International Journal of Geosciences, 2013, 4, 850-862
http://dx.doi.org/10.4236/ijg.2013.45079 Published Online July 2013 (http://www.scirp.org/journal/ijg)
Integrated Geophysical and Geochemica l M ethods for
Environmental Assessment of Municipal Dumpsite System
Elijah Adebowale Ayolabi1, Adetayo Femi Folorunso1,2*, Olusola Titilope Kayode1
1Department of Geosciences, University of Lagos, Lagos, Nigeria
2College of Marine Geosciences, Ocean University of China, Qingdao, China
Received April 18, 2013; revised May 21, 2013; accepted June 29, 2013
Copyright © 2013 Elijah Adebowale Ayolabi et al. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
ABSTRACT
Leachate originating from open refuse dumpsite systems can be delineated through an integration of qualitative and
quantitative methods. This study was designed to examine extent of leachate and pollution from one of the numerous
open refuse dumpsites in Lagos metropolis. Qualitative assessment was determined using electrical resistivity tomo-
graphy (ERT), vertical electrical sounding (VES) and induced polarization geophysical methods. Both ERT and VES
methods revealed persistent low resistivity (1 - 20 Ωm) of leachate to the depth above 35 m. The two methods were
projected to produce 3-D view of the site which shows a NW-SE flow pattern of the leachate and possibly, the ground-
water. IP values observed over the polluted zone was −2.9 - 8 ms, indicating a sandy layer. Quantitative assessment was
achieved by analysis of geochemical substances in the water samples taken from wells and boreholes in the precinct of
the dumpsite. Here, we examine the macroelements, salts (sulphates, nitrates and chlorides), heavy metals, radioactive
metals contents and physical parameters of the water samples. The analyses reveal the presence of these substances in
the water and their strong correlations justified the provenance as the same. As part of the quantitative evaluation,
physical parameters (pH, TDS, DO, salinity, total hardness, turbidity, electrical conductivity EC and temperature) of the
water samples were also determined. The samples pH plotted in the acidic domain unsuitable for human consumption.
Leachate flow direction was generated from the decreasing concentration of measured parameters (geochemical ele-
ments and physicals properties) in NW-SE direction which agrees with similar flow pattern deduced from ERT results.
Keywords: Dumpsite; Leachate; Electrical Resistivity; Hydrochemical Analysis; Pollution Depth; Heavy Metals;
Contaminant Plume
1. Introduction
Waste disposal dumps are common phenomena espe-
cially in industrial and highly populated cities where
dumps are generated in tons on a daily basis and thus
becomes a more important and efficient way of main-
taining a clean environment in urban settings. In devel-
oping countries unregulated landfills are commonly lo-
cated adjacent to large cities, releasing harmful contami-
nants into a leachate and thereby polluting underlying
aquifers [1-6]. Similar groundwater contamination occurs
in well waters due to leachate from household septic
tanks [7] and from settlement around dumps [8-10].
Municipal solid waste landfills/dumpsites have been
identified as major environmental problem when located
at high proximity to inhabited areas [11]. The challenges
in solid waste dumping, handling, and management, all
pose great threats to the environmental wholesomeness
[12]. In most cases, dumpsites were originally located far
from urban areas, but increasing expansion due to ever-
increasing population and urbanization have resulted in
development of land adjacent to dumps as either public
buildings or residential houses. Humans are therefore
exposed to a range of environmental hazards but particu-
larly percolation of polluted leachate into the shallow
aquifers which is the main source of drinking water in
developing countries. In most cases in developing coun-
tries, disposal sites are not properly planned. Thus, peri-
odical environmental auditing exercises become an in-
evitable task to ascertain the conditions of waste site with
view to gain the knowledge of possible interaction be-
tween its dumps and the environment.
Over the years, geochemical approaches have gained
*Corresponding author.
C
opyright © 2013 SciRes. IJG

E. A. AYOLABI ET AL. 851
tremendous popularity in dumpsite leachate delineation
[13-15]. The environmental challenges of waste dumps
include:
 contamination of groundwater by pollutants generated
by the dumps;
 migration of the pollutants away from the site via
groundwater, surface water, or air routes;
 a combination of these, fire and explosion at the site,
and direct contact with hazardous substances [6].
Each year about two million people die as a result of
poor sanitation and contaminated water, ninety percents
(90%) of the victims are children [16]. These hazardous
effects emanate from the presence of toxic elements of
environmental concern in the waste; elements such like
Pb, Cd, As and Cr. Many of these metals have been
found to act as biological poisons even at low concentra-
tion (parts of per billion—ppb) levels [17]. [18] also ob-
served that the elements are toxic in the form of cations
and when bonded to short chains of carbon atoms may
not be toxic as free elements. Even most celebrated met-
als with important commercial uses are also not left out
and hence undesirable for indiscriminate release into the
environment [19].
This research work aims to showcase the effectiveness
of integrating non-invasive geophysical methods with
widely employed geochemical approach in environmental
assessment of waste disposal site [9]. While the later is a
quantitative phenomenon, the former elaborately displays
qualitative conditions of the site. Both can map the con-
taminant plume and groundwater flow direction. The
geophysical methods we introduced are electrical resis-
tivity tomography ERT, vertical electrical sounding VES
and induced polarization IP methods.
Electrical Resistivity Tomography (ERT) is a tech-
nique for imaging the subsurface electrical structure us-
ing electrical currents. From a series of electrodes, low
frequency electrical current is injected into the subsur-
face, and the resulting potential distribution is measured.
Early development of ERT in geophysics was confined
to imaging rock core samples in the laboratory [20], but
prototype data-collection hardware and research-grade
inverse codes suitable for field scale applications soon
followed [21]. The method has been developed to detect
leaks from large storage tanks [21], monitor underground
air sparging [22] and mapping movement of contaminant
plumes [23]. More recently, ERT has been used for lo-
cating shallow cavities, fractures, fissures and mapping
groundwater flow [24], identification of geological struc-
tures [25], engineering and environmental surveys [26-
32], and in agriculture [33].
2. The Study Area
Lagos was the capital city of Nigeria until early 1990’s
when the capital territory was moved to Abuja in the
center of Nigeria geographical center. Lagos remains the
commercial and economic centre of the nation, the most
populous and most urban centre in Africa and one of the
most populated cities in the world [34]. Such geographic
and demographic factors have resulted in its growing
population and consequently, high rate of waste genera-
tion. In addition, there are many dumpsites located in
various parts of the metropolis and almost all are sur-
rounded by residential buildings including the study site
and most have not been monitored. In Lagos each person
generates around 0.5 Kg of waste per day and with a
population of around eighteen million people Lagos gen-
erates close to 10,000 MTPD (million tons per day) [35].
The study dumpsite is an open dumping system which
began over twenty years ago (Figure 1). Dumping at the
site is indiscriminate and unsorted. Wastes types dumped
on the site are mainly domestic and non-hazardous in-
dustrial wastes. Some components of these wastes in-
cluding food, papers etc, oxidize thereby changing the
redox potential of the water in the dump. Percolating
groundwater provides a medium through which the
wastes particularly organics can undergo degradation
into simpler substances through biochemical reactions
involving dissolution, hydrolysis, oxidation and reduc-
tion processes. The percolating liquid dissolves different
compositions of waste to form a complex mixture called
leachate. This leachate mainly organic carbon largely in
the form of fulvic acids migrate downward and contami-
nate the groundwater. Thus, shallow sources of ground-
water, hand-dug wells, which constitute about 85% of
sources for domestic and irrigation water systems, are at
high risk of contamination from the dumpsite.
The dumpsite covers an area of about 200 to 400
square meters sloping from the west to the east and it is
located near the Oke-Afa canal (Figure 2). The site was
initially used as an abattoir for slaughtering and market-
ing cattle and sheep, before it was converted to a refuse
dump by the local refuse collectors. However, a portion
of the land is still being used as an abattoir.
Speculative information gathered during the course of
investigation suggests the possibility of converting the
dumpsite to an international market in the future while
winding up the refuse dumping at the site. The long term
environmental effects of creating a commercial facility
on the site combined with pollution of groundwater and
therefore any future wells are beyond the scope of this
paper. However, this study hopes to evaluate the extent
of groundwater pollution.
2.1. Geology and Hydrogeology
The City of Lagos sits on a flat and low-lying plain with
altitude generally below 17 meters on a sedimentary ba-
in, variously described as the Eastern portion of Da- s

E. A. AYOLABI ET AL.
852
Figure 1. The dumping site as at the time of this survey.
Figure 2. Data acquisition map of the study area.
homey Basin, the Nigerian sector of Benin Basin or Ni-
gerian Southwestern basin. The basin is made up of a
sequence of clays and sands, with shale and limestone
intercalations [36]. Various workers have described the
stratigraphy to consist of Abeokuta group (Ise, Afowo
and Araromi Formations), Ewekoro, Oshosun, and Ilaro
Formations and Benin formation (coastal plain sands)
[36-41].
Lagos annual rainfall ranges from 2031 mm in the
western half of the state to 2032 mm in the East. The
Coastal Plains Sands aquifer is a multi-aquifer system
consisting of three aquifer horizons separated by silty or
clayey layers [42]. A shallow phreatic aquifer in present
in the most recent sediment is exploited by hand-dug
wells and shallow boreholes. This aquifer is (2.0 - 15.0 m
below the surface) is prone to pollution from surficial
activities. The deeper aquifers in the Ilaro Formation,
[42,43] are less prone to pollution. These aquifers are
often confined less prone to pollution and exploited
through boreholes for domestic and industrial water sup-
ply.
3. Materials and Methods
3.1. Geophysical Method
The electrical resistivity method and hydrochemical
analysis of water samples from wells and boreholes were
used for the investigation of possible contamination of
groundwater by leachate from an open dumpsite. A total
of six Electrical Resistivity Tomography (ERT) lines
were surveyed covering the dumpsite (Figure 2). ERT
was measured using ABEM terrameter SAS 1000, auto-
mated land imaging system with 64 electrodes. The
measurement protocol is computer controlled using a
laptop microcomputer together with an electronic switch-
ing unit used to automatically select the relevant four
electrodes for each measurement [44,45]. Selection of
minimum electrode spacing must be based on the target

E. A. AYOLABI ET AL. 853
depth [45]. Wenner electrode configuration was chosen
for its relative sensitivity to vertical changes in the sub-
surface resistivity below the center of the array and for its
ability to resolve vertical changes (i.e. horizontal structures)
[45]. Minimum electrode spacing of 3 m for all the pro-
files was maintained to attain a reading within the depth
range of polluted aquifer in the area [42]. The traverses
were oriented in NW-SE direction paralleled to each
other and according to the geometry of the dumpsite, (Fig-
ure 2) and to ensure maximum site coverage and maxi-
mum recovery of data beneath the dumpsite. Profile one
was established 70 m away from the dumpsite as a con-
trol while the other profiles were rightly located on the
dumpsite.
Resistivity data were inverted using the Earth Imager,
AGI resistivity computer program. Each commercial
system (e.g. ABEM, AGI, Campus, Geofysika, Geomet-
rics, Iris, OYO, Pasi and Scintrex) comes with its con-
version program [45]. The Earth Imager computer pro-
gram automatically reduce the measured resistance to ap-
parent resistivity values, based on smoothness-constrained
least-square technique of [46,47], modified by [48] and
applied by [42,49,50]. The subsurface is divided into
small rectangular blocks with position and size fixed by
forward modelling. The resistivity of the block is then
determined so that the calculated apparent resistivity val-
ues agree with the measured values from the field survey
by adjusting the resistivity of the model blocks and con-
sequently iterate to reduce the difference between the
calculated and measured (field) apparent resistivity [51].
These differences are expressed in form of RMS error.
Moderate RMS errors were obtained from the survey as
electrode coupling had to be improved by using water to
aid conductivity.
Beside 2-D inversion of ERT data, 1-D resistivity data
were extracted at notable points from each profile, proc-
essed and iterated to obtain typical 1-D resistivity model
to project cross-profile geoelectrical sections for a 3-D
view of the site. 1-D resistivity model samples were
shown in Figure 3. We consider this necessary to reveal
the subsurface condition below the depth probed with
ERT, which we found useful in understanding leachate
movement under the dumpsite.
In addition to resistivity data, attempts were made to
measure the Induced Polarization (IP) simultaneously
with the ERT data according to standard practices [52].
Measuring IP with ERT enables inversion and interpreta-
tion of the data in 2-D as previously noted by [32]. This
is one of the more recent developments in the instrumen-
tation of electrical imaging surveys [45]. The same resis-
tivity software was employed to invert the IP data in
similar process of subdividing the earth to smaller mod-
els block by forward modelling, iterating to reduce the
difference between the calculated and measured apparent
data; and expressing the differences in RMS error. Dif-
ferences in the RMS values obtained in IP compared to
ERT indicates the independence of IP data inversion
from its counterpart ERT though data were acquired and
recorded at the same time as well as inverted by the same
computer program.
3.2. Hydrochemical and Hydrophysical Analyses
Methods
Ten water samples were collected from water boreholes
and hand-dug wells around the dumpsite—eight hand-
dug wells at a distance range of 4 to 400 m from the
dumpsite and two water boreholes located at a distance
of 4 to 250 m away from the dumpsite—to determine the
presence of possible contamination and the degree. Our
main task is not to evaluate the impact of the contami-
nated water on the inhabitants of the area but to delineate
and ascertain the possible linkage of the groundwater
chemistry with exotic substances from the adjoining
dumpsite. Our aim is achieved by juxtaposing the chem-
istry with threshold values which is usually WHO stan-
dard. Further details concerning health implication of
excess and deficiency of these trace elements can be
found in [53-57].
Samples W2 and W8 are borehole water while W1, W3,
to W7, W9 and W10 are well water. All samples were well
labeled in situ, prepared in accordance with standard
practice and sent to Acme Laboratory, Canada for analy-
sis. Anions such as PO4, SO4, NO3, Cl, and 72 trace ele-
ments of including those of environmental concern were
tested and analyzed for. Some in situ data collected on
the water samples include conductivity (EC), total dis-
solved solids (TDS), pH, temperature (T), while turbidity,
total hydrocarbon content (THC) and dissolved oxygen
(DO) were determined locally in the Department of Che-
mistry laboratory, University of Lagos. The static water
levels of the hand-dug wells were also taken and found to
vary between 2 m to 13 m.
4. Results, Interpretation and Discussion
4.1. ERT and IP Results
The resistivity distribution derived from 2-D inversions
of ERT and IP data are presented and discussed here with
their resistivity-depth models (Figurs 4(a) and (b)).
Generally, the subsurface below the dumpsite was
characterized by low resistivity possibly influenced by
contaminants emanating from the dumps. The maximum
depth penetrated is 36 m with resisitivity values of
contaminated layers below 20 Ωm except some few cases
of high resistivity in the top layer and isolated high re-
sistivity at depth under some profiles. The chargeability
value is generally low within the impacted region (−2.9 -
8 ms, Figure 4(b)) which suggest possible high

E. A. AYOLABI ET AL.
854
Figure 3. VES curves of extracted data from ERT.
(a) (b)
Figure 4. The dumpsite (a) ERT (b) IP tomography models for the six profiles.

E. A. AYOLABI ET AL. 855
porosity and may compose of sand that has been highly
impacted with leachate.
A critical look at the resistivity-depth model from ERT
profile 2 to 6 shows high infiltration of leachate to the
subsurface soil. From profile 2 and 3, subsurface under
these profiles was characterized by resistivity between 10
and 20 Ωm. Generally, the result reflects high level of
impact of leachate from the decomposed materials from
the dumpsite with resistivity 10 - 20 Ωm prevalent on the
entire traverse. The depth of pollution with low resistiv-
ity values is indicative that the leachate from the decom-
posed refuse material has impacted the subsurface as a
result polluting the groundwater particularly the first and
second aquifers [42,43]. High resistivity encountered
between electrode positions 18 and 36 at the depth of 4 -
30 m under profile 3 possibly reflects the presence of a
non-conductive waste since the IP measured over it has
no indication of any geologic relevance compared with
the IP range of geologic materials according to [52].
Similar buried exotic non-conductive materials were de-
lineated from ERT and IP inverted section at a land rec-
lamation site within Lagos metropolis [32]. It should also
be noted that waste dumped at the site were not sorted as
earlier mentioned.
Similarly, models from profiles 4 - 6 reflect resistivity
from 1 - 20 Ωm for the polluted area but more pro-
nounced in the first half of profiles 5 and 6 than in the
last parts. Pockets of high resistivity from profiles 4 to 6
could possibly be attributed to non-conductive, non-de-
compose waste buried by other waste residues dumped
after. Also, at electrode positions 105 - 135 m (9 m depth
downward), was a suspected uncontaminated imperme-
able exotic material (177 - 800 Ωm) attesting to the in-
discriminate dumping system and unsorted nature and
varieties of the dumps being deposited at the site.
Worthy of note is the control profile (profile 1) which
indicates more contamination than other profiles far from
it. The possibility we think responsible for this is whether
the place has been part of the dumpsite site before being
cleared to pave way for buildings presently located on it.
If the later being the case, it is then expected to find the
wells around the area contaminated with leachate from
the dumpsite, which is confirmed by geochemical analy-
sis of the well water (Well 8).
4.1.1. Pollution Depth Estimate
The pollution depth was estimated by mapping out depths
of pollution at intervals on the ERT traverses, based on
the inverted resistivity value (<20 Ωm) and the GPS co-
ordinates, to produce pollution depth estimate map (Fig-
ure 5) showing the extent of pollution. A depth range of
0 to 35 m was marked out as polluted cutting across the
profiles. The anti-synclinal nature at the center (point of
highest depth) possibly suggests the center of dumping
activity and the first place dumping began many years
ago. A critical view of the map also helps to decipher the
possible migration path as N-S and NW-SE directions.
Water moves from region of high concentration and alti-
tude to region of low concentration and low altitude. How-
ever, groundwater, unlike surface water, has no clear
paths. Migration is controlled by such factors as porosity
and permeability of the media as well as concentration of
pore liquid. It implies that all the permeable layers within
the depth range must have been invaded by the scaveng-
ing substance (leachate). Static water level (for hand-dug
wells) in the area ranges from 2 m to 9 m, an indication
that the first aquifer has been complete overthrown by
the intruding discharge from the waste while the sec-
ond aquifer is gradually being infiltrated in the same
way.
4.1.2. Extracted VES Interpretation
An attempt was made to extract the Vertical Electrical
Sounding (VES) data from the 2D data using Earth
Imager Software. The data were extracted at selected
locations along the traverse and inverted using 1-D in-
version model of Earth Imager computer program to
produce the 1-D model Curves as shown in Figure 3.
From the inverted VES, we intended to view resistivity
distributions across the profiles. Approximately equal
surface positions on each profile are connected to make a
2-D view (geo-electric section, Figure 6) and the results
discussed in traverses. The first traverse cut across pro-
files 2, 4 - 6 with top material thickness of 1.33 - 3.2 m.
The thickness of waste material/contaminated region
varies from 10 - 15 m while the underlying sandy soil
(groundwater aquifer) is not spared from the pollution
effect. The second traverse extracted from surface posi-
tions 92 - 96 m of traverses 1 - 5 has 1.01 - 4.07 m thick
top materials and 5.93 - 20.24 m thickness of waste/
contaminated region. The sandy horizon here is also in-
filtrated by the discharge from decomposed wastes.
Combining the ERT view with the extracted VES
gives a 3-D view of the subsurface under the dumpsite
(Figure 6). It shows an underground soil completely in-
vaded by discharge from the overlying decomposed re-
fuse material to a depth above 35 m. By interpretation,
the second aquifer harnessed through boreholes, which
was the basis of mini-water works in Lagos metropolis
has been affected in the study site.
4.2. Hydrochemical Analysis
Many authors have noted that, besides the vertical in-
filtration of leachate from the solid waste, the hydro-
logical groundwater flow also play a prominent role in
contaminant distributions beneath the subsurface of a
landfill or dumpsite, [11,58]. This accounts for the con-
tamination of groundwater aquifer not directly or vertical

E. A. AYOLABI ET AL.
856
Figure 5. Pollution depth estimate map from ERT traverses from the study area. Note the anti-synclinal center (point of
highest depth) possibly pointing to the center of dumping activity and the first place dumping began many years ago.
located on dumpsite or landfills across the globe. Table 1
provides the pH and major elemental compositions of
water from wells and boreholes in the immediate sur-
roundings of the site. Because of the persistent and in-
discriminate burning coupled with heterogeneous nature
of the waste, pH value in the acidic domain is expected
since the residue after burning dissolves and percolates
the subsurface making the water more acidic (pH of 5.15 -
6.35 are predominant). Only Na and K show high val-
ues but not necessarily at toxic level. The elements are
essential in humans, though may cause some health ef-
fects in susceptible individuals while elevated concentra-
tion may give rise to unacceptable taste [57]. The S con-
tent is high. Table 2 represents the heavy metal contents
(mg/l) of the ten water samples, showing relatively ele-
vated values for Br.
The anion contents, electrical conductivity, and other
physical parameters measured on the water samples col-
lected from wells and boreholes in the precinct on the
dumpsite are provided in Table 3. 60% of the EC meas-
ured are above the threshold value [59]. Most elevated
EC values obtained attest to the presence of electrically
charged ions as reflected in the resistivity surveying ear-
lier explained (resistivity of 20 Ωm is predominant).
Around 50% of the water samples collected showed TH
(total hardness) values greater than 200 mg/l and about
30% showed DO (dissolved oxygen) above 5. In contrast,
nitrates, sulphate and phosphate are extremely lower than
the threshold values. [59] requirements for TDS in
drinking water differs from WHO owing to variety in
environmental, social, cultural, economic, dietary and
other conditions affecting potential exposure as recog-
nized by the world body [57]. 40% of the water showed
elevated TDS values (by [59] standard), an indication of
the presence of inorganic salts (principally calcium, mag-
nesium, potassium, sodium, bicarbonates, chlorides and
sulfates) [57].
In addition, we observed high correlations between EC
and Cu, Ni, pH, Mg, PO4, SO4, TDS and TH and be-
tween chloride and As, Mg, Co, Ni, K, Na, and salinity
(Figure 7). These physical and geochemical parameters
ere strongly correlated which also gives credence to w

E. A. AYOLABI ET AL. 857
Figure 6. A 3-D block model of the dumpsite projected from ERT and cross-profile 1-D geoelectric sections.
able 1.und the
pH Ca Mg K Na P S Al B
T pH, macroelements and Boron contents (mg/l) of water samples obtained from wells and boreholes aro
dumpsite.
Samples
W1 6.55 6 4 5 0. 0. 3.0511.158.664.08nd 16 001343
W2 5.15 36.21 7.01 26.84 83.74 0.
0.
1
0.
5.136.2.94 5.724..729..50.0263.7 0.01 0.063
ST 0.45 19.17 16.6 80.1 46.42 0.13 13.17 0.5124 0.67
0253 0.025 0.09
W3 6.35 80.74 10.31 36.54 83.54 nd 10 0.013 0.177
W4 6.26 93.94 9.64 32.87 62.28 nd 22 0.01 0.117
W5 6.59 48.84 7.13 30.5 161.1 nd 12 1.641 0.02
W6 6.17 61.6 10.83 57.03 81.64 32619 0.013 0.149
W7 6.26 39.7 5.7 24.66 29.7 0.153 4 0.089 0.172
W8 6.25 48.95 4.85 76.41 104.3 nd 47 0.026 0.061
W9 6.89 56.78 50.52 118.2 58.62 nd 30 0.007 1.438
W10 6.17 82.2 43.38 286.7 175.5 08912 0.018 2.063
Range 5 - 6.87 1 - 930 - 50.52 66 - 28670 - 17525 - 0.30 - 401- 1.6420 - 2.0
Mean 6.26 61.2 17.05 73.84 89.45 0.148 17.5 0.1843 0.463

E. A. AYOLABI ET AL.
858
Table metntents (µg/l) of wateles obtarom wd bors arou
Sam
2. Heavyals cor sampined fells aneholend the dump.
ples ACdZn Ba Cu Co CrNi s Mn PbBr
W1 nd 0.06 5.4 29.05 nd 10.3 0.12 7.4 4.8 nd 370
W2 0.7 0.42.482
3
Range 0.2 0.0.24 2.0.9 20.22.60.10.40.2 0.0 137
0.
28 7.1 46 0.7 5.1 0.18 6.7 1.8 nd
W3 0.9 0.06 2 33.15 0.9 2.8 0.16 8.6 0.3 nd 700
W4 0.5 0.1 9 38.28 0.5 4.3 0.12 9.1 nd nd 278
W5 1.4 0.23 5.4203.4 1.4 4.2 2.18 0.7 3.8 2.3 371
W6 1 nd 9.6 32.92 1 6 0.21 7.6 1.7 nd 266
W7 0.8 nd 25.1 33.08 0.8 8.5 0.12 4.4 1.6 0.1 138
W8 1.1 0.14 45.9 127.5 1.1 9.2 0.57 3.8 2.2 7 890
W9 1.4 nd 4.3 76.14 1.4 19.6 0.43 13.4 7.3 0.2 269
W10 4.2 nd 3.2 116.8 4.2 8.5 1.49 21.4 9.2 nd 3547
5 - 4.6 - 0 - 459 - 203.45 - 4.8 - 19.2 - 2.187 - 21.3 - 9.1 - 7.8 - 354
Mean 1.33 14514.7 73.28 1.33 7.85 0.56 8.31 3.63 2.4 731
ST 1.12 0.092 15.32 58.46 1.12 4.82 0.708 5.73 2.96 3.23 1014
ble 3. Anions co andal pters ter ced frols andholendmps
Cl
Tantents phy sicarameof waollectm wel bores ar ou the duite.
NO3 PO4 SO4 EC TDS Salinity DO TH Turb Temp SWL
Samples µg/l µg/l µg/l µg/l µS/cm µg/l µg/l µg/l µg/l NTU (˚C) m
W1 70
8.
Range 4 1.5 0.0.2 0.04532120.04.0.4122 1.5 27..92.0.0
1. 6.
1.2 0.09 0.07 952 480 0.18 4.4 200 4.5 28.2 8
BW2 93 2.3 0.06 0.09 454 211 0.22 4.2 140 2.7 27.9
W3 107 2.5 1.2 1.21 954 388 0.23 4.3 236 2.9 28.3 6
W4 62 2.6 0.1 1.27 1014 249 0.09 4.1 240 1.5 28.4 6
W5 187 1.9 0.7 1.01 1151 573 0.4 4.2 228 3.2 28.4 13
W6 85 2.2 0.05 0.06 994 496 0.17 4 188 6.9 28.3 5
W7 40 1.76 2.1 0.08 1007 504 0.08 4.3 120 2.2 28.2 6
BW8 163 1.24 1.7 0.05 1120 561 0.34 4.1 164 2.9 29.9
W9 102 3.5 3.2 2.09 1643 822 0.18 4 652 22.3 29.9 2
W10 387 2.9 3 2.12 1123 399 0.69 4.2 428 22.5 27.2 4
0 - 3872 - 3.5 - 35 - 2.12 4 - 1641 - 828 - 0.69 - 40 - 655 - 22.2 - 29 - 3
Mean 130 2.21 220.81 1041 468.3 0.26 4.18 259.6 7.16 28.47 58
ST 101 0.71 1.23 0.85 289 174 0.18 0.13 161.9 8.17 0.83
samourrigiichrobabe dumte ef-
uents.
Figu a)); anil, NO4 a4, Figure
8(b)); total heavy metals (As, Cd, Zn, Ba, Mn, Cu, Co,
e sce on wh is ply thpsi
fl
Of significant importance is the decreasing level of all
measured parameters (total physical parameters, total
anions, total heavy metals and total radioactive metals)
from NW-SE direction (wells 8 - 10 to wells 1 - 7). Fig-
ure 8 was derived from the combine contributions of
physical parameters (EC, TDS, Salinity, DO and TH,
Cr, Ni and Br, Figure 8(c)); and total radioactive metals
(U, Sr, Rb, Nd, Sb, Sm and V, Figure 8(d)) measured
from water samples around the dumpsite.
For each group of parameters, we found the combine
contributions of the measured parameters at each location
using the equation.
re 8(total ons (CO3, Pnd SO

E. A. AYOLABI ET AL. 859
Figure 7. Scatter plots for the correlation of some measured parameters. Correlation of some of the elements, ions and
physiccal parameters wth the EC and Cl is a direct indication of same provenance for these parameters.
(a) (b)
(c) (d)
Figure 8. Leachate flow path deduced from decreasing concentrations of (a) physical parameters (b) total anions (c) total
heavy metals and (d) total radioactive metals measured from water samples around the dumpsite. The parameters decrease
in concentrations from the dumpsite to the surrounding groundwater, meaning that the groundwater at close proximity to
the dumpsite has high concen trations of the measured physical and geochemical par a me ters.
1
nPn
 (1)
where P = concentration measured parameter,
And n = number of the parameters added together to
make up “P”. For example, for total anions,
con
Cl NOP3con4con 4con POSO;

 (2)

E. A. AYOLABI ET AL.
860
Table 4. Radioactive contents (µg/l) water samples colle cted from wells and boreholes around the dumpsite.
Samples U Nd Sb Sm Sr Rb V
W1 0.35 240.5 72.68 nd 0.47 nd 0.9
W2 0.07 127.8 41.65 0.08 0.21 0.02 0.5
W3 0.76 271.5 52.33 0.04 0.16 nd 0.4
1.276.7 53.0.5.
52.
W6 0.25 204.3 89.8 0.29 0.52 0.06 19.2
0. 17.
W9 2.6 640.5 251.4 0.62 3.26 0.11 2.4
W
Range 0.07 -53 127.21.05 -0 0.04 -10 0.11 -36 0.02 -76 0.4 -2
Mean 1.51 295.8 110.3 7.174 0.78 1.47 5.19
2. 7.
W4 92 15 51 0.41 0.07 3
W5 0.36 167.5 21.05 1 0.16 9.6 0.9
W7 0.13 150.6 54.89 0.31 1.3 06 2
W8 0.08 228.9 38.44 10.48 0.11 1.76 1.3
10 8.53 649.8 428 0.14 1.17 0.05 3.8
8.5 - 649 428. 52. 3. 1. 19.
ST 61 190.5 129.2 17.18 0.97 3.34 05
and n each l
Plois againe sampltions give
combstributionsese param the area.
The parameters wserved tease in c-
ations from the dumpsite to the surrounding groundwa-
dwater at close proximity to
th
r
fr
we could not adduce any
re
in Lagos. Our geophysical
o map and delineate the contaminant
eneath the aged open dumping system
to or enal as
wae. The End VES ite a polluepth
of over 35 m beneath the surface which coincide with the
uption of thond aquifhe area, ca-
tion of a complete submerge of the first groundwater
16/0022-1694(83)90221-4
= 4 atocation.
tting th
ine di
st th
of th
e loca
eters in
es th
ere obo decroncen
tr
ter, meaning that the groun
e dumpsite has high concentrations of the measured
physical and geochemical parameters more than those fa
om the dumpsite. It shows underground resultant flow
path of the leachate and possibly of the groundwater as
envisaged from ERT survey.
In this study, we include radioactive elements detected
in the water samples as some existed in concentrations
(Table 4) above other geochemical elements widely re-
ported in most dumpsite studies (example: [11]). Sr and
Rb are especially high. while
ason to the presence of these radioactive metals in the
water samples, it is however suspected that some could
arise from various unidentified waste usually dumped on
the site, ranging from plastic to vegetation, electronics,
waste cooked food, corroded metals, and other metallic
and household materials.
5. Conclusion
Integration of electrical and geochemical methods has
been used to assess the subsurface conditions under a
municipal dumpsite system
method was able t
plume (leachate) b
being recently cleared in preparation for its possible con-
version into shopping complex. The integrated methods
aquifer harness by majority through shallow wells. In the
same vein, statistical analyses of geochemical and phy-
sical parameters determined in situ on groundwater from
wells and boreholes located in the precinct of this site
also agree to the contamination status of the site, having
have provenbe tools fvironmentsessment of
ste sitRT andicated d
per sece secer in tan indi
elevated concentrations of some macro-elements and
heavy metals. The parameters also show high correlation
to as a proof of same provenance. The pH obtained from
water samples indicates high acidic content (5.15 - 6.87
µg/l) while about 60% of the water show high EC. Con-
centrations of all geochemical elements measured follow
a NW-SE decreasing trend suggesting the possible flow
of the leachate and consequently of the groundwater,
which also agrees with similar flow pattern deduced from
ERT results.
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