What is vapor intrusion? Vapor intrusion (VI) is the upward migration of soil gases into buildings.
The migration of soil gases into a building occurs when a source contaminant is drawn into a building through permeable soil and stone below the concrete slab. The most common entry pathways are seams or cracks in the slab, utility and plumbing penetrations, floor drains, French drains, deteriorated seals around pipes, and block wall openings. The driving force of VI is the air pressure differentials between the inside and outside of a building. Soil gases enter the building when the air pressure in the building is lower than the pressure below the slab.
The contaminant gases most often associated with vapor intrusion are classified as Volatile Organic Compounds (VOCs) and primarily consist of TCE, PCE, Carbon Tetrachloride, and petroleum hydrocarbons. All of the contaminants have one thing in common: their negative effects on human health.
The harmful, odorless, and tasteless gases are almost always in concentrations undetectable by human senses. Most VI problems are diagnosed only after proper testing due to health issues arising among building occupants or the building changes ownership and the problem is detected in the due diligence phase.
A vapor plume can easily travel through the soil and along underground utilities and aquifers to impact buildings on the other side of town, potentially creating a very widespread problem. Common places where VI occurs include gas stations, dry cleaners, buildings with underground storage tanks, facilities used for industrial processes, and the manufacturing of finished metal or pharmaceutical products.
Building owners should be aware of VI issues because the VOCs involved are closely linked to several types of cancer, as well as organ and reproductive toxicity. Prolonged exposure to VOCs, such as that associated with living or working in a building experiencing a VI problem can negatively impact human health.
A properly designed and installed vapor intrusion mitigation system (VIMS) can mitigate a vapor intrusion problem. A custom-design VIMS, based on the unique challenges of the building in which it is being installed, is necessary for maximum effectiveness and protection of the people served by the system. There are no one-size-fits-all solutions when it comes to mitigating VI.
Vapor intrusion can occur in both new construction and existing buildings. There are different solutions for every type of building. New construction or redevelopment projects that are known to have soil contaminants can be mitigated more cost-effectively than a retro-fit and the VIMS can be more easily integrated into the building’s overall aesthetic and design. Existing buildings can be retro-fitted with a VIMS to eliminate a VI problem.
As more buildings and brownfield sites are repurposed, understanding the potential impact of vapor intrusion is essential to project development. Taking preventative action to control VI can significantly reduce the long-term health concerns of people occupying the building and minimize liability for building owners and responsible parties.