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Geotechnical Stability Exhibit <br />Geologic features at the Topaz Mine that may have associated hazards include natural highwalls <br />at the portal area and the constructed slopes of the waste rock area (WItA). Additionally, <br />explosives will be used during mining. Explosives have the potential to create geotechnical <br />instability. It is not expected that failure of any of these geologic features will result in off-site <br />impacts. <br />1.1 Naturalllighwalls <br />Surface excavations with attendant highwalls are not proposed, as all mining will be done using <br />underground methods. Natural highwalls exist in the portal area. L` areas of loose rock on the <br />highwalls present a safety concern, the loose rock will be pried down or stabilized in place with <br />rock bolts and metal mesh. <br />1.2 Waste Rock Area <br />Constructed slopes at the Topaz Mine include the WRA. The WRA will have a maximum bench <br />height of 70 feet and will be left at the angle of repose (approximately 1.5:1) during mine <br />operation. The WRA will be regraded to achieve final slopes of 2H:1 V or less steep. Based on <br />experience at the Topaz Mine and other mines in the Sunday Mine Complex, the constructed <br />slopes are expected to remain stable during mine operations. <br />1.3 Use of Explosives <br />Use of explosives at the Topaz Mine will occur inside the mine during production. Currently the <br />mine decline extends 4,000 feet south and is at an average depth of 500 feet below the ground <br />surface. Based on the distance from surface facilities and depth of the mine workings, explosives <br />are not expected to adversely affect any on-site or off-site surface aeeas. <br />S-IS-2007 Geotechnical Stability GS-1 <br />