Sewer Overflows

There are multiple points throughout The Metropolitan St. Louis Sewer District’s (MSD) service area where a combination of stormwater and wastewater may discharge from the sewer system during moderate to heavy storms. These constructed wastewater overflow points (Wastewater Overflows), also known as constructed sanitary sewer overflows or SSOs, were designed decades ago to act as relief valves when too much stormwater enters the wastewater sewer system and help to reduce wastewater backups into homes and businesses.

For your information, there are a number of factors that determine if an overflow discharges, including how much rain falls over a given period of time. The result is that not all Wastewater Overflows discharge every time it rains. In fact, some Wastewater Overflows will go months or years without discharging.

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