Workers to begin underwater blasting at Lake Mead site

Workers stationed on a floating barge will start blasting holes in the bed of Lake Mead this week as construction of a $700 million water intake for Las Vegas enters a complicated new phase.

The National Park Service has closed a portion of the lake around the barge to keep boaters away from the construction zone.

The work will start with a series of small test explosions, but the blasting will grow in size and complexity as workers seek to excavate a pit 50 to 60 feet deep in the rock at the bottom of the reservoir.

The pit eventually will hold the intake structure for the Southern Nevada Water Authority's new straw into Lake Mead.

During the next six months, crews plan to blast and remove 25,000 cubic yards of rock from the bottom of the lake. That's enough material to bury a football field under a pile almost 12 feet tall.

Authority spokesman Bronson Mack said the controlled blasts will be directed into solid rock some 300 feet underwater, so the contractor does not expect to see any evidence of the explosions at the surface. There should be no watery eruptions, waves, or clouds of dead fish, Mack said.

The closed area, which extends in a 100-yard radius around the construction barge, is near Black Island in the waterway of Boulder Basin. Its perimeter is marked by buoys and patrolled by safety boats.

"This safety zone is necessary to ensure our visitors remain safe by keeping clear of the hazardous area during the construction operations," said Bill Dickinson, superintendent for the Lake Mead National Recreation Area.

The blasting is expected to continue intermittently for the rest of the year.

The work site is too far down for divers, so workers will use submersible robots guided remotely from the surface to plant the explosives.

After the rock is cleared from the blast area using a giant vacuum, a concrete pad will be poured under more than 250 feet of water. Then, sometime in mid-2011, the precast intake structure -- 95 feet tall and weighing 1,200 tons -- will be towed across more than two miles of open water, carefully lowered into position and cemented in place with more concrete.

At the same time, a massive tunnel boring machine beneath the lake bed will be chewing its way toward the intake structure to complete the 20-foot diameter pipe that eventually will stretch three miles from Saddle Island to a spot in one of the deepest parts of Boulder Basin.

When the project is finished in early 2013, the authority's so-called "third straw" will keep water flowing to Las Vegas despite drought and shortages on the Colorado River that could force one of the two existing intakes to shut down.

The Las Vegas Valley draws about 90 percent of its drinking water supply from Lake Mead.

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