Apparent CFC and 3H/3He age differences in water from Floridan Aquifer springs

The apparent CFC-11, -12 and -113 ages of Upper Floridan Aquifer water discharged from 31 springs located in Florida and Georgia ranged from 11 to 44 years when samples were collected in 2002 and 2003. Apparent 3H/3He ages in these springs ranged from 12 to 66 years. Some of the springs sampled did not yield valid CFC ages because one or more of the CFCs were contaminated by non-atmospheric sources. Of the 31 springs sampled, six were contaminated with all three CFCs and nine were contaminated with one or two CFCs. Of the remaining 16 springs, the CFC distributions of four could be modeled assuming a single source of water, and 11 were best modeled by assuming two sources of water, with one of the water sources > 60 years old. The CFC and 3H/3He apparent ages and the simple mixing models applied to these ages suggest that past impacts to the water quality of water recharging the sampled springs may take anywhere from 0 to ∼60 years or more to appear in the discharging spring water. In 27 springs where both 3H/3He ages and CFC ages were available, five springs gave similar results between the two techniques, while in the other 22 cases the 3H/3He apparent ages were 8-40 years greater than the CFC ages. Large excesses of 4He were observed in many of the springs, consistent with a source of older water. This older water may also carry an additional and unaccounted for source of 3He, which may be responsible for the greater 3H/3He ages relative to the CFC ages. We believe that the large excess 3He and 4He values and apparent age differences are related to regional climate variations because our samples were obtained at the end of a 4-year drought.