Island County’s Septage Treatment Facility treats all septage generated on Whidbey Island along with waste-activated sludge from several municipal treatment plants. The project team prepared an engineering report, evaluated energy conservation options for aerobic digestion, and recommended improvements to make the best use of the existing infrastructure and to extend the life of the facility for 20 years. Upgrades to the facility included a new mechanical screen in the headworks, two new aerobic digesters, a new pump building, and construction of a 5.5 MG storage lagoon for Class B biosolids.



Client Name

Island County Public Works Department


Coupeville, WA


  • Pre-Design Report
  • 20-Year Design Capacity
  • Energy Conservation Evaluation
  • Design for Aerobic Digester
  • Renovation of Biosolids Holding Lagoons
  • Structural Engineering Design
  • Land Surveying