Per- and polyfluoroalkyl substances (PFAS) is the emerging contaminants of critical concern. Comprehensive understanding of the transport and fate of PFAS in the vadose-zone, a type of water-unsaturated porous media, is key to determination of the risks of the PFAS contamination in the subsurface and to the development of the effective remediation strategies. PFAS transport in the unsaturated porous media is a complex process. In order to disclose the main factors controlling the PFAS transport in unsaturated porous media, we develop the theoretical model based on the dimensionless governing equations for the transient water flow and PFAS transport. The effects of the dimensionless parameters and numbers on the PFAS transport in 2D unsaturated porous media are uncovered based on the second order accurate finite volume method. We find that the retardation numbers and the dimensionless parameters relevant to the properties of porous media as well as the relation between the surface tension and the PFAS concentration play an important role in the PFAS transport in the unsaturated porous media. The effects of the Péclet numbe, Damköhler numbers, and fraction of instantaneous sorption are not significant, however. These findings provide a better understanding of the PFAS transport in vadose zone.
Supporting Information for Dimensionless parameters and numbers controlling PFAS transport in unsaturated porous media
Table S1 in SI presents the values of parameters used in the present study. Fig. S1 illustrates Schematic of the computational domain and the boundary conditions. Fig. S2 presents the flow chart of the calculation procedures. Fig. S3 compares the numerical and experimental results for PFAS transport in unsaturated porous media. Fig. S4 shows the variation of water content with h* for different C*. Fig. S5 shows the variation of the distribution of the water content with time for the case of K* = 0.01. Figs. S6 and S9 shows the effects of Pe, Da,s, Da,aw, Fs and Faw on Cave* and average water content.