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ABSTRACT
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.
TABLE OF CONTENTS
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
CHAPTER 1
INTRODUCTION
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
2.7.2.1 Confined
aquifer 45
2.7.2.2 Unconfined aquifer 45
2.7.2.3 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
2.9.9.1 Porosity 64
2.9.9.2 Permeability 65
2.9.9.3 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
2.10.1.2 Statistical methods (empirical methods) 75
2.10.1.3 Overlay and index methods 76
2.10.1.3.1 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
CHAPTER
5: CONCLUSION AND
RECOMMENDATIONS
5.1 Conclusion 195
5.2
Recommendations 198
REFERENCES 200
APPENDIX 217
LIST
OF TABLES
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
LIST
OF FIGURES
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
LIST
OF PLATES
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
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
OF THE STUDY
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):
where
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.
1.2 LOCATION
OF THE STUDY AREA
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).
Fig. 1.1: Location map of the study area
1.3 GEOLOGY
OF THE STUDY AREA
The study area falls within the Cenozoic
Niger Delta basin geologically. The Niger Delta is situated in the Gulf of
Guinea and extends throughout the Niger Delta Province. From Eocene to the
present, the delta has prograded southwestward, forming depobelts that
represent the most active portion of the delta at each stage of its development
(Doust and Omatsola, 1990).
The Niger Delta is divided into three
formations, representing prograding depositional facies that are distinguished
mostly on the basis of sand-shale ratios namely: Akata, Agbada and Benin
Formations. The Akata Formation at the
base of the delta is of marine origin and it comprises of thick shale sequence
(potential source rock), turbidite sand (potential reservoirs in deep water),
and minor amounts of clay and silt.
Deposition of the overlying Agbada Formation,
the major petroleum-bearing unit, began in the Eocene and continues into the
Recent. The Agbada Formation is overlain by the third Formation, the Benin
Formation, a continental late Eocene to Recent deposit of alluvial and upper
coastal plain sands that are up to 2,000m thick (Avbovbo, 1978).
Fig. 1.2: Geologic outline map of Nigeria showing basement and sedimentary basins
Ehime
Mbano and environs falls within
Anambra –Imo sedimentary basin of
South-eastern Nigeria and is underlain by Benin Formation (–miocene – recent) (youngest) Bende-Ameki Formation (Eocene) and Imo Shale
Formation (Paleocene) and oldest in
the area (Reyment 1965). The major aquiferous
formation is Benin Formation (Parkinson, 1970;
http://www.sciencepub.net/rural).
Table 1.1: Stratigraphic
sequence in south-eastern Nigeria
|
Age (my) |
Abakaliki-Anambra Basin |
Afikpo Basin |
|
|
30 |
Oligocene |
Ogwashi-Asaba
Formation |
Ogwashi-Asaba
Formation |
|
54.9 |
Eocene |
Ameki/Nanka Formation/Nsugbe
Sandstone |
Ameki Formation |
|
65 |
Paleocene |
Imo Formation Nsukka Formation |
Imo Formation Nsukka Formation |
|
73
83 |
Maastrichtian
|
Ajali Formation Mamu Formation Nkporo/Owelli
Sandstone/Enugu Shale (Including Lokoja
Sandstone and Lafia sandstone
|
Ajali Formation Mamu Formation Nkporo
Shale/Afikpo Sandstone |
|
Campanian |
|||
|
Santonian |
Agbami
Sandstone/Agwu Shale |
Non-deposition/erosion |
|
|
87.5
88.5
93
100
119 |
Coniacian
|
|
|
|
Turonian
|
Ezeaku Group
Asu River Group |
Ezeaku Group (Incluing Amasiri
Sandstone) |
|
|
Cenomanian-Albian |
|||
|
Aptian Barrenian
Hauterivian |
Unnamed units |
||
|
Precambrian |
Basement complex |
||
Source: (Nwajide and Reijers, 1996)
Fig.
1.3: Geologic map of the study area
1.3.1 Benin Formation
Benin
Formation is among the sub-surface stratigraphic components in the contemporary
Tertiary Niger delta. It spreads from the west across the whole Niger delta
district of Nigeria and southward beyond the present coast-line (Short and
Stauble, 1978; Ehirim and Ofor, 2011).This Formation is the youngest of
Oligocene. It is almost found at the top most part of the earth. The thickness
varies from one place to another. It is above ninety percent sandstone with
shale intercalations. It is coarse grained, gravelly, locally fine grained, poorly
sorted, and sub-angular to well-rounded and bears lignite streaks and wool
fragments. The Formation is a continental latest Eocene to Recent deposit of
alluvial and upper coastal plain sands. Various structural units such as point
bars, channel fills, natural levees, back swamp deposits and oxbow fills are
identifiable within the Formation indicating the variability of the shallow
water depositional medium.
1.3.2 Bende-Ameki
Formation
Bende-Ameki
Formation constitutes the main bulk of Eocene strata overlying the Imo Shale
Formation. This Formation consists of sequence of highly fossiliferous grayish-green sandy- clay
with calcareous concretions and white clay sandstones. It consists of two
lithological groups: the lower with fine-to-coarse sandstones and
intercalations of calcareous shale and thin, shaly-limestone and the upper with
coarse, cross- bedded sandstones, bands of fine, grey to green sandstone and
sandy clay. Bende-Ameki layers consist of speedily interchanging shale, sandy
shale, mudstone, clayey sandstone and good grained argillaceous sandstone with
thin limestone bands. In some places, the inter-bedded sandstone attains a
thickness of about 33m and is richly fossiliferous.
The
beds dip gently between 5o and 7o S. In general,
Bende-Ameki strata show steeper dips than the overlying Imo Shale Formation (strata)
which indicates unconformable relationship. The age of the Bende-Ameki
Formation is generally considered to be Lutetian to lower Bartonian age (Kogbe,
1976). The Formation is richly fossilifereous, foraminifera (dead plants) and
corals predominating.
1.3.3 Imo shale
Formation
Imo
Shale Formation consists of thick clayey shale, fine-textured dark grey to
bluish grey with occasional mixture of clay ironstone and thin sandstone bands.
Carbonized plants are locally common and the Formation becomes sandier towards
the top where it may consist of an alteration of bands of sandstone and shale.
The type area is along the Imo River between Umuahia and Okigwe with a
thickness of approximately 50m (Wilson, 1925; Simpson et al., 1955; Kogbe, 1976). It rests conformably on the Nsukka Formation
and shows lateral variation into sandstones in some places. These arenaceous
lateral equivalents are the Igbabu sandstone, Ebenebe sandstone and Umuna
sandstone (Reyment, 1965; Kogbe, 1976).
1.4 STATEMENT OF THE PROBLEM
Surface
and groundwater resources in Ehime, Mbano area are threatened by contamination
and consequently, rendering them unfit for consumption. In addition, few
government aided borehole projects and shallow wells by individuals have failed
due to seasonal recharge problems. Therefore, greater parts of the rural
population depend on the available surface water sources, such as rivers, lakes
and streams which are highly vulnerable due to surface contaminants which
result: water borne diseases e.g. guinea
worm, typhoid and cholera are prevalent within Ehime Mbano etc. Incidentally
most of the shallow private and commercial wells in the basin are hand-driven,
and some constructed with inferior casings.
The
lack of public water supply to people of Ehime Mbano over decades of years has
denied the people access to good and quality water. This has provoked my
research on analysis of groundwater quality and direction of flow in Ehime
Mbano South-Eastern Nigeria in order to proffer solutions to these perennial
problems. Hence, the surface water is not sustainable throughout the year.
This
makes the region depend on the largest available source of quality fresh water
which lies underground and this is referred to as groundwater. It is the water
found beneath the surface of the earth in underground streams and aquifers
(Anomohanran, 2011; Ariyo and Banjo, 2008). Groundwater can be in alluvial
landscape where it is fewer challenging to exploit excluding for its chemical
configuration. It can as well be in the basement multifaceted landscape where
it can be a minute problematic to discover principally in spaces triggered by
crystal-like unfractured or unweathered rocks. This study will involve the
geophysical and geochemical analyses. It will improve/provide knowledge of ground
water scarcity in the area and it will bridge the gap and improve the living
standard of the inhabitants.
1.5 AIM AND OBJECTIVES
The aim of this study is to analyze the
groundwater quality and direction of flow in Ehime Mbano such that cases of
abortive or failed water well projects could be minimized in the area.
Specific objectives that will be executed in
order to achieve the purpose of this study include:
i.
To undertake resistivity data analysis and characterization of various
geological Formations of the study area, delineating areas suitable for
sustainable groundwater development using state-of-the-art soft wares.
ii.
To map out aquifer systems or hydro geologic units by assessing the
groundwater vulnerability and DRASTIC Indices.
iii.
To develop an understanding of the groundwater flow systems indicating
the direction of flow within the study area, Ehime Mbano.
iv.
To determine the groundwater quality in Ehime Mbano and its environs.
1.6 JUSTIFICATION
FOR THE STUDY
Unavailability
of groundwater prospect map of an area for public consumption is believed to
have contributed greatly to the increasing failure of water well projects in
Ehime Mbano. Groundwater prospect map is a vital tool to government in water
well allocation decision making process. Thus, individuals, establishments,
societies, and governments could envisage regions expected to be difficult for
groundwater development and then be committed to alternative water sources in
such areas. This will reduce incidents of failure, perched, abortive, or abandoned
public wells and non-functionality of domestic water wells common in South East
Nigeria. It is therefore very necessary to do everything possible to reduce
incidents of abortive wells, sub-standard domestic wells, and non-functional
wells. With good groundwater model and prospect maps, government or private
individuals would approve contracts of water well projects to only viable
areas, excluding areas where difficult subsurface geology does not allow
successful groundwater development. This will reduce economic wastes, and
environmental degradation as well as disappointment and hardship to the
affected communities.
1.7 SCOPE OF
THE STUDY
The study is limited
to Ehime Mbano local government area of Imo State Nigeria which is comprises of
11 electoral wards (Wikipedia, 2016). The study covers the entire Ehime Mbano
Local Government Area with the following Formations: Benin, Bende-Amaeke,
Ogwashi Asaba Formation and Imo Shale.
This study has three major aspects Viz: the resistivity (VES) aspect,
the vulnerability assessment aspect and groundwater quality analysis aspect.
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