Résumé : A methodology to characterize the main hydro-geothermal parameters of saturated and unsaturated ground layers, such as intrinsic thermal conductivity, volumetric heat capacity and groundwater velocity is proposed, based on the monitoring of the temperature plume around an activated borehole heat exchanger (BHE). The methodology is applied on an experimental platform composed of four BHEs. Based on the expected lithology and approximative groundwater fluxes direction, one BHE is thermally activated with a pre-determined heat injection and duration. The temperature evolution is recorded by means of PT100 sensors in the activated BHE and in the three non-activated BHEs, at three different depths in the saturated and unsaturated domain of an unconfined aquifer crossed by the BHEs. From an analytical solution considering conductive, advective and dispersive heat transfers, the hydro-geothermal parameters of the ground are obtained by fitting the measured to the predicted temperatures evolution. The effect of the possible inclination of the measuring boreholes is evaluated with the analytical solution. The obtained hydro-geothermal parameters demonstrate the important role of the saturated aquifer that significantly enhances the apparent thermal conductivity of the ground and, in case of groundwater flows, induces an anisotropic propagation of the temperature plume.