User:Redhairrockstar/Floridan aquifer

Geochemistry of Groundwater in the Upper Floridan Aquifer
The most permeable layer within the Upper Floridian Aquifer System is comprised of carbonate rocks, specifically limestone that is almost completely calcite mineralogically. Other minerals found in the lower units include dolomite, gypsum, and apatite. Organic carbon, as peat, is also found throughout the rock units. These inorganic and organic materials affect the alkalinity and pH of the water throughout the aquifer. The pH of this system, from sampled wells, ranges from 7.16 to 8.10. Carbon dioxide (CO2) concentrations affect the geochemistry of the aquifer water, as does the dissolution of carbonate rocks, which is affected by changing water temperatures and CO2 levels. If a water sample is taken from a well that penetrates both the Upper and Lower Floridan Aquifer, then the sample is usually more geochemically of the Upper Aquifer and not the Lower Aquifer because of differences in permeability. This has limited understanding the water quality of the Lower Aquifer.

The chemical composition of the Upper Floridan Aquifer is characterized as being either a calcium-bicarbonate water type, or a calcium-magnesium-sulfate water type, or a sodium-chloride water type. The hardness of the aquifer increases with depth for the Upper Aquifer, due to the increase of dissolved gypsum with increasing depth. Hardness is determined by the concentration of calcium and magnesium ions, although calcium concentrations are among the highest in this aquifer. Higher concentrations of magnesium exist where there is dolomite. Where freshwater and ocean water mix, such as near the coasts, the brackish water can become geochemically supersaturated with respect to calcite. Precipitation of calcite within pore spaces reduces aquifer permeability.

High concentrations of sulfate and chloride are found throughout the aquifer as a result of various geochemical reactions. Gypsum mineral dissolution increases sulfate concentrations in the aquifer. Gypsum is more soluble in seawater, due to the higher ionic strength, and the source rock for gypsum is the Sub-Floridan confining bed. Where the Upper Aquifer is confined, sulfate concentrations are higher than in the unconfined portion of the aquifer. Sea water is a source for chloride, so wells with brackish water have higher chloride concentrations than freshwater wells that are away from the coast.