Gas Station located in Jacksonville, Florida

Site Summary

Leaking underground storage tanks resulted in contamination to ground water at a former gas station in Jacksonville, Florida. After removing the tanks and delineation of the nature and extent of the contamination, bioremediation was selected for treatment of the residual contamination. Bioremediation was selected for its cost-effectiveness and minimal disruption of the current property use. Petrox microbes were injected in the source area in October 2004. After a single treatment, the contaminant concentrations were reduced to nearly non-detect levels.

Geology

The setting of the site is a beach complex of mainly sand deposits.

Hydrogeology

The affected aquifer was a shallow unconfined sandy formation. The water table fluctuated between 1 to 4 feet below grade.

Ground Water Contamination

The size of ground water plume that resulted from leaching soil contaminants was estimated to be approximately one half acre. The contaminants of concern were benzene, toluene, ethylbenzene, and xylene (BTEX) compounds.

Remediation Design

To provide complete coverage of the plume, 28 injection points were installed in the contaminated ground water area.

Since the dissolved oxygen level was unknown, a slurry of 100 pounds of calcium peroxide was injected into the ground water. The calcium peroxide was added 2 days prior to the inoculation to boost the dissolved oxygen levels. Within the treatment area, 17 units of Petrox (935 gallons) were evenly injected into the ground water. Approximately 30 to 35 gallons of Petrox was injected into each point.

Results

Ground water samples were taken from monitoring wells located in and surrounding the plume 30 days after the inoculation. The sampling results show significant contamination reduction in the plume as shown in the graph. The monitoring points outside of the plume showed that the contamination was not displaced during the injections.

The combined Petrox and calcium peroxide cost was $14,000, including shipping. The contractor’s costs for injection wells, field time, and monitoring are not known.