Using Suction Lysimeters for Determining the Potential of Per- and Polyfluoroalkyl Substances to Leach from Soil to Groundwater: A Review

In-situ porewater samples were proposed to best represent the fraction of perfluoroalkyl and polyfluoroalkyl substances (PFAS) with the potential to migrate to groundwater. While there are many techniques for collecting porewater samples, suction lysimeters are frequently being used for PFAS investigations. Suction lysimeters use vacuum to extract porewater from vadose zone soils, typically fine to medium sands, which retain and release enough porewater for analysis. Importantly, determining the rate of PFAS migration to groundwater requires an independent measure of water percolation. This review covers the installation and sampling methods for suction lysimeters and provides suggestions to improve the utility and reduce the variability of the results. Because the volume of soil represented by the porewater sample varies significantly depending on the soil-water content, which is spatially and temporally variable, many suction lysimeters may be required to accurately represent soil heterogeneity. A similar limitation applies to soil or leaching protocol samples. Suction lysimeters may not provide a representative sample for all PFAS due to interactions with lysimeter materials, air-water interfaces, and the use of vacuum. Consequently, lysimeter data are best applied in combination with soil-leaching protocols, groundwater transects, and soil analysis when making remedial decisions.