Superfund Research Program
Indoor Air Concentration Dynamics and Vapor Intrusion
Project Leader: Eric M. Suuberg
Grant Number: P42ES013660
Funding Period: 2009-2021
This project has a new set of foci, a new co-investigator, and new student personnel. At its core, the project remains focused on providing a better understanding of organic vapor exposure pathways. It has built further on the results of the last program period, with a recognition from that work that earlier idealized mixture concepts were far too simple when dealing with mixtures of polycyclic aromatic hydrocarbons (PAH) and, more generally, polycyclic aromatic compounds (PAC). A surprisingly complex thermodynamic behavior was uncovered experimentally and is now being explored through use of advanced computational tools. Much greater emphasis now is being turned to the behavior of halogen-containing PACs. Phase behavior now is being explored using not only the previously employed vapor-pressure measurement techniques but also differential scanning calorimetry, phase-transition analysis such as mixture thaw and liquidus point determinations, X-ray diffraction, and soon, high-resolution transmission electron microscopy. There are surprisingly few data on this aspect of the thermodynamics of PACs, and it is hoped that this will shed new light on how these materials, which have been implicated in many roles as chemicals of concern for human health, can interact with other molecular systems.
Meanwhile, there is a much greater emphasis on fate and transport that play a critical role in determining human exposure to organic vapors through the so-called vapor-intrusion (VI) route. This project, which grew out of a research translation-catalyzed effort in the last program period, is now an equally important aspect of this project. Here the emphasis continues to be on the development of mathematical models for describing the VI process. It is hoped that these tools will be adopted by those engaged in field work as a way of better understanding the complexity that has characterized the heretofore mostly empirical efforts. The models will help not only in analyzing the problem but in suggesting how it may be mitigated or remediated. The philosophy is to provide those concerned with these issues a procedure that can be implemented easily using commercial codes. Results already obtained suggest where several aspects of regulatory guidance might be inadequate for protecting human health. Focus has turned from the development of the basic model structure to adding in complicating factors that make understanding field data particularly difficult. These include transient effects associated with pressure variations and wind, movement or depletion of a contaminant plume and biodegradation. The program has received a major boost with the funding of an American Recovery and Reinvestment Act supplement that involves close collaboration with the Boston University Superfund Research Program, in which an actual impacted neighborhood will be examined using both field testing and modeling, thereby contributing greater understanding to the modeling approach as well as taking an important next step in its field validation.