Utilizing 2-D Resistivity Method for Seawater Intrusion Study at Benteng Kuta Lubok, Aceh-Indonesia Dr. Muhammad Syukri Senior Lecturer at Geophysics Section, Department of Physics, Faculty of Sciences, Syiah Kuala University, Banda Aceh, Indonesia e-mail: m.syukri@unsyiah.ac.id Zul Fadhli Postgraduate Student at Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: zulcmc@gmail.com Dr. Rosli Saad Senior Lecturer at Geophysics Section, School of Physics,11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: rosli@usm.my ABSTRACT Research has been conduct using 2-D resistivity method to identify seawater intrusion. The study was conduct at Benteng Kuta Lubok, Aceh Besar, Aceh (Indonesia) which is Lamuri kingdom, built by Portuguese in 1600 AD. Nine survey lines (40 m each) of Pole-dipole array with minimum electrode spacing of 1 m and the spacing between lines is 20 m was design for the study. The 2-D resistivity inversion models show the study area consists two layers. The first layer with thickness of 5 m has interpreted as marine alluvium and the second layer with depth 0-8 m has interpreted as colluvium. The seawater intrusion with resistivity value of <10 Ohm.m was detected at line R1, R2 and R5 at depth <2 m and 15 m respectively. KEYWORDS: 2-D Resistivity, Seawater Intrusion, Benteng Kuta Lubok, Marine Alluvium. I NTRODUCTI ON Seawaters intrusion or infiltration of seawater into pores of rock will contaminate ground water. The difference between seawater and groundwater is Sodium Chloride (NaCl) ions that cause changes in the electrical properties. The value of groundwater resistivity is 10 - 100 Ohm.m, while seawater is <10 Ohm.m. Seawater intrusion occurs in all coastal aquifers, where - 165 -