Wilsonville Wastewater Treatment Plant Project
Clean Water for Tomorrow   

Frequently Asked Questions

We try to anticipate questions you might have about this project and provide the answers here. The links on the right provide general technical and process information. If you need additional information please send an email to Eric Mende at mende@ci.wilsonville.or.us.



Why is this project needed?

The wastewater treatment plant improvement project will replace old equipment and structures, incorporate new technology, address odor issues, meet current and future capacity needs, ensure compliance with future regulatory requirements and convert from a  liquid biosolids by-product to a more easily managed solid biosolid by-product.


When will the work take place?

Operations by the DBO contractor (CH2M Hill) began in September 2011. Design of the improvements will be completed in March 2012. Construction is scheduled for completion in February 2014.


What is the cost of the project?

The budgeted cost to improve and expand the wastewater treatment plant is $41.2 million, $35.7 million of that is for construction and the remaining $5.5 million is for project management including specialized technical and legal support during the pre-bid, design and construction management phases of the project.


How will the project affect my rates?

The average Wilsonville resident uses six units of water during the winter months (one unit of water is the equivalent of 748 gallons). Residential sewer bills are based on average winter-time water use. The current average residential sewer bill is $39. At the end of the full rate phase-in, the average monthly residential sewer bill will increase to $54. The anticipated increase is $6 in 2012, $5 in 2013 and $4 in 2014.


How will the project be funded? 

The wastwater treatment plant improvements will be funded through a combination of customers' monthly sewer rates and SDC (systems development charges) paid by new development. The City of Wilsonville's bond sale has a true interest cost rate over 20 years of 3.447 percent. The average annual savings to the city is $325,000 and savings over the 20 year life of the bonds will be about $6.5 million. 



What will be done about the odors from the plant?

Odor control is a key project goal. Approximately $1.4 million of the construction cost is specific to odor control, and the operations contract includes an "odor guarantee" which containts specific penalties to the DBO contractor for odor violations.


What opportunities does the public have to provide input?

Citizens can attend a City Council meeting where the first part of the meeting is always open to citizen comments and questions, you can also submit questions and comments via Ask the City on the City's website at www.ci.wilsonville.or.us ; or contact Eric Mende at mende@ci.wilsonville.or.us or 503-570-1538.

8. How long will these improvements last?

The current treatment plant capacity is approximately 2.25 million gallons/day (MGD). After the upgrades are completed, the capacity will be approximately 4 MGDm which should be adequate to serve the city until approximately 2025, depending on flows. Additional features are being incorporated into the design to allow future expansion to 7 MGD - the projected "build out" capacity needed in year 2035.

Click on the following series of articles for an overview of the Wastewater Treatment Plant and individual unit processes.

Improving the WWTP

Liquid Treatment Process


Odor Control

Biosolids Processing

Filtration and Disinfection

Fact Sheet

Project Performance Report August 2013