Since August, Southern Nevada Water Authority officials have been hinting about another delay in the completion of the new water intake under construction at Lake Mead.
Now we know how much of a delay.
Today, water authority board members will be asked to vote to extend the completion date for the third intake by about 13 months to July 4, 2015.
“We trust this will get us to the end of the project,” said Marc Jensen, director of engineering for the water authority. “Unless we encounter more surprises.”
General contractor Vegas Tunnel Constructors needs more time because conditions underground have proved to be worse than expected, slowing progress on the three-mile-long intake tunnel and requiring major structural repairs to the giant digging machine specially built for the job.
The delay could put the community’s water supply at risk, though authority officials consider that it’s only a remote possibility they are “not terribly concerned about,” Jensen said.
Roughly 90 percent of the valley’s water arrives here by way of two intake pipes in Lake Mead.
One of those pipes could be forced to shut down if the reservoir keeps shrinking amid ongoing drought on the overdrawn Colorado River. If that happens before the third intake goes on line, the valley will be literally down to its last straw.
The latest federal projections call for enough water to flow down the Colorado through September 2015 to keep the surface of Lake Mead at least 23 feet above the level at which the valley would lose one of its intakes.
But the forecast could change with another unusually dry winter in the mountains that feed the river.
The current completion date of May 31, 2014, is the result of a previous change order approved in March 2011 that added 593 days and almost $40 million to the now $817 million project.
The new change order does not include any additional money for Vegas Tunnel Constructors, which is a subsidiary of the Italy-based construction giant Impregilo.
The third intake project has been called one of the most complicated tunneling operations in the world.
Authority General Manager Pat Mulroy has said the job is so complex and dangerous that it took her agency more than a year just to find someone willing to insure the work.
It involves digging a tunnel three miles long and large enough for a 20-foot diameter pipe beneath the bed of Lake Mead.
Construction began in 2008 with excavation of vertical shaft extending 600 feet into the ground at the lake’s Saddle Island. From there, the tunneling went horizontal, the start of a journey through solid rock to a pre-built intake structure already waiting in the cold, dark water at one of the lake’s deepest spots.
On June 11, 2012, a worker was killed in an accident underground. Some equipment was lost during a series of floods in 2010 and 2011 that filled tunnel with water and debris, forcing the contractor to abandon the site and dig in a new direction.
Things are going far more smoothly now. Jensen said the massive tunnel boring machine advanced more than 1,000 feet in September and more than 1,500 feet in October.
The machine and its crew have left the shoreline behind and are working directly beneath Lake Mead and its 4 trillion gallons of water.
Jensen said workers expect to encounter several more sections of troublesome rock like the fractured, water-filled mess the machine had to crawl its way through earlier in the project.
They should hit the next bad patch in a month or two, as the tunneling machine approaches and then crosses 50 feet beneath the channel carved by the old Las Vegas Wash back before Hoover Dam was built.
Before they enter that stretch, they plan to stop to conduct a full maintenance check of the machine.
As of now, the tunnel is a mile and a half long and growing at a breakneck pace of an inch or two a minute. Jensen said the machine is running wide open, halfway home.
Contact reporter Henry Brean at firstname.lastname@example.org or 702-383-0350. Follow @RefriedBrean on Twitter.