What happens when a combined sewer system exceeds its capacity?

When a combined sewer system exceeds its capacity, it usually results in discharging untreated wastewater into nearby water bodies. This situation occurs during heavy rainstorms or snowmelt when the volume of stormwater and sewage surpasses the system's capacity to manage both. As the system becomes overwhelmed, the excess water is often released through designated overflow structures known as Combined Sewer Overflows (CSOs) to prevent backups and potential flooding in urban areas. This practice, while necessary to maintain system functionality and prevent local flooding, poses significant environmental and health risks because the untreated wastewater can contain pathogens, nutrients, and pollutants that adversely affect water quality and aquatic life. Consequently, managing and mitigating these CSO events is crucial for public health and environmental protection.