Field-scale modeling of PFAS transport and transformation at a biosolids land disposal site

Biosolids derived from wastewater sludge are ideal soil fertilizers because of their rich content of organic carbon and nutrients. However, biosolids can also contain elevated concentrations of contaminants, thus posing a risk to the environment when applied to the land as a disposal approach. This work presents and demonstrates a modeling approach to describe the reactive transport of per- and polyfluoroalkyl substances (PFAS) at land application sites. Consistent with state-of-the-art formulations for the fate and transport of PFAS in natural porous media, this approach incorporates unsaturated water flow and PFAS retention mechanisms that include sorption to the solid phase and competitive adsorption at the air-water interface. Furthermore, the model accounts for the phase-out of some of the compounds and the transformation of PFAS precursors. This work underscores the need to model the seemingly opposite effects that each biosolids applications can have on the PFAS availability in soils: the increase in total PFAS concentrations and the potential decrease of pore water levels due to an enhanced retention because of the organic carbon introduction. Overall, this work provides a data-driven modeling framework for predicting the long-term behavior of PFAS that can be used to inform management practices at biosolids-amended sites.