CFC and SF_6 concentrations in shallow groundwaters :implications for groundwater age determination. In : 13 th Water-Rock Interaction 2010, Guanajuato, México, Aug 16-20, P. Birkle ans I.S. Torres-Alvaredo (Eds.) Taylor and Francis Group

CFC12, CFC-111, CFC-113 and SF6 measurements have been carried out during two hydro-logical cycles in a granitic catchment, western France. The well network allowed the variability of the CFC and SF6 concentrations to be investigated in the large, variably saturated zone from 2-3 m down to 6-8 m. All gases show an important variation range which is clearly related to the water table variation. A strong dis-agreement is observed between SF6 and CFC, the later showing systematically older ages, especially before 1990. Laboratory experiments support potential SF6 production and a slight CFC sorption and/or degradation.