Clearing the Air: Understanding Vapor Intrusion and Vapor Intrusion Mitigation Systems – Part 1

Vapor intrusion assessments and vapor mitigation system implementations have increasingly become essential elements in projects with environmental concerns, particularly in projects involving a change in property use. Conversion of former industrial properties to commercial/residential mixed-use buildings has become the norm for optimizing real estate, which often requires solutions mitigating exposures for future occupants. Vapor intrusion is often one of these exposure environmental professionals assist in mitigating. This article will help you understand vapor intrusion and how we can mitigate its harmful effects.

Vapor Intrusion: A Threat to Indoor Air Quality

Vapor intrusion refers to the migration of vapors from volatile chemicals from contaminated soils and/or groundwater into buildings. It can occur in residential and commercial buildings and is particularly prevalent in areas with a history of industrial activity. Vapor Intrusion occurs when there is a pressure difference between indoor and outdoor air spaces. Typical modes of migration can occur through cracks in the foundation, gaps around windows and doors, stairwells, sumps, pipe penetrations, and other pathways giving access to the building envelope. These chemicals include volatile organic compounds (VOCs), such as benzene, trichloroethylene (TCE), tetrachloroethylene (PCE), and vinyl chloride (VC). These volatile chemicals pose a potential threat to indoor air quality. They can originate from a multitude of sources, such as leaking underground storage tanks, gas stations, new or historical chemical spills, current or former industrial operations, and dry cleaning facilities.

The volatile chemicals typically associated with vapor intrusion cause a wide range of impacts on occupants’ health. The type and severity of health effects depend on several factors, including the type and concentration of the chemical, the duration of exposure, and the age and health status of the exposed individual. Once inside, the chemicals can accumulate in the indoor air, posing a potential health hazard to the building's occupants. In addition to the health risks, vapor intrusion can impact property values and make buildings challenging to sell or lease.

Identifying Vapor Intrusion

Identifying vapor intrusion can be challenging and involves investigating multiple lines of evidence. However, some signs may indicate the presence of vapor intrusion.

• Unusual odors: If you notice an unusual or persistent odor in your home or workplace, this could be a sign of vapor intrusion. Toxic vapors from contaminated soil or groundwater can have a distinct smell similar to gasoline or other chemicals.
• Health symptoms: If you or others in your building experience unexplained health symptoms such as headaches, dizziness, or respiratory problems, this could be a sign of vapor intrusion. The inhalation of toxic chemicals can cause these symptoms.
• Proximity to a contaminated site: If your building is located near a contaminated site, such as a former gas station or industrial facility, there may be a higher risk of vapor intrusion. The contaminants in the soil or groundwater can easily migrate into nearby buildings.
• History of contamination: If your property has a history of contamination, either through previous use or nearby contamination, there may be a higher risk of vapor intrusion. This can include one-time use as a gas station, industrial facility, or proximity to known contaminated sites.

A way to confirm a vapor intrusion issue is to collect environmental samples from the soil, groundwater, sub-slab soil vapor, and/or indoor air. Most states have established or adopted vapor intrusion screening levels to determine if the presence of contamination will potentially cause a vapor intrusion issue. The United States Environmental Protection Agency (US EPA) also has a Vapor Intrusion Screening Level (VISL) calculator that environmental professionals can use to make the conditions more specific to a particular exposure scenario. Working with an environmental professional when utilizing the VISL calculator is critical to ensure the variables are used correctly.

What’s the Solution?

Vapor intrusion is a severe environmental problem that can pose significant health risks. It is vital to take action as soon as possible to mitigate the effects of vapor intrusion. It might seem like it is all doom and gloom. But there are solutions available to mitigate vapor intrusion impacts. We’ll discuss these solutions in Part 2.