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| Resource Library > Technology Transfer > Programs and Initiatives > Bioventing > Overview |
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Bioventing is the process of aerating soils to stimulate in situ biological activity and promote bioremediation. Bioventing typically is applied in situ to the vadose zone (i.e., unsaturated soils) by injecting oxygen in the form of air. Bioventing systems are designed to maximize biodegradation while minimizing volatilization. The technology is applicable to any chemical that can be aerobically biodegraded; however, to date has been implemented primarily at petroleum-contaminated sites.
Much of the hydrocarbon residue at a fuel-contaminated site is found in the vadose zone soils, in the capillary fringe, and immediately below the water table. Seasonal water table fluctuations typically spread residues in the area immediately above and below the water table. Conventional physical treatment in the past involved pump-and-treat systems where groundwater was pumped out of the ground, treated, and either discharged or reinjected. Although useful for preventing continued migration of contaminants, these systems rarely achieved typical cleanup goals. Bioventing systems are designed to biologically degrade the contaminant source within the vadose zone, thereby preventing future and/or continued contamination of the groundwater.
A typical bioventing system injects air at a low rate into the vadose zone. Although bioventing is related to the process of soil vacuum extraction (SVE), the primary objectives of these two bioremediation technologies are different. SVE is designed and operated to maximize the volatilization of low-molecular-weight compounds, with some biodegradation occurring. In contrast, bioventing is designed to maximize biodegradation of aerobically biodegradable compounds, regardless of their molecular weight, with some volatilization occurring. Bioventing reduces vapor treatment costs, which typically constitute 50 to 80% of total remediation costs. SVE may be best employed for unique conditions where high volatility hydrocarbons are in close proximity with basements or other subsurface conduits to occupied buildings (e.g., utility lines etc.).
Candidate Bioventing Sites
One can use standard soil gas techniques to confirm the appropriateness of bioventing at a site. A good candidate site for bioventing should display the following profile (A more detailed discussion can be found found in Addendum One, Test Plan and Technical Protocol for A Field Treatability Test for Bioventing
- Using Soil Gas Surveys to Determine Bioventing Feasibility and Natural Attenuation Protocol):
- Low oxygen in soil gas (less than 2% vol/vol) compared to background (e.g., 15 - 21%)
- High carbon dioxide in soil gas (greater than 2%) compared to background (e.g., 0.5%)
- Elevated volatile hydrocarbons in soil gas
- Contaminants of concern above cleanup goals
AFCEE Bioventing Initiative
AFCEE Technology Transfer has demonstrated that properly designed bioventing systems are safe, effective, and cost-effective. This conclusion is based on the system design, installation, and performance monitoring of over 150 bioventing systems installed in every US EPA Region, across 32 states and 61 bases. The technology has been applied at waste oil, heating oil, diesel, jet fuel, and gasoline contaminated sites.
Bioventing is particularly effective in quickly treating the most toxic, soluble, and mobile constituents in fuels (i.e., benzene, toluene, ethyl benzene, and xylenes). Results are typically seen within less than one year. This preferential removal provides a substantial reduction in potential risk and compliance with risk-based cleanup goals.
The application of bioventing at those sites included in the AFCEE bioventing initiative realized an estimate 3:1 return on investment as compared to the application of SVE. Volume 1 and Volume 2 of the Bioventing Principles and Practices Manual were developed by the AFCEE and published through both the US EPA and DOD. These documents, as well as the Bioventing Design Tool, provide all the information necessary to understand where bioventing is appropriate through how to properly design and monitor a system. Additional bioventing references and tools were also developed and are available through this web site.
The AFCEE Bioventing Initiative proved to be very effective and successful:
- Bioventing was found to be effective under a variety of soil and climatic conditions
- Based on soil sampling data from over 100 sites, an average BTEX reduction of 97$ was achieved during the first year of testing
- The average cost for design, installation, and one year of operation and monitoring at a single vent well bioventing site was less than $60,000 per site, based on actual costs incurred at the test sites.
- Regulatory acceptance of bioventing was obtained in 38 states and all 10 EPA regions. The Bioventing Initiative greatly accelerated the use of the technology in the private sector.
- At nearly half of the sites tested, the pilot systems were converted into full-scale remediation systems, saving the Air Force an estimated $5M to $10M in design and construction costs.
- At the majority of the bioventing sites, the reductions in BTEX achieved during the first year of bioventing were sufficient to meet the most conservative EPA risk-based cleanup criteria for soils.
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