Laboratory investigation on longitudinal dispersivity of sand-illite mixtures

The longitudinal dispersivity of soil is critical for predicting contaminant transport through a subsurface porous medium. This study conducted laboratory soil-column experiments to investigate the longitudinal dispersivity of sand-illite mixtures as a function of the travel length and illite content. In addition, the longitudinal dispersivity was evaluated separately from breakthrough and tailing curves to identify the difference between breakthroughs and tailings in the sand–illite mixtures. The longitudinal dispersivity increased as the illite content and the travel length increased, which led to a larger fitted standard deviation from the derivatives of the breakthrough curves. In addition, the trends of the Peclet numbers for the sand-illite mixtures were different from the database of previous studies on pure coarse-grained soils. This suggested that the clay content should be considered when predicting contaminant transport through clay-containing soils.