John Upton/The Bay Citizen

A welder clambers on top of a tunnel boring machine at the bottom of a shaft in East Palo Alto. The machine will burrow five miles under the Bay to Newark over two years.

Updated 5:30 p.m., June 17, 2011.

Construction on the first tunnel to go underneath San Francisco Bay is about to begin. The San Francisco Public Utilities Commission is building the tunnel, which will house a pipe carrying drinking water from the East Bay to the Peninsula.

Unlike BART's Transbay Tube, which sits on the floor of the Bay, the 5-mile long tunnel will require crews to bore under the Bay.

A tunnel-boring machine is being assembled at the bottom of a 125-foot shaft in Menlo Park. The digging itself is expected to begin in late July or August and last for two years. Construction of the Bay Tunnel is expected to finish in 2015.

The SFPUC says the tunnel is needed because the pipelines that transfer its water over the Bay are at risk of rupture, especially during an earthquake.

“They’re aging pipelines that have reached the end of their useful life,” said Maureen Barry, spokeswoman for the SFPUC’s $4.6 billion Water System Improvement Program.

The program will replace, reinforce, and expand the network of pipes and treatment facilities between the Central Valley and its customers along the San Francisco Peninsula and in southern stretches of the East Bay. “We can’t even maintain them properly because of their location in sensitive marshlands," Barry said.

The SFPUC estimates the tunnel will cost $313 million. The SFPUC's customers will see their water rates increase to pay for the tunnel.

Check out the following slideshow to learn more about the project.

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