Sump pumps gather ground water from around the house and move the water away from the house. The goal is to reduce the water pressure on the foundation which will prevent water entry into the house.
I see quite often where the sump discharges into the sewerage pipe. The city limits of Chicago does allow this, but none of the suburbs allow it.
The reasoning I get from the suburbs is that the water from the sewerage needs to be cleaned and treated before it can be returned to Lake Michigan. If all the homes discharged ground water into the sewerage system, the sewer system would be overwhelmed.
We do identify this as something that should be addressed.