Addressing a hot topic, the Maine Department of Environmental Protection (DEP) just issued “Supplemental Guidance for Vapor Intrusion (VI) of Chlorinated Solvents and other Persistent Chemicals” superseding guidance issued in 2010.   

VI is a significant indoor air issue most often at or near properties with volatile organic chemical releases (especially current and former dry cleaners) or releases of petroleum products.  Those concerns may arise from detected odors by residents or employees, from environmental site assessments, or from spills or tank releases that may reach foundation penetrations, such as utility conduits.  The ability to measure contaminants at very low levels has raised concerns even if the levels are unlikely to cause health impacts, and the potential for interference and background levels of chemicals in indoor air are well-established confounding factors.

DEP’s VI Guidance is not a regulation, but is intended to be a start-to-finish approach for determining when a VI investigation should be conducted, the substance of a VI investigation plan, and evaluation of VI data.  VI from chemicals that decay relatively rapidly in the subsurface, such as petroleum compounds, however, are not within the scope of the proposed DEP guidance, nor is VI risk from polychlorinated biphenyls (PCBs), hydrogen sulfide, and elemental mercury.

The state recognizes that EPA’s VI Guidance (issued in 2015) is intended for larger sites, which are rare in Maine. The state’s supplemental guidance will have “presumptive” applicability for sites with 10 or fewer inhabitable buildings at risk, and is intended to offer reasonable cost-effective alternative approaches for investigating and mitigating vapor intrusion risks.  Among the most important parts of the guidelines is the five part “completed pathway” analysis. DEP also indicates it is trying to be flexible by stressing the “multiple lines of evidence” approach and by offering sampling protocols that are less costly than EPA's VI Guidance.  Nevertheless, DEP’s guidance states that ideally four sampling events about three months apart showing acceptable concentrations at the exposure point will be necessary to close out a VI site.

Addressing VI issues and application of the VI Guidance raise multiple legal and strategic issues including whether and when the guidance applies, what legal standards apply, what notifications are required and to whom, whether to test soil or indoor air, the “due care” and “reasonable steps to prevent or limit exposures” obligations as contemplated by federal and state laws (even for non-source property owners), and what cleanup may be required.  Importantly, under the VI Guidance, indoor air targets will be used by DEP to determine when mitigation or remediation is needed, and the priority of that remediation.  Further, the DEP VI Guidance does not address how cleanup may apply under other programs such as the Hazardous Waste Corrective Action program.