A combined sewer system has pipes that collect both storm water runoff and sanitary sewage. Combined sewers have existed in Upper Sandusky since the early 1900’s and at that time all combined sewers drained directly or indirectly to the Sandusky River. It was not until the early 1950’s the Upper Sandusky constructed a wastewater treatment facility.
Some of these early combined sewers are still in use today. During dry weather these combined sewers transport wastewater directly to the sewage treatment facility. In periods of heavy rainfall or excessive snowmelt, the wastewater volume in the combined sewer system can exceed the capacity of the sewer system or the treatment facility. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to the Sandusky River. With these overflows, pressure is relieved from the sewer system thus helping to prevent back-ups in basements. These overflows are called CSO’s.