(AP) - A small leak in one of the oldest radioactive waste tanks at the Savannah River Site has been found, but an official said Wednesday that there is no immediate health or environmental concerns.

Westinghouse Savannah River spokesman Dean Campbell said the leak on the nearly 50-year-old tank dried up and plugged itself. It was found Monday, but it’s unclear exactly when the liquid escaped.

The underground tank is one of 51 at SRS, the former nuclear weapons complex near Aiken. It holds about 191,000 gallons of sludge from Cold War bomb making and was scheduled to be emptied next year.

The first step in that removal process, which was adding water to the tank, began in November.

The tank had three previous leaks but none were active. The new leak is similar in size, location and makeup as the others.

The process of removing the waste from the tanks and closing them has come under scrutiny from environmentalists concerned about the Department of Energy’s plan to leave about one percent of the sludge behind.

The process has been challenged in courts, but Congress agreed last year to allow the sludge to be left in tanks at SRS and a federal facility in Idaho instead of being shipped to a central repository.