The problem is too much water. Sanitary sewer systems can only handle a certain amount of water. During a rainstorm, water gets into the sewer from connected downspouts and sump pumps. In a neighborhood of 200 homes it only takes six to eight sump pumps working full time in wet weather to cause sewer backups. When there is too much water for the system, the excess has to go somewhere, and that somewhere is often somebody's basement, a manhole, or the Grand Calumet River.
The City of East Chicago has a legal requirement, (Ordinance Number 2835) which was passed on May of 1964 to stop rain water from flowing to our sanitary sewers. With an increase in water flow, this becomes a problem, because the wastewater treatment plant has to treat the extra water.