Terraphase conducted the first investigations of per- and polyfluoroalkyl substances (PFAS) in sediment pore water in the San Francisco Bay, California. The study was initiated to address regulatory concerns about potential migration of PFAS into the bay from shallow groundwater at an industrial facility, potentially impacting aquatic receptors.
Scope of Services
Terraphase performed hydrogeologic investigations, including a tidal influence study and slug testing, to develop a conceptual site model and estimate the groundwater discharge zone. Pore-water samples were collected at two depths from 12 locations along 6 transects perpendicular to the shore, between 5 and 50 feet offshore, using a custom-modified, PFAS-free Trident probe. PFAS concentrations in pore water were compared to regional background values and ecological screening criteria.. Data were used to calculate dilution-attenuation factors (DAFs) and to propose site-specific groundwater screening levels for perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), which were accepted by the San Francisco Bay Regional Water Quality Control Board (RWQCB).
Notable Accomplishments
- Completed the first PFAS pore-water investigation in the San Francisco Bay
- Identified no exceedances of PFAS aquatic-receptor screening criteria in pore water
- Demonstrated attenuation of PFAS from groundwater to sediment pore water
- Calculated site-specific DAFs for PFOS (33) and PFOA (10)
- Developed and received regulatory acceptance of site-specific groundwater screening levels
