CHAPTER ONE: INTRODUCTION                                          

1.0        General Statement………………………………………………………………..1-5

1.1        Aim and Objectives of the study…………………………………………………5

1.2        Relief and Drainage………………………………………………………………5-6

1.3        Climate and Vegetation…………………………………………………………..6

1.4        Literature Review…………………………………………………………………6-9

CHAPTER TWO: GENERAL GEOLOGY OF NIGERIA

2.1        Introduction……………………………………………………………………….10

2.2        Basement Complex………………………………………………………………..11-14

2.2.1      The Schist Belts…………………………………………………………………..14-15

2.2.2      Charnokitic, Gabbroic and Dioritic Rocks……………………………………….15

2.2.3      Older Granite……………………………………………………………………..15-16

2.2.4      Younger Granites………………………………………………………………....16-17

2.2.5      Tertiary-Recent Volcanic Rocks………………………………………………….17

2.2.6      Evolutions and Geochronology of the Basement Rocks…………………………17-18

2.3         Hydrogeology of South-Western Nigeria……………………………………..….18-21

2.4         Geology of Precambrian Basement Rocks of South-Western Nigeria………..…21

2.5          Local Geology………………………………………………………………..….22

2.5.1       Geology of the Study area………………………………………………….…...22-23

CHAPTER THREE: METHODOLOGY

3.1        General Statement…………………………………………………………….….24

3.2        Theory of Electrical Resistivity Method………………………………………...24-27

3.3        Electrode Array………………………………………………………...………..27

3.3.1     Wenner Array…………………………………………………………..……….27-28

3.3.2     Dipole-Dipole Array………………………………………………….………...28

3.3.3     Wenner-Schlumberger Array………………………………………….…….…28

3.3.4     Pole-Pole Array…………………………………………………….…………..31

3.3.5     Pole-Dipole Array………………………………………………….…………..31

3.4        Data Interpretation for VES Survey…………………………………………...32

3.4.1.    Computer Iteration Techniques………………………………………………..33

3.4.2.    Partial Curve Matching………………………………………………………..33-35

3.5        Instrumentation………………………………………………………………..35-36

3.6        Precautions taken during field survey…………………………………………36-37

3.7        Limitations of Electrical Resistivity method…………………………………..37-38

3.8        The GODT Modeling Approach……………………………………………….38-40

3.9        Field Procedure………………………………………………………………....40-43

CHAPTER FOUR: RESULTS AND DISCUSSION

4.1        VES Curves……………………………………………………………………44

4.2        Interpretation of Vertical Electrical Sounding…………………...……………44-63

4.3        Geo-Electric Parameters………………………………………………………..63

4.3.1     Overburden Thickness………………………………………………………….63-64

4.3.2     Reflection Coefficient and Resistivity Contrast of the Basement Rock……….64

4.3.3     Total Longitudinal Conductance………………………………………………64-65

4.3.4     Electrical Anisotropy/Coefficient of Anisotropy………………………………65

4.5        GODT Parameters……………………………………………………………...75-76

4.6        Groundwater vulnerability potential modeling-based on the GODA-index results…76

4.7        The deductions and the findings of the GODA vulnerability index method……...76

4.8        Geo-Electric Sections……………………………………………………………82-90

CHAPTER FIVE: SUMMARY, CONCLUSION AND RECOMMENDATION

5.1        Summary………………………………………………………………………….91-92

5.2        Conclusion………………………………………………………………………...92

5.3        Recommendation………………………………………………………………….92-93

             Reference………………………………………………………………………….94-103

             Appendix………………………………………………………………………….104-118

LIST OF FIGURES

Figure

1.1        Location, accessibility and drainage map of the Study area

2.1        Geological Map of Nigeria (Oyawoye 1972)

2.2        Geological Map of Ibadan

3.1        Dipole-Dipole Array

3.2        Wenner-Schlumberger Array

3.3        Pole-Dipole Array

4.1        VES points of the study area

4.2        Map of the 2D and 3D of groundwater hydraulic confinement of the study area.

4.3        Map of the 2D and 3D of aquifer overlying strata of the study area.

4.4        Map of the 2D and 3D of depth to aquifer table of the study area.

4.5        Map of the 2D and 3D of topography of the study area.

4.6        The groundwater vulnerability map of the study area.

4.7.1     Interpretation of transverse one.

4.7.2     Interpretation of transverse two.

4.7.3     Interpretation of transverse three.

4.7.4     Interpretation of transverse four.

4.7.5     Interpretation of transverse five.

4.7.6    Interpretation of transverse six.

4.7.7    Interpretation of transverse seven.

4.7.8    Interpretation of transverse eight.

4.7.9    Interpretation of transverse nine.

LIST OF TABLES

Tables

4.1       Electrical Resistivity Data taken within the Study area.

4.2       The curve type of the Study area.

4.3       Subsurface lithology of the study area.

4.4       Attribution of scoring notes for GODA model parameters (modified after Khemiri et al., 2013).

4.5       The GODA modeling computed results.

4.6       The groundwater vulnerability potential classification and the areal coverage percentage    obtainable (Modified after Murat et al, 2003).

agement in the area.

Geophysical investigation involving electrical resistivity method was carried out with the aim of using geo-electric parameters to assess groundwater vulnerability in Alagbagba and environs, Ibadan, South-Western Nigeria. It is underlain by rocks which include migmatite-gneiss, quartz, mica and granites

Forty (40) Vertical Electrical Soundings (VES) were acquired within the area adopting Schlumberger electrode configuration with maximum current electrode separation (AB) of 200 m. The acquired field data were interpreted using partial curve matching and were further subjected to computer iteration program with the aid of WINRESIST. Parameters such as the layer resistivity, the depth at which each layer is identified and the overburden thickness were calculated and used to produce the groundwater vulnerability of the area. The developed model christened as GODT model was applied to assess groundwater vulnerability in a multi-faceted crystalline geologic terrain.

The predominant VES curve types are H, A and KH. The results revealed three to four geo-electric layers, namely, topsoil (37.3 to 469.1Ωm), sandy clay (106.4 to 341.0Ωm), fractured bedrock (259.9 to 1842.5Ωm) and fresh basement (414.2 to 7428.5Ωm). The GODT model yielded 2.5% moderate vulnerability, 7.5% low moderate vulnerability and 90% low vulnerability.

The study area has predominantly low vulnerability which indicates that the area has good confining capability against pollution. The results produced in this study can form part of decision making model for environmental planning and groundwater man