Inside the New Tunnel 100 Feet Below San Francisco Bay

By Molly Samuel and Amy Standen

Thursday is the 24th anniversary of the Loma Prieta Earthquake, which, aside from damaging the Bay Bridge and disrupting a World Series game, reminded Bay Area residents that our water system is on shaky ground. (Well, it probably didn’t really remind everyone of that.)

So in 2002, San Francisco got around to passing a ballot measure to seismically retrofit the water system. And in 2010, the San Francisco Public Utilities Commission started construction on a tunnel under the Bay that’s intended to be able to deliver our drinking water, rain or shine or earthquake. The $286 million tunnel is the first that’s actually beneath the Bay; BART’s Transbay Tube sits on the bottom of the Bay.

The tunnel is five miles long and 15 feet in diameter, built with concrete and steel pipeline. (Molly Samuel/KQED)

It’s not quite finished, but to commemorate the earthquake anniversary, the SFPUC invited media down into the tunnel, to see the thing before it fills up with water from the Hetch Hetchy.

One end of the tunnel is in Menlo Park, the other end is in Newark. An elevator on the Menlo Park side goes down more than 100 feet to the opening of the tunnel. (Molly Samuel/KQED)

Sorry for the graininess; it’s pretty dark in there. (Amy Standen/KQED)

To dig the tunnel, the SFPUC brought in a $10 million custom-made tunnel-boring machine from Japan. Engineers here like to say the machine “eats dirt and spits out concrete tunnel.” Driving the machine were miners who spent ten-hour work days 100 feet below daylight. When they got to the other side of the tunnel, they were less than a quarter of an inch off target — “well within the margin of error,” says Program Director Julie Labonte.

The SFPUC expects to finish working on the tunnel in late-2014, six months ahead of schedule. (Molly Samuel/KQED)

To learn more about the project, watch a TV segment we did about it: