| Abstract | Coastal aquifers are precious freshwater storage, which are susceptible to seawater intrusion that refer to movement of seawater in subsurface . The deleterious effect of seawater intrusion is reduction of available freshwater reserve. Additionally, contamination o f freshwater in coastal aquifer normally occur, thereby one percent of seawater result in freshwater unfit for drinking . To design method of protecting seawater intrusion, appropriate measurement and monitoring methods are very needed. Geophysical methods especially electric and induced polarization imaging have widely been used for seawater intrusion monitoring and mapping because of differe nce in electrical properties between freshwater and seawater. This research was studied in Phuket , where is the big gest island of Thailand . Phuket is the most popular place, where tourist usually visit. In additional, Phuket is also industrial and agricultural city, which normally use high amount of water. Groundwater has become importance since water demand in Phuket would increase to 101,000,000 m 3 in 20 37, w hereas, water reserve is only 46,000,000 m 3 . While water demand is increasing, improper discharging of groundwater from coastal aquifers is conducted, which leads to seawater intrusion problem in Phuket. In this study electric and induced polarization imaging w ere conduct ed to investigate seawater intrusion both by laboratory experiment and field survey, where were investigated at a coastal site, Phuket, Thailand . In laboratory experiment was successfully delineated salt water - freshwater interface, which 97.24 Ω m of resistivity refer to freshwater, whereas, contaminated freshwater with Cl - concentration 1,500 mg/L to 3,000 mg/L present 15 Ω m to 33 Ω m of resistivity and chargeability 0.72 mV/V to 5.76 mV/V. Field investigation in Chalong display seawater intrusion at 5 m. to 26 m. below ground surface, extension of seawater intrusion is 175 m. into coastal aquifer. Contaminated freshwater shows 3 Ω m t o 22 Ω m of resistivity, wh ile 74 Ω m to 119 Ω m of resistivity represent freshwater aquifer. In addition, chargeability result of less than 20 mV/V represent sand aquifer, while more than 20 mV/V show clay layer. |