LEARNING OBJECTIVES  

     Degradation of our surface water and groundwater resources is a serious problem, the effects of which may not be fully known for some time.  There are a number of steps we can take to treat water and to minimize pollution.  This section should foster your understanding of the major categories of pollutants, biochemical oxygen demand, how urban processes may cause shallow aquifer pollution, and methods used to restore polluted waters. 

ENVIRONMENTAL ISSUE  -  How Can Polluted Waters Be Restored? 

     The Illinois River begins in the northeast region of the state and flows west and south, draining parts of Indiana and Wisconsin (see map).  From Chicago's Lake Michigan, which is connected to the river by a canal, to the confluence with the Mississippi, is a distance of 327 miles.  The surrounding flood plains, once a mixture of prairie and oak-hickory forest, are now primarily used for raising crops.  Formerly, the river was highly productive, especially in the lower 200 miles; it produced 10% of the U.S. Freshwater fish catch in 1908 (11 million kg, or 24 million lb; 200 kg/ha, or 178 lb/acre).  By the 1970s, the same stretch of river produced a mere 0.32% of the total freshwater fish harvest (4.5 kg/ha or 4 lb/acre).  Two major factors are responsible for the change in the productivity of the Illinois River: diversion of Chicago's sewage from La e Michigan to the river, and agriculture.  A brief history of events related to water quality in the Illinois River is given in the table below. 

 Year                Critical Event                   Environmental Impact 

1854-1855	Heavy rains resulted in untreated sewage from Chicago entering Lake Michigan and then the city's drinking water	Cholera and typhoid epidemic in Chicago
1900	Chicago Sanitary and Ship Canal built to convey sewage away from Lake Michigan and into Illinois River	Waste entered Illinois River; commercial fish yield from river reached peak in 1908
1920	.	Fish populations declined in river
1920-1940	Most cities along river build sewage treatment plants	Some recovery in fish population
1940-1960	Rapid population growth in Chicago and other cities along the river; increase in agricultural acreage	Lower oxygen levels in river; further declines in fish populations; sport fish and ducks declined in backwaters and lakes of the river
1977-199?	Construction of Chicago Tunnel and Reservoir Plan (TARP) to capture and treat sewage overflows initiated	Some improvement in water quality by 1990, but no change in turbidity or total phosphorus; sodium increased

 
 

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