HYDROGEOLOGY AND SUBSURFACE IDENTIFICATION USING GEOELECTRIC AND DRILLING METHODS IN THE CIRANJANG AREA AND SURROUNDINGS

• Main Author: Farandy, Alvito
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/78260
• Institution: Institut Teknologi Bandung

The research area is located in the Ciranjang region and its vicinity, Ciranjang District, Cianjur Regency, West Java. Geographically, the research area is situated at coordinates UTM 923800 - 924600 mN and 747000 - 752000 mE. The research area covers an area of 40 km². The area faces groundwater quantity issues in the Bantargebang Village. The research methodology includes geological mapping aimed at understanding the geological and hydrogeological characteristics of the research area, groundwater quality for drinking water, and subsurface layer identification using geoelectric and drilling methods. The geomorphology of the research area is divided into three geomorphological units: the Piroclastic Stream Ridge Unit of Bojongpicung, the Ciranjang Lahar Stream Plain Unit, and the Ciranjang Alluvial Plain Unit. The stratigraphy of the research area is divided into four unofficial rock units, ranging from Pliocene to Holocene in age. These rock units were deposited in terrestrial environments and are, in order from older to younger, Volcanic Breccia Unit, Breccia Unit, the Lahar BrecciaTuffaceous Sandstone Unit, and the Alluvial Deposit Unit. The geological structure in the research area is the Right Slip Normal Fault. These geological structures were formed by tectonic phases trending northeast-southwest. Aquiclude and aquifers in the research area are found within Lahar Breccia Aquifer Unit, Volcanic Breccia Aquiclude Unit, and Breccia Aquiclude Unit. The types of aquifers in the research area are unconfined and confined aquifers, with the general groundwater flow direction being from south to north. Confined aquifer units in the research area include the Tuffaceous Sandstone Aquifer Unit and the Lahar Breccia Aquiclude Unit. This research aims to examine the groundwater facies in the research area, which falls under the Calcium Bicarbonate (Ca(HCO3)2) group, and analyze the chemical processes influencing it, particularly the impact of rainwater/surface water and silicate mineral weathering. Water quality observations based on the Ministry of Health Regulation No. 492/MENKES/PER/IV/2010 revealed that two points in the northern part of the research area did not meet the pH requirements, while one point did not meet the TDS requirements. Based on field geological data, geoelectric surveys, and drilling, wet soil (low resistivity: 5-10 ?) indicates good potential for water infiltration, dry soil (high resistivity: 56-100 ?) suggests possible impermeability, breccia as an aquifer (low resistivity: 18-30 ?) at approximately 4.8 - 15m depth, breccia as an aquiclude (high resistivity: 50-100 ?) at approximately 20 - 40m depth, tuffaceous sandstone as an aquifer (low resistivity: 8-12 ?) at approximately 40 - 100m depth, and breccia as an aquiclude (medium resistivity: 32-35 ?) at approximately 100-120m depth.