Long‐Term Trends Show Improvements in Water Quality in the Chicago Metropolitan Region With Investment in Wastewater Infrastructure, Deep Tunnels, and Reservoirs

Abstract

AbstractThe ecological degradation of streams draining urban land, known as the urban stream syndrome, is characterized by elevated nutrients and contaminants, increased hydrologic flashiness, and altered biotic assemblages. This study demonstrated an improvement in chemical characteristics by evaluating water quality trends from 1975 to 2012 and from 2013 to 2018 in the Chicago, Calumet, and Des Plaines River Systems in Cook County, Illinois. Data from 41 monitoring locations were compiled and 11 water quality parameters were analyzed for long‐term monotonic trends and differences in water quality parameters between select time periods to investigate the outcomes from improvements in water reclamation plant (WRP) and tunnel and reservoir infrastructure carried out by the Metropolitan Water Reclamation District of Greater Chicago. From 1975 to 2012, significant decreasing trends in concentrations were demonstrated at most sampling locations for total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonium nitrogen (), total suspended solids (TSS), fecal coliform (FC), and sulfate. Significant increasing trends were demonstrated for dissolved oxygen (DO) and chloride concentrations and temperature. Total phosphorus (TP) concentrations increased downstream of the Stickney, Kirie, and Calumet WRPs from 1975 to 2012, but decreased downstream of the Kirie WRP and had no trends downstream of the Stickney and Calumet WRPs from 2013 to 2018. Improvements in TKN, , TOC, TSS, FC, TP, and DO concentrations over four decades demonstrated the benefits of expanding secondary wastewater treatment and implementing the Tunnel and Reservoir Plan System, instream and side‐stream elevated pool aeration stations, and effluent disinfection.