Preventing sewage from backing up into your basement is our highest priority when too much rain gets into the sanitary sewer system. Unfortunately, our only weapon in that battle is a relief valve that sends excess water to the nearest river or lake, an overflow pipe. As a region, we've invested more than $4 billion to reduce sewer overflows, a massive effort that is paying off.
Prior to the Deep Tunnel, this region used to pollute Lake Michigan with an average 8 billion to 9 billion gallons of sewage every year. Here's the record since 1994, the first full year of operation for the Deep Tunnel system: