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Ralston Quarry —Permit No. M-1974-086/AM-03 Stability Analysis, Preliminary Adequacy <br />Review <br />Page 2 <br />March 6, 2015 <br />The results table in Section 1.4 of the July 22, 2014 Brierley letter does not provide <br />results for a north dipping analysis. Please address the FOS for the north dipping slope. <br />3. July 22, 2014 Letter, Section 1.5 — The first paragraph on the top of page 3 states "...east <br />dipping slopes will be controlled by the shale/basalt contact." It is unclear from this <br />statement whether the dip refers to the shale - basalt contact plane or the slope of the <br />mined highwalls, especially when considering the third column in the table of results in <br />Section 1.4, "Slope Dip Angle ", which appears to be vertical for both the "West Dipping" <br />analyses. The Division is concerned about how the analyses performed relates to the <br />proposed mine plan with respect to the amount of basalt left after mining between the <br />shale layer and the corner at the intersection of the highwall toe and the top of a given <br />bench. In other words, if each bench were drilled to contact with the shale layer, the <br />basalt wedge would most likely be unstable. Please clarify the configuration modeled in <br />SWEDGE and how it relates to the proposed mine benching plan as it relates to the <br />basalt/shale contact. A geologic cross - section might be helpful in explaining the <br />correlation here. <br />Greg Lewicki And Associates Comment <br />4. Geotechnical Stability Exhibit, Section 1.1 and Map C -4 — According to Brierley's July <br />22, 2014 "Additional Slope Evaluation Letter ", the analysis for the East Dipping Overall" <br />requires a Slope Dip Angle of 73 degrees (reference Section 1.4 Results Table). Sections <br />D -Q' and E -E' on Map C -4 call out "Detail A" for the West Slope (east dipping). <br />Section 1. Lc, d of the Geotechnical Stability Exhibit state a minimum bench width of 14 <br />feet and a maximum bench height of 80 feet, presumably as limits to reach the overall dip <br />slope of 73 degrees. Based on the Division's calculations, the 14 feet to 80 foot ratio <br />results in a dip angle of 80.1 degrees, which of course exceeds the 73 degree dip analyzed <br />by Brierley required to achieve the 1.35 FOS. Please explain how the 14 -foot minimum <br />bench width maintains the maximum 73- degree overall dip slope or revise both Map C -4, <br />Detail A and Section 1.1 of the Geotechnical Stability Exhibit. <br />If either you or the applicants have any questions regarding the comments above, please call me <br />at (303) 866 -3567, extension 8169. <br />