Présentations Colloques

Oral Presentation
8.04
Session 8.04: Isotopic and residence time tracers
Henriot Abel
Inferring groundwater ages in complex aquifers using gas tracers and tritium.
The determination of transit time distributions in complex aquifers with environmental tracers might be affected by a series of processes. We compare results from a 50-years’ time series of a water-bound tracer (3H) and a complete set of gaseous environmental tracers (85Kr, 39Ar, CFCs, SF6) sampled at a single date. Study area is the complex aquifer system of Evian (French Alps).The interpretation using lumped parameter models and 3H data is not sensitive to distinguish between residence times in the unsaturated (USZ) and saturated zone. Since gas tracers behave differently in the USZ they provide a differenced view on the water flow path including some estimates about the recharge area and process. The comparison of 85Kr data with CFCs allow for a quantification of degradation processes of the latter.Due to the prolonged gas residence time in the USZ the initial 39Ar activity is possibly affected by cosmogenic production by the 39K(n,p)39Ar reaction. **It is concluded that the combination of time series measurements and a multi tracer snapshot in time complete each other and provide also an assessment of the transient behavior of a groundwater flow system. Furthermore, hydrogeological conceptualization in order to pre-design the possible schemes for the lumped parameter models (e.g. models in series or in parallel), highly helps to converge towards more realistic sets of parameters.**
France