Vapor Intrusion of VOCs and Indoor Exposure Risk: A Field Study in an Urban Neighborhood

Abstract

Background: Characterizing vapor intrusion (VI) exposure risk often involves the collection of indoor air samples from affected buildings. Interpretation of field data and the assessment of health risks are widely recognized as challenging. Aims: To conduct field measurements at a well characterized site with the goal of improving VI models of transport mechanisms and risk characterization. Methods: Owners of three different properties (each with different foundation-types) were recruited to participate in our assessment in a Boston area neighborhood (USA) where VI of chlorinated solvents (VOCs) was known to be occurring and regulatory action underway. Ten (10) exterior soil gas sampling locations (nested at multiple depths) and three subslab sampling locations were installed. We conducted five quarterly sampling events. At each event, soil gas, indoor air, and groundwater samples were collected. Soil moisture content was also monitored and the soil geology was qualitatively described and evaluated. We communicated results with property owners and regulatory agencies. Results: Saturated soil zones appear to act as impervious barriers to vapor transport. Geologic features may also affect vapor transport. In several locations geologic stratigraphy correlated with soil gas concentrations. We identified the infiltration of sewer gas at one property resulting in PCE concentrations in indoor air that were nearly two-orders of magnitude higher compared to when infiltration of sewer gas was not known to be occurring. We are identifying implications of how our research can inform and improve VI characterization methods. Conclusion: Site models for VI should consider sewer lines as potential sources of volatile organic chemicals to indoor air, as well as geologic features that may restrict vapor transport. The integration of modeling results and field data, can be used to better understand site conditions and the potential for vapor intrusion exposure and health risk.