Until recently, vapor intrusion was not a major concern at contaminated sites. Now there is a realization that indoor air impacts can be the most direct exposure to people from subsurface contamination. In addition, the new ASTM Phase I standard creates much greater visibility for the potential for vapor intrusion. While measuring concentrations of VOCs in indoor air is a well-established practice, determining the source of the VOCs has often been problematic:
- Is subsurface contamination actually contributing to indoor air VOCs?
- Are outdoor air concentrations of VOCs a major contributor to indoor levels?
- Are potential indoors sources of VOCs, such as dry cleaning, aerosols, paint, solvents, etc., distinguishable from vapor intrusion?
- Do VOC concentrations continue to show up inconsistently, even after remediation, but you cannot exclude the possibility of residual soil vapor as a source?
The increased focus on vapor intrusion has led to the development of better tools for determining the source(s) of VOCs in indoor air. One such tool is compound specific isotope analysis (CSIA). This is a well-established method for fingerprinting of pure chemicals and groundwater contamination. CSIA compares molecular structures between two samples of the same material in order to determine the likelihood that they originated from the same source. While this approach has been applied to VOCs in indoor air, there has been some hesitation to use it in a litigation context given the lack of an established methodology. However, in the last month or so, two major developments have occurred that pave the way for utilizing this methodology for litigation related to vapor intrusion source attribution.
- The 9th Circuit, in City of Pomona v. SQM North America Corporation, issued 5/2/14, held that stable isotope analysis (for perchlorate in this case) meets the Daubert standard for admissibility.
- The US Department of Defense’s environmental technology demonstration and validation program, ESTCP, issued a report titled “Use of Compound-Specific Stable Isotope Analysis to Distinguish between Vapor Intrusion and Indoor Sources of VOCs”. This report provides the documentation needed for establishing a standard methodology and method validation to meet legal standards for admissibility and withstand Daubert challenges or state-specific expert witness thresholds (such as Sargon in CA).
These developments facilitate the use of isotope analysis techniques analysis that can be effectively and efficiently employed to reduce uncertainty and answer questions that otherwise would be extremely difficult and costly to address.