The effectiveness of PFAS management options on groundwater quality in contaminated land using numerical modelling

Abstract

The concentrations of PFOS and PFHxS in a contaminated site in regional New South Wales, Australia, were above the human health screening values for industrial land use. In this study, the effects of different management options on the quality of groundwater were investigated through numerical modelling. At first, a complete transfer model including the main features of advection, dispersion, adsorption and decay, was developed to simulate the long-term migration of PFOS from topsoil subjected to full climate interaction for 100 years. The sorption isotherm characteristics of the contaminated soil were determined from chemical analysis using LC/MS equipment. The model results were confirmed by PFOS values measured from a monitoring well in the proximity of the site. The model showed that PFOS values in groundwater increased gradually and exceeded the guideline values for drinking water. Three management options were suggested: a do-nothing approach, cut and replacement, and immobilisation of the topsoil up to 2 m depth. The numerical models showed that although all these strategies reduced the PFOS level in the groundwater significantly, the values were still higher than the guideline values for drinking water. This was because PFOS migrated in the ground beyond the site location. The cut and replacement and immobilisation strategies ensured that the PFOS values were lower than the guideline values for soil screening, but PFOS levels in the groundwater were not necessarily lower than the guideline values for drinking water after a long time.

Keywords: Contaminant transport modelling; Cut and replacement; Groundwater; PFOS; Soil immobilisation.