City of Wilsonville Wastewater Treatment Plant & Improvements Project

Cost: $44 million
Location: Wilsonville, Ore.
Year: 2014-12-15
Size: 4 mgd
Owner: City of Wilsonville
Designers: CH2M Hill
Contractor: Wildish Building Co., Power City Electric, University Mechanical Contractors

Originally built in the early 1970s, the wastewater treatment plant in Wilsonville, Ore., was home to aging infrastructure and numerous odor complaints. The 2.25-million-gal-per-day (mgd) plant was in need of increased capacity, upgraded infrastructure and biosolids handling for regulatory compliance, improved odor control, and maximized plant space for future expansion. 

As the first wastewater design-build-operate (DBO) project in the state of Oregon, the $44-million project included permitting, design, construction and commissioning. Additionally, CH2M Hill, the DBO delivery firm, will handle long-term operations, operations and maintenance (O&M), repair, and replacement of the upgraded plant. The 15-year operations contract includes an annual O&M fee of approximately $2 million per year. 

Located in a residential neighborhood surrounded by trees, the site’s tight footprint was a challenge for the construction crew. This, combined with the need to keep the plant fully operational throughout construction, proved difficult as most of the equipment was being repurposed or removed. Because of these issues, careful sequencing of construction was required. In addition, the trees presented environmental challenges, and buffer zones were created to protect the environmentally sensitive areas near the construction site.

Ultimately, plant capacity was expanded to 4 mgd and infrastructure modifications included improvements to the headworks, aeration basins, clarifiers, biosolids processing, and filtration and disinfection. The plant now is capable of producing Class A biosolids on site and it employs redundant equipment so the facility can operate with one major piece of equipment or process unit out of service. Functional and hydraulic equipment from the existing plant was repurposed to be used in the upgraded facility both during and after construction.

“This was an excellent project completed on schedule and within budget. The new facility resolves longstanding community complaints concerning odor from the plant, improves water quality and increases capacity to facilitate future growth for the city,” said Eric Mende, project manager for the city of Wilsonville. “The teamwork approach and cooperative attitude amongst all of the project participants—the city, owner’s representative, CH2M Hill and all of its subcontractors—created a true partnership, of which we are all proud.”