Hydrology and Chemistry of Ground Waters in the Central Florida Phosphate District
Published Online: 15 MAR 2013
Copyright 1989 by the American Geophysical Union.
Florida Phosphate Deposits: Tampa to Jacksonville, Florida June 30-July 7, 1989
How to Cite
Scott, T. and Cathcart, J. (1989) Hydrology and Chemistry of Ground Waters in the Central Florida Phosphate District, in Florida Phosphate Deposits: Tampa to Jacksonville, Florida June 30-July 7, 1989, American Geophysical Union, Washington, D. C.. doi: 10.1029/FT178p0039
- Published Online: 15 MAR 2013
- Published Print: 1 JAN 1989
Print ISBN: 9780875906317
Online ISBN: 9781118666982
- Floridan aquifer system;
- Ground waters in Central Florida Phosphate District;
- Intermediate aquifer system;
- Pollution and chemical plants;
- Surficial aquifer system
Ground-water quality in the central Florida phosphate district is remarkably good. The only major concerns involve radiation and localized contamination around agrichemical plants.
There are three hydrostratigraphic horizons in the district. The water chemistry of each reflects the composition of the host rock. The surficial aquifer system is predominantly quartz sand. Water in this system is unconfined and usually slightly acid-, iron- and organic-rich. The surficial aquifer system is separated from an uppermost artesian aquifer, a component of the intermediate aquifer system, by clay-rich sediments of the phosphatic Hawthorn Group. The uppermost aquifer (artesian) is a highly localized series of permeable, sandy strata within the upper Hawthorn Group. Water quality is highly variable and concentrations of phosphorus, fluorides and radionuclides are of concern. Clays and silts in the lower Hawthorn Group comprise the intermediate confining unit which separates the secondary artesian aquifer or upper Floridan aquifer system from the uppermost artesian aquifer. The upper Floridan aquifer system consists of limestones and dolostones of the Arcadia Formation, especially the Tampa Member. The Floridan aquifer system often lies below a regionally persistent clay horizon in the Tampa Member and consists of the lower Tampa Member of the Arcadia Foramtion, Suwannee Limestone, Ocala Group and Avon Park Formation. Floridan aquifer system horizons are karstic and water quality is typical of carbonate aquifers.
Radiation in ground water is a result of weathering of uranium-bearing phoshorites. The radionuclides of concern are radium-226, radon-222, and polonium-210. Other uranium and thorium daughters are present, but are not considered hazardous. Gross-alpha and radium activities exceed state and federal standards in scattered wells. In general, these high radiation activities are not considered to be a result of phosphate mining. They are a result of natural releases from mineralized strata. Mining activities do, however, redistribute the radioactive materials.
Chemical processing of the phosphate ore involves dissolution of fluorapatite with sulfric acid. This process results in large accumulations of slightly radioactive waste-gypsum and highly acidic waste process water. Both are contained at plant sites and pose little threat to regional ground water; however, concern remains and examples of ground-water contamination have been documented.