Pentafluorobenzoic acid

PFOS (CAS# 1763-23-1, Sigma-Aldrich, 98% purity) and PFOA (CAS# 335-67-1, Alfa Aesar, 95%) were used as representative PFAS in the experiments. Additionally, perfluoropentanoic acid (PFPeA) was used for interfacial-tension measurements (CAS# 2706-96-3, TCI America, 98%). Pentafluorobenzoic acid (Strem Chemicals, 99% purity), which is not a PFAS, was used as the nonreactive tracer (NRT). Trichloroethene (CAS# 79-01-6, Sigma-Aldrich, >99.5% purity) and decane (CAS # 124-15-5, Sigma-Aldrich, 99% purity) were used as representative dense (DNAPL) and light (LNAPL) NAPLs, respectively. Experiments were conducted with either 0.01 M NaCl or synthetic groundwater (SGW) solutions. A commercial quartz sand (Accusand, Unimin Corp., Ottawa, Mn) was used in the column experiments. SGW and sand characteristics are detailed in section S1 of the SI.

The experiments were conducted with PFOS (CAS# 1763-23-1, Sigma-Aldrich, 98% purity) and PFOA (CAS# 335-67-1, AIKE Reagent, 98% purity) as the representative PFAS. Pentafluorobenzoic acid (99%, Strem Chemicals), which is not a PFAS, was used as the nonreactive tracer (NRT). Two soils and a commercial natural quartz sand (Accusand, Unimin Corp., Le Sueur, MN) were used in the experiments. The media have similar median grain diameters, but different geochemical properties (Table S1 in the Supplemental Information file). A synthetic groundwater solution was used for the experiments conducted with the soils. A 0.01 M NaCl solution was used for the experiments conducted with the sand. Details of the soils and synthetic groundwater composition are provided in the Supplemental Information (SI-I).