An $800 million effort to sink a new straw into Lake Mead has hit another snag, this time in the connector tunnel that will link the new intake to the existing water system.
Excavation of the half-mile connector tunnel has been slowed by unexpected amounts of water seeping into the work site 480 feet underground.
The trouble will add almost $5 million to the cost of the connector tunnel and delay its completion until January, about seven months later than expected.
The new deadline is not expected to delay completion of the so-called third intake as a whole, which is already running roughly 20 months behind schedule.
The Southern Nevada Water Authority board unanimously approved the change order Thursday.
Before the vote, board member and Las Vegas City Councilman Bob Coffin said such complications and cost increases are to be expected on such a project.
"It's important to note that this is unpredictable geology. It's predictable only in that it is unpredictable," he said.
Marc Jensen, director of engineering for the Southern Nevada Water Authority, echoed that sentiment.
"Underground construction has uncertainties, and we're just coping with those uncertainties," he said.
Board members previously approved an additional $2.4 million for the job, which was originally slated to cost $42.3 million and be completed by the end of this month. That change order extended the completion date by 95 days and came on top of several smaller change orders totaling almost $2.8 million.
The connector tunnel is being excavated by KW Pipeline, a Henderson-based construction company currently operating under the name Renda Pacific.
Work began on the tunnel in May 2009, and the job remained slightly ahead of schedule until last year, when the contractor began to encounter more water underground than expected.
Jensen said there have been no floods or cave-ins as a result of the extra water and "no hint" that there could be.
But the same cannot be said of the adjacent third intake tunnel.
The trouble there began on July 1, 2010, when a crew excavating a starter tunnel for the tunnel-boring machine hit a fault zone, causing water and debris to flood the work area 600 feet below Lake Mead's Saddle Island.
The company hired to design and build the intake, Vegas Tunnel Constructors, spent weeks trying to stabilize the fault, but the area flooded twice, forcing the contractor to abandon the tunnel and excavate a new one in a different direction.
The resulting change order, approved by the water authority board in February 2011, added $39.5 million to what was already the single largest construction contract the agency has ever issued. It also extended the timeline for the project by 593 days to the summer of 2014.
By all accounts, the third intake is the most complicated and expensive construction job in the history of the water authority. It involves digging a tunnel 23 feet in diameter and three miles long through solid rock beneath Lake Mead.
Most of that work will be done by a specially made tunnel boring machine, but so far the $25 million digger has only advanced a little over 300 feet.
Jensen said the machine is expected to start regular mining operations in a month or two, once its support network of conveyor belts and other infrastructure is in place.
When finished, the new intake is expected to keep water flowing to Las Vegas even if the lake shrinks enough to force one of the two existing straws to shut down.
The Las Vegas Valley depends on the Colorado River's largest reservoir for about 90 percent of its drinking water.
The water authority board approved a rate increase earlier this year to help cover the last $360 million of the intake project.
Even with the change order approved Thursday, Jensen said, the cost of the connector tunnel remains well under the second lowest bid the authority received for the work.
He added that by building the connector tunnel, the authority was able to defer construction of a pumping station expected to cost about $150 million.
Contact reporter Henry Brean at email@example.com or 702-383-0350.