Metropolitan Water Reclamation District of Greater Chicago

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The Metropolitan Water Reclamation District of Greater Chicago (District) protects the health and safety of the public in its service area, protects the quality of the water supply source (Lake Michigan), improves the quality of water in watercourses in its service area, protects businesses and homes from flood damages, and manages water as a vital resource for its service area. The District’s service area is 883.5 square miles of Cook County, Illinois. The District is committed to achieving the highest standards of excellence in fulfilling its mission.


The District’s seven modern water reclamation plants provide excellent treatment for residential and industrial wastewater, meeting permitted discharge limits virtually at all times. The treatment process is protected by a pretreatment program to guard against hazardous substances and toxic chemicals. These are strictly regulated pursuant to federal and state requirements. The District routinely monitors all industries and non-residential sources to assure that wastes are disposed of in an environmentally responsible and lawful manner.

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Treated wastewater, along with runoff from rainfall, enters local canals, rivers and streams that serve as headwaters of the Illinois River system. Stormwater in the separate sewered area is controlled to reduce flood damages by a number of stormwater detention reservoirs. In the combined sewer area, the District’s tunnel and reservoir project has significantly reduced basement backup and overflows to local waterways.

Flow within the District’s waterway system and the Lake Michigan discretionary diversion flow are controlled by three inlet structures on Lake Michigan: Wilmette Pumping Station, Chicago River Controlling Works and O’Brien Lock and Dam. The single outlet control structure is the Lockport Powerhouse and Controlling Works.

While exercising no direct control over wastewater collection systems owned and maintained by cities, villages, sewer districts and utilities, the District does control municipal sewer construction by permits outside the city of Chicago. It also owns a network of intercepting sewers to convey wastewater from the local collection systems to the water reclamation plants.


The District is located primarily within the boundaries of Cook County, Illinois. The District serves an area of 883 square miles which includes the City of Chicago and 125 suburban communities. The District serves an equivalent population of 10.35 million people; 5.25 million real people, a commercial and industrial equivalent of 4.5 million people, and a combined sewer overflow equivalent of 0.6 million people. The District’s 554 miles of intercepting sewers and force mains range in size from 12 inches to 27 feet in diameter, and are fed by approximately 10,000 local sewer system connections.

The District’s Tunnel and Reservoir Project (TARP) is one of the country’s largest public works projects for pollution and flood control. Four tunnel systems total 109 miles of tunnels, 9 to 33 feet in diameter and 150 to 300 feet underground. One reservoir is in operation and construction is in progress on the two remaining reservoirs.
The District owns and operates one of the world’s largest water reclamation plants, in addition to six other plants and 23 pumping stations. The District treats an average of 1.4 billion gallons of wastewater each day. The District’s total wastewater treatment capacity is over 2.0 billion gallons per day.

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The District controls 76.1 miles of navigable waterways, which are part of the inland waterway system connecting the Great Lakes with the Gulf of Mexico . It also owns and operates 30 stormwater detention reservoirs to provide regional stormwater flood damage reduction. The District owns approximately 9,500 acres of property in Cook County for its operations

In conjunction with its biosolids beneficial utilization and farm land application program, the District recycles all biosolids in land application programs in northeast Illinois, and owns over 13,500 acres of land in Fulton County, Illinois, formerly used for biosolids application.

Continuous Dissolved Oxygen Monitoring Program

In 1998, the Metropolitan Water Reclamation District of Greater Chicago (District), initiated a comprehensive field-monitoring program in order to locate and identify reaches in the Chicago River System where the dissolved oxygen (DO) concentration is less than the appli¬cable Illinois Pollution Control Board (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 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 District’s Continuous Dis¬solved Oxygen Monitoring (CDOM) Program.

The CDOM program currently has eighteen active monitoring stations of which twelve are in Chicago area deep-draft waterways and six are in Chicago area wade¬able streams. Each location has a continuous DO monitor installed and set-up to record DO, temperature, and specific conductivity measurements hourly. The monitors are ex¬changed bi-weekly and the data is downloaded into a custom designed Oracle® database. Data is carefully reviewed for accuracy each week according to the quality assurance project plan.

The continuous water quality monitors used to collect this data are manufactured by YSI Incorporated of Yellow Springs, Ohio. In order to protect and safeguard the monitors from marine navigation and vandalism, the monitors are deployed in the field into a fixed length of 8-inch diameter stainless steel pipe, with multiple 2-inch circular openings, vertically mounted on the side of a bridge abutment. Verification of representative data is conducted three times each year to determine if the fixed CDOM location represents the DO concentration across the waterway.

Ambient Water Quality Monitoring Program

The District routinely collects and analyzes water samples from Chicago area waterways within its service area. The waterways are composed of approximately 225 miles of natural and modified rivers or streams, and man-made canals. This monitoring has been undertaken by the District to determine water quality on an ongoing basis and establish a historical record. A historical water quality database exists back to project inception in 1970.

The District’s current program is referred to as the Ambient Water Quality Monitoring (AWQM) program. Monitoring for the AWQM program at 59 sampling stations on 21 waterways began in 2001. Water samples are collected at least monthly at these stations to assess water quality. Surface grab samples are collected at each sample location for the analysis of most measured analytes. These water samples are analyzed for a wide range of parameters including alkalinity, turbidity, biochemical oxygen demand, solids, ammonia, nitrate, chloride, fluoride, phosphorus, total metals, dissolved metals, cyanide, phenol, fecal coliform, escherichia coli, organic priority pollutants, nonylphenol, fats, oils, and grease, and radiochemistry. A special sampling device is used to collect samples for dissolved oxygen analysis and bacterial analysis. Water temperature and pH are measured onsite at each sampling location.
Following collection, the samples are transported to the Cecil Lue-Hing Research and Development Complex at the Stickney Water Reclamation Plant (WRP) and the Organic Compounds Analytical Laboratory at the John E. Egan WRP for analysis. The waterways monitoring data are maintained in computer databases. Exceedances of water quality standards are reported quarterly. Annual summary reports are prepared that assess compliance with applicable IPCB water quality standards and identify long-term trends in water quality.
In addition to the water quality data being collected, the District’s Environmental Monitoring and Research Division collect biological, habitat, and sediment quality at each of the 59 AWQM sampling stations. The biological monitoring portion of the AWQM Program operates on a 4-year cycle, with a primary focus each year on a different river system in the Chicago area. Fifteen of the 59 stations located across all of the waterways are monitored annually.