Sewer Overflows

There are hundreds of points throughout MSD’s service area where a combination of stormwater and wastewater discharges into local waterways from the sewer system during moderate to heavy rainstorms.  These sewer overflow points act as relief valves when too much stormwater enters the sewer system, and without them, our community could experience thousands of basement backups and/or extensive street flooding (even with these sewer overflows, residential customers do still experience basement backups).  Depending on where sewer overflows are located within MSD’s system, they are classified as constructed separate sewer overflows or combined sewer overflows.

If an overflow discharges or not is dependent upon a number of factors, including how much rain falls over a given period of time.  The result is that not all overflows discharge every time it rains — in fact, some overflows will go months or years without discharging.  Though both types of overflow points generally have the same function, the distinction between constructed separate sewer overflows and combined sewer overflows is made for engineering and regulatory purposes.

Many of the overflows that exist throughout MSD’s service area are a legacy of our aging sewer system.  Even though most overflows predate MSD’s creation in 1954, they are still our responsibility,and efforts to address the issue must continue.

The United States Environmental Protection Agency (EPA) required MSD to place signs in multiple areas that could be impacted by activated overflows. The EPA ordered signs placed at all constructed separate sewer overflow points For overflow points where no easily identifiable structure exists, the signage was posted nearby.

In addition, a letter was mailed to all MSD customers regarding the signage. A separate letter and brochure was sent to customers whose property might contain an overflow.

The letters, brochure, a map showing the location of all sewer overflows in the MSD service area and the EPA order can be found in the links below.

If you have questions about these materials, the signage or overflows, please contact us at (314) 768-6260.

Letter to Customers
Sewer Overflow Locations Map
Overflow Notification Brochure
Signage Order 
Amended Signage Order
Letter to EPA
Letter from EPA
Long-Term Control Plan Exec. Summary 2011
Long-Term Control Plan 2011 
Long-Term Control Plan 2013 Update – Supplement No. 1
Long-Term Control Plan 2013 Update – Supplement No. 2
CSO Volume Reduction Green Infrastructure Program: Pilot Final Report and Full Implementation Plan without Appendices
CSO Volume Reduction Green Infrastructure Program Report: Appendix A-O
CSO Volume Reduction Green Infrastructure Program Report: Appendix P-V
CSO Volume Reduction Green Infrastructure Program Report: Appendix W-Z
CSO Volume Reduction Green Infrastructure Program Report: Appendix AA-EE