Petaluma main drinking water pipeline redirected ahead of Highway 101 widening

The fit of the cement-coated steel pipe needed to be snug so construction workers cutting and shaping sections of a redirected water channel beneath Highway 101 in Petaluma could weld the new pieces into place.

By 10 a.m. Tuesday, a pipe-laying vehicle was carefully lowering the nearly 3-foot-wide cylinder into one of two sections being installed. They were the final two pieces of a two-month $1.3 million project to relocate 600 feet of an aqueduct that transports water to about 309,000 people in Petaluma and parts of Marin County.

The vehicle operator and workers guiding it soon realized another foot of the water line needed to be cut, lengthening a job that had to be perfect so water could flow again within 15 hours before the stored water supply ran out.

Ghilotti Construction and Sonoma Water performed what officials likened to open heart surgery on the south county’s water system. The detailed work was required to finish relocating a portion of the 32-mile aqueduct so new bridge piers could be built by the SMART train underpass and support a wider highway.

"The aqueduct is the lifeline for the south county and into Marin in terms of delivering potable water,“ Sonoma County Supervisor David Rabbitt said. ”It’s 57 years old, but it’s still in great shape, and that’s been confirmed now on three separate occasions. This is the third opening of the aqueduct for projects we’ve had.“

Tuesday’s installation was the final adjustment made to the Petaluma aqueduct since 2011, when Caltrans began expanding 16 miles of highway through the Marin-Sonoma Narrows to provide three lanes in each direction. Before that, the pipeline had gone untouched since 1963 when it was first constructed.

Linking the new pieces required temporarily shutting down a portion of the system, and coordination with multiple cities who buy filtered Russian River water from the regional agency and distribute it to their community.

Sonoma Water cut lines north and south of Petaluma around 5 a.m. and the county agency had prepared to go as long as 15 hours without the 17 million gallons of water that flow daily through the aqueduct, general manager Grant Davis said.

Storage tanks in Cotati, Kawana and Kastania were topped off with a total of 100 million gallons to ensure every spout in Petaluma, Novato and as far south as Sausalito flowed without interruption.

“For customers, it was just another day,” said David Royall, Sonoma Water’s operations and maintenance manager.

Completing the final steps of the tedious project, which was funded by water rates to the nine cities and special districts across Sonoma and Marin counties, was an involved process, Ghilotti Construction project manager Nick Keane said.

Every new piece of the aqueduct was custom fabricated for the new route, and then surveyed before and after it was brought to the site. A 4-foot-wide tunnel was built to house the relocated pipeline beneath the highway.

About 420 feet of the former aqueduct will be filled with concrete and left underground, and a few smaller pieces will be scrapped, Keane said.

Sonoma Water will keep one segment for its engineers to analyze, Davis said. A project like this helps the region’s water supplier enhance its system, get a sense of how well the pipeline has aged and if future repairs might be needed.

“This is a niche (project) with infrastructure, emergency preparedness,” the water agency’s Davis said. “A lot of this makes us more resilient to know the condition of the pipe and to know that’s been installed safely for years to come.”

You can reach Staff Writer Yousef Baig at 707-521-5390 or yousef.baig@pressdemocrat.com. On Twitter @YousefBaig.