Shallow soil vapor samples collected across a commercial property during a Phase II property transaction screening revealed the solvent trichloroethylene (TCE) at concentrations above the USEPA Short-Term Action Level requiring expedited indoor air sampling. Weber, Hayes and Associates was retained to complete the investigation and subsequent mitigation of TCE vapor intrusion for a large commercial building at the property. Work tasks completed following the discovery included:
- In close coordination with the Santa Clara County Department of Environmental Health, a vapor intrusion assessment was designed in accordance with Department of Toxic Substances Control guidelines to determine potential risk to future building occupants.
- Initial and follow-up indoor air sampling confirmed elevated concentrations of TCE were isolated to the building’s bathrooms only, which suggested that the TCE vapor had been entering through the bathroom floor drains and other plumbing fixtures that penetrate the concrete slab foundation. The bathroom-isolated concentrations were in exceedance of applicable Environmental Screening Levels.
- A standard method for abating vapor intrusion to commercial buildings having heating ventilating and air conditioning (HVAC) systems that control facility air circulation is to adjust the equipment to allow more fresh air to be drawn into the building. A HVAC contractor
adjusted the facility HVAC system (i.e., economizers on the roof top units permanently adjusted to 50 percent intake) with the fresh air intake fan for each unit operating continuously. In addition, all bathroom floor drains were permanently sealed, which were suspected TCE vapor entry points. - Almost immediately following these building alterations, real-time high-resolution sampling over a 5-day period via a portable gas chromatograph showed concentrations of TCE decrease to non-detectable levels.
- With the implementation of these building alterations, concentrations of TCE inside the building have been eliminated and routine testing has confirmed the building is safe to occupy.
