Combined Sewer Overflow
Did you know that in the state of Pennsylvania, more than twenty four billion gallons of raw sewage enters our streams and rivers every year? It’s not just a problem in Pennsylvania - during the Paris 2024 Olympics, sewage pollution made the River Seine too polluted for triathletes to swim in. But why is there sewage in our rivers in the first place? To understand why this happens, we must first explore our wastewater systems. Read on to learn more!
What are combined sewers?
Combined sewer systems are sewer pipes that handle both stormwater and sewage. Many US cities built before 1900 have this type of sewer system because sewage treatment was not available before the 20th century. Thus, the most efficient way for cities to manage stormwater and sewage was to pipe them both directly to the local river.
When sewage treatment became available, it was too costly for cities with these systems to separate stormwater pipes from sewage pipes. Therefore, combined sewer pipes were redirected to treatment plants where both stormwater and sewage were treated together. To this day, some suburbs and cities throughout our state still have these systems in place.
Combined Sewer Overflow
The main issue with combined sewers is that when there is a large rainfall event, treatment plants cannot handle the large volume of both stormwater and sewage. These systems are designed to overflow, which means that when the system is overwhelmed, stormwater and sewage overflow into our streams and rivers. This type of event is called a combined sewer overflow (CSO).
Unfortunately, this can occur frequently. For example, five out of the six watersheds local to Philadelphia receive raw sewage at least 64 times a year. As you can imagine, this not only impacts aquatic life but also restricts us from using our waterways for fishing, swimming, and drinking. Wondering if your community has combined sewers? Check out this PA DEP spreadsheet to see a list of CSO communities in Pennsylvania.
Normally sewage flows as it should
Rain can make it overflow
What is being done about this issue?
There are many efforts underway to reduce overflows throughout our state, especially in major cities. Philadelphia is currently implementing a $2 billion plan called “Green City, Clean Waters”. This plan aims to significantly reduce the frequency of overflows by implementing over 12,000 acres of green stormwater infrastructure (GSI). GSI like rain gardens, infiltration trenches, and green roofs reduce the amount of stormwater entering the combined system by storing it temporarily or infiltrating it into the soil.
Pittsburgh is currently implementing a similar project that focuses on adding about 183 acres of GSI and increasing the volume capacity of water treatment plants. Instead of strictly focusing on gray infrastructure improvements such as holding tanks, cities are opting for GSI as it provides additional benefits like improving air quality, cooling our neighborhoods, and increasing property values. To learn more, visit our green stormwater infrastructure webpage!
Solutions for Residents and Community Organizations
If you’re a property owner in an area with combined sewers, you can help reduce CSOs by reducing runoff from your property. Some GSI solutions you could consider include downspout disconnection, downspout planters, or rain barrels. Most CSO communities have programs in place to assist residents in addressing these issues, so make sure to check in with your local government for more information. For example, Philadelphia’s program is called PWD Rain Check.
If your community does not have a program in-place, consider volunteering with your local Environmental Advisory Committee or even starting your own rain garden program. Be sure to check out the various pages under the “taking action” tab above to learn more.