(Reuters) - A slightly elevated level of tritium was found in one monitoring well on the site near Exelon's Three Mile Island nuclear generating station in Pennsylvania, but the amount found posed no health or safety risks, the company said on Wednesday.

The well is located in an area where groundwater is re-circulated back into the plant and used for non-potable purposes throughout the facility, the company said in a statement.

Tritium is a mildly radioactive isotope of hydrogen that is a byproduct of nuclear power production and also occurs naturally in very small amounts in ground water.

The slightly elevated level was identified in a monitoring well sample and confirmed by an independent laboratory, Exelon said.

"Subsequent samples show declining concentrations," it said.

A team of technical and environmental experts is working to track down the source, Exelon said.

No unusual levels of tritium have been found in the other wells or stations, it added.

(Reporting by NR Sethuraman in Bangalore; editing by Jim Marshall)