VOC Vapor Intrusion and Mitigation Methods

Vapor intrusion is a concern that may come up during environmental due diligence, site redevelopment, or property evaluation. It occurs when volatile organic compounds (VOCs) in soil or groundwater release vapors that rise through the ground and enter a building. These vapors may enter through cracks in a slab, gaps around utility lines, sump openings, crawlspaces, construction joints, or other openings in the foundation.

While mitigation for VOC vapor intrusion shares some similarities with radon mitigation, there are several important differences. Radon is a naturally occurring radioactive gas, while VOCs are chemical vapors often associated with petroleum products, dry-cleaning solvents, industrial activity, or other contamination sources.

While the contaminants are very different, from a building perspective the concern is similar: unwanted, potentially harmful vapors can move from beneath the structure into indoor air.

One of the most common methods is sub-slab depressurization, which creates a pressure difference beneath the building slab. By drawing air or vapor from below the slab and exhausting it outdoors, the system helps vapors move toward the mitigation system rather than into indoor air.

When sub-slab depressurization is used for VOC vapor intrusion, the system is intended to create lower pressure beneath the slab than inside the building. A typical system may include:

VOC vapor intrusion projects are usually more site-specific than a standard radon project. The design may be influenced by environmental testing, soil gas data, indoor air sampling, groundwater conditions, contaminant type, building construction, and regulatory expectations.

Sub-membrane depressurization, another radon mitigation technique, may be used for VOC vapor intrusion where a building has a crawlspace, exposed soil, or another area that can be covered with a sealed membrane. The concept is similar: vapors are collected beneath the membrane and vented away before they can enter occupied space.

Soil gas collector mats or venting layers may also be used, especially in new construction. These materials can create a pathway for soil gas to move beneath the building and toward a venting system. Depending on the project, they may be paired with a vapor barrier and designed as part of a passive or active mitigation approach.

Pressure field extension testing may also be part of the evaluation process. This testing helps determine whether a depressurization system is influencing the intended area beneath the slab. For existing buildings, pressure testing can help guide suction point placement, system design, and post-installation verification.

Essentially, a radon system and a VOC vapor mitigation system may look similar, but the evaluation behind them can be very different.

Identifying a need for vapor intrusion mitigation is a specialized service requiring environmental professionals to identify a potential problem, evaluate site conditions, and determine if remediation is necessary.

As such, Southwest Radon Eliminators does not offer VOC vapor intrusion mitigation as a direct, independent service to commercial builders. However, as one of the leading radon mitigation companies in the southern United States, we work with environmental consultant firms who have identified a need in order to deliver expert mitigation to VOC vapor intrusion projects.

Sources:

U.S. Environmental Protection Agency: https://www.epa.gov/vaporintrusion/vapor-intrusion-database

Interstate Technology and Regulatory Council: https://vim-1.itrcweb.org/active-mitigation-fact-sheet/