Detailed characterization of solute transport in a heterogeneous field soil

There is a necessity for improved physical understanding of solute transpor t processes in heterogeneous soil systems. In situ nondestructive technique s like time domain reflectometry (TDR) and fiber optic miniprobes (FOMPs) p ermit the collection of unique measurements of solute transport processes i n soils for the purposes of model development and validation. This study ex amined the application of TDR and FOMPs to measure solute transport at vari ous points laterally and at two depths in a heterogeneous clay-loam soil. A miscible displacement experiment was performed at a constant irrigation pm to examine the applicability of these probes to field soils. In their firs t application to a field soil, the FOMPs were successfully calibrated and p erformed well in measuring solute breakthrough curves. Two now regimes were identified in the soil profile, the first where lateral spreading of the s olute occurred in the surface horizon, followed by convergence into prefere ntial flow pathways in the second transport zone. The measured transport re sponse was heterogeneous with at least two identifiable vertical now phases . It was demonstrated using transfer function modeling and data from a corr esponding laboratory study that the FOMPs were measuring the slower phase, while the TDR probes captured a composite of the fast and slow phases. The combination of these two techniques may be a means to separate solute trans port phases in heterogeneous media and relate laboratory column results to field studies.