Milwaukee Case Study in Example Evolution of Sewer Controls

The Milwaukee Metropolitan Sewerage District (MMSD) operates a sewer interceptor system with the aid of one of the most extensive real time control networks in the country. This sophisticated system began 90 years ago when the interceptor sewers were installed with mechanically operated movable gates that restricted flows into the interceptors in response to increasing flow depths in the trunk sewers. By the 1960s, the controls included the original tilting gates, several pump stations operated in response to wet well levels, and about 25 sluice gates that were manually adjusted twice each year in response to seasonal precipitation patterns to direct flows towards, or away from, the Milorganite production. In the 1980s MMSD incorporated evolving remote sensing instrumentation, telemetry, and computer controls to automate the system. Since 2000 MMSD has refined telemetry, instrumentation, and operating strategies to further the continuous improvement of this innovative system. Most recently the real time controls were expanded to aid the Department of Transportation in achieving stormwater quality objectives for downtown highway interchange drainage. This paper summarizes the unique components of the controls incorporated into the system at each stage in the nearly 100 year evolution. The paper also summarizes the motivation, costs and system performance improvements associated with each major stage of the real time controls evolution. For the more recent innovations (those since 1980), the paper discusses the alternatives considered and the reasons for selection of those options implemented. The paper concludes with a summary of the benefits attributed to the real time control network. The benefits include reduced capital costs to achieve high levels of wet weather performance, improved tracking and reporting of system performance, improved real time identification and resolution of system problems, and decreased safety and environmental risks associated with maintenance of the diversions.