Contaminant sorption on soil and indoor materials and its possible impact on transients in vapor intrusion- An example based upon trichloroethylene (TCE).

Although building materials are well recognized as potential sources and sinks of indoor volatile organic compounds (VOCs), knowledge about how they affect indoor air concentrations and measurements in vapor intrusion scenarios is limited. This study investigates the potential influence of sorption processes on indoor air contamination in vapor intrusion, relying upon laboratory measurements at relevant concentration levels, and applying these in a numerical transient vapor intrusion model. It was found that the sink effect of adsorption on building materials can lower indoor air concentrations or delay their achieving a steady state, thus cautioning that these processes can affect observed indoor air concentration variability. Building materials can also serve as secondary sources of pollutants in vapor intrusion mitigation scenarios, which might affect the evaluation of the efficiency of mitigation efforts. For example, it was predicted that in a cinderblock structure it could take up to 305 hours to reduce indoor trichloroethylene (TCE) concentrations by 50% due to the re-emission of TCE from the cinderblock, whereas it would take only 1.4 hours without the re-emission process.