144 CONSERVATION OF GROUND WATER 



satisfactory as a source of ground-water recharge than the 

 streams in many another of the nation's watercourses. Hy- 

 drologic interpretation of water analyses has confirmed this 

 conclusion and shown that only about a third of the water 

 pumped from wells is replaced by river infiltration. Of the 

 37 million gallons a day pumped in the Peoria and East 

 Peoria well fields, only about 14 per cent was concluded to 

 be of river origin, and most of that came from the small 

 tributary, Farm Creek. On the other hand, about 75 per 

 cent of the 1 1 million gallons a day pumped from the Pekin 

 well field is evidently replaced from the river. The Pekin 

 field, however, is below the dam on the Illinois River which 

 stabilizes Peoria Lake by maintaining a minimum pool stage 

 440 feet above sea level. The silt which has accumulated in 

 this lake to an average depth of 10 feet may well impede 

 recharge near Peoria. In the past 17 years the greatest de- 

 cline of water levels in several observation wells occurred 

 during the three years after the dam was placed in opera- 

 tion. Recharge to the ground-water reservoir apparently oc- 

 curs only when the river rises well above the pool stage 

 created by the dam. 



The Illinois Water Survey has had favorable results in 

 experiments to recharge the ground-water reservoir by 

 pumping river water into large filter beds. In addition, 

 buried glacial valleys with large volumes of permeable 

 gravel have been located northwest of Peoria and about 

 20 miles east of Peoria. These ground-water reservoirs con- 

 stitute potential additional sources of water. 



This listing of problems encountered in developing ground 

 water along some watercourses does not give a fair picture of 

 the potentialities of such sources for additional supply in many 

 places. One should also cite Dayton, Ohio, where wells pump 

 about 90 million gallons a day and receive full replenishment 

 from the Miami and Mad Rivers. Or the East St. Louis-Alton, 

 111., industrial area where 85 million gallons a day are 

 pumped: in an area of about 2 square miles the water table 



