Just six miles from where the Hoover Dam holds back the largest reservoir in the nation, workers are struggling against solid rock, geologic faults and seeping water to construct an intake tunnel to keep drinking water flowing from shrinking Lake Mead to thirsty Las Vegas.
Their work in a hot, humid cavern some 600 feet below ground goes largely unnoticed by local residents and tourists enjoying icy drinks in glittery Sin City casinos and nightspots.
But the perils of tunneling beneath the lake bed were cast in stark terms this week, when a veteran tunnel worker died on the daunting $817 million, five-year project that officials compare with building the dam itself. They cast the so-called "Third Straw" project as the most complex current effort of its kind in the U.S.
"It has factors that are very unique to this project and make it very complicated," said Heidi Dexheimer, a Las Vegas civil engineer and regional representative of the American Society of Civil Engineers. Dexheimer once worked at the Southern Nevada Water Authority and is familiar with the project, but isn't involved with it.
She compared the 3-mile tunnel project to work on the 1.5-mile Lincoln Tunnel that connected New York City and New Jersey beneath the Hudson River in 1937 and the nearly 1.7-mile Eisenhower Tunnel through the Continental Divide on Interstate 70 west of Denver that opened in the 1970s.
"There's a lot of risk and a very small margin for error," Dexheimer said Friday. "It takes a really highly trained team of experts to do it."
The Lake Mead Intake No. 3 project has already had several setbacks. The tunnel flooded in July 2010 when a drilling machine hit a geologic fault. It flooded again in December 2010, forcing contractor Vegas Tunnel Constructors to abandon the tunnel and start a new one in a different direction. The completion date was pushed back several months, to summer 2014.
Ninety percent of Las Vegas water currently comes from Lake Mead, which has shrunk in recent years due to ongoing drought and increasing demand from seven states and more than 25 million people sharing Colorado River water rights under agreements dating to 1922.
The water authority is aggressively working on other ways to ensure a future water supply for Las Vegas' nearly 2 million residents and more than 40 million annual visitors. One is a controversial plan to build a $3.5 billion, 300-mile surface pipeline to pump billions of gallons of water south to Las Vegas from rural areas along the Nevada-Utah border.
In a city that averages just over four inches of rain per year, officials say they have no choice but to press on with the Lake Mead project. It promises to ensure the ability to fetch water no matter how low the reservoir gets.
Even the Occupational Safety and Health Administration administrator in the region said he expects drilling will resume after an investigation.
"A human life was lost," said Stephen Coffield, chief of the Nevada OSHA office in Henderson. "We need to know what happened and get it corrected so it doesn't happen again."
But, "the lake is dropping," Coffield added. "The first straw is going to be sucking air."
Two initial Lake Mead water intakes were built along with Hoover Dam, an engineering marvel that authorities estimate cost the lives of about 100 workers during five years of construction. It was completed in 1936.
The lake behind the dam is fed by Rocky Mountains snowmelt and managed by the U.S. Bureau of Reclamation in tandem with the Lake Powell reservoir upstream and lakes Mojave and Havasu downstream.
The Lake Mead surface level has dropped about 100 feet in elevation since the lake was full in 2000, bureau spokeswoman Rose Davis said. It is about half-full today _ displaying a distinctive white mineral "bathtub ring" between the low and high water lines.
The lake surface elevation was just beneath 1,118 feet on Friday, about 68 feet above the first intake elevation of 1,050 feet. A second intake draws water from an elevation of 1,000 feet.
"It's really hard to say when we're going to get there, but if the drought continues as it has over the last 12 years, we have to expect that first intake is in danger," said Scott Huntley, a Southern Nevada Water Authority spokesman.
The current lake level also is only 43 feet above a mark that would trigger a mandatory reduction in water deliveries to Nevada and Arizona. In November 2010, the reservoir water level dropped to 1,081 feet _ just six feet above the mark _ before a heavy winter snowfall pushed the lake level back up.
At the bottom of a shaft 600 feet beneath Lake Mead's Saddle Island, 125 workers face more immediate dangers _ in conditions that Huntley described as loud, wet, humid and busy.
"It's a huge cavern down there, with large machines, welders, everyone doing a job," he said.
The death of Thomas Albert Turner, 44, was the first directly associated with the project.
On Monday, Turner _ a married father of two from Henderson whose brother also works on the pipeline _ died when he was hit in the head by a pressurized stream of a grout mixture containing fist-sized rocks, pebbles, sand, fly ash, water and cement.
Huntley said it appeared the pressurized slurry hit Turner after a segment of curved concrete wedged loose before it could be cemented in place, creating a 4-inch-by-2-foot gap. The slurry mix was being injected into a void between the pipeline wall and the tunnel wall at 200 pounds per square inch of pressure _ about twice the flow from a fire hose.
A nearby co-worker was hurt but is recovering, Huntley said. A third co-worker on the team escaped injury.
OSHA has inspected the work site eight times since August 2008, and 14 safety violations were found during two of the visits, according to U.S. Department of Labor data. Coffield said the contractor corrected the violations and paid $800 in fines.
Officials with Vegas Tunnel Constructors, based in Boulder City, and corporate parent SA Healey Co. of Lombard, Ill., didn't immediately respond to messages. The company is a subsidiary of Gruppo Impreglio S.p.A. of Milan, Italy.
This week's accident happened some 55 stories underground, where a $25 million machine has, so far, slowly bored through 1,000 feet of solid rock. It has about 13,000 feet to go.
When finished, the 23-foot-high tunnel will reach almost three miles, connecting an existing water treatment plant to a funnel-like structure already cemented in place on the lakebed.
The pipeline itself, measuring 20 feet in diameter, is being constructed of some 2,500 concrete rings weighing 17 tons each, cemented into place like kitchen tile by the slurry mixture.
Water authority officials called the accident tragic _ a private family memorial service for Turner was to be held Friday _ and vowed to prevent it from happening again. But they left little doubt that drilling will resume.
"The third intake is the most demanding and difficult project the SNWA has undertaken," agency chief Pat Mulroy said in a statement.
"It is quite possibly also the most important. As the drought on the Colorado River continues, and even intensifies this year, the critical importance of this project to the security of our community's water supply is heightened."