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Tucked away in a ravine along Puget Sound in an annexed portion of Edmonds, the City of Lynnwood’s Wastewater Treatment Plant has quietly done its job for more than six decades. Now, City officials say it’s time for a full reboot.
Lynnwood is planning a decade-long overhaul of the plant, a project now estimated at about $330 million, to replace worn-out equipment, accommodate population growth and comply with stricter environmental rules. The upgrade would reshape how wastewater from Lynnwood and parts of Edmonds is treated before being discharged into Puget Sound.
The plant was built in 1962 and last expanded in the 1980s, when Lynnwood’s population was about 22,000. Today, the city has more than 41,600 residents, and officials say the system is stretched thin. Planning for the overhaul began in 2020, with the City Council adopting a facility plan in 2022. Construction is tentatively scheduled to begin in early 2028.
The plant serves most of Lynnwood, more than 1,000 acres of Edmonds and parts of unincorporated Snohomish County — about 49,000 people by 2026 and more than 74,000 by 2050. While the facility can handle 7.4 million gallons per day under normal conditions, projected average daily flows could reach nearly 10 million gallons by 2050, with peak flows approaching 30 million gallons, according to the facility plan.
What’s new?
Updated cost estimates released in September 2024 pushed the price tag up sharply from $208 million in 2021. Public Works Program Manager Ehsan Shirkhani said the increase reflects inflation, labor shortages, higher material costs and intense competition for infrastructure funding — not an expansion of the project’s scope. Annual operating costs are also expected to rise, from about $3.4 million to more than $5.4 million.
To pay for the project, Lynnwood plans to use a mix of bonds, grants and sewer rate increases. The City’s 2024 General Sewer Plan shows that cash reserves will cover about 27% of the 10-year plan, with more than $240 million expected to be financed through debt. Sewer rates rose more than 24% annually between 2023 and 2026 and are scheduled to continue increasing through 2030. The City Council also approved a higher utility tax and raised the residential sewer connection charge to $11,700.
Edmonds, whose customers account for about 11% of the plant’s capacity, is expected to share in the cost. The two cities are negotiating a new agreement to replace a cost-sharing deal dating to 1965. Shirkhani said Lynnwood has proposed that Edmonds help pay to replace aging infrastructure, but not for added capacity tied to Lynnwood’s growth. Talks stalled earlier this year amid staff turnover in Edmonds, he said.
The Lynnwood City Council on Nov. 24 approved a $6.2 million design contract with engineering firm Hazen and Sawyer to develop a “basis of design” report refining assumptions, costs and schedules. In February, the council also approved a $400,000 contract with KBA Inc. to serve as the project’s owner-adviser.
The state-mandated environmental impact review (known as the SEPA review) won’t begin until design is between 30% to 60% completed, Shirkhani said. This review will determine the project’s impacts on both the environment and the people living nearby and detail potential mitigation strategies, if needed.
Within the next year the City also plans to hire a general contractor/construction manager to help with design. Traditionally, a contractor isn’t hired until after design is completed. Joining the project in early design allows a general contractor to identify risks and potential cost savings early in the project, rather than after the City already paid for full design, according to the Washington Department of Enterprise Services.
City officials say they are seeking outside funding aggressively but face long odds. A Department of Ecology loan request is pending after a similar application was denied last year. “There’s a lot more competition and less money available,” Shirkhani said.
Some Edmonds residents living near the plant say they were caught off guard by the scope of the project and criticized what they described as limited communication from Lynnwood. Neighbors have questioned why there is little signage at the site and said requests for information went unanswered. Shirkhani said outreach is ongoing and will increase as designs are finalized. City records show that staff have exchanged hundreds of emails with residents, and Shirkhani said they also distributed flyers to nearby residents inviting them to information sessions.
“I want to make it clear that we are still in the very early stages of this project,” Shirkhani said. He said there are still several phases before the City can even start to apply for permits, begin the state environmental review or alter the land in any way. “We have to know what we’re doing first before we can tell others.”
Why is this necessary?
The overhaul is driven by three main factors: aging infrastructure, population growth and environmental regulations.
Since 2023, the Environmental Protection Agency has cited Lynnwood twice for air and water quality violations, costing the city more than $550,000. Plant Manager Tanner Boyle said there have been no violations since 2024 when the city shut down the plant’s 60-year-old sludge incinerator and switched to a temporary system. The system in place dewaters solids and ships them by rail to an Oregon landfill. The change initially triggered odor complaints, but Boyle said adjustments have reduced odors by about 90%.
New state regulations also add pressure. The Washington Department of Ecology’s Puget Sound Nutrient General Permit requires wastewater plants to sharply reduce nitrogen discharges, which harm marine life by depleting oxygen. City officials say meeting those limits will require major upgrades, not minor retrofits.
Before electing to upgrade the existing plant, City officials ruled out building a new wastewater treatment plant, after studies found it to be costly and disruptive. A new facility would require up to 21 acres — land the city does not own — forcing Lynnwood to buy and convert property at uncertain cost, per the facility plan. Relocating the plant would also require major sewer reconfigurations and new pump systems, and treated wastewater would still need to be routed back to the existing Puget Sound outfall.
The city also rejected connecting to a regional system, such as King County’s, after finding it would raise costs, eliminate local control and strain capacity. Buying into King County’s system alone was estimated to cost more than $340 million, not including construction. Instead, Lynnwood plans to redevelop the existing plant in phases, allowing it to remain operational during construction despite the site’s tight footprint.
Project scope
The plan is divided into three phases to keep the plant operating during construction.
Phase 1: Site preparation
The first phase focuses on reshaping the site to make room for new treatment infrastructure, with an estimated cost of $26 million. Work includes clearing trees, excavating the hillside, rerouting a fish-bearing creek and realigning Bertola Road and a major sewer pipe. The creek relocation will require coordination with tribal, state and federal agencies and could include additional environmental protections – but those won’t be determined until after the SEPA review, Shirkhani said.
Shirkhani and Boyle said the City remains proactive, preparing ahead of time for big decisions set to come in the coming months and years. The City is in regular communication with tribes, government and environmental agencies, and other involved parties. About a month ago, plant staff met with local tribal leaders to discuss their preferences for environmental mitigation.
To keep the plant operational during construction, the City will need extra room. This year, Lynnwood purchased two nearby homes in Edmonds for a combined $2.7 million and plans to demolish them for temporary use. City officials said the purchases were made early to avoid rising land costs, and there are no current plans to acquire additional properties.
One property at 17014 Bertola Road in Edmonds was purchased for $1.5 million in February 2025. A second property at 17018 76th Ave. W., also in Edmonds, was acquired in November 2025 for $1.2 million. The latter sale included $162,000 in relocation assistance for the elderly owners, according to city documents. The couple, the only property owners listed in county records, did not initially list their home for sale. City staff approached them with an offer sometime in the fall.
Phase 2: Liquid stream improvements
The second and most complex phase would overhaul how wastewater is treated to meet nutrient limits and future capacity needs. Estimated at $191 million, the work eliminates primary treatment, adds new headworks and aeration basins uphill, retrofits existing clarifiers and replaces chlorine gas disinfection with an enclosed ultraviolet system capable of handling peak flows.
Phase 3: Solids handling
The final phase replaces the aging incinerator and ends long-term sludge hauling by installing a permanent solids-handling system, estimated at $111.8 million. An official new system hasn’t been selected and won’t be until further design is completed. However, after weighing five total solids handling options, a 2021 study identified a vapor recompression “paddle wheel dryer” as the preferred option. The system uses heated thermal oil to dry solids into a nutrient-rich Class A biosolid.
According to the Washington Department of Ecology, Class A biosolids are treated to remove pathogens to below detectable levels making them safe to handle and suitable for use as fertilizer — potentially generating revenue for the city.
“We’re going for tried and true,” Boyle said in an interview. “We’re not going to try anything experimental… we’re doing a lot of upfront homework to make sure what we’re getting is going to work and work the right way.”
The full project documents and more information is available at the City’s website.
— Contact Ashley at ashley@myedmondsnews.com.
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