Board approves 4% sewer rate while warning of large King County pass-throughs and lake‑line unknowns
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Summary
The Mercer Island Utility Board voted to adopt a 4% local sewer rate increase for 2026 but highlighted materially larger pass‑through charges from King County Metro and flagged technical and permitting uncertainties on the island's lake sewer line and 17 pump stations that could drive future costs.
The Mercer Island Utility Board on Oct. 28 approved a 4% local sewer rate increase for fiscal year 2026, while repeatedly warning that King County Metro’s external wastewater charges — which are passed through to city customers — will add substantially more to customer bills in coming years.
Consultant Angie Sanchez Vernaz and staff said King County’s most recent forecasts show Metro pass‑through increases of about 7–7.5% for 2026 and projected double‑digit percentage increases in later years. Those external charges, staff warned, account for the majority of the total sewer bill increase customers will see and are not subject to local approval.
“King County Metro does set a pass‑through that your customers will see on their bills,” Angie said. She described the formal Municipal Wastewater Pollution Abatement Advisory Committee (MUPAC) process cities use to review Metro proposals and said member jurisdictions have formally expressed concern and asked Metro to re‑examine the scope of future increases.
Board members and operations staff also spent substantial time on the island’s sewer infrastructure. Jason Kennedy described the system as complex: 17 pump stations, a 'lake line' sewer reach under the lake with challenging inspection and permitting needs, and multiple localized overflows that prompted Department of Ecology orders and a reprioritization of the capital program. Staff said they are launching Reach 1 assessments and will return to the board with findings.
“Those are all big, unfortunately, there’s dollar signs associated to it,” Kennedy said of the lake line and pump station work. Staff described the Reach 1 capacity improvement project as the start of a multi‑year engineering effort to assess remaining useful life and repair options.
Action: The board moved to adopt staff’s revised recommendation — a 4% local sewer increase for 2026 (reduced from a previous 4.5% proposal) — and the motion carried unanimously. Staff emphasized that the overall sewer bill impact to customers will be larger after King County Metro charges are added.
What’s next: Staff plan to update the board on the Reach 1 study and to continue engagement through MUPAC and partnerships with nearby jurisdictions to press King County for additional analysis and moderation of future pass‑through increases.
