underground tunnel below street with equipment

NS 12 – Collector System Improvements

Project Update

Stage 1 and Stage 2 detour plans are now in effect. Construction of shafts in Hopkins is ongoing. The tunneling boring machine has been delivered to the site and is currently tunneling in Hopkins. Milwaukee County Transit System has posted signs redirecting riders to temporary locations for pickup and drop off.

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

Get Involved/Stay informed:

  • Sign up to receive NS 12 project updates in your inbox.
  • Follow MMSD on social media (TwitterInstagramFacebook ) for updates on MMSD projects.

Comments / Questions


Project Resources

  • slide

    Removing a tunnel boring machine after sewer is installed

  • slide

    Tunnel Boring Machine at bottom of workshaft about to launch