ESTIMATON OF PRIMARY CHARACTIRISTIC OF AQUIFER USING VERTICAL ELECTRICAL SOUNDING: A CASE STUDY OF ALIERO LOCAL GOVERNMENT, KEBBI STATE, NIGERIA

TABLE OF CONTENT

TITLE PAGE i

CERTIFICATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

TABLE OF CONTENT vi

LIST OF FIGURES viii

LIST OF TABLES x

ABSTRACT xi

CHAPTER ONE 1

1.1   AQUIFER 2

1.2 CLASIFICATION 3

1.3 SATURATED AND UNSATURATED 3

1.4 SATURATED 4

1.5 UNSATURATED 4

1.6     AQUIFER VERSUS AQUITARD 4

1.7 AQUITARD 4

1.8 CONFINED VERSUS UNCONFINED 4

1.9 AQUIFER CHARACTERISTICS 5

1.10 AIMS AND OBJECTIVES 5

1.11 SIGNIFICANCE OF THE STUDY 6

1.12 STATEMENT OF THE PROBLEM 6

1.13 SCOPE OF THE RESEARCH 6

CHAPTER TWO 7

2.0 LITERATURE REVIEW 7

2.1 Brief geology of Nigeria 7

2.2 GEOLOGY OF KEBBI STATE 8

2.3 DRAINAGE 9

2.4 CLIMATE 9

2.5 SOIL 10

2.6 VEGETATION 10

2.7 DEPTH 11

2.8 GEOLOGY OF THE STUDY AREA 11

2.9 REVIEW OF LITERATURE WORK 11

CHAPTER THREE 14

3.0 MATERIALS AND METHOD 14

3.1 INSTRUMENTS USED 14

3.2 METHODOLOGY 14

3.3 ELECTRICAL RESISTIVTY TECHNIQUE 15

3.4 BASIC THEORY OF ELECTRICAL RESISTIVITY TECHNIQUE 16

3.5 SCHLUMBERGER CONFIGURATION 17

3.6       WENNER CONFIGURATION 18

CHAPTER FOUR 19

4.0   DATA PROCESSING AND INTERPRETATION OF RESULT 19

4.1   DATA PRESENTATION 19

4.2   INTERPRETATION OF VES RESULT 19

Table 4.1: Summaries of VES results 25

CHAPTER FIVE 27

5.0  CONCLUSION, RECOMMENDATION REFFERENCES 27

5.1  CONCLUSION 27

5.2   RECOMMENDATIONS 27

5:3  REFERENCE 28

LIST OF FIGURES

FIGURE 1.1: DESCRIPTION OF THE STUDY AREA

FIGURE 3.1: SCHLUMBERGER ARRAY

FIGURE 3.2: WENNER ARRAY

FIGURE 4.0: PSEODUSECTION EQUIVALENT OF EOELECTION FORMATION

FIGURE 4.1a: VERTICAL ELECTRICAL SOUNDING (VES 1) PLOT OF CURVE MATCHING  USING MICROSOFT EXCEL 

FIGURE 4.1b: VERTICAL ELECTRICAL SOUNDING (VES 1) PLOT OF  COMPUTERITERATION TECHNIQUES  USING  THE  SOFTWARE CALLED IPI-2 WIN.

FIGURE 4.2a: VERTICAL ELECTRICAL SOUNDING (VES 2) PLOT OF  CURVE MATCHING  USING MICROSOFT EXCEL.

FIGURE 4.2b: VERTICAL ELECTRICAL SOUNDING (VES 2) PLOT OF COMPUTER ITERATION TECHNIQUES USING THE SOFTWARE CALLED IPI-WIN

FIGURE 4.3a: VERTICAL ELECTRICAL SOUNDING  (VES 3) PLOT OF CURVE MATCHING  USING  MICROSOFT EXCEL.

FIGURE 4.3b: VERTICAL ELECTRICAL SOUNDIN  (VES 3) PLOT OF COMPUTER  ITERATION TECHNIQUES  USIN G THE SOFTWARE  CALLED IPI-2 WIN

FIGURE 4.4a: VERTICAL ELECTRICAL SOUNDING  (VES 4) PLOT OF CURVE MATCHING  USING MICROSOFT EXCEL

FIGURE 4.4b: VERTICAL ELECTRICAL SOUNDING  (VES 4) PLOTOF COMPUTER ITERATION TECHNIQUES  USING THE SOFTWARE  CALLED IPI-2 WIN.

FIGURE 4.5a VERTICAL ELECTRICAL SOUNDING (VES 5) PLOT OF CURVE MATCHING USING MICROSOFT EXCEL.

FIGURE 4.5b: VERTICAL ELECTRICAL SOUNDING  (VES 5) PLOT OF  COMPUTER   ITERATION TECHNIQUES  USING THE  SOFTWARE  CALLED IPI-2 WIN.

LIST OF TABLES

TABLE  4.1: SUMMARIES  OF  THE  (VES) RESULT.

ABSTRACT

The aim of this study is to assess the resistivity layer in some selected area of Aliero, Nigeria. This was carried out by evaluating the geoelectrical and hydrogeological characteristics of the aquifer in the area. The Vertical Electrical Sounding (VES) technique using the Schlumberger array configuration was applied to investigate the geoelectrical characteristics. The data obtained were interpreted first by partial curve matching, computer iteration techniques. The result of interpretation indicates the presence of (3-4) three to four geo electric layers which are composed of fine sand formation clayey sand and loose sand mud stones peaty soil medium grain. The result also revealed the presence of confined aquifer located in layer (4) four and unconfined in layer (3) three. The various geoelectrical interpretations and hydrogeological results depict that the best sites for locating wells or boreholes in Aliero, within study areas are VES stations 2, 3, and 4. While probability of getting good ground water in VES station 1 is very infinitesimal, this might result from the presence of high accumulated pollutant in the station

 CHAPTER ONE

Introduction

The need for the quality and availability of water resources has always been the primary concern of our societies especially in semiarid and arid region, and even the areas with abundant rainfall such as tropical region. The problem of gaining an adequate supply of quality water is generally becoming more severe effect due to ever increasing of population, irrigation and industrialization. Due to this situation, surface water cannot be dependable throughout the year; hence other alternative is needed in order to supplement for surface water. The groundwater is sthe water lies under ground and it is the best quality fresh water which the world depend on its availability source. It is the water held in the sub-surface within the saturated zone under hydrostatic pressure below water table. The groundwater can be in sedimentary terrain where it is less difficult to exploit or in the basement complex terrain in which it can be a bit difficult to locate especially in areas underlined by crystalline rocks (Fadele, et al., 2013).

Nowadays the used of geophysical techniques for groundwater exploration and water quality evaluation has increases due to rapid advances in computer software and other numerical modeling techniques. The use of vertical electrical sounding (VES) has become very popular with groundwater prospecting due to simplicity of the techniques. The purpose of electrical geophysical survey method is to detect the surface effects that produce by the flow of electric current inside the earth. These techniques have been used in a wide range of geophysical investigation such as mineral exploration, archaeological investigation, engineering studies, geothermal exploration, permafrost mapping and geological mapping. 

Electrical method are generally classified according to energy source involved that is either natural or artificial. Those under natural source method include self-potential (sp), telluric current and magneto telluric while those under artificial source methods are relatively, electromagnetic (EM) and induced polarization (IP) methods. The present research used one of the artificial methods, which is the use of electric D.C resistivity method using Instrument Called ABEM (SAS300) terrameter which were taken using schlumberger array. 

1.1   AQUIFER

An aquifer is a body of saturated rock through which water can move. Aquifer must be both permeable and porous and include such rock types as sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel. Fractured volcanic rocks such as columnar basalts also make good aquifers. 

It has been established in Nigeria that aquifers consist of:

Weathered zones of hard rocks.

Fractured basement rocks.

Alluvium layer (along stream channels and rivers channels).

Figure 1.1 Aquifer  (Ajiobade et al., 1979)

1.2 CLASIFICATION

The above diagram indicates typical flow direction in a cross section view of a simple confine or unconfined aquifer system. The system shows two aquifers within one aquitard (a confining or impermeable layer) between them, surrounding by the bedrock aquiclude, which  is in contact with a gaining stream (typical in humid regions).

1.3 SATURATED AND UNSATURATED

Ground water can be found at nearly every point in the earth shallow surface to some degree, although aquifer does not necessarily contain fresh water. The earth’s crust can be divided into two regions. The saturated zone (e.g. aquifer and aquitards etc.), where all available space are filled with water, and the unsaturated (also called vadose zone), where there are still pockets of air that contain some water.

1.4 SATURATED 

Saturated mean the pressure head of the water is greater than atmospheric pressure ( it has a gauge pressure greater than zero). The definition of the water table is the surface where the pressure head is equal to atmospheric pressure (where gauge pressure = 0).

1.5 UNSATURATED

Unsaturated conditions occur above the water table where the pressure head is negative (absolutely pressure can never be negative, but gauge pressure can) and the water that incompletely fills the pores of the aquifer material under sunction. The water content in the unsaturated zone is held in place by surface adhesive forces and it rises above the water table.

1.6     AQUIFER VERSUS AQUITARD

Aquifer are typically saturated regions of the subsurface that produce an economically feasible quantity of water to a well or spring (e.g. sand and gravel or fractured bedrock often makes good aquifer materials).

1.7 AQUITARD

An aquitard is a zone within the earth that resist the flow of ground water from one aquifer to another. A completely impermeable aquitard is called an aquiclude or aquifuge. An aquitard comprises layers or either clay or non porous rocks with hydraulic conductivity.

1.8 CONFINED VERSUS UNCONFINED

There are two end members in the spectrum types of aquifer, confined and unconfined. Unconfined aquifers are sometimes called water table or phreatic aquifers, because their upper boundary is table or phreatic surface. The shallowest aquifer at a giving location is unconfined meaning it does not have a confining layer between it and the surface. Confined aquifers have very low storativity values (much lesser than 0.01, and as little as 10ˉ5), which means the mechanism of aquifer matrix expansion and the compressibility of water, which typically are both quite small quantities.

1.9 AQUIFER CHARACTERISTICS

The aquifer characteristics of the study area classified base on similarity or nearly similar hydro geological characteristics of geological structure. One of the basic element of Hydrological study is production of Hydrological characteristics of hydro stratigraphic units, basically the geological characteristics of the area that include degree of fracturing and degree of weathering, geological structure that favorite groundwater storage and movement and other parameters play significant role in designing capture and dewatering system of the groundwater. Besides, schematizing the natural hydro geological conditions, it is important to know the hydraulic/hydro geological parameters. There are several important physical properties that govern the capability of aquifer to store, transmit, and yield groundwater. Reliable interpretations and conclusion about the whole aquifer performance in an area are not possible without the accurate determination of these basic aquifer’s physical properties.

1.10 AIMS AND OBJECTIVES

The aim of this research is to:

Investigate the depth thickness and resistivity of aquifer using vertical electrical sounding.

To determine water quality assessment.

To determine which software will give correct interpretation of primary aquifer characteristic.

      The specific objective of this research is to determine the electrical estimation of primary aquifer characteristics using vertical electrical sounding (VES), correct interpretation of the software used can assist in mapping of the depth, thickness and resistivity to the water table and bedrock and locate AIMS AND OBJECTIVES correct anomaly of the sub surface such as minerals, water, and petrol etc.

1.11 SIGNIFICANCE OF THE STUDY

            The study of geophysical investigation of resistivity layer and classification using vertical electrical sounding (VES) method could provide base line information which could be useful to both governmental agencies interested in the country (Nigeria). The study would in addition aid in demonstrating and alternative technology for exploiting different type and classification in the study are that may be relevant to students of geophysics, hydrogeology, soil science and researchers in similar disciplines.

1.12 STATEMENT OF THE PROBLEM

The demand for water has increased due to increase in population. The traditional Electrical Resistivity method is the commonly used method in ground water investigation. Electrical resistance survey is one of a number of methods used in wide span for investigation, leading to problems with horizontal resolution.

1.13 SCOPE OF THE RESEARCH

The scope of this research is to investigate the characteristics of aquifers by employing vertical electrical sounding (VES) method in selected areas in Aliero local government, Kebbi state.

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 Brief geology of Nigeria

Nigeria lies in an extensive pan-African mobile belt which separates the West African and Congo cratons. The belt is interpreted to have evolved from the continental collusion between the West African craton and the pan-African belt (Burke and Dewey 1972). The latter part of pan-African orogeny was characterized by brittle deformation which resulted in a very consistent conjugate strike –slip fault system consisting of fault trending Northeast-Southwest (Grant, 1979).

The surface area of Nigeria, 923,768 square kilometers is covered, almost in equal proportions, by the crystalline rocks of the Basement Complex and sedimentary rocks.  The sediments are mainly Upper Cretaceous to recent in age, while the Basement Complex rocks are further divided into three main groups, viz; the Basement Complex, younger Granites, and the tertiary recent volcanic.  The Basement complex rocks include the undifferentiated metamorphic and igneous rocks, and their insitu weathering products (over burden). On the other hand, the sedimentary rocks are divided into eight main basins. These include Lower Benue Trough (Anambra Basin), Middle Benue Trough, Upper Benue Trough, Borno Basin (Chad Basin), Bida Basin,Niger-Delta Basin, and Sokoto Basin (Figure 2.1).

Figure 2.1: Region geological map of Nigeria (Ajiobade et al., 1979)

2.2 GEOLOGY OF KEBBI STATE

The geology of Kebbi State is dominated by two formations; Precambrian Basement Complex in the southern and south east young sedimentary rocks in the north. The Basement Complex region is composed of very old volcanic and metamorphic rocks such as granites schists, gneisses, quaetzites and migmatites. In addition there are met sediments such as phyllites and met Conglomerates. The sedimentary region consists of the Gwandu, Illo and Rima groups whose ages range from the cretaceous to the Ecocene. The Gwandu group consist of massive clay grits inter bedded with sand stone while the Illo and Rima groups consist of pebby grits, sand stone and clays mudstone and siltstone respectively. Minerals that can be found in the State include quartz, kaolia, piotoltitic bauxite, clay, potassium silica sand and salt.

Kebbi State can be divided into three relief regions, namely the high plains in the south and southeast, the plain land scape in the north and the reverine lowland of the Niger and low Rima valleys. The high plain are characterized by dissected crystalline rocks with hills ranges and domical rises (inselbergs). It is approximately 700m above sea level. The plain landscape forms parts of the vast Sokoto plain which is an end tertiar plantation surface (Ajiobade, 1979). It is a monotomous lowland, sedimentary in origin, with average height of about 300m above sea level. The plain surface is interrupted by isolated flat-topped laterite capped hills and ridges. The reverend lowlands are mainly the flood plains of the major rivers which are very wckide, up to 8km in many areas. They are characterized by leaves, backswamos and terraces on the natural vegetation.

2.3 DRAINAGE

The drainage system in Kebbi State is dominated by River Rima system with major tributaries like Gawon, Zamfara, and Gubinka. These tributaries rise in the basement complex region of Sokoto State and flow westward to join the Rima. However, in the southern part of the State, there are other less important rivers such as Danzaki, Soda and Kasanu, all of which flow to join the river Niger to the south of the Sate. Most of the rivers first flow through deep and narrow valleys with step gradients on the Basement Complex rocks, and then through broad shallow valleys when they flow through the sedimentary formations. The Rima itself flows in abroad sweeping valley through the Sedimentary area and then into River Niger in the south west, creating extensive flood plans that have no semblance to present discharges, thus indicating that it is a product of a more humid quaternary period in the past.  In terms of flow regimes, most of the rivers are storm channels maintaining bank full discharges after individual rainstorm events only to dry out with the cessation of rainfall. This characteristic is also reflected in seasonal flow situations.

2.4 CLIMATE

Kebbi State enjoys a tropical Continental type of climate. This is largely controlled by two air masses, namely Tropic Maritime and Tropical Continental, blowing from the Atlantic and Sahara desert respectively. These air masses determine the two dominant seasons wet and dry. The wet season last from April to October in the south and May to September in the North; while the dry season last for the remaining period of the year. Mean annual rain is about 800mm in the North and 1000mm in the South. Temperature is generally high with mean annual temperature of about 26 º in all locations. However, during the harmattan season (December to February) the temperature can go down to about 21º and up to 40 ºc during the months of April to June Night temperature are generally lowered (Caby et al., 1981). Relatively humidity is generally low 40% for most of the year except during the wet season when it reaches an average of 8%. This explains the hot dry environment which is a sharp contrast to a hot humid environment in the southern part of Nigeria.

2.5 SOIL

In the northern part of the State, two groups of soil can be identified; the upland and the fadama soil group are generally characteristics of the Sokoto Rima Basin. While the upland soils are sandy and well drained, the fadama soils are generally clay and hydro morphic, especially in the back swamp. In the south and south eastern parts, the weathering of the Basement Complex rocks has given rise to three types of soils. These are the ferruginous tropical soils, back cotton soils and litho soils. These soils are subject to stripping by erosion as a result of topographic characteristics typical of the area.

2.6 VEGETATION

The natural vegetation of the State consists of a Northern guinea Savannah in the South Southern. They are characterized by medium sized trees such as the South Southern. They are characterized by medium sized trees such as Parkia Clapperoniana (locust been trees) and bytrosperium (shear butter trees) and Combretum species. In the North, the sudan Savannah consists of open wood land with scattered trees such as acacia (Gawo). Parkia clappetoniana, porassus and dum palms, have allowed the hydro geological characteristics of the basic to be evaluated. They defined the boundaries of the basic and the sediment thickness. (Onuoha, 1988) used electrical resistivity measurements, he conclude that the study would be very helpful for finding suitable sites for studies of recharge, contaminates and dewatering of aquifers.

2.7 DEPTH

Aquifer may occur at various depths, those closer to the surface are not more likely to be used for water supply and irrigation, but are also more likely to be topped up by the local rainfall. Many desert areas have limestone hills or mountains within them or close to them that can be exploited as ground water resources. 

2.8 GEOLOGY OF THE STUDY AREA

The present study are Aliero and the entire land mass lies within the young sedimentary rocks, the sedimentary region consist of rocks of the Gwandu, Illo, Rima group whose  ages range from the cretaceous to the Eocene. The Gwandu group consist of massive clay grits, sandstones and clays mudstone and siltstones respectively and present of the some minerals like clay,quark, Kaolin,silica, sand and salt, etc. The study area has a plain landscape relief form part of the vast Sokoto plain which is an end tertiary plantation surface (McCurry, 1977). It is monotonous lowland sedimentary in origin with average height of about 300m above the sea level. The plain surface is interrupted by isolated flat topped laterite capped hills ridges.

2.9 REVIEW OF LITERATURE WORK 

The literature review contain considerable information, methods and techniques employed during data acquisition and interpretation, several researchers have carried out geophysical exploitation for ground water using vertical electrical sounding (VES) this include Ujuanbi (2000) used this method to map clay deposit in a dual geological environment. This method was used in the assessment of the ground water resources potentials within the Obudu basement, Okwueze (1996). Etu-Efeotor et al. (1989) carried out an assessment of the near surface underground water resources potential within the eastern Niger Delta. Olorufemi et al. (1995) carried out a Pre-drilling ground water development in the proterozoic basemen of the Kaduna State. Nigeria, using Electromagnetic and resistivity methods. The VES was carried out with both the wenner and Schlumberger arrays. A total of 150 VES station was established and 76 rural areas investigated. 

The quantitative interpretation of VES data involved partial curve marching and computer iteration. They concluded that the EM method is sensitive to shallow water bearing, unconfined sheet-like fractures. It is not amenable to the delineation of confined fractures that are concealed by infinitely resistive, fresh, Precambrain basement rocks. Sultan and Mohammed (2009) carried out a total of vertical electrical soudings, using Schlumberger configuration in Cairo University in Egypt, in order to investigate the aquifer characteristics and ground water potential of the surface 1P17.63. The depth and resistivity of the subsurface layers were determined. Also, the iso-apparent resistivity maps, the geoelecric sections, the iso-thickness map of the aquifer and the resistivity map of aquifer were drawn. The results of the interpretation of the VES data revealed the presence of the following electric layers:

Near-surface layers and dry alluviume with resistivity ranging from 1 to 15000 km and thickness varies from 16 to 23m. 

The second layer, which constitutes aquifer for study area, has resistivity value varying from 0.3 to 6.4 Ωm while the thickness varies from 6.9-10.7m. it is composed of fine-grained sand.

The third layer, which constitutes Marly bedrock, characterized by electrical resistivity value varying  from 6.8 to 37Ωm in most part of area  and with depth ranges from 23.8 to 33m.  The resistivity value of this layer in two sounding is 120 and 131 Ωm. this is probably caused by existing many lime stone in these sounding.

The forth geoelectric layer, has resistivity values ranging from 0.4 -4 Ωm.Nkankwo and Olashinde (2013). Carried out a combine use of sounding profiling resisting measurement with electrode arrays. They showed that the combination of the maximum information about distribution of resistivity’s in the earth and that resistivity data from such measurements can be presented as electrical normal sounding curve. They concluded that with three electrodes arrays, thin concluded that with three electrode arrays, thin conductors and contact lithological units of different resistivity’s can be accurately located. Application of surface geophysics to ground water investigation has been carried out  the work on automatic interpretation of Schlumberger sounding curves. 

Alile et al. (2008). Carried out geophysical exploration involving the use of vertical electrical sounding (VES) in a sedimentary environment to determine the suitability of the method for underground water study. In their work, the Schlumberger electrode array configuration and Schlumberger automatic analysis method of interpretation was adopted.

CHAPTER THREE

3.0 MATERIALS AND METHOD

3.1 INSTRUMENTS USED

ABEM Tetrameter SAS 300 power by a 12.8v DC Battery

Four (4) electrodes of stakes.

Two (2) sets of measurement tapes.

Coiled wires.

 (2) set of Hammers

GPS (Global positioning system).

3.2 METHODOLOGY

The following procedures are followed during the data acquisition:

The Terrameter was powered by the DC source and further adjustment on Terrameter was made such as; setting the number of cycles to 4, automatic reading of values in Ohms and setting a 50mA of current into the ground.

Data acquired was plotted on a log-log graph sheet and the resultant curved was quantitatively interpreted.

 Terrain level of the VES station was located and using the Schlumberger array.

When the ratio of the distance between the current electrodes and the potential electrodes became too large, the potential electrodes were displaced outwards otherwise the potentials difference becomes too small to be measured with sufficient accuracy.

The four (4) electrodes were position symmetrically along a straight line i.e. the current electrode (C1 and C2) on the outside and the potential electrodes (P1 and P2) at the inner, placed in between C1 and C2.

The steps were repeated at subsequent VES stations.

To change the depth of penetration, the current electrodes were displaced outwards while the potential electrodes remains fixed.

The maximum current electrode spacing (AB/2) was 100m and the Terrameter was used to measure and record the resistance of the subsurface.

The values of resistance obtained in the field were multiplied with their respective Geometric factor (K) which gave the required apparent resistivity results.

The (GPS) instrument was used in locating the longitude and the latitude of each VES station.

3.3 ELECTRICAL RESISTIVTY TECHNIQUE

The most useful electrical resistivity technique is the application of vertical electrical sounding (VES) using Schlumberger and Wenner array. The resistivity ρ and half the distance between the two current electrodes (AB/2), are plotter on a log-log graph, and the curved formed is curve matched using model and auxiliary curves for different layers types. Hence, the curve matching techniques involves the comparison of the field curves with master curve. Resistivity measurement are made to obtain the resistivity of the earth layer by using vertical electrical sounding (VES) which probes down into the various layer present including the aquifer layer if present.

Naturally, these two operations describe above (i.e. parameters from pumping test and vertical electrical sounding) are usually carried out independently by different apparatus, instrument and techniques. Application of the field hydro geological of assessment method is the standard technique for evaluating aquifer parameters. However, estimating hydraulic conductivity or permeability (K), transitivity (T) and storability (S) values from field pumping test and down well-log data is expensive and time consuming, therefore, surficial resistivity methods which probe vertically can provide rapid and effective technique for groundwater exploration and aquifer evaluation (Niwas and Singhal 1981). The electrical resistivity method is one of the most relevant geophysical methods applied in the groundwater investigation in the basement terrain.

 3.4 BASIC THEORY OF ELECTRICAL RESISTIVITY TECHNIQUE

In the Principle of electrical resistivity survey, electric current is usually sent to the ground through the current electrodes. The variation in the potential difference (pd) between the two electrodes is usually measured. The current electrode is usually outside while the potential electrode is inside. Ohms law stated that, the current flowing through a wire is proportional to the potential difference across its end, governs the current movement in a material.

i.e.  V = IR                                (1)

DV = IV,                                                                                                                                (2)

Where

 DV = Potential difference,

I = Current,

R = Resistance,

 Therefore,                                                                                                                        (3)

The inverse of R, is the conductance (S) or (Ω-1) calculate micros/cm or Siemens. Resistance varies for the some material depending on the dimension on the equation. The relationship between resistance (R), length (L) and cross section area (A) is giving a                 (4)

                                                                                                                              

Where ρ = proportionality constant called resistivity, indicates the ability of a material to oppose the flow of charge. Hence from equation (5)

RA = ρ                                (6)

        This is the resistance of a material, it defined as the resistance in Ohms between the opposite face of a unit cube of the material. The unit is (Ωm). The inverse of the resistivity is the conductivity of the material, the S. I. unit as Siemens per meter i.e.                                                                                                                                                                                                                                                                                                                                                           

3.5 SCHLUMBERGER CONFIGURATION

           For certain type of work, e.g. where high resolutions is required, the Schlumberger confirmation is preferred to that of winner configuration. For a Schlumberger array, the two current electrodes and the two potential electrodes are placed in line with other, centered on some location, but the potential and current electrodes are not placed equidistant from one another. In the field operations the inner (potential) electrodes remain fixed, while the other (current) electrode are left adjust to the distance S. the spacing is adjusted  due to decreasing sensitivity of measurement. The spacing must be large than 0.45m or the potential gradient assumption is no longer valid. The resistivity values obtained are plotted against electrode spacing and the resulting curves are used for interpretation.

Figure 3.1 Schematic diagram of Schlumberger array

3.6       WENNER CONFIGURATION 

        The Wenner configuration consist of four electrodes in line, separated by equal intervals, the Wenner array demands less instruments sensitivity and data reduction is marginally easier, in this research, the Shclumberger array was adopted.

                                                       I                                  

                                                     V

                      a                              a                              a                    

            A             M                                             N               B    

Figure 3.2 Schematic diagram of Wenner array

CHAPTER FOUR

4.0   DATA PROCESSING AND INTERPRETATION OF RESULT

4.1   DATA PRESENTATION

For the resistivity studies, the apparent resistivity data are presented as depth sounding curves. The curves were obtained by plotting the apparent resistivity data (in Ohm-meter) as ordinate against electrode spacing (in meters). The curve types are classified primarily on the basis of the shape of curves, but at the same time is related the geological situation of the subsurface. The quantitative interpretation of the VES curves was carried out in two stages. Which are:

Curve Matching.

Computer iteration Techniques using the software called IPI-2 Win.

4.2   INTERPRETATION OF VES RESULT

The typical sounding curved obtained from the computer iteration of resistivity data are presented in figure 4.2 to 4.5 from the resistivity curve the geoelectric layers varies from 3-4m in all the profiles. The geoelectric layers delineated correspond to the top soil, dry wet sand, mud stones and clay. The summarized table is in Table 4.1.

Co-linear VES points were also processed to obtain apparent resistivity against current electrode AB/2 Plot section in the study area. As presented in Figures 4.2(a-b)-Fig. 4.5(a-b).

The resistivity and thickness of the top soil varies from 892Ωm - 2326Ωm and from 0.5m-9.06m respectively. The second layer is dry wet sand with resistivity and thickness of 51.4Ωm - 273Ωm and from 3.48m-33.2m. It resistivity varies with degree of saturation. The third layer represent the mudstone. The resistivity of this layer varies from 2.21Ωm-20792Ωm and from 0m-10.1m respectively. The last layer is the less compacted claycompacted clay which has resistivity which ranges from 2.05 Ωm to 1352 Ωm.The resistivity Peudo-section show continuos high resistivity zone on the surface VES 1, VES3, VES4 (Fig. 4.2a- 4.5b). This is zone due to it high resistivity may be regarded as the dry layer. The geoelectric plot sections Fig. 4.1 show variation in lithology from one VES point to another (Fig. 4.2a-4.5b). With the depth to bedrock generally less than 7.17m.

Fig. 4.1: Pseudo-Section Equivalent of Eoelection Formation

VES 1:

The resistivity of the top soil shows higher degree of variation from 0Ωm -1243Ωm and thickness from 0m – 9.06m. The second layer has a decrease in resistivity from 1243Ωm-273Ωm and thickness increase from 9.06 m-33.2m the top soil which is probably dry wet sand. The third layer is mud stones which indicates the presence of high resistivity from 273Ωm -20792Ωm. In the third layer, toward last layer there is indication of high resistivity which could be considered to be water bearing layer. This is a clear indication of varying lithology at vertical progression at some profile at depth.

Figure 4.2a: Vertical Electrical sounding (VES 1) plot of Curve Matching Using Microsoft Exce

VES 2: 

The result of this study in comparison to lithologic log has shown a (4) four layered formation. The first layer is mainly fine sand formation. The resistivity of this layer ranges from 0Ωm-892Ωm while the thickness ranges from 0m-0.2. The second layer with resistivity range from 892Ωm-175Ωm it is composed of medium grain with thickness ranging from 2.03m-  4.02m.the Third layer is made up of sandy clay with resistivity ranging from 175Ωm– 1414Ωm while the thickness ranges from 4.02m- 10.1m, The forth layer composed of Peaty soil with resistivity of 1414Ωm-2.05Ωm.    

Figure 4.3a: Vertical Electrical sounding (VES 2) plot of Curve Matching Using Microsoft Excel

 Figure 4.3b: Vertical Electrical sounding (VES 2) plot of Computer iteration Techniques

VES 3:

The analysis of this results has shown four layers formation, the first layer of which is made up of peaty soil with resistivity from 0Ωm-2326Ωm. while the thickness range from 0m-0.5m.the second layer is mainly fine sand formation. The resistivity of this layer ranges from 2326Ωm- 51.4Ωm, while the thickness ranges from 0.5m-4.86m.the third layer which is composed of  sandy clay  with resistivity range from 51.4Ωm-2.21Ωm,and the thickness ranges from 4.86m-5.71m.the fourth layer also made up of clayey sand and loose sand with resistivity range from 2.21Ωm-1352Ωm. And it indicate that groundwater exist in the second and forth layers. While the second layer aquifer is unconfined and prone to pollution, the second aquifer in the fourth layer is confined and therefore of good quality. 

 

Figure 4.4a: Vertical Electrical sounding (VES 3) plot of Curve Matching Using Microsoft Excel

 Figure 4.4b: Vertical Electrical sounding (VES 3) plot of Computer iteration Techniques

VES 4:

The result of this study in comparison to lithologic log has shown a (3) three layered formation. The first aquifer is found in the first layer with resistivity ranging from 0Ωm-895Ωm. It is composed of fine sand formation with thickness ranging from 0m – 3.17m. This is a very thin unconfined bed and will therefore be prone to contamination. Consequently, this aquifer is unreliable and will not yield water for the residents of the area. while the second layer is mainly clayey sand and loose sand. The resistivity of this layer ranges from 895Ωm-65.6Ωm while the thickness ranges from 3.13m – 3.48m.the Third layer is made up of mud stones with resistivity ranging from 65.6Ωm-1156Ωm.

 Figure 4.5a: Vertical Electrical sounding (VES 4) plot of Curve Matching Using Microsoft Exc

Figure 4.5b: Vertical Electrical sounding (VES 4) plot of Computer iteration Technique

Table 4.1: Summaries of VES results

VES 

Curve Type

No of Layers

Resistivity (Ω.m)

Thickness (m)

Depth to the Bedrock (m)

Remarks (expected formation)

VES 1

KH

1

2        

3

1243

273

20792

9.06

33.2

42.3m

Top soil

Dry wet sand

Mud stones.

VES 2

KH

1           2          3           4         

892

175

1414

2.05

2.03

4.02

10.1

16.2m

Fine  sand formation

Medium grain

Sandy clay

Peaty soil

Clayey sand and loose sand

VES 3

Q

1         2          3            4

2326

51.4

2.21

1352

0.5

4.86

5.71

11.1m

Peaty soil

Fine sand formation

Sandy clay

Clayey sand and loose sand

VES 4

HKH

1           2              3                               

895

65.6

1156

3.17

3.48

6.65m

Fine sand formastation.

Clayey sand and loose sand Mudstones Peaty soil Medium grain.

CHAPTER FIVE

5.0  CONCLUSION, RECOMMENDATION AND REFFERENCES

5.1  CONCLUSION

The study has shown that (3-4) three to four geo-electrical layers exist in the study area which is made up of a multi aquifer formation. While layer three is taught to be an unconfined aquifer with thickness ranging from 3.0m to 13.0m, layer four is a confined aquifer having thickness range of 7.0m to 17.7m. The various geoelectric interpretations and hydrogeological results depict that the best sites for locating wells or boreholes in Aliero in respect to the (4) four studied areas are VES stations 2, 3, and 4. While probability of getting good ground water in VES station 1 is very infinitesimal, this might result from the presence of high accumulated pollutant in the station.

5.2   RECOMMENDATIONS

It would be of experimental justification, if further researchers verify the accuracy of this work within the study areas using magnetic method and vertical electrical sounding method to compare the difference between the two.

5:3  REFERENCE

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