Part of the Hetch Hetchy water system delivers water to the Moccasin Creek power generation facility near Groveland. Photo by Flickred!.
A $350 million tunnel is being drilled beneath San Francisco Bay as part of an ambitious plan to update the aging Hetch Hetchy water system. The tunnel will create a 21-mile stretch of new piping between the East Bay and the Peninsula to help secure the water supply to San Francisco and Peninsula communities in the event of another major earthquake like Loma Prieta or the 1906 quake whose fires devastated San Francisco.
The piping planned beneath the Bay under the WSIP will be part of the fifth major pipeline installed in the Hetch Hetchy system between the East Bay and the Peninsula since the 1920s.
The existing four pipelines are aging and could rupture during an earthquake. They were built between 1925 and 1973 using now-outdated construction materials.
Two of the pipelines veer south and wind around the Bay, passing through Silicon Valley.
The other two pipelines cross over the Bay on a custom-built bridge that runs parallel to the Dumbarton Bridge between Newark and Menlo Park.
The pipes that cross the water leak badly, leading vegetation to flourish at their corroded metal seams. But the ramshackle 1920s-era bridge crosses sensitive wetlands that are protected by federal environmental laws. Those laws effectively prevent water officials from accessing or maintaining the pipeline.
“You basically can’t walk on it,” Project Manager Joe Ortiz said. “We have some pretty extensive environmental regulations — certainly the most that I’ve seen on any project that I’ve worked on in 23 years. In the ’20s, they could do anything. But nowadays, with our regulations, it’s almost impossible to step on the land.”
An underwater 9-foot-wide metal pipeline is planned to eventually replace both Bay-crossing pipes, although it’s not known whether they will be removed because dismantling efforts could disrupt wetland wildlife. (SF Examiner)
The tunnel will be constructed using a custom-built boring machine similar to the one that bored the tunnel from England to France under the English Channel. Construction is expected to begin next year and last until 2015. The tunnel will run 100 feet beneath the floor of the Bay. Dirt and sediment removed during the tunnel boring operations will be used as fill to help restore native marshlands in the area.