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Lahor Dam is located in Karangkates Village, Sumber Pucung District, Malang Regency serves as an alternative connecting road between Malang regency and Blitar regency. Lahor Dam also functions as an area irrigation system and hydroelectric power plant. Of the 18 piezometer units in the impermeable core of the Lahor dam and there is only one active piezometer unit. This caused the water table surveillance in the impermeable layer of the Lahor dam to be disrupted. The purpose of this study was to determine the location of the water table using the georadar method in the impermeable core of the Lahor dam so that it can determine the type of material contained in it as well as the value of pore pressure from upstream to downstream of the dam. The georadar method is one method in geophysics that uses the principle of electromagnetic waves propagation. This research was carried out by scanning 7 tracks at the top of the dam from the south end to the north end and vice versa. The results of the data obtained are interpreted using Geoscan32 software to determine the location of the water table used to determine the type of material based on the calculation of the propagation speed of electromagnetic waves. The water pore pressure value is obtained by calculating the hydrostatic pressure where the water table is located on the piezometer location. Based on the results of analysis and interpretation of the data, it was found that the type of material in the impermeable of the Lahor dam is clay soil. The condition of the impermeable core of the Lahor dam is monitored safely, which can be seen from the decrease in the pore pressure value of the water from upstream to downstream of the dam.