Mapping spatial and temporal variability of community exposure to PCE from vapor intrusion

The migration of subsurface contaminants into indoor air is a potential health threat at thousands of sites across the country. As more information is collected about vapor intrusion, the exposure is characterized by spatial and temporal heterogeneity within a site. It is difficult to predict and assess exposure at a community level. This study attempted to examine short-term temporal fluctuations in concentrations of chlorinated organic compounds in the indoor air of residential homes due to vapor intrusion in an environmental justice community. Using a community-based participatory design, we collected 72-hour samples for tetrachloroethylene (PCE) using sorbent packed passive diffusion samplers. Samples were collected over 10 days in 20 homes throughout the community that sit atop the contaminated shallow groundwater plume in southwest San Antonio, Texas. Any potential confounding indoor sources were removed. Indoor air samples were analyzed using gas chromatography/ mass spectrometry instrumentation, following EPA Method TO-17 procedures. Preliminary results demonstrate significant variability across both space and time. The data set will be analyzed for correlations with barometric pressure, temperature differentials and wind speed using longitudinal statistical analysis techniques. Results will also be compared with a house-level predictive model previously developed. Passive sampling technique coupled with community partnerships provides a less intrusive and more cooperative approach to data collection and show particular value in environmental justice settings. This study contributes to the body evidence on exposure screening and variability to estimate the occurrence of vapor intrusion in a home. This information will be used to update a probabilistic-based community exposure map and model to predict and screen for indoor air contamination as a result of subsurface contaminant migration.