Vapor intrusion in the spotlight

10 Jul 2013

How clean is “clean enough” is a significant question faced as part of most brownfield redevelopment and cleanup projects. For many years, the answer to that question was driven by whether water at the site was clean enough to be consumed safely. In the last few years, the issue of vapor intrusion (as well as surface water bodies impacted by venting groundwater and their more sensitive wildlife) has begun to drive the “how clean is clean” question.

Vapor intrusion is explained in this link but, basically, it is the threat that some contaminants may migrate upward from soils and groundwater into buildings at unsafe levels.

The MDEQ has issued both generic baseline standards and guidance on the subject.  The MDEQ’s guidance applies when some previously adopted generic standards are exceeded and when there are pathways which might be outside the MDEQ generic baseline assumptions – such as when impacted groundwater may be shallow and near foundations and basements.  The guidance includes the following steps:

1. Evaluating existing information to determine if the vapor pathway is of concern;
2. If it is, and there are buildings nearby assess the risk and whether response actions are needed;
3. In some cases, conduct a building-specific investigation to evaluate the risks posed by the contaminants;
4. Conduct response actions, if necessary, which may include remedial actions or other mitigation measures.

In some cases, the MDEQ guidance has levels far more stringent than were previously the case.

The EPA has also issued draft guidance which is more complex and requires more than MDEQ’s guidance – including more vapor intrusion assessment; building mitigation and subsurface remediation; preemptive mitigation (“Early Action”); and community outreach and involvement.

While there are some creative and inexpensive measures to deal with vapor intrusion, this is a relatively new concern – particularly for residential developments.  This is a new layer of complexity which may make closures and brownfield redevelopments much harder to pursue.

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