The Michigan Department of Environmental Quality (MDEQ) recently announced that it will be evaluating the vapor intrusion (VI) pathway at 4,000 sites, including as many as 375 Resource Conservation and Recovery Act (RCRA) corrective action sites. With this, Michigan joins a growing number of states (e.g., New York, Massachusetts and New Jersey) in reevaluating the VI pathway at waste sites where the VI pathway was either never evaluated or may not have been properly or fully evaluated. These sites likely include some that were previously closed, ones still in the process of being remediated, and newly discovered sites as a result of recent public health or safety concerns.

Michigan's move to reevaluate the VI pathway at waste sites follows multiple highly publicized incidents where the state evacuated residents and tenants of commercial structures due to potential VI and required the installation of vapor mitigation measures. It also is occurring while MDEQ is working with various stakeholders to develop the new cleanup criteria under part 201 of Michigan's Natural Resources and Environmental Protection Act, 1994 PA 451, as amended (NREPA), including VI criteria. While the outcome of the process to establish new part 201 criteria is not yet complete, there are some certainties. The VI screening process will become more stringent, criteria will be lowered for some chemicals, and there will heightened regulatory scrutiny of the VI pathway due to the potential for it to present a public health concern.

Anyone who may question this outcome only needs to look as far as Governor Snyder's earmarking $4.9 million to address VI and MDEQ Director Heidi Grether's recent statement that "a 'significant public health threat' is brewing in Michigan because of chemical vapors that percolate up from the ground of former industrial or commercial sites and can leak into nearby homes."

So what does this mean to the regulated community? Here are six ways Michigan's review of VI sites could impact you:

1. While Governor Snyder earmarked VI funds, it clearly will not be enough to address the estimated 4,000 VI sites identified by MDEQ. Although MDEQ has indicated that previously closed sites may not be "reopened" per se, one may expect that, when there is a known potential responsible party (PRP) at a closed site where chemicals of VI concern were previously documented, a request for information or notice letter may be issued by MDEQ asking that the VI pathway be evaluated as a potential new release. New releases are generally carved out of any administrative consent order or closure approval, and a PRP who thought it had no further obligations at a site, may find itself being required to further evaluate the VI pathway or implement vapor mitigation measures.

2. When there is no viable PRP, site owners of previously remediated sites may be contacted by MDEQ to request that they test the groundwater and air in and around their buildings to see if there is a VI issue. Remember that an owner of a "facility" has certain due care obligations under section 20107a of part 201, including the obligation to prevent unacceptable human exposure to contamination. This would include preventing those exposures that may arise from vapors entering a building. This may result in an obligation to evaluate the VI pathway or implement mitigation measures to protect building occupants.

3. With lower screening levels, regulatory triggers and criteria, more sites will likely require detailed VI evaluations, be considered "facilities" under part 201, and be required to implement mitigation measures.

4. A party submitting a Baseline Environmental Assessment (BEA) or Due Care Plan (DCP) to MDEQ pursuant to part 201 can expect increased scrutiny of the VI pathway and its evaluation. This likely will result in an MDEQ follow-up, potentially requiring additional investigation and evaluation of the VI pathway, engineering or institutional controls, or mitigation measures. The same is true at Superfund sites, where

5. The regulated community may find that the agency driving VI evaluations and consideration of mitigation measures will be the Michigan Department of Health and Human Services (MDHHS), not MDEQ. For example, iMDEQ procedures or criteria; however, this memorandum is now being used by both agencies, driving VI evaluation and evacuation triggers. It also is understood that MDHHS has developed a new guidance document covering many more chemicals, with lower screening levels for some constituents.As of the date of writing this article, this guidance document was not available for review.This may be just the first step in a shift from part 201's risk-based program to what appears to be more of a zero-risk approach by MDHHS in handling VI sites.

6. One can expect MDEQ to be hypersensitive to potential VI issues. As a result, MDEQ will likely be very conservative, and it may even look to expand its interpretation of part 201 and its rules or attempt, as it has in the past, to impose agency guidance as if it has the force of law. As an example of an expanded interpretation of part 201, under section 20120a(18), a person can demonstrate compliance with indoor air inhalation criteria for a hazardous substance at a facility by meeting the Michigan Occupational Safety and Health Act criteria - i.e., complying with the OSHA permissible exposure limits (PELs) - instead of the part 201 criteria, if the facility is an establishment covered by certain sectors of the North American Industry Classification System (NAICS). However, MDEQ recently argued that application of the OSHA PELs is limited to the active manufacturing area and the lower part 201 criteria apply to the non-manufacturing area, such as office space, even though the entire site or establishment falls squarely within an NAICS code identified in section 20120a(18) of part 201. This is despite the fact that section 20120a(18) does not require such an approach, that NAICS does not allow an establishment to be classified into multiple sector codes (except in very limited circumstances), and that OSHA equally applies to all employees within the establishment (same OSHA PELs apply, although the exposure assumptions may change based on where an employee works within a facility). Since part 201 VI criteria are lower (and only likely to become lower) than OSHA PELs, additional VI investigations and VI mitigations measures are likely to be triggered under such an interpretation.

This new emphasis on VI in Michigan's site remediation program raises concerns about remedial obligations and represents potential litigation challenges, particularly given the use of "screening" levels instead of promulgated remedial action criteria and the seeming trend toward a more "better to be safe than sorry" or zero-risk approach.