Oil leak at Xcel’s Monticello nuclear plant reaches Mississippi River, testing public trust

When an industrial motor at Xcel Energy’s Monticello nuclear plant leaked lubricating oil into a cooling system this week, the company moved quickly to reassure residents along the Mississippi River.

The spill had been contained, officials said, and booms in the plant’s discharge canal were holding the oil back. “None of the oil has reached the Mississippi River,” local outlets quoted the company as saying.

By the next day, that had changed. Xcel acknowledged a light sheen of mineral oil on the river’s shoreline just downstream of the plant.

The incident—about 200 gallons of nonradioactive lubricating oil—is minor by the standards of industrial spills. The plant was already shut down for scheduled maintenance, and state and company officials say there has been no radiological release and no threat to public health.

But it comes less than three years after a much larger leak of tritium-contaminated water at the same facility, and after repeated criticism that Xcel and state regulators were slow and incomplete in disclosing that problem. For residents of this Mississippi River town and communities downstream that rely on the river for drinking water, the oil sheen is the latest test of trust at an aging nuclear plant that federal regulators have cleared to operate until 2050.

What happened

Xcel said the oil leak began when a mechanical component in a large motor at the Monticello Nuclear Generating Plant failed earlier in the week. The motor helps circulate nonradioactive cooling water through the plant, drawing from and returning to the Mississippi.

A piece of equipment designed to keep lubricating oil and cooling water separate malfunctioned, allowing the oil to mix with water flowing toward the facility’s discharge canal. The plant has been offline for maintenance since Feb. 20.

In initial statements carried Tuesday by several Minnesota outlets, including CBS Minnesota and FOX 9, Xcel said workers discovered the problem “Tuesday morning” during testing and immediately shut down the equipment. The company said roughly 200 gallons of oil escaped the system before the motor was taken out of service.

As part of its response, Xcel said, crews “immediately isolated the equipment from the water supply and notified federal, state and local governments.” The company said it deployed floating booms and absorbent barriers within the concrete-lined discharge canal and placed additional booms near the point where the canal meets the Mississippi.

At that point, the message was clear: the oil was contained in the canal.

“There has been no impact to the Mississippi River,” the company said in remarks relayed by local stations, emphasizing that the leak involved only “non-radiological mineral oil” and that the plant’s reactor systems were unaffected.

A revised timeline—and a sheen on the river

By Wednesday, however, Xcel was offering a more detailed—and somewhat different—account.

In a statement provided to KSTP-TV, the company said its first sign of “abnormal oil levels” had come Monday afternoon, not Tuesday morning as previously described. Xcel said plant staff identified the leak and isolated the equipment within a few hours and notified the state that same day.

The updated statement also acknowledged what earlier ones had ruled out: some oil appeared to have escaped the containment systems and reached the river.

“There’s always a possibility that a small amount of mineral oil seeped past the containment system,” Xcel said. “During ongoing monitoring, we observed a small amount of mineral oil appearing as a sheen near the shoreline.”

The company described the amount of oil on the river as “small” and said cleanup crews were working along the affected stretch of shoreline. It has not provided a public estimate of how much oil left the canal.

The Minnesota Pollution Control Agency said it was in contact with the utility.

“We are aware of this situation and working with Xcel to understand the impact,” the agency said in a brief statement. The agency has not yet released its own sampling results or said whether it will pursue enforcement action.

Limited hazard, but heightened sensitivity

Regulators and the company stress that the risk from the oil itself is limited. The lubricant, often described as mineral oil, is commonly used in large industrial motors and transformers. Unlike radioactive releases, which are tightly regulated by the Nuclear Regulatory Commission, such spills are typically handled under state and federal water-quality and pollution-control rules.

Still, the sight of any sheen on the Mississippi is sensitive in Monticello, where trust in the plant’s operators and regulators was shaken by a far larger leak of radioactive water in 2022 and 2023.

In that earlier case, Xcel discovered in November 2022 that a pipe between two plant buildings had leaked water containing radioactive tritium into the ground. The company reported the leak to the Nuclear Regulatory Commission and the Minnesota Pollution Control Agency, but the public was not informed until March 2023.

At first, the utility said about 400,000 gallons of contaminated water had seeped into the ground and that the leak remained on plant property. Over the following months, Xcel increased its estimate to more than 750,000 gallons; federal documents now put the total at roughly 829,000 gallons.

In July 2023, after installing additional monitoring wells, the company said testing showed groundwater with very low levels of tritium near the edge of the Mississippi River. One sampling point about 30 feet from the river detected around 1,000 picocuries per liter, well below the federal drinking water limit of 20,000 picocuries per liter. Xcel and state officials continued to say there was no health risk.

The Pollution Control Agency later fined Xcel $14,000 for storing large volumes of tritium-contaminated water in temporary tanks at the site without a required permit. Agency officials defended their decision not to alert the public sooner, saying the leak posed no immediate danger and that they wanted more complete information before making an announcement.

Residents and advocacy groups criticized both the delay and the shifting numbers, saying the episode eroded confidence that they were being told the full story about problems at the nuclear plant.

A plant cleared to run until 2050

Monticello, which began operating in 1971, is a single-unit boiling water reactor on the south bank of the Mississippi about 40 miles northwest of Minneapolis. It is the city’s largest employer and a major source of property tax revenue. Xcel says the plant produces enough carbon-free electricity to power roughly 500,000 homes and is a cornerstone of its plan to retire coal-fired units and cut greenhouse gas emissions.

In January 2025, the Nuclear Regulatory Commission approved a second 20-year license renewal for Monticello, allowing it to run until 2050. The decision followed a safety and environmental review and came as Xcel was still working to remediate the tritium leak.

Environmental and anti-nuclear organizations opposed the extension, arguing that the plant’s age, incident history and location on a major drinking-water source made long-term operation risky. Supporters, including Xcel and some local officials, countered that the plant’s safety record met federal standards and that shutting it down early would complicate efforts to decarbonize the region’s power supply.

What’s still unknown

The latest oil leak is far smaller than the tritium release and involves a different set of hazards. But for critics, the pattern is familiar: a problem at the plant, early assurances that impacts are contained, and later acknowledgments that more contamination occurred or that key details were initially off.

Regulators have not suggested that the spill jeopardizes Monticello’s license or that it posed a threat to drinking water. The Mississippi’s flow in this stretch of river is large, and even a few dozen gallons of oil dispersing into that volume would be quickly diluted, though thin films can still affect near-shore habitat and are visible on the surface.

What remains unclear is exactly how much oil left the plant’s canal, how far it traveled along the riverbank, and whether the mechanical failure that caused the leak points to broader maintenance issues in the plant’s cooling systems.

Xcel says it continues to monitor the discharge canal and nearby river reaches and is working with state agencies on cleanup. The Pollution Control Agency said residents may see increased activity along the shoreline while response crews are present.

For people in Monticello and downstream, the reassurance is once again that the immediate risk is low. The larger question—after a tritium leak that grew in scope on paper and an oil spill that went from “contained” to visibly on the Mississippi in a day—is whether future assurances will be believed.