Présentations Colloques

Oral Presentation
Session 8.04: Isotopic and residence time tracers
Dwi Putra Rahmad
Using radioactive and stable isotope (tritium, oxygen-18, and deuterium) in determining groudwater age and recharge area of spring complex area in west java, indonesia
A spring complex area in Bandung and Garut Regency, West Java, roles as a major water source for inhabitant. Based on field observation, one spring point can provide clean water for three villages by using pipe to distribute the water. The groundwater age and recharge area analyses were performed in the spring complex, as important to manage the groundwater as vulnerable resource. **The study was carried out by conducting geological mapping, groundwater sampling of 45 spring points, and isotope analyses.The radioactive isotope (tritium) analysis was performed to determine the age of groundwater of the research area, and stable isotope (deuterium dan oxygen-18) analysis for determining the processes occuring in groundwater and estimation of recharge area. **The geology of research area, volcanostratigraphically, from youngest to the oldest unit, i.e. Khuluk Pra-Pulus comprises of Gumuk Mt. Pulus, Mt. Pasir Jugul, dan Mt. Putri+ Khuluk Pra-Mandalawangi involves Gumuk Mt. Mandalawangi, Mt. Buleud, dan Mt. Pangrajin. Generally, the lithologies of those units are pyroclastic tuff, pyroclastic breccia, igneous rock (andesite lava).**The 45 spring points are classified as depression springs due to the absence of geological structure and contact of lithology. Based on deuterium and oxygen-18 analyses, recharge area is located in Mt. Guntur-Mt. Kamojang complex at an elevation of 1500-2240 masl, about eight kilometres south of the spring complex area. The elevation is confirmed by the slope direction heading to the research area.The analyses also indicate that evaporation process takes place in the study area, as the evaporation held due to shallow aquifer or the water was being evaporated when discharged.**Refer to tritium analysis, the groundwater is classified as modern groundwater (<5 to 10 years) which confirmed by calcium bicarbonate water. By using Darcy equation for water velocity calculation using hydraulic conductivity and head gradient, it supports that the hydraulic conductivity of the aquifer about 1.04 x 10-3 m sec which could be gravel exists as weathered rock or unconsolidated material.**
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