Unsaturated flow effects on solute transport in porous media

A major contaminant transport process in soils is hydrodynamic dispersion by affecting the spreading and arrival of surface-applied pollutants at underlying groundwater reservoirs. When a soil is unsaturated, hydrodynamic dispersion is very much affected by soil water saturation. Centimeter- and decimeter-scale column experiments were carried out to explore the effects of fluid saturation and particle size on the unsaturated solute dispersivity. Measured in-situ breakthrough curves were analyzed in terms of both classical advection-dispersion and dual-porosity (mobile-immobile) type transport equations. A clear non-monotonic relationship was found between the dispersivity and soil water saturation. The extent of non-monotonicity was more pronounced for a relatively coarse-textured sand compared to a finer sand. This finding has been reported rarely before; it explains some of the inconsistencies of saturation-dispersivity relationships in the literature.

Automated summary

Hydrodynamic dispersion in soils is significantly influenced by soil water saturation, and there is a non-monotonic relationship between fluid saturation and solute dispersivity. The extent of non-monotonicity is more pronounced for a relatively coarse-textured sand compared to a finer sand, which helps explain some inconsistencies in the literature regarding saturation-dispersivity relationships.