Ground-Water Investigation Used 131 I and Fallout Cesium as Tracer

A method for ground water investigation is described which employs I131 and fallout cesium as tracer. To demonstrate the feasibility of the method, measurements were made on ground water samples from the Mamigasakigawa Fan''. From the measurements which employed I131 as tracer, the velocity of the free ground water was 0.6 m per hour at a place located at the top part of the Fan and was 2.0 m per hour at another place which was not far from the former. It showed that there exists considerable fluctuation in velocity from place to place. The deep ground water would be considerably slower than the free ground water. It was found that the artesian ground water at the edge part of the Fan was contaminated with fallout cesium. From this fact and measurements of fallout cesium since 1957 it can be supposed that the artesian ground water soaking into ground at the top of the Fan reaches the edge part of the Fan in 3 or 4 years.