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. Depending on where sewer overflows are located within MSD's system, they are classified as constructed separate sewer overflows — or— combined sewer overflows (CSOs).
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 CSOs and constructed separate 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 to the right.
If you have questions about these materials, the signage or overflows, please contact us at (314) 768-6260.