Foundational studies

Beginning with the 1958 Metropolitan Seattle Wastewater and Drainage Study, regional agencies have collaborated on studies to identify major environmental protection needs and to identify and prioritize corrective actions.

The studies identified CSO impacts as being an important but relatively small part of the larger problem. No updated characterization has been required since the 1988-1997 CSO characterization because pollutants have remained stable or have decreased. The county now tracks West Point influent, biosolids quality, and industrial monitoring as indicators of change that should be evaluated for CSO implications. Superfund listings of Harbor Island, the East and West Waterways, and the Lower Duwamish Waterway set in motion more recent studies that further refine our understanding of the Duwamish environment. Now, together with studies being done for the Puget Sound Partnership, attention is turning to ways beyond industrial source control to address stormwater pollution. The next step may very well be to focus on how pollution is deposited from the air.

In the 2008 CSO control plan update, WTD reviewed new information and conducted studies to assess--both quantitatively and qualitatively--the health benefits to the public, environment, and endangered species of controlling all county CSOs. The assessment drew from studies describing existing environmental conditions and predicted conditions at the completion of the program. It built on the findings of the county's 1999 CSO Water Quality Assessment of the Duwamish River and Elliott Bay and 1999 Sediment Management Plan--both done in support of the RWSP--and on annual water quality monitoring reports.

Studies conducted to better understand how to protect fish species listed as threatened under the Endangered Species Act (ESA) provided insight into the life stages of these species and the effects of degraded water, sediment, and habitat on their survival. WTD helped to generate some of this information through its participation in Watershed Resource Inventory Area (WRIA) groups in King County, initiation of a Habitat Conservation Plan, and review of CSO occurrence in relation to presence of juvenile chinook salmon. Also reviewed were published findings from studies being conducted in support of contaminated sediment cleanup in the Duwamish Waterway, which present some of the most current science available that is relevant to CSO control planning. Finally, the most recent science on climate change and sea-level rise in the Puget Sound was reviewed for issues that may affect CSO planning.