On this page (10 sections)
Biology enters a brownfield cleanup once assessment and risk analysis show organic contamination at levels microbes can work on, and only if the redevelopment schedule allows months to years for treatment. Where metals dominate, concentrations pose an immediate risk, or a developer is waiting on the ground, it fits poorly. Former gas stations and other petroleum sites are the clearest match. Below, the brownfield process stage by stage, with the points where biology comes in.
What counts as a brownfield
EPA defines a brownfield as property whose expansion, redevelopment or reuse may be complicated by the presence or potential presence of a hazardous substance, pollutant or contaminant. The definition comes from CERCLA section 101(39), the federal Superfund law, and covers residential, commercial and industrial property [1]. EPA treats petroleum brownfields as their own category, including abandoned gas stations, auto service businesses, factories, mills, shipyards and junkyards [2].
Since the definition includes “potential presence,” some brownfields turn out to be nearly clean and others heavily contaminated, and only assessment sorts them.
The process, and where biology enters
EPA’s risk-based framework has three main stages: site characterization, risk assessment, and cleanup planning and implementation [3]. The table adds the assessment steps and marks where biology comes in.
| Stage | What happens | Where biology enters |
|---|---|---|
| Phase I site assessment | Review of records and government databases, a site visit, and interviews with owners, neighbors, and past workers, to find out whether contamination is likely [4]. | Nowhere yet. The record of past use hints at which compounds to expect. |
| Phase II site assessment | Further investigation, usually including sampling and analysis, to confirm contamination and its extent [3][4]. | The contaminant list decides whether biology is a candidate at all. |
| Risk assessment | Estimate of the nature and probability of harm to people and the environment, based on exposure pathways [3]. | Sets how clean the soil needs to be for the planned use. |
| Cleanup planning | A remedy is chosen to meet specific cleanup and redevelopment objectives, with options and cost estimates tied to future use [3][4]. | Biology is one candidate remedy, tested first in a bench-scale treatability study [5]. |
| Implementation | The remedy is carried out. Where contamination remains, engineering controls (such as soil caps) or institutional controls (such as land use restrictions) manage exposure [3]. | Treatment runs and is sampled on schedule. |
Risk-based cleanups, EPA says, aim to reduce risk for the property’s intended reuse and may leave contamination in place where that is protective for the planned use [3]. A parking lot and a day care don’t need the same endpoint, and EPA’s petroleum brownfields page notes that residential properties call for more stringent remediation than industrial ones [2].
Petroleum brownfields
EPA’s technical paper on biological treatment cites a 2001 survey of leaking underground storage tank programs. Biodegradation technologies such as land farming and biopiles were used at 33% of the soil sites, and in-place bioremediation and related approaches, including monitored natural attenuation, at 79% of the groundwater plumes [6]. Those figures cover that program, not all brownfields.
Landfarming has been used on diesel, No. 2 and No. 6 fuel oils, jet fuel and oily sludge. It works best on heavier hydrocarbons, and lighter volatile compounds are better handled by vapor extraction [7]. Our post on microbes that eat oil covers the organisms; see also petroleum hydrocarbons and brownfields.
Where biology fits poorly
- Metals are a poor fit, since FRTR states bioremediation is not applicable to inorganic contaminants [8], and former plating shops and foundries often leave metals. See what microbes can and cannot do with metals.
- Where contamination poses an immediate risk, EPA says excavation with offsite disposal or ex situ treatment is often the fastest way to handle it [9].
- Tight schedules are hard to meet, because bioremediation may take a few months or several years, per EPA’s public guide [10].
- Some compounds are hard to degrade, and FRTR notes chlorinated contaminants degrade very slowly in place while some compounds break down into more toxic by-products [8]. Our fit chart sorts these.
- Small lots are a problem, since landfarming needs a lot of land [7], and biopiles still require excavation and aboveground treatment enclosures [11].
Land, schedule and neighbors
Urban brownfields are often small, close to homes and served by streets with poor truck access. EPA’s public guide notes that bioremediation keeps contaminated soil on site, cutting truck traffic compared with some other methods [10]. Excavation brings trucks, noise and contaminated material moving through neighborhoods, which FRTR lists as a source of community resistance [9][12].
One practical point: parcels often sit idle for months or years waiting on financing or a buyer. A slow method running during that wait costs the project far less schedule than the same method started after a developer is ready to build. A treatability study and a realistic timeline in the proposal let you make that call.
Funding
EPA’s Brownfields Program offers assessment, cleanup and revolving loan fund grants. A cleanup grant requires site characterization sufficient for remediation to begin, certified by an environmental professional, and a 20% cost share from the recipient [13]. Caps and rules change, so check current terms on EPA’s website or with your regional contact before planning around a figure.
State voluntary cleanup programs are another route. EPA’s technical paper notes that Superfund accounts for only a fraction of bioremediation work nationwide, with far more sites handled under RCRA, state-led programs, underground storage tank programs and state voluntary cleanup programs [6]. Each has its own regulator, so start with the state program that holds your site.
Questions for a municipal brownfield coordinator
- Do we have Phase II data naming the contaminants and their concentrations?
- Is the target tied to the intended reuse, and has the regulator accepted it?
- Does the schedule leave time for treatment, or does it need a hybrid with hot-spot excavation?
- Has anyone run a treatability study on this soil?
The full list is in our guide to evaluating a bioremediation proposal, and bioremediation vs. dig-and-haul compares the two main options.
Where Elm Dirt fits
We make living-soil biological products, work directly with applicators and can be on site. Where a site needs excavation or another engineered remedy, biology doesn’t replace it. Independent lab analysis by Biome Makers identified 291 microbial species in our Plant Juice. We have not published product-level degradation data, and we plan on months to a year or more, verified by independent lab testing.
Your parcel
Whether biology suits a given parcel depends on its Phase II data, the regulator’s target and the redevelopment schedule, none of which a general guide can judge. Bring us your site details.
Sources
- U.S. EPA. About the Brownfields Program. Link. Accessed 2026-10-01.
- U.S. EPA. Petroleum Brownfields. Link. Accessed 2026-10-01.
- U.S. EPA. Risk-Based Brownfields Cleanups. Link. Accessed 2026-10-01.
- U.S. EPA. Assessing Brownfield Sites (Phase I and Phase II environmental site assessments). Link. Accessed 2026-10-01.
- U.S. EPA. Guide for Conducting Treatability Studies Under CERCLA: Biodegradation Remedy Selection, Interim Guidance. EPA/540/R-93/519a, August 1993. Link. Accessed 2026-10-01.
- U.S. EPA. Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites. EPA/625/R-06/015, October 2006, citing Kostecki and Nascarella (2003). Link. Accessed 2026-10-01.
- Federal Remediation Technologies Roundtable. Remediation Technologies Screening Matrix, section 4-13: Landfarming. Link. Accessed 2026-10-01.
- Federal Remediation Technologies Roundtable. Remediation Technologies Screening Matrix, section 3.1: In Situ Biological Treatment for Soil, Sediment, and Sludge. Link. Accessed 2026-10-01.
- U.S. EPA. A Citizen’s Guide to Excavation of Contaminated Soil. EPA 542-F-12-007, September 2012. Link. Accessed 2026-10-01.
- U.S. EPA. A Citizen’s Guide to Bioremediation. EPA 542-F-12-003, September 2012. Link. Accessed 2026-10-01.
- Federal Remediation Technologies Roundtable. Remediation Technologies Screening Matrix, section 4-11: Biopiles. Link. Accessed 2026-10-01.
- Federal Remediation Technologies Roundtable. Remediation Technologies Screening Matrix, section 4-28: Excavation, Retrieval, and Off-Site Disposal. Link. Accessed 2026-10-01.
- U.S. EPA. Types of Brownfields Grant Funding. Link. Accessed 2026-10-01.