2015-04-13_REVISION - M1974086 (6)

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Tim Cazier Item 3. July 22, 2014 Letter, Section 1.5 — The first paragraph on the top of page 3 states "..east dipping slopes will be controlled by the shale/basalt contact. "It is unclear from this statement whether the dip refers to the shale - basalt contact plane or the slope of the mined highwalls, especially when considering the third column in the table of results in Section 1. 4, "Slope Dip Angle"; which appears to be vertical for both the "West Dipping" analyses. The Division is concerned about how the analyses performed relates to the proposed mine plan with respect to the amount of basalt left after mining between the shale layer and the corner at the intersection of the highwall toe and the top of a given bench. In other words, if each bench were drilled to contact with the shale layer, the basalt wedge would most likely be unstable. Please clam the configuration modeled in SWEDGE and how it relates to the proposed mine benching plan as it relates to the basalt /shale contact. A geologic cross - section might be helpful in explaining the correlation here. See the April 2, 2015 Brierley letter attached to this response. Geologic information can also be found on Map B -2. Tim Cazier Item 4. Geotechnical Stability Exhibit, Section 1.1 and Map C -4 — According to Brierley's July 22, 2014 'Additional Slope Evaluation Letter ", the analysis for the East Dipping Overall" requires a Slope Dip Angle of 73 degrees (reference Section 1.4 Results Table). Sections D- D' and E -E' on Map C -4 call out "Detail A "for the West Slope (east dipping). Section 1.1. c, d of the Geotechnical Stability Exhibit state a minimum bench width of 14 feet and a maximum bench height of 80feet, presumably as limits to reach the overall dip slope of 73 degrees. Based on the Division's calculations, the 14 feet to 80 foot ratio results in a dip angle of 80.1 degrees, which of course exceeds the 73 degree dip analyzed by Brierley required to achieve the 1.35 FOS. Please explain how the 14 foot minimum bench width maintains the maximum 73- degree overall dip slope or revise both Map C -4, Detail A and Section 1.1 of the Geotechnical Stability Exhibit. The bench height and width minimums and maximums are not the primary controlling factor in the final configuration of the East Dipping slope. The overall slope dip of 73 degrees will be the controlling factor. As an example, if Asphalt Paving Co. wishes to mine a bench with a width of 14 feet, they must maintain a suitable bench height that will maintain an overall slope of greater than 73 degrees. Similarly in the event of an individual bench being mined to a height of 80 feet, the bench must then be wide enough to maintain the overall slope angle of 73 degrees or less. 3