The present WWTP has been in operation since 1987.  The pipe system from your home to the  treatment plant is maintained by the Public Works Maintenance crews.

Once in the pipe system domestic sewage, commercial and industrial  wastewater are conveyed to the treatment plant (WWTP), by gravity flow. There are also seven pump stations that push wastewater from the outlying areas of the city to the WWTP and one large pump station at the WWTP. 

The WWTP is an oxidation ditch activated sludge treatment system designed to treat up to 4.0 mgd (million gallons per day) in the summer and 6.5 mgd in the winter.

The activated sludge system is biological using the organic material in the wastewater as food for bacteria and microorganisms in the sludge. Oxygen is supplied to the microorganisms by aerators in oxidation ditches. The activated sludge is then separated from the water in settling tanks (clarifiers).

The majority of the settled sludge is recirculated back to the oxidation ditches. A portion is pumped to the solids handling facility where it is dehydrated and composted. The compost produced is available to the public for a nominal charge.

The clear water from the top of the clarifiers is disinfected and then dechlorinated to protect aquatic organisms before being discharged to the Willamette River.

Up to 1 million gallons per day can be further treated by microfiltration and used as recycled water for irrigation.  

Effluent water discharged to the river is required to meet pollutant limits set by the Oregon Department of Environmental Quality (DEQ). These limits, and other constraints, are listed in the City’s National Pollutant Discharge Elimination System (NPDES) permit, issued by DEQ, as authorized by the federal Clean Water Act.

A copy of the City’s NPDES permit is available upon request.