State experts outline post‑fire drinking‑water risks, sampling rules and multi‑month recovery from recent California fires

State water officials on Nov. 20 told the California Water Quality Monitoring Council that wildfires can contaminate drinking‑water distribution systems and that recovery can take weeks or months.

The Division of Drinking Water (DDW) described how negative‑pressure events during fires — when lines dewater because of leaks and firefighting use — can draw smoke, gases and debris into service lines. ‘‘Benzene is by far the most prevalent contaminant that shows up over an MCL,’’ Yvonne, a DDW presenter, said, noting California’s benzene MCL is 1 part per billion (the federal MCL is 5 ppb).

DDW assistant deputy director Andrew Altavote and field staff outlined the agency’s emergency response steps: gather information on affected systems, spin up district coordination, work with local emergency managers and mutual‑aid partners, and prioritize public health protection through notices and sampling. Jason Spots (DDW emergency management) described reporting to the State Operations Center and coordination with Cal OES, EPA Region 9 and FEMA when events are large.

Laboratory oversight and data quality were central to the presentations. Christine Sotelo, program manager for California’s Environmental Laboratory Accreditation Program (ELAP), said all drinking‑water VOC analyses conducted for regulatory purposes must be run by ELAP‑accredited labs and uploaded to the California Laboratory Intake Portal (CLIP) so regulators can see the results. ELAP certified roughly 500 laboratories statewide and can help identify surge capacity in emergencies, she said.

Guidance on sampling for wildfire‑related volatile organic compounds (VOCs) is evolving, DDW staff said. When DDW requires VOC testing after qualifying fires, agencies typically use EPA method 524.2 with a modified collection technique. DDW recommended that, for service‑line samples, water should stagnate at the tap for 72 hours before collection and that lines should not be flushed prior to the sampled stagnation period because flushing can remove the very contaminants the test seeks to detect. Those VOC results are publicly available via CLIP, though DDW noted public entries currently appear as single data points and identify location only at system level.

Case study: Los Angeles January fires

Sean McCarthy (DDW Southern Branch) reviewed sampling and recovery from the Palisades and Eaton fires in January. Nine community water systems required coordinated response; systems collected more than 1,500 VOC samples (mostly at service lines). About 12% of samples had at least one VOC detection; benzene was detected in roughly 8% of samples and exceeded California’s 1 ppb MCL in 80 samples. McCarthy emphasized that contamination was highly localized — many samples were non‑detect — and that the areas of concern clustered around dead‑ends or pressure‑zone edges. Recovery steps included damage assessments, isolating broken service lines, targeted flushing, repeated sampling and, in some cases, temporary interconnections to neighboring systems to supply clean water.

Research and operational gaps

Academic and agency researchers urged further study to explain why contamination appears in some places and not others. Allison Tilze, a PhD student at UC Irvine, presented a volunteer point‑of‑use study showing mostly low VOC levels at standing homes after the fires; benzene exceedances were rare in her sampling. Her preliminary lab microcosm work showed that added VOCs can stimulate microbial activity in stagnant water, raising questions about how chemical intrusions might alter distribution‑system microbiology.

Council discussion and next steps

Council members and presenters discussed practical next steps: improve public messaging about water safety (DDW noted that more than 97% of Californians receive safe tap water daily), prepare sampling plan templates and data‑quality checklists that agencies and smaller systems can adapt, and coordinate with ELAP to identify laboratory surge capacity. The council’s new post‑fire monitoring work group will continue developing a statewide approach and consider issuing guidance or a sampling‑plan library for different incident scenarios.

What happens next

DDW staff said decisions to lift precautionary do‑not‑drink or do‑not‑boil notices are based on repeated rounds of sampling and the demonstration that targeted areas return to nondetect for VOCs; the agency will continue to refine protocols and work with researchers, ELAP and field offices to improve timeliness and comparability of data. The council’s post‑fire work group will incorporate lessons from the LA response and consider drafting ready‑to‑use data‑quality templates and communications resources.