The Water Quality Assessment and Monitoring Study set out to examine water, sediment, and fish and shellfish tissue quality for the waterbodies where CSOs currently discharge.  This evaluation used data previously collected from a variety of monitoring programs and studies.  Data gaps and limitations were evaluated and new studies were chosen to be conducted to improve the understanding of existing conditions. The data gaps identified were: bacteria sources and pathways to the study areas, current sediment conditions in Lake Union, tissue chemistry in Lake Union, sources of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) to King County CSO basins, concentrations of contaminants of emerging concern in the study areas, an effective sewage tracer to help quantify the contribution of sewage to pollutant loads, concentrations of metals, organic compounds, PCBs, and PBDEs in Elliott Bay surface waters, and concentrations of PBDEs in the Duwamish Estuary.

These data gaps and potential new studies were scored and ranked based on various criteria.  After prioritization of the new studies, three were chosen: a bacteria study to better understand the sources and pathways of bacteria in the study areas (collect and analyze new data), a literature review to understand if other researchers have identified chemicals that can be used to effectively track sewage in surface waters (sewage tracers), and a water column survey of a select group of contaminants of emerging concern in the study areas (collect and analyze new data).