On April 13, 2021 the Department of Environment, Great Lakes, and Energy signed an Addendum to the May 2013 Remediation and Redevelopment Division’s Guidance Document for the Vapor Intrusion Pathway.
In order to promote a consistent and informed approach for compliance with the Part 213 requirement that upon confirmation of a release from an underground storage tank system a person must identify and mitigate acute vapor hazards (Section 21307), this addendum to the 2013 VI Guidance Document was developed. Information regarding the identification, investigation, and evaluation that RRD will find acceptable to satisfy the requirements to identify an acute vapor hazard consistent with Section 21307 are provided in this addendum. Leslie DeBoer of BLDI presented the Site characterization data and examples for several trainings with EGLE staff on how to apply the various scenarios presented in the addendum.
The risk-based screening levels (RBSLs) for the volatilization to the indoor air pathway (VIAP) for certain regulated substances reflect long-term (chronic) exposures. EGLE’s Toxics Steering Group (TSG) in 2020 identified that the substances identified in Attachment 1 of the referenced addendum, are an acute (short-term) risk at concentrations less than levels that present chronic risks. The identification of short-term (acute) risks for these regulated substances are not assessed with the Part 213 Risk Based Screening Levels (RBSLs) and must be evaluated with site-specific target levels (SSTLs) that address the acute risks. Attachment 1 of the addendum includes a list of hazardous petroleum and nonpetroleum regulated substances under Part 213 that represent an acute risk for the VIAP. When present at concentrations that represent a vapor source as part of a release, these regulated substances represent an acute vapor hazard if detected at concentrations exceeding soil or groundwater SSTLs.
To comply with the obligations of Section 21307(2)(a), the liable owner or operator after discovery of a release, must conduct actions sufficient to:
- Identify if an acute vapor hazard is, or is likely, present for the VIAP for any structures located within the source of vapors (i.e., the area exceeding the residential SSTLs), as well as within the lateral inclusion zone, and
- Mitigate the hazard, if necessary.
Prior to the issuance of this addendum, if a potential acute vapor hazard was identified during investigation, closure at petroleum release sites was delayed due to uncertainties associated with how to evaluate and determine the need to address the acute vapor hazard. This addendum outlines the process to identify acute vapor hazards and determine the need to mitigate using representative soil vapor sampling data associated with the presence of a vapor source for hazardous substances that represent an acute risk, or how a successful demonstration is made that mitigation is not warranted.
With the application of the scenarios outlined within the addendum there may be other ways in which your site conditions can be further investigated to show that the acute vapor hazard is not a risk to inhabitants of the property. The scenarios outlined in the addendum consist of the following:
The source of the vapors is adjacent to, but not in contact or beneath a structure that is within the lateral inclusion zone
The source of vapors extends beneath a structure but is not in contact with the structure
The source of vapor is in contact with the structure