Avaliação hidrogeológica quali-quantitativa do aquífero fraturado Serra Geral, localizado no noroeste do Rio Grande do Sul

The Serra Geral fractured aquifer (SASG) is one of the largest aquifers in Rio Grande do Sul state, Brazil, and it constitutes an important source of water supply for 46% of the counties. The present study aims to assess the influence of the SGAS fracture system on the productivity and groundwater quality. For this purpose, statistical tests were carried out, integrating structural, hydrodynamic, and hydrochemical parameters, by using PAST statistical software. The study area is the county of Frederico Westphalen. Most of the pumping wells (75%) do not exceed 186 m in depth. The wells that intercept more than one fracture zone have higher specific capacity (up to 19.8 m3/h/m) and are less deep than those that intercept a single fracture zone. The flow rate is around 8 m3/h. In comparison with wells close to smaller lineaments, those close to the largest lineaments often intersect several fracture zones and have inflow, dynamic, and static levels which are less deep, and higher flow rate and specific capacity. Potenciometric levels show a regional trend flow from west to east and northeast. Waters are mostly sodium bicarbonated, and well waters that intercept a single fracture zone are more carbonated and chlorinated; pH ranges from 7 and 9.9, increasing with the proximity of the lineament and with the increasing depth of the well. Water quality of 78% of wells is within standards for human consumption, but there are some cases with total iron and fluoride concentrations above the allowed levels. There is evidence of saline water contribution from deeper aquifers (upward flow) in wells that explore the SASG.