application of electrical resistivity methods and ...

2 downloads 0 Views 3MB Size Report
G. Ogubazghi. Eritrea Institute of Technology, Eritrea .... The generalized geology map of the study area showing road networks and some geological features.
Academic Journal of Science, CD-ROM. ISSN: 2165-6282 :: 05(01):147–166 (2016)

APPLICATION OF ELECTRICAL RESISTIVITY METHODS AND CHEMICAL ANALYSIS IN THE STUDY OF LEACHATE CONTAMINATION AT INACTIVE OPEN DUMPSITE, OSUN GROOVE AREA, OSOGBO, SOUTHWESTERN NIGERIA

N.U. Ugwu, R.T. Ranganai and R.E. Simon University of Botswana, Botswana G. Ogubazghi Eritrea Institute of Technology, Eritrea

Electrical resistivity surveys and soil sampling analyses were conducted on the accessible side of the inactive dumpsite, Osun Groove area, Osogbo, Southwestern Nigeria to investigate the degree and extent of the impact of the waste dumped on the farmland and the quality of the groundwater in the study area. Three 2-D imaging profiles and Six Vertical Electrical Soundings (VES) were acquired on the established traverses. The 2-D imaging delineated low resistivity (< 30 ȍm) at zones suspected to be the shrinking pollution plume along traverse TR1G. The VES interpreted results also delineated five to six subsurface layers comprising thin sand/dried lateritic topsoil, weathered layer with clay/sandy clay materials; partial weathered basement, weathered basement and fresh basement Twenty-two soil samples were collected on the surface and at 1 m depth within and around the dumpsite and analyzed for heavy metals. The soil sample analysis showed a higher elemental concentration of manganese, zinc, copper, chromium, lead and cadmium on the dumpsite than about 25 – 50 m away from the dumpsite. The order of concentration level is Mn > Zn > Cu > Cr > Pb > Cd. However, the statistical parameters analyzed at the level of concentration reveals that the area is uncontaminated of heavy metals. This could be attributed to continuous farming in the area which might have absorbed part of the metals over the years, the washing away of the metal elements deposited and scavenging of materials for recycling. The pollution plume detected by the 2-D imaging in traverse TR1G could be from degradation of organic materials. The study area is considered safe for groundwater and farming. Keywords: Southwestern Nigeria, Electrical Resistivity, Heavy metals, Pollution plume, Groundwater, Farmland.

Introduction Generally, groundwater is considered as the most abundant source of potable water in comparison to surface water as it is often protected from direct human activities. Supply of water from the Osun state surface water scheme to Osogbo, the state capital, has been inadequate due to growing population. This has made the residence to shift attention to groundwater as an alternative source of water for domestic and industrial use. However, pollution of groundwater resources can arise from industrial discharges, oil 

147

148

Application of Electrical Resistivity Methods ...

spillage, medical waste, agricultural waste, urban runoff, landfills or waste dump. In Nigeria, municipal solid wastes are mostly disposed through an open dumpsite (e.g. Geoffrey, 2005) and as rain washes through the waste, some of the solids are dissolved while liquids are mixed. The water can become acidic and act on the waste, hence producing leachate (eg. Becker 2001). Leachate formed becomes a groundwater contaminant which results in major health risks (Lee and Jones-Lee 1993a, b; Christensen et al. 2001; Longe and Enekwechi 2007). Osazua and Abdullahi (2008) explained that leachate from municipal dumpsite contains organic substances (e.g. vinyl chloride, benzene 1,1,1-Trichloroethene) and inorganic substances (e.g. Silver, mercury, chromium, lead, copper, manganese) which is harmful. Inorganic substances pollution of the environment is due principally to anthropogenic sources caused by indiscriminate disposal of wastes from home, hospital and industrial processes, such as metal plating or from some organic liquids used for cleaning metallic products (Olajire and Ayodele 1998; Bear and Cheng 2010) and from agriculture and land practices (Uba et al. 2008). The rising of heavy metals (e.g.. Manganese, arsenic, mercury, chromium, lead and cadmium) in soil from anthropogenic sources have been reported to be harmful to crops and human health (e.g. Smith et al. 1996; Brady and Weil 1999; Abdus-Salam and Adekola 2005a). The concentrations and transformations of heavy metals in solid municipal wastes lead to their accumulation in the food chain (Gimmler et al. 2002). The views of many researchers are that municipal waste disposal may increase the heavy metal burden of the soil and underground water (Albores et al. 2000; Okoronko et al. 2006; Elaigwu et al. 2007). Therefore, metals considered in the study include those which are natural and micro-nutrient such as manganese, zinc and copper and the anthropogenic and non-essential/toxic heavy metals, chromium, lead and cadmium, which are toxic to plants (Abdus-salam, 2009). The open dumpsite, Osun groove area, Osogbo, Southwestern, Nigeria was operated for about thirty years and became inactive about six years ago. There is the likelihood that the groundwater within the surroundings of the dump site is contaminated. It is imperative, therefore, to carry out a geophysical investigation of the area around the waste dump site, with the focus to delineate the lithological sequences, identify the aquifer units; carrying out chemical analysis of soil samples on and around the dumpsite; and use it to assess the degree and extent of the impact of the waste dumped on the farmland and quality of the groundwater in the study area. The Study Area The survey area is located within geographical coordinates of latitudes N07° 45.505ƍ and N07° 48.552ƍ and longitudes E04° 29.611ƍ and E04° 34.321ƍ (Figure 1a). It is characterized by a sub-humid climate and about 1241 mm precipitation falls annually (Kottek et al., 2006). In a year, the warmest month is March with an approximate temperature of 34°C while August has the lowest average temperature of 19 °C with an annual mean temperature of about 24°C (Oyelami et al. 2013). The study area Osogbo is underlain by the crystalline rock of the Precambrian basement complex of the southwestern Nigeria (Rahaman, 1988; 1989). The major metamorphic rock types discovered around the area include highly fractured quartzite and banded gneiss (Fig. 1b). The mineralogy of the quartzite is mainly quartz with little mica. The structures found in these rocks are banding and joints. The strike is S160SE and S140SE on the rocks studied while the dip is 24°NE. The joint strike directions (Fig. 1b) are S172SE, E120SE, E120SE, E128SE, E110SE, and the dip 80°NE. The fractured bedrock generally occurs in a typical basement terrain (Odusanya and Amadi, 1989) in tropical and equatorial regions, weathering processes create superficial layers, with varying degree of porosity and permeability. These geological events gave rise to such structures as folds, faults and fractures that are geologically associated with zones of weakness.

N. U. Ugwu et al.

149

Figure 1a. The generalized geology map of the study area showing road networks and some geological features

Figure 1b. Banded Gneiss with joints and dips in the study area

3. Methods of Study 3.1 Geoelectric resistivity survey Three traverses ranging between 90 m and 125 m were established in the NE – SW direction. The geophysical resistivity data were acquired with the Ohmega d.c. resistivity meter along these traverses (Fig. 2). 2-D imaging using dipole-dipole survey was used to determine the lateral and vertical variation in apparent resistivity of the subsurface beneath the three established traverses (TR1G – TR3G). Interelectrode spacing of a = 5 m and expansion factor (n) varied from 1 to 5 were adopted. The dipole – dipole data were inverted into the 2-D resistivity structure using the DIPPRO for windows (2000)

150

Application of Electrical Resistivity Methods ...

software. Six vertical electrical soundings (VES) were conducted using the Schlumberger electrode array (Zhody et al., 1974) along the traverses with maximum electrode spacing (AB/2) of 65 m. The electrical resistivity data were processed by plotting the apparent resistivity values against the electrode spread (AB/2). The field curves were interpreted through partial curve matching (Koefoed, 1979), engaging master curves and auxiliary point charts (Orellana and Mooney, 1966). This was subsequently interpreted quantitatively using the partial curve matching method (Koefoed, 1979) and computer-assisted 1-D forward modelling with WinResist software (Vander Velpen, 2004) which successfully reduced the interpretation error to acceptable levels (Barker, 1989). Maximum information about the subsurface lithology and overburden thickness was generated.

A UHO B V1

G J

C

V2 V4

25m

K

V5

D

V3

H

E

I

V6

TR1G

F

TR2G TR3G

Soil sample point

Figure 2. Data acquisition and soil sampling map of the study area.

Soil Chemical Analysis Sample collection and analysis Twenty – two soil samples were collected within and outside of the dumpsite as shown in (Figure 2) into clean polyethylene bags. At each position, samples were taken at the surface (depth of about 15-20 cm) and at a depth of 1 m below the earth's surface. The samples collected at the surface were labelled A1 – K1 while those collected at 1 m were labelled A2 – K2.The soil samples were thoroughly mixed to form composite and spread on a clean plastic sheet and air dried at room temperature for 24 hours.

N. U. Ugwu et al.

151

The soil was sieved using a 0.5 mm sieve to obtain fine particles and 0.5 g was weighed from each sample into a Pyrex beaker. 10 ml of Perchloric/nitric acid mixture of ratio 1:2 was added to each sample. The beaker was then covered with a lid and placed on a hot plate at 105 0C for 30 minutes in a fume cupboard for digestion. The mixture was allowed to cool and filtered. The filtrates were made up to 25 ml with distilled water. The chemical analysis of the elemental concentration of heavy metals (Mn, Cu, Zn, Cd, Cr and Pb) was carried out using atomic absorption spectrophotometer (AAS) at Centre for Energy Research and Development (CERD), Obafemi Awolowo University (OAU) Ile – Ife, Nigeria. Also, the pH of each soil sample was determined by a calibrated pH meter. The results of the chemical analysis are tabulated and presented under results and interpretation. Data Analysis The results obtained were subjected to analysis to determine the Contamination factor (CF), Geo-accumulation Index (GeoI) and Pollution load index (PLI) of the metals in the environment. Contamination factor (CF) Contamination factor (CF) is a quantifier of the degree of contamination relative to either the average crustal composition of the respective metal or to measure background values from geologically similar and uncontaminated area (Tijani et al., 2004). It is expressed as CF = Cm / Bm, where Cm is the mean concentration of metal m in the soil and Bm is the background concentration (value) of metal m. Bm can either be taken from the literature (average crustal abundance) or directly determined from a geologically similar material. CF values were interpreted as suggested by Hakanson (1980), where: CF < 1 indicates low contamination; 1 < CF < 3 is moderate contamination; 3 < CF < 6 is considerable contamination; and CF > 6 is very high contamination. Geo-accumulation index (GeoI) Geo-accumulation index (GeoI) as proposed by Mueller (1979) has been widely used to evaluate the degree of heavy metal contamination in terrestrial and aquatic environments as expressed by

GeoI

ln (Cm /1.5* Bm)

where Cm and Bm are as defined above, while 1.5 is a factor for possible variation in the background concentration due to lithologic differences. GeoI is classified into seven descriptive classes (e.g. Mueller, 1981; Lokeshwari and Chandrappa 2006; Bhuiyan, 2010; Yisa et al 2012) as shown in table 1. Table 1. Contamination classifications of Geo-Accumulation Index of Metals GeoI Class 0 1 2 3 4 5 6

GeoI Values GeoI ” 0 0< GeoI < 1 1 < GeoI < 2 2 < GeoI < 3 3< GeoI < 4 4< GeoI < 5 5 < GeoI

Dumpsite Soil Quality Uncontaminated uncontaminated to moderately contaminated moderately contaminated moderately contaminated to heavily contaminated heavily contaminated Heavily to extremely contaminated extremely contaminated

Pollution load index (PLI) For the entire sampling site, PLI has been determined as the nth root of the product of the n CF: PLI

(CF1 u CF2 u CF3 u···uCFn )1/ n 

Application of Electrical Resistivity Methods ...

152

This index provides a simple, comparative means for assessing the level of heavy metal pollution. When PLI > 1, it means that a pollution exists; otherwise, if PLI < 1, there is no metal pollution (Tomlinson, 1980). Results and Interpretation 1. Vertical Electrical Sounding (VES) The resistivity type curves identified include HKH and QHKH. The number of subsurface layers delineated from the VES ranges between 5 and 6. Table 2 gives a summary of the interpretation results of the VES curves at the studied locality. Table 2. Quantitative interpretation of VES showing geoelectric parameters obtained from inactive dumpsite VE S 1

CURVE –TYPES

HKH

NO OF LAYERS

RESISTIV ITY (ȍm) 465 239 443 203 983

THICKN ESS (m) 0.4 3.1 7.8 19.6

DEPTH (m)

LITHOLOGICAL UNIT.

0.4 3.5 11.2 30.9

5

1145 243 1006 212 4927

0.7 3.9 3.2 19.3

0.7 4.6 7.8 27.1

5

440 39 507 11 2239 236 153 653 100 17347

0.4 0.9 3.1 16.0

0.4 1.3 4.4 20.4

0.4 1.3 3.3 14

0.4 1.7 5.0 19.0

6

296 89 60 341 34 6588

1.0 1.3 1.4 5.2 13.9

1.0 2.4 3.7 9.0 22.9

5

416 107 545 122 17525

0.5 2.1 5.1 30.7

0.5 2.6 7.8 38.4

Topsoil Weathered layer Partly Weathered Layer Weathered Basement Fresh Basement Topsoil (dried laterite) Weathered layer Partly Weathered Layer Weathered Basement Fresh Basement Topsoil Clay Weathered layer Weathered Basement Fresh Basement Topsoil Weathered layer Partly Weathered Layer Weathered Basement Fresh Basement Topsoil Clay Weathered layer Partly Weathered Layer Weathered Basement Fresh Basement Topsoil Weathered layer Partly Weathered Layer Weathered Basement Fresh Basement

5 U1>U2U4U2U4U2U4U2U4U2U4U2U4 100 ȍm may suggest sandy clay, clayey sand, sand, compact sand or lateritic column (eg. Ako and Olorunfemi, 1989; Olayinka and Olorunfemi, 1992; Olorunfemi and Okhue, 1992; Omosuyi et al., 2003; Oladapo et al., 2004). The weathered layer has resistivity and thickness range from 39 ȍm to 243 ȍm and 0.9 to 3.9 m respectively. This could be interpreted as clay/sandy clay. A partly weathered layer (hardpan) has resistivity varies from 443 í 1006 ȍm with thickness ranges between 3.1 m and 7.8 m. The weathered basement resistivity and thickness vary from 11 í 212 ȍm and 16.0í19.6 m respectively, while the fresh basement resistivity ranges from 983 í 4927 ȍm. 465 VES 1

VES 2

1145

39 VES 3

440

A

A' 239

243

507

1006

443

KEY 11

Topsoil Clay Weathered Layer

212 203

Partly Weathered Layer Weathered Basement 2234 4929 983

(a)

Distance (m)

Figure 3a. Geoelectric sections along Traverse TR2G.

Figure 3b. Geoelectric sections along Traverse TR3G.

Fresh Basement Resistivity ( m)

154

Application of Electrical Resistivity Methods ...

Figure 3b shows the geoelectric section B-Bƍ produced from the VES points (4, 5 and 6) along traverse TR3G. The geoelectric section depicts five subsurface geologic layers except VES 26 which has six layers. The topsoil has resistivity varying from 236 í 416 ȍm and thickness (0.4 í 1.0 m). The topsoil is indicative of sand, compact sand or lateritic. A thin (1.3 m thick) layer with resistivity 89ȍm is seen in VES 5. The weathered layer resistivity and thickness vary from 60 ȍm to 153 ȍm and 1.3 m to 2.1 m respectively. Also delineated is a partly weathered layer (compacted sand/hard pan) with resistivity varying from 341í 653 ȍm and thickness ranges between 3.3 m and 5.2 m. The weathered basement has resistivity and thickness values vary from 34 ȍm í 122 ȍm and 13.9 m í 30.7 m respectively. Also, the fresh basement has a resistivity ranging from 6588 í 17525 ȍm. 2. 2-D Resistivity Structure Figure 4 shows the inverse model 2-D resistivity sections for traverses TR1G, TR2G. In figure 4a, low resistivity values (mostly less than 30 ȍm) could be observed at an approximate depth of 7 m. This is within presumed topsoil/weathered layer. The low resistivity value materials filtrated into the weathered basement as seen between 26 í 30 m, 70 – 75 m and 95 – 105 m within an approximate depth of 11 m. A suspected fracture is noticed between two high resistivity (4921 í 27195 ȍm) intrusive fresh basements.

Figure 4a. 2íD Resistivity structure of profiles along traverse TR1G





Figure 4b. 2íD Resistivity structure of profiles along traverse TR2G.

N. U. Ugwu et al.

155

In figure 4b the topsoil/weathered layer within an approximate depth of 2.5 m has resistivity values range from 116 – 578 ȍm) except between 15 í 25 m and 85 í 110 m lateral distance that has resistivity values vary from 49 í 89 ȍm. This is a combination of clay, sandy clay and lateritic materials. A partly weathered layer (hardpan) with resistivity and thickness vary from 422 í 1041ȍ and 2.5 – 15 m respectively were delineated between 35 – 80 lateral distance. At a depth range of 15 í 25 m, suspected fracture occurred with resistivity values vary from 52 í 110 ȍm between distances 10 í 33 and 86 í 100 m. The 2-D profile in figure 4c was carried along traverse TR3G and it covered a distance of 90 m. The topsoil/weathered layer exhibited high resistivity values varying between 129 and 644 ȍm. High resistivity values between 358 – 1775 ȍm of the partly weathered layer were observed between 0 í 20 m, 55 í 70 and 75 í 85 m lateral distance with the clay of slightly low resistivity between 61-99 ȍm occurring between 42 and 50 m. Also, between lateral distance 60 – 85 m resistivity varies from 47 í 132 ȍm) is seen within a depth range of 10 í 24 m.



Figure 4c. 2íD Resistivity structure of profiles along traverse TR3G

3. Soil Chemical Analysis Result The elemental concentration of manganese, zinc, copper, chromium, lead and cadmium, from ten sample points on the dumpsites, are analyzed. Based on the results obtained, there was a gradual decrease in the concentration of heavy metals from the dumpsite to distance about 50 m from the dumpsite. In most cases there was a significant difference between the elemental concentrations of most metals at the dumpsite to those at 25 to 50 m away from the dumpsite. Tables 2 (a, b) show the elemental concentration (mgkg-1) of the extracted metals on the surface (A1 - K1) and at 1 m depth (A2 - K2) respectively. The pH values measured from the samples ranges between 9.73 and 11.40. The order of level of concentration is Mn > Zn > Cu > Cr > Pb > Cd. The histograms of the concentration levels of the analyzed elements of the sampling points are shown in figure 5 for samples at the surface and figure 6 for the sample at 1 m depth. Highest levels of The elemental concentration levels of sample points A1, B1, C1, D1, E1 and F1which are located at the dumpsite are slightly higher than the elemental concentration levels of sample points G1, H1, I1, J1 and K1 located between 25 m to 50 m from the dumpsite (Figure 5 (a-f)). The elemental concentration levels of samples at 1 m depth followed the same trend as these on the surface (figure 6 (a-f)). The concentrations at 1 m depth in most samples are higher than the concentration found at the surface.

156

Application of Electrical Resistivity Methods ...

. Tables 3a. Concentration of extracting metals at the surface (5-15cm) CONCENTRATION (mg/kg ) Sample points

Mn

Zn

Cu

Cr

Pb

Cd

A1

33.25

10.53

5.80

1.060

0.600

0.044

B1

62.50

15.75

4.00

0.850

0.653

0.066

C1

30.13

8.50

8.30

0.770

1.060

0.036

D1

32.25

7.38

3.00

0.800

0.700

0.056

E1

12.51

6.60

2.50

0.470

0.480

0.060

F1

26.45

10.20

4.17

0.400

0.430

0.047

G1

17.06

1.70

0.98

0.339

0.600

0.025

H1

16.50

5.50

0.40

0.287

0.410

0.030

I1

15.22

1.30

3.80

0.450

0.370

0.020

J1

38.88

15.75

0.85

0.306

0.450

0.040

K1

10.16

1.10

0.20

0.250

0.400

0.010

Mean

26.81

7.67

3.09

0.544

0.559

0.040

Tables 3b. Concentration of extracting metals at 1m depth CONCENTRATION (mg/kg ) Sample points

Mn

Zn

Cu

Cr

Pb

Cd

A2

43.63

20.63

6.70

1.810

0.700

0.060

B2

64.38

19.87

7.83

1.516

0.690

0.072

C2

40.63

14.63

10.75

2.000

1.100

0.047

D2

41.50

8.88

4.83

1.335

0.680

0.059

E2

20.70

12.10

2.90

1.040

0.511

0.062

F2

15.34

8.43

5.45

2.100

0.800

0.051

G2

16.62

1.80

3.58

0.700

0.460

0.029

H2

2.00

3.88

0.30

0.259

0.415

0.016

I2

14.50

1.80

3.85

1.080

0.450

0.023

J2

24.88

15.38

0.97

0.311

0.510

0.046

K2

3.32

0.70

0.70

0.660

0.390

0.010

Mean

26.14

9.83

4.35

1.16

0.610

0.043

N. U. Ugwu et al.

Figure 5 (a-f). Concentration levels of heavy metals in a soil sample at the surface (a) Mn, (b) Zn, (c) Cu, (d) Cr, (e) Pb and (f) Cd.

157

158

Application of Electrical Resistivity Methods ...

Figure 6(a-f). Concentration levels of heavy metals a in soil sample at 1 m depth (a) Mn, (b) Zn, (c) Cu, (d) Cr, (e) Pb and (f) Cd.

N. U. Ugwu et al.

Table 4a. Metal contamination factors (CFs) and pollution load indices (PLIs) for the soil sample at the surface in the study area Contamination factors (CFs)

PLI

Sample points

Mn

Zn

Cu

Cr

Pb

Cd

A1

0.033

0.078

0.083

0.009

0.038

0.293

0.0527

B1

0.063

0.119

0.057

0.007

0.041

0.440

0.0361

C1

0.030

0.064

0.119

0.006

0.066

0.240

0.0528

D1

0.032

0.056

0.043

0.007

0.044

0.373

0.0455

E1

0.013

0.050

0.036

0.004

0.030

0.400

0.0322

F1

0.027

0.077

0.060

0.003

0.043

0.313

0.0414

G1

0.017

0.013

0.014

0.003

0.038

0.167

0.0197

H1

0.017

0.042

0.006

0.002

0.026

0.200

0.0188

I1

0.015

0.010

0.054

0.004

0.023

0.133

0.0215

J1

0.039

0.119

0.012

0.003

0.028

0.267

0.0328

K1

0.010

0.008

0.003

0.002

0.025

0.067

0.0096

Mean

0.027

0.058

0.044

0.005

0.035

0.267

0.0267

Table 4b. Metal contamination factors (CFs) and pollution load indices (PLIs) for the soil sample at 1 m depth in the study area Contamination factors (CFs) Sample points

Mn

Zn

Cu

PLI Cr

Pb

Cd

A2

0.044

0.156

0.096

0.015

0.044

0.400

0.0747

B2

0.064

0.151

0.098

0.012

0.043

0.480

0.0785

C2

0.041

0.110

0.154

0.016

0.069

0.313

0.0788

D2

0.042

0.067

0.069

0.011

0.043

0.390

0.0574

E2

0.021

0.092

0.041

0.009

0.032

0.413

0.0460

F2

0.015

0.064

0.078

0.017

0.050

0.340

0.0528

G2

0.017

0.014

0.051

0.003

0.029

0.193

0.0243

H2

0.002

0.029

0.004

0.002

0.026

0.107

0.0104

I2

0.015

0.014

0.055

0.009

0.028

0.153

0.0276

J2

0.025

0.117

0.014

0.003

0.032

0.307

0.0326

K2

0.003

0.005

0.010

0.005

0.024

0.067

0.0103

Mean

0.026

0.074

0.062

0.010

0.038

0.287

0.0485

Table 5a. Metal contamination factor and geo-accumulation index of metals in soil from the dumpsite Overall summary of contamination level

Parameters

Cm

Bm

CF

GeoI

Mn

26.81

1000

0.027

- 4.02

Uncontaminated

Zn

7.67

132

0.058

- 3.25

Uncontaminated

Cu

3.09

70

0.044

- 3.53

Uncontaminated

159

160

Application of Electrical Resistivity Methods ...

Cr

0.544

122

0.005

- 5.82

Uncontaminated

Pb

0.559

16

0.035

- 3.76

Uncontaminated

Cd

0.040

0.15

0.267

- 1.73

Uncontaminated

Table 5b. Metal contamination factor and geo-accumulation index of metals in soil from the dumpsite Parameters

Cm

Bm

CF

GeoI

Overall summary of contamination level

Mn

26.14

1000

0.026

- 4.05

Uncontaminated

Zn

9,14

132

0.070

- 3.08

Uncontaminated

Cu

4.35

70

0.062

- 3.18

Uncontaminated

Cr

1.16

122

0.010

- 5.06

Uncontaminated

Pb

0.610

16

0.038

- 3.67

Uncontaminated

Cd

0.043

0.15

0.287

- 1.65

Uncontaminated

CF- contamination factor; GeoI- geo-accumulation index; Cm- mean concentration of the metal in the soil; Bm- average crustal abundance (background value) in an uncontaminated soil, adopted from (Dineley et al., 1976; Amadi and Nwankwoala, 2013).

Discussion Electrical resistivity The subsurface geology delineated by the geoelectric section showed that the study area has thin topsoil with thickness and resistivity range between 0.4 – 1.0 m and 234 – 1145 ȍm indicative of clayey sand/dried lateritic surface. Laterite being a highly resistant material is serving as a firm hardpan which tends to prevent intensive percolation of the leachate from penetrating into the neighboring groundwater (Ojo et al., 2014). This was underlain by clay/sandy clay weathered layer with a resistivity value vary from 39 – 243 ȍm and thickness between 0.9 – 3.9 m. A partial weathered basement which could be hard pan was delineated between the weathered layer and the weathered basement. It has resistivity and thickness range of 341 - 1006 ȍm and 3.1 - 7.8 m respectively. Low resistivity value (11 – 212 ȍm) weathered basement delineated has a thickness range of 13.9 – 30.7 m. The overburden thickness, which constitutes the groundwater aquifer ranges approximately between 19.0 – 38.4 m. The 2-D resistivity structure stacked on the base map figure 6 shows the resistivity distribution in the surveyed area. Even though the geoelectric sections presented the topsoil as being covered by hard laterite, low resistivity values (mostly less than 30 ȍm) were observed in the 2-D resistivity structure on traverse TR1G which was approximately 1.0 m away from dumpsite. These low resistivity values were seen at lateral distances between 10 – 25 m and 60 – 95 m at an approximate depth of 7 m. The shrinking pollution plume caused by leachate is seen at the low resistivity zones (Figure 7). The low resistivity materials filtrated into the suspected weathered basement as seen between 26 í 30 m, 70 – 75 m and 95 – 105 m within an approximate depth of 11 m. The shrinking pollution plume is also noticeable within a suspected fracture between two high resistive zones. Low resistivity values less than 30 ȍm were not observed within 25 m and beyond from the dumpsite, as seen in traverses TR2G and TR3G indicating that pollutant in the area has decreased or the pollutant might have been absorbed by plants due to continuous farming.

N. U. Ugwu et al.

Cg1

V30

161

A

Cg6

UHO B

Cg10

V29

Cg7

V25

C

Cg2

25m

D V28

Cg8

V26

Cg3

Cg11

E

TR1G

Cg12

V27

TR3G

90m

TR2G

125m

F

110m

Soil sample position

Figure 6.The pattern of 2-D resistivity structure in the study area

Soil Analysis The result of the soil analysis in table 2(a, b) also revealed that the level of elemental concentration of the heavy metals is from the dumpsite to the farmland area along traverse TR2G and TR3G. In general, the concentration level of the metals at 1.0 m depth is slightly higher than that at the surface which indicates that there was no fresh dumping of waste on the site. Manganese Manganese, Mn elemental concentration at the surface ranges from 10.16 - 62.50 mgkg-1 with a mean value 26.81 mgkg-1. Amadi and Nwankwoala (2013) reported a mean concentration value of 48.12 mgkg-1 manganese from Enyimba dumpsite in Aba, Southeastern, Nigeria. Dineley et al. (1976) and Abbasi et al. (1998) gave an accepted value of 1000 mgkg-1 for manganese in an uncontaminated soil. The manganese in the soil is an essential nutrient for plants and animals. Manganese in dumpsite could come from products such as batteries, glass and fireworks (Huang and Lin, 2003; Aboud and Nandini, 2009) and oxidant materials for cleaning, bleaching and disinfection. Other manganese sources include fertilizer, fungicides and as well as livestock feeding supplements.

162

Application of Electrical Resistivity Methods ...

Copper In the soil analysis copper concentration levels vary from 0.20 – 8.30 mgkg-1 at the surface with mean value 3.09 mgkg-1 and 0.30 – 10.75 mgkg-1 at 1 m depth with a mean value of 4.35 mg kg-1. The values are higher than 0.068-8.00 ppm obtained by Adebayo et al. (2015) while delineating contamination Plumes at Olubonku dumpsite at Ede Southwestern Nigeria. The mean Cu extracted contents are higher than 1.3ppm and 2.1ppm reported respectively by Adepetu et al. (1979) in their study of surface soils of Ondo State in Nigeria, and Fagbami et al. (1985) in their study of the basement complex soils of the tropical dry rain forest of South-Western Nigeria. However, these values are lower than the mean concentration in world soils of about 20.0 ppm of Cu (Alloway, 1995) and also lower than 21.4 mgkg-1 reported by Zauyah et al. (2004) in their study of some cultivated soils of Malaysia Peninsula. Furthermore, the value of the Cu concentration level is lower than the agriculturally acceptable limit of 63ppm in Canadian soil Quality Guidelines for the protection of Environmental and Human Health (CCME, 1999). Zinc The Zinc concentration level varied from1.10 – 15.75 mgkg-1 at the surface with a mean value of 7.67 mg kg-1 and 0.700 – 20.63 mgkg-1 at 1 m depth with an average value of 9.83 mgkg-1. The average Zn concentrations obtained from the analyses soils of the dumpsite farmland were lower than the mean content of 20 mgkg-1 found in Florida agricultural surface soils (Holmgren et al., 1993), and also lower that the average 45ppm value reported in the literature for world sandy soils by Kabata-Pendias and Pendias (1992). The Zn concentrations of the study area are higher than 2.8 – 12 mg kg-1 reported by Gough et al. (1994) in their investigation of the baseline elemental contents of the Bull Island soils and 0.418-0.832 mgkg-1 obtained by Francis (2005) in his study of heavy metals in contaminated soils in the vicinity of livestock farmland in Southern Nigeria. Chromium Chromium elemental concentration levels range from 0.25-1.06 mgkg-1 with a mean value of 0.544 mgkgat the surface and 0.259 – 2.100 mgkg-1 with a mean value of 1.160 mgkg-1 at 1 m depth. This same range (0.110 – 2.000 ppm and mean 0.89 ppm) was obtained by Adebayo et al. (2015). The sources of chromium are materials like alloys, electroplated items, pigments, paints, fungicides, glass and tanned leather. Chromium is carcinogenic by inhalation and corrosive to tissue where it is found in abundance (Lin et al., 2002; Aboud and Nandini, 2009).

1

Lead In table 2 (a, b) the concentration level of lead deposited at the inactive dumpsite and periphery farmland range 0.040 - 1.06 mgkg-1 with a mean concentration of 0.559 mgkg-1 at the surface and 0.010 – 1.10 mgkg-1 with mean value of 0.610 mgkg-1 at 1 m depth. When lead is above the recommended limit, reduces sperm count, damage kidney, liver, blood vessels, nervous system and other tissues in humans (Anglin-Brown et al., 1995). In dumpsites, it is absorbed into soil from materials like lead-acid batteries, solder, alloys, cables sheathing, paints, ammunition, glass and plastic (McAllister et al., 2005). Cadmium The concentration of cadmium ranges from 0.010 – 0.066 mgkg-1 with a mean concentration of0.040 mgkg-1 at the surface and 0.010 – 0.02 mgkg-1 with mean concentration of 0.043 mgkg-1 at 1 m depth. The USEPA, based on their own risk assessment, estimated that 20 mg/kg of Cd in the top soil represents no

N. U. Ugwu et al.

163

significant health risk to highly exposed individuals from dietary ingestion of Cd-contaminated food crops (McBride 2003). Cadmium contains in materials like plastics, batteries and in various electronic components. Cadmium, when ingested by humans, accumulates in the intestine, liver and kidney and chronic exposure to Cd causes proximal tubular disease and osteomalacia (Pascual et al., 2004). The calculated metal contamination factors (CFs) in tables 3 and 4 in all metals are CF < 1 indicating low contamination Hakanson (1980) and pollution load indices (PLIs) also are PLI < 1, showing that there is no metal pollution (Tomlinson, 1980). The evaluated degree of heavy metal contamination GeoI using the mean values (Table 4a, b) of the metal concentration levels vary from – 4.05 to – 1.65 which indicate uncontaminated (Bhuiyan, 2010; Amadi and Nwankwoala, 2013). Conclusion The VES clearly delineated subsurface sequences and the geological parameters. The geoelectric sections show 5 – 6 layers. These include thin topsoil with sand/dried lateritic surface, weathered layer with clay/sandy clay materials; partial weathered basement which covered the weathered basement. The weathered layer with a resistivity value vary from 39 – 243 ȍm and a thickness between 0.9 – 3.9 m and weathered basement with resistivity value (11 – 212 ȍm) and thickness (13.9 – 30.7 m) which forms the major groundwater aquifers. The 2-D imaging delineated low resistivity (30 ȍm) zones suspected to be the shrinking pollution plume caused by leachate from the inactive dumpsite on traverse TR1G. However, low resistivity values were not dictated along Traverses TR2G and TR3G showing a decrease in pollution. The soil sample analysis showed the higher elemental concentration of manganese, zinc, copper, chromium, lead and cadmium on the dumpsites than about 25 – 50 m away from the dumpsite. The order of level of concentration is Mn > Zn > Cu > Cr > Pb > Cd. However, the statistical parameters analyzed at the level of concentration reveals that the area is uncontaminated of heavy metals. This could be attributed to continuous farming in the area, heavy rain that might have washed away the metal elements deposited in the inactive dumpsite over the years and the activities of scavengers that scavenge metals, plastics and other materials for recycling. The pollution plume detected by the 2-D imaging in traverse TRG1 could be from organic materials. The study area is considered safe for groundwater and farming. References 1. 2. 3. 4. 5.

6. 7. 8. 9.

Abbasi S A, Abbas N, Soni R 1998 Heavy metals in the environment (1st ed., p. 314). Mittal Publ. Abdus-Salam N Adekola FA 2005 Physico-chemical characterization of some Nigerian goethite mineral samples. Ife J. Sci. 7(1), 131 – 137. Abdus-Salam N 2009 Assessment of Heavy Metals Pollution in Dumpsites in Ilorin Metropolis. Ethiopian Journal of Environmental Studies and Management Vol.2 No.2. Aboud SJ, Nandini N 2009 Heavy metal analysis and sediment quality values in urban lakes. Am. J.Environ. Sci., 5(6), 678-687. Adebayo EA, Ariyibi MO, Awoyemi GC, Onyedim AS 2015 Delineation of Contamination Plumes at Olubonku Dumpsite Using Geophysical and Geochemical Approach at Ede Town, Southwestern Nigeria. Geosciences, 5(1): 39-45 DOI: 10.5923/j.geo.20150501.05 Adepetu JA, Adebayo AA, Aduayi EA, Alofe GO 1979 “A Preliminary Survey of the Fertility Status of Soils in Ondo State under Traditional Cultivation”. Ife Journal of Agriculture. 1: 134 – 149. Ako BD, Olorunfemi MO (1989) Geoelectric survey for groundwater in the Newer Basalts of Von. Plateau State. Nig. J. Mining & Geol. 25(1&2), 247-251. Albores AF, Perez-Cid B, Gomes EF, Lopez EF 2000 Comparison between sequential extractions procedures and single extraction procedures for metal partitioning in sewage sludge samples. Analyst, 125, 1353-1357 Alloway BJ 1995 Heavy Metals in Soils. 2nd ed. Glasgow, U.K: Chapman and Hall.

164

Application of Electrical Resistivity Methods ...

10. Amadi AN, Nwankwoala H. O 2013 Evaluation of Heavy Metal in Soils from Enyimba Dumpsite in Aba, Southeastern Nigeria Using Contamination Factor and Geo-Accumulation Index. Energy and Environment Research; Vol. 3, No. 1p125 http://dx.doi.org/10.5539/eer.v3n1p125 11. Anglin-Brown B, Armour A, Lalor G C 1995 Heavy metal pollution in Jamaica 1: Survey of cadmium, lead and zinc concentrations in the Kintyre and Hope flat district. Environ. Geochem. Health, 17, 51-56. 12. Barker RD 1989 Depth of investigation of collinear symmetrical four-electrode arrays. Geophysics 54, 10311037 13. Bear J, Cheng AHD 2010 Modeling Groundwater Flow and Contaminant Transport. Springer Dordrecht Heidelberg London. DOI 10.1007/978-1-4020-6682-5 14. Becker CJ 2001 Hydrogeology and leachate plume delineation at a closed municipal landfill, Norman, Oklahoma. Water Resources Investigations Report 01-4168. U.S. Geological Survey. 15. Bhuiyan M.A.H., Parvez L, Islam M. A., Dampare S.B., Suzuki S. 2010 Heavy metal pollution of coal mineaffected agricultural soils in the northern part of Bangladesh, J. Hazard. Mater. 173 384–392. 16. Brady Nweil R1999 The nature and properties of soil. Prentice Hall, Upper saddle River, New Jersey, pp 7492. 17. Canadian Council of Ministers of the Environment 1999 Canadian soil quality guidelines for the protection of environmental and human health: Summary tables. In: Canadian environmental quality guidelines. (1999) Canadian Council of Ministers of the Environment, Winnipeg. 18. Christensen TH, Kjeldsen P, Bjerg PL, Jensen DL, Christensen JB, Baun A, Albrechtsen HJ, Heron G 2001 Biogeochemistry of landfill leachate plumes. Appl. Geochem. 16:659-718. 19. Dineley D, Hawkes D, Hancock P, Williams B 1976 Earth resources – a dictionary of terms and concepts (p. 205). London: Arrow Books Ltd. 20. Dippro for Windows. 2000. DipproTM Version 4.0 Processing and Interpretation software for Dipole-Dipole electrical resistivity data. KIGAM, Daejon, South Korea. 21. Elaigwu SE, Ajibola VO, Folaranmi FM 2007 Studies on the impact of municipal waste dumps on surrounding soil and quality of two cities in Northern Nigeria. J. Applied Sci., 7 (3), 421-425 22. Fagbami A., Ajayi SO, Ali EM 1985 Nutrient distribution in the basement complex soils of tropical dry rain forest of South-Western Nigeria. 2. Micronutrients – zinc and copper. Soil Science 139: 531 – 537. 23. Francis DA 2005 Trace heavy metal contamination of soils and vegetation in the vicinity of livestock in Nigeria. Electron J. Environ. Agric. Food Chem. 4: 863 – 870. 24. Geoffrey IN 2005 The urban informal sector in Nigeria: towards economic development, environmental health, and social harmony. Global Urban Development Magazine 1(1). 25. Gimmler H, Carandang J, Boots A, Reisberg E, Woitke M 2002 Heavy metal content and distribution within a woody plant during and after seven years continuous growth on municipal solid waste MSW bottom slag rich in heavy metals. J. Appl. Bot., 76, 203-217 26. Gough LP, Severson RC, Jackson LL 1994 Baseline element concentrations in soils and plants, Bull Island, Cape Romain National Wildlife, Refuge, South Carolina, U.S.A. Water Air Soil Pollut. 74: 1 – 17. 27. Hakanson L 1980 Ecological risk index for aquatic pollution control. A sedimentological approach, Water Res. 14 975–1001. 28. Holmgren GGS, Meyer MW, Chaney RL, Daniels RB. 1993 Cadmium, lead, zinc, copper and nickel in agricultural soils of United States of America. J Environ Qual; 22: 335–348. 29. Huang K., Lin S 2003 Consequences and implication of heavy metal spatial in sediments of Keelung River drainage basin, Taiwan. Chemosp., 53, 1113-1121. 30. Kabata-Pendias A., Pendias H 1992 ‘Trace elements in soils and plants’.London: CRC Press. 31. Koefoed O 1979. Geosounding Principles 1. Resistivity sounding measurements. Elsevier Scientific Publishing Company, Amsterdam, p. 275. 32. Kottek M, Grieser J, Beck C, Rudolf B, Ru F 2006 World map of the Köppen-Geiger climate classification updated. Meteorologische Zeitschrift, 15(3), 259-263. 33. Lee GF, Jones-Lee A 1993 Groundwater pollution by municipal landfills. Leachate composition, detection and water quality significance. Proceeding of the 4th International Landfill Symposium, Sardinia, Italy, pp.10931103.

N. U. Ugwu et al.

165

34. Lee GF, Jones-Lee A 1993 ‘Revisions of State MSW Landfill Regulations: Issues for Consideration for the Protection of Groundwater Quality’. Environmental Management Review, No. 29, Third Quarter, pp. 31-54. 35. Lin YP, Teng TP, Chang TK. 2002 Multivariate analysis of soil heavy metal pollution and landscape in Changhua Country in Taiwan. Landscape Urban Plan., 62:19-35. http://dx.doi.org/10.1016/S01692046(02000094-4 36. Lokeshwari H, Chandrappa GT 2006 Impact of heavy metals content in water, water hyacinth and sediments of Laibagh tank, Bangalore. Indian J. Environ. Sci. Eng., 48, 183-188. http://www.neeri.res.in/jesevo14803006.pdf 37. Longe EO, Enekwechi LO 2007 Investigation on potential groundwater impacts and influence of local hydrogeology on natural attenuation of leachate at a municipal landfill. Int. J. Environ. Sci. Tech, 4(1):133140., Res. J. Appl. Sci. Eng. Technol. 2(1):39-44. 38. McAllister JJ, Smith BJ, Baptista NJA, Simpson JK. 2005 Geochemical distribution and bioavailability of heavy metals and oxalate in street sediments from Rio de Janeiro, Brazil: A preliminary investigation. Environ. Geoch. Heal, 27:429-441. 39. McBride MB 2003 ‘Toxic metals in sewage sludge-amended soils: Has proportions of beneficial use discounted the risks. Adv. Environ. Res., 8:5–19. 40. Mueller G 1979 Schwermettale in den sedimenten des Rheins – Veraenderungen seit. Umschau, 79:778-783. 41. Mueller G 1981 Die Schwermetallbelstung der sedimente des Neckars und seiner Nebenflusse: eine estandsaufnahme, Chem. Zeitung 105:157–164. 42. Odusanya BO, Amadi UMP 1989 An Empirical Resistivity Model for Predicting Shallow Groundwater Occurrence in the Basement Complex. Water Res. J. Nig. Asso. Hydrogeol. 2:77-87. 43. Ojo AO, Oyelami CA, Adereti AO 2014. Hydro-geochemical and Geophysical Study of Groundwater in the Suburb of Osogbo, South Western Nigeria. J Earth Sci Clim Change 5:205.doi:10.4172/2157-7617.1000205 44. Okoronkwo NE, Odemelam SA, Ano OA 2006 Level of toxic elements in soils of abandoned waste dumpsites. Afr, J. Biotechnol., 5 (13):1241-1244 45. Oladapo MI, Mohammed MZ, Adeoye OO, Adetola BA 2004 Geoelectrical Investigation of the Ondo State Housing Corporation Estate, Ijapo Akure, Southwestern Nigeria. Journal of Mining and Geology, Vol.40 (1):41-48 46. Olajire AA, Ayodele ET 1998 Heavy metals analysis of solid municipal waste in the western part of Nigeria. Water, Air and Soil Pollut., 103: 219-228 47. Olayinka AI and Olorunfemi MO 1992 Determination of Geoelectric Characteristics in Okene Area and Implications for Borehole Siting. Journal of Mining and Geology, 28 (2): 403 - 411. 48. Olorunfemi M O and Okhue E T 1992 Hydrogeological and Geologic significance of a geoelectric survey at IleIfe, Nigeria Journal of Mining and Geosciences Society, 28:221-229 49. Omosuyi GO, Ojo JS and Enikanselu PA 2003. Geophysical Investigation for Groundwater around Obanla – Obakekere in Akure Area within the Basement complex of South-Western Nigeria. Journal of Mining and Geology. 39(2):109 – 116. 50. Orellana E Mooney HM 1966 Master tables and curves for vertical electrical sounding over layered structures. Inteciencis, Madrib, 34pp. 51. Osazua LB, Abdullahi NK 2008 Geophysics Techniques for the study of Groundwater Pollution: A Review. Nigerian Journal of Physics, 20(1):163 – 174. 52. Oyelami AC, Ojo AO, Aladejana JA, Agbede OO 2013 Assessing the Effect of a Dumpsite on Groundwater Quality: A Case Study of Aduramigba Estate within Osogbo Metropolis, Journal of Environment and Earth Science 3(1):2224-3216. 53. Pascual B, Gold-Bouchot G, Ceja-Moreno V, del Ri’o-garci’a M 2004 Heavy metal and hydrocarbons in sediments from three lakes from san Miguel, Chiapas, Mexico. Bull. Environ. Contam. Toxicol., 73, 762-769. 54. Rahaman, M. A. 1989. Review of the basement geology of southwestern Nigeria: In Geology of Nigeria (Kogbe CA Ed.). Elizabeth Publishing. Co. Nigeria, 11:41-58. 55. Rahaman MA 1988 Recent advances in the study of the basement complex of Nigeria. In Precambrian Geology of Nigeria, Geological Survey of Nigeria, Kaduna South p 11- 43.

166

Application of Electrical Resistivity Methods ...

56. Smith CJ, Hopmans P, Cook FJ 1996 Accumulation of Cr, Pb, Cu, Ni, Zn and Cd in soil following irrigation with untreated effluents in Australia. Environ. Pollut., 94:317-323 57. Tijani MN, Jinno K, Horoshiro Y 2004 Environmental Impact of Heavy Metals Distribution in Water and Sediments of Ogunpa River, Ibadan Area, Southwestern Nigeria. J. Mining and Geol. 40(1):73. 58. Tomlinson DC, Wilson JG, Harris CR, Jeffery DW 1980 Problems in the assessment of heavy metals levels in estuaries and the formation of a pollution index, Helgol. Wiss. Meeresunters 33:566–575. 59. Uba S, Uzairu A, Harrison GFS, Balarabe ML, Okunola OJ. 2008 Assessment of heavy metals bioavailability in dumpsites of Zaria Metropolis, Nigeria. African Journal of Biotechnology. 7(2):122-130. 60. Vander-Velpen BPA 2004 WinRESIST Version 1.0 Resistivity Depth Sounding Interpretation Software. M. Sc Research Project, ITC, Delf Netherland. 61. Yisa J, Jacob JO, Onoyima CC 2012 Assessment of Toxic Levels of Some Heavy Metals in Road Deposited Sediments in Suleja, Nigeria. American Journal of Chemistry 2(2):34-37 DOI:10.5923/j.chemistry.20120202.08 62. Zauyah S, Julian B, Noorhafizh R, fauzih CI, Rosenami B 2004 Concentration and Speciation of Heavy metals in some cultivated and uncultivated ultisols and Inceptisols in Peninsular Malaysia. Super Soil. The Regional Institute Ltd. 63. Zohdy AAR, Eaton GP, Mabey DR 1974 Application of surface geophysics to groundwater investigations: Techniques of water resources investigations of U.S. Geol. Survey: Book 2, Chapter DI, U.S. Government Printing Office, Washington, pp.66.