underground tunnel below street with equipment

NS 12 – Collector System Improvements

Project Update

Project construction continues with work now occurring in both N 31st St. and in W Hopkins St. This new phase of work requires additional road closures.  Stage 2 detour plans will go into effect on April 4th with W Hopkins St. closed to through traffic between W Capitol Dr. and N 27th St.

Stage 1 detour remains in place with N 31st St. closed to through traffic north of W Capitol Dr. except for school traffic. The construction site map and detour plans are available to help you plan travel in the area. If you have questions or concerns, please use the comment form below. Thank you for your patience during the construction of this project.

Project Overview

Since before 2003, MMSD has experienced hydraulic issues with the North Shore 12 (NS12) near surface collector system. This dual-purpose system conveys flows from the City of Milwaukee combined sewer in West Hopkins Street to the MMSD’s Inline Storage System (Deep Tunnel) when available and to Lincoln Creek during extreme wet weather events. Currently, the system cannot deliver enough combined sewage to the Deep Tunnel when it is available.

The NS 12 – Collector System Improvements project resolves to accomplish two goals. First, the construction of approximately 2,600 feet of tunneled 84-inch sewer will increase capacity to the Deep Tunnel reducing the risk of premature overflows. Second, the construction of 530 feet of double 72-inch by 120-inch box culvert will provide greater capacity to handle excess combined sewage during extreme wet weather events. The level of service for this improvement will only increase once the MMSD’s West Basin Stormwater Management Project is complete and online.


Project Map

Project Goals:

  • Help prevent unintended Combined Sewer Overflows (CSOs)
  • Help prevent combined sewage from discharging to grade during large storm events

Timeline –

  • Design: Completed July 2023
  • Construction – December 2023 to June 2025
  • Post-construction – September 2025

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Comments / Questions


Project Resources

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    Removing a tunnel boring machine after sewer is installed

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    Tunnel Boring Machine at bottom of workshaft about to launch