Superfund Research Program
Indoor Air Concentration Dynamics and Vapor Intrusion
Project Leader: Eric M. Suuberg
Grant Number: P42ES013660
Funding Period: 2009-2021
Studies and Results
This project is focused on providing a better understanding of organic vapor exposure pathways and has involved two complementary activities. One activity is related to gaining a better understanding of the properties of polycyclic aromatic SVOCs. This includes the tar-like contaminant mixtures found in many Superfund and brownfield sites but was extended to consider other SVOCs of increasing environmental concern: brominated flame retardants. The focus of the second activity concerns vapor intrusion (VI) into structures built atop or near VOC-contaminated sites and has received the most attention this year.
Researchers have developed rigorous mathematical simulation tools that describe the VI process based on commercially and readily available finite element solvers, which means that they can be widely deployed without requiring any particular group of experts to run the simulations. These tools already had been shown in previous years to address some important common misunderstandings that result from relying on empirical sampling methods. Not all field practitioners are equipped to run full three-dimensional numerical simulations of VI. Sometimes quick estimates are needed. To address this need, researchers have developed analytic approximations of the results that the full 3-D models would provide using a closed-form analytical solution to estimate the vapor concentration beneath the sub-slab. This has been extended to the development of an analytical approximation method for prediction of sub-slab contaminant concentrations in petroleum vapor intrusion (PVI). Unlike vapor intrusion of chlorinated compounds, the vapor intrusion hazard from petroleum compounds is lessened by natural degradation of the compounds by soil bacteria. This model can be used to determine the required vertical source-building separation defining whether a particular structure is at risk for petroleum vapor intrusion.
This project continued a major effort in the direction of developing mathematical modeling tools for improved characterization of vapor intrusion sites. As noted above, most of the site characterization efforts are still highly empirical, involving environmental consultants taking air or soil gas samples at suspected sites. This is a highly intrusive process, as these sites are often residential neighborhoods. Moreover, in many cases, some feel that the only reliable measurements of the hazard posed by the chemicals of concern are those taken either within or directly beneath the homes of interest. Clearly, there is a strong incentive to try to understand the nature of the contamination problem to as great an extent as possible without taking the alarming step of entry into a home. Mathematical models of the VI process can help guide the process of sampling. They can help develop a site conceptual model to as great a degree as possible before undertaking intrusive sampling procedures. Moreover, once developed, these same models can provide environmental professionals a tool for design of mitigation systems to address the problem, if it is confirmed to exist.