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The Milwaukee Metropolitan Sewerage District (District) has recently completed the initial phase of its Central Metropolitan Interceptor Sewer (MIS) System Improvement Project. This multi-year project was undertaken to clean, inspect, and repair nearly 50 miles of the District's oldest (75 to 115 years) interceptors, siphons, and flow control structures. The Central MIS, located within the heart of Milwaukee, had not been available for inspection until the Inline Storage System (ISS) or “deep tunnel” was put on line in 1994, providing a means for flow diversion.

The goal of this undertaking was to identify the facilities requiring rehabilitation, replacement or other improvements required to achieve an additional 50 years of service life, correct maintenance/operational deficiencies and optimize the hydraulic performance of the Central MIS over this period.

A two-year cleaning and inspection effort utilized robotic closed-circuit television, manentry hand held cameras, and sonar inspection equipment to evaluate the 50 miles of 12- inch to 84-inch diameter interceptors and siphons, 504 manholes, and 137 intercepting structures. The system was found to be generally in sound structural condition but not anticipated to last another 50 years.

Hydraulic modeling revealed system bottlenecks and determined minimum acceptable pipe diameters for repaired or replaced piping. One bottleneck determined by the hydraulic model, in the most downstream portion of the Central MIS, was the siphon system under the Milwaukee Harbor leading to the Jones Island Wastewater Treatment Plant. The siphons were determined to be restricting flow to below the plant capacity. Improvements now under final design will increase flow delivery to above the plant capacity, thereby utilizing the full capacity of the interceptors and plant and diverting less flow to the Inline Storage System. Modeling was also utilized to determine improvements needed to regulate flow from combined sewers to the interceptors in order to optimize the performance of the Central MIS.

Geotechnical, archaeological and environmental field investigations also influenced improvement options.

From this work, 36 preliminary engineering reports, 6 technical memoranda, 2 conceptual improvement plans and a master hydraulic plan were generated, recommending approximately 240 million of improvements, that will be accomplished through 50 to 60 design and construction packages to be completed by 2010.

Design and construction phases are now underway. Improvements include replacement and rehabilitation of much of the system. Much of the rehabilitation will be accomplished by “trenchless technologies”, utilizing some of the latest innovations in the rehabilitation industry. Large diameter cured-in-place lining, sliplining, segmental lining, cementitious and epoxy coatings all have applications in this improvement effort. Selections have been based upon structural condition, diameter, depth, hydraulic limitations, pipe configuration and constructability considerations. Where feasible, rehabilitation contracts are being let with repair alternative options, thereby increasing competition and resulting in very favorable bid prices.

This paper will describe how the improvement project is managed, with emphasis on pipe rehabilitation methodologies and bidding procedures.
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Document Type: Research Article

Publication date: 2002-01-01

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