Petroleum Vapor Intrusion Precluding Factors Checklist Update
The Department of Environment, Great Lakes, and Energy (EGLE), Remediation and Redevelopment Division (RRD) has updated the 2013 Guidance Document for the Vapor Intrusion Pathway (2013 VI Guidance). The update will promote a consistent and informed approach to determine where to characterize and assess risks to human health with the volatilization to indoor air pathway (VIAP) at petroleum release sites. This addendum provides an updated checklist to help determine if certain factors are present at a site that would preclude the use of the Interstate Technology and Regulatory and Council (ITRC) screening process for the VIAP. The screening process presented in the ITRC 2014 Petroleum Vapor Intrusion (PVI) guidance (ITRC PVI guidance[1]) is a means of utilizing soil and groundwater data with lateral and vertical separation distances to screen out properties and/or buildings for the VIAP to reduce unnecessary data collection while remaining protective of human health and the environment. When certain factors are present at a site, the assumptions from the data used in the screening model are no longer valid and preclude the use of ITRC screening distances. When the certain factors are absent, it allows for the establishment of a lateral inclusion zone for assessment and the utilization of vertical separation distances within the lateral inclusion zone.
Lateral Inclusion Zone
The lateral inclusion zone is used in the ITRC PVI screening process to determine whether a building or property is close enough to a petroleum vapor source to warrant an evaluation of the VIAP. A conservative distance of 30-feet from the extent of a vapor source (nonaqueous phase liquids [NAPL], soil contamination, and/or groundwater contamination) may be used in accordance with the ITRC PVI guidance when the conceptual site model supports its use and there are no precluding factors present.
The default lateral inclusion distance of 30 feet is a conservative buffer developed to account for the uncertainty with contaminant stability or with the lateral edge of contamination due to the typical spacing of borings or monitoring wells laterally from the vapor source area. Once the site is fully delineated and well characterized (the extent of the soil contamination, NAPL, and groundwater plume boundary are known and the NAPL body and groundwater plume has been shown to be stable), the vertical screening distances of 5 feet from a dissolved groundwater or a contaminated soil source or 15 feet from NAPL may be applied in the lateral direction, measured from points where target levels are met.
All structures and properties within the lateral inclusion zone must be evaluated for the VIAP. This could include screening out by vertical separation, soil gas sampling, sub-slab sampling, etc. Structures or properties outside of the lateral inclusion zone do not require further evaluation for the VIAP as the lateral inclusion zone is the conservative maximum distance vapors are expected to migrate. The lateral inclusion zone is applied for the entire release and may be used independently of the vertical separation distance. Additional site characterization (e.g., soil gas data) may allow for further reduction of the lateral inclusion zone; however, those approaches are site-specific and not included as part of the ITRC screening process. Additional information and guidance on reducing or developing a site-specific lateral inclusion zone using soil gas data will be provided in the future.
Vertical Separation Distances
The vertical separation distances are applied within the area established as the lateral inclusion zone and therefore cannot be used unless the precluding factors identified for the lateral inclusion zone are absent. The vertical separation distance for dissolved groundwater contamination, soil contamination, and/or NAPL zones may be used on a property-by-property or structure-by-structure basis.
The use of the screening process is not a statutory requirement for compliance with the VIAP under Part 213, Leaking Underground Storage Tanks or Part 201, Environmental Remediation, of the Natural Resources and Environmental Protection Act,1994 PA 451, as amended. However, if a party is providing a submittal to RRD using the ITRC screening process, the Precluding Factors Assessment for PVI Lateral Inclusion Zone and the Precluding Factors Assessment for PVI Vertical Separation Distance checklists should be used and provided to RRD with the submittal to ensure that a more consistent and efficient review is completed. Training on the use and applications of the checklists is planned for February.
Please contact Nick Swiger, Technical Support Unit Manager, at 231-429-8926 or SwigerN@Michigan.gov, Matthew Williams, Volatilization to Indoor Air Specialist, at 517-881-8641 or WilliamsM13@Michigan.gov, or Dr. Steve Beukema, Part 213 Program Specialist, at 269-547-0125 or BeukemaS@Michigan.gov with any questions.
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