Duke Paired Soil Study at only 0.14% of Total Loss Lots

A Duke-led analysis of residential soils and structural ash from more than 30 properties affected by the Eaton and Palisades fires found highly variable lead and arsenic levels. Lead was highest in structural ash from some homes built before the 1970s, likely reflecting lead-based paint.

Researchers later compared more than 100 individual post-cleanup samples from just 17 residences with nearby pre-cleanup samples and found reduced lead and arsenic concentrations in the areas scraped by the EPA and Army Corps, particularly where initial levels were highest. The paired samples could provide useful information about what occurred at those specific properties, particularly because the Army Corps did not conduct post-cleanup testing. However, those 17 properties represent approximately 0.14% of the estimated 11,900 burned lots across the two fire zones—about 5,900 in the Palisades and 6,000 in the Eaton Fire area. Duke’s paired study size is a fraction of a percent of total loss lots and should be questioned whether any conclusions can be defensibly drawn from such a small and potentially unrepresentative sample.

Such a small percentage should not be presented as proof that Army Corps of Engineers debris removal consistently removed enough hazardous contamination across thousands of burned lots without a much larger, representative post-remediation testing program. EFRU encourages property owners to independently test their soil to understand the remaining impact on their specific property. Testing should not be limited to lead and arsenic; property owners should consider the full CAM 17 metals panel, along with lithium, manganese, and other contaminants associated with urban wildfire debris that if found above threshold can pose a health risk.

Duke also references the federal threshold for lead of 200 ppm. Residents should be aware that the state of CA set the safety threshold of 80 ppm for lead in 2009 and since then 80 ppm has been the standard for soil recovery in every CA fire recovery since then.
The Duke Nicholas School of the Environment publication can be found here.
On May 15, 2025, 12 soil researchers from nine universities sent Governor Newsom a letter outlining recommended soil-sampling methods. Read it here.