Vapor intrusion, the migration of a volatile chemical from subsurface contamination into the indoor air of a building, was not viewed as a significant exposure pathway in 1995 when Act 2 was written into law. It is viewed as significant now. The emerging importance of this pathway poses unique challenges for DEP and responsible parties under Act 2. It also has the potential to undermine some of the predictability that Act 2 is designed to provide. Managing the risks related to vapor intrusion under Act 2 requires understanding the issues, including the steps that DEP has already taken to address them and the changes that are likely to come. We cover these issues briefly in this post.
Part of the challenge of vapor intrusion for DEP, and the regulated community, is structural -- vapor intrusion exposures are not considered in development of Statewide Health Medium Specific Concentrations (MSCs) for soil and groundwater under Act 2. Perhaps more in theory than practice, this means that achieving MSCs for a volatile contaminant below a building does not ensure that the contaminant is not present at unacceptable levels in the indoor air – the MSCs are not calculated to be protective for vapor migration to indoor air (though they may be protective for most substances in any event). More problematic is that the “point of compliance” for attainment of groundwater MSCs is the property boundary. This means that under the attainment criteria established in the Act 2 statute itself, high levels of a volatile chemical – a source for vapor intrusion to indoor air -- could be left in groundwater under an on-site building as long as the groundwater MSC is achieved at the property boundary.
DEP has taken steps to address these issues.
In January 2004, the DEP Clean Standards Science Advisory Board (CSSAB) issued Section IV.A.4 of the Technical Guidance Manual -- Pennsylvania Vapor Intrusion into Buildings from Groundwater and Soil under the Act 2 Statewide Health Standard (2004 SHS VI Guidance). This guidance states, “Indoor air quality (IAQ) from the vapor intrusion of contaminants into buildings from groundwater and soil is not assessed under the Statewide Health standard in the Act 2, Chapter 250 regulations.” Though not itself a regulation, the guidance provides “additional screening requirements . . . to prevent unacceptable risk” from vapor intrusion in the context of Statewide health standard sign-offs. The guidance provides decision matrices to be followed under the Statewide health standard; includes MSCs for Indoor Air Quality; screening values that can be used to evaluate groundwater and soil data if site conditions match the underlying assumptions; and a framework for evaluating vapor intrusion risks. DEP also developed valuable questions and answers on vapor intrusion in the Land Recycling Q and A Database (Category: Vapor Intrusion).
In January 2011, DEP made the evaluation of vapor intrusion part of the law in promulgating a regulatory provision at Section 250.312 for Statewide Health Standard signoffs: “The final report must include, as appropriate, an assessment of the vapor intrusion pathway.”
In addition, in March 2011, DEP re-convened the CSSAB Vapor Intrusion Subcommittee, to support an update of the 2004 SHS VI Guidance. Preliminary work was done by the DEP and the subcommittee in 2011. After a hiatus, the next meeting of the subcommittee is scheduled for late January 2013. As a member of that subcommittee I will keep you posted as appropriate. At this point, I expect a guidance more focused on sub-slab and indoor air sampling -- consistent with recent New Jersey VI Guidance and the recently ‘leaked’ revision of the USEPA guidance, substantial revision to some of the screening values, and that includes discussion of proceeding directly to the installation of mitigation systems in lieu of extended investigation. Mitigation systems can be relatively inexpensive and work well. The downside is the environmental covenant that will be required if mitigation is to be relied on in a release of liability.
One recommendation, if you plan to rely on an existing Act 2 release of liability for any site where volatile contaminants remain, seek out good advice on whether vapor intrusion has the potential to undermine the certainty you expect from the release of liability.