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Publication Abstract

7-Day, 10-Year Low Flows of Streams in Northeastern Illinois Singh, Krishan P., and Ganapathi S. Ramamurthy, 1993  Illinois State Water Survey, Champaign, IL,  ISWS CR-545    Full Text Available

The 7-day, 10-year low flows, or Q7,10 ,values for Illinois streams, under the 1970 condi- tions of municipal and industrial effluent discharges, were derived and presented in Illinois State Water Survey (ISWS) Bulletin 57 (Singh and Stall, 1973). The Bulletin contains 11 maps, which show the Q7,10 flows for all rivers and streams in Illinois, together with the effluent discharges and their locations, adjusted for effects of any flow regulation and consumptive use of water. These low flow values have been used by the Illinois Environmental Protection Agency (IEPA) in assessing the desirable level of treatment at a wastewater treatment facility, depending on the Q7,10 value in the receiving stream. The Q7,10 values for streams in northeastern Illinois (map 2 in Bulletin 57) were updated for 1980 conditions of effluents and water withdrawals in ISWS Contract Report 307 (Singh, 1983). The Q7,10 values for streams in the remainder of the state were updated for 1984 conditions of effluents and water withdrawals in ISWS Contract Reports 440 and 441 (Singh et al., 1988a, 1988b). The Q7,10 map for the northeastern region of Illinois covers the area drained by the Chicago Sanitary and Ship Canal and its tributaries, and Des Plaines, Du Page, and Fox Rivers. The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) operates three major wastewater treatment plants: Northside, West-Southwest (Stick- ney), and Calumet. Since the mid-1970s three new medium-sized plants have been put into operation: Hanover Park, John Egan, and O'Hare. The North Shore Sanitary Dis- trict (NSSD) is also operating three new wastewater plants: Waukegan, Gurnee, and Clavey Road. The population in certain areas has increased or decreased and there have been changes in industrial activities. These have led to changes in municipal and indus- trial effluent discharges. Many industries have also decreased their effluent discharges through recycling and conservation measures. These changes for northeastern Illinois and similar changes for the rest of the state necessitate that the Q7,10 flows and relevant information be updated for the 1990 conditions of effluent discharges and any flow regulation. The information on municipal and industrial effluent discharges was collected from the IEPA office in Springfield, Illinois, and from various municipalities and industries by correspondence or telephone inquiries. The change in town populations from 1970 to 1990 was analyzed with regard to change in effluent flow for purposes of verification and identification of any special circumstances. The daily streamflow data at the streamgaging stations in northeastern Illinois were analyzed to develop values of 7-day lowest flow each year as well as the Q7,10 flow, both with and without effluent contributions. Finally, a map was prepared showing the Q7,10 flows (adjusted for the 1990 conditions of effluent discharges to the streams and any water withdrawals for industrial uses) of the various streams and rivers in northeastern Illinois.

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