The radiation limit for soil contaminated by the Fukushima nuclear disaster in an experiment to reuse it in construction was lowered from 8,000 becquerels per kilogram to 3,000 becquerels per kilogram after strong opposition from a local mayor, it has been learned.

The experiment is to be carried out at a temporary storage site in Minamisoma, Fukushima Prefecture, where around 1,000 bags of contaminated soil will be opened, made into construction foundations, and their radiation levels measured. The experiment will be done to check, among other things, whether the radiation exposure dose remains at the yearly limit of 1 millisievert or less. The experiment will cost around 500 million yen. The results are expected to be put together next fiscal year or later.

From soon after the Great East Japan Earthquake in 2011, municipalities including Minamisoma asked the national government to separate out lower-radiation level concrete and other debris for reuse in things like groundwork for coastal forests used to defend against tsunami. At first, the Ministry of the Environment was negative about this, but in December 2011 the ministry allowed such reuse for debris with a limit of 3,000 becquerels per kilogram. According to documents released in response to a release of information request made by the Mainichi Shimbun, some 350,000 metric tons of this kind of debris have been used in Minamisoma and the towns of Namie and Naraha in projects such as groundwork for coastal forests.

Then in June last year, the Ministry of the Environment decided on a policy of reusing contaminated soil with 8,000 becquerels or less per kilogram in structures such as soil foundations for public works projects.

The same month, Minamisoma's Mayor Katsunobu Sakurai visited then vice-minister of the environment Soichiro Seki, where he questioned Seki about the 3,000 becquerel limit that had been used until being replaced by the 8,000 becquerel limit. Sakurai reportedly called for the 3,000 becquerel limit to be used in the upcoming experiment in Minamisoma.

Sakurai says, "If they don't use the 3,000 becquerel limit it is inconsistent. It doesn't make sense for a ministry that is supposed to protect the environment to relax the standards it has set."

The ministry confirmed to the Mainichi Shimbun that the experiment will only use soil up to the 3,000 becquerel limit, and said that the soil used will on average contain about 2,000 becquerels per kilogram.