An experimental study on the determination of dispersion coefficient in layered soils

Dispersivity is a measurable parameter in soil porous media that is used for studying the transport of contaminants to groundwater. The value of this parameter depends on various factors, including the kind of porous media (homogeneous or heterogeneous), flow velocity, initial contaminant concentration, travel distance, and sampling method. A physical model with dimensions of 0.10 m in width, 0.80 m in height, and 1.10 m in length was constructed to investigate the effects of these parameters on the dispersivity value. The stratified soil used consisted of three 20-cm-thick layers containing fine-grained, medium-grained, and coarse-grained soil. Sodium chloride solutions with electrical conductivity values of 10, 14, and 19 dS/m were used as the contaminants. Flow was forced through the layered heterogeneous soils at three discharge velocities of 17.58, 22.02, and 26.18 × 10−5 m/s. The point and mixed sampling methods were used. The results indicated that the soil dispersivity values in layered heterogeneous soils and homogeneous soil were influenced by contaminant concentration, flow velocity, and travel distance. Moreover, the dispersivity values obtained by point sampling were lower than those obtained using the mixed sampling method, and the mean dispersivity value in the layered heterogeneous soils was lower than that of the homogeneous soil.