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HYDC03 12/5/05 5:36 PM Page 82

82 Chapter Three

BO X
Continued
3.2

A sequence of hydrochemical evolution is observed starting with
calcite dissolution in recharge areas that produces a Ca-HCO dom-
3
inated water type with a TDS concentration of generally less than
−1
250 mg L . Downgradient, dissolution of dolomite leads to a Ca-
Mg-HCO hydrochemical facies. Where gypsum is abundant, sul-
3
phate becomes the predominant anion. In coastal areas, as shown
in Fig. 1, seawater increases the TDS concentrations and the hydro-
chemical facies changes to Na-Cl. Leakage from underlying or adjac-
ent sand aquifers in south-central Georgia enters the Floridan
aquifer and lowers TDS concentrations but does not change the
hydrochemical facies. In the western panhandle of Florida, cation
exchange leads to the development of a Na-HCO water type.
3
The hydrogeological and hydrochemical sections shown in Figs 2
and 3 illustrate the main features of the hydrochemical environ-
ment in south Florida. The confining unit of the Upper Floridan
aquifer is thick along this section and there are evident changes in
the concentrations of the major ions in the general direction of
groundwater flow. Chemical stratification of the Upper Floridan
2+
aquifer may be indicated by the fact that concentrations of Ca ,

Fig. 3 Hydrochemical section along line A–A′ (see Fig. 2)
showing the variation in the concentrations of major ions
downgradient in the direction of groundwater flow. After
Sprinkle (1989).

Mg 2+ and SO 4 2− in water from the Lake June in Winter (LJIW) well
are greater than in water from the downgradient Fort Ogden well,
which is about 100 m shallower than the LJIW well. However, the
−
+
Fig. 2 Hydrogeological section of part of the Upper Floridan Fort Ogden well is nearer the coast and Na and Cl concentrations
aquifer. The line of section A–A′ from Highlands County to increase by about three times compared with concentrations at the
Charlotte County is shown in Fig. 1. After Sprinkle (1989). LJIW well.