A few weeks after the devastating 2017 Tubbs Fire raged through parts of northern California, Gerald and Serene Buhrz returned to their Santa Rosa home, turned on the kitchen sink faucet, and were hit with a stinging smell.
“The water smelled like diesel,” Gerald Buhrz, 77, said. “It smelled like you could probably light it with a match.”
He immediately alerted city officials, who tested his neighborhood’s water system and found high levels of potentially carcinogenic compounds like benzene. Buhrz waited a year until the water was deemed safe to drink. But his complaint highlighted a possible health risk that had gone largely unrecognized: water contamination after a wildfire.
Public officials anticipate such contamination to be all the more pressing this year, as record blazes burn vegetation and homes along vast stretches of the West Coast. Some neighborhoods in California are already witnessing benzene levels that exceed state and federal permissible limits as evacuees return to “do not drink/do not boil” warnings.
“The number of water systems that we expect to see impacted could be the highest yet,” said Daniel Newton, assistant deputy director of California water board’s division of drinking water. “It is a concern.”
Recent research suggests fires can lead to water contamination by heating up plastic pipes, which then leach chemicals into water. It’s also possible for damaged, depressurized water systems to suck smoke and pollutants — including compounds such as benzene — from the air into the pipes.
Benzene is a colorless chemical found in gasoline fumes, burnt wood, and plastic smoke. It’s quick to evaporate into the air and easily dissolves in water. During and after wildfires, exposure to benzene can occur either by drinking water, inhaling it when water is boiled for cooking, or during showers, when it might also get absorbed through the skin. In the short-term, benzene exposure is associated with a bout of light-headedness or nausea — but prolonged exposure is tied to increased cancer risk.
The U.S. Environmental Protection Agency has set 5 parts per billion as the maximum permissible level of benzene in drinking water, the same standard adopted by Oregon and Washington, but a higher threshold than the 1 part per billion limit in California. But benzene levels as high as 40,000 parts per billion were recorded after the 2017 Tubbs Fire and as high as 2,217 parts per billion following the 2019 Camp Fire. This year, at least one drinking water sample from California’s CZU Lightning Complex Fires-affected region had 42 times more benzene than the state’s acceptable limit. It’s possible more contaminated samples will soon turn up.
“We’re still early in the fire season,” said Stefan Cajina, chief of the north coastal section of California water board’s division of drinking water. “It takes a bit of time for the water systems to get back in and to start sampling and get laboratory results.”
Risks to human health depend on how contaminated the water is, and how long people are exposed. Health officials in California, for example, estimate benzene concentrations exceeding 26 parts per billion to be harmful in the short-term, and dangerous beyond 1 part per billion over the long run.
“Benzene is tricky,” said Gina Solomon, a clinical professor of medicine at the University of California, San Francisco. At lower levels, “it may not have any signs or symptoms and people would not be expected to get sick right away.”
“That’s why we want to make sure people aren’t exposed,” she said.
For water agencies, that requires speedy and frequent testing of main water supply lines and sometimes service lines. If tests reveal benzene levels beyond permissible limits, freshwater is injected into the system to flush out contaminated water. This process is repeated until benzene levels drop.
“Time is of the essence,” Newton said. “The quicker we’re able to flush the system, the more effective it is at minimizing the amount of contamination that occurs.”
But after the Tubbs Fire in Santa Rosa, for instance, three months of flushing did not bring down the benzene to acceptable limits in some cases, noted Andrew Whelton, an associate professor of civil, environmental, and ecological engineering at Purdue University. Layers and layers of toxic compounds had built up in hydrants, pipes, and meters, which continued to taint the water. These were eventually replaced.
Experts say that to minimize potential health risks, officials need to issue quick and comprehensive alerts to the public about potentially contaminated water.
But recent and past fires have seen inconsistent warnings and inadequate measures, Whelton said. In late August, officials with the state of California and San Lorenzo Valley Water District, issued a “do not drink, do not boil” advisory in the wake of water mainlines destroyed by the CZU Lightening Complex Fire.
Residents in the area weren’t restricted from using the water to shower, although they were asked to limit showering time, use cold or lukewarm water, and ventilate the area. At that point in time, it wasn’t yet clear what toxins might be in the water or how high the levels might be.
A few days later, limited testing revealed benzene in the water.
In such uncertain times, Whelton recommends a blanket “do not use” order to protect people from inhaling volatile compounds like benzene, which can readily evaporate at room temperature.
Benzene is far from Whelton’s only concern. He and his colleagues assessed several months of water contamination data from Tubbs and Camp Fires and found evidence of other hazardous compounds — including naphthalene, styrene, and methylene chloride — that exceeded either state or federal permissible limits. All are considered potential carcinogens.
That’s why Whelton cautions against using benzene alone as an indicator of whether drinking water might be contaminated, which is the approach taken by some agencies.
“Nobody has actually figured out which compounds are of most consequence,” he said. “In the case of Camp Fire, for instance, Paradise Irrigation District sometimes found benzene at levels that didn’t pose a risk, but other chemicals were there that did.”
His team is now trying to figure out possible compounds that could be used as an indicator to show whether or not water is safe to use during disastrous fires. Having such a benchmark will be increasingly critical as wildfires become more common and intense in the western U.S. with climate change.
“You’re going to continue to have wildfires and all these concerns will surface again and again,” Whelton said. “You have to start thinking about all the vulnerable points in the system and hardening them against future damage.”
Correction: A previous version of this story misstated where benzene levels that exceed state and federal limits have been detected. It is in California.