Geophysical Mapping of Saltwater Intrusion using ERT and TEM Methods at Pantai UMT, Terengganu, Malaysia

Saltwater intrusion is a common problem in a coastal setting and can contaminate the groundwater source. The depth of saltwater intrusion can also be heterogeneous in relative to the distance from the shoreline, which is highly dynamic in the coastal setting due to the rising sea level. Typically, saltwater intrusion is identified by drilling wells and carrying out water sampling, although this method can be time-consuming and unreliable for a large area. In this study, geophysical surveys (i.e., ERT and TEM) were carried out at Pantai UMT to determine the depth of saltwater intrusion. Two resistivity survey lines (L1, L2) were set up parallel and perpendicular to the shoreline by using ABEM Terrameter LS2. Three electromagnetic data (P1, P2, P3) also were collected using ABEM WalkTEM 2. The findings show the seawater is correlated with significantly low resistivity values (ca. < 1 Ωm), saltwater-freshwater is correlated with medium resistivity values (ca. < 10 Ωm) and sandy beach is correlated with high resistivity values (ca. > 10 Ωm). This study indicates that both ERT and TEM methods can identify shallow saltwater intrusion (ca. 2 – 10 m depth), but TEM method can detect a deeper saltwater intrusion at 90 – 120 m depth. This study also reveals that the rising sea level can reduce the saltwater intrusion depth and contaminate the groundwater in a coastal setting.