What describes a 'combined sewer'?

A combined sewer is designed to carry both wastewater and stormwater in a single system. This configuration allows for efficient management of sewage and rainwater runoff, particularly in urban areas where space might be a premium. When it rains, the combined sewer system manages stormwater along with domestic and industrial wastewater, which can be beneficial because it reduces the need for separate systems, thus minimizing infrastructure costs.

However, one of the challenges with combined sewers is that during heavy rainfall, the capacity can be overwhelmed, leading to combined sewer overflows (CSOs). These occurrences can discharge untreated wastewater directly into nearby bodies of water, posing environmental and public health risks. Understanding the design and function of a combined sewer helps in grasping the complexities of urban wastewater management and the importance of mitigating CSOs through various techniques such as storage tanks or treatment plants.

Options that limit the function to only stormwater or wastewater do not accurately reflect the dual purpose of a combined sewer, while a sewer with multiple pipes relates more to separate systems rather than a combined approach.