GROUNDWATER QUALITY ASSESSMENT OF WELLS IN IFEWARA, OSUN STATE

Study was carried out in Ifewara, Osun state with an objective of evaluating the quality and suitability of local groundwater for domestic purposes. Twenty six groundwater samples from hand dug wells and one borehole sample and were subjected to physicochemical analysis. Results from the study shows that the cationic and anionic concentrations vary as follows: Na(0.2-3.5 mg/l), K (0.1-15.1 mg/l) Ca (16-96 mg/l), HCO3 (16-176 mg/l), Mg (3104 mg/l), NO3(0.18-11.43 mg/l), SO4,(1.24-21.3 mg/l), Cl (2-52 mg/l), and PO4(0.01-0.75 mg/l).The study also shows that the water is fresh with TDS value (avg. 93.8 mg/l) and a neutral pH (avg. 6.8) within the permissible range (6.5-8.5).Hydrogeochemical evaluation of the groundwater reveals that it is predominantly of the CaHCO3 type while others belong to the Mixed CaMgCl type. The water chemistry was observed to have been influenced by the dilution and weathering processes at shallow depth.


INTRODUCTION
Sustainable provision of portable and adequate water resource for immediate and future use are of regional to global concern. Water supports all forms of life (Vanloon and Duffy, 2005) and the challenge of obtaining clean portable water is a concern for most people living in the rural area in most developing countries. The quality of water available for the population is often a function of natural as well as anthropogenic activities (Sajjad, et al., 1998).
Water is sourced from two principal sources; surface waters such as fresh water lakes, rivers, streams, etc. and ground water such as borehole and well water. Groundwater refers to underground fresh water which can be abstracted for domestic, agricultural and industrial uses and it accounts for 98% of the world's fresh water (Buchanan, 1983;Bouwer, 2002). Fresh water resource in most communities is under threat due to immense natural and anthropogenic influences as a result of factors such as overpopulation and activities (including agriculture, indiscriminate refuse disposal and use of septic tanks, soak away and latrines) which are capable of producing run-offs and leachate which could infiltrate into and pollute groundwater formation.
Many households depend on wells due to the frequent interruptions or non-availability of supply of treated water. The aim of this study is to investigate the water quality and hydrogeochemical process (evolution, origin and mixing) of water resource in Ifewara.

Study Area
The study area in located in Atakumosa local government area of Osun State, Southwestern Nigeria. It covers an area of approximately 14,875 Km 2 . The study area enjoys a tropical climate with distinct wet and dry seasons. Ifewara falls within the Ilesha schist belt and it is underlained by gneiss, migmatite and metasediments ranging from Precambrian to Paleozoic age ( Fig. 1).

Methodology
Field investigation of groundwater samples were carried out on water samples from 25hand dug wells and one borehole samples in Ifewara. A pair of samples were collected in carefully rinsed and labelled bottles for both cationic and anionic analyses. Dilute Nitric acid was added to the samples for cationic analysis on the site to preserve and retard the chemical and metal changes while the anions were preserved with ice blocks. Hydrogeochemical properties of representative samples from the wells such as; temperature, pH, Electrical Conductivity (EC) and total dissolved solids(TDS)were measured on the field using Hanna 98130 digit multi-meter. The concentration of cation species such as Ca 2+ , Mg 2+ , K and Na in the samples were determine with the use of spectrophotometer while the Anions; SO 4 2-, HCO 3 -, Cl and NO 3 were determined using digital titration method.
Data from the hydrogeochemical analysis were subjected to statistical analysis in order to classify the water resource into distinct group and sub-groups. Water quality assessment were also carried out by comparing the results against WHO standards for domestic use.

Study Area
The study area in located in Atakumosa local government area of Osun State, Southwestern Nigeria. It covers an area of approximately 14,875 Km 2 . The study area enjoys a tropical climate with distinct wet and dry seasons. Ifewara falls within the Ilesha schist belt and it is underlained by gneiss, migmatite and metasediments ranging from Precambrian to Paleozoic age ( Fig. 1).

Methodology
Field investigation of groundwater samples were carried out on water samples from 25hand dug wells and one borehole samples in Ifewara. A pair of samples were collected in carefully rinsed and labelled bottles for both cationic and anionic analyses. Dilute Nitric acid was added to the samples for cationic analysis on the site to preserve and retard the chemical and metal changes while the anions were preserved with ice blocks. Hydrogeochemical properties of representative samples from the wells such as; temperature, pH, Electrical Conductivity (EC) and total dissolved solids(TDS)were measured on the field using Hanna 98130 digit multi-meter. The concentration of cation species such as Ca 2+ , Mg 2+ , K and Na in the samples were determine with the use of spectrophotometer while the Anions; SO 4 2-, HCO 3 -, Cl and NO 3 were determined using digital titration method.
Data from the hydrogeochemical analysis were subjected to statistical analysis in order to classify the water resource into distinct group and sub-groups. Water quality assessment were also carried out by comparing the results against WHO standards for domestic use.

RESULTS AND DISCUSSION
The results of the physiochemical parameters determined for water samples in the study area are presented in Table 1

Study Area
The study area in located in Atakumosa local government area of Osun State, Southwestern Nigeria. It covers an area of approximately 14,875 Km 2 . The study area enjoys a tropical climate with distinct wet and dry seasons. Ifewara falls within the Ilesha schist belt and it is underlained by gneiss, migmatite and metasediments ranging from Precambrian to Paleozoic age ( Fig. 1).

Methodology
Field investigation of groundwater samples were carried out on water samples from 25hand dug wells and one borehole samples in Ifewara. A pair of samples were collected in carefully rinsed and labelled bottles for both cationic and anionic analyses. Dilute Nitric acid was added to the samples for cationic analysis on the site to preserve and retard the chemical and metal changes while the anions were preserved with ice blocks. Hydrogeochemical properties of representative samples from the wells such as; temperature, pH, Electrical Conductivity (EC) and total dissolved solids(TDS)were measured on the field using Hanna 98130 digit multi-meter. The concentration of cation species such as Ca 2+ , Mg 2+ , K and Na in the samples were determine with the use of spectrophotometer while the Anions; SO 4 2-, HCO 3 -, Cl and NO 3 were determined using digital titration method.
Data from the hydrogeochemical analysis were subjected to statistical analysis in order to classify the water resource into distinct group and sub-groups. Water quality assessment were also carried out by comparing the results against WHO standards for domestic use.

RESULTS AND DISCUSSION
The results of the physiochemical parameters determined for water samples in the study area are presented in Table 1   The physical description of the water is clear and colorless. The pH values of water samples is neutral (varying between 6.3 and 7.4, avg. 6.8) and it falls within the limits (6.5 -8.5) recommended for drinking water WHO (2006).However samples A11, A12 and A14 are slightly acidic with pH of 6.37, 6.36 and 6.29 respectively. Electrical conductivity signifies the amount of total dissolved solids and it is the most important parameter to identify salinity and suitability of water for irrigation purposes (Ramesh and Bhuvana, 2012). The EC values in the water ranges between26 to 495 µS/cm. The hydrogeochemistry of the water was evaluated by plotting the concentrations of the major ions such as Na + , K + , Ca 2+ , HCO 3 -, Mg 2+ ,SO 4 2and Clin milli-equivalent per liter in a Piper diagram (1994) using Rock Ware AqQA software. The result show that the samples plotted in fields that suggesting the facies type of the water are predominantly CaHCO 3 type while the others are of Mixed CaMgCl type (Fig.5). The physical description of the water is clear and colorless. The pH values of water samples is neutral (varying between 6.3 and 7.4, avg. 6.8) and it falls within the limits (6.5 -8.5) recommended for drinking water WHO (2006).However samples A11, A12 and A14 are slightly acidic with pH of 6.37, 6.36 and 6.29 respectively. Electrical conductivity signifies the amount of total dissolved solids and it is the most important parameter to identify salinity and suitability of water for irrigation purposes (Ramesh and Bhuvana, 2012). The EC values in the water ranges between26 to 495 µS/cm. The hydrogeochemistry of the water was evaluated by plotting the concentrations of the major ions such as Na + , K + , Ca 2+ , HCO 3 -, Mg 2+ ,SO 4 2and Clin milli-equivalent per liter in a Piper diagram (1994) using Rock Ware AqQA software. The result show that the samples plotted in fields that suggesting the facies type of the water are predominantly CaHCO 3 type while the others are of Mixed CaMgCl type (Fig.5). The physical description of the water is clear and colorless. The pH values of water samples is neutral (varying between 6.3 and 7.4, avg. 6.8) and it falls within the limits (6.5 -8.5) recommended for drinking water WHO (2006).However samples A11, A12 and A14 are slightly acidic with pH of 6.37, 6.36 and 6.29 respectively. Electrical conductivity signifies the amount of total dissolved solids and it is the most important parameter to identify salinity and suitability of water for irrigation purposes (Ramesh and Bhuvana, 2012). The EC values in the water ranges between26 to 495 µS/cm. The hydrogeochemistry of the water was evaluated by plotting the concentrations of the major ions such as Na + , K + , Ca 2+ , HCO 3 -, Mg 2+ ,SO 4 2and Clin milli-equivalent per liter in a Piper diagram (1994) using Rock Ware AqQA software. The result show that the samples plotted in fields that suggesting the facies type of the water are predominantly CaHCO 3 type while the others are of Mixed CaMgCl type (Fig.5). The provenance of the chemical constituent of the water was also classified based on the meteoric gneiss index (r 2) using; (( ) ⁄ The meteoric gneiss index and the concentrations of Na + , K + , SO 4 2and Cl were expressed in meq/l. groundwater with r2 greater than 1 (r2 > 1) suggest shallow meteoritic water percolation type while r2 < 1 suggest a provenance of deep meteoric water percolation type. The meteoric gneiss values of all the sample were observed to be greater than 1 indicates they are from the shallow meteoric water percolation type. This can also be supported with the depth of all the hand dug wells ranging between 9.15 and 19.98 m.
Gibbs ratio and plots are widely sued to assess the functional sources of the dissolved chemical constituents and it could be; precipitation dominance, rock dominance or evaporation dominance (Ramesh, 2012). The mechanism controlling the groundwater chemistry of the samples were observed to be precipitation and rock dominance (Fig.  4).

Figure 4:
Plot of TDS against Na/(Na+Ca) ratio (after Gibbs, 1970) Two predominant water types were identified based on water classification Ca-Mg-HCO 3 andMg-Ca-CO 3 However, water samples A5 and A25 have water type Ca-Mg-Cl both having unusual abundance of Cl. Possible source of the Ca-Mg ions in the water could imply a provenance from plagioclase feldspars, mafic minerals and clays from the underlying weathered basement (Anudu, 2011).

Irrigation water quality
All ground water contains dissolved salts and trace elements which are from the process of weathering, erosion or effluent from Industries, municipal sewage or irrigated farmlands. The suitability of groundwater for irrigation depends upon the chemical composition of the water. For agricultural purposes, salinity levels in groundwater is a primary concern, since GROUNDWATER The provenance of the chemical constituent of the water was also classified based on the meteoric gneiss index (r 2) using; (( ) ⁄ The meteoric gneiss index and the concentrations of Na + , K + , SO 4 2and Cl were expressed in meq/l. groundwater with r2 greater than 1 (r2 > 1) suggest shallow meteoritic water percolation type while r2 < 1 suggest a provenance of deep meteoric water percolation type. The meteoric gneiss values of all the sample were observed to be greater than 1 indicates they are from the shallow meteoric water percolation type. This can also be supported with the depth of all the hand dug wells ranging between 9.15 and 19.98 m.
Gibbs ratio and plots are widely sued to assess the functional sources of the dissolved chemical constituents and it could be; precipitation dominance, rock dominance or evaporation dominance (Ramesh, 2012). The mechanism controlling the groundwater chemistry of the samples were observed to be precipitation and rock dominance (Fig.  4).

Figure 4:
Plot of TDS against Na/(Na+Ca) ratio (after Gibbs, 1970) Two predominant water types were identified based on water classification Ca-Mg-HCO 3 andMg-Ca-CO 3 However, water samples A5 and A25 have water type Ca-Mg-Cl both having unusual abundance of Cl. Possible source of the Ca-Mg ions in the water could imply a provenance from plagioclase feldspars, mafic minerals and clays from the underlying weathered basement (Anudu, 2011).

Irrigation water quality
All ground water contains dissolved salts and trace elements which are from the process of weathering, erosion or effluent from Industries, municipal sewage or irrigated farmlands. The suitability of groundwater for irrigation depends upon the chemical composition of the water. For agricultural purposes, salinity levels in groundwater is a primary concern, since GROUNDWATER The provenance of the chemical constituent of the water was also classified based on the meteoric gneiss index (r 2) using; (( ) ⁄ The meteoric gneiss index and the concentrations of Na + , K + , SO 4 2and Cl were expressed in meq/l. groundwater with r2 greater than 1 (r2 > 1) suggest shallow meteoritic water percolation type while r2 < 1 suggest a provenance of deep meteoric water percolation type. The meteoric gneiss values of all the sample were observed to be greater than 1 indicates they are from the shallow meteoric water percolation type. This can also be supported with the depth of all the hand dug wells ranging between 9.15 and 19.98 m.
Gibbs ratio and plots are widely sued to assess the functional sources of the dissolved chemical constituents and it could be; precipitation dominance, rock dominance or evaporation dominance (Ramesh, 2012). The mechanism controlling the groundwater chemistry of the samples were observed to be precipitation and rock dominance (Fig.  4).

Figure 4:
Plot of TDS against Na/(Na+Ca) ratio (after Gibbs, 1970) Two predominant water types were identified based on water classification Ca-Mg-HCO 3 andMg-Ca-CO 3 However, water samples A5 and A25 have water type Ca-Mg-Cl both having unusual abundance of Cl. Possible source of the Ca-Mg ions in the water could imply a provenance from plagioclase feldspars, mafic minerals and clays from the underlying weathered basement (Anudu, 2011).

Irrigation water quality
All ground water contains dissolved salts and trace elements which are from the process of weathering, erosion or effluent from Industries, municipal sewage or irrigated farmlands. The suitability of groundwater for irrigation depends upon the chemical composition of the water. For agricultural purposes, salinity levels in groundwater is a primary concern, since GROUNDWATER QUALITY ASSESSMENT OF WELLS IN IFEWARA, OSUN STATE salt can affect soil structure and yield (Fipps, 2003). High salinity is capable of posing salinity hazard to plants by creating an artificial drought condition whereby the roots of plants are unable to absorb water even when the soil is well moistured. Salinity hazard can be measured using both conductivity and dissolved solids.
The effect of salinity hazard on plants can vary from low, medium, high to very high. Low salinity have no detrimental effects on plants; Medium salinity have detrimental effects to sensitive crops; High salinity, adverse effects on many crops and very high salinity are only suitable only for salt tolerant plants Salinity hazard of the ground water in the study based on the SAR vary between 0.12 and 1.67 which shows that 62% of the water samples in the study area was observed to have Low values while 38% have high SAR values. (Table 2).

CONCLUSION
Hydrochemistry evaluation suggest the cations in the water are from plagioclase feldspars, mafic minerals and clays in the weathered basement aquifer. Results from the study shows that the water in Ifewara and environ is safe for drinking with a low salinity hazard making it suitable for irrigation purposes. The water chemistry was observed to have been strongly influenced by dilution and weathering processes at shallow depth.

ACKNOWLEDGEMENT
The author acknowledges the assistance of the residents of Ifewara community for giving access to their wells. The efforts of Laboratory Staff of EMT, FUNAAB in carrying out the laboratory analysis is also much appreciated