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Subslab Depressurization (SSDS)

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What is Subslab Depressurization?

A Subslab Depressurization System (SSDS) is an engineering control method that significantly reduces or even eliminates vapor intrusion of Volatile Organic Compounds (VOC’s) into a building. Many times SSDS is used in combination with sealants that close off floor cracks and floor openings to mitigate VOC’s.  Vapor intrusion (VI) occurs when there is a migration of vapor-forming chemicals from any subsurface source into an overlying building. (USEPA). Common contaminants that cause problems are Volatile Organic Compounds (VOCs) like PCE from dry cleaners and TCE from manufacturing facilities.  SSDS is considered to be both practical and effective to mitigate vapor intrusion risk. The main goal of SSDS is to prevent and/or reduce Vapor Intrusion at concentrations that exceed human risk levels.   SSDS typically works by venting vapors through a series of collection points placed in the floor slab. SSDS can be either active or passive. “Active” SSDS are defined by the use of an operating fan to vent vapors outdoors. Meanwhile “passive” SSDS 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 the steps performed to consider and complete a Subslab Depressurization System (SSDS)

  1. Identify that there is a Vapor Intrusion Indoor Air Human Health Risk
  2. Consider alternatives to mitigate the vapors considering using SSDS and alternatives
  3. Seal the floors and openings as necessary
  4. Design and Perform a Pilot Test of a mini-scaled system for 24 to 48 hours
  5. Based on the Pilot Test, Design a Full Scale System with Piping and Fans
  6. Drill and install shallow sub-slab collection points
  7. Procure and install a fan (blower) with the proper capacity to perform the desired SSDS
  8. Connect the collection points via a piping network to the active 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 (SSDS) throughout Southern California. TRG is able to mitigate VI and reduce Human Health Risk.


Contact The Reynolds Group to work through your “VI” mitigation challenges!

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