Preliminary Study of Groundwater Quality Using Hierarchical Classification Approaches for Contaminated Sites in Indigenous Communities Associated with Crude Oil Exploration Facilities in Rivers State, Nigeria

Background: Groundwater is an important source of water. Since the control and removal of pollution are expensive, it is essential to identify the possible sources of contamination and to correctly classify groundwater on the basis of its intrinsic and integrated vulnerability. Objectives: To group ground water chemical ions and heavy metals parameters into similar groups. Method: The investigation made use of standard analytical procedures. All sampling, conservation, transportation and analysis followed standard procedures described in APHA (2012). To prevent degradation of the organic substances, all obtained samples were transferred to the laboratory, while kept in an ice-box. Results: Sampling records from the same area are generally assigned to the same cluster during hierarchical cluster analysis (HCA). The cluster diagram shows the grouping of the heavy metal in the study area during wet and dry seasons. It reveals that 5 distinct clusters were identified for wet season and 4 clusters were identified during dry season. Also, it reveals that 5 distinct clusters were identified for wet season and for dry season, 4 distinct clusters were identified. Conclusion: The findings of this study are significant for po-licymakers and agencies in terms of dealing with the issues identified to enhance sustainable livelihood practices in the oil rich Niger Delta region of Nigeria. Therefore, decision-makers should take proper initiatives to get local people aware of the endangered zones before use, as drinking water is key to good health. Similarly, multinational oil companies will find quest for viable social corporate responsibility and remediation plans in their respective host communities. The method proved to be a useful and objective tool for environmental planning.


Introduction
Approximately half of the world's population is affected by one or more of the six major diseases linked to water supply and sanitation at any one time 1) Diarrhea caused by a number of microbial and viral pathogens in food and water; 2) Ascaris; 3) Dracunculiasis; 4) Hookworm; 5) Schistosomiasis, all by infestation with various worms leading to disability, morbidity and sometimes death; 6) Trachoma caused by a bacterium, leading to blindness) [1]- [16]. In the underdeveloped world, almost 400 children under the age of five die every hour from watery diarrheal illnesses [16]. Longevity, decreased infant mortality, improved health, productivity, and material well-being are all considered benefits of development [1] [2]. In general, the inhabitants of developing nations do poorly on these indicators when compared to those of industrialized countries. The availability of abundant and safe water for residential use, as well as proper sanitation to dispose of waste, has long been recognized as critical to development, with advantages such as increased labor productivity extending across all sectors [3] [4] [5] [6] [7] [9] [10] [11] [12] [14]. Increased rivalry among water users for dwindling supplies of unpolluted water may be linked to water quality issues [17]- [25]. Pollutants can be human-made (such as salinization, microbiological contamination, eutrophication, excess nutrients, acidification, metal pollutants, toxic wastes, saltwater contamination, thermal pollution, and increases in total suspended solids) or natural pollutants (like fluoride as well as arsenic) [3] [4] [5] [8] [11] [12] [15] [16]. In highly populated areas where water is scarce and wastewater treatment is inadequate, poor water quality is progressively limiting agricultural and commercial growth [1] [2]. Water pollution has a negative impact on agricultural productivity and poses a health risk to fish, other aquatic life, especially humans [4] [5] [17] [18].
As a consequence of the ineffective and inefficient public water provision in the Ebocha-Obrikom region of Rivers State, which is caused by non-operational public water stations across the LGA, rural inhabitants resort to other sources of water like private boreholes for drinking and other domestic purposes [17]- [25].
This phenomenon has led to the proliferation of all kinds of water vending enterprises most of which do not meet the purification standard, thereby predis-  [12] [13] [16]. As groundwater (GW) quality remain crucial for indigenous population of Nigeria's oil rich communities, their health, food system, societal stability and welfare [17]- [25]. While groundwater is extremely important as a life-sustaining factor, in view of this, an effort has been made for grouping heavy metals parameters into similar groups in Ebocha-  [25]. This result is of great significance for insightful guidelines on domestic and management for agricultural activists, policymakers, as well as water managers. Also, it would provide pollution prevention and control of gas flaring and oil spillage in the core Niger Delta region of Nigeria.

The Study Area [Niger Delta-Ebocha-Obrikom Geology]
Geographically the Niger Delta basin is one of the seven sedimentary basins in Nigeria. It is considered as the most significant owing to its petroliferous nature and consequent active hydrocarbon exploration and production operations occurring both onshore and offshore. The Niger Delta basin has three major formations namely, the Agbada, Akata and Benin Formations. The Benin Formation is the uppermost consisting of considerable amounts of non-sea sand predominantly sandstone together with deposits of gravels [60]. The formation contains negligible amounts of hydrocarbon [61]. The Agbada Formation lies beneath the Benin formation and overlies the Akata Formation. The formation encompasses reservoir rocks and seals [61]. The Akata Formation, which is at the base is about 7000 m thick and consists of basically clay and shale. The formation is rich in organic matter and is believed to be the major rock generating hydrocarbons in the study area.

Field Sample Collection
The sampling strategy employed for the current research investigation was similar to that utilized by Morufu and Clinton [25]; Raimi and Sabinus [24]; Olalekan et al. [23] in which sampling was targeted in some vulnerable quarters at a densely populated location. These quarters are places predisposed to all kinds of contamination not only because of their geographical situation but also because of the presence of crude petroleum exploration and exploitation. From the sample location (see Table 1 below), extracted water samples from groundwater sources utilized mostly for drinking as well as domestic activities. Sample collections were limited to only groundwater from dug wells or shallow pumping wells built for household uses exclusively. The depth of the wells varies between 10 to 28 m, which is a phreatic aquifer. The sampling locations sites were documented using portable GPS mobile devices. In the vicinity of the depot, ground water sources were selected randomly but at various distances from each other for the purpose of this investigation. Furthermore, the samples were manually collected from nine (9)

Sampling, Preservation and Analysis
The standard methods outlined in American Public Health Association (APHA) (2012) [63]; Morufu and Clinton [25]; Raimi and Sabinus [24]; Olalekan et al. [23] have been strictly followed by water sampling, conservation, transportation as well as analysis. In-situ measurements of the following parameters viz: temperature, pH, electrical conductivity (EC), dissolved oxygen (DO), total dissolved substance (TDS), turbidity and total dissolved solids (TDS) were carried out in the field using HANNA water quality checker [63].

Ground Water Collection
For the analyses of physico-chemical parameters, ground water samples were collected using pre-rinsed 1litre plastic containers. Pre-rinsed ground water samples for heavy metal analyses were collected with nitric acid of 1litre containers as well as treated with 2 ml nitric acid (assaying 100%, Trace Metal Grade, Fisher Scientific) prior to storage. These were done to stabilize the metals oxidation conditions. Groundwater samples were collected in two groups of 250 ml glass-stoppered-reagent bottles per sampling location for Biological Oxygen Demand (BOD), and Dissolved Oxygen (DO) determinations. The BOD samples have been properly filled without air trapping as well as the bottles are covered in black polythene bags. This was done to eliminate light, which is present in the samples and capable of producing DO by autotrophes (algae). The BOD samples were incubated for five days, which was added to 2 ml of each sample. In order to retard additional biological activities, Winkler solutions I and II use different dropping pipettes for each sample. The bottles were thoroughly shaken to precipitate the floc, which lay at the bottom of the bottles. Further, Winkler solution I is a solution of manganese sulphate, while solution II is sodium or potassium iodide, sodium or potassium hydroxide, sodium azide (sodium nitride) and sodium hydroxide. The DO samples were collected in clear bottles and also tightly stoppered. With samples of dissolved oxygen preserved on the spot with Winkler I and II solutions similar to that of the BOD samples [63]. All samples had been clearly identified and controlled at 4˚C for easy identification. Determination was carried out on site to know the concentrations of unstable as well as sensitive water quality characteristics including total dissolved solids (TDS), electrical conductivity (EC), pH, alkalinity (Alka.), and temperature (Temp). Thus, the fundamental approaches for investigating the groundwater composition are described in Figure 2 above.

Quality Assurance and Quality Control (QA/QC)
Furthermore, using high purity analytical reagents and solvents, all analytical operations were thoroughly monitored using quality assurance and control methodologies. The instruments were calibrated using calibration standards. The analytical technique validation included the use of procedure blanks, triplicate analysis, as well as the examination of certified reference materials (CRM). The limit of detection (LoD), repeatability, precision, reproducibility, as well as ac-Open Journal of Yangtze Gas and Oil curacy of each organic contaminant in groundwater samples was determined.

Results
The cluster diagram in Figure 3 and Figure 4 show the grouping of heavy metal in the study area wet and dry season.   The cluster diagram in Figure 5 and Figure 6 reveals the grouping of physicochemical parameters in the study area wet and dry season.

Hierarchical Cluster Analysis (HCA) of Groundwater Chemical Variables
Because of inherent toxicity, endurance, and bioaccumulation, heavy metals are the most frequently occurring substances in the environment [ (Figures 3-6). Sampling records from the same region are generally assigned to the same cluster during HCA. The cluster diagram in Figure 3 and Figure 4 show the grouping of chemical ions and heavy metal in the study area for wet and dry season. seasons. Thus, all this is mainly controlled by the geogenic factor and can be corresponded with mineral dissolution and rock-water interactions which regulate the characteristics of groundwater in the study area [88]. While cluster 4 comprised of only Mg. For the physicochemical parameters that had similar characteristics were grouped using dendogram Hierarchical cluster [89]. The parameters were distinctively grouped into clusters and the cluster diagram in Figure 5 and Figure 6 reveals the grouping of some physicochemical parameters in the study area for wet and dry season. Figure 5 reveals that 5 distinct clusters were identified with the following physicochemical parameters in each of the cluster, cluster 1: alkalinity, hardness, this TH is a combination of Ca 2+ and Mg 2+ ions, it is considered as a result of total dissolution of all ions, which gives information on the hardness and degree of quality of groundwater, reflecting a wide variation in geochemical processes prevailing in the present study area.
Therefore, Cluster I is considered as alkalinity and hardness-controlled cluster.
In cluster 2, it was conductivity, DO and COD, showing a result of decaying organic matter and root respiration, which in turn, combines with recharge water.
The higher concentration of conductivity, DO and COD infers a dominance of organic matter and mineral dissolution [90]. Thus, Cluster II is considered as conductivity, DO and COD controlled cluster, acidity was in cluster 3, pH, tur- Radha-Krishnan et al. [91], Praveen et al. [92]; Oparaocha et al. [93] and Basamba et al. [94] which attribute concentration of Ca to anthropogenic activities and natural processes within the aquifers as major sources of groundwater hardiness. Thus, the present study indicates the influence of anthropogenic origin on the aquifer chemistry [95]. Therefore, the excess concentrations of various

Conclusion and Implications of the Study
In addition to the human and environmental consequences, groundwater contamination has a monetary cost in the billions of Naira. As a result, precise and reliable data on groundwater pollution is critical for promoting social health initiatives in Nigeria's oil-rich Niger Delta. The intake of water polluted with physicochemical characteristics might provide a health concern to local residents and surrounding consumers, since drinking water is one of the ways of human exposure to a variety of components. Thus, early monitoring of human sensitivity to environmental pollution is critical for fast action to minimize pollution as well as, the negative health impacts. To regulate and forestall heavy metal toxicity, national collaboration is required to develop successful strategies, policies, and practices through coordinated engagement with all stakeholders in order to achieve an integrated as well as holistic implementation. The present study has successfully carried out an overall suitability assessment by grouping ground water heavy metals parameters into similar groups in the Ebocha-Obrikom Area of Rivers State Nigeria using an integrated Hierarchical Cluster Analysis (HCA) approach. It was found that the quality of water within the study area is degraded owing to elevated levels of heavy metals (such as Cd and Pb); thus, these metals are seen as the main influencers of the poor drinking water quality.
Therefore, the data obtained in the present study could be useful in comparing groundwater resources in oil rich Niger Delta region of Nigeria with groundwaters in different parts of the world. The following highlights are offered after the broad research findings:  Chemometric analysis unveiled that the variation in the hydro geochemistry and water quality within the study area is mainly a result of the influence of both geogenic (weathering and dissolution of silicate and carbonate minerals) and anthropogenic activities such as oil spillage, agricultural and gas Open Journal of Yangtze Gas and Oil flaring activities, which play significant roles in groundwater contamination by physicochemical and heavy metals in the study area. Thus, as it is likely that physicochemical and heavy metals will increase in the groundwater in the future, it is suggested that more research be done to establish the effect of heavy metal bioavailability.  Ensure the mandatory implementation of a detailed Environmental and Health Impact Assessment in the Niger Delta region of Nigeria, while also introducing stringent quality standards for various oil and gas operations.  Ensuring that remedial measures toward mitigating the negative impact of the oil and gas industry are built into the industry creating shared value.  Implement post environmental audits that ensure that the in-built mitigating measures satisfactorily address the anticipated environmental and public health concerns.