Subslab Depressurization System (SSD) Installation

Subslab Depressurization System (SSD) Installation

Terra-Petra was engaged by the attorney representing the owner of a former dry cleaner in southern California that was experiencing vapor intrusion.

Specifically, indoor ambient air was monitored and determined to have concentrations exceeding commercial screening levels for the following (as well as others):

  • Toluene
  • Tetrachloroethene
  • Dichlorodifluoromethane (CFC 12)

The attorney had requested a way to mitigate the vapor intrusion issues at the site so that the property could be commercially viable again.  As we always do with any existing building Terra-Petra completed an extensive investigation of the building of concern to gain an understanding of what type of Subslab Depressurization System (SSD) would be most effective in mitigating the issue. Terra-Petra completed the pressure field extension testing to determine how much vacuum would be required to extend a minimum sub-slab negative pressure field of -0.016 ” w.c. Understanding how much vacuum is required and where it should be applied is the objective of the permeability mapping portion of any investigation and shall serve as the foundation for our design.

The design of the mitigation plan is the most critical component in the entire process because it determines the remedial design and scope of work. This is the part that eliminates the ad hoc guess work and provides a defined plan. It also eliminates installing a system that is not effective in reducing soil borne contaminants. Additionally, the process eliminates the possibility of overdesigning the system to compensate for uncertainties. Over-designed systems result in excessive installation and operational costs. Once a plan is in place, definite implementation costs can be determined.

As such, Terra-Petra completed the design, which we permitted through the local building department and began installing the system in early February of this year. The system will be online before the end of this month after we complete the installation and run our start up testing.

Installation Progress Photos

Need Vapor Intrusion Mitigation? Contact Terra-Petra Today For Assistance

Feel free to contact Terra-Petra for any of your vapor intrusion mitigation needs.  One of our experienced and friendly team members is standing by to assist you.

Vapor Intrusion Mitigation System – Fontana, CA

Terra-Petra has been chosen to provide environmental engineering services for the design of the vapor intrusion mitigation system (VIMS) design for a new logistics center in Fontana, CA.

Over the last couple of years, we have seen an increased demand for vapor intrusion mitigation systems to be designed and installed at large commercial warehouse type buildings. The main driving force appears to be the environmental personality of the property in which the buildings are being constructed. The site history will vary, but a history of industrial or commercial use where the site was subject to a chemical release of some sorts is the commonality.

Whether it be a petroleum hydrocarbon (TPH) impact from a former oil field/oil well or a Volatile Organic Compound (VOC) release from a dry cleaner or manufacturing facility the potential impacts on the health and safety of the future occupants of the building is what needs to be addressed.

Terra-Petra is well equipped at designing these systems for the current conditions, as well as building in contingency design features for potential future changes. Essentially, we design passive venting systems that are easily upgradable to active subslab depressurization systems (with remote telemetry and remote system monitoring and maintenance built into it if such a conversion is warranted in the future).

The proposed development in Fontana will consist of the construction of a new warehouse building having an approximate 260,650 SF footprint. The vapor mitigation measures will specifically include a “passive” vapor barrier beneath the office areas of the planned warehouse building, and the installation of  a passive ventilation layer beneath the vapor barrier. Inclusion of a ventilation layer beneath the vapor barrier would enable it to be made “active” at a later date by adding in-line fans, such as those used for radon mitigation, to the vertical riser pipes inside the warehouse.