The M Street Trunk Rehabilitation Project is planned to begin construction in summer 2025 and will repair approximately 2.6 miles of concrete sewer pipe in the City of Auburn. The project will also repair 45 maintenance holes, install new maintenance holes, and over 100 sewer connections to homes and businesses.

The M Street Trunk is a King County sewer pipe located in Auburn that carries untreated wastewater from homes, businesses, and schools in your neighborhood to the South Treatment Plant in Renton, where it is cleaned and safely released into the Puget Sound.

We understand construction can be disruptive. Here are ways we are minimizing the impacts to our community. While construction work is underway, wastewater from your homes and businesses will be sent into a temporary pipe called a sewer diversion pipe or bypass. This will allow construction crews to work inside the existing sewer pipe while maintaining services to the community. Noise and odor control equipment will be used at critical points in the sewer diversion system.

The M Street Trunk was installed in 1963 and has deteriorated due to the long-term effects of hydrogen sulfide exposure. Hydrogen sulfide is a normal and expected byproduct of wastewater and can be corrosive to our infrastructure. We will rehabilitate the trunk pipe to ensure our systems remain safe and reliable for decades.

The project is organized into four work zones, based on the rehabilitation method and sewer pipe diameter: Zones, 18, 24, 30 and 36.

Construction will take place during the summer months when sewer flows are lower. In summer 2025, the project team will complete the repair work of Zone 18, 24, and some sections of Zone 30 on M Street Northeast, starting from the intersection on 14th Street Northeast to south of 22nd Street Northeast. This early work will help us complete the entire rehabilitation project in 2026 as planned and coordinate with the City of Auburn's planned road widening project on M Street beginning in 2026.

The construction of the remaining portion of Zone 30 and the full length of Zone 36 will be done in summer 2026. We will provide updates to the schedule on the project website as the design progresses.

The project is organized into four work zones, based on the rehabilitation method and sewer pipe diameter: Zones 18, 24, 30 and 36. Across these work zones, King County Wastewater Treatment Division will be using two methods for relining the M Street Trunk: cure-in-place piping and spiral-wound lining.

Cure-in-place piping (also known as “cured-in-place pipe lining” and abbreviated CIPP) is an efficient method for repairing sewers that require little to no digging and therefore reduces impacts to neighbors. CIPP involves inserting new, flexible lining into the existing sewer pipe, inflating the lining to the size of the inside of the existing pipe, and then hardening it using heat or ultraviolet (UV) light to stay in place. The lining then forms a smooth, water-tight seal on the inside of the existing pipe. CIPP will be used for Zones 30 and 36.

Spiral-wound pipe lining is an efficient method for sewer repair that requires little to no digging and can sometimes be done while water is still flowing through the sewer. This method uses a flexible material that can be wound in a spiral around the inside of an existing sewer pipe. Imagine wrapping a ribbon around your finger, overlapping it just enough as you wrap it down your finger so that none of your skin is showing. That is what the spiral winder does inside the pipe. The edges of the lining material are often self-sealing, so it forms a water-tight bond as it is wound down the length of the pipe. Spiral-wound technology will be used for Zones 18 and 24.