In the weeks after March 11, 2011, what to do with the mountains of debris that had once been people's homes and possessions before the quake and tsunami, and how to do it quickly, cheaply and safely, became the top priority of the cleanup effort in Tohoku.

In response, the Environment Ministry called on local governments across the nation to assist stricken parts of the northeast by accepting portions of the debris for incineration and burial.

But two years on, the amount of debris the government says needs to be moved out of the region for disposal has been revised to just one-sixth of the original estimate. Meanwhile, continuing concerns about radioactive contamination and transport costs have led some municipalities in central and western Japan to alter their plans to help.