One pipeline in the Hetch Hetchy system was built in the late 1960s to meet the growing demand for water along the Peninsula. Located seven stories below the surface, it typically carries water for more than a million people. No one has been inside it to inspect it since the water was turned on more than four decades ago -- until now.
"This tunnel went into service in approximately 1967 and it hasn't been inspected since," inspector Blake Rothfuss said.
Rothfuss is the lead quality assurance inspector on the three-mile stretch of pipeline running along Highway 280 in San Mateo County
"We're inspecting system infrastructure that rarely gets inspected but is so critical to the population that you rarely have the opportunity to unwater the tunnel, to get inside and check on them," Rothfuss said.
The stretch of tunnel was carefully walked by engineers and water officials looking for anything that may affect the flow or quality of the water being sent through it.
"We're looking for signs of distress in the concrete lining that might be indicated by cracks, might be indicated by leaking water, water leaking into the tunnel," Rothfuss said.
It can be dangerous work. Communication is by radio and an air horn letting everyone outside the tunnel know everyone inside is OK. Working in a nine-foot tall tunnel underground has unseen dangers. The air quality is constantly measured for dangerous levels of carbon monoxide or possibly explosive methane gas. To keep the air moving, a high powered fan forces air through the opposite end of the tunnel.
To keep water out during the inspection, every valve supplying water to the tunnel is turned off and locked until everyone is out of the tunnel.
"The opportunity for the SFPUC to inspect the condition of the tunnel is a rare opportunity," Rothfuss said.
It is an opportunity made possible by one of the largest water infrastructure upgrades in California history. Since the 1920s, water from Hetch Hetchy in Yosemite National Park has provided 2.5 million people in Northern California with some of the most pristine and valuable water in the nation. It is an engineering marvel managed by the San Francisco Public Utilities Commission, but years of deferred maintenance and old construction techniques have made the system vulnerable in major earthquake.
In 2002, San Francisco voters approved a bond measure to pay for their share of repairs to the aging system. It will be paid back over time with increases in water rates. Some of the largest projects are ramping up to start this year.
"We're going to be probably dedicating a project a month for the next six months," SFPUC General Manager Ed Harrington said.
Harrington is heading up the $4.5 billion project to upgrade the Hetch Hetchy water system. It includes replacing pipes over San Francisco bay with a tunnel, a new dam and upgrading water treatment facilities.
"We have $2 billion in construction going on right now," Harrington said.
Harrington says the goal is to completely upgrade the Hetch Hetchy water system by 2015.
One of the fundamental problems we have with this capital improvement project is rebuilding it while it remains online and that's a tremendous challenge," SFPUC water treatment manager David Briggs said.
That is why they are putting in a new tunnel near Crystal Springs Reservoir. It will provide an alternative path to keep water flowing to customers during routine maintenance and emergencies. But the older tunnel is still an important part of the system and that is why this inspection was so critical.
"It turns out the tunnel is in fantastic shape and were lucky enough not to have to go back into the tunnel for repairs for the foreseeable future," Briggs said.
"This opportunity is maybe one time in 100 years that the city gets a chance to get inside and verify that the condition of the tunnel is very good and the condition for the level of operation of it is at a high level of confidence," Rothfuss said.
The water was scheduled to be shut off for 20 days. In the end, workers finished in half the time, by working around the clock.
Written and produced by Ken Miguel