CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF STUDY
Water is an essential liquid to human lives and continuous existence of the ecosystem. Water has some physical characteristics that guaranteed its wholesomeness: it must be colourless, odourless, tasteless, and readily foam with soap or detergents. The human body and blood is composed of 60-75% of water as such needed enough water; at least 2-3 litres for adult to enhance the effective functioning of the circulatory and metabolic systems of the body. Safe water must be used for domestic (drinking, washing, bathing, and cooking), agricultural, industrial processes, and recreational activities. This water is gotten from sources such as: rain, snow, stream, lake, river, sea and aquifer (groundwater). Safe water is dependent on the chemical components of the water.
Groundwater is an important natural resource that supplies billions of gallons of water for domestic, agriculture, industrial purposes and other uses. The known surface water bodies in the area under study are severely polluted by anthropogenic activities, as such about 85% of the population of the area now solely depends on groundwater as their source of water. Thus, harnessing and preservation of clean and safe groundwater becomes imperative.
The considerable thickness of the aquifers, the high transmissivity of water through these aquifers due to the high degree of porosity and permeability and the adequate groundwater recharge capacity enhanced by the high annual rainfall in the area, makes the aquifers of the area reliable water resources that can yield and supply reasonable millions of volume of water to satisfy the water needs of the people and industries of the area through both public and private abstractions (Todd, 1959; Krivochieva and Chouteau, 2003, Tamunobereton-ari et al, 2010a; Tamunobereton-ari et al, 2010).
The characterization and delineation of aquifer in the area becomes imperative as water samples from some existing wells and boreholes in the study area fall short of the acceptable characteristics of groundwater and during the dry season most wells and boreholes drop to a minimum yield and sometimes get dried up; perhaps due to lack of hydrogeological information of the area and improper delineation of the aquifer to facilitate the precise identification of desired aquifer before drilling and well completion for sustainable supply of potable water to the people of the area (Edlefsen, and Anderson. 1941; Tamunobereton-ari et al, 2013).
It is an established fact that a quick, non-invasive, cost effective means of subsurface characterization is the geoelectrical or electrical resistivity method. These combined hydro-geophysical methods which employs vertical electrical sounding in conjunction with 2D wenner electrical resistivity tomography (ERT), is majorly the geophysical application methods used for hydro-geological investigation which is directed towards aquifer characterization and ground water quality studies (Olayinka and Mbachi, 1992; Ismail Mohamaden, 2005; Astahani, 2006; Bello and Mankinde, 2007 in Mogagi et al, 2011).
These methods image the subsurface geologic stratigraphy for characterization of the subsurface in a bid to delineate zones characterized with high porosity, permeability as well as saturation for sufficient ground water exploitation and determination of depth, thickness and boundary between saline and potable fresh water aquifer zones (Khalil, 2006; El-waheidi et al, 1992; Bello and Mankinde, 2007; Astahani, 2006; Ismail Mohamaden, 2005). Ground water exploration involves the use of numbers of Geophysical techniques available in the location of water bearing rocks called Aquifer (Ariyo and Adeyemi, 2012; Emenike, 2001). Mogaji, et al, (2011) defined aquifer as any mass of permeable rock material from which significant amount of water can be recovered from. Sabongida- Ora Edo State is characterized with limited boreholes and ephemeral stream, thus water is a priceless commodity.
The need for water in adequate supply and quantity is a necessity for every life that is for domestic and industrial uses (Ariyo and Adeyemi, 2012). This study aimed at shielding light on the subsurface geology for the determination of geo-electrical and hydro-geophysical characteristics of potable aquifer for optimal groundwater exploration. Both Schlumberger and Wenner array configurations were used in this study.
The schlumberger method has a greater penetration than the Wenner therefore, it is suitable for depth and thickness investigation whereas Wenner configuration discriminates between resistivities of different geoelecric lateral layers (Olowofela et al, 2005 cited in Adegbola et al, 2010). Consequently, the application of hydro-geophysical method proffer the existence of a perched water aquifer within a window depth of 15m to 35m and a deep seated confined aquiferous unit at depth of investigation beyond 240m with good characteristic for potable water exploration and its supply in the study area.
Methods for applying geophysical techniques in groundwater exploration have been already presented (Van Dongen and Woodhouse 1994) but as MacDonald et al. (2001) pointed out, ‘‘areas with complex geology and hydrogeology are not covered by the general approach and require special methods for particular problems’’. Many geophysical methods have been used for groundwater resources investigation, but the electrical and electromagnetic methods have the greatest success and can be used for studying fresh and/or contaminated aquifers around the world (Meju et al. 1999; Peavy and Valentino 1999; Sørensen and Søndergaard 1999; Gwaze et al. 2000; Corriols et al. 2000; Mendoza et al. 2000; Miele et al. 2000; Maillol et al. 2000; Wynn et al. 2000; Farrell et al. 2000; Paine et al. 2000; Soupios et al. 2010).
1.2 STATEMENT OF THE PROBLEM
The groundwater potentials and its environs are enormous based on the positive indicators of high resistivity values, clean coarse sand formation materials, the thickness of the established aquiferous saturated zone and the shallow depth to locating the aquifer, which is about from 22m that can facilitate the easy harnessing and supply of safe, sustainable and portable water to the people of the area. Lack of expertise might be a leading problem that might bring about poor water production or drilling. This is a situation whereby the drillers are not able to properly decipher the rudiment of borehole drilling and they just stop into the line of business without knowing the right thing to do. Finally, several studies has been carried out on delineation of aquifer depth but not even a single research has been carried out on the delineation of aquifer depths and its characterisation using geophysical method.
DELINEATION OF AQUIFER DEPTHS AND ITS CHARACTERISATION USING GEOPHYSICAL METHOD
