Tunnel Under Bay Will Be Water Lifeline to San Francisco, San Mateo and Santa Clara Counties

Bay City News —   The San Francisco Public Utilities Commission gave a guided tour today of the Bay Tunnel project, a planned $286 million, earthquake-resistant water pipeline and the first tunnel to be built beneath the floor of the San Francisco Bay.

The Bay Tunnel, which is about 90 percent complete, is to be part of the 176-mile Hetch Hetchy Regional Water System that pipes fresh water from reservoirs outside Yosemite National Park to San Francisco, serving 2.5 million people. The tunnel runs from Newark down to a maximum of 125 feet under the floor of the bay to the edge of Menlo Park, a mile south of the Dumbarton Bridge, according to Julie Labonte, director of the SFPUC's water system improvement program.

To be completed by next summer, it is the first tunnel constructed under the bottom of the bay. BART's Transbay Tube was built on top of the bay's floor, Labonte said.

The tunnel is part of a series of 81 projects the SFPUC began 10 years ago after the agency conducted studies and found that a major earthquake in the Bay Area could "create a catastrophic failure of the Hetch Hetchy system which in turn could result in parts of our service area to be without water for up to two months," Labonte said.

The San Francisco Bay Area sits on what is known as the "Ring of Fire" along the Pacific Ocean where 90 percent of the world's earthquakes occur and the U.S. Geological Survey predicted in 2008 that the Bay Area had a 63 percent chance of a major earthquake within 30 years, Labonte said. "So, those probabilities are now so much higher," Labonte said.

 In light of the dangers posed by earthquakes, the SFPUC approved a $4.6 billion water improvement plan a decade ago to repair and replace aging sections of the water system to make them seismically safe, including building the Bay Pipeline, Labonte said. So far, 62 of the 81 projects in the plan, across seven counties from California's Central Valley to downtown San Francisco, have been completed, she said.

The Bay Tunnel is considered a key part of a "lifeline" to deliver fresh water across the bay to SFPUC customers in San Francisco, San Mateo and Santa Clara counties even in the event of an earthquake, according to Labonte. "It is the one that will survive a major earthquake," she said. "It is possible that other (pipeline) conduit could fail. But this one has been designed to withstand a maximum credible earthquake on all the major faults here in the Bay Area."

 The project, to be completed by sometime next summer, is also meant to replace a pair of aging water pipes, built across the bay on wooden trestles in 1925 and 1932, still in use today, Labonte said.

Pressurized water coming down via gravity on sloping pipelines from the Hetch Hetchy Reservoir near Yosemite will start flowing through the Bay Tunnel and into the existing system to San Francisco in late 2014, Labonte said.