Defense
Student: Angélica Aparecida dos Santos
Program: Geophysics
Title: "Hydrogeological characterization of a spring area in sedimentary terrain using geoelectrical methods, in the region of Itaí – SP."
Advisor: Prof. Dr. Vagner Roberto Elis
Judging Comitee:
- Prof. Dr. Vagner Roberto Elis – IAG/USP (Chair and Advisor)
- Profa. Dra. Alice Marques Pereira Lau - UFBA
- Dr. Otávio Coaracy Brasil Gandolfo - IPT
Other Members:
- Prof. Dr. Jorge Luís Porsani - IAG/USP
- Dr. Alexandre Lisboa Lago - CPRM
- Prof. Dr. Auberto José Barros Siqueira - UFMT
- Prof. Dr. Sérgio Júnior da Silva Fachin - UFMT
Abstract:
The municipality of Itaí is located in the Alto Paranapanema region, within the Paraná Sedimentary Basin. In the study region, the geological units are related to Paleozoic events, characterized by the deposition of the Passa Dois Group, with sediments deposited in glacial, marine, and lacustrine environments that promoted basin subsidence, resulting in compaction and the formation of lithologies less favorable to groundwater storage. In addition, the geological framework includes sandstones of the Botucatu Formation, basaltic flows of the Serra Geral Formation, and intrusive dikes and sills of Mesozoic age. The hydrogeology of the area corresponds to the Passa Dois Aquiclude, presenting fractured rock that provides some groundwater productivity, although with low capacity for water supply. The objective of this research is to carry out a hydrogeological characterization around a perennial spring located at Fazenda Triunfo, using geo-electrical methods in order to contribute to subsurface mapping studies for regional knowledge and to support the search for better groundwater prospecting alternatives, considering that the region, predominantly occupied by monoculture, is currently experiencing a water crisis. For the hydrogeological mapping, five acquisition lines were established, namely 00, 01, 02, 03, and 04. Two methods were applied: the Electrical Resistivity (ER) method, aiming to obtain information on the resistivity (ρ) of subsurface material properties through Electrical Resistivity Profiling (CE) to identify possible geological units and their structures, and Vertical Electrical Sounding (VES) to obtain details regarding lithological thickness and potential saturated zones. The Frequency Domain Electromagnetic (FDEM) method provided information on the conductivity of these properties using the EM-34 instrument, allowing the acquisition of characteristics related to possible geological units and fracturing, although at greater investigation depths compared to the ER method. With the inversion of the data and the integration of the results from the inverted sections (profile models), anomalies associated with fractures, lithotypes, thickness variations, and possible saturation zones were identified based on resistivity and conductivity responses. Zones with higher resistivity responses are related to massive rocks, whereas less resistive and more conductive zones indicate weathered, moist, or saturated areas. The applied methods proved to be effective for spring studies, showing potential for similar applications, especially in the region of the farm and the municipality, for the identification of strategic and reliable locations for groundwater spring’s prospecting.
Keywords: Electrical Resistivity, Frequency Domain Electromagnetics, Hydrogeology, Spring, Paraná Basin