A model of PCB fate in the Upper Hudson River

A mechanistic model of PCB fate, transport, and bioaccumulation in the Uppe r Hudson River was developed to provide a quantitative tool to assess the e ffectiveness of natural recovery and active remediation in reducing PCB lev els in water, sediment, and biota. The fate and transport modeling, which i s the subject of this paper, builds on previous approaches by using a mecha nistic 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 a spect of the model is the calibration and validation for both the short tim e scale of erosion events and the decade-long lime scare associated with tr ends in sediment contamination. The model demonstrates differences between PCB fate in cohesive and noncohesive sediments that are important to effort s to reduce perceived human health and ecological risks. Burial due to the deposition of solids with lower PCB concentrations is the principal mechani sm responsible for the approximately 90% decline in surface sediment PCB co ncentrations since the late 1970s. The more moderate decline seen in noncoh esive sediments is due principally to the movement of PCBs from these sedim ents 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 exte rnal source located near the General Electric facility upstream of the cont aminated sediments and sediments throughout the river. Elimination of the u pstream source will increase the rate at which PCB levels decline in the co hesive sediments because it will reduce the concentration of PCBs on deposi ting particles. It will also immediately reduce the PCB flux to the Lower H udson River by as much as 20% and affect future reductions as surface sedim ent PCB levels decline.