interpretation of groundwater quality using statistical techniques … · 2018. 3. 5. · world...

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( Received 18 February 2018; Accepted 04 March 2018; Date of Publication 05 March 2018 )

WSN 95 (2018) 124-148 EISSN 2392-2192

Interpretation of Groundwater Quality Using Statistical Techniques in Federal University, Otuoke

and Environs, Bayelsa State, Nigeria

C. D. Abadom and H. O. Nwankwoala*

Department of Geology, Faculty of Science, University of Port Harcourt, Nigeria

*E-mail address: [email protected]

ABSTRACT

This study aims at assessing and interpreting groundwater quality using statistical techniques in

Otuoke and environs, Bayelsa State, Nigeria. Fourteen (14) groundwater samples were collected in the

rainy season and analyzed for their physico-chemical and heavy metal contents. Heavy metals were

analyzed using Atomic Adsorption Spectrometer. Assessment for drinking purposes revealed that the

water is predominantly acidic, with iron and manganese contents exceeding regulatory guidelines in

most locations. All other parameters were within WHO and NSDWQ regulatory limits for safe potable

water. Water Quality Index revealed that over 73% of the groundwater in the area (11 samples) had

good to excellent quality; while the remaining 27% of the groundwater (3 samples) have poor to

unsuitable quality for consumption. Assessment of water quality for irrigation purposes was achieved

using Sodium Adsorption Ratio (SAR), Potential Salinity (PS), Permeability Index (PI), Sodium

percentage (Na%), Kelly’s ratio (KR), and Magnesium Adsorption Ratio (MAR). On average SAR

(4.19), PI (68.51%), MAR (37.45%) and PS (0.77) revealed excellent water quality, whereas Na%

(66.46%) revealed doubtful water quality while KR (2.00) revealed unsuitable water quality. Using

Piper and Stiff diagrams, hydrochemical facies defined from groundwater in the area includes; Na+K

– Cl facies; Na+K - Mg – Cl facies; and Na+K - Ca – Cl facies. Gibb’s diagrams revealed that the

dominant control on the hydrochemical facies and overall groundwater quality in the area has been

attributed to precipitation and chemical weathering of subsurface rocks. Various ionic ratios including

Mg/Ca (0.642), HCO3ˉ/Cl (0.040), (Na+K)/Cl (7.026) and Cation Exchange Values (-6.026) revealed

low salt inland origin with respect to provenance. Pearson correlation matrices showed both positive

and negative inter-relationships between the physico-chemical and heavy metals in groundwater

within the study area. This study has proven the effective use of water quality index as a tool for

defining the overall quality of water in Otuoke and its environs, along with hotspots that needs

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immediate attention. The results could also serve as a decision making tool that will aid in

establishment of treatment facilities to improve the quality of water in the study area.

Keywords: Groundwater quality, water quality index, potable water, hydrochemistry

1. INTRODUCTION

Water is not only essential for life, but also one of the most significant factors in

determining the quality of life of humans. Groundwater is one of the most refined forms of

water available in nature. It is a valuable natural resource and an important source of water for

agriculture and domestic use. Groundwater is a preferred source of drinking water in most

developing countries including Nigeria because of its higher quality, and unlike surface water,

it is less vulnerable to contamination (Oborie and Nwankwoala, 2014). Groundwater quality

is determined by the solutes, flow paths and soil gases dissolved in the water, as well as the

matter suspended in and floating on the water. Hence, groundwater quality is a consequence

of the natural physical and chemical state of the water as well as any alteration factors that

may have occurred as a consequence of human activity and microbial activities in soils

(Hwang et al., 2017).

The quality of groundwater is of vital concern, since it is directly linked with health and

human welfare. Ranjana (2010) clearly stated that the quality of public health depends greatly

on the quality of groundwater. Groundwater in the preferred source of potable water in the

Niger delta, because it is less prone to contamination as a result of its natural filtration

(Agbalagba et al., 2011). Although groundwater quality is more preffered when compared to

surface water, its quality is the sum of natural and anthropogenic influences (Chapman, 1996).

Water quality parameters reflect the level of contamination in water resources and show

whether water is suitable for human consumption, irrigation and/or industrial usage. Drinking

contaminated water is unacceptable because of its adverse health effects (Suthra et al., 2009).

In the last decade, Bayelsa State has witnessed a continuous influx of companies and

people due to the oil exploration and exploitation activities. Though, Bayelsa State is

surrounded by water, it lacked the quality for human consumption due to pollution occasioned

by the activities of the multi-national oil companies. Recently, illegal bunkering and crude oil

refining activities by the locals had aggravated an already bad case. This is further

compounded by the non-availability of municipal water supply, compelling most residents to

depend largely on boreholes or hand-dug wells for their domestic water supply. Bayelsa State

is located within the transition zone of the Coastal sedimentary lowlands hydro-geologic

province in Southern Nigeria. The area is underlain by a thick series of sedimentary rocks.

The consequence is that the area has thus been taken for granted as a sustaining source

of good quality groundwater. The general approach to water supply however, is

indiscriminate sinking of boreholes without preliminary geological, geo-physical and

hydrogeological investigation. This has generally resulted in very low success rate in that

many boreholes are abandoned due to high iron content, seasonal or temporally functional

boreholes. Also, due to paucity of relevant studies in the area, the subsurface geological

structures have not been adequately studied, and thus lack adequate knowledge of the

groundwater quality variation in the area.


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In addition to rapid urbanization, waste generation have increased, hence a common

feature in the area is that refuse dumps are ubiquitous. Additionally, the uncontrolled location

and leakage of facilities most especially underground storage tanks of petroleum products,

septic tanks of various households and shallow subsurface piping facilities are other potent

sources that can provoke permanent damage of the underlying aquifers. This suggests that the

ground water is susceptible to pollution if there is leakage of buried underground storage

tanks thereby releasing organic contaminants or infiltration of leachate from decomposed

refuse dumps. The need therefore arises to evaluate the protective capacity of the overburden

materials in the area in order to establish the level of safety of the hydro-geologic system

within the area. Therefore, it becomes obligatory to undertake a groundwater hydrochemical

survey in the area to ascertain its quality for drinking, domestic use and other purposes. The

results of this study will serve as a guide for government agencies, researchers and other

development organizations like NGO’s to develop strategies, policies and institutional

infrastructures to provide quality and accessible groundwater resources to the affected

communities in the area.

2. THE STUDY AREA

Figure 1(A). Map of Bayelsa State showing the study area and sample locations.


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Figure 1(B). Map of Bayelsa State showing the study area and sample locations.


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The study area Federal University Otuoke and environ is located within the lower

section of the upper flood plain deposits of the sub-aerial Niger Delta (Allen, I965).

Geographically, it lies between latitudes 4°46’N and 5°51’N and longitudes 6°15’E and

6°23’E (Fig. 1(A,B). The area is bounded on the North by Yenagoa, the capital of Bayelsa

State and on the south by Brass and Nembe local government areas of Bayelsa State, to the

West by southern Ijaw and Ahoada-west local government areas of Bayelsa State and Rivers

State respectively. The area can be accessed from the north by the Mbiama-Yenagoa road and

on the south by the Nembe and Brass Rivers. Most part of the area is motor-able; hence there

is a network of roads that links the different parts of the area.

Geology/Hydrogeology of the Study Area

Figure 2. Stratigraphic column showing the various stratigraphic units of

the Niger Delta basin.


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The study area lies in the coastal Niger Delta sedimentary basin. The geology of the

Niger Delta has been described in details by various authors. The formation of the Delta

started during Early Paleocene and resulted mainly from the buildup of fine grained sediments

eroded and transported by the River Niger and its tributaries. The Tertiary Niger Delta is a

sedimentary structure formed as a complex regressive offlap sequence of clastic sediments

ranging in thickness from 9,000 - 12,000 m. Starting as separate depocenters, the Niger Delta

has coalesced to form a single united system since Miocene. The Niger Delta is a large and

ecologically sensitive region, in which various water species including surface and sub-

surface water bodies exist in a state of dynamic equilibrium (Abam, I999). Stratigraphically,

the Niger Delta is sub-divided into Benin, Agbada and Akata Formations in order of

increasing age (Fig. 2).

The Benin Formation is the water bearing zone of the area (Nwankwoala, 2013). It is

overlain by quaternary deposits (40-I50 m thick) and generally consists of rapidly alternating

sequence of sands and silty clays with the latter becoming increasingly more prominent

seawards (Etu-Efeotor and Akpokodje, I990). The clayey intercalations within the Benin

formation have given rise to multi-aquifer system in the area (Etu-Efeotor and Akpokodje,

I990). The first aquifer is commonly unconfined while the rest are confined. The study area

has been noted to have poor groundwater quality due to objectionable high concentration of

certain groundwater parameters and encroachment of saltwater or brackish water into the

freshwater aquifers (Nwankwoala & Udom, 2011) The static water level in the area ranges

from 0-2 m during the rainy season and 1-3 m during the dry season (Nwankwoala and

Daniel, 2016). The main source of recharge is through direct precipitation where annual

rainfall is as high as 3000 mm (Amajor and Ofoegbu, I988). The water infiltrates through the

highly permeable sands of the Benin Formation to recharge the aquifers. Groundwater in the

area occurs principally under water table conditions (Udom and Amah, 2006).

3. METHODS OF STUDY

3. 1. Groundwater Sampling

Groundwater samples were collected from fourteen (14) boreholes in Federal University

of Otuoke and its environs during the rainy season. The boreholes utilized for this study were

selected from eight communities at random. Both private and public water sources were

sampled in this study. Sterilized water bottles were used to collect representative water

samples to prevent contamination. At each borehole location, the sample bottles were washed

and rinsed thoroughly with the sample water before being sampled. The samples were

collected close to the well head to maintain the water integrity. The boreholes were allowed to

flow for about 3 minutes to ensure stable conditions before samples were collected. The bottle

was filled to the brim with the sample water, and the lid immediately replaced to minimize

oxygen contamination and escape of dissolved gases. Sampling was done using two sets of

prelabelled bottles of one litre capacity for ionic and heavy metals analysis respectively.

Water samples for the determination of cations were stabilized by adding few drops of diluted

HCl to them after collection. To maintain the integrity of the water samples, physico-chemical

parameters sensitive to environmental changes such as pH, conductivity and temperature were

measured and recorded in-situ using portable digital meters. The co-ordinates of all the

sampling locations were recorded using a Garmin 78 model Geographic Positioning System


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(GPS). The samples were later transported to the laboratory in an ice chest for chemical

analysis. Table 1 shows the borehole sampling locations along with the geographic cordinates.

3. 2. Analytical Methods

The quality parameters were analyzed using the American Public Health Association

(APHA, 1989) and American Standard for Testing Materials (ASTM, 1969) standard

procedures. The detectable limit of the AAS was set at < 0.001 mg/l for the heavy metals.

Table 1. Borehole sample locations within the study area

S/N Borehole location Sample

code Latitude Longitude

1 Kolo1(State Secondary School) BH1 04° 48′ 27.2″ 06° 22′ 31.7″

2 Otuoke 1 (skill acquisition centre) BH2 04° 48′ 04.8″ 06° 19′ 24.8″

3 Otuoke 2 (community hospital) BH3 04° 47′ 38.4″ 06° 18′ 43.3″

4 Fuo 1 (vice-chancellor’s lodge) BH4 04° 47′ 27.8″ 06° 19′ 51.8″

5 Fuo 2 (registrar’s lodge) BH5 04° 47′ 39.4″ 06° 19′ 50.8″

6 Fuo 3 (business centre) BH6 04° 47′ 41.0″ 06° 19′ 28.1″

7 Fuo 4 (student hostel) BH7 04° 47′ 35.6″ 06° 19′ 42.6″

8 Kolo 2 BH8 04° 48′ 38.1″ 06° 22′ 36.2″

9 Kolo 3 BH9 04° 47′ 51.6″ 06° 22′ 35.0″

10 Efriwo BH10 04° 48′ 11.4″ 06° 18′ 49.6″

11 Otuaba BH11 04° 47′ 06.0″ 06° 18′ 46.9″

12 Abaye BH12 04° 47′ 10.0″ 06° 18′ 30.9″

13 Elabio BH13 04° 47′ 34.9″ 06° 19′ 18.5″

14 Obruba BH14 04° 46′ 34.2″ 06° 16′ 30.0″

Heavy metals were determined using an Atomic Absorption Spectrophotometer (AAS)

as described in APHA 3111B and ASTM D3651. This involved direct aspiration of the

sample into an air/acetylene or nitrous oxide/acetylene flame generated by a hollow cathode

lamp at a specific wavelength peculiar only to the metal programmed for analysis. For every

metal investigated, standards and blanks were prepared and used for calibration before

samples were aspirated. Concentrations at specific absorbance displayed on the data system

monitor for printing. The equipment limit of detection is <0.001 mg/L.


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3. 3. Water Quality Index Determination

Water quality index (WQI) gives an overall assessment of the water quality in any given

area. Eighteen parameters were utilized in calculating WQI for the study area. Each parameter

was assigned a given weight (wi) based on the perceived health effect or the importance of the

parameter on the overall water quality for drinking purposes (Vasanthavigar et al., 2010).

Parameters that were considered not to be harmful to health were assigned a value of 1 while

parameters that had the most impact on health were assigned a value of 5. Based on overall

impact, other parameters were between 1- 5. The method of WQI determination in this study

was based on Dhakad et al., (2008). The method involves first calculating the quality of the

parameters (qi) as follows;

(1)

where: qi – quality rating of each parameter for n number of samples

va – value of parameter as obtained from laboratory analysis

vs – value of parameter obtained from WHO water quality standard

The relative weight (Wi) was calculated as follows:

∑ (2)

WQI was determined as follows:

∑( ) (3)

The WQI was then used to classify the water quality in the area based on data from

Vasanthavigar et al., (2010) as follows; 0-25 (Excellent), >25 – 50 (Good), >50 – 75 (Poor),

>75 – 100 (Very poor), > 100 (Unsuitable for drinking purposes).

3. 4. Irrigation Water Indices

Various indices were used to determine the quality of groundwater for irrigation in the

study area. The various indices are discussed in the following sub-headings.

3. 5. Sodium Adsorption Ratio (SAR)

The SAR was calculated after Richards (1954) as follows:

√( )

(4)

All parameters are in meq/L.


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3. 6. Magnesium Adsorption Ratio (MAR)

The MAR was calculated after Raghunath (1987) as follows:

(5)


3. 7. Kelly’s Ratio

The KR was calculated after Sundaray et al., (2009) as follows:

(6)


3. 8. Sodium Percentage (Na%)

The Na% was calculated after Wilcox (1955) as follows:

(7)


3. 9. Permeability Index (PI) The PI was calculated after Doneen (1964) as follows:

(⌊( √ )⌋ ⌊( )⌋) (8)


3. 10. Potential Salinity (PS)

The PS was calculated after Doneen (1954) as follows:

√ (9)


3. 11. Statistical Analysis

Microsoft Excel (2016 Edition) was used for the construction of histograms, scatter

plots and descriptive analysis. Statistical software for social science (SPSS, ver. 22) was used

for developing correlation matrices and determining inter-relationships. Rockware (ver. 15)

was used to generate spatial variation maps and flow direction map. ArcGIS (ver. 2010.3) was

used to generate the map of the study area.


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4. RESULTS AND DISCUSSION

Groundwater temperature in the study area ranges from 24.60 to 29.5 °C with mean of

27.31±1.12 °C and variance of 1.25 (Table 2). Groundwater pH which is a measure of acidity

or alkalinity, ranges from 4.78 to 7.01 with mean, standard deviation (SD) and variance of

6.27±0.56 and 0.32. The highest pH values were obtained from BH7 (7.01) and BH8 (6.83)

whereas the lowest pH was obtained at BH3 (4.98) (Table 2). This shows that the water in the

area is predominantly acidic. The EC ranges from 53.20 to 130.30 μS/cm with mean of

94.81±22.12 μS/cm and variance of 489.13. The high standard deviation and variance shows

that there is wide degree of variability in the EC of the groundwater resources in the area.

Groundwater turbidity ranges from 3.71 to 5.14 NTU, with mean, SD and variance of

4.37±.46 NTU and 0.21 respectively (Table 2). Total soluble solids ranged from 4.72 to 13.02

mg/L while hardness ranged from 32.0 to 61.0 mg/L. Water is said to be hard when it contains

large amount of dissolved salts, such as calcium and magnesium ions. Total Dissolved Solids

ranges from 4.11 to 92.10 mg/L with mean, SD and variance of 36.02±23.30 and 542.92

respectively (Table 3). Alkalinity ranged from 10.34 to 12.01 mg/L with mean and SD of

11.19±0.35 mg/L. Table 3 shows the results of statistical analysis for measured parameters in

the area along with regulatory guidelines while Table 4 is the results interpretation of the

various groundwater quality models for the study area.

Table 2. Results of physicochemical and heavy metals in groundwater from the study area

Parameters Units

BH1 BH2 BH3 BH4 BH5 BH6 BH7

Kolo 1 Otuoke1 Otuoke2 Fuo 1 Fuo 2 Fuo 3 Fuo 4

Temperature °C 27.50 27.10 27.30 27.20 27.30 27.2s0 27.10

pH

6.31 6.52 4.98 6.71 6.53 6.21 7.01

Conductivity μS/cm 53.20 118.70 96.30 73.00 75.00 90.50 83.60

Turdidity NTU 3.75 4.73 4.16 5.00 5.14 3.71 4.77

TSS mg/L 10.60 6.27 13.01 12.75 4.72 5.89 5.99

TDS mg/L 22.82 13.51 27.56 12.75 33.55 21.06 4.11

Chloride mg/L 23.89 26.71 14.33 15.74 19.51 41.31 25.04

Bicarbonate mg/L 3.00 0.40 1.60 0.90 0.80 0.90 1.94

Hardness mg/L 51.00 32.00 35.00 37.00 39.00 50.00 61.00

Calcium mg/L 25.00 23.10 28.31 26.02 24.10 23.03 26.40

Magnesium mg/L 7.82 9.33 9.91 8.88 8.30 7.91 8.33

Sulphate mg/L 0.09 0.03 0.05 0.06 0.03 0.07 0.04

Phosphate mg/L 5.01 0.03 0.06 0.01 0.02 0.07 0.05


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Alkalinity mg/L 10.90 10.83 10.44 11.02 12.01 11.05 11.02

Iron mg/L 0.07 0.11 1.25 10.00 0.11 0.56 0.00

Nitrate mg/L 0.07 0.20 0.10 0.06 0.03 0.04 0.01

Sodium mg/L 100.00 102.00 111.00 103.00 93.00 112.00 96.00

Manganese mg/L 0.01 0.12 0.15 0.16 0.11 0.10 0.15

Potassium mg/L 4.20 1.47 1.55 0.76 1.20 1.43 4.65

Lead mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Copper mg/L 0.01 0.003 0.002 0.006 0.035 <0.001 0.021

Barium mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Cobalt mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Arsenic mg/L 0.0012 <0.001 <0.001 <0.001 <0.001 0.0012 0.0011

Boron mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Table 2(continue). Results of physicochemical and heavy metals in groundwater from

the study area

Parameters Units

BH8 BH9 BH10 BH11 BH12 BH13 BH14

Kolo 2 Kolo 3 Eferiwo Otuaba Abaye Elabio Obruba

Temperature °C 29.50 28.20 25.90 24.60 27.40 28.30 27.70

pH

6.83 5.76 6.72 6.90 5.73 6.22 6.77

Conductivity μS/cm 120.40 130.30 81.30 98.40 94.50 87.70 124.50

Turdidity NTU 3.99 4.55 4.21 4.75 3.88 4.55 4.29

TSS mg/L 4.73 12.01 6.77 8.91 11.11 13.02 10.02

TDS mg/L 68.00 92.10 53.50 40.10 36.30 40.57 38.30

Chloride mg/L 23.90 19.30 16.03 17.89 39.33 47.80 31.51

Bicarbonate mg/L 1.60 0.92 2.50 1.20 4.80 1.60 0.90

Hardness mg/L 49.00 37.00 32.00 39.00 53.00 50.00 46.00

Calcium mg/L 29.01 29.01 28.10 30.01 14.99 55.03 44.41

Magnesium mg/L 11.12 11.12 13.14 11.01 15.05 7.93 10.22

Sulphate mg/L 0.09 0.09 0.03 0.02 0.01 0.06 0.07

Phosphate mg/L 0.21 0.21 0.04 0.05 0.07 0.04 0.01

Alkalinity mg/L 11.60 11.60 10.34 11.00 11.08 11.88 11.92

Iron mg/L 0.09 0.12 0.32 0.12 0.06 0.01 0.41

Nitrate mg/L 0.03 0.02 0.05 0.03 0.11 0.21 0.15


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Sodium mg/L 100.00 101.00 101.00 103.00 102.00 102.00 98.00

Manganese mg/L 0.10 0.91 0.12 0.10 0.15 0.17 0.12

Potassium mg/L 1.80 2.62 2.50 1.80 2.25 2.13 4.00

Lead mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Copper mg/L 0.011 <0.001 0.013 0.01 <0.001 <0.001 <0.001

Barium mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Cobalt mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Arsenic mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Boron mg/L <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Table 3. Results of statistical analysis for measured parameters in the area along

with regulatory guidelines

Parameters Minimum Maximum Mean SD Variance WHO

(2011)

NSDWQ

(2007)

Physical parameters

Temperature 24.60 29.50 27.31 1.12 1.25 NA NA

pH 4.98 7.01 6.37 0.56 0.32 6.5-8.5 6.5-8.5

Conductivity 53.20 130.30 94.81 22.12 489.13 1250.00 1000.00

Turdidity 3.71 5.14 4.39 0.46 0.21 5.00 5.00

TSS 4.72 13.02 8.99 3.18 10.09 NA NA

TDS 4.11 92.10 36.02 23.30 542.92 1200.00 500.00

Hardness 32.00 61.00 43.64 8.92 79.63 500.00 150.00

Alkalinity 10.34 12.01 11.19 0.53 0.28 400.00 NA

Cations and Anions

Sodium 93.00 112.00 101.71 5.00 24.99 200.00 200.00

Potassium 0.76 4.65 2.31 1.19 1.41 55.00 200.00

Magnesium 7.82 15.05 10.01 2.14 4.59 50.00 30.00

Calcium 14.99 55.03 29.04 9.77 95.36 75.00 75.00

Chloride 14.33 47.80 25.88 10.46 109.34 250.00 250.00

Bicarbonate 0.40 4.80 1.65 1.15 1.33 600.00 NA

Sulphate 0.01 0.09 0.05 0.03 0.00 500.00 100.00

Phosphate 0.01 5.01 0.42 1.32 1.75 5.00 NA

Nitrate 0.01 0.21 0.08 0.07 0.00 50.00 50.00


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Heavy metals

Iron 0.00 10.00 0.95 2.63 6.90 0.30 0.30

Manganese 0.01 0.91 0.18 0.21 0.05 0.20 0.20

Copper <0.001 0.04 0.01 0.01 0.00 1.00 1.00

Lead <0.001 <0.001 <0.001 <0.001 <0.001 0.01 0.01

Barium <0.001 <0.001 <0.001 <0.001 <0.001 0.30 0.30

Cobalt <0.001 <0.001 <0.001 <0.001 <0.001 1.00 1.00

Arsenic <0.001 <0.001 <0.001 <0.001 <0.001 0.05 0.01

Boron <0.001 <0.001 <0.001 <0.001 <0.001 0.30 0.30

Table 4. Results interpretation of the various groundwater quality models for the study area

Classification scheme Categories Range

(mg/L)

Percent of

Samples

Number of

samples

Sodium adsorption ratio

(SAR)

Excellent <10 100 14

Good 10-18 0 Nil

Fair >18-26 0 Nil

Poor >26 0 Nil

Hard >200-300 0 Nil

Very hard >300 0 Nil

Sodium Percentage

(Na%)

Excellent up to 20 0

Nil

Good >20-40 0 Nil

Permissible >40-60 14 2

Doubtful >60-80 86 12

Unsuitable >80 0 Nil

Permeability Index

(PI)

Excellent > 75 0 Nil

Good 25-75 100 14

Unsuitable < 25 0 Nil


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Magnesium adsorption ratio

(MAR)

Acceptable <50 93 13

Non acceptable >50 7 1

Kelly's ratio

(KR)

Suitable <1 0 Nil

Unsuitable >1 100 14

Potential soil salinity

(PS)

Excellent to good <5 100 14

Good to injurious 5-10 0 Nil

Injurious to

unsatisfactory >10 0 Nil

4. 1. Groundwater Classification and Genesis

Groundwater classification in the study area was achieved using Piper (1944) and Stiff

(1951) diagrams.

4. 2. Piper Diagram

The piper's trilinear diagram is useful for geochemical evaluation and it was used to

determine the hydrochemical facies of the groundwater in the study area (Fig. 3). On the

graph, the major cations are presented on the lower triangle to the left while anions are

presented on the lower right triangles, respectively. The hydrochemical facies are plotted on

the diamond shape. The diagram revealed two hydrochemical facies; Na+K – Cl water type

and Ca – Mg water type.

4. 3. Gibbs Diagram

Gibbs diagram of Na+

+ K+/(Na

+ + K

+ + Ca

2+) versus TDS (Fig. 5a) and Clˉ/(Clˉ +

HCO3ˉ) versus TDS (Fig. 5b) were used to determine the mechanism controlling groundwater

hydrochemistry. The plots revealed that precipitation was the main controlling factor that

governed the groundwater quality in the area, along with some contribution from chemical

weathering of subsurface rocks.

4. 4. Stiff Diagram

The objective description of the hydrochemical properties of groundwater in the area

was supported by Stiff diagram (Fig. 6a,b). Diagrams with similar shapes are believed to have

similar hydrochemical properties and similar origin. Three distinctive shapes were

recognized; i) Na+K – Cl water type; which includes BH1 to BH11; ii) Na+K - Mg – Cl water

type, which include BH12, and; iii) Na+K - Ca – Cl water type, which includes BH13 and

BH14. Figure 4.10 is a map showing the distribution of water types in the study area based on

stiff diagrams.

The ionic concentrations in were in the order; Na > Ca > Mg > K, and Cl > PO4 > HCO3

> SO4 > NO3. Schoeller diagram which is a graphical presentation of cations and anions

shows that cations predominate over anions in the groundwater (Figure 4).


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4. 5. Correlation Matrices

Pearson’s correlation method was used to determine the inter-relationships amongst the

physico-chemical and heavy metals in groundwater of the study area (Table 5). A correlation

coefficient (r) of +1 indicates that two variables are perfectly related in a positive linear sense,

but r = -1 indicates a negative linear correlation. However, no relationship between two

variables exists if r = 0. Strong positive inter-relationships exist between EC and TDS (r =

0.537), TDS and Mn (r = 0.668), TH and K (r = 0.570), TH and Cl (r = 0.593), Mg and HCO3

(r = 0.575), Cl and NO3 (r = 0.523), EC and Mn (r = 0.498), TDS and Mg (r = 0.477), while

strong negative inter-relationships exist between pH and TSS (r = -0.564), pH and Na (r =

-0.565), turbidity and HCO3 (r = -0.536), Na and alkalinity (r = -0.511), EC and PO4 (r =

-0.517), Na and K (r = -0. 412), turbidity and Na (r = -0. 481) and between turbidity and PO4

(r = -0. 416). The positive inter-relationships suggest that the pairs of concerned ions

originated from common source whereas negative inter-relationships suggest dissimilar

origin. Cross plots reveal that the total dissolved solids in groundwater in the area are

dependent on the water conductivity. As TDS increases, so does the EC of the water. Very

weak negative correlation exists between pH and temperature (Table 5), while no significant

trend was found between sodium and chloride.

Table 5. Pearson’s correlation coefficients for groundwater samples in the study area

pH

EC

Tu

rb

TS

S

TD

S

TH

Alk

Ca

Mg

Na

K

Cl

HC

O3

SO

4

NO

3

PO

4

Fe

Mn

pH

1

EC

-.078

1

Tu

rb

.355

.001

1

TS

S

-.564

*

-.052

-.042

1

TD

S

-.166

.537

*

-.146

.090

1

TH

.167

-.202

-.350

-.100

-.234

1

Alk

.20

5

.29

5

.27

0

-.046

.33

0

.28

3

1


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Ca

.130

.190

.147

.337

.197

.072

.490

1

Mg

-.166

.340

-.263

.075

.477

-.171

-.234

-.301

1

Na

-

.565

*

.062

-.481

.318

-.100

-.180

-.511

-.096

.004

1

K

.215

-.063

-.245

.010

-.047

.570

*

.046

.190

-.049

-.412

1

Cl

-.071

.068

-.364

.059

-.116

.593

*

.383

.341

-.098

.142

.109

1

HC

O3

-.251

-.350

-.536

*

.200

.005

.436

-.290

-.315

.575

*

-.040

.328

.225

1

SO

4

-.059

.155

-.343

.164

.353

.180

.311

.306

-.396

.098

.230

.037

-.261

1

NO

3

-.200

.193

-.026

.357

-.213

-.100

.115

.485

-.067

.118

-.056

.523

-.019

-.124

1

PO

4

-.041

-.517

-.416

.143

-.126

.242

-.150

-.125

-.280

-.096

.459

-.059

.340

.422

-.059

1

Fe

.096

-.273

.342

.370

-.300

-.256

-.145

-.091

-.153

.160

-.404

-.307

-.205

.082

-.078

-.109

1

Mn

-.338

.498

.174

.321

.668

**

-.223

.231

.045

.182

-.022

.018

-.147

-.193

.317

-.203

-.194

-.032

1

*. Correlation is significant at the 0.05 level (2-tailed).

**. Correlation is significant at the 0.01 level (2-tailed)

5. CONCLUSIONS

The assessment of groundwater quality in the area based on physicochemical and heavy

metals has shown that water is fairly good for consumption and irrigation purposes, but fit for

industrial use. The groundwater quality at the vicinity of the Vice Chancellor’s lodge is most

deteriorated. Also the dominant control on the groundwater quality in the area has been

attributed to precipitation and chemical weathering of subsurface rocks.

Sodium adsorption ratio, Permeability index, Kelly’s ratio and Potential soil salinity

reveals that all the groundwater samples are in excellent condition and can be used for

irrigation purposes. Sodium percentage reveals that 14% (2 samples) of the groundwater

samples are permissible, while 86% (12 samples) of the groundwater samples are doubtful for


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irrigation purposes. Magnesium Adsorption ratio reveals that 93% (13 samples) of the

groundwater samples are good for irrigation while the remaining 7% (1 sample) is unsuitable

for irrigation. Kelly’s ratio shows that all the water samples are unsuitable for irrigation.

Overall assessment of the water quality on the basis of Water Quality Index (WQI)

revealed that over 73% of the groundwater in the area (11 samples) had good to excellent

quality; while the remaining 27% of the groundwater (3 samples) have poor to unsuitable

quality for consumption. The water quality in the vicinity of the Vice-Chancellor’s lodge

shows the most unsuitable conditions and are defined in this study as hotspots that needs

immediate attention.

Hydrochemical facies defined from groundwater in the area includes; Na+K – Cl facies;

Na+K – Mg – Cl facies; and Na+K – Ca – Cl facies. The dominant control on the

Hydrochemical facies and overall groundwater quality in the area has been attributed to

precipitation and chemical weathering of subsurface rocks.

Various ionic ratios including Mg/Ca, HCO3ˉ/Clˉ, (Na+K)/Cl and CEV shows an inland

origin for the groundwater with respect to provenance. Pearson correlation has also shown the

inter-relationships between the physico-chemical and heavy metals in groundwater within the

study area.

From the research findings, the following recommendations were proffered;

1. Groundwater pH should be treated with sodium bicarbonate in order to reduce the

acidity. Iron can be removed through the process of filtration.

2. The borehole situated at the vicinity of the Vice-Chancellor’s lodge should be shut-

down until remediation is completed.

3. Constant monitoring and quality assessment on the groundwater is necessary to ensure

that groundwater in the area is within regulatory requirements.

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Figure 3. Piper Trilinear diagram showing the water type in the area


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Figure 4. Schoeller diagram showing the concentration of major cations and anions in

groundwater


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Figure 5(a). Gibbs plot of Na+

+ K+/(Na

+ + K

+ + Ca

2+) vs TDS for the groundwater samples


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Figure 5(b). Gibbs plot of Clˉ (Clˉ + HCO3ˉ) versus TDS for the groundwater samples


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Figure 6(a). Stiff diagram showing the various distinct shapes for the groundwater samples

in the study area


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Figure 6(b). Stiff diagram showing the various distinct shapes for the groundwater samples

in the study area

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