Study shows how PFOS moves, attaches to organic carbon in groundwater

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Remediation at the firefighting site began in the 1990s and groundwater monitoring has occurred since 2000, including measuring for PFAS and PFOS since 2015. Data collected between 2015 and 2018 showed a PFOS plume in the groundwater with two peaks in concentration — one near the training site and another farther away, with lower concentrations between the two hot spots, the scientists said. Photo credit: Jana, stock.adobe.com

Penn State researchers have completed new research that helps to improve understanding of how per-and polyfluoroalkyl substances, or PFAS, move as chemicals in groundwater.

In particular, the study focused on perfluorooctanesulfonic acid, or PFOS, which made its way into groundwater near a former firefighter training base in Centre County, Pennsylvania. PFOS is commonly used in firefighting foams. The researchers discovered that its molecules quickly attach to organic carbon and other minerals, so higher concentrations of the pollutant may be present in areas with more organic carbon.

“Our analysis demonstrates that preferential retention and transport resulting from simple heterogeneity in bedrock sorption, as caused by organic carbon content variability, provides a plausible explanation for plume separation,” the study states.

Remediation at the firefighting site began in the 1990s and groundwater monitoring has occurred since 2000, including measuring for PFAS and PFOS since 2015.

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Data collected between 2015 and 2018 showed a PFOS plume in the groundwater with two peaks in concentration — one near the training site and another farther away, with lower concentrations between the two hot spots, the scientists said.

Kalle Jahn, a researcher at the U.S. Geological Survey, who conducted the PFOS work as a doctoral candidate at Penn State, explained that authorities should be trying to limit how much PFAS escapes into the environment, but once it’s discovered, “we need to be aware of the complexities that exist in trying to constrain our predictions of its movement with the limited information we can collect,” wrote Jahn. This work may give people a starting point for thinking about contamination elsewhere.”

Jahn explained that what makes PFAS unique is that their chemical structure makes it hard to predict their movement in the environment.

“Pretty much all PFAS are hydrophobic — part of their molecular structure makes it so they don’t want to be in water, and they will attach to organic material because of that,” he wrote.

Physical measurements from the firefighting site suggested changes in the water table or hydraulic conductivity, or how fast the water moves underground, were not responsible for the split.

Demian Saffer, former head of geosciences at Penn State and now a professor of geological sciences at the University of Texas, and Sara Lincoln, former lab manager in Penn State’s Energy and Environmental Sustainability Laboratories and now a researcher at the U.S. Geological Survey, also participated in the study.

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