts (next paragraph), specific <br /> mitigation measures are recommended in this report. Potential impacts: <br /> 1) Damage to ground surface on east and south sides of the site, due to mass <br /> movement (primarily slip circle failure). <br /> 2) Damage to metal pipe fencing along north side of site, due to mass movement <br /> (slip circle failure) or erosion. Unable to calculate FS due to erosion. <br /> 3) Damage to power poles on north side of site, due to mass movement (slip circle <br /> failure) or erosion. Unable to calculate FS due to erosion. <br /> 5) There is no significant potential for seismic impact on this site. <br /> 6) Backfill using engineered fill against the excavated face of the in-situ materials <br /> increases factor of safety for slope stability and can be further increased by use of <br /> geo-reinforcement, based on engineering evaluation of highwalls and benches. <br /> (Necessary actions identified in the "recommended actions.") <br /> Technical Revision to M1985-001 J&J Pit, LaPlata County, dated 24 AUG 2016 Page 27 <br />