Xcel Energy reports on tritium levels in well near Mississippi River

The Minneapolis-based energy company shared the readings as part of an update about its ongoing recovery work stemming from a large leak into the ground beneath its Monticello nuclear power plant in 2022.

The test showed tritium at 19,800 picocuries per liter, and the EPA’s drinking water standard is 20,000 pCi/L. However, the sample was taken from a well about 40 feet underground, much deeper than the nearby riverbed, and shallower wells tested at the location are not detecting tritium, the company said in a statement.

Tritium is a naturally occurring form of hydrogen present in the environment that emits low levels of radiation and is commonly generated as part of nuclear energy production’s chain reaction. It is found in trace amounts in groundwater worldwide and the radiation it emits cannot penetrate the skin, according to the Nuclear Regulatory Commission.

“While 20,000 picocuries per liter (pCi/l) of tritium may sound like a high number, the EPA’s Maximum Containment Level for tritium in drinking water corresponds to a radiation dose of about 4 millirem per year—assuming someone drinks two liters of that water every day, all year,” said Emily Caffrey, an assistant professor and director of the graduate-level Health Physics Program at the University of Alabama—Birmingham.

“For perspective, this is a very small dose compared to the 310 millirems of natural background radiation the average American receives annually, mostly from exposure to radon, cosmic rays, and to naturally occurring radioactive materials—including granite countertops and even bananas,” Caffrey added.

While nuclear plants routinely release diluted amounts of tritiated water, the NRC monitors the safety of the process.

Quotable: “Tritium still has not been detected in the river above naturally occurring levels, despite the increased sampling we and state regulators have conducted today and in the past. Small amounts of tritium reaching the river would likely be at such low levels and diluted so quickly that it cannot be detected, even by highly sensitive instruments. The leaked tritium has also not affected any drinking water sources near Monticello or downstream along the river. Residents in the area do not need to take any action and can continue drinking the water they currently use,” said Xcel spokesperson Kevin Coss, adding that “while the recent readings do not require any mandatory actions according to state or federal law or our operating permit, we are providing this update for awareness and transparency.”

Background: In November 2022, plant workers discovered that a broken pipe at the Monticello plant was responsible for a leak of between 750,00 and 900,000 gallons of tritiated water. Since then, Xcel has worked to contain and recover the tritium, and Coss said the team has successfully driven down tritium concentrations in the groundwater by more than 90 percent of the initial recordings.

In 2023 Xcel announced it would begin building an underground barrier wall—600 feet long and 40 feet deep—along the edge of Monticello’s boundary with the Mississippi River to improve the plant’s ability to manage groundwater flow and impede interaction between the river water and groundwater at the plant.

The 671-MWe boiling water reactor at Monticello has been in commercial operation since 1971.

Oversight: A statement from the Minnesota Pollution Control Agency, the Minnesota Department of Natural Resources, and the Minnesota Department of Health also noted that tritium readings in the river have been below detection limits, but still said that, based on testing on Xcel’s property last month, “there has been a change” in the situation at Monticello, the Minnesota Star Tribune reported.

Since April, “monitoring strongly suggests the plume of tritiated groundwater is moving toward the Mississippi River,” MPCA spokesman Dan Ruiter told the Star Tribune, but added that there is no threat to human health or the environment.

The NRC said in a statement that tritium levels are routinely assessed from samples taken in dozens of monitoring sites on and off site, including from the drinking water supply for Minneapolis (downstream from Monticello) and from surface water in the Mississippi.

“We are aware of the recently reported elevated tritium levels in a monitoring well near the plant. We continue to conclude that there is no danger to the plant, the public, or the environment connected to the leak,” according to the commission. “The elevated tritium levels are a result of the movement of the original leak plume. The monitoring of multiple monitoring wells on site indicates there is no new leak from the plant, and the elevated tritium levels do not trigger any additional reporting criteria.”

What’s next: Coss said Xcel is adjusting the amount of water it pumps to pull the leaked tritium away from the vicinity of the river more effectively.

“We expect measurements to fluctuate over time as we continue to retrieve the leaked water," he said. "We remain committed to being good neighbors and stewards of the environment, as well as following all regulations, as we continue the clean-up.”