FLORIDA GEOLOGICAL SURVEY has occurred in some parts of the county since about 1948, because of an increase in water use. Determinations of the chloride content of the artesian water indicate saltwater contamination in a zone about 3 to 10 miles wide along the coast. The degree of contamination increases with depth and seaward. Throughout most of the zone, the water in the Tampa formation contains less than 250 parts per million (ppm) of chloride and is suitable for most purposes, but some wells in the vicinity of Palma Sola Bay yield water from the Tampa formation containing more than 400 ppm of chloride. The chloride content of the water in the Suwannee limestone is more than 2,000 ppm at some places but is generally less than 500 ppm. The water in the Eocene formations along the coast is probably too salty for most uses. Periodic analysis of the water from many wells shows that the chloride content varies with the seasonal Huchwtions of artesian pressure head. Some wells that show a progressive decline in artesian pressure head also show a progressive increase in chloride content of the water, indicating that significant declines in head result in upward movement of salty water from the deeper formations. This upward movement is probably retarded considerably by the beds of low permeability that separate the principal water-bearing zones.
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