Project 3: Indoor Air Concentration Dynamics and Vapor Intrusion

Overview

People spend a majority of their lives indoors and this environment offers potential for human exposure to harmful chemicals, including those entering by vapor intrusion (VI) from the soil. Their concentrations may vary widely over time, and this project will examine the dynamics of such contaminant exposure, developing modeling tools to describe and predict it, and performing field measurements of the variability at actual VI sites.

Significance

Vapor Intrusion (VI) is a recently recognized, priority environmental health concern in the U.S. The VI problem involves volatile organic compounds (VOCs), which vaporize from contaminated soil or groundwater beneath homes and other structures, entering these buildings directly from the soil. VI represents a chronic, low-level exposure pathway in homes and schools, and there is increasing concern about associated health risks. A major problem in managing VI risk is the highly variable indoor contaminant concentrations that empirical field investigative methods can easily miss. This project will provide those tasked with managing VI sites new computational tools for better understanding the variability in concentrations that may be expected, and allow them to make more realistic predictions of exposures than are possible now.  This is critical to developing a truly human health-protective response.

Approach

The project focuses on developing a full three dimensional model of VI that can reliably predict dynamic variability in indoor concentration levels. The modeling work will be informed by, and tested against, actual field measurements at two chlorinated solvent (TCE and PCE) VI sites in Rhode Island. Working with the RI Department of Environmental Management, and with the Research Translation and Community Engagement Cores, we will perform indoor measurements to establish the variability of indoor contaminant concentrations at well-characterized sites. The indoor measurements will include determining concentrations of VOCs, as well as factors that are important to the modeling work, such as air exchange rates, relevant indoor volumes, indoor depressurizations, and the inventory of sorption materials and surfaces that may be involved in storing the harmful chemicals. The dynamics of VOC partitioning to indoor surfaces requires further study to establish the role that such processes play in determining the variability in indoor concentrations. Thus, this project also involves laboratory measurements of dynamic partitioning of VOCs of VI concern to common indoor materials.

Specific Aims

  1. To develop a 3-D computational tool to predict time-varying indoor VOC concentrations
  2. To conduct field sampling at Rhode Island VI sites for model development and validation
  3. To measure dynamic VOC partitioning on diverse materials in indoor environments as an input to the dynamic modeling.

Sub-slab depressurization systemsSub-slab depressurization systems

An example of the predicted influence of sub-slab depressurization systems on the VOC contaminant concentration beneath a house (red indicates high concentrations, blue, low concentrations; the right panel shows the “unprotected” house, and the left the same house with a depressurization system activated). This is an example of how three dimensional engineering modeling of a vapor intrusion situation can guide the design of measures aimed at protecting residents. 

Project Leader

Eric Suuberg, Ph.D.
eric_suuberg@brown.edu