Dispersivity is one of the measurable parameters in soil porous media that is used for studying of the transport of a contaminant in groundwater. The value of this parameter depends on various factors, including kinds of porous media (homogeneous or heterogeneous), flow velocity, initial contaminant concentration, travel distance, and sampling method. In order to investigate the effects of these parameters on the dispersivity value in layered heterogeneous soils, a physical model constructed with dimensions of 10 cm in width, 80 cm in height, and 110 cm in length, respectively. The stratified soil consisted of three 20-cm thick layers containing fine-grained, medium-grained, and coarse-grained soil. Sodium chloride solutions with electrical conductivity values 10, 14, and 19 dS/m were used as the contaminant. Flow was forced through the layered heterogeneous soils at three discharge velocities of 17.58, 22.02, and 26.18 × 10-5 m/s. Two methods of sampling included point, and mixed methods sampling were used. The results of the layered heterogeneous soil were also compared with those of homogeneous soils. The results indicated that soil dispersivity values in the layered heterogeneous soils, and also homogeneous soil were influenced by contaminant concentration, flow velocity, and travel distance. Moreover, the dispersivity values obtained in point sampling were lower compared to those in the mixed methods sampling, and the mean dispersivity value in the layered heterogeneous soils was lower than that of the homogeneous soil.
