The Tri-City Water Pollution Control Plant uses physical, biological and chemical treatment to clean approximately 8.4 million gallons of wastewater per day, created by the cities of Gladstone, Oregon City and West Linn. Following the treatment process, clean water is released into the Willamette River.

Originally installed as plugs in the fall of 2010, there are a total of three roofs on the project. The roofs are irrigated with greywater, and the water treatment personnel monitor the water quality of the runoff from the roofs.