Frequently Asked Questions....

Example schematic of a combined sewer system.

Example schematic of a combined sewer system.

What is a combined sewer?
Combined sewer is a type of sewer system that collects rainwater runoff, domestic sewage, and industrial wastewater in a single pipe network.

What is a sanitary sewer?
Sanitary sewer is a type of sewer system that collects domestic sewage and industrial wastewater in a separate pipe network.

What is a storm sewer?
Storm sewer is a type of sewer system that is designed to collect surface runoff and certain infiltration sources, such as foundation drains and sump pumps, in a separate pipe network.  

What is a combined sewer overflow (CSO)?
A combined sewer overflow is the discharge of excess wastewater from a combined sewer system directly into nearby rivers, streams, or other water bodies.

What causes a CSO?
Combined sewer overflows are caused by large variations in flow between dry and wet weather periods.  During periods of heavy rainfall or snowmelt, the stormwater volume in a combined sewer system can exceed the capacity of the sewer system or wastewater treatment plant.

Why are CSO's an issue?
CSO's discharge pollutants into receiving bodies of surface water and can include untreated human and industrial waste, pathogens, toxic materials, and debris.

 

For more information regarding the City of Des Moines Long Term Control Plan (LTCP), please click on the navigation link below.