200 CONSERVATION OF GROUND WATER 



are left each year in the area, an average of 1 ton per irri- 

 gated acre. The increasing salinity of the soil has been ac- 

 companied by declining per-acre yields of alfalfa, flax, and 

 winter vegetables. Excess irrigation to remove this salt 

 creates another problem, for the water accumulates in the 

 Salton Sea, and that saline body has been gradually rising 

 to inundate the lowermost cultivated lands. 



Disposal of Wastes 



There are numerous examples of local contamination of 

 ground water by the disposal of wastes, in some cases forcing 

 abandonment of wells. If artificial recharge of underground 

 reservoirs becomes a general practice, such contamination is 

 likely to become more common, unless adequate precautions 

 are taken to prevent recharge by contaminated water. 



sewage 



The disposal of sewage, estimated at 80 to 100 gallons per 

 day per capita, has caused gross pollution of many rivers, and 

 not a stream draining inhabited regions can currently be con- 

 sidered safe for drinking without treatment. Although a siz- 

 able proportion of the sewage goes into cesspools, septic tanks, 

 ponds, or shallow underground leaching devices, the danger 

 of drawing polluted water from wells is far less than in the 

 case of streams. In the recorded instances of polluted water 

 drawn from wells, the great majority have been traced to 

 introduction of contamination at the well and thus indicate 

 faulty well construction; records of an aquifer yielding con- 

 taminated water are rare. 



If powerful influences of protection or purification were 

 not at work in nature, it would be almost impossible to find 

 unpolluted water anywhere. As far as intestinal bacteria are 

 concerned, the accepted standard of safety of water for domes- 

 tic purposes is in the order of one organism per 100 cubic 

 centimeters, or one ten-millionth the degree of pollution that 

 is in sewage. In a large part of the country the ground-water 



