The Elliott Bay Seawall in Seattle, Washington provides protection from coastal storms and shoreline erosion, in addition to housing major utilities and infrastructure for the Alaskan Way Viaduct, Colman Dock Ferry Terminal, and Burlington Northern Santa Fe rail lines. Replacement of the seawall is a critical public safety project which was approved by voters in 2013. WaterTectonics worked with joint venture partners, Mortenson-Manson, to provide treatment system design, consultation, on-site equipment and turnkey operational services. The first phase of treatment utilized a 500gpm electrocoagulation system equipped with dissolved air flotation, ultrafiltration, and granular activated carbon polishing. The influent water contained a mix of seawater, stormwater and contaminated groundwater. Treated effluent was discharged to Elliot Bay and met all Washington State Department of Ecology Construction Stormwater General Permit as well as site specific Administrative Order discharge limits.