6 CONSERVATION OF GROUND WATER 



movement of water through earth materials. If water is unable 

 to move toward a well rapidly enough to replace the water 

 pumped out, the pump inevitably takes water from progres- 

 sively greater depth in the immediate vicinity of the well, the 

 pumping lift and cost of pumping increase, and the well even- 

 tually may be pumped dry. This certainly indicates a shortage 

 of water at the well but not necessarily an insufficiency of 

 water in the ground-water reservoir. Indeed, water levels have 

 declined markedly in small portions of some reservoirs whose 

 recharge areas are annually filled to overflowing; but the re- 

 charging water moves too slowly to the areas where wells are 

 pumped. In ground-water reservoirs being emptied because 

 the total replenishment is less than the draft, pumping from 

 closely spaced wells accelerates the declining trend of water 

 levels in some areas. 



Pumping from closely spaced wells has caused significant 

 declines of water level in parts of nearly every state (see Plate 

 III), chiefly in municipal or industrial areas that use large 

 quantities of ground water. Water levels have reached ap- 

 proximate equilibrium in some of those areas, indicating that 

 the pumped water is now being replaced by water transmitted 

 through the aquifer. In other areas the water levels are still 

 declining each year. Concentrated draft has induced inflow 

 of ocean water or other unusable water to some wells. In 

 several places along the Atlantic, Gulf, and Pacific Coasts, 

 wells have been abandoned because of this contamination. 



The greatest recorded declines of water levels have been in 

 areas of concentrated draft from artesian aquifers. Wells in 

 many localities reach water that once was under sufficient 

 pressure to flow at the surface, or at least to rise above the top 

 of the aquifer that holds the water. The artesian pressure is 

 created by a capping layer of impermeable material over the 

 aquifer, and the water taken from artesian wells must be re- 

 plenished by movement from recharge areas that may be many 

 miles distant. If the pumpage exceeds the underground flow 

 from the recharge areas, a decline of water levels is inevitable. 



In the areas of local overdraft perennial supply can be as- 



