Colville Wastewater Treatment Plant

Varela improved wastewater treatment and water quality for this NE Washington city

Historically, the City of Colville treated its wastewater for 4,800 residents via an aerated lagoon system followed by disinfection and discharge to the Colville River.

Due to the aging and obsolete lagoon system, and with advent of more stringent water quality and treatment standards, the City was faced with requirements of a major treatment upgrade needed to meet regulatory standards and comply with the City’s National Pollutant Discharge Elimination System (NPDES) permit.

Stringent standards required a cost-effective solution.

A new, state-of the-art, treatment facility was proposed with design and implementation handled by Varela.

The central process consisted of an extended aeration, activated sludge biological reactor in an oxidation ditch configuration. Other components included peak flow equalization, anoxic selector tanks, clarification, ultraviolet disinfection, and effluent polishing/equalization. 

During the design phase, “value engineering” was conducted to provide outside input and further optimize the final plan for improved cost-effectiveness.

Varela assisted the City of Colville with assembling and procuring a comprehensive funding package through the following agencies: USDA Rural Development, WA State Dept of Ecology, Public Works Trust Fund, and the US Forest Service.

Treatment improvements included:

• 1.45 MGD average and 5.33 MGD peak hour wastewater influent capacity
• Year-long, high tech, pre-loading and engineered settlement of the highly compressive treatment plant site, prior to construction
• 1850 gpm triplex raw sewage influent lift station
• Preliminary treatment improvements facility with fine screening and grit removal and processing