The Michigan Department of Environmental Quality (MDEQ) and the Michigan Department of Health and Human Services have collaboratively developed recommended interim action screening levels for indoor air. These vapor intrusion screening levels (VISLs) and new conservative media-specific interim response screening levels for soil, groundwater, and soil vapor were issued on Monday, August 7th to replace the previous 2013 VISLs presented in the Guidance Document for the Vapor Intrusion Pathway that were rescinded on June 20, 2017.
How are these Vapor Intrusion Screening Levels (VISLs) different than the last ones?
Though still in the process of completing the official formal regulatory update, the August screening levels present the most significant guidance available. They are likely close to the final numbers that will be part of the rules package for Environmental Contamination Response Activity, legislative passage of which is expected by the end of 2017.
In many instances, screening levels and criteria for many compounds are lower than those used in the past. For example, with PCE (tetrachloroethylene), a common dry cleaning solvent, the current soil level that requires additional sampling or considerations for nonresidential properties is 21,000 ppb. The new level with the updated rules package will be lowered to 19 ppb. Nonresidential soil vapor levels for PCE were 23,000 μg/m3 in the 2013 guidance document and is 2,700 μg/m3 in the newly issued document.
What does this mean to you?
An existing Phase II report that required no additional sampling or calculations could now have a considerable amount of additional work.
The lower VI levels, specifically for chlorinated compounds, means being proactive may save you time and money in the future.
In addition to pre-purchase due diligence, current owners will want to review any existing reports to determine if additional investigation and/or mitigation of potential vapor intrusion concerns are required based on the changing screening levels before the regulatory agencies request the information.