California wildfires caused unexpected benzene contamination of drinking water

As the 2018 wildfire season begins in the western U.S., part of Northern California is still grappling with previously unrecognized and wholly unanticipated damage from fires that burned 15,000 hectares and devastated the state’s wine country last year.

In addition to destroying more than 8,000 structures and killing 44 people, those fires unexpectedly also caused persistent contamination by the carcinogen benzene in the water infrastructure in a Santa Rosa neighborhood.

First detected in November, the benzene levels persisted for months, and Santa Rosa city officials feared a large portion of their water system would have to be replaced­—a project they estimated would take two years and cost $43 million. Gradually, however, benzene levels dropped, most dramatically in the past few weeks, and a full system replacement may not be necessary. Nevertheless, the city will still be replacing up to 500 service lines at a cost of $3.4 million and supplying activated-charcoal filters to affected residents to ensure benzene levels fall below California’s limit of 1 ppb for drinking water.

The situation took the water supply industry and government agencies by surprise. Water experts say it’s likely to spur new research on the relationship between fires and water contamination and on ways to prevent such contamination.

The benzene, initially detected in some places at levels as high as 500 ppb, is largely contained in an 8-km² section of the water supply in Santa Rosa’s Fountaingrove district. Only 13 of 350 houses served by that supply survived the fires.

After benzene was first detected, the city embarked on a program of testing, research, and consultation with water scientists and engineers.

The likely contamination process, city officials reported at a public meeting in April, began when the fire’s exceptional intensity created extreme heat that melted the plastic water pipes on burned properties as well as other plastic components in the water system. Ash, debris, and burned plastic resins were sucked into the open pipes. At the same time, firefighters were drawing great quantities of water. This created a pressure drop, and contaminated water surged through the water system.

The city drained the system, expecting the problem to be solved, but further testing showed that benzene was still present. After more research, the city and its consultants realized that benzene had absorbed into the pores of the plastic pipes and was gradually leaching out.

This kind of fire-related contamination has never been reported before, city and federal officials say.

The many types of plastic used in the water system make it impossible to predict how long it will take for the contaminants to leach all the way out, says Emma Walton, a civil engineer for Santa Rosa. The city initially concluded that the Fountaingrove neighborhood’s entire water system would have to be replaced, much to the distress of homeowners eager to rebuild. But testing since January has shown a gradual drop in benzene levels, with benzene now undetectable in some water lines. Given the new results, the city may need to replace only service lines to properties and not main distribution lines. It begins that project this month and expects to finish in August.

The benzene contamination “will engender a lot of research,” says Bruce Macler, a water toxicologist with the U.S. Environmental Protection Agency. “We will hopefully have good advice for others and figure out how to not let this happen again,” he says.

Tony Radoszewski, president of the Plastics Pipe Institute, a trade association, agrees. “We encourage the entire water industry to study this issue,” he says.

Andrew J. Whelton, an engineering professor at Purdue University and plastic pipe expert, says Santa Rosa’s experience underscores the need for more research on plastic water pipes. The relative flexibility of plastic pipes is crucial in earthquake-prone areas like California. But their propensity for soaking up organics like a sponge can cause lingering contamination. Such pipe absorption was also seen in 2014 in Charleston, W.Va., when a storage tank containing 4-methylcyclohexanemethanol leaked into water supplies there.

The need to understand the newly-discovered, fire-driven contamination process is even more urgent than in the past because urban growth and its associated infrastructure are encroaching upon wildlife areas at an accelerated pace (Proc. Natl. Acad. Sci. USA 2018, DOI: 10.1073/pnas.1718850115), and fires are becoming larger and more intense because of climate change (Nat. Ecol. Evol. 2017, DOI: 10.1038/s41559-016-0058). In recent weeks, wildfires have begun blazing across the western U.S., in California as well as Arizona, Colorado, Idaho, New Mexico, Oregon, Texas, Utah, and Washington as of C&EN deadline.

The situation facing Santa Rosa should sound an alarm, Whelton says. “Urban areas prone to fire damage should pay attention.”

Elizabeth Wilson is a freelance writer based in the San Francisco Bay Area.