Wastewater Treatment Plant

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Edmonds Regional Wastewater Treatment Plant

City of Edmonds WWTP receives Utility of the Future Today 2020 Energy Efficiency Award
Wastewater Treatment Plant cuts energy cost by 45 percent and that's just the start!

2020 Utility of the Future Today Honorees Video
Edmonds project starts at the 17:54 minute mark

Utility Future Today

The Edmonds Wastewater Treatment Plant (WWTP) is a regional facility.

The original Primary Treatment plant was built in 1957. The plant was upgraded two times by 1967 to handle the increased flows. Partnerships with Mountlake Terrace and Ronald Sewer District were established in 1959 and with Olympic View Water and Sewer District in the late 1960's.

From 1986 to 1991 the treatment plant was expanded to incorporate secondary treatment. The $35 million construction cost was funded by Federal grants (50%) and by the four (4) partners (50%): MLT, OV, and RSD (together constitute 49%), and the City of Edmonds (51%). The original 30 year agreement stated that while the plant is owned and operated by the City of Edmonds, the other 3 partners own their purchased capacity and they pay their portion of the annual operating and capital expenses. The original agreement focused on construction of the new facility. A new thirty (30) year Agreement that is in the final stages of approval focusses on new regulatory requirements, joint use areas, and supporting the partnership that will enable The City of Edmonds to keep treatment costs low for its citizens.

In 1988 the City entered into an agreement with King County (Metro). This agreement contained the following provisions:

  • Sewage from Metro's Richmond Beach service area would be treated at Edmonds. Metro would abandon the Richmond Beach Treatment Plant (due to regulatory issues and not wanting to add secondary treatment) and turn it into a pumping station.

  • Metro would build a pump station and sewer line(s) to facilitate a flow swap to West Point from Edmonds East, which alleviated the need of MLT to upgrade their pump station.

  • The agreement detailed the construction project, flow exchange, and payment methodologies.

The original agreement was amended in 1993, 2000, and 2012. The agreement expires in 2036.

Regulatory Compliance

The WWTP must comply with all local, State, and Federal Laws. The operating performance is directed and regulated by:

  • WA State Department of Ecology who issues the NPDES permit.

  • Puget Sound Clean Air Agency who issue the construction permit for the gasification process and oversees air emissions.

Each agency's permit requires various monthly, semi-annually, annually, and "as needed" reports.

Design and operating information

  • Treatment Process

Activated Sludge

  • Rated Capacity

11.8 Million Gallons per Day (MGD)

  • Average Flow Winter

6.5 MGD Summer 4 MGD

Staff: Currently there are 20 FTE's authorized. The majority of staff require specialized training, knowledge, experience, and certifications. Based on need, the plant is staffed 14 to 24 hours/day, 365 days/year.

The plant maintains an accredited laboratory where the chemical, physical, and bacteriological processes that treat the wastewater are analyzed. The analysis of wastewater is necessary for the plant to demonstrate compliance with its discharge permit. The laboratory is staffed five days a week by a Laboratory Technician. Certified Operators provide laboratory support on the weekends.

The treated wastewater (effluent) from the plant either flows by gravity or may be pumped (depending on tidal influence) to the two (2) outfall pipes. The outfall pipes are located approximately 1300 feet offshore in Puget Sound at an average depth of 70 feet. Ocean current modeling demonstrates that this location provides excellent mixing of the treated wastewater within Puget Sound. Treatment plant staff monitor effluent quality to ensure compliance with all regulatory requirements and to ensure that the waters of Puget Sound are protected.

In December of 2022 the new gasification process will come online. Stay tuned for further updates.

Contact Public Works

Public Works & Utilities Administration
Operations & Maintenance Center
7110 210th St SW
Edmonds, WA 98026

Phone: (425) 771-0235
Fax: (425) 744-6057
[email protected]

Public Hours:
8:00am to 4:30pm M-F
Closed Weekends and Holidays

For Emergencies Call 911

Wastewater Treatment Plant
200 2nd Ave S
Edmonds, WA 98020

Phone: (425) 771-0237
Fax: (425) 771-0255
[email protected]