Anthropogenic sources of contamination recognition — Sines coastal aquifer (SW Portugal)

Sines coastal sedimentary basin, a tectonic ditch with a NE–SW orientation filled with Mesozoic and Cenozoic deposits, presents two hydrogeological systems: the Mio-Pliocene and the Jurassic. Both systems are supplying water to the entire region with highly populated and industrialized areas. The aquifers recharge occurs on the outcrop areas, while the Jurassic areas also receive some contribution from the overlain Miocene rocks. The main groundwater flow direction of the Jurassic aquifer is E to W towards the Atlantic Ocean.In order to confirm the influence of the anthropogenic activities on the water quality, the application of statistical principal components analysis (PCA) was used as one useful tool. PCA was based on the in physical–chemical data of groundwater samples in both aquifers. Four components were obtained in the Jurassic and three in the Miocene. The principal components analyses indicate water–rock interaction process as the major mechanism responsible for the groundwater salinity (mainly calcium-bicarbonate type), invoking the lithological composition dominated by calcareous and dolomitic units. Anthropogenic contamination was identified in the influence of the water mineralization, corresponding to local polluting inputs (PC 3 in Jurassic and PC 2 in Miocene) that justify about 13% of the system's total variance in the Jurassic aquifer and near 23% in Miocene one.