As part of its Plan to Protect Seattle’s Waterways, SPU committed to constructing green and/or gray infrastructure that will bring the Vine basin into compliance with Combined Sewer Overflow (CSO) regulatory requirements by the end of 2025. Serving as GSI Lead, RKI helped SPU develop and evaluate GSI options and select the preferred option to be advanced to final design and construction.

King County Wastewater Treatment Division is updating their Combined Sewer Overflow (CSO) Long-term Control Plan (LTCP). As GSI Lead, RKI was responsible for basin planning to integrate GSI techniques, such as roadway bioretention, permeable pavement, and green alleys, with conventional gray storage facilities to develop alternatives for reducing stormwater contributions to the combined system and reducing the required size of gray storage facilities to meet the regulatory control standard.

The West Duwamish Combined Sewer Overflow (CSO) Control Project will control CSOs for King County’s West Michigan and Terminal-115 basins to the Washington State regulatory requirement of one-event per year on a rolling 20-year average. As Design Team Manager, RKI led the GSI alternatives analysis to identify and compare various combinations of grey and green technologies to achieve the control strategy and help protect the Duwamish River and Puget Sound.

RKI led the 2016 update of the City’s Stormwater Management Plan to address population growth, land use development, and requirements of the National Pollutant Discharge Elimination System (NPDES) Phase II Eastern Washington Permit. The plan characterizes existing drainage and water quality issues, identifies and prioritizes projects and programs that provide residents with the greatest value and protection, provides a financial plan and rate forecast, and helps the City prepare for possible future MS4 program audits.