A probabilistic evaluation of PFOS contamination of aquifers under municipal waste landfills with a single composite liner

Per- and poly-fluoroalkyl substances (PFAS) are persistent contaminants associated with a range of adverse health impacts and are widely detected in municipal solid waste landfills (MSWLs) around the world. MSWLs commonly rely on a single composite liner system to limit the migration of contaminated leachate into neighbouring aquifers. However, these liner systems have not been designed specifically for PFAS and a question has hence been raised as to whether they can protect groundwater from PFAS contamination. The paper addresses this issue in relation to Perfluorooctane sulfonic acid (PFOS), one of the most concerning PFAS. A Monte Carlo framework enhanced by polynomial chaos expansion is developed to simulate PFOS transport through a typical single composite liner system, using best available experimental evidence. Probability distributions of the maximum PFOS concentration in the underlying aquifer (C aq-max ) are generated and compared with reference concentrations (C ref ) taken from drinking water guidelines/standards of four jurisdictions around the world. Even under excellent liner construction quality, the probability of C aq-max exceeding C ref is found to be greater than 90% for all guidelines/standards considered. Equally concerning is that C aq-max may not peak until more than a century after the onset of landfill operations.