In hydrological and water quality models aiming to reproduce stream solute dynamics, we need to represent the contribution of all the watershed’s compartments: the surface, the vadose zone and the groundwater. Actually, each compartment has different properties, inducing different hydrologic behaviors (rapid or slow flows) impacting differently the pollutants fate and transport. For hard rock catchments, modeling the groundwater compartment is crucial. The aquifer contributes to the largest part of flow in the river throughout the year and thus controls significantly its quality. It supplies water in recessions and low flow periods, but also during floods, diluting the surface and subsurface inputs. The underground module for hard-rock catchments proposed here will be coupled with a surface/subsurface model (Rouzies & al., 2019). It is based on a hybrid modeling approach mechanistic for water and conceptual for pesticides: The transient groundwater/subsurface interactions in crystalline aquifers have a significant impact on the remobilization of pesticides: it is therefore assumed that a physical-based approach, is necessary for groundwater flows in order to take into account the impact of the water table dynamics on the transfer of pollutants; The residence time of the groundwater (or water age), , is a relevant indicator characterizing the hydrogeological behavior of aquifers. We make the assumption that this of water ages distribution, combined with knowledge on the pollutants physicochemical properties (governing the degradation and retention processes) can be used in a conceptual and mathematical approach to evaluate the transfer and the fate of pollutants. The approach chosen for the estimation of the residence time distribution is based on the “StorAge Selection functions” (Botter & al., 2010) which are functions that describe how systems hold and release water. This approach has shown good performance and robustness in several studies and succeeded, in a parsimonious way, to reproduce the dynamics of pollutants at the scale of the watersheds. However, it has often been applied to represent the solute dynamics in the basin as a whole hydrologic unit while in our study, we implement this method only on the groundwater compartment. Moreover, the method was always used with a conceptual representation of water fluxes while we couple it with a physical representation for the water in order to better understand the interactions of the aquifer with the other compartments. At last, the SAS functions have been less applied for pesticides. In this study, the method will be tested on multiple pesticides with different properties and also for their degradation products. To constrain the residence time distributions on our study catchment (La Morcille, a vineyard basin located in the North of the Beaujolais region in France), concentrations of dissolved gas Chlorofluorocarbons (CFCs that are known to be good tracers for water age in groundwater) will be measured. The objective is to characterize the mean residence time during two different seasons (dry and humid) which will allow to understand the hydrogeological behavior of the shallow aquifer of our catchment and its impact on the pesticides fate.