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Guidance
Documents Vapor
IntrusionFact Sheet: Subsurface Depressurization Systems
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Fact Sheet:
Subsurface Depressurization Systems
November 2008
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. In general, the goal
at these sites is to remove the source
of the vapors by cleaning up the contaminated
soil or ground water. Since
this can be a lengthy process, interim
measures are often needed to protect
occupants of the buildings from
breathing the vapors while the
cleanup is underway.
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.
A subsurface depressurization system fan
on the exterior of a building. |
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Sub-slab depressurization systems
are installed in buildings with slab
(concrete) floors. Sub-membrane
depressurization systems are installed
at buildings with earthen or gravel
crawl spaces or floors instead of
slabs.
A sub-slab depressurization system
consists of PVC piping installed
through the slab floor and a fan connected
with the piping. When the system
is on, the fan applies a vacuum
beneath the slab and the vapors in
the soil beneath the building are directed
outside, as shown above.
With sub-membrane depressurization
systems, an impermeable membrane (such as plastic sheeting) is
placed over the earthen or gravel area
and the ventilation piping is installed
through the membrane.
Subsurface depressurization systems
are also used throughout the country
to prevent naturally occurring radon
gas from entering buildings.
Sub-slab and sub-membrane depressurization
systems must operate
continuously to be effective. They use
little electricity, are relatively quiet and
require little maintenance. A professional
contractor should periodically
check your system to ensure it is
working properly. |
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A subsurface depressurization system prevents vapor intrusion by directing hazardous
vapors in the soil to the exterior of the building.
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