Full text
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| Author(s): |
Ingo Daniel Wahnfried
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Geociências (IG/BT) |
| Defense date: | 2010-06-23 |
| Examining board members: |
Ricardo Cesar Aoki Hirata;
Chang Hung Kiang;
Claudio Riccomini
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| Advisor: | Ricardo Cesar Aoki Hirata |
| Field of knowledge: | Physical Sciences and Mathematics - Geosciences |
| Abstract | |
The main objectives of the present thesis were to test the existence of leakage through the fractured Serra Geral Aquifer (SGA) to the Guarani Aquifer System (GAS), create a conceptual flow model for both aquifers, and obtain their hydraulic parameters, at a location where the SGA-forming basalt has 100 m thickness. The chosen area is 9 km to the south of Ribeirão Preto, São Paulo State, Brazil. The study is part of a research project called FRATASG, from the Geological Institute (São Paulo Environmental Secretariat). Surface geophysical methods (vertical electrical sounding, electric resistivity survey and controlled source audiomagnetotelluric survey - CSAMT) were used to locate fractures in the basalt that are possibly hydraulically active, and also to determine the contact depths between overburden, basalt, and the eolian sandstones that form the GAS. Vertical low electric-resistivity planar features were identified in the basalt, at locations were lineaments were described, in half of the electric resistivity and CSAMT surveys, and one of the latter showed continuity of the feature down to the GAS. This was interpreted as possible water bearing fractures, and was used to define the location of three wells in the SGA. Two piezometers were also drilled, open to both SGA and GAS, close to an existing production well in the GAS (Esmeralda Well - PE). To collect discrete depth samples in the SGA, a pneumatic packer system was built, based on models used by the USGS, adapting equipment that is available in Brazil. The system, as well as other equipment used, the procedures and interpretation of the hydraulic tests and sample collection at discrete depths, are described. A 171 hour long pumping test was executed in the GAS, where anisotropy was identified, probably caused by the sedimentary layering present in the eolic dunes in the sandstone. The highest transmissivity, \'T IND.max\' = \'T IND.x\', is 160 m²/d, and the lowest transmissivity, \'T IND.min\' = \'T IND.y\', is 103 m²/d. The correlation between Tmax / Tmin is 1,55. Hydraulic conductivity (K) is 4,6x\'10 POT.-1\' m/d and 7,0x\'10 POT.-1\' m/d, and storativity (S) is 1,6x\'10 POT.-3\' and 8,4x\'10 POT.-4\', determined respectively at piezometers PPE-1G and PPE-2G, located at different directions from PE. Dye-tracer tests were also conducted, with injection in GAS and SGA, and collection in the GAS. The effective porosity was determined, ranging from 18,8 to 20,3%. Several hydraulic tests were done in discrete depths in the SGA, in one well. The transmissivity (T) of small intervals ranges between 5x\'10 POT.-2\' and 3x\'10 POT.-1\' m²/d. The highest T of individual features is always associated to sub-horizontal fractures. The drawdown curve showed double porosity behavior in the basalt, caused by vesicules and sub-vertical fractures connected to the sub-horizontal ones. Water samples were collected during all pumping tests, in the GAS, in two open wells in the SGA and in discrete zones in this aquifer, for hydrochemical analysis. Stable and radioactive isotope analysis (³H, ²H, \' ANTPOT.18 O\', \'ANTPOT.13 C\' and \' ANTPOT.14 C\') were done with selected samples, both from GAS and ASG. The fractured aquifer shows and hydrochemical evolution with depth, with Na+K increase. Samples can thus be grouped as shallow (around 16 m depth), intermediate (around 25 m) and deep (around 55 m). The same groups are found in the stable isotope results, whereas the radioactive show an age increase with depth. Samples from GAS are isotopically and hydrochemically closer to the shallow waters from the SGA. It can thus be concluded that the connection between both aquifers is very limited, or not present, and water flow in the SGA is mostly horizontal and shallow. (AU) | |
| FAPESP's process: | 04/15543-0 - Guarani Aquifer System recharge through Serra Geral Aquitard: definition of protection zones |
| Grantee: | Ingo Daniel Wahnfried |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |