Paula Wallis, Reporter

Section to the new intake structures

Five bids came in last month - all well below the Engineer’s Estimate of $105 million - but it wasn’t enough. Funding shortfalls forced the owner to reject the bids and postpone construction of the new pumping station shaft on the deep intake project at Lake Mead.

Since advertising the contract, the Southern Nevada Water Authority (SNWA) has had to scale back its budget and funding projections for the coming fiscal year and was forced to cancel the contract.

“The local impacts of the developing global economic crisis are continuing to exert financial strain on our capital program budget,” said Robin Rocky, spokesperson for the Authority. “Revenues from charges for new water connections have dropped dramatically and we are assessing every opportunity for limiting capital expenditures as much as possible.”

Lake Mead intake tunnel plan

According to the SNWA revenue from new water hookups dropped from $188.4 million in 2006 to a mere $61.5 million in 2008. In the first six weeks of 2009 reserves in its construction fund dropped 6%
 to $480 million putting severe strain on the Authority’s ability to repay the $500 million in bonds it plans to start selling later this year to complete the Lake Mead 
project.

As a result the SNWA is deferring major components of the Lake Mead Intake No. 3 project for several years and will add more pumps to increase capacity of the exiting Intake No. 2 instead. KW Pipeline Inc, doing business as Renda Pacific entered the lowest bid for the Intake No. 3 pumping shaft contract at $78.7 million, and was followed by the 
Vegas Tunnel Constructors JV, lead by Impregilo, at $86. 1 million; Clark Construction Group with a bid of $86.5; 
Kiewit Western Company at $88.2 million; and 
Barnard of Nevada at $99.1 million. The Engineer’s Estimate was $105 million.

“Rejecting all bids on the pumping station will give our staff time to reevaluate and repackage the work to include only those components deemed necessary to assure water supplies are reliably conveyed through the new Intake No. 3,” said Rocky.

The Authority’s decision does not impact the major tunneling component of the Intake No. 3 project. The intake shaft and tunnel contract was awarded in March 2008 to the Vegas Tunnel Constructors JV of Impregilo andImpregilo and its US subsidiary, SA Healy.

Site mobilization

Construction of the $513 million design-build contract with Arup as designer began in June 2008 with the access shaft on Saddle Island. By late March 2009March 2009 crews had excavated about 300ft of the roughly 640ft (nearly 200m) deep shaft.

Once complete, a Herrenknecht pressurized TBM of exceptional design, currently in production in Germany, will excavate the three mile (4.8km) tunnel to an intake shaft on the bottom of Lake Mead about 600ft (182m) below water level.

“This is a challenging project,” said Michael Feroz of Parsons Water Infrastructure and Principal Construction Manager of SNWA. “The new intake lies 200ft (60m) deeper in the lake than the existing intakes, both of which are tunneled structures - the first built in the 1970s and the second in 2000.”

Feroz said, while those tunnels were drill+blast excavations, the new tunnel is a TBM operation starting in the open mode but having to go into closed pressurized mode as it advances into softer formations where the heading might be subjected to the full 600ft (182m) hydrostatic pressure of the lake. The JV’s contract also includes a connection tunnel from the new Intake No. 3 to the existing No. 2 intake at the Saddle island landfall end, a distance of about 3000ft (915m).

Geological investigations indicate that Saddle Island is a block of Precambrian amphibolites and gneiss with the oldest known rocks in the area dating back 1.7 billion years. The alignment then moves into softer rocks and the water bearing silts and sands of the Muddy Creek Formation created by ancient rivers that flowed five to 11 million years ago.

The project is being driven by the worst 10-year drought to hit the region in recorded history. Lake levels have been dropping about 1% a year since 1999 and by 2012 its surface could drop below the existing intake that delivers 40% of the Las Vegas water supply.

Intake No. 3 is expected to be online by 2012.

References

Intake No. 3 tunnel contract award -TunnelTalk, Jun 2008
Funding woes affect water projects in Las Vegas -TunnelTalk, Apr 2009
Lake Mead intake project design -TunnelTalk, Sep 2006