The evaluation of potential contaminant sources in Elliott Bay and the lower Duwamish River, Seattle, has two major components: identification and ranking of CSO's (Combined Sewers Overflows) and storm drains based on concentrations of chemical contaminants measured in drain sediments; identification of relationships between potential contaminant sources and the high-priority problem areas identified in the receiving environment. Available information on drainage basin areas, discharge locations, contaminant loading, flow rates, permitted facilities and historical problem sites was used to identify, evaluate and rank potential sources of contaminants. Potential sources can be divided into seven major categories: wastewater treatment plants, CSO's, industrial discharges, groundwater, atmospheric deposition, surface runoff and accidental spills. Problem chemicals in each drain were identified on either of the following criteria: levels exceeded highest Apparent Effects Threshold (AET) values for chemicals where AET values have been derived, or levels exceeded 90th percentile of all concentration values. Problem drains were ranked on the following criteria: number of problem chemicals in a drain; magnitude of Elevation Above Reference (EAR) sediment chemistry; contaminant loading index for each drain. Sediment samples were collected from 7 CSO's, 20 storm drains and 15 CSO/storm drains.