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Vol. 10 (1968) No. 1 p. 11-23



The utilization of natural tritium plays the most important role in surveying large areas for the development of groundwater resources.
The flow velocity and flow distribution of the groundwater in a large water system could not be directly calculated by other methods in the past.
In the study reported here, bomb-produced tritium was used as a tracer to estimate mean groundwater velocities by the distance of seepage from the groundwater recharge zone.
At present, the concentration of natural tritium is obtained by the following: 10 1-groundwater in the deep layer intercepted from the shallow water by clay layer is concentrated into one-hundreds ml by 2-step electrolysis after distillation its tritium concentration is measured by the liquid scintillation spectrometer.
The tritium unit (T. U. ) of the groundwater in the Kanto plain showed 2 to 406 T. U.
Natural tritium content of levels is less than 5 T. U. Therefore, the 1954 front are estimated to have moved 40 km along the basin of the River Tone and 48 km along the basin of the River Kinu. The groundwater velocities were computed 9 mid and 11 mfel respectively. It was clarified that the deep groundwater in the Kanto Plain is strongly followed by the geological structure of the Kanto structural basin and flow out towards the Tokyo Bay according to the past results.

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