In June 2017, the Michigan Department of Environmental Quality (MDEQ) issued a bulletin that rescinded Attachment D of the 2013 Guidance Document for the Vapor Intrusion (VI) Pathway. The guidance document provides a thorough discussion of the VI pathway and presents procedures for conducting investigations and mitigation activities at sites with known or potential VI issues.
Attachment D of the document presented screening values that were used to determine whether contaminants in soil, groundwater, soil gas or indoor air were present at concentrations that could result in a potential unacceptable vapor inhalation exposure to occupants of a residential or non-residential structure.
Based on recent studies showing in utero developmental effects and risk to sensitive populations from low doses and acute exposure to certain chemicals, the MDEQ has determined that the screening values included in the 2013 VI Guidance Document are not protective of the indoor air inhalation (VI) exposure pathway.
The MDEQ is in the process of finalizing a comprehensive update of the Cleanup Criteria Requirements for Response Activity (Part 201), which will include revised generic cleanup criteria and screening levels for the VI pathway. The update will include an online calculator that can be used to develop site-specific VI screening levels based on certain conditions at a facility including soil type, depth to groundwater and building construction. The revised VI criteria and/or the online calculator will not be available to the public until after the proposed changes to Part 201 are promulgated, which is not expected to occur until early 2018.
In the interim, those evaluating the VI pathway must generate their own site-specific criteria to determine if soil gas beneath their facility may present an unacceptable risk, and submit the necessary information to the DEQ for review and approval. Or they may contact their local District Office and request for the MDEQ to develop site-specific VI criteria for their facility. The MDEQ has indicated that it may take up to two or more weeks to develop site-specific VI criteria.
Based on recent updates by the MDEQ, the new VI criteria and site-specific screening values are expected to be significantly lower than the previous values for many contaminants, especially for chlorinated compounds, which were used historically at industrial facilities. Thus, it is anticipated that additional investigation will be required at many sites to evaluate the VI pathway. This will affect facilities that were previously closed, as well as sites that are undergoing a transfer of ownership.
The MDEQ has begun to collaborate with the Department of Health and Human Services (DHHS) to enforce response action at sites with potential VI issues, including contaminated facilities that had been previously closed and sites where chlorinated solvents were detected during the course of a property transfer and disclosed through a Baseline Environmental Assessment (BEA). The MDEQ and DHHS have developed a table of Action and Trigger Levels for VI sites, which dictates when vapor mitigation is necessary and/or evacuation of a building is warranted. The MDEQ and DHHS are aggressively pursuing these response actions at potential VI sites.
Due to the costs associated with investigation and mitigation of VI issues and, more importantly, the risk to human health and public safety, it is imperative that you and/or your environmental professional have a thorough understanding of VI risks, including building assessment, soil gas and indoor air investigations, design and operation of mitigation systems and regulatory requirements. Failure to understand VI at your site may result in unnecessary costs to investigate or mitigate a potential VI issue or in an unacceptable exposure to your family, employees or visitors.
Let Envirologic help. We have comprehensive experience in all aspects of vapor intrusion, including:
If you have questions regarding VI testing, system design or regulatory issues, please contact Project Manager Paul French.
Explore more about Vapor Intrusion in our recent blog post What is Vapor Intrusion?
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michigan department of environmental quality • mdeq • vapor intrusion • vi • 2013 vi guidance document • vi pathway • envirologic