Identification for a Favorable Area of Groundwater Exploitation Based on Structural and Geoelectrical Data in Fractured Aquifer in Southern Brazil

Abstract

The inherent structural complexity of fractured aquifers, which controls the groundwater accumulation and flow in restricted zones, can lead to a high number of non-productive tube wells. The combined analysis of geomorphological features and indirect investigations like geophysics methods allows the identification of favorable targets for groundwater exploitation. This paper deals with regional and local structural surveys coupled with electrical resistivity tomography data in order to identify favorable targets for groundwater exploitation for urban consumption in a fractured granite located in Caçapava do Sul city, southern Brazil. The structural control is manifested in the regional landforms and clearly conditions the orientation of main drainages. Based on this structural control, four parallel electrical resistivity tomography lines were performed in an area of interest for groundwater exploitation, followed by the generation of 2D inversion models and pseudo 3D models. The contact between the very thin superficial soil and the underlying granite massif determines the existence of a regional free aquifer and the probable recharge of the fractured aquifer. In the 2D inversion models, abrupt variations of resistivity related to locally recognized vertical fractures in the field occur, although they do not show lateral continuity (out of plane). The analysis of the geophysical maps from 40 meters depth allows the recognition of three alignments of low resistivity (around 500 Ω m) within a granite context where high values predominate (above 15000 Ω m). These alignments show a triple fracture intersection pattern also recognized in satellite images, which are highly favorable for groundwater accumulation and exploitation.