Subslab Depressurization for Vapor Intrusion Issues

Vapor IconVapors from volatile organic contamination in soil or ground water can enter nearby homes and other buildings through openings like foundation cracks and holes, causing serious issues for the structure and its inhabitants. Since air pressure in most homes and buildings is usually lower than the pressure in the surrounding soil, vapors may be drawn into the building. There are several approaches to mitigating this intrusion of subsurface vapors. Subslab depressurization (SSD) is, by most standards, viewed to be the most practical and efficient vapor intrusion mitigation strategy for existing buildings and new construction.

Subslab depressurization is a system that uses a blower, fan or vacuum pump-powered ventilation system to lower sub-slab air pressure relative to indoor air pressure. As a result, holes, cracks, or other pathways between the building and the subsurface are no longer a problem because the vapors will now flow downward instead of upward. If the depressurization system is well-designed, it will prevent any toxic vapors from intruding into structures above.

In the case of new construction, a subslab venting layer is typically installed below the slab. A blower, fan or vacuum pump is used to draw soil vapor through the gravel underlying the slab before the vapor is discharged into the atmosphere. Multiple points of pipe installation and horizontal perforated pipe installed beneath the structure have been effective in reducing vapor intrusion in larger buildings.

For existing structures, installing subslab depressurization system involves cutting a hole or multiple holes in the slab and removing a small quantity of soil from beneath the slab. This creates a suction pit or hole into which vertical suction pipes are placed. Connected to a manifold containing an exhaust fan, blower or vacuum pump, the pipes carry the vapors, which are vented outdoors.

Gasho is experienced in developing subslab depressurization systems for a variety of structures. Contact us today to discuss your project.