Natural Occurrence of Sulphates in Ground and Surface Waters in Aosta Plain (Italy)Engineering Geology for Society and Territory - Volume 5

This research originates from a wider three-year hydrogeological study about Aosta Plain (Italy), from Villeneuve to Pontey municipalities (12 ground and surface waters sample surveys leading to the chemical analysis of more than 800 samples). The hydrogeochemical characterization of the unconfined aquifer shows that 80 % of the groundwater sampled from June 2006 to May 2009 has Ca-HCOs composition. Instead, 8.4 % of the samples shows sulphates concentration higher than carbonate and chlorides one. This predominant inversion is detected in few wells, located in a delimited area. Considering the absence of hazard sources connected to human activities, it is reasonable to introduce the hypothesis of natural occurrence of sulphates. Therefore, the delimited research area has been the object of geological, geomorphological and hydrochemical observations to trace the sulphates occurrence back to soluble lithotypes or to pyrite mineralization, both present in the area. Different data elaborations reveals that the predominant sulphates source is represented by gypsum formations normally associated with particular carbonate rocks.