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Research ArticleAssessment of Economically Accessible GroundwaterReserve and Its Protective Capacity in Eastern Obolo LocalGovernment Area of Akwa Ibom State Nigeria UsingElectrical Resistivity Method
N J George1 E U Nathaniel1 and S E Etuk2
1 Department of Physics Akwa Ibom State University Ikot Akpaden 53001 Nigeria2 Department of Physics University of Uyo Uyo 53001 Nigeria
Correspondence should be addressed to N J George nyaknojimmyggmailcom
Received 30 December 2013 Accepted 27 February 2014 Published 14 April 2014
Academic Editors E Liu G Mele F Monteiro Santos and B Tezkan
Copyright copy 2014 N J George et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The application of geophysical method employing vertical electrical sounding (VES) method in combination with laboratoryanalysis of aquifer sediments has been used to access the economically accessible groundwater reserve and its protective capacityin some parts of Eastern Obolo Local Government area the eastern region of the Nigerian Niger Delta Schlumberger electrodeconfiguration was used to sound twelve VES to occupy the areas that have borehole locations and accessibility for the spread ofcurrent electrodes to at least 1000m Based on the results the safe and economic aquifer potential has groundwater reserve ofabout 168480558 plusmn 18532861m3 The desired aquifer thickness and its depth of burial have average value of 5202m and 7314mrespectively The area has a fair protective capacity This is indicated by 5833 weak 1667 moderate and 25 good protectivecapacity for the areaThis study was done in one of the oil cities where contaminated Salt River water is used as the major source ofwater for domestic uses and it is believed that the settlers will appropriate this result and sue for safe groundwater at the indicateddepths
1 Introduction
The need to assess safe groundwater repositories is increas-ingly important in Eastern Obolo Local Government Area(EOLGA) located in Eastern Niger Delta region of Nige-ria because of the extant health hazards posed by surfaceand underground contaminations which are associated withchemical microbial and physical contaminant plumes Thefocus of groundwater quality protection is on the preventionof groundwater pollution however where groundwater hasbecome polluted it must be cleaned up and managed toensure the ongoing protection of human health and theenvironment Access to clean water is a human right andbasic requirement for economic development The world-wide development of past civilisations as well as the recentsocioeconomic evolution of nations is based on and strongly
controlled by the availability of water which can be obtainedeither as surface or subsurface water
The Niger Delta region (the site for which the studyarea is located) is one of the most industrialised parts inthe entire Gulf of Guinea These industries have contributedimmensely to economic growth and development of thestates within the region The region which is one of the tenmost important wetland and marine ecosystems in the worldhas suffered immensely from these unsustainable industrialactivities [1] Some of the human activities that have impactednegatively on the Niger Delta environment include industrial(hydrocarbon exploration and exploitation noise pollutiongas flaring oil spillage and waste disposal) removal of back-shore vegetation construction of barges and other coastalcontrol works river dredging agricultural (excessive anduncontrolled application of inorganic fertilizers pesticides
Hindawi Publishing CorporationISRN GeophysicsVolume 2014 Article ID 578981 10 pageshttpdxdoiorg1011552014578981
2 ISRN Geophysics
Sandy formation
Rive
rs S
tate
Ikot Abasi
Alluvium
SiltstoneBH
1
1 1
2
20
3
4
5
67
8
9
10
11
12
A
B
C
D
E
F
Nigeria
N
BH
BH
BH
BH
(km)
BH
BH
BH BH
BH
BH
BH
BH
BH
Atabrikang Aquaha
Atabrikang Ekeme
Bight of Bonny Onna
Okoro EteIko town
Okoro Inyang
Queen townKalasunju
Opobo town
Obianga
Okpukalama
Mkpat Enin
State boundary
Major roadMinor road
TributaryLGA boundaryRiver
LGA headquartersSettlementVES station VES traverseA B
7∘30
998400E 7∘32
998400E 7∘34
998400E 7∘36
998400E 7∘38
998400E 7∘40
998400E 7∘42
998400E
7∘30
998400E 7∘32
998400E 7∘34
998400E 7∘36
998400E 7∘38
998400E 7∘40
998400E 7∘42
998400E
4∘30
998400N
4∘32
998400N
4∘25
998400N
4∘20
998400N
4∘15
998400N
Figure 1 Location map showing the study location VES points and VES traverses
and herbicides) municipal waste disposal urbanisation andmining activities [2 3] Environmental problems like lossof biodiversity coastal and riverbank erosion flooding landdegradation loss of soil fertility and deforestation are nowcommon [1 4] Most of the numerous surface water resourceendowments of the area which the entire population usedto be solely dependent on for their domestic agriculturalindustrial and social needs are currently seriously pollutedby both natural and anthropogenic sources [4] Recently theactivities of criminals who are involved in illegal pipelinevandalism and crude oil theft and refining have compoundedthe environmental problems in the Niger Delta region Thequality of the groundwater resources in many parts of theregion is gradually being degraded [5]There is urgent need tounderstand the extent of natural protection the distributionsof the economically safe aquifer repository and possibly thepollutant flow path in order to design appropriate mitigationremediation and protection strategies especially now thatsuch plans are in the drawing board by governmentalenvironmental and other international partners Designof appropriate groundwater management strategies in anygeologic environment depends to a reasonable extent on thenature of subsurface materials whose properties (physicaland chemical) and spatial distribution constitute the goalof all hydrogeological and hydrogeophysical investigationsThe surface water is found to be grossly degraded in qualitybecause of its exposure to physical biological or chemicalcontaminants [6] Groundwater on its own has less degreeof contaminations when relatively compared with surface
water Inadequate public water supply has led to increaseddemand for alternative sources of water supply in EOLGAdue to rapidity in human growth in recent times [7] Todaywe are witnessing the increasing number of boreholes drilledby the government nongovernmental organizations andindividualsThis clearly shows that groundwater is effectivelycomplementing other sources of water supply in the areaThis is due to the rate of contamination of surface waterthrough the effect of inordinate quest for developmentWildcat drilling which does not support any scientific searchfor the location of the water bearing sediments in the areahas exposedmany groundwater resources to contaminationsIn view of this the area was mapped in order to access thequantitative reserve distribution of the safe and economicwater bearing units its depth of burial and the protectivecapacity of the groundwater repositories in the study area
2 Location and Geology of the Study Area
The study area shown in Figure 1 lies between longitudes7∘301015840 and 7∘ 421015840 E and latitudes 4∘151015840 and 4∘321015840N in the NigerDelta region of Southern Nigeria The study was designedto cover some areas of Eastern Obolo Local GovernmentAreas of Akwa Ibom State of Nigeria one of the oil richregions of the Arcuate Niger Delta surrounded by both freshand saline water The study area is located in an equatorialclimatic region that is characterised by two major seasonsThe seasons are the rainy season (MarchndashOctober) anddry season (NovemberndashFebruary) [7 8] The dry season is
ISRN Geophysics 3
a period of extreme aridity characterized by excruciatinghigh temperatures that do reach 35∘C The area has beenseverely affected by the current global climatic changes insuch a way that there have been shifts in both the upperand lower boundaries of these climatic conditions [9ndash13]Thestudy area is located in the tertiary to quaternary coastal plainsands (CPS) (otherwise called the Benin Formation) andalluvial environments of the Niger Delta region of SouthernNigeria (Figure 1) The Benin Formation which is underlainby the paralic Agbada Formation covers over 80 of thestudy area The sediments of the Benin Formation consistof interfringing units of lacustrine and fluvial loose sandspebbles clays and lignite streaks of varying thicknesseswhile the alluvial units comprise tidal and lagoonal sedimentsand beach sands and soils [14ndash16] which are mostly foundin the southern parts and along the river banks The CPS iscovered by thin lateritic overburden materials with varyingthicknesses at some locations but is massively exposed nearthe shorelines The CPS forms the major aquiferous unitsin the area It comprises poorly sorted continental (finemedium and coarse) sands and gravels that alternatewith lig-nite streaks thin clay horizons and lenses at some locationsThe thin clayshale horizons truncate the vertical and lateralextents of the sandy aquifers thereby building upmultiaquifersystems in the area [17] Thus both confined and partiallyconfined aquifers can be found in the area Southward flowingrivers like the Kwa River and their tributaries that emptydirectly into the Bight of Bonny drain the area
3 Data Acquisition and Analysis
Surface electrical methods have been used in investigatingdifferent types of geological geotechnical and environmentalproblems for many years due to the dependence of earthresistivity on some geologic parameters Generally the elec-trical resistivity method involves injecting electrical currentinto the ground through a pair of electrodes (called currentelectrodes) and monitoring the potential difference createdby the passage of the electrical current through the earthmaterials using another pair of electrodes technically calledpotential electrodes Details of this can be found in [18ndash20] Many electrode configurations and field procedures existthat can be used to perform geoelectrical investigations [18]but the Schlumberger array which was performed using thevertical electrical sounding field procedure was adopted toassess the subsurface electrical resistivity and the depth ofthe economically accessible aquifers The Schlumberger elec-trode configuration used in measuring apparent resistivity 120588
119886
is shown in the following equation
120588119886= 120587 sdot ((1198601198612)
2minus (1198721198732)
2
(119872119873)) sdot 119877119886 (1)
whereAB is the distance between two current electrodes119872119873is the distance between two potential electrodes and 119877
119886is
the apparent electrical earthrsquos resistance measured from the
equipment The term in the equation shown below is calledthe geometric factor (119866)
119866 = 120587 sdot ((1198601198612)
2minus (1198721198732)
2
119872119873) (2)
The electrical resistivity investigations were conducted intwelve (12) locations across the study area between 2011 and2012 using a SAS1000model of ABEMTerrameterMaximumcurrent electrode spacing (119860119861) was constrained by settlementpattern and other space limiting conditions to vary fromone location to another This confined the VES points tothe locations shown in Figure 1 In locations with goodaccess paths andor roads the current cables were extendedup to 1000m in order to ensure that depths above 200mwere comfortably sampled assuming that penetration depthvaries between 025119860119861 and 05119860119861 [21 22] Correspondingreceiving (potential) electrode separation (119872119873) varied froma minimum of 05m at119860119861 = 2m to a maximum of 50mat119860119861 = 1000m At all the electrode positions great care wastaken to ensure that the separation between the potentialelectrodes did not exceed one-fifth of the separation of thecurrent electrodes [23] VES data quality was generally goodespecially in the wet season but in the dry season theelectrode positions were usually wetted with water and saltsolution (where necessary) in order to lower the contactresistance and consequently ensure good electrical contactbetween the ground and the steel electrodes
Information generated from the analyses of geophysicaldata was used to constrain drillingThe drilling phase startedas soon as the geophysical reports were submitted to theAkwa Ibom State Millennium Development Goal [24] thatfunded the borehole projects Manual drilling technique wasadopted in drilling 6-inch borehole in all locations since thesubsurface condition in the entire area was favourable to suchdrillingmethod Some of the boreholes were cited adjacent tothe VES stations while some that are located at where therewas no access path to spread the cables at the vicinity of theboreholes were separated by more than 150m (see Figures2 3 and 4) The drill cuttings were logged geologically inall 12 locations and from the desired aquifer samples werecollected for laboratory measurement of porosityThe drilledboreholes were cased using 75mm high pressure PVC casingmaterials The PVC casings were slotted at various depthswith sizable thicknesses and the slotted region of the wellannulus was gravel packed to ensure good delivery of water tothe borehole Gravel packing is also important in checking theingress of sediments into the borehole Amixture of sand andcement was used to grout the boreholes to prevent backflowof water at the surface into the well [25] The wells weredeveloped
The core samples were prewashed with distilled waterto remove traces of clay and other argillaceous materialsthat might have originated from the coring operation [26]The samples were later put into a vacuum desiccator andevacuated at a pressure of 03mBar for a period of 1 hour (see[27]) Deaerated distilled water was gently poured into thedesiccator until the water completely covers all the samplesAll the samples were later soaked for a period of 24 hours
4 ISRN Geophysics
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 4
VES 1
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
RMSEBH BH
24 25 NANA
VES
4
VES
1
6804 9499
14886 27155
14645
5492
37452
12487
Gra
velly
sand
Gra
velly
sand
Pene
trat
ion
dept
h (m
)
Loamy
Fine
sand
Fine
sand
topsoilLoamytopsoil
(b)
Figure 2 Samples of modelled VES curves along119860119861 profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 5
VES 7
Half current electrode configuration [AB2] (m)
Resis
tivity
(Ωm
)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
RMSE 21 NA 25 NA
VES
5
VES
7
BH BH
7184
18449
2058
7503
Sandytopsoil
Fine
sand
Gra
velly
sand
Silts
tone
Fine
sand
13622
14408
526
668
Loamytopsoil
(b)
Figure 3 Samples of modelled VES curves along CD profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
ISRN Geophysics 5
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 12
VES 10
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
90
100
110
NA not applicable
RMSE root-mean square error
VES
12
26
12410
1182
6112
48930
26
2107
3979
17214
2282
RMSE NA NA
VES
10
BH BH
Silts
tone
Fine
sand
Fine
sand
Silts
tone
Loamytopsoil
Loamytopsoil
(b)
Figure 4 Samples of modelled VES curves along EF profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
in order to ensure that any trace of salt and other relatedsoluble contaminants within the samples diffused out intothe surrounding water The cleaned samples were later driedin a temperature controlled oven at 105∘C for 16 hours inorder to check any irreversible change in the composition ofthe samples (see [27 28]) The oven dried core samples wereallowed to cool to normal air temperature in a desiccatorTheweight of the cool and dry core samples 119882
119889was measured
using an electronic weighing balance five times and the meanwas computed and recorded The samples were soaked withdistilled water that has been boiled for 30 minutes in avacuum pressure of 03mBar for 18 hours The weight of thewet samples119882
119908was also measured five times and the mean
was computed and recorded Effective porosity (120601) of thesamples was calculated using (6) as
120601 = 100 sdot (119882119908minus119882119889
119881) (3)
where119881 is volume of the samples Details of the experimentalprocedure can be found in [26ndash28]
4 Results and Discussion
The field data consisting of the apparent resistivity (120588119886) and
the current electrode spacing (1198601198612) were partially curvematched smoothened and manually plotted against eachother on a bilogarithmic scale with 120588
119886on the ordinate and
current electrode 1198601198612 on the abscissa It was performedby either averaging the two readings at the crossover pointsor deleting any outlier at the crossover points that did notconform to the dominant trend of the curve Also deletedwere data that stood out as outliers in the prevalent curvetrend which could have caused serious increase in root meansquare error (RMSE) during themodelling phase of the workWhere observed such outliers constitute less than 2 of thetotal data generated in each sounding station and since wemeasured over ten data per decade deleting such noisy datadid not alter the trend of the sounding curve Some of thedeleted data might have been the electrical signatures of thethin clay materials that might have suffered suppression fromthe over- and underlying thick sandy aquifers [29 30] Anydiscontinuity observed in the smoothened curves was exclu-sively attributed to vertical variation of electrical resistivitywith depth Preliminary interpretation of the smoothenedcurves wasmade using the traditional partial curvemarchingtechnique to estimate primary layer parameters The partialcurve matching technique uses master curves and chartsdeveloped by [31] A computer basedVESmodelling softwarecalled RESIST [32] that can perform automated approxima-tion of the initial resistivity model from the observed datawas later used to improve upon the preliminary interpretedresults using the inversion technique The RESIST softwareuses the initial layer parameters to perform some calculationsand at the end generates a theoretical curve in the process Itthen compares the theoretical curve with the field data curve
6 ISRN Geophysics
Table1Summaryof
locatio
ncoordinatesgeoelectric
allay
erprop
ertie
sand
protectiv
estre
ngth
ofthes
tudy
area
VES
number
Latitud
e(degree)
119910(m
)
Long
itude
(degree)
119909(m
)
Bulkresistiv
ityof
layersfro
mtopto
botto
mof
thee
cono
micaquifer(Ωm)
Thickn
esso
flayersfrom
topto
botto
mof
econ
omicaquifer(m)
Depth
toecon
omicaquifer
(m)
Long
itudinal
cond
uctance
119878(Ω
m)
Econ
omic
aquiferfractional
porosity
Protectiv
estr
ength
Curve
type
1205881
1205882
1205883
1205884
ℎ1
ℎ2
ℎ3
12982
176
6604
14886
5492
12487
1336
478
527
009
0305
Weak
KH2
2828
357
4186
19130
3921
mdash17
1123
mdash114
0006
0350
Weak
K3
2836
607
1304
57202
20494
mdash12
15512
674
005
0278
Weak
H4
2882
794
9499
27155
1464
537452
05
39
161
206
001
0301
Weak
KH5
1850
1009
7184
1844
913622
1440
805
16389
829
003
0280
Weak
KH6
1423
210
14330
2100
8605
83673
194
431
496
1124
028
0260
Mod
erate
HA
71950
1328
2058
7503
526
668
29
118
682
829
133
0195
Goo
dKH
81363
1586
18268
1075
401
647
36
246
452
734
136
0312
Goo
dAH
9581
104
34555
18256
3939
20304
06
20
892
918
023
0276
Goo
dQH
109562
150
2107
3979
17214
2282
07
128
552
687
007
0256
Weak
AK
119740
209
13351
33725
9242
16816
44
556
509
1109
007
0289
Weak
KH12
1867
356
17214
1182
6112
48930
916
567
368
1151
059
040
6Mod
erate
HA
ISRN Geophysics 7
Table 2 Protective capacity ratings of longitudinal conductance
Range Strength119878 gt 10 Excellent5 lt 119878 lt 10 Very good07 lt 119878 lt 49 Good02 lt 119878 lt 069 Moderate01 lt 119878 lt 019 Weak119878 lt 01 Poor
Since quantitative interpretation of geoelectrical soundingdata is usually difficult due to the inherent problem ofequivalence [33] borehole data were used to constrain alldepth andminimise the choice of equivalentmodels by fixinglayer thicknesses and depths while allowing the resistivitiesto vary [34] The total number of observed minima andmaxima on the smoothened VES curves was usually usedas the starting number of layers (or models) over a half-space for the data inversion exercise The software worksiteratively by calculating at the end of each step updatedparameters of the model and calculates the extent of fitbetween the calculated and the observed data using theroot mean square error (RMSE) technique in which 5 waspreset as the maximum acceptable value Figures 2 3 and 4show some of the modelled VES curves observed andtheir correlation between the nearby borehole lithology andinterpreted results A good correlation was observed betweenthe borehole lithology log data and the inverted results overhalf-space in many locations These noticed distortions weresuspected to have possibly originated from the failure of the1D assumption of the shallow subsurface of the half-space[29] The result of the computer iterations gave the layers ofthe subsurface penetrated by current true resistivity of eachlayer the thickness (ℎ) depth (119889) of each layer and the totaldepth of overburden to the safe and economically accessibleauriferous layers as shown in Table 1 Three to four layerswith different curve types were delineated The availabilityof H and K curve types indicates the high and low valuesof resistivities in sediments which translate from unsaturatedzones into saturated zones Specifically the curve types inthe areas occupied by VES are KH which takes 417 K HAH AK and QH which respectively take 83 of the totalcurve distributions The other curve type also noticed is theAH curve type which takes 167 of the curve distributions(see Table 1 and Figure 5 for curve distributions) From theinferred layer resistivities and thicknesses the longitudinalconductance known as one of the Dar Zarrouk parameterswas used to classify the degree of protection of each of VESsites according to rating in Table 2 intoweakmoderate goodand excellent aquifers based on the numerical values assignedto each point Based on the longitudinal conductance theprotective capacity of the overburden showed that 5833 ofthemapped area has weak protective capacity 1667moder-ate protective capacity and 25goodprotective capacityThisis an indication that the chosen economic aquifer repositoryapart from having a sizeable thickness of average value of5205m and average depth of 7314m also has a fair protection
0
10
20
30
40
Curv
e fre
quen
cy (
)
KH K H HA AH AK QHCurve type
417
833 833
167
833 833 833
Figure 5 Bar chart showing frequency of curve type distribution inthe study area
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
North of reference coordinate (m)
Long
itudi
nal c
ondu
ctan
ce (m
Ωminus1)
1000 1500500
Figure 6 Distribution of longitudinal conductance map showinghigh values of S in VES 6 7 and 8 in the north-eastern zone of themapped area
from the surface flow despite its open nature The sizeablethickness and the average depth of the aquifer located inaquifer units ranging from fine sand to coarse or in siltstonecan be economically exploited for domestic and industrialuses by the settlers of the region
The longitudinal conductance (119878) is given by
119878 =
119899
sum
119894=1
ℎ119894
120588119894
=ℎ1
1205881
+ℎ2
1205882
+ℎ3
1205883
+ sdot sdot sdot +ℎ119899
120588119899
(4)
where ℎ119894and 120588
119894are the saturated thickness of each of the
layers and their corresponding true resistivities respectivelyThe earthrsquos medium acts as a natural filter to percolatingfluid The ability of the earth to retard or accelerate and filterpercolating fluid is a measure of its protective capacity [3536] The total longitudinal conductance is a parameter usedto define the target areas of groundwater potential High 119878values indicate relatively thick geologic succession and shouldbe accordedwith the highest priority in terms of groundwaterpotential while low 119878 reflects thin geologic successions withlow groundwater potential [35] The contour map showing 119878distribution is given in Figure 6
The results of the thickness and total depth of groundwa-ter repository in Table 1 were respectively used in generatingthe 2D and 3D representation of the subsurface economicgroundwater repository and 3Dmap showing the total depth
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
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Geological ResearchJournal of
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Geology Advances in
2 ISRN Geophysics
Sandy formation
Rive
rs S
tate
Ikot Abasi
Alluvium
SiltstoneBH
1
1 1
2
20
3
4
5
67
8
9
10
11
12
A
B
C
D
E
F
Nigeria
N
BH
BH
BH
BH
(km)
BH
BH
BH BH
BH
BH
BH
BH
BH
Atabrikang Aquaha
Atabrikang Ekeme
Bight of Bonny Onna
Okoro EteIko town
Okoro Inyang
Queen townKalasunju
Opobo town
Obianga
Okpukalama
Mkpat Enin
State boundary
Major roadMinor road
TributaryLGA boundaryRiver
LGA headquartersSettlementVES station VES traverseA B
7∘30
998400E 7∘32
998400E 7∘34
998400E 7∘36
998400E 7∘38
998400E 7∘40
998400E 7∘42
998400E
7∘30
998400E 7∘32
998400E 7∘34
998400E 7∘36
998400E 7∘38
998400E 7∘40
998400E 7∘42
998400E
4∘30
998400N
4∘32
998400N
4∘25
998400N
4∘20
998400N
4∘15
998400N
Figure 1 Location map showing the study location VES points and VES traverses
and herbicides) municipal waste disposal urbanisation andmining activities [2 3] Environmental problems like lossof biodiversity coastal and riverbank erosion flooding landdegradation loss of soil fertility and deforestation are nowcommon [1 4] Most of the numerous surface water resourceendowments of the area which the entire population usedto be solely dependent on for their domestic agriculturalindustrial and social needs are currently seriously pollutedby both natural and anthropogenic sources [4] Recently theactivities of criminals who are involved in illegal pipelinevandalism and crude oil theft and refining have compoundedthe environmental problems in the Niger Delta region Thequality of the groundwater resources in many parts of theregion is gradually being degraded [5]There is urgent need tounderstand the extent of natural protection the distributionsof the economically safe aquifer repository and possibly thepollutant flow path in order to design appropriate mitigationremediation and protection strategies especially now thatsuch plans are in the drawing board by governmentalenvironmental and other international partners Designof appropriate groundwater management strategies in anygeologic environment depends to a reasonable extent on thenature of subsurface materials whose properties (physicaland chemical) and spatial distribution constitute the goalof all hydrogeological and hydrogeophysical investigationsThe surface water is found to be grossly degraded in qualitybecause of its exposure to physical biological or chemicalcontaminants [6] Groundwater on its own has less degreeof contaminations when relatively compared with surface
water Inadequate public water supply has led to increaseddemand for alternative sources of water supply in EOLGAdue to rapidity in human growth in recent times [7] Todaywe are witnessing the increasing number of boreholes drilledby the government nongovernmental organizations andindividualsThis clearly shows that groundwater is effectivelycomplementing other sources of water supply in the areaThis is due to the rate of contamination of surface waterthrough the effect of inordinate quest for developmentWildcat drilling which does not support any scientific searchfor the location of the water bearing sediments in the areahas exposedmany groundwater resources to contaminationsIn view of this the area was mapped in order to access thequantitative reserve distribution of the safe and economicwater bearing units its depth of burial and the protectivecapacity of the groundwater repositories in the study area
2 Location and Geology of the Study Area
The study area shown in Figure 1 lies between longitudes7∘301015840 and 7∘ 421015840 E and latitudes 4∘151015840 and 4∘321015840N in the NigerDelta region of Southern Nigeria The study was designedto cover some areas of Eastern Obolo Local GovernmentAreas of Akwa Ibom State of Nigeria one of the oil richregions of the Arcuate Niger Delta surrounded by both freshand saline water The study area is located in an equatorialclimatic region that is characterised by two major seasonsThe seasons are the rainy season (MarchndashOctober) anddry season (NovemberndashFebruary) [7 8] The dry season is
ISRN Geophysics 3
a period of extreme aridity characterized by excruciatinghigh temperatures that do reach 35∘C The area has beenseverely affected by the current global climatic changes insuch a way that there have been shifts in both the upperand lower boundaries of these climatic conditions [9ndash13]Thestudy area is located in the tertiary to quaternary coastal plainsands (CPS) (otherwise called the Benin Formation) andalluvial environments of the Niger Delta region of SouthernNigeria (Figure 1) The Benin Formation which is underlainby the paralic Agbada Formation covers over 80 of thestudy area The sediments of the Benin Formation consistof interfringing units of lacustrine and fluvial loose sandspebbles clays and lignite streaks of varying thicknesseswhile the alluvial units comprise tidal and lagoonal sedimentsand beach sands and soils [14ndash16] which are mostly foundin the southern parts and along the river banks The CPS iscovered by thin lateritic overburden materials with varyingthicknesses at some locations but is massively exposed nearthe shorelines The CPS forms the major aquiferous unitsin the area It comprises poorly sorted continental (finemedium and coarse) sands and gravels that alternatewith lig-nite streaks thin clay horizons and lenses at some locationsThe thin clayshale horizons truncate the vertical and lateralextents of the sandy aquifers thereby building upmultiaquifersystems in the area [17] Thus both confined and partiallyconfined aquifers can be found in the area Southward flowingrivers like the Kwa River and their tributaries that emptydirectly into the Bight of Bonny drain the area
3 Data Acquisition and Analysis
Surface electrical methods have been used in investigatingdifferent types of geological geotechnical and environmentalproblems for many years due to the dependence of earthresistivity on some geologic parameters Generally the elec-trical resistivity method involves injecting electrical currentinto the ground through a pair of electrodes (called currentelectrodes) and monitoring the potential difference createdby the passage of the electrical current through the earthmaterials using another pair of electrodes technically calledpotential electrodes Details of this can be found in [18ndash20] Many electrode configurations and field procedures existthat can be used to perform geoelectrical investigations [18]but the Schlumberger array which was performed using thevertical electrical sounding field procedure was adopted toassess the subsurface electrical resistivity and the depth ofthe economically accessible aquifers The Schlumberger elec-trode configuration used in measuring apparent resistivity 120588
119886
is shown in the following equation
120588119886= 120587 sdot ((1198601198612)
2minus (1198721198732)
2
(119872119873)) sdot 119877119886 (1)
whereAB is the distance between two current electrodes119872119873is the distance between two potential electrodes and 119877
119886is
the apparent electrical earthrsquos resistance measured from the
equipment The term in the equation shown below is calledthe geometric factor (119866)
119866 = 120587 sdot ((1198601198612)
2minus (1198721198732)
2
119872119873) (2)
The electrical resistivity investigations were conducted intwelve (12) locations across the study area between 2011 and2012 using a SAS1000model of ABEMTerrameterMaximumcurrent electrode spacing (119860119861) was constrained by settlementpattern and other space limiting conditions to vary fromone location to another This confined the VES points tothe locations shown in Figure 1 In locations with goodaccess paths andor roads the current cables were extendedup to 1000m in order to ensure that depths above 200mwere comfortably sampled assuming that penetration depthvaries between 025119860119861 and 05119860119861 [21 22] Correspondingreceiving (potential) electrode separation (119872119873) varied froma minimum of 05m at119860119861 = 2m to a maximum of 50mat119860119861 = 1000m At all the electrode positions great care wastaken to ensure that the separation between the potentialelectrodes did not exceed one-fifth of the separation of thecurrent electrodes [23] VES data quality was generally goodespecially in the wet season but in the dry season theelectrode positions were usually wetted with water and saltsolution (where necessary) in order to lower the contactresistance and consequently ensure good electrical contactbetween the ground and the steel electrodes
Information generated from the analyses of geophysicaldata was used to constrain drillingThe drilling phase startedas soon as the geophysical reports were submitted to theAkwa Ibom State Millennium Development Goal [24] thatfunded the borehole projects Manual drilling technique wasadopted in drilling 6-inch borehole in all locations since thesubsurface condition in the entire area was favourable to suchdrillingmethod Some of the boreholes were cited adjacent tothe VES stations while some that are located at where therewas no access path to spread the cables at the vicinity of theboreholes were separated by more than 150m (see Figures2 3 and 4) The drill cuttings were logged geologically inall 12 locations and from the desired aquifer samples werecollected for laboratory measurement of porosityThe drilledboreholes were cased using 75mm high pressure PVC casingmaterials The PVC casings were slotted at various depthswith sizable thicknesses and the slotted region of the wellannulus was gravel packed to ensure good delivery of water tothe borehole Gravel packing is also important in checking theingress of sediments into the borehole Amixture of sand andcement was used to grout the boreholes to prevent backflowof water at the surface into the well [25] The wells weredeveloped
The core samples were prewashed with distilled waterto remove traces of clay and other argillaceous materialsthat might have originated from the coring operation [26]The samples were later put into a vacuum desiccator andevacuated at a pressure of 03mBar for a period of 1 hour (see[27]) Deaerated distilled water was gently poured into thedesiccator until the water completely covers all the samplesAll the samples were later soaked for a period of 24 hours
4 ISRN Geophysics
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 4
VES 1
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
RMSEBH BH
24 25 NANA
VES
4
VES
1
6804 9499
14886 27155
14645
5492
37452
12487
Gra
velly
sand
Gra
velly
sand
Pene
trat
ion
dept
h (m
)
Loamy
Fine
sand
Fine
sand
topsoilLoamytopsoil
(b)
Figure 2 Samples of modelled VES curves along119860119861 profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 5
VES 7
Half current electrode configuration [AB2] (m)
Resis
tivity
(Ωm
)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
RMSE 21 NA 25 NA
VES
5
VES
7
BH BH
7184
18449
2058
7503
Sandytopsoil
Fine
sand
Gra
velly
sand
Silts
tone
Fine
sand
13622
14408
526
668
Loamytopsoil
(b)
Figure 3 Samples of modelled VES curves along CD profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
ISRN Geophysics 5
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 12
VES 10
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
90
100
110
NA not applicable
RMSE root-mean square error
VES
12
26
12410
1182
6112
48930
26
2107
3979
17214
2282
RMSE NA NA
VES
10
BH BH
Silts
tone
Fine
sand
Fine
sand
Silts
tone
Loamytopsoil
Loamytopsoil
(b)
Figure 4 Samples of modelled VES curves along EF profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
in order to ensure that any trace of salt and other relatedsoluble contaminants within the samples diffused out intothe surrounding water The cleaned samples were later driedin a temperature controlled oven at 105∘C for 16 hours inorder to check any irreversible change in the composition ofthe samples (see [27 28]) The oven dried core samples wereallowed to cool to normal air temperature in a desiccatorTheweight of the cool and dry core samples 119882
119889was measured
using an electronic weighing balance five times and the meanwas computed and recorded The samples were soaked withdistilled water that has been boiled for 30 minutes in avacuum pressure of 03mBar for 18 hours The weight of thewet samples119882
119908was also measured five times and the mean
was computed and recorded Effective porosity (120601) of thesamples was calculated using (6) as
120601 = 100 sdot (119882119908minus119882119889
119881) (3)
where119881 is volume of the samples Details of the experimentalprocedure can be found in [26ndash28]
4 Results and Discussion
The field data consisting of the apparent resistivity (120588119886) and
the current electrode spacing (1198601198612) were partially curvematched smoothened and manually plotted against eachother on a bilogarithmic scale with 120588
119886on the ordinate and
current electrode 1198601198612 on the abscissa It was performedby either averaging the two readings at the crossover pointsor deleting any outlier at the crossover points that did notconform to the dominant trend of the curve Also deletedwere data that stood out as outliers in the prevalent curvetrend which could have caused serious increase in root meansquare error (RMSE) during themodelling phase of the workWhere observed such outliers constitute less than 2 of thetotal data generated in each sounding station and since wemeasured over ten data per decade deleting such noisy datadid not alter the trend of the sounding curve Some of thedeleted data might have been the electrical signatures of thethin clay materials that might have suffered suppression fromthe over- and underlying thick sandy aquifers [29 30] Anydiscontinuity observed in the smoothened curves was exclu-sively attributed to vertical variation of electrical resistivitywith depth Preliminary interpretation of the smoothenedcurves wasmade using the traditional partial curvemarchingtechnique to estimate primary layer parameters The partialcurve matching technique uses master curves and chartsdeveloped by [31] A computer basedVESmodelling softwarecalled RESIST [32] that can perform automated approxima-tion of the initial resistivity model from the observed datawas later used to improve upon the preliminary interpretedresults using the inversion technique The RESIST softwareuses the initial layer parameters to perform some calculationsand at the end generates a theoretical curve in the process Itthen compares the theoretical curve with the field data curve
6 ISRN Geophysics
Table1Summaryof
locatio
ncoordinatesgeoelectric
allay
erprop
ertie
sand
protectiv
estre
ngth
ofthes
tudy
area
VES
number
Latitud
e(degree)
119910(m
)
Long
itude
(degree)
119909(m
)
Bulkresistiv
ityof
layersfro
mtopto
botto
mof
thee
cono
micaquifer(Ωm)
Thickn
esso
flayersfrom
topto
botto
mof
econ
omicaquifer(m)
Depth
toecon
omicaquifer
(m)
Long
itudinal
cond
uctance
119878(Ω
m)
Econ
omic
aquiferfractional
porosity
Protectiv
estr
ength
Curve
type
1205881
1205882
1205883
1205884
ℎ1
ℎ2
ℎ3
12982
176
6604
14886
5492
12487
1336
478
527
009
0305
Weak
KH2
2828
357
4186
19130
3921
mdash17
1123
mdash114
0006
0350
Weak
K3
2836
607
1304
57202
20494
mdash12
15512
674
005
0278
Weak
H4
2882
794
9499
27155
1464
537452
05
39
161
206
001
0301
Weak
KH5
1850
1009
7184
1844
913622
1440
805
16389
829
003
0280
Weak
KH6
1423
210
14330
2100
8605
83673
194
431
496
1124
028
0260
Mod
erate
HA
71950
1328
2058
7503
526
668
29
118
682
829
133
0195
Goo
dKH
81363
1586
18268
1075
401
647
36
246
452
734
136
0312
Goo
dAH
9581
104
34555
18256
3939
20304
06
20
892
918
023
0276
Goo
dQH
109562
150
2107
3979
17214
2282
07
128
552
687
007
0256
Weak
AK
119740
209
13351
33725
9242
16816
44
556
509
1109
007
0289
Weak
KH12
1867
356
17214
1182
6112
48930
916
567
368
1151
059
040
6Mod
erate
HA
ISRN Geophysics 7
Table 2 Protective capacity ratings of longitudinal conductance
Range Strength119878 gt 10 Excellent5 lt 119878 lt 10 Very good07 lt 119878 lt 49 Good02 lt 119878 lt 069 Moderate01 lt 119878 lt 019 Weak119878 lt 01 Poor
Since quantitative interpretation of geoelectrical soundingdata is usually difficult due to the inherent problem ofequivalence [33] borehole data were used to constrain alldepth andminimise the choice of equivalentmodels by fixinglayer thicknesses and depths while allowing the resistivitiesto vary [34] The total number of observed minima andmaxima on the smoothened VES curves was usually usedas the starting number of layers (or models) over a half-space for the data inversion exercise The software worksiteratively by calculating at the end of each step updatedparameters of the model and calculates the extent of fitbetween the calculated and the observed data using theroot mean square error (RMSE) technique in which 5 waspreset as the maximum acceptable value Figures 2 3 and 4show some of the modelled VES curves observed andtheir correlation between the nearby borehole lithology andinterpreted results A good correlation was observed betweenthe borehole lithology log data and the inverted results overhalf-space in many locations These noticed distortions weresuspected to have possibly originated from the failure of the1D assumption of the shallow subsurface of the half-space[29] The result of the computer iterations gave the layers ofthe subsurface penetrated by current true resistivity of eachlayer the thickness (ℎ) depth (119889) of each layer and the totaldepth of overburden to the safe and economically accessibleauriferous layers as shown in Table 1 Three to four layerswith different curve types were delineated The availabilityof H and K curve types indicates the high and low valuesof resistivities in sediments which translate from unsaturatedzones into saturated zones Specifically the curve types inthe areas occupied by VES are KH which takes 417 K HAH AK and QH which respectively take 83 of the totalcurve distributions The other curve type also noticed is theAH curve type which takes 167 of the curve distributions(see Table 1 and Figure 5 for curve distributions) From theinferred layer resistivities and thicknesses the longitudinalconductance known as one of the Dar Zarrouk parameterswas used to classify the degree of protection of each of VESsites according to rating in Table 2 intoweakmoderate goodand excellent aquifers based on the numerical values assignedto each point Based on the longitudinal conductance theprotective capacity of the overburden showed that 5833 ofthemapped area has weak protective capacity 1667moder-ate protective capacity and 25goodprotective capacityThisis an indication that the chosen economic aquifer repositoryapart from having a sizeable thickness of average value of5205m and average depth of 7314m also has a fair protection
0
10
20
30
40
Curv
e fre
quen
cy (
)
KH K H HA AH AK QHCurve type
417
833 833
167
833 833 833
Figure 5 Bar chart showing frequency of curve type distribution inthe study area
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
North of reference coordinate (m)
Long
itudi
nal c
ondu
ctan
ce (m
Ωminus1)
1000 1500500
Figure 6 Distribution of longitudinal conductance map showinghigh values of S in VES 6 7 and 8 in the north-eastern zone of themapped area
from the surface flow despite its open nature The sizeablethickness and the average depth of the aquifer located inaquifer units ranging from fine sand to coarse or in siltstonecan be economically exploited for domestic and industrialuses by the settlers of the region
The longitudinal conductance (119878) is given by
119878 =
119899
sum
119894=1
ℎ119894
120588119894
=ℎ1
1205881
+ℎ2
1205882
+ℎ3
1205883
+ sdot sdot sdot +ℎ119899
120588119899
(4)
where ℎ119894and 120588
119894are the saturated thickness of each of the
layers and their corresponding true resistivities respectivelyThe earthrsquos medium acts as a natural filter to percolatingfluid The ability of the earth to retard or accelerate and filterpercolating fluid is a measure of its protective capacity [3536] The total longitudinal conductance is a parameter usedto define the target areas of groundwater potential High 119878values indicate relatively thick geologic succession and shouldbe accordedwith the highest priority in terms of groundwaterpotential while low 119878 reflects thin geologic successions withlow groundwater potential [35] The contour map showing 119878distribution is given in Figure 6
The results of the thickness and total depth of groundwa-ter repository in Table 1 were respectively used in generatingthe 2D and 3D representation of the subsurface economicgroundwater repository and 3Dmap showing the total depth
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Applied ampEnvironmentalSoil Science
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Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
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International Journal of
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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
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Geological ResearchJournal of
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Geology Advances in
ISRN Geophysics 3
a period of extreme aridity characterized by excruciatinghigh temperatures that do reach 35∘C The area has beenseverely affected by the current global climatic changes insuch a way that there have been shifts in both the upperand lower boundaries of these climatic conditions [9ndash13]Thestudy area is located in the tertiary to quaternary coastal plainsands (CPS) (otherwise called the Benin Formation) andalluvial environments of the Niger Delta region of SouthernNigeria (Figure 1) The Benin Formation which is underlainby the paralic Agbada Formation covers over 80 of thestudy area The sediments of the Benin Formation consistof interfringing units of lacustrine and fluvial loose sandspebbles clays and lignite streaks of varying thicknesseswhile the alluvial units comprise tidal and lagoonal sedimentsand beach sands and soils [14ndash16] which are mostly foundin the southern parts and along the river banks The CPS iscovered by thin lateritic overburden materials with varyingthicknesses at some locations but is massively exposed nearthe shorelines The CPS forms the major aquiferous unitsin the area It comprises poorly sorted continental (finemedium and coarse) sands and gravels that alternatewith lig-nite streaks thin clay horizons and lenses at some locationsThe thin clayshale horizons truncate the vertical and lateralextents of the sandy aquifers thereby building upmultiaquifersystems in the area [17] Thus both confined and partiallyconfined aquifers can be found in the area Southward flowingrivers like the Kwa River and their tributaries that emptydirectly into the Bight of Bonny drain the area
3 Data Acquisition and Analysis
Surface electrical methods have been used in investigatingdifferent types of geological geotechnical and environmentalproblems for many years due to the dependence of earthresistivity on some geologic parameters Generally the elec-trical resistivity method involves injecting electrical currentinto the ground through a pair of electrodes (called currentelectrodes) and monitoring the potential difference createdby the passage of the electrical current through the earthmaterials using another pair of electrodes technically calledpotential electrodes Details of this can be found in [18ndash20] Many electrode configurations and field procedures existthat can be used to perform geoelectrical investigations [18]but the Schlumberger array which was performed using thevertical electrical sounding field procedure was adopted toassess the subsurface electrical resistivity and the depth ofthe economically accessible aquifers The Schlumberger elec-trode configuration used in measuring apparent resistivity 120588
119886
is shown in the following equation
120588119886= 120587 sdot ((1198601198612)
2minus (1198721198732)
2
(119872119873)) sdot 119877119886 (1)
whereAB is the distance between two current electrodes119872119873is the distance between two potential electrodes and 119877
119886is
the apparent electrical earthrsquos resistance measured from the
equipment The term in the equation shown below is calledthe geometric factor (119866)
119866 = 120587 sdot ((1198601198612)
2minus (1198721198732)
2
119872119873) (2)
The electrical resistivity investigations were conducted intwelve (12) locations across the study area between 2011 and2012 using a SAS1000model of ABEMTerrameterMaximumcurrent electrode spacing (119860119861) was constrained by settlementpattern and other space limiting conditions to vary fromone location to another This confined the VES points tothe locations shown in Figure 1 In locations with goodaccess paths andor roads the current cables were extendedup to 1000m in order to ensure that depths above 200mwere comfortably sampled assuming that penetration depthvaries between 025119860119861 and 05119860119861 [21 22] Correspondingreceiving (potential) electrode separation (119872119873) varied froma minimum of 05m at119860119861 = 2m to a maximum of 50mat119860119861 = 1000m At all the electrode positions great care wastaken to ensure that the separation between the potentialelectrodes did not exceed one-fifth of the separation of thecurrent electrodes [23] VES data quality was generally goodespecially in the wet season but in the dry season theelectrode positions were usually wetted with water and saltsolution (where necessary) in order to lower the contactresistance and consequently ensure good electrical contactbetween the ground and the steel electrodes
Information generated from the analyses of geophysicaldata was used to constrain drillingThe drilling phase startedas soon as the geophysical reports were submitted to theAkwa Ibom State Millennium Development Goal [24] thatfunded the borehole projects Manual drilling technique wasadopted in drilling 6-inch borehole in all locations since thesubsurface condition in the entire area was favourable to suchdrillingmethod Some of the boreholes were cited adjacent tothe VES stations while some that are located at where therewas no access path to spread the cables at the vicinity of theboreholes were separated by more than 150m (see Figures2 3 and 4) The drill cuttings were logged geologically inall 12 locations and from the desired aquifer samples werecollected for laboratory measurement of porosityThe drilledboreholes were cased using 75mm high pressure PVC casingmaterials The PVC casings were slotted at various depthswith sizable thicknesses and the slotted region of the wellannulus was gravel packed to ensure good delivery of water tothe borehole Gravel packing is also important in checking theingress of sediments into the borehole Amixture of sand andcement was used to grout the boreholes to prevent backflowof water at the surface into the well [25] The wells weredeveloped
The core samples were prewashed with distilled waterto remove traces of clay and other argillaceous materialsthat might have originated from the coring operation [26]The samples were later put into a vacuum desiccator andevacuated at a pressure of 03mBar for a period of 1 hour (see[27]) Deaerated distilled water was gently poured into thedesiccator until the water completely covers all the samplesAll the samples were later soaked for a period of 24 hours
4 ISRN Geophysics
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 4
VES 1
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
RMSEBH BH
24 25 NANA
VES
4
VES
1
6804 9499
14886 27155
14645
5492
37452
12487
Gra
velly
sand
Gra
velly
sand
Pene
trat
ion
dept
h (m
)
Loamy
Fine
sand
Fine
sand
topsoilLoamytopsoil
(b)
Figure 2 Samples of modelled VES curves along119860119861 profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 5
VES 7
Half current electrode configuration [AB2] (m)
Resis
tivity
(Ωm
)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
RMSE 21 NA 25 NA
VES
5
VES
7
BH BH
7184
18449
2058
7503
Sandytopsoil
Fine
sand
Gra
velly
sand
Silts
tone
Fine
sand
13622
14408
526
668
Loamytopsoil
(b)
Figure 3 Samples of modelled VES curves along CD profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
ISRN Geophysics 5
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 12
VES 10
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
90
100
110
NA not applicable
RMSE root-mean square error
VES
12
26
12410
1182
6112
48930
26
2107
3979
17214
2282
RMSE NA NA
VES
10
BH BH
Silts
tone
Fine
sand
Fine
sand
Silts
tone
Loamytopsoil
Loamytopsoil
(b)
Figure 4 Samples of modelled VES curves along EF profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
in order to ensure that any trace of salt and other relatedsoluble contaminants within the samples diffused out intothe surrounding water The cleaned samples were later driedin a temperature controlled oven at 105∘C for 16 hours inorder to check any irreversible change in the composition ofthe samples (see [27 28]) The oven dried core samples wereallowed to cool to normal air temperature in a desiccatorTheweight of the cool and dry core samples 119882
119889was measured
using an electronic weighing balance five times and the meanwas computed and recorded The samples were soaked withdistilled water that has been boiled for 30 minutes in avacuum pressure of 03mBar for 18 hours The weight of thewet samples119882
119908was also measured five times and the mean
was computed and recorded Effective porosity (120601) of thesamples was calculated using (6) as
120601 = 100 sdot (119882119908minus119882119889
119881) (3)
where119881 is volume of the samples Details of the experimentalprocedure can be found in [26ndash28]
4 Results and Discussion
The field data consisting of the apparent resistivity (120588119886) and
the current electrode spacing (1198601198612) were partially curvematched smoothened and manually plotted against eachother on a bilogarithmic scale with 120588
119886on the ordinate and
current electrode 1198601198612 on the abscissa It was performedby either averaging the two readings at the crossover pointsor deleting any outlier at the crossover points that did notconform to the dominant trend of the curve Also deletedwere data that stood out as outliers in the prevalent curvetrend which could have caused serious increase in root meansquare error (RMSE) during themodelling phase of the workWhere observed such outliers constitute less than 2 of thetotal data generated in each sounding station and since wemeasured over ten data per decade deleting such noisy datadid not alter the trend of the sounding curve Some of thedeleted data might have been the electrical signatures of thethin clay materials that might have suffered suppression fromthe over- and underlying thick sandy aquifers [29 30] Anydiscontinuity observed in the smoothened curves was exclu-sively attributed to vertical variation of electrical resistivitywith depth Preliminary interpretation of the smoothenedcurves wasmade using the traditional partial curvemarchingtechnique to estimate primary layer parameters The partialcurve matching technique uses master curves and chartsdeveloped by [31] A computer basedVESmodelling softwarecalled RESIST [32] that can perform automated approxima-tion of the initial resistivity model from the observed datawas later used to improve upon the preliminary interpretedresults using the inversion technique The RESIST softwareuses the initial layer parameters to perform some calculationsand at the end generates a theoretical curve in the process Itthen compares the theoretical curve with the field data curve
6 ISRN Geophysics
Table1Summaryof
locatio
ncoordinatesgeoelectric
allay
erprop
ertie
sand
protectiv
estre
ngth
ofthes
tudy
area
VES
number
Latitud
e(degree)
119910(m
)
Long
itude
(degree)
119909(m
)
Bulkresistiv
ityof
layersfro
mtopto
botto
mof
thee
cono
micaquifer(Ωm)
Thickn
esso
flayersfrom
topto
botto
mof
econ
omicaquifer(m)
Depth
toecon
omicaquifer
(m)
Long
itudinal
cond
uctance
119878(Ω
m)
Econ
omic
aquiferfractional
porosity
Protectiv
estr
ength
Curve
type
1205881
1205882
1205883
1205884
ℎ1
ℎ2
ℎ3
12982
176
6604
14886
5492
12487
1336
478
527
009
0305
Weak
KH2
2828
357
4186
19130
3921
mdash17
1123
mdash114
0006
0350
Weak
K3
2836
607
1304
57202
20494
mdash12
15512
674
005
0278
Weak
H4
2882
794
9499
27155
1464
537452
05
39
161
206
001
0301
Weak
KH5
1850
1009
7184
1844
913622
1440
805
16389
829
003
0280
Weak
KH6
1423
210
14330
2100
8605
83673
194
431
496
1124
028
0260
Mod
erate
HA
71950
1328
2058
7503
526
668
29
118
682
829
133
0195
Goo
dKH
81363
1586
18268
1075
401
647
36
246
452
734
136
0312
Goo
dAH
9581
104
34555
18256
3939
20304
06
20
892
918
023
0276
Goo
dQH
109562
150
2107
3979
17214
2282
07
128
552
687
007
0256
Weak
AK
119740
209
13351
33725
9242
16816
44
556
509
1109
007
0289
Weak
KH12
1867
356
17214
1182
6112
48930
916
567
368
1151
059
040
6Mod
erate
HA
ISRN Geophysics 7
Table 2 Protective capacity ratings of longitudinal conductance
Range Strength119878 gt 10 Excellent5 lt 119878 lt 10 Very good07 lt 119878 lt 49 Good02 lt 119878 lt 069 Moderate01 lt 119878 lt 019 Weak119878 lt 01 Poor
Since quantitative interpretation of geoelectrical soundingdata is usually difficult due to the inherent problem ofequivalence [33] borehole data were used to constrain alldepth andminimise the choice of equivalentmodels by fixinglayer thicknesses and depths while allowing the resistivitiesto vary [34] The total number of observed minima andmaxima on the smoothened VES curves was usually usedas the starting number of layers (or models) over a half-space for the data inversion exercise The software worksiteratively by calculating at the end of each step updatedparameters of the model and calculates the extent of fitbetween the calculated and the observed data using theroot mean square error (RMSE) technique in which 5 waspreset as the maximum acceptable value Figures 2 3 and 4show some of the modelled VES curves observed andtheir correlation between the nearby borehole lithology andinterpreted results A good correlation was observed betweenthe borehole lithology log data and the inverted results overhalf-space in many locations These noticed distortions weresuspected to have possibly originated from the failure of the1D assumption of the shallow subsurface of the half-space[29] The result of the computer iterations gave the layers ofthe subsurface penetrated by current true resistivity of eachlayer the thickness (ℎ) depth (119889) of each layer and the totaldepth of overburden to the safe and economically accessibleauriferous layers as shown in Table 1 Three to four layerswith different curve types were delineated The availabilityof H and K curve types indicates the high and low valuesof resistivities in sediments which translate from unsaturatedzones into saturated zones Specifically the curve types inthe areas occupied by VES are KH which takes 417 K HAH AK and QH which respectively take 83 of the totalcurve distributions The other curve type also noticed is theAH curve type which takes 167 of the curve distributions(see Table 1 and Figure 5 for curve distributions) From theinferred layer resistivities and thicknesses the longitudinalconductance known as one of the Dar Zarrouk parameterswas used to classify the degree of protection of each of VESsites according to rating in Table 2 intoweakmoderate goodand excellent aquifers based on the numerical values assignedto each point Based on the longitudinal conductance theprotective capacity of the overburden showed that 5833 ofthemapped area has weak protective capacity 1667moder-ate protective capacity and 25goodprotective capacityThisis an indication that the chosen economic aquifer repositoryapart from having a sizeable thickness of average value of5205m and average depth of 7314m also has a fair protection
0
10
20
30
40
Curv
e fre
quen
cy (
)
KH K H HA AH AK QHCurve type
417
833 833
167
833 833 833
Figure 5 Bar chart showing frequency of curve type distribution inthe study area
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
North of reference coordinate (m)
Long
itudi
nal c
ondu
ctan
ce (m
Ωminus1)
1000 1500500
Figure 6 Distribution of longitudinal conductance map showinghigh values of S in VES 6 7 and 8 in the north-eastern zone of themapped area
from the surface flow despite its open nature The sizeablethickness and the average depth of the aquifer located inaquifer units ranging from fine sand to coarse or in siltstonecan be economically exploited for domestic and industrialuses by the settlers of the region
The longitudinal conductance (119878) is given by
119878 =
119899
sum
119894=1
ℎ119894
120588119894
=ℎ1
1205881
+ℎ2
1205882
+ℎ3
1205883
+ sdot sdot sdot +ℎ119899
120588119899
(4)
where ℎ119894and 120588
119894are the saturated thickness of each of the
layers and their corresponding true resistivities respectivelyThe earthrsquos medium acts as a natural filter to percolatingfluid The ability of the earth to retard or accelerate and filterpercolating fluid is a measure of its protective capacity [3536] The total longitudinal conductance is a parameter usedto define the target areas of groundwater potential High 119878values indicate relatively thick geologic succession and shouldbe accordedwith the highest priority in terms of groundwaterpotential while low 119878 reflects thin geologic successions withlow groundwater potential [35] The contour map showing 119878distribution is given in Figure 6
The results of the thickness and total depth of groundwa-ter repository in Table 1 were respectively used in generatingthe 2D and 3D representation of the subsurface economicgroundwater repository and 3Dmap showing the total depth
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
4 ISRN Geophysics
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 4
VES 1
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
RMSEBH BH
24 25 NANA
VES
4
VES
1
6804 9499
14886 27155
14645
5492
37452
12487
Gra
velly
sand
Gra
velly
sand
Pene
trat
ion
dept
h (m
)
Loamy
Fine
sand
Fine
sand
topsoilLoamytopsoil
(b)
Figure 2 Samples of modelled VES curves along119860119861 profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 5
VES 7
Half current electrode configuration [AB2] (m)
Resis
tivity
(Ωm
)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
RMSE 21 NA 25 NA
VES
5
VES
7
BH BH
7184
18449
2058
7503
Sandytopsoil
Fine
sand
Gra
velly
sand
Silts
tone
Fine
sand
13622
14408
526
668
Loamytopsoil
(b)
Figure 3 Samples of modelled VES curves along CD profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
ISRN Geophysics 5
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 12
VES 10
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
90
100
110
NA not applicable
RMSE root-mean square error
VES
12
26
12410
1182
6112
48930
26
2107
3979
17214
2282
RMSE NA NA
VES
10
BH BH
Silts
tone
Fine
sand
Fine
sand
Silts
tone
Loamytopsoil
Loamytopsoil
(b)
Figure 4 Samples of modelled VES curves along EF profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
in order to ensure that any trace of salt and other relatedsoluble contaminants within the samples diffused out intothe surrounding water The cleaned samples were later driedin a temperature controlled oven at 105∘C for 16 hours inorder to check any irreversible change in the composition ofthe samples (see [27 28]) The oven dried core samples wereallowed to cool to normal air temperature in a desiccatorTheweight of the cool and dry core samples 119882
119889was measured
using an electronic weighing balance five times and the meanwas computed and recorded The samples were soaked withdistilled water that has been boiled for 30 minutes in avacuum pressure of 03mBar for 18 hours The weight of thewet samples119882
119908was also measured five times and the mean
was computed and recorded Effective porosity (120601) of thesamples was calculated using (6) as
120601 = 100 sdot (119882119908minus119882119889
119881) (3)
where119881 is volume of the samples Details of the experimentalprocedure can be found in [26ndash28]
4 Results and Discussion
The field data consisting of the apparent resistivity (120588119886) and
the current electrode spacing (1198601198612) were partially curvematched smoothened and manually plotted against eachother on a bilogarithmic scale with 120588
119886on the ordinate and
current electrode 1198601198612 on the abscissa It was performedby either averaging the two readings at the crossover pointsor deleting any outlier at the crossover points that did notconform to the dominant trend of the curve Also deletedwere data that stood out as outliers in the prevalent curvetrend which could have caused serious increase in root meansquare error (RMSE) during themodelling phase of the workWhere observed such outliers constitute less than 2 of thetotal data generated in each sounding station and since wemeasured over ten data per decade deleting such noisy datadid not alter the trend of the sounding curve Some of thedeleted data might have been the electrical signatures of thethin clay materials that might have suffered suppression fromthe over- and underlying thick sandy aquifers [29 30] Anydiscontinuity observed in the smoothened curves was exclu-sively attributed to vertical variation of electrical resistivitywith depth Preliminary interpretation of the smoothenedcurves wasmade using the traditional partial curvemarchingtechnique to estimate primary layer parameters The partialcurve matching technique uses master curves and chartsdeveloped by [31] A computer basedVESmodelling softwarecalled RESIST [32] that can perform automated approxima-tion of the initial resistivity model from the observed datawas later used to improve upon the preliminary interpretedresults using the inversion technique The RESIST softwareuses the initial layer parameters to perform some calculationsand at the end generates a theoretical curve in the process Itthen compares the theoretical curve with the field data curve
6 ISRN Geophysics
Table1Summaryof
locatio
ncoordinatesgeoelectric
allay
erprop
ertie
sand
protectiv
estre
ngth
ofthes
tudy
area
VES
number
Latitud
e(degree)
119910(m
)
Long
itude
(degree)
119909(m
)
Bulkresistiv
ityof
layersfro
mtopto
botto
mof
thee
cono
micaquifer(Ωm)
Thickn
esso
flayersfrom
topto
botto
mof
econ
omicaquifer(m)
Depth
toecon
omicaquifer
(m)
Long
itudinal
cond
uctance
119878(Ω
m)
Econ
omic
aquiferfractional
porosity
Protectiv
estr
ength
Curve
type
1205881
1205882
1205883
1205884
ℎ1
ℎ2
ℎ3
12982
176
6604
14886
5492
12487
1336
478
527
009
0305
Weak
KH2
2828
357
4186
19130
3921
mdash17
1123
mdash114
0006
0350
Weak
K3
2836
607
1304
57202
20494
mdash12
15512
674
005
0278
Weak
H4
2882
794
9499
27155
1464
537452
05
39
161
206
001
0301
Weak
KH5
1850
1009
7184
1844
913622
1440
805
16389
829
003
0280
Weak
KH6
1423
210
14330
2100
8605
83673
194
431
496
1124
028
0260
Mod
erate
HA
71950
1328
2058
7503
526
668
29
118
682
829
133
0195
Goo
dKH
81363
1586
18268
1075
401
647
36
246
452
734
136
0312
Goo
dAH
9581
104
34555
18256
3939
20304
06
20
892
918
023
0276
Goo
dQH
109562
150
2107
3979
17214
2282
07
128
552
687
007
0256
Weak
AK
119740
209
13351
33725
9242
16816
44
556
509
1109
007
0289
Weak
KH12
1867
356
17214
1182
6112
48930
916
567
368
1151
059
040
6Mod
erate
HA
ISRN Geophysics 7
Table 2 Protective capacity ratings of longitudinal conductance
Range Strength119878 gt 10 Excellent5 lt 119878 lt 10 Very good07 lt 119878 lt 49 Good02 lt 119878 lt 069 Moderate01 lt 119878 lt 019 Weak119878 lt 01 Poor
Since quantitative interpretation of geoelectrical soundingdata is usually difficult due to the inherent problem ofequivalence [33] borehole data were used to constrain alldepth andminimise the choice of equivalentmodels by fixinglayer thicknesses and depths while allowing the resistivitiesto vary [34] The total number of observed minima andmaxima on the smoothened VES curves was usually usedas the starting number of layers (or models) over a half-space for the data inversion exercise The software worksiteratively by calculating at the end of each step updatedparameters of the model and calculates the extent of fitbetween the calculated and the observed data using theroot mean square error (RMSE) technique in which 5 waspreset as the maximum acceptable value Figures 2 3 and 4show some of the modelled VES curves observed andtheir correlation between the nearby borehole lithology andinterpreted results A good correlation was observed betweenthe borehole lithology log data and the inverted results overhalf-space in many locations These noticed distortions weresuspected to have possibly originated from the failure of the1D assumption of the shallow subsurface of the half-space[29] The result of the computer iterations gave the layers ofthe subsurface penetrated by current true resistivity of eachlayer the thickness (ℎ) depth (119889) of each layer and the totaldepth of overburden to the safe and economically accessibleauriferous layers as shown in Table 1 Three to four layerswith different curve types were delineated The availabilityof H and K curve types indicates the high and low valuesof resistivities in sediments which translate from unsaturatedzones into saturated zones Specifically the curve types inthe areas occupied by VES are KH which takes 417 K HAH AK and QH which respectively take 83 of the totalcurve distributions The other curve type also noticed is theAH curve type which takes 167 of the curve distributions(see Table 1 and Figure 5 for curve distributions) From theinferred layer resistivities and thicknesses the longitudinalconductance known as one of the Dar Zarrouk parameterswas used to classify the degree of protection of each of VESsites according to rating in Table 2 intoweakmoderate goodand excellent aquifers based on the numerical values assignedto each point Based on the longitudinal conductance theprotective capacity of the overburden showed that 5833 ofthemapped area has weak protective capacity 1667moder-ate protective capacity and 25goodprotective capacityThisis an indication that the chosen economic aquifer repositoryapart from having a sizeable thickness of average value of5205m and average depth of 7314m also has a fair protection
0
10
20
30
40
Curv
e fre
quen
cy (
)
KH K H HA AH AK QHCurve type
417
833 833
167
833 833 833
Figure 5 Bar chart showing frequency of curve type distribution inthe study area
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
North of reference coordinate (m)
Long
itudi
nal c
ondu
ctan
ce (m
Ωminus1)
1000 1500500
Figure 6 Distribution of longitudinal conductance map showinghigh values of S in VES 6 7 and 8 in the north-eastern zone of themapped area
from the surface flow despite its open nature The sizeablethickness and the average depth of the aquifer located inaquifer units ranging from fine sand to coarse or in siltstonecan be economically exploited for domestic and industrialuses by the settlers of the region
The longitudinal conductance (119878) is given by
119878 =
119899
sum
119894=1
ℎ119894
120588119894
=ℎ1
1205881
+ℎ2
1205882
+ℎ3
1205883
+ sdot sdot sdot +ℎ119899
120588119899
(4)
where ℎ119894and 120588
119894are the saturated thickness of each of the
layers and their corresponding true resistivities respectivelyThe earthrsquos medium acts as a natural filter to percolatingfluid The ability of the earth to retard or accelerate and filterpercolating fluid is a measure of its protective capacity [3536] The total longitudinal conductance is a parameter usedto define the target areas of groundwater potential High 119878values indicate relatively thick geologic succession and shouldbe accordedwith the highest priority in terms of groundwaterpotential while low 119878 reflects thin geologic successions withlow groundwater potential [35] The contour map showing 119878distribution is given in Figure 6
The results of the thickness and total depth of groundwa-ter repository in Table 1 were respectively used in generatingthe 2D and 3D representation of the subsurface economicgroundwater repository and 3Dmap showing the total depth
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
ISRN Geophysics 5
Resis
tivity
(Ωm
)
105
104
103
103
102
102
101
100
101
ObservedCalculated
VES 12
VES 10
Half current electrode configuration [AB2] (m)
(a)
10
20
30
50
60
40
70
80
Pene
trat
ion
dept
h (m
)
90
100
110
NA not applicable
RMSE root-mean square error
VES
12
26
12410
1182
6112
48930
26
2107
3979
17214
2282
RMSE NA NA
VES
10
BH BH
Silts
tone
Fine
sand
Fine
sand
Silts
tone
Loamytopsoil
Loamytopsoil
(b)
Figure 4 Samples of modelled VES curves along EF profile showing correlations between VES derived 1-D subsurface models and boreholelithologs
in order to ensure that any trace of salt and other relatedsoluble contaminants within the samples diffused out intothe surrounding water The cleaned samples were later driedin a temperature controlled oven at 105∘C for 16 hours inorder to check any irreversible change in the composition ofthe samples (see [27 28]) The oven dried core samples wereallowed to cool to normal air temperature in a desiccatorTheweight of the cool and dry core samples 119882
119889was measured
using an electronic weighing balance five times and the meanwas computed and recorded The samples were soaked withdistilled water that has been boiled for 30 minutes in avacuum pressure of 03mBar for 18 hours The weight of thewet samples119882
119908was also measured five times and the mean
was computed and recorded Effective porosity (120601) of thesamples was calculated using (6) as
120601 = 100 sdot (119882119908minus119882119889
119881) (3)
where119881 is volume of the samples Details of the experimentalprocedure can be found in [26ndash28]
4 Results and Discussion
The field data consisting of the apparent resistivity (120588119886) and
the current electrode spacing (1198601198612) were partially curvematched smoothened and manually plotted against eachother on a bilogarithmic scale with 120588
119886on the ordinate and
current electrode 1198601198612 on the abscissa It was performedby either averaging the two readings at the crossover pointsor deleting any outlier at the crossover points that did notconform to the dominant trend of the curve Also deletedwere data that stood out as outliers in the prevalent curvetrend which could have caused serious increase in root meansquare error (RMSE) during themodelling phase of the workWhere observed such outliers constitute less than 2 of thetotal data generated in each sounding station and since wemeasured over ten data per decade deleting such noisy datadid not alter the trend of the sounding curve Some of thedeleted data might have been the electrical signatures of thethin clay materials that might have suffered suppression fromthe over- and underlying thick sandy aquifers [29 30] Anydiscontinuity observed in the smoothened curves was exclu-sively attributed to vertical variation of electrical resistivitywith depth Preliminary interpretation of the smoothenedcurves wasmade using the traditional partial curvemarchingtechnique to estimate primary layer parameters The partialcurve matching technique uses master curves and chartsdeveloped by [31] A computer basedVESmodelling softwarecalled RESIST [32] that can perform automated approxima-tion of the initial resistivity model from the observed datawas later used to improve upon the preliminary interpretedresults using the inversion technique The RESIST softwareuses the initial layer parameters to perform some calculationsand at the end generates a theoretical curve in the process Itthen compares the theoretical curve with the field data curve
6 ISRN Geophysics
Table1Summaryof
locatio
ncoordinatesgeoelectric
allay
erprop
ertie
sand
protectiv
estre
ngth
ofthes
tudy
area
VES
number
Latitud
e(degree)
119910(m
)
Long
itude
(degree)
119909(m
)
Bulkresistiv
ityof
layersfro
mtopto
botto
mof
thee
cono
micaquifer(Ωm)
Thickn
esso
flayersfrom
topto
botto
mof
econ
omicaquifer(m)
Depth
toecon
omicaquifer
(m)
Long
itudinal
cond
uctance
119878(Ω
m)
Econ
omic
aquiferfractional
porosity
Protectiv
estr
ength
Curve
type
1205881
1205882
1205883
1205884
ℎ1
ℎ2
ℎ3
12982
176
6604
14886
5492
12487
1336
478
527
009
0305
Weak
KH2
2828
357
4186
19130
3921
mdash17
1123
mdash114
0006
0350
Weak
K3
2836
607
1304
57202
20494
mdash12
15512
674
005
0278
Weak
H4
2882
794
9499
27155
1464
537452
05
39
161
206
001
0301
Weak
KH5
1850
1009
7184
1844
913622
1440
805
16389
829
003
0280
Weak
KH6
1423
210
14330
2100
8605
83673
194
431
496
1124
028
0260
Mod
erate
HA
71950
1328
2058
7503
526
668
29
118
682
829
133
0195
Goo
dKH
81363
1586
18268
1075
401
647
36
246
452
734
136
0312
Goo
dAH
9581
104
34555
18256
3939
20304
06
20
892
918
023
0276
Goo
dQH
109562
150
2107
3979
17214
2282
07
128
552
687
007
0256
Weak
AK
119740
209
13351
33725
9242
16816
44
556
509
1109
007
0289
Weak
KH12
1867
356
17214
1182
6112
48930
916
567
368
1151
059
040
6Mod
erate
HA
ISRN Geophysics 7
Table 2 Protective capacity ratings of longitudinal conductance
Range Strength119878 gt 10 Excellent5 lt 119878 lt 10 Very good07 lt 119878 lt 49 Good02 lt 119878 lt 069 Moderate01 lt 119878 lt 019 Weak119878 lt 01 Poor
Since quantitative interpretation of geoelectrical soundingdata is usually difficult due to the inherent problem ofequivalence [33] borehole data were used to constrain alldepth andminimise the choice of equivalentmodels by fixinglayer thicknesses and depths while allowing the resistivitiesto vary [34] The total number of observed minima andmaxima on the smoothened VES curves was usually usedas the starting number of layers (or models) over a half-space for the data inversion exercise The software worksiteratively by calculating at the end of each step updatedparameters of the model and calculates the extent of fitbetween the calculated and the observed data using theroot mean square error (RMSE) technique in which 5 waspreset as the maximum acceptable value Figures 2 3 and 4show some of the modelled VES curves observed andtheir correlation between the nearby borehole lithology andinterpreted results A good correlation was observed betweenthe borehole lithology log data and the inverted results overhalf-space in many locations These noticed distortions weresuspected to have possibly originated from the failure of the1D assumption of the shallow subsurface of the half-space[29] The result of the computer iterations gave the layers ofthe subsurface penetrated by current true resistivity of eachlayer the thickness (ℎ) depth (119889) of each layer and the totaldepth of overburden to the safe and economically accessibleauriferous layers as shown in Table 1 Three to four layerswith different curve types were delineated The availabilityof H and K curve types indicates the high and low valuesof resistivities in sediments which translate from unsaturatedzones into saturated zones Specifically the curve types inthe areas occupied by VES are KH which takes 417 K HAH AK and QH which respectively take 83 of the totalcurve distributions The other curve type also noticed is theAH curve type which takes 167 of the curve distributions(see Table 1 and Figure 5 for curve distributions) From theinferred layer resistivities and thicknesses the longitudinalconductance known as one of the Dar Zarrouk parameterswas used to classify the degree of protection of each of VESsites according to rating in Table 2 intoweakmoderate goodand excellent aquifers based on the numerical values assignedto each point Based on the longitudinal conductance theprotective capacity of the overburden showed that 5833 ofthemapped area has weak protective capacity 1667moder-ate protective capacity and 25goodprotective capacityThisis an indication that the chosen economic aquifer repositoryapart from having a sizeable thickness of average value of5205m and average depth of 7314m also has a fair protection
0
10
20
30
40
Curv
e fre
quen
cy (
)
KH K H HA AH AK QHCurve type
417
833 833
167
833 833 833
Figure 5 Bar chart showing frequency of curve type distribution inthe study area
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
North of reference coordinate (m)
Long
itudi
nal c
ondu
ctan
ce (m
Ωminus1)
1000 1500500
Figure 6 Distribution of longitudinal conductance map showinghigh values of S in VES 6 7 and 8 in the north-eastern zone of themapped area
from the surface flow despite its open nature The sizeablethickness and the average depth of the aquifer located inaquifer units ranging from fine sand to coarse or in siltstonecan be economically exploited for domestic and industrialuses by the settlers of the region
The longitudinal conductance (119878) is given by
119878 =
119899
sum
119894=1
ℎ119894
120588119894
=ℎ1
1205881
+ℎ2
1205882
+ℎ3
1205883
+ sdot sdot sdot +ℎ119899
120588119899
(4)
where ℎ119894and 120588
119894are the saturated thickness of each of the
layers and their corresponding true resistivities respectivelyThe earthrsquos medium acts as a natural filter to percolatingfluid The ability of the earth to retard or accelerate and filterpercolating fluid is a measure of its protective capacity [3536] The total longitudinal conductance is a parameter usedto define the target areas of groundwater potential High 119878values indicate relatively thick geologic succession and shouldbe accordedwith the highest priority in terms of groundwaterpotential while low 119878 reflects thin geologic successions withlow groundwater potential [35] The contour map showing 119878distribution is given in Figure 6
The results of the thickness and total depth of groundwa-ter repository in Table 1 were respectively used in generatingthe 2D and 3D representation of the subsurface economicgroundwater repository and 3Dmap showing the total depth
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
6 ISRN Geophysics
Table1Summaryof
locatio
ncoordinatesgeoelectric
allay
erprop
ertie
sand
protectiv
estre
ngth
ofthes
tudy
area
VES
number
Latitud
e(degree)
119910(m
)
Long
itude
(degree)
119909(m
)
Bulkresistiv
ityof
layersfro
mtopto
botto
mof
thee
cono
micaquifer(Ωm)
Thickn
esso
flayersfrom
topto
botto
mof
econ
omicaquifer(m)
Depth
toecon
omicaquifer
(m)
Long
itudinal
cond
uctance
119878(Ω
m)
Econ
omic
aquiferfractional
porosity
Protectiv
estr
ength
Curve
type
1205881
1205882
1205883
1205884
ℎ1
ℎ2
ℎ3
12982
176
6604
14886
5492
12487
1336
478
527
009
0305
Weak
KH2
2828
357
4186
19130
3921
mdash17
1123
mdash114
0006
0350
Weak
K3
2836
607
1304
57202
20494
mdash12
15512
674
005
0278
Weak
H4
2882
794
9499
27155
1464
537452
05
39
161
206
001
0301
Weak
KH5
1850
1009
7184
1844
913622
1440
805
16389
829
003
0280
Weak
KH6
1423
210
14330
2100
8605
83673
194
431
496
1124
028
0260
Mod
erate
HA
71950
1328
2058
7503
526
668
29
118
682
829
133
0195
Goo
dKH
81363
1586
18268
1075
401
647
36
246
452
734
136
0312
Goo
dAH
9581
104
34555
18256
3939
20304
06
20
892
918
023
0276
Goo
dQH
109562
150
2107
3979
17214
2282
07
128
552
687
007
0256
Weak
AK
119740
209
13351
33725
9242
16816
44
556
509
1109
007
0289
Weak
KH12
1867
356
17214
1182
6112
48930
916
567
368
1151
059
040
6Mod
erate
HA
ISRN Geophysics 7
Table 2 Protective capacity ratings of longitudinal conductance
Range Strength119878 gt 10 Excellent5 lt 119878 lt 10 Very good07 lt 119878 lt 49 Good02 lt 119878 lt 069 Moderate01 lt 119878 lt 019 Weak119878 lt 01 Poor
Since quantitative interpretation of geoelectrical soundingdata is usually difficult due to the inherent problem ofequivalence [33] borehole data were used to constrain alldepth andminimise the choice of equivalentmodels by fixinglayer thicknesses and depths while allowing the resistivitiesto vary [34] The total number of observed minima andmaxima on the smoothened VES curves was usually usedas the starting number of layers (or models) over a half-space for the data inversion exercise The software worksiteratively by calculating at the end of each step updatedparameters of the model and calculates the extent of fitbetween the calculated and the observed data using theroot mean square error (RMSE) technique in which 5 waspreset as the maximum acceptable value Figures 2 3 and 4show some of the modelled VES curves observed andtheir correlation between the nearby borehole lithology andinterpreted results A good correlation was observed betweenthe borehole lithology log data and the inverted results overhalf-space in many locations These noticed distortions weresuspected to have possibly originated from the failure of the1D assumption of the shallow subsurface of the half-space[29] The result of the computer iterations gave the layers ofthe subsurface penetrated by current true resistivity of eachlayer the thickness (ℎ) depth (119889) of each layer and the totaldepth of overburden to the safe and economically accessibleauriferous layers as shown in Table 1 Three to four layerswith different curve types were delineated The availabilityof H and K curve types indicates the high and low valuesof resistivities in sediments which translate from unsaturatedzones into saturated zones Specifically the curve types inthe areas occupied by VES are KH which takes 417 K HAH AK and QH which respectively take 83 of the totalcurve distributions The other curve type also noticed is theAH curve type which takes 167 of the curve distributions(see Table 1 and Figure 5 for curve distributions) From theinferred layer resistivities and thicknesses the longitudinalconductance known as one of the Dar Zarrouk parameterswas used to classify the degree of protection of each of VESsites according to rating in Table 2 intoweakmoderate goodand excellent aquifers based on the numerical values assignedto each point Based on the longitudinal conductance theprotective capacity of the overburden showed that 5833 ofthemapped area has weak protective capacity 1667moder-ate protective capacity and 25goodprotective capacityThisis an indication that the chosen economic aquifer repositoryapart from having a sizeable thickness of average value of5205m and average depth of 7314m also has a fair protection
0
10
20
30
40
Curv
e fre
quen
cy (
)
KH K H HA AH AK QHCurve type
417
833 833
167
833 833 833
Figure 5 Bar chart showing frequency of curve type distribution inthe study area
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
North of reference coordinate (m)
Long
itudi
nal c
ondu
ctan
ce (m
Ωminus1)
1000 1500500
Figure 6 Distribution of longitudinal conductance map showinghigh values of S in VES 6 7 and 8 in the north-eastern zone of themapped area
from the surface flow despite its open nature The sizeablethickness and the average depth of the aquifer located inaquifer units ranging from fine sand to coarse or in siltstonecan be economically exploited for domestic and industrialuses by the settlers of the region
The longitudinal conductance (119878) is given by
119878 =
119899
sum
119894=1
ℎ119894
120588119894
=ℎ1
1205881
+ℎ2
1205882
+ℎ3
1205883
+ sdot sdot sdot +ℎ119899
120588119899
(4)
where ℎ119894and 120588
119894are the saturated thickness of each of the
layers and their corresponding true resistivities respectivelyThe earthrsquos medium acts as a natural filter to percolatingfluid The ability of the earth to retard or accelerate and filterpercolating fluid is a measure of its protective capacity [3536] The total longitudinal conductance is a parameter usedto define the target areas of groundwater potential High 119878values indicate relatively thick geologic succession and shouldbe accordedwith the highest priority in terms of groundwaterpotential while low 119878 reflects thin geologic successions withlow groundwater potential [35] The contour map showing 119878distribution is given in Figure 6
The results of the thickness and total depth of groundwa-ter repository in Table 1 were respectively used in generatingthe 2D and 3D representation of the subsurface economicgroundwater repository and 3Dmap showing the total depth
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
ISRN Geophysics 7
Table 2 Protective capacity ratings of longitudinal conductance
Range Strength119878 gt 10 Excellent5 lt 119878 lt 10 Very good07 lt 119878 lt 49 Good02 lt 119878 lt 069 Moderate01 lt 119878 lt 019 Weak119878 lt 01 Poor
Since quantitative interpretation of geoelectrical soundingdata is usually difficult due to the inherent problem ofequivalence [33] borehole data were used to constrain alldepth andminimise the choice of equivalentmodels by fixinglayer thicknesses and depths while allowing the resistivitiesto vary [34] The total number of observed minima andmaxima on the smoothened VES curves was usually usedas the starting number of layers (or models) over a half-space for the data inversion exercise The software worksiteratively by calculating at the end of each step updatedparameters of the model and calculates the extent of fitbetween the calculated and the observed data using theroot mean square error (RMSE) technique in which 5 waspreset as the maximum acceptable value Figures 2 3 and 4show some of the modelled VES curves observed andtheir correlation between the nearby borehole lithology andinterpreted results A good correlation was observed betweenthe borehole lithology log data and the inverted results overhalf-space in many locations These noticed distortions weresuspected to have possibly originated from the failure of the1D assumption of the shallow subsurface of the half-space[29] The result of the computer iterations gave the layers ofthe subsurface penetrated by current true resistivity of eachlayer the thickness (ℎ) depth (119889) of each layer and the totaldepth of overburden to the safe and economically accessibleauriferous layers as shown in Table 1 Three to four layerswith different curve types were delineated The availabilityof H and K curve types indicates the high and low valuesof resistivities in sediments which translate from unsaturatedzones into saturated zones Specifically the curve types inthe areas occupied by VES are KH which takes 417 K HAH AK and QH which respectively take 83 of the totalcurve distributions The other curve type also noticed is theAH curve type which takes 167 of the curve distributions(see Table 1 and Figure 5 for curve distributions) From theinferred layer resistivities and thicknesses the longitudinalconductance known as one of the Dar Zarrouk parameterswas used to classify the degree of protection of each of VESsites according to rating in Table 2 intoweakmoderate goodand excellent aquifers based on the numerical values assignedto each point Based on the longitudinal conductance theprotective capacity of the overburden showed that 5833 ofthemapped area has weak protective capacity 1667moder-ate protective capacity and 25goodprotective capacityThisis an indication that the chosen economic aquifer repositoryapart from having a sizeable thickness of average value of5205m and average depth of 7314m also has a fair protection
0
10
20
30
40
Curv
e fre
quen
cy (
)
KH K H HA AH AK QHCurve type
417
833 833
167
833 833 833
Figure 5 Bar chart showing frequency of curve type distribution inthe study area
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
North of reference coordinate (m)
Long
itudi
nal c
ondu
ctan
ce (m
Ωminus1)
1000 1500500
Figure 6 Distribution of longitudinal conductance map showinghigh values of S in VES 6 7 and 8 in the north-eastern zone of themapped area
from the surface flow despite its open nature The sizeablethickness and the average depth of the aquifer located inaquifer units ranging from fine sand to coarse or in siltstonecan be economically exploited for domestic and industrialuses by the settlers of the region
The longitudinal conductance (119878) is given by
119878 =
119899
sum
119894=1
ℎ119894
120588119894
=ℎ1
1205881
+ℎ2
1205882
+ℎ3
1205883
+ sdot sdot sdot +ℎ119899
120588119899
(4)
where ℎ119894and 120588
119894are the saturated thickness of each of the
layers and their corresponding true resistivities respectivelyThe earthrsquos medium acts as a natural filter to percolatingfluid The ability of the earth to retard or accelerate and filterpercolating fluid is a measure of its protective capacity [3536] The total longitudinal conductance is a parameter usedto define the target areas of groundwater potential High 119878values indicate relatively thick geologic succession and shouldbe accordedwith the highest priority in terms of groundwaterpotential while low 119878 reflects thin geologic successions withlow groundwater potential [35] The contour map showing 119878distribution is given in Figure 6
The results of the thickness and total depth of groundwa-ter repository in Table 1 were respectively used in generatingthe 2D and 3D representation of the subsurface economicgroundwater repository and 3Dmap showing the total depth
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
8 ISRN Geophysics
9000
8000
7000
6000
5000
4000
3000
2000
1000
Nor
th o
f ref
eren
ce co
ordi
nate
(m)
125
1
075
05
025
0
East of reference coordinate (m)1000 1500500
Thic
knes
s of l
ayer
(m)
(a)
1000
500
1500
200030
00400050
00600070
00800090
00
110
90
70
50
30
North reference coordinates (m) East of reference
coordinates (m)
Thick
ness
Thickness (m)100
50
(m)
(b)
Figure 7 (a) 2D distribution of aquifer thickness in the mapped area (b) 3D distribution map of the preferred aquifer thickness in themapped area used in computing the groundwater reserve
1000
500
1500
2000
3000
400050
00600070
00800090
00
100
80
60
40
2030
50
90
North of reference coordinates (m)East
of refer
ence
coordinate
s (m)
Dep
th (m
)
Depth to aquifer (m)70100
50
Figure 8 3D distribution map of depth to aquifer in the mappedarea
in a continuum (see Figures 7(a) 7(b) and 8) ApplyingSURFER programme to the thickness geometry the totalvolume of the unconfined aquifer geometry was computedas 576396025m3and the porous volume based on the averageporosity of the unconfined aquifer of 2923 (02923) was168480558m3 using the latitude of each of the survey lines asthe119910-axis and the longitude as119909-axis The porosity distribu-tion was also produced using fractional porosities in Table 1and the porosity variation is shown in Figure 9 These mapsdescribe the variations of the aquifer and can explain the flowpattern of groundwater The thickness of the economic andsafe aquifer repository to the estimated depth was consideredas the z-axisThe error in porous volumewas computed usingthe equation below
Δ119881
119881=Δ119897
119897+Δ119908
119908+Δℎ
ℎ+Δ120601
120601 (5)
where Δ119881 Δ119897 Δℎ Δ119908 120601 and Δ120601 are error in volumeV errorin length 119897(0) error in thickness ℎ(0) error in width119908 and
9000
8000
7000
6000
5000
4000
3000
2000
1000Nor
th o
f ref
eren
ce co
ordi
nate
(m)
038
041
032
026
029
035
023
East of reference coordinate (m)1000 1200 1400400200 600 800
Frac
tiona
l por
osity
02
Figure 9 3D distribution map of porosity of the preferred aquiferin the mapped area
error in porosity The error in length and width is negligibleHence
Δ119881
119881= 0 + 0 + 01 + 001 = 011 (6)
Δ119881 = 119881 sdot 011 = 168480558 sdot 011 = 18532861m3 (7)
Therefore the approximate volume of porous zone is 2923of the considered aquifer total volume Hence there exists168480558plusmn18532861m3 of water residing in the study area
5 Conclusion
The inferred safe and economic aquifer repository locatedin fine to gravelly sands does not show any interaction inthe reference location based on the resistivity the converseof conductivity The estimated reserve shows that moreboreholes can be drilled to exploit the described aquifer sothat the reasonable population who relies on the Salt Riverwater in the area can avoid the biological chemical andphysical adverse consequences associated with river water
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
ISRN Geophysics 9
The protection of the aquifer based on the overburden mate-rials is commendable as the area has on the average goodaquifers mostly within the vicinity of VES 6ndash12 Laboratorychecks can be conducted from time to time in order toaccess the protective capacity of aquifers within the regionsof VES 1ndash5 described as weak The average depth of theoverburden to the aquifer repository the highly resistivetopsoil and estimated protective capacity on the averageindicate that the safe economically recommended aquifer canbe free from surface or near-surface contaminant plumesThe porosity longitudinal conductance thickness and depthto aquifer distribution maps drawn could be used to deriveinput parameters for contaminant migration modelling andto improve the quality of model The method is unique asthe calculated aquifer parameters are well defined within therange of observed aquifer parameters
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] A A Kadafa ldquoOil exploration and spillage in the Niger Delta ofNigeriardquo Civil and Environmental Research vol 2 no 3 pp 38ndash51 2012
[2] H I Ezeigbo and B N Ezeanyim ldquoEnvironmental pollutionfrom coal mining activities in the Enugu area Anambka stateNigeriardquoMineWater and the Environment vol 12 no 1 pp 53ndash61 1993
[3] A E Edet and C S Okereke ldquoA regional study of saltwater in-trusion in southeastern Nigeria based on the analysis of geo-electrical and hydrochemical datardquo Environmental Geology vol40 no 10 pp 1278ndash1289 2001
[4] United Nations Environmental Programme ldquoEnvironmentalassessment of Ogonilandrdquo Executive Summary UNEP 2011
[5] K S Okiongbo and E Akpofure ldquoDetermination of aquiferproperties and groundwater vulnerability mapping using geo-electricmethod in Yenagoa city and its environs in Bayelsa stateSouth Nigeriardquo Journal of Water Resource and Protection vol 4no 6 pp 354ndash362
[6] A Edet and R H Worden ldquoMonitoring of the physical param-eters and evaluation of the chemical composition of river andgroundwater inCalabar (SoutheasternNigeria)rdquoEnvironmentalMonitoring and Assessment vol 157 no 1ndash4 pp 243ndash258 2009
[7] N J George A E Akpan and I B Obot ldquoResistivity study ofshallow aquifers in the parts of Southern Ukanafun Local Gov-ernment Area Akwa Ibom state Nigeriardquo E-Journal of Chem-istry vol 7 no 3 pp 693ndash700 2010
[8] U F Evans N J George A E Akpan I B Obot and A N IkotldquoA study of superficial sediments and aquifers in parts of UyoLocal Government Area Akwa Ibom state Southern Nigeriausing electrical sounding methodrdquo E-Journal of Chemistry vol7 no 3 pp 1018ndash1022 2010
[9] A G Martınez K Takahashi E Nunez et al ldquoA multi-institu-tional and interdisciplinary approach to the assessment of vul-nerability and adaptation to climate change in the PeruvianCentral Andes problems and prospectsrdquo Advances in Geo-sciences vol 14 pp 257ndash260 2008
[10] D Rapti-Caputo ldquoInfluence of climatic changes and human ac-tivities on the salinization process of coastal aquifer systemsrdquoItaian Journal of Agronomy vol 3 pp 67ndash79 2010
[11] E S Riddell S A Lorentz andD C Kotze ldquoA geophysical anal-ysis of hydro-geomorphic controls within a headwater wetlandin a granitic landscape through ERI and IPrdquo Hydrology andEarth System Sciences vol 14 no 8 pp 1697ndash1713 2010
[12] GWagner and R J Zeckhauser ldquoClimate policy hard problemsoft thinkingrdquo Climatic Change vol 110 no 3-4 pp 507ndash5212012
[13] B K Farauta C L Egbule A E Agwu Y L Idrisa and N AOnyekuru ldquoFarmersrsquo adaptation initiatives to the impact of cli-mate change on agriculturein Northern Nigeriardquo Journal of Ag-ricultural Extension vol 16 no 1 pp 132ndash144 2012
[14] T J A Reijers SW Petters and C S Nwajide ldquoTheNiger deltabasinrdquo in African Basins R C Selley Ed vol 3 of SedimentaryBasin of the World pp 151ndash172 Elsevier Science AmsterdamThe Netherlands 1997
[15] T J A Reijers and S W Petters ldquoDepositional environmentsand diagenesis of Albian carbonates on the Calabar Flank SENigeriardquo Journal of Petroleum Geology vol 10 no 3 pp 283ndash294 1987
[16] T N Nganje A E Edet and S J Ekwere ldquoConcentrations ofheavymetals and hydrocarbons in groundwater near petrol sta-tions and mechanic workshops in Calabar metropolis South-eastern Nigeriardquo Environmental Geosciences vol 14 no 1 pp15ndash29 2007
[17] N J George A I Ubom and J I Ibanga ldquoIntegrated approachto investigate the effect of leachate on groundwater around theIkot Ekpene dumpsite in Akwa Ibom state Southeastern Nige-riardquo International Journal of Geophysics vol 2014 Article ID174589 12 pages 2014
[18] WMTelford L P Geldart R E Sheriff andDAKeysAppliedGeophysics Cambridge University Press 2nd edition 1990
[19] G V Keller and F C Frischknecht Electrical Methods in Geo-physical Prospecting Pergamon London UK 1966
[20] M S Zhdanov and G KellerThe Geoelectrical Methods in Geo-physical Exploration Methods in Geochemistry and Geo-physics Elsevier 1994
[21] K K Roy andHM Elliot ldquoSome observations regarding depthof exploration in DC electrical methodsrdquo Geoexploration vol19 no 1 pp 1ndash13 1981
[22] K P Singh ldquoNonlinear estimation of aquifer parameters fromsurficial resistivity measurementsrdquoHydrology and Earth SystemSciences vol 2 pp 917ndash938 2005
[23] S S Gowd ldquoElectrical resistivity surveys to delineate ground-water potential aquifers in Peddavanka watershed AnantapurDistrict Andhra Pradesh Indiardquo Environmental Geology vol46 no 1 pp 118ndash131 2004
[24] Akwa Ibom State Millennium Development Goal (AKSMDG)ldquoBorehole completion report from the thirty one Local Govern-ment Areas of Akwa Ibom Staterdquo Tech Rep 2011
[25] A C Ibuot G T Akpabio and N J George ldquoA survey of therepository of groundwater potential and distribution using geo-electrical resistivity method in Itu Local Government Area(LGA) Akwa Ibom State SouthernNigeriardquoCentral EuropeanJournal of Geosciences vol 5 no 4 pp 538ndash547 2013
[26] American Petroleum Institute (API) ldquoRecommended practicefor core analysis procedurerdquo Tech Rep no 40 1990
[27] DW Emerson ldquoLaboratory electrical resistivityrdquo Proceedings ofthe Australian Institute of Mining and Metallurgy vol 230 no51 1969
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
10 ISRN Geophysics
[28] J S Galehouse ldquoSedimentation analysisrdquo in Procedures in Sedi-mentary Petrology R F Carver Ed p 653 Wiley-InterscienceNew York NY USA
[29] V V S G Rao G T Rao L Surinaidu R Rajesh and JMaheshldquoGeophysical and geochemical approach for seawater intrusionassessment in the Godavari Delta Basin AP IndiardquoWater Airamp Soil Pollution vol 217 no 1ndash4 pp 503ndash514 2011
[30] M A Sabet ldquoVertical electrical resistivity sounding locategroundwater resources a feasibility studyrdquoWater Resources Bul-letin vol 73 p 63 1975
[31] E Orellana andAMMooneyMaster Curve and Tables for Ver-tical Electrical Sounding over Layered Structures IntercienciaEscuela Spain 1966
[32] B P A V Velpen ldquoA computer processing package for DC re-sistivity interpretation for an IBM compatiblesrdquo ITC Journalvol 4 1988
[33] R A van Overmeeren ldquoAquifer boundaries explored by geo-electrical measurements in the coastal plain of Yemen a case ofequivalencerdquo Geophysics vol 54 no 1 pp 38ndash48 1989
[34] A T Batayneh ldquoA hydrogeophysical model of the relationshipbetween geoelectric and hydraulic parameters Central JordanrdquoJournal of Water Resource and Protection vol 1 pp 400ndash4072009
[35] R Barker T V Rao and M Thangarajan ldquoDelineation of con-taminant zone through electrical imaging techniquerdquo CurrentScience vol 81 no 3 pp 277ndash283 2001
[36] A O Olawepo A A Fatoyinbo I Ali and T O Lawal ldquoEvalua-tion of groundwater potential and subsurface lithologies inUni-lorin quarters using resistivity methodrdquo The African Review ofPhysics vol 8 pp 317ndash323 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ClimatologyJournal of
EcologyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
EarthquakesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom
Applied ampEnvironmentalSoil Science
Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal of
Geophysics
OceanographyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
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