Miners call it a "hole through" -- that's where two tunnels dug from opposite ends come together; 450 feet below the Fremont hills. Two separate crews were finally able to shake hands after 13 months of digging.
"Today marks a milestone," said tunnel superintendent Curtis Bahten. "We have now completed a 4,500-foot run."
When it is completed, this new tunnel will travel three and a half miles underground, supplementing an older pipe built in 1934. That existing pipe currently supplies water to 2.1 million people in San Francisco, the Peninsula, the South Bay and parts of Alameda County.
"We still have pipe to go in here -- 8-foot in size diameter pipe the entire way," said Bahten. "I mean there's still a lot of work to do here."
This is dangerous work. Explosives are used daily and monster machines work within inches of miners. Add to that the fact this project is sandwiched between two active earthquake faults.
The tunnel is expected to cost $230 million and completed in the fall of 2014.
The project will be paid for with money from a bond measure voters passed in 2002 to upgrade the aging Hetch Hetchy water system, a network of tunnels, pipes, dams and reservoirs that deliver water 167 miles from Hetch Hetchy Reservoir in Yosemite National Park to Crystal Springs Reservoir along Interstate 280 in San Mateo County.