Remediation and Redevelopment Division rescinds the 2021 Addendum to the 2013 guidance document for the vapor intrusion pathway for the acute vapor hazards associated with petroleum releases at Part 213 sites
The Michigan Department of Environment, Great Lakes, and Energy (EGLE), Remediation and Redevelopment Division hereby rescinds the 2021 Addendum to the 2013 Vapor Intrusion Guidance Document (Acute Addendum) for acute vapor hazards (toxicants) associated with petroleum releases at Part 213 sites. The Acute Addendum was created to clarify expectations for complying with Section 21307 and to address vapor hazards from acute toxicants for leaking underground storage tank releases.
Note that the Acute Addendum addressed only Part 213 releases, which are mostly only petroleum compounds, and the vapor intrusion to the indoor air pathway. While most Part 213 releases are petroleum, it is possible for a Part 213 release to include chlorinated compounds and other hazardous substances. In instances where chlorinated compounds or other hazardous compounds are released at a Part 213 site, additional consideration of the vapor intrusion to indoor air pathway is necessary.
To ensure EGLE’s guidance is protective of public health and representative of real-world scenarios, EGLE has evaluated data collected at over 90 petroleum contaminated sites. Of the 19 chemicals addressed in the Addendum, ethanol, diisopropyl ether, n-propylbenzene, and toluene are either additives of petroleum or the base components of petroleum and are the acute toxicants associated with Part 213 petroleum releases. EGLE’s data evaluation determined soil gas screening levels were not exceeded for any of these compounds except toluene. Toluene did not exceed soil gas screening levels at most sites; however, at a small number of sites where soil gas samples were collected very near or within a petroleum non-aqueous phase liquids (NAPL) body, toluene concentrations exceeded screening levels. Petroleum vapors, including toluene, rapidly degrade under aerobic conditions, therefore, the likelihood of an acute exposure from a petroleum hydrocarbon is extremely low. Based on the data evaluation, EGLE determined the sampling plan outlined in the addendum is unnecessary and the potential risks from acute petroleum hydrocarbons can be evaluated the same as other hydrocarbons at Part 213 sites.
Section 21307(2)(a) requires that acute vapor hazards from a petroleum release be evaluated. For acute hazards from potentially acute toxicants, if a potential source of vapors is present (NAPL is present or soil and/or groundwater screening levels are exceeded), there are generally 2 options for the evaluation: 1) Use vertical or horizontal separation distances to screen out a structure; 2) Use a hierarchy of soil gas and air data – if soil gas exceeds screening levels, collect sub-slab samples; if sub-slab samples exceed screening levels, collect indoor air samples. Site specific or alternative options may also be proposed for evaluation. This evaluation of the acute vapor hazards is only applicable to new releases and releases conducting initial response actions. If, at any point in the evaluation, petroleum odors have been identified in a structure, NAPL has been found to be entering directly into the structure, and/or fire and explosion hazards potentially exist, then mitigation and/or increased monitoring frequency will be necessary as part of the initial response actions under Section 21307.
Guidance on petroleum vapor intrusion and sampling for the risk evaluation from non-aerobically degrading acute toxicants will be released in the near future. In the interim, these will be evaluated on a site-by-site basis.
Questions regarding this rescission may be directed to Nick Swiger, Technical Support Unit Manager, at SwigerN@Michigan.gov or 231-429-8926 or Matt Williams, Volatilization to Indoor Air Specialist, at WilliamsM13@Michigan.gov or 517-881-8641. Questions regarding the toxicology may be directed to Dr. Shane Morrison at MorrisonS5@Michigan.gov or 517-230-7570. Questions regarding the application of the guidance to a specific site should be directed to district staff where the site is located.
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