Completing a shift to renewable energy, Kennecott Utah Copper will shut down its last coal-fired power plant in Magna, shrinking its carbon footprint by as much as 65% — a total of more than 1 million tons of carbon dioxide a year, according to its owners.

Rio Tinto, Kennecott’s corporate parent, announced Wednesday that power to the copper producer will come from 1.5 million megawatt hours of renewable energy certificates purchased from Rocky Mountain Power, which will be primarily sourced from its Utah-allocated portfolio, including wind power generated in Wyoming.

The move formalizes a transition that has been underway at Kennecott Utah Copper, which mines and processes copper ore at its vast industrial network on the west side of the Salt Lake Valley, for the past several years, according to spokesman Kyle Bennett.

“This ensures we are offsetting the electrical demand we use across our Utah operations with certified renewable energy certificates,” Bennett said. “Rio Tinto wants to be carbon neutral by 2050. Every operation within the portfolio would have to look at ways to achieve that.”

Kennecott’s 75-megawatt Unit 4, added in 1960 and idled for the past two years, is the last coal-fired power plant on Utah’s crowded Wasatch Front and perhaps the oldest in Utah.

Western Resource Advocates welcomed the announcement as a step toward improving an airshed burdened with seasonal pollution spikes that sometimes violate federal standards for human health.

"This move will help improve air quality along the Wasatch Front, particularly in the summer, when the Salt Lake metropolitan area is experiencing increasingly severe concentrations of ozone pollution,” said Joro Walker, the environmental group’s general counsel, who is based in Salt Lake City.

Gov. Gary Herbert also praised Kennecott’s announcement as “a win-win for our community. Their decision will simultaneously support Utah’s shift toward a low-carbon economy and improve air quality in the Salt Lake Valley."

Rio Tinto’s chief executive officer, Jean-Sébastien Jacques, said the company “is committed to playing a part in the transition to a low-carbon economy.”

“This move will significantly reduce emissions associated with our operations in Kennecott and allow us to offer customers copper, gold and silver with a reduced carbon footprint," he said in a statement. “… Rio Tinto will continue to work with partners and customers to develop new sustainable solutions.”

According to Rio Tinto, the renewable energy certificates are Green-e Energy certified and meet the nonprofit Center for Resource Solutions' environmental and consumer-protection standards.

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Kennecott has made numerous investments to reduce energy use and cut emissions, according to Bennett, but retiring the four-unit power plant may have the biggest impact.

“That’s going to take 6,000 tons of particulate and particulate precursors out of our airshed annually," Bennett said. “We live in a constrained airshed, and we wanted to look at ways to reduce our contribution."

The company has not used the plant during the wintertime inversion season since the early 1990s, according to Bennett.

Kennecott installed the first of its four coal units in 1944 and expanded the station through the years to four units capable of generating 175 megawatts of electrical power. In 2016, the mining company agreed to retire the three oldest units ahead of schedule and convert the fourth to clearer-burning natural gas.