King County tells Mercer Island board repairs on sewer intertie are complete; finish date pushed to October 2026

King County project manager Meredith Redmond told the Mercer Island Utility Board on March 10 that the North Mercer sewer intertie project — a multi‑work‑zone effort that includes a triple‑barrel siphon across Lake Washington and pump station upgrades — remains on track for a coordinated system start this year but now targets substantial completion in October 2026.

Redmond said the single capital effort is being delivered through two construction contracts (conveyance and pump station), both awarded to Walsh Construction in January 2022. She described the work on Mercer Island as roughly four miles of new conveyance divided into 12 work zones, including 7,000 linear feet of 16‑ and 18‑inch force mains in the north zones and a 3,400‑foot transition to 24–30‑inch gravity sewer in the middle sections.

The project schedule has been extended, Redmond said, primarily because contractor‑installed force mains in work zones 1–4 failed pressure testing and required rework. "These new force mains were not passing pressure tests," she said, and crews had to locate leaks, insert sleeves, replace whole pipe sections and change gaskets where installations did not meet contract requirements. Redmond told the board the county has completed the repair work and that pressure testing could be finished as early as the end of the month.

Redmond and other county staff described the milestone sequencing that governs the work: Milestone 1 for the conveyance contract is successful pressure testing and the system being ready to receive flows from the North Mercer Pump Station; that milestone must be achieved before the pump station contract can complete its operational testing. She said Lift Station 11 has already completed initial commissioning and operational testing and that North Mercer pump station testing awaits the conveyance milestone.

On project finances, Redmond reviewed the awarded low bid and subsequent change orders. The conveyance contract bid was cited as $62,200,000; executed change orders raised the revised contract total (presentation cited a figure near $67.9 million) and the county’s remaining balance to be billed is roughly $6.7 million. Redmond said nonconforming work is the contractor’s responsibility and that the county is enforcing contract requirements to ensure long service life for ratepayers.

Board members pressed county staff on long‑term capacity. Redmond said the design is sized for 2060 growth projections developed in coordination with the regional planning body. "Our modeling and comp planning accounts for that," she said. The county noted it used Puget Sound Regional Council numbers in modeling and offered to share more detailed model outputs if the board wished.

Redmond said the county has conducted targeted community outreach — door‑to‑door flyers, email notices to near neighbors and same‑day notifications when last‑minute contractor work arose — and is coordinating traffic control plans with the city. Board members asked whether upcoming local events and the light‑rail opening would conflict with construction; county staff said they do not expect significant construction in those specific spots at the critical times but will coordinate with city projects to minimize cumulative impacts.

King County staff also discussed rate implications. Olivia Robinson of King County WTD told the board the county has proposed sewer rate changes to its advisory group (MUPAC) and that rising regulatory and capital costs — including compliance with a long‑standing federal consent decree to control combined sewer overflows into Puget Sound — are among the drivers of rate increases. The county expects next steps in the rate process in April.

The board thanked county staff for the update and asked for follow‑up materials on modeling, pressure testing results and any forthcoming schedule adjustments. No formal action was required.