King County outlines Coal Creek sewer upgrade, warns of traffic and trail impacts

King County wastewater officials briefed the Newcastle City Council on July 15 on a multi‑year plan to replace an aging sewer trunk that runs adjacent to and in places inside Coal Creek.

The project will replace a pipe built in the 1960s, relocate most of the line away from the creek, add a tunneled segment through the Red Cedar Trailhead and construct open‑cut sections where needed. King County said the work advances two goals: meet 20‑year peak flow capacity and reduce environmental vulnerability by moving the pipe away from the stream.

King County Wastewater Treatment Division Director Cameron Gural called the work “a very important project.” Project manager Scott Dingus said most of the existing alignment (the presenter showed it in red) will be removed and replaced with new pipe and a tunnel (shown in orange on project maps). Dingus said the tunnel reduces surface impacts in neighborhoods and on roads but that the team still expects traffic disruptions where the work must cross or use the roadway.

County staff outlined the primary construction impacts: two points on Coal Creek Parkway will be reduced to one lane in each direction during active work, and there will be truck turn lanes and staging areas that affect traffic. Dingus said tunneling at the Red Cedar trailhead will be permitted to run 24/7 once it begins because “once it starts, they really can’t stop.” He also said work in the roadway will follow the City of Bellevue permit hours (work in the right of way generally Monday–Friday during daytime hours) and that an approved contractor schedule was not final at the time of the briefing.

Environmental work is integral to the design. County staff said they will remove some pipe segments in the stream, stabilize erosion, install high‑flow and low‑flow channels for salmon habitat, use woody debris to protect banks, and replant with native species. Dingus said the restored areas will have required maintenance for a minimum of 10 years and that the project has a Salmon‑Safe certification with performance criteria that must be met post‑construction.

Council members pressed the county on traffic and construction timing. Council member Quick asked directly, “How much do I what do I gotta do to call Bellevue and say, please let them do all the construction 24 7?” and urged the county to seek more nighttime work to reduce daytime congestion. County staff replied that nighttime roadway work raises safety and cost concerns and that they have not yet asked Bellevue to change normal right‑of‑way hours beyond the tunneling allowance.

County staff said they have conducted outreach since 2017, maintain a project website and listserv, and will operate a 24‑7 hotline during the tunneling phase. They also said translated materials will be available as needed and that the county will coordinate with both Bellevue and Newcastle on notices to residents.

No formal action or local approvals were requested at the July 15 briefing; the presentation was informational and councilmembers asked questions about schedule, traffic mitigation and habitat restoration. King County staff said they will finalize contractor scheduling and deliver additional materials to the council and the public once the schedule is approved.

Nearby residents and trail users should expect periodic lane reductions on Coal Creek Parkway, intermittent construction staging near the Red Cedar Trailhead, and bursts of activity associated with tunneling when that phase begins. King County encouraged residents to sign up for the project listserv and sign notifications on the project website for the latest construction timing.