Post-Fire Bioremediation Guidance for Residential Properties

Fire-Resilient Bioremediation and Landscape Recovery Consortium

Purpose

This document explains when and how bioremediation may be appropriate for residential properties impacted by urban fire-related soil contamination. It is intended to support informed decision-making. It does not replace professional or regulatory guidance.

What Bioremediation Is

Bioremediation works with living systems such as plants, fungi, and soil microbes to reduce contamination in place.

There are three main biological approaches:

Phytoremediation

Certain plants can extract metals into their above-ground tissues or stabilize metals in their root zones.

Mycoremediation

Certain fungi, especially decomposer fungi, can degrade some organic contaminants such as petroleum hydrocarbons and polycyclic aromatic hydrocarbons. Others, such as mycorrhizal fungi, can help plants survive in poor soil conditions and may contribute to metal uptake. 

Microbial Remediation

Soil microbes can transform or degrade certain organic contaminants under the right conditions.

Different Contaminants Need Different Remediation Approaches

Heavy Metals

• Examples include lead (Pb), arsenic (As), cadmium (Cd) and others 

• They are elemental and inorganic, so do not biodegrade 

• Since they do not biodegrade, they stay in soils forever 

• Remediation of metals involves moving them around:

  • Remove the soil with the metals and dispose of it as hazardous waste.

  • Remove the metals from the soil with special plants and fungi and dispose of the plants/fungi as hazardous waste.

• Alternatively, you can prevent / reduce exposures to metals by:

  • Covering the soil and ensuring it remains covered.

  • Diluting the metal concentrations by adding soil or compost so they are below screening limits.

    
    

Organic Contaminants 

• Examples include diesel oil, PAH’s, dioxins and PFAS

• They are carbon-based, which means most of them can be broken down for food by fungi and microbes 

• some are more complex than others and fungi can typically handle the most complex organic contaminants 

  
  

Important Clarification:

Metals such as lead, arsenic, and cadmium do not break down over time. Biological approaches can extract them into plant tissue or reduce their mobility, but they do not make metals disappear.

When Bioremediation May Be Appropriate

Bioremediation may be appropriate under the following conditions:

• Soil testing has confirmed contamination, meaning at least one contaminant has concentrations higher than residential screening limits set by the EPA.

• Contamination levels are elevated but not extremely high, especially for lead (Pb).

• The property owner has 12 months or more for treatment and monitoring. NOTE: This can sometimes happen at the same time as rebuilding, if in different areas of a site.

• Immediate excavation is not feasible due to cost, logistics, or site constraints.

• Biological approaches are combined with exposure reduction strategies such as soil cover or targeted hotspot removal.

Bioremediation is often most effective when used as part of a combined strategy rather than as a standalone solution.

When Bioremediation Is Likely Not Appropriate

Bioremediation is unlikely to be appropriate as a primary strategy when:

• Contaminant levels are very high and exceed levels where rapid removal is indicated. This is especially true for lead levels higher than 500 ppm.

• Immediate move-in or rebuild timelines require fast clearance.

• Insurance or resale requirements demand rapid, EPA-verified soil removal.

Sensitive populations such as young children, pregnant individuals, or pets will have ongoing soil contact and no interim protection plan is in place.

In cases of very high lead or mixed contamination at high concentrations, excavation and removal may be the most protective option.

The Bioremediation Process

If biological remediation is selected, the typical process includes:

1. Soil Testing and Site AssessmentTesting must identify contaminant type, concentration, and distribution.

2. Site-Specific DesignTreatment plans are based on contamination levels, land use goals, irrigation availability, and household risk factors.

3. InstallationSelected plants are installed. Fungal inoculants may be added where appropriate. Soil may be covered with compost, mulch, or clean soil to reduce dust and exposure.

4. MonitoringSoil is re-tested at defined intervals to evaluate progress.

5. Plant Removal and DisposalIf metal extraction is used, plant biomass must be handled and disposed of appropriately.

6. Final Testing and DocumentationFinal soil testing confirms whether remediation goals have been met.

Timelines

Timelines vary depending on contaminant type and concentration.

• Petroleum hydrocarbons and some organic contaminants may show measurable reductions within months under optimal conditions.

• Metal reduction through extraction may require one year or longer.

• Highly contaminated sites may require staged or combined approaches.

Bioremediation should not be presented as a rapid solution.

Verification and Oversight

Follow-up soil testing is required to confirm progress. Professional oversight is strongly recommended to:

• Design and conduct soil sampling using EPA-recognized methods.

• Interpret soil test results accurately.

• Select appropriate plant species and fungal treatments.

• Prevent contaminant spread during installation.

• Manage and dispose of contaminated plant material safely.

• Prepare documentation suitable for insurance, resale, or regulatory purposes.

Bioremediation without monitoring and documented verification does not constitute confirmed remediation.

Exposure Reduction During Treatment

While remediation is ongoing:

• Keep soil covered.

• Avoid disturbing bare soil.

• Practice good indoor hygiene, including wet mopping and removing shoes.

• Prevent children and pets from contacting contaminated soil.

  
  

Bioremediation is compatible with these protective measures but does not replace them.

Food Growing

If soil contamination exceeds residential or agricultural screening limits:

• Do not grow food directly in contaminated soil.

• Use raised beds with clean soil.

• Keep native soil covered beneath beds.

Even where biological treatment is underway, food safety should be verified through soil or plant tissue testing before consuming produce.

Conclusion

Bioremediation is one of several soil management options available after wildfire. It may offer a lower-cost, in-place strategy in certain situations, particularly when time allows and contamination levels are moderate. It is not appropriate for all sites and does not replace the need for testing, monitoring, and professional oversight.

Choosing a remediation approach should balance:

• Contamination level

• Urgency

• Household risk

• Budget

• Long-term property plans

No single method is right for every property.