Groundwater radiation levels at Japan’s crippled Fukushima nuclear plant have soared near a tank that leaked 300 tons of toxic water in August, struggling operator Tokyo Electric Power Co said Saturday. TEPCO said water samples collected from a well on Thursday contained 400,000 becquerels per liter of beta-ray emitting substances, the highest reading since the nuclear accident was triggered in March 2011. Samples in previous days had been showing levels of just 60 to 90 becquerels per liter. The reading for radioactive tritium also shot up to a record high of 790,000 becquerels, TEPCO said. The leaking storage tank was discovered in August and TEPCO said measures taken since then had included transferring water from the tank and removing the surrounding soil. “Other wells are not showing such a high level. We need to take additional measures for the areas around this well,” Masayuki Ono, TEPCO spokesman, told a press conference on Friday evening. TEPCO has removed most of the soil contaminated by the August spill, but might have failed to collect some radioactive materials, Ono said. Heavy rain over recent weeks could have washed contaminated materials into the well, he added, saying TEPCO would remove the toxic soil and groundwater. TEPCO has poured thousands of tons of water onto the reactors to keep them cool in an ongoing operation. Radioactive water is being stored in around 1,000 tanks but the company has admitted contaminated liquid has made its way into the sea.