Meaning
Mechanical mitigation equipment maintains a continuous negative pressure differential across sub-slab aggregate to prevent gas movement into occupied indoor space. An active depressurization system utilizes inline powered blowers connected to sub-slab extraction points to draw volatile organic compounds out of soil matrix before vapors breach the floor slab. The installation relies on sealed penetration points and dedicated exhaust piping to transport extracted soil gas into the atmosphere above the building eaves.
The boundary of this mechanism ends at the stack discharge point where exhaust vents dissipate vapors into ambient air.
Pressure Differential
Suction pits excavated beneath concrete slabs establish a zone of influence that counters stack effects and building HVAC influences. Operational capability relies on creating measurable vacuum field extension across the entire slab footprint. Pilot tests establish baseline permeability, whereas full production runs require continuous differential pressure monitoring across diagnostic sampling points to verify zero vapor bypass.
Operation Envelope
Dynamic seasonal water table shifts alter sub-slab airflow resistance, requiring adjustable fan speeds to preserve pressure targets. Excessively high extraction rates draw moisture into ductwork and elevate electricity demand without expanding negative pressure field boundaries. Premature system certification based on dry season data risks indoor air contamination when saturated soils restrict air permeability during rainy periods.
Verification Standard
Diagnostic micro-manometer readings verify that sub-slab vacuum levels meet baseline design targets. Differential pressure measurements confirm operational integrity before post-mitigation sampling commences. System verification fails whenever sub-slab depressurization collapses.
