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Electrical resistivity investigation was carried out at Olabisi Onabanjo University campus, Ago-Iwoye, Southwestern Nigeria with the aim of evaluating groundwater potential and aquifer protective capacity of the overburden units in the area. The underlain rocks are predominantly porphyroblastic and banded gneiss, quartzschist and biotite-hornblende granite. Twenty-Four Vertical Electrical Sounding (VES) were probed using Schlumberger array with maximum current electrode spacing (AB/2) of 100 m at each point using the OHMEGA Allied resistivity meter. The data were interpreted using the partial curve matching and computer iteration programme using WINRESIST. Parameters such as overburden thickness, basement resistivity, reflection coefficient and longitudinal conductance were calculated and used for evaluating the groundwater potential and aquifer vulnerability of the study area. The predominant VES curve types obtained are KH, H, A, AKH, HKH and HA. The geoelectric sections show that the area is underlain by 3-5 layers: the topsoil (72.4-1735.6 Ω m), clay/clayey sand/sand/laterite (18.9-1349.5 Ω m), fractured basement (430.7-1021.4 Ω m) and the fresh basement (433.3-7146.4 Ω m). The plotted isopach map showed an overburden thickness range of 4.9-28.2 m with values greater than 20 m at the southeastern and southwestern parts of area. The reflection coefficient range is between 0.62 and 0.98 while protective capacity range is between 0.03 and 0.28. Groundwater potential of the area were classified as high (overburden thickness > 13 m and reflection coefficient < 0.8); medium (overburden thickness > 13 m and reflection coefficient ≥ 0.8); and low (overburden thickness < 13 m and reflection coefficient > 0.8). The protective capacity rating falls between poor to moderate, thus, vulnerable to infiltration of leachate and other surface contaminants. The study therefore helped in identifying favourable groundwater potential and the aquifer vulnerability of the area.

Background. Exposure to heavy metals emanating from cement production and other anthropogenic activities can pose ecological risks. Objectives. A detailed investigation was carried out to assess the contamination and ecological risk of heavy metals associated with dust released during cement production. Methods. Sixty samples, including 30 soils and 30 plants, were collected around Lafarge Cement Production Company. Control samples of soil and plants were collected in areas where human activities are limited. Samples were dried, sieved (for soil; 65 μm), packaged and analyzed using inductively coupled plasma mass spectrometry at Acme Laboratory in Canada. Results. The average concentration of heavy metals in soils of the area are: copper (Cu): 41.63 mg/kg; lead (Pb): 35.43 mg/kg; zinc (Zn): 213.64 mg/kg; chromium (Cr): 35.60 mg/kg; cobalt (Co): 3.84 mg/kg and nickel (Ni): 5.13 mg/kg. Concentrations of Cr in soils were above the recommended standards, while other metals were below recommended limits. The average concentrations of heavy metals in plants were: Cu: 26.32 mg/kg; Pb: 15.46 mg/kg; Zn: 213.94 mg/kg; Cr: 30.62 mg/kg; Co: 0.45 mg/kg and Ni: 3.77 mg/kg. Levels of heavy metals in plants were all above international limits. Geo-accumulation of metals in soils ranged between −0.15 and 6.32, while the contamination factor ranged between 0.53 and 119.59. Ecological risk index of heavy metals in soils ranged between 49.71 and 749. Discussion. All metals in soils of the study area except for Cr were below the allowable limits, while the levels of metals in plants were above the permissible limits. Levels of heavy metals reported in this study were higher than those from similar cement production areas. Soils around the Ewekoro cement production area were low to extremely contaminated by toxic metals. Cement production, processing, transportation in conjunction with the abandoned railway track in the area greatly contribute to the high degree of contamination observed in the area. Metal transfers from soil to plant are a common phenomenon. The metals pose low to considerable ecological risk. Conclusions. Anthropogenic sources, especially cement processing activities, release heavy metals which leads to progressive pollution of the environment and poses high ecological risk. Competing Interests. The authors declare no competing financial interests

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The geophysical assessment of groundwater in Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is predominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very low frequency electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES) methods. The VLF-EM survey was at 10 m interval along eight traverses ranging between 290 and 700 m in length using ABEM WADI VLF-EM unit. The VLF-EM survey was used to delineate areas with conductive/fractured zones. Twenty-three VES surveys were carried out with the use of Campus Ohmega resistivity meter at different location and at locations areas delineated as high conductive areas by VLF-EM survey. The result of VLF-EM survey along its traverse was used in delineating high conductive/fractured zones, it is, however, in agreement with the delineation of the VES survey. The VES results showed 3-4 geoelectric layers inferred as sandy topsoil, sandy clay, clayey and fractured/fresh basement. The combination of these two methods, therefore, helped in resolving the prospecting location for the groundwater yield in the study area.