ENVIRONMENTAL HYDROGEOCHEMISTRY OF THE BENIN FORMATION OF THE PORT HARCOURT, ABA AND OWERRI AXIS IN THE NIGER DELTA, NIGERIA

ABSTRACT

Soil and water pollution are major environmental problems facing many coastal regions of the world due to high population, urbanization and industrialization. The Environmental Hydrogeochemistry of the Benin Formation of the Port Harcourt, Aba and Owerri axis in the  Niger  Delta,  Nigeria  was  investigated  in  this  study.  The  study  area  lies  between latitudes 440IN to 5º40IN and longitudes 6º50IE to 7º50IE covering parts of Port Harcourt, Aba and Owerri a total area of about 12,056 km2. Hydrogeological investigations show that the aquifers in the area are largely unconfined sands with intercalations of gravels, clay and shale. Results of geoelectric sections, boreholes logs and sieve analysis confirm the dominance of sandy horizons in the area. Pumping test results show that the transmissivity ranged between 152.0 m2/day and 2835.0 m2/day with an average value of 1026.0 m2/day while the specific capacity varied between 828.0m3/day and 15314.0 m3/day with a mean value of 6258.0 m3/day. Well discharge ranged between 1624.0 m3/day and 7216.0 m3/day with an average value of 3218.0 m3/day while hydraulic conductivity varied between 3.2 m/day and 478.4 m/d with a mean value of 98.6 m/day. These findings indicate that the aquifer in the area is porous, permeable and prolific in groundwater. The observed wide ranges and high standard deviations and mean in the geochemical data are evidence that there are substantial differences in the quality/composition of the groundwater within the study area. The plot of the major cations and anions on Piper, Durov, and Scholler diagrams indicated six hydrochemical facies in the area: Na-Cl, Ca-Mg-HCO3, Mg-Ca-SO4, Ca-Mg- Cl, Na-Fe-Cl and Na-Fe-Cl-NO3. Heavy metal enrichment index revealed 12 elements in the decreasing order of: Fe > Ni > Cu > Zn > Mn > Cd > V > Co > Pb > Cr > As > Hg. The study identified salt intrusion, high iron content, acid-rain, hydrocarbon pollution, use of agrochemicals, industrial effluents and poor sanitation as contributors to the soil and water deterioration in the area. Saltwater/freshwater interface occurs between 5 m and 185 m while iron-rich water is found between 20 m and 175 m. The first two factors are natural phenomenon  due  to  the  proximity  of  the  aquifer  to  the  Ocean  and  probably  insitu weathering and mobility of marcasite, a sulphite mineral contained in the rock. The occurrences of the marcasite are localized at depths between 150m and 180m. The last four factors are results of various anthropogenic activities domiciled in the area. DRASTICA model, a modification of DRASTIC model was developed and used in the construction of aquifer vulnerability map of the area. Modern sanitary landfill that ensures adequate protection for the soil and groundwater was designed and recommended to replace the existing open-dumpsites. Owing to the monumental and devastating effects of hydrocarbon pollution in the area, the need to eradicate gas flaring and minimize oil spills in the area was advocated. Bioremediation and phytoremediation techniques were recommended to be applied in the clean-up of soils and water contaminated with hydrocarbon in the area. The efficiency of multivariate statistical techniques in evaluating hydrogeochemical data have been demonstrated in this study.

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background

Land  and  water  are  precious  natural  resources  on  which  rely  the  sustainability  of agriculture, industrialization and the civilization of mankind. Unfortunately, they have been subjected to severe exploitation and contamination due to anthropogenic activities resulting from  industrial  effluent,  solid  waste  landfills,  gas  flaring,  oil  spillage  and  petroleum refining leading to the release of heavy metals into the environment (Bellos and Swaidis, 2005; Ahmad, Islam, Rahman, Haque and Islam, 2010). The areas around Port-Harcourt, Aba and owerri are coastal areas which have been experiencing high urbanization and industrialization as a result of exploration and exploitation of the petroleum resources of the areas. It is necessary to undertake a comprehensive study of the hydro-facies of the groundwater system of the region,  to be able to assess the aquifer characteristics and consequently   suggest   remediation   methods   and   processes.    Industrialization   and urbanization of the area necessitated the choice of the study area, considering the impact which various anthropogenic activities may have on the groundwater system of the area. The aquifer system in the area is largely unconfined, highly porous and permeable and the tendency of contaminants infiltrating into the shallow water table is quite obvious. This study has provided the means of identifying and characterizing the contaminants. This research has provided hydrogeologically based aquifer vulnerability map of the area, which is vital in aquifer security, utilization and management.

The increase in groundwater demand for various human activities has placed great importance on water science and management practice world-wide (Nouri, Mahvi, Babaei and Ahmadpour, 2006). Each source of contaminant has its own damaging effects to plants, animals and ultimately to human health, but those that add heavy metals to soils and waters are of serious concern due to their persistence in the environment and carcinogenicity to human beings. Unlike the organic pollutants which are biodegradable (Ammann, Michalke, and Schramel, 2002; Adams, Guzman-Osorio and Zavala, 2008) heavy metal ions are not biodegradable (Bird, Brewer, Macklin, Balteanu, Driga, Serban and Zaharia, 2003; Lee, Li, Zhang, Li, Ding and Wang, 2007), thus making them a source of great concern. Through food chain, the heavy metals bioaccumulate in living organism and reach levels that cause toxicological effects (Kraft, Tumpling and Zachman, 2006; Aktar, Paramasivam, Ganguly, Purkait and Sengupta,2010). Human health, agricultural development and the ecosystem are all at risk unless soil and water systems are effectively managed (Akoto, Bruce and Darko,  2008).  Close  relationship  exists  between  groundwater  quality  and  land  use  as various land use activities can result in groundwater contamination.

Eastern Niger Delta is the operational base of major oil producing and servicing companies in Nigeria. Petroleum exploration and exploitation have triggered adverse environmental impacts in the Delta area of Nigeria through incessant environmental, socio-economic and physical disasters that have accumulated over the years due to limited scrutiny and lack of assessment  (Achi,  2003;  Caerio,  Costa,  Ramos,  Fernandes,  Silveira,  Coimbra,  Painho, 2005). In Nigeria, immense tracts of mangrove forests have been destroyed as a result of petroleum exploitation in the mangroves and these have not only caused degradation to the environment and destroyed the traditional livelihood of the region but have caused environmental pollution that has affected weather conditions, soil fertility, groundwater, surface water, aquatic and wildlife (Olujimi, 2010). If this trend is allowed to continue unabated, it is most likely that the food web complexes in this wetland might be at a higher risk of induced heavy metal contamination. This unhealthy situation continues to attract the interest of environmental observers and calls for evaluation of the impact of exploration and exploitation activities in the coastal areas of Nigeria and these were part of what this research intended to address.

To meet the ever-increasing water demand in the region, groundwater is being extensively used to suppliment the surface water thereby subjecting it to over-exploitation for domestic, agricultural, urban and industrial uses which results in the deterioration of groundwater in coastal areas (Macklin, Brewer, Balteanu, Coulthard, Driga, Howard and Zaharia, 2003). Increasing urbanization is taking place along the coastlines of the Niger Delta and causing increased use of groundwater and it has a large impact on the quality and quantity of groundwater system in the area. The quality of groundwater is measured in terms of its physical, chemical and biological parameters (Sargaonkar and Deshpande, 2003). In many countries around the world, including Nigeria, groundwater supplies may have become contaminated through various human activities, which have impact on the health and economic status of the people. The discharge of untreated waste water, soakaway, pit- latrine as well as agricultural water runoff from farms can all lead to the deterioration and contamination of groundwater in coastal aquifers via infiltration  through the overlying formation (Abdel-Satar, 2001; Adams et al., 2008).

The deterioration of water quality in the coastal region due to saltwater pollution of the freshwater aquifers of Eastern Niger Delta, Nigeria has become a major concern to stakeholders in the water sector (Oteri, 2013). Saltwater pollution is the movement of saline water into freshwater aquifers, which leads to contamination of groundwater sources which in turn leads to waterborne diseases such as typhoid fever, dysentry, cholera, meningitis and diarrhea. Seawater intrusion is a natural process due to the hydraulic connection between groundwater and seawater. Saltwater is denser with low hydraulic head than freshwater because of its higher mineral content and has the capacity to migrate inland below the freshwater (Nwankwoala, 2011; Oteri and Atolagbe, 2003). Human activities such as pumping of groundwater from coastal freshwater wells, construction of canals and drainage networks provide conduits for saltwater to be carried inland (Oteri, 2013). Studies have shown that many of the coastal aquifers in the world already experience salt water intrusion caused by both natural and anthropogenic processes (Kar, Sur, Mandal, Saha and Kole, 2008; Venugopal, Giridharan and Jayaprakasa, 2009). Oteri, (2003) and Nwankwoala, (2011) revealed that boreholes are abandoned along the Nigerian coastlines as a result of saltwater  intrusion.  Some  of  the  identified  causes  include  indistriminate  drilling  of boreholes and uncontrolled abstraction of groundwater. It is therefore necessary to understand the pattern of movement and interaction between the fresh water and the salt water as well as the conditions that can influence these processes. Considering the water resources in areas bordering the ocean such as in Nigeria, the Benin Formation is a major source of groundwater (Karbassi, Nouri and Ayaz, 2007; Vinodhini and Narayanan, 2008). The aquifer constitutes a hydrological unit formed by the alluvial and shallow features as they are spread along the fluvial valley of the basin.

The shallow depth and high permeability of the coastal plain-sand aquifer of Niger Delta has made the groundwater system highly vulnerable to contamination (Amadi and Olasehinde, 2009). According to Amadi, (2007), the Benin Formation of Niger Delta is characterized  by  shallow  water  table,  high  porosity  and  hydraulic  conductivity.  The strategic position of the Niger Delta in the socio-economic activities of Nigeria makes it imperative to have a good knowledge of the groundwater quality status in the area.

With the discovery of oil in Nigeria, more than fifty years ago, there has been no concerted and effective effort on the part of the government, let alone the oil operators, to evaluate and control environmental and health problems associated with the industry while the host communities are on the receiving end. Niger Delta is an oil-rich region with high amount of gas reserves. It covers about 20,000 km² within wetlands of 70,000 km² formed primarily by sediment deposition (Akpokodje, 2001). It is home to over 20 million people and 40 different ethnic groups. This floodplain makes up 7.5% of Nigeria’s total land mass (Nwankwoala, 2005). It is the largest wetland and maintains the third-largest drainage basin in Africa (Adelana, Olasehinde and Vrbka, 2000; Adegoke, 2002). The region sustains a wide variety of crops, economic trees and a variety of fresh water fish than any ecosystem in West Africa. But this region, if care is not taken can lose most of its natural endowments due to uncontrolled gas flaring, oil spillage and poor sanitary situation in the area (Teme, 2002;  World  Bank,  2004).  The  Niger  Delta  is  among  the  world’s  largest  petroleum provinces and its importance lies on its hydrocarbon resources. It has been rated as the sixth largest oil producer and twelfth giant hydrocarbon province (Adegoke, 2002).   The oil sector provides 20% of Nigerian’s GDP and 95% of foreign exchange earnings as well as 75% of budgetary revenues (World Bank, 2004).

The practice of gas flaring and incidence of oil spillage are as old as oil production in Nigeria. In Europe 99% of associated gas (AG) is used or re-injected into the ground but in Nigeria, over 75% of gas production is flared, out of which 95% is associated gas (World Bank, 2004). Statistically, about 2.5 billion standard cubic feet (scf) of gas is flared in Nigeria in a day. This is equal to about 25% of the UK’s daily gas consumption and about 40% of Africa’s daily gas consumption and this amounts to an annual loss of $2.5billion to the Nigerian economy apart from the associated health and environmental hazards. According to the World Bank (2004), more gas is flared in Nigeria than anywhere in the world and flaring in the country has contributed more greenhouse gases to the earth’s atmosphere than all the other sources in Sub-Saharan Africa combined.

From available literature (Odero, Semu and Kamau ,2000; Ngah, 2002; Njenga, 2004; Ofoma and Ngah, 2006; Adekunle, Adetunji, Gbadebo, and Banjoko, 2007; Nwankwoala and Udom, 2008), some of the chemicals released in a flare include benzene, toluene, xylene, naphthalene, styrene, hydrogen sulphide, carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen dioxide, methane, ethane ethylene and acetylene. Most of these chemicals that are released are carcinogenous and have the potentials to cause other health hazards to humans after prolonged exposure while the gaseous components combine with water molecules in the atmosphere to produce acid-rain.

1.2 Statement of the Problem

The impact of hydrocarbon pollution in terms of gas flaring and oil spillage on the environment and health of host communities in Niger Delta, Nigeria is of great concern. The upsurge in human activities due to the presence of oil companies in the area and the propensity of contaminant infiltrating through the porous and permeable formation into the shallow groundwater table has necessitated the study, which is intended to provide useful information on the degree of aquifer contamination resulting from anthropogenic activities in  the  area.  This  is  important  because  the  physical,  chemical  and  bacteriological characteristics of groundwater determine its application, management and remediation processes.    In  view  of  the  economic  activities  domiciled  in  the  region,  it  becomes imperative to undertake a comprehensive study of the effects of human activities on the aquifer/groundwater quality in the area.

1.3 Aim and Objectives of the Research

The study seeks to provide baseline information on the hydrofacies of the aquifer system as well as the suitability of the groundwater in the area for domestic purposes. The specific objectives of this study include:

(i) To carryout geophysical investigation on selected locations in the area in order to obtain lithostratigraphic information on the subsurface geology.

(ii) To determine the hydraulic properties of the aquifer through pumping test and lithological logging of drilled boreholes.

(iii) To carryout laboratory analyses of groundwater, soil, surface water and rainwater samples from the area in order to determine their quality status.

1.4 Justification of the Research

The need to identify, evaluate and categorize the hydrofacies in Eastern Niger Delta is long overdue. For more than 50 years now, petroleum prospection, exploration, exploitation and refining as well as other industrial and agricultural activities have been going on in the area and the impact of these human activities on the environment in general and groundwater in particular has not been determined and this is what this study intended to achieve. No study has provided a platform to evaluate the impact, the various human activities might have on the groundwater system as well as design a pollution control and protection measures that will prevent pollutant coming in contact with groundwater system. The present study is targeted at addressing these deficiencies.

1.5 Study Area Description

The study area lies within the eastern Niger Delta region of Nigeria between latitude

440IN and 5º40IN and longitude 6º50IE and 7º50IE (Figure 1.1). It covers parts of Port- Harcourt, Aba and Owerri and a total area of approximately 12,056 km2. The area is low lying with a good road network system and is drained by Imo, Aba, Kwa-Ibo and Bonny Rivers and their tributaries. The topography is under the influence of tides which results in flooding especially during the rainy season (Nwankwoaloa and Mmom, 2007). The prevalent climatic condition in the area comprises of the rainy (March to October) and dry (November to February) seasons characterized by high temperatures, low pressure and high relative humidity throughout the year. A short spell of dry season referred to as the ‘August break’ is often felt in August and is caused by the deflection of the moisture-laden current. Due to vagaries of weather, the ‘August break’ sometimes occurs in July or September.

Figure 1.1: Map of Niger Delta, Nigeria

(Modified from Weber and Daukoru, 1976)

1.5.1 Physiography

The area is characterized by a fairly flat topography underlain by the Benin Formation and slopes  towards  three  major  rivers  (Imo,  Aba,  Kwa-Ibo  and  Bonny).    It  has  a  gentle elevation that ranges from 40m – 84m above sea level, and the landform is related to the geology of the region. Several gulley erosion sites exist in the area which can be attributed to the friable nature of the coastal plain sand dominant in the area. The slope ranges from 0 to 3% and is generally towards the rivers from north to south. The area is drained mainly by the four perennial rivers and their tributaries and flows north-south joining the Atlantic Ocean (Figure 1.2). There are swampy grounds close to the river channels due to the flat topography.

Figure 1.2: Drainage map of Niger Delta, Nigeria

(After Ibe, Sowa and Osondu 1992)

1.5.2 Climate and Vegetation

The climate of the region is humid and characterized by two seasons; the dry season (November to March) and a rainy season (April to October) although on the average no month of the year is entirely devoid of rainfall. Analysis of the rainfall data of the area shows that the mean monthly rainfall figure of about 172.34 mm with a maximum of about 353.33 mm recorded in September and a minimum of 5.62 mm in December (Etu-Efeotor and Akpokodje, 1990). A high percentage of this rain falls between the months of April and October. The average rainfall is about 2217.29 mm/year, but it averaged 2613.9 mm in 1999 being the maximum to have been recorded over the ten years period (Table 1.1). The mean minimum temperature and mean maximum temperature are 21.3oC and 30.0oC respectively. The dry season temperature could be as low as 17oC, and as high as 34.4oC. On the average the maximum temperature is recorded in November and December and the minimum temperature is recorded in January and February (Tables 1.2 and 1.3). The mean annual evaporation loss is estimated for the area as 969.5mm with the highest monthly evaporation loss of 113.8mm during the dry season and about 89.6mm in the rainy season. The area has an average monthly relative humidity that ranged between 50% and 93% over 24 hours during the day (Edet, 1993; Etu-Efeotor and Odigi, 1983) and between 66.5% and 86.0% (Federal Ministry of Water Resources, Port-Harcourt, 2010; Table 1.4). The average monthly relative humidity by Federal Ministry of Water Resources, Port-Harcourt was adopted in the study because it is recent and from a Federal Government Ministry.

Tropical vegetation is found along streams/river channels and often covers uncultivated farm lands. Due to intense cultivation, grasses are taking over the original tropical forest characteristic of the area. Rodents and reptiles inhabit the grassy areas.  There is abundant sunshine all the year round. The temperature is highest in December and lowest in February due to the harmattan. The dry season in the area is from November to March and is characterized by dry, cold and windy weather, with little or no rainfall. This period in the region is referred to as harmattan and is usually accompanied with dust. Palm trees are very abundant in the area, which is favoured by the abundant rainfall and high temperature. Raffia palms are also grown in the area.  Other crops are bananas, plantain, maize, cassava, yams and cocoyams including various vegetables. Hydro-meteorological data of the area from 1998 to 2007 was obtained from the Federal Ministry of Water Resources, Port- Harcourt (FMWR, 2010) and are summarized in Tables 1.1 to 1.4.

Table 1.1: Summary of monthly rainfall in Eastern Niger Delta from 1998 to 2007

Year/ Month	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007
Jan.	9.07	35.20	0.00	0.00	0.00	15.02	99.01	0.00	0.00	26.00
Feb.	49.04	62.05	20.05	100.00	98.23	2.23	0.08	0.00	15.00	13.02
March	103.18	101.31	72.34	146.05	69.21	98.23	73.67	111.02	185.17	143.07
April	97.02	54.18	106.04	125.29	18.33	122.05	63.79	105.68	133.16	102.06
May	177.41	463.21	131.07	207.37	274.49	174.04	113.51	226.05	351.57	149.44
June	347.63	220.38	275.69	205.49	484.53	256.98	230.64	212.58	321.00	319.21
July	407.98	554.84	218.28	165.46	172.32	296.77	474.01	371.77	285.31	290.02
Aug.	118.33	226.30	260.65	341.75	423.54	386.78	204.81	433.74	211.23	339.87
Sept	444.54	559.85	518.64	513.10	344.53	283.68	355.76	188.33	276.03	448.86
Oct.	131.99	226.30	101.26	74.49	325.05	317.92	293.09	457.66	105.14	211.03
Nov.	70.14	110.34	106.10	47.01	99.25	91.32	153.31	64.33	80.24	124.12
Dec.	0.00	0.00	12.07	5.01	5.01	0.00	0.00	12.02	22.04	0.00
Mean	163.03	217.83	151.86	160.92	192.87	170.42	171.81	181.93	165.49	180.56
Total	1956.3	2613.9	1822.2	1931.0	2314.4	2045.0	2061.6	2183.1	1985.8	2166.7

(Source: Federal Ministry of Water Resources, Port-Harcourt, 2010)

Table 1.2: Monthly minimum temperature (oC) in Eastern Niger Delta from 1998 to 2007

Year/Month	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007
January	18.0	19.0	22.0	17.0	25.0	22.0	22.0	22.0	22.0	19.0
February	22.0	22.0	22.0	22.0	22.0	22.0	21.0	23.0	22.0	21.0
March	22.0	23.0	24.0	21.0	22.0	20.0	22.0	23.0	21.0	21.0
April	21.0	22.0	25.0	22.0	22.0	21.0	21.0	22.0	17.0	21.0
May	22.0	23.0	23.0	21.0	21.0	19.0	19.0	21.0	21.0	22.0
June	21.0	23.0	22.0	22.0	22.0	19.0	19.0	21.0	20.0	21.0
July	18.0	21.0	19.0	21.0	21.0	18.0	21.0	23.0	22.0	22.0
August	24.0	21.0	23.0	22.0	19.0	21.0	23.0	20.0	21.0	18.0
September	24.0	19.0	23.0	23.0	18.0	22.0	22.0	19.0	22.0	20.0
October	21.0	22.0	22.0	24.0	20.0	22.0	22.0	19.0	22.0	21.0
November	21.0	24.0	21.0	24.0	21.0	21.0	23.0	18.0	21.0	22.0
December	18.0	25.0	19.0	23.0	19.0	20.0	22.0	19.0	22.0	22.0
Mean	21.0	22.0	22.1	21.8	21.0	20.6	21.4	20.8	21.1	20.8
Total	273.0	286.0	287.1	283.8	273.0	267.6	278.4	270.8	274.1	270.8

(Source: Federal Ministry of Water Resources, Port-Harcourt, 2010)

Table 1.3: Monthly maximum temperature (oC) in Eastern Niger Delta from 1998 to 2007

Year/Month	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007
January	34.3	32.0	23.2	23.2	29.0	30.0	28.5	29.6	27.6	28.4
February	26.5	32.2	26.0	26.2	28.3	30.2	25.5	30.5	29.5	30.2
March	30.2	31.0	26.2	34.0	29.2	34.0	28.5	32.0	28.6	30.4
April	32.1	31.0	28.3	31.0	30.3	31.6	29.4	29.7	28.8	29.3
May	28.2	30.0	29.4	32.0	29.2	27.6	30.5	25.6	28.4	30.0
June	30.0	27.0	30.2	30.0	28.3	26.5	29.0	28.4	30.2	32.4
July	34.4	28.0	27.0	29.1	30.0	24.2	28.2	26.2	28.4	29.7
August	28.0	29.2	30.0	29.3	28.3	26.0	30.5	27.0	29.3	31.2
September	29.2	32.2	31.0	30.2	30.2	31.3	26.0	27.0	30.3	33.3
October	32.3	26.4	32.2	31.3	34.0	30.4	29.2	26.0	33.2	32.,4
November	32.4	31.0	32.0	33.2	34.0	28.5	28.0	28.4	34.2	34.3
December	32.0	33.3	34.3	35.0	34.4	31.8	30.6	30.5	35.3	34.7
Mean	30.8	30.3	29.2	31.2	30.4	29.3	28.7	28.4	30.3	31.4

(Source: Federal Ministry of Water Resources, Port-Harcourt, 2010)

Table 1.4: Monthly relative humidity in Eastern Niger Delta from 1998 to 2007

Year/Month	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007
January	80.5	77.0	80.5	80.5	79.0	84.5	78.0	77.0	81.0	78.5
February	80.5	78.5	79.0	trace	78.5	85.5	75.5	75.5	77.0	82.5
March	80.0	79.5	79.0	80.0	81.5	66.5	83.0	80.5	73.0	74.5
April	81.0	80.5	72.0	76.5	79.5	84.5	80.5	83.0	75.5	82.0
May	81.0	81.5	81.5	73.5	81.0	81.0	79.5	78.5	76.0	81.5
June	84.0	83.5	78.0	83.5	79.0	82.5	78.5	82.5	79.0	82.0
July	84.5	80.5	82.5	84.5	81.5	85.0	88.0	80.5	82.0	82.5
August	83.0	82.5	86.0	83.0	80.5	80.0	81.0	84.0	82.0	86.5
September	82.0	80.5	80.5	85.0	81.0	80.0	81.0	83.5	83.0	85.0
October	79.5	80.0	79.0	81.0	84.5	81.0	83.5	83.0	84.0	83.0
November	81.0	78.0	78.5	80.5	82.5	80.5	78.0	85.5	83.0	78.5
December	82.0	77.5	79.0	81.5	86.5	81.5	82.0	82.5	84.0	82.5
Mean	81.9	80.0	80.0	80.7	81.3	81.0	80.7	81.3	80.0	81.6

(Source: Federal Ministry of Water Resources, Port-Harcourt, 2010)

1.6 Scope of Present Work

The study involved deskwork during which preliminary assessment of feasibility of the research project and evaluation of existing data on the hydrogeology of the study area were compiled. This was followed by fieldwork which involved collection of data for geological, hydro-geophysical and hydrochemical evaluations. The detail activities of the field study involve:

i) Geological and hydrogeological mapping of the study area in order to have direct and detailed information on the aquifer system in the area. This involved rock unit mapping and logging of exposures, borehole drilling and pumping test.

ii)   Geophysical surveys using Vertical Electrical Resistivity Sounding (VES) were conducted in order to delineate the subsurface geo-electrical variations/sections, depth to the aquifer and pollution (plume) mapping. The underlying factors in the choice of survey points in the study area are:

Spatial distribution Proximity to major waste dumpsite/gas flaring station/flow station and The observed groundwater flow direction.

iii) Borehole well inventory data such as well depth, depth to water table, well location coordinates and elevations.

(iv) Collection of soil, surface water, groundwater and rainwater samples for chemical and microbial analyses. This stage also included in-situ measurement of physical parameters, such as pH, electrical conductivity (EC), total dissolved solids (TDS), and temperature of the sampled geomaterials using standard techniques.

However, due to the constraint regarding generation of all the relevant data needed for complete  evaluation  in  this  type  of  study,  secondary data  were  sourced  from  reliable government agencies, oil companies, chemical industries, hospitals, borehole drilling and water  engineering outfits  to  complement  the  field  data  collected.  These data  were  all subjected to careful and objective analyses, followed by data processing and evaluation using manual, iterative, statistical, and analytical techniques; and the use of specialized computer software suitable for the various analyses.

Hydrofacies determinations are useful for evaluating flow patterns, origins and chemical histories of groundwater masses. They describe bodies of groundwater in an aquifer that differ in their physical, chemical and bacteriological composition. The facies are a function of  the  lithology,  prevailing  climatic  condition,  topography,  residence  time,  solution kinetics, flow pattern of the aquifer and anthropogenic interference (Raghunath, Murthy and Raghavan, 2002; Abdullah, Musta, Aris and Annamala, 2004; Lambarkis, Antonakos and Panagopoulos, 2004). Hydrochemical facies can be classified on the basis of the dominant ions in the facies by means of Piper, Durov, Stiff and Schoeller diagrams. These methods combine chemically similar elements together and large data are usually cumbersome to handle. Their demerits were overcome in this study by the application of principal component analysis (PCA), factor analysis (FA), water quality index (WQI) and a newly evolved DRASTICA model. These geostatistical techniques allow for elemental analysis and interpretation of multiple mixing trends thereby providing greater precision in identifying groundwater hydrofacies and interpreting their sources and this is part of what make this research unique. The study has helped to ascertain the level of aquifer/groundwater pollution in the area and to suggest ways to efficiently utilize and manage groundwater resources while providing the stakeholders with useful information on the aquifer/groundwater vulnerability of the area.

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