What are the circumstances that cause the sewer system to combine and then overflow?
In the combined sewer service areas, one pipe exists to convey both sewage and storm water. When the runoff from rain adds to the sewage component of the flow in sewer, the system relieves itself to a creek or river at the CSO outfall. If there were no designed overflow point, the excess sewage mixture would overflow at other low-lying locations, like basement floor drains.
