An active vapour-intrusion mitigation system that uses a fan-driven suction point beneath a building slab to maintain a negative pressure differential, so soil gas migrates to the venting stack rather than into indoor air.
SSD systems install one or more suction pits in permeable material below the slab, connected by sealed PVC piping to a continuously operating in-line fan that discharges above the roofline. Effective design depends on slab permeability, sub-slab communication testing, and verification with pressure-field extension surveys. Continuous monitoring of differential pressure and periodic indoor air sampling are typical performance requirements.
SSD pairs naturally with a vapour barrier: the membrane blocks bulk diffusion while the active depressurization removes any vapours that defeat the membrane. For occupied buildings over chlorinated solvent or petroleum plumes, SSD is often the fastest mitigation path because it can be retrofitted with limited interior disturbance.
Also known as: sub-slab depressurization, SSD, sub-slab ventilation.
Vapor Intrusion: treatment approach
The subsurface-to-indoor-air migration pathway for volatile contaminants. It is investigated with sub-slab and indoor-air sampling and mitigated primarily by sub-slab depressurization systems that reverse the pressure gradient driving vapor into the building.
An ex-situ soil treatment process that heats contaminated soil to volatilize and separate organic contaminants from the soil matrix, after which the liberated vapors are captured and treated, usually in a high-temperature oxidizer.
A thermal desorption configuration where the heat source contacts the soil directly inside the rotary unit, delivering high heat-transfer efficiency and supporting higher treatment temperatures.
A thermal desorption configuration where heat is conducted through the wall of the treatment vessel without combustion gases contacting the soil, producing a concentrated, lower-volume vapor stream suitable for condensation and recovery.
Treatment that heats contaminated soil and groundwater in place, typically with electrical resistance, thermal conduction, or steam injection, to volatilize and recover contaminants without excavation. Used where excavation is impractical or where the contaminant zone sits beneath active infrastructure.