Occurrence and fate of chlorofluorocarbon plumes in groundwater

Chlorofluorocarbons (CFCs) are stable volatile organic compounds that have been manufactured since about 1930 and appeared thereafter in the atmos- and hydrospheres. Oceanographers use CFC analyses in the pg 1-1 range as tracers for ocean mixing processes. In hydrogeology, it has been suggested that CFCs may be used similarly for age-dating of groundwater. We reviewed studies that report on CFCs in groundwater from 16 porous and fractured aquifers on three different continents. In 12 aquifers, groundwater was found to be locally contaminated with CFCs in concentrations exceeding equilibrium with respect to modem air. Reported sources of contaminants include direct industrial solvent spills, river water infiltration, and landfills. Natural attenuation of CFCs in aerobic aquifers is limited. Evidence that reductive dechlorinat- ion of CFCs is occurring in anaerobic aquifers is provided. Possible degradation products known to be toxic (HCFC-21) or even carcinogenic (HCFC-31) are rarely studied. In order to assess the vulnerability of aquifers, there is a need to better identify these compounds.