"Kennecott’s tailings pond may be leaking into the Great Salt Lake", 16 July 2025

A polluted tailings pond at the Kennecott Utah mine has sunk 20 feet or more, raising concerns that it has seeped contamination into the neighboring Great Salt Lake.

But the state regulator charged with protecting the lake’s water, the Division of Water Quality, allowed the mining company to edit this information out of a recent groundwater permit, documents show. The division also allowed Kennecott to quietly nix a study that would have investigated the tailing pond’s connectivity to and impact on the Great Salt Lake.

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Division director John Mackey said it’s common to let regulated companies weigh in on their permits.

“It’s necessary for us to coordinate with them on that,” Mackey said, “because they’re the ones who need to do the study.”

Kennecott denied settlement of its tailings pond posed an environmental concern in an emailed statement from the mine’s parent company, Rio Tinto.

“We stand by the safety of our tailings impoundment,” a spokesperson wrote, “and affirm that it meets, and in some cases exceeds, the required standards.”

At issue is selenium, a mineral that can be toxic for humans at high concentrations. It also poses a threat to the millions of migrating birds that visit the Great Salt Lake every year. The material weakens eggs and deforms embryos. It can bioaccumulate in the wetland bugs those birds eat, and work its way up to hunters harvesting waterfowl.

More than a century of mining at the Kennecott facility has resulted in two groundwater plumes with selenium pollution that have impacted at least some the lake’s wetlands.

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Last year ... regulators detected elevated levels of selenium in migratory bird eggs collected near the discharge point.

Given the rise of selenium in eggs, and Kennecott’s “inability” to manage selenium-impacted groundwater, the EPA determined in September that the wetlands and groundwater near the tailings pond are not protective of human health and the environment in a five-year review.

The agency’s report noted the Utah Division of Water Quality had alerted the federal agency about a 20-foot settlement of the tailings pond, which has a natural clay liner meant to prevent pollution from mingling with the shallow aquifer.

But deterioration of the pond that is causing it to sink at a rate of 0.9 feet a year could mean there’s a pathway for tailings water to mix with groundwater and the surrounding wetlands, EPA noted.

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The [Utah Division of Water Quality] gave the mining company one year to analyze how the pond’s sinking has impacted its clay liner and whether it was seeping.

It also gave Kennecott two years to file a “Great Salt Lake Connectivity and Influence Analysis,” studying water quality and how the lake’s briny water mixes with surrounding fresh water and groundwater.

A division scientist shared the draft permit language with Rio Tinto on June 5, 2024, emails show.

A staffer for the mining company responded three weeks later, attaching a document with significant red lining and revisions.

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The revised language requires Kennecott to compile “previously submitted reports” on the pond’s clay layer and hydrology — suggestions made by the company in its revisions. The Division did, however, insert that its director “may” later require an investigation.

That same month it approved the groundwater permit, the division received a report that detected selenium in five shorebird eggs at levels that trigger a regulatory response. It’s the first time the state has detected such high concentrations of the contaminant, Mackey confirmed, although the state has not reported egg selenium data since 2017.

That’s because receding lake levels made egg collection difficult, he said.

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In December, after receiving reports on the shorebird eggs, Mackey issued letters to both Kennecott and Jordan Valley Water Conservancy District, notifying both to prepare to take actions reducing selenium unless they could prove they were not the source of increased pollution.

The water district declined to comment, but Mackey’s letter notes it had reduced selenium discharge during the nesting season.

Kennecott, meanwhile, has not released surface water to the Great Salt Lake for more than a year, Mackey said. The mining company mostly recycles water from its ponds.

In both cases, Mackey wrote he did not have sufficient evidence to determine whether the entities were in the clear.

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