The railway access to the Outer Ferrol harbor requires the construction of the 5.5 km long Brión tunnel. The tunnel is excavated with the so-called new Austrian method through highly-fractured granodioritic rocks. The tunnel intersects a major fault zone, several fracture zones and two other existing tunnels: the A Graña road tunnel and the A Malata seawage emissary tunnel. The tunnel runs 200 m below the ground Surface. Several finite element 2D numerical models have been constructed to evaluate the construction, geotechnical and environmental effects of the tunnel. The numerical models rely on a conceptual model of the hydrogeology of the study area which accounts for a shallow layer of 1-5 m thickness of quaternary deposits and weathered granodiorite, an underlying layer of 10-15 m thickness of altered and decompressed granodiorite, and two deep layers of fractured granodiorites. The deepest layer is assumed to have the smallest hydraulic conductivity. Numerical models of vertical profiles were performed at three representative locations. The models were calibrated first under steady state conditions and then, they were used to evaluate the water pressures at the back of the tunnel, the water inflows into the tunnel and the groundwater drawdowns in deep and shallow wells for several hypotheses about the drainage conditions and waterproofing (undrained, drained and resine injection). Model results have provided very useful recommendations for the Ferrol Habor Authority.