One of the reasons that VI receives so much attention is because, unlike dermal exposure, for example, chemicals typically enter the bloodstream more easily through inhalation. Furthermore, the chemicals that are associated with VI (TCE, benzene) are fairly pervasive.
Vapour Intrusion in Ontario and other Jurisdictions
Last fall we discussed some of those more dicey issues, as well as other complications and controversies, including developments in the United States (for additional perspective on VI in the US see: New VI Guidance Documents and How they Impact You and Vapor Intrusion: The New Tiered Approach under Michigan’s Part 201).
Dr. Khaled Chekiri conducting an outdoor presentation on Vapour Intrusion (VI) several years ago (Photo Credit: Dragun Corporation).
Update on Vapour in Ontario
Recently, I attended Maxxam Analytics Ontario Soil Vapour Workshop (Mississauga, Ontario) where I learned that the Ministry of the Environment and Climate Change (MOECC) is developing refined soil vapour Risk Management Measures (RMMs) as part of a Tier 2 Modified Generic Risk Assessment (MGRA).
The MOECC retained a consultant to conduct research studies on the soil vapour intrusion mitigation (SVIM) systems to:
- Evaluate the different mitigation methods
- Review empirical data and evaluate system effectiveness
- Apply modelling to the SVIM systems
- Estimate VI reduction
- Set up a SVIM monitoring framework
Briefly, the preliminary results of the studies provide the following:
- Sub-slab depressurization (SSD) methods work best for existing buildings. A typical reduction in VOC concentrations in residential homes is greater than 80%. For new buildings, the optimal SVIM system depends on the contaminant, the concentration reduction needed, and the building type.
- The Johnson and Ettinger (J&E) model has been modified to include a sub-building ventilated layer or a barrier layer.
- A new Reduction Factor (RF) quantifies mitigation performance where:
RF = Vapour Attenuation Factor (AF) / Mitigation Attenuation Factor
RF ranges from 2 to 560 for the passive SVIM systems and from 100 to 9300 for the active systems. - The SVIM monitoring framework presented incorporates a new exceedance ratio concept, as well as the type of mitigation system in place.
If you want more detailed information, you can contact the MOECC or call me and I can share more information about what was covered.
As with other environmental regulatory issues, the vapour issue is dynamic. After all, the Ontario VI Guidance was developed six years ago and may be in the process of being reviewed and updated. We’ll do our best to keep you informed on this and other environmental issues that may affect the regulated community.
One final point that is important: Before committing to any (potentially costly) remediation or mitigation efforts, make sure you have a robust conceptual site model (CSM) to understand the potential vapour issues. See our article from several years ago for a more in depth discussion (Vapour intrusion from soil or groundwater: A challenge for property owners).
In the meantime, if you have any questions or would like additional information related to vapour intrusion, please feel free to contact me (kchekiri@dragun.com) at 519-979-7300, ext. 138.