The Illinois Tollway must balance the need to move people safely while protecting water quality. Many natural areas that provide aquatic habitat border the Tollway system, and municipalities rely on clean surface and groundwater for recreational opportunities and municipal water supply.
Pollutants from Tollway construction activities and roadway runoff can potentially reach downstream waters and shallow aquifers. Common pollutants of interest are suspended sediment from land-surface disturbance, heavy metals from automotive sources, and chloride from road salt application. The Illinois Tollway has implemented best management practices (BMPs) to reduce discharge and pollution reaching the Chicago Area Waterways System (CAWS). The Illinois State Geological Survey (ISGS) monitors hydrology and water quality to determine the effectiveness of roadside treatment wetlands, such as bioswales, for removing these contaminants. Further, impaired waterways that receive runoff from the Tollway and are monitored for concentrations of roadway-derived target contaminants regulated by IEPA.