Superfund Research Program
Indoor Air Concentration Dynamics and Vapor Intrusion
Project Leader: Eric M. Suuberg
Grant Number: P42ES013660
Funding Period: 2009-2021
Drs. Suuberg and Pennell's research remains focused on providing a better understanding of organic vapor exposure pathways, and it continues to have two complementary activities. One is related to better understanding the properties of the tar-like contaminant mixtures found on a great many Superfund and brownfields sites, and the other is concerned with vapor intrusion into structures built atop or near to organics contaminated sites.
The researchers have looked into very basic questions concerning the thermodynamic properties of what are commonly termed "tars" or "tar mixtures." One of the questions that has been addressed is: How many PAH components in a mixture does it take to get tar-like behavior? Mixtures of just a few PAHs are seen in many respects to be rather poor models for real tars, even though they may seem to be the "right" choice. The researchers studied—and published several papers on—the complicated phase behavior of few-component PAH systems and saw how they approached the usually assumed near-ideal behavior only when the number of components exceeded about a half dozen.
At the same time, Drs. Suuberg and Pennell are looking at computational methods for predicting properties such as vapor pressures and water solubility of such PAH compounds and mixtures in order to avoid having to resort to their experimental characterization. Rather than using the empirical group additivity approach that is widely discussed in the literature, they are using a quantum chemical approximation method that is fundamentally more appealing and may offer more hope for prediction of properties for compounds outside of the measured set. In addition, the researchers are continuing to build up their database on vapor pressure and phase behavior of halogenated aromatics.
This research also continues a major effort in the direction of developing modeling tools for characterization of vapor intrusion of hazardous materials from in-ground sources. The program has received a major boost with the funding of an ARRA supplement that involves close collaboration with the Boston University SRP in which an actual impacted neighborhood is being examined using both field testing and modeling. In addition to that work, the research group is continuing to explore the broad range of variables that impact vapor intrusion exposures. For example, the researchers have been examining the transient phenomena that may confound simple field-based empirical characterizations of the process. They have also critically examined the assumptions in the EPA-recommended one-dimensional screening model for the phenomenon and pointed out where use of the simple model can provide useful results and under what conditions the results can be misleading. The researchers will continue to work towards fuller validation of the modeling approach and still hold out as a goal teaching the community concerned vapor intrusion characterization and mitigation and how to use these computational tools as an aid in proposing solutions for contaminated sites.