Arsenic in the aquifer systems of Viterbo Region, Central Italy: Distribution and Geochemistry

Groundwater arsenic (As) levels exceed the allowable limit of 10 µg/L in some areas of Viterbo region. In order to examine the extent of the As enrichment and the factors influencing this enrichment in the groundwater of Viterbo Region, Central Italy, water samples were collected from 231 different wells and springs. Based on the dominance of major anions and cations of water samples three hydrochemical facies identified: (i) Facies A- Na-HCO3 type water, (ii) Facies B- No dominant type, Na-Ca-HCO3 (water type in which none of the ions is dominant and/or results of mixing of two or more different facies) and (iii) Facies C- Ca-HCO3. The distribution of Arsenic varies in different hydrochemical facies and can be linked to different parameters such as lithology, mineralogy, local hydrology and hydrogeology. Accordingly, the processes responsible for As enrichment have been proposed for the different types of water in relation to groundwater evolution.