Untreated stormwater has been identified as a major contributor of contaminants and habitat degradation in urban water bodies. As new stormwater controls and treatment facilities are implemented, it is necessary to assess their effectiveness in the field and their potential to improve water quality in receiving water bodies. This study evaluates the effectiveness of stormwater treatment facilities recently added along the Aurora Corridor (part of State Route 99) in Shoreline, Washington, where highway, commercial and residential stormwater is received by Echo Lake. The goals of the Aurora Corridor Project include improving traffic safety, traffic flow, streetscape amenities, and stormwater quality along the three-mile stretch of the Aurora highway within the City of Shoreline. Construction within the Echo Lake drainage basin began in 2011 and is scheduled to be completed at the end of 2015.

This study was designed to address data gaps identified by the Washington State Stormwater Work Group (SWG) in the effectiveness of stormwater treatment technologies used in the Puget Sound Region. The SWG represents several layers of government, economic stake holders, and researchers, and was formed under the leadership of the Puget Sound Partnership (PSP) and Washington State Department of Ecology (Ecology) in 2008 to develop a Stormwater Monitoring and Assessment Strategy for the Puget Sound Region. The Regional Stormwater Monitoring Program (RSMP), through which this and several other effectiveness studies are funded, was created out of this process.