Third Lake Mead Intake Tunnel Tough Job for Water Authority
The Southern Nevada Water Authority�s largest single contract to date just got a little pricier.
A starter tunnel for a third raw water intake at Lake Mead flooded three times in six months last year, prompting its contractor, Vegas Tunnel Constructors LLC �a joint venture of S.A. Healy Co., Lombard, Ill., and Impreglio S.p.A., Sesto San Giovanni, Italy�to drill in a drier direction. Costs for the design-build project, awarded in early 2008, have swollen to $526.6 million, up 15% from its original $447-million price tag. Who will pay for the added costs is uncertain.
Authority board members delayed a Feb. 17 vote on a $39.5-million change order until further review of the project�s contract intricacies, surety bonds and insurance policies. VTC has agreed to absorb any future project cost overruns if the change order goes through. The insurer has paid about $4.5 million so far, although future payouts are expected. Lake Mead Constructors LLC�a joint venture of Traylor Bros., Evansville, Ind., Obayashi Corp., San Francisco, and Barnard of Nevada Inc., Las Vegas�had a $588-million runner-up bid that was 24% higher than the winning offer.
VTC, who based its estimate on 50 owner-performed geotechnical core samples, spent months pumping out water and stabilizing rock fractures with grout following a June 28, 2010, incident that flooded a 200-ft-long, 37-ft-high staging vault and ruined some mining equipment. The joint-venture team includes geotechnical consultants Brierley Associates LLC, Denver, and Arup, New York City. Further, water seepage occurred two more times before the contractor went back to the drawing board.
�We�re investigating an alternate alignment roughly 20� east from the current 200-ft-long starter tunnel,� says VTC project manager James McDonald, who has taken another 10 core samples since the seepage. �It will eventually rejoin the original alignment.�
The project, which calls for a three-mile-long tunnel, has yet to use a $25-million customized Herrenknecht tunnel-boring machine. This fall, VTC hopes to begin lowering TBM components down a 30-ft-dia, 600-ft-long access shaft and assemble piecemeal the 1,500-ton, 600-ft-long mechanical earthworm with a jack-and-rail system. The TBM will form a 20-ft-dia tunnel reinforced with 2,500 precast ring segments. The project, which already has been delayed by a year, now is expected to finish in 2014.
�Underground construction has more uncertainty and greater risk than other types of construction,� says Marc Jensen, SNWA engineering director. �We are disappointed that we ran into difficult ground conditions at the beginning of the project, but we�re addressing it.�
A third intake provides crucial water insurance at Lake Mead, now at 40% below capacity. At $700 million, the tunnel is the largest piece of the multiphase project.
