Hydrogeochemistry of the Serra Geral Aquifer System in the Alto Uruguai River region, northwest of the Rio Grande do Sul State and its spatial relationship with the brittle tectonics

Abstract

The present study aims to improve the knowledge about the hydrogeochemistry of the Serra Geral Aquifer System (SGAS), recognizing different geochemical Facies of groundwater and testing the existence of structural relationships conditioning the aquifer system in the Alto Uruguai River region, northwestern of the State of Rio Grande do Sul. The methodology was conducted through the initial acquisition of georeferenced database of tubular wells in the area, recovering of tectonic lineaments through satellite imagery and filtering in a Geographic Information System (GIS), generating thematic maps and statistical analysis of the database. 1.981 tectonic lineaments were drawn and separated by length and pattern directions. Short lineaments and directions NE-E and NW-W are dominant in the area. The variation of hydrogeochemical Facies shows positive correlation with the lineament density. The CaMg and Mixed Waters Facies exhibit characteristics of low residence time, related to recharge areas of SGAS, the first one being linked to NE-E and N-NW directions and the second one with the NW-W direction. The Na Facies is related to lineaments NE-E and NW-W directions and alkaline pH and high total dissolved solids (TDS) contents, suggesting mixing with waters from the underlying Guarani Aquifer System (GAS). The FeK and F Facies are related to areas of ascending recharge of GAS or even deeper aquifers, the first one presenting relationship with the NE-E and NW-W directions and the second strongly related to N-NE lineaments.