236 CONSERVATION OF GROUND WATER 



rate of movement of water through the reservoir and therefore 

 in the yield of wells or springs. These several geologic and 

 hydrologic characteristics of an aquifer, plus information con- 

 cerning the position of the water table or piezometric surface 

 throughout the ground-water reservoir, are the basis for quan- 

 titative determinations of storage and movement within the 

 reservoir. Thereafter, changes in storage and movement may 

 be calculated from fluctuations of water level in representative 

 wells. 



The amount of recharge may be indicated by the losses from 

 the soil zone, stream, or other ground-water reservoir which 

 has contributed the water. Any increment to storage must also 

 affect the position of the water table in the recharge area. 

 Therefore a coordinated analysis of records of infiltration, 

 soil-moisture storage and discharge, stream seepage, and 

 ground-water storage in the recharge area is needed for a 

 thoroughgoing determination of ground-water recharge. Sim- 

 ilarly, determinations of natural discharge from a ground- 

 water reservoir require adequate data as to evapotranspira- 

 tion, outflow in springs, and seepage to streams, as well as 

 decreases in ground-water storage. 



The quality of ground water is a field in itself, of especial 

 interest to the chemist, but of concern to all users of water 

 because most of the mineral matter in water is dissolved from 

 rock materials and therefore comes from ground water. An 

 understanding of variations in quality of water in various 

 parts of a ground-water reservoir requires also a knowledge of 

 the geology and the movements of water in the reservoir. 



For several ground-water reservoirs, particularly in the 

 West, hydrologic studies are sufficiently advanced to permit 

 calculation of seasonal changes in storage and of recharge and 

 discharge; estimates have been made of the total volume of 

 water stored in some ground-water reservoirs, for instance, in 

 the High Plains in Texas (page 28). Experience has shown that 

 considerable expense is entailed in the quantitative determi- 

 nation of the hydrologic characteristics of aquifers, particularly 

 where test drilling and special pump installations are involved. 



