Subsurface soils in many locations are polluted with poly- and perfluoroalkyl substances (PFASs), a class of highly persistent chemicals with known adverse health impact at trace concentration. During wetting events, they can be released into infiltrating stormwater and eventually reach the groundwater, if the adsorption capacity of the soil is low. Thus, accurate groundwater risk assessment requires a better understanding of PFAS leaching processes in subsurface soil subjected to natural weather variabilities such as dry-wet and freeze-thaw cycles. However, it is unclear whether and how these natural conditions may affect leaching of PFASs from subsurface soils. To reveal these processes, soil and sand in packed columns were first contaminated by applying water spiked with perfluorooctanoic acid (PFOA), perfluorobutyrate  (PFBA) and perfluorooctanesulfonic acid (PFOS) and followed by application of uncontaminated water to flush PFASs from pore water. Contaminated media were then subjected to flow interruption when columns were subjected to one of three types of conditions: saturated, drained by gravity to initiate drying, or freeze-thaw cycles. Injection of uncontaminated groundwater was ensued, and the effluent was measured for PFAS concentration. The result indicates that leaching potential of PFASs from subsurface is sensitive to PFAS type and the hydrologic condition the soil is subjected to between rainfall events.  The hydrological conditions affected not only the quantity of PFASs leached from soil but also the phases—dissolved and particulate—of PFASs in the solution. The results link PFAS leaching potential in subsurface soil to PFAS behavior at solid-water, water-air, or ice-water interfaces. Overall, the results help quantify the contamination risk of groundwater due to long-term PFAS leaching from subsurface subjected to natural weather variability.

Leaching of poly- and perfluoroalkyl substances from soil subjected to dry-wet and freeze-thaw cycles

2019 Fall National Meeting

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