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~. <br />NUMBERED RESPONSES TO QUESTIONS AND CONCERNS STATED DURING MEETING <br />OF AUGUST 27, 1979: <br />4. A discussion of the pre-mine and post-mine hydrology will be submitted <br />during the week of September 17. <br />5. The following discussion regarding pit wall stability was taken from the <br />Pit Design Engineer's report to the Manager of Engineering. <br />"The initial set of computer generated pit designs contained several <br />slopes in the 500-60 range. A qualitative review of the lithology and <br />potential structure indicated that these slopes were excessively steep. <br />The high ore value combined with the generally non-gradational nature <br />of the mineralization indicated that the ultimate pit economics would <br />probably not be overly sensitive to slope angle. <br />"Consequently, slopes were selected by setting the inter-ramp slopes <br />at the estimated angle of repose for various rock types, followed by <br />judiciously combining estimated inter-berm slopes with desired berm <br />widths to a geometrically viable configuration. The overall effect <br />is to eliminate the possibility of a major wall failure by limiting <br />potential failures to the inter-berm slopes which are steeper than <br />the angle of repose. <br />"The predominant rock types are mudstone and sandstone, but the sugar <br />sand has been included as a separate design unit due to its highly in= <br />competent nature. The following slopes have been utilized: <br />Sandstone Mudst~e Su ar and <br />Inter-Ramp Slope 44b1 352 2401 <br />Inter-Berm Slope 55 45 32 <br />Vert. Berm Interval 60' 60' 60' <br />Berm Width 20' 25' 20' " <br />-6- <br />