Diffusion Impacts Solute Transport in Macroporous Media

Contaminant transport in soils is driven by a number of physical, chemical, and biological factors. Among these various factors, two physical processes are omnipresent: advection by the water flow and molecular diffusion due to thermal motion. In soil physics, the combination of these two processes leads to the so-called phenomenon of dispersion (i.e., spreading of the plume of contaminants as they are transported within a soil), and it is generally hypothesized that this macroscopic behavior is not affected by molecular diffusion.