Investigation of the Origin of Hexavalent Chromium in a Greek Ophiolitic Aquifer

High levels of hexavalent chromium (Cr(VI)) in groundwater are typically attributed to anthropogenic sources. However, scientific reports over the last decade have demonstrated that relatively high levels of Cr(VI) in groundwater may also be due to natural processes. Cr(VI) is among the most significant groundwater contaminants, since it is a potential carcinogenic compound that is commonly found in contaminated groundwater. The complexity of physicochemical processes, combined with the variable environmental conditions inherent in a subsurface, can highly influence the behavior of chromium. The aim of this study was to investigate the origin and concentration of Cr(VI) in the ophiolitic aquifer of the Vergina area. The selection of this aquifer was based on groundwater sampling and analysis among several areas in Greece where high concentrations of Cr(VI) were observed. The applied criteria were: a) elevated chromium concentrations, b) geological background with ophiolites and ultrabasic formations and c) large distance from anthropogenic activities. The area that was finally chosen to be studied, according to the above criteria, was the ophiolitic aquifer of Vergina in northern Greece. Soil and groundwater samples from existing and new boreholes were obtained and analyzed. The results of this study show that although concentration of Cr(tot) in the soil increases with increasing depth, this was not the case for Cr(VI) which demonstrates the opposite behavior. Finally, although Cr(tot) and Cr(VI) seem to have similar concentrations across the water column down to 78 m depth, their levels decrease by half when the depth is further increased.