Construction crews reached a significant milestone Tuesday in their effort to complete a 3.5-mile tunnel designed to protect the Hetch Hetchy Reservoir water supply from a major earthquake.
At 9:46 a.m., miners from the Irvington Portal heading in Fremont and the West Vargas shaft heading about 4,400 feet away met underground in what is called a hole through.
The segment is part of the ongoing $226.6 million New Irvington Tunnel project that is scheduled to be finished in fall 2014.
The tunnel will stretch from Sunol Valley to Fremont's Mission San Jose District and help provide water for 2.6 million Bay Area customers.
"Right now we're 90 days ahead of schedule, we're on budget and the job is proceeding fairly well," Superintendent Curtis Bahten said. "It's been good."
Excavation for the hole through Tuesday began in May 2011 when a 55-ton roadheader -- a machine powerful enough to cut through rock -- was put down a 115-foot shaft and started grinding west.
A crew at the Irvington Portal began grinding east a month later, and the two teams met Tuesday.
The next segment of the tunnel, stretching from the Vargas East shaft to the Alameda West heading in Sunol, is much longer (14,400 feet) and expected to hole through in fall 2013.
"Every step we get is a big step toward securing the Hetch Hetchy Water System," said Francis Zamora, a spokesman for the San Francisco Public Utilities Commission.