International Research Journal of Geology and Mining (IRJGM) Vol. 1 (1) pp. 001-011, November 2011
Available online http://www.interesjournals.org/IRJGM
Copyright © 2011 International Research Journals
Full Length Research Paper
Geology and hydrogeology of Northern Ishan district,
Edo state, Southwestern Nigeria
O.C. Okeke, S.O. Onyekuru*, G. Uduehi and H. O. Israel
Department of Geology, Federal University of Technology, Owerri, Nigeria.
Accepted 23 August, 2011
o
o
o
Northern Ishan District of Edo State, Nigeria, lies between Latitudes 6 41' – 6 5' and Longitudes 6 00' –
o
6 30' and covers an area of about 150 square kilometers. The major towns in the area include Ekpoma,
Irua, Uromi and Ubiaja. Their elevations range from 243.9m (800ft) to 426.6m (1400ft) above mean sea
level. About 14 of the 27 boreholes drilled in the area were abortive. The study investigated the
influence of the local geology on groundwater potential of the area. The geologic formations in the area
are Ameki Formation and Ogwashi -Asaba Formation which consist of sandstone, clay and shale
(Ameki Formation) and sandstone, clay and lignite (Ogwashi - Asaba Formation). Some of the aquifer
characteristics include transsmisivity (average, 9.0 x 10-3 m2/s), storativity (average, 1.85x10-2), yield
(average, 1.42x10-2 m3/s) and hydraulic conductivity (average, 1.47x10-2m/s). Sands of various sizes
constitute the aquifer material in the area. The pH values of 4.80 - 6.00 in some of the borehole water
samples and Fe content of 1.08 - 1.55 mg/l in all the water samples are outside the WHO acceptable
limits of 6.5 - 8.5 and less than 0.3mg/l, respectively, for safe drinking water. The water may be
classified as acidic, soft, and fresh and is generally good for domestic and agricultural purposes.
Key words: Geology, Hydrogeology, Ameki Formation, Ogwashi-Asaba Formation, Aquifer Characteristics,
Water Quality.
INTRODUCTION
The quantity and quality of ground water resources of any
area are controlled by the climate and geology of the
area. The climate through rainfall and surface water
resources ensure constant supply or recharge to
groundwater resources of an area in a complex
hydrological cycle. The geology of the area determines
the aquiferous zones where exploitable groundwater may
occur and influences the geochemical characteristics of
the groundwater, amongst other factors such as human
activities
(Domenico,
1972).
The
geochemical
characteristics of the groundwater in turn influence the
quality of the groundwater resources. Earlier works by
Demenico, and Schwartz (1998), Ahiarakwem and
Ejimadu (2002),
Downey (1984),
Aniya and,
Schoenekeck K (1992), Idowu et al. (1999) and Awalla
and Ezeigbo (2002) have confirmed the influence of local
geology on the aquifer characteristics and quality of
groundwater resources of any area. Human activities
*Corresponding author E-mail: onyekuru2001@yahoo.com
may also influence the quality of groundwater in the area
(Alagbe, 2006).
Northern Ishan District, in Edo State of Nigeria, lies
between Latitudes 6040' - 60 51’ and Longitudes 6000' - 60
30' and covers an area of about 150 square kilometers
(TAHAL, 1977). The distinct feature of the area is its
higher elevation compared to the elevation of the
surrounding towns outside the district. The major towns in
the area include Ekpoma, Irua, Uromi and Ubiaja (Figure
1). The elevation of the towns within the district ranges
from 243.9m (800ft) to 426.6m (1400ft) above mean sea
level while the elevation of surrounding towns including
Benin, Agbor and Auchi ranges from 60.96m (200ft) to
182.88m (600ft) (TAHAL 1977; Figure 2). The area is
accessible through Benin - Auchi and Benin - Agbor
Federal Highways (Figure 2).
The area experiences tropical climate with distinct rainy
and dry seasons that occurs from April to October and
November to March, respectively. The average annual
rainfall in the area is 1704mm with a range of 1562 1867mm for ten years record (Nigeria Meteorological
002 Int. Res. J. Geol. Min.
Figure 1: Location map of the study area
Figure 2: Topographic map of the study area
Okeke et al. 003
Table 1: Stratigraphic sequence of sediments in the study area (Kogbe et al., 1976; Reyment, 1965)
Age
Miocene-Recent
OligoceneMiocene
Formation
Benin Formation
Ogwashi-Asaba
Formation
Eocene
Ameki Formation
Paleocene
Imo Formation
(Imo Shale)
Nsukka Formation
Maastrichtian
Lithology
Thickness (m)
Unconsolidated sandstone with lenses of clay
200
Unconsolidated
300
sandstone and clays with lignite seams
Sandstone, clays and
84
Shales
Blue to gray dark shales and sandstone members
314
Sandstones and shales
Agency, 2007). According to TAHAL (1977), the major
rivers in the area with their flow rates include Ena River
(3.41m3/sec or 2.2 million gallons per hour); Ubiaja River
(0.03 m3/sec or 24000 gallons per hour); Ekpoma River
(0.158 m3/sec or 125000 gallons per hour), and Ugbalo
River (0.214 m3/sec of 170000 gallons per hour). The
groundwater resources comprise the aquifers of the
sedimentary formations in the area.
The population of the area according to the 2005
population record is 834750, and assuming an annual
growth rate of 3% for most towns in Nigeria, the
estimated population of the study area will well be over
1million people in 2010. There have been several efforts
to provide borehole water for this teeming population,
which have led to reports of several cases of abortive
water boreholes in the area. About 14 of the 27 boreholes
(52% drilled in the area were abortive (Federal Ministry of
Water Resources, 1989). It is believed that this is
because of the complex geology of the area. In this study
therefore, the geology and hydrology of the area were
investigated with the aim of evaluating the influence of
local geology on the groundwater resources of the area.
Geology of the study area
According to Reyment (1965), the study area, northern
Ishan District, lies on the southwestern extension of the
Niger Delta Basin which geologically consist of:
a.
Ameki Formation;
b.
Ogwashi -Asaba Formation; and
c.
Various Quaternary Deposits.
The Niger Delta Basin is part of southern Nigerian
Sedimentary Basin. Its origin and evolution have been
discussed by several workers including Horspers (1965),
Burke et al. (1972) and Nwachukwu (1972). The origin is
believed to be linked to a series of tectonic activities that
occurred in the south Atlantic region during the late
Cretaceous times (Murat, 1972).
The Sediments penetrated by the Gbakebo “B” well
located at Okitipupa Ridge on the western flank of Niger
Delta form part of the late Cretaceous and Tertiary
with coal seams
233
sequences of the southern Nigerian Basin (Kogbe et al.,
1976). Deposition of sediments in the Niger Delta Basin
began in the Tertiary and continued into post Tertiary
times. The Niger Delta sediments include Benin, Agbada
and Akata Formations and they range in age from
Eocene to Recent (Short and Stauble, 1967; Asseez,
1976). The Agbada Formation is a down -dip continuation
of Eocene-Miocene Ameki and Ogwashi-Asaba
Formations, while the Akata Formation is a down-dip
continuation of Paleocene Imo Formation (Frankl and
Cordy, 1967).
Table 1 shows the stratigraphic sequence of the study
area and environs as recorded in Gbakebo AB@ well
(Kogbe et al., 1976; Reyment, 1965). Figure 3 shows the
geologic map of the study area.
MATERIALS AND METHODS
The data concerning the geology, hydrology and water
boreholes in the study area were obtained from the Benin
offices of Nigerian Geological Survey Agency, Federal
Ministry of Water Resources/Benin-Owens River Basin
Authority and Edo State Water Board. Table 2 shows
location description of water boreholes in the study area.
Field investigations consisted of visits to some
functional water boreholes in the study area and
collection of water samples (both rainy season, June to
October; and dry season, December) for laboratory
analysis. The chemical characteristics including pH, Total
dissolved solids, major clarion and anions were
measured based on the procedures outlined in Hem
(1970) and APHA (1971).
The Total Hardness (TH) of the sample was
determined with the expression below (Freeze and
Cherry, 1979):
2+
2+
TH = 2.5 (Ca 4.1 (Mg ) .............................. (1)
where TH is expressed in mg/l CaCo3
The Sodium Absorption Ratio (SAR) that expresses the
sodium hazard of the soil was determined using the
expression below (Freeze and Cherry, 1979);
004 Int. Res. J. Geol. Min.
Figure 3: Geological map of the study area
Table 2: Location of water boreholes used in the study
Borehole No.
Uromi 1
Uromi 2
Uromi 3
Ekpoma 1
Ekpoma 2
Ekpoma 3
Irua 1
Irua 2
Ubiaja 1
Amendokien 1
Iruekpan 1
Ugboha 1
Ugboha 2
Description
Central School Compound
Central School Compound
Km 4, Uromi – Ubiaja Road
General Hospital
Ambrose Ali University Campus
Ihumudum Village, Ekpeoma
Town Hall
Central School Compound
Mr Joseph Ikaro Compound
Near motor park (Uzehe Street)
Town Hall
General Hospital
Km 6, Ugboha-Ubiaja Road
Okeke et al. 005
SAR
=
Na+
√ (Ca2+ + Mg2+)/2
……… (2)
RESULTS AND DISCUSSION
Table 3 shows aquifer characteristics of some water
boreholes in northern Ishan District, while Table 4 and 5
show chemical characteristics of groundwater samples in
the area, expressed in mg/l and, in miliequivalent/l,
respectively. Table 6 is a description of groundwater
potential of an aquifer on the basis of trasimissivity
values.
Considering Table 3, the parameters storativity,
transmissivity, yield and hydraulic conductivity are aquifer
characteristics
that
quantitatively
express
the
groundwater resource potential of the area (Davis and
Dewiest 1966; Schwartz and Zhang, 2003; Chatterjee,
2005). These properties are usually controlled by the
local geology of an area. The values obtained in the
-4
study area include transmissivity (range, 1.37x10 -2 2
-3
2
3.14x10 m /s; mean, 9.0 x 10 m /s), storativity (range,
1.05 x 10-4 - 7.41 x 10-2; mean, 1.85x 10-2), yield (range,
2.2 x 10-3 - 4.5 x 10-2 m3/s; mean, 1.42 x 10-2 m3/s) and
hydraulic conductivity (range, 2.74 x 10-6m/s - 1.81 x 103
m/s; mean, 1.47 x 10-3m/s).
The average values and ranges of the aquifer
properties cannot be assigned to particular geologic
formations. However, boreholes with high yield have
generally high transmissivity and storativity values. The
Storativity of most unconfined aquifers range from 1x10-3
- 1x 10-5 (Schwartz and Zhang, 2003). Idowu et al. (1999)
and Aniya and, Schoenekeck K (1992) reported similar
results in multi–aquifer systems in the Dahomey Basin
(southwestern Nigeria) and Bauchi area (northern
Nigeria), respectively.
Table 3 and Figure 4 also show that all the boreholes in
the area have multi-aquifer systems. Moving in eastwest
direction, boreholes at Iruekpan, Ekpoma, Irua Uromi
which geologically lie within Ogwashi-Asaba Formation
have 3 - layered multi-aquifer systems while boreholes at
Ubiaja and Ugboha which geologically lie within Ameki
Formation have 2 –layered multi-aquifer system.
The relatively shallow unconfined aquifer in most of the
boreholes are less than 120m deep while the deeper
confined aquifers in all the boreholes are greater than
120m. The confining layers in boreholes at Iruekpan,
Ekpoma, Irue and Uromi (Ogwashi-Asaba Formation) are
lignite/clays and shales while the confining layers in
boreholes at Ubiaja and Ugboha (Ameki Formation) are
shales and clays.
Figure 5 is the water table map of the area prepared
from the elevation of the static water level of Table 3. The
groundwater flow directions are generally in all the
geographic directions (west-east; east-west; south-north
and north-south). This is evidenced by many springs and
rivers that exist in all the corners of the district/ plateau
(Figure 5).
Considering Table 4, the pH values range from 4.80 to
7.10 (average, 6.28), while Total Hardness, Ca2+, Mg2+,
Fe (total iron), No3 - and CL- and HCO3- values range from
15.36 to 23.17mg/l (average, 19.28mg/l), 2.60 to 3.50mg/l
(average, 2.95mg/l), 2.10 to 3.70mg/l (average,
2.92mg/l), 1.08 to 1.55mg/l (average 1.46mg/l), Nil to
0.03mg/l (average 0.02mg/l) 8.00mg/l to 25.50mg/l
(average 15.16mg/l (and 15.00 to 25.00mg/l average,
18.00mg/l), respectively. Compared with WHO Drinking
Water Standard, (2005), only pH values at Uromi (6.00)
and Iruekpan (5.00) are below the acceptable limits of
6.50 - 8.50; and Fe values in all the water samples (1.08
to 1.55mg/l) are above the acceptable limits of less than
0.2mg/l. The groundwater in the area is generally slightly
acidic (average pH = 6.28). Acidic waters such as the
groundwater of the study area can lead to corrosion of
plumbing materials in water distribution systems. The
high iron content of the water may cause stains on
clothing materials when the water is used for laundry,
however iron generally do not have adverse physiological
effect on humans. The high acidity and high iron content
of the water may be corrected with addition of lime and
aeration, respectively during water treatment processes
(Charttergee, 2005). On the basis of Total Hardness of
less than 60mg/l (Table 7; Hem, 1970), Total Dissolved
Solids of less than 1000mg/l (Table 8; Carrol, 1962) and
Sodium Adsorption Ratio (SAR) of less than 10 in Table 4
(Table 9; Freeze and Cherry, 1979), the groundwater of
the study area may also be classified as soft, fresh and
excellent for irrigation purposes, respectively. SAR values
are used to measure the potential dangers posed by
excessive sodium in irrigation water. According to Davis
and Dewiest (1966), sodium reduces soil permeability
and encourages hardening of the soil. The SAR values of
groundwater in the study area that range from 0.33 to
0.89 (average, 0.63) will not cause any sodium hazard in
the soil, and is therefore very good for irrigation.
The high concentration of Fe and moderate
concentration Ca2+, Mg2+, Na+, Cl- HCO3 are due to the
local geology of the area. Ameki Formation is known for
its content of calcareous shales and high amount of
Fe203, which is a common geologic parameter that
constitute most sediments of southeastern and
southwestern Nigeria. The Na+ and Cl- contents may be
as a result of indiscriminate use of fertilizer in the study
area. The elements may enter the groundwater in
boreholes drilled in relatively unconfined aquifers.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
The underlisted conclusions may be made from the
study:
a.
the geologic formations that underlie the study
006 Int. Res. J. Geol. Min.
Uromi -1
255.8
Uromi -2
280.0
Uromi i -3
228.8
Ekpoma 1
216.4
Ekpoma 2
280.4
Ekpoma 3
289.4
Irua 1
335.0
Irua 2
331.0
Ubiaja 1
225.5
Amendokian
318.5
90.00 -110.00
225.0 -240.00
245.0 – 253.0
85.0 – 120.00
232.0 – 255.0
285.0 – 320.0
224.0 – 259.0
260.0 – 290.0
300.0 – 320.0
40.5 – 60.0
136.0 – 148.0
206.0 – 230.0
50.8 – 81.00
168.2 – 183.4
201.1 – 216.4
155.0 – 192.5
220.0 – 250.0
261.0 – 275.0
70.0 – 120.0
183 – 232.0
285.0 – 320.0
190.3 – 225.0
233.0 – 255.0
40.0 – 60.0
170.0 – 190.0
191.0 – 221.0
70.0 – 110.0
180.0 – 230.0
265.0 – 280.0
-2
19/6/94
335.2
195.2
149.0
215.5
6.01x10
18/7/2000
335.2
190.2
149.2
198.0
7.41x10 -2
18/8/2003
335.2
205.2
130.0
218.2
5.21x10
5/2/84
345.2
188.3
156.9
197.4
9/2/96
345.2
190.0
155.2
3/4/99
345.2
190.0
23/9/2000
426.2
4/9/200
-2
-2
-2
Remarks
Hydraulic
Conductivity (m/s)
Yield (m3/s)
Transmissivity
(m2/s)
Storativity
Depth to Dynamic
water level (m)
(m) (m (m)
Static Water
Elevation level
Depth to Static
water table (m)
Ground Surface
Elevation (m)
Date of
Completion
of Borehole
Aquiferous
Zone (m)
Borehole
Location/No
Total Depth of
Borehole (m)
Table 3: Aquifer characteristics of some water boreholes in Northern Ishan District, Southwestern Nigeria (Compiled from FMWR, 1999 and Uduehi, 2004)
-3
1.03x10
2.30x10
1.0 x10
Abortive
3.14x10-2
1.90x10-2
1.8 x10-3
Operational
-4
-2
-3
1.92x10
1.3x10
1.21 x10
Operational
6.86x10 -3
1.02x10-2
1.x10-2
3.4 x10-4
Operational
200.5
9.75x10 -3
9.63x10-2
16x10-2
1.25 x10-4
Abortive
150.2
200.5
1.24x10
210.3
215.9
230.0
274.3
216.5
209.7
24/8/92
335.2
134.5
16/7/92
335.2
195.0
-2
-2
-2
-4
1.31x10
1.0x10
2.61 x10
Operational
2.68x10 -3
2.65x10-3
1.59x10-2
1.30 x10-2
Abortive
235.0
1.05x15 -2
2.62x10-2
4.50x10-3
1.30 x10-6
Abortive
139.8
172.65
4.44x10
140.2
201.10
3.52x10 -4
-4
-4
-3
-6
1.37x10
3.0x10
2.74 x10
Operational
1.38x10-4
2.2x10-3
3.35 x10-6
Abortive
Okeke et al. 007
Table 3 continue
Iruekpan 1
251.0
Ugboha 1
195.4
Ugboha 2
186.0
Uzea 1
310.0
100.0 – 120.0
140.0 – 160.0
201.9 – 249.0
70.0 – 110.0
142.5 – 182.0
40.00 – 85.0
120.0 – 185.0
60.1 – 110.4
160.0 – 200.0
20/8/87
335.2
135.5
199.7
163.64
1.32x10 -3
2.44x10-4
8.0x10-3
5.08 x10-6
Abortive
21/8/95
252.4
145.1
106.7
161.24
1.05x10 -4
3.36x10-4
1.1x10-2
8.44 x10-6
Abortive
5/2/89
252.4
155.4
87.9
178.04
1.01x10 -2
-
1.6x10-2
-
Operational
6/4/87
426.6
208.3
217.7
220.0
-
-
2.6x10
-2
-
Operational
1.85x10-2
Average
9.00x10-3
1.42x10-2
1.47x10-3
Table 4: Chemical characteristics of groundwater from Northern Ishan District
Parameters
pH
TDS (mg/l)
Total Hardness (mg/l
CaCo3)
Ca2+ (mg/l)
Mg2+ (mg/l)
Na+ (mg/l)
K+ (mg/l)
Fe (Total Iron) mg/l
No3- (mg/l)
Cl- (mg/l)
(So42- (mg/l)
HC03- (mg/l)
Uromi 1
6.00
10600
21.69
Uromi 2
6.80
98.00
15.36
Ekpoma1
7.00
85.00
16.34
Irua 1
6.50
109.00
22.09
Irua 2
6.50
110.00
23.17
3.10
3.40
8.40
0.75
2.53
Nil
25.5
1.00
18.00
2.70
2.10
5.80
0.40
1.49
Nil
23.50
1.00
15.00
2.60
2.40
4.30
0.70
1.50
0.07
12.80
0.50
16.00
3.50
3.40
9.60
1.00
1.49
0.03
7.40
0.40
25.00
3.20
3.70
9.90
1.20
1.50
0.10
8.00
0.60
23.00
Location/Standards
Ubiaja 1 Iuekpan 1 Ugboha 1
6.30
5.0
7.10
87.00
105.00
110.00
16.75
18.89
19.8
2.60
2.50
3.30
0.80
1.35
0.01
14.00
1.00
23.00
2.80
2.90
4.80
0.90
1.48
0.03
10.50
1.00
18.00
2.91
3.00
5.10
0.85
1.08
0.01
23.20
0.80
23.00
Uzea 1
4.80
106.00
19.67
Average
6.28
102.00
19.28
WHO Standard (1984)
6.50 – 8.50
1000.00
100 – 500
3.11
2.90
8.70
1.00
1.34
Nil
11.00
0.80
20.00
2.95
2.92
6.66
0.84
1.46
0.02
15.16
0.79
18.00
75.00
200.00
200.00
200.00
0.3.00
10.00
250
200
500
008 Int. Res. J. Geol. Min.
Table 5: Concentration of the chemical constituents in miliequivalent/l and Sodium Adsorption Ration
(SAR) Values
Location
Uromi 1
Uromi 2
Ekpoma 1
Irua 1
Irua 2
Ubiaja 1
Iruekpan 1
Ugboha 1
Uzea1
Average 1
Ca2+
0.16
0.14
0.14
0.18
0.16
0.14
0.14
0.15
0.16
0.15
Mg 2+
0.28
0.18
0.20
0.28
0.31
0.21
0.24
0.25
0.24
0.24
Concentration in mequile and SAR values
Na+
K+
ClNo3So42- HCo30.37
0.02 0.73
0.02
0.30
0.25
0.01 0.67
0.02
0.25
0.19
0.02 0.37 0.0007 0.01
0.26
0.42
0.03 0.21 0.0005 0.01
0.41
0.43
0.03 0.23 0.0002 0.02
0.38
0.14
0.02 0.40 0.0002 0.02
0.30
0.21
0.02 0.30 0.0005 0.02
0.38
0.22
0.02 0.66 0.0002 0.02
0.38
0.38
0.03 0.31
0.02
0.33
0.29
0.02 0.43 0.0004 0.02
0.33
SAR
0.78
0.63
0.46
0.88
0.89
0.33
0.48
0.49
0.85
0.63
Table 6: Gheorghe Standard for Transimissitivity (T) (Gheorghe, 1978)
Transmissitivity Range
Greater than 500m 2/dy (5.79 x 10-3m2/s)
Between 50 and 50 m2/dy (5.58 x10-3and 7.3910-3x10-3m 2/s)
Between 5 and 50 m2/dy (9.06 x 10-3 and 5.50 x 10-3 m2/s)
Between 0.5 are sm2/dy 5.01x10-3 and 5.58 10-3m2/s
Below .5m2/dy (5.01 x 10-3 m2/s)
Figure 4: Acquire system of natural Ishan District (W – E)
Transmissitivity Potentials
High Potential
Moderate Potential
Low Potential
Very low potential
Negligible flat
Okeke et al. 009
Figure 5: Water table contour map of Nortern Ishan district
Table 7: Classification of water based on Total Hardness (TH)
(From Hem, 1970)
Total Hardness (mg/l) as CaCo3
0 – 60
61 - 120
121 – 180
> 180
Water Class
Soft
Moderately Soft
Hard
Very Hard
Table 8: Classification water based on Total Dissolved
Solids (TDS) (From Carrol, 1962)
Total Dissolved Solids (mg/l)
1 – 1000
1000 – 10,000
> 10,000
Water Class
Fresh
Brakish Saline
Brine
010 Int. Res. J. Geol. Min.
Table 9: Classification of water based on Sodium
Adsorption Ratio (SAR) (From US Salinity Laboratory,
1954)
Sodium Adsorption Ratio
0 – 10
10 – 18
18 – 26
> 26
area, northern Ishan District are Imo Shale, Ameki
Formation and Ogwashi – Asaba Formation; and the
lithology consists of clays, shales, lignites and
sandstones;
a.
all the boreholes drilled in the area penetrated
only Ogwashi-Asaba and Ameki Formations;
.
multi-aquifer systems exist in the area, 3-layer
aquifer system occur in boreholes drilled into the
Ogwashi -Asaba Formation and 2-layer aquifer system
occur in boreholes tapping water from the Ameki
Formation.
d.
all the boreholes have unconfined aquifers (less
than 120m depth) (1st layer in all the boreholes) and
confined aquifer (greater than 120m depth) (2nd and 3rd
layers in some boreholes).
e.
some of the aquifer characteristics include
-2
2
transmissivity (range, 1.37 x 154 - 3.14 x 10 m /s, mean
-3
2
-4
9.0 x 10 m /s), storativity (range, 1.05 x 10 - 7.4 x 10-2,
mean, 1.85 x 10-2), yield (range, 2.2 x 10-3 - 4.5 x 10-2
m3/s; mean, 1.42 x 10-2 m3/s) and hydraulic conductivity
(range, 2.74 x 10-6 - 1.81 x 10-3 m/s, mean 1.47x10-3m/s).
f.
sands and sandstones are the mean aquifer
sediment materials because of their characteristic high
hydraulic conductivity (1.47 x 10-3m/s) and high yield
-2
3
(1.42 x 10 m /s).
g.
the low pH values (4.80 - 6.00) measured in
water samples from some boreholes (at Uromi and
Iruekpan) and high total iron (Fe) values (1.08 -1.55mg/l)
measured in water samples from all the boreholes are not
within the WHO standards acceptable limits of 6.5 - 8.5
and less than 0.20 mg/l, respectively.
h.
The high values of Fe and moderate values of
2+
2
-1
Ca , Mg and HCo3 are traceable to the geology
(mineralogical/chemical composition of the rocks) of the
area; while moderate values of Na+ and Cl- may be due
to use of fertilizers in the area.
i.
The groundwater of northern Ishan District may
be classified as acidic, soft, fresh and excellent irrigation
water on the basis of its pH, Total Hardness, Total
Dissolved solids and SAR values, respectively.
Recommendations
Adequate geological and geophysical investigations
should be conducted prior to drilling of any water
Water Class
Excellent
Good
Fair
Poor
borehole in the area to reduce the incidence of abortive
boreholes.
In order to improve the quality of groundwater from the
area to be used for domestic and industrial purposes, it
should undergo pH correction (by addition of lime) and
iron removal (by aeration), which are aspects of water
treatment to bring their values to fall within acceptable
WHO standards.
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