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350 South 5th Street
RM 203 City Hall
Minneapolis, MN  55415-1390

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Combined Sewer Overflows

What is a Combined Sewer Overflow (CSO)?

CSOs occur when heavy rain or melting snow causes sanitary sewers to overflow into stormwater drainpipes. This allows sewage to mix with runoff from buildings, parking lots and streets and flow, untreated, into the Mississippi River.

Compared to many other cities, CSO events are rare in Minneapolis. The City has been actively working on sewer separation since the 1960s. Most of the City’s sewer system has been separated. When a CSO does occur, it can cause serious health and environmental problems.

The threats posed by CSOs are serious enough that federal and state mandates have been issued that require the City of Minneapolis to stopping a CSO event from entering the Mississippi River. Non-compliance with these mandates could lead to fines and other legal action.

Stopping CSOs

Fixing the remaining problems that can cause CSOs in Minneapolis won't be easy. Here is why:

It is the goal of the City of Minneapolis, along with the Metropolitan Council Environmental Services (MCES) , to eliminate CSOs. Key components of the plan included passage of the Chapter 56 Ordinance. The goad of this ordinance is to prevent discharges to the sanitary sewer system from homes and commercial buildings, that can contribute to the occurrence of a CSO event.

Commitment to Eliminate CSOs

The City is committed to investing in and giving higher priority to capital improvement and repair projects that will contribute to eliminating CSOs. Examples of these projects include:

Learn more about the Chapter 56 Ordinance by reading the Rainleader Ordinance Fact Sheet.

Last updated Feb 5, 2019



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