Elevated concentrations of trichloroethylene (TCE) were detected in indoor air at an active school facility in Oakland, California. The issue was identified during due diligence investigations for a property transaction, just one month before the start of the school’s summer break. The TCE levels were found to be two orders of magnitude higher than the regulatory action level. Terraphase rapidly implemented overnight emergency interim measures to protect occupants and ensure the continuity of school operations.

Scope of Work

Terraphase immediately constructed and installed a dozen air filtration units using granular activated carbon (GAC) to address areas impacted by TCE.

Additional interim controls included sealing wall and floor penetrations with expanding foam, sealing entire walls with plastic sheeting, and adjusting building heating, ventilation, and air conditioning (HVAC) systems to control vapor intrusion from below the building. Air sampling verified the effectiveness of the interim measures, and students only missed one day of school due to indoor air quality issues.

During the summer break, Terraphase installed a permanent, 200-cubic-feet-per-minute sub-slab depressurization system (SSDS) utilizing soil-vapor extraction (SVE) wells to control vapor intrusion from the subsurface. The system operated under an enforcement agreement with the Bay Area Air District (BAAD) until a permit could be issued following a mandatory 30-day public comment period.

Terraphase maintained and monitored the SSDS throughout the school year. Differential pressures and sub-slab volatile organic compound (VOC) concentrations were measured monthly and indoor air samples were collected quarterly for laboratory analysis. The school was permanently relocated at the end of the school year, and the SSDS was subsequently decommissioned.

Notable Accomplishments

• Deployed emergency air filtration overnight to restore indoor air safety
• Installed and operated a full-scale SSDS within weeks
• Maintained indoor air quality throughout the school year with minimal disruption