TEPCO, operator of the plant, has been checking below-ground water on the advice of the Nuclear Safety Commission of Japan.

The company says radioactive water was detected beneath the ground near the turbine buildings of five of the 6 reactors. The remaining reactor, No. 4, could not be checked because it was blocked by debris.

TEPCO says radioactive substances dispersed into the atmosphere may have seeped into the soil through rain and sprayed water.