In December 1956 the U. S. Geological Survey, in cooperation
with the Florida Geological Survey and the Board of
County Commissioners of Pinellas County, collected waterlevel
and chloride content of water in 94 wells in Pinellas
County. First sampled in 1947, resampling and reanalyzing the water
from these wells was used to determine the change in the chloride
content of the ground water from 1947 to 1956. The chloride
content of ground water is generally a reliable indication of
the contamination of ground water by sea water, as 90 percent of the dissolved solids of sea water are chloride salts. (PDF contains 15 pages.