Integrated approach for groundwater assessment in Yetunde Brown, Ifako, Gbagada, Lagos State, Nigeria
The poor quality of potable water sourced from boreholes and hand dug wells at Yetunde Brown, Gbagada, Lagos informed the integration of geophysical, physicochemical and Water Quality Index (WQI) to assess the condition of groundwater in the study area. Twenty-Five (25) Vertical Electrical Sounding (VES) data were acquired and complemented with water samples collected from three boreholes and two hand-dug wells within the neighborhood of the study area. The VES data were partially curve matched and inverted. Physicochemical parameters were measured in water samples. The results of the VES data revealed four to five geo-electric layers which correspond to the topsoil (with layer thickness and resistivity values from 0.6 to 1.3 m and 20.1 to 361.4 Ωm respectively), clay (with layer thickness and resistivity of 1.7 to 5.2 m and 2.8 to 22.1 Ωm), sandy clay (with layer thickness and resistivity values of 2.8 to 5.9 m and 12.4 to 56.8 Ωm) and clayey sand (with layer thickness and resistivity values of 23.8 to 31.8 m and 7.2 to 94.2 Ωm). The sand in VES 7, 9, 12-18 and 20 has resistivity values ranging from 151 to 331.5 Ωm. The depth to the identified aquifers fluctuates between 23.8 and 90.4 m. The measured iron, chloride and lead ions are above World Health Organization (WHO) recommendation for potable water in some water samples. WQI calculated reflected poor quality for two boreholes only, which could be due to the unconfined aquifers delineated in the second and fourth geo-electric layers making the water vulnerable to contamination. The study recommended that bore hole should be sunk at VES 7, 9, 12, 13, 18 and 20 at depth between 31.8 to 66.6 m for exploitation of good quality water.
Keywords: Groundwater, Electrical resistivity, Water quality index, physicochemical analysis, Aquifer