Groundwater Contamination Prediction Using Finite Element Derived Geoelectric Parameters Constrained by Chemical Analysis around a Sewage Site, Southwestern Nigeria

Abstract

Vertical Electrical Sounding, the Finite Element Technique (FET) and chemical analysis of soil samples were used to map the pollution plume around two oxidation sewage ponds in Ile-Ife, Southwestern Nigeria. The elemental concentrations of the soil samples at 5 m depth around the sewage ponds were obtained using partial extraction of exchangeable metals ions of (0.05 HCl + 0.025 N H2SO4) or 0.075 N acid mixture. The VES interpreted results delineated three to four geoelectric subsurface layers comprising topsoil, laterite, weathered layer and the fresh basement. The elemental concentration of Cu, Zn, Pb and Cr in the soil samples located at the periphery of the sewage ponds are much higher than those of the control sample point indicating pollution. The finite element generated isopach map of the overburden indicates easterly direction of groundwater flow and weathered layer isoresistivity map generated using the finite element technique identifies low resistivity zone characteristic of pollution zone in the eastern flank. The study concluded that the groundwater in the area around the sewage ponds may have been polluted

Surface DC resistivity survey of contamination Beneath Ido-Osun dumpsite, southwestern Nigeria

“…Figures 3B and 3C represent the observed dipole-dipole pseudo-section, and 2-D Inversion Model respectively. The 2-D resistivity structure reveals relatively low resistivity values in the range of 5 and 14 Ωm typical of contamination zones (Adepelumi et al, 2005;Urish, 1983;Bayowa et al, 2012) between stations 2 and 8 at a depth range between 3 and 12 m; stations 10 and 12 at about 5 m depth and between stations 14 and 19.5 at depth range between 5 to 15 m. At the depth of detection of the plumes, it is apparent that the groundwater is contaminated.…”

“…Only H and KH type curves were obtained beneath this traverse as indicated in Table 1 (Adepelumi et al, 2005;Urish, 1983;Bayowa et al, 2012) are observed between stations 2 and 4 at a depth range between 0 and 15 m; stations 5 and 6 at a depth of about 5 m and; stations 6 and 8 at a depth beyond 30 m.…”

“…Figure 4A is a VES geoelectric section that relates VES 13,14,15,16,17,18,19,and 20. respectively. The 2-D image indicates distinct low resistivity zones (Adepelumi et al, 2005;Urish, 1983;Bayowa et al, 2012) of possible contamination between stations 2 and 7 at about 10 m depth; stations 8 and 10 at a depth of 3 m and between stations 12 and 16 at a depth range between 0 and 8(11?) m.…”

“…For these reasons, there is widespread interest in applying noninvasive and relatively inexpensive geophysical techniques, such as electrical resistivity imaging (ERI), electromagnetic methods, electrical conductivity (EC) logging, and seismic surveys, as means for mapping the occurrence and movement of leachate and for facilitating decision making regarding the location of monitoring wells (Bernstone and Dahlin, 1997;Butler et al, 1999;Buselli and Lu, 2001). These geophysical methods have been used prior to waste disposal installations and for evaluation of possible leachate flow after dumping of waste because they generate nearly continuous image of the subsurface that can significantly reduce the risk of undetected contaminants (Zume et al, 2006;Olorunfemi and Mesida, 1987;Sharma, 1997;Schulmeister et al, 2003;Abu-Zeid et al, 2004;Naudet et al, 2004;Bayowa et al, 2012). This article reports the application of the electrical geophysical method involving the vertical electrical sounding (VES) and 2D profiling (Dipole-Dipole) techniques to map possible leachate distribution and migration processes from the abandoned Ido Osun landfill site, Osun State, southwestern, Nigeria.…”