The environmental community continues to focus on the vapor intrusion pathway — guidance has been issued by ASTM, ITRC and more than 25 States. Most recently, the U.S. Environmental Protection Agency’s (EPA or Agency) Office of Underground Storage Tanks (OUST) just published an information paper entitled, “Petroleum Hydrocarbons And Chlorinated Hydrocarbons Differ In Their Potential For Vapor Intrusion.” The purpose of this paper is to amplify the discussion of why petroleum hydrocarbons (PHCs) warrant a different analysis and approach than do chlorinated hydrocarbons (CHCs) when investigating the issue of vapor intrusion. The conclusion is that petroleum hydrocarbons in many cases do not produce a vapor intrusion risk.
In the vadose zone, PHCs behave differently than do CHCs because PHCs biodegrade easily in the presence of the oxygen in the soil, and because PHC free product is lighter than water. In contrast, CHCs typically are more resistant to biodegradation and its free product is denser.
Given these distinct characteristics, it is likely that regulators in the near future will be able to develop exclusion criteria for petroleum contaminated sites whereby, with sufficient depth of soil between the source and receptor, the vapor intrusion concern can be eliminated without further testing. See, Hartman, B., The Vapor-Intrusion Pathway: Petroleum Hydrocarbon Issues, Lustline, No. 66. The ability to screen out candidate sites without need for intrusive testing would be of substantial benefit in streamlining regulatory decision-making.
EPA’s information paper is one in a series of steps being taken by EPA’s OUST group with the goal of producing final PHC guidance in 2012, as a compliment to the vapor intrusion guidance update expected by Office of Solid Waste and Emergency Response before December 2012. See www.epa.gov/oswer/vaporintrusion.