What is a potential environmental concern with combined sewers during heavy rain?

The potential environmental concern with combined sewers during periods of heavy rain revolves around overflow leading to contamination. Combined sewer systems are designed to carry both sewage and stormwater in a single pipe. During heavy rainfall, when the volume of water exceeds the capacity of the sewer system, these combined sewers can overflow. When this occurs, untreated sewage, along with stormwater, can be discharged directly into local water bodies, such as rivers, lakes, or coastal waters.

This type of overflow can have severe environmental impacts, including the introduction of pathogens, nutrients, and harmful pollutants into the aquatic ecosystem. Such contamination can harm aquatic life, disrupt ecosystems, and pose health risks to humans, particularly those who swim or fish in affected waters. These considerations underscore the importance of managing combined sewer overflow (CSO) situations effectively to protect both public health and the environment.

The other options do not highlight the significant environmental risks associated with combined sewer overflow during heavy rain events, focusing instead on unrelated issues.