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07/11/1996 10:37 303-24 04 MINERALS & GE( Y PAGE 03 <br /> b. Partial versus full replacement. The operator has assumed <br /> that only partial failure of the bulkhead seals would occur. <br /> However, given the apparent lack of empirical data on the <br /> long term performance of this type of bulkhead seal, and the <br /> tremendous pressures acting on the seals (the American Tunnel <br /> seal in particular) , it would seem prudent to include costs* <br /> for complete reconstruction of the bulkhead seals, including <br /> establishing coffer dams and/or water diversions, 100% form <br /> building and bracing, and placing debris screens and <br /> limestone. As I recall, some of the periodic •blowouts" of <br /> the Argo Tunnel in Idaho Springs were quite spectacular and <br /> aptly demonstrated the effects of the tremendous forces <br /> generated by release of water that had built up in the <br /> tunnel. Such forces would seem to be capable of completely <br /> destroying the bulkhead(s) . <br /> 2. Tunnel rehabilitation costs. Although I do not have any <br /> information in our Durango office files showing how far from the <br /> surface the seals are located in the underground workings, it <br /> would seem prudent to include costs for possible tunnel <br /> rehabilitation work that may be necessary to ensure safe and <br /> efficient access back into the workings by a contractor to re- <br /> install bulkhead seals. The condition of the tunnels may have <br /> deteriorated (rock falls, sludge/sediment/debris deposition on <br /> tunnel floor) to some extent over time after the tunnels have been <br /> closed, flooded, and no longer maintained. Additionally, there <br /> may be some specific MSHA requirements associated with re-opening <br /> the tunnel that may result in additional costs to a Division hired <br /> contractor. If electrical power is necessary_ and cannot be <br /> provided with portable generators due to possible MSHA <br /> restrictions, there may be additional costa associated with <br /> providing electrical power to the installation sites. <br /> 3 . Replacement of upper seals. Although I do not have all of the <br /> design and installation information for the seals in the Durango <br /> Office files, I know there were additional bulkheads (I do not <br /> know how many) installed behind the main seals. It would seem <br /> reasonable to assume that failure of the main bulkhead may result <br /> in part from failure of the upper seal (s) which would cause <br /> additional pressure to be exerted on the lowermost seal, causing <br /> it to fail. If this were to occur, the upper seals would probably <br /> need to be replaced in order to maintain the integrity of the <br /> entire sealing system as originally designed. The cost of <br /> replacing the upper seal(s) would involve both the direct bulkhead <br /> re-installation costs plus additional costs for further tunnel <br /> rehabilitation, hoist refurbishing or replacement, and possible <br /> expansion/extension of the ventilation system. <br /> 4. Additional contractor costs. Since this work is fairly <br /> specialized, it is doubtful that qualified contractors would be <br /> located near the project site. This would likely result in higher <br /> mobilization/demobilization costa which do not appear to have been <br /> included in the operator' s estimate. Additionally, since it is <br /> assumed that the surface facilities will have been partially or <br />