The City of Chicago, in cooperation with the Illinois Environmental Protection Agency (IEPA), holds an MS4 permit governing stormwater discharges. The City of Chicago ensures that all required projects at O’Hare obtain coverage under General Permit ILR10. The City of Chicago's annual MS4 report contains a list of ILR10 permitted projects. The most recent report is available online at https://www.chicago.gov/city/en/depts/water/provdrs/engineer/svcs/MS4_2017.html