TL;DR

LA Post Fire: PostFire: Soil Expert Q&A #6 

Host: iO Tillet- Wright, wildfire survivor and activist 

https://www.iolovesyou.com/, postfirela.org 

Guests: Professor Seth John, Soil Expert, Associate Professor of Earth Sciences, University of Southern California. https://dornsife.usc.edu/profile/seth-john/ 

Main Concerns About Soil Contamination & Debris Removal 

● Homeowners must choose between private debris removal or Army Corps of Engineers. ● Army Corps and EPA are not testing soil, only removing six inches from burned structures. 

● Uncertainty remains about contamination in the rest of the property. 

Findings on Lead Contamination 

● Research focuses on lead levels in soil post-fire. 

● Lead concentrations in burned areas are elevated compared to non-burned areas. ● Uses X-ray fluorescence spectroscopy to measure contamination. 

Lead Levels & Safety Guidelines 

● Lead is not a safe nutrient; ideally, it should be at zero. 

● Various safety thresholds: 

○ EPA past standard: 1,600 PPM for residential soil. 

○ EPA play area standard: 400 PPM. 

○ New EPA residential standard (2023): 200 PPM. 

○ California threshold: 80 PPM. 

● Findings in Altadena: 

○ Burned area ash contains 200-300 PPM lead. 

○ Comparable to EPA’s new standard but not alarmingly high. 

Practical Implications for Homeowners 

● Debris Removal: Necessary for burned structures. 

● Gardening: 

○ Testing soil before growing vegetables is advised. 

○ Fruit trees are less concerning since roots go deeper. 

● Child Safety: 

○ The lead levels in some affected areas are similar to USC campus soil.

○ The expert allows his daughter to help with sampling, suggesting it's not critically hazardous. 

● Lead contamination is mostly in the topsoil where ash settled. 

Lead Contamination and Testing 

● Lead contamination is high within burned areas, especially where structures have burned. 

● Outside burned areas, lead levels are not significantly elevated, even with ash deposition. 

● Lead is persistent in soil and is a major concern for remediation. 

Other Contaminants to Test For 

● Asbestos: Harmful if inhaled; should be remediated from ash on properties. ● Polycyclic Aromatic Hydrocarbons (PAHs): Organic compounds formed during fires. ● Volatile Organic Compounds (VOCs): Less studied but could be a concern. 

Soil Remediation Process 

● Removing 6 inches of soil from burned areas is considered a safe approach. ● Testing of topsoil near burned structures has shown elevated lead levels, but contamination decreases with depth. 

● For gardens or areas with heavy ash deposition, deeper removal may be advisable. ● Raised garden beds with new soil are a good option for planting. 

Testing Options 

● Hiring an EPA or state-certified contractor is the most thorough but costly option. ● USC is working on a program allowing community members to submit soil samples for lead testing. 

Alternative Remediation Methods 

● Zeolites: Minerals that absorb and lock in lead permanently. 

● Concrete & Turf: Sealing soil with non-permeable materials reduces exposure. ● Washing Surfaces: Spraying driveways and patios with water helps remove contaminants. 

Depth of Soil Removal for Safety 

● Burned areas: Remove at least 6 inches. 

● Non-burned areas with ash deposition: 2-3 inches should be sufficient. ● Children’s play areas (e.g., sandboxes): Replace soil entirely.

● Gardens: If planting food, consider replacing the topsoil or using raised beds. Impact on Outdoor Living 

● Dogs digging in soil and outdoor activities raise concerns for contamination. ● If lead levels are below 400 PPM, it is considered safe by University of Maryland standards. 

● If concerned, err on the side of caution by replacing the top 2-3 inches of soil. Toxins & Their Behavior in Soil & Water 

● Mobile Toxins (e.g., Arsenic): 

○ Found in burned wood (used in construction). 

○ Can dissolve in water and wash away over time. 

○ Rain helps dilute arsenic levels; no significant impact detected in LA River or ocean. 

● Immobile Toxins (e.g., Lead, Asbestos): 

○ Do not wash away easily and remain in the soil long-term. 

○ Can pose ongoing health risks if not properly capped. 

Impact on Plants & Food Safety 

● Heavy Metal Uptake by Plants: 

○ Plants may absorb some contaminants, but lead uptake into fruits/vegetables is typically low. 

○ Eating produce from home gardens in affected areas is likely safe, but soil testing is advisable. 

Testing for Contaminants 

● Lead as an Indicator for Other Toxins: 

○ High lead levels likely correlate with asbestos and other burn-related 

contaminants. 

○ Research is ongoing to confirm these correlations. 

● Commercial Soil Testing Costs & Accessibility: 

○ Professional testing is available but expensive. 

○ Efforts are underway to provide low-cost or free community testing. 

○ Testing primarily identifies lead, but other contaminants require different analyses.

Comparison to Previous Wildfires & Testing Decisions 

● Differences from Camp Fire (2018): 

○ Post-remediation testing in Camp Fire areas often required multiple rounds of soil removal. 

○ Los Angeles has a historic background of lead contamination from leaded gasoline & paint. 

○ Deeper soil layers may contain pre-existing urban lead contamination, unrelated to the fire.The Army Corps of Engineers is conducting remediation work in the burn zone. 

○ California has passed laws affecting how the county will bill residents for the "free" debris removal program. 

○ If residents have insurance, they can undertake additional remediation before the Army Corps bills them. 

○ The county will bill on behalf of the Army only for any remaining remediation costs. 

● Decision Not to Conduct Widespread Testing: 

○ Officials may be concerned that deeper soil testing would continue to detect existing lead. 

○ The focus is on surface-level mitigation (removal & capping) rather than deep remediation. 

Rebuilding & Community Considerations 

● Properties with proper remediation may have higher resale value post-fire. ● Coordinated neighborhood-wide soil removal efforts are ideal to minimize exposure risks. 

● Unremediated neighboring yards can still pose an exposure risk to pets and children. ● In past fires, authorities used all available insurance funds for debris removal. ● Further research will be conducted to confirm details of the billing process. ● Some residents may consider hiring private companies for additional soil and debris removal before the Army Corps' billing process. 

Groundwater & Mudslide Concerns 

● Some lead may leach into groundwater, but levels detected so far are below EPA safety thresholds. 

● Mudslides primarily pose physical hazards but are unlikely to significantly redistribute contaminants.