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Biodegradation of Petroleum Hydrocarbon in the Vadose Zone
Citation:
WILSON, J. T., K. JEWELL, C. PAUL, R. Davis, AND J. Menatti. Biodegradation of Petroleum Hydrocarbon in the Vadose Zone. Presented at The EPA Region 3 States LUST Technical Workshop, Shepherdstown, WV, September 08 - 10, 2009.
Impact/Purpose:
Looking at two major impediments to a better understanding of the influence of biodegradation on the risk of intrusion of petroleum vapors
Description:
There are two major impediments to a better understanding of the influence of biodegradation on the risk of intrusion of petroleum vapors. We describe the contribution of biodegradation as an attenuation factor between the source and the receptor. The use of attenuation factors implies that the extent of biodegradation is only controlled by the concentration of vapor at the source, and that the geometry of the subsurface has no role. In fact, the attenuation of vapors is a sensitive function of the depth of clean soil above the spill. We tend to look for contaminated ground water, and tend to use concentrations in contaminated ground water to calibrate models of vapor intrusion. It is more likely that the important sources of vapors are residual fuel in the unsaturated zone. As an alternative to calibrating a J&E model with ground water data from wells, well logs should be examined for PID hits that might indicate residual fuel above the water table. Soil vapor probes should be installed at the depth interval represented by the PID hits. The J&E model should be calibrated with real vapor data. If soil vapor probes are not available, but cores samples were taken at the site and data are available on concentrations of TPH and benzene in the core samples, Raoult’s law can be used to estimate the concentration of benzene or other contaminants in the pore water, and these estimates can be used to calibrate the J&E model.