After the fire, what’s in the soil?

By Judy Abel · Fri Aug 14 2026

New guide outlines steps for testing and remediating potentially contaminated soil

For Malibu residents rebuilding after the 2025 fires the question remains: What was left behind in the soil? When homes and other structures burn, materials including lead-based paint, appliances, machinery, and car batteries release hazardous substances. Ash, smoke, and debris can settle on surrounding properties, potentially introducing contaminants into the soil that we will rebuild on. A cross-sector collaboration, including UCLA and USC researchers known as CONSORTIUM, has developed a guide to help fire-affected homeowners, renters, and businesses understand those risks and determine what steps may be necessary to address them. The organization established a soil remediation working group to develop practical recommendations for post-fire soil cleanup.

The guide's central message is that residents do not have to solve everything at once.

In the short term, reducing direct contact with potentially contaminated soil can lower exposure while residents arrange testing and consider whether remediation is necessary.

Among the contaminants identified in post-fire testing are heavy metals such as lead, polycyclic aromatic hydrocarbons, or PAHs, and per- and polyfluoroalkyl substances, known as PFAS or “forever chemicals.” CAP.LA and USC CLEAN have tested more than 6,000 lots across Los Angeles County following the 2025 fires, according to the guide.

CONSORTIUM has focused much of its guidance on lead because it has been found frequently in post-fire soil testing.

For Malibu residents living on or returning to fire-affected properties, the guide recommends several immediate measures. Bare soil should be covered when possible. Residents should remove shoes before entering their homes, wet-mop floors and wipe down surfaces rather than dry sweep, and limit children and pets from digging in exposed soil. HEPA filtration can also help reduce contaminated dust indoors.

Children playing in soil and gardening are identified as higher-exposure activities, while walking through a yard is considered lower risk, primarily because soil can be tracked indoors. Rebuilding can also increase exposure if dust-control measures are not used.

For families with children or pets who remain on a property while deciding what to do, CONSORTIUM recommends temporarily covering bare soil with 2 to 4 inches of clean material, such as clean soil, quartz sand, gravel, or compost.

Testing comes first

According to CONSORTIUM, soil testing is the only way to determine whether remediation is necessary. Testing should focus on exposed soil, children's play areas, gardens, downspouts, ash and debris areas, and locations likely to be disturbed during rebuilding.

The guide emphasizes that contamination can vary significantly even within a single property. Multiple samples from different areas are therefore important, and a neighbor's soil test should not be considered a substitute for testing one's own property.

Residents can hire professionals to collect samples or, where available, participate in free testing programs. CONSORTIUM recommends professional laboratory testing for CAM 17 heavy metals, lithium, hexavalent chromium and, if available, PAHs. Homeowners should also request chain-of-custody documentation.

USC CLEAN offers free self-submitted testing that primarily looks for lead. However, the guide cautions that self-submitted testing may not be sufficient to develop a professional remediation plan or support certain legal claims.

Understanding the results

For homeowners receiving soil test results, one important figure may be the concentration of lead.

California's residential screening limit for lead is 80 parts per million, while the U.S. Environmental Protection Agency's limit is 200 ppm. CONSORTIUM stresses that screening levels are not a strict dividing line between “safe” and “unsafe.” Actual risk depends on the level of contamination, frequency of contact, whether soil is covered and who is exposed.

For properties with lead concentrations above 80 ppm, the guide recommends considering additional testing, particularly when children under 6 or pregnant women regularly use the property. At concentrations above 200 ppm, professional remediation is recommended.

Four options for cleanup

CONSORTIUM outlines four primary approaches to remediation: excavation and disposal, capping, immobilization, and bioremediation.

Excavation removes contaminated soil and replaces it with clean soil, providing the greatest certainty but potentially at a higher cost. Capping covers contaminated soil with a protective barrier such as clean soil, gravel, concrete, or pavement, while immobilization uses materials that can bind contaminants and reduce their movement.

Bioremediation uses plants, bacteria or fungi to remove, break down or reduce certain contaminants. It can be effective for organic contaminants such as PAHs, but metals such as lead cannot be broken down biologically.

Costs vary by property and method. The guide estimates excavation can cost up to $50,000 or more, while capping, immobilization and bioremediation can range from approximately $10,000 to $100,000.

CONSORTIUM advises homeowners to have test results reviewed by an independent environmental professional before beginning remediation and to use licensed contractors experienced in residential post-fire contamination. Residents should also ask how dust will be controlled, how cleanup will be verified, and where contaminated soil will be taken if excavated.

The guide warns this is not a do-it-yourself project because digging and moving soil can increase exposure and spread contamination.

The Los Angeles County Public Health free soil testing program is ending with last day to submit soil samples August 14, 2026. Going forward for soil testing services visit the USC CLEAN Program website: public-exchange.org/usc/project/soil-testing