ABSTRACT
In situ biological remediation of unsaturated soils is a treatment technology that utilizes naturally occurring soil microorganisms to degrade petroleum hydrocarbons to carbon dioxide, water, and humus. Indigenous microorganisms present in the soil are stimulated by providing those elements, usually oxygen and nitrogen, that are limiting the degradation of the petroleum hydrocarbons. Vapor phase delivery maintains unsaturated conditions throughout the affected soil and minimizes the downward migration of chemicals that would occur under saturated conditions. The depth to groundwater, groundwater flow direction and gradient, the presence or absence of floating product, and petroleum hydrocarbon concentrations in the groundwater should be understood prior to implementation of the in situ bioremediation, to avoid recontamination of cleaned soil from the groundwater. Bench-scale tests conducted at these sites determined that no elements other than nitrogen and oxygen were limiting bioremediation. Changes in soil microbiology and soil nitrogen levels were measured throughout the treatment.
