The Master Plan for the expansion of the Port of Barcelona includes, in terms of a potential impact on the strategic aquifers of the Llobregat Delta, two important actions: dredging of the breakwater to increase the berthing depth and expanding the quays to gain ground from the sea. In 1999, the Department of Land Engineering of the School of Civil Engineering of the UPC assessed these impacts and determined that they could be summarised as a possible increase in the piezometric levels of the surface aquifer and a possible increase in the conductivity of the water in the deep aquifer. This analysis was used for the construction period 2000-2010. To quantify the follow works in the harbour, and more specifically concerned about the possible increase in conductivity of the deep aquifer, the CUADLL has been carrying out a study commissioned by the Port of Barcelona with the contribution of CSIC-IDAEA, through numerical modelling with different approaches, from the most local to the regional level, taking into account all the aquifers of the Low Valley and Llobregat delta. The results of the modelling quantify a small, compatible and acceptable impact. An environmental monitoring plan has also been designed based on a control network to detect, as far as possible, variations indicative of the possible impacts of the works that will be carried out during this decade.