A Comparative Study of Borehole Water Quality from Sedimentary Terrain and Basement Complex in South-Western, Nigeria
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.
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.
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.
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,
sampling parameters results
||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)
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
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.
1: Adegoke, O.S., 1969. Ecocene stratigraphy of southern Nigeria. Bill Geol Men No. 60.
2: Agagu, O.K., 1985. A geological guide to bituminous sediments in South Western Nigeria of geology. Report, University of Ibadan, Nigeria, pp: 2-16.
3: Alexander, P., 2008. Evaluation of ground water quality of mubi town in adamawa state, Nigeria. Afr. J. Biotechnol., 7: 1712-1715.
Direct Link |
4: Aseez, L.O., 1971. Hydrogeology of Southwestern Nigeria: The Nigerian engineer. J. Nig. Soc. Eng., 7: 22-44.
5: Balogun, O.Y., 2000. Senior Secondary Atlas. 2nd Edn., Longman, Nigeria.
6: Ezeigbo, H.I., 1988. Geological and hydrogeological influence on the Nigeria environment. Water Resour., 1: 37-44.
7: Gibbs, R.J., 1970. Mechanisms controlling world water chemistry. Science, 170: 1088-1090.
CrossRef | Direct Link |
8: 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.
Direct Link |
9: 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.
Direct Link |
10: Jain, C., K. Omkar and M.K. Sharma, 1996. Ground water technical report, CS (AR) 196. National Institute of Hydrology, Roorkee, 1995-1996.
11: Jain, C.K., K.K.S. Bhatia and T. Vijay, 1995. Ground water quality monitoring and evaluation in and around kakinada, andhra pradesh. Technical Report, CS (AR) 172. National Institute of Hydrology, Rorkee.
12: Offodile, M.E., 1983. The occurrence and exploitation of ground water in Nigerian Basement Rocks. Niger. J. Mining Geol. Vol., 20.
13: Omatsola, M.E. and O.S. Adegoke, 1981. Tectonic evaluation and cretaceous stratigraphy of the dahomey basin. J. Mining Geol., 18: 130-137.
14: 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.
Direct Link |
15: Todd, D.K., 1980. Groundwater Hydrogeology. John Willey and Sons Inc., New York, pp: 555.
16: WHO. (World Health Organization), 2003. Guidelines for Drinking Water. World Health Organization, Geneva.