Random walk particle tracking for quantifying anomalous transport in laboratory-scale, heterogeneous porous formations

Intermediate-scale laboratory solute transport experiments on heterogeneous porous media were conducted in a 1 m length, 1 m height and 0.03 m thickness sandbox with small blocks of fine sand. Use of visualization of dye solution linked with spatial moment analysis was applied to the identification of the changes in anomalous transport in longitudinal and transverse directions caused by the presence of physical heterogeneities. Random Walk Particle Tracking (RWPT) was employed to reconstruct the dye tracer behavior in the abrupt changes of physical properties of the porous materials. The applicability of RWPT was also verified numerically through macrodispersivity estimation using spatial moment approaches based on dye tracer distributions, demonstrating a good agreement between the experimental and numerical results. Experimental and numerical results adequately displayed the macrodispersivity evolution subject to the existence of abrupt change of hydraulic conductivity. Furthermore, the results demonstrated that the physical heterogeneity relevant to the hydraulic conductivity is not a unique factor to define the longitudinal macrodispersivity.