Vapor Intrusion, or “VI” occurs when there is migration of vapor-forming chemicals from any subsurface source into an overlying building, negatively effecting the quality of the indoor air. VI quickly became and has continued to be a hot button topic for the environmental consulting field. This is due to the fact that, based on the current science and current screening levels, VI is the most likely potential exposure pathway to people at and/or near contaminated sites.
While environmental professionals have been collecting and evaluating soil and groundwater samples for decades, collecting empirical data to evaluate for the VI pathway is relatively new. Further, representative air samples can be difficult to collect due to a variety of reasons. Different seasons, various heating, ventilation, and air conditioning (HVAC) settings, differing atmospheric conditions, numerous building construction approaches (specifically foundations and subsurface utility connections, etc.) lead to potentially biased results. Possibly most importantly, the chemicals that are stored at a house or facility (be it cleaning supplies, gas for equipment, paints, materials for hobbies, or even if the occupants smoke or burn candles, etc.) can have a big effect (and the representativeness) on the data collected.
With the spotlight on VI from many regulators, and the fact that the data collected frequently drives the next steps for a project, it is imperative to understand how to collect representative data in order to correctly evaluate this potential exposure pathway. As such, many state regulatory agencies have adopted guidance that includes a series of steps to follow that assist in collecting air data and interpreting the results.