Publication Summary

This is the study plan for the loading of contaminants to the Lower Duwamish Waterway from suspended sediments in the Green River.

Predictions of contaminant loading to the Lower Duwamish Waterway sediment cleanup site are based on a computer model of sediment transport and contaminants measured in relatively few whole water samples. Contaminants associated with incoming suspended sediments have not been measured. Field measurements of suspended sediment contaminants, transport pathways, and deposition patterns will increase confidence in model predictions.

The goals of this study are to (1) estimate contaminant loading from suspended Green River sediment, (2) measure contaminants in two size ranges of suspended particles, and (3) provide field results to confirm predictions of the short-term transport and fate of suspended sediments.

Contaminant loading will be estimated by combining river flows, determined by the U.S. Geological Survey (USGS) and the Washington State Department of Ecology (Ecology), with contaminants measured in suspended Green River sediments. Suspended sediments will be collected by pumping river water through flow-through centrifuges. The centrifuged material will be tested for levels of PCBs, dioxins and furans, arsenic, PAHs, and organic carbon. These parameters will sometimes be measured separately in fine-grained (<63 µm diameter) and sandy (>63 µm diameter) sediments. Specific conductivity, suspended solids, in-situ particle size distribution, and organic carbon will also be measured.

Fluorescent sediment particles, manufactured to mimic native suspended and surface sediments, will be released into the Lower Duwamish Waterway where they will act as tracers. Results from analysis of tracers in recovered water and sediment samples will be compared to predictions of transport pathways and short-term patterns of deposition.

Note: Each study conducted by Ecology must have an approved Quality Assurance Project Plan. The plan describes the objectives of the study and the procedures to be followed to achieve those objectives. After completion of the study, a final report describing the study results will be posted to the Internet.

Link to EIM data for User Study ID LDW_08