Getting A Handle On Sewer Overflows

A surge in storm activity is triggering more intense peak flows at wastewater treatment plants served by both combined sewer and sanitary sewer systems.

The combined sewer systems, commonly found in urban areas, capture surface water runoff, domestic sewage, and industrial waste to be sent through one pipe to the plant for treatment. Periods of heavy rainfall or snowmelt — known as wet weather events — cause combined sewer overflows (CSOs), where untreated excess capacity is discharged to nearby streams, rivers, and other waterbodies. (By comparison, the broader stormwater category includes runoff that doesn’t flow to a combined storm sewer.)