Study of penetration behavior of PCB-DNAPL in a sand layer by a column experiment

•Infiltration performance of PCB-DNAPL in a sand layer was investigated.•Residual PCB-DNAPL under saturated and unsaturated conditions was measured.•Residual PCB-DNAPL in the PCB–air phase was more abundant than in the PCB–water phase.•PCB-DNAPL was not directly transported but dissolved in an aqueous phase.•PCB infiltration rate is governed by the degree of PCB saturation in a sand layer. To better understand the infiltration performances of high concentration PCB oils (KC-300 and KC-1000 polychlorinated biphenyl (PCB) mixtures), representative dense non-aqueous phase liquid (DNAPL), under both saturated and unsaturated conditions, we conducted experiments on a sand column filled with Toyoura Standard Sand. When PCB oil with the volume comparable to the total porosity in the column was supplied, the residual PCB concentrations under PCB–water conditions were 4.9×104mgkg−1 in KC-300 and 3.9×104mgkg−1 in KC-1000. Under PCB–air conditions, residual PCB concentrations were 6.0×104mgkg−1 and 2.4×105mgkg−1 in the upper and lower parts for KC-300 and 3.6×104mgkg−1 and 1.5×105mgkg−1 in those for KC-1000, respectively, while the rest of the PCBs were infiltrated. On the other hand, when a small amount of PCB oil with the volume far smaller than the total porosity in the column was supplied, the original PCBs were not transported via water permeation. However, lower-chlorinated PCB congeners—e.g., di- or tri-chlorinated biphenyls—preferentially dissolved and were infiltrated from the bottom of the column. These propensities on PCB oil infiltration can be explained in conjunction with the degree of PCB saturation in the sand column.