City troubleshoots persistent sewer odors plaguing City Park area

It’s a problem that just won’t go away.

For years, residents living between City Park and the Woodway town line have been periodically assaulted by sewer odors rising through residential roof vents and vault covers along 3rd Avenue South.

While the city has taken measures to address this, residents in the area continue to report unpleasant sewage gas odors, and the city responds by working to address the issue.

“We continuously monitor this issue and we have taken several steps to mitigate it — some of those are effective, some not so much — so we are constantly investigating what is possible,” said Edmonds Public Works and Utilities Director Oscar Antillon.

My Edmonds News first reported on the problem in December 2020. At that time, the main culprit appeared to be fumes rising from a King County sewage line through vents in the vault covers along 3rd Avenue South. This line carries waste from King County – no Edmonds homes or businesses are connected. Plugging the vault cover vent holes appeared to afford some relief, but over time these plugs deteriorated and the problem would recur. King County is responsible for maintenance of this line, including periodic inspections and replacement of vault cover plugs as needed.

Our earlier report also noted a secondary source of odor originating from sewage pumped from Edmonds’ Lake Ballinger neighborhood east of Highway 99. While this flow originates from within the City of Edmonds, it travels to the Edmonds wastewater treatment plant through a King County line and is pushed by a King County-owned pumping station near Lake Ballinger. This second line also flows under 3rd Avenue and is connected to homes in the area. At the time of our report, city officials speculated that the pump could be over-pressurizing the line, causing sewage gases to backflow into residential sewage vent systems and be discharged — along with the odors — through rooftop vents.

To address the problem, the city installed a scrubbing station just inside City Park adjacent to the Pine Street/2nd Avenue South intersection. The facility employs a forced-air carbon filtration system designed to depressurize the air in the sewage line and scrub odors at the same time.

While this affords some relief, the problem persists and the city continues efforts to address it.

“We believe that some of the issues are caused during peak flow from King County,” Antillon explained. “We are actively working with them to reduce any peak flows. Starting July 31, they plan to [level this out to] a steady flow, and we will be monitoring to see if that makes a difference.”

In addition, the city is increasing the capacity of the City Park odor scrubber by replacing the carbon filters and increasing the vent motor speed by 18%.

“We have met with numerous residents and explain the challenges with eliminating the odors,” Antillon said, adding the city has ongoing monitoring in place. “We encourage citizens to report these issues via our Fix It Edmonds App. This will help us track and monitor the issue,” he added.

— Story and photos by Larry Vogel