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City engineers propose rerouting siphon sewer under I‑894 to reduce failure risk
Summary
Engineering staff briefed the Board of Public Works on a plan to eliminate a 1965 cast-iron siphon sewer beneath I‑894 by rerouting flows via Layton Avenue and tying into an existing public sewer serving English Meadow; design work will proceed and an easement from the apartment owner will be required.
City engineering staff told the Board of Public Works on Sept. 23, 2025 that the city plans to redesign a section of sanitary sewer that currently functions as a siphon under Interstate 894.
Staff said the existing siphon is an always-full, cast-iron sewer installed in 1965 and that a failure would affect a swath of properties north of Layton Avenue. Because the pipe lies under the freeway and carries flow under pressure, routine camera inspection is ineffective and repairs under the freeway would be technically difficult and very expensive.
To reduce the risk, engineers proposed running a new sewer along Layton Avenue and connecting a north-side neighborhood segment into an existing sewer serving the English Meadow apartment complex, thereby eliminating the siphon. The purple segments shown in the presentation represent new pipe in the proposed alignment; staff said they are proceeding with design and will seek an easement from the apartment owner to place the pipe through the site’s driveway area.
Engineering staff emphasized the project is proactive. A full inspection of the siphon would be costly; staff said past study work had been on the order of "a couple hundred thousand dollars" for inspection alone. If the siphon were to fail, bypass or emergency repairs under the freeway could be extremely expensive and would likely disrupt service to many homes.
The presentation was informational; a construction project request will return to the Board for authorization once design is complete and right-of-way/easement agreements are in place.
Engineering staff answered questions about whether other siphons exist (this is the only siphon system the city uses, staff said) and confirmed the northern sewer reaches the gravity system that continues eastward. The Board accepted the briefing and will be updated as design advances.
