A study conducted by researchers at North Carolina State University has found that per- and polyfluoroalkyl chemicals (PFAS) could take over 40 years to flush out of contaminated groundwater in Cumberland and Bladen counties in North Carolina. The study utilized a combination of PFAS data, groundwater age-dating tracers, and groundwater flux to predict PFAS concentrations in groundwater discharging to tributaries of the Cape Fear River. The researchers sampled groundwater in two watersheds near the Fayetteville Works fluorochemical plant in Bladen County, discovering a significant area of PFAS contamination that impacts both private well users and downstream users of river water in and near Wilmington.
By analyzing the PFAS types and levels in the groundwater samples, coupled with atmospheric contamination data provided by the N.C. Department of Environmental Quality, the researchers were able to create a model that estimated past and future PFAS concentrations in the groundwater discharging to tributary streams. They found that PFAS was present in groundwater up to 43 years old, with concentrations of the most common PFAS compounds, hexafluoropropylene oxide-dimer acid (HFPO-DA) and perfluoro-2-methoxypropanoic acid (PMPA), averaging 229 and 498 nanograms per liter (ng/L) respectively. The maximum contaminant level (MCL) set by the U.S. Environmental Protection Agency for HFPO-DA in public drinking water is 10 ng/L.
The researchers concluded that it could take decades for the groundwater PFAS contamination from the ‘high emission years’ between 1980 and 2019 to be fully flushed out through natural groundwater flow. Additionally, they noted that PFAS may be diffusing into and out of low-permeability zones, such as clay layers and lenses, which could prolong the flushing process. Despite reduced air emissions of PFAS post-2019, some atmospheric deposition is still occurring, potentially feeding into the groundwater and continuing the contamination cycle.
Even in a best-case scenario where atmospheric deposition ceases, the researchers estimate that it will still take around 40 years for past PFAS emissions to completely flush out of the groundwater and surface water. This extended time frame for groundwater remediation underscores the long-term nature of the PFAS contamination problem in the area. The researchers plan to further investigate future PFAS levels at individual drinking water wells and collaborate with toxicologists to study the health outcomes related to past PFAS exposure levels. By quantifying the extent and duration of PFAS contamination, the research provides valuable insights into the ongoing challenges posed by these persistent chemicals in groundwater.