NASCLA Accredited Commercial General ContractorSite WorkHard
An environmental consultant is assessing a brownfield site prior to redevelopment. One of the primary concerns is the potential for vapor intrusion from volatile organic compounds (VOCs) in the subsurface. Which engineered control measure is specifically designed to mitigate vapor intrusion into a new building?
- ASheet piling
- BSub-slab depressurization system
- CGeotextile fabric
- DSlurry wall
Show answer & explanationAnswer & explanation
Correct answer: B. Sub-slab depressurization system
A Sub-slab Depressurization System (SSDS) is an active mitigation technique that creates a negative pressure field beneath the building's slab, drawing soil gas (and VOCs) away from the building and safely venting it to the atmosphere, preventing intrusion.
Why the other options are wrong
- A. Sheet piling is used for excavation support or temporary cofferdams, not for vapor intrusion mitigation.
- C. Geotextile fabric is used for separation, filtration, reinforcement, or drainage, not as a primary vapor barrier or active vapor intrusion control.
- D. A slurry wall is used for groundwater control or deep foundations, not directly for vapor intrusion mitigation.
Sub-slab Depressurization System (SSDS)
An active mitigation system that uses a fan to draw air from beneath a building's concrete slab, creating negative pressure to prevent soil gases (like radon or VOC vapors) from entering the indoor environment.
- Creates a pressure differential to prevent vapor entry.
- Commonly used for radon and VOC vapor intrusion mitigation.
- Includes a fan, piping, and a sealed slab.
Memory trick: Sub-Slab Sucks Vapors Out, Barriers Block Them.