Tuesday, June 12, 2012 | 4:15 p.m.
As the investigation begins into a Monday accident at a Lake Mead construction site that left one man dead, officials released new details Tuesday about what happened in the tunnel 600 feet underground.
The accident occurred about 4:30 p.m. when a large concrete tunnel ring slipped forward, releasing a pressurized stream of grout, mud and small rocks that struck two workers, the Southern Nevada Water Authority said in a statement Tuesday. Officials are still investigating why the ring, which previously had been installed, slipped.
Thomas Albert Turner, 44, of Henderson was killed and another man suffered minor injuries, officials said.
A total of 2,500 tunnel rings, each about six feet thick, are being placed in the tunnel below Lake Mead that will connect to a new intake straw to protect Southern Nevada’s water supply. So far, 133 rings have been installed in the tunnel, which will eventually stretch three miles.
A team from Vegas Tunnel Constructors, the project contractor, entered the accident site Monday evening and determined the area was safe, the SNWA said. No cave-ins or flooding were found.
The company is preparing to seal the approximately four-inch by two-foot gap opened when the tunnel ring slipped.
The Nevada Occupational Safety and Health Administration is also investigating to identify the cause of the accident, but there is no timeline for when its findings will be released.
The construction site will remain closed until whatever caused the breach has been corrected and the “safety of the tunnel has been verified,” OSHA said in a statement.
This is the first fatality on the troubled, $800 million project, which has been hampered by delays and cost increases since construction began in 2009.
The project was started while Southern Nevada was struggling through a decade of drought. Plunging lake levels threatened to drop below the existing two intakes, which were drilled at shallower depths.
Las Vegas depends on the Colorado River reservoir for about 90 percent of its drinking water.
The third intake will allow the region to continue drawing water from the lake, even if lake levels continue to drop. The project was initially scheduled to be finished in 2013, but the completion date was pushed back to 2014 after several mishaps.
In July 2010, work on the tunnel that would carry water from the straw into the valley’s water system was slowed when crews struck a geographical fault, releasing water and muck into the construction area. Attempts were made to stabilize the fault with grout, but after two more leaks, the tunnel was abandoned and crews began excavating a different direction.
Monday’s accident occurred in the new tunnel. It will be lined with the concrete rings, which are lowered in pieces and assembled underground.
The grout that hit the workers holds the rings in place and counteracts the immense pressure from the earth and water above the tunnel, said Erika Mooning, SNWA’s engineering project manager.