to Ground Water along Coasts. 279 



the penetration of salt water inland is affected by the 

 character and structure of the rocks along the shore. As 

 just indicated on sandy parts of the Florida coast fresh 

 water saturates the ground almost to the shore line. Yet 

 Sanford 6 says that the main Florida Keys, which are 

 composed chiefly of limestone very full of seams and 

 crevices, "may be underlain by salt water about at tide 

 level; this is the condition in islands as wide as 3 or 4 

 miles in the Bermudas and also on many Florida Keys." 



Sea water in deeper, drilled wells. 



Most of the deeper wells on the New Haven coast were 

 drilled with the percussion type of drill rig and are 6 

 inches in diameter. Wells from 100 to 300 feet deep are 

 fairly common as sources of domestic supply. A few 

 wells of greater depth have been drilled by manufacturing 

 concerns in the hope of obtaining industrial supplies, but 

 most of these have been failures because the quantity of 

 water was insufficient or its quality was unsatisfactory. 

 Out of 29 wells examined, 10 were definitely contaminated 

 by sea water and 2 others probably were slightly contam- 

 inated. Moreover, as wells that yield bad water are 

 generally abandoned and forgotten, and their records are 

 almost impossible of verification, the ratio is really 

 higher. It is not unlikely that half the drilled wells in 

 a zone a few hundred feet wide along the shore are more 

 or less contaminated. 



Xearly all the drilled wells on the New Haven coast 

 penetrate bedrock and draw their water from open joints 

 and crevices. The possibility of obtaining water at all 

 in the crystalline rocks is difficult of prediction, and the 

 likelihood of obtaining salt water in deep wells is doubly 

 uncertain. One well very near the shore may penetrate 

 crevices connected only with the fresh ground water and 

 yield water of good quality; another may penetrate 

 crevices connected with the sea and yield only salt water. 

 Undoubtedly the danger of obtaining salt water increases 

 rapidly with the depth of drilling, and once salt water is 

 struck there is very little chance of finding fresh water 

 at greater depth. The distance inland at which salt 



Matson, G. C, and Sanford, Samuel : Geology and ground waters of 

 Florida, U. S. Geol. Survey Water-Supply Paper 319, p. 261. 



