Petroleum vapor intrusion (PVI) is a subset of vapor intrusion (VI) and is the process by which volatile petroleum hydrocarbons (PHCs) released as vapors from light nonaqueous phase liquids (LNAPL), petroleum-contaminated soils, or petroleum-contaminated groundwater migrate through the vadose zone and into overlying buildings. Fortunately, in the case of PHC vapors, this migration is often limited by microorganisms that are normally present in soil. The organisms consume these chemicals, reducing them to nontoxic end products through the process of biodegradation. The extent and rate to which this natural biodegradation process occurs is strongly influenced by the concentration of the vapor source, the distance the vapors must travel through soil from the source to potential receptors, and the presence of oxygen (O2) in the subsurface environment between the source and potential receptors.
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This ITRC petroleum vapor intrusion (PVI) guidance document provides an 8-step process for the effective assessment and management of vapor intrusion at sites contaminated with petroleum hydrocarbons. The guidance presents a method of screening petroleum-contaminated sites for potential vapor intrusion, as well as providing the tools and strategies that offer the most efficient means of evaluating the vapor intrusion pathway at these sites. The fundamental principle of this screening method is the “vertical separation distance,” which was developed using empirical data from hundreds of petroleum-contaminated sites. Use of separation distance to screen petroleum-contaminated sites allows managers to better focus scarce resources on sites with greater potential for petroleum vapor intrusion.