Big Gulch Wastewater Treatment Plant

The Big Gulch Wastewater Treatment Facility was completed in August, 1970 and has been in continuous service since that time as a modern and state-of-the-art facility. As technology and and the understanding of the microbiological processes in wastewater change, the treatment plant has undergone updates and design modifications to address these changes. Major updates include:

Headworks Construction 2012


The staff’s primary responsibility is managing the treatment process, ensuring compliance with the District’s National Pollution Discharge Elimination System (NPDES) permit. This permit is issued through the Washington State Department of Ecology (WDOE). In addition, staff members, who are all certified wastewater treatment plant operators through the State of WA, are responsible for the maintenance of the plant, all related sub systems, and equipment used in operating the facility. Likewise, District staff operates a State certified laboratory used in evaluating permit indicators throughout the treatment process. Laboratory findings are submitted to WDOE for review regularly throughout the year.

U.V. Disinfection

uv lamps

SecondaryTreatment - Clarifier

MARCH 2018

Secondary Facility

The District operates an oxidation-ditch secondary wastewater treatment facility, which has a maximum daily treatment capacity of 2.625 million gallons per day (mgd). The facility, which is operated seven days per week, utilizes an ultraviolet (UV) disinfection process before discharging treated effluent directly into the Puget Sound. The Water Environment Federation (WEF) has an excellent wastewater treatment diagram similar to the District treatment process.