We Can Fix That: Ten Years of Seattle Public Utilities Retrofit Program Successes

Seattle Public Utilities (SPU) operates and maintains a combined sewer system (CSS) within the City of Seattle (City) service area with 87 permitted combined sewer overflow (CSO) locations. CSOs, the discharge of both stormwater and untreated human and industrial waste, toxic materials, and debris, are a major water pollution concern throughout the United States, and particularly in the Puget Sound region. Since 1972, both the federal and state governments have passed laws to regulate the occurrence of CSOs, thereby reducing their impact on receiving water quality. The State of Washington has defined the greatest reasonable reduction of CSOs as an average of one overflow per site year. This performance standard is reiterated in the City's current National Pollutant Discharge Elimination System (NPDES) permit issued by the Department of Ecology (Ecology).SPU has a three tier approach to reducing CSOs: 1) Optimize the existing system through retrofits; 2) Implement green stormwater infrastructure on both private property and street rightof-way; and 3) Construct CSO reduction facilities (e.g., underground storage, pipelines, and/or pump stations).The objective of this paper is to present the results of SPU's Retrofit Program at reducing CSOs and minimizing the impact of the overall CSO reduction program on the City's rate payers. The three key lessons learned from this program are: implementing textbook program/project planning results in successful projects; developing an integrated planning team representing project stakeholders maximizes ownership and accountability of the results; and gaining detailed knowledge of site specific hydraulics and performing innovative design resolve large problems with simple solutions. These lessons are demonstrated through five project examples. Each project narrative includes the opportunity, solution, and major project outcomes.