Evidence for the removal of CFC-11, CFC-12, and CFC-113 at the groundwater–surface water interface in the Everglades

Authors

James D. Happell, Division of Marine and Atmospheric Chemistry, Rosenstiel School of Marine and Atmospheric Science, University of MiamiFollow
René M. Price, Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, University of Miami, MiamiFollow
Zafer Top, Division of Marine and Atmospheric Chemistry, Rosenstiel School of Marine and Atmospheric Science, University of MiamiFollow
Peter K. Swart, Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, University of Miami,Follow

Abstract

Poor agreement between ³H/³He ages and CFC-11 and CFC-12 ages suggests that CFCs may not be conservative tracers in the Everglades National Park. ³H/³He ages were used to calculate the expected concentration of CFC-11 and CFC-12 in groundwater from wells 2 to 73 m deep. The expected concentrations of CFCs were compared to the measured concentrations and plots of the % CFC-12 and CFC-11 remaining offered no evidence that significant CFC removal was occurring in the groundwater at depths ≥2 m, suggesting that CFC removal occurs at shallower depths. Except where CFC contamination was suspected, CFC-11, CFC-12 and CFC-113 concentrations in fresh surface water were nearly always below solubility equilibrium with the atmosphere. Measurements of CFC-11, CFC-12 and CFC-113 in pore water indicate a 50–90% decrease in concentration 5 cm below the groundwater–surface water (GW–SW) interface. In the same 5 cm interval CH₄ concentrations increased by 300–1000%. This suggested that CFCs were removed at the GW–SW interface, possibly by methane-producing bacteria. CFC derived recharge ages should therefore be viewed with caution when recharging water percolates through anoxic methanogenic sediments.

Comments

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Recommended Citation

Happell, J.D., R.M. Price, Z. Top, P.K. Swart. 2003. Evidence for the removal of CFC-11, CFC-12, and CFC-113 at the ground water-surface water interface in the Everglades. Journal of Hydrology 279: 94-105.