Influence of geological discontinuities on the groundwater flow of the Serra Geral Fractured Aquifer System

Abstract

Groundwater circulation in fractured aquifer systems is a topic of worldwide interest as they are heterogeneous and peculiar environments. In Brazil, little is known about the groundwater flow within fractured rocks. This knowledge gap motivated the investigation of (1) the statistical variance of the exploited discharges and their relationship with the directions of geological lineaments, (2) the analyzes of the relationship between of the groundwater flow with the different characteristics of the discontinuities and (3) the correlation between the acting stresses with the fracturing geometries that present groundwater flow. To reach these objectives, this paper is circumscribed within the following methods: frequency graphs, normality assumptions test, non-parametric homogeneity tests, multiple correspondence analysis, scanline profiles, and in situ stress analysis. This study was carried out in the Serra Geral Fractured Aquifer System, in Caxias do Sul, Rio Grande do Sul, Brazil. The results showed that most the exploited water wells are associated with the NW-SE and NE-SW lineament directions. There was a predominance of four sets of subvertical fractures (S1, S2, S3, and S4) and one sub-horizontal (S5). Sets of fractures S3, S4, and S5 showed the greatest persistence of fractures and presence of exudation. The tension axes σ1 and σ3 were identified in the (310°; 113°–141°) and (218°; 020°–051°) directions, respectively. The groundwater circulation in sets of fractures S3 and S4 is related to tensions σ1 and σ3 and the most exploited lineament directions NW-SE and NE-SW, while S5 is correlated to tension σ2 and behaves as a facilitator of the groundwater circulation in the underground flow network.