Single region substitute models for dual-porosity advection–dispersion migration process based on contaminant distribution

Dual-porosity (DP) model is recommended for describing the complex non-Fickian contaminant transport in soil, while advection–dispersion-equation (ADE) model is the most popular transport model due to its simplicity and convenience. In this study, single region substitute approaches for the DP model were established based on the contaminant distribution in the mobile and immobile phases. A time dependent parameter Ω was used to determine the participation degree of the immobile phase in contaminant transport. The single region substitute (SRS) model was modified by combining the mobile phase retardation factor with the adsorbed concentration of immobile phase. Furthermore, dispersion-modified SRS (DSRS) model was established for calculating the equivalent dispersion coefficient of the coupled mobile-immobile mass transfer and advection via Fourier transformation. Correlation analyses of the modified models shown that the SRS model fits DP well when advection velocity or the mobile-immobile mass transfer rate is relatively slow under both Cauchy and Dirichlet inlet boundary, whereas that the DSRS model is applicable when mobile-immobile mass transfer rate is relatively higher. Both SRS and DSRS models can provide better understanding to the contaminant transport process of DP model.