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In 2011, a number of radioactive substances were released as a result of the accident at the Fukushima Daiichi Nuclear Power Plant, Japan, which was caused by the Tohoku region Pacific coast earthquake. The radioactive substances that were released fell onto the surrounding ground and into the sea. Therefore, decontamination measures for the ground have been conducted at the field site. However, the safety and validity of modern decontamination measures were uncertain because no analytical verification had been performed that considered the various properties of the ground. Moreover, selection of the site where storage containers for radioactive materials could be constructed was a critical issue that required a solution. Therefore, it was necessary to evaluate quantitatively the behaviour of radioactive substances in soils to prepare new decontamination methods for the ground. In this study, the advection–dispersion equation was added to the radioactive half-life to evaluate the transportation of radioactive substances. As the results of this study show, this analytical method could recreate the on-site situation through comparison of the analysis results with the measurement results. Furthermore, modern decontamination techniques were effective for the section under analysis for ground with a silt or a clay layer. However, these techniques were not effective for sand layers.