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Engineering Blog: New Mass DEP Vapor Intrusion Guidance

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By Michael Bricher,  Senior Environmental Engineer

Over the past two years, there has been an increase concern from the regulatory community, its Licensed Site Professionals (LSPs), and environmental attorneys regarding Mass DEP's implementation of vapor intrusion requirements at Massachusetts Contingency Plan (MCP) sites.

Over a 100 MCP audited sites have been recently re-opened by Mass DEP due to potential vapor intrusion concerns which include some sites that have been closed for more than 15 years. As a result, the responsible parties have been required to perform additional environmental response actions at a significant expense. In many cases, the audited sites were closed out in accordance with the regulations that applied at that time.

As a result of Mass DEP's revised approach and more stringent requirements (some of which are still in draft) to address potential vapor intrusion, there's much more uncertainty concerning what it takes to achieve MCP closure for VI sites. For example:

• Can you really rely on vapor intrusion modeling now?
• Do you need Mass DEP review and approval of every vapor intrusion site in order to be comfortable that real closure has been achieved?

In response to the increasing degree of uncertainty from the public regarding Mass DEP's policies for addressing potential vapor intrusion at MCP sites, Mass DEP has convened an Indoor Air Workgroup to develop an Updated Vapor Intrusion Guidance Document. In order to stay current with Mass DEP's approach and requirements for potential vapor intrusion, Triumvirate recommends that you review the latest draft version of the Assessment section in the New Vapor Intrusion Guidance (dated March 27, 2009). The link is provided below: