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JOHN F. ABEL, JR. <br />MINING ENGINEER <br />310 LOOKOUT VIEW COURT <br />GOLDEN, CO 80401 <br />303279/801 <br />FA?C 278-8183 <br />JFAbsI~C«nup.net <br />July 14, 2003 <br />Mr. Steve Fearn <br />Silver Wing Co. <br />P.O. Box 299 <br />Silverton, CO 81433 <br />Reference: Bulkhead design, Mogul Mine, No. 1 Level <br />Dear Steve: <br />This letter report presents the bulkhead design for the No. 1 <br />Level drainage tunnel for the Mogul Mine. A 9-ft thick bulkhead <br />is recommended for the 8-ft wide, 8-ft high tunnel section between <br />Stations 2+41 and 2+50, indicated on the Figure 1 plan view and <br />Figure 2 cross section. The bulkhead sill elevation is <br />approximately 11,422-ft. The bulkhead requires two-way cage of 60 <br />ksi #6 rebar (3/4-in diameter) on 12-in centers for tensile, <br />shrinkage and temperature reinforcement at the downstream side and <br />the same rebar cage for shrinkage and temperature reinforcement at <br />the upstream side. The bulkhead will include a 6-in schedule 40 <br />stainless steel bypass pipe and gate valve to allow the mine pool <br />to be drawn down if and when required. <br />DESIGN CRITERIA <br />The purpose of the bulkhead is to impound the maximum 150 gpm <br />of acidic (range from a pH of 1 to a pH of 5) and sulfate bearing <br />(range from 600 to 900 ppm) water that flows out the No. 1 Portal <br />during an annual cycle. Figures 1 and 2 indicate a direct <br />connection between the tunnel and the ground surface through a <br />crosscut from the tunnel to the "212-ft Raise to Surface". The <br />maximum static hydraulic head will develop on the bulkhead if <br />water flows out the lowest collar elevation of the "212-ft Raise <br />to Surface", approximate elevation of 11,640-ft. The maximum <br />static hydraulic head is 218-ft above the bulkhead, a hydraulic <br />pressure of 94 psi. The design maximum 0.094 g horizontal <br />earthquake acceleration was calculated from the maximum credible <br />6.5 magnitude earthquake along the Ridgeway Fault, 24 miles to the <br />north-northwest. Previous earthquake studies for the Sunnyside <br />Gold Corp. tailings at Gladstone (Sullivan, et al, 1980; Weisser, <br />1982; Knight Piesold Co., 1988) predicted a maximum credible <br />horizontal acceleration of 0.087 g at Gladstone, 25 miles <br />