. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. WATER SUPPLY AND USE 2000. 1000 1961 1966 1971 1976 1981 1986 Figure 1. Total water use for the 162 largest PWS facilities 1991 and reduction in turbidity, and 2) unless a community is located near a river with sustained flow, then surface water storage (usually an impounding reservoir) must be created, which requires significant capital expendi- ture. Nevertheless, in terms of volume, surface water
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. WATER SUPPLY AND USE 2000. 1000 1961 1966 1971 1976 1981 1986 Figure 1. Total water use for the 162 largest PWS facilities 1991 and reduction in turbidity, and 2) unless a community is located near a river with sustained flow, then surface water storage (usually an impounding reservoir) must be created, which requires significant capital expendi- ture. Nevertheless, in terms of volume, surface water accounts for more than 75 percent of the PWS use in Illinois, and approximately two-thirds of the total popu- lation's domestic supply. Surface water supply systems have been developed in cases where the sustainable yield of the available ground-water resources is inade- quate to serve the needs of the community. Conjunctive use of surface and ground-water resources is also becom- ing an increasingly viable option when a community outgrows the yield of their original source of supply. Sources of Surface Water Supply For the purposes of this project, four surface water supply sources were defined: 1) Lake Michigan, 2) border rivers, 3) intrastate rivers with sustained flow, and 4) reservoirs (both impounding reservoirs and side- channel reservoirs). Table 3 lists the approximate number of facilities by category for four separate years: 1930, 1954, 1970, and 1992. It is not unusual for the number of facilities in each category to differ from one year to the next, given typical changes in water supply practices. Figure 3 lists the change in overall use from 1961 to 1991 for each of these categories. With the exception of Lake Michigan and the border rivers, most surface water supply systems are located in the southern half of Illinois, where ground-water yields are particularly low. Figure 4 shows the location of all surface water withdrawals used for PWS. Lake Michigan. The lake
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