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Chicago is home to the two largest water treatment plants in the world – the James W. Jardine Water Purification Plant and South Water Filtration Plant – both located on the shores of Lake Michigan. The massive size of the plants alone is overwhelming, not to mention the amount of water that is processed through the facilities each day.
Last year, the plants pumped an average of 1,048 million gallons per day combined, to provide water to over 5 million people throughout Chicago and approximately 118 surrounding communities. The rigorous process followed must meet both United States Environmental Protection Agency and Illinois Pollution Control Board standards.
Each facility uses intake cribs located 2 to 21/2 miles off the shore of Lake Michigan. Water travels from the cribs through large intake shafts, then flows through traveling screens which weed out fish, weeds and other large particles within the water. "Low Lift" pumps are used to raise the water from this point (approximately 20 feet) after which it follows the rest of the process by gravity. The water is treated through the process by chlorine, alum and polymer, blended phosphates, carbon, and fluoride. These chemicals help with disinfection, coagulation, corrosion and lead leaching within pipes, along with taste and odor control. Coagulation of the water is followed by movement into the settling basins.
At the end of the process, water travels through conventional sand and gravel filters and then is routed into the reservoirs. Water is delivered to the pumping stations located throughout the City of Chicago by large underground tunnel systems. (The system is capable of supplying more than 2.5 billion gallons of water each day.) The average pumpage through Jardine and South Water is 661 and 387 million gallons per day, respectively.
In the past few years, the water coming in from Lake Michigan has been exceptionally clean due to the influx of zebra mussels. An adult zebra mussel, a small snail-like water inhabitant, can filter up to one liter of water each day.
The City of Chicago started full operation of the Jardine facility in the fall of 1964. This man-made complex was constructed over part of Lake Michigan, built by a process involving a cofferdam around what would eventually be the perimeter of the plant. The water was then pumped out and the dam filled in with concrete to become what we know today as a massive city works (larger than two football fields) located about 40 yards from the famous Navy Pier. Built in the 1940s, the South Water facility is noted for its age, size, and quality of water.
Monitoring, Data Acquisition
Of course, with such size and responsibility to the community, a large amount of planning and monitoring is required. The Jardine plant has 92 chemical tanks in use, while the South Water facility has 56. These include receiving, storage, and day tanks. These tanks are monitored 24 hours a day at the South Water Plant by the Chemical Application Control Center and the Transfer Center at the Jardine Facility.
Originally, the facility acquired tank data through a simple float gauging system. The Jardine facility upgraded its original system in the early 1980s. Today, levels are monitored to an accuracy of just under one-eighth of an inch with over 90 of L&J Engineering’s MCG 2000 transmitters, coupled to conventional tape and float gauges. These units are equipped with redundant systems to automatically indicate when preset levels are reached.
South Water uses the same data acquisition system as the Jardine Facility. The ranges of flow depend on the demand of each particular chemical. Alum, also used in the coagulation process to settle impurities, is fed at an approximate rate of 20 lbs.—100 lbs. per million gallons of water dependent on water quality (Jardine). Carbon, used from mid-May to November, is strictly for taste and odor control. The range of flow varies upon demand and can be set from a low range of 0—4.5 gallons per minute up to the higher range of 0—40 gpm. This chemical can be fed into 10 different feeders along the process (Jardine Facility). While the Jardine facility has notable ranges of flows, South Water is not lagging behind.
Carbon and alum are fed at an average rate of 25,000 lbs. and 26,500 lbs. per day respectively. Dependent on the need at each facility, the tanks have a side-mounted or top-mounted tape gauge; the installation of these tape gauges is dependent upon the amount of work clearance, which is only a few feet at certain points at Jardine. Fluoride tanks, and most carbon tanks, use an ultrasonic-type gauging system which is connected to L&J Engineering’s 1200SS transmitter.
This system converts an analog signal to digital, displays the data, and transmits the data via the L&J 4-wire digital highway to the system computer. The data from the both types of gauges is fed to the Chemical Applications Control Center/Transfer Center and read continuously.
L & J Engineering’s 3600 mini computer/receiver system, which is an embedded microprocessor, is used throughout the system. This microprocessor is used to gather local information and pass it to the host. At the heart of the system is the MCG 3400 (DOS based) which gathers the data from six satellite clusters of 3600s that are constantly acquiring data.
Each facility soon will upgrade its current system to an L&J Engineering MCG 3900 Inventory Management System. This is a tank gauging and inventory management system designed to run in the Windows 95/98 or NT environment. This system readily interfaces with most PLCs, including the Allen Bradley that is in use at both plants at this time.
Both facilities will upgrade their systems for several reasons: 1) to meet Y2K compliance, 2) to change from a DOS based system to more of a "point and click" system, 3) to get plant-wide data, 4) to enable remote gauging, and 5) to readily link with the SCADA systems currently in use at each facility.
Unlike the Jardine facility, the South Water plant has room for expansion as needed. Both facilities exceed the standards they must meet to provide pure, safe drinking water to the City of Chicago. Neither facility sees a need for changing any part of the process that works so efficiently.