Landslides in sensitive clays are among the most significant geohazards in the province of Québec, occurring primarily within the former Champlain Sea's footprint. These clays become sensitive through the gradual leaching of salts over long timescales. Although the leaching process remains poorly understood, gaining deeper insight into its driving mechanisms could improve our ability to predict the distribution of sensitive clays. Such knowledge would provide valuable support for land-use planning and risk management. This study employs a two-dimensional, density-dependent flow and solute transport model to investigate the influence of hydrogeological controls on salt leaching over the 10,000 years since land emergence following the regression of the Champlain Sea. By comparing two conceptual models (one in which a till layer recharges directly at the surface, and another where the till is confined) it is shown that surface-connected till markedly enhances salt leaching. Parametric analysis demonstrates that salt leaching is highly sensitive to clay permeability, despite its generally low values. This finding highlights the importance of long-term flow within the clay layer. Structural analysis further reveals that factors affecting the hydraulic gradient (e.g., deep river incision) or creating preferential pathways (e.g., permeable interbeds) exert a strong influence on leaching. Overall, this research underscores the need for landslide risk assessments to incorporate both regional hydrogeological settings and localized flow pathways, as these factors govern the vertical and lateral extent of sensitive clay development.