Modeling solute transport in heterogeneous soil column using continuous time random walk

Solute transport in heterogeneous media always occurs in the non-Fickian process with early arrival and long-tail. We analyze the data of the breakthrough curves(BTCs)measured in a 1 250 cm long heterogeneous soil column with the continuous time random walk(CTRW)and the advection-dispersion equation(ADE). It is found that Fickian behavior occurs in the transport at the distances from the inlet to 100 cm with a β value larger than 2,which is attributable to relatively homogeneous packing. Within the distances from 200 cm to 700 cm,the transport has significant non-Fickian behavior with β=0.915±0.024,this is due to the highly heterogeneity when packing the column. While the moderate non-Fickian transport isfound within the distances from 800 cm to 1200cm,and theβvalue is 1.19±0.0691 Compared with the dispersion coefficient of ADE,βvalue is relative stable. Better simulation results are also obtained especially for the tails of BTCs by using CTRW with respect to ADE. It implies that CTRW is a useful method to describe the scale-dependent transport and non-Fickian trans-port.