Hydrogeochemical Assessment of Chemical Composition of Groundwater; a Case Study of the Aptian-Albian Aquifer Within Sedimentary Basin Nigeria

: The research was carried out to evaluate major source influencing chemical quality of groundwater within suburban area of Abakaliki. It lies between latitudes 6°15' and 6°35'N and longitudes 7°40' and 8°15'E. A total of twenty one (21) groundwater samples were collected and analyzed. Parameter analyzed were; EC, pH, TDS, Cl¯, Na , Mg , NO ¯, SO ¯, Ca , HCO ¯, K , CO ¯ these parameterwere analyzed using American Public + 3 Health Association standard method. Various hydrogeochemical approach and model were used to assess chemical quality of groundwater within the study area. These include; Gibbs, Mg /Ca . End-member, Diamond 2+ 2+ field of Piper and Parson plots were used to indentify major source influencing groundwater chemistry within the study. Finding, from Gibbs plot and Mg /Ca against Mg /Na revealed that rock dominance is the major 2+ 2+ 2+ + process that control groundwater chemistry, while End-member plot showed that silicate and carbonate weathering are the two weathering process that influence groundwater chemistry within the study area. Diamond field of Piper by Lawrence and Bal-Subramanian modified, revealed that groundwater fell within High Ca + Mg & SO + Cl. Parson plot revealed that 65 % of groundwater fell within Ca - Mg – Cl water type, while 4 35 % fells within Ca - Mg - SO . Relationship between TDS vs TH plots showed that groundwater samples fell 4 within soft - fresh water category. The results of the geochemical survey reveal major ionic components trend in other of Mg>Ca>Na>HCO3>SO4>Cl, result reveal that there is no particular trend of ions movement in groundwater.


INTRODUCTION
various authors has also stated that anthropogenic The continuous and severe increase of water [12][13][14]. Domenico and Schwartz [15], Edmunds, et al. [16] demands, due to the rapid population growth, have led to went further, to state that unsustainable groundwater over-exploitation of water bearing fractured aquifer within development, overexploitation andimproper management the study area. Recent, studies carried out within Asu of mining waste, wastewater from miningareas have River Group of Southern Benue Trough revealed that caused adverse impact on quality of groundwater.Decline groundwater within the area is considered hard [1,2].
in groundwater quality may be directly or indirectly Further studies, revealed that water quality is on decrease influencedby the leaching of contaminants through within the area, this is mostly attributed to anthropogenic mining activities as a result of rock-water interaction, activities such as improper disposal of refuges waste, during the process ofpercolation water moves through a leakage from septic tanks and mining related activities, hydrologicalcycle it transfers both inorganic and organic these activities has rendered water quality unsafe for components from soilto water thereby decreasing its various use [3][4][5][6][7][8][9]. Although, geology formations has chemical quality [17]. Assessment of groundwater directly or indirectly influenced the origin and chemical quality is usually based on the availability of a large constituents of groundwater in south-south and amount of information concerning its chemistry [18,19]. southeastern part of Nigeria [10,11]. On a global scale, Its chemistry, depends on a number of factors, such as activities has negative influence on groundwater quality The study area belongs to the various rock types, quality of recharge water and inputs rainforest region of Nigeria as described by Igbozuruike, from sources other than water rock interaction. Such [24]. The vegetation is characterized by orchard bush of factors and their interactions result in a complex short trees with varying densities of dominant elephant groundwater quality [20]. Murray [21], Rosen and Jones grasses. Two major seasons are experienced in the [22] further pointed out that the interaction of all factors area-the wet and dry season. The wet season starts from has leads to various water facies.Previous studies carried March and ends in October, while the dry season begins out on water quality within Ebonyi state revealed that the in November and ends in February. These two seasons major factor that influences groundwater quality are are dependent on the two prevailing winds blowing anthropogenic activities such as mining activities and across the country at different times of the year-the dry water-rock interaction. Although various studies has been harmattan Wind, the North East Trade Wind from the carried out on hydrogeochemical assessment of water Sahara Desert that prevails in the dry season and the resources in Ebonyi state for domestic and irrigation marine wind, the SW Trade Wind, from the Atlantic Ocean use [23]. But detailed, studies have not been carried out which introduces the rainy season. Temperature in the dry within the study area to evaluate factors that influence season and rainy season ranges from 20 to 38°C and 16 to chemical quality of groundwater within the study area.
28°C, respectively. The average monthly rainfall ranges The objective of this paper was to determine factors that from 3.1 mm in January and 270 mm in July. The average influence chemical quality of groundwater within the area annual rainfall varies from 1750 to 2250 mm. The climate of of study and to know the dominant factor that influences the area, no doubt, favours the dispersion of the resultant its chemistry.
pollutants from the mining activities.Eyankware, et al. [6] MATERIALS AND METHODS that moves the pollutants and also assists percolation.

Study Area:
The study area is located in the sub-urban area of Abakaliki, Ebonyi state, southeastern Nigeria. Geology and Hydrogeology of the Study Area: The The area is quite accessible through a network of major Benue Trough is a linear NE-SW trending trough that is roads and footpaths as shown in Fig. 1.
divided into three parts, namely the Upper, Middle and stated that high amount of rainfall results in surface run-of The drainage pattern of the area is dendritic.   ze-Aku Formation is found [28]. The hydrogeology of shown in Table 3.Various factors are responsible for the study area is typified by poor aquifer conditions. change in pH value. It is important to highlight the This is a result of the dominant shale units (Aquiclude) mechanism of processes taking place in this area, When which are neither porous nor permeable and do not water is in equilibrium with both CO from the atmosphere transmit water to wells found in the area. Eyankware et al.
and carbonate containing rock, the resultant solution will [6] further pointed out that groundwater on a regional be a buffer with a pH of 8.3, this is close to the pKa of the scale is impossible to find. However, conditions for the weak acid bicarbonate ion HCO¯ (pKa = 8.4). This will presence of groundwater may occur at weathered/ resist further changes in pH to any added acid or base. fractured zones or at points of sandstone intercalations. This is a natural mechanism for balancing the The structure and hydrogeology of the fractured aquifer considerable dissolution of lime from the underlying in the study areaare typical of a multilayer complex formation and precipitation of lime from the waterbody system. Obviously, due to drilling distribution on [29] Further studies revealed that groundwater pH varies aquifer.As water bearing formation within the study area depending on the composition of the sediments that exists in fractured shale and limestone Nwachukwu, [1].
surround the travel pathway of the recharge water The major sources ofwater are stream, hand-dug well, infiltrating to the groundwater and also due to prolong manualborehole and motorized borehole. stay in particular rock that serves as aquifer which host Method: Twenty one (21) water samples were randomly interaction [29]. collected from boreholes see (Fig. 2). Sampling was carried out during the dry season when there was a decrease in Total Dissolved Solid (TDS): The water samples were the water level and the concentration of cations and classified with regard to total dissolved solids (TDS). anions were more stable. Though the study area consists The results of geochemical analysis (Table 3) indicated of two geology formation, groundwater sampling was that Total dissolved solids (TDS) ranged from 68 mg/L carried within the Asu River Group. Precautionary to 602 mg/L with mean value as 293.73 mg/L. Table 4 measures were taken by washing the bottles with clean shows that sampling points within the study area were water and cleaning reagents and thoroughly rinsing with classified under freshwater category. The sources of distilled, de-ionized water prior to collection of water material in TDS can come from nature, i.e. geological samples from the site. The samples were analyzed for condition and seawater and from human activities, eleven parameters, namely pH, electrical conductivity, i.e. domestic and industrial waste and also agriculture total dissolved solids, magnesium, calcium, chloride, [30][31][32]. nitrate, sulphate, potassium, sodium and bicarbonate following APHA, 2012 standard (Table 2).
Electrical Conductivity (EC): EC is one of the important DISCUSSION electrical current in the water.Electrical conductivity in pH: pH is a term used universally to express the intensity minerals, salts, metals, cations or anions that dissolved in of the acid or alkaline condition of a solution. From the water. EC values of the water samples ranged from 72 to Table 3, the measured pH is found to be slightly acidic to 1042 µS/cm with mean value of 480.04 µS/cm as shown in basic and ranges from 6.3 to 7.9 with mean value of 7.15 as Table 3.   2   3 the water, the longer the stay, the larger the rock water water quality parameters that shows the ability of water is due to ionization of dissolved inorganic solids  Major Factors Influencing the Groundwater Chemistry and the results' area is shown in Fig. 3a, b, respectively.

Work Rock Interaction: Freeze and Cherry [33] has been
These diagrams suggest that rock weathering is the main used in determination of the major mechanisms controlling mechanism controlling the chemical constituents of water chemistry and are widely used in studies of the groundwater in the study area.An important process of relationships between water chemical composition and water rock interaction is mineral dissolution [35] and the climate or geological characteristics. It is represented as assessment of ionic meq/L ratios can indicate which plots of TDS versus Na /(Na + Ca ) and TDS versus minerals are likely to have the largest influence on Cl¯/(Cl¯ + HCO¯) and the controlling hydrochemical groundwater quality. 3 mechanisms can be divided into three zones: evaporation, Gaillardet et al.
[36] used End member plot in precipitation and water rock interaction [34]. Most determining rock-weathering sources related to the groundwater samples were plotted in the middle of the hydrochemical characteristics of groundwater. They diagram except for samples AI/03 and 07 that is been further identified the following chemical composition of influenced by precipitation. (Fig. 3), indicating that rock Ca /Na = 0.35 ± 0.15, Mg /Na = 0.24 ± 0.12 and weathering is the primary factor controlling the HCO3¯/Na = 2 ± 1 for the silicate end member and groundwater chemistry.In addition to the Gibbs diagram, Ca /Na = 50, Mg /Na = 10 and HCO3¯/Na = 120 for the the ratio of Mg /Na and Mg /Ca can also be used to carbonate end member. Fig. 4 diagrams were applied to the data obtained in this study shown in Fig. 4.  The water classification of hydrogeo chemical facies TH ranges from 2.8 -73.5 mg/L, sampled points were of Piper diagram was reconstructed by Lawrence and classified as soft water category, EC ranges from 72 -1042 Balasubramanian [37] in the new reconstructed diamond us/cm. Chemical quality of groundwater was evaluated field (Fig. 5). It classifiedwater in the various zones on using the following models; Gibbs plot, Mg /Ca against the basis of various reactions occurring in the Mg /Na , End-member plot, Diamond field of Piper groundwater aquifer system. The reconstructed diamond modified after Lawrence and Balasubramanian and Parson field shows that groundwater sample lies within High plot. Gibbs plot, Mg /Ca against Mg /Na revealed that Ca + Mg + SO + Clhydrogeochemicalfacies as shown in groundwater is highly influenced by rock dominance, two 4 Fig. 5. This implies that, Ca and Mg, are the primary major that of weathering process was observed to courses of hardness in water. Any water with high Ca + influence groundwater, these are silicate and carbonate Mg is said to be hard.
weathering, Diamond plots showed that groundwater is of From Fig. 6. It was observed that groundwater High Ca + Mg & SO + Cl type, while Parson plot revealed were within the three category of water type; Na -SO4, that 65 % of groundwater were within Ca -Mg -Cl water Ca -Mg -SO4 and Ca -Mg -Cl water type. That implies type, while 35 % were categorize as Ca -Mg -SO water that groundwater is of different origin.
type. From modified Diamond plot and Piper diagrams it TDS and total hardness (TH) indicate that all the groundwater is soft, fresh and moderately hard fresh water type Fig. 7 showed that groundwater within the study area falls within moderately, hard fresh. This is in-line with previous research within the study area that stated that groundwater within the area is considered hard Eyankware et al. [3], Edeh and Nnabo [7], Ojobor and Nnabo [8].
different dissolved constituents and classification of water on the basis of its chemical characters. The triangular cationic field of Piper diagrams reveals that Ca + Mg + HCO3 are the dominant ionic specie. It also reveals that geochemical zone of the groundwater in the study area are magnesium bicarbonate type and that the alkaline earth exceed the alkaline in the groundwater see Fig. 8. However, from the Scholler diagram. It shows a hydrogeochemical trend of Mg>Ca>Na>HCO3>SO4>Cl. The result also reveal that groundwater, this implies that the groundwater is not of the same origin as shown in Fig. 9 and 10.

CONCLUSION
The presented research has helped to establish factors that influence chemical quality of groundwater within the study area and its environs, Ebonyi state southeastern Nigeria.From the analysis, it was observed range shows that groundwater is of fresh water category, was observed that groundwater(s) are of various origin. 6. Eyankware, M.O., V.S. Nnajieze and C.G. Aleke, The results of the geochemical survey reveal major ionic components trend in other of Mg>Ca>Na>HCO3>SO4>Cl, result reveal that there is no particular trend of ions movement in groundwater.

ACKNOWLEDGEMENTS
The author sincerely and graciously acknowledge Prof. Dr. Wahid M. Ahmed, Editor-in-Chief ofGlobal journal of Environmental Research. The anonymous reviewers are also appreciated for their constructive suggestions in bringing the manuscript to its present form. Not left out is Dr. Akakuru, O. C. a lecturer at theDepartment of Geography and Environmental Studies, AlvanIkoku University of Education, Owerri for his assistance with AquaChem software which was used to plot the Piper diagram and Schoeller semi logarithmic diagram. Lastly, I sincerely appreciate the owner of the borehole and hand-dug wells, from which water was source for physicochemical analysis.
Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or non-profit sectors.

Conflicts of Interest:
The author declare no conflicts of interest regarding the publication of this paper.