Two construction joint ventures hired to wash radioactive substances off buildings in two Fukushima Prefecture communities in December allowed the tainted water to run off into street gutters, an Environment Ministry official said Tuesday.

Although not illegal, the conduct of Taisei Corp., Maeda Corp. and other firms involved in the venture illustrates the types of corners that contractors cut in doing cleanup work.

A special law passed for the nuclear disaster makes dumping of contaminated substances into the environment punishable by up to five years in prison or a fine of up to ¥10 million. However, contractors are only asked to collect tainted runoff, with no penalty for failing to do so.

Recent media reports that contractors were possibly illegally dumping radiation-tainted waste into rivers and elsewhere in Fukushima Prefecture prompted the Environment Ministry's Fukushima office for environmental restoration to question managers of four joint ventures Monday. They were all hired by the government to do decontamination work near the stricken Fukushima No. 1 nuclear power plant.

The ministry investigation turned up the cases of tainted runoff in the village of Iitate and the town of Naraha.

In Iitate, workers washing a post office and its premises allowed some of the contaminated water to run freely into a gutter in the street, said the ministry official, who declined to be named, citing ministry policy.

Though workers blocked the gutter at one end, contaminated water was allowed to flow away in the other direction.

In Naraha, contractors used high-pressure water hoses to decontaminate the roof and walls of a house without taking steps to collect the tainted runoff, he said.

On Monday, a ministry task force ordered the contractors to re-examine their methods for dealing with contaminated waste. The ministry plans to come up with countermeasures by the end of next week, he said.

"We must figure out why this happened, and what is really going on at decontamination sites first," the official said.

As of Monday, 50 ministry officials and hired supervisors were monitoring decontamination work in Naraha, Iitate, Tamura and Kawauchi.

But work is currently halted in some areas in the prefecture due to a lack of temporary storage sites for tainted waste, the official said.