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

Abstract

Abstract. We calibrate a stoichiometrically coupled soil gas diffusion model with spatially resolved observations of oxygen, carbon dioxide, total hydrocarbon, and trichloroethylene vapor concentrations in the unsaturated zone above a weathered jet fuel/solvent spill at Plattsburgh Air Force Base in upstate New York. The calibration suggests that aerobic microorganisms in the capillary fringe degrade jet fuel vapor at a steady rate of 9.5 hydrocarbons (m -2 s-l). The solvent does not degrade in the fringe, however, and the model and data estimate a steady evaporation rate of 1.2 x 10 -2/xg TCE (m -2 s-•).Barometric pumping slightly alters the steady concentration profile at Plattsburgh, although the transient advective flux is the same order of magnitude as the steady diffusive flux. We derive a simple perturbation theory for the second-order transient concentration corrections and include it in the calibration. The perturbation theory is valid at Plattsburgh because the soil is uniform and permeable with a relatively deep capillary fringe. 1.Introduction 0 0 at (O•c + OC) + •zz (v•c + vC)We use concentration data and a set of steady and transient, stoichiometrically coupled, one-dimensional, analytical transport models to estimate the flux of soil gas constituents through a uniform, permeable, unsaturated zone. 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.Wallach [1998] applies perturbation theory to the reactive term of a groundwater contaminant transport model. We compliment this approach by considering perturbations to the transport mechanisms of a soil gas constituent. Gaseous diffusion is assumed to dominate the steady profile and barometric pressure fluctuations drive the transient profile. The barometric pressure distribution is described by a diffusion equation [Shah, 1995] and induces a second-order, transient correction to the steady concentration profiles if the capillary fringe is uniform and relatively deep. The constraints validating the perturbation theory are easily satisfied at Plattsburgh. Soil Gas Transport Theory Steady and Transient Soil Gas Transport EquationsWe assume that the advective, dispersive, and diffusive vertical flux of a dissolved and gaseous phase constituent through the unsaturated zone is balanced by a reaction and the temporal change of aqueous c and soil gas C concentrations

Evaluation of Vapor Attenuation at Petroleum Hydrocarbon Sites: Considerations for Site Screening and Investigation

“…Pasteris et al (2002) found that aerobic biodegradation of the petroleum vapors was the primary mechanism that limited migration away from the NAPL source, and that this biodegradation accounted for most of the mass loss from the experimental system. MTBE, which was not found to biodegrade under these controlled conditions, was the only compound detected in groundwater 1.2 m below the Downloaded by [Simon Fraser University] at 05:09 19 November 2014 Ostendorf et al (2000) found similar results at a spill site with a mixed petroleum and trichloroethylene (TCE) LNAPL source present at the water table at Plattsburgh AFB in upstate New York. Ostendorf et al (2000) found that the diffusive flux of oxygen from the ground surface was sufficient to support essentially complete biodegradation of all petroleum VOCs evaporating from the LNAPL source.…”

“…MTBE, which was not found to biodegrade under these controlled conditions, was the only compound detected in groundwater 1.2 m below the Downloaded by [Simon Fraser University] at 05:09 19 November 2014 Ostendorf et al (2000) found similar results at a spill site with a mixed petroleum and trichloroethylene (TCE) LNAPL source present at the water table at Plattsburgh AFB in upstate New York. Ostendorf et al (2000) found that the diffusive flux of oxygen from the ground surface was sufficient to support essentially complete biodegradation of all petroleum VOCs evaporating from the LNAPL source. This biodegradation occurred in close proximity to the capillary fringe and resulted in production of carbon dioxide at a rate that stoichiometrically matched the estimated evaporation rate for the petroleum VOCs from the LNAPL.…”

Transport of BTEX Vapours Through Granular Soils with Different Moisture Contents in the Vadose Zone

“…Ostendorf and Kampbell (1991) concluded that aerobic biodegradation of hydrocarbon vapours in the unsaturated zone prevents the escape of appreciable contamination to the atmosphere from an aviation gasoline spill. Moreover, Ostendorf et al (2000) observed that aerobic microorganisms in the subsurface degrade jet fuel vapour and nearly all of the evaporating jet fuel is consumed in the contaminated capillary fringe. Additionally, Lahvis et al (1999) underscored the importance of aerobic biodegradation in limiting the transport of hydrocarbon vapours in the unsaturated zone and implied that vapour-plume migration into basements and other points of contact may only be significant if a source of the free product is present.…”

Estimating diesel degradation rates from N2, O2 and CO2 concentration versus depth data in a loamy sand

“…In the steady‐state methods, one‐dimensional gas diffusion models based on Fick’s law are calibrated against measured CO 2 (De Jong & Schappert, 1972; Osozawa & Hasegawa, 1995; Hashimoto & Suzuki, 2002) or O 2 and CO 2 concentration versus depth data (Ostendorf et al , 2000) to predict soil respiration. Kerfoot (1994) discussed the use of both O 2 and CO 2 concentration gradients measured in situ to determine the degradation rate of saturated‐zone hydrocarbon contamination.…”

“…Time‐averaged concentrations of hydrocarbon vapours and O 2 were used to calibrate the model by estimating the hydrocarbon degradation rate, described by two parameters, namely the maximum reaction rate, V , and the half‐saturation constant, K . Another stoichiometrically coupled soil gas diffusion model was developed by Ostendorf et al (2000). They used concentration data and a set of steady‐state and transient one‐dimensional, analytical transport models to estimate the flux of soil gas constituents through a uniform, permeable, unsaturated zone.…”