Limestone exploration has numerous advantage to the nation’s economy. However,

major anthropogenic activities such as mining of such mineral deposits causes environmental

contamination due to heavy metals pollution.The presence of heavy metals such as lead,

cadmium, mercury and arsenic can interfere with the biochemical pathways by interaction with

enzymes and proteins. They equally have the capacity to alter the DNA repair mechanism and

act as the inducers of carcinogenesis. The focus of the research is therefore to detect the extent

of heavy metals contaminations within the sampled Ewekoro limestone, southwestern Nigeria

and to ascertain the risks they posed to the quarry workers, miners and the people residing in

the study area

Aizebeokhai, A. P.

Akinsiku, A.A.

Anake, W. U.

Ayara, Williams A.

Jonathan, Hassana

Olofinnade, O. M.

Oyeyemi, Kehinde D.

Sanuade, O. A.

Covenant University Repository

IOP Conference Series: Materials Science and EngineeringPAPER • OPEN ACCESSInvestigating the near surface leachate movement in an open dumpsiteusing surficial ERT methodTo cite this article: K D Oyeyemi et al 2019 IOP Conf. Ser.: Mater. Sci. Eng. 640 012109 View the article online for updates and enhancements.This content was downloaded from IP address 165.73.223.243 on 12/11/2020 at 16:01Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd1st International Conference on Sustainable Infrastructural DevelopmentIOP Conf. Series: Materials Science and Engineering 640 (2019) 012109IOP Publishingdoi:10.1088/1757-899X/640/1/0121091      Investigating the near surface leachate movement in an open dumpsite using surficial ERT method K D Oyeyemi1 A P Aizebeokhia1 A N Ede2 O J Rotimi3 O A Sanuade4 O M Olofinnade2 O A Ekhaguere5 O Attat1 1Department of Physics, Covenant University, Ota, Ogun State, Nigeria 2Department of Civil Engineering, Covenant University, Ota, Ogun State, Nigeria 2Department of Petroleum Engineering, Covenant University, Ota, Ogun State, Nigeria 3Geosciences Department, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia 4 Department of Physics, Federal University of Agriculture, Abeokuta, Nigeria  *kdoyeyemi@yahoo.com, kehinde.oyeyemi@covenantuniversity.edu.ng  Abstract. Geoelectrical resistivity imaging technique was conducted at Abule-egba open dumpsite, Lagos with intentions to monitor the movement of the contaminant leachate within the near surface. The two survey traverses (T1 and T2) of 2D electrical resistivity tomography were conducted using Wenner array configuration with minimum electrode spacing of 1 metre and maximum data levels of seven. The inversion models revealed the two delineated geoelectrical layers which are sandy-clay and sand units. The leachate fluids has the resistivity values of 5.75 – 10.4 Ωm at depth range of 2.5 – 4.0  metres along T1 and T2 moving from NW to the SE section. The leachate fluids are capable of polluting shallow groundwater aquifer within the study area and the residents are advised to drill deeper in the subsurface for clean and portable groundwater resources.     Keywords: Environmental Geophysics, Leachates, Near-surface geophysics, Open dumpsite, Electrical resistivity tomography (ERT)  1.  Introduction Leaching of both inorganic and organic contaminants from dumpsites is constituting a serious environmental challenge to both surface water and aquifers. Groundwater pollution from organic and inorganic contaminants is one of the hazards that endangered environments most especially in industrial areas. Contaminations sources are divided into two, which are point source and area contaminations. The point source contaminations include those of accidental spills, landfills, industrial waste disposal sites and gasoline tanks leakage. Whereas, those of area contaminations include fertilizer and pesticides contaminations in agriculture. Landfills and solid waste disposal are the most common point source contaminations and they can produce contamination leachate plumes [1-3]. The migration of the leachate plume can also pollute the aquifers and surface waters for a long period of time thereby causing a long term serious health and environmental risks [4, 5].  1st International Conference on Sustainable Infrastructural DevelopmentIOP Conf. Series: Materials Science and Engineering 640 (2019) 012109IOP Publishingdoi:10.1088/1757-899X/640/1/0121092      In order to properly evaluate these risks, mapping and characterizing the leachate plume is pertinent. There are several techniques for these purposes, however, several of them only provide limited spatial subsurface information which might generate incomplete site investigation thereby resulting into inadequate remedial designs. Geophysical surveys can reduce this gap in provision of spatial information by generating an extensive lateral coverage without jeopardizing the needed high resolution information. Geophysical techniques are non-invasive and have been extensively used for subsurface characterization, in particular electrical resistivity tomography (ERT) has been used for groundwater exploration and pollution studies [6-12]. In this research, we used surficial ERT method to monitor the lateral coverage and migration of leachate plume within the subsurface of an open dumpsite around Abule-Egba, Lagos (Figure 1).     Figure 1: Abule-Egba Dumpsite. 2.  Methodology  2.1 Study Area The area of study is a dumpsite situated between the easting of 3°18'1.31'' to 3°18'16.03'' and northing 6°38'15.08'' to 6°38'15.43'' (Figure 2) located along Abule-egba to Iyana-ipaja Road, Lagos state, SW Nigeria. The study area lies geologically within the Eastern Dahomey Basin with east-westward trend sediments deposition and six lithostratigraphic units comprising Benin, Ilaro, Oshosun, Akinbo, Ewekoro and Abeokuta Formations from youngest to the oldest geological formation. Ewekoro Formation is known to be a Paleocene shallow marine deposit of non-crystalline and non-fossiliferous limestone strata. The Ilaro Formation consisting of clays and shales followed by the poorly sorted coastal plain sands of Benin Formation and recent alluvial deposits. Within the Lagos metropolitan area, the coastal plain sand units of Benin Formation are the major aquifers generally exploited by low and medium income earners for water supply.  2.2 ERT Data Acquisition and Processing   The 2D electrical resistivity tomography survey consist of two traverses (T1 and T2) situated within the north-west portion of the dumpsite (Figure 2). Wenner array was used for data acquisition with minimum electrode spacing of 1 m and maximum data levels of seven (7). The electrode positions were clearly pegged prior to the survey in order to avoid electrode positioning error. SAS 1000/4000 series ABEM Terrameter was used for the data measurement. The equipment was set for measurement repetition with minimum and maximum data stacking of 3 and 6 respectively. The minimum and maximum current 1st International Conference on Sustainable Infrastructural DevelopmentIOP Conf. Series: Materials Science and Engineering 640 (2019) 012109IOP Publishingdoi:10.1088/1757-899X/640/1/0121093      injected into subsurface for apparent resistivity measurements were 20.0 mA and 100.0 mA. During the survey, we ensured that electrodes were firmly in contact with the ground and effective contact were maintained between the electrodes and the connecting cables. The acquired apparent resistivity datasets for both traverses were processed and inverted with the use of RES2DINV inversion code that employs nonlinear optimization technique to compute the subsurface 2D inverse models.     Figure 2: Google earth map showing the survey area with survey traverses TR1 and TR2.  3.  Results and Discussion  The inverse model of the 2D ERT along TR1 (Figure 3) shows two geoelectrical layers of sandy-clay unit with resistivity values range 14.9 – 50.5 m  and sand unit with resistivity values range 92.9 – 314 m . A low resistivity layer of sandy-clay unit impregnated with high density leachate fluids with resistivity values less than or equal to 4.40 m  that percolate downward to the depth range of 2.5 m to 4.00 m in the subsurface. The inverse resistivity model for TR2 shows two geoelectrical layers of sandy-clay unit with resistivity values range 18.4 – 72.0 m  and sand unit with resistivity 1st International Conference on Sustainable Infrastructural DevelopmentIOP Conf. Series: Materials Science and Engineering 640 (2019) 012109IOP Publishingdoi:10.1088/1757-899X/640/1/0121094      values range 142 – 558 m . A low resistivity layer of sandy-clay unit impregnated with high density leachate fluids with resistivity values less than or equal to 4.69 m  that percolate downward to the depth range of 2.5 m to 4.00 m in the subsurface. Generally, the leachate fluids are observed to flow south-eastward in the study area. The contaminant plume is predominant within the shallow and central portions of the study area. Consequently, any shallow aquifers present in the study area seem to have been polluted by the leachate.      Figure 3: 2D ERT Inverse resistivity model for traverse TR 1    Figure 4: 2D ERT Inverse resistivity model for traverse TR 2.   1st International Conference on Sustainable Infrastructural DevelopmentIOP Conf. Series: Materials Science and Engineering 640 (2019) 012109IOP Publishingdoi:10.1088/1757-899X/640/1/0121095      4.  Conclusions 2D electrical resistivity tomography has been used to determine the near surface occurrence of leachate plume within a dumpsite around Abule-Egba, Lagos Nigeria. The preferential flow movement of the leachate fluid is investigated. The geoelectrical imaging results show that the contaminant leachates occur in the near surface depths at about 2.5 m to 4 m and flow south-eastwards. The residents are admonished to drill deeper for clean groundwater source as any shallow aquifers would have been contaminated by the leachate plume. Hydrogeochemical analysis of the groundwater in the area is recommended so as to ascertain the extent of groundwater pollution in the area.     Acknowledgments The authors thank Covenant University centre for research, innovation and development (CUCRID) for the conference support. References [1] Cozzarelli I M Boehlke J K Masoner J Breit G N Lorah M M Tuttle M L W Jaeschke J B 2011 Biogeochemical evolution of a landfill leachate plume, Norman, Oklahoma Ground Water 49 663–687 [2]     Oyeyemi K D Aizebeokhai A P Oladunjoye M A 2015 Integrated geophysical and           geochemical investigations of saline water intrusion in a coastal alluvial terrain, Southwestern            Nigeria International Journal of Environmental Sciences 10(4) 1275–1288         [3] Oyeyemi K D Aizebeokhai A P and Okagbue H I 2017 Geostatistical exploration of dataset assessing the heavy metal contamination in Ewekoro limestone, Southwestern Nigeria Data in Brief 14 110–117 [4]        Bjerg P L Albrechtsen H J Kjeldsen P Christensen T H Cozzarelli I M 2014 The             biogeochemistry of contaminant groundwater plumes arising from waste disposal facilities A2 - Holland, Heinrich D. In: Turekian, K.K. (Ed.), Treatise on Geochemistry, second ed. Elsevier, Oxford 573–605 [5] Oyeyemi K D Aizebeokhai A P Attat O F 2018 Evaluation of groundwater near municipal solid waste landfill site using ERI technique: A case in southwestern Nigeria Nature Environment and Pollution Technology 9(6) 765–772 [6]    Aizebeokhai A P Oyeyemi K D 2014 The use of the multiple-gradient array for geoelectrical resistivity and induced polarization imaging Journal of Applied Geophysics 111 364 – 376  [7]  Aizebeokhai A P Oyeyemi K D 2018 Geoelectrical characterization of basement aquifers: the case of Iberekodo, southwestern Nigeria Hydrogeology Journal 26(2) 651 – 664 [8]  Oyeyemi K D Olofinnade O M 2016 Geoelectrical-Geotechnical studies for near surface characterization, case history: Lagos, SW Nigeria Electronic Journal of Geotechnical Engineering 21(10) 3735 – 3750 [9] Oyeyemi K D Aizebeokhai A P Adagunodo T A Olofinnade O M Sanuade O A Olaojo A A 2017 Subsoil chracterizatin using geoelectrical and geotechnical investigations: Implications for foundation studies International Journal of Civil Engineering and Technology 8(10) 302 – 314 [10]  Aizebeokhai A P Oyeyemi K D Kayode O T 2015 Assessment of soil petrophysical parameters using electrical resistivity tomography (ERT) and induced polarization techniques. Research Journal of Applied Sciences 10 (9) pp 479 – 485 [11]  Oyeyemi K D Aizebeokhai A P Olofinnade O M Sanuade O A 2018 Geoelectrical investigations for groundwater exploration in crystalline basement terrain, SW Nigeria: Implications for groundwater resources sustainability 9(6) 765 – 772  [12]  Aizebeokhai A P Ogungbade O Oyeyemi K D 2017 Integrating VES and 2D ERI for near-surface characterization in a crystalline basement terrain. SEG Technical Program Expanded Abstracts 5401 – 5406  

Geospatial distribution of heavy metal contamination in Ewekoro

Limestone, SW Nigeria

http://eprints.covenantuniversity.edu.ng/13734/1/Oyeyemi_2019_IOP_Conf._Ser.%20_Mater._Sci._Eng._640_012109.pdf

Geospatial distribution of heavy metal contamination in Ewekoro Limestone, SW Nigeria

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