518p. SIMPSON, A., 1954. The Nigerian coalfield, the geology of parts of. Onitsha, Owerri and Benue provinces. Geological Survey. Nigeria Bulletin 24, pp1-85.
Journal of Mining and Geology Vol. 43(1) 2007, pp. 79 – 89 © Nigerian Mining and Geosciences Society (NMGS) - Printed in Nigeria
1116-2775
Hydrogeochemical and bacteriological investigation of groundwater in Agbor area, southern Nigeria S.B. OLOBANIYI, J. E. OGALA and N.B. NFOR Department of Geology, Delta State University P.M.B. 1, Abraka, Nigeria Abstract Agbor, a town in southwestern Nigeria, is underlain by the Miocene to Recent Benin Formation. Groundwater occurrence within the formation has been investigated for its quality, from which inferences are drawn on its usability and the prevalent hydrogeochemical processes in the water systems. The results indicate a chemical attribute of low pH, low total dissolved solids (TDS) and salinity. Cationic concentrations including Na+, K+, Ca2+, Mg2+ have values ranging from 0.9 to 18.9 mg/l, 0.1 to 4.2 mg/l, 1.2 to 12.8 mg/l and 0.2 to 3.5 mg/ l respectively. Concentration values of Fe2+, Zn2+, Mn2+ and Pb2+ range from 0.08 to 1.92mg/l, 0.12 to 4.35 mg/l, 0.0 to 0.42 mg/l and 0.0 to 0.04 mg/l respectively. Anions including HCO3-, CO32-, Cl-, SO42-, NO32-, PO42- have respective concentration values ranging from 1.0 to 10.0 mg/l, 0.1 to 0.9 mg/l, 3.2 to 24.0mg/l, 0.0 to 10.3 mg/l, 0.0 to 18.4 mg/l and 0.0 to 2.4 mg/ l. The bacteriological constituents of the water samples include Total aerobic bacteria counts (5 - 535cfu/ml) and Total coliform (10 - 70MPN/100ml). A comparison of these results with various quality guidelines, suggests that the groundwater may be suitable in its untreated state for crop irrigation, but will require pH remediation and microbial disinfection to upgrade its quality for potability and use in food processing industries. Factor analysis reveals three main hydrogeochemical activities operative within the groundwater system. Factor 1 is dominant and can be related to water-soil interaction and incorporation of leached formation water along the groundwater flow path. Factor 2 is related to pollution by biochemical related substances resulting from agricultural practices in the area. Factor 3 indicates fresh groundwater recharge. An inter-play of these processes, and base exchange reactions produced dominant chloride water types (Ca-Cl, Ca-Mg-Cl, Mg-Ca-Cl, Na-Ca-Cl and NaCl), and localized occurrences of bicarbonate types (NaHCO3 and Na-Ca-HCO3.
Introduction
Location of study area and geology
In southern Nigeria, especially in areas underlain by sedimentary formations, groundwater is usually present in abundance. This is partly because of the prevalent equatorial climate that fosters abundant rainfall and hence ensures adequate aquifer recharge, coupled with the availability of suitable aquifers and impervious sediments that favour the storage of the recharging water. Despite its abundance, groundwater may still be unusable when its quality is considerably degraded by chemical and bacteriological contamination that results predominantly from the impact of man on his environment. Apart from the influence of man, considerable alteration in water quality attributed to its residence history often results. A close assessment therefore of the chemical and bacteriological constituents of groundwater is often necessary for effective monitoring of its quality status. Several such studies have been conducted within the sedimentary formations of southern Nigeria (Etu-Efuotor, 1981; Ezeigho, 1987; Amadi et al., 1989; Edet, 1993; Ajayi and Umoh, 1998; Akpoborie et al., 2000; Olobaniyi and Owoyemi, 2004 ). In Agbor area, groundwater constitutes the predominant source of water for domestic use. This is partly because of the paucity of surface water, and the pollution of the few available ones due to indiscriminate disposal of solid and liquid wastes. This paper assesses the physico-chemical and bacteriological aspects of groundwater quality in Agbor and its environs and discusses its suitability for domestic, agricultural and industrial purposes. It also examines the prevalent hydrochemical facies with emphasis on the underlying hydrogeochemical processes.
Agbor is located in southwestern Nigeria within latitudes 6007| and 6020|N, and longitudes 6005| and 6020|E, and covers an area of about 650 km2 (Fig. 1). It has a population in excess of 240,000 people and is located along a major route connecting southeastern and northwestern Nigeria. Consequently, it is a flourishing center of trade and agriculture. The physiography of the area shows two topographic highs separated by a valley. Within the valley is River Asimiri, which flows in a southwest-northeast direction (Fig. 1). The area lies within the subequatorial climate, with annual rainfall over 2000mm, long wet season (about 8 months), high humidity and atmospheric temperature of between 24 - 270C (Iloeje, 1981), which supports the rainforest-type vegetation. The study area is underlain by the Miocene - Recent Benin Formation. This formation previously recognized as the Coastal Plain Sands (Tattam, 1943; Simpson, 1954) stretches over a considerable portion of the coastal region of Nigeria, adjacent to the Deltaic Plain Sediments. The formation generally consists of unconsolidated and friable sandy beds, with intercalations of gravely units and clay lenses. It has been reported to contain good aquifers (Oteze, 1981; Offodile, 1992) that are probably the most prolific water producers in southern Nigeria. Within the area, the Benin Formation is capped by lateritic soil in the first few metres (Fig. 2), followed by fine grained sand that varies in thickness from 9 to 58 metres. Underlying these, is a sequence of medium to coarse grained sand with several horizons of intercalated discontinuous 79
80
Fig. 1. Map of Agbor, showing topography and sampling points (insert:: map of Nigeria showing location of Agbor)
lenses of clay. The medium to coarse grained sandy beds constitute the main aquifer tapped in the area. Groundwater occurs at a depth generally greater than 60 metres, predominantly under unconfined conditions. Deductions from groundwater level contouring shows that River Asimiri (the main river that drains the area) is partly recharged from the aquifer (Fig. 3).
Methods of investigation
Water samples were obtained from 32 boreholes, distributed within Agbor and environs. Of these, 10 representative boreholes were sampled for bacteriological investigation. Logging during drilling operations was carried out on 6 boreholes to determine their lithologic profiles, characteristics and sequence within the study area. This was accompanied by a laboratory grain size analysis of collected drill cutting samples. From the lithological logs, a geologic fence diagram for the study area was constructed (Fig. 2). Water level depths were determined
in each borehole using the water level meter, while topographic elevation was measured at each sample points with a Garmin model 72 GPS. With these information, the groundwater level contour map (Fig. 3) of the area was constructed. At each borehole site, the well was pumped for 5 minutes to ensure obtaining fresh water samples. For chemical analysis, replicate water samples were collected into clean 1 litre plastic cans from each sampling point, one of which was stabilized (with acid) for metal concentration determination. For bacteriological investigation, water samples were collected into sterilized 1 litre plastic cans. These samples were kept in ice bags before being transported to the laboratory for analysis. Analytical procedures for physical, chemical and bacteriological parameters are generally in accordance with the specifications of American Public Health Association (1985). Unstable parameters such as electrical conductivity (EC), pH and temperature were measured in-situ on the field. The TDS contents of the water samples were
81
Fig. 2. Geologic fence diagram for Agbor area
Fig. 3. Groiundwater level contour map of Agbor and environs
82 estimated with the Oakton TDS meter. The concentrations of Na+ and K+ were determined with a Flame Emission Analyser. Ca 2+ and Mg 2+ were measured by EDTA titrimetry, while Cl-, HCO32-and CO32- were measured using titrimetric methods. NO3- was measured by colorimetry while SO42- was determined by precipitation using BaCl2 and measurement of absorbency with a spectrophotometer. The concentrations of heavy metals (Fe, Pb, Zn, and Mn) were determined with a model SP2900 Pye-Unicam Atomic Absorption Spectrophotometer (AAS). Total aerobic bacterial counts were determined by the Pour-Plate
technique, while Total coliform counts were performed by the Most Probable Number (MPN) technique.
Results and interpretation Water quality The results of physical, chemical and bacteriological parameters analyzed for the 32 water samples are presented in Tables 1, 2 and 3 respectively. A statistical summary of these parameters is given in Table 4, while evaluation and interpretations are presented in the following sections.
Table 1. Result of physical parameters of groundwater samples and measured groundwater levels in the study area Borehole no
pH
Temp oC
TDS
EC
TH
SAR
Water Level (m)
1
6.8
27.6
23.0
45.2
20.0
0.61
82.4
2
6.4
26.0
42.0
79.6
30.0
0.82
85.4
3
5.4
26.6
13.1
25.8
10.1
0.75
85.4
4
5.5
29.0
12.9
24.8
30.0
0.25
85.4
5
5.4
27.0
10.5
21.0
5.0
0.37
85.4
6
4.9
27.4
44.1
87.8
17.0
0.83
85.4
7
5.7
28.4
7.6
16.0
12.5
0.27
85.4
8
6.2
29.7
12.2
24.9
10.0
0.30
85.4
9
5.2
29.3
10.6
21.2
15.0
0.37
30.5
10
4.8
28.4
12.2
24.8
20.0
0.31
30.5
11
5.1
29.0
10.3
20.8
5.0
0.40
54.9
12
4.9
29.3
9.7
19.0
20.0
0.38
67.1
13
6.3
28.8
47.6
95.7
35.0
0.91
30.5
14
5.1
32.7
13.4
27.2
10.0
0.40
36.6
15
5.1
28.6
10.8
21.6
10.0
0.42
67.1
16
4.8
28.6
13.9
27.2
10.0
0.72
64.1
17
4.9
28.2
9.7
19.2
10.0
0.50
67.1
18
6.6
27.3
50.4
102.1
30.0
0.83
67.1
19
5.4
28.9
12.3
24.9
15.0
0.13
30.5
20
4.7
27.1
12.3
25.2
20.0
0.12
32.1
21
4.4
28.0
66.7
133.8
15.0
0.93
12.2
22
6.0
27.2
8.0
16.1
10.0
0.33
85.4
23
5.8
26.5
9.7
19.2
10.0
0.40
100.7
24
5.7
29.2
11.5
28.9
25.0
0.32
100.7
25
4.8
32.7
11.0
22.1
5.0
0.37
36.6
26
4.9
29.0
8.9
17.2
10.0
0.48
30.5
27
4.4
31.7
80.6
162.1
20.1
1.21
15.3
28
4.0
31.6
32.7
65.3
25.0
0.66
30.5
29
4.0
32.5
51.5
102.6
10.0
0.75
54.9
30
4.7
30.0
8.3
17.3
10.0
0.14
70.2
31
4.8
30.0
17.2
35.2
15.0
0.36
88.5
32
4.6
32.1
18.8
39.6
25.0
0.38
67.1
TDS = Total dissolved solids in mg/l; EC = electrical conductivity in us/cm TH = Total hardness as CaCO3 in mg/l; SAR = sodium absorption ratio
4.7 9.2 3.8 2.2 2.2 9.3 1.5 2.1 2.1 2.3 2.0 2.1 10.2 2.7 2.3 4.0 2.5 10.3 1.1 1.0 6.3 1.8 2.2 2.1 2.0 3.1 18.9 7.1 10.4 0.9 2.8 2.9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Concentrations in mg/l
Na+
Borehole no 1.3 2.4 0.9 0.3 0.3 4.0 0.3 0.6 1.0 0.3 0.7 0.7 3.9 0.5 0.5 0.7 0.5 4.1 0.2 0.2 4.2 0.3 0.5 0.4 0.8 1.8 4.1 1.4 2.0 0.2 1.2 1.2
K+ 4.2 7.4 1.2 2.6 2.4 8.1 1.2 2.8 1.5 2.0 1.7 1.9 7.8 2.6 1.9 1.6 1.5 8.4 4.5 4.4 2.5 1.8 1.6 2.8 1.8 2.6 12.8 6.6 10.9 2.8 2.8 3.6
Ca2+ 0.2 1.3 0.5 1.8 0.2 0.9 0.7 0.6 0.6 1.3 0.2 0.3 1.0 0.4 0.2 0.4 0.3 2.0 0.6 0.6 0.6 0.3 0.4 0.3 0.2 0.4 3.5 1.5 2.2 0.2 1.1 0.4
Mg2+ 0.10 0.24 0.15 0.10 0.10 0.17 0.10 0.08 0.10 0.08 0.10 0.12 0.15 0.10 0.18 0.10 0.13 0.12 0.18 0.10 1.92 0.10 0.10 0.15 0.13 0.25 0.10 0.10 0.12 0.10 0.15 0.35
Fe2+ 0.50 0.50 0.62 0.18 0.16 0.45 0.12 0.14 0.17 0.15 0.40 0.28 0.83 0.34 0.47 0.32 0.15 0.48 0.68 0.30 4.35 0.33 0.38 0.42 0.58 0.58 1.08 0.20 0.20 0.15 0.40 1.43
Zn2+ 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.02 0.01 0.42 0.01 0.01 0.01 0.02 0.02 0.01 0.01 0.01 0.01 0.04 0.05
Mn2+ 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.03 0.00 0.00 0.00 0.02 0.01 0.00 0.00 0.00 0.00 0.02 0.04
Pb 2+ 10.0 10.0 2.0 2.0 2.0 1.0 2.0 6.0 2.0 1.0 1.0 1.0 8.0 2.0 2.0 1.0 0.0 10.0 2.0 1.0 1.0 4.0 2.0 2.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
HCO30.9 0.6 0.7 0.7 0.4 0.1 0.5 0.1 0.3 0.1 0.8 0.7 0.8 0.1 0.2 0.3 0.3 0.2 0.3 0.2 0.1 0.4 0.3 0.1 0.1 0.2 0.1 0.2 0.1 0.3 0.2 0.2
CO323.8 3.2 4.1 7.4 8.2 18.1 4.5 4.9 4.2 8.0 8.5 3.5 15.2 5.0 3.8 5.4 5.5 20.9 7.7 7.9 8.8 4.5 4.5 6.0 6.0 4.0 24.0 10.5 16.1 4.1 4.5 4.5
Cl -
Table 2. Results of chemical parameters of groundwater samples from the study area
0.1 3.5 0.6 0.2 0.1 1.8 0.0 0.1 0.1 0.1 0.2 0.2 0.3 0.1 0.2 0.3 0.2 0.3 0.1 0.1 2.2 0.1 0.2 0.1 0.1 1.1 10.3 2.6 4.2 0.2 1.4 2.2
SO420.0 2.2 0.5 0.1 0.1 1.6 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.0 0.1 0.1 0.1 0.2 0.1 0.1 18.4 0.1 0.1 0.1 0.1 1.0 5.2 1.6 2.7 0.2 1.1 1.1
NO3-
0.0 1.2 0.2 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.1 0.0 0.0 2.4 0.0 0.0 0.0 0.0 0.2 0.3 0.5 1.6 0.0 0.4 0.4
PO 42-
83
84
Physico-chemical parameters
Table 3. Result of the bacteriological analysis of borehole water samples Borehole No.
Total Aerobic Counts (cfu/ml)
Total Coliform (MPN/100ml)
8
10
25
9
30
50
11
135
35
13
344
20
14
20
35
15
5
45
18
52
70
19
535
14
21
96
10
25
128
50
The chemistry of the groundwater generally indicates low dissolved solute and hence low salinity as reflected by low values of TDS and EC in the range of 7.6 to 80.6 mg/l and 15.9 to 162.1 µs/cm respectively. This low TDS status ( Ca2+ >K+ > Mg2+ > Zn2+ > Fe2+ for cations, while anions show the order Cl- > HCO3- > NO3- > SO42- > PO42-.
Bacteriological quality
The result of the bacteriological composition of the water samples is presented in Table 3. The Total aerobic bacteria counts values range between 5 cfu/ml to 536 cfu/ml while Total coliform counts have values from 10 MPN/100ml to 70 MPN/100ml. The presence of aerobic bacteria may not pose a significant health threat, because they could be derived from many sources including, saprophylitic
microorganisms growing on decaying plant matter. It may however, suggest that the water supply facilities (boreholes) have deteriorated significantly in quality, thus allowing the ingress of such micro-organisms. The occurrence of coliforms in excess of WHO (1996) guideline for potability (Table 4), suggests that the water sources might be contaminated with pathogenic microorganisms of faecal origin. An assessment of the relationship between the microbial load and groundwater level depth is shown in Fig. 4. This diagram indicates that neither Total aerobic bacteria counts nor Total coliform counts show direct correlation with water depth. This implies that the microbial population encountered in each of the boreholes may be more related to the sanitary habits of the users. Other plausible reasons may be the entrance of contaminated surface run-offs during heavy downpours or contamination from nearby soak-away pits and/or damaged septic tanks.
Fig. 4. Plot of groundwater depth versus microbial load in boreholes
Water usability
Water quality requirements for different purposes differ; hence standards have been developed to appraise water usability for the various purposes. Water is used predominantly for domestic, agricultural and industrial purposes.
Domestic use The criteria for water potability are defined by Davis and DeWeist (1966) to include, the absence of objectionable tastes, odours, colour and substances of adverse health effects. A quantitative measure of these criteria is stipulated by WHO (1993 and 1996). A comparison of the ionic and bacteriological components of groundwater in the Agbor area with these standards (Table 4) shows that the water samples generally possess pH values lower than the WHO mandatory lower limit of 6.5 for drinking water and higher than required
microbial load. These two factors significantly degrade its quality for domestic use. Remediation such as, lime treatment and sand filtration to upgrade the pH, and chlorine disinfection to reduce the microbial load, are suggested to improve its quality. However, the low total hardness values recorded in the samples ( 2000mm) experienced yearly in the study area, ensures a continuous leaching of the sediments thereby reducing its soluble components with time. This, in addition to the significant dilution of groundwater resulting from abundant recharge by precipitation, and rapid circulation of water through the soil because of the high permeability and slopy landscape, probably account for the low solute concentration of groundwater in the study area. The water types encountered in the study area include the bicarbonate types Na-HCO3 and Na-Ca-HCO3 and more prominently chloride facies of several cationic associations namely; CaCl2, Ca-Mg-Cl, Mg-Ca-Cl, Na-Ca-Cl and NaCl. While the bicarbonate type indicates areas of recent water recharge with base exchange processes, the chloride type suggests water-rock interaction and dissolution of formation water, accompanied by some cation exchange activities. Studies of groundwater chemistry in areas with contrasting topography have revealed that the chemical facies of groundwater could also be influenced by topographic setting (Raji and Alagbe, 2000; Adams et al, 2001). In topographic highs (hills and upslope areas) that represent areas of recharge, bicarbonate water accompanied by low TDS can be dominant. Middle slope locations often contain significant bicarbonate-chloride water. In downslope areas (valleys and plains) where groundwater is relatively static, sulphate-chloride facies with concomitant
increase in TDS values are often noticed. Although considerable topographic contrasts occur in Agbor area, this study does not reveal such contrasts in the groundwater chemistry. This may imply that the influence of this factor is minimal in the study area and/or it is effectively masked by the activities of other factors. Deductions from this study, indicate that the groundwater is generally suitable for crop irrigation. Nevertheless, appropriate pH remediation and microbial disinfection are needed to upgrade its quality for industrial and domestic use. Inferences from factor analysis (Factor 2) suggest an on-set of the aquifer contamination from agricultural related activities. This may intensify with the further use of nitrogen-rich fertilizers, such as NPK, that ensures adequate agricultural yield. Although the nitrate level in groundwater is still within the WHO acceptable limits, the possibility of a rise in its concentration is a potential cause for concern. Nitrate pollution of groundwater arising from long-term use of nitrogen fertilizers has been widely reported (Burkart and Kolpin, 1993). The environmental health effects in such districts are, a drastic rise in cancer mortality in adults (Mandel and Shiftan, 1991) and Methemoglobinemia (blue baby syndrome) in infants (Johnson et al., 1987). Reduction in nitrogen-rich fertilizer applications to the minimum needed or the use of alternative slow-release fertilizers may help reverse this pollution trend (Montgomery, 1992).
References ADAMS, S, TITUS, R., PIETERSON, K., TREDOUX, G. and HARRIS, C. 2001. Hydrochemical characteristics of aquifer near Sutherland in Western Karoo, South Africa. Jour. of Hydrology 241, pp 91-103. AJAYI, O. and UMOH, O.A., 1998. Quality of groundwater in coastal plain sands aquifer of Akwa Ibom state, Nigeria. Journal of African Earth Science 27/2, pp.259-275 AKPOBORIE, I.A., EKAKITIE, O.A. and ADAIKPOH, E.O., 2000. The quality of groundwater from dug wells in parts of the Niger Delta. Knowledge Review 2/5, pp72-79 AMADI, P.A., OFOEGBU, C.O. and MORRISON, T. 1989. Hydrochemical assessment of groundwater in parts of Niger delta, Nigeria. Environmental Geology 14/3, pp.195-202. AMERICAN PUBLIC HEALTH ASSOCIATION, 1985. Standard method for the examination of water and waste water. APHA, New York. 1800p AMERICAN WATER WORKS ASSOCIATION, 1971. Water quality and treatment. McGraw-Hill. New York. 654p. BURKART, M.R. and KOLPIN, D.W., 1993. Hydrologic and landuse factors associated with herbicides and nitrate in near-surface aquifers. Journal of Environmental Quality 22 pp646-656 BRIZ-KISHORE, B.H. and MURALI, G., 1992. Factor analysis for revealing hydrochemical characteristics of a water shed. Environmental Geology 19, pp3-9. DAVIS, S.N and DEWEIST, R.J.M, 1966. Hydrogeology. John Wiley and Sons, Inc. 463p. DRISCOLL, F.G., 1986. Groundwater and wells. Johnson Filtration System Inc, Minnesota. 1089p EDET, A.E. 1993. Groundwater quality assessment in parts of Eastern Niger Delta. Environmental Geology 22, pp.41-46 EZEIGBO, H.I., Quality of water resources in Anambra State, Nigeria.
Journal of Mining and Geology 23, pp.97-103 ETU-EFEOTOR, J.O., 1981. Preliminary hydrochemical investigation of sub-surface waters in parts of the Niger Delta. Journal of Mining and Geology 18/1, pp103-107 HEM, J.D., 1984. Study and interpretation of chemical characteristics of natural water. USGS Water Supply Paper no. 1473, 264p. ILOEJE, N.P., 1981. A new geography of Nigeria. Longman, Nigeria. 201p. JOHNSON, C.J., BONRUD, P.A., DOSCH, T.L., KILNESS, A.W., SENGER, K.A.,BUSCH, D.C., and MEYER, M.R., 1987. Fatal outcome of Methemoglobinemia in infant. Journal of the American Medical Association 257, pp2796-2797. LAWRENCE, F. W. and UPCHURCH, S.B., 1993. Identification of recharge areas using geochemical factor analysis. Groundwater 20, pp. 680-687. MONTGOMERY, C.A., 1992. Environmental Geology. Wm. C. Brown Publishers, Dubuque. 466p. MANDEL, S and SHIFTAN, Z. I., 1991. Groundwater resource investigation and development. Academic Press Inc., New York. 269p OFFODILE, M.E., 1992. An approach to groundwater study and development in Nigeria. Mecon Services Ltd, Jos. 243p. OLOBANIYI, S.B. and OWOYEMI, F.B., 2004. Quality of groundwater in the Deltaic Plain Sands aquifer of Warri and environs, Delta State, Nigeria. Water Resources (journal of the Nigerian Association of Hydrogeologists) 15, pp.38-45 OLOBANIYI, S.B. OGBAN, F.E., EJECHI, B.O. and UGBE, F.C., 2004. Assessment of groundwater across Delta State: effects of man, geology and hydrocarbon exploitation.Final Report. Delta State University. 100p OLOBANIYI S.B. and OWOYEMI, F.B., 2006. Characterization by
89 factor analysis of the chemical facies of groundwater in the Deltaic Plain Sands aquifer of Warri, Western Niger Delta, Nigeria. UNESCO/African Journal of Science and Technology: Science and Engineering Series 7, pp.73-81 OTEZE, G. 1981. Water resources of Nigeria. Environmental Geology 3, pp. 171-184. PIPER, A. M., 1944. A graphical procedure in geochemical interpretation of water analysis. Trans. American Geophysics Union 25, pp. 914-923. RAJI, B.A and ALAGBE, S.A., 2000. A topo-geochemical sequence study of groundwater in asa drainage Basin, Kwara State, Nigeria. Environmental Geology 39(6), pp.544-548. RICHARDS, L.A., 1954. Diagenesis and improvement of saline and alkali soils. Agric. Handbooks 60, U.S. Dept. Agric. Washington, D.C. 160p. ROSE, A. W., HAWKES, H. E. and WEBB, J. S., 1979. Geochemistry in mineral exploration. Academic Press, London. 655p SAWYER, C.N and MCCARTHY, P. L., 1967. Chemistry for sanitary engineers. 2nd ed. McGraw-Hill, New York. 518p. SIMPSON, A., 1954. The Nigerian coalfield, the geology of parts of Onitsha, Owerri and Benue provinces. Geological Survey
Nigeria Bulletin 24, pp1-85. SUBBARAO, C., SUBBARAO, N. V. and CHANDU, S.N., 1996. Characterisation of groundwater contamination using factor analysis. Environmental Geology 28(4), pp.175-180. TATTAM, C.M., 1943. A review of Nigerian stratigraphy. Geological Survey of Nigeria Report, Lagos pp. 27-46. TIJANI, M. N., 1994. Hydrogeochemical assessment of groundwater in Moro area, Kwara State, Nigeria. Environmental Geology 24, pp.194-202. TIJANI, M.N., Onibalusi, S.O. and Olajide, A.S., 2002. Hydrochemical and environmental impact assessment of Orita Aperin waste dumpsite, Ibadan, southwestern Nigeria. Water Resouces (Journal of Nigerian Association of Hydrogeologists) 13, pp.78-84. WORLD HEALTH ORGANISATION, 1993. International standard for drinking water and guidelines for water quality. WHO, Geneva. WORLD HEALTH ORGANISATION, 1996. Guidelines for drinking water quality. 2nd edition: Health criteria and other supporting information. WHO, Geneva.
Received 1 September, 2005; Revision accepted 18 December, 2006
90
