Evaluating the representativeness of suction lysimeter for sampling PFAS porewater concentration in the vadose zone
Min Ma1, Jicai Zeng1, Bo Guo1,*
1 Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA
Per- and poly-fluoroalkyl substances (PFAS) have accumulated significantly in the vadose zone at many sites due to decades of contamination. This acts as long-term sources of contamination to groundwater underneath. As a direct sampling and measurement of in-situ solute porewater concentrations in the soil, suction lysimeters is starting to be widely used for estimation of PFAS mass leaching potential in source zones. However, the sampled porewater concentrations of PFAS by suction lysimeters may lack representativeness compared with the in-situ concentration due to the unique interracially-active properties of PFAS. When the in-situ soil wetting conditions are disturbed during porewater sampling, PFAS mass can move from the aqueous phase to the air-water interfaces, leading to reduced PFAS porewater concentrations. We employed an advanced three-dimensional mathematical model to simulate the sampling process in field applications of suction lysimeters, and quantify the impacts of potential disturbances on the sampling accuracy in multiple scenarios. Our results reveal that the sampling errors can be significant for some longer-chain PFAS—up to 35% depending on the specific operative and environmental conditions. The detailed analyses and insights can be used to optimal sampling operation for improving field sampling accuracy, which will ultimately contribute to cost-effective management and remediation of PFAS-contaminated sites.