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Mr Raymond Lazuk June 28, 2017 <br /> Climax Molybdenum Company, Climax Mine 8 1661214 006 RSP RevO <br /> 1.3 Built in Conservatism <br /> Golder would like to summarize some of the conservative assumptions used in the stability analysis. <br /> Changes to any of these assumptions to represent more realistic or expected conditions would increase <br /> the FoS. <br /> ■ Cross sections cut in worst-case locations using worst case OSF geometry. Stability <br /> performed using 2D methods that do not account for potential 3D buttressing effects. <br /> ■ Conservative seismic reoccurrence interval events selected for use in analysis (OBE and <br /> MDE) <br /> ■ Conservative approach (Hynes and Franklin 1984) used for pseudo-static analysis <br /> ■ Residual (not peak)strengths used in analysis <br /> ■ Material strengths reduced by 20%for pseudo-static analysis <br /> ■ Overburden strengths are considered conservative. Strength is based on large scale direct <br /> shear testing (12-inch diameter shear box) of finer portion of material. Including <br /> consideration for oversize materials would increase strength considerably. <br /> ■ Strengths for Lincoln, Maroon, and Minturn formations are conservative. Strengths are <br /> based on laboratory testing of the "worst case" residual soil weathered from these <br /> formations. Golder is aware that the CGS performed a review of the Golder(2017) stability <br /> evaluation. CGS noted that in other locations the Minturn Formation is known to have lower <br /> shear strengths than those used in the analysis. The Minturn Formation is known to be <br /> thousands of feet thick, spanning across multiple quadrangles, with significant variations <br /> in makeup between different members (CGS 2004). The material tested in Golder(2017) <br /> represented the lowest strength portion of the formation encountered below the proposed <br /> Climax OSFs, consisting of the most weathered, finest grained, highest clay content <br /> material Outside of the OSF area in other parts of the state lower strength, material <br /> undoubtedly exists. However, the materials tested in Golder (2017) do represent the <br /> weakest portion of the Minturn Formation encountered across the borings and test pits <br /> within the OSF footprint. <br /> ■ Cross-sections do not consider increase in average formation strength with depth as <br /> weathering decreases. For example, Minturn sandstone at a depth of 100 feet was <br /> modeled using the same strength parameters as the residual soils. <br /> 4.0 CLOSING <br /> Golder appreciates the opportunity to present this additional information to justify the use of the stability <br /> design criteria as presented in Golder(2017). Should you have any questions or comments pertaining to <br /> the information presented herein, please do not hesitate to contact the undersigned. <br /> Sincerely, <br /> GOLDER ASSOCIATES INC. <br /> �" 4X,01 "/a� <br /> David Geier Brent Bronson, PE <br /> Senior Project Engineer Project Director and Principal Engineer <br /> DG/BB/rjg <br /> Golder} <br /> 1661214 006 RSP RM Responses to DRMS Comments 28JUN17 docx xnodates <br />