Tokyo Electric Power Company (Tepco) said that radioactive water has again overflowed from a drainage channel, spilling into the sea following heavy rain.
Tepco said rainwater samples taken from the channel two hours after the spill contained 830 becquerels per litre of radioactive caesium which exceeds the government standard for water allowed to be released into the sea. The water also had 1100 becquerels of beta-ray emitting radioactive substances.
Tepco suspects that the rain has washed away mud and soil that also contains radioactive materials and that the amount of rainwater has exceeded the pump's capacity.
The company said it cannot stop the spill anytime soon and has been monitoring the density of the radioactive substances.
Radioactive rainwater spilled into the sea from the same channel in February. The company built a barrier at channel's downstream to pump up water before it leaks into the sea.