A government task force on the nuclear emergency will allow sludge containing 8,000 becquerels or less per kg of radioactive cesium to be buried in waste disposal sites, providing there are no future residential developments at the locations.
It also said Thursday the safety of sludge containing between 8,000 and 100,000 becquerels per kg of cesium must be evaluated case by case before it is buried.
Sludge measuring more than 100,000 becquerels per kg should be kept sealed, and a final disposal method remains undecided.
The announcement came as radioactive materials have been detected in water and wastewater treatment plants in many regions, including Tokyo, since the Fukushima No. 1 nuclear power plant was crippled by the March 11 disaster.
Goshi Hosono, a special adviser on the nuclear crisis to Prime Minister Naoto Kan, said at a news conference that the central government is considering bearing the costs of disposal.
The task force said the decision concerns 13 prefectures, including Fukushima, Tokyo and Shizuoka.