The Science of Sustainability

From Tunnel to Tap: Quake-Proofing Our Water Supply

  • share this article
  • Facebook
  • Email
tunnel boring machine

Next time we see this machine, it'll be on the other side of the Bay, in Newark.

As you head past East Palo Alto, toward the soon-to-be western end of the new Bay tunnel, it is easy to start thinking you're in the wrong place. There's nothing to see, just acres of flat bayside grassland off of Highway 101.

And then, suddenly, there it is: a big, deep hole in the ground.

What looks like a round elevator shaft the width of a five-lane freeway is the start of a tunnel that will, eventually, stretch five miles across the Bay. Bob Mues, like a lot of people here, says it’s one of the most exciting engineering projects he’s ever worked on.

Like me, he’s wearing a hard hat, neon vest, and safety glasses. (See them for yourself in the slide show farther down on this page.) He’s a construction manager for the San Francisco Public Utilities Commission, which is running this project. Mues says this is the first tunnel ever dug beneath the bay, despite what many BART riders may believe.

"I was around when we built the BART tunnel," he says. "The BART tunnel is a sunken tube."

(Scroll down to the bottom of this page to see an amazing 1940 silent film about Hetch Hetchy's construction — a colossal undertaking at the time — starring the ever-thirsty "Miss San Francisco." A few highlights: a 28.5 mile tunnel "the longest ever driven by man," workers being searched for tobacco before they enter the mine… probably a good idea when you're working with explosives, and the moment, on October 28, 1943, when the first trickle of water from Hetchy Hetchy reached the Peninsula.)

Mues points to the bottom of the shaft, to a white steel cylinder the size of a school bus, with a red tip. This is the star of the show, a state-of-the-art tunnel boring machine, arrived from Japan in May. To picture how it works, think about a circular cheese grater. The kind where you crank the wheel, and grated cheese falls out the middle.

But the machine does more than just dig. Mues says it functions like an underground factory. "The machine eats dirt, and extrudes finished concrete pipe in 5-foot lengths," he says.

All that discarded dirt (with a consistency like potters' clay, Mues says) will ooze out past the drill and onto conveyor belts that snake back through the tunnel, to Palo Alto. From there, it'll be trucked to Bair Island, near Redwood City, where it'll be used for wetland restoration.

And the next time anyone sees the drill, it’ll be on the other side of the Bay, in Newark. Mues says tunnel construction will take about 23 months. On average, that's 50 feet of tunnel a day.

Hetch Hetchy's Overhaul

The Bay tunnel is just one part of a vast overhaul of the Hetch Hetchy system, which carries water 167 miles from the Tuolumne River, near Yosemite, to Bay Area taps. There are 81 projects in all: pipes, water treatment centers, dams, reservoirs, all replaced or retrofitted with stronger, more durable parts.

All together, these projects will cost 4.6 billion dollars, and if you drink Hetch Hetchy water, you’re helping pay for it, thanks to a ballot measure that voters approved in 2002.

If it seems surprising, especially in this current budget climate, that Hetch Hetchy customers would have approved such an expensive project, one that essentially doubles many customers’ water bills (at a time when water systems seemed to be working just fine), consider what was then still a recent memory: Loma Prieta.

"Really, 1989 was a catalyst," says David Schwartz, an earthquake geologist with the United States Geological Survey. "It told everyone 'Hey, wake up Bay Area. You know, we’ve gone a long time, since 1906 with nothing happening, but we have big quakes in our future.'"

Schwartz and other geologists believe the next big quake is likely to come from the Hayward Fault, which runs through Berkeley and Oakland. Carbon dating shows that over the last 1700 years, the Hayward Fault has erupted approximately once every 140 years. The last major quake on it was in 1868, 143 years ago.

"So certainly in the next couple decades we really expect to see a 6.8 or a 6.9, maybe a 7 on the Hayward Fault," says Schwartz.

Learning from Earthquakes

All earthquakes are wake-up calls. Take the 1906 quake, which rendered San Francisco, and its fire stations, virtually without water for days.

"Essentially the entire city burned down," says Julie Labonte. She's a civil engineer tasked with overseeing all 81 projects of the Water System Improvement Program, as it's called. Labonte says after 1906, city officials vowed never to let the city burn again.

"That’s when city officials went to the Department of the Interior, to petition for the rights to water on the Hetch Hetchy Valley," she says.

That decision — to build a dam in Yosemite — sparked a bitter battle with the Sierra Club. Some environmentalists still want the dam torn down. But today, Hetch Hetchy supplies 90 percent of the water to San Francisco and Penninsula residents. It’s some of the cleanest water in the country. The 1906 earthquake is what got the system built.

Engineers at the Bay tunnel hope they can get it done before the next big quake hits. The tunnel is designed to last a century. It’s projected to cost $313 million and be complete by 2015.

Related

Explore: , , , , , ,

Category: Engineering, Environment, Geology, News, Radio

  • share this article
  • Facebook
  • Email

About the Author ()

Amy Standen is a radio reporter for KQED Science. Her email is astanden@kqed.org and you can follow her on Twitter at @amystanden.