What are Combined Sewer Overflows (CSOs)?

Combined Sewer Overflows (CSOs) occur when the infrastructure designed to manage both stormwater and wastewater becomes overwhelmed, typically during heavy rainfall or rapid snowmelt. In a combined sewer system, both types of wastewater—household sewage and storm runoff—are channeled through the same pipes. When precipitation is excessive, the capacity of the system can be exceeded, resulting in the discharge of a mixture of untreated sewage and stormwater directly into nearby water bodies. This not only poses environmental risks but also raises public health concerns, as the overflow can lead to contamination of local waterways. Understanding CSOs is crucial for sewage treatment workers, as they play a role in managing and mitigating these overflow events to protect water quality and public health.