Two carcinogenic compounds have been discovered in Sevastopol’s aging water wells, sparking concern among city council leaders, especially as the city lacks funding to repair its infrastructure.

Specifically, traces of arsenic were detected in three city wells, according to a recently released city report. Tetrachlorethylene, commonly known as PCE, was also detected in one of these three wells.

But levels of arsenic and PCE in the city’s drinking water remain below thresholds deemed unsafe by state and federal regulators, city officials say. Indeed, filtration or treatment systems have been installed to eliminate most of the contaminants, and well water is mixed to reduce them even further.

“Our infrastructure is very old,” Sebastopol Public Works Superintendent Dante Del Prete told the council Tuesday. “But our water is safe.”

Unlike much of Sonoma County, Sebastopol does not get its water from Sonoma Water, the government agency that draws water from Lake Sonoma, Lake Mendocino and the Russian River.

Instead, it draws water from the Wilson Grove Highlands Formation Water Basin, an underground spring that produces nearly a million gallons of water per day for Sebastopol residents. The arsenic in the wells is present because of natural volcanic layers in the Wilson Grove, according to Del Prete.

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According to the California State Water Resources Board, “Arsenic is ubiquitous in nature and is commonly found in California drinking water sources.”

In Sebastopol, it was found in Wells Nos. 4, 6, and 7, along Petaluma Avenue, Highway 116, and Village Way, respectively. That’s according to monitoring by city staff as reported in the city’s annual Consumer Confidence Report, a federally mandated annual disclosure to its water customers.

Arsenic levels in the three wells averaged 4 parts per billion. The maximum level of contaminants allowed is 10 parts per billion.

“Although your drinking water meets federal and state standards for arsenic, it contains low levels of arsenic,” the report states. “The Arsenic Standard balances current understanding of the possible health effects of arsenic with the costs of removing arsenic from drinking water. The U.S. Environmental Protection Agency continues to research the health effects of low levels of arsenic, a mineral known to cause cancer in humans at high concentrations and which is linked to other effects on health such as skin lesions and circulatory problems.

To keep arsenic levels in drinking water at acceptable levels, the city relies on filtration and treatment systems for all three wells. It then mixes the water pumped from well No. 6 with the water pumped from wells No. 7 and 4.

“We mix the water to reduce arsenic levels so that it is at a safe enough level to meet regulations,” Del Prete told the council.

Well No. 4, however, presents an additional problem. Since 2012, PCE has been recorded in the well following contamination from a former dry cleaning company. But the water produced by this well is filtered to remove the contaminant.

“Dry cleaning chemicals are processed by a carbon system originally designed for gas station contaminants, which fortunately are no longer measurable,” Del Prete said. “We monitor and maintain, and our goal is to have non-detectable levels.”

The system works, he says. PCE levels in Well #4 range from 2.7 to 6.2 micrograms per liter before treatment. After being filtered, PCE levels are undetectable, says Del Prete.

The council prioritized the replacement of Well No. 4, installed in 1953 and which is the oldest well in the city. The city plans to borrow $3.7 million during its 2026-2027 fiscal year to complete this project.

Other projects to more permanently guarantee the city’s water supply would be “very expensive” and are not currently budgeted. Such projects include a complete overhaul and reconstruction of Well No. 6, which Del Prete said would likely cost $4 million.

Even though the city raised water and sewer rates in July, city staff say it will be years before the city coffers have enough money to begin maintenance and construction, long deferred. Of course, this would have to change if monitoring revealed increased levels of carcinogens.

Amie Windsor is the community journalism team leader at The Press Democrat. She can be reached at [email protected] or 707-521-5218.