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Going to School on Vapor Intrusion

New awareness for harmful vapor pathways brings mitigation solutions that work

Not everyone looks forward to the start of the new school year. AKT Peerless was recently retained by a small public school system that was hoping to acquire a former charter school building to support the city’s growing population. Since the building was a former school, environmental due diligence was thought to be a formality. However, during the course of a Phase I Environmental Site Assessment (ESA), a potential problem was identified.

The building’s boiler was previously fueled with heating oil. An underground storage tank (UST) was discovered during building expansion in the early 2000s. The UST and grossly impacted soil were properly removed in accordance with regulatory standards at that time. But times have changed…

Vapor Intrusion occurs when vapors from volatile chemicals in contaminated soil or groundwater migrate into the breathing space of overlying/nearby buildings. In the 1980s, vapor intrusion into buildings and other enclosed spaces was recognized as a concern mainly due to radon, a naturally-occurring  carcinogenic gas. In the ensuing years, there has been an increasing awareness that volatile chemicals found in soil, groundwater, and even sewers can also pose a threat to indoor air quality via the vapor intrusion pathway. With this new-found awareness, regulators at all levels of government have been developing new or revised screening levels and cleanup criteria based on a more complete understanding of the vapor intrusion exposure pathway. In most cases, the new criteria are significantly lower than those previously used to evaluate potential vapor intrusion concerns.

On August 7, 2017, the Michigan Department of Environmental Quality (MDEQ) and the Michigan Department of Health and Human Services (MDHHS) circulated Recommended Interim Action Screening Levels for Indoor Air (“Interim Screening Levels”). The MDEQ considers these Interim Screening Levels a replacement of the vapor intrusion screening levels provided in the May 2013 MDEQ Guidance Document for the Vapor Intrusion Pathway.

The recent Interim Action Screening levels are currently the best available guidance from the MDEQ and the MDHHS for evaluating vapor intrusion risks at properties in Michigan. The MDEQ and MDHHS are using these Interim Action Screening levels to direct due diligence, cleanup, and enforcement actions on Part 201 and 213 sites in Michigan. In many cases, the Interim Action Screening levels are significantly lower than the screening levels previously used to evaluate potential vapor intrusion issues.

These changes in the regulatory approach to vapor intrusion meant the previously “clean” UST removal at the local school now represented a potential vapor intrusion threat to the future occupants. Armed with new information and regulatory awareness, AKT Peerless acted quickly, conducting sub-slab soil gas sampling, indoor air testing, and diagnostic pressure field extension testing to support development of a mitigation strategy. Using the data generated during these investigations, AKT Peerless designed and installed a cost-effective, sub-slab depressurization system (SSDS) that prevents harmful petroleum vapors from impacting the children and faculty, just in time for the start of the school year. AKT Peerless continues to monitor the effectiveness of the school’s vapor mitigation system to ensure that the client meets ongoing statutory due care obligations. Parents, faculty and staff can breathe easier. Sorry kids, back to school.


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