Placing of ice blocks in underground trenches, which will freeze highly toxic water pooled, is a necessary step for the construction of a 1.5-km ice wall to keep groundwater out, The Japan Times reported.

Tepco is working to freeze 1.5km of soil around the basements of the four reactor buildings aimed to keep groundwater from becoming contaminated and spilling into the ocean.

Refrigeration rods were initially inserted by the company in April into the trenches in order to freeze the water but abandoned its efforts after some 11,000t of highly toxic water flowed into the trenches through the No. 2 and No. 3 reactor buildings.

The company will consider placing dry ice blocks in the trenches to help freeze the water, a Tepco official said.