A Model of PCB Fate in the Upper Hudson River

A mechanistic model of PCB fate, transport, and bioac cumulation in the Upper Hudson River was developed to provide a quantitative tool to assess the effectiveness of natural recovery and active remediation in reducing PCB levels in water, sediment, and biota. The fate and transport modeling, which is the subject of this paper, builds on previous approaches by using a mechanistic sediment-transport model that describes erosion and deposition with sufficient accuracy to remove the requirement to adjust sediment transport as part of the contaminant calibration process. An additional significant aspect of the model is the calibration and validation for both the short time scale of erosion events and the decade-long time scale associated with trends in sediment contamination.The model demonstrates differences between PCB fate in cohesive and noncohesive sediments that are important to efforts to reduce perceived human health and ecological risks. Burial due to the deposition of solids with lower PCB concentrations is the principal mechanism responsible for the ap proximately 90% decline in surface sediment PCB concentrations since the late 1970s. The more moderate decline seen in noncohesive sediments is due principally to the movement of PCBs from these sediments to the water column. The PCB load passing from the Upper Hudson River to the tidal Lower Hudson River is attributable to a combination of an external source located near the General Electric facility upstream of the contaminated sediments and sediments throughout the river. Elimination of the upstream source will increase the rate at which PCB levels decline in the cohesive sediments because it will reduce the concentration of PCBs on depositing particles. It will also immediately reduce the PCB flux to the Lower Hudson River by as much as 20% and affect future reductions as surface sediment PCB levels decline.