Abstract : The development of hydrodynamic models at regional scale requires to take into account the aquitards layers and their hydrogeological behaviour on the long term. These leaky units have specific geological and hydrodynamical properties and sometimes large scale heterogeneities. The area of Bordeaux which is subject to large withdrawals, is used to support the study for understanding the role of aquitards in the hydrodynamic behavior of a multilayered complex. Various methods were used to assess the geological characteristics of these low permeability formations. The well logging tool allowed a reinterpretation of the geology and resulted in the updating of the geometry of the hydro-geological study area and a new vertical structure of aquifers and aquitards units. The installation of a specific borehole, with the analysis of core samples and permanent pressure monitoring device, at different levels, provided an estimation of the geological and hydrodynamical properties of the aquitard. Finally, the quantitative approach of the role of aquitards in the hydrodynamic behavior of the aquifer system was carried out using a hydrodynamic model. This model takes into account the new geometry obtained from the use of well loggings, and integrates the values of hydrodynamic parameters obtained by laboratory and in situ measurements. The model is used to identify the leakage flows in the multilayer system. The results demonstrate the impact and the role of a leaky unit within a thick aquitard. Ultimately, integration of heterogeneities within an aquitard is essential to the development of quantitative and qualitative management tools for groundwater resources, at different time scales, for complex multilayered aquifer systems.