[Purpose] Waste disposal, particularly, radioactive waste disposal has become a grave social problem. In order to solve this problem appropriately for the purpose, "a method for disposing of waste by displacement of deep-seated bottom sediments" (JP3000193) was invented in 1999. The purpose of the present invention is to improve this technique and make use of the improved technique for solving the problem. [Problem] Faults, sand layers or gravel layers exist in deep-seated bottom sediments and form a groundwater artery. There is a risk that contaminated water resulting from the waste which has been disposed of by the displacement may pass through a stratum and/or the groundwater artery to cause groundwater contamination. [Solution] A method for disposing of waste by the displacement of deep-seated bottom sediments via the injection of a waterproof (radioprotective) clay, characterized by previously injecting a waterproof (radioprotective) clay into deep-seated bottom sediments before the injection of waste th
