ASSESSMENT OF THE IMPACT OF CLIMATE CHANGE TO CONFINED ALLUVIAL AQUIFER: IMPLICATIONS ON THE CONTAMINATION TRANSPORT MECHANISMS E. Romano 1, S. Camici 2, L. Brocca 2, T. Moramarco 2, F. Pica 1, E. Preziosi 1 1CNR - Water Research Institute, Area della Ricerca di Roma 1-Montelibretti, via Salaria km 29,300, PB 10 – 00015 Monterotondo Stazione, Rome, Italy, [email protected] 2CNR - Research Institute for Geo-Hydrological Protection, via della Madonna Alta 126, 06128, Perugia, Italy,[email protected] The alluvial aquifer of the Umbra Valley is exploited for human consumption since the 1970s through the Petrignano and the Cannara well field, the first one exploiting a phreatic zone, the second one a confined zone. In the last years, a contamination of organochlorinated compounds has been detected by ARPA Umbria in a wide area (about 72 km 2) including the towns of Torchiagina, Petrignano d’Assisi, Bastia Umbra, Assisi, Foligno and Spoleto. The Umbra Valley aquifer is mainly fed by the effective infiltration from the ground surface; as a consequence, changes in the temperatures and precipitation regime because of climate change, could significantly affect the recharge to the aquifer and the related piezometric heads field; the related changes in the velocity field could significantly affect the dynamic of transport of possible contaminants, modifying the guardianship zones for the well fields of Petrignano and Cannara. The goal of this paper is to investigate the impact of possible climate change both quantitatively, analyzing possible evolution of the piezometric heads due to a decrease in precipitation and qualitatively, assessing the changes in the mechanisms of transport of contaminants. To this aim, a 2D flow model has been developed for the Umbra Valley aquifer through the finite-difference code MODFLOW2005: the model has been calibrated and validated for the present climate adopting both the undisturbed (1974) and under exploitation (1998-2010) conditions as target. The General Circulation Model PCM (from the National Center for Atmospheric Research) has been adopted to obtain scenarios for present and future climate; GCM’s time series for present climate (1952-2010) have been downscaled to the observed temperature and precipitation time series collected at the stations located within the study area through statistical methods (a quantile-quantile procedure and the delta-change method); the relationships between CGMs and observations obtained through downscaling have been finally applied to the GCM’s future scenarios to get the future local temperature and precipitation. The latters, turned to effective infiltration time series by means of the Thorntwaite-Mather model, have been used as input to the flow model. The assessment of the risk related to possible contamination both for the Petrignano and the Cannara pumping station in relation to significant changes in the velocity field of the aquifer has been investigated through a transport model developed through the MT3D numerical code. .