Application of vertical electrical sounding (VES) in subsurface geological investigation for potential aquifer in Lahad Datu, Sabah

40 Vertical Electrical Sounding (VES) stations were established to investigate the subsurface geology and aquifer potentials in the area of Dent Group sedimentary rock. Dent Group sedimentary rock consists of Sebahat, Ganduman and Togopi Formation with the age of Late Miocene until Pleistocene. VES technique was performed by measuring the resistivity change with depth. The resistivity measurements were conducted using ABEM SAS 300C Terrameter by using Schlumberger electrode configuration with maximum current electrode separation of 500m. Interpreted VES data in the Sebahat Formation produces three to four geo-electrical resistivity layers. Most of the geo-electrical layers show low resistivity value (1-10 Ohm-m) that indicate the formation was mainly made of clay or shale materials. VES results in the Ganduman Formation indicates that the formation dominated by layers of sandstone and mudstone mixed with siltstone layer. Generally, the Ganduman Formation gives four to five geo-electrical resistivity layers. While Togopi Formation produced 3 to 4 geo-electrical layers interpreted as sandstone for the first layer, mudstone for the second layer and followed by layer containing several block of limestone. The geo-electrical resistivity results indicate that Ganduman and Togopi Formations have the potential to become aquifer. The VES method has successfully detected the soil material layers in Ganduman and Togopi formations which were supported by the existing borehole data. Combination of sandstone and mudstone layers indicate that the Ganduman Formation possibly become semi-confined aquifer. Furthermore, the Ganduman Formation also producing artesian wells in some areas that were found at a number of production wells in the study area. Similarly, the Togopi Formation is also having dominated sandy layer that can be a potential aquifer. In addition, the limestone blocks in the Togopi Formation could also become a potential aquifer, whilst for the Sebahat Formation which consist of mudstone is interpreted to be an aquitard layers.