In the present study we present a methodology of how structural geology and geophysics techniques, together with hydrochemical and hydraulic data, can help in identifying the main fractures that conduct most of the groundwater flow in a granitic pluton (low-permeability fractured media). Using the values of transmissivities obtained from 3-D numerical models of the local hydraulic test interpretation, we have been able to reproduce the effect of a large-scale and long-term pumping test.