Identifikasi Intrusi Air Laut Menggunakan Metode Geolistrik Resistivitas 2D di Kecamatan Puger, Kabupaten Jember

Abstract

The coastal area of Puger Subdistrict, Jember Regency, is vulnerable to seawater intrusion due to geological conditions characterized by sandy alluvial deposits and high groundwater extraction by the local community. Seawater intrusion causes a decline in groundwater quality, rendering it unsuitable for consumption or domestic use. This study aims to determine the distribution of subsurface resistivity and identify seawater intrusion zones based on resistivity values obtained from field measurements. The method used is the two-dimensional (2D) resistivity geophysical method with the Wenner–Schlumberger configuration, which provides information on horizontal and vertical variations in subsurface structure. Data processing was performed using Microsoft Excel for initial calculations and Res2Dinv software to generate 2D models. The study was conducted on four transects with lengths of 30 m, 60 m, 80 m, and 60 m, respectively, and electrode spacing ranging from 1.5 m to 4 m with a value of n equal to 5. The results of the study show that subsurface resistivity values range from 0.113 Ωm to 4702 Ωm, with constituent materials consisting of clay, silt, sand, gravel, and sandstone. The seawater intrusion zone is characterized by very low (<1 Ωm) to low (<10 Ωm) resistivity values. Intrusion was identified along all transects with distinct characteristics: transects 2 and 4 were dominant at shallow depths (0.75–4.06 m), transect 3 at deeper depths (10,7 – 13,8m), while transect 1 showed a transition zone ranging from brackish water to potentially saline water. The results of this study indicate that the coastal area of Puger Subdistrict has experienced seawater intrusion with an uneven distribution pattern both laterally and vertically.