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Two gypsum (phosphogypsum) stack complexes, the AMAX, Inc., plant at Piney Point in Manatee County and the U.S. Steel Agri-Chemicals plant at Bartow in Polk County, were chosen for intensive study of the movement and chemical modification of process water seeping into ground water. A third site, a slime pond at the International Minerals and Chemical Corporation mine near Bartow, was also selected for intensive study. The composition of the process water in the entire system of gypsum stacks, ponds, and ditches is virtually the same. This highly acidic water has a dissolved-solids concentration of about 28,000 milligrams per liter, a pH of 1.4 to 1.8 units, and contains sodium, phosphate, fluosilicate, hydrogen, and sulfate ions as major constituents. The concentration of most other ions are also higher in the process water than in the native ground water and surface water of central Florida. The native ground water has a dissolved-solids concentration of less than 500 milligrams per liter and is calcium bicarbonate water with a pH near 7.0 units; the ambient ground water at the plant sites is similar in composition. Water drawn from shallow, water-table test holes within a few hundred feet of circulating process water reflects the contaminant source by increased concentrations of almost all constituents compared to the native ground water, although no contaminant-enriched ground water sampled showed ionic concentrations as high as the contaminant source. Migration of process water to great distances or into deep artesian zones is less easily recognizable because of dilution and reactions of process water with aquifer materials. For all wells sampled, water-quality constituents related to health were found to be within safe limits at distances of 1,500 feet or more from a contaminant source except for one sulfate concentration of 750 milligrams per liter. Water from many wells, however, were within safe limits at much shorter distances from a source. Sodium and sulfate ions are the most mobile of the contaminant-source constituents in process water. Migration of radionuclides, fluosilicates, phosphates, and trace metals is largely controlled by the degree of acid neutralization as the result of reaction with aquifer materials, and is generally restricted to areas immediately adjacent to the source. Iodide, bromide, and ammonium are useful as tracers near gypsum stacks. These tracers may distinguish the contaminant plume of process water where the existence of the contaminant is more subtle because of reduction in overall concentration of the contaminant due to acid neutralization and chemical precipitation. All contaminants are removed or reduced in concentration in the ambient ground water with distance traveled. Concentrations of contaminants are controlled by the degree of reaction with aquifer materials and dilution by native water; thus, the movement and chemical modification of the contaminant-enriched plume can be documented. The mechanisms involved, which includes adsorption, dispersion, dilution, radioactive decay, and other chemical and physical processes, can be inferred for some constituents the degree of acid neutralization with aquifer materials being the most significant mechanism. Ion indices for the major ions have been developed as an approach to distinguish between native and industrial sources of solute. Results of ion indices and concentrations of selected constituents suggest that both surficial and underlying artesian aquifers are contaminated in the recharge area at the Bartow site and also at the Piney Point site, which can be either a recharge area or a discharge area depending on the time of year. Phosphate slimes from mining and beneficiation operations were found to contain phosphorus, trace metals, and radiochemicals. These substances were associated with solid materials and were effectively retained by the slime pond. The quality of water of the slime pond after settling was good for constituents determined and satisfies primary (U.S. Environmental Protection Agency, 1976) and secondary drinking water regulations (U.S. Environmental Protection Agency, 1977). Water with elevated specific conductance was associated with high water levels in the artesian aquifer near the slime pond, indicating that a hydraulic connection exists between the pond and the first artesian aquifer. The spatial distribution of water with high specific conductance with respect to the slime pond and mining pit suggests that the slime pond is contributing some water and, thus, some solute to the surficial aquifer, although solute contributions are much less than that associated with gypsum stacks. Rainfall associated with haze and stagnant air at Bartow had specific conductances of 290 and 347 micromhos per centimeter. After the atmosphere was cleansed by wind and rain, rainfall samples had specific conductances of 23 and 43 micromhos per centimeter. Calcium, ammonia, bicarbonate $ and sulfate were the predominant ions found in rainfall. Knowledge of local and regional geology and geohydrology are important for site selection and site interpretation. This report documents the nature, magnitude, and extent of the process-water movement into the adjacent ground water. The report will assist the phosphate industry and regulatory agencies in determining the seriousness and significance of this movement as well as managing water resources and the storage of solid waste more effectively.

Effects of three phosphate industrial sites on ground-water quality in central Florida, 1979 to 1980