An estimated 61.1 million m<sup>3</sup>yr<sup>-1</sup> of leachate is generated in the United States. Studies suggest that most leachates contain per- and polyfluoroalkyl substances (PFAS) that may pose a risk to the environment following release of raw or treated leachate. The objectives of this project were to 1) optimize strategies for analysis of total PFAS composition and concentrations in field-collected landfill leachate using a combination of analytical techniques; 2) apply optimized techniques to study occurrence of PFAS in leachate; and 3) assess sorption and diffusion of  PFAS in flexible membrane liner materials. Leachates and leachates spiked with aqueous film foam (AFFF) were prepared using liquid liquid extraction (LLE), solid phase extraction (SPE), and the total oxidizable precursors (TOP) assay. Samples were analyzed using targeted analysis and high resolution mass spectrometry (HRMS) with suspect screening to evaluate which preparation method would yield optimal internal standard (IS) recovery, retention of anionic, neutral, cationic and zwitterionic PFAS, and total PFAS estimates. SPE led to low recovery (&lt;50%) of 15 (Leachate A) to 17 (Leachate C) of 20 internal standards (IS).  Relative to SPE, LLE led to increased IS recovery in all but 3 IS. HRMS analysis of AFFF-spiked leachates demonstrated that LLE also retained the greatest number of PFAS. TOP assay results demonstrated that measurable precursors remained in some leachates following oxidation at multiple oxidant concentrations. C4-C10 perfluoroalkyl carboxylates, C4-C8 perfluoroalkyl sulfonates, 6:2 fluorotelomer sulfonate, and 5:3 fluorotelomer carboxylates were present in all leachates, consistent with prior studies. Four perfluoroalkyl ethers were detected in Leachate C that, to our knowledge, have never been previously detected in leachate. Multiple homologous series of polyfluoroalkyl ethers were also detected during suspect screening of Leachate C. Sorption of PFAS in leachate to polypropylene (PP) and linear low density polyethylene modified with ethylene vinyl alcohol (LLDPE) up to 1000 ng/L was linear and increased with increasing chain length. PFAS sorption to PP was greater than LLDPE, particularly at higher chain lengths. Side-by-side diffusion cells with field collected leachate are being used to evaluate diffusion of PFAS through the same materials/ Preliminary results suggest diffusion coefficients will be of similar magnitude as those in limited prior studies.

Occurrence and fate of per and polyfluoroalkyl substances in landfill leachate

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