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 TitleiCertificationiiDedicationiiiAbstractivAcknowledgementvTable of contentsviList of figures xList of tablesix CHAPTER ONE 1.1 Introduction 1Aims, objectives Justification of the study 3 1.4 Location and accessibility of the study area 3Topography and drainage Climate 631.7 Land use / vegetation6 Review of previous work done 8Basic resistivity theory 9
Electrical properties of earth materials 12
1.9 Electrical method 16
CHAPTER TWO2.1 Regional Geology 18 2.2 Regional stratigraphic setting of Eastern Dahomey Basin 212.3 Geology of the study area 25 2.4 Hydrogeology of the study area 26
3.1 Methodology27 3.1.1 Cleaning of the reagent bottles 273.1.2 Sample collection and analysis 273.1.3 Sample analysis 283.2 Procedures 283.2.1 Cleaning of reagent bottles and collection vessels 283.2.2 Sample collection and presentation 283.2.3 Sample analysis 283.3 Cations32 3.4 Anions33 3.5 2- D geophysical investigation CHAPTER FOUR37 Results and discussion Geophysical dataPhysio chemical data Chemical characteristics41 63 414.1.1pH64 4.1.2 TDS(Total Dissolved Solids)64 4.1.3 EC( Electrical Conductivity)64 4.1.4 Temperature64 4.2 Chemical assessment65 Cations 4.2.1 Calcium 674.2.2 Magnesium67 4.2.3 Sodium68 4.2.4 Potassium Anions68 4.3.1 Chloride 684.3.2 Bicarbonate68 4.4 Parameters for Irrigation Purposes71 4.4.1 SAR (Sodium Adsorption Ratio)71 4.4.2 SSP (Soluble Sodium Percent) 714.4.3 RSBC (Residual Bicarbonate) 714.4.4 PI (Permeability Index) 714.4.5 MAR (Magnesium Adsorption Ratio 724.4.6 KR(Kelly’s Ratio)72
Conclusions 73Recommendations 74
LIST OF FIGURES FigurePage1: Location map of the study area (Alapoti) 42: Drainage map of the study area 53: Vegetation map of Nigeria showing the study area7 4a: Direction of current flow 104b: Four electrode array measurement of sub surface resistivty 114c: Common arrays used in resistivty surveys and their geometric factors 115: Map of eastern Dahomey Basin 206: Showing the field physical characteristics analysis35 7: Showing the laboratory sample analysis procedure36 8: 2- D measurement using Wenner array configuration 389: Showing the placing of electrodes 394.0 Layout of Area covered during geophysical investigation42 Pseudo section for traverse one 43Pseudo section for traverse two 49Pseudo section for traverse three 53Pseudo section for traverse four 57Pseudo section for traverse five 61
LIST OF TABLES
TablePage 1: Resistivity of rocks and Minerals 172: Stratigraphy of Nigerian Part of Dahomey Basin 244.0: Resistivity value for traverse one 434.1: Resistivity value for traverse two47 4.2: Resistivity value for traverse three51 4.3: Resistivity value for traverse four55 4.4: Resistivity value for traverse five59 4.5: Summary of 2- D resistivity investigation62 4.6: Physical parameters of water samples 634.7: Chemical parameters (Cations and Anion66 4.8: Summary of Physico chemical parameters, SON and WHO standard 694.9: Parameters from water samples in Alapoti with regards to Irrigation 70
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