Stormwater Treatment Facility
The 5,500-square-foot project features a series of six cascading pools that channel runoff from streets and properties as far south as North 30th Street.
- 8 million gallons: That’s how much the bio-rentention facility can handle each day.
- 5,500 square feet: This little space treats water from 754 acres – all the way up Pearl Street to North 30th Street.
- Gravity does the heavy lifting: Stormwater drops via gravity into the facility’s treatment cells without requiring additional energy.
- Plants don’t mind: Evergreen huckleberry and other drought-tolerant plants that can tolerate wet winters top the treatment cells.
- Defender of Puget Sound: Polluted stormwater is one of the biggest threats to Puget Sound. The Point Defiance Regional Stormwater Treatment Facility helps counter the threat.
Defending Puget Sound
Before this facility was built, polluted stormwater from the 754-acre watershed flowed untreated before spilling into the Sound near Point Defiance Marina. That changed in late 2015 with the completion of this facility, which became the largest of its kind in the world.
After researching several options, the City received grant funding from the state Department of Ecology.
The aim is to capture the worst pollutants before they wash into an area of the Sound already overloaded with heavy metals from the Tacoma Asarco Smelter Plume.
The facility employs a mechanism that first traps some contaminated runoff and floatable materials. Runoff shunted into the system flows from pools to a series of concrete boxes filled with filtering material and topped with mulch and plants.
The system makes use of biology as well as chemistry; the plants were selected specifically to take root in the filter media and thrive on polluted waters.
Besides defending Puget Sound, the facility is a learning laboratory. Students at Tacoma’s Science and Math Institute have had the opportunity to do water quality testing and experiments at the site, and professors from local universities have recognized the project’s value. Elementary school students learning about stormwater have visited the facility to see how it works up close.