A valuable approach in a quantitative seawater intrusion interpretation from the geoelectrical resistivity data for groundwater investigation in Dumai area, Indonesia

An improvement of geoelectrical resistivity interpretation has been done through this research. Up to now, the geoelectrical resistivity data was interpreted qualitatively especially in the case of the aquifer intruded by seawater, and the percentage of seawater mixture content in the aquifer cannot be predicted. In this research, a valuable approach was used in the prediction of percentage seawater mixture in the shallow aquifer that is intruded by seawater. The study was conducted in the coastal area which is mainly covered by peat soil. The research employed the direct soil resistivity measurement and the ground surface resistivity survey. Geoelectrical resistivity with the Wenner configuration was used for both measurements. The soil character and the fluid content in the soil were measured to obtain their correlation to the direct soil resistivity value. The results show that resistivity value is about 2-5 ohm.m for 50% seawater content mixture in aquifer and it increase to be 5-10 ohm.m for 25% seawater mix to freshwater in the aquifer. The increasing seawater content in the pore soil caused the decreases in resistivity value drastically. The percentage of seawater mixture in the fluid pore soil has been successfully predicted through the geoelectrical resistivity measurement on the surface.