The groundwater monitoring system in Tuscany according to the EU Directive 2000/60 and the groundwater As contamination in the Versilia coastal plain

The EU Water Framework Directive 2000/60/EC commits European Union Member States to achieve good qualitative and quantitative status for all water bodies. Its application requires periodic monitoring of selected water bodies. Concerning groundwater bodies, the Tuscany Region selected monitoring wells for periodic sampling and performing chemical analyses. Results of these analyses are used to assess the qualitative status according to the EU Directive. In some cases, this groundwater monitoring can highlight some water pollution, hence activating more detailed investigations. In this work, we present the case of high arsenic concentrations in groundwater, reaching about 1000 μg/L, from domestic wells located in southern Versilia (Tuscany, Italy), close by the Baccatoio stream which receives acidic waters from a former mining site. Initially, the arsenic has been related to acid mine drainage from the nearby sites in the Baccatoio Valley. As-rich pyrite weathering was supposed to be the primary source for As in groundwater despite the Baccatoio stream is As-free. Although the evaluation of the amount of pyrite in sediments needs further investigations, alternative hypothesis were formulated. The highest As concentration is often accompained by high amounts of iron and ammonium ions reflecting reducing environments. This suggests the occurrence of secondary As-sources such as ferric oxyhydroxide and organic matter, likely in peat layers, undergoing reductive dissolution. The aim of this work is to carry out a preliminary assessment of the origin of the As contamination in groundwater of the Versilia coastal plain.