The Asahi Shimbun sent a team of reporters to observe the cleanup for several days in December. They reported seeing water contaminated with radioactive material being allowed to drain instead of being disposed of properly.
Workers directly involved in the cleanup told the newspaper they were acting as instructed by supervisors. They said they were ordered to cut corners and ignore the rules on disposal of nuclear material.
"If the reports are true, it would be extremely regrettable," Fukushima Gov. Yuhei Sato told a news conference Friday. "I hope everyone involved will clearly understand how important decontamination is to the people of Fukushima."
The plant on the northeast coast of the island of Honshu was damaged by a March 2011 earthquake and the tsunami that followed. Several of its reactors went into meltdown when the cooling system failed.
The government has allocated 650 billion yen ($7.4 billion) for environmental cleanup. The goal is to remove contaminated materials within 65 feet of buildings, roads and agricultural land.