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MassDEP Issues Draft Comprehensive Guidance on Addressing Vapor Intrusion Sites in Massachusetts

Beveridge & Diamond, P.C. - Massachusetts Client Alert, December 14, 2010

On December 14, 2010, the Massachusetts Department of Environmental Protection (MassDEP) posted for public review and comment its new, “interim-draft” comprehensive guidance for addressing sites with vapor intrusion issues in Massachusetts.  Vapor intrusion refers to the ability of volatile contaminants to move from the groundwater or soil into the indoor air of buildings.  MassDEP states that its goal in developing this guidance is to provide “clear, practical and health protective guidance on vapor intrusion assessment and mitigation approaches.”  Comments are due February 1, 2011.   

As part of developing this guidance, in late 2008 MassDEP convened an Indoor Air Workgroup consisting of representatives from the licensed-site-professional, risk assessment, and legal communities, along with MassDEP staff and other interested groups.  Jeanine Grachuk of Beveridge & Diamond, P.C. is participating in this workgroup. 

The 83-page draft guidance addresses assessment, mitigation, the regulatory framework, and public involvement.  The guidance goes into detail on what, when, how, and where to sample environmental media for the purpose of evaluating vapor intrusion.  The document also provides detailed guidance on mitigation measures, including MassDEP’s preference for sub slab depressurization systems to be “active” and requirements for demonstrating that performance standards are met for any system, including indoor air sampling. 

Based on discussions at the work group meetings, at least three specific issues are of significant interest to the regulated community:  (a) if and when can modeling be used to evaluate vapor intrusion concerns, as opposed to indoor air testing; (b) how to achieve site closure when a mitigation measure is already in place, such as a sub-slab depressurization system, at a residential site; and (c) how to address the potential for future construction at vacant properties. 

Modeling.  Modeling is used to calculate the estimated concentration of VOCs in indoor air based on sub-slab soil gas concentrations.  The draft guidance document confirms that modeling can be a useful tool as one of several lines of evidence, but disallows the use of modeling alone to determine whether a vapor intrusion pathway exists.  The draft guidance also states a clear preference for measured indoor air values for risk assessment purposes when it is feasible to sample indoor air.

Site Closure.  Under the regulations implementing the site cleanup program in Massachusetts, which are known as the Massachusetts Contingency Plan or MCP, detections of any concentration of site contaminants in the indoor air of a residence require prompt reporting to MassDEP and—regardless of risk—prompt measures to prevent, mitigate or eliminate the vapor intrusion pathway.  These measures may include installation of an active sub slab depressurization system.  The guidance confirms that when site cleanup standards are met based on the subsequent comprehensive site assessment and potentially cleanup efforts, the site can be closed even if detectable levels of contaminants continue to exist in indoor air at the residence, and the existing active sub slab depressurization system can be turned off.  However, the draft guidance “encourages” continuation of these systems on a voluntary basis. 

Future Construction.  The MCP typically does not require evaluation of vapor intrusion at sites without a building.  As such, a vacant site could be closed under the MCP without addressing vapor intrusion.  A building could later be constructed on that site, possibly resulting in exposure of building occupants to contaminated indoor air.  In the guidance, MassDEP is recommending that a deed restriction, known in Massachusetts as a Notice of Activity and Use Limitation (AUL) be placed on certain vacant sites that may pose vapor intrusion concerns in order to inform future owners of this potential and their obligations under the MCP.  In the draft guidance, MassDEP states that the AUL should require any future building to be constructed with a vapor barrier and active sub slab depressurization system with specified ongoing monitoring.

The draft guidance is available for review at http://indoorairproject.wordpress.com/, and the public comment period ends February 1, 2011. 

For further information on vapor intrusion issues in Massachusetts, please contact Jeanine Grachuk at jgrachuk@bdlaw.com