Anomalous transport in "classical" soil and sand columns

We re-examine - in light of recent theoretical developments - classical experiments on dispersion of a passive tracer in fully and partially saturated porous columns. We rind that the dispersion breakthrough curves (BTCs) exhibit anomalous (non-Fickian) early arrival times and late time tailing, which can be explained by the Continuous Time Random Walk (CTRW) theory. The CTRW framework includes as a special case the classical advection-dispersion equation (ADE) for Fickian transport. We argue that existing measurements and interpretations of dispersion should be carefully reconsidered in the framework of these advances in conceptual understanding and quantification.