PEORIA, Ill. (WMBD) — Do people ever wonder where stormwater goes when it rains heavily? It’s called combined sewer overflow, or CSO, and it drains into the Illinois river.

A combined sewer system collects rainwater runoff, sewage, and wastewater into one pipe. It transports all the wastewater it collects into a body of water.

Specifically, CSOs carry untreated or partially treated human and industrial waste, toxic materials, and debris, as well as stormwater. They are a priority water pollution concern for approximately 700 municipalities across the U.S. that have combined sewer systems.

“Eventually that stormwater and sanitary sewage, that pipe that it flows through that combines sewer, it’ll get overwhelmed on days like this when there is a substantial amount of rainfall that falls in such a short period of time. When that does happen, sewage does end up in the river,” said Nick McMillion, communications specialist at the Department of Public Works.

One project at a time, Peoria Public Works is trying to diminish the amount of waste draining into the river.

“At the end of the 18 years, what we would hope to do is have the majority of an average rain to be taken into the system and not get to the river,” said Public Works Director for Peoria Rick Powers.

This year, the department is building bumpout planters and permeable pavers on Laveille, Caroline, and Mary Street, right by Lincoln K-8th.

“We’re going to work around those areas kind of network them, and then divert water toward a collector, or a storage tank, so we can hold it and then release it at a metered rate into the interceptor,” said Powers.

While each yearly project is different, the total cost remains the same.

“Year one is $3.6 million, it’s a $120 million investment over 18 years,” said McMillion.

While it may sound costly, the smallest amount of water can cause an overflow, dirtying up the river.

“Today, as little as a quarter of an inch of rain can cause a surcharge on our system, so that gives you an idea of the magnitude of the undertaking we’re in now,” said Powers.

For those who would like to lessen their stormwater footprint, there are things they can do at home.

“We’re encouraging homeowners to consider rain gardens, try to hold the water that rains and comes off your roof in rain barrels, anything that you can to plant a garden. Contact us at public works, and we’ll even show you some designs on how you can participate and keep water from getting into the systems,” said Powers.

Once the project is complete in 18 years, McMillion said it’ll make the environment cleaner, along with the river. “It ultimately creates a better city, better area, just overall better experience and livelihood for everyone.”