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Biodegradation of Petroleum Hydrocarbon Vapors in the Vadose Zone
Citation:
WILSON, J. T., K. JEWELL, AND C. PAUL. Biodegradation of Petroleum Hydrocarbon Vapors in the Vadose Zone. Presented at 21st Annual National Tanks Conference and Expo, Sacramento, CA, March 30 - April 01, 2009.
Impact/Purpose:
To offer an alternative approach to Henry's Law and the J& E model.
Description:
The current state of practice to estimate the risk from intrusion of vapors of petroleum hydrocarbons from spills of gasoline is to measure the concentration of the chemical of concern in ground water under the spill, use Henry’s Law to estimate a concentration of the chemical in soil gas in equilibrium with the ground water, and then assume that the chemical is transported by molecular diffusion in soil gas to the point where it enters the building (The Johnson and Ettinger or J&E model). This approach can be problematic for compounds such a benzene that can be removed for soil gas by aerobic biodegradation. This presentation offers an alternative approach. First, collect core samples at various depths. Then extract the cores and determine concentrations of TPH and Benzene in the sediment (mg/kg), and determine weight loss of core sediment on drying. Use this information to calculate the concentration of benzene in pore water in the core samples. Then multiply the concentration of benzene in pore water by the Henry’s Law Constant to calculate the concentration of Benzene in soil gas. Finally, compare the calculated concentration to the concentration expected from vapor diffusion (the transport mechanism in the J&E model). If the calculated concentrations are significantly lower than would be expected from diffusion of the chemical from ground water, then calibrate J&E with the estimated concentration of the chemical in pore water in the unsaturated zone at the appropriate depth of the core sample. The approach was applied to field data from a fuel spill in Green River, Utah. Core samples were acquired and extracted and analyzed for concentrations of TPH and individual petroleum hydrocarbons. The predicted concentrations of benzene in soil gas were compared to measured concentrations of soil gas sampled from adjacent vapor monitoring wells. Concentrations of benzene in shallow vapor monitoring wells were one hundred to one thousand-fold lower than would be expected from vapor diffusion alone. The predicted concentrations of benzene in soil gas were in general good agreement with concentrations of benzene in soil gas sampled from the vapor monitoring wells. (the abstract will not be published)
URLs/Downloads:
Biodegradation of Petroleum Hydrocarbon Vapors in the Vadose Zone (PDF, NA pp, 416 KB, about PDF)2009 Conference URL
2010 Conference URL