Environmental Compliance 101

Vapor intrusion (VI), the migration of contaminant vapors from subsurface soils and groundwater to buildings, is a leading concern for regulatory agencies across the country and in Indiana. Vapor intrusion can result in impacts hundreds or even thousands of feet from the source of the contamination, and therefore, can greatly affect off-site properties. The primary source of VI is contaminated groundwater migrating from off-site properties. However, contaminant vapors from the source area also can migrate through utility corridors a considerable distance.

VI Mitigation
Advancements have recently been made in VI mitigation that may increase the overall effectiveness and reduce the cost of mitigation. The most common methods of mitigating VI are very similar to radon mitigation technologies, and include: installation of barriers to prevent migration of vapors/gases into structures; passive venting of vapors; and depressurization systems that use fans to actively remove vapors accumulating beneath the building.

There are several manufacturers of barrier systems, and although the barriers are similar, the manufacturers of these barriers have developed innovative venting materials that are placed beneath the barriers. These venting systems increase the effectiveness of the barriers by decreasing the potential for accumulation of vapors/gases beneath the barriers. Among the more notable advancements has been the concept of “aerated floor systems.” These systems have the appearance of large “egg containers” and are meant to be placed under the concrete slab during construction. Vents and stacks are attached to these systems to facilitate movement of air beneath the slab. In some cases these also can be installed post-construction on existing slabs, but the venting material would have to be covered with an additional slab. These systems can be operated as vents, or actively as depressurization systems (which utilize fans to actively remove accumulating vapors).

Other developments in VI mitigation include more reliance on wind and solar power fans and vents to depressurize (i.e., apply vacuum to) the area beneath the concrete slab of a building. The advantage of these options is that there can be lower maintenance costs and increased energy savings.