Blue Island

The city of Chicago conducts ongoing monitoring for Cryptosporidium, Giardia and E. coli in source water as part of its comprehensive water quality program. To date, Cryptosporidium has not been detected in these samples, though Giardia was identified in one raw lake water sample collected in September 2010.

Treatment processes have been specifically optimized to create effective barriers against Cryptosporidium oocysts and Giardia cysts in source water, successfully removing these microorganisms during treatment. By maintaining low turbidity through contaminant removal, the risk of these organisms entering the municipal water system is significantly reduced.

In 2017, the Department of Water Management (DWM) continued monitoring for hexavalent chromium (chromium-6). The USEPA has not established a standard for chromium-6, a contaminant with both natural and industrial origins. For questions about this monitoring program, please contact DWM's Water Quality Department at 312-742-7499. Reports on the chromium-6 monitoring program are available at: http://www.cityofchicago.org/city/en/depts/water/supp_info/water_quality_resultsandreports/city_of_chicago_emergincontaminantstudy.html

SOURCE WATER ASSESSMENT OVERVIEW
The Illinois EPA implemented a Source Water Assessment Program (SWAP) to assist with watershed protection of public water supplies. The SWAP identifies potential contamination sources and evaluates source water susceptibility to contamination. The Illinois EPA has completed the assessment for our source.

SOURCE WATER AREA
Chicago utilizes Lake Michigan as its source water via two water treatment plants. The Jardine Water Purification Plant serves northern areas of the city and suburbs, while the South Water Purification Plant serves southern areas. Lake Michigan is the only Great Lake entirely within the United States. It borders Illinois, Indiana, Michigan, and Wisconsin, and is the second-largest Great Lake by volume (1,180 cubic miles) and third largest by area.

SUSCEPTIBILITY TO CONTAMINATION
The Illinois EPA considers all surface water sources of community supply to be susceptible to potential pollution problems. The very nature of surface water allows contaminants to enter intakes with no protection other than dilution. Chicago's offshore intakes are positioned far enough from shore that shoreline impacts are rarely considered a factor in water quality. However, at certain times, there is potential for contamination due to wet-weather flows and river reversals. Additionally, the crib structures may attract waterfowl, gulls and terns that frequent the Great Lakes area, thereby concentrating fecal deposits at the intake and compromising source water quality. Conversely, the shore intakes are highly susceptible to storm water runoff, marinas and shoreline point sources due to the influx of groundwater to the lake.

.. ...