“Conceptualizing Controlling Factors for PFAS Salting Out in Groundwater Discharge Zones Along Sandy Beaches,” published in June 2024, reflects the continued importance of research that helps advance understanding of PFAS behavior in groundwater systems.

Its coauthors were Hiroko M. Hort, Yue Li, David T. Adamson, Charles J. Newell, Clare E. Robinson, Audrey H. Sawyer, and Douglas Roff.

Sophia is a Principal Geologist based in California with more than 10 years of experience focused on hydrogeologic modeling, remedial investigations, water resilience, PFAS investigations and remediation, and environmental restoration for governmental and private clients worldwide. Sophia is a recognized subject matter expert in integrating groundwater modeling into remedial investigations at environmental cleanup sites.

Rebecca is a Principal Geologist based in California with more than 20 years of professional experience in the fields of CERCLA and federal site management, hydrogeologic investigation, PFAS research and site inspections, and vapor intrusion.

Groundwater is the leading international journal focused exclusively on groundwater. Founded in 1963, it publishes a dynamic mix of papers on topics including groundwater flow and well hydraulics, hydrogeochemistry and contaminant hydrogeology, application of geophysics, groundwater management and policy, and history of groundwater hydrology.

More Information on PFAS Remediation, Groundwater Modeling, and the Article

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For more information on PFAS remediation, hydrogeologic investigations, and groundwater modeling, contact Sophia at Sophia.Lee@geosyntec.com or Rebecca at Rebecca.Cardoso@Geosyntec.com.
Learn more about Sophia: Sophia Lee, PG
Learn more about Rebecca: Rebecca Cardoso, PG

Abstract

Understanding fate and transport processes for per- and polyfluoroalkyl substances (PFAS) is critical for managing impacted sites. “PFAS salting out” in groundwater, defined herein, is an understudied process where PFAS in fresh groundwater mixes with saline groundwater near marine shorelines, which increases sorption of PFAS to aquifer solids. While sorption reduces PFAS mass discharge to marine surface water, the fraction that sorbs to beach sediments may be mobilized under future salinity changes. The objective of this study was to conceptually explore the potential for PFAS salting out in sandy beach environments and to perform a preliminary broad-scale characterization of sandy shoreline areas in the continental United States (US) While no site-specific PFAS data were collected, our conceptual approach involved developing a multivariate regression model that assessed how tidal amplitude and freshwater submarine groundwater discharge affect the mixing of fresh and saline groundwater in sandy coastal aquifers. We then applied this model to 143 US shoreline areas with sandy beaches (21% of total beaches in the USA), indirectly mapping potential salinity increases in shallow freshwater PFAS plumes as low (<10 ppt), medium (10–20 ppt), or high (>20 ppt) along groundwater flow paths before reaching the ocean. Higher potential salinity increases were observed in West Coast bays and the North Atlantic coastline, due to the combination of moderate to large tides and large fresh groundwater discharge rates, while lower increases occurred along the Gulf of Mexico and the southern Florida Atlantic coast. The salinity increases were used to estimate potential perfluorooctane sulfonic acid (PFOS) sorption in groundwater due to salting out processes. Low-category shorelines may see a 1- to 2.5-fold increase in sorption of PFOS, medium-category a 2.0- to 6.4-fold increase, and high-category a 3.8- to 25-fold increase in PFOS sorption. The analysis presented provides a first critical step in developing a large-scale approach to classify the PFAS salting out potential along shorelines and the limitations of the approach adopted highlights important areas for further research.