The use of indoor air measurements to evaluate intrusion of subsurface VOCvapors into buildings

The implementation of a risk-based corrective action approach often require s consideration of soil vapor migration into buildings and potential inhala tion exposure and risk to human health. Due to the uncertainty associated w ith models for this pathway, there may be a desire to analyze indoor air sa mples to validate model predictions, and this approach is followed on a som ewhat frequent basis at sites where risks are considered potentially signif icant. Indoor air testing can be problematic for a number of reasons. Soil vapor intrusion into buildings is complex, highly dependent on site-specifi c conditions, and may vary over time, complicating the interpretation of in door air measurements when the goal is to deduce the subsurface-derived com ponent. An extensive survey of indoor air quality data sets highlights the variability in indoor volatile organic compound (VOC) concentrations and nu merous sources that can lead to elevated VOC levels. The contribution from soil vapor is likely to be small relative to VOCs from other sources for mo st sites. In light of these challenges, we discuss how studies that use ind oor air testing to assess subsurface risks could be improved. To provide ad ded perspective, we conclude by comparing indoor air concentrations and ris ks arising from subsurface VOCs, predicted using standard model equations f or soil vapor fate and intrusion into buildings, to those associated with i ndoor sources.