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Using localized green infrastructure to combat CSOs in Milwaukee Metropolitan Sewerage District

Milwaukee Metropolitan Sewerage District

Milwaukee, WI

Comprehensive localized green infrastructure strategies across public and private properties to combat flooding.

Topics Covered

Stormwater Management
Water Supply & Drought
Water Quality


Initial: 11 Million USD


General obligation bond

Utility rates

Project Status

Operational since 2013

Problem Addressed

In Milwaukee, one inch of rainfall amounts to 7.1 billion gallons of water.

To control this influx of stormwater, the local utility, Milwaukee Metropolitan Sewerage District (MMSD), receives flows from two sewer systems – a combined system constructed over 130 years ago and a separate system built following World War II. Faced with sewer overflows and basement backups, MMSD made significant updates to these systems in 1993 by installing a network of over 19 miles of tunnels 300 feet below ground. Through the mid-1990s, MMSD invested $3 billion in gray infrastructure and in 2010, another $1 billion in an overflow reduction plan that expanded the deep tunnel system to 28.5 miles and allowed it to store up to 521 million gallons of stormwater. Despite these massive investments and time-intensive infrastructure upgrades, the Milwaukee community continued to voice concerns about sewer overflows.

Solutions Used

Responding to the community’s flooding concerns, MMSD decided to prioritize ratepayer involvement in a solution.

MMSD recognized that because localized infrastructure can be installed right on a home or business owner’s property, it is more likely to gain public support since it is easily visible and accessible to the community. In 2002, MMSD began deploying localized strategies including bioswales, permeable pavement, stormwater trees, rain gardens, and more to help capture stormwater where it falls, reduce the strain on centralized infrastructure, minimize pollution caused by overflows, and improve water quality.

In 2013, MMSD decided to scale existing localized infrastructure and approved a regionwide strategic plan to implement this goal. The goal of this new plan was to “achieve zero sewer overflows, zero basement backups, and improved water quality by the year 2035” by capturing the first 0.5 inch of rainfall from impervious surfaces with localized infrastructure. A key element included ongoing public education and outreach to the 28 communities in MMSD’s service area through its “Green Solutions” program.

The Green Solutions program promoted 10 localized strategies across both public and private properties, including: rain barrels, rain gardens, green roofs, bioswales, porous pavement, soil amendments, native landscaping and stormwater-capturing trees, wetlands, green alleys, streets, and parking lots. For public installations, MMSD coordinated localized infrastructure installations with other municipal projects, like street improvements. With strategies implemented on private property, MMSD prioritized widespread access and feasibility, using interactive promotions like technology giveaways to reach more local households and communicate benefits. For example, the utility provided an average 75 to 100 free rain barrels each year.



Economic Benefits: MMSD’s investment in green infrastructure are expected to reduce the utility’s future infrastructure costs by tens of millions of dollars.


Environmental Benefits: MMSD installed green infrastructure projects that capture 39-40 million gallons of water during each storm & helped reduce CSOs to 2.3 overflows per year.


Social Benefits: MMSD’s investment in localized infrastructure is expected to improve quality of life through new green spaces, recreational opportunities, and enhanced community aesthetics.

Last Updated

Jan 30th, 2020

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