It took four months for workers to clear out a flooded cavern at the site of the new water intake tunnel under construction at Lake Mead.
Their efforts were answered with more water and mud.
Excavation has been halted once again on the $700 million third intake project as a team of contractors and consultants tries to figure out how to dig through a fault line filled with water and fractured earth.
Marc Jensen, director of engineering for the Southern Nevada Water Authority, said it could take several months and "a few tens of millions of dollars" to get the job back on track.
The intake was originally scheduled to go on line in 2013. A series of delays has now pushed the likely completion date into 2014, Jensen said.
The Las Vegas Valley draws roughly 90 percent of its drinking water from Lake Mead. The third intake will pull from deeper in the reservoir, allowing the flow of water to continue even if the reservoir shrinks enough to shut down one of the two existing straws.
The project was already about three months behind on July 1, when workers excavating the cavern 600 feet underground hit a fault zone, causing water and debris to pour into the work area.
Efforts to seal off the fault proved unsuccessful, and the entire cavern quickly filled with muck.
The workers all safely evacuated, but some mining equipment was lost to the flood.
Vegas Tunnel Constructors, the project’s general contractor, spent weeks trying to stabilize the fault by drilling down from the surface and injecting grout into the fracture zone. Once that was done, workers went back underground to drain and clean out the cavern.
They had just reached the original spot where the July 1 mishap occurred when "another event" sent more water, rock and clay into the cavern, Jensen said.
A bulkhead was quickly installed about 40 feet back from the unstable area to keep the entire cavern from flooding again. Now a team of mining and grouting experts are trying to figure out how to proceed.
Jensen insists the overall project is "not at risk from a practical or economical standpoint."
"We still have a great deal of confidence in our contractor," he said. "We still believe this is a viable project. We wouldn’t have started it if we didn’t."
It is too soon to say exactly how long the work will be stalled, but Jensen predicted it would take "certainly weeks, likely months" for large-scale excavation to resume.
Each day the project is delayed can add $20,000 to $30,000 to the final price tag, he said.
As for who will pick up the tab for such cost overruns, Jensen said, "That will be a topic of discussion in the future, but I’m sure the authority will bear some of it."
The potential impact on ratepayers, if any, could not be immediatedly determined Tuesday.
Construction of the third intake involves mining a 3-mile tunnel beneath the reservoir and connecting it to an intake structure that will stick up from the lake bed at one of the deepest spots in the reservoir’s Boulder Basin.
The tunnel under the lake will be excavated using a massive tunnel boring machine that will be lowered in pieces down the 600-foot vertical access shaft and put together underground, assuming the contractor can figure out a way to keep the assembly area from flooding.
Jensen said the contractor laid off "two or three folks" after excavation ground to halt, but most of the workers were kept on the payroll and shifted to other parts of the job.
"They’ve been busy. It’s not like they’ve let the grass grow under their feet," he said.
The project continues to employ 120 to 150 people, many of them at the other end of the straw, where the intake structure is nearing completion.
Once that concrete-and-steel funnel is finished, it will be hauled out onto the reservoir on a barge and carefully submerged above a hole in the lake bed now being excavated by deepwater blasting two to three times a day.
The tunnel boring machine will complete its 3-mile journey beneath the bottom of the lake by actually digging into the side of the completed intake structure.
Despite the most recent delay, Jensen said the authority has enough water available to meet peak demand over the next four years, even if Lake Mead continues to fall and the valley’s growth spikes back up.
Contact reporter Henry Brean at email@example.com or 702-383-0350.