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| Connection: Keeping Bay Area drinking water supplies safe during earthquakes involves boring new tunnels. (John Upton/The Examiner) |
Tunnel below Bay will pipe water
By: John Upton
12/29/09 9:41 AM PST
The first tunnel bored beneath San Francisco Bay will carry drinking water five miles from Fremont to San Mateo County.
Boring of the $350 million Bay Tunnel is one step that’s planned as part of an effort to create a 21-mile stretch of new piping between the East Bay and the Peninsula to ensure that water continues to reach millions of customers after an earthquake.
The project is part of the multibillion-dollar Water System Improvement Program, which aims to overhaul the Hetch Hetchy water system that holds and transports drinking water for 2.5 million Bay Area residents.
As part of the program, the San Francisco Public Utilities Commission is replacing and reinforcing water pipes and tunnels throughout a 167-mile network that carries snowmelt from Hetch Hetchy Reservoir in Yosemite National Park west to San Francisco and surrounding cities.
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 They were built between 1925 and 1973 using now-outdated construction materials.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.
Tunnel construction efforts using a heavy-duty tunnel-boring machine are expected to begin next year and last until 2015. The tunnel will pass up to 100 feet beneath the Bay floor.
Dirt and other fill that’s removed from the tunnel as it is bored will be used by an unrelated but adjacent project that aims to restore industrial salt ponds to native marshland, Ortiz said.
Other projects to improve the earthquake resilience of the system of piping that carries water west from the East Bay will increase the number of interconnections between pipes.
Interconnections between pipes are important because they allow water officials to redirect water from one pipeline to another following a rupture or maintenance and repair efforts, without completely switching off the westerly flow of water.
New San Mateo pipeline to replace aging passages
A custom-made tunnel-boring machine is helping dig a 12-foot-wide tunnel for a new water pipeline beneath Polhemus Road in San Mateo County.
While other pipelines in the area are being rebuilt or repaired, the Crystal Springs Bypass Tunnel will house a new pipeline.
The 4,200-foot pipeline is needed because aging underground pipes in the area, which carry all of the water from the East Bay to the Peninsula and San Francisco, are vulnerable to landslides and earthquakes.
Work on the tunnel and pipeline is expected to finish in late 2011 and cost $95 million.
Tailor-made: A custom tunnel-boring machine is laying the foundation for a new San Mateo County water pipeline, which will travel through a 12-foot-wide tunnel.
Bay Tunnel by the numbers
229 million gallons Water carried west through Bay Division pipelines on a typical winter day
21 miles Planned new Bay Division Pipeline
5 miles Length of pipeline that will pass beneath Bay floor
10 feet Width of tunnel planned beneath Bay floor
9 feet Width of steel piping that will occupy tunnel
3,000 feet Existing pipeline that sits on Bay floor
Source: SFPUC
Protecting water delivery
The Water System Improvement Program is a $4.4 billion to $4.6 billion, 12-year effort to rehabilitate and protect the system of pipes, reservoirs and equipment from earthquakes. The entire system delivers water — largely from the Hetch Hetchy Reservoir in Yosemite National Park — to 2.5 million Bay Area customers.
