Vapor intrusion occurs when vapors from volatile organic contamination in soil or ground water enter nearby buildings through cracks and holes in the foundations or slabs or via crawl spaces. An effective method to prevent vapor intrusion during the cleanup process is to install subsurface depressurization systems at the affected buildings. The two most common types are the sub-slab depressurization system and the sub-membrane depressurization system. This fact sheet from NJDEP provides information on these two types of subsurface depressurization systems.