Indikasi Intrusi Air Laut Berdasarkan Resistivitas 2D dan Kualitas Air Tanah di Penjaringan dan Tambora, Jakarta

Abstract

Groundwater salinity in coastal Jakarta is difficult to identify solely from low-resistivity values because saturated clay deposits can also produce conductive responses. This study aims to map the lateral and vertical distribution of low-resistivity zones and evaluate their relationship with groundwater quality and geological conditions in Penjaringan and Tambora, Jakarta. Two-dimensional resistivity surveys were conducted along two profiles using an ARES II system with a Wenner–Schlumberger configuration, a 5 m electrode spacing, and profile lengths of 235 m and 355 m, respectively. The data were inverted using RES2DINV with topographic correction. Interpretation was supported by measurements of electrical conductivity and total dissolved solids from four groundwater wells, together with local geological information. The Penjaringan profile is dominated by resistivity values of 0.5–2.0 Ωm to a depth of approximately 45 m, whereas the Tambora profile shows resistivity values of 0.5–4.5 Ωm to a depth of about 70 m, with several local resistive anomalies ranging from 15 to 100 Ωm. Electrical conductivity values range from 1.144 to 3.414 dS/m, while TDS values range from 763 to 2,277.14 mg/L. Three samples are classified as brackish water, whereas one sample is classified as fresh water. The integrated results indicate that pore-water salinity contributes to the low-resistivity response, although clay content, silt content, and saturation level also play important roles. These findings indicate groundwater salinization consistent with the possible influence of seawater intrusion, but they do not yet confirm its source, flow direction, or regional extent.