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Sulfate Concentration in Water


The Floridan aquifer, which underlies all of Florida, yields water with a sulfate content of less than 50 parts per million in the north-western part and throughout most of the center of the State. In the southern part of Florida and along the most of the east coast, the sulfate concentration generally exceeds 100 parts per million and is as much as 1,700 parts per million. The sulfate concentration tends to be higher in the deeper zones of the aquifer. This map shows the sulfate concentration in the upper part of the aquifer.

Sulfate is found in almost all natural water. Sulfate in rainwater is dissolved from impurities and gasses in the atmosphere. Rankama and Bahama (1955, p. 314) report that the average sulfate content of rainwater is two parts per million; however, concentrations have been as high as 283 parts per million. Much of the sulfate in rainwater comes from hydrogen sulfide gas which is generated in shallow water on the continental shelves. The combustion of bituminous coal used for heating and industrial purposes seems to be an important local source of sulfate.

Sulfate may also be dissolved from materials on the surface of the ground. Decaying organic matter such as leaves and trees is the primary source of this sulfate. The amount of sulfate contributed from this source will generally be small. Sulfate may be discharged in numerous industrial wastes such as those from tanneries, pulp mills, textile mills, and other industries that use sulfate compounds.

After the water enters the ground, the sulfate concentration may increase. This increase may be a result of leachings from gypsum and other sulfate minerals as the water percolates through the ground. Other sources include connate water (water that was trapped in the rocks when they were formed), salt water from the ocean, or by pollutants.

The U. S. Public Health Service recommends the sulfates not exceed 250 parts per million in drinking water except where a more suitable supply is not available. This limit is not based on taste or physiological effects other than a laxative action on new users. Public water supplies with sulfate concentrations above 250 parts per million are commonly used without adverse effects.

William J. Shampine, "Sulfate Concentration in Water from the Upper Part of the Floridan Aquifer In Florida" Prepared by United States Geological Survey in cooperation with the Bureau of Geology, Florida Department of Natural Resources Tallahassee, Florida, 1965, revised 1975.


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