CLEVELAND — It's the most expensive infrastructure project in Northeast Ohio history and it's one you'll never see. There are signs promoting Project Clean Lake in key locations like University Circle, but the bulk of the $3 billion project is going on out of sight, deep below the ground.

The project is the Northeast Ohio Regional Sewer District's response to a federal mandate years ago to reduce the amount on untreated water that flows into the Cuyahoga River and in turn Lake Erie during storms.

The sewers that carry our house waste to be treated are also filled with rainwater that flows in from our gutters and street drains — a volume of water during a storm that the water treatment system simply cannot handle. Project Clean Lake will see the construction of seven underground tunnels, some three to five miles in length that will be used to store storm water and sewage during a heavy rain event until it can be pumped out, cleaned and released into the lake.