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Wastewater Treatment Plant Expansion
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What's New

Updated April 10, 2016 -
The new solids thickening facility went online last October, with workers retiring the old gravity belt thickeners and supporting equipment. The last original primary clarifier sludge pump was recently replaced.

New aeration basins and secondary clarifiers are going through final testing, taking over treatment for existing facilities in March. This allows workers to begin demolition of the existing basins, and converting them to allow for the new DEMON, or de-ammonification, treatment processes the county studied in 2011.

Construction crews continue to make progress on two new anaerobic digesters at the plant, with the goal of bringing them both online later this year. The new structures nearly double the plant’s solids processing capacity. Additionally, construction of a new reclaimed water facility will provide treated irrigation water for Chambers Creek Properties.

Treatment plant staff are eagerly awaiting the completion of new offices, locker rooms, and warehousing facilities, allowing for offices currently scattered across the plant to be consolidated.

Overall, the plant expansion is about 80 percent complete. In total, more than 1 million man hours have been spent working on the expansion since the county broke ground in 2012.

Updated April 7, 2015 -
Construction is now over 50% complete and continues to move forward at a pace of approximately $7 million per month.  For the past couple of years the 4 tower cranes were a large part of the construction site.  The major equipment is now in place and most of the 60,000 cubic yards of concrete has been poured, the tower cranes will be taken down.  With 300 construction workers there will still be a flurry of activity during 2015 to get some key components running and ready to start treating wastewater in the new facilities.  While the site was dominated by concrete structures work it is now shifting to piping and electrical work necessary to tie the various existing and new facilities together.  Once the new facilities are treating wastewater the construction focus shifts to the renovation of the existing plant.

The next major milestones include start-up of the new solids thickening facility in Spring-Summer 2015 followed by preparation for the new aeration basins start-up in late 2015.

Updated Aug. 20,2014 - The expansion project reached several milestones in the second quarter:

  • Received a notice to proceed on Construction Package 4 on June 23
  • Executed the final Maximum Allowable Construction Cost for Construction Package 4 on June 5
  • Reached final completion of Construction Package 2 on May 21
  • Finished the design phase of the expansion project on March 24
  • Completed the Pretreatment Lab, Vactor Decant Facility, Electrical Service Building and Maintenance Storage Building
The contractor continues to work on the Aeration Basins, Secondary Clarifier, Digester, Solids Thickening Building, Biological Process Building, Reclaimed Water Building and Utilidors as part of Construction Package 3. A vast majority of the work is concrete for all new facilities.
About the project

Work has begun on a $353 million project to increase capacity and environmental benefit at the Chambers Creek Regional Wastewater Treatment Plant. As our population increases and new customers connect, we need to expand the treatment capability of the plant and replace aging infrastructure before it wears out.

Benefits include:
  • Increased sewer capacity
  • Repair and replace aging infrastructure 
  • New technologies that help protect the environment

Project Location

Project Timeline

Project Photos

DEMON (Anammox)
Pilot Study


Project Funding

Total Project Cost: Approximately $353 million

Project Funding Sources:
  • $511,000 grant received from Washington State Department of Ecology (WSDOE) in March of 2011. This grant is from the ‘Clean Up Toxic Sites – Puget Sound’ fund and was approved by the State in the 2010 Supplemental Capital Budget Proviso Section 3010.
  • $60,000,000  loan received from WSDOE in August of 2014. This loan was funded by the Washington State Water Pollution Control Revolving Fund, 2014 funding cycle.
  • $196,090,000 sewer revenue bonds received in 2012.
  • $53,660,000 sewer improvement bonds received in 2010.
  • Sewer rate revenue.
  • Capacity charge revenue.

Design Engineer: Brown & Caldwell 

General Contractor/Construction Manager: Mortenson Construction

Contact Us
For More Information

Ryan Dooley, P.E.
Project Manager
Ph: (253) 798-4280

Arnie Sheppard,
Construction Manager
Ph: (253) 798-4647

Contact Us
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