Influence of Tectonics on the Hydrogeochemistry of the Serra Geral Aquifer System in the Ijuí River Basin, Rio Grande do Sul State

Abstract

This study aimed to integrate hydrogeological, tectonic, and hydrogeochemical data from the Serra Geral Aquifer System (SGAS) in the Ijuí River Basin, in the Northwest of Rio Grande do Sul, Brazil, in order to recognize characteristics that permit an improvement in the understanding of the subterranean water resources of the region. The methodology used in the structural characterization included assembling of hydrogeological data from water wells, tectonic lineaments mapping through satellite images, creation of thematic maps and statistical analyses. As for the hydrogeochemical characterization, laboratory data was treated statistically through a factor analysis, allowing the grouping of samples into three facies: Na Facies, CaMg Facies and Mixed Water Facies. The results demonstrate that the medium-sized geological structures (2-4 km) are predominant in the area, with NE-E and N-NE preferential directions. There is a positive correlation between the wells with higher flow rates and the zones with a high density of lineaments. As for the hydro geochemistry, the study indicates that the groundwater has different sources, with the CaMg facies related to the meteoric replenishment and the Na Facies being related to the mixing with waters from the Guarani Aquifer System, which ascend through faults and fractures in the volcanic rocks. This understanding was corroborated by the identification of a positive correlation between the Na facies wells and the zones with a high density of lineaments.