Geophysical and Geochemical Approach for Seawater Intrusion Assessment in the Belawan Coast and the Medan Industrial Area, North Sumatera Utara, Indonesia

Abstract

The uncontrolled underground water exploitation and inadequate domestic and industrial wastewater control systems have contributed significantly to groundwater degradation. The groundwater degradation potentially initiates the seawater intrusion especially on the coastal area. The present study aims to analyze the seawater intrusion using geophysical and geochemical approach in the coastal area of Belawan and Medan Industrial Area which close to the coastal area. 15 borehole water samples collected were analyzed to determine anions, cations concentrations, and facies. The results showed that the lithostratigraphy of the study area consisted of alluvial in form of watery gravel and clay layers. The investigation of the groundwater using the geoelectricmethod showed that the resistivity values for track 1 (GL-1) and track (GL-02) are 129Ω to 371Ω. These values are interpreted as layers of sand that have experienced seawater intrusion at a depth of 40-60 meters. Furthermore, the water quality tests at the point of wells 1 and 2 on the chloride parameter, where the highest chloride concentration with values of 205.8 mg/l and 203.2 mg/l, was polluted. The result proved that the seawater intrusion has stimulated the groundwater in the coastal area of Belawan and Medan Industrial Area, Indonesia.