Tokyo Electric Power Co. said Thursday it found a new leak late Wednesday at the Fukushima Dai-Ichi nuclear power plant, near tanks holding contaminated water.

The utility company, known as Tepco, is collecting soil that absorbed an estimated 26,400 gallons of water spilled from a concrete barrier. Tepco doesn’t believe any water reached the ocean, company executives said at a briefing in Tokyo.

“Such a water leak was found despite a variety of measures taken by the company,” Masayuki Ono, an official at the power plant, said. “We are sorry to have caused concern.”

Tepco has been managing the plant’s cleanup of radioactive water for nearly three years after a massive earthquake and tsunami in 2011 caused cores of three reactors to melt at the plant and release substantial amounts of harmful radioactive material.

A sample collected from the leaked tank was tested for beta radiation and found to contain 230 million becquerels per liter, far above Japan’s safety limit for radioactive materials in drinking water at 10 becquerels per liter.

The contaminated water overflowed from a 10-meter-long tank after two valves that were supposed to remain shut were opened, Ono said. The leakage ended just 0.4 miles from the ocean.