Textural heterogeneities in clayey-dominant superficial formations result in preferential flow paths, thus in spatial variability in both unsaturated water fluxes and pollutant transport velocities. Such heterogeneities are often neglected in hydrogeological studies that could lead to an underestimation of groundwater recharge rate and aquifer vulnerability. The purpose of this study, conducted at the Hydrogeological Experimental Site (HES) of Poitiers (France), was to characterize the Tertiary clayey-dominant unsaturated zone overlaying the Dogger limestone aquifer, which corresponds to a major regional groundwater resource. Geophysical investigations (Tomography approaches) and soil sampling were performed and showed that the Tertiary deposits contain localized silty to sandy lenses with plurimetric lateral extension. This result leads to reconsider the conceptual models developed for groundwater management in the area: (i) the Dogger aquifer, assumed confined locally, could be affected by direct groundwater recharge processes; and (ii) the low vulnerability level associated to the Tertiary deposits in risk assessment studies need to be increased.


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