Wastewater Department

Combined Sewer Overflows

There are three types of sewers: separate sanitary sewers that transport sanitary waste only; separate storm sewers that transport storm water only; and combined sewers that transport sanitary wastewater and storm water. The Butler Wastewater System has more than 8 miles of sewers, of which about 60% are combined sewers. No new combined sewers have been constructed since the late 1950s.

Combined sewers transport only sanitary wastewater during periods of dry weather. However, during periods of wet weather, such as rain or snowmelt, the combined sewers transport storm water along with the sanitary wastewater. The problem with combined sewers is that their capacity is limited and when the volume of storm water entering the combined sewers exceeds the capacity of the combined sewer, an overflow at a designated outfall may occur into Big Run Ditch. There is only one permitted combined sewer overflow (CSO) Outfall in the Butler sewer system.

The overflow may contain untreated sanitary wastewater. The untreated sanitary wastewater contains large amounts of bacteria and those bacteria represent a risk to human health if a person ingests or comes into contact with the untreated wastewater in the receiving stream.

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