Vapour intrusion occurs when volatile contaminants in soil or groundwater migrate upward through the subsurface and enter buildings through cracks in foundations, utility penetrations and other openings. This exposure pathway has received significant regulatory attention in BC over the past several years.
When is a Vapour Assessment Required?
Vapour intrusion assessments are typically required when:
- Volatile organic compounds (VOCs) are present in soil or groundwater at a site
- Petroleum hydrocarbon contamination exists near occupied buildings
- A property is being redeveloped and historical contamination includes volatile substances
- The CSR vapour standards are potentially exceeded based on soil or groundwater data
The Assessment Process
A vapour intrusion assessment typically follows a phased approach:
- Screening - Review soil and groundwater data to determine if vapour standards could be exceeded. Apply attenuation factors from CSR Protocol 4.
- Soil Vapour Sampling - Install soil vapour probes at appropriate depths and locations. Collect samples following BC guidance documents.
- Indoor Air Sampling - If soil vapour results suggest potential indoor air impacts, collect indoor air samples during building operation conditions.
- Risk Evaluation - Compare results against CSR vapour standards or conduct a detailed risk assessment.
- Mitigation - If unacceptable risk is identified, install vapour mitigation systems (sub-slab depressurization, vapour barriers, ventilation).
Common Contaminants of Concern
The most common volatile contaminants driving vapour intrusion assessments in BC include petroleum hydrocarbons (gasoline, diesel), chlorinated solvents (TCE, PCE), BTEX compounds (benzene, toluene, ethylbenzene, xylenes) and naphthalene.
As building science and environmental toxicology advance, expect vapour intrusion requirements to become more stringent. Proactive assessment protects building occupants and avoids costly retrofit mitigation.