Geoelectrical resistivity imaging using both 2D and Vertical Electrical Sounding (1D) method was carried out in Atan , Ado/Odo Ota Local Government, Ogun State ,Nigeria using the PAS earth resistivity meter.Three profiles was carried out using both Wenner and Schlumberger array configuration. The data was interpreted using RES2DINV for 2D and computer iteration method (WinResist) for VES. Results showed that there are five major layers which described the geological structure of the study area. The resistivity values ranges between 1200Ωm to 4000Ωm,

500Ωm to 1000Ωm, 400Ωm to 800Ωm , 200Ωm to 400Ωm and 60.7 Ωm to approximately 100Ωm respectively according to the structures. VES1,VES 2, VES 3 and VES 4 apparent resistivity curve shows the different layers with their corresponding thicknesses. The study area revealed that the depth to the aquifer ranges between 130m t0 140m.

Certification ii

Dedication iii

Acknowledgements iv-v

List of Tables viii

List of Figures viii -ix

Abstracts x

1.1 Introduction 1 - 3

1.2 Geological Description of Underground Water 3 - 4

1.2.1 Occurrence of Groundwater 4

1.2.2 The movement of Groundwater 5 - 6

1.2.3 Transmission of Groundwater 6 - 8

1.2.4 Recharge 8

1.2.5 Leakage 8 - 9

1.2.6 Withdrawal 9

1.2.7 Aquifers 9- 11

1.3 Location of the study area 12

1.4 Aim and Objectives 14

1.5 Scope of the Study 14

1.6 Justification of the study 14

2.1 Literature Review and Geological Setting 15-21

2.2 Geological Setting of the study area. 21-22

3.1 Electrical Resistivity Theory and Methodology 23

3.1.1 Single Current Electrode at Depth 24

3.1.2 Single Current Electrode at Surface 25

3.1.3 Two Current Electrode at the Surface 25

3.2 Apparent Resistivity and Electrode Configuration 25 â€" 26

3.3 Resistivity Survey 27 - 28

3.4 Field Measurement Procedure 28- 30

3.5 The Field Work Procedure 30-34

4.1 Results and Interpretation 35-36

4.2 Data Collected for Profile 1 37-40

4.3 Data Collected for Profile 2 41-44

4.4 Data Collected for Profile 3 44

5.1 Result, Discussion, Conclusion and Recommendation 45

5.1.1 Profile 1 Discussion 45-47

5.1.2 Profile 2 Discussion 48-50

5.1.3 Profile 3 Discussion 51-53

5.2 Conclusion 54

5.3 Recommendation 54-55

5.4 Contribution to Knowledge 55

Table 4.1: Raw Data for 2D in Profile 1 37

Table 4.2: Raw Data for 2D in Profile 1 38

Table 4.3: Raw Data for 2D in Profile 1 38

Table 4.4: Raw Data for 2D in Profile 1 39

Table 4.5: Raw Data for 2D in Profilr 1 39

Table 4.6: Raw Data for 2D in Profile 1 39

Table 4.7: Raw Data for 2D in Profile 1 40

Table 4.8: Raw Data for 2D in Profile 1 40

Table 4.9: Raw Data for 2D in Profile 1 40

Table 4.10: Raw Data for 2D in Profile 1 40

Table 4.11: Raw Data for 2D in Profile 2 41

Table 4.12: Raw Data for 2D in Profile 2 42

Table 4.13: Raw Data for 2D in Profile 2 42

Table 4.14: Raw Data for 2D in Profile 2 43

Table 4.15: Raw Data for 2D in Profile 2 43

Table 4.16: RawData for 2D in Profile 2 44

Table 4.17: Raw Data for VES in Profile 3 44

Figure 1.1: Approximation of time varying infiltration rate 8

Figure 1.2: Sketch diagram of (a) homogeneous (b) Inhomogeneous (C) Anistropy aquifers 9

Figure 1.3: Hydrological cycle and aquifers type 11

Figure 1.4: Base map of the study area 12

Figure 1.5: Geological map of Ogun State showing the study area 13

Figure 3.1: A conventional four electrode array to measure the subsurface Resistivity 27

Figure 3.2: Common arrays used in resistivity surveys and their geometric factors (Loke, M.H 1997; 1999) 28

Figure 3.3: 2D measurement Using Wenner Arrangement Configuration (Loke, 1999) 30

Figure 3.4: Schlumberger Array Configuration 32

Figure 4.1: Showing the PAS Earth Resistivity Meter used for Data Aquistion 40

Figure 5.1: Showing the measured data of the study area for profile 1 46

Figure 5.2: Showing the measured apparent resistivity, calculated  apparent resistivity and inverse model resistivity section for profile 1 of the study area 47

Figure 5.3: Showing the field work survey in progress 48

Figure 5.4: Showing the measured data of the study area for profile 2 49

Figure 5.5: Showing the measured apparent resistivity, calculated apparent resistivity and inverse model resistivity section for profile 2 of the study area 50

Figure 5.6: Showing typical curve for VES 1 51

Figure 5.7: Showing typical curve for VES 2 51

Figure 5.8: Showing typical curve for VES 3 52

Figure 5.9: Showing typical curve for VES 4 52