First Tritium-Helium Dating Results of Groundwater in Eastern Taiwan and Further Implications

Thursday, 18 December 2014
Ai-ti Chen1, Tsanyao F Yang1, Tsung-Kwei Liu1, Yuji Sano2, Naoto Takahata2, Kuan-Yu Chen3 and Yunshuen Wang4, (1)National Taiwan University, Taipei, Taiwan, (2)Atmosphere and Ocean Research Institute University of Tokyo, Kashiwa, Japan, (3)Industrial Technology Research Institute, Taipei, Taiwan, (4)Central Geological Survey, Taipei, Taiwan
We applied Tritium-Helium (T-He) dating method, for the first time, to obtain the ages of groundwater from eastern part of Taiwan as a case study. The groundwater wells are located on the recharge area of LiWu and Hualien river basins. 10 groundwater samples have been collected from different monitoring wells, which are artificial and all around 21-97 meters deep, and the altitude of them are less than 125-953 meters. Samples sent to University of Tokyo for further T-He dating analysis. We could obtain total helium-3 concentrations in groundwater samples, although they might contain different signatures other than radiogenic source from tritium decay. In order to obtain the radiogenic helium-3 concentration, we needed to eliminate helium-3 concentrations of air-saturated water and terrigenic source in spite of air contamination. In this study, we can successfully separate the radiogenic source of helium-3 from terrigenic (crustal and mantle) source, as well as air contamination for the studied samples. After helium-3 corrections, we can obtain the age results, which are not older than 40 years, with terrigenic signature of 0.13 Ra. The result suggests that the T-He dating technique could be a good method for determining the age of young groundwater in Taiwan.