Analytical study of boreholes water quality in both sedimentary terrain and basement complex were carried out with 16 samples from different boreholes, collected from two different States (regions) representing the lithology in South Western Nigeria. It is in no doubt that the composition of a terrain has influence on the water quality and from both terrains, it was observed that the pH ranges from 5.30 to 7.60, Iron, Nitrite, Nitrate and Manganese contents have maximum values of 2.70, 2.00, 7.30 and 0.10 mg L-1, respectively. Total alkalinity ranges from 12.00-155.0 mg L-1, total hardness ranges from 21.00-275.00 mg L-1, salinity ranges from 15.00-566.00 mg L-1, chloride ranges from 5.50-70.00 mg L-1, but sulphate is absent in all the water samples. The obtained results showed how elemental compositions vary with lithology and how water qualities in the two zones are almost suitable for use/consumption of the populace. Although, some samples from the Sedimentary basin have slight high Iron content, this calls for attention.
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Water is of fundamental importance to human life, animals and plants, it is of equal importance with the air we breathe in maintaining the vital processes to life and it makes up about 60% of body weight in human being.
Among the various sources of water, groundwater is known to be more appropriate and often meets the criteria of quality of water, the most widely used as sources of water in most African countries, Nigeria inclusive. The quality of groundwater is the resultant of all the processes and reactions that act on the water from the moment it condensed in the atmosphere to the time it is discharged by a well or spring and varies from place to place and with the depth of the water table (Jain et al., 1995; Todd, 1980). Ground waters have unique features, which render them suitable for public water supply (Alexander, 2008; Offodile, 1983). They have excellent natural quality, usually free from pathogens, color and turbidity and can be consumed directly without treatment (Jain et al., 1996). Its widely distributed and can frequently develop incrementally at points near the water demand, thus avoiding the need for large-scale storage, treatment and distribution system (Alexander, 2008). Groundwater is particularly important as it accounts for about 88% safe drinking water in rural areas, where population is widely dispersed and the infrastructure needed for treatment and transportation of surface water does not exist. Nevertheless, there are various ways groundwater may suffer pollution e.g., land disposal of solid wastes, sewage disposal on land, agricultural activities, urban runoff and polluted surface water (Jain et al., 1995).
The chemistry of rocks and soils and the rock geological conditions in any borehole has a great influence on the quality of water which determines the concentration of introduced cations and anions such as Na+, K+, Mg2+, Fe2+, NO3¯, CO32¯, SO42¯, Cl¯ and so on.
The comparison of hydro geochemistry of the borehole water will help to ascertain the water quality in those terrains, however, the assessment of groundwater quality will be based on the physical and chemical characteristics while the physical characteristics of groundwater includes the electrical conductivity, Total dissolve solids, pH value, color, turbidity and hardness. The interplay between turbidity and contour current processes on the Columbia Channel fan drift, Southern Brazil Basin.
Thus, this study was aimed at determining the physicochemical parameters concentrations in the boreholes which is one of the main sources of water supply in Oyo and Lagos States and at the same time sets to review and compare the qualities of borehole water in the said studied areas.
MATERIALS AND METHODS
The two study areas are located in South-Western, Nigeria. Oyo State is lies between latitude 7° and 10°N and longitude 2° and 5°E (Fig. 1a). on the other hand Lagos State is lies between latitude 6° and 7°N and longitude 2° and 5°E (Fig. 1b).
Geology of the Study Areas
Five tectonic events were recognized using radiometric dating in the West African craton to which the Nigerian Basement complex belongs. Basement complex underlines virtually every part of the country, but occur mainly in the South-Western, Eastern and North Central part of Nigeria. It also extends Western-wards and is apparently continuous with the Precambrian rocks of Dahomey (Omatsola and Adegoke, 1981). The basement complex rocks of Nigeria, based on their petrology are composed predominantly of five classes namely: Migmatite gneiss, Schist, Charnockitic rocks, older granites and non-metamorphosed dolerite dykes.
Sedimentary rocks predominantly compose of sands, sandstones and limestone; cover about half of the surface of Nigeria. Crystalline igneous and metamorphic rocks generally referred to as the basement rock cover the rest of the country.
Oyo State is underlain by Pre-Cambrian rocks which forms part of the Basement complex of South Western Nigeria. On the other hand, Lagos is located on sedimentary rock of the southwestern part of Nigeria, it lies within the Dahomey basin, which termed the Benin basin (Adegoke, 1969; Agagu, 1985; Aseez, 1971) (Fig. 2, 3).
The study was conducted over a period of 6 months, precisely between August 2007 and Feb. 2008 between two main States representing the sedimentary and basement formations (Lagos and Ibadan respectively) within the South-Western part of Nigeria.
Eight water samples were collected in four LGAs in Oyo State with 1 sampling point each in Lagelu, Ibadan North, Ibadan North-West and 5 sampling points in Ibadan South-West.
Study area of Nigeria, (a) Oyo State and (b) Lagos State
The samples were taken from boreholes in areas like Ring Road, Felele, Adeoyo State Hospital, Lajoogan House, Idi-Ape, Iwo Road. On the other hand, in Lagos State, 1 sampling points each in Alimosho and Surulere LGAs, 2 each in Eti-Osa, Ikeja and Somolu LGAs. The samples were taken in the following area; Shasha, Ikeja, Alausa, Shomolu, Ikoyi and Surulere.
The samples were taken with 2 L container and transported to the laboratory the same day. The geochemical analysis were carried out according to the approved standards.
Geological setting of Oyo State, Source: After Balogun (2000)
Geology setting of Lagos, Source: After Balogun (2000)
RESULTS AND DISCUSSION
It w as observed that all the water samples were odorless, tasteless and colorless (Table 1). The color values are found to be between 5 and >10 TCU. Turbidity is generally low and between 1.4 and 9.7 NTU in the two zones except point K which is extremely high of about 140 NTU (Table 1, Fig. 4b). On the average the results of conductivity, turbidity,
Borehole sampling parameters results
|Fig. 4:||Distributions of the various analyzed parameters, (a) Turbidity, (b) Conductivity, (c) Total Dissolve Solid (TDS), (d) Iron (Fe), (e) Total alkality, (f) Hardness, (g) Nitrate, (h) Salinity, (i) Chloride and (j) pH|
Total Dissolve Solid (TDS), total alkalinity, hardness (CaCO3, Calcium hardness and Magnesium hardness), Nitrate, Salinity, Chloride and pH are lower in sedimentary zone than the basement complex (Table 1, Fig. 4b, c and e-j, respectively). Electrical conductivity values ranged from 34 to 340 μs. TDS values in the 2 zones are generally below WHO limits except
Lithology of the Boreholes and their distances apart
point F. Iron in basement complex was observed to be lower than sedimentary zone on average (Table 1, Fig. 4d). Samples from basement had iron contents within the WHO recommendations while some of the water samples in sedimentary have Iron contents higher than the World Health Organization (2003) recommendation which may be due to iron encrustation which is caused by ferrous iron which is soluble in water and are deposited as ferric iron. Similarly, Manganese may form encrusted when the bicarbonate reacts with oxygen to form insoluble Manganese Hydroxide.
According to Gibbs (1970), water chemistry is mainly influenced by dilution and slightly from weather product of the rock type.
The relatively high levels of turbidity and variation in color could be attributed to the presence of decaying organic matter (Hiscott et al., 1997; Coulibaly and Rodriguez, 2003; Rim-Rukeh et al., 2006). While the groundwater in the two zones (Basement and sedimentary) varies between slightly acidic and slightly alkaline, according to the classifications of Ezeigbo (1988) but rather falls within the range of WHO recommendation standard for pH value within 5.30-7.50.
From this study, it can be seen that the chemical analysis revealed the water quality from basement complex and sedimentary terrain to have almost the same quality and is good for purposes such as drinking and domestic use, it was also noticed that some of the water from Lagos, that is sedimentary have slightly higher iron content. Meanwhile, as water seeps through the ground and adds to its mineral content, much of its suspended matter, color and bacteria content are filtered out. Thus, a deep well is likely to produce water that is clear, colorless and low in bacteria count as found in the two zones of study. In conclusion, its apparent that the composition/lithology (Table 2) of a terrain has no matter how little-influence on the borehole water quality.
The authors will like to say a big thank you to the International Centre for Theoretical Physics (ICTP), Trieste, Italy for their support with useful materials for this study.
- Alexander, P., 2008. Evaluation of ground water quality of mubi town in adamawa state, Nigeria. Afr. J. Biotechnol., 7: 1712-1715.
- Gibbs, R.J., 1970. Mechanisms controlling world water chemistry. Science, 170: 1088-1090.
- Hiscott, R.N., K.T. Pickering, A.H. Bouma, B.M. Hand, B.C. Kneller, G. Postma and W. Soh, 1997. Basin-floor fans in the North Sea: Sequence stratigraphic models vs. sedimentary facies: Discussion. Am. Assoc. Petroleum Geol. Bull., 81: 662-665.
- Coulibaly, H. and M.J. Rodriguez, 2003. Portrait of drinking water quality in small quebec municipal utilities. Water Qual. Res. J. Canada, 38: 49-76.
- Rim-Rukeh, A., G.O. Ikhifa and P.A. Okokoyo, 2006. Effects of agricultural activities on the water quality of orogodo river, agbor Nigeria. J. Applied Sci. Res., 2: 256-259.