Fitting a highly technical treatment facility into just 2.5 operational acres posed multiple challenges. The design team responded by stacking buildings vertically, using gravity to move water through the system and dramatically reducing energy consumption, maintenance needs and physical footprint.

Photo by Lara Swimmer

Geotechnical upgrades were also critical due to the high water table. Liquefaction-prone soils that turn to quicksand during earthquakes required ground reinforcement with stone columns to create solid bearing for heavy processing buildings. A 35-ft-deep concrete slab anchored the underground 100-ft-deep, 100-ft-dia equalization basin, resisting groundwater buoyancy. Crews installed secant and sheet piles before excavating through contaminated soils, sequencing earth-retention structures and turbidity curtains to protect adjacent waterways.

Photo by Lara Swimmer

Processing up to 70 million gallons of combined rainwater and wastewater daily during approximately 20 annual storm events, the project significantly reduces Duwamish River pollution. The project also achieved more than 85% waste diversion, reusing wood in interior finishes and recycling concrete for subgrade fill.

In recognition of its social, economic and environmental benefits, the project earned Washington state’s first Platinum Envision certification.