Hydrochemical response of a fractured carbonate aquifer to stress variations: application to leakage detection of the Vouglans arch dam lake (Jura, France)

Leakage detection and the prediction of the behavior of fractured rocks subjected to variations in hydrostatic pressure are important issues in hydropower engineering. Some large water reservoirs are constructed in karstic carbonate areas. In order to understand underground circulation in the limestone/dolomite foundation of the Vouglans dam (Jura, France), groundwater chemistry analysis, according to geological conditions, is used. Statistical analyses (PCA and DFA) are carried out: (1) to accurately characterize the contrast in chemical composition resulting from the interaction between surface and groundwater in a poorly contrasted environment, due to the shared carbonated context, and (2) to reassign individuals into homogeneous groups with respect to the variables studied. PHREEQC is used to determine the potential for the precipitation of secondary minerals from the water chemistry mainly in order to determine the geochemical control of clogging. Three types of hydrodynamic behavior were identified in the sector. The origin and transfer time of inflows vary with respect to seasons. The area of influence of the rapid transit of the lake water varies predominantly in response to changes in the lake water level. The hydrostatic pressure of the water column influences the opening and closing of cracks at the bottom of the dam. Drains intercepting an upstream fissure are highlighted by hydrochemical measurements. Inflows are oversaturated with respect to calcite and are thus likely to precipitate this mineral. Zones with a strong clogging capacity correspond to the zones with slow transit groundwater.