Bioventing and biosparging at a site contaminated with JP-4 and TCE
During the 1950's, 60's and 70's, a great number of military and civilian airfields dumped thousands of gallons of fuel, waste oils and solvents into the subsurface environment as part of routine fire training activities. These areas now pose a threat to humans and wildlife. This research investigates bioventing and biosparging as remedial alternatives at Plattsburgh Air Force Base (PAFB) where soils are heavily contaminated with JP-4 and solvents.
To begin the investigation, site geology and contaminant constituents were thoroughly characterized. Installation and sampling of soil gas monitoring points confirmed the presence of hydrocarbon and TCE vapors in the vadose zone as well as a gradient of decreasing oxygen and increasing carbon dioxide from the ground surface to the water table indicative of aerobic hydrocarbon degradation. New models were developed and used to determine soil gas constituent mass fluxes during ambient and bioventing/biosparging conditions. Mass fluxes of hydrocarbons, TCE, oxygen and carbon dioxide were calculated during ambient conditions based on the soil gas profiles. Combining this information with contaminant characterization and extent yielded an estimated cleanup time of approximately 150 years.
After the initial characterization, the bioventing system, operating above the water table, was activated followed by sampling and analysis of O2, CO2, TCE, and HCs. Following 6 months of operation, compound mass fluxes under the pilot scale bioventing system indicated an increase in the hydrocarbon degradation rate by a factor of 4 for an estimated cleanup time of 37 years.
After ending the bioventing phase, the biosparging system, injecting air below the water table, was subsequently activated and the same soil gas constituents measured over a period of 4 months. Compound mass flux results indicated a hydrocarbon degradation rate increase over ambient conditions by a factor of 2 (75 years). A new, near surface soil gas measurement tool was developed allowing sample collection in shallow (1m) soils with high resolution (2cm).
Based on the pilot scale bioventing and biosparging results, either one or a combination of both of these remedial alternatives would accelerate the cleanup process at PAFB for a reasonable cost.
0768: Environmental science