Identification of seawater intrusion using geoelectrical resistivity method in the Goa Cina Beach Malang Area, Indonesia

Seawater intrusion can cause groundwater that is looked fresh initially but becomes brackish and even salty. It makes decreasing the quality of groundwater in the area. The Goa Cina Beach, Malang has a geological structure of rock in limestone, sand, and gravel. These rocks have greater porosity, so that the potential to pass water or water infiltration is also quite large, both freshwater and saltwater. Starting from these problems, it is needed to identify groundwater distribution that is not affected by the seawater intrusion process. The geoelectric method effectively determines geological parameters such as depth of bedrock, minerals, fluids, and shallow exploration to identify groundwater aquifers. Data acquisition was carried out using the geoelectrical resistivity method with Wenner configuration with three measurement points. Furthermore, the data processing used Res2dinv Software. The results showed that the measured resistivity value between 0.01000-501 Ωm with a maximum depth of 19.9 meters. The seawater intrusion distribution is assumed to be on lines 1 and 2 at an average depth of 10-19.9 meters with a resistivity value of 0.01000-0.230 Ωm. At the same time, the area that is not expected to experience seawater intrusion is on Line 3. The making of wells for coastal areas needs to consider the distance from the shoreline and rock porosity for minimizing the potential for seawater intrusion.