MILWAUKEE'S EXPERIENCE IN COLLECTION SYSTEM CONTROLS
Abstract:During the past century, Milwaukee's metropolitan sewers grew from simple discharges to the rivers and Lake Michigan to a complex system of interconnected sanitary and combined sewers, interceptors, and treatment plants. By the mid-1970s this network conveyed and treated most of the sewage generated by 1.3 million people in the 425-square-mile service area, but only during dry weather. During wet weather, hundreds of bypasses activated from the tributary separated sewer service areas and 114 combined sewer overflows discharged untreated wastewater to the rivers and lakes. Many homes in the separated sewer service area also suffered sewage backups, some more often than once a year. The Milwaukee Metropolitan Sewerage District (MMSD), spurred by local environmental concern as well as national and state legislation and court action, undertook a water pollution abatement program to address the problem.
The collection system controls portion of the program was completed in 1986. A 400 million gallon deep tunnel storage and conveyance system was added to the system and became fully operational in 1994. The number and frequency of combined sewer overflows were significantly reduced, from a pre-program average of more than 60 overflows per year to a post-program average near 2 per year. For several years, sewer backups in residences were virtually eliminated, but recently reappeared during extreme storms.
This paper explains how controlling the interceptor system, rather than just relieving it, has enabled the MMSD to achieve far more than merely reducing bypass and overflow frequency. The collection system controls allow the MMSD to meet tight overflow restrictions in a manner flexible to variable precipitation patterns, growth patterns, and lake and groundwater levels. The paper further explains how the development and operation of the controls have assisted the MMSD in such varied activities as troubleshooting blockages, identifying and responding to system anomalies, and even improving budgeting and user charge cost allocations for operations.
The paper is presented in four sections: description of the original problem and objectives of the collection system, components of the collection system controls, performance of the collection systems, and lessons learned in 5 years operating the real time collection system controls. An Acronym List is appended at the end of the paper for the readers convenience.
Document Type: Research Article
Publication date: January 1, 2001
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