Arsenic and fluoride in groundwater of a loessical unconfined aquifer, Córdoba, Argentina

Abstract

La Colacha basin (Córdoba province, Argentina) is a piedmont rural area where groundwater is used for different activities. The objective of this work is to assess the controls on geochemistry processes in the unconfined loessical aquifer, especially those related to arsenic and fluoride. Low groundwater velocities and bicarbonate sodium water types predominate. The results of the numerical models show that salt dissolution and cation exchange are the main geochemical processes in the aquifer. High values of As and F were identified and although they do not follow clear trends with major ions, the multivariate statistical analysis shows that there is affinity between As and F with pH and alkaline waters. Furthermore, As and F are positive correlated, which account for their similar origin (lithological control) and their entering in solution under similar geochemical aquifer conditions. It is assumed that the volcanic glass, in a moderate to high pH aquifer environment, may be altered, supplying As and F ions to the solution. Fluoride may be supplied also from other F earing minerals identified in this geological setting (fluorite and fluoroapatite). In this oxidant aquifer environment, arsenates may also be desorbed from the surface of secondary amorphous Fe and Mn oxides.