4Clark I, Fritz P. 1998. Environmental Isotopes in Hydrogeology 178～175. LEWIS.
5Guan Bingjun. 1996. Tritium value Evaluating of precipitation in China. Hydrogeology and Engineering Geology, ( 2 ): 38 ～ 42 (in Chinese with English abstract).
6Wang Hengchun. 1990. Foundment of Environmental Isotope Hydrogeology. Beijing: Geological Press House (in Chinese).
7Lian Yanqing, Zhou Hong, Wang Hengchun. 1988. Envirnmental isotope studies of karst water system of the Guozhuang springs,Shanxi, China. Carsologica Sinica, (4): 318～ 323 (in Chinese with English abstract).
8Ma Zhiyuan, Gao Wenyi. 1997a. Environmental study for recharging of covered karst water in Dacha valley, Pingliang City.Northwestern Geology, 18 (1) : 29 ～ 33 (in Chinese with English abstract).
9Ma Zhiyuan, Gao Wenyi, Guo Jianqing. 1997b. Evaluation of residence time and aquifer parameters of covered kaster water by national tritium. Coal Geology and Exploration, (4): 34～38 (in Chinese with English abstract).
