Are hydrocarbons really bioattenuating in the shallow vadose zone, or is it propaganda by the oil companies in an attempt to minimize their vapor-intrusion problems?
A vast number of studies have been performed that clearly demonstrate the bioattenuation of hydrocarbon vapors in aerobic soils. Many, but not all of these studies, were performed by the oil industry (go to www.API.org to read published studies). In general, the studies show that when oxygen levels are 10 percent or greater and at least two feet of vadose zone exists between the contaminant source and the overlying structure, the hydrocarbons aren’t likely to pose an unacceptable risk. (A published study by the New Jersey Department of Environmental Protection suggested oxygen levels as low as 6 percent are sufficient). While there is a current effort to try and quantify the bioattenuation process and add a quantitative term to the existing models, it is more likely to expect that the bioattenuation rate will be extremely site dependent. The more accepted alternative is to document that this process is occurring by collecting vertical profiles of the soil gas for the hydrocarbons, oxyg
