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Borehole Logs and Physico-chemical Investigation of Some Presumptive Springs in Akoko, South-western Nigeria

41

treatment needed is determined by the quality of the

groundwater source (Macrea et al. 1993). Research

has shown that rural water wells are not tested as

suggested by professionals, and are contaminated with

pathogens and chemicals from various sources

(Charrois 2010). Some other research has shown that

33% of documented outbreaks of water-related

infections could be attributed to groundwater systems

(Reynolds et al. 2008).

Fieldwork studies have also shown that aquifers

in crystalline basement terrains are highly localized

and are mainly controlled by weathered regoliths, and

secondary porosities resulting from joints and

fractures (Adelusi et al. 2000; Bala and Ike 2001;

Olorunfemi et al. 2001; Abdullahi 2005). The

potentiality of fractured crystalline rocks to store,

transmit and yield appreciable quantity of water

depends on thickness and continuity of fractures

(Bayode 2000). Because of the discontinuous

(localized) nature of basement aquifer, successful

exploitation of groundwater in basement terrains

requires proper understanding of geo-hydrological

characteristics.

The Federal Ministry of Health presented

statistics in 1994 that only about 30% of Nigerians

have access to potable water (Dada and Ntukekpo

1997 while in the same year, United Nations

estimated that 1.2 billion people lacked access to

potable water globally (Oyeku et al. 2001). These

springs are not potable, and to monitor potability and

safety of this water, a physico-chemical analysis must

be assessed to see their conformity with regulatory

standards. This work serves as preliminary assessment

for careful evaluation of physico-chemical analysis of

the springs and boreholes and carries a hope that the

results will provide informative update on the quality

of water from these sources in line with the World

Health Organization (WHO) standards.

This study has applied an electrical resistivity

method (vertical electrical sounding) and physico-

chemical analyses of a selected spring to determine

groundwater subsurface geometry and quality in the

parts of Akoko areas of Ondo state, south-western

Nigeria

2. Geology of the study area

The study area is the selected locations in Akoko

areas of Ondo state, south-western Nigeria as shown

in (Figure 1). The area lies within the Precambrian

basement complex terrain in south-western Nigeria

and has been affected by the Pan African orogeny.

Major lithologic units include the migmatite gneiss

complex which is made up of three main lithologies:

the early gneiss; the amphibolites, the biotite-gneiss

and Pan African granites (Rahaman and Ocan 1978).

Moreover, minor pegmatite vein and quartz vein

intrusions and noticeable geologic structures include

faults, folds and joints. Rahaman (1976) recognized

that the migmatite-gneiss complex might have

resulted from a complex association of a deformative,

shearing, folding, granitization and migmatization

process. A barrovian type of metamorphism has

affected the area and metamorphic grade is from

green schist to amphibolite facies (Rahaman 1989).

Figure 2 shows the location relief map of the study

area indicating longitude, latitude and elevation of the

study areas.

Fig.1. Geological map of Ondo State (Geological survey of Nigeria, Ondo State, 1989)

F

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eva

mp

ndar

oxy

erm

sp

ero d

five

ion

gen

ing

d (A

2–

Fe

2–

ed

olv

ely,

5).

pora

apor

ple

rd m

yge

mine

peci

diss

e di

n of

n de

the

Aph

– S

NH

– S

So

ved

as

atio

rati

of

met

en

ed

fied

solv

sso

f dil

ema

e re

ha

SO4

H2–

SO4

lid

so

s s

1

on d

ing

eff

thod

dem

us

d i

ved

olve

lutio

and

eflu

198

2u

– S

u

(T

olid

spe

00

dish

dis

flue

d (A

man

sing

in a

/

d ox

ed o

on a

(C

ux m

85).

used

SO4

used

TDS

w

cifi

00

h;

sh a

ent

Aph

nd

g

a s

/

xyge

oxyg

and

COD

met

.

d fo

4u

d fo

S).

was

ied

!

and

wa

ha 1

(B

the

stan

en;

gen

d is

D) o

thod

or b

used

r sa

Sam

ev

in

res

as

198

BOD

e u

ndar

n;

giv

of th

d a

lan

d;

amp

mpl

vapo

n a

"

sidu

def

5).

D)

unm

rd

ven

he s

s sp

nk;

ple.

le a

orat

a s

"

ue.

fine

of

mod

me

as:

sam

pec

.

ana

ted

stan

ed a

f th

difie

etho

(1

:

(2

mple

cifie

(3

alys

an

ndar

as

he

ed

od

1)

2)

es

ed

3)

sis

nd

rd

((4)

Borehole Logs and Physico-chemical Investigation of Some Presumptive Springs in Akoko, South-western Nigeria

43

! = 1000! − " (5)

4. Results

Resistivity results show a delineation of three to

four subsurface horizons, namely, the top soil,

weathered basement, fracture basement and fresh

basement. The fractured basement rock aquifers occur

immediately beneath weathered basement rock

aquifers in most places and serves as a main source of

water for the spring within the study areas. The curve

types are A, H, Q and HA: A curve type P1< P2< P3

is a three layer curve, it is composed of topsoil,

clayey, weathered basement and fresh bedrock. Three

layer curves occurred in the first phase of VES

location 7 & 9, and second phase of VES location 1-

10, while 1-6, 8 and 10 as well as VES 5 have a four

layer model in the first phase and second phase of

locations, respectively. It is predominant of all curve

types, it covers about 20 % of the total curve type.

Geoelectric sequence of H type P1>P2 < P3, it is a

three layer sequence with a clayey lateritic layer,

weathered layer and fracture / fresh basement. It is

found to occur in VES location 10, it covers about

10% of the total curve type. The geoelectric sequence

of HA curve type P1> P2 < P3< P4, is topsoil,

lateritic / sandy layer / weathered layer, fracture

basement and fresh basement. It is found in VES

location 1, 2, 3, 4, 5, 6 and 8, it covers about 70 % of

the total curve type. In the second phase locations H

curve type covers 50% of the total curve type, A

curve type is 30%, HA curve type is 10%, while Q

curve type is 10% in that respect.

Extensive geoelectrical investigations by means

of VES technique by Olorunfemi et al., 1991, have

shown that a generalized basement complex vertical

profile is made up of four geologic layers comprising

topsoil, weathered basement, partial

weathered/fractured basement and the fresh basement

bedrock which are best to yield groundwater.

4.1 Interpreted borehole log in selected springs in

Akoko areas in the first phase of location 1-10

(Fig. 3.1 and Fig. 3.2)

Location 1: Omidu spring Ikare, longitude

5045.262E, latitude 7030.508N and elevation 204 ft.

The HA type curve in location 1 comprises four layers

which are topsoil, weathered basement, partial

weathered/fractured basement and fresh basement. It

is 1.4 m thick which is not significant for good

groundwater yield.

Location 2: Along Akungba-Ikare road,

longitude 5044.689E, latitude 7029.365N and

elevation 357ft.This location also consists of four

layers and HA type that is made up of topsoil,

weathered basement, potentially weathered,

fracture/fresh basement. The potentially weathered

basement has a thickness of 3.5m which is quite

appreciable for groundwater yield.

Location 3: (Opp. CCC parish (Ikare- Akungba

road), longitude 50 44.655E, latitude 70 29.373N and

elevation 496ft. The HA type curve consists of four

layers that is topsoil, weathered basement, partial

weathered/fracture basement and fresh basement. The

appreciable thickness of the weathered/fractured

basement has led to the groundwater accumulation

and discharge to the surface as a spring.

Location 4: (Ayere Abekoko) Ikare, longitude 50

45.337E, latitude70 30.628N and elevation 479ft. This

location has a greater depth and thickness of 11.6 m -

14.6 m, respectively, with an HA curve type

appreciable enough for significant groundwater yield.

Location 5: Alafa spring (Supare), longitude 50

41.544E, latitude 70 27.528N and elevation 203ft. This

HA curve type comprises four layers: topsoil,

weathered basement, partially weathered/fracture

basement and fresh basement. The partially

weathered/fracture basement has 11.6 m thickness,

which is significant for spring formation and

appreciable for groundwater yield.

Location 6: Araromi (Supare), longitude: 50

41.405E, latitude 70 27.467N and elevation 215ft. This

HA curve type comprises four layers with the

partially/weathered basement having thickness of 4.2

m. This type of spring is a seasonal driven type that

dries up during a dry season and accumulates during a

wet season.

Location 7: Ogangan (Supare), longitude 50

42.720E, latitude 70 27.339N and elevation 43ft. This

A curve type comprises 3 layers, top soil, weathered

basement and fresh basement. Due to its less

overburden, less depth and the resistivity value, it will

not yield sufficient groundwater throughout the year.

Location 8: Araromi (Etioro), longitude: 50

43.370E, latitude 70 26.374N and elevation 78ft. This

HA type comprises four layers of a greater depth and

thickness of 12.7-7.6 m, respectively.

Location 9: Omi Alafa (Etioro), longitude: 50

43.38E, latitude 70 26.439N and elevation 241 ft. This

location has A curve type and comprises three layers:

topsoil, weathered basement and fresh basement. It is

little overburden, with less depth and resistivity value.

It may not be able to yield sufficient groundwater for

the community.

Location 10: Ebo- Oka Odokunlogbo spring

(Iwaro), longitude: 50 46.444E, latitude70 26.37N and

elevation 688ft. This location has H curve type and

comprises three layers: topsoil, weathered basement

and fresh basement, although the depth is a little bit

higher than that of an A curve type with little

overburden and a resistivity value higher than that of

the A curve type. It will yield ground water which

may not be sufficient enough.

The borehole log section contains VES stations

1,2,3,4 shown in Figure 4. Three layers were

delineated for VES 1, 2, 3 and 4. The first layer is top

soil with resistivity of 76.2(Ωm), 634.6(Ωm),

352.1(Ωm) and 301.4(Ωm) to thickness of 0.9m,

0.5m, 0.8m and 0.5m.

C. C. Okpoli

44

Fig. 3.1. Borehole log in selected spring in Akoko areas in the first phase of location 1-5

Fig. 3.2. Borehole log in selected spring in Akoko areas in the first phase of location 6-10

4.2 Interpreted borehole log in selected springs in

Akoko areas in the second phase of location 1-10

Their second layer is a weathered layer with

resistivity of 200.9 (Ωm), 100(Ωm), 197.3(Ωm) and

256.1(Ωm) and thickness of 2.7m, 3.1m, 5.0m and

2.3m. When the weathered layer is significantly

thick, it has the capacity to constitute an aquifer unit

and to discharge as a spring to the surface through the

fracture pathway. A third layer is fresh basement

which has resistivity values of 285.3 (Ωm),

170.8(Ωm), 626.6(Ωm) and 4574.2(Ωm) with an

infinite thickness because the curve terminated at this

layer.

A borehole log section contains VES stations

5,6,7,8 (Figure 4). Three layers were delineated in

VES 6, 7 and 8, while four layers were observed in

VES 5. For VES 5, 6, 7 and 8, the first layer is topsoil

with resistivity of 229(Ωm), 421.9(Ωm) and

121.4(Ωm) to thickness of 0.8m, 1.1m and 0.7m.

Their second layer is a weathered layer with

resistivity of 109.1(Ωm), 34.4(Ωm) and 72.2(Ωm) to

thickness of 4.6m, 5m and 2.5m.

For VES 6, 7, and 8 their third layer which is the

basement of 2186.7(Ωm), 1447.5(Ωm) and 446.4

(Ωm) to infinite thickness because the curve

terminated at this layer. VES 5 was inferred with

resistivity of 152.1(Ωm) for topsoil, 31.3(Ωm) for the

weathered layer, with low resistivity usually for clay

VES 1 VES 2 VES 3 VES 4 VES 50

5

10

DEPTH(m

)

TOPSOIL

WEATHERED LAYER

FRACTURED LAYER

BEDROCK

G

SCALE (m)

20 40

5

10

VES 6 VES 7 VES 8 VES 9 VES 10

DE

PT

H (

m)

LEGEND

TOPSOIL

WEATHERED LAYER

FRACTURED LAYER

BEDROCK

SCALE (m)

5

10

15

20 40

0

5

10

G

Borehole Logs and Physico-chemical Investigation of Some Presumptive Springs in Akoko, South-western Nigeria

45

and 1146.4(Ωm) for the fractured zone which it is also

the main aquifer unit, to thickness of 0.4m, 1.1m, and

2.4m and the fourth layer was inferred with resistivity

of 22918.5 (Ωm) with infinite thickness. Therefore,

both the second layer of VES 6, which is the

weathered layer, is taken as the major aquifer unit for

groundwater development and the third layer of VES

5, which is the fractured basement, constitute spring

water.

Fig. 4. Borehole log in selected spring in Akoko areas in the second phase of location 5-8

This result contains VES 9 and 10 (Figure 5).

Three layers were observed. The first layer which is

top soil has resistivity of 191.8(Ωm) and 109.9 (Ωm)

with thickness of 0.7m to 0.5m. Their second layer

which is weathered layer was inferred with resistivity

of 185.0(Ωm) to 47.6(Ωm) with appreciable thickness

of 8.0m and 2.0m. Beyond this layer there is the

basement complex with resistivity of 1456.0 (Ωm) to

2056 (Ωm) to infinite thickness.

Therefore, VES 9 constitutes the major aquifer

unit for spring water development for weathered layer

at high resistivity and VES 10 has low resistivity,

which is clay i.e. not good groundwater development

due to permeability.

Fig. 5. Borehole log in selected spring in Akoko areas in the second phase of location 9-10

4.3. Physico-chemical results

Table 1 shows WHO 2004 drinkable water

standards, adopted in comparison the results of

physico-chemical analysis of twenty (20) samples

taken in the study areas, as shown in Table 2. The bar

chart format is represented in Figure 6. WHO 2004

results are compare to those obtained from selected

springs in the study area, and there is little variation in

the values of pH, temperature and EC of the sample.

Turbidity is also of little variation, which is a

measure of relative clarity of liquid (Matheis G.

1

DE

PT

H (

m)

VES 5 VES 6 VES 7 VES 8

TOPSOIL

WEATHERED LAYER

FRACTURED LAYER

BASEMENT

LEGEND

152.1 (Ohm-m)

31.3 (Ohm-m)

1146.4 (Ohm-m)

22918.5 (Ohm-m)

229 (Ohm-m)

109.1 (Ohm-m)

2186.7 (Ohm-m)

421.9 (Ohm-m)

34.4 (Ohm-m)

1447.5 (Ohm-m)

121.4 (Ohm-m)

72.2 (Ohm-m)

446.4 (Ohm-m)

N

VES 9 VES 10

1

2

4

5

6

DEPTH

(m

)

LEGEND

191.8 (Ohm-m)

185 (Ohm-m)

1456 (Ohm-m)

109.9(Ohm-m)

47.6(Ohm-m)

2056(Ohm-m)

TOPSOIL

WEATHERED LAYER

BASEMENT

GL

N

1

t

r

t

T

T

t

s

w

h

l

c

t

e

m

c

p

q

198

that

rang

that

Tab

To

Te

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PH

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Bi

[B

Ch

Tab

S/N

the

sam

whi

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littl

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t of

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atm

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d as

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WHO

DS]

man

nd [C

al a

art s

bits

d (

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trati

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they

mit

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al o

and

mm

e d

ter

som

bee

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nd

COD

analy

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sho

litt

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ntra

trat

ion

ca

anal

y sh

for

c ma

oxyg

d (

mon

deg

sam

me

en o

e th

and

D]

lysis

emp

2

2

2

2

2

2

2

win

tle v

DS).

atio

tion

va

n b

lyse

how

po

atte

gen

(CO

me

gree

mpl

dis

obse

he le

dard

s of

p

25

25

25

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25.8

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25.3

25.3

25.0

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ng re

vari

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on v

n va

alue

be

ed w

wed

tab

er in

n de

OD)

easu

e o

les

scre

erv

east

d 20

Ma

250

Ma

6.5

Ma

Lim

Lim

Ru

f sam

6

2

0

0

esul

iati

onc

valu

alue

e an

us

wer

d th

bility

n w

ema

). T

ure

of o

is c

epan

ed

t va

004

A

ax 10c-2

ax 2

5-8.5

ax 1

mit

mit

ural

mple

lts o

on

cen

ue

e, an

nd i

ed

re c

hat T

y.

wate

and

Tw

es o

org

com

ncie

wh

alue

Acc

000

260c

25

5

0µs

6mg

3-6

area

es

Ec

2

1

2

1

1

2

2

1

1

1

of ph

in v

ntrat

is

nd

it m

for

com

TD

er h

d (B

wo

of t

ani

mpa

es

hich

e an

cept

0

c

s/cm

g/l

mg/

a re

2.4 x

1.3 x

2.2 x

1.4 x

1.2 x

2.1 x

2.3 x

1.5x

1.4 x

1.3 x

hys

val

tion

0.0

sam

may

r h

mpa

S d

have

BOD

of

the

c m

ared

in

h sh

nd

table

m

/l in

spe

x 10

x 10

x 10

x 10

x 10

x 10

x 10

x 10

x 10

x 10

ico-

ues

n w

02m

mpl

y ne

hum

ared

did n

e be

D) a

th

wa

mat

d to

the

how

are

e le

n Ur

ctiv

02

02

02

02

02

02

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02

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-che

s of

with

mg/l

le 8

eed

man

d to

not

een

and

ese

ater

tter

C. C

46

o

e

w

e

vel

rban

vely

emic

f

h

l

8

d

n

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n

d

e

r

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6

cl

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lim

n an

y

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cal

po

of

de

su

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su

in

eq

sa

di

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po

do

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lear

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rom

mit

nd

rbid

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ana

ollu

f d

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ubst

nact

quiv

amp

ichr

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OD

ollu

ome

li

rer

0.

m th

t for

St

B

ch

N

R

A

bl

L

L

dity

0.0

0.0

0.0

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0.0

0.0

0.0

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alys

utio

diss

omp

as

only

tanc

tive

vale

ple

rom

D va

D t

utio

esti

wh

The

he s

r th

tom

Bone

hild

Naus

Rusti

Anae

lood

Liver

Liver

02

03

05

01

06

10

01

03

03

01

is

on o

olv

posi

bac

y to

ces

e o

ent

th

mate

alue

than

on c

ic a

hen

e a

sele

he w

Ef

mach

e dis

dren

sea,

ing

emia

d.

r ca

r ca

of w

ved

ition

cter

o m

s su

rga

of

hat

e. C

es.

n B

cont

and

co

anal

ecte

wate

ffect

h di

seas

n ma

cra

and

a; li

ance

ance

TD

wat

ox

n o

ria.

meas

uch

anic

f th

is

COD

In o

BOD

trol

ind

omp

lysi

ed

er q

t

scom

se p

ay g

amp

d ca

iver

er

er

DS

0.2

0.0

0.3

0.4

0.3

0.5

0.1

0.5

0.0

0.5

er B

xyg

of o

CO

sure

h a

c m

he

s s

D t

oth

D.

l bo

dust

pare

is h

spr

qual

mfo

pain

get m

ps, d

ance

r, ki

25

02

33

44

36

54

19

55

09

54

BO

gen

orga

OD

e th

as b

matt

tot

susc

test

her c

Th

oard

tria

ed t

has

ring

lity

ort

and

mott

diarr

er

dne

OD

(D

anic

is a

he a

bac

ter

tal

cept

re

cas

hese

ds

al w

to s

sh

gs d

y sta

d ten

tled

rhoe

ey o

B

is a

DO)

c m

a w

amo

cteri

in

org

tibl

sult

es o

e p

to a

waste

sam

how

do

and

nde

d tee

ea a

r sp

BOD

a m

) in

matte

wate

ount

ia

wa

gan

le

ts a

of t

para

ass

e.

mple

wn t

not

ard

erne

eth.

and

plee

D

3.5

3.2

3.4

4.1

3.3

2.8

2.6

3.3

4.3

4.8

meas

n m

er b

er q

t of

but

ater

nic

to

are

the

am

ess

P

T

E

T

T

B

C

e 6

tha

t ex

d.

ss o

asso

n da

sure

mg/

by m

qual

f bi

t a

r. I

ma

ox

a g

Tab

eter

wa

PH

Tem

Ec

Turb

TDS

BOD

COD

6 w

at w

xce

of th

ocia

ama

e o

/l n

mic

lity

iolo

also

It i

atter

xid

goo

ble

rs

ater

mp

bid

S

D

D

whos

wate

eed

he b

ated

age,

C

f th

nec

cro-

me

ogic

o b

is a

r in

ant

od e

the

are

r po

ity

se v

er s

the

bone

d hea

, cha

OD

he q

cess

-org

easu

cally

biolo

an

n a

t s

esti

ere

e u

ollu

valu

sam

e W

e,

ad a

ang

D

4.8

3.2

6.4

5.6

6.4

6.4

4.0

4.8

5.6

3.2

qua

sary

gan

ure

y a

ogi

ox

a w

such

ma

is m

used

utio

ue

mple

WH

ache

ges i

8

2

4

6

4

4

0

8

6

2

antit

y fo

nism

use

activ

cal

xyge

wat

h a

ate o

mor

d b

on b

is

es

HO

es

in

ty

for

ms

ed

ve

ly

en

er

as

of

re

by

by

Borehole Logs and Physico-chemical Investigation of Some Presumptive Springs in Akoko, South-western Nigeria

47

Results of BOD and COD from the study area

show that they exceeded the maximum allowable

limit of the WHO standard. BOD ranges from 2.8 to

4.1, while COD ranges from 3.2 to 6.4 respectively.

The World Health Organization (WHO) recommends

a BOD limit of 6mg/l for drinking water as shown

Table 1. The same is true with the European Union. In

view of ease of determination of COD over BOD,

China has set the maximum allowable COD 3 mg/l

for drinking water in urban areas and 6mg/l in rural

areas. The organic pollution of drinking water in the

study area indicates that people in these selected areas

will be prone to liver cancer, because results of the

analyses are greater than the acceptable level. They

differ from those in the report by Edema et al (2001)

where samples of analyzed drinking water in

Abeokuta have unpleasant odour and taste.

5. Conclusions

A geophysical survey method involving the use

of Vertical Electrical Resistivity Sounding technique

was applied in twenty (20) different locations in

Akoko area of south-western Nigeria. Results

obtained in the study area have revealed that

weathered and fractured basement constitutes a major

aquifer unit in the area. Fractured basement rock

aquifer occurs immediately beneath the weathered

basement rock aquifers in most places and serves as

the main source of water that springs out as spring

water. In addition BOD concentration in spring water

within the study area can be considered safe for

drinking purposes (with respect to its BOD

concentration). As BOD and COD levels in all

analyzed samples were lower or higher than the

permissible length (6mg/l) recommended by WHO

location, water from springs 3, 5 and 6 is not safe for

drinking because of a higher COD concentration

than the permissible limit, hence that water requires to

be treated before it can be safe for drinking purposes.

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Okpoli C. C. is from the Department of Geology, Adekunle

Ajasin University; assistant lecturer.

Main research area:Environmental geophysics

Address: Akungba- Akoko, Ondo State, Nigeria.

Phone: +2348064488625

E-mail: okpolicyril@gmail.com

Galimų vandens šaltinių fizikiniai bei cheminiai ir gręžinių pjūvių

tyrimai Akoko teritorijoje, Pietų ir Vakarų Nigerijoje

Cyril Chibueze Okpoli Adekunle Ajasin universitetas, Geologijos katedra, Akungba-Akoko, Nigerija

(gauta 2013 m. gegužės mėn., priimta spaudai 2013 m. rugsėjo mėn.)

Šiame darbe, taikant Schlumbergerio konfigūracijos metodą, buvo atliktas geologinis ir fizikinis tyrimas. Nustatyti vandens mėginių fizikiniai ir cheminiai parametrai dvidešimtyje atrinktų Akoko vietų, Ondo valstijoje, kuri yra įsikūrusi pietvakarių Nigerijoje. Galimi vandens šaltiniai kartografuojami atsižvelgiant į gylį, storį, varžą ir derlingas nuosėdas. Taikant kompiuterinį iteracinį procesą, buvo analizuojami gauti duomenys. Tiriant dirvožemio paviršiaus sudūlėjusį ar išsisluoksniavusį ir giluminį sluoksnius, buvo nubraižytos A, HA ir Q tipinės kreivės. Tiriant gręžinio pjūvį, daugiausia dėmesio buvo skiriama sudūlėjusiam sluoksniui dėl jo pakankamo storio, kuris reikalingas vandens šaltiniams formuotis ir sezoniniam derliui gauti. Surinktų vandens mėginių fizikiniai ir cheminiai parametrai svyravo taip: pH – nuo 6,57 iki 7,20; elektros laidumas (EC) – nuo 1.2× 102 iki 4.2 × 102 (Uhr / cm); ištirpusių medžiagų kiekis – nuo 0,01 iki 0,55 (mg/l); drumstumas nuo 0,01–0,1; ištirpusio deguonies koncentracija – nuo 7,8 iki 9,6 (mg/l); BOD – nuo 2,8 iki 4,8 (mg/l) ir ChDS 1,6–6,4 (mg/l); temperatūra – nuo 25 °C iki 26 °C. Dauguma tirtų mėginių atitinka Pasaulinės sveikatos organizacijos (PSO) nustatytas ribines vertes, kurios yra žemesnės negu 10 mg/l, išskyrus ChDS ir temperatūrą, viršijančią PSO rekomenduojamas vertes 3.5 ir 6 vietovėse. Kadangi šiose vietovėse yra padidėjęs žmonių sergamumas vėžiu, rekomenduojama prieš vartojant vandenį maisto reikmėms jį pirmiausia išvalyti.