Dissolved Oxygen in the Chicago Area Waterway System – Using A CDOM Program to Support Water Quality Improvement Efforts

The Chicago Area Waterway System (CAWS) consists of 78 miles of canals, which serve the Chicago area for two principal purposes, the drainage of urban storm water runoff and treated municipal wastewater effluent and the support of commercial navigation. Approximately 75 percent of the length is composed of man-made canals where no waterway existed previously and the remainder is composed of natural streams that have been deepened, straightened and/or widened to such an extent that reversion to the natural state is not possible. The flow of water in the CAWS is artificially controlled by hydraulic structures. The CAWS has two river systems, the Calumet River System and the Chicago River System.Over the years, increased pollutant loading from urbanization throughout the Chicago metropolitan area and low stream velocities in Chicago area deep-draft waterways have caused dissolved oxygen (DO) concentrations to fall below DO standards established by the Illinois Pollution Control Board (IPCB). More than 30 years ago, the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) determined that applicable IPCB DO standards for Chicago area waterways could not be met exclusively by advanced wastewater treatment. In order to increase the DO concentration in the Chicago and Calumet River Systems, the MWRDGC designed and constructed artificial aeration systems (instream diffuser and sidestream elevated pool aeration [SEPA] stations) during the late 1970s and early 1990s, respectively.In August 1996, the MWRDGC's Research and Development Department began developing a comprehensive field-monitoring program in order to locate and identify reaches in the Chicago River System where the DO concentration is less than the applicable IPCB DO standard. Initially, the program focused on the Chicago River System and in 2001 the study area was expanded to include the Calumet River System. In 2005 eleven new monitoring stations were installed in shallow stream or wadeable locations in the Des Plaines River System, Chicago River System, and Calumet River System. This comprehensive field-monitoring program is referred to as the MWRDGC's Continuous Dissolved Oxygen Monitoring (CDOM) Program.The CDOM program currently has thirty-two active monitoring stations of which twenty are in Chicago area deep-draft waterways and twelve are in Chicago area wadeable streams. Each location has a continuous DO monitor installed and set-up to record DO temperature, and specific conductivity measurements hourly. The monitors are exchanged weekly and the data is downloaded into a custom designed Access® database.Because results of the CDOM program demonstrate non-compliance with water quality standards, the MWRDGC has developed a model of the CAWS to assist in the assessment of alternatives to improve DO in the system. This model has been used to evaluate the influence of flow augmentation to the Upper North Shore Channel using North Side WRP effluent. The MWRDGC has also used the model to investigate installation of additional supplemental aeration stations to meet target DO standards in parts of the CAWS. Finally, the MWRDGC has investigated the use of combining supplemental aeration with flow augmentation to meet proposed DO standards in the South Fork of the South Branch of the Chicago River.