292 J. S. Brown — Relation of Sea Water 



The variation shows the influence of variations in pre- 

 cipitation and apparently also in temperature. The 

 extremely high chloride in June and the first part of July 

 represents the effect of a month of very light rainfall, 

 accompanied by rising temperature. The steady de- 

 crease of chloride from July 12 to July 26 is the result 

 of heavy, well-distributed rainfall, and the increase in the 

 week of July 26 to August 2 coincides with a week of 

 light rainfall. The great decrease in chloride between 

 August 2 and September 6 is. evidently the result of heavy 

 rains, particularly on September 2 and 3, when 3.72 inches 

 fell. The increase noted in the following week, Septem- 

 ber 6-13, apparently represents the effect of gradual 

 rediffusion of salt after the flood of fresh ground water 

 had subsided. Undoubtedly careful tests at more fre- 

 quent intervals would show many irregularities of the 

 curve due chiefly to the variable precipitation, but the 

 general form would agree more or less closely with that 

 of a yearly temperature curve, although the spring rise 

 would lag considerably behind the rise in the temperature 

 curve, because the frost is slow to leave the ground in 

 spring — that is, the ground warms more slowly than 

 the air. 



The influence of temperature appears in different ways. 

 Higher temperature increases evaporation. It also 

 greatly increases the rate of percolation, so that ground 

 water seeps out to sea more freely and salt water diffuses 

 landward faster. Slichter 17 states that a change of tem- 

 perature from 32° to 75° F. will practically double the 

 power of a soil to transmit water, and that a change from 

 50° to 60° will increase the rate of flow 16 per cent. The 

 influence of humidity is also a factor, and the rate of 

 transpiration by plants is important. The island on 

 which the well is situated supports a grove of trees and 

 a grassy lawn, which transpire much of the precipitation 

 in the summer season. The net result, as indicated, is a 

 remarkable increase of salinity in summer. 



Observations on two drilled wells in bedrock, although 

 not so complete as those on the Beattie well, strengthen 

 the evidence that certain contaminated wells are most 



17 Slichter, Chas. S. : Field measurements of the rate of movement of 

 underground waters, U. S. Geol. Survey Water-Supply Paper, 140, p. 13, 

 1905. 



