US: Contaminants’ havoc after fires

Parts of L.A. could go days without clean water. As authorities across the Los Angeles area warn against using some municipal water supplies to drink and bathe because of wildfire-borne contaminants, experts cautioned that it could be days, weeks, even months before some water supplies become safe to use again.

During wildfires, water systems can become contaminated in a number of different ways. When a fire hydrant is not in use but water is flowing beneath it, negative pressure can pull debris and contaminants into a water main. When a house or property loses water pressure because of damage or destruction, contaminants can freely backflow into the water system.  And when water pipes and tanks made of thick plastic are burned or heat up, contamination can leach into supplies. 

More than 9,000 structures have been destroyed or damaged in the Palisades and Eaton fires, according to preliminary estimates that are likely to increase. How long water will remain unusable depends on the scale of contamination. Other major disasters have seen areas go weeks, and in extreme cases months, before water was usable again.

More frequent wildfires also strip the landscape, making it less able to retain water during significant winter rains, said Kurt Schwabe, a professor of environmental economics and policy at UC Riverside. That in turn causes caustic compounds present in the soil, including fire retardant dropped by aircraft, to “percolate those chemicals into streams and ground water,” Schwabe said.

Read the full article in the San Francisco Chronicle
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