LADES
Espace performance
Batiment C1-C2
35769 Saint Gregoire

Phone. +33 2 99 23 74 40
Fax. +33 2 99 23 78 11
Mail : info lades.fr

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Water infiltrating records atmospheric signature and keeps it all along its underground travel. Dating is based on analysis of dissolved atmospheric gases: CFC (chlorofluorocarbons) and SF6 (sulfur hexafluoride).

CFC and SF6 are anthropogenic gases produced since the middle of the XXth century: consequently they are ideal tracer for young groundwater (<50 years). Most of pollutants that lead to the tap water production cessation are more or less related to the intensification of anthropogenic activities during these last 50 years (agricultural and industrial).

CFC and SF6 analysis also shows the vulnerability of groundwater. Any trace of these gases in deep old aquifers indicates a non-negligible proportion of recent water (0-50 years) potentially marked by anthropogenic activities.

A CFC and SF6 analysis allows a real dating for recent groundwater. Their concentration in the atmosphere atmospheric concentrations has increased through the 2nd half of the century. The younger the water is, the higher the gases concentration is. In the most favorable cases, groundwater age could be estimated within +/- 5 years.

Nevertheless even if it’s more difficult to give a precise age, the presence or the absence of such gases in the aquifer could provide a better understanding of the hydrogeological functioning and the potential disturbances linked to its use.