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Third Lake Mead Intake Tunnel Tough Job for Water Authority

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The Southern Nevada Water Authority’s largest single contract to date just got a little pricier.

Drier days Workers in 2010 in staging vault that later flooded twice.
Photo: Tony Illia for ENR Southwest
Drier days Workers in 2010 in staging vault that later flooded twice.
Tunnel-boring machine head will drill for three miles.
Photo: Tony Illia for ENR Southwest
Tunnel-boring machine head will drill for three miles.
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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.

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