Estimation of Rates of Aerobic Hydrocarbon Biodegradation by Simulation of Gas Transport in the Unsaturated Zone

Abstract

The distribution of oxygen and carbon dioxide gases in the unsaturated zone provides a geochemical signature of aerobic hydrocarbon degradation at petroleum product spill sites. The fluxes of these gases are proportional to the rate of aerobic biodegradation and are quantified by calibrating a mathematical transport model to the oxygen and carbon dioxide gas concentration data. Reaction stoichiometry is assumed to convert the gas fluxes to a corresponding rate of hydrocarbon degradation. The method is applied at a gasoline spill site in Galloway Township, New Jersey, to determine the rate of aerobic degradation of hydrocarbons associated with passive and bioventing remediation field experiments. At the site, microbial degradation of hydrocarbons near the water table limits the migration of hydrocarbon solutes in groundwater and prevents hydrocarbon volatilization into the unsaturated zone. In the passive remediation experiment a site‐wide degradation rate estimate of 34,400 g yr−1 (11.7 gal. yr−1) of hydrocarbon was obtained by model calibration to carbon dioxide gas concentration data collected in December 1989. In the bioventing experiment, degradation rate estimates of 46.0 and 47.9 g m−2 yr−1(1.45 × 10−3 and 1.51 × 10−3 gal. ft.−2yr−1) of hydrocarbon were obtained by model calibration to oxygen and carbon dioxide gas concentration data, respectively. Method application was successful in quantifying the significance of a naturally occurring process that can effectively contribute to plume stabilization.

Soil gas transport above a jet fuel/solvent spill at Plattsburgh Air Force Base

“…We postulate aerobic biodegradation of hydrocarbons in the contaminated capillary fringe, so that, to leading order, oxygen diffuses steadily down from the atmospheric source at the ground surface, while carbon dioxide and hydrocarbon vapors diffuse steadily upward from a separate phase source at the edge of the fringe. The steady carbon dioxide and oxygen fluxes are evaluated above a jet fuel/solvent spill at Plattsburgh Air Force Base and found to be consistent with steady values found by Lahvis and Baehr [1996] and Lahvis et al [1999] over automobile gasoline spills.…”

Part 1: Vadose-Zone Column Studies of Toluene (Enhanced Bioremediation) in a Shallow Unconfined Aquifer

“…The results of these gas and solution analyses were used to evaluate the nutrient's overall effectiveness in stimulating aerobic bioremediation of the substrate at different column depths under optimal conditions. Results from previous studies suggest that microbial degradation of hydrocarbons near the water table inhibits the migration of hydrocarbon solutes in ground water and prevents hydrocarbon volatilization into the unsaturated zone, and the rates of degradation kinetics are approximately first order (Lahvis and Baehr, 1996). However, these and other studies were performed on sites where spills occurred a decade or more earlier, which precludes speculation on the fate of toluene compounds if remediation techniques are applied directly after the spill occurs.…”

“…However, these and other studies were performed on sites where spills occurred a decade or more earlier, which precludes speculation on the fate of toluene compounds if remediation techniques are applied directly after the spill occurs. Lahvis and Baehr (1996), Lahvis et al (1999) and Ostendorf and Kampbell (1991) all cited that in situ bioremediation rates were limited by the rate at which oxygen could diffuse through the unsaturated zone and spatial heterogeneity (Kota et al, 2004). Thus, this study examined the nutrient's continual effectiveness in stimulating aerobic, microbial degradation of toluene under decreasing oxygenated conditions.…”

In Situ Bioremediation of a Gasoline‐Contaminated Vadose Zone: Implications from Direct Observations

“…Concurrent monitoring of the depletion of both O 2 and VOC concentrations and the accumulation of CO 2 in soil gas is another common method for demonstrating biodegradation (Suchomel et al, 1990;Lahvis and Baehr, 1996;Hers et al, 2000;Lamy et al, 2013). However, this method does not provide definitive evidence for the degradation of a specific compound.…”

“…Water-gas and NAPL-gas partitioning and diffusion, together with biodegradation, affect the isotopic signature of a compound in the gas and liquid phases (Bouchard et al, 2008a). Nevertheless, isotopic effects from biodegradation may dominate the overall isotopic signatures in the dissolved phase Kuder et al, 2005) and in vadose zone vapor (Bouchard et al, 2008b).Concurrent monitoring of the depletion of both O 2 and VOC concentrations and the accumulation of CO 2 in soil gas is another common method for demonstrating biodegradation (Suchomel et al, 1990;Lahvis and Baehr, 1996;Hers et al, 2000;Lamy et al, 2013). However, this method does not provide definitive evidence for the degradation of a specific compound.…”