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r <br /> Sunnyside Gold Corp. Page 3 March 10, 1993 <br /> EXECUTIVE SUMMARY <br /> This report contains designs for the four reinforced concrete <br /> bulkheads needed to impound the water currently passing through the <br /> Sunnyside Mine workings. The purpose of these bulkheads is to <br /> restore the pre-mining hydrology as best as possible to that <br /> present prior to mining. The bulkheads will prevent surface and <br /> ground water entering the Sunnyside Mine from moving through the <br /> low resistance mining developed flow paths, as is currently the <br /> situation. The four bulkheads will impound water in the mine, the <br /> water that is flowing through low resistance paths presented by <br /> mine workings. After completing bulkhead construction, impounded <br /> water will only be able to exit the Sunnyside Mine through either <br /> natural groundwater channels or at the maximum elevation of the <br /> mine pool, the 12210-foot elevation of the Lake Emma out-flow <br /> drainage ditch, or a variable combination of both. <br /> Impoundment of water within the Sunnyside Mine workings will <br /> significantly reduce the oxidation rate of sulfide minerals <br /> presently exposed to air in abandoned stopes, drifts and tunnels. <br /> Oxidation of metallic sulfides produces the metallic and sulfate <br /> ion contamination of the water draining from the Sunnyside Mine <br /> through the Terry Tunnel and the American Tunnel. The only oxygen <br /> available to oxidize sulfide minerals below the mine pool water <br /> level will be that dissolved in the water. Obviously, the oxygen <br /> content of even fully oxygen saturated water is lower than in air. <br /> once the oxygen in the impounded water is depleted it can only be <br /> replaced by water circulation to the mine pool surface. Once the <br /> bulkheads are closed, differential rock temperature should be the <br /> only energy source available to replenish depleted oxygen below the <br /> surface of the mine pool. This extremely low energy source will be <br /> resisted by the restricted and complicated potential flow paths <br /> within the mine. Careful design and construction of the bulkheads <br /> is essential because bulkhead leakage would serve as a gravity <br /> driven source of oxygen for sulfide mineral oxidation. <br /> The bulkhead locations were chosen to maximize the length of <br /> natural hydraulic flow paths and to minimize the potential for <br /> water leakage through the jointed rock adjacent to the bulkheads. <br /> Table 1 presents the geometric conditions at the four selected <br /> bulkhead locations. The factors of safety listed in Table 1 are <br /> for the critical flexural bending stress. These factors of safety <br /> are in relation to American Concrete Institute' s (ACI) Building <br /> Code Requirements for Reinforced Concrete (ACI 318-89) . The <br /> critical deep-beam, i.e. the bulkheads, flexural stresses will be <br /> resisted by two-way, horizontal and vertical, rebar reinforcement. <br /> The ACI code (Section 9 . 2 . 1) requires the design strength for a <br /> dead or fluid loaded reinforced concrete deep-beam structure to <br /> support 1. 4 times the maximum dead or fluid load. In addition, the <br /> ACI code requires a strength reduction factor for reinforced <br /> concrete in flexure of 0.90 (Section 9. 3 . 2 . 1) . This results in a <br /> minimum actual factor of safety of 1. 56 against flexure. In the <br /> case of shear, ACI requires a strength reduction factor of 0.85 <br /> (Section 9 . 3 . 2 . 3) . The actual minimum factor of safety against <br /> shear is 1 . 65. <br />