Which system is designed to carry both sanitary wastewaters and stormwater runoff?

The combined sewer system is specifically designed to carry both sanitary wastewater from homes and businesses, as well as stormwater runoff from rainfall and snowmelt. This integrated approach allows the movement of all types of wastewater through a single piping system, which can simplify infrastructure requirements in some urban areas.

During dry weather, the combined sewer system generally functions effectively, directing the flow to wastewater treatment facilities for proper treatment. However, it is important to note that during heavy rainfall events, the system can become overwhelmed. When this occurs, a combined sewer overflow (CSO) can happen, releasing untreated or partially treated sewage directly into local water bodies to prevent backups into homes and streets.

In contrast, a sanitary sewer system is designed only for wastewater coming from households and industrial sources. A stormwater collection system exclusively handles rain and surface runoff, while a POTW (Publicly Owned Treatment Works) refers to the facility that treats wastewater, rather than the system that collects it. Thus, the combined sewer system uniquely addresses both types of wastewater flow, making it the correct answer to the question.