JOURNAL OF ENVIRONMENTAL GEOGRAPHY Journal of Environmental Geography 6 (1–2), 29–36. DOI: 10.2478/v10326-012-0004-2 ISSN: 2060-467X EVALUATION OF GROUNDWATER QUALITY USING WATER QUALITY INDICES IN PARTS OF LAGOS-NIGERIA Isaiah S. Akoteyon Department of Geography and Planning, Lagos State University,Ojo, P.M.B. 1087, Apapa, Lagos e-mail: sewanuakot@gmail.com Research article, received 14 January 2013, published online 15 April 2013 Abstract Water samples collected from forty-five hand dug wells and thirteen boreholes using random sampling technique were measured for pH, electrical conductivity and total dissolved solids. Calcium, chloride, bicarbonate and carbonates were analyzed using titrimetry method. Magnesium, potassium and sodium by Atomic Absorption Spectrophotometer (AAS) and sulfate was analyzed using a spectrophotometer. The study aims to evaluate groundwater quality using water quality indices in parts of Lagos-Nigeria. The sample locations and spatial variations in the concentration of bicarbonates, Revelle and Water quality indices were mapped using surfer 6.0 software. The result shows that pH indicate extremely acidic to strongly alkaline condition, EC shows medium and high enrichment of salts from location 28 and 21 respectively. Spatially, about 31% and 29.3% of bicarbonate are under poor and moderate zones respectively. The computed Revelle index shows that 41.4% and 1.7% are slightly and strongly influenced by groundwater saliniza- tion respectively. Unlike the water quality index, about 12.1% and 1.7% indicate poor and water unfit for drinking respectively. The paper concludes that groundwater salinization is on the increase since over half of the samples are influenced by salinity. Unlike the water quality, it was concluded that the water is of good quality since about 86.2% is suitable for drinking purposes. Based on these findings, it was recommended that waste water treatment and disposal methods should be avoided and appropriate treatment methods to make it more potable and fit for human consumption should be employed in critical locations of the study area. Keywords: groundwater, Lagos-Nigeria, water quality, Revelle Index, Water Quality Index INTRODUCTION Fresh water, as a valuable and finite resource, is a central issue of sustainable development, economic growth, social stability, and poverty alleviation. Fresh water quality has grown to become the major international issue in recent years (Rejith et al., 2009). Urban growth, increased industrial activities, intensive farming, and overuse of fertilizers in agricultural production have been identified as drivers responsible for these changes (Patwardhan, 2003). Studies have shown that the pol- luted environment has a detrimental influence on human health, fauna and flora species (Sujatha and Reddy, 2003). Contamination of groundwater (resulting from human activities or from inherent aquifer material) im- pairs water sources and poses threat to public health (Renji and Panda, 2007). Rapid population growth and increased anthropogenic activities result in huge dis- charge and diverse pollutants reaching sub-surface wa- ter. Excessive groundwater withdrawals have been re- ported to result in hydro-chemical changes in the physi- cal, chemical and microbiological water quality, decline of the water table, reverse hydraulic gradient and conse- quently water quality deterioration in coastal areas (Esteller et al., 2012; Jamshidzadeh and Mirbagheri, 2011). Poor water quality results in incidences of water- borne diseases and consequently reduces the life expec- tancy (WHO, 2006). Thus, concern for clean and safe drinking water and protection from contamination is justified because a large proportion of the population in the study area depends on sub-surface sources e.g. dug wells and boreholes etc. for domestic and drinking uses. Water quality evaluation is based on the physical, chemical and biological parameters ascertaining the suitability for various uses such as consumption, agricul- tural, recreational and industrial use (Boyacioglu, 2007; Sargaonkar and Deshpande, 2003). Traditional methods of assessing water quality are based on the comparison of experimentally determined parameter values with existing guidelines. This method allows proper identifi- cation of contamination sources essential for checking legal compliance (Boyacioglu, 2007). One of the advan- tages of water quality index (WQI) is that it serves as a useful and efficient method for assessing the suitability of water quality for various purposes. It also serves as a mean of communicating information on the overall qual- ity of water using a single number both temporarily and spatially (Christiane et al., 2009; Boyacioglu, 2007). Water quality indicators have been applied to as- sess the overall water quality in different parts of the mailto:sewanuakot@gmail.com 30 Akoteyon (2013) globe efficiently (Bharti and Katyal, 2011). These indi- cators are based on the comparison of water quality parameters using regulatory standards to give a single value to the water quality of a source. WQI computation involves four steps: parameter selection, development of sub-indices, assignment of weights and aggregation of sub-indices to produce an overall index. WQI helps to reveal the temporal and spatial variation of water quality (Bharti and Katyal, 2011). It also serves as a useful tool for summarizing large amounts of water quality data into simple terms such as excellent, good, bad, etc. for easy communication to the public. Literature abounds on water quality assessment. Akoteyon et al. (2010), Yidana and Yidana (2010), Akoteyon and Soladoye (2011), Jamshidzadeh and Mirbagheri (2011), Partey et al. (2010), Celik and Yildirim (2006) Mishra et al. (2005), Edmunds et al. (2003) among others applied WQI in evaluating groundwater. For instance, Shah et al. (2008) co m- pared groundwater quality in Gandhinagar Taluka in India and developped the water quality index for the area. Zaharin et al. (2009) classified salinization of groundwater in the shallow aquifer of a small tropical Island in Sabah, Malaysia using Revelle index (i.e. Cl / (HCO3 + CO3). Lobo-Ferreira et al. (2005), Chachadi and Lobo – Ferreira (2001) also adopted this index to evaluate seawater intrusion into the coastal aquifer in India. Thus, this study is aimed at evaluat- ing groundwater quality using water quality indices in parts of Lagos-Nigeria as an alternative method for disseminating information on water quality status using indices for better understanding both by the public and relevant agencies. STUDY AREA The study area is located approximately between lati- tudes 6 o 23’ 30’ N and 6 o 34’15 N and longitudes 3 o 28’0 E and 3 o 38’45 E . It is bounded in the East by Ibeju- Lekki, in the North by the Lagos Lagoon and in the South by the Atlantic Ocean and parts of the metrop o- lis in the West. The climate is tropical, hot and wet and the area is characterized by coastal wetlands, sandy barrier islands, beaches, low-lying tidal flats and estuaries (Adepelumi et al., 2009). The average temperature is about 27 0 C with an annual average rainfall of about 1,532 mm (Adepelumi et al., 2009). The major seasons are the wet and dry seasons. The wet season lasts for 8 months (April to Nove mber) and the dry season covers a period of 4 months (De- cember to March (Adepelumi et al., 2009). The domi- nant vegetation consists of tropical swamp forest (fresh waters and mangrove swamp forests and dry lowland rain forest). The area is drained by Lagos Lagoon (Emmanuel and Chukwu, 2010). The geology is underlain by the Benin Formation and is made up of highly porous sand and gravel with thin shale/clay inter-beds (Oteri and Atolagbe, 2003). The groundwater flow direction shows a general North to South direction with two small cones of depression in Apapa and Ikeja because of intense groundwater extraction (Coode et al., 1997; Oteri and Atolagbe, 2003). The hydrogeology is characterized by unfos- siliferous sandstone and gravel weathered from unde r- lying precambrian basement rock (Longe, 2011). It consists of Abeokuta and Ewekoro Formations, Coastal Plain Sands (CPS) and recent sediments. The CPS aquifer is the most productive and exploited aquifer in Lagos state. CPS is categorized into four types namely the recent sediments, the second and third aquifers also known as (upper and lower) CPS aquifer and the fourth aquifer is the Abeokuta forma- tion (Longe, 2011). The upper coastal plain sand aquifer (UCPS) is a water table aquifer and ranged from 0.4–21m below ground level with a relatively annual fluctuation be- low 5m (Asiwaju-Bello and Oladeji, 2001). This aqui- fer is usually tapped by hand dug well. The major limitation of this aquifer is that, it is prone to poll u- tion because it is near to the ground surface. Unlike the lower coastal plain sand (LCPS) aquifer, it is tapped through boreholes. MATERIALS AND METHODS Fifty-eight samples including 45 hand dug wells (samples 1–45) and 13 boreholes (samples 46–58) were randomly selected for evaluation of groundwater salinization and quality assessment in the study area. Samples were collected in clean 150ml polyethylene bottles and preserved in ice chests for delivery to the chemistry department of the University of Lagos, Akoka for laboratory analyses using standard methods (APHA, 1998). In-situ parameters were measured for electrical conductivity (EC), pH and total dissolved solids (TDS) using a portable hand held (HI98303, Hanna model), (PH-102, RoHS model) and TDS/TEMP HM Digital model respectively. The in- situ measurements were necessary because these pa- rameters are likely to change on transit to the labor a- tory. Chloride, calcium, carbonate and bicarbonate were determined using titrimetry method. Atomic Absorption Spectrophotometer (AAS) HI 98180 model was used to analyze magnesium, potassium and sodium, and sulfate was determined using spectrophotometer, HACH DR/2000 model. The indi- vidual sample co-ordinate and the computed Revelle and water quality indices were exported to the Surfer 6.0 software package for mapping the spatial varia- tions of bicarbonate, the Revelle index and the water quality index using the Kriging method. The statistical analysis of the examined groundwater parameters were computed using SPSS software 17.0 version. Evaluation of groundwater quality using water quality indices in parts of Lagos-Nigeria 31 Co-ordinates of the sampled wells were recorded using Global Positioning System (GPS) and thereafter were plotted using ArcMap 9.3 software on the geo- logical map of Lagos, sheet 68 on 1:250,000 scale to generate a map of the sampling locations (Fig.1). Evaluation of groundwater salinity and the drink- ing water quality assessment were executed applying: Revelle Index (RI): R = rCl - / (rHCO3 – + rCO3 2– ) (1) where: r = milliequivalents per litre (meq/l) RI < 0.5 (unaffected), 0.5- 6.6 (slightly affected) > 6.6 (strongly affected) (Zaharin et al., 2009; Revelle, 1941) The Water Quality Index (WQI) was evaluated using the World Health Organization (2004) standard. The stages of calculating the WQI include: qn = 100 [Vn – Vio ] / [Sn – Vn] (2) where: n is the water quality parameter and quality rating or sub index (qn) corresponding to n th parameter (i.e a number reflecting the relative value of this parame- ter with respect to its standard (maximum permissi- ble value) qn = Quality rating for the n th water quality parameter Vn = Estimated value of the n th parameter at a given the sampling point Sn = Standard permissible value of the n th parameter Vio =Ideal value of n th parameter in pure water (i.e. 0 for all other parameters except pH and Dissolved Oxy- gen (7.0 and 14.6 mg/l respectively). The Unit weight (Wn) is calculated by a value inversely proportional to the recommended standard value (Sn) of the corresponding parameter. Wn = K/Sn (3) where: Wn= unit weight for the n th parameters Sn = standard value for the n th parameters K = constant for proportionality The overall WQI is calculated by aggregating the qual- ity rating with the overall WQI which is calculated by aggregating the quality rating with the unit weight linearly as: WQI=ƩqnWn/ƩWn (4) RESULTS AND DISCUSSION The measured parameters and the descriptive statistics of the groundwater characteristics of the study area are shown in Table 1. The pH of the sampled wells varied from 3.4 to 8.55 indicating an extremely acidic to strongly alkaline condition that may affect the taste (Todd and Mays, 2005). Fig.1 Sampling locations 32 Akoteyon (2013) Table 1 Detected parameters of groundwater and their descriptive statistics Sample No. pH EC (µS/cm) TDS (mg/l) Na + (mg/l) K + (mg/l) Ca 2+ (mg/l) Mg 2+ (mg/l) Cl - (mg/l) HCO3 - (mg/l) SO4 2- (mg/l) CO3 2- (mg/l) 1 6.84 630 424 13.4 4.16 69 45 38 176 9 153 2 7.33 285 200 10.11 2.05 96 30 40 169 7 148.4 3 6.8 380 264 7.61 1.54 160 16 38 UDL 11 445.2 4 5.96 748 515 13.65 2.28 316 26 82 50.4 17 339.2 5 5.92 204 141 3.7 0.45 86 30 18 UDL 5 339.2 6 6.02 375 257 6.95 1.8 72 44 34 UDL 9 275.6 7 6.52 222 153 6.33 2.12 90 22 20 UDL 5 254.4 8 6.4 182 128 3.85 0.74 102 15 14 67.2 4 148.4 9 4.54 206 143 4.27 1.89 82 74 80 UDL 6 314.4 10 5.58 763 533 32.3 5.12 110 112 176 UDL 19 826.8 11 6.01 310 219 7.22 3.51 12 2 36 100.8 8 127.2 12 5.31 348 240 6.99 4.2 64 56 48 UDL 8 402.8 13 5.48 174 124 4.16 1.89 30 26 32 117.8 5 84.8 14 5.5 360 250 5.59 2.34 150 20 44 369.6 8 106 15 5.32 40 30 0.63 0.19 16 2 8 UDL 2 106 16 3.79 659 453 16.52 4.88 234 22 142 UDL 14 360 17 3.4 213 150 2.79 0.87 92 16 30 UDL 5 233.2 18 6.09 658 440 29.64 4.52 190 32 116 UDL 8 848 19 6.86 327 223 9.2 1.76 94 28 36 252 6 63.6 20 6.61 145 99 4.09 0.36 44 16 16 50.4 4 84.8 21 6.57 4040 6112 1080.1 52.32 1200 580 3400 184.8 1250 106 22 6.7 442 302 17.89 2.72 52 74 70 67.2 7 275.6 23 7.14 648 449 25.56 3.97 114 96 100 621.6 12 127.2 24 6.41 490 341 15.89 2.71 76 94 62 218.4 7 190.8 25 6.8 738 492 69.7 10.58 118 106 246 210 10 UDL 26 6.43 438 296 47.38 6.42 50 34 166 110 8 UDL 27 5.48 648 442 41.53 5.65 138 54 140 120 9 UDL 28 6.29 1575 1020 122.51 15.75 414 106 448 570 16 40 29 6.1 1053 705 112.42 14.63 328 86 374 456 14 26 30 6.67 806 537 104 16.3 406 92 356 380 12 38.5 31 5.48 318 202 5.27 3.12 138 26 40 104 8 29.7 32 5.89 369 242 3.4 2.42 140 24 16 86 6 UDL 33 6.03 611 400 32.69 4.78 142 74 114 140 9 UDL 34 6.39 790 541 38.24 5.17 184 16 130 240 12 UDL 35 5.34 425 290 22.6 4.15 144 8 75 128 4 UDL 36 5.61 490 305 10.46 5.2 100 12 114 104 6 UDL 37 6.5 472 296 31.88 4.58 108 26 120 70 9 UDL 38 5.09 68 47 1.3 0.5 12 2 8 UDL 2 84 39 6.03 191 125 9.8 1.35 22 6 6 UDL 2 96 40 6.3 115 81 6.2 0.17 14 4 10 UDL 4 42 41 6.22 63 44 2.6 0.48 38 12 32 UDL 4 48.4 42 8.55 103 72 3.6 4.8 60 10 46 UDL 8 28 43 5.9 676 479 52.7 8.12 202 26 176 130 10 UDL 44 5.64 201 134 24.6 6.18 196 48 166 146 10 UDL 45 8 116 59 4.31 0.28 46 UDL 16 0.08 4 UDL 46 6.2 312 240 5.21 2.7 88 34 20 30.4 5 276.4 47 6.02 289 154 6.53 1.9 76 38 26 26.4 4 344.8 48 6 403 301 8.35 3.5 81 42 31 28 6 398.2 49 6.8 175 137.5 8 2.15 6.4 2.3 17.1 149.05 11.7 UDL 50 7.1 210 147.4 26.3 12.25 22 10 11 48.23 5.4 UDL 51 5.9 185 132.8 20.2 10.5 3.1 1.1 25.8 43.4 12.3 UDL 52 6 70 23 30 5.2 UDL UDL 23 31.2 45 UDL 53 6 72 22 30 4.8 UDL UDL 25 30 43 UDL 54 6 70 23 31 4 UDL UDL 22 33.1 44 UDL 55 5.4 66 66.9 2.2 1.2 2.1 0.77 11.6 29.5 1.2 UDL 56 5.3 50 46.9 2.2 1 2.1 0.77 8.4 29.15 0.2 UDL 57 5.4 66 66.9 2 1.6 2.1 0.77 11.6 25.2 0.6 UDL 58 6 52 23 1.3 UDL 24 UDL 5 UDL 1 UDL UDL-Under detection limit. Evaluation of groundwater quality using water quality indices in parts of Lagos-Nigeria 33 The Electrical Conductivity (EC) varied between 40 and 4,040μScm -1 with a mean value of 433.36µScm -1 . According to the classification in Rao et al. (2012), samples from locations 1 to 20, 22 to 27 and 29 to 58 are of low enrichment of salts while location 21 and 28 depict medium and high enrichment of salts respec- tively. TDS varied between 22 and 6,112 mg/l with a mean value of 351.44mg/l. According to Todd and Mays (2005), the samples from locations 1 to 20, 22 to 27 and 29 to 58 are of the fresh water type while loca- tions 21 and 28 depict the brackish water type. Cal- cium, Magnesium, Sodium and Potassium varied be- tween under the detection limit to 1, 200, under detec- tion limit to 580, 0.63 to 1,080.10 and under detection limit to 52.32 mg/l with a mean value of 118.24, 41.03, 38.77 and 4.82 mg/l, respectively (Table 1). Carbonate, chloride, bicarbonate and sulfate varied between under the detection limit and 848, under the detection limit to 621.6, 5 and 3,400 and 0.2 to 1,250mg/l with mean values of 134.70, 133.04, 102.46 and 30.73 mg/l respectively. According to Stuyfzand (1989), the classification of chloride shows that about 46.6% of Cl in the samples ac- counts for fresh water while 37.9%, 8.6%, 5.2%, and 1.7% accounted for oligohaline, fresh-brackish, brackish and brackish-salt respectively (Table 2). The spatial variation of bicarbonate in the study area is presented in (Fig. 2). According to the WHO (2004) classification, the variation in HCO 3 concen- tration revealed that about 31% of the samples are under poor zone, 29.3% moderate zone and 10.3% good zone respectively. Evaluation of groundwater salinization The computed Revelle index varied from 0.05 and 14.62meq/l. The relationship between the ratios of Cl/HCO3 + CO3 indicates a strong positive linear rela- tion with Cl concentrations (r = 0.94, p < 0.01). This linear relationship indicates the mixing of saline water and fresh groundwater (Zaharin et al., 2009). Figure 3 shows the spatial variation of the extent of the ground- water salinization in the study area. About 56.9% of the samples (n = 33) were unaffected by salinity, 41.4% (n = 24) were slightly influenced and the remaining 1.7% (n = 1) was strongly influenced by salinity. Areas of critical concern include locations 21, 25-30, 33-37, 41-44, and 51-58 in the study area. Thus, effort must be made to curtail the current groundwater salinization in the area in order to ensure groundwater sustainability. Assessment of drinking water quality The suitability of groundwater quality for drinking pur- pose in the study area was determined using World Health Organization (WHO, 2004) guidelines. Accord- ing to Sahu and Sikdar (2008), the computed water qual- ity index (WQI) ranged from 15.27 to 550.97mg/l. The spatial variations in the samples revealed that about 37.9% of the sampled wells had excellent water quality and 48.3%, 12.1% and 1.7% indicate good, poor and water unfit for drinking respectively (Fig.4). Critical areas that require urgent attention include locations 9-10, 16-17, 21 and 28. Others are 12, 23, 25 27, 33 and 43-44. These locations pose a threat to human health and water resources management in the study area. Table 1 (cont.) Detected parameters of groundwater and their descriptive statistics pH EC (µS/cm) TDS (mg/l) Na + (mg/l) K + (mg/l) Ca 2+ (mg/l) Mg 2+ (mg/l) Cl - (mg/l) HCO3 - (mg/l) SO4 2- (mg/l) CO3 2- (mg/l) Min 3.40 40.00 22.00 0.60 UDL UDL UDL 5.00 UDL 0.20 UDL Max 8.60 4040.00 6112.00 1080.10 52.30 1200.00 580.00 3400.00 621.60 1250.00 848.00 Mean 6.07 433.36 351.40 38.80 4.80 118.24 41.03 133.04 102.50 30.70 134.70 Std. Dev 0.80 563.66 794.12 141.60 7.38 172.73 78.67 446.28 139.20 163.20 187.71 Skewness -0.27 4.88 6.93 7.23 4.99 4.63 5.86 7.13 2.11 7.58 2.08 WHO Std. 8.5 1000 500 200 10 75 30 200 300 200 300 Min-minimum, Max-maximum, Std. Dev-standard deviation; WHO-World Health Organization; Std-standard Table 2 Classification of Chloride in the study area (Source: Stuyfzand (1989)) Chloride Type Chloride (mg/l) Sample Numbers Very Oligohaline < 5 - Oligohaline 30.0-150 (n=23) 5, 7–8, 15, 17, 20, 32, 38–40, 45–47, 49–58 Fresh 30-150 (n=26) 1–4, 6, 9, 11–14,16, 18, 19, 22–24, 27, 31, 33–37, 41–42, 48 Fresh-Brackish 150-300 (n=5) 10, 25–26, 43–44 Brackish 300-1,000 (n=3) 28–30 Brackish-Salt 1,000-10,000 (n=1) 21 Salt 10,000-20,000 - Hypersaline >20,000 - 34 Akoteyon (2013) 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <100mg/L Poor 100-250 - Moderate >250 -Good 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <100mg/L Poor 100-250 - Moderate >250 -Good <100 mg/l - poor 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <100mg/L Poor 100-250 - Moderate >250 -Good 100-250 mg/l - moderate 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <100mg/L Poor 100-250 - Moderate >250 -Good >250 mg/l - good Fig.2 Spatial variation of bicarbonate 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 373839 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <0.5meq/L- Unaffected 0.5-6.6meq/L - Slightly affected >6.6meq/L- Strongly affected 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <100mg/L Poor 100-250 - Moderate >250 -Good <0.5 meq/l - unaffected 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <100mg/L Poor 100-250 - Moderate >250 -Good 0.5-6.6 meq/l – slightly affected 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <100mg/L Poor 100-250 - Moderate >250 -Good >6.6 meq/l – strongly affected Fig.3 Spatial variation of Revelle index 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <50 -Excellent 50-100 - Good 100-200 - Poor 200-300 - Very poor > 300 - Water unfit for drinking 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <50 -Excellent 50-100 - Good 100-200 - Poor 200-300 - Very poor > 300 - Water unfit for drinking <50 - excellent 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <50 -Excellent 50-100 - Good 100-200 - Poor 200-300 - Very poor > 300 - Water unfit for drinking 50-100 - good 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <50 -Excellent 50-100 - Good 100-200 - Poor 200-300 - Very poor > 300 - Water unfit for drinking 100-200 - poor 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <50 -Excellent 50-100 - Good 100-200 - Poor 200-300 - Very poor > 300 - Water unfit for drinking 200-300 - very poor 3.4 3.5 3.5 3.6 3.6 3.7 6.4 6.5 6.5 6.6 12 3 4 5 6 7 8 910 11 12 13 14 15 1617 18 19 20 212223 24 25 26 27 2829 3031 32 33 343536 37 38 39 40 4142 43 44 45 4647 48 49 5051 525354 5556 57 58 <50 -Excellent 50-100 - Good 100-200 - Poor 200-300 - Very poor > 300 - Water unfit for drinking >300 - water unfit for drinking Fig.4 Spatial variation of Water quality Index Evaluation of groundwater quality using water quality indices in parts of Lagos-Nigeria 35 CONCLUSION Groundwater is increasingly gaining significance as the main solution to the water supply problems in Nigeria, especially in the sub-urban and rural areas. The pH indi- cates extremely acidic to strongly alkaline conditions. About 96.6% of the EC values are characterized by low enrichment of salts, 12.1% medium enrichment of salts, and 1.7% high enrichment of salts. Major cations are in the order of: Ca 2+ > Mg 2+ > Na + > K + and the major ani- ons are in the order of: CO3 2- > Cl - > HCO3 - > SO4 2- . 46.6% of the samples accounts for fresh water and 37.9%, 8.6%, 5.2%, and 1.7% accounts for oligohaline, fresh-brackish, brackish and brackish-salt based on Chloride. Similarly, the classification of bicarbonate show that 31% of the samples fall under poor zone, 29.3% moderate zone and 10.3% good zone. Groundwater salinization shows that 56.9% of the samples are unaffected, 41.4% are slightly influenced and 1.7% of groundwater was strongly affected. This infers that fresh groundwater contamination by salinity is a major concern for the fresh water supply in the study area especially around locations 21, 25-30, 33-37, 41-44 and 51-58. Thus, the need for the regulating groundwater exploitation through monitoring by concerned agencies for sustainable groundwater resource management. The suitability of groundwater for drinking purpose shows that about 37.9% of the samples had excellent water qual- ity and 48.3%, 12.1% and 1.7% indicate good, poor and water unfit for drinking respectively. It is deduced that locations around 9-10, 16-17, 21 and 28 pose a great threat to water quality in the study area. However, the study concluded that the water quality of the study area is of good quality, since about 86.2% is suitable for drink- ing purposes. However, appropriate treatment methods to make it more potable and fit for human consumption should be employed in areas with poor quality. The study has contributed to knowledge by proffering methods of disseminating information on water quality status using indices for better understanding by the public and rele- vant agencies as well. References Adepelumi, A.A., Ako, B.D., Ajayi, T.R., Afolabi, O., Omo- toso, E.J. 2009. Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula, Lagos, Nige- ria. Environ Geology 56 (5), 927–933. doi:10.1007/s00254-008-1194-3. Akoteyon, I.S., Soladoye, O., Mbata, U.A. 2010. Assessment of groundwater quality in Eti-Osa LGA, Lagos- Nigeria. Ife Res. Pub. Geography 9 (1), 195–207. Akoteyon, I.S., Soladoye, O. (2011) .Groundwater Quality Assessment in Eti-Osa, Lagos-Nigeria using Multivari- ate Analysis .J. Appl. Sci. Environ. Manage. 15 (1), 121–125. American Public Health Association (APHA) 1998. Standard methods for the examination of water and wastewater, (20 th ed.), APHA, Washington DC, 2005–2605. Asiwaju-Bello, Y.A., Oladeji, O.S. 2001. Numerical model- ling of ground water flow patterns within Lagos me- tropolis, Nigeria. Nigerian Journal of Mining and Geol- ogy 37, 185–194. Bharti, N., Katyal, D. 2011.Water quality indices used for surface water vulnerability assessment. Inter. J Environ. Sci 2 (1),154–173. Boyacioglu, H. 2007. Development of a water quality index based on a European classification scheme.Water SA 33 (1), available on website http://www.wrc.org.za. Celik, M., Yildirim, T. 2006. Hydrochemical evaluation of groundwater quality in the Cavuscayi Basin, Sungurlu- Corum, Turkey, J. Environ. Geol. 50, 323–330. Chachadi A.G., Lobo-Ferreira, J.P. 2001. Sea water intrusion vulnerability mapping of aquifers using GALDIT method, In: Proc. Workshop on Modeling in Hydrogeol- ogy, Anna University, Chennai,143-15. Christiane, C., Roberto, T., Túlio, A.P.R., Renata, T. G.Souza, Daniela, A. P. 2010. Water quality index using multivariate factorial analysis. Revista Brasileira de Engenharia Agrícola e Ambiental 14 (5), 517–522, Campina Grande, PB, UAEA/UFCG http://www.agriambi.com.br Coode Blizard Ltd., Akute Geo-Resource Ltd and Rofe Ken- nard and Lapworth. 1997 .Hydrogeological Investigation of Lagos State. Final Report, Vol I & II, submitted to Lagos State Water Corporation. Edmunds, W.M., Shand, P. Hart, P., Ward, R.S. 2003. The natural (baseline) quality of groundwater: A UK pilot study, Sci. Total Environ. 310, 25–35. Emmanuel, B. E., Chukwu, L.O. 2010. Spatial distribution of saline water and possible sources of intrusion into a tropical freshwater lagoon and the transitional effects on the lacustrine ichthyofaunal diversity. African J. of Envi- ron Sci and Tech 4 (7), 480-491. Esteller, M.V., Rodríguez, R., Cardona, A., Padilla-Sánche, L. 2012.Evaluation of hydrochemical changes due to inten- sive aquifer exploitation: case studies from Mexico. En- viron Monit Assess 184 (9), 5725–5741. doi 10.1007/s10661-011-2376-0. Jamshidzadeh, Z., Mirbagheri, S.A. 2011. Evaluation of groundwater quantity and quality in the Kashan Basin, Central Iran. Desalination 270, 23–30. Lobo-Ferreira, J.P, Chachadi, A.G., Diamantino, C., Henriques, M.J. 2005. Assessing aquifer vulnerability to sea-water intrusion using GALDIT method: Part 1 – Application to the Portuguese Aquifer of Monte Gordo. IAHS and LNEC, Proceedings of the 4th The Fourth In- ter Celtic Colloquium on Hydrology and Management of Water Resources, held at Universidade do Minho, Gui- marães, Portugal, July 11-13, 2005. Longe, E.O. 2011 .Groundwater Resources Potential in the Coastal Plain Sands Aquifers,Lagos, Nigeria. Research Journal of Environmental and Earth Sciences 3 (1), 1–7. Mishra, P.C., Behera, P.C, Patel, R.K.. 2005. Contamination of water due to major industries and open refuse dump- ing in the steel city of Orissa: A case study, ASCE, J. Environ.Sci. Eng. 47 (2), 141–154. Oteri, A. U., Atolagbe, F.P. 2003 .Saltwater Intrusion into Coastal Aquifers in Nigeria, The Second International Conference on Saltwater Intrusion and Coastal Aquifers — Monitoring, Modeling, and Management. Mérida, Yucatán, México. Environments and the 1st Arab Water Forum, 1-15. Partey, F.K., Land, L.A., Frey, B. 2010. Final Report of the Geochemistry of Bitter Lakes National Wildlife Refuge, New Mexico Bureau of Geology and Mineral Resources, Roswell, New Mexico, 2010, 19p. Patwardhan, A . 2003. Changing status of urban water bodies and associated health concerns in Pune, India. Proceed- ings of the Third International Conference on Environ- ment and Health, Chennai, India (339–345). Chennai, 36 Akoteyon (2013) India: Department of Geography, University of Madras and Faculty of Environmental Studies, York University. Rao, N.S., Rao, P.S., Reddy, G.V., Nagamani, M., Vidyasa- gar, G., Satyanarayana, N.L. 2012. Chemical character- istics of groundwater and assessment of groundwater quality in Varaha River Basin, Visakhapatnam District, Andhra Pradesh, India. Environ Monit Assess 184 (8), 5189–214. doi: 10.1007/s10661-011-2333-y Rejith, P.G., Jeeva, S.P., Vijith, H., Sowmya, M., Mohamed, A.A.H. 2009. Determination of Groundwater Quality Index of a Highland Village of Kerala (India) Using Geographical Information System. Journal of Environ Health 71 (10), 51–58. Renji, R., Panda, R. K . 2007. Groundwater Quality Mapping Using GIS: A Study from India’s Kapgari Watershed. Environmental Quality Management John Wiley & Sons, Inc., 41–60. / doi 10.1002/tqem.20130 Revelle, R. 1941. Criteria for Recognition of Sea Water in Ground Water,” Transactions of American Geophysical Union 22, 593–597. Sahu, P., Sikdar, P.K . 2008. Hydrochemical framework of the aquifer in and around East Kolkata wetlands, West Ben- gal. India. Environ Geol 55, 823–835. Sargaonkar, A., Deshpande V. 2003. Development of an overall index of pollution for surface water based on a general classification scheme in Indian context, Envi- ronmental Monitoring and Assessment 89, 43–67. Shah, M.C., Shilpkar, P.G., Acharya, P.B. 2008 .Ground water quality of Gandhinagar Taluka, Gujarat, India, E- J. Chem. 5 (3), 435–446. Stuyfzand, P.T. 1989. A New Hydrochemical Classification of Water Types with Examples of Application, IAHS (In- ternational Association of Hydrological Sciences) 184, 89–98. Sujatha, D., Reddy, B.R. 2003. Quality Characterization of groundwater in the south-eastern part of the Ranga Reddy District, Andhra Pradesh, India.Environ Geol 44, 579–586. Todd, D.K., Mays, L.W. 2005. Groundwater Hydrology, 3rd edition. John Wiley and Sons Inc. World Health Organization (WHO) 2004. Guidelines for drinking water quality. Geneva: World Health Organiza- tion. 540 p. World Health Organization (WHO) 2006. Guidelines for drinking water quality. First Addendum, (3rd ed.) 1, 491–493. Yidana,S.M and Yidana, A . 2010. Assessing water quality using water quality index and multivariate analysis En- viron Earth Sci 59, 1461–1473. doi: 10.1007/s12665- 009-0132-3. Zaharin, A.A., Abdullah, M.H., Praveena, S.M. 2009. Evolu- tion of Groundwater Chemistry in the Shallow Aquifer of a Small Tropical Island in Sabah, Malaysia. Sains Malaysiana 38(6), 805–812. http://www.ncbi.nlm.nih.gov/pubmed?term=Rao%20NS%5BAuthor%5D&cauthor=true&cauthor_uid=21931947 http://www.ncbi.nlm.nih.gov/pubmed?term=Rao%20PS%5BAuthor%5D&cauthor=true&cauthor_uid=21931947 http://www.ncbi.nlm.nih.gov/pubmed?term=Reddy%20GV%5BAuthor%5D&cauthor=true&cauthor_uid=21931947 http://www.ncbi.nlm.nih.gov/pubmed?term=Nagamani%20M%5BAuthor%5D&cauthor=true&cauthor_uid=21931947 http://www.ncbi.nlm.nih.gov/pubmed?term=Vidyasagar%20G%5BAuthor%5D&cauthor=true&cauthor_uid=21931947 http://www.ncbi.nlm.nih.gov/pubmed?term=Vidyasagar%20G%5BAuthor%5D&cauthor=true&cauthor_uid=21931947 http://www.ncbi.nlm.nih.gov/pubmed?term=Satyanarayana%20NL%5BAuthor%5D&cauthor=true&cauthor_uid=21931947