Determination of Groundwater Seepage into a River by Radon-222 Concentration in Water

In Japan, the amount of infiltration from paddy fields is about 50 billion m3 per year, and most of the infiltration flows into rivers. It is necessary to determine groundwater seepage into rivers in order to use water resources effectively. Generally, river discharge is measured to determine groundwater effluent. The practice is, however, very troublesome and not conducted easily. Furthermore, the results tend to contain errors and cannot be used to clarify groundwater seepage behavior. To solve these problems, the authors directed their attention to radon-222 (222Rn), and measured the concentration in a river.