|Northwest Side Deep Tunnel
|Newly Finished Deep Tunnel Boosts MMSD Storage Capacity by 21%
Like many U.S. cities, Milwaukee faced a serious and growing problem. Population growth and continuing development produced ever-increasing volumes of sewage and stormwater. Aging and undersized infrastructure was woefully inadequate to handle the increase, resulting in sewer overflows and basement backups during wet weather.
In 1998, the Milwaukee Metropolitan Sewerage District formulated a farsighted proposal to accommodate growth, protect water quality and safeguard public health within its 420-square-mile service area. The Northwest Side Relief Sewer was the number-one priority Capital Improvement Project in the District's 2010 Facilities Plan, and its successful completion is a key achievement in realizing the Plan's goals.
It took over $121 million, more than a year to dig, a machine powerful enough to cut a 22-foot diameter hole through bedrock, and thousands of truckloads of concrete to complete this massive project. More than seven years of planning, design and construction went into the 7.1-mile sewer tunnel, which serves seven northwestern Milwaukee County communities.
The project demonstrates important strategies to confront capital-intensive sewer overflow challenges, where available funding often falls short and pressure to meet regulatory compliance is intense. 130-180 feet below ground, the large scale, multi-functional tunnel both transports and stores wastewater. Its design makes shrewd use of the existing system—not a band aid” approach to the problem, but a carefully considered design that enables the community to prosper through future growth and development.
The project firmly establishes advanced risk management techniques as critical to success in largescale underground construction. Through progressive risk management and an intelligent bidding strategy, the team achieved on-schedule, under-budget performance with no significant disputes or delays despite the many risks inherent in construction of a tunnel of this magnitude.
Quietly and out-of-sight, the Northwest Side Relief Sewer is producing notable results for the MMSD and enhancing quality of life in Milwaukee:
New Deep Tunnel Nearing Completion
(Milwaukee, WI) – It took more than a year to dig, a machine powerful enough to cut a 22-foot-diameter hole through bedrock, and thousands of truckloads of concrete to complete this massive project.
After more than seven years of planning, design, and construction, the Milwaukee Metropolitan Sewerage District's (MMSD) newest Deep Tunnel is getting closer to its first full day on the job of helping to protect Lake Michigan.
Part of the District's $900 million Overflow Reduction Plan, the 7.1-mile long Northwest Side Relief Sewer is a Deep Tunnel that can hold up to 89 million gallons of wastewater during heavy rain, storage that is needed when wastewater treatment plants are operating at full capacity and cannot handle anymore flows.
"This is a positive step forward. Although, I can't stress enough that this Deep Tunnel is not the cure all that will put an end to all sewer overflows," said MMSD Executive Director Kevin Shafer.
"It will significantly reduce basement backups in the northwest side of our 420-square mile service area,” said Shafer. "However, this tunnel only helps us prevent sewer overflows if the rain hits that northwest side. If storms are light in the northwest, but heavy in the south, there's still a chance we could have an overflow."
Before this new tunnel can go on-line, construction workers need to finish installing equipment that controls the flows into and out of the tunnel. That includes computer control devices and operating logic to allow remote control operation.
Designed to accommodate future growth
The Northwest Side Relief Sewer will only handle sanitary flows from the separate sewer area, unlike phase one of the Deep Tunnel system, 19.4 miles of tunnels that also service the combined sewer areas of the City of Milwaukee and Village of Shorewood.
Providing additional storage capacity for projected future growth, the new Deep Tunnel will service northwest Milwaukee, Wauwatosa, Mequon, Brookfield, Germantown, Menomonee Falls and Butler.
Tunneling for the Northwest Side Relief Sewer began in March 2003 when a massive boring machine went to work, capable of drilling a 22-foot diameter hole in bedrock. At peak drive, the tunnel boring machine required enough electricity to power 4,000 to 5,000 homes. The machine used on this project was more than 800-feet long and had to be assembled underground.
Computer and laser guided, the boring machine negotiated curves and miles of drilling with amazing accuracy. Even at 165 feet underground with no freeway signs saying "turn here," the machine was within one half inch of engineer's projections when it reached the midway point in the project.
Click on this link for more information on the boring machine.
Chips of bedrock carved out by the boring machine were transported through the tunnel by train and lifted up to the surface by a conveyor belt system. At the top, the chips were loaded into dumped trucks and hauled away.
It took approximately 69,000 dump-truck loads to remove the excavated rock from the construction site.
With excavation complete, crews switched over to lining the entire 7.1-mile long tunnel with one-foot thick concrete, reducing the 22-foot diameter excavated hole to a 20-foot diameter Deep Tunnel.
It took approximately 11,500 truckloads of concrete to complete the task. Construction on the relief sewer began in April 2002.