The pipeline, which would provide a backup water supply to the drought-ridden Las Vegas Valley, has repeatedly flooded with water, rock and muck, causing authorities to consider drilling a new starter tunnel.

Extending from a 600-foot vertical shaft near Lake Mead, a 350-foot horizontal starter tunnel was blasted into place to make room for the massive, custom-made tunnel-boring machine that would drill a 3-mile path to the deepest part of Lake Mead. However, the starter tunnel crosses a fault line, where crumbling rock has causes lake water to flood the tunnel.

"If the tunnel-boring machine was in place, we could go through it easily," says Robin Rockey of the Southern Nevada Water Authority. But for the drill-blast team that's extending the starter tunnel, the fault line represents a significant obstacle. "It looks like we'll be retreating and abandoning our starter tunnel," she says.

A new starter tunnel that would extend from the 600-foot vertical shaft is now being proposed. It would be drilled at an angle that is 20 to 23 degrees from the original starter tunnel. This should provide enough space to build the tunnel-borer, blast through or skirt the fault line and resume the planned 3-mile path under the deepest parts of Lake Mead.

The Water Authority will go before its board of directors in mid-February to propose this new plan and assess the setbacks in money and time.

The reroute is expected to delay completion of the tunnel, which was originally set for early 2013 and has now been moved to 2014. The pipeline will serve residents of the valley, whose concerns heighten as an 11-year drought continues to grip Nevada. Since 1999, Lake Mead's water elevation has dropped from 12,014 feet to 10,082 last November, its lowest point ever.

Currently, Lake Mead provides 90 percent of the region's fresh water through two intake pipelines. As the drought continues, water levels threaten to fall below the intake levels, potentially cutting off water supplies to millions of residents. The current water elevation of 10,090 is dangerously close to Intake No. 1 at 10,050 feet.

Bronson Mack, spokesperson for Southern Nevada Water Authority, which collects water-usage data, says the organization is optimistic. "We're confident that the third intake will be built before we lose our first intake," he says.

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