Combined Sewer Overflow, or CSO, is a method for conveying both stormwater and sewage in one combined system. These systems were built in hundreds of communities across the US in the past, before indoor plumbing became commonplace. During periods of normal rainfall, the systems function properly by conveying both stormwater and sewage to wastewater treatment facilities. But during floods or periods of heavy rainfall, this combined system can cause raw sewage to overflow into our streams and rivers, causing a threat to public health. Under the EPA’s Clean Water Act, Indianapolis and other communities must develop plans to reduce these overflows and protect human health and the environment.

Click here to see why CSOs are such a problem in the City of Indianapolis