GEOLOGI DAN STUDI GEOKIMIA AIR UNTUK PENENTUAN BATAS SISTEM PANAS BUMI DAERAH PATENGAN, KABUPATEN BANDUNG, PROVINSI JAWA BARAT

• Main Author: Rachmawati, Cindytami
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/34121
• Institution: Institut Teknologi Bandung

Research area is located in Patengan Village, Rancabali District, Bandung Regency, West Java Province, adjacent to Patuha Geothermal Field. Geographically, research area is located in the UTM coordinate 9207000 – 9211000 mN and 763000 – 767000 mE 48 Southern Hemisphere Zone, with an area of 16 km2. The objective of this research is to determine the northern boundary of geothermal system from geological study and water geochemistry data of hot and cold springs in the research area, which is obtained in the early stage of geothermal exploration. Patuha Geothermal System is a volcanic hydrothermal system. Boundary of this system is characterized by a lateral outflow, characterized by the occurence of acidic to neutral bicarbonate-chloride or chloride thermal springs manifestation. The absence of this thermal spring will be a difficulty in determining the geothermal system boundary. In other side, its occurrence is predicted to contaminate shallow groundwater. Contaminated cold spring will be enriched with cations and anions, as well as the anomaly of pH and temperature from its common trend. The boundary of a geothermal system is expected to be found by examining cold water springs that are not contaminated by the steam heated thermal water. This research is conducted by classifying cold springs and thermal spring associated with geological analysis, including geomorphology, volcanostratigraphy, geological structure, hydrogeology, and geological synthesis from field data and literature. It was done to determine their relation with the occurrence of cold springs and thermal springs in the research area and its association with Patuha geothermal system. Geochemical analysis, taken from one hot spring, six warm springs, and nine cold springs, is done to determine which cold water springs has been contaminated with thermal fluid. This water geochemistry analysis was completed by using temperature, pH, TDS, anions, cations, and isotopes. Laboratory data that consists of anions, cations, and isotopes, are further evaluated by Piper Diagram, Schoeller Diagram, and isotope graph. Boundary of geothermal system is determined and validated using resistivity data from DC-current and MT, also subsurface temperature gradient from well data. Based on geological study, cold springs in the research area can be classified into springs that are located in Khuluk Patuha and Khuluk Masigit. Springs in Khuluk Patuha consist of thermal spring from Patuha Geothermal System, contaminated cold springs, and one uncontaminated cold spring, which is Legok Kondang spring (ADLK). Cold springs from Khuluk Masigit, which is located 1 to 1,5 km from the farthest thermal spring, are uncontaminated cold springs. Thermally contaminated cold springs show increasing value of water temperature and TDS, decreasing of pH, and also changes in ions and isotope characteristics due to thermal fluids from Patuha geothermal system. The geothermal system boundary location is estimated to be in between uncontaminated cold springs and the farthest thermal springs from upflow zone or the closest contaminated cold springs to outflow zone. This boundary is validated by using low resistivity value (?20 ohm.m) and temperature gradient data that shows similarity in the boundary location, and it can be concluded that the method used is valid.