Radioactive material has leaked into the groundwater below a nuclear power plant north of New York City, prompting a state investigation on Saturday and condemnation from Governor Andrew Cuomo.

Cuomo, a Democrat, ordered an investigation into “alarming levels of radioactivity” found at three monitoring wells at the Indian Point energy center in Buchanan, New York, about 40 miles north of Manhattan.

“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 wrote in a letter that directed health and environmental officials to investigate.

In one location radioactivity levels rose nearly 65,000%, from 12,300 picocuries per liter to over 8,000,000 picocuries per liter.

The Environmental Protection Agency’s maximum contaminant level for tritium in drinking water is 20,000 picocuries per liter, though Entergy, the company that owns the plant, emphasized that only groundwater, and not drinking water, were contaminated.

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The Governor’s office said the contamination had not moved offsite. Cuomo has encouraged Entergy to shut down Indian Point, but to keep its other plants further upstate open.

He directed health and environmental officials “to determine the extent of the release, its likely duration, cause and potential impacts to the environment and public health.”

“While elevated tritium in the ground onsite is not in accordance with our standards, there is no health or safety consequence to the public”, Entergy said in a statement released late Saturday. “Releases are more than a thousand times below federal permissible limits. The tritium did not affect any source of drinking water onsite or offsite.”

The plant supplies roughly 30% of the electricity consumed by New York City. Indian Point had three emergency shutdowns in December, prompting the governor’s office to launch, and then expand, an inquiry into operations and safety standards at the facility.

“This latest failure at Indian Point is unacceptable”, Cuomo said in a statement. “This is not the first such release of radioactive water at Indian Point … this failure continues to demonstrate that Indian Point cannot continue to operate in a manner that is protective of public health and the environment.”

Both reactors operating without licences

An astonishing aspect of the matter is that Indian Point units 1 and 2 are both operating without licences from the Nuclear Regulatory Commission.

Unit 2’s licence expired in September 2013, and Unit 3’s licence expired on 12th December 2015. However in both cases the NRC his given permission for the plants to keep on running while Entergy’s renewal applications for 20-year extensions were under way.

Since their licence expiries both reactors have been involved in unauthorized radiation releases, of tritium in particular, and numerous unscheduled closures.

Tritium is a relatively short-lived radioactive hydrogen isotope that cannot penetrate the skin, however it can be consumed in food and water and be taken up in tissues. It is considered a health risk for illnesses, including cancer.

There have been many tritium leaks at the plant in recent years, though Saturday’s leak appears to be the most serious so far. Public Service Commission chair Audrey Zibelman faces a deadline for the results of the pre-existing investigation by President’s Day, 15th February.

The Governor’s office did not immediately respond to request for further comment on the beginning of the leak and its duration. But as Cuomo told reporters last October:

“It is a nuclear power plant that is in the most dense community on the planet. They’re supposed to have an evacuation plan for the entire surrounding area. The surrounding area is New York City. You cannot evacuate New York City. What’s the plan? Jump in the river and swim to New Jersey?”

Sam Thielman covers the business of technology for Guardian US.

Alan Yuhas is a reporter for the Guardian US. You can follow him on Twitter @alanyuhas

This article was originally published by Guardian Environment and is republished here with thanks via the Guardian Environment Network. Some additional reporting by The Ecologist.