Tokyo Electric Power Co. said Wednesday that it found radioactive water dripping out one of the newly installed steel above-ground tanks it was using at the crippled Fukushima No. 1 nuclear plant in place of the leaky covered storage reservoirs.

Tepco told reporters that only about 1 liter of water leaked and poses no serious impact on the environment, adding the utility is investigating to determine the cause of the leak.

The tank was installed on the south side of the plant in May so Tepco could transfer part of the more then 20,000 tons of radioactive water held in the trenchlike, triple-lined reservoirs, which have coamings and covers, that were found to be leaking into the soil in April.

According to Tepco, workers found radioactive water leaking from the surface of the steel tank at a rate of one drip per several seconds at 12:15 p.m. Wednesday.

The tank is built of steel plates bolted together, and the leak came from a seam.

Tightening the bolts failed to stop the leak so Tepco removed some of the contents inside the tank so the water level was lower than the point of the leak.

Tepco spokesman Masayuki Ono said the latest incident will not cause the utility to drastically alter the way it is handling the radioactive water accumulating at the site as a result of it being injected as coolant into the plant’s three reactors that experienced core meltdowns in March 2011.

Ono noted three similar tanks suffered leaks in 2012.