Spatial and temporal variation in groundwater quality in Makurdi sedimentary
formation, Nigeria.
Ocheri Maxwell1(Lecturer)Corresponding author
1 Department of Geography, Benue State University,P.M.B .102119,Makurdi,Nigeria
Mile Iyange I2 (Lecturer)
2 Department of Social and Environmental Forestry, University of Agriculture,
Makurdi,Nigeria.
Abstract
This study examines the spatial and temporal characteristics of groundwater quality in
Makurdi sedimentary formation.A total of 15 water samples were collected from hand
dug wells and analysed for physico-chemical concentrations as they affect the quality of
drinking water for both wet and dry seasons.The analysis was done according to standard
method of water examination and reported in WHO guide limit for drinking water.The
results of analyses show that PH, total dissolved solids,turbidity, iron , chromium and
nitrate have concentrations in these wells above WHO prescribed limit for drinking
water. The concentrations of all the parameters analysed vary spatially across the
residential area and among the seasons.Parameters whose concentrations were higher in
the wet season include PH,turbidity, electrical conductivity, chloride,iron,
calcium,chromium,nitrate and Biochemical oxygen Demand. This suggests season has a
strong influence on the concentration level of the physico-chemical parameters on the
quality of groundwater in Makurdi area. Other factors identified to influence the quality
of groundwater in the study area include geology of the environment, location of well
close to soakaway, use of chemical fertilizers on farms, indiscriminate dumping of refuse
and lack of protection of the well. Water generally from these hand dug well is not safe
for drinking except some form of treatment is carried out.
Introduction
Groundwater make up 95% of the world’s available water resources and constitutes the
main source of drinking water for a large percentage of the world
population(Rajagopal,1978;Shiklomanov,1993;UN/WWAP,2003)..In many parts of the
world groundwater is generally considered to be ready available, good quality source of
water for drinking and for agricultural uses. However, increasing demands, significant
changes in land use pattern, climate change,and vast industrial effluent entering the
hydrological
cycle
stresses
the
quality
and
quantity
of
groundwater(Mackey,1990).Beside, the natural geology and geochemistry of the
environment in addition to providing beneficial nutrient and bioessential elements to
groundwater, also give rise to undesirable or toxic properties through deficiency or
excess of various elements(Edmund and Smedley,1996).
In Nigeria, the pressure of urbanization characterized by high degree of
population densities and concentration of socio-economic activities is fast threatening
the quality of life
and urban infrastructural services as observed by these
authors(Mabogunje,1986;Adebayo
and
Rowland,1973;Onokerhoraye,1995;Ocheri,2006.Urban water supply in Nigeria is one of
the most problematic issues inhabitants contend with almost on daily basis. The public
water supply is generally inadequate and in most cases inaccessible, the supply is
intermittent and unreliable,thus resulting in high dependency on unsafe supplementary
sources such as streams, ponds and hand dug wells(Ayoade and
Akintola,1980;Ezenwaji;1990;Ocheri,2004).
Hand dug wells are systems through which groundwater is abstracted at relatively
shallow depths.They are constructed using simple implements such as diggers, hoes, The
are common in most households in Nigeria urban areas.In Makurdi town, due to the
general inadequacy and inaccessibility of public water supply well over 85% of the
inhabitants rely on water from hand dug wells. Hand dug wells are generally more
vulnerable to pollution because of their shallow depths and landuse change/land cover.
Consumers of water from these wells stands a high risk of water related diseases. This
concern has attracted studies on quality of water in different parts of Nigeria(Ovrawah
and
Hymore,2001;Ogunbadewa,2002;Ehinola
and
Coker,2002;Nnodu
and
Ilo,2002;Alexander,2008;
Jatau,Bajeh
and
Innocent,2008;Olobaniyi
and
Owoyemi(2006);Omofonmwam and Eseigbe2009;Adebo and Adetoyinbo,2009). In this
study, attempt is made to assess the spatial and temporal characteristics of groundwater
quality in an urban setting. While most studies focused on the quality of groundwater in
general, the spatial and temporal dimension is not given attention.
The Study Area
The study area is Makurdi town, the capital city of Benue state in the North C
entral Nigeria. Makurdi lies between Lat. 7O 44N and Long.80 54N .It is located within the
flood plain of lower River Benue valley.The physiographic characteristics span between
73m to 167m above sea level. Due to the general low relief sizeable portions of Makurdi
is water logged and flooded during heavy rainstorms. This is reflected in the general rise
in the level of groundwater in wells during dry seasons.The drainage system is
dominated by River Benue which traverse the town into Makurdi North and South banks.
Temperatures are generally high throughout the year due to constancy of
insolation with the maximum of 320 C and mean minimum of 260C.The hottest months
are March and April.The rainfall here is convective,and occurs mostly between the
months of April and October and is derived from the moist and unstable southwest trade
wind from St. Helena subtropical anticyclones(STA).Mean annual rainfall total is
1190mm and ranges from775mm to 1792mm.Rainfall distribution is controlled by the
annual movement and prevalence of inter-tropical discontinuity(ITD).The mean monthly
relative humidty varies from 43% in January to 81% in July-August
period(Tyubee,2009).
The geology is of cretaceous sediments of fluvio-deltaic origin with well-bedded
sandstones of hydrogeological significance in terms of groundwater yield and
exploitation (Kogbe et al 1978).Makurdi town which started as a small river port in 1920
has grown to a population of 297,393 people (NPC,2006).
Materials and Methods
Data for this study generated from the analyses of water samples collected from
hand dug wells across the residential area of Makurdi town.Two sets of water samples
were collected from 15 hand dug wells in the months of September for the wet season
and January for the dry season. Parameters analysed in the water sample include
PH,alkalinity, acidity,total dissolved solids,turbidity,electrical conductivity,Biochemical
oxygen Demand,Nitrate, chloride,iron,calcium,cadmium,chromium To ensure quality
assurance, adequate measures such as the use of sterilized containers in water sample
collection, proper preservation and storage at temperature of 40 before laboratory
analyses.
The analyses of the water samples were based on the principles and procedures as
specified in the
standard methods of water examination(APHA-AWWAWPCF,1985).The techniques includes titrimetric, flame photometer and Atomic
Absorption spectrophotometer UNICAM Sp 6-550 model was used to determine the
ionic concentrations in water sample. PH and electrical conductivity were determined
using Jenway meters model,titrimetric method was used for total dissolved
solids,chloride,nitrate,biocmical
oxygen
demand
determination;
iron,calcium,cadmium,chromium were determined using Atomic Absorption
spectrophotometric technique.Water samples (1000ml) were acidified with 103 of
concentrated nitric acid and concentrated to 25cm3 using evaporation method. After
chelation,extraction and subsequent minerialization, these element were determined using
AAS.The instruments were operated as per instrument’s manual. The blank was used for
zeroing the instruments before each analysis. The result of analyses is presented below
for discussion.
Results and discussion
The physical and chemical characteristics of groundwater from hand dug wells
inMakurdi is presented in Tables 2 and 3.Seasonal variation in physico-chemical
characteristics is presented in Table 4 and WHO drinking water guide value in Table 1.
Table 1: Quality criteria for drinking water
Quality characteristics
WHO Guide value
PH
7-9.2
Total dissolved solids(TDS)
500-1,500
mg/l
Turbidity(TB)
5-25
FTU
Electrical conductivity(EC)
750-2,500
μmhos/cm
Chloride(Cl)
200-600
Mg/l
Iron(Fe)
0.1-1.0
Mg/l
Calcium(Ca)
75-200
Mg/l
Cadmium(Cd)
0.01
Mg/l
Chromium(Cr)
0.05
Mg/l
Nitrate(No3)
45
Mg/l
Biochemical Oxygen Demand(BOD)
6
Mg/l
Source: World Health Organisation Drinking water guide value(2006)
Table 2: Values of physico-chemical parameters of hand dug wells for the wet season
Code PH
W1
W2
W3
W4
W5
W6
W7
W8
W9
W10
W11
W12
W13
W14
W15
5.9
6.6
6.9
6.8
6.9
5.7
6.4
5.8
6.2
5.7
6.1
6.5
6.3
6.9
6.3
TDS
mg/l
440
260
1,200
180
360
1,800
1,700
660
420
280
220
520
580
380
1,860
TB
mg/l
188
56
120
144
84
164
150
132
168
42
85
33
228
136
282
EC
nhos
450
320
850
390
390
940
790
500
300
150
200
310
470
420
980
Cl
mg/l
38
115
126
61
29
158
245
81
23
140
28
129
19
17
25
Fe
mg/l
0.22
0.12
0.01
0.10
0.06
0.08
0.00
0.26
0.17
0.11
0.03
0.11
0.32
0.06
0.07
Ca
mg/l
6.4
12.2
8.5
18.8
112.3
27.5
20.8
3.3
10.7
135
106
17.3
24.5
0.75
0.66
Cd
mg/l
0.00
0.00
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
0.00
Ch
mg/l
0.45
0.20
0.40
0.31
0.01
0.76
0.58
0.40
0.49
0.31
0.53
0.41
0.20
0.35
0.18
No3
mg/l
50
48
46
58
62
85
148
40
49
43
120
87
36
128
132
BOD
mg/l
2.2
0.6
1.8
2.8
1.3
3.3
3.6
2.8
1.3
0.4
0.2
0.6
2.5
1.7
0.8
Table3:Values of physico-chemical parameters of hand dug wells for the dry season
Code PH
W1
W2
W3
W4
W5
W6
W7
W8
W9
W10
W11
W12
W13
W14
W15
5.3
6.0
7.0
6.9
6.3
5.0
6.0
5.8
6.3
6.0
6.6
6.8
6.2
7.0
6.5
TDS
mg/l
665
450
1,448
610
810
1,950
1,813
560
600
80
528
520
800
590
1,388
TB
mg/l
170
60
135
156
113
170
150
186
88
53
66
48
193
110
120
EC
μhos/c
480
350
600
460
520
930
840
350
300
200
250
340
470
500
800
Cl
mg/l
28
21
99
49
30
120
180
68
44
115
19
98
14
23
28
Fe
mg/l
0.05
0.03
0.10
0.06
0.09
0.01
0.14
0.18
0.07
0.08
0.04
0.09
0.23
0.05
0.07
Ca
mg/l
6.3
18.1
13.6
23.1
72.8
24.1
16.4
5.4
14.3
76
68.8
22
48.6
9
15
Cd
mg/l
ND
0.00
ND
ND
ND
ND
ND
ND
ND
0.02
ND
ND
ND
ND
0.02
Ch
mg/l
0.38
0.18
0.35
0.32
0.13
0.68
0.55
0.43
0.45
0.26
0.43
0.44
0.31
0.31
0.30
No3
mg/l
39
40
47
60
53
66
89
33
35
45
98
80
40
110
115
BOD
mg/l
0.8
0.3
2.3
2.2
1.5
2.2
2.4
1.9
0.9
0.6
0.8
0.5
1.3
1.0
1.3
Table4:Summary of
wells
Wet
Parameters
Min
PH
5.7
TDS
180
TB
33
EC
150
Cl
17
Fe
0.00
Ca
0.66
Cd
ND
Ch
0.09
No3
36
BOD
0.20
seasonal variation of physico-chemical parameters of the hand dug
Max
6.9
1,860
282
980
245
0.66
135
ND
0.76
148
3.6
Season
Dry
Mean CV(%) Min
6.3
6.6
5.0
724
83
80
134
51
48
497
53.3 200
82
82.1 14
0.15 107.6 0.01
33
132
5.41
ND
ND
ND
0.37 46.1 0.13
75
51.0 33
1.7
63.8 0.03
Max
7.0
1,950
193
930
180
0.23
76
ND
0.68
115
2.4
Season
Mean CV(%)
6.2
9.4
854
63.0
121
40.2
492
44.2
62
78.9
0.08 67.7
28
85.6
ND
ND
0.36 37.7
63.3 44.9
1.33 53.3
ND-Not detected
From Tables 2 and 3, physico-chemical parameters whose concentrations in hand dug
wells exceeded WHO prescribed limit for drinking water include PH, total dissolved
solids,turbidity,iron, and chromium.Other parameters such as electrical conductivity,
chloride, calcium,and cadmium are within the guide limit.
The PH of water in the wells were below the WHO minimum limit of 7 for
drinking water.The mean PH of 6.3 and 6.2 were recorded for wet and dry seasons. The
water is more less acidic both in the wet and dry seasons.The acidity here may result
from presence of organic acids as well as hydrolyzing salts such as ironII and aluminium
suphate.The water in hand dug well will contribute to corrosiveness of materials.
TDS in water has not been proved to have health implications,rather it is found to
affect the palatability of drinking water.Water with TDS is rated by panel of tasters as
follows: Excellent TDS less than 300mg/l;good TDS 300-600mg/l;fair 600-900mg/l;poor
900-1,200mg/l;unacceptable greater than 1,200mg/l.Based on this rating water in hand
dug wells in Makurdi may generally be classified as good. However, there exceptions to
this ,as there are some wells with TDS of 1,800mg/l(W6),1,700mg/l
(W7),1,860mg/l(W15),1,448(W3),1,950mg/l(W6),1,813mg/l(W7),1,388mg/l(W15)
above WHO guide maximum limit of 1,500mg/l which are completely unacceptable.
Most of these wells are located within wadata and High level residential of Makurdi and
they fall in high density area.High TDS in these wells may originate from natural
sources,sewage, urban and agricultural run-off,and industrial wastes.Water with high
TDS may be objectionable to consumers owing to the resulting taste and to excessive
scaling of in water pipes, heaters,boilers, and household appliances.
All the hand dug wells in Makurdi have turbidity concentrations far above the
WHO guide limit of 5-25FTU for drinking water.Turbidity is not an inherent property of
water as temperature and PH,the recognition of turbidity as indicator of environmental
health of water bodies has increased over the past decade,resulting in a growing demand
water for high quality and objective measurements.The cause of high concentrations of
turbidity in Makurdi hand dug wells may traced to the presence of suspended and
dissolved matter,such as clay,silt, finely divided organic matter. Makurdi geology is
predominantly sandstone with high infiltration properties of permeability and
porosity.Stormwater discharge easily percolate into these wells thereby polluting
them.People that ingest water with high level of turbidity stand a very high risk of
developing gastrointestinal diseases.
Few wells have iron concentrations above the WHO guide limit of 1.0mg/l for
drinking water. Iron in water is perceived more as aesthetic contaminant rather than a
health problem.However, health problem may arise if communities decide not to use
improved supplies because of staining ,taste and return to old polluted
sources(MacDonald, et al,2005).Water from wells have been rejected as result of
excessive iron concentrations due to coloration effects on cooking utensil and
food(Peligba et al,1991;Gyan-Boaky and Dapaah-Siakwam,1991).
From Table 2and 3, 80% of the wells have nitrate concentrations above WHO
prescribed limit of 45mg/l for drinking water in wet season,and 67% of the wells for the
dry season.This implies that consumers of water from these well stand very high risk of
metheamoglobinea (blue-baby syndrome).The causes of high nitrate concentrations in
these well is attributed to urban agriculture using chemical fertilizers, improper disposal
of human and animal wastes, and soak ways.
For cadmium there was no detection in any of the wells .Four wells have
chromium concentration above the WHO guide limit for drinking.This may be attributed
to mineral leaching and waste incineration.
From Table 4,physico-chemical parameters all showed variation among the seasons.
PH range from 5.70 -6.9, with a mean of 6.3 and CV of 6.67% for the wet season
as against 5.0-7.0, mean of 6.2 and CV of 9.46% for the dry season. From the CV the
season variation of PH is less in the wet season than the dry season. However, the water
is still acidic.
Total dissolved solids have a range , mean,and CV for the wet season as
follows:180-1860mg/l; 65.8;83.2% and 80-1,950mg/l,mean of 854mg/l and CV 63.0%
for the dry season.
Turbidity has a mean of 134 and CV 51%for wet season and mean of 121,CV
40%. Water is more turbid during wet due precipitation, stormwater discharge /run off
activities. They infiltrate in most cases to pollute groundwater sources. Since water is
tapped at shallow depths these well are highly vulnerable to pollution.
The mean conductivity and CV is 497and 53.3% for wet season as against a mean
of 492 and CV 44% for dry season. The coefficient of variation suggest a homogenous
environment.
Calcium concentrations in well have a mean of 82,and CV of 82.1% for wet
season and a mean of 62 and CV of 78.9%. Calcium levels in hand dug well are higher in
the wet season than the dry season. This may be attributed to the influence of rainwater in
contact with calcium rich rocks like limestone that can lead to water hardness.
Iron has a mean and CV of 0.15and 107.6% for wet season and a mean of 0.08
and CV 67.7%. Iron concentrations in wells vary widely in the study area.
The mean and CV of chloride for wet season are 33 and 132% and a mean of 28
and CV 85.6% for the dry season. Wide variation in calcium concentration in wells
suggests the influence of season. Chloride concentrations in well may be traced to saline
intrusion as the study area is located at River Benue Valley.
From the analyses cadmium could not be detected in the hand dug wells.
Nitrate has a mean of 75, CV 51% for wet season as against a mean of 63.3% and
44.9% for dry season. Nitrate level in hand dug wells are higher in season than in the dry
season. Agricultural run off is believed to be the major cause of nitrate in these well as
urban farming using chemical fertilizers is practiced in the study area.
Biochemical Oxygen demand has a mean of 1.7 and CV63.8% for wet season as
against a mean of 1.33 and CV53.3%. BOD is higher in wet season than in the dry
season.
Implication of the study
This study has shown that water from hand dug wells in the study area is not safe for
drinking. For instance, elevated concentrations of nitrate in well above WHO prescribed
limit for drinking poses serious health implications especially children. The same goes
for chromium. Using water from hand dug wells for drinking in the study will require
some form of treatment. Characteristics of these well shallow in respect of depths.
location close to soakaways, pit latrines , refuse dumps can contribute to pollution of the
water.
Conclusion
Hand dug well although very common in the study area are of health risk to consumer of
water from them.This there therefore require close monitoring of the quality of water
from these hand dug wells to avoid water related epidemics. Sanitary surveillance of
these waterpoints is very essential. The public should be enlightened on the danger of
using water for drinking from these wells.
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Suggested referees
Prof. R.N.C Anyadike , Department of Geography, University of Nigeria, Nsukka.
Prof. O.Ekanade, Department of Geography,Obafemi Awolowo University,IleIfe,Nigeria.
Prof.O.Osibanjo, Department of Chemistry, University of Ibadan, Nigeria
Prof. S.K.A Danso, Director, EcoLab, University of Ghana