What are the implications of combined sewer overflows (CSOs)?

The implications of combined sewer overflows (CSOs) are significant, particularly concerning environmental and public health impacts. During periods of heavy rainfall, combined sewer systems— which collect both stormwater and sanitary sewage—can become overwhelmed. When the capacity of the system is exceeded, untreated wastewater is discharged into nearby water bodies. This can result in pollution that degrades water quality, introduces harmful pathogens and nutrients, and poses a risk to aquatic life and human health.

Discharging untreated wastewater during storm events leads to a variety of problems, including contamination of drinking water sources, adverse effects on recreational water activities, and degradation of habitat for aquatic organisms. Environmental regulations often address CSOs, necessitating that municipalities develop strategies for managing these overflows, which might include infrastructure upgrades, retention basins, or green infrastructure solutions.

This answer highlights the environmental and health challenges posed by CSOs, distinguishing it from the other options related to wastewater treatment and ecosystem health, which do not adequately reflect the primary concern associated with CSOs.