How the Times tested for soil toxins after the L.A. fires

Over three days in late March, four Los Angeles Times environment reporters and an editor fanned out across the Eaton and Palisades burn scars to collect 40 soil samples from residential properties: 10 in each burn area from properties where debris removal was completed by the Army Corps of Engineers and 10 in each burn area from the yards of standing homes.

At each stop, the team donned vinyl gloves and boot coverings to prevent the spread of contamination and collected five evenly spaced samples with a hand-held tool that takes 4-inch soil cores. At standing homes, we sampled throughout the yard. At destroyed properties, we sampled within the former structure’s footprint, where the federal cleanup crews had cleared debris and scraped up to 6 inches of soil.

Times journalists mixed these five samples in a lined bucket to create one “composite” sample to be tested in the lab. This sample pattern is designed to account for a wide range of soil conditions on each property and serve as an average, since it is possible that one part of a given property might be fully devoid of metal contamination while another might be heavily polluted. Composite sampling is a common practice in wildfire recovery.

Between every property, the team sanitized all soil collection equipment with distilled water and wipes, and changed gloves and boot covers — so that no potential toxins could accidentally track from one site to another.

We stored the samples in lab-provided jars, and kept the samples refrigerated at 38-40 degrees. At the end of the collection week, our editor drove the samples to BSK Associates, a state-certified environmental testing laboratory that tested soil on behalf of the government following the 2018 Camp fire and 2024 Mountain, Park and Borel fires.

BSK used an Environmental Protection Agency-approved method to test for 17 metals most often studied in post-fire recovery. To do this, BSK used an instrument that sorts out different elements from within the soil by mass and counts the atoms. Since each of these 17 elements has a unique atomic mass — for example, only lead has an atomic mass of 0.34 trillion billionths of a gram — BSK could then determine the concentration of the metals.

At each step of the process, our team and BSK meticulously documented the chain of custody for the samples, creating a record of, at each moment, which individual was responsible for the safekeeping of each individual sample.

The Times’ methodology rigorously followed soil-testing practices from previous official post-wildfire efforts. Our team reviewed documents outlining the response for the Camp and Woolsey fires, and spoke with soil-testing experts familiar with the standard methodology for California wildfires.

To find participants, we identified standing properties using the California Department of Forestry and Fire Protection’s damage inspection data and properties that had finished debris removal using the Army Corps’ dashboard. All participants consented to testing on their properties, and their exact addresses have been anonymized.

The testing methodology used by The Times is a conservative reading. By using composite samples, high levels of contamination from one part of the property can become diluted by relatively uncontaminated sections elsewhere on the property.

Further, due to cost considerations, The Times’ methodology differed from typical postfire soil testing practices in one key way: In previous fires, soil testers would collect multiple composite samples for larger properties, roughly one sample per 500 square feet. Our team took only one composite sample per property, regardless of size.

This means The Times’ results had a greater potential to miss smaller contamination hot spots on properties.

The Times found two properties cleared by the Army Corps in Altadena still had contamination above the state’s typical health-based cleanup goals: one arsenic, one lead. Altadena’s standing homes had arsenic, lead and mercury levels above typical cleanup goals, across three of the 10 homes our team tested. The Times found only a single reading above typical cleanup goals in the Palisades: a standing home with high levels of arsenic.