Use of geophysical logs in hydrogeological studies and borehole designs: case study of Apapa coastal area, Lagos, Nigeria

Abstract

Abstract The hydrogeological study of Apapa, a coastal part of Lagos, Nigeria, has been investigated using combined geophysical borehole logs, consisting of natural gamma and electrical resistivity components and ditch cutting samples. This study utilized data from 10 boreholes to delineate freshwater aquifer and proposes the best borehole design and construction for optimum groundwater developments in the study area. The electrical resistivity log data show that the depth to the freshwater interface varies across the study area occurring between 150 and 160 m and as shallow as 110 m in a borehole. The variations in depth of the freshwater interfaces are attributed to the extent of saline/brackish water contamination and distribution of rock types. Based on these differences and the inability to identify water quality from ditch cuttings, borehole geophysical logging is a vital tool in providing in situ subsurface information of the rock types and fluid contents in groundwater studies. This further demonstrates that geophysical borehole logs play an important part in borehole design for development of water wells.

Keywords

• Geophysical borehole logs
• Electrical resistivity
• Natural Gamma
• Groundwater
• Coastal aquifer
• Freshwater–saltwater intrusion