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 assumptions for major consent‑decree CSO projects. Crystal Fleet, capital portfolio planning and analysis manager, said the division’s regulatory category alone includes about $6,000,000,000 over the next decade and that regulatory projects remain the largest single driver of capital need.

The Mouth of the Duwamish program (MDCSO) is the single largest change in the forecast. Stan Hummel, CSO delivery unit manager, said the project was chartered in 2023 with a planning‑level cost of $2 billion and that preliminary design and updated climate modeling have increased both capacity assumptions and costs. "We are basing our design on a 1 and a half year reoccurrence interval," Hummel said, noting that the design capacity basis and on‑site storage assumptions have grown and that SoDo site conditions (contaminated soils, fill and liquefaction potential) add substantial site‑preparation cost.

Crystal Fleet explained how MDCSO shifted "from being mostly outside the 10‑year forecast window to being largely inside the 20‑year window," and showed a crosswalk illustrating that roughly $1.4 billion of the forecast increase in the first decade is attributable to MDCSO. Fleet said the division sequences projects to reflect constrained internal delivery capacity and that the large CSO megaprojects rely heavily on outsourced delivery teams, not the county’s internal workforce.

Committee members and the Municipal Utility/Private Agency Committee (MUPAC) raised policy and process questions. John McClellan, MUPAC chair, said his advisory group supported the 2026 rate "with the understanding that the system requires significant and growing investment," but urged additional oversight and predictability measures, including third‑party oversight of the capital improvement program and consideration of a multi‑year rate commitment. McClellan characterized his group's letter as "an expression of frustration and of hope."

On financing and cash‑funding options, Chief Financial Officer Courtney Black described the division’s use of cash funding, State Revolving Fund and WIFIA loans, and revenue bonds. She said the division is pursuing low‑interest, long‑term loans where available and that those choices affect how much is collected from rates versus replaced with debt service. "After we've used our cash, that's where we're looking at that portfolio financing," she said, explaining that principal and interest on borrowed funds are major components of the future revenue requirement.

Staff stressed uncertainty in the second decade of the 20‑year forecast. Several committee members suggested presenting ranges rather than a single point estimate for the later years. Commissioner Clark and others suggested that ranges could better reflect the known unknowns — especially for regulatory requirements such as nutrients and contaminants of emerging concern (PFAS) — and reduce the risk of apparent overconfidence in long‑range percentage projections.

Division director Gurel and staff also briefly reviewed legislative and regulatory items under monitoring: a biosolids bill under consideration in Olympia, Senate Bill 5360 (environmental penalties language the division said could expose ratepayers to risk unless amended), and Ecology’s evolving approach to the Puget Sound Nutrient General Permit. Gurel said the county had received a letter from Ecology describing a voluntary option after the Pollution Control Hearings Board invalidated the prior general permit; the division will review and intends to provide an update potentially for the committee’s May 7 meeting. The division also noted completion of a 12‑month PFAS sampling study and signaled a commitment to brief the committee on those results.

What the committee will do next: the county executive is scheduled to transmit the proposed 2026 sewer rate ordinance to the council April 24. The King County Council’s Budget and Fiscal Management committee is slated to begin review May 28, with a possible committee decision June 11 and final council action on June 17 or June 24. Chair Claudia Balducci asked staff to draft a committee letter for discussion at the May meeting and asked members to submit suggested language within roughly one week so staff could circulate a draft in time for May packet deadlines.

The committee did not take a formal vote on the 2026 rate at the April 2 meeting; members asked staff for more information and to return in May with additional briefings, including a planned executive‑session discussion on legal risks related to consent‑decree obligations.

Ending: committee members repeatedly stressed the need to pair technical forecasting with clear policy direction on predictability, oversight and affordability. Several members encouraged stronger regional coordination among contract agencies and earlier opportunities for advisory groups such as MUPAC to examine alternatives and delivery approaches, including financing and potential multi‑year rate structures. The division committed to return with additional briefings on long‑range forecast methodology, the MDCSO project, the Ecology nutrient permit, PFAS results and a draft capacity charge methodology.