GEOPHYSICAL AND PHYSICO- CHEMICAL CHARACTERISTICS OF GROUNDWATER IN ALAPOTI AND ITS ENVIRONS, OGUN STATE, SOUTH- WESTERN NIGERIA

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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  
Titlei
Certificationii
Dedicationiii
Abstractiv
Acknowledgementv
Table of contentsvi
List of figures x
List of tablesix 
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    63
1.7 Land use / vegetation6 
  1. Review  of previous work done                                                             8
    1. 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 Basin 21
2.3 Geology of the study area 25 
2.4 Hydrogeology of the study area  26

CHAPTER THREE

3.1 Methodology27 
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 Cations32 
3.4 Anions33 
3.5 2- D geophysical investigation     CHAPTER FOUR37 
Results and discussion Geophysical dataPhysio chemical data Chemical characteristics41     63  41
4.1.1pH64 
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 67
4.2.2 Magnesium67 
4.2.3 Sodium68 
4.2.4 Potassium Anions68 
4.3.1 Chloride 68
4.3.2 Bicarbonate68 
4.4 Parameters for Irrigation Purposes71 
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  
FigurePage
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 area7 
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 analysis35 
7: Showing the laboratory sample analysis procedure36 
8: 2- D measurement using Wenner array configuration 38
9: Showing the placing of electrodes 39
4.0 Layout of Area covered during geophysical investigation42 
  • 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

TablePage 
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 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 63
4.7: Chemical parameters (Cations and Anion66 
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