Effect of layered sandy soil configuration on dispersion coefficient of nonreactive contaminant

In this research, the transport process of a non-reactive contaminant through layered sandy soils and dispersion coefficient behavior in different configurations of these soils were investigated. Tracer tests included pollution and leaching experiments conducted in a sandbox with dimensions of 130 cm×10 cm×60 cm. Three types of homogeneous sandy soils (coarse, medium and fine) as a control and six types of layered sandy soils were studied. The results showed that in the homogeneous sandy soils, the dispersion coefficient increased with increasing particle size of sand. For example, the dispersion coefficients of the coarse sandy soil in the pollution and leaching experiments were 8.46 and 7.91 orders of magnitude larger than the dispersion coefficients of the fine sandy soil, respectively. In the layered sandy soils, the type of configuration and the order of layers at each configuration influenced dispersion coefficient. In the pollution and leaching experiments, the least values of dispersion coefficients were equal to 12.50 cm2/min and 17.16 cm2/min, respectively, which were observed in the perpendicular configuration with stratification of coarse-medium-fine. However, the most values of dispersion coefficients in the pollution and leaching experiments were equal to 32.56 cm2/min and 37.31 cm2/min, respectively, which were obtained in the parallel configuration with stratification of coarse-fine- medium (from bottom to top). The dispersion coefficients of the layered sandy soils differed significantly from those of the homogeneous sandy soils. The transport process in the layered sandy soils, compared to the homogeneous sandy soils, had a more deviation from Fickian transport.