Sub-Slab Depressurization Systems
- Marc Boogay
- May 12
- 2 min read
Soil-vapor Intrusion risk; Initial Considerations
Every site is different with respect to how areas of a hazardous release to soil can be responsible for vapors returning from that soil to occupied spaces. Findings of a soil-vapor survey, overlain with usage/architectural information, indoor air-quality (IAQ) assessments, and more may lead to a proposal of design effort as should limit soil-vapor intrusion.
Other approaches to mitigating soil vapor intrusion.
Removal of all known materials, wastes, and, as feasible soil, containing the Volatile Organic Compound(s) of interest,
Thorough assessment of the floor, with improvements attempted as could minimize soil vapor intrusion (sealing of joints, cracks, utility penetrations).
Consideration of imposed air flow (from outside to inside) as may reduce vapor intrusion driven by pressure differential.
If less-invasive approaches such as these are unfeasible or do not adequately mitigate IAQ, and the floor is a typical slab-on-grade, a Sub-Slab Depressurization System (SSDS) should be considered.
SSDS; Initial Considerations
The primary aspects of geometry of the site structure and availability for saw-cutting floor-slabs to create vacuum-application points. In addition, considerable measurements must be made to assess a breathable-character beneath the slab. This is done by applying vacuum through the slab at one or more central points and measuring pressure-change at a distance away. If these findings indicate potential for successful use of an SSDS, one or more variations of vacuum-application area and natural or induced-draft pressure differential for disrupting the path toward occupied indoor spaces.
Government Participation; The Goal of Case-Closure in San Diego County
Governmental oversight of many kinds of sampling is not required, and findings can remain private. But placement of re-sampleable well-points, any issues involved with underground tanks, and issues driving from accidental release must be done by permit, typically with the San Diego County Department of Environmental Health (DEH). The DEH offers a Voluntary Assistance Program (VAP) which is often recommended to document satisfaction of key aspects of risk, etc., allowing DEH to issue a status of "case-closed."
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