Contamination of groundwater with per- and polyfluoroalkyl substances (PFAS) from legacy landfills in an urban re-development precinct

The extent of per- and polyfluoroalkyl substances (PFAS) in groundwater surrounding legacy landfills is currently poorly constrained. Seventeen PFAS were analysed in groundwater surrounding legacy landfills in a major Australian urban re-development precinct. Sampling locations (n = 13) included sites installed directly in waste material and down-gradient from landfills, some of which exhibited evidence of leachate contamination including elevated concentrations of ammonia-N (<= 106 mg/L), bicarbonate (<= 1,740 mg/L) and dissolved methane (<= 10.4 mg/L). Between one and fourteen PFAS were detected at all sites and PFOS, PFHxS, PFOA and PFBS were detected in all samples. The sum of detected PFAS (Sigma(14)PFAS) varied from 26 ng/L at an ambient background site to 5,200 ng/L near a potential industrial point-source. PFHxS had the highest median concentration (34 ng/L; range: 2.6-280 ng/L) followed by PFOS (26 ng/L; range: 1.3-4,800 ng/L), PFHxA (19 ng/L; range: <LOQ - 46 ng/L) and PFOA (12 ng/L; range: 1.7-74 ng/L). Positive correlations between Sigma(14)PFAS, PFOA and other perfluoroalkyl carboxylic acids (PFCAs) (e.g. PFHxA) with typical leachate indicators including ammonia-N and bicarbonate were observed. In contrast, no such correlations were found with perfluoroalkyl sulfonic acids (PFSAs) (e.g., PFOS and PFHxS). In addition, a strong positive linear correlation (R-2 = 0.69) was found between the proportion of PFOA in the sum of detected perfluorinated alkylated acids (PFOA/Sigma PFAA) and ammonia-N concentrations in groundwater. This is consistent with previous research showing relatively high PFOA/Sigma PFAA in municipal landfill leachates, and more conservative behaviour (e.g. less sorption and reactivity) of PFCAs during subsurface transport compared to PFSAs. PFOA/Sigma PFAA in groundwater may therefore be a useful indicator of municipal landfill-derived PFAA. One site with significantly elevated PFOS and PFHxS concentrations (4,800 and 280 ng/L, respectively) appears to be affected by point-source industrial contamination, as landfill leachate indicators were absent. (C) 2019 Elsevier Ltd. All rights reserved.