From its source high in the Sierra, snow melt trickles down to the Tuolumne River into the Hetch Hetchy Reservior in Yosemite National Park. This is some of the most pristine and valuable water in the nation – 265 million gallons of per day travel some 160 miles to homes and businesses in the Bay Area. It is an engineering marvel.
But time has taken its toll. Now just maintaining the region's largest water system has become an engineering feat in itself. The aging network of reservoirs, pipes, pumps, tunnels and treatment facilities crosses five earthquake faults, including the Hayward Fault, which is well overdue for a major quake.
"We want to be able to tell you that if there is a major earthquake on the Hayward Fault, or something else, you'll still get water within a very short period of time," says Ed Harrington, with the San Francisco Public Utilities Commission.
Harrington is in charge of the San Francisco PUC, which owns Hetch Hetchy.
In 2002, San Francisco voters approved a bond to pay for their share of repairs to the aging system. It will be paid back over time with increases in water rates. It set the stage for upgrades that secure a source of water for nearly two-thirds of the Bay Area.
"Much of it has aged, so you're talking 80 projects worth over $4 billion dollars that we'll seismically retrofit and really strengthen the entire system," says Harrington.
Some of those projects have started or are in the works. South of the Dumbarton Bridge, aging pipelines need to be replaced. Engineers are planning to run new pipes under the bay from Newark to Menlo Park.
"It's going to be a five mile tunnel. It's going to be the first tunnel underneath the bay. The BART doesn't count. That's a tube," says Joe Ortiz, senior project manager.
Near Sunol, the Earthen Calaveras Dam will be torn down and a new one will be built. The water level has been reduced for fear it may collapse. The replacement is critical to securing the water supply during dry years.
"The dam is not seismically safe to keep the full reservoir level in the reservoir. So, right now, the reservoir is down to about 40 percent of the total capacity," says Dan Wade, Calaveras Dam Replacement Project.
On the Peninsula, the spillway at the Crystal Springs Dam will be improved and a nearby pumping station will be upgraded less than 100 feet from the San Andreas Fault.
"These generators behind me are actually outdated as we speak. We are having a very hard time getting any spare parts. It's critical that we replace these generators in the next few years," says Julie Labonte, seismic improvement director.
Work has already started on San Francisco's largest water storage facility -- an eight city block reservoir in the Sunset District is operating at half capacity while workers shore up the massive project.
"In the event of an earthquake, if we did not perform some of that work, there would be the possibility that we could loose this reservoir or the ability to store water in this reservoir," says Labonte.
In Fremont, where the Hetch Hetchy pipeline crosses the Hayward Fault, work was recently completed on emergency valves on either side of the fault.
"We can close these valves and shut down the water to either one of the pipelines that may have ruptured, then it will be much more easier for us to go in and fix it. Also, we would prevent a big water discharge," says Ortiz.
But even with all this work, much of the system is still vulnerable. There are still dozens of other projects to be completed. Environmental reviews are underway. Major construction is expected to begin next year. The entire project is currently on track to be finished by 2015.
There were no homes there when the pipes were laid along much of the pipeline's route, but that's not so today. The major impact will be when work begins on the portion that slashes across Menlo Park and Redwood City.
Written and produced by Ken Miguel.