THE USE OF OXYGEN INFUSION FOR THE BIOREMEDIATION OF A GASOLINE CONTAMINATED SITE

A gasoline station had a release of gasoline that impacted the groundwater of the shallow unconfined fractured bedrock system and the deeper confined systems beneath the site. A pump and treat system was installed at the site to cleanup and hydraulically control the groundwater systems. Gasoline contaminated groundwater is extracted from four wells; one deep well that is constructed in the shallow and deeper groundwater systems and three wells that are constructed in the shallow system. The extracted groundwater is treated in aerobic bioreactors and then discharged to leachfields.

The pump and treat system has been effective, especially in the cleanup of the deeper groundwater systems. The remediation system has not cleaned up the shallow groundwater system, which is not as permeable as the deeper systems, as quickly. To expedite the cleanup of the shallow system, oxygen infusion was used to increase the dissolved oxygen (DO) in the shallow system and thereby enhance in situ bioremediation. The oxygen infusion technology utilizes microporous hollow fiber to provide a large surface area for contact between oxygen and groundwater and, hence, allow for the efficient mass transfer of the oxygen into groundwater.

Oxygen infusion units were installed in three monitoring wells that are constructed in the shallow groundwater system. The selection of the monitoring wells was based on their relatively close location to three of the groundwater extraction wells. Immediately following the installation of the units, the DO concentrations in the wells increased. The average concentrations of DO in the wells has been approximately 40 mg/l. The analytical results of samples that have been collected from the monitoring wells in which the infusion units are installed and the results of samples from the extraction wells indicate significant decreases in the concentrations of gasoline compounds.