Deep Tunnel Clean-Out for MMSD

The challenge

Not only was it a massive and unconventional undertaking, but the Deep Tunnel clean-out project in Milwaukee, Wisconsin was a perfect fit with Veolia's advanced capabilities. Constructed in 1993, Milwaukee's Deep Tunnel is 19.4-miles long and thirty feet wide, and runs 300 feet below ground level to collect storm water and wastewater during heavy or prolonged rains. The complex tunnel network was designed to hold more than 520 million gallons of water to protect the city from flooding and prevent downstream contamination of Lake Michigan. Over the course of its life the Deep Tunnel has prevented 348 million gallons of pollution from entering Lake Michigan. Wastewater that accumulates in the Deep Tunnel is pumped to the surface and treated at Jones Island sewage treatment plant.

The project challenges are:

  • One of the challenges of Milwaukee's Deep Tunnel is that over the past 18 years heavy trash (i.e. floatables, such as assorted jugs, bottles, bags, lumber scraps, and leaves) have accumulated and clogged the system.
  • The debris in the system was constricting the removal and treatment of wastewater by blocking key suction grates used by industrial pumps.
  • In order to restore operational efficiency, the tunnel needed to be cleared of these floatables.

The solution

Innovative project plan:

  • Veolia North America operates the Milwaukee Metropolitan Sewerage District's (MMSD) Jones Island wastewater treatment plant and Deep Tunnel system.
  • Veolia's water experts engaged our industrial cleaning experts to collaboratively develop, plan and execute the Deep Tunnel clean-out project.
  • Working for several months, Veolia's industrial cleaning, confined space, water treatment and safety experts worked to develop an innovative project plan to complete the clean-out project in the safest, most efficient manner.

Customized solution:

  • Veolia's custom solution for the MMSD required a crane to lower personnel and equipment into the Deep Tunnel's access shaft.
  • The largest piece of equipment, a Veolia-designed 16-foot pontoon boat equipped with an industrial 10-foot conveyor belt, motored from the access point to the end of the tunnel below Jones Island, a distance of about one mile.
  • From there, the conveyor boat pushed all of the floating debris back towards the access point, with Veolia's two-man crew using wide rakes to help direct floating debris onto the boat's conveyor.
  • The conveyor transferred the floatables into a specially-designed waste container that was lifted by an industrial crane to the surface for disposal.

Experienced crew:

  • Once lowered, Veolia crews were hundreds of feet from an outside exit; working in what would otherwise be complete darkness, if not for their equipment.
  • Thanks to stringent safety planning, crews were prepared with all of the necessary equipment, including an emergency evacuation boat and a 16-foot tri-hull boat carrying first aid equipment and oxygen tanks.
  • Crews were ready to evacuate themselves and their equipment at a moment's notice in the event of rapidly-developing storms that could lead to heavy rainfall and rising water levels in the tunnel.

Benefits for our clients


According to John Hogan, Division Manager for Veolia North America's Industrial Business, the extensive waste clean-up effort removed approximately 90 cubic yards of plastic trash, wood and other floating debris that had collected in the tunnel for 18 years. One of the most unlikely floatables recovered from the tunnel was a bowling ball, which surprisingly did float.

Surpassed goals:

  • The project was completed in only 10 days, well ahead of the estimated 40-day schedule, with Veolia employees working six days a week.
  • Thanks to the hard work and diligence of the team on the job, 99% of the floatable debris was removed from the Deep Tunnel, keeping an essential part of Milwaukee's infrastructure clean and efficient for years to come.

Learn more about our solutions:

Water Solutions
Waste Solutions
Energy Solutions