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The Milwaukee Metropolitan Sewerage District's (MMSD) future growth and flow projections indicated that portions of the existing metropolitan interceptor system (MIS) would be approximately 60 percent below the required wet weather peak capacity by year 2010. As part of MMSD's commitment to the environment and its proactive approach to meeting growing demands, the challenges are being resolved through an innovative 132 million relief and storage tunnel project. The Northwest Side Relief Sewer (NWSRS) tunnel, when completed in January 2006, will provide 88 million gallons of additional wastewater storage capacity and help alleviate basement flooding in a significant portion of the MMSD's service area.

The NWSRS is designed to function simultaneously as a wastewater storage tunnel component of the city's collection system, a relief sewer providing additional capacity to the MIS, and as a conveyance facility delivering wastewater to the treatment plants. The tunnel is 7.1 mile long and 20-foot diameter located in dolomite bedrock at 120 and 165 feet below ground. The project was awarded for construction in December 2001; the construction began in April 2002. The mechanized excavation of the tunnel was completed in April 2004 and the concrete lining has been completed in May 2005.

This paper summarizes the design and flexibility built-in to maximize the project benefits. Other general information such as description of the facilities as well as topographic and geologic setting is also provided. Finally, this paper presents the critical risk management, design, operations and maintenance elements involved in the deep tunnel storage and conveyance projects. The NWSRS tunnel is an outstanding project accomplishment for wastewater utilities and the tunneling industry where multiple design and construction challenges have been turned into success stories and ultimately resulted in happy project partners. The project continues to be on a successful track for an on-time and within budget completion.

Document Type: Research Article


Publication date: 2005-01-01

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