Petaluma aqueduct to receive upgrades

A project to protect a vital pipeline that supplies the vast majority of Petaluma’s drinking water is expected to get underway as soon as July, potentially snarling traffic along Petaluma Boulevard South.

The $1.3 million project will update anti-corrosion systems already in place along the Petaluma aqueduct, a more than five-decade old pipeline that serves 600,000 residents in Petaluma, Cotati, Rohnert Park and northern Marin County. The underground aqueduct, which runs from downtown Santa Rosa to southern Petaluma, carries an average of 2.24 million gallons of water daily, according to information from a Sonoma County Board of Supervisors staff report and Sonoma County Water Agency Community and Government Affairs Manager Ann DuBay.

The pipe carries 98 percent of Petaluma’s water, Director of Public Works and Utilities Dan St. John said. The other 2 percent comes from local sources and groundwater, and the city also uses recycled water to irrigate some urban and agricultural areas, Operations Manager Kent Carothers said.

“Petaluma depends on this pipeline to deliver pretty much all its drinking water and so this project will help extend the life of that pipeline by another 50 years,” DuBay said. “That saves people in Petaluma in the long run a lot of money by not having to replace the pipeline and they continue get clean, inexpensive drinking water.”

The project will upgrade the pipeline’s cathodic protection system which uses so-called “sacrificial metal anodes,” which stop the pipe from rusting or corroding. The update will implement a new system with a longer life span that’s easier to replace, DuBay siad.

In 2007, the Sonoma County Water Agency performed a corrosion survey along the aqueduct, determining that 60 percent of the pipe was no longer adequately protected from corrosion based on National Association of Corrosion Engineers standards, DuBay said. The decreased protection could have happened because the anodes installed with the old system could be depleted and need to be replaced or the anodes could have been disconnected from the pipeline, DuBay said.

“This is an aqueduct that’s been there many, many years, and it’s in good condition, but we want to prevent it from getting corroded,” DuBay said. “What the contractor does is dig these very narrow but very deep wells where they put a piece of metal into the well and that metal attracts all the minerals and things that potentially corrode the pipeline, and instead of corroding the pipeline, all these elements are attracted to and corrode the metal in this well.”

Otherwise, the pipeline is in good condition and there were no indications of leaks or other issues after a limited assessment study was done, she said. The agency is in the process of implementing a rigorous assessment on the entire aqueduct, which will take several years to conduct.

The project to replaced anodes is set to kick off in Santa Rosa in April and will work its way down the pipeline, reaching Petaluma by July or August, DuBay said.

Several anodes will be replaced in the Penngrove area without traffic disruptions before work reaches Petaluma.

The replacement of the anodes will take place at six sites along Petaluma Boulevard, beginning near Brewsters Beer Garden and Restaurant and ending at the Petaluma Veterans Memorial Building, she said.

The agency will work with the city for traffic control plans, but details about traffic disruptions were not yet available, DuBay said. At each site, there may be lane closures lasting up to one week, but construction noise will be limited to normal working hours on weekdays, according to a notice sent by the water agency to affected Petaluma residents.

Work will also potentially cause a disruption in the front parking lot of the DMV on Southpoint Boulevard, she said.

Each site will take about two weeks, with work to include excavating the pipeline and drilling the wells, she said. The project will be wrapped up in Petaluma within a couple months, she said.

Funding for the project comes from Sonoma County ratepayers.

Sonoma County Supervisor David Rabbitt lauded the update to critical infrastructure.

“We have to continue to invest in infrastructure, we don’t have the luxury not to,” said Rabbitt, who also functions as a director of the Sonoma County Water Agency.

“We too many times build something and when we’re done with that, we go away and look at the next shiny thing. It’s kind of like roads and everything else – it’s important to make sure we continue to keep in the best shape possible all pieces of infrastructure. There’s no more vital piece than a pipeline that supplies water.”

Vice Mayor Mike Healy said the city several years ago thought a new “parallel aqueduct” would be necessary, prompting a temporary urgency moratorium that delayed the Target shopping center project.

Increased water conservation assuaged concerns about capacity, but worries about reliability remained, he said.

“The Petaluma Aqueduct is always in use and can’t be shut down for maintenance,” Healy, who also serves as the city council representative to the Sonoma County Water Agency Sustainability Agency, wrote in an email. “So this new cathodic protection is a cheap way to extend the aqueduct’s life for decades and avoid several tens of millions of dollars in expenses for a new aqueduct. That expense would have caused a bump to in rates but now we can avoid it. Very good news all around.”