BUCHANAN, N.Y. -- Gov. Andrew Cuomo is calling for an investigation after an apparent overflow at the Indian Point nuclear power plant spilled highly radioactive water into an underground monitoring well, but nuclear regulators said the public isn't at risk.

Officials at Indian Point in Buchanan reported on Friday that water contaminated by tritium leaked into the groundwater under the facility.

The contamination has remained contained to the site, said Cuomo, who ordered the state's environmental conservation and health departments to investigate.

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"Our first concern is for the health and safety of the residents close to the facility and ensuring the groundwater leak does not pose a threat," Cuomo said Saturday in a statement, according to CBS New York. "This latest failure at Indian Point is unacceptable and I have directed Department of Environmental Conservation Acting Commissioner Basil Seggos and Department of Health Commissioner Howard Zucker to fully investigate this incident and employ all available measures, including working with Nuclear Regulatory Commission, to determine the extent of the release, its likely duration, cause and potential impacts to the environment and public health."

The leak occurred after a drain overflowed during a maintenance exercise while workers were transferring water, which has high levels of radioactive contamination, said Neil Sheehan, a spokesman for the Nuclear Regulatory Commission.

Normally, a sump pump would take the water and filter it into another treatment system, but the pump apparently was out of service, Sheehan said. After the drain overflowed, the water seeped out of the building into the groundwater.

It was unclear how much water spilled, but samples showed the water had a radioactivity level of more than 8 million picocuries per liter, a 65,000 percent increase from the average at the plant, Cuomo said. The levels are the highest regulators have seen at Indian Point, and the normal number is about 12,300 picocuries per liter, Cuomo said.

Contaminated groundwater would likely slowly make its way to the Hudson River, Sheehan said, but research has shown that water usually ends up in the middle of the river and is so diluted that the levels of radioactivity are nearly undetectable.

"We don't believe there's any concern for members of the public," Sheehan said. "First of all, this water's not going anywhere immediately -- and, again, because of the dilution factor, you wouldn't even be able to detect it were you to take a direct sample."

A spokesman for Entergy Corp., the New Orleans-based company that operates Indian Point, said the overflow was "likely the cause of the elevated tritium levels."

"While this instance of tritium in the ground is really not in accordance with our standards, there really is no health or public safety consequence," spokesman Jerry Nappi said.

In a statement, Entergy also said, "While the effect of these elevated values is less than one-tenth of one percent of federal reporting guidelines, Entergy made voluntary notification to the NRC, state agencies and key stakeholders."

There has been a history of groundwater contamination at Indian Point. A federal oversight agency issued a report after about 100,000 gallons of tritium-tainted water entered the groundwater supply in 2009, and elevated levels of tritium also were found in two monitoring wells at the plant in 2014. Officials said then the contamination likely stemmed from an earlier maintenance shutdown.