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Tiny bubbles disappearing from SF, Peninsula water

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Water supplies are clearing up in San Francisco and on the Peninsula after a historic pipeline shutdown led to 41 days of cloudy tap water.

The 1930s-era pipeline that carries fresh water to the Bay Area from the Hetch Hetchy Reservoir and other dams east of San Joaquin County was dried out during most of January and early February.

The longest-ever closure of the 25-mile Coast Range Tunnel allowed San Francisco Public Utilities Commission officials and contractors to proceed with $175 million worth of projects designed to improve and protect water supplies.

Bay Area reservoirs were filled prior to the pipeline closure, which was scheduled to coincide with times of low water usage.
When the pipeline wasn’t in use, millions of SFPUC customers received their water directly from local storage and treatment facilities, including the Harry Tracy Water Treatment Plant in Sunol.

But the plant treated more water than is normally carried by pipelines from Sunol to customers, leading to tiny air bubbles becoming trapped in the unusually turbulent stream of water, according to David Briggs, the SFPUC’s water supply and treatment manager.

“It’s not a contaminant,” Briggs said recently. “The water is perfectly safe.”

At times, it took days for the cloudy water to reach taps from the Sunol treatment plant, leading to a rash of complaints about the apparent milkiness of customers’ water more than a month after the shutdown began, according to spokeswoman Maureen Barry.

Murky water wasn’t the only surprise during the shutdown. Two minor earthquakes struck at the nearby Calaveras Fault, Barry said.

Additionally, the Sunol treatment plant was knocked offline Jan. 19 for eight hours after it was hit by lightning.

“People who had worked there for many years had never seen this happen,” Barry said. “Everybody in operations was planning for the unexpected.”

The shutdown ended Feb. 13, one week ahead of schedule, according to Barry. Residents should be advised it could take some time before water supplies return to their normal, nonfizzy state.

jupton@sfexaminer.com


No easy task

A water-delivery pipeline was shut down for repairs.

85 percent: SFPUC water that travels through the Coast Range Tunnel

10.5 feet: Diameter of Coast Range Tunnel

25.2 miles: Length of Coast Range Tunnel, all of which was shut down temporarily

41 days: Duration of Coast Range Tunnel shutdown

2: Minor earthquakes on nearby Calaveras Fault during shutdown

1: Lightning strike at Harry Tracy Water Treatment Plant during shutdown

12: Workers killed by a 1930s methane explosion while building the tunnel

Source: San Francisco Public Utilities Commission