Geochemical Characterization and Assessment of Groundwater Quality in Owerri Metropolis, South- Eastern Nigeria

Journal of Geography, Environment and Earth Science International

19(1): 1-24, 2019; Article no.JGEESI.32939 ISSN: 2454-7352

C. Chukwuemeka Onyeanuna1*, Patience John2 and N. Temple Nwankwo3

1Department of Environment, Land and Infrastructure, Polytechnic University of Turin, Piedmont, Italy. 2Department of Geosciences, Federal University of Technology Owerri, Imo State, Nigeria. 3Department of Agricultural Technology, Federal Polytechnic Oko, Anambra State, Nigeria.

Authors’ contributions

This work was carried out in collaboration between all authors. Author CCO designed the study, performed the statistical analysis and wrote the protocol. Author PJ performed the sampling, laboratory measurement and wrote the first draft of the manuscript. Author NTN reviewed the analyses of the study and literature searches. All authors read and approved the final manuscript.

Article Information

DOI: 10.9734/JGEESI/2019/32939 Editor(s): (1) Dr. Kaveh Ostad-Ali-Askari, Department of Civil Engineering, Isfahan (Khorasgan) Branch, Islamic Azad University, Iran. (2) Dr. Wen-Cheng Liu, Department of Civil and Disaster Prevention Engineering, National United University, Taiwan and Taiwan Typhoon and Flood Research Institute, National United University, Taipei, Taiwan. Reviewers: (1) Gopal Krishan, National Institute of Hydrology, India. (2) S. Selvakumar, Centre for Geotechnology, Manonmaniam Sundaranar University, India. (3) Ahoussi Kouassi Ernest, Universite Felix Houphouet Boigny, Cote D’ivoire. (4) Dorota Porowska, University of Warsaw, Poland. Complete Peer review History: http://www.sdiarticle3.com/review-history/32939

Received 04 November 2018 Original Research Article Accepted 23 January 2019 Published 07 February 2019

ABSTRACT

A total of five borehole samples were collected from five towns in Owerri metropolis, South-eastern Nigeria and subjected to physio-chemical analysis using atomic absorption spectrophotometer (AAS) and other standard equipment with the aim of characterizing and analysing the groundwater quality indicators. These quality indicators are namely: pH, temperature, total hardness, turbidity, electrical conductivity, total dissolved solids, total suspended solids, dissolved oxygen, Ca2+, Mg2+, + + - 2- - - 2+ 2+ 2+ 2+ 2+ 2+ Na , K , HCO3 , SO4 , Cl , NO3 , Fe , Zn , Pb , Cu , Mn , and Cr . With the aid of geochemical diagrams acquired using Aquachem 2014.2, we classified the groundwater samples into their respective hydrogeochemical facies, identified their relative similarity and demonstrated the irrigability of the groundwater. The results showed that the groundwater quality indicators occur in ______

*Corresponding author: E-mail: [email protected];

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the groundwater in amounts that fall within their respective permissible limits as set by World Health Organization (WHO) Drinking Water Standard, and therefore ascertained the groundwater portable and suitable for drinking. The pH of the groundwater has a mean value of 6.7 with a standard deviation of 0.26. The relative abundance of the majority of cations follows this sequence - Na+ > 2+ + 2+ - - 2- - Ca > K > Mg , while that of the anions follow this sequence - HCO3 > Cl > SO4 > NO3 . Heavy metals constituents of the groundwater follow this order of relative abundance - Zn2+ > Fe2+ > Mn2+ > Cu2+ > Cr2+ > Pb2+. Three hydrogeochemical facies were identified in the area and they are: the + - 2+ + - 2+ 2+ - Na —Cl water type, the Mixed Ca -Na -HCO3 water type and the Ca -Mg -HCO3 water type. Great similarities were identified between the geochemical composition of the samples and they are all evidently suitable for irrigation purposes. The TDS level and concentration of Ca2+, Mg2+ and Cl- demonstrated the freshness and softness of the groundwater, with no laxative effects. From series of computations and plots, silicate weathering and seawater intrusion were deduced to be the dominant factors controlling the groundwater chemistry, though there is evidence of poor rock dissolution – immature water-rock equilibrium.

Keywords: Groundwater; aquifer; water quality; concentration; geology; geochemical; fresh water.

1. INTRODUCTION soil quality indices but equally affected the productivity of agroecosystems [3]. Land use Water is essential for livelihood and socio- change has significant impact on the feedback of economic development of any community. Fresh hydro-climatic processes on the surface water resources are unevenly distributed hydrology [4]. Kigne [5] stated that urbanization throughout the world and their availability are is the most forceful of all the changes that affect becoming scarce day by day owing to population the hydrology of an area; this forcefully results to growth and diverse human activities. In quest to a decrease in the infiltration rate of water into the fill up the gap created by the absence of fresh soil as the excess flow becomes runoff. Changes surface water resources, groundwater is in groundwater quality with subsequent exploited to meet the demand exerted by various contamination can undoubtedly, affect human sectors. Groundwater may become surface water health [6]. Groundwater quality depends, to some through springs and drainage into rivers, lakes degree, on its chemical composition which may and wetlands. Conversely, surface water bodies be modified adversely by natural and may seep into the ground and recharge the anthropogenic sources [7]. Rapid urbanization, aquifers, e.g. when flood water percolates especially in developing countries like Nigeria, through the vadose zone to the saturated zone has affected the availability and quality of [1]. Movement of faults and other forms of groundwater due to improper and uncontrolled tectonism on the earth is predictably influenced waste disposal practice, especially in urban by the interplay of groundwater lubrication. areas. Groundwater may not be confined only to earth; the formation of some of the landforms observed Groundwater pollution is a growing on Mars may have been influenced by environmental problem, especially in developing groundwater, there is also evidence that liquid countries and impairs the usefulness of water, water may also exist in the subsurface of causing hazard to public health through toxicity Jupiter's moon Europa [2]. or spread of disease [8]. Wastes generated in the study area are disposed of in open dumps, along In Nigeria, many major cities, suburbs and river banks, erosion sites, septic tanks, pit villages depend on groundwater for water latrines, abandoned borrow and quarry-pits. Oil supplies, mainly because of its abundance, and gas spills from the numerous petrol stations, stable quality and because it is inexpensive to industrial efﬂuents, and wastes from agricultural exploit. Owerri and its environs have witnessed a activities are also potential sources of pollution in substantial industrial and population growth the area. Particularly, open dumps are sited during the past two decades. Demography and indiscriminately in Owerri without consideration fast urbanization of Owerri metropolis have led to of the protection of the underlying aquifer [9]. profound social, economic and ecological This results in aquifer deterioration, since some alterations to the extent that poses an increasing of these waste products may be discharged threat to the attainment of a healthy environment. directly into the aquifer system [10]. Through Land use trend in Owerri not only affected the precipitation, irrigation waters or liquid wastes,

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water soluble wastes can be dissolved and the set standards. Some of these constituents eventually seep through the vadose zone of the occur in significant amounts while others are of soil into the saturated zone to pollute the minor importance or are present as trace groundwater. Once groundwater is elements. Spatial variation in groundwater quality contaminated, its quality cannot be restored by in response to local geologic set-up and stopping the pollutants from source [11,12]. As anthropogenic factors warrants the evaluation of groundwater has a huge potential to ensure the quality for many purposes including that of sustainable water supply, it is important that human consumption [7]. Since groundwater human activities on the surface do not negatively occur in geologic setting which is dynamic, it affect the precious resource [13]. Poor possible for near-surface aquifer that produced environmental management creates havoc on clean water in a given year to produce polluted the water supply and hygiene and undermines water in the following year. Therefore, constant public health [14]. monitoring of groundwater quality is vital to ascertain their fitness for human consumption In sub-Saharan Africa, the water use efficiency and to determine the appropriate remediation estimated for the year 2005/07 and projected for measure to be taken if significant alterations to the year 2050 is 22 and 25 percent respectively, the quality are observed. which is by far less than the world average which is 44 and 46 percent respectively [15]. Although, Some scholars who have studied some aspects the current water withdrawal for agriculture and of the hydrogeology in South-eastern Nigeria other purposes is lower than the total annual include: Nwankwo [10], who investigated some renewable water resource, this low water use aspects of hydrogeology of Umuosinta spring; efficiency will undoubtedly challenge the Ahiarakwem [18] studied physiochemical sustainable use and management of water in the characteristics of the urban springs, all in Imo region [16]. Thus, expanding the irrigated area state; Ahuja [19] investigated the discharge rate, under the present agricultural water management flow type and microbial assay of urban spring characterized with low irrigation efficiency rates water. This study will fill the research gaps in the will result in severe water scarcity in the coming previous studies by undertaking hydrological and decades. The growing importance of geochemical study of groundwater resources in groundwater for agriculture can largely be the region. explained by the capacity of groundwater to act as a reliable water source for irrigation, providing 2. STUDY AREA water on demand, while being largely unaffected by seasonal surface hydrological variation [1]. Continued abstraction results in the lowering of 2.1 Geology of the Study Area water tables, which in turn increases the cost of pumping and could possibly create a “race to the Owerri municipal and its environs are located in bottom” among producers [16]. Where use is Imo State within South-eastern Nigeria, intensive, reaching unsustainable level, positioned at latitude 5°47’E and longitude 7°2’N. groundwater overdraft has further resulted in The town has an urban setting and is the significant negative externalities with direct landlord to most government ministries, impacts on agriculture production. Intensive departments and agencies in the state. It is also groundwater withdrawals for agriculture have the epicenter of all socio-economic and religious contributed to depleted streams, rivers and lakes activities in the State. It is one of the constituent in some regions and caused the sometimes- areas of the well-known Benin formation in the irreversible salinization of aquifers in coastal Anambra basin. Principal elements of the areas, impacting all surface water users, geologic framework of the stratigraphic including farmers, and damaging ecosystems [1]. succession within the study area are summarized Intensive pumping is also responsible for land in Table 1. The Benin formation is made up of subsidence in some regions, causing costly friable sands with minor 'intercalation of clay. The damage to infrastructure in urban and rural sand units are mostly coarse-grained pebbles areas, while diminishing the capacity of aquifers [20]. The grains are sub angular to surround in to store water for future uses. Small holder drip sharp. The lithology according to Asseez [21], is irrigation technique improves water productivity made up of over 90% sandstone with few shale and, of course, water use efficiency [17]. intercalations. The shale is greyish brown, sandy to silty and contains some part remains and For groundwater to be considered safe and dispersed lignites. The formation starts as a thin portable, its contents must concurrently satisfy age at its contact with the Ogwashi-Asaba

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formation in the north of the area and thickens the source of surface water supply in the area. In seawards. The average thickness of the addition, there are vast interfluves characterized formation at the study area is 800 m [22]. In by dry valleys that gulp in surface drainage in many places within the study area, the formation high precipitation periods. The porous and is overlain by a considerable thickness of the red permeable sands and the interfingering sandy earth composed of iron stained regolith formed clay and gravels of the Benin Formation form a by the withering and the subsequent multi-aquifer system in which aquifer units are ferrugination of the withered material. Several separated by semi-permeable sandy clay structural units such as point bars, chicalfills, and aquitards [32]. Three aquifer units characterized natural levees, back swap deposits and ox-bow by high storativity and transmissivity delineates fills are identified in the formation. Petrographic the lower Imo River basin which, namely: upper studies show several thin sections [20]; quartz water-table (unconfined) aquifer, middle semi- make up about 99% of all grains. The quartz confined aquifer, and a lower confined aquifer grains show undulose extension, the rock is [32]. The base of the unconfined aquifer is at a mineralogically matured and texturally immature. maximum depth of 100 m. The middle semi- The Benin formation conformably overlies the confined aquifer has an average thickness of 80 Ogwashi-Asaba formation. The Ogwashi-Asaba m, while the lower confined aquifer has an formation was formerly known as “lignite series” estimated thickness of more than 600 m. The [23,24,25], “lignite group” [26], and “lignite aquifer in the study area is largely unconfined but formation” [27]. Reyment [28] formalized it and becomes semi-confined to confined in some described the lithology as consisting of seams locations [9]. Water table mounding and direct and clays. The average thickness is 300m. infiltration of leachates form the major path ways Kogbe, [29] suggested that part of the formation for the entry of contaminants into the maybe of oligocene age. The complete groundwater system which is comprised stratigraphic sequence of the study area showing generally of an extensive permeable/porous all the formations, their lithology and depositional overburden. The unconfined nature of the aquifer environment are presented in Table 1. is of strategic importance in the supply of potable water to the populace [9]. The terrain’s 2.2 Hydrogeology of the Study Area phenomenal monotony may be accounted for by the absence of tectonic disturbances and by the The study area is drained the Otamiri, Njaba, and homogeneous rock structure [31]. Oramiriukwa rivers (all some of which have very few tributaries), plus the Nwaorie Stream and the ephemeral Okitankwo Stream. Apart from 2.3 Land Use and Land Cover of Owerri Imo River, which runs through the area Metropolis underlain by Imo Shales, other rivers rise within the coastal plain sands. Generally, river valleys Land Use and Land Cover in the study area are constitute the major physical features, which classified into five groups namely: built-up are often marshy [31]. They recharge mainly environment occupying up to 30%, forest from surface runoff and groundwater base flow; vegetation - 40.68%, farmland - 25.8%, peak discharge occurs in September and bare/eroded surfaces - 1% and water body - October [32], and these watersheds represents 2.52%. Presently, variation in the outlying

Table 1. Showing the stratigraphic succession within the study area [28] and [30]

Age Formation Lithology Depositional environment Miocene-Recent Benin formation Medium-Coarse grained sandstone, poorly Continental consolidated with shale intercalations Oligocene- Ogwashi-Asaba Unconsolidated sand with lignite seams at Continental Miocene formation various layers Eocene Ameki formation Grey clayey-sandstone and sandy clay Marine stone. Paleocene Imo shale Laminated clayey-shale Marine Maastrichian Nsukka Formation Sandstone intercalated with shale and coal Marine beds

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peri-urban areas of the forest vegetation class Calabar in Cross River State with its apex near have changed substantially compared to its state Ahoada of Rivers State. Its western banks in 1991 [33,34]. Over the past 27 years (1991- parallel the Niger River while its south-eastern 2018), the built-up environment has rapidly parts almost reach the coast line. expanded within the municipality and the suburbs, with high intensity at the central, Nigeria like of all West Africa has a tropical northwest and southwest of the study area. climate with main regimes as dry season and Increasing development pressure and urban rain season. These two regimes originate over expansion in these areas led to the conversion of the Atlantic. Besides the dominant influence of other classes to built-up environment, especially the air masses, the Climate is influenced by the the bare/eroded surfaces, farmlands and forest geographic position of Nigeria on the one hand, vegetation. Expansion of the already existing altitude and proximity to the sea on the other urban fabrics through rapid construction of hand. Thus, Nigeria maybe divided into four residential, commercial and industrial units, road climate regions. (a) Subequatorial region (b) networks, pavements, leisure facilities and other Tropical Continental North (c) Tropical Hinterland infrastructures, all together led to continuous (d) The High Plateau [35]. The study area expansion of built-up environment in the different witnesses two seasons; the wet and dry with an corners of the area [34]. Urban growth and loss even distribution of rainfall, temperature and of forest, farmland and open space were the humidity all year round; this is typical of most conversion in the area. equatorial climate. Rainfall distribution in the area is bimodal, with peaks in July and September However, the largest inter-class change since and a two week break in August. The rainy 1986 occurred between the farmland and the season resumes in March and terminates in forest vegetation classes. This conversion October or early November. Rainfall is often at its occurred mainly around the semi-urban outlying maximum at night and during the early morning areas. This is due to increased subsistence hours. Annual rainfall varies from 1,990 to 2,200 farming in the outlying areas of Orji, Naze, Irete, mm [36]. The mean annual temperature over Orogwe, Amakohia, Uratta and Akwakuma and most of the region is about 27°C with deviations Egbu/Awaka suburbs [33]. The increased from the mean related largely to the degree of farming is in turn a ripple effect of urbanization to cloudiness. The mean daily temperature attains meet the demands of the rising population of its highest value (28-30°C) around March and its Owerri and its environs. The bare/eroded surface lowest values (23-24°C) around August [37]. The class have been highly converted to the built-up humus content of the land area favours environment, observed mainly around the core of agriculture, hence farming activities is intensive Owerri metropolis over the past 27 years. in the area as well as livestock rearing. Conversion from bare/eroded surfaces to the farmlands has been minimal. The water body 2.5 Soil Type and Properties class increases in the rainy season through overflowing of riverbanks and increase of flooded The soil type in the study area belongs to the and water-logged areas due to the high rainfall; it ferralic soil and consists of the plain sand and reduces tremendously in the dry season. sometimes loamy layer, with thickness approximately up to 100 meters. The soil has a 2.4 Geomorphology and Physiography strong foothold which is good for arable crops. The soil particle size distribution is unaffected The geomorphology of an area involves the under different land use systems [38,39]. High classification of Landforms based on physical sand fractions in the area are attributed to the and chemical processes. Interactions between overlying parent material - coastal plain sand the earth’s surface and the natural forces acting [40]. With exception of coastal plain sand of upon it differs from one to another and the result Benin formation, the clay distribution increases of such interactions depends on such factors as slightly downward, thus revealing the relief, geology, climate and base level. homogeneity of horizons and precludes the Geomorphologically, the study area falls within a existence of well-developed argillic horizons in coastal plain that is one of the largest of the the soil profiles [41]. Clay has high rate of geomorphological zones in southern Nigeria. Its adsorption and can retain water easily. In boundaries continue far beyond Imo state, accordance, moisture content increases forming a triangle whose base extends over 250 downward with increasing clay content as clay kilometres from Onitsha in Anambra State to impairs drainage especially at the sub-surface

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horizons [42,43]. The heavy rainfall coupled with Due to clay movement, there is downward deep water drawing nature of the trees in the soil increase in clay content with well-developed contributes to the high infiltration of rainwater. argillic horizon in soils derived from coastal plain Variations in soil bulk density, soil total porosity sand, while there is kandic horizon in soils and gravimetric moisture content are attributed to derived from Ameki Shale [3]. Soils developed different agronomic practices in the different land from the different parent materials have varying use types [11]. colours. Reddish brown to reddish orange and

Fig. 1. Location map showing the study area

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loamy sand textured for soils derived from groundwater content of the area. A total 15 unconsolidated sand of Ogwashi-Asaba samples were collected in the study area from formation; grayish brown to brownish red and the main area of each town during the rainy sandy loam to loamy sand textured for soils season (in the morning of different days in the derived from Ameki Shale; reddish brown to red month of July 2018), when there was a maximum with clayey texture with sub-angular blocky chance for leachate and contamination of structure for soils derived from coastal plain groundwater in surrounding area. The sterile sand. The colour variation in the soils colour is bottles were carefully labelled before collection to due to varied iron content, organic carbon differentiate each sample from another with content, soil water content, texture and indication of the time of sampling, name of topography [39,44]. location, well depth and depth of water table. Sampling protocols included the following Soil pH is strongly acidic due to the inherent precautions for avoiding contamination: characteristics of soils of the study area irrespective of their parent materials [45,46].  Only new sample containers were used for Exchangeable sodium percent of the soil which sample collection. identifies the degree to which the exchange  All new sample containers were complex is saturated with Na is very low. Soil appropriately cleaned by soaking them in organic matter decreases downward probably hot 50% nitric acid for 2 days, rinsed with due to surface incorporation and mode of deionized water, then leached in 1% nitric deposition of organic residues. Top soil organic acid for 2 weeks before they were taken to matter contents are directly related to organic the field. carbon inputs and there have been several  Container lids were double-checked for studies demonstrating improvements in soil liners that may cause contamination or quality and fertility after organic carbon additions adsorb particular analytes. [47]. Generally, soils of Ameki Shale contain  We ensured the inside of the containers higher quantity of organic matter compared to and lids did not come in contact with hands those of coastal plain sand and unconsolidated or objects. sand [48,49]. Nitrogen contents of the surface  Disposable gloves were used while horizons are higher than the sub-surface in handling sample containers at every stage correlation to the organic contents of these during sampling. horizons (Table 6).  Sample containers were kept in a clean environment away from potential 3. MATERIALS AND METHODS contaminants, including dust, dirt and fumes after sample collection. Groundwater samples from borehole wells were collected from five towns, namely, Obinze, For physio-chemical analysis, we selected some Ikenegbu, Orji, Naze and Orogwe as shown in parameters for measurement and assessment the location map in Fig. 1. For sample collection, based on guidelines set by the World Health the American Public Health Association (APHA) Organization (WHO) for drinking water-quality standard protocol was adopted [50,51]: Run the assessment [54,55,56]. The parameters tap supplying water from a service pipe measured are as follows: pH, temperature, total connected directly to the pump submerged in the hardness, turbidity, electrical conductivity (EC), well at maximum flow for about 2-3 minutes to total dissolved solids (TDS), total suspended clear the service line, and then collect the sample solids (TSS), dissolved oxygen (DO), calcium after reducing the flow to prevent splashing on (Ca2+), magnesium (Mg2+), sodium (Na+), + - the bottle. The samples were collected in new potassium (K ), bicarbonate (HCO3 ), sulphate 2- - - 2+ and cleaned 500 ml sterile bottles with corks and (SO4 ), chloride (Cl ), nitrate (NO3 ), iron (Fe ), then put in an ice box. This process was carried lead (Pb2+), zinc (Zn2+), copper (Cu2+), out thrice at a 15-minute interval in order to Manganese (Mn2+) and Chromium (Cr2+). obtain three samples from each sampling location, after which they transferred immediately While on site, we determined pH, Temperature, to the laboratory where they were stored at 4°C Turbidity, EC, TDS and DO of groundwater with before laboratory analysis [52,53]. The aim for the aid of a portable water analyzer kit that collecting three samples at each sampling contains a pH meter, a thermometer, a location is to obtain a mean value for each turbidimeter, a conductivity meter, a TDS meter parameter that is a true representative of the and a DO meter. Other parameters were

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- - analyzed in the laboratory. HCO3 and Cl were coefficient of variation. In addition, we performed determined by complexometric EDTA titration a reliability check on the datasets using a system methods. The alkaline earth ions (Ca2+ and Mg2+) set by Hounslow [57]. The mean value of these and the heavy metals (Fe2+, Pb2+, Zn2+ and Cu2+) measured parameters obtained from the results were determined using the atomic absorption of the statistical analysis were plotted into spectrophotometer while the alkali ions (Na+ and geochemical diagrams with the aid of Aquachem K+) were measured using the atomic emission 2014.2 maintenance release geochemical - 2- spectrophotometer. NO3 and SO4 were software [58], and then compared with literatures determined by a colorimetric method using a UV- that dealt with classification and designation of Visible spectrophotometer type. We determined ionic nature of water. The illustrations of ionic total hardness from calcium and magnesium signature helped us in revealing the principal concentrations using the total hardness ions controlling the water chemistry. formula: Geochemical plot like Piper diagram, Durov diagram, Schoeller diagram, Wilcox diagram, 2.5[] + 4.1[] Giggenbach’s triangle, Gibbs plot and other water quality criteria like Correlation matrix, SAR, All parameters were determined according to the TDS were used to assess the portability and measurement protocols prescribed in 2005 and suitability of the groundwater for domestic and 2012 by the American Public Health Association irrigation purpose. (APHA), Water Environment Federation (WEF) and American Water Works Association (AWWA) 4. RESULTS AND DISCUSSION [50,51]. A quick look at the percent coefficient of variation Following measurement protocols, we calibrated (CV%) in Table 3, which is also known as relative the equipment used for field and laboratory standard deviation (RSD), expressed as a measurements before using them on site and in percentage of the ratio of standard deviation to the laboratory respectively. For the pH meter, we the mean; shows that Pb2+ and Cr2+ calibrated it by placing the electrode in three measurements for Naze and Ikenegbu sampling different buffer solutions of known pH values of sites respectively retains the highest CV% of 4.01, 7.01 and 10.01, and subsequently setting 35.36, followed by Cu2+ and Cr2+ for Ikenegbu the meter to the buffer’s pH value. We used the and Obinze respectively with CV% of 17.68%. ice water method to calibrate the mercury in Fe2+ for Ikenegbu and Mn2+ for Naze follows in glass thermometer. For the turbidimeter, we descending order each with CV% of 16.33. This performed stabilized formazin standard implies that among all the measured values, recalibration on it before it was used for those of Pb2+ for Naze and Cr2+ for Ikenegbu are measurement. We calibrated the conductivity the most unreliable, followed by other meter by inserting its probe into a sodium parameters with decreasing unreliability down chloride standard poured into a plastic cup and the sequence. However, the CV% values for all allowing it to interact with the functional parts of measured parameters in all sampling locations the probe before adjusting the meter to the fall within acceptable limits. Parameters with zero standard’s value. We also adjusted and (0) CV% in some of the sampling locations recalibrated the TDS meter by partially retains the most reliable measurement values immersing the meter into a commercial standard with intangible or negligible unreliability. NaCl-based solution. For DO measurements, we subjected the DO sensor and temperature According to the reliability analysis presented in sensor to a 100% air-saturated water of a known Table 4, the datasets obtained a pass mark for DO value, then compared the reading and all series of reliability checks. The datasets for all adjusted the meter accordingly. samples exhibit a good ion balance (Fig. 2); with the cations being greater than the anions by The values obtained at each sampling location values less than 5%. A pass mark below 5% for were compared with the World Health the reliability check of the measured TDS (TDS Organization (WHO) standards for drinking entered) implies that the major constituents of water. For quality assurance and quality control, the groundwater were accounted for in this we performed statistical analysis on the three assessment. The percentage ratio of TDS and samples obtained from each of the five sampling EC falls within reliable limits of 55%-75% and by locations to determine their mean value, implication validates the measured TDS and of variance, standard deviation and percent course EC. EC of water being a function of the

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2- - amount of ions present in water showed a good SO4 > NO3 . The pH of the groundwater in the balance when checked with the sum of cations metropolis has a mean value of 6.7 and a (in meq); all results falling within reliable limits. standard deviation of 0.26 and 3.83% coefficient This implies that EC and the major cationic of variation. constituents of the groundwater were reliably measured. The K+/(Na+ + K+) percentage ion The correlation matrix presented in Table 4 ratios are all below 20%, and are therefore indicates a strong positive relationship as the reliable since potassium is more readily removed values tend close to 1 and a strong negative from solution by plants and clay minerals than relationship as values tend close to -1. Unity (1) sodium. The Mg2+/(Ca2+ + Mg2+) follows the in the matrix implies the parameters are same same trend being below 40%. Ca2+/(Ca2+ + and no quantitative or qualitative difference SO42-) and Na+/(Na+ + Cl-) percentage ion ratios exists while zero (0) implies there is no are all above the reliable limit of 50% since the correlation at all. The pH of water is strongly major sources of sulphate and chloride in negatively correlated with magnesium ion. A groundwater are CaSO4 and NaCl respectively. strong positive correlation exists between EC Having successfully passed the datasets through and TDS, similar to the correlation between EC all data quality and reliability checks, the and TSS, plus EC and bicarbonate. By datasets can most assuredly be used for further implication, when bicarbonate ion concentration, analysis and characterization of the groundwater TDS, and TSS also increases in the of the study area. groundwater, EC also increases. TDS, TSS and bicarbonate ion are strongly positively correlated Generally, the statistical analysis of the entire to each other; increase in bicarbonate ion implies study area (Table 5) shows that the Pb2+ increase in TDS and TSS. It is important to parameter exhibits the highest measure of mention that bicarbonate ions have the strongest dispersion with a range of 0.0005 and a CV% of influence on the EC and TDS of the groundwater 47.14. This implies that the Pb2+ constituent of in the study area. As expected, TSS retains a the groundwater varies spatially over the study strong positive correlation between potassium area more than any other constituent. Cr2+, Mn2+, ions and zinc ions. Magnesium ions and sodium K+, TSS, Zn2+, Mg2+ and Cu2+ parameters follow ions, sodium ions and sulphate ions are strongly this spatial variation trend in a descending order. positively correlated. Increase in chloride ions in Low values of CV% observed for temperature, groundwater implies a strong reduction in the Na+, pH, and Cl- implies that the spatial amount of bicarbonate ions, TDS and TSS while distribution of these parameters across the study it strongly favours manganese ions. Nitrate ions area are even. The relative abundance of are strongly positively correlated to sulphate majority of the cations in meq/l follows this ions, and sodium ions also. Increase in ferrous sequence - Na+ > Ca2+ > K+ > Mg2+, while that of ions indicates a strong decrease in magnesium - - the anions follows this sequence - HCO3 > Cl > ions, sodium ions and sulphate ions.

Fig. 2. Ion balance diagram for all sampling locations

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Table 2. Physio-chemical parameters of groundwater samples in the study area alongside with WHO guideline values [54,55,56]

Parameter Orogwe Naze Orji Ikenegbu Obinze WHO Samples 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 Well Depth (m) 55 55 55 60 60 60 80 80 80 75 75 75 55 55 55 Depth of Water Table (m) 20.5 20.5 20.5 23.8 23.8 23.8 49.5 49.5 49.5 28.7 28.7 28.7 18.2 18.2 18.2 pH 6.54 6.51 6.51 6.54 6.53 6.59 7.24 7.16 7.2 6.7 6.67 6.65 6.55 6.56 6.54 6.5-8.5 Temperature (°C) 26.8 26.8 26.8 27.4 27.4 27.4 26.8 26.8 26.8 27.5 27.5 27.5 26.8 26.8 26.8 Total Hardness (mg/I CaCO3) 15.92 15.35 16.01 17.76 16.28 16.03 14.46 14.05 14.39 15.65 15.24 15.44 13.28 13.33 13.23 500 Turbidity (NTU) 0.83 0.85 0.83 0.9 0.9 0.93 0.77 0.75 0.76 1.56 1.53 1.53 0.85 0.89 0.87 4 EC (µS/cm) 78 76.6 77.6 71 72.5 71.3 69.9 70.3 69.5 66.2 66.4 66 62.2 62.6 62.1 1000 TDS (mg/I) 56.5 56.1 56.3 50.5 50.2 50.2 46.3 47.6 46.2 44.8 45.3 44.6 43.2 44.2 43.4 600 TSS (mg/l) 3.38 3.5 3.4 2.5 2.5 2.45 2.78 2.75 2.74 1.58 1.56 1.51 1.76 1.82 1.82 250 DO (mg/I) 6.7 6.4 6.4 6.7 6.7 6.7 5.8 6.1 6.1 7 6.9 7.1 6.8 6.3 6.4 5 Ca2+ (mg/l) 4.5 4.4 4.6 5.3 5.2 5.1 4.7 4.7 5 4.2 4.2 4.2 4 4.02 3.98 200 Mg2+ (mg/I) 1.14 1.06 1.1 1.1 0.8 0.8 0.6 0.5 0.4 0.95 0.85 0.9 0.8 0.8 0.8 150 Na+ (mg/l) 7.4 7.45 7.35 6.5 6.9 7 6.28 6.32 6.3 6.86 6.82 6.78 6.6 6.6 6.9 200 K+ (mg/I) 3.12 3.08 3.1 1.43 1.39 1.38 2.65 2.58 2.57 1.4 1.4 1.4 2 1.9 2.1 200 - HCO3 (mg/l) 22.4 22 21.9 18.5 18.6 18.7 15.9 16.4 16 14.92 14.91 14.87 13.45 13.55 13.5 500 2- SO4 (mg/l) 3.5 3.5 3.5 3.1 3.13 3.07 2.8 2.8 2.8 2.94 2.88 2.88 3.2 3.2 3.2 250 Cl- (mg/l) 8.7 8.6 8.8 9.5 9.1 9 8.85 8.9 8.95 9.2 9.2 9.5 10.1 9.6 9.7 250 - NO3 (mg/l) 3.3 2.7 3 2.4 2.8 2.3 2.11 2.1 2.12 2 2.1 2.5 2.6 2.6 2.9 50 Fe2+ (mg/I) 0.04 0.04 0.05 0.05 0.06 0.06 0.07 0.06 0.07 0.05 0.04 0.06 0.05 0.05 0.05 2 Pb2+ (mg/I) 0.003 0.003 0.003 0.001 0.002 0.001 0.004 0.003 0.003 0.002 0.002 0.002 0.005 0.005 0.006 0.01 Zn2+ (mg/l) 0.3 0.32 0.28 0.19 0.23 0.21 0.3 0.3 0.3 0.11 0.15 0.11 0.2 0.19 0.21 3 Cu2+ (mg/l) 0.03 0.03 0.03 0.04 0.04 0.05 0.04 0.04 0.04 0.02 0.03 0.03 0.04 0.03 0.04 2 Mn2+ (mg/l) 0.03 0.02 0.03 0.05 0.04 0.06 0.02 0.02 0.02 0.04 0.045 0.04 0.06 0.05 0.055 0.4 Cr2+ (mg/l) 0.003 0.003 0.003 0.002 0.002 0.002 0.001 0.001 0.001 0.002 0.001 0.001 0.002 0.003 0.003 0.05

Onyeanuna et al.; JGEESI, 19(1): 1-24, 2019; Article no.JGEESI.32939

Table 3. Standard deviation and percent coefficient of variation of samples collected in each sampling location in Owerri

Parameter Orogwe Naze Orji Ikenegbu Obinze Statistical parameters Mean SD CV% Mean SD CV% Mean SD CV% Mean SD CV% Mean SD CV% pH 6.52 0.014 0.22 6.55 0.0262 0.40 7.2 0.033 0.45 6.673 0.021 0.31 6.55 0.008 0.12 Temperature (°C) 26.8 0 0 27.4 0 0 26.8 0 0 27.5 0 0 26.8 0 0 Total Hardness (mg/I CaCO3) 15.76 0.292 1.85 16.69 0.7635 4.57 14.3 0.179 1.25 15.44 0.167 1.08 13.28 0.041 0.31 Turbidity (NTU) 0.84 0.009 1.13 0.91 0.0141 1.55 0.76 0.008 1.07 1.54 0.014 0.92 0.87 0.016 1.88 EC (µS/cm) 77.4 0.589 0.76 71.6 0.6481 0.91 69.9 0.327 0.47 66.2 0.163 0.25 62.3 0.216 0.35 TDS (mg/I) 56.3 0.163 0.29 50.3 0.1414 0.28 46.7 0.638 1.37 44.9 0.294 0.66 43.6 0.432 0.99 TSS (mg/l) 3.43 0.052 1.53 2.48 0.0236 0.95 2.76 0.017 0.62 1.55 0.029 1.90 1.8 0.028 1.57 DO (mg/I) 6.5 0.141 2.18 6.7 0 0 6 0.141 2.36 7 0.082 1.17 6.5 0.216 3.32 Ca2+ (mg/l) 4.5 0.082 1.81 5.2 0.0816 1.57 4.8 0.141 2.95 4.2 0 0 4 0.016 0.41 Mg2+ (mg/I) 1.1 0.033 2.97 0.9 0.1414 15.71 0.5 0.082 16.33 0.9 0.041 4.54 0.8 0 0 Na+ (mg/l) 7.4 0.041 0.55 6.8 0.216 3.18 6.3 0.016 0.26 6.82 0.033 0.48 6.7 0.141 2.11 K+ (mg/I) 3.1 0.016 0.53 1.4 0.0216 1.54 2.6 0.036 1.37 1.4 0 0 2 0.082 4.08 - HCO3 (mg/l) 22.1 0.216 0.98 18.6 0.0816 0.44 16.1 0.216 1.34 14.9 0.022 0.14 13.5 0.041 0.30 2- SO4 (mg/l) 3.5 0 0 3.1 0.0245 0.79 2.8 0 0 2.9 0.028 0.98 3.2 0 0 Cl- (mg/l) 8.7 0.082 0.94 9.2 0.216 2.35 8.9 0.041 0.46 9.3 0.141 1.52 9.8 0.216 2.20 - NO3 (mg/l) 3 0.245 8.16 2.5 0.216 8.64 2.11 0.008 0.39 2.2 0.216 9.82 2.7 0.141 5.24 Fe2+ (mg/I) 0.04 0.005 10.88 0.06 0.0047 8.32 0.07 0.005 7.07 0.05 0.008 16.33 0.05 0 0 Pb2+ (mg/I) 0.003 0 0 0.001 0.0005 35.36 0.003 0.0005 14.14 0.002 0 0 0.005 0.0005 8.84 Zn2+ (mg/l) 0.3 0.016 5.44 0.21 0.0163 7.78 0.3 0 0 0.123 0.019 15.29 0.2 0.008 4.08 Cu2+ (mg/l) 0.03 0 0 0.043 0.0047 10.88 0.04 0 0 0.027 0.005 17.68 0.037 0.005 12.86 Mn2+ (mg/l) 0.03 0.005 17.68 0.05 0.0082 16.33 0.02 0 0 0.04 0.002 5.66 0.06 0.004 7.42 Cr2+ (mg/l) 0.003 0 0 0.002 0 0 0.001 0 0 0.001 0.0005 35.36 0.003 0.0005 17.68 SD – Standard Deviation; CV% - Percent Coefficient of Variation

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Table 4. Quality Assurance/Quality Control: Reliability analysis for the measured parameters

Sample Designation Orogwe Naze Orji Ikenegbu Obinze Check Unit Attention value Analysis value Analysis value Analysis value Analysis value Analysis value Balance (C-A)/(C+A)*100 meq/l <5% 3.34% 3.51% 4.91% 4.65% 4.51% TDS: (Entered - Calculated)/Entered*100 mg/l <5% 4.44% 4.45% 4.63% 4.51% 1.27% TDS Entered/EC mg/l 55%< ## <75% 72.7% 70.3% 68.8% 67.8% 70.0% Conductivity/Sum MEQ Cations mg/l 90< ## <110% 106% 105.60% 106.80% 105.90% 100% K+/(Na+ + K+) meq/l <20% 19.8% 10.8% 19.6% 10.8% 15.0% Mg2+/(Ca2+ + Mg2+) meq/l <40% 28.9% 22.4% 14.8% 26.3% 25.0% 2+ 2+ 2- Ca /(Ca + SO4 ) meq/l >50% 75.5% 80.1% 80.4% 77.7% 75.0% Na+/(Na+ + Cl-) meq/l >50% 56.8% 53.3% 52.2% 53.1% 51.3% N/B: TDS Entered = TDS measured. The Unit column represents the unit of parameters with which their different percentage ratios were calculated

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Table 5. Measures of central tendency and dispersion for groundwater samples in Owerri

Statistical parameters Minimum Maximum Range Mean Variance SD CV% pH 6.51 7.24 0.73 6.70 0.07 0.26 3.83 Temperature (°C) 26.80 27.50 0.70 27.06 0.10 0.32 1.18 Total Hardness (mg/I CaCO3) 13.23 17.76 4.53 15.09 1.55 1.25 8.26 Turbidity (NTU) 0.75 1.56 0.81 0.98 0.08 0.28 28.77 EC (µS/cm) 62.10 78.00 15.90 69.48 26.13 5.11 7.36 TDS (mg/I) 43.20 56.50 13.30 48.36 20.98 4.58 9.47 TSS (mg/l) 1.51 3.50 1.99 2.40 0.46 0.67 28.07 DO (mg/I) 5.80 7.10 1.30 6.54 0.13 0.35 5.41 Ca2+ (mg/l) 3.98 5.30 1.32 4.54 0.19 0.43 9.58 Mg2+ (mg/I) 0.40 1.14 0.74 0.84 0.04 0.21 25.05 Na+ (mg/l) 6.28 7.45 1.17 6.80 0.14 0.37 5.46 K+ (mg/I) 1.38 3.12 1.74 2.10 0.45 0.67 31.93 - HCO3 (mg/l) 13.45 22.40 8.95 17.04 9.23 3.04 17.83 2- SO4 (mg/l) 2.80 3.50 0.70 3.10 0.06 0.25 7.92 Cl- (mg/l) 8.60 10.10 1.50 9.18 0.17 0.41 4.44 - NO3 (mg/l) 2.00 3.30 1.30 2.50 0.14 0.38 15.01 Fe2+ (mg/I) 0.04 0.07 0.03 0.05 0.000089 0.009 17.68 Pb2+ (mg/I) 0.001 0.006 0.005 0.003 0.000002 0.0014 47.14 Zn2+ (mg/l) 0.11 0.32 0.21 0.23 0.0047 0.07 30.17 Cu2+ (mg/l) 0.02 0.05 0.03 0.04 0.0001 0.007 20.32 Mn2+ (mg/l) 0.02 0.06 0.04 0.04 0.0002 0.014 36.72 Cr2+ (mg/l) 0.001 0.003 0.002 0.002 0.0000007 0.0008 40.82

Orogwe Orji 80 80 Obinze > = Naze 4 60 60 < O = Ikenegbu S C + a l + C 40 40 M g 20 20

Mg SO4

80 80

60 60

40 40

20 20

8 6 4 2 0 0 0 0 0 0 0 0 2 4 6 8 Ca Na+K HCO3 Cl

Fig. 3. Piper diagram plot for groundwater samples in Owerri metropolis

Onyeanuna et al.; JGEESI, 19(1): 1-24, 2019; Article no.JGEESI.32939

Table 6. Correlation matrix of some measured parameters

2+ 2+ + + - 2- - - 2+ 2+ 2+ 2+ 2+ 2+ pH EC TDS TSS Ca Mg Na K HCO3 SO4 Cl NO3 Fe Pb Zn Cu Mn Cr pH 1 -0.21 -0.30 0.11 0.24 -0.88 -0.76 0.25 -0.26 -0.74 -0.32 -0.73 0.79 0.02 0.38 0.33 -0.70 -0.70 EC µS/cm 1 0.99 0.86 0.52 0.56 0.69 0.51 0.99 0.57 -0.85 0.49 -0.31 -0.46 0.56 -0.43 -0.47 0.24 TDS mg/L 1 0.88 0.44 0.61 0.75 0.57 0.99 0.70 -0.78 0.63 -0.40 -0.33 0.60 -0.40 -0.38 0.41 TSS mg/L 1 0.50 0.19 0.40 0.80 0.87 0.50 -0.84 0.46 -0.07 -0.11 0.90 -0.10 -0.60 0.31 Ca2+ mg/L 1 -0.14 -0.14 -0.06 0.50 -0.15 -0.52 -0.18 0.56 -0.73 0.38 0.36 -0.30 -0.26 Mg2+ mg/L 1 0.96 0.02 0.59 0.79 -0.13 0.74 -0.88 -0.20 -0.18 -0.67 0.29 0.57 Na+ mg/L 1 0.29 0.71 0.87 -0.31 0.82 -0.90 -0.09 0.07 -0.71 0.08 0.62 K+ mg/L 1 0.53 0.46 -0.62 0.45 -0.21 0.43 0.87 -0.18 -0.61 0.37 - HCO3 mg/L 1 0.64 -0.80 0.57 -0.35 -0.40 0.58 -0.39 -0.41 0.34 2- SO4 mg/L 1 -0.15 0.99 -0.80 0.25 0.31 -0.33 0.23 0.91 Cl- mg/L 1 -0.07 -0.03 0.43 -0.67 0.39 0.86 0.18 - NO3 mg/L 1 -0.77 0.32 0.31 -0.25 0.30 0.95 Fe2+ mg/L 1 -0.24 0.17 0.72 -0.28 -0.66 Pb2+ mg/L 1 0.19 0.19 0.21 0.51 Zn2+ mg/L 1 0.19 -0.60 0.26 Cu2+ mg/L 1 0.29 0 Mn2+ mg/L 1 0.47 Cr2+ mg/L 1

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4.1 Water Quality and Hydrogeochemical while samples from other towns falls into the no- Facies dominant class. Generally, there is a + + 2+ 2+ predominance of Na + K over Ca and Mg in Characterization of water body geochemically, the metropolis. Although, samples from four of the five towns fall into the no-dominant type, presents the water condition with respect to its - - HCO3 predominates over Cl which in turn quality-measuring parameters considered under 2- the study. The use of interpretive diagrams and predominates SO4 . tables are for understanding the nature and origin of the water quality. From the Durov diagram plot, the groundwater type can be classified as sodium-dominated Comparison of the datasets obtained from waters (alkali-rich waters) according to the samples collected in Orogwe, Naze, Orji, cationic triangle (Fig. 4). The sample from Ikenegbu and Obinze of Owerri Metropolis with Orogwe is within the bicarbonate-dominated the World Health Organization (WHO) drinking while others are in the non-dominated water type water standard for each parameter (Table 2), due to substantial levels of chloride in the sample ascertains and approves the ground water in from the other four locations within the Owerri Metropolis as suitable for drinking metropolis. The groundwater sample from purposes. All the parameters were found to be Orogwe has the highest EC values and within the recommended standards, indicating consequently the highest TDS, seconded by the their presence is not harmful to humans, living Naze sample. The Obinze sample exhibited the organisms, and aquatic life [56,55]. The TDS of lowest EC and hence the lowest TDS. Although Owerri ranges from 42.2 - 49.8mg/l and with a the different samples collected from different mean value of 48.36mg/l for the analysed towns in the metropolis are classified into samples. This shows that the groundwater within different water types, with the aid of Durov Owerri and its environs is fresh and good for diagram we were able to identify the human consumption with reference to Table 7. relative similarity between the samples by The TSS of the study area ranges from 1.51 - plotting the datasets into a single graphical 3.50mg/l and a mean value of 2.4mg/l, therefore representation (the square plot at the centre of the total amount of solids in the groundwater is Fig. 4). The square plot clearly displays a cluster averagely 50.76 mg/l. of sample datasets which indicates that the sample is strongly similar to each other. The Table 7. Water classification by TDS level [59] similarity of the samples from different towns within Owerri metropolis implies spatial uniformity of the groundwater geochemical composition. Category TDS (mg/l) This is assertion is further strengthen considering Fresh water 0-1,000 the CV% of parameters in Table 5; no measured Brackish water 1,000-10,000 parameter exceeded the CV% of 50 mark across Saline water 10,000-100,000 the study area and most being below 20%. Brine water > 100,000 The Schoeller diagram (Fig. 5) further Using the Piper diagram classification scheme demonstrates the uniformity and similarity of presented by Ravikumar et al. [60], three composition among the groundwater samples by hydrogeochemical facies were identified the cluster of the lines of concentration from among the five samples. Samples from Orji, cations to anions. And so, uniformity of Ikenegbu and Obinze are classified into the groundwater constituents across the study Na+—Cl- water type, the sample from Orogwe area. 2+ + - falls into the Mixed Ca -Na -HCO3 water type class while the sample from Naze lies in between However, a thin line of difference exists in the the Na+—Cl- water type and the Mixed Ca2+- cation and anion concentrations of the samples. 2+ - 2+ + + - Mg -HCO3 water type. In the cations triangle, Mg , Na + K and HCO3 groundwater every other sample is classified into the Na+ + K+ constituents are highest in the Orogwe sample type while the sample from Naze lies at the while Orji sample exhibits the lowest + + 2+ 2- border between the Na + K type and the no- concentration of Mg and SO4 ions. The dominant type. In the anions triangle, the sample Obinze sample tops the list in chloride content - 2+ - from Orogwe is classified into the HCO3 type but the lowest in Ca and HCO3 .

Onyeanuna et al.; JGEESI, 19(1): 1-24, 2019; Article no.JGEESI.32939

SO4

Orogwe 80 20 Orji 60 40 Obinze

40 60

3 Total Dissolved Solids (mg/L) Naze

1 O

20 80 2 4 6 0

C 0 0 l 0 0 0 0

a C Ikenegbu 80 C 60 40 20 Mg 80 60 40

+20 K Na 60

40 EC (µS/cm)

Fig. 4. Durov diagram plot for groundwater samples in Owerri metropolis

1.00 Orogwe Orji Obinze Naze Ikenegbu

0.10 Concentration (meq/L)

0.01 Mg Ca Na + K Cl SO4 HCO3

Fig. 5. Schoeller diagram of major cations and anions in Owerri groundwater samples

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4.2 Hardness ascertains the Owerri groundwater suitable for drinking purposes with little or no health Hardness results from the presence of divalent concerns. Although all the heavy metals in the cations of the calcium and magnesium. The total groundwater occur within recommended limits, it hardness for Owerri groundwater samples is important to note that the concentration of ranges from 13.23 - 17.76 mg/l CaCO3 with a manganese exceeds its natural occurrence of 10 mean value of 15.09 mg/l CaCO3. It therefore µg/l in groundwater. Low levels of heavy metals implies that the water sample is soft when cross- in the study area strongly indicates that the referenced with Table 8. inefficient control of refuse dump in the area have had little or no effect on the groundwater. Table 8. Showing the classification of water However, in the long term such disposal practice by hardness [61] will increase the heavy metal content and adversely affect the groundwater and consequently render the groundwater unfit for Hardness mg/l CaCO3 Water class 0-75 Soft drinking. 75-150 Moderately hard 150-300 Hard Over 4.5 Rock Source Deduction 300 Very hard Here, we adopted the system and steps set by 4.3 Sodium Absorption Ratio (SAR) Hounslow [57] to deduce the rock source or water constituent source since the pH of the samples are all above the convenience value of The sodium absorption Ratio (SAR) was adopted 5. Using the system helped us to determine the to determine the suitability of the water for dominant processes affecting the groundwater in irrigation purpose because irrigability of water the metropolis; the results are tabulated in Table depends on the level of sodium absorbed in the 7 and they are a general overview based on ionic soil [62]. According to the Wilcox diagram in Fig. ratios found in the samples. 6, all five samples collected in Owerri metropolis poses a low sodium and salinity hazard. Sodium A holistic view at summary of reasoning for reacts with the soil thereby reducing permeability source-rock deduction (Table 7) and Gibbs plot of the soil [62]. Therefore, low sodium hazard or (Fig. 8) shows that that the dominant source of SAR of the groundwater implies high sodium in the groundwater for all samples permeability of the soil; thus, validating the collected in Owerri metropolis is through natural groundwater as suitable for irrigation purposes. ion exchange from sources other than halites. While the SAR for all five samples are similar, Knowing that the sodium that occurs on cation- the salinity level of the samples differs slightly, exchange minerals probably originates from with that of Orogwe leading in salinity, followed rainwater or from weathered sodium-rich clay by those of Naze, Orji, Ikenegbu and Obinze in [63]. It is therefore important to mention that their descending order. Again, here (Fig. 6) the rainwater contributes to a significant amount of samples are clustered together thus confirming sodium in the groundwater of the area but not their similarity. enough to outweigh the contributions from weathered clay silicates in the area. The high 4.4 Heavy Metals annual rainfalls in the study area support this claim. The calcium source is deduced to have Occurrence of heavy metals in water is one of resulted from minerals other than gypsum, the most important concerns that may cause especially carbonates and silicates. With respect severe health problems. For the study area, the to the TDS level, we can precisely conclude that relative abundance of heavy metal constituents weathered silicates are the dominant source of of the groundwater follows this order (in meq/l) - calcium in the metropolis. This assertion is Zn2+ > Fe2+ > Mn2+ > Cu2+ > Cr2+ > Pb2+ as seen congruent to the geology of the study area which in Fig. 7. Heavy metals distribution in the we presented earlier. Benin formation which groundwater of the study area follows this order overlies the study area starts as a thin-age north with respect to the sampling locations - Orji > of the area and thickens seawards; this makes Orogwe > Naze > Obinze > Ikenegbu. Generally, the study area liable for seawater intrusion in the the heavy metal composition of the groundwater area. Consequently, seawater or brine is the samples is classified as low and falls within the dominant source of bicarbonate in the limits of WHO standards for drinking water, which groundwater (Table 7).

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C1 250 C2 750 C3 2250 C4 Orogwe 30 Orji Obinze Naze Ikenegbu

Sodium (Alkali) hazard: 20 S4 S1: Low S2: Medium S3: High S4: Very high Salinity hazard: C1: Low C2: Medium

Sodium Hazard (SAR) C3: High 10 C4: Very high S3

S1 0 10 100 1000 Salinity Hazard (EC in µS/cm)

Fig. 6. Wilcox Diagram plot showing the viability of the samples for irrigation purposes

1.000 Orogwe Orji Obinze Naze Ikenegbu

0.100 (mg/L)

0.010

0.001 Iron Lead Zinc Copper Manganese Chromium

Fig. 7. Schoeller diagram for majority of heavy metals in the study area

Onyeanuna et al.; JGEESI, 19(1): 1-24, 2019; Article no.JGEESI.32939

Fig. 8. Gibbs diagram showing factors controlling the groundwater chemistry

Fig. 9. Giggenbach triangle plot showing the water-rock equilibrium level of Owerri groundwater samples. Sqr(Mg) in the plot, is √Mg

Onyeanuna et al.; JGEESI, 19(1): 1-24, 2019; Article no.JGEESI.32939

Table 9. Source-rock deduction summary of reasoning for Owerri groundwater samples [57]

Sample designation Orogwe Naze Orji Ikenegbu Obinze Result Parameter Attention Value Conclusion Value Value Value Value Value (Na/(Na+Cl) >0.5 Sodium source other than 0.5249 0.5071 0.5289 0.5141 0.5024 Sodium source other than halite - albite, ion exchange halite (albite), 0.5 Halite solution <0.5, TDS >500 Reverse Softening, seawater <0.5, TDS <500 and >50 Analysis Error <0.5, TDS <50 Rainwater Ca/(Ca+SO4) 0.5 Gypsum dissolution 0.7847 0.8013 0.7445 0.7931 0.7713 <0.5, and pH <5.5 Pyrite oxidation Calcium source other than <0.5, and pH neutral Calcium removal - ion gypsum - carbonate or exchange or calcite silicates precipitation >0.5 Calcium source other than gypsum - carbonate or silicates TDS >500 Carbonate weathering or 49.60 46.30 44.70 44.80 42.60 Silicate weathering brine or seawater <500 Silicate weathering HCO3-/Sum >0.8 Silicate or carbonate 0.562 0.511 0.485 0.455 0.417 Seawater or brine Anions weathering <0.8 sulfate high Gypsum dissolution <0.8 sulfate low Seawater or brine

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