New Research Reveals Shortcomings in Vapor Intrusion Investigations

A recent paper in the journal, Environmental Science & Technology (December 2013, v. 47, pp. 13347-13354) describes perhaps the most thorough temporal data set to date for vapor intrusion. This research was conducted by Dr. Paul Johnson of Arizona State University and coworkers at a specially instrumented home which is situated over a chlorinated solvent groundwater plume in Utah. The researchers collected indoor air measurements taken at 2-to-4 hour intervals for 2.5 years. Findings include documentation of indoor air concentrations varying by over three orders of magnitude and an analysis showing that sparse sampling protocols typically employed for vapor intrusion studies (such as just a single round of indoor air or subslab sampling) have a very high probability of mischaracterizing the degree of vapor intrusion and (in particular) mischaracterizing long-term average concentrations.

These studies demonstrate in great detail the dynamic fluctuations of soil gas and indoor air, adding momentum to the theories and observations presented in the book entitled, “Continuous Soil Gas Monitoring: Worst Case Parameters” coedited by our chief scientist, Dr. Lorne Everett.

Since decisions about risk to human health are often based on long-term average concentrations of contaminants in indoor air, the findings of this paper are profound. It suggests that future vapor intrusion evaluations should include multiple monitoring events or continuous monitoring across the range of conditions such as climate factors (on daily to seasonal time scales), soil moisture variability and indoor air exchange rates of the building. State and federal regulatory agencies may respond to these findings by revisiting prior risk decisions which may have been based on what is now seen as incomplete data sets. It is even conceivable that closed cleanup sites will be reopened in response to these findings.