Intake work progresses under Lake Mead

After a year of setbacks, the Southern Nevada Water Authority finally has some good news to report about its $700 million effort to build a new straw into Lake Mead.

Construction crews working 600 feet underground are now making "slow but steady progress" on a starter tunnel that was originally scheduled for completion a year ago, said Marc Jensen, director of engineering for the authority.

The tunnel is now about 310 feet long and roughly 50 feet from completion, Jensen said. If work proceeds at about 10 feet a week, it should be finished by next month.

Then the general contractor can begin lowering a massive digging machine into the ground for the largest part of the job, the excavation of a 23-foot tunnel through three miles of solid rock beneath the bottom of Lake Mead.

The tunnel-boring machine will be lowered in pieces and assembled underground, where it will eventually stretch the length of two football fields and weigh more than three Boeing 747 jetliners.

Jensen said the machine could be in place and ready to start digging by the end of the year.

And all it took to get things back on track was the largest change order in water authority history.

In February, the authority board agreed to add another $39.5 million to what was already the single largest construction contract the agency ever issued.

In exchange for the money, the project's designer and general contractor, Vegas Tunnel Constructors, accepted liability for any additional problems until the tunnel-boring machine is underground and chewing rock.

The change order also extended the timeline for the project by 593 days to the summer of 2014.

The 310 feet mined so far represents about 2 percent of the tunnel's total length.

"We still have a long way to go," Jensen said.

The Las Vegas Valley currently depends on two intake pipes to draw roughly 90 percent of its drinking water from Lake Mead.

The third intake will pull from deeper in the reservoir, allowing the flow of water to continue even if the lake shrinks enough to shut down one of the two existing straws.

The project is especially important to Henderson and Boulder City, which get all of their water from Lake Mead. As water authority chief Pat Mulroy put it, "Their plumbing doesn't connect to the rest of the valley."

Work on the third intake was already about three months behind on July 1, 2010, when a crew excavating the starter tunnel hit a fault zone, causing water and debris to flood the work area.

Vegas Tunnel Constructors spent weeks trying to stabilize the fault, but the area flooded again on Oct. 27 and Dec. 31.

The contractor eventually abandoned that tunnel and started excavating a new one in a different direction in hopes of skirting the troublesome fault line. So far, the tactic appears to be working, Jensen said.

The new starter tunnel is now more than twice as long as the old one.

To reach the work area, miners have to descend to the bottom of a vertical access shaft roughly the same height as a 55-story building. The tunnel-boring machine's sections will be lowered down the same shaft, which took more than a year to dig near the valley's two existing straws on the western shore of Lake Mead's Boulder Basin.

There are 130 people now working on the third intake, roughly 70 of them at the starter tunnel.

A crew of about 20 people are at the opposite end of the project, blasting a hole in the bottom of Lake Mead from a floating barge. The hole will eventually house a massive intake structure that will be lowered into it from the surface of the water.

Authority spokesman J.C. Davis said that part of the project remains on schedule.

The change order approved on Feb. 25 is the authority's largest in terms of pure dollars, but not by percentage.

That honor belongs to the River Mountains Water Treatment Facility, which was already being constructed in 2000 when authority officials decided to expand the design. The resulting change order totaled $31.3 million, or 21 percent of the project's total cost of $146.6 million.

The regional water agency also ran into cost overruns in the late 1990s during excavation work on its second Lake Mead intake.

That project was completed in 2000 but not before racking up change orders that increased the total cost from $68 million to $83 million.

Contact reporter Henry Brean at hbrean@reviewjournal.com or 702-383-0350.