Same Building, Different Concerns
Overcoming Vapor Intrusion Concerns in Adaptive Reuse Projects
While subsurface contamination is often only considered on new development projects, contaminated vapors care very little about a building’s age when they make their way inside. Therefore, it is prudent for developers and property owners to consider the potential for vapor intrusion in existing properties, during transactional due diligence, and when properties are used as financial collateral.
Subsurface vapors have a tendency to migrate through high permeability zones such as loose fill, gravel, and utility trenches, and their exact migration pathway can be difficult to pinpoint. Additionally, on-site contamination may not be the only source of contaminated vapors. Vapors can also off-gas from groundwater contaminant plumes or migrate from a neighboring source (i.e. dry cleaner, gas station).
The primary vapor intrusion concern is the health risk associated with exposure to contaminated vapors (i.e. solvent vapors, petroleum vapors, radon, methane, elemental mercury). To prevent exposing building occupants to contaminants in indoor air, property owners should assess their buildings for potential impacts and integrate mitigation measures as needed.
Is your building at risk? One way to identify potential vapor intrusion risks is to review historical uses and regulatory databases associated with your property and the surrounding neighborhood. Representative sub-slab vapor or indoor air samples can also be collected to assess risk at your property. Keep in mind, some states require that property owners notify tenants and local health departments of indoor air sample results that exceed applicable guidelines.
One well-known technology for vapor intrusion mitigation in buildings is a sub-slab depressurization (SSD) system. Active SSD systems use fans to pull subsurface vapors from below the building and exhaust these vapors above the roof. Although the components and operation of such a system may appear simplistic in nature, designing and operating an effective SSD system for a building has its own set of unique challenges beyond developing an efficient design. Vinicius De Paula, an environmental engineer in Langan’s New York City office, explains: “Working in occupied buildings can be tricky. The engineer has to consider the current use of the space with the constructability of the design while minimizing interruptions to building operations. A walk-through during design development with the engineer, contractor, and building occupants is a must.” Langan has industry-leading computational pneumatic design modeling capabilities, which allows site-specific constraints to be considered and future system performance demonstrated so a system can be designed effectively without being oversized.
It is important to note that you will have to incorporate SSD system operation into your ongoing building management. These systems require periodic inspection and maintenance, and must continue to operate throughout the life of the building. A suitable approach is installing technology to remotely monitor and control your system, which streamlines operation and maintenance and promptly notifies property operators if the system turns off. Langan has extensive experience designing, incorporating, and operating such alarm interlock and remote telemetry systems.