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Subslab Depressurization

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What is Subslab Depressurization?

Subslab depressurization (SSD) is an engineering control that significantly reduces, or even eliminates, vapor intrusion (VI) of volatile organic compounds (VOCs) into a building. Vapor intrusion occurs when vapor-forming chemicals from any subsurface source migrate into an overlying building. Often, SSD systems are enhanced by sealing cracks and floor penetrations in the building slab. Common contaminants that cause problems are VOCs like PCE from dry cleaners and TCE from manufacturing facilities. 

Subslab depressurization is considered to be both practical and effective to mitigate vapor intrusion risk. The main goal of subslab depressurization is to prevent and/or reduce vapor intrusion to concentrations below human health risk levels. Subslab depressurization typically works by drawing air through a series of collection points installed through the slab of a building. Subslab depressurization systems (SSDSs) can be either active or passive. Active SSDSs use powered fans or blowers to produce a vacuum directly beneath the building slab. Passive SSDSs do not rely on the use of a fan but rely on pressure differentials to vent the vapors.

Steps to Using a Subslab Depressurization System  (SSDS)

The following steps are generally performed to consider and install a subslab depressurization system 

  1. Identify that there is a Vapor Intrusion/Indoor Air Human Health Risk
  2. Consider methods to mitigate the vapors using SSDS and alternatives
  3. Seal the slab and openings as necessary
  4. Design and perform a pilot test of a mini-scaled system
  5. Based on the pilot test, design a full scale system 
  6. Core the slab and install shallow sub-slab collection points
  7. Procure and install a fan (blower) with the proper capacity to achieve the necessary  subslab depressurization
  8. Connect the collection points via a piping network to the fan
  9. Start up and shake down the system
  10. Perform routine operations, maintenance (O&M) and sampling to confirm performance.

Subslab Depressurization System (SSDS) Services

In addition to a full suite of environmental consulting services such as soil vapor sampling, indoor air sampling, and human health risk assessments (HHRA’s), The Reynolds Group designs, permits, pilot tests, constructs and provides O&M services for subslab depressurization systems throughout Southern California and surrounding states. TRG mitigates vapor intrusion and reduces human health risk.

Contact The Reynolds Group to work through your vapor intrusion mitigation challenges!

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