J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 Journal of the Nigerian Society of Physical Sciences Groundwater Quality Assessment Using Multivariate Analysis and Water Quality Index in some Saline Fields of Central Nigeria N. D. Umara, O. V. Omononab,∗, C. O. Okogbuec aDepartment of Geology, Federal University of Lafia bDepartment of Geology/Geophysics, Alex Ekwueme Federal University, Ndufu Alike Iko cDepartment of Geology, University of Nigeria Abstract The groundwater of Awe-Keana saline fields central Nigeria was studied to investigate physicochemical processes that influence its groundwater chemistry and quality and hence determine its quality for drinking and irrigation purposes. Twenty groundwater samples were collected from hand dug wells and borehole for the purpose of identifying the hydrochemical characteristics and assessing the quality of groundwater of the Awe-Keana saline fields. Principal component analysis was performed to identify the hydrochemical controlling processes while water quality index (WQI) was used to determine the overall quality of the water samples. Multiple regression analysis however, revealed the parameter(s) that impact the overall water quality the most. The results showed that the chemical compositions of the groundwater of the area is influence by weathering of host rocks, salinity and anthropogenic activities. Four hydrochemical facies were deciphered (Ca− Mg− HCO3, Na− K − HCO3, Na− K −Cl−S O4, and Ca − Mg − Cl − S O4) and this revealed the diversity in the chemical controlling processes that yield different facies. Two clusters of water groups were identified from cluster analysis, namely, groundwater characterized with very high salinity, high nitrate contamination and high Ca, Cl, Na, and HCO3 ionic concentrations and groundwater with high Mg, K, and S O4 ionic concentrations. Saturation indices in relation to different minerals showed that precipitation and dissolution processes gave rise to the concentrations of different ions in the groundwater. Water quality assessment showed that about 85 % of the groundwater of the area is unsuitable as drinking water but, generally suitable for irrigation. Multiple regression analysis revealed that NO3 ion among the hydrochemical parameters measured was observed to be the major pollutant in groundwater of the study area. DOI:10.46481/jnsps.2021.183 Keywords: Awe-Keana, Multivariate analysis, Saline field, Water quality, Water quality index Article History : Received: 17 March 2020 Received in revised form: 17 June 2021 Accepted for publication: 16 July 2021 Published: 29 November 2021 c©2021 Journal of the Nigerian Society of Physical Sciences. All rights reserved. Communicated by: O. J. Abimbola 1. Introduction The Awe – Keana saline fields is located in parts of the Cen- tral Benue Trough (CBT), Nigeria. The occurrence of saline groundwater as springs, lakes and ponds is common in parts of ∗Corresponding author tel. no: +(234)8036145840 Email address: victor.omonona@funai.edu.ng (O. V. Omonona) the sedimentary basin. Different hypothesis has been given to explain the origin of saline water in the Trough, however, the theories postulated by [1] are widely acceptable. The saline groundwater in the southern and central sections of the Be- nue Trough is frequently associated with tectonic elements such as intrusive and mineralized veins. Prominent outcrops which commonly support local table salt industries are found in the CBT. These industries serve as sources of employment to the 267 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 268 locals who engage in the table salt production business. The area is also known for agricultural activities, mainly crop production. Domestic and agricultural water supply in the Central Benue Trough is largely through groundwater sources. Groundwater supports human existence on earth therefore, its quantity and quality are very important with regard to drinking, irrigation and industrial water supplies. The world over, there is decline on the available of high-quality groundwater for human consumption [2]. This quality can be impacted significantly by land usage, geology and anthropogenic activities. Groundwater is preferred to surface water because it is read- ily available throughout the year as surface water in the area usually becomes unavailable during the long dry season. Be- sides, it is cheaper to access groundwater than exploring for and exploiting surface water. Groundwater is also more potable and not easily contaminated as surface water but is more difficult to remediate a contaminated groundwater source. However, ad- vances in the physicochemical characteristics of groundwater with respect to drinking and agricultural purposes has not been prioritized, as water from these hand-dug wells and boreholes are put to use without any quality consideration and hence its health implications. The determination of groundwater quality for human consumption is important for the wellbeing of the increasing population [3]. It is important therefore to establish those quality criteria for human health and food security consid- ering the growing population and increased agricultural activi- ties in the study area. It is thus pertinent to know the possible sources of contaminants and quality of groundwater supply for various purposes in area. [4] identified natural processes as the controlling factors of the hydrochemistry of groundwater chemistry while, anthro- pogenic contaminations, natural mineralisation and cation ex- change as factors controlling the hydrochemistry. Groundwa- ter quality for drinking and agricultural or other purposes has been studied by [5, 6 and 7]. Water quality index (WQI) have been identified as an important technique for define groundwa- ter quality and its potability. [2, 6 and 8] used the WQI to clas- sify groundwater for drinking. Previous works on groundwater quality for drinking and agricultural or other purposes around the Benue Trough are available likewise studies on the hydrochemical characteristics of groundwater [5, 6 and 7] but no hydrochemical work has been carried out around the saline field of the Awe-Keana re- gion. This present study seeks to investigate physicochemical processes that influence the groundwater chemistry and qual- ity, decipher the underlying contaminants imparting the quality of groundwater of the area and hence determine its quality for drinking and irrigation purposes. 2. The Study Area 2.1. Location Awe-Keana lies within latitudes 8◦06 ′ N to 9◦ 09 ′ N and longitudes 8◦ 47 ′ E to 9◦ 09 ′ E. The area forms part of the saline fields in Central Nigeria (Figure 1). It is generally a lowland area with few scattered hills with elevation that ranges from 115 - 165 m above mean sea level. The River Keana and River Tunga, which are major tributaries of the River Benue constitute the main drainage system of the area. The climatic condition is made up of two major and distinct seasons: a wet season and a dry season. The former lasts from May to October while the latter lasts from November to April. The mean annual rainfall varies between 1000 and 1500 mm and the relative hu- midity between 60 and 80 %. The average annual humidity and temperature are 70 % and 28.50 ◦C respectively [9]. Figure 1. Google Earth view of the Awe-Keana area showing the sample collection points. 2.2. Geology and Hydrogeology In the Middle Benue Trough, six Upper Cretaceous lithogenic formations (Asu River Group, Ezeaku Formation, Keana For- mation, Awe Formation, Awgu Formation and Lafia sandstone) comprise the stratigraphic succession (Figure 2). The Asu River Group comprises of limestones, shales, micaceous siltstones, mudstones and clays [10, 11 and 12]. These are overlain by the Cenomanian-Turonian Ezeaku Formation which deposition marked the beginning of marine transgression in the Late Ceno- manian which took place in a presumably shallow marine coastal environment. The sediments are made up mainly of calcareous shales, micaceous fine to medium friable sandstones and beds of limestones which are in places shelly. The Keana Formation resulted from the Cenomanian regression which deposited flu- viodeltaic sediments. The Formation consists of cross-bedded, coarse grained feldspartic sandstones, occasional conglomer- ates, and bands of shales and limestones towards the top. Mas- sive outcrops occur at Keana, Azara and Daudu. This was fol- lowed by the Awe Formations which was deposited as passage 268 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 269 (transitional) beds during the Late Albian Early Cenomanian regression. Its typical sections occur around the town of Awe, where [10] estimated the thickness to be about 100 m. The for- mation consists of flaggy, whitish, medium to coarse grained calcareous sandstones, carbonaceous shales and clays. The Late Turonian-Early Santonian coal-bearing Awgu For- mation lies conformably on the Awe Formation. The deposi- tion of the Awgu Formation marked the end of marine sedi- mentation in this part of the Benue Trough. The formation is made up of bluish-grey to dark-black carbonaceous shales, cal- careous shales, shaley limestones, limestones, sandstones, silt- stones, and coal seams. The major outcrop of the coal-bearing Awgu Formation is at the bank of River Dep in Shankodi, 7 km to the west of the village of Jangwa. The post-folding Campano-Maastrichtian Lafia Formation ended the sedimentation in the Middle Benue Trough, after which widespread volcanic activities took over in the Tertiary. It is lithologically characterized by ferruginized sandstones, red, loose sands, flaggy mudstones, clays and claystones. Outcrops and sections of the Lafia Formation occur in and around the town of Lafia, and along the bank of River Amba on the Lafia- Doma Road. Figure 2. Stratigraphic succession in the Middle Benue Trough (Obaje, 2009). The Awe-Keana saline field of the CBT is underlain by the following geological sequence: the Asu River Group (marine), the Ezeaku (marine), the Keana/Awe Formation (continental) the Awgu Formation (marine) and the Lafia Sandstone (con- tinental). Detailed discussions on the geology of the Central Benue Trough were presented by many authors notably [10, 11 and 12]. Awe-Keana brine fields are known to have very strange and difficult hydrogeological situations. These condi- tions arise from the fact that most of the potential aquifers are either limited in extent, thinly developed with consistent clay and shale interbeddings or even highly indurated that only the development of secondary voids created by fractures, joints and solutions channels can attract hydrogeological interest. The stratigraphic sequence (Table 1) shows that the study areas are made up of alternate shale and sandstone horizons which are suspected to correspond to the sources of the saline and fresh- water respectively. Ezeaku, Keana and Awe Formation aquifers are the main aquifer units in study area [13]. The uppermost aquifer is the sandstone member of the Ezeaku Formation which is composed of series of shale-limestone and sandstone beds. Keana Forma- tion aquifer is composed of more heterogeneous, massive and predominantly fine, coarse and pebbly sandstone beds. Keana Formation is a good aquifer but is limited in extent which ren- ders it unproductive for groundwater exploration. However, Keana together with Ezeaku Formations form a very thick pro- ductive aquifer when encountered in a borehole. Awe Formation aquifer is the lowest aquifer and is com- posed of series of shale and porous sandstone beds and is highly productive. However, the presence of salt in it renders it un- favourable for groundwater exploration as the water from wells tapping the aquifer around Old Awe Town (Tsohon Gari) show high saline concentration because of the out-cropping brine- bearing Awe Formation [14]. 3. Materials and Methods Twenty (20) groundwater samples were collected from shal- low hand dug wells and boreholes in the study area. Sampling was done early in the morning before water abstraction com- menced by the residents of the study area. The study area was gridded into ten quadrants for even distribution of sample loca- tions and two samples were collected from each quadrant at an arbitrary distance. At each location, two water samples were collected and filtered in situ through a 0.45 µm membrane filter, collected in labelled 125 ml bottles and kept under cold condi- tion for the detection of anions and cations. Samples for cation analytes were acidified to a pH less than 2 with concentrated nitric acid in water solution at 0.15 % concentration by weight. Transient physicochemical parameters (temperature, total dissolved solids, electrical conductivity and redox potential) were measured immediately in the field using Portable T/pH/EC /TDS meter (H19813-5 model) and portable Eh meter while the cations and anions were collected in a fresh new high-density polyethylene (HDPE) bottles for laboratory analysis. The con- centrations of the cations were determined using ICP-ES/ICP- MS at Acme Analytical Laboratories Ltd, Canada, while the an- ions were analyzed using HACH DR 2000 spectrophotometer at UNICEF assisted Water Supply and Sanitation Laboratory, Ibadan, Nigeria. [15] quality assurance programme was em- ployed to check the validity of the field measurements and lab- oratory analytical results. Quality control measures applied in- 269 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 270 Table 1. Hydrostratigraphic units of Rocks in the study areas (Modified from Offodile, 2002). EPOCH AGE GEOLOGIC FORMATION ROCK UNIT AQUIFERS Santonian-Campanian Volcanic Cretaceous Maastrichtian Lafia Formation Fine to coarse grained, friable and feldspartic sandstone, brownish at top and whitish at depth. Coniacian Awgu Formation Greybedded shale with occasional sandstone bed and limestone. Late Turonian- Early Turonian Ezeaku Formation Thick calcareous shales, micaceous and fine to medium grained sandstones. Late Cenomanian Keana Formation Crystalline fine, coarse and pebbly sandstone. Aquifer Early Cenomanian Awe Formation Flaggy, whitish, medium to coarse grained feldspartic sandstones, calcareous sandstones, limestone interbedded with carbonaceous shale. Aquifer Early Cretaceous Mid-Late Albian Asu River Group Marine shales, clays siltstones and mudstones. Pre Cambrian Basement Complex and Meta-sediments Crystalline rock cluded the use of blank samples and estimation of the cation–anion ratios [16, 17, 18 and 19]. Saturation index of calcite, dolomite, halite, gypsum, siderite, and hematite was estimated using pH-REEQC 3.3.8-11728. WQI was calculated according to [3, 20 and 21 and was used to clas- sify groundwater quality into the different degree of quality on the overall quality of water for human consumption [22 and 23]. Statistical analyses were performed using Statgraphics Cen- turion XVI.I which includes (mean, minimum, maximum, coef- ficient of variation, and standard deviation). Pearson’s correla- tion matrix, principal components analysis (PCA), cluster anal- ysis (CA), and multiple regression analysis. PCA and CA were carried out using standardized data. Standardization of the data for the statistical tests was done in order to resolve the effect of differences in the units of measurements and large variations between the data units. PCA were performed on the correla- tion matrix of the data and the number of extracted principal components was based on a minimum Eigen value of 1.0. CA was carried out based on Ward’s method and the Squared Euclidean distance metric mode. The clusters defined by the CA were based on the similarity in chemical compositions of the various water sampling stations [24]. Multiple regression analysis was conducted on the data to determine the parame- ter(s) that most influenced the character of the WQI. WQI val- ues were the dependent variable while the concentrations of the parameters used in the estimation of WQI were the indepen- dent variables. The model was fitted upon the forward stepwise selection procedure. 4. Results and Discussion 4.1. Physicochemical characteristics The summary of the results of the hydrochemical parame- ters along with the WHO standard for drinking water are pre- sented in Table 1. The pH of the groundwater samples ranges from 5.52 to 7.72, with a mean value of 6.46. Low pH is pre- dominant around Awe area and could be attributed to the pres- ence of humic shale found around that area, while the low pH around Keana could attributed to photosynthetic processes. Wa- ter with low pH (below 6.5) is unacceptable for drinking pur- poses, as such water is reported to cause acidosis [25 and 26]. The redox potential (Eh) value ranges from 8 to 281 mV with an average value of 175.3 mV. It was observed that Eh has neg- ative correlations with all the physicochemical parameters ex- cept CO3 and S O4. The positive correlation coefficient values of CO3 and S O4 with Eh may be attributed to the high ten- dency of C and S to participate in redox reactions because of their variable oxidation states. Eh has significant negative cor- relation coefficient values (-0.519) with Cl and salinity. This shows that high salinity and chloride concentration in ground- water in the area is favoured under a low redox condition (an anoxic environment). Electrical conductivity (EC) values ranged from 56.1 to 1059 µ S/cm with a mean value of 591.45 while total dissolved solids (TDS) ranged from 37.58 to 709.53 ppm with a mean value of 396.27. The higher variations in the EC value are partly as a re- sult of the wide variation in the water table and saturated zone in the area and partly due to the effect of increased temperature and pressure with depth which increased the rate of reaction and dissolution of ions. A linear relationship occurs between EC and TDS (correlation coefficient of 1.0). This imply that 270 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 271 TDS is the dominant factor in the EC of the study area. About 65 % of the groundwater samples from the area have EC values above the stipulated guideline value while 40 % of the water samples have TDS values above the guideline value [24]. Salinity values of the groundwater samples ranged from 0.011 to 15.510 ppt with a mean value of 0.885. At Awe area, high salinity is confined to the southwest zone (salinity value ¿ 15 ppt was measured). However, in Keana, high salinity is spread throughout the area (Figure 2). 4.2. Cation and anion: concentrations and relationships The concentration of sodium varied ranges from 4.22 to 3024 ppm, potassium from 0.84 to 79.18 ppm while calcium and magnesium varied from 3.63 to 137.30 ppm and 0.96 to 48.66 ppm respectively. Magnesium concentration in all the groundwater studied is below the guideline value of 50 ppm while 25 % of the water samples have calcium concentrations above the [24] guideline value of 75 ppm. Bicarbonate con- centrations varied from < 1 ppm (below detection limit) to 888.2 ppm, chloride concentration ranges from 5.99 to 8584.95 ppm while sulphate concentration range from 2 to 60 ppm (Ta- ble 2). Generally, there is high variability in the concentra- tions of the major ions which could be the results of differences in the geologic units and lithogenic processes of the aquifers, recharge rate variability, and anthropogenic factors. The fol- lowing cation-anion pairs with correlation coefficients greater than 0.5 (P < 0.005) (Table 3) predominate in the groundwa- ter: Ca − HCO3 (0.7342), Mg − HCO3 (0.7537), Na − HCO3 (0.7923), Na − Cl (0.7107), Ca − NO3 (0.5281), Na − NO3 (0.5751), Mg−NO3 (0.5748), K−S O4 (0.5407), and Mg−S O4 (0.5526). The high correlation coefficient values of these ionic pairs suggest that they may have come from the same source(s) and or have been produced by the same process(es). 4.3. Hydrochemical facies Groundwater in the study area was characterized using Piper (1944) trilinear diagram. [27 and 28] classifications were used to classify the groundwater of the study area into different hy- drochemical facies. From the diagram (Figure 3), four (4) dif- ferent hydrochemical facies namely Ca − Mg − HCO3, Na − K − HCO3, Na − K − Cl − S O4, and Ca − Mg − Cl − S O4 (in the order of geochemical evolution) were deciphered. The Ca−Mg−HCO3 facies (constituting 65 %) is the most dominant facies in the area and it reflects water from recharge zone and prevalence of rock weathering. The Ca−Mg−Cl−S O4 ranked second in abundance (constituting 25 %) and it reflects groundwater of reverse ion exchange. Ca − Mg − Cl − S O4 facies is a mixed water type with Ca − Mg − HCO3 and Na − K − Cl − S O4 as the two end members. The Na − K − HCO3 facies constituted 5 % of the total facie types. This facie reflects base ion exchange; exchange of Ca and Mg by Na and K in the initial Ca − Mg − HCO3 facies. The Na − K −Cl − S O4 facies (5 %) reflects water formed as a result of evaporation or mixing with seawater or saline water. A geochemical evolution model may be defined here, with water facies beginning with the Ca − Mg − HCO3 to Na − K − HCO3, then Na−K−Cl−S O4 and again from Ca−Mg−HCO3 to Ca − Mg − Cl − S O4. Figure 3. Piper (1944) diagram showing the different hydrochemical facies. 4.4. Sources of ions Gibbs diagram (Figure 4) revealed that rock weathering is the dominant physicochemical process controlling the chem- istry of the groundwater in the area. Table 4 presents the sat- uration indices (SI) in relation to different minerals. The ta- ble reveals, that all the groundwater samples were undersatu- rated (< 0) with respect to halite, gypsum, and siderite. There- fore, the concentrations of Na and Cl in the groundwater is attributed to the dissolution of halite while S O4 and total Fe (Fe2+ and Fe3+) is attributed to the dissolution of gypsum and siderite respectively. Eleven of the groundwater samples con- stituting 55 %, were undersaturated with respect to both calcite and dolomite, and the remaining nine samples (constituting 45 %) were oversaturated with respect to calcite and dolomite. Ca and Mg concentrations may be considered to be as a re- sult of the dissolution of calcite and dolomite respectively. It was observed that the samples from Awe area were character- ized more with undersaturation of calcite and dolomite while, those from the Keana area were characterized more with over- saturation with respect to calcite and dolomite. The oversatu- ration with respect to calcite and dolomite is evidenced by the presence of limestone deposits around the Keana segment. No limestone quarries exist around the Awe segment. It is observed that throughout the entire study area, the lateritic cap is very rich in iron and hence the groundwater is super oversaturated with hematite. The high concentration of NO3 (from 0.32 to 90.23 mg/l) detected in some parts of the Awe-Keana saline fields, indicated 271 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 272 Table 2. Summary Statistics of the Hydrochemical Data. Parameter Unit Average Standard Deviation Coefficient of Variation Minimum Maximum WHO (2008) Limit pH Nil 6.46 0.54 8.38 5.52 7.72 6.5 - 8.5 Eh mV 175.3 76.35 43.55 8 281 - EC µS/cm 591.46 349.52 59.09 56.1 1059 500 TDS ppm 396.28 234.18 59.09 37.59 709.53 500 Salinity Ppt 0.89 3.44 389.04 0.01 15.51 - Cl ppm 489.92 1905.97 389.04 5.99 8584.95 250 HCO3 ppm 285.24 253.83 88.99 0 888.2 500 CO3 ppm 36.60 44.45 121.46 0 120.00 - PO4 ppm 1.64 1.80 109.49 0 5.11 - NO3 ppm 27.76 28.45 102.47 0.32 90.23 45 S O4 ppm 24.50 19.36 79.04 2 60.00 250 K ppm 28.19 30.60 108.54 0.84 79.18 - Na ppm 339.00 890.14 262.58 4.22 3024 - Ca ppm 58.76 38.78 66.02 3.63 137.30 75 Mg ppm 18.20 13.73 75.40 0.96 48.66 50 Table 3. Pearson’s correlation matrix. Ca Cl CO3 EC Eh HCO3 K Mg Na NO3 pH PO4 Salinity S O4 TDS Ca 0.4881 0.2007 0.7536 -0.330 0.7342 0.6257 0.6865 0.676 0.5281 -0.056 0.4797 0.4881 0.4229 0.7536 Cl 0.4881 -0.188 0.3167 -0.519 0.5583 0.3572 0.2976 0.7107 0.5123 -0.085 -0.069 1 0.0259 0.3167 CO3 0.2007 -0.188 0.2407 0.3795 0.1655 0.2401 0.4752 -0.258 0.164 0.001 -0.059 -0.188 0.8708 0.2407 EC 0.7536 0.3167 0.2407 -0.133 0.5123 0.5766 0.4375 0.4194 0.4302 -0.267 0.253 0.3167 0.4697 1 Eh -0.330 -0.519 0.3795 -0.133 -0.426 -0.385 -0.134 -0.742 -0.266 -0.042 -0.193 -0.519 0.1637 -0.133 HCO3 0.7342 0.5583 0.1655 0.5123 -0.426 0.3251 0.7537 0.7973 0.8299 -0.243 0.3658 0.5583 0.2974 0.5123 K 0.6257 0.3572 0.2401 0.5766 -0.385 0.3251 0.3769 0.4956 0.1127 0.1209 -0.004 0.3572 0.5407 0.5766 Mg 0.6865 0.2976 0.4752 0.4375 -0.134 0.7537 0.3769 0.4191 0.5748 0.1711 0.2519 0.2976 0.5526 0.4375 Na 0.676 0.7107 -0.258 0.4194 -0.742 0.7973 0.4956 0.4191 0.5751 -0.102 0.2689 0.7107 -0.016 0.4194 NO3 0.5281 0.5123 0.164 0.4302 -0.266 0.8299 0.1127 0.5748 0.5751 -0.303 0.2829 0.5123 0.2477 0.4302 pH -0.056 -0.085 0.001 -0.267 -0.042 -0.243 0.1209 0.1711 -0.102 -0.303 -0.33 -0.085 -0.017 -0.267 PO4 0.4797 -0.069 -0.059 0.253 -0.193 0.3658 -0.004 0.2519 0.2689 0.2829 -0.33 -0.069 -0.081 0.253 Salinity 0.4881 1 -0.188 0.3167 -0.519 0.5583 0.3572 0.2976 0.7107 0.5123 -0.085 -0.069 0.0259 0.3167 S O4 0.4229 0.0259 0.8708 0.4697 0.1637 0.2974 0.5407 0.5526 -0.016 0.2477 -0.017 -0.081 0.0259 0.4697 TDS 0.7536 0.3167 0.2407 1 -0.133 0.5123 0.5766 0.4375 0.4194 0.4302 -0.267 0.253 0.3167 0.4697 Correlation coefficient > 0.5 are in bold. 272 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 273 Table 4. Saturation indices in relation to Calcite (CaCO3), Dolomite (CaMg(CO3)2), Gypsum (CaS O4 · 2H2O), Halite (NaCl), Hematite (Fe2O3) and Siderite (FeCO3) minerals. (nd => not determined) Location CaCO3 CaMg(CO3)2 CaS O4 · 2H2O NaCl Fe2O3 FeCO3 Awe 1 -0.17 -0.45 -2.62 -5.42 nd nd Awe 2 -0.28 -0.63 -2.65 -3.35 nd nd Awe 3 -2.33 -4.69 -3.81 nd 15.42 -0.36 Awe 4 -2.44 -4.81 -3.43 nd 7.88 -1.08 Awe 5 -0.58 -1.25 -2.82 -7.16 13.50 -0.28 Awe 6 2.10 3.68 -2.10 -7.75 14.37 -13.17 Awe 7 2.10 4.02 -2.18 -7.08 13.46 -13.40 Awe 8 -0.11 -0.32 -2.46 -6.90 17.00 -0.08 Awe 9 -1.46 -3.44 -3.14 -8.52 11.99 -0.98 Awe 10 -0.98 -2.27 -2.75 -6.46 15.20 -0.45 Keana 11 1.90 3.49 -1.92 -6.75 15.22 -11.27 Keana 12 1.78 3.42 -2.11 -7.09 17.49 -7.47 Keana 13 2.04 4.12 -2.11 -6.44 14.70 -12.11 Keana 14 1.72 3.09 -2.12 -6.75 14.90 -12.47 Keana 15 1.72 3.15 -2.22 -6.72 15.96 -10.58 Keana 16 1.73 3.69 -2.54 -7.19 15.48 -12.94 Keana 17 -1.46 -3.16 -3.76 -8.70 17.80 0.18 Keana 18 2.00 3.78 -2.16 -6.59 16.43 -9.15 Keana 19 -2.52 -5.22 -4.29 -9.12 16.41 -0.28 Keana 20 -1.97 -4.24 nd -8.38 20.56 -1.68 Table 5. Saturation indices in relation to Calcite (CaCO3), Dolomite (CaMg(CO3)2), Gypsum (CaS O4 · 2H2O), Halite (NaCl), Hematite (Fe2O3) and Siderite (FeCO3) minerals. PC 1 PC 2 PC 3 Ca 0.335818 0.293805 0.135665 Cl 0.360345 -0.105957 -0.0336973 Eh 0.307956 -0.0532982 -0.234097 HCO3 0.374573 -0.0145737 0.00042887 K 0.17127 -0.28981 0.591508 Mg 0.150976 0.554345 0.035744 Na 0.390315 -0.0936606 -0.00266831 NO3 0.302649 -0.060511 -0.0534841 pH -0.0458886 0.518323 -0.336216 Salinity 0.360345 -0.105957 -0.0336973 S O4 -0.273386 0.0726313 0.454219 TDS 0.139542 0.458819 0.501138 Eigen Value 5.57428 1.84474 1.0301 % of Variance 46.452 15.373 8.584 Cumulative % 46.452 61.825 70.409 Table 6. Table of Principal Component Scores. Location PC 1 PC 2 PC 3 Awe 1 3.99 -0.24 0.135665 Awe 2 8.50 -0.85 -0.14 Awe 3 0.43 0.53 0.37 Awe 4 0.02 1.63 -0.60 Awe 5 -1.62 -0.50 -1.32 Awe 6 0.17 -0.80 -1.44 Awe 7 -0.76 0.02 -0.69 Awe 8 -1.09 -0.52 -1.08 Awe 9 -0.93 0.58 -0.32 Awe 10 -0.97 0.22 -0.37 Keana 11 -1.90 -1.67 1.65 Keana 12 -1.46 -1.54 -0.01 Keana 13 -0.90 3.32 -0.31 Keana 14 -0.90 -1.31 1.08 Keana 15 -1.66 -1.01 -1.29 Keana 16 0.31 -0.90 -0.41 Keana 17 -0.45 1.18 0.99 Keana 18 -0.90 -1.22 1.88 Keana 19 0.16 1.08 1.72 Keana 20 -0.052 2.20 0.18 273 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 274 Table 7. Water Quality Index (WQI) Classification for Water of Awe-Keana Area. Location WQ1 Value Type of Water Awe 1 694.83 Water Unsuitable for Drinking Purposes Awe 2 4181.90 Water Unsuitable for Drinking Purposes Awe 3 127.50 Poor Water Awe 4 93.72 Good Water Awe 5 313.06 Water Unsuitable for Drinking Purposes Awe 6 552..58 Water Unsuitable for Drinking Purposes Awe 7 510.35 Water Unsuitable for Drinking Purposes Awe 8 379.89 Water Unsuitable for Drinking Purposes Awe 9 163.31 Poor Water Awe 10 403.33 Water Unsuitable for Drinking Purposes Keana 11 356.69 Water Unsuitable for Drinking Purposes Keana 12 291.05 Water Unsuitable for Drinking Purposes Keana 13 413.45 Water Unsuitable for Drinking Purposes Keana 14 466.34 Water Unsuitable for Drinking Purposes Keana 15 332.60 Water Unsuitable for Drinking Purposes Keana 16 559.42 Water Unsuitable for Drinking Purposes Keana 17 132.49 Poor Water Keana 18 378.37 Water Unsuitable for Drinking Purposes Keana 19 32.64 Excellent Keana 20 48.51 Excellent Table 8. Multiple Regression Analysis. Parameter Estimate Standard Error Statistic P-Value Constant −4.7676 × 10−9 1.4758 × 10−5 −3.2303 × 10−4 0.9997 Ca 1.32267 3.880021 × 10−7 3.40875 × 106 0.0000 Cl 0.3968 4.66743 × 10−9 8.50147 × 107 0.0000 HCO3 0.1984 7.19455 × 10−8 2.75764 × 106 0.0000 Mg 1.984 9.96068 × 10−7 1.99183 × 106 0.0000 NO3 2.20444 4.67962 × 10−7 4.71074 × 106 0.0000 S O4 0.3968 4.7444 × 10−7 8.36355 × 105 0.0000 TDS 0.1984 4.99819 × 10−8 3.96943 × 106 0.0000 274 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 275 that unconfined aquifers predominate in the area. It was ob- served further that, nitrate concentrations did not relate linearly with well depth. Most of the nitrate-contaminated groundwa- ter sources are located very close to farmlands and areas with very poor sanitary control and protection (this was from reports obtained during the field investigations and the interaction with the people of the locality). Increased nitrate concentrations in the groundwater of the area could be attributed to wastes em- anating from fertilized crop fields and runoffs and discharges from livestock. Figure 4. Gibbs diagrams of the hydrochemical data of A) Keana and B) Awe. 4.5. Statistical analysis Cluster analysis (Figure 5) grouped the various sampling stations (20 locations) into two clusters, based on the similar- ities among the chemical parameters involved in the ground- water quality. Cluster 1: Groundwater characterized with very high salinity, high nitrate contamination and high ionic (Ca, Cl, Na, and HCO3) concentrations and Cluster 2: groundwater with high ionic (Mg, K, and S O4) concentrations. Table 4 presents the results of Principal component (PC) including component-loading matrix, eigen values, percentage variance and total cumulative variance and cumulative percent- age. Three components were extracted that accounted for 70.41 % of the total variance. PC 1 describes 46.45 % of the total vari- ance and has high positive component-loadings on Eh, salinity, Ca, Na, Cl, NO3, and HCO3. PC 1 could be attributed to weathering and leaching of the host rocks, salinity and nitrate pollution factors. PC 2 has high positive component-loadings on pH, Mg, and TDS and accounts for 15.37 % of the total variance. PC 2 may therefore, be said to reflect TDS factor. The dissolution and migration of the ions are strongly influenced by pH. PC 3 ac- counted for 8.58 % of the total variance and has high positive loadings on K, S O4 and TDS, but high negative loadings on pH. This PC reflects the effects of sulphate minerals dissolution. Principal Component Score (PCS) loadings on the ground- water sample locations are presented in Table 5. PCS loadings at and above ±1.0 were considered significant controlling pro- cesses on the sample locations. From the table, PC 1 reflect the effect of weathering and leaching of host rocks, salinity and ni- trate pollution has high impacts in the groundwater chemistry of sample locations 1, 2, 5, 8, 11, 12 and 15. The chemical composition and chemistry of groundwater of sample locations 4, 5, 11, 12, 13, 14, 15, 17, 18, 19, and 20 are strongly influ- enced by TDS, while those of sample locations 5, 6, 8, 11, 14, 15, and 18 are strongly influenced by sulphate minerals dissolu- tion. Figure 6 presents the distributions and spatial relationships between sampling point loading characteristics. Figure 5. Cluster analysis dendrogram showing the different water classes. Figure 6. Principal component score scatterplot for the Awe-Keana area. 4.6. Groundwater quality Evaluation of the groundwater quality for drinking and other uses was done through water quality index (WQI). The WQI technique was first introduced by [29] and has been employed by different authors [2, 30, 31, 32 and 33]. The results of the calculated WQI are presented in Table 6. Four classes of water quality were defined, namely, “excellent 275 Umar et al. / J. Nig. Soc. Phys. Sci. 3 (2021) 267–277 276 water” (10 %), “good water” (5 %), “poor water” (15 %) and “water unsuitable for drinking purposes” (70 %). The results showed that groundwater in the area is generally of very poor quality for drinking purposes. The results of the analysis (Table 7) revealed that nitrate, mainly from nitrate-rich-fertilizers and domestic wastes ema- nating from septic storages, magnesium and calcium released from dissolutions of dolomite, and calcite minerals in that or- der are the principal parameters contributing to the pollution and contamination of groundwater of the area. The suitability of the groundwater for irrigation purposes on the other hand, was evaluated from the [34] Wilcox (USSL, 1954) diagram. From the diagram (Figure 7), groundwater from the area plotted within the following fields, low sodium alkali hazard-low salinity hazard (C1-S1), medium salinity hazard- low sodium alkali hazard (C2-S1), high salinity hazard -low sodium alkali hazard (C3-S1) and high salinity hazard-medium sodium alkali hazard (C3-S2). Most of the groundwater sam- ples plotted within the C1-S1 field and hence, can be used for irrigation. However, those that plotted C3-S2 should be used with caution for irrigation. Figure 7. Wilcox diagram for groundwater of the area. 5. Conclusion Hydrochemical characteristics of groundwater from the Awe- Keana saline field, CBT Nigeria have been studied and different indices used to assess the quality of the groundwater. Results of the hydrochemical analysis revealed that the groundwater in the area is slightly acidic to neutral and that anoxic conditions prevailed during the period the groundwater formation. The concentrations of the major ions showed high variabil- ity which could be attributed to differences in the underlying ge- ologic materials, prevailing lithogenic processes, recharge rates, and anthropogenic factors. Four hydrochemical facies were de- ciphered, namely, Ca−Mg−HCO3 (65 %); Ca−Mg−Cl−S O4 (25 %); Na − K − HCO3 (5 %) and Na − K − Cl − S O4 (3 %) in that order. The prevalence of the Ca − Mg − HCO3 could be attributed to the increased action of CO2 on H2O, low water- rock interactions rate, and low residence time. Different sources and processes were contributed by the concentration of the var- ious ions in the groundwater. Prominent controlling processes include dissolution and precipitation of calcite and dolomite, precipitation of hematite and dissolution of gypsum, halite and siderite. Cluster analysis identified two types of sample locations cluster based on their chemical composition similarities (Clus- ter 1: Groundwater characterized with very high salinity, high nitrate contamination and high ionic (Ca, Cl, Na, and HCO3) concentrations and Cluster 2: groundwater with high ionic (Mg, K, and S O4) concentrations) while principal component analy- sis revealed three hydrochemical processes controlling the ground- water chemistry (weathering and leaching; dissolution and mi- gration of ions and dissolution of sulphate minerals). Evaluation of the groundwater quality for drinking and other domestic purposes showed that 85 % of the groundwater sources examined are not potable while only 15 % is suitable for drink- ing and other domestic purposes. NO3 was found to be the most paramount parameter impairing the quality of groundwater in the area. The groundwater is generally suitable for irrigation particularly for halophytes but not for the cultivation of glyco- phytes. 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