Advances in the science of vapor intrusion (VI) have shown that there can be considerable degradation of petroleum hydrocarbons in the subsurface soil vapor. In March of 2008, the U.S. EPA (EPA) released their VI Database which expanded upon their original database which was released in 2002.  The goal of this database was to collect observations during VI investigations which would improve the knowledge and understanding of the VI pathway; in particular, the attenuation of vapors between the subsurface and indoor air.  While the EPA’s current database contains observations from 15 states, 41 sites, 913 buildings and 2,989 paired measurements of subsurface and indoor air concentrations, there are only limited observations from sites contaminated with petroleum hydrocarbons.  The collection of more observations from petroleum hydrocarbon sites is critical to demonstrate that biodegradation readily occurs, which thereby leads to greater attenuation in the subsurface than is generally seen at chlorinated sites.
Buildings located near former MGP sites can be particularly vulnerable to conventional predictions for VI studies, which can lead to unnecessary investigations and remedial efforts. High-quality, representative, and reproducible measurements of soil gas, and indoor air contaminant concentrations were collected from former MGP sites in New York.  A database was developed to compare the attenuation factors between the MGP sites and the EPA’s database attenuation factors.  This presentation will discuss the former MGP sites’ empirical data and compare them to indoor air background values and VI model predictions. 
The collection and presentation of this data will assist in improving the understanding of the VI pathway, and will also help regulators and practitioners evaluate and improve predictive models and screening criteria for evaluating the VI pathway at former MGP sites.