Polychlorinated Biphenyl Transport from Consolidation of Contaminated Sediments During In Situ Capping

The management of sediments contaminated with polychlorinated biphenyls (PCBs) is an issue of significant contemporary concern. The application of an in situ cap to isolate and contain the contaminants is a desirable management option that is hindered by a lack of detailed information regarding the fate of the contaminants after cap installation. In this study, we evaluate the fate and transport of PCBs in fine-grained, organic-rich sediments during and after the application of an in situ cap, with the goal of estimating the release of dissolved and colloid-bound contaminants from consolidating sediments under a variety of capping scenarios. Three capping materials were evaluated for their propensity to hinder PCB release; quartz sand, activated carbon, and a proprietary organoclay. Consolidation tests to simulate in situ rapid dewatering were conducted using contaminated sediment dredged from the Grand Calumet River in Gary, Indiana. The results of tests conducted without a cap indicate that rapid transient flow caused by consolidation results in the release of colloid-bound PCBs at concentrations exceeding 10 µg total PCBs per liter of effluent pore fluid, which was far above the calculated dissolved PCB concentration. Tests conducted to simulate release from capped sediments showed all three capping materials reduced the release of particles and associated PCBs by over 80 %. The dissolved organic carbon content also decreased significantly. The organoclay and activated carbon were more effective than sand for both particle and PCB removal. This work demonstrates that reactive caps help to mitigate contaminant release due to sediment consolidation and should be considered as a viable management option for in situ remediation of PCB-contaminated sediments.