ABSTRACT
Electrical resistivity method involving the 2- D surveying was carried out within the sedimentary complex terrain of Alapoti Ogun State South Western Nigeria with a view of estimating the geo electric layer parameters ( resistivity and thickness), to identify the aquifer types and evaluate the groundwater potential and overburden protective capacity over the aquifer.
Sixty three (63) 2- D electrical resistivity readings were taken around the area using the Wenner Beta array. The preliminary layer parameters obtained were forward modelled using the win resist software to obtain the final layer parameters, and pseudo sections were created. Five traverses were covered. Each traverse was 100m long and were taken in the West –East direction in community High School, Alapoti
Fresh water/Aquifers/Surface water is encountered at depth ranging from 1.25m to 9.26m with thickness ranging from 2,5m to 8.01m. The location of the fresh water/ surface water/aquifer is indicated in the pseudo section. The water is slightly acidic with pH ranging from 4.28 to 5.22, while Ca2+, Mg2+, K+, are below the W.H.O
recommendation. The average values for the Sodium Adsorption Ratio, Soluble Sodium Percent, Magnesium Adsorption Ratio, Kelly’s Ratio, Permeability Index, and Residual Bicarbonate were: 64.84, 79.0, 133.7, 5.87, 649.7, and 7.33 respectively and all of them except Permeability index are above the recommended values.
Based on the findings, the groundwater is slightly acidic with relatively shallow depth, odourless and potable, but poor for irrigation purposes.
Key words: 2–D Resistivity, Alapoti, Aquifer, Irrigation, Potability.
| TABLE OF CONTENTS | ||
| Title | i | |
| Certification | ii | |
| Dedication | iii | |
| Abstract | iv | |
| Acknowledgement | v | |
| Table of contents | vi | |
| List of figures | x | |
| List of tables | ix | |
| CHAPTER ONE 1.1 Introduction | 1 | |
| Aims, objectives Justification of the study | 3 | |
| 1.4 Location and accessibility of the study area | 3 | |
| Topography and drainage Climate | 6 | 3 |
| 1.7 Land use / vegetation | 6 |
- Review of previous work done 8
- Basic resistivity theory 9
Electrical properties of earth materials 12
1.9 Electrical method 16
CHAPTER TWO
| 2.1 Regional Geology | 18 | ||
| 2.2 Regional stratigraphic setting of Eastern Dahomey Ba | sin | 21 | |
| 2.3 Geology of the study area | 25 | ||
| 2.4 Hydrogeology of the study area | 26 |
CHAPTER THREE
| 3.1 Methodology | 27 | |
| 3.1.1 Cleaning of the reagent bottles | 27 | |
| 3.1.2 Sample collection and analysis | 27 | |
| 3.1.3 Sample analysis | 28 | |
| 3.2 Procedures | 28 | |
| 3.2.1 Cleaning of reagent bottles and collection vessels | 28 | |
| 3.2.2 Sample collection and presentation | 28 | |
| 3.2.3 Sample analysis | 28 | |
| 3.3 Cations | 32 | |
| 3.4 Anions | 33 | |
| 3.5 2- D geophysical investigation CHAPTER FOUR | 37 |
| Results and discussion Geophysical dataPhysio chemical data Chemical characteristics | 41 63 | 41 |
| 4.1.1pH | 64 | |
| 4.1.2 TDS(Total Dissolved Solids) | 64 | |
| 4.1.3 EC( Electrical Conductivity) | 64 | |
| 4.1.4 Temperature | 64 | |
| 4.2 Chemical assessment | 65 | |
| Cations | ||
| 4.2.1 Calcium | 67 | |
| 4.2.2 Magnesium | 67 | |
| 4.2.3 Sodium | 68 | |
| 4.2.4 Potassium Anions | 68 | |
| 4.3.1 Chloride | 68 | |
| 4.3.2 Bicarbonate | 68 | |
| 4.4 Parameters for Irrigation Purposes | 71 | |
| 4.4.1 SAR (Sodium Adsorption Ratio) | 71 | |
| 4.4.2 SSP (Soluble Sodium Percent) | 71 | |
| 4.4.3 RSBC (Residual Bicarbonate) | 71 | |
| 4.4.4 PI (Permeability Index) | 71 | |
| 4.4.5 MAR (Magnesium Adsorption Ratio | 72 | |
| 4.4.6 KR(Kelly’s Ratio) | 72 |
CHAPTER FIVE
- Conclusions 73
- Recommendations 74
References 75
| LIST OF FIGURES | ||
| Figure | Page | |
| 1: Location map of the study area (Alapoti) | 4 | |
| 2: Drainage map of the study area | 5 | |
| 3: Vegetation map of Nigeria showing the study area | 7 | |
| 4a: Direction of current flow | 10 | |
| 4b: Four electrode array measurement of sub surface resistivty | 11 | |
| 4c: Common arrays used in resistivty surveys and their geometric factors | 11 | |
| 5: Map of eastern Dahomey Basin | 20 | |
| 6: Showing the field physical characteristics analysis | 35 | |
| 7: Showing the laboratory sample analysis procedure | 36 | |
| 8: 2- D measurement using Wenner array configuration | 38 | |
| 9: Showing the placing of electrodes | 39 | |
| 4.0 Layout of Area covered during geophysical investigation | 42 |
- Pseudo section for traverse one 43
- Pseudo section for traverse two 49
- Pseudo section for traverse three 53
- Pseudo section for traverse four 57
- Pseudo section for traverse five 61
LIST OF TABLES
| Table | Page | |
| 1: Resistivity of rocks and Minerals | 17 | |
| 2: Stratigraphy of Nigerian Part of Dahomey Basin | 24 | |
| 4.0: Resistivity value for traverse one | 43 | |
| 4.1: Resistivity value for traverse two | 47 | |
| 4.2: Resistivity value for traverse three | 51 | |
| 4.3: Resistivity value for traverse four | 55 | |
| 4.4: Resistivity value for traverse five | 59 | |
| 4.5: Summary of 2- D resistivity investigation | 62 | |
| 4.6: Physical parameters of water samples | 63 | |
| 4.7: Chemical parameters (Cations and Anion | 66 | |
| 4.8: Summary of Physico chemical parameters, SON and WHO standard | 69 | |
| 4.9: Parameters from water samples in Alapoti with regards to Irrigation | 70 |
GEOPHYSICAL AND PHYSICO- CHEMICAL CHARACTERISTICS OF GROUNDWATER IN ALAPOTI AND ITS ENVIRONS, OGUN STATE, SOUTH- WESTERN NIGERIA
