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Cross Mine(M1977-410) Technical Revision No.5 <br /> At a distance of approximately 250 ft from the new portal,the tunnel opening is known to increase to 12 <br /> ft x 12 ft as a result of exploration conducted during the 1950's and will not be enlarged as part of the <br /> proposed rehabilitation effort. <br /> Ground support for the proposed tunnel rehabilitation is anticipated to consist of various combinations <br /> of steel sets and lagging, shotcrete and rock bolts, rock bolts and wire mesh,fiber-reinforced shotcrete, <br /> spilt sets, and grouted thread-bar, as required by the specific ground conditions encountered. In some <br /> areas, forepoling and spilings installed ahead of tunnel advance will be required to provide adequate <br /> stand-up time for the installation of permanent ground support. Ground support required during the <br /> actual rehabilitation efforts will be determined by a qualified engineer licensed as a Professional Engineer <br /> in the State of Colorado. <br /> Enlarging the tunnel to a nominal 10 ft x 10 ft cross section will generate less than 500 cubic yards or 850 <br /> tons of waste rock,along with waste mine timbers,cribbing,steel rails,etc. Waste rock produced during <br /> the Idaho Tunnel rehabilitation efforts will be placed in the existing waste rock pile located adjacent to <br /> the upper(western)entrance to the Caribou mine(Map 4). During use of any of the waste rock stockpiles, <br /> BMP's such as mulch,straw waddles,silt fences,etc.will be used to provide runoff and drainage control, <br /> as needed. <br /> As timbers used as the original ground support are removed,they will be salvaged and used for creating <br /> retaining structures to form wing-walls for the portal opening that extend beyond the limits of the <br /> shotcrete facing. Steel rails removed from the portion of the tunnel being rehabilitated will be sold for <br /> scrap or used on site for barriers, railings,etc. <br /> 5.3. Mine Water <br /> As rehabilitation efforts approach the caved area(approximately 200 feet into the tunnel)backed-up mine <br /> water will be drained by pumping.The pumped water will then be discharged with the other mine water <br /> in accordance with NPDES discharge permit CO-00322751. <br /> During rehabilitation of the remaining portions of the Idaho Tunnel,water discharged from the tunnel will <br /> be collected at the portal and routed to the sediment ponds per the existing water management system. <br /> However,full access to the Idaho Tunnel water may not be achieved until rehabilitation of the portal is <br /> complete. A skid mounted water treatment system may be temporarily operated on site to treat the <br /> impaired water such that it is acceptable for discharge under the NPDES permit until construction in the <br /> Idaho Tunnel is complete. <br /> Upon completion of Idaho Tunnel rehabilitation, new mine water outflow piping will be installed. This <br /> piping will be 10-in diameter Schedule 40 PVC routed to the sediment pond system(Figure 1). <br /> No other changes to the water management system are proposed in this TR. <br /> 10 <br />