The Point Defiance Regional Stormwater Treatment Facility is located just outside the entrance to the Point Defiance Park. The 5,500 square foot facility treats stormwater from 754 acres using a treatment train of two TAPE approved technologies – a hydrodynamic separator followed by media filtration cells. The hydrodynamic separator provides pretreatment, removing trash and larger solids and extending the maintenance cycle of the downstream media filtration cells.
After leaving the hydrodynamic separator, stormwater flows through a series of six cascade pools, troughs, and filtration cells filled with engineered media. The filtration cells also contain plants that improve the effectiveness of the treatment media. Stormwater filters through the engineered media, removing pollutants through a combination of filtration, adsorption, and absorption. Treated stormwater enters an underdrain system then flows into a bioswale before rejoining the city’s stormwater drainage system and being conveyed to Commencement Bay.
Overall, the treatment facility has the ability to remove sediment, heavy metals, nutrients, and oil and grease from up to 8 million gallons of water each day. These are contaminants that would otherwise flow into untreated and unimpeded to the Point Defiance Marina, Commencement Bay, and Puget Sound.