Federal investigators are searching for the cause of a spike in radioactive material in the groundwater beneath the Indian Point Power Plant.

The radioactive isotope tritium was first confirmed in groundwater under the power plant a decade ago.

Since then, monitoring wells have shown a steady decline in the levels of contamination until April, when samples from two wells near Indian Point Unit Two saw a sudden spike.

The spike was detected after the reactor for Unit Two was shut down for refueling.

Nuclear Regulatory Commission officials tell News 12 that the prime suspect is a canal that is flooded to move used fuel from the reactor to a water-filled pool, where it cools off. A previous leak was blamed on a faulty weld in the metal lining of that canal.

Even though the levels of tritium under the plant went up earlier this year, both the NRC and Entergy contend there's no immediate threat to the public. They say that levels have dropped significantly since the spike was found, but the NRC wants to make sure the problem is quickly fixed.

Critics say that the fact there may be a leak in an area where there was previously a leak shows that Indian Point is aging and systems are failing. They also add that if the material is getting into the Hudson River, it may then become too diluted to detect.

The Nuclear Regulatory Commission is currently considering Entergy's application for a 20-year renewal of its licenses for both Indian Point Units Two and Three.