Groundwater quality is pivotal for sustainable resource management, necessitating comprehensive investigation to safeguard this critical resource. This study introduces a novel methodology that integrates stiff diagrams, geostatistical analysis, and geometric computation to delineate the extent of a confined aquifer within the Chahrdoly aquifer, located west of Hamadan, Iran. For the first time, this approach combines these tools to map the boundaries of a confined aquifer based on hydrochemical characteristics. Stiff diagrams were used to calculate geometric parameters from groundwater chemistry data, followed by simulation using a linear model incorporating the semivariogram parameter γ(h). The Root Mean Square Error (RMSE) of the linear model was used to differentiate confined from unconfined aquifers based on hydrochemical signatures. Validation was conducted by generating a cross-sectional hydrogeological layer from well logs, confirming the presence of aquitard layers. The results successufully delineated the confined aquifer's extent, showing strong agreement with hydrogeological log data. By integrating stiff diagrams with semivariogram analysis, this study enhances the understanding of hydrochemical processes, offering a robust framework for groundwater resource identification and management.