to Ground Water along Coasts. 275 



water. 3 Some valuable information also was obtained 

 during a few days spent on the coast of Florida in 

 April, 1920. 



Previous investigations. — In the United States many 

 geologists and engineers have described contamination of 

 ground-water by sea water, and a few writers have dis- 

 cussed at some length phases of the problem incidental 

 to other investigations. However, there has been no 

 systematic investigation of the problem or serious attempt 

 to assemble and apply the data already published. In 

 Europe, the denser settlement and more intensive devel- 

 opment of water supplies caused the problem to be recog- 

 nized earlier, and in Holland, Belgium, France, and 

 Germany many data have been collected and numerous 

 papers published on the subject. The present writer has 

 used the published material to supplement the informa- 

 tion obtained on the New Haven coast and confirm the 

 conclusions reached. 



Methods of investigation. — In the course of this investi- 

 gation a geologic map of the region was made. Records 

 of wells, springs, and pumping plants and details of their 

 construction, use, and operation were collected. Topo- 

 graphic features were noted carefully. In order to deter- 

 mine the degree of contamination by sea water many 

 samples of water were analyzed. As in many previous 

 investigations, the chloride 4 content of the samples has 

 been used as the chief criterion for determining the 

 presence or absence of sea water. Chloride is not always 

 a reliable indicator of contamination by sea water, for it 

 may come either from salt in the rocks or from sewage 

 and factory wastes. The rocks of Connecticut, however, 

 yield very little salt, and in areas free from polluted 

 drainage the ground water contains but little chloride, — 

 in fact, 10 or 12 parts per million is usually the maximum 

 quantity present from both these sources. 5 In this inves- 

 tigation, it was generally possible to tell from the sur- 

 roundings whether chloride from sewage or waste was to 



3 A complete report, of which this paper is a summary, entitled ' ' A study 

 of coastal ground water, with special reference to Connecticut, " is to appear 

 as a Water-Supply Paper of the U. S. Geological Survey. 



4 The term chloride is used here to denote the chloride radicle (CI). 



5 See Jackson, D. D., The normal distribution of chlorine in the natural 

 waters of New York and New England: U. S. Geol. Survey Water-Supply 

 Paper 144, 1905. 



