Combined Sewer Overflow -
A Minneapolis Solution
What is a Combined Sewer Overflow (CSO)?
Combined Sewer Overflows (CSO) 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, CSOs are relatively rare in Minneapolis. The City has been actively working on sewer separation, a key strategy for preventing CSOs, since the 1960s. Most of the City’s system has been separated.
When a CSO does occur, however, it can cause serious health and environmental problems that affect City residents and all who live, work or play downstream.
The threats posed by CSOs are serious enough that federal and state mandates have been issued that require the City of Minneapolis to stop combined sewer overflows into the Mississippi River. Not complying with these mandates could lead to fines and other legal action against the City.
Stopping CSOs
Fixing the remaining problems that can cause CSOs in Minneapolis won't be easy. Here is why:
- The combined sewers that remain were left for last because they will be the most difficult and expensive to separate.
- The entire system is large, complex, and has been in place for a long time. While the City has found and addressed many of the problems that could contribute to the risk of a CSO, there are some that have not yet been detected.
- Some solution strategies require action by home and building owners -- at their own expense.
See History of Combined Sewer Separation in Minneapolis for more information about how the City's sewer systems have evolved and how it has addressed sewer separation issues over time.
A Five-Year Plan
The City of Minneapolis has joined forces with the Metropolitan Council to eliminate combined sewer overflows. Key components of the plan include:
Passage of an ordinance to prevent the kinds of discharges to the sanitary sewer system from homes and commercial buildings that can contribute to CSOs:
Chapter 56. Prohibited Discharges to Sanitary Sewer System (pdf), also known as the "Rainleader Ordinance," was passed by the City Council in May 2003. It requires disconnection of all roof and area drains or other stormwater or clearwater connections to the City’s sanitary sewer system. Inspections of public and private property and buildings are being conducted to verify compliance.
High priority areas will be targeted first. Teams will then inspect all remaining areas of the City. Every parcel and building has been inspected to check for prohibited connections to the sanitary sewer system.
For more information about the ordinance and how you might be affected, see the Rainleader Ordinance Fact Sheet.
Commitment to significant investment in capital improvements and maintenance repairs to our sewer systems:
The City has committed to giving higher priority to capital improvement and repair projects that will contribute to eliminating CSOs. Examples of such projects include:
- Sewer separation and sanitary main restoration projects
- Use of hydraulic modeling of the sanitary sewer system to identify improvements that will maximize storage capacity, locate problem areas, and evaluate the effectiveness of CSO program work that has been completed
- Continued research to find inlets and cross-connections to storm drains and eliminate them through maintenance repairs
Launching of a community outreach program to educate residents and business owners about CSOs and ways to prevent them
This CSO website is part of this outreach. How-to-disconnect brochures and other instructional pamphlets have been produced and been distributed to residents and business owners directly affected by rainleader ordinance compliance requirements.
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