Application of Radon Isotopes to Determine Permeable Zones in Rajabasa

Applied Mechanics and Materials Vol 771 (2015) pp 165-169 © (2015) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.771.165

Application of Radon Isotopes to Determine Permeable Zones in
Rajabasa Geothermal Field, Indonesia

Nandi Haerudin1,2,a*, Wahyudi1,b, Dikdik Risdianto3,c and Wiwit Suryanto1,d

1Department of Physics, Faculty of Mathematics and Natural Sciences, Gadjah Mada University,
Sekip Utara No. 1,Yogyakarta 55281, Indonesia
2Department of Geophysics Engineering, Faculty of Engineering, Lampung University,
Jl. Sumantri Brojonegoro No. 1, Bandar Lampung 35145, Indonesia
3Center of Geological Resource, Geology Agency of Indonesia, Jl Soekarno Hatta no 444,
Bandung 40254, Indonesia
anandi_haerudin@ugm.ac.id, bpwahyudi2002@yahoo.com, cdikrisdi@yahoo.com, dws@ugm.ac.id

This study aims to determine permeable zones (i.e. fault or fracture zones) in the Rajabasa geothermal field using radon isotopes. Radon concentration of soil gas was measured by Scintrex Radon detector RDA 200 consisting of 123 measurement station. The measurement site spacing was between 200 m and 350 m. The radon concentration was classified based on a statistical approach, i.e. low, high and very high. Very high value of radon concentration, called radon anomaly, associated with permeable zones. From the radon anomaly contour map, a 2D Radon migration from the source to the surface was modelled by means of numerical simulation. Finally, the radon contour map was overlaid with the surface geological map and the resistivity contour map in the area of study. It suggests that the radon anomaly correlates with the location of permeable zone in the centre part of the study area i.e. mud pool manifestation at the Kunjir and the Cugung (Bulakan) fumarole. Based on numerical simulation, the width of the fault is 2,800 m; velocity of fluid is 0.08 m/s and the Radon concentration is 860,000 Beq/m3. The resistivity contour map results in low resistivity of 0 to 100 Ωm indicating the conductive zone coincide with permeable zones based on radon measurements. Furthermore, the peak of the profile curve of Radon concentration could be an indication of fault systems in this area.

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