STUDY ON REMOVAL OF CONTAMINATED SOIL ON FOREST SLOPE FOCUSING ON DIFFERENCE IN DENSITY OF SUBSURFACE GROUND

A large amount of radioactive cesium was released from the Fukushima Daiichi nuclear power station. Decontamination in living area has been almost completed for seven years. However, decontamination has not progressed much in forests where people do not enter. The decontamination of soil on forest slope cannot be done using heavy machinery unlike that on flatland. The effective decontamination method for the forest slope is desired. Therefore, in this study, the collecting method of slope surface soil through flushing water and the soil separation method focusing on the difference in the density of minerals were proposed and examined. In the proposed method, it is expected to reduce the volume of contaminated soil through the separation of the contaminated part and non-contaminated one. In this study, the laboratory test is conducted to evaluate the usefulness of the proposed method. In the test, a device of simulating the slope and a device to flush the soil by flowing water is produced. When an actual soil is utilized for the experiment, it is difficult to ensure the experimental repeatability due to soil variability. Therefore, simulated soil consists of Toyoura standard sand and vermiculite. To simulate soil contaminated with cesium, cesium standard solution is added into the simulated soil. The soil is set on the slope, and the test is conducted to flush and collect the soil by running water from upside to downside. As a result, it is clarified that only soil containing cesium can be removed by separating the soil after flushing.