Distribution of Free Groundwater Aquifers in Rumpin and Surrounding Areas, Bogor Regency, West Java

The geology of the Tangerang area, including the Rumpin area, is mostly formed by Quaternary surface deposits (Alluvium, Pematang Pantai, Alluvium Fan and Banten Tufa) and a small part (southern) is Tertiary sedimentary rock (Genteng Formation and Serpong Formation). The boundary of the groundwater basin at the surface is estimated to be located along the Cisadane river, as well as at the boundary of tertiary rock outcrops (southern) that pass and impermeable to groundwater. The problem that arises is how the relationship between surface data (outcrop) and subsurface data (based on estimation of geoelectrical data) which is validated with drilling data becomes a model of the hydrogeological system in the research area. The purpose of this study was to determine the hydrogeological conditions and distribution characteristics of the aquifer, as well as to calculate the groundwater potential in the Rumpin area and its surroundings based on outcrop data, subsurface geological data and drill log data. Based on the research results, the lower boundary of the groundwater basin can be in the form of compact rock or very thick clay and is estimated to be more than 100 meters deep. The hydrogeological system of the Rumpin area and its surroundings is the result of geoelectrical data, then validated with surface outcrop data and drill logs, can be grouped into aquifers which include the Free Groundwater Aquifer Group, has a depth range of 0– 15 and 15–45 meters with 1-2 aquifers thick ranged from 2-7 meters. The shallow/free groundwater level (0–10 m) data has a groundwater level ranging from 0 to -5 m (mts). The results of the geoelectrical analysis show that the distribution of the aquifer layer is uneven and there is an impression that the free groundwater aquifer can reach a depth of 3–20 meters (mts). The distribution of isoresistivity maps with resistivity at a depth of 3–20 meters has the potential for fresh groundwater. Keywords— Rumpin, Aquifer, Geoelectric, Groundwater.