EPA Releases Technical Report on Screening Approach for Petroleum Vapor Intrusion

Last month EPA's Office of Underground Storage Tanks released a report on its evaluation of subsurface empirical data from petroleum-impacted sites for the purpose of developing a new soil vapor intrusion screening approach for petroleum hydrocarbons. EPA primarily evaluated underground storage tank sites, but also considered data from other sites such as fuel terminals, petroleum refineries, and petrochemical facilities. We note that the report is expected to be used in developing EPA's upcoming and long-awaited vapor intrusion guidance. 

EPA's evaluation of the data that forms the basis of the report resulted in an "inclusion distance approach" (vertical source-to-building distance) for screening petroleum-impacted sites for vapor intrusion. The report concludes that "[t]he inclusion distance approach is based on the observed attenuation of petroleum hydrocarbons over a characteristic separation distance beyond which there is limited potential for a complete petroleum vapor intrusion pathway." In addition to vertical separation distance, EPA identified two other important metrics for petroleum vapor intrusion screening: facility type, which influences the size of the release, and petroleum hydrocarbon source type, because the vapor source concentration is higher if it results from separate phase liquids (LNAPLs) rather than petroleum compounds dissolved in groundwater. Vertical inclusion criteria for various types of facilities and petroleum sources are described in the report. The report was peer-reviewed by a panel of independent experts last year and, as noted, will significantly influence the broader vapor intrusion guidance expected to be released this year.