Edmonds officials outline new gasification system, PFAS destruction and future nitrogen rules affecting Mountlake Terrace costs

Edmonds interim public works director Phil Williams told the Mountlake Terrace City Council that the regional wastewater treatment plant serving Mountlake Terrace is undergoing a major technology replacement for biosolids handling and that the change will affect partner agencies’ bills.

The discussion centered on the plant’s new gasification system, its expected financial effect and broader regulatory pressures such as PFAS control and future nitrogen limits for Puget Sound.

Williams said the plant is a conventional activated sludge facility with a hydraulic capacity of “11,800,000 gallons a day” and that Mountlake Terrace owns “23.17% of that capacity.” He described a multiagency ownership and cost-sharing arrangement and said the city of Edmonds currently pays a slightly smaller share of annual operating and maintenance costs because of flow-based reconciliation.

“We were looking for a replacement technology,” Williams said of work to replace a worn-out incinerator. After evaluating a biochar process, Edmonds contracted for a gasification system that dries biosolids, heats them to about 2,000 degrees Fahrenheit and produces a sterile mineral product or carbon-rich “biochar”-type material that can be sold. Williams said the project cost was “a little over $26,000,000.”

He described partner shares and the near-term financial impact for partner cities: the project caused Edmonds’ costs to rise by about 7.67 percent and reduced operating and maintenance costs by roughly $341,000 per year. Williams said the single-family retail bill in Edmonds changed in the neighborhood of “about $3 a month” as a result of the project. He gave a rough breakdown that showed Mountlake Terrace’s share at about $6,000,000 (projected) and Edmonds’ ownership at about 50.787 percent of the project.

Williams highlighted a compliance advantage of the new technology. “The nice thing about this technology which we didn’t know when we went into it was it completely destroys PFAS. So we won’t we won’t have to worry about that as an issue going forward,” he said when answering a council question about forever-chemical risks in biosolids.

He also warned that new state nutrient regulations — particularly controls on nitrogen discharged to Puget Sound — could require additional, costly treatment upgrades. Williams described past and planned pilot projects to reduce nitrogen and said full-scale systems to meet future permits are likely to cost “approximately $10,000,000 plus” for a plant of this size, and that such changes often reduce hydraulic capacity because they require additional residence time in treatment basins.

Council members asked how regional growth would affect capacity and rates. Williams and Mountlake Terrace public works director Gary Schmick discussed infiltration-and-inflow reduction efforts, and Williams said the plant has some physical space for expansion but that decisions will be required if projected regional population growth materializes. Williams said operators are certified to Group 4 standards and noted the facility’s age and other capital needs beyond the current project.

Mountlake Terrace staff and councilmembers pressed for more detail on the Mountlake Terrace share of costs and the municipality’s proportion of flows; staff committed to providing a more detailed percentage of the city’s wastewater budget that pays into the Edmonds partnership.

The council discussion ranged from near-term rate impacts to longer-term capital planning tied to growth and state nutrient rules. Williams said the gasifier construction was about 95 percent complete at the time of his presentation and that the plant had completed prescriptive commissioning runs and was preparing for full-time operation.

Mountlake Terrace did not take any formal action at the meeting; staff said they would follow up with more detailed budget impacts and coordination for future comprehensive-plan updates.

Ending

Edmonds’ gasification project shifts biosolids management away from incineration and adds resilience on PFAS, but state nutrient rules and long-term capital needs mean partner cities including Mountlake Terrace should expect further decisions on treatment upgrades and rate impacts in coming years.