This Combined Sewer Overflow (CSO) system was built in the middle of Seward Park to help the City divert storm and sewer flows to prevent overflows and outfalls into Lake Washington. The project involved construction of a large 2.65 million gallon underground concrete storage tank with real time controls and pumping.

The project was built within 20 feet of Lake Washington’s shoreline, requiring extensive and complicated shoring, dewatering, and excavation efforts. Henderson required a system capable of pumping 2,000 gallons of water per minute.

To handle the load, Hoffman used a specialized dewatering system that can perform real-time treatment, although typically water is pumped and sent to Lake Washington with no treatment required. If turbid water starts to run through it, the system detects it and automatically treats it before returning it to the lake.