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Aquifer Vulnerability Using Geophysical and Physiochemical Methods in Parts Of Ethiope West Local Government Area Delta State, Nigeria

Authored by Julius Otutu Oseji



This study was carried out to determine the aquifer vulnerability and groundwater quality using geophysical and physiochemical methods in parts of Ethiope West Local Government Area of Delta State. Thirty vertical electrical soundings and four dipole-dipole profiling were administered using Abeam Terameter SAS 1000 AB. The field data were curve matched and Iterated using Win resist and Dipro software. The auriferous zone was found in the fourth layer with resistivity ranging from 159 Ωm – 100234 Ωm, thickness ranging from 12m – 156 m and depth of 32m – 162m except VES 25 whose aquifer is in third layer. The dipole – dipole resistivity structure shows low resistivity values along areas where waste dump was sited with resistivity ranging from 300 Ωm to 630 Ωm. This finding suggests that the leachate from the dumpsite is affecting the characteristics possessed by the subsurface close to it. The first order geoelectric and Dar-Zarrouk parameters study of aquifer protective capacity revealed a protection capacity value of less than 0.1 for VES 1 – 18 and 20 – 30 while VES 19 revealed a value of 0.24. Thus, Oghara communities are extremely unprotected and the aquifer is prone to contamination. Physiochemical analysis carried out indicates that groundwater is slightly acidic with pH value ranging from 5.40 – 6.40 when compared with WHO permissible limit. The groundwater flow direction depicts flow from the East to the West; this will assist policy planners to decide places where dumpsites and other companies generating waste could be sited to preserve groundwater potential.

Water is among the natural resources of great need to man all over the world, and groundwater that is responsible for the springs, lakes and wells [1] is a major source of water to man especially in developing nation and rural communities where availability of requisite public infrastructure for surface water treatment, reticulation and supply are inadequate or non-existent.

The Electrical Resistivity methods were used in this investigation due to the use of simple instrument; easy and straight forward field logistics, less tedious and economic analysis of data. This is the reason why many researchers such as [2-11] used the method for the determination of aquifer boundary.

The availability of groundwater depends on the presence and hydraulic properties of auriferous (groundwater bearing) units; and its portability depends on its hydro geochemical properties and vulnerability to contamination/ pollution [12-16]. Aquifer vulnerability refers to the degree of protection against contamination offered by the overlying strata and the potential for purification of contaminated water in the aquifer [17-20].

Oghara located in the oil rich Niger Delta Basin in Delta State, Nigeria, can be regarded as a fast-developing town characterized by relatively high population density occasioned by the large number of industries, commercial centers and civil service institutions.

Supply of potable water in Oghara communities in particular and parts of Ethiope West Local Government Area of Delta State in general is inadequate as a result of increasing population and development activities in the area.

The regional water crises in nations of the world can be resolved and sustained, if groundwater resources are effectively managed. In Oghara Communities, groundwater has not been properly explored before embarking on drilling boreholes which results in large number of low yielding and/or failed boreholes. Foster [21] observed that there has been success in groundwater development through borehole drilling in area underlain by crystalline hard rocks in Nigeria. Development of secondary porosity and permeability within the basement rocks are responsible for the availability of groundwater which results from weathering and fracturing [22]. Fresh water supply is increasingly sourced from ground water which act as the supply of fresh water under the earth’s surface in an aquifer that forms a natural reservoir for human use Udosen [23]. Moreso, surface water is all the naturally open to the atmosphere (rivers, lakes, reservoir, streams seas etc) and all spring wells or other collectors which are directly influenced by surface FEPA [24]. Surface water can be polluted when there are presences of pollutants like radioactive isotopes, heavy metals bacteria and viruses among others. There is a global concern on water pollution as it affects human health and one of the causes of ground water pollution is the disposal of waste materials directly onto the surface Waziri, et al. [25], Wells [26], WHO [27,28]. The waste if contains soluble material will insinuate thereby leading to ground water pollution Waziri et al., [25], Kola & Baba [29].

For successful groundwater exploitation in order to limit dry borehole and loss of resources there is need to determine aquifer vulnerability using geophysical and physiochemical methods in parts of Ethiope West Local Government Area Delta State.

Oghara is a town in Ethiope West Local Government Area of Delta State, Nigeria and is located between latitude 5O35′1’’N and longitude 5O51’16’’E. The Communities include: Ogharefe, Oghareki, Edjemuonyavwe, Ijomi, Otefe, Ovade, Ugbenu and Mosogar. The base map of the study area is shown in Figure 1. It has road intersections connecting Sapele to Warri and Benin. It resides within the equatorial region having two climatic regimes which is the rainy season and dry season. Typically, the region has the characteristic feature of the humid tropical wet and dry climate governed primarily by the rainfall. The dry season is from November to February and the wet season is from March to October. Oghara community is in the Niger Delta Basin characterized by three majors depositional (sedimentary) environments (marine, mixed, and continental).

The people are predominantly farmers producing food crops, like cassava (starch and garri), maize, plantain, yam and other variety of vegetable products. They are big time timber merchants and also into palm oil production. Oghara has a good number of Tertiary Institutions such as the Delta State University Teaching Hospital located in Edjemuonyavwe, the Western Delta University in Ogharefe, the Delta State Polytechnics in Otefe, the Electoral Institute (INEC) in Edjemuonyavwe, and a campus of the National Teachers Institute Kaduna in Oghareki where Teachers are trained for the Teacher’s grade two Certificate (TC II) and the Nigeria Certificate of Education (NCE). There is also the Pan - Ocean Oil Corporation in Ovade, the Nigeria Gas Company Ovade and about fifteen oil tanks farms/wells which distribute petroleum products to many parts of Nigeria. There is JK Rubber Industries Ltd, Ogharefe, Pamol Rubber Company Ltd, Edjemuonyavwe and Pamol Oil Palm Company Ltd Ajagbodudu. It has a mini Stadium in Ogharefe that has hosted many National and International Football Competitions. It also has the Nigerian Naval logistics headquarters in Ogharefe and a Mobile Police base in Oghareki. Local Geology: Three major depositional (sedimentary) environments (marine, mixed, and continental) are observable in the area.

Based on the sedimentary environmental classification, three rocks formations namely the Benin, Agbada, and Akata formation are used to describe the sedimentary sequence. In the Niger Delta oil producing communities, the source rocks and seal rocks are the marine/deltaic, plastic and over-pressured shales of Akata and Agbada Formations. The geology of the study area shows the presence of clay, sand, pebbles, sandstone, gravel, shales, mangrove swamp, lignite, and Alluvium.

 

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