Drought stricken Lake Mead needs a third straw to ensure water for the Las Vegas Valley.
The drought gripping the southwest has forced fast growing communities like Las Vegas to undertake new water-related construction projects. On March 20, the Southern Nevada Water Authority awarded a $447-million design-build contract to Vegas Tunnel Constructors LLC – a joint-venture of S.A. Healy Co., Lombard, Ill. and Impreglio S.p.A., Sesto San Giovanni, Italy. The JV will build a third raw water intake tunnel at Lake Mead, the Las Vegas Valley's water lifeline. The additional straw is needed since lake levels have dipped 110 ft since 2000. Lake Mead now operates at 1,117 ft. or about half of its capacity. One or both of the existing water inlets will be forced to shut down if the lake level drops another 70 ft. The new intake, SNWA's largest project to date, will be able to draw water deeper than its counterparts at 860-ft.
“It's not going to add to capacity,” says Marc Jensen, SNWA's director of engineering. “It's insurance in case our current intakes become inoperable. It will also draw water lower ensuring a better water quality.”
Construction entails a 20-ft-dia., 15,000-ft-long concrete panel reinforced tunnel under the lake bed. The contracting team is purchasing a hybrid tunnel boring machine from Herrenknecht AG, Schwanau, Germany, created specifically for the project. The TBM will be able to operate in both open and closed modes, meaning the drill face is pressurized, for more efficient ground and water control, says Jim McDonald, Vegas Tunnel's project manager. The TBM will have a trailer installing 2,500 supporting concrete rings, each weighing 3,500 tons. Each ring consists of six separate pieces that will be manufactured onsite. Other tunneling work entails a 16-ft.-dia., 60-ft-to-80-ft.-deep water intake shaft and a 32-ft-dia., 600-ft-deep access shaft along Saddle Island's western shore line.
“We expect to have about 200 people onsite during the peak of construction activity,” says McDonald. “The TBM will take about four months to assemble and test. We could break ground within six weeks.”
The erection, schedule and price played a key in role in Vegas Tunnel Constructors securing the contract. Runner-up, 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 bid that was 24% higher than Vegas Tunnel Constructors. Yet they still received a $600,000 stipend for their submission effort. A third competitor, Frontier-Kemper Constructors JV, dropped-out. All three teams were furnished with 10% complete bridging documents prepared by Broomfield, Colo.-based MWH Americas/CH2M-Hill Inc.
The intake tunnel has a 1,571-day project schedule that's expected to finish in July 2012. However, there are four other associated projects that still have yet to bid, including a 600-mgd pumping station; a 14-ft-wide, 16-ft-tall connection to the second intake; a 120-in.-dia. discharge pipeline from the pumping station to the Alfred Merritt Smith Water Treatment Plant; and, a large power substation and lines. The entire raw water intake project is expected to cost $817 million, and finish by early 2013.
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