Vapor intrusion (VI) is back in the news with the Ohio EPA publication of a guidance document recommending response action levels and timeframes for common contaminants of concern at vapor intrusion sites in Ohio.
“Rapid” Response to Vapor Issues
Ohio has joined a group of States and EPA Regions, including Region IX, Region X, Massachusetts, New Jersey, and California, in adopting short-term action levels and recommending action timeframes for trichloroethylene (TCE) in residential and industrial settings. Various adjectives are used to express the urgency of the required actions: “short-term,” “rapid,” “accelerated,” “imminent,” or “immediate.” The residential action level is set at 2.1 micrograms per cubic meter (µg/m3) for Ohio, 6 µg/m3 for Massachusetts, 4 µg/m3 for New Jersey, 2 µg/m3 for California, and 2 µg/m3 for Regions IX and X (learn more about Michigan’s Tiered Approach in our June 7, 2016 blog).
The wave of implementing these short-term action-level concentration values started in September 2011 when the EPA lowered the non-cancer inhalation reference concentration (RfC) value from 10 µg/m3 to 2 µg/m3. In order to address a specific health concern for women in the first trimester of pregnancy (because of the potential of cardiac malformations to the developing fetus), the regulatory bodies adopted the non-cancer risk as the driving mechanism to regulate TCE.
Despite some caveats in the guidance to allow for more qualifications, such as “further analysis may be warranted if…” or “where appropriate” or “EPA has the flexibility to determine that case-specific conditions do not warrant a removal action,” the EPA Region and State guidance implies that if the TCE concentration of the residential indoor air sample exceeds the action level, some type of mitigating actions must be undertaken within weeks, if not within days or hours! For more information on recommended response times see tables beginning on page 5.
Sufficient Information to Act?
What happened to “making sure” you have a robust conceptual site model (CSM) to understand the potential vapor issues before committing to any (potentially costly) remediation or mitigation efforts? Where are the multiple lines of evidence? Why are we relying today so heavily on indoor air sampling and disregarding the valuable data from sub-slab sampling, soil gas sampling, and establishing a pathway from the contaminated soil and/or groundwater to indoor air? Did we forget the wide spatial and temporal variability of TCE concentrations observed in indoor air samples by so many researchers?
Dr. Khaled Chekiri conducting a field demonstration of the dynamics of vapor intrusion (Image Credit: Drgun Corporation).
In June 2011, the EPA published a compilation of statistics of background indoor air concentrations of volatile organic compounds (VOCs). The publication gathered test results of indoor air concentrations in North American residences from 1990 to 2005. Approximately 2,500 background air samples were collected and tested for TCE. TCE was detected in no less than 42.7% of the background samples tested. After all, varnishes, lubricants, and other adhesives containing TCE are commonly used in homes. The laboratory reporting limits (RL) varied between 0.02 and 2.7 µg/m3. The detected concentrations ranged from the RL to 3.3 µg/m3. Most action-level concentrations listed above are within the background concentrations range.
Fortunately, some states like Colorado and Indiana do not follow the rush to mitigate when residential indoor air TCE concentrations are greater than the action level. Colorado calls for further study to determine the source of TCE. Indiana concluded that “an accelerated response is not scientifically supportable based upon current information.”
The bottom line is that the VI landscape continues to change, and keeping a pulse on these changes can be challenging. We’ll continue to do our best to keep you informed on these changes as we see them. In the meantime, if you have any questions or would like additional information related to vapor intrusion, please feel free to contact me (kchekiri@dragun.com) at 248-932-0228, ext. 138.