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significantly greater than 1.50, which is used a basis for long -term stability, in our opinion, <br />the slope of the Gob Pile #4 is stable as constructed. Figure 1 below presents the results of <br />the analysis showing the slope as constructed and with the Bishop Simplified Method <br />results. Note that the failure plane is surficial and results in small - scale, localized failure <br />sites. No deep seated failure planes result from surfaces of the pile that approach 2.0 H: 1V. <br />Figure 1. Analysis results for Bishop Simplified method which resulted in the lowest and <br />therefore most conservative Factor of Safetv for the Gob Pile #4 slope as- constructed. <br />5ntetp Ene[oc <br />f <br />0.000 <br />i <br />t5 <br />0.500 <br />1.000 <br />� <br />File Name ORMS Re iced Pile #4.2012 As- &,k .sli <br />1.500 <br />Material. Name <br />Strength Type: Mohr - Coulomb <br />2.000 <br />t <br />Unit Weight: 125 bW <br />Cohesion: 100 psf <br />2.500 <br />Friction Angle 34 degrees <br />Water Surface: None <br />3.000 <br />Material Gob <br />3.500 <br />Strength type: Mohr- Coulomb <br />4.000 <br />Unit Weight: 110.5 bM <br />Cohesion: 0 list <br />4.500 <br />Friction Angle: 34 degrees <br />Water Surface- None <br />5.000 <br />5.500 <br />Method bishop simplified <br />FS. 1.536230 <br />6. 000f <br />Gob <br />Natna Sal <br />eoo uao r400 <br />CONCLUSIONS <br />Since the analyses presented in this letter indicate that small, surface related failures may <br />occur on slopes at or near 2.0 H: 1V, we recommend that the areas highlighted in the DRMS <br />letter of October 31, 2012 be surveyed to confirm the slopes in those areas. Any areas <br />steeper than 2.0 H: 1V should be re- graded to achieve a slope with a minimum F.S. of 1.5 as <br />required. <br />Thank you for the opportunity to work with you on this long -term project at the Bowie Mine <br />#2. If you have any questions about this analysis, please contact me at (970) 497 -8852 or <br />dan(@buckhorngeo.com. <br />Respectfully submiitted, G/ <br />J <br />Daniel C. Quigley, PE, PG 334 <br />Buckhorn Geotech, Inc. <br />NAL <br />Bowie Mine #2 — CWDA Pile # 4 <br />DRMS Response Analysis <br />Page 2of2 <br />PN 05- 126 -GEO <br />