Hundreds of feet below ground workers tore through the final bits of earth to complete a 3.5-mile-long tunnel. Video, provided by the San Francisco Public Utilities Commission, shows the moment when miners drilling from Fremont met another crew from Sunol.
"And both came together in the middle of a mountain about two miles in from behind us," said Daniel McMaster, the project construction manager.
Miners call it "holing through." The $227 million project is part of a massive plan to secure the water supply for more than 2.5 million customers in four Bay Area counties.
This new tunnel will ultimately replace a pipeline built in the 1930s. Mining here was tough back then as you can imagine, and it still is today. Workers crossed fault lines, ripped through tough soil and ran into pockets of ground water.
"Every single foot of this tunnel was different, so that presented many, many, challenges in how to approach the ground, and how to actually mine the ground," said Curtis Bahten, the tunnel superintendent.
"We had to grout the tunnel before we actually mined through it with over seven million pounds of cement grout," said McMaster.
Voters approved a $4.6 billion ballot measure in 2002 to repair and replace the aging Hetch Hetchy water system.
An engineering marvel at the time, the system of pipes, dams, and reservoirs carries water 167 miles from Yosemite National Park, across the Central Valley, and into the South Bay before going up the peninsula to San Francisco.
Work funded by the bond measure is now one major step closer to being completed.
"It's roughly 80-percent done, the excavation is a 100 percent done, but we have quite of bit to do on the surface," said David Tsztoo, the tunnel project manager.
The tunnel is scheduled to be completed next fall.
Written and produced by Ken Miguel.
