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This study focuses on the analysis of groundwater quality and direction of flow in Ehime Mbano South-Eastern Nigeria with the aim of minimizing cases of abortive water well projects in the area. Ehime Mbano is located within Anambra-Imo sedimentary basin of South-Eastern Nigeria. The study area is underlain by Benin Formation (miocene-recent), Bende-Ameki Formation (Eocene) and Imo Shale Formation (Palocene). It is located from latitude 5o 37' N to 5o 46' N; and longitude 7o 14' E to 7o 21' E. Elevation, Vector Grid and 3-D surface maps were used to ascertain the direction of water flow which slopes in two directions: North-West to South-East and North-West to South-South West with a point of convergence noticed at Umunakanu, Umuezeala 1, Umuakagu and Umunumo. A total of 60 vertical electrical soundings, using Schlumberger configurations with AB/2 = 400m was undertaken to estimate aquifer parameters within the study area. The VES data were interpreted using state of the art soft wares e.g. IP12WIN and Surfer 12 to obtain the final model for each VES. Isoresistivity studies were carried out in the area and contoured at specific distances of AB/2 = 1m, 8m, 15m, 50m, 150m, 200m, 250m, 300m and 350m. Results revealed significant variations of electrical resistivity with depth. Regions of low resistivities such as Nzerem, Lowa,and Agbaja were identified. Places of high resistivities were also observed in the Southern and South- regions especially around Ikperejere and Ibeafor. The results of this study using electrical resistivity method to characterize the aquifer revealed various aquifer parameter values within the area. The resistivity values indicate the presence of clay, top soil, sand and sandstone lithologies. The average resistivities of rock units within the study area vary between 1000Ωm and 10,000Ωm. The central and southern parts of the study area like Ikperejere, Ibeafor have relatively higher resistivity values making them more viable for groundwater exploitation than the Northern parts which have relatively low resistivity values like Agbaja, Nzerem and Lowa. The most abundant resistivity curves are with KK, KHK and HK types with a percentage abundance of 21.7%, 18.3% and 16.7% respectively revealing major sustainable aquifers and their depth of occurrence. Majority of the locations have transmissivities between 50m2/day and 500m2/day while few places have high values of 501m2/day to1100m2/day especially at Umuchienta in the southeast, Umueleke and Umuawuchi. Aquifer vulnerability assessment carried out revealed areas with high, low and moderate vulnerability based on the DRASTIC Index. Locations with high vulnerability rating of 126 -165 include: Umuokiri Umunumo and Ikperejere. Locations with moderate vulnerability rating of 86-125 include: Ikpem, Ikweii Nzerem while locations with low vulnerability rating of 70-85 include: Umuokara Uzinomi and areas close to Umueze II. Water quality analysis was conducted for fifteen water samples within the study area. Analysis of physicochemical, heavy metals and microbiological characteristics (pH, Conductivity, Turbidity, Total Dissolved Solids (TDS), Acidity, and Alkalinity), was carried out using standard laboratory techniques. The results were compared with World Health Organization (WHO) Standard and Nigerian Standard for Drinking Water Quality (NSDWQ). Some water samples had concentration of five parameters being clearly above both WHO and NSDWQ permissible limits. This raises concern of contamination and health risk, hence the need for periodic treatment and monitoring of ground water in the area. It is recommended that a regional water scheme should be established at locations such as Ezeoke Nsu with possible high yield so that it can serve other communities where groundwater prospect is slim. In all, a good aquifer characterization has been presented which can serve as a guide to hydrogeophysical and hydrogeological information for groundwater in the area.


Title page                                                                                                                    i

Certification                                                                                                                ii

Declaration                                                                                                                  iii

Dedication                                                                                                                  iv

Acknowledgements                                                                                                    v

Table of contents                                                                                                        vi

List of Tables                                                                                                              x

List of Figures                                                                                                             xi

List of Plates                                                                                                               xiv

Abstract                                                                                                                      xv




1.1        Background of the Study                                                                               1

1.2       Location of the Study Area                                                                            5

1.3       Geology of the Study Area                                                                            8

1.3.1    Benin Formation                                                                                             12

1.3.2    Bende-Ameki Formation                                                                                12

1.3.3    Imo shale Formation                                                                                       13

1.4       Statement of the Problem                                                                               13

1.5       Aim and Objectives                                                                                        14

1.6       Justification for the Study                                                                              15

1.7       Scope of the Study                                                                                         16


CHAPTER 2:                        LITERATURE REVIEW

2.1       Literature Review of Previous Works                                                               17

2.2       Literature on Studies on other Geological Provinces in Nigeria                       19

2.3       Literature Review of Works in other Parts OF the World                                20

2.4       Hydrogeology of the Study Area                                                                     26

2.5       Geophysical Methods in Groundwater Studies                                                28

2.5.1    Basic theories of electrical resistivity                                                                28

2.5.2    Application of resistivity method                                                                     31

2.5.3    Resistivity of earth materials                                                                             31

2.5.4    The real and apparent resistivity                                                                       32

2.5.5    Electrical properties of rocks                                                                             33

2.5.6    Electrical resistivity surveys                                                                              35

2.5.7    Limitations of the restivity method                                                                  35

2.6       Electrode Configuration                                                                                   36

2.6.1    Schlumberger electrode configuration                                                              38

2.6.2    Types of sounding curves                                                                                 39

2.7       Groundwater Occurrence                                                                                  41

2.7.1    Aquifer characteristics                                                                                      44

2.7.2    Types of aquifers                                                                                               44 Confined aquifer                                                                                               45 Unconfined aquifer                                                                                           45 Perched aquifer                                                                                                 46

2.7.3    Anisotropy of aquifers                                                                                      46

2.7.4    Recharge and discharge of groundwater                                                                      47

2.8       Groundwater Management                                                                               48

2.8.1    Monitoring groundwater                                                                                   49

2.8.2    Water balance                                                                                                    50

2.8.3    Control of human activity                                                                                 50

2.8.4    Pollution                                                                                                            51

2.9       Hydrogeological Concepts                                                                                53

2.9.1    Groundwater flow and confinement                                                                54

2.9.2    The water- table                                                                                                 56

2.9.3    The hydraulic head                                                                                            57

2.9.4    Hydraulic gradient (i)                                                                                        59

2.9.5    Hydraulic conductivity (K)                                                                               60

2.9.6    Transmissivity                                                                                                   61

2.9.7    Transverse resistance                                                                                         62

2.9.8    Longitudinal conductance                                                                                63

2.9.9    Porosity and permeability of rocks                                                                   64 Porosity                                                                                                             64 Permeability                                                                                                      65 Water saturation                                                                                                68

2.9.10  Groundwater storage                                                                                        69

2.10     Review of Previous Works on Groundwater Vulnerability                              72

2.10.1 Groundwater vulnerability assessment methods                                               75 Statistical methods (empirical methods)                                                         75 Overlay and index methods                                                                            76 Drastic                                                                                                          76


CHAPTER 3:                        MATERIALS AND METHODS

3.1       Instrumentation                                                                                               79

3.2       Data Acquisition                                                                                             80

3.3       Precautions                                                                                                      82

3.4       Vulnerability                                                                                                   82

3.5       The Application of the Drastic Model to the Study Area                              83

3.5.1    Depth to the water table                                                                                 84

3.5.2    Net recharge                                                                                                    84

3.5.3    Aquifer media                                                                                                 84

3.5.4    Soil media                                                                                                       85

3.5.5    Topography                                                                                                     85

3.5.6    Impact of the vadose zone                                                                              85

3.5.7    Hydraulic conductivity                                                                                   86

3.6       Weights and Ratings for the Drastic Parameters                                            86

3.7       Development of an Understanding of the Flow System                                89

3.8       Groundwater Quality Assessment                                                                  89


CHAPTER 4:                        RESULTS AND DISCUSSION

4.1       Curve Types                                                                                                    91

4.2       Apparent resistivity, Co-ordinates and Elevation                                           114

4.2.1    Iso-resistivity at AB/2 = 1m and at AB/2 = 8m                                             127

4.2.2     Iso-resistivity at AB/2 = 15 m and 50 m                                                        130

4.2.3    Iso-resistivity at AB/2 = 150 m and at AB/2 = 200 m                                   133

4.2.4    Iso-resistivity at AB/2 = 250 m and at AB/2 = 300 m                                   136

4.2.5    Iso-resistivity at AB/2 = 350 m                                                                      139

4.3       Interpretation of Profiles (Cross Sections)                                                     141

4.3.2    Geoelectric section (B-B')                                                                               146

4.3.3    Geoelectric section (C-C')                                                                               148

4.4       Aquifer Parameters and Characterization                                                      150

4.4.1    Aquifer restivitity                                                                                           153

4.4.2    Water tables                                                                                                    155

4.4.3    Aquifer Thickness                                                                                           157

4.4.4    Transverse resistance                                                                                       159

4.4.5    Transmissivity                                                                                                 161

4.4.6    Hydraulic Conductivity                                                                                  163

4.4.7    Storativity Distribution                                                                                   165

4.5       Aquifer Vulnerability Ratings                                                                        167

4.6       Water Quality Analysis                                                                                   173

4.6.1    pH and turbidity of the water samples                                                           177

4.6.2    Dissolved oxygen (DO) and nitrite concentrations of the water samples      180

4.6.3    Iron concentration and colour of the water samples                                       183

4.6.4    Electrical conductivity (EC), Total dissolved solids (TDS), dissolved

            solids and other micro elements                                                                      186

4.7       Elevation and Direction of Water Flow                                                         191



5.1       Conclusion                                                                                                      195

5.2       Recommendations                                                                                         198


REFERENCES                                                                                                        200

APPENDIX                                                                                                               217



1.1:                  Stratigraphic sequence in south-eastern Nigeria                                 10

2.1:                  Resistivity ranges of rock types (Telford et al., 1976)                        32

2.2:                  Order of magnitude of K for different kinds of rock                        61

2.3:                  Porosity of different geological materials                                           65

2.4:                  The relative assigned weight(s) of DRASTIC model parameters

                        and its description                                                                               77

3.1:                  Depth to water table                                                                           87

3.2:                  Net recharge rating in inches                                                              87

3.3:                  Aquifer media characteristics                                                             87

3.4:                  Soil media                                                                                           88

3.5:                  Topography                                                                                         88

3.6:                  Impact of the vadose zone                                                                  88

3.7:                  Net recharge showing the rating based on the hydraulic

                        conductivity                                                                                        89

3.8:                  DRASTIC index ranges for qualitative risk categories                      89

4.1:                  Curve types and their characteristics                                                  113

4.2:                  Apparent resistivity data for the 60 VES points for ρ1 - ρ3                     115

4.3:                  Apparent resistivity data for the 60 VES points for ρ4 – ρ10                   117

4.4:                  Apparent resistivity data for the 60 VES points for ρ11 – ρ17                 119

4.5:                  Apparent resistivity data for the 60 VES points for ρ18 – ρ20                                 121

4.6:                  True resistivities and depths of modelled geoelectric layers              123

4.7:                  Aquifer parameters of the study area                                                 151

4.8:                  Aquifer Vulnerability Obtained from DRASTIC Index                    170

4.9:                  Location of different aquifer vulnerability categories and their                                 associated colours ramp                                                                172

4.10:                Location of water samples and their coordinates                               175

4.11:                Result of water quality analysis                                                          176








1.1:                  Location map of the study area                                                          7

1.2:                Geologic outline map of Nigeria showing basement and sedimentary

                      basins                                                                                                    9

1.3:                Geologic map of the study area                                                            11

2.1:                  General four electrode configuration for resistivity measurement

                        consisting of a pair of current electrodes (A, B) and a pair of

                        potential electrodes (M, N)                                                                 30

2.2:                  Schlumberger arrangement of electrodes                                            38

2.3:                  Two-layer master set of sounding curves for the Schlumberger

                        Array                                                                                                   40

2.4:                  Types of three-layer Schlumberger sounding curves                          41

2.5:                  The hydrological cycle                                                                        43

2.6:                  Confined and unconfined aquifers                                                     45

2.7:                  Perched aquifer                                                                                   46

2.8:                  Recharge and discharge of groundwater                                            48

2.9:                  Groundwater pollution                                                                       52

2.10:                Pollution sources                                                                                 53

2.11:                Groundwater flow and confinement                                                  55

2.12:                Hydraulic head                                                                                   58

2.13:                Darcy’s Law                                                                                       59

2.14:                Permeability of rock                                                                            65

2.15:                Schematic representation of aquifer storativity                                  71

3.1:                  The schematic diagram of electrical resistivity operating

                        Principles                                                                                             81

4.1(a):              Computer modelled curves of VES 1 to 3                                         93

4.1(b):              Computer modelled curves of VES 4 to 6                                         94

4.1(c):              Computer modelled curves of VES 7 to 9                                         95

4.1(d):             Computer modelled curves of VES 10-12                                         96

4.1(e):              Computer modelled curves of VES 13 to 15                                     97

4.1(f):              Computer modelled curves of VES 16 to 18                                     98

4.1(g):              Computer modelled curves of VES 19 to 21                                     99

4.1(h):              Computer modelled curves of VES 22 to 24                                     100

4.1(i):               Computer modelled curves of VES 25 to 27                                     101

4.1(j):               Computer modelled curves of VES 28 to 30                                     102

4.1(K):             Computer modelled curves of VES 31 to 33                                     103

4.1(l):               Computer modelled curves of VES 34 to 36                                     104

4.1(m):             Computer modelled curves of VES 37 to 39                                     105

4.1(n):              Computer modelled curves of VES 40 to 42                                     106

4.1(o):              Computer modelled curves of VES 43 to 45                                     107     

4.1(p):              Computer modelled curves of VES 46 to 48                                     108

4.1(q):              Computer modelled curves of VES 49 to 51                                     109

4.1(r):              Computer modelled curves of VES 52 to 54                                     110

4.1(s):              Computer modelled curves of VES 55 to 57                                     111

4.1(t):              Computer modelled curves of VES points 58 to 60                           112

4.2:                  The various categories of iso-resisitivity range at AB/2 = 1m            128

4.3:                  Various categories of iso-resisitivity at AB/2 = 8m                            129

4.4:                  Various hotspots of iso-resisitivity range at AB/2 = 15m                   131

4.5:                  Several points of iso-resisitivity range at AB/2=50m                         132

4.6:                  Iso-resisitivity range at AB/2=150m                                                   134

4.7:                  Highest, moderate and lowest range of iso-resisitivity at AB/2=200m 135

4.8:                  Various spots of io-resisitivity range at AB/2 = 250m                       137

4.9:                  Isoresistivity of the study area at AB/2=300M                                  138

4.10:                Various spots of isoresistivity at AB/2=350M                                   140

4.11:                Map showing VES profile in the study area                                       143

4.12:                Geoelectric section (A-A') of N-S direction of the study area           145

4.13:                Geoelectric section (B-B') of NW-SE direction of the study area     147

4.14:                Geoelectric section (C-C') of E-W direction of the study area          149

4.15:                Aquifer resistivity map of the study area                                           154

4.16:                Water table map of the study area                                                      156

4.17:                Aquifer thickness map of the study area                                            158

4.18:                Transverse resistance map of the study area                                       160

4.19:                Aquifer transmissivity map of the study area                                     162

4.20:                Hydraulic conductivity map of the study area                                   164

4.21:                Aquifer storativity map of the study area                                           166

4.22:                Aquifer vulnerability index map of the study area                             169

4.23:                pH contour map                                                                                  178

4.24a:              Turbidity Contour Map                                                                       178

4.24b:              Turbidity Concentration Chart of Water Samples                              179

4.25a:              Dissolved oxygen contour map                                                          181

4.25b:              Dissolved oxygen concentration chart of water samples                    181

4.26a:              Nitrite contour map                                                                             182

4.26b:              Nitrite concentration chart of water samples                                      182

4.27a:              Iron contour map                                                                                184

4.27b:              Iron concentration chart of water samples                                          184

4.28:                Colour contour map                                                                            185

4.29:                Electrical conductivity concentration chart of water samples            187

4.30:                Total dissolved solids contour map                                                    187

4.31:                Dissolved solids contour map                                                             188

4.32:                Nitrate contour map                                                                            188

4.33:                Phosphorus contour map                                                                     189

4.34:                Alkalinity contour map                                                                       189

4.35:                Zinc contour map                                                                                190

4.36:                Elevation contour map of the study area                                            192

4.37:                Groundwater flow direction                                                               193

4.38:                Vector grid map showing flow direction                                            194

4.39:                3-D Surface map of study area                                                           194





Supervisor with the research students                                                            217

The field crew                                                                                                 217

Researcher with field crew mounting the equipment                                     218

The researcher fixing the electrode firmly to the ground                               218







Water as a massive forceful fluid form conveys with it occasionally toxins of fluctuating and unpredictable amounts therefore quality groundwater availability has come under severe threat due to anthropogenic causes. This has led to the contamination of ground and surface water. In Ehime Mbano for instance, there seem to be increased rate of water pollution or unhealthy groundwater drilled for consumption; water contamination are chiefly due to urban and agricultural activities. Such contaminated water when consumed gives rise to some diseases like cholera, diarrhea, dysentery, hepatitis A and typhoid fever (Nwachukwu et al., 2010b). In severe cases it can lead to fatalities with children and pregnant women being the most affected. This hampers their socio-economic development, stability and overall welfare of the community (Public Health Madison and Dane County, 2017). The Wisconsin Department of Natural Resources, Bureau of Drinking Water and Groundwater (2005) recommended that well water should be atleast tested annually preferably at the end of raining season, and when ever a well is serviced including changing of submersible pump. Well qater should also be tested whenever a change in taste, odour or colour is noticed. This research tends to investigate the safety and quality as well as the abundance of water in Ehime Mbano with a view to reducing the cases of abortive wells in Ehime Mbano.

Water is indispensable in life and serves for drinking, domestic, industrial, and agricultural purposes. Groundwater makes up more than 90% of the biosphere’s freely accessible stream resources with residual 10% in lagoons, pools, streams and swamps (Basewinkel, 2000; Asonye et al., 2007). Most of the earth’s liquid freshwater is not found in lakes and rivers, but is stored underground in aquifers. Groundwater is a globally relevant, cherished and renewable resource. It is described as the water found beneath the surface of the earth in underground streams and aquifers (Anomohanran, 2011). However, an aquifer is defined as a permeable geologic unit which will yield useful quantities of water. The thickness of the aquifer refers to the volume of ground water in the location. It is contained in geological Formations. During the periods of no rainfall, these aquifers proffer an appreciable base flow distributing water to rivers. Due to the vast growing awareness in the capacity of groundwater development and sustainability, a quantitative description of aquifers has turn out to be a dynamic mandate to report and deal with multitudes of hydrogeological issuess. These aquifers, therefore require conservation so that groundwater can remain to sustain the human race and the outstanding ecosystems that rely heavily on it.

Due to an ever-increasing population in the society and industrialization, the demand for water increased, hence the need for sustainable groundwater development to compensate the depleting surface water. Ehime Mbano local government area has experienced high rate of abortive boreholes drilled over the years without previous knowledge of the subsurface stratification. With this in mind, active geophysical technique (electrical resistivity method) has been employed in this study and groundwater models are designed to serve as appreciated projecting implements for controlling of groundwater in the study area. A model is an implement aimed to symbolize a basic version of reality. Models are used in our everyday life. Groundwater models are scientific simulations resulting from Darcy’s law which is beneficial in estimating the proportion cum flow of groundwater via the aquifer cum restraining components in the sub-units (Chowdhury et al., 2010; Igboekwe and Achi, 2011).

Using groundwater models, it is promising to investigate several supervision and controlling patterns in order to forecast the impact of certain actions. The soundness of the prediction depends on how well the model approximates field conditions. Groundwater model are indispensable tool in forecasting the effect of pumping on groundwater levels.  They might as well be advantageous to foretell certain prospective ground-water current system in the area. Generally, groundwater current simulations are vital in describing the extent of groundwater accessible or route of liquefied movement. It also supports in outlining the perimeter of an apprehended region for a pollution reclamation well or for describing a liquid well shield region (or rejuvenate zone in lieu of water provision (Igboekwe and Udoinyang, 2011).

Dissolved substances or suspended ones in groundwater reveal its worth. In most subsurface materials, deferred resources are not conveyed to a superior degree but often filtered out. The distribution of subsurface geological materials plays a large role in these models to see whether the prediction made with the numerical models are representative of the true natural system.  In general, groundwater flow rest on the penetrability of the sub-unit resources and eqaully the hydraulic slope (gradient of the compression for artesian situations). The flow of some fluid through a porous medium is expressed in Darcy’s law based on the results of experiments on the flow of water through beds of sand. It states that the rate of flow is directly proportional to the drop in vertical elevation between two places in the medium and directly proportional to the distance between them.

The flow of water (and other liquids) via a leaky intermediate is explained in Darcy’s law (equation 1.1):


K                     = Permeability

Q                     = groundwater flow rate (m3/s)

(H1-H2)            = piezo metric head drop (m)

A                     = Cross sectional area (m2)

L                      = distance between wells (m)

According to UNEP 2002, Freshwater quality and availability remains unique out of the utmost critical environmental and sustainable issues of the 21st century. One reason why groundwater has become more popular as a foundation of drinkable water is due to its quality, and it is relatively easy and cheap to use when compared to other water sources. It is known to be free most times from pollutants and hence requires little or no decontamination before use. Lawrence and Ojo (2012) noted that groundwater is most generally free from odour, colour and has very low dissolved soliaquiferd. It is also not usually affected by natural factors such as drought since it is stored in s which are natural underground reservoirs.

In Mbano, there is proliferation of shallow private/commercial wells of poor stands owned by indviduals. This is as a result of financial paucity/poverty and lack of purposeful communal water stock. The shallow well implies that the groundwater in the area is polluted especially by percolation of contaminated water by nearby laterines and some unhealthy heavy metals in the vicinity of wells. Citizens are therefore constrained to the proliferation of shallow substandard wells often recharged by surface water through fractures, and harvested rain water stored in under ground tanks of all manners. This might be attributable to the tenacity of water associated ailments in the basin (Nwachukwu et al., 2013). Proliferation of shallow private/commercial wells of poor standards by individuals also implies financial incapability for outstanding bores. This is owing to absence of purposeful communal water stock, and the extreme aspiration of inhabitants to be self-dependent. The most contaminated wells are usually the shallow hand-dug rather than drilled, and having poor casing material (Comely, 1987). According to Nwachukwu et al., (2010b), the greatest problem of manual drilling is the impunity at which the operators declare the drilling terminated, soon as the crew penetrates the water table, or run out of energy. Ibe et al., (2007); Nwachukwu et al. (2010a), and Nwachukwu et al. (2010c), have confirmed that environmental pollution in the Imo River basin increases from the shale north to the sandy south. They hold that human activities also follow a similar trend, representing the primary source of water pollution in the Imo River basin.


Ehime Mbano is situated within Anambra-Imo sedimentary basin of South-eastern Nigeria. It is bounded by latitude 5° 37' N to 5 °46' N and longitude 7° 14' E to 7° 21' E. Ehime Mbano is one of the Local Government Areas in Imo State occupying an area of 169 kilometer square with a population of 130,931 as at the 2006 census and is projected to be 204,340 people in 2015. It is surrounded at the North by Onuimo and at the South by Ahiazu Mbaise and from the East and West by Ihitte/Uboma and Isiala Mbano/Onuimo/Okigwe local government areas correspondingly. Its drainage pattern is dendritic, typical of sedimentary rocks with uniform resistance and homogenous geology (Dever and James, 1985). A tropical climate exists in the region and it witnesses two air commonalities: equatorial marine air commonalities, related with fall bearing South west breezes commencing via Atlantic Ocean around March to September (Egbueri et al., 2020) and the arid and dirty hamattan breezes from Sahara desert blowing around December to February. The yearly total average rainfall is around 230mm and temperature arrays from 29°C during arid periods to around 33°C in drizzling period. The relative humidity in the area the ranges from 65% to 75% (Egbueri et al., 2020). The physiography is dominated by a segment of Northern, Southeastern trending Okigwe regional escarpment which stands at elevation of between 61m and 122m above sea level (Alfred, 1992). The vegetation of the study area is tropical rain forest which is predominant in the Southern states of Nigeria. Due to excessive request of land in the area combined with extra man actions particularly excessive grazing, the rain forest has been populated by certain profitable produce like oil palm forest. In the area, the soil is loamy with dispersed gravels (Batayneh, 2013). Bushy vegetative concealments shield soil erosion in the region, nevertheless, erosion is noticeable in the regions where path cuts, and where forest clearing and excessive vegetation have widened up the soil (Stephen, 2004). The presence of Benin Formation is a contributory factor to soil erosion especially where they are exposed unprotected by vegetation (Onunkwo– Akunne and Ahiarakwem, 2001).