Geophysical assessment for vertical leachate migration profile and physicochemical study of groundwater around the Olusosun dumpsite Lagos, south-west Nigeria

Applied Water Science (2018) 8:142 https://doi.org/10.1007/s13201-018-0775-x ORIGINAL ARTICLE Geophysical assessment for vertical leachate migration profile and physicochemical study of groundwater around the Olusosun dumpsite Lagos, south‑west Nigeria Anthony Aduojo Ameloko1 · Elijah Adebowole Ayolabi2 Received: 20 April 2016 / Accepted: 31 July 2018 / Published online: 13 August 2018 © The Author(s) 2018 Abstract The study was aimed at assessing the vertical movement of leachate from 2001 through 2015, and groundwater physicochemical parameters analysis around the Olusosun dumpsite, through a time-lapse study.Tracking the leachate vertical migration profile was achieved through analysis of VES time-lapse data obtained from previous investigations on the dumpsite between 2001 and 2006, and 2D resistivity data acquired from this study in 2014 and 2015. Seventeen borehole and hand-dug well water samples were obtained randomly from 17 sampling locations around the dumpsite, first, in August 2014 (wet season) and then a repeat in December 2015 (dry season). The results of the VES data and 2D resistivity analysis showed that there is a constant and progressive increase in the depth of migration of the contaminants generated on this site into the subsurface environment over the years. It also showed that the contaminated zones are characterised by resistivity values ranging from 0.63 to 12.5 Ωm, and a maximum depth of 120 m has been impacted by the contaminants. The results of the water sample analysis showed clear variations for the various elemental constituents analysed for. Most of the physicochemical parameters analysed fell within the World Health Organisation (WHO) and the Nigerian Standard for Drinking Water Quality (NSDWQ) standard limit. Comparing the wet and dry season results, there was generally an increase in the mean concentrations of TDS, EC, temperature, hardness, Ca2+, Mg2+, K+, Na+,Cl−,NO−3 , Zn, Cu, Pb and Cr from the dry season study, particularly the samples with close proximity to the dumpsite. On the other hand, there was reduction in the mean concentrations of SO2− PO3− 4 , 4 , Fe, pH, and Ni from the dry season study when compared with the wet season. This trend could be attributed to the fact that in the absence of rainfall during the dry season period, contaminant accumulation in groundwater continued undiluted due to continuous breakdown of the biodegradables units with time, and this led to the generally high concentration of the physicochemical properties during the dry season. The implication is that the water around the study area has lower quality in the drier season when compared to the quality of water during the wet season, and so water treatment should be given more priority during the dry season before consumption and usage for other domestic purposes to avoid waterborne diseases. Generally, the information obtained from the geophysical study will facilitate decisions on improving protection for groundwater resources around the study area. Keywords Concentration · Physicochemical · Landfill · Wet season · Dry season Introduction * Anthony Aduojo Ameloko 1 Department of Petroleum Engineering, Covenant University, Ota, Nigeria 2 Department of Geosciences, University of Lagos, Lagos, Nigeria An integrated geophysical survey consisting of 2D electrical resistivity imaging, time-lapse vertical electrical sounding (VES) and seasonal physicochemical measurement of groundwater parameters was conducted at the dumpsite with the aim of assessing and investigating the vertical migration profile of leachate contamination over time. The impact of seasonal variation on the physicochemical properties of groundwater around the dumpsite was also to be examined. One of the greatest challenges associated with landfilling activities is 13 Vol.:(0123456789) 142 Page 2 of 15 that of pollution to the environment, and more challenging is how to determine the extent of environmental pollution to the surface and subsurface environment. When it rains on a landfill, water percolates through the cells and soils in the landfill. As this continues, the water dilutes the decomposed materials (organic and inorganic chemicals, metals, biological waste products of decomposition) on the site to form what we refer to as leachates, and it is typically acidic. In landfills without liners, there might be migration of different organic and inorganic chemical compounds to the unsaturated zone of the soil which may reach the saturated zone (Mondelli 2004). These contaminated liquids may leave the disposal site, enter the underlying groundwater system and make the groundwater unpotable. If this water is used, the health of users is put at risk (Soupios et al. 2007). Theoretically, the electrical resistivity method measures variation in subsurface resistivity when a current is driven into the earth. From the measurements on earth surface of the electrical potential and the current, it is usually possible to obtain information about the variation of subsurface resistivities. Usually the methods are not used to detect contamination directly, but rather, they reveal contamination through sharp variation in subsurface resistivities as a result of the presence of these contaminants. Studies abound in the literature on groundwater contamination. Such work includes (Bably and Kumari 2000). They concluded that there is need to monitor water quality on regular basis. This is because the increase in concentration of trace metals in potable water will increase the threat to man’s health and life. The variation of groundwater quality in an area is a function of physical and chemical parameters that are greatly influenced by geological formations and anthropogenic activities (Subramani et al. 2005). Recent studies around the Olusosun dumpsite revealed continuous degradation of the groundwater quality. According to Adeyi and Majolagbe (2014), almost all the groundwater collected around Olusosun dumpsite showed level of nitrate higher than that of WHO permissible limit of 10 mg/L. This situation is of great health risk as nitrate pollution has been linked to myth and sometimes death. The groundwater vulnerability index analysis around the dumpsite showed values between 61.8 and 205, indicating good–poor–very poor class of water, and about sixty per cent of water collected around the dumpsite are unsafe for human consumption without further treatment (Abdulrafiu et al. 2016). The uncontrolled disposal of lead acid batteries and spent petroleum products probably caused relatively higher levels of Pb, Cu and Fe found in groundwater around the study area (Oyeku and Eludoyin 2010). Also, statistical analyses of physical parameters determined in situ on groundwater from the work of Ayolabi et al. (2014) around the dumpsite showed elevated concentrations of total dissolved solid, electrical conductivity, temperature and high acidic content. They concluded that the high level of polluti (...truncated)