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07/11/1996 10:37 303-247-5104 MINERALS & GEOLOGY PAGE 03 <br />~ ! b. Partial vereui 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 thin typo of bulkhead sisal, and the <br />tremsndoua pressures acting oa the scale (the American Tunnel <br />i eeai in particular), it would seem prudent to i.nalude coats <br />for aomplate reconetruatioa of the bulkhead seals, including <br />eatablishiag coffer damn and/or water diversior.~s, 1001 form <br />building and bracing, sad placing debri^ screens sad <br />limeatoae. Ae I recall, some of the periodic ''blowouts" of <br />the Argo Tunnel is Idaho Spriag^ were quite eparetacular sad <br />aptly demonstrated the affects of the treme:ndoue forces <br />generated by release of water that had built up in the <br />tunnel. Such forces would seem to ba capable of completely <br />destroying the bulkhead(s). <br />2. 3Vaaei rehabilitation coats. Although I do not have nay <br />information is our Durango office files ahowiag how far from the <br />surface the aeale are located is the underground workings, it <br />would seam prudent to include coats for posrible tunnel <br />rehabilitation work that may ba aeeeaaary to secure safe and <br />efficient aaoess back into thn workings by a contractor to re- <br />install bulkhead seals. The condition of the tuanela may have <br />deteriorated (rock fella, sludge/sediment/debris deposition on <br />tunnel floor) to soma extent over time after the tuns-ela have been <br />• closed, flooded, and no longer maintained. Additionally, there <br />may be ^ome specific l[SHA requirements associated with re-opening <br />the tunnel that may result is additional costs to a irlvisioa hired <br />contractor. If electrical power ie necessary, sad cannot be <br />provided with portable generators dun to poeaible D~SHA <br />reetrictioae, there may be additional costa aeraociated with <br />providing electrical power to the installation cites. <br />3. Aeplacesant of upper seals. Although I do not have ali of the <br />design and installation information !or the aeala is 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) whia]z would cause <br />additional pressure to be exerted oa the lowermost seal, causing <br />it to fail. If this wary to occur, the upper scale would probably <br />need to be replaced in order to maintain the iat:egrity of the <br />satire sealing eyatem ae originally designed. The coat of <br />replacing the upper scal(e) would involve both the d.ireet bulkhead <br />re-installation eost^ plus additional coats for :Further tunnel <br />rehabilitation, hoist refurbishing or replacement, and possible <br />expansion/extension of the ventilation system. <br />4. additional contraator costa. Biace this work is fairly <br />specialized, it ie doubtful that qualified contractors would be <br />~ located agar the project site. This would likely result is higher <br />• mobilisation/demobilisation coats 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 />