Mass balance modeling of polychlorinated biphenyls in the Lower Duwamish Waterway

Abstract

Remediation is most effective when a site is properly characterized. The Lower Duwamish Waterway (LDW) in Seattle, Washington is contaminated with polychlorinated biphenyls (PCBs). A zero dimensional mass balance of the 5 mile long waterway, which ends in Elliott Bay, helps to determine the different sources and concentrations of PCBs within the Lower Duwamish Waterway to aid future remedial activities. There are four unknown state variables: freshness, suspended sediment concentration, dissolved phase total PCB concentration, and sorbed phase total PCB concentration. The sole freshness source was the Green River and the freshness sink was the flushing at the downstream mouth. PCBs exist in sorbed and freely dissolved phases. Sorbed PCB sources include: the incoming Green River, laterals, and erosion. Sinks of sorbed PCBs include: deposition, flushing, and desorption. The Green River, laterals, diffusion, and desorption are all dissolved PCB sources, while the sinks are flushing and volatilization to the atmosphere. The calculated four state variables were compared to measured values and a sensitivity analysis was performed on the sources.