The state is launching a new investigation into radioactive material that leaked from the Oyster Creek Generating Station twice last year.

The state Department of Environmental Protection invoked the Spill Act on Friday to take over the cleanup from the plant's owner, Exelon Corp. The move gives the state broad discretion over the cleanup.

The agency said 180,000 gallons of tritium-tainted water gushed from two leaks at the plant on April 9, 2009.

Tritium, a low-level nuclear material, was found in the groundwater of Ocean County in the Cohansey aquifer at 50 times higher concentrations than DEP safety standards for drinking water.

DEP Commissioner Bob Martin on Friday said in a statement there was no imminent public health threat. The tainted water is believed to be 2 miles from the nearest residential wells, he said.

"The fact that this is a major source of drinking water for much of South Jersey is very worrisome," DEP spokesman Lawrence Ragonese said.

Exelon is cooperating in the investigation, he said. Under the Spill Act, the company faces the prospect of triple the state fines if it does not cooperate.

Tritium has been detected in leaks at 33 of the nation's 104 nuclear power plants, including a spill last month at Salem 2 in Lower Alloways Creek Township. The state is also investigating that radioactive spill.

Exelon Corp. reported leaks at Oyster Creek in Lacey Township in April and August of last year.

Exelon spokesman David Benson said Friday disputed the DEP's suggestion that that company has not taken appropriate action to address the spill. Invoking the Spill Act was unnecessary, he said.

"We don't believe such action by the state is warranted," he said. "Exelon has taken a series of significant actions without any kind of compulsion. "There were no detectable levels of tritium off-site. The plume is about 200 by 100 feet."

The company has spent about $6 million and 10,000 work hours in environmental monitoring and pipe repairs since last year with plans to spend about $7 million more, he said.

"I don't want to minimize this in any way. In our sampling of the wells, we're seeing a steady reduction in tritium levels," he said.

The DEP said polluting the aquifer is a violation of the law. They ordered the company to install deeper monitoring wells into the aquifer to track the pollution.

The plume is migrating about three feet per day, according to the state. At that rate it would take about 15 years for the contaminated water to reach the wells. Tritium has a relatively short half-life of 12.3 years, further reducing the potential risk to human health.

The radioactive water tested at 1 million picocuries. The federal safe-drinking-water standard is 20,000 picocuries.

Cleaning up tritium leaks is difficult. PSEG is still cleaning up a 2002 spill that measured at 15 million picocuries, the highest radiation level ever recorded in any tritium spill nationwide.