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<br />2.3.1 Tunnel Sealing <br />Obviously, the aforementioned scenario would not be left unattended; it is presented only as a <br />worst case. The alternate closure plan would seal the haulage tunnel with a concrete bulkhead <br />plug. This plug would be placed approximately 1000' into the tunnel from the portal as <br />conceptually illustrated in Figure 3. Exact location would be selected based upon location of <br />geological structures and rock competency. Of note is the fact that rock in the haulage tunnel is <br />highly competent and timbering is not required for support; a situation which simplifies both <br />engineering and construction. <br />The bulkhead proposed for this closure plan is similar to bulkheads currently in use within the <br />Urad Mine. The design is heavily influenced by South African experience with plugs as old as 40 <br />years. These bulkheads were designed to: 1) insure that any leakage could be fully controlled, <br />and 2) assure structural integrity under the highest pressure predicted for the flooded mine. The <br />design pressure is 350 psi which represents predicted pressures if flooding were to occur to the <br />level of the Henderson glory hole. Using this maximum probable pressure and a 1.25 safety <br />factor, the bulkhead would be 22 feet in length. Concrete for this plug would be sulfate resistant, <br />type V with a design strength of 2500 psi. The concrete would contain fly ash to reduce <br />hydration heat and cracking and polypropylene fibers to further reduce cracking. A 3 mil thick <br />plastic film would be placed on the upstream side of the bulkhead to reduce the reaction of low <br />pH water with the face. <br />In order to monitor pressures behind the bulkhead, a 6 inch diameter 316 stainless steel pipe with <br />a gate valve would be placed in the plug. A polypropylene screen would be installed upstream of <br />the plug to catch debris that might clog the pipe. All of the piping and fittings would be rated for <br />600 psi or greater operating pressures, and all would be manufactured of 316 stainless steel. <br />2.3.2 Pumping and Water Discharge <br />Once the bulkhead was installed, the 200-300 gpm of water entering the mine through the tunnel <br />would be halted; slowing the length of time needed to flood the mine and ultimately reducing the <br />amount of water to be pumped and treated. Once bulkead construction was complete, the <br />Henderson Mine workings would be allowed to flood naturally to the 8100' level (Figure 1); still <br />887' below the tunnel portal. When the water level reached the 8100' level, the existing pumping <br />station at that level in the No. 2 Shaft (Figure 1) would be reactivated. Water would be pumped <br />to the surface, heated via alkaline precipitation (present technology) at the No. 1 Shaft surface <br />treatment facilities, and discharged as per conditions of the CPDS Permit then in effect. <br />A critical and obvious question i^ this alternate closure plan regards flooding timelines and rates. <br />4 <br />