Home Abstract Introduction - Purpose and Scope > Previous Investigations - Acknowledgments Hydrogeology of S. Florida Ground-Water Movement Subsurface Storage Summary and Conclusions References PDF Version

Introduction: Previous Investigations

Regional aspects of the hydrogeology of the Floridan aquifer system (also referred to as the "Vicksburg artesian limestones," the "principal artesian formation," the "principal artesian aquifer," the "Floridan aquifer," and the "Tertiary limestone aquifer system") in southern Florida were reported by Sellards and Gunter (1913), Stringfield (1936, 1953, 1966), Parker and others (1955), Kohout (1965, 1967), Vernon (1970, 1973), and Miller (1982a, 1982b, 1986). Hydrogeologic studies of a local nature were reported by Schroeder and others (1954), Bishop (1956), Lichtler (1960), McCoy (1962), Klein and others (1964), Meyer (1971, 1974), Sproul and others (1972), Boggess (1974), Sutcliffe (1975, 1979), Cram and others (1975), Wilson (1977), Reece and others (1980), Smith and others (1982), and Wedderburn and others (1982). Potentiometric surface maps, which indicate the direction of ground-water movement in the upper part of the aquifer system, were compiled by Stringfield (1936), Parker and others (1955), Healy (1975a, 1975b, 1982), and Johnston and others (1980, 1981). The various uses of the Floridan aquifer system in southern Florida are presented by Garcia-Bengochea (1970), Garcia-Bengochea and Vernon (1970), Vernon (1970), Vecchioli and others (1979), Merritt and others (1983), and Merritt (1985).

The use of natural isotopes as tracers in studies of ground-water movement in the Floridan aquifer system began in the early 1960's with estimates of ground-water velocities in the upper part of the aquifer system in central Florida by Hanshaw and others (1965), who used carbon-14. Results of their study indicated that although absolute ages of the ground-water samples may be unreliable, the relative ages of the samples are reason-ably reliable for estimating rates and direction of ground-water movement. In a later study of the same area, Plummer (1977) examined transient changes in water chemistry in relation to the earlier carbon-14 ages, and new ages (slightly younger) were assigned to the Hanshaw samples on the basis of mass-transfer reaction coefficients.

Pearson and Bodden (1975, p. 143) reported the first results of carbon-14 analyses of ground water from the Floridan aquifer system in southeastern Florida. The samples were obtained from the upper and middle parts of the aquifer system, and the uncorrected activities of 5.6 and 4.3 percent of modern carbon (PMC) were anomalous compared with Hanshaw's results in central Florida (that is, the samples seemed to become younger with increasing distance from the recharge areas in central Florida). Hanshaw and Back (1971), in studies of the origin of dolomite in the Floridan aquifer system, used stable isotope ratios of carbon-13/carbon-12 (¹³C) and oxygen-18/oxygen-16 (¹⁸O) to distinguish between marine (primary) dolomite and nonmarine (stoichiometric) dolomite. Tamers and others (1975) related carbon-14 ages to ground-water movement in the surficial aquifer of southeastern Florida.

The use of naturally occurring uranium isotopes as tracers of ground-water movement in the Floridan aquifer system also began in the early 1960's (Osmond and others, 1968). The alpha-activity ratio (AR) of uranium-234/uranium-238 and uranium concentrations were used to infer circulation patterns (Osmond and others, 1968). Cowart and others (1978) compared the alpha-activity ratios and uranium concentrations in three samples of saltwater from the lower part (Boulder Zone) of the Floridan aquifer system in southeastern Florida with ratios and concentrations in modern seawater. They concluded that the saltwater originated in the Straits of Florida, thereby supporting Kohout's hypothesis. Cowart and others (1978) also concluded that low alpha-activity ratios (less than unity) in samples of brackish water from the upper part of the system in the Florida Keys may indicate the presence of highly transmissive zones containing relic waters that are residual of rapid circulation from the recharge area when sea level was much lower.