Nuclear watchdog and environmental groups have criticized Southern California Edison for how long it took to notify the media and public of an ammonia leak at a nuclear power plant that led to an emergency alert.

The public was not alerted until more than an hour after the leak began Tuesday. A phone line reserved for media calls was for a time not working properly and officials with Edison, which operates the San Onofre Nuclear Generating Station, did not return multiple emails and calls from The Associated Press until more than two hours after the leak started.

"That's losing precious time if it had been a more serious event," said Gary Headrick, with San Clemente Green, a group that has called for the station to be shut down until various issues are dealt with. "We're basically at the mercy of them telling us if there's a problem or not...I think it's important for the public to be aware of when it's safe too."

Gil Alexander, a spokesman for Edison, called the concerns an exaggeration adding that because this is a nuclear facility "everything is taken extremely seriously."

"In this case there was no public notification that would normally take place at this low level of an emergency," he said. "If this had been any other facility other than a nuclear plant the fact is we wouldn't be talking about it this morning."

Officials are continuing to investigate the cause of the leak which was discovered before 3 p.m. PDT in a storage tank in the water purification system of San Onofre Nuclear Generating Station's Unit 3. As a precaution some workers were evacuated before it was contained two hours later.

The emergency alert was required because fumes could prevent access to certain areas of the plant, said Todd Adler, the plant's engineering manager to reporters at a media information center in Irvine, Calif. The alert, the second lowest of four federal classifications for emergencies at commercial nuclear power plants, was canceled at 6:07 p.m. and evacuated workers were allowed to return.

The leak was in the non-nuclear section of the plant, which is operated by Southern California Edison. No radioactive material was released, no injuries were reported and there was no danger to the public, the company said.

Approximately 25 gallons of leaked ammonia were collected in a basin underneath the tank that was designed for that purpose.

Exposure to high levels of ammonia can cause irritation, serious burns, lung damage and even death. It is used at the plant to treat water that is turned into steam, which runs the turbines that produce electricity. The treated water also is used to remove heat from the reactor's cooling system.

Officials are continuing to investigate the cause of the leak that triggered the alert.

The plant is located about 45 miles north of San Diego, just south of San Clemente, and is jointly owned by Edison, San Diego Gas and Electric and the city of Riverside.

U.S. Rep. Ken Calvert, whose district includes the station, said San Onofre followed federal nuclear regulatory commission requirements but called it an opportunity to learn and improve the public notification process at nuclear facilities across the country.

"The public should always be notified as soon as possible in the event of a leak or other emergency at a nuclear facility," he said.

Bernadette Del Chiaro, director of clean energy programs at Environment California, said she remains concerned by the time it took officials to get the word out.

"No matter how small an incident it's a haunting reminder of the dangers of a nuclear power plant," she said. "Ammonia today, the next incident could be radioactive and instead of evacuating employees we may be evacuating Los Angeles."