44 CONSERVATION OF GROUND WATER 



is tapped by most wells, is thus confined between bad waters. 

 Many wells are perforated in both upper and middle 

 aquifers for the purpose of drawing some water from the 

 upper horizon and diluting it with the more usable water 

 that comes from below. Needless to say, this construction 

 provides means of access of bad water into the heavily 

 pumped middle zone when the wells are idle. 



It is possible that the reservoir can eventually be re- 

 charged artificially through wells, but the methods at- 

 tempted to date have not been successful. If the present 

 irrigation economy is to be perpetuated, it appears that 

 water must be imported from other areas. 



A few ground-water reservoirs receive very little replenish- 

 ment because of unfavorable geologic conditions. There un- 

 doubtedly are some reservoirs where the water was accumu- 

 lated long ago and is now trapped with little opportunity for 

 either recharge or discharge under present conditions. En- 

 trapment of water in rocks is not uncommon, and there are 

 numerous localities where water has remained in rocks since 

 their deposition. Connate water has been encountered in many 

 wells, but generally it is saline and unusable, a remnant of 

 the sea in which the rocks were deposited. Some ground-water 

 reservoirs may contain fresh water entrapped since the deposi- 

 tion of the rock materials, but no specific examples are yet 

 recorded. 



Several reservoirs contain appreciable amounts of water in 

 storage but are prevented from receiving more than negligible 

 recharge by enclosing or overlying impermeable materials. 

 The waters in such reservoirs may be exceptions to the rule 

 that ground water is a renewable resource, for the aquifers 

 obviously cannot be counted on for perennial supply. It is 

 inevitable that the reservoirs will be depleted when wells 

 pump from them. The examples cited below are remarkable 

 for their contrasts: in the Drift Prairie the aquifers hold only 

 small quantities of water, but in the High Plains and the 

 Grand Prairie there is a vast amount of water stored under- 



