Radioactive tritium was in a newly installed groundwater monitoring well at the Pilgrim nuclear power plant in Plymouth, MA.
Plant owner, Entergy, submitted an event notification to the Nuclear Regulatory Commission (NRC) informing them of the situation.
A sample taken from the well on Dec. 30 indicated a tritium concentration of 69,000 picocuries per liter, which dropped to 20,000 on Jan. 6 and 14,300 on Jan. 9.
The EPA limit for tritium in groundwater used for drinking purposes is 20,000 picocuries per liter.
In 1991 the EPA calculated it would take a year-long ingestion of water containing 60,900 picocuries per liter of tritium to yield a radiation exposure dose of 4 millirems, a fraction of the approximately 620 millirems of radiation exposure that Americans receive each year from natural and manmade sources.