48 CONSERVATION OF GROUND WATER 



from wells that tap thin lenses of sand and gravel in the 

 glacial drift. Some lenses are so thin that their initial yield 

 is insufficient for a farm dwelling; others carry enough water 

 to supply a town of several hundred for years. Many of these 

 aquifers are completely enclosed in impervious glacial till, 

 and when water is pumped from them there is no evidence 

 of the replenishment that is required for a perennial supply. 



The situation in Fessenden, N.D., is an example. Under 

 that town there is a sand and gravel lens having an areal 

 extent less than 100 acres and a maximum thickness of about 

 30 feet. Wells in that aquifer supplied the water for the 

 town for 20 years, but only the lower 14 feet of aquifer was 

 still saturated in 1939, and by 1945 all but a 3-foot thickness 

 had been unwatered. In 1941, another sand lens 19 feet 

 thick was located 5 miles northeast of town by test drilling; 

 initially producing 100 gallons a minute, the yield had 

 dropped to 10 gallons a minute by 1944, when there re- 

 mained only 7 feet of saturated sand. In 1945, the town was 

 obtaining only about 20,000 gallons from these two wells, 

 and hauling 15,000 gallons from the town of Heimdal, 12 

 miles away. Subsequently another aquifer was discovered 7 

 miles north of Fessenden and was producing about 70,000 

 gallons per day in 1950. 



The rates at which these aquifers are unwatered suggests 

 that practically all the water is taken from storage — water 

 that may possibly have been in the sand since the glacial 

 epoch. Water in such aquifers constitutes a nonrenewable 

 resource, comparable to petroleum, and the technique of 

 maintaining a perennial supply is similar — prospecting and 

 locating additional aquifers for utilization as fast as the de- 

 veloped sources are depleted. It is possible that there is slow 

 replenishment of unwatered aquifers from the enclosing 

 clay, so that they may be refilled and usable again in several 

 decades. In general, the inhabitants of the area make every 

 effort to locate other and more permanent sources of supply: 

 gravel in present stream valleys or in buried glacial channels, 



