Hydrogeochemical, Geophysical and Geological Assessment of the Recharge Zone of Guarani Aquifer System in Alegrete, southern Brazil

Abstract

The state of Rio Grande do Sul has a huge part of the Guarani Aquifer, having a recharge area in its central and western region and, therefore, this investigation was focused on the city of Alegrete. There is no annual plan for water resources in the state and, hence, it is required to evaluate the hydrogeochemical, geophysical and geological characteristics where the aquifer has its recharge regions. Thus, some data were acquired, having chemical analysis of the water in different wells (mostly in rural areas) and refraction seismic and geoelectrical surveys. In addition, the geological information was obtained from the public database SIAGAS (Sistema de Informações de Águas Subterrâneas – ground water information system). Then, different maps of chemical parameters and a Piper diagram were made. Moreover, the refraction seismic and geoelectrical data were processed and interpreted, concatenating these results with the geological data obtained from the SIAGAS wells, mapping the different formations and static levels of the aquifer. A high concentration of lead, chromium and cadmium along with phosphate was found. Additionally, by means of geophysical surveys, a line was pointed out as a possible aquifer, which could be used for human, agropastoral or industrial activities after treatments of altered values.