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, 6 were contaminated with all 3 CFCs and 9 were contaminated with 1or 2 CFCs. Of the remaining 16 springs, the CFC distributions of 4 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, 5 springs gave similar results between the two techniques, while in the other 22 cases the ³H/³He apparent ages were 8 to 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.