Sonoma County well owners advised to test water for contaminants as a result of two-year drought

Concern over ‘naturally occurring contaminants’ in about 45,000 private wells

With groundwater levels lower than normal after two years of drought, Sonoma County and state officials are recommending private well owners test their water for natural contamination.

“Well owners should test their well water to ensure it is safe to consume,” Christine Sosko, county director of environmental health, said in a news release.

Shrinking aquifers that caused some wells to run dry last year may have increased concentrations of substances that “can be harmful to human health,” Sosko said.

Testing for “naturally occurring contaminants is highly recommended,” she said, adding that residents should contact a private water treatment expert for assistance if tests detect any unhealthy substances.

There are about 45,000 water wells in the county, the most per capita of any California county, officials said in the release.

Most residents who depend on wells are beyond the reach of city and special district water systems fed largely by Sonoma Water, the county agency that serves more than 600,000 residents in parts of Sonoma and Marin counties.

“Testing the quality of private drinking water wells is a critical component to protecting public health,” Matt St. John, executive director of the North Coast Regional Water Quality Control Board, said in the release.

Private wells should be checked every year for the presence of coliform bacteria, nitrates and any other contaminants of local concern, the Centers for Disease Control and Prevention website says.

Arsenic, nitrates and hexavalent chromium are naturally occurring contaminants in Sonoma County groundwater that also have links to industrial and agricultural processes, according to the state water board.

“Those three are on our list,” confirmed Tyler Judson, president of Sebastopol-based Weeks Drilling & Pump, which does groundwater testing.

When underground water tables are high these substances can be diluted to a point below the maximum contaminant level set by the Environmental Protection Agency, said Christoper Watt, a senior engineering geologist with the water board.

The contaminant level can rise when there is less dilution from rainwater, he said.

Judson said there has been no recent uptick in requests for water testing, which he thinks might make sense now.

“If your water hasn’t been tested in a few years it’s never a bad idea,” he said.

Arsenic occurs naturally in the environment and also comes from industrial and agricultural activities including pesticides, while nitrates — found naturally in mineral deposits, soil and water — also come from fertilizer, feed lots and sewage, according to the U.S. Geological Survey.

Hexavalent chromium, a toxic and carcinogenic metal, was the object of consumer advocate Erin Brockovich’s successful lawsuit in the 1990s faulting PG&E for contaminating the water in Hinkley, California.

Stanford scientists in 2018 announced a finding that naturally occurring chromium affects more wells and more Californians than industrial sources of the toxin from faulty industrial waste disposal.

Arsenic is by far the most prevalent of the three groundwater contaminants exceeding federal safety levels in Sonoma County private wells, according to maps posted online by the Community Water Center, a nonprofit aimed at providing safe drinking water.

There are impacted tracts in Sonoma Valley, west of Petaluma, Rohnert Park and Santa Rosa and surrounding Healdsburg. Visit the interactive maps at https://bit.ly/3tEu3CV.

Along the coast from Jenner to about halfway north toward Sea Ranch are numerous tracts where arsenic concentration is more than double the federal standard for drinking water.

Nitrates and hexavalent chromium appear in small, isolated tracts, including a lone pocket of the latter north of Windsor.

Despite heavy rains in October and December that have turned the landscape green and recharged local reservoirs, officials are also urging private well owners to conserve water for sustenance should the drought continue this year.

Since the start of the dismal 2019-2020 water year on Oct. 1, 2019, Santa Rosa has received only 54 inches of rain, 30% short of its historic average, the release said.

The city would typically get an average of 77 inches of rain during the same period.

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.