King County committee hears steep long‑term sewer rate outlook as Mouth of Duwamish CSO costs rise

King County’s Regional Water Quality Committee received a detailed briefing April 2 on the wastewater division’s proposed 2026 sewer rate and capacity charge and on a longer 20‑year forecast that shows higher near‑term increases driven mainly by the Mouth of the Duwamish combined‑sewer‑overflow (CSO) program and other regulatory and asset‑management needs.

The proposed 2026 residential equivalent sewer rate in the division’s transmittal is $62.66, with a 2026 capacity charge of $77.99. Committee members and advisers flagged large projected increases in the 2027–2029 period and urged faster, clearer work on long‑term forecasting, oversight and affordability.

Why it matters: the sewer rate funds both near‑term operations and a multibillion‑dollar capital program. Committee members said the size and timing of capital projects — together with uncertain future regulatory requirements such as nutrient limits and emerging contaminants — make the near‑term rate path and long‑term affordability a policy concern for elected officials across the region.

Wastewater Treatment Division Director Cameron Gurel told the committee that the division is expanding transparency and engagement around the forecast and that it is responding to motions the committee has adopted on long‑term forecasting. "We know that higher rate forecast present real work or concerns for all of us, including us here at King County WTD," Gurel said, adding that the division is pursuing financing options and additional public briefings.

The division said two structural changes make this year’s forecast substantially different from prior years: extending the forecast horizon from 10 to 20 years, and updated cost and schedule…