Long-term hydraulic and containment response of geosynthetic clay liners to PFAS-impacted leachates

• Provides the first long-term evidence of geosynthetic clay liners' (GCLs) ability to contain PFAS-laden leachate, setting a new benchmark for landfill barrier performance. • PFAS breakthrough time was strongly influenced by molecular structure; longer perfluorocarbon chains and specific terminal groups exhibited longer retention times. • The activated carbon amended GCLs significantly delayed the breakthrough of 28 environmentally relevant PFAS, outperforming conventional GCLs, especially for long-chain compounds. • The limited retention of short-chain PFAS highlights the urgent need for more robust landfill liner systems to ensure long-term environmental protection. This paper explores the efficacy of individual geosynthetic clay liner (GCL) components and an activated carbon-amended GCL (ACA-GCL) in attenuating per- and polyfluoroalkyl substances (PFAS) from leachates obtained from two Australian landfills, denoted herein as leachates A and B. Batch sorption tests were performed on GCLs and their components to evaluate their sorptive affinity for 20 environmentally significant PFAS. Long-term hydraulic conductivity tests were also performed on activated carbon-amended GCLs subjected to leachates for 660 to 1111 days. Batch test results indicated that PFAS sorption increases with longer carbon chain lengths, likely attributed to enhanced hydrophobic interactions. Conversely, all sorbents exhibited minimal to negligible sorption of short-chain PFAS. Hydraulic conductivity tests yielded values of k = 7.6 × 10 −11 m s⁻¹ and k = 6.2 × 10 −11 m s⁻¹ for activated carbon-amended GCL specimens permeated by leachates A and B, respectively, indicating a moderate increase compared to conventional GCLs. Furthermore, sampling of hydraulic conductivity effluents at various intervals throughout the testing period demonstrated that the activated carbon-amended GCL specimens significantly retarded the breakthrough of 28 target PFAS compared to conventional GCLs. PFAS breakthrough time varied depending on the terminal head group and the carbon chain length, with longer perfluorocarbon chains exhibiting extended breakthrough times. Overall, the results suggest that while activated carbon-amended GCLs can effectively retard the migration of long-chain PFAS until their sorptive capacity is reached, they are less effective in addressing the migration of short-chain compounds, which presents a significant challenge. To prevent PFAS migration over time, robust landfill liner designs may be required, such as those incorporating materials capable of attenuating short-chain PFAS.