304 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



are indeed very large, and the quantities that they will yield from 

 storage merely through the compression that results from the release 

 of artesian pressure of the confined water apparently may amount 

 to millions of gallons a day for many years. It is believed that the 

 phenomenon of compression with decrease in artesian pressure 

 has been demonstrated to be of primary importance in the study of 

 the perennial yield of these artesian sandstones, but the mode of com- 

 pression has not been given much investigation. Presumably com- 

 pression occurs largely in the strata of relatively fine grain which feed 

 into the strata of coarser grain that supply the wells. The phenom- 

 enon of reexpansion with increase in artesian pressure is also known to 

 occur to a considerable extent. It is more difficult to explain than 

 the compression but is probably also more characteristic of strata of 

 relatively fine grain than of the most productive water-bearing beds. 



It appears that the spectacular discharge of artesian water from 

 the Dakota sandstone for more than half a century has been supplied 

 to a great extent from storage, largely as a result of the elastic or com- 

 pressive properties of the system. It remains to be determined 

 whether the more moderate withdrawals that are likely to be made in 

 the future will be replaced by recharge or will result in further pro- 

 gressive depletion. The 800-foot sand in the Atlantic City area has 

 yielded water freely for several decades and is currently yielding 

 several millions of gallons a day. It shows encouraging recovery of 

 head whenever the rate of pumping from wells is diminished. How- 

 ever, a 13-year record obtained by the investigators in that area 

 seems to show that the regional cone of depression is still expanding, 

 and that with the resulting compression some water is still being 

 taken from storage. Other great artesian sandstones, such as those 

 which for many years have furnished the water supplies of Memphis 

 and Houston, are known to have large annual recharge, but neverthe- 

 less further records are needed to determine definitely the source of 

 the current pumpage — to what extent the pumped water is replaced 

 by recharge and to what extent it is derived from storage by the 

 further development of the regional cones of depression. 



About 6,500 public watenvorks in this coimtry are supplied from 

 wells. Many of these obtain their water from surficial formations 

 with true water-table conditions and many others from recognized 

 artesian formations. However, there is another large group of water- 

 works that are supplied from aquifers, largely in the glacial drift, 

 that are not usually regarded as artesian and yet underlie more or less 

 effective confining beds and are recharged by somewhat devious 

 percolation of the ground water. More attention ought to be given to 

 the problems of depletion and safe yield of these aquifers of inter- 

 mediate character. 



