MATERIALS AND METHODS

Study Areas
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).

Experimentation
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.

Fig. 1:	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.

Fig. 2:	Geological setting of Oyo State, Source: After Balogun (2000)

Fig. 3:	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,

Table 1:	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

Table 2:	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, it’s apparent that the composition/lithology (Table 2) of a terrain has no matter how little-influence on the borehole water quality.

ACKNOWLEDGMENTS

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.