Michael Risinit

mrisinit@lohud.com

Entergy monitors the groundwater under its Indian Point nuclear power plant.

The company this spring detected higher than usual levels of tritium in two wells.

Because the levels were decreasing%2C the matter was possibly thought to be a spike.

But fluctuating levels%2C the NRC now says%2C may potentially illustrate an ongoing leak.

Radioactive tritium in the groundwater beneath the Indian Point nuclear power plant could be part of an ongoing leak and not a momentary spike as first thought, federal regulators said Thursday.

Elevated levels of tritium — a low-energy radioactive form of hydrogen — were found in two monitoring wells in late March near Indian Point Unit 2. Samples in April and May showed decreasing levels, suggesting the contamination might have been related to the movement of used nuclear fuel during a maintenance shutdown.

But samples collected this month showed the concentration rising again and then decreasing. There is no health threat to either the public or Indian Point workers, the Nuclear Regulatory Commission said.

"Is it accurate to describe these increases as 'spikes' if there are several significant variations in tritium levels in monitoring wells?" NRC spokesman Neil Sheehan said in an e-mail. "(Plant owner) Entergy acknowledges that it could be indicative of an ongoing source of leakage rather than one attributable to the most recent Indian Point 2 refueling and maintenance outage."

A byproduct of nuclear power, the Environmental Protection Agency characterizes tritium as "one of the least dangerous" radioactive particles because it emits very low radiation and, if ingested, leaves the body relatively quickly.

Entergy is testing drains, pipes and tanks for damage and making sure there were no unidentified spills during the March shutdown, company spokesman Jerry Nappi said. Such fluctuations aren't uncommon and could be due to the bedrock's formation beneath the plant and how rainwater filters through the rock, he said.

"While the overall trend in this instance is still a downward one, we have not ruled any source out and continue to aggressively investigate to find the cause of the elevated tritium," Nappi said in an email, adding the company's inquiry was still pointing toward a one-time event.

The monitoring wells were installed after sampling in 2005 found tritium in the groundwater, a leak traced to a failed weld in a canal leading to Unit 2's spent fuel pool.

The current problem might not have been detected without those wells, said Dave Lochbaum, director of the Nuclear Safety Project at the Union of Concerned Scientists. But until the source is found, he said, the leak's seriousness can't be fully assessed.

"I think the good news is at least the flag has been raised," Lochbaum said.

Indian Point isn't the only U.S. nuclear plant with tritium-groundwater issues. A list maintained by the NRC shows 44 other plants with tritium leaks or spills, as far back as 1979.