United States Solid Waste and EPA 510-F-93-022 Environmental Protection Emergency Response October 1993 Agency 5403W Soil Remediation For UST Sites In Situ Bioremediation: Bioventing In situ bioremediation—bioventing—is a technique for removing biodegradable contaminants from unsaturated soils. The technique injects oxygen into contaminated soil. The oxygen stimulates the aerobic biodegradation of the organic contaminants in the soil. Oxygen is delivered at a low rate to encourage biodegradation rather than volatilization. Bioventing is most effective in coarse-grained soils such as sand and gravel. It requires a minimum 5-foot-thick unsaturated zone. This technique can be used in conjunction with air sparging or groundwater pumping systems. This technique is able to treat large volumes of soil effectively and with minimal disruption to business operations. It also can remove contamination from near or under fixed structures. Bioventing also reduces the need for aboveground treatment because it works to degrade contaminants in place. Petroleum Types And Constituents » Fresh or weathered gasoline, diesel, jet fuel, kerosene, motor oil, heavy fuel oil, lubricating oils, and crude oils « Volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylene fBTEX); residual semlvolatfle organic compounds (SVOCs) such as polynuclear aromatic hydrocarbons; and nonvolatile constituents ------- In Situ Bioremediation: Bioventing Advantages Degrades semivolatile organic compounds (SVOCs) and nonvolatile organic compounds Effectively treats large volumes (> 1,000 cu yd) of soil Causes minimal disruption to business operations Degrades contaminants near or under fixed structures Degrades volatile organic compounds (VOCs) in place, which reduces air emissions and subsequent need for treatment Limitations Targets only biodegradable constituents Is a relatively slow process Requires sufficient nutrients, moisture, active indigenous microbial population, and pH of 6-9 to degrade contaminants Effectiveness limited in heterogeneous soils System Components • Vertical or horizontal extraction wells • Trenches • Vacuum blower or pump • Injection and passive inlet wells • Vapor treatment (optional) • Nutrient delivery equipment (optional) Wastestream Treatment Vapor treatment options (might be needed for high concentrations of contaminants): • Vapor phase biofilter • Granulated activated carbon • Internal combustion engine • Catalytic oxidation unit • Thermal incinerator Parameters to Monitor1 • Vapor concentration • Airflow rate • In situ respiration rate (oxygen consumption and carbon dioxide production) • Soil contaminant concentration • Microbial population • Soil pH, moisture, and nutrients Cleanup Levels and Timing2 • Treats > 90% of biodegradable constituents • For an ideal site3, ~90% in 1 to 2 years • For an average site4, ~90% in 1 to 4 years • Longer time required to degrade heavier hydrocarbons Costs5 For an ideal site3, $40,000 to $120,000 For an average site4, $100,000 to $150,000 Vapor treatment and longer treatment times increase costs ''Parameters to monitor" are for performance purposes only; compliance monitoring parameters vary by state. An Ideal site" assumes no delays in corrective action and a relatively homogenous, permeable subsurface. 4An "average sle" assumes mWmal (Ways in cotredive action andarrKxleratelyrieteroc^nec)usandpemieablestJMurface. ^Costs include equipment, and operation and maintenance. ------- |