COTRANSPORT OF CADMIUM AND HEXACHLOROBIPHENYL BY DISSOLVED ORGANIC-CARBON THROUGH COLUMNS CONTAINING AQUIFER MATERIAL

The cotransport of an ionic contaminant (cadmium) and two nonionic contaminants (2,2',4,4',5,5'-hexachlorobiphenyl and 2,2'4,4',6,6'-hexachlorobiphenyl) by naturally occurring dissolved organic carbon (DOC) was evaluated using columns containing aquifer material. Contaminant mobility was found to increase as solution DOC concentrations were incrementally changed from 0 to 20.4 mg of DOC/L for polychlorinated biphenyl (PCB) and from 0 to 58.1 mg of DOC/L for cadmium. Desorption processes were similarly affected by the presence of mobile DOC. Experimental adsorption breakthrough curves (BTCs) were predicted independently of column experiments using measured contaminant distribution coefficients (batch technique) and the convection-dispersion (CD) transport equation. The increased contaminant mobility, observed in the presence of mobile DOC, was explained by incorporating a three-phase system (two mobile, one stationary) into the CD transport equation. Results support the hypothesis that contaminants can be cotransported by mobile DOC in groundwater systems.