Insights from Detailed Subsurface Characterization of a Plume of Poly- and Perfluoroalkyl Substances on Cape Cod, MA

Poly- and perfluoroalkyl substances (PFASs) are persistent contaminants introduced to the environment through their use in firefighting, industry, and commercial products. Owing to growing evidence of potential adverse human health outcomes such as cancer, obesity, and thyroid disease from PFAS exposure, the U.S. Environmental Protection Agency recently issued drinking water health advisories for two PFASs—perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). Aqueous film-forming foams (AFFFs) used for firefighting are a significant source of PFASs in groundwater. At hundreds of locations throughout the United States, AFFFs were used regularly over several decades at fire training areas (FTAs). Leaching of contaminated soil beneath often unlined FTAs has resulted in PFAS plumes in aquifers that are sources of drinking water.

Groundwater sampling in 2014-15 near an FTA on Cape Cod, MA, where AFFFs were used from 1970 to 1985 revealed a plume of PFAS contamination that extends more than 1.2 km downgradient from the FTA and passes beneath wastewater infiltration beds (WWIBs) used for disposal of treated municipal wastewater from 1936 to 1995. PFASs in samples collected near the water table at the FTA and WWIBs indicate that both sites are continuing sources of PFASs to the aquifer despite several decades since their last use, although PFAS concentrations from the WWIBs are much lower than those from the FTA. The shallow groundwaters beneath the two sites have different PFAS compositions, a finding that may be useful for differentiating PFAS source types at other locations. Results from total oxidizable precursor assays conducted using groundwater from the plume showed the presence of mobile perfluoroalkyl acid precursors that can degrade into perfluoroalkyl acids such as PFOS and PFOA, indicating that the total mobile mass of PFASs can be greater than what is typically measured directly with current laboratory techniques.