FirstEnergy Corp. said Friday it will shut down or sell the last unit it has in operation at its 58-year-old Bay Shore power plant in Oregon by October, 2020.

That announcement was made concurrently with a statement from the utility that it will close four of the seven units of its massive coal-fired W.H. Sammis power plant in eastern Ohio by May, 2020, each built between 1959 and 1962.

That plant, on the Ohio River near Steubenville, is one of the nation’s largest and historically one of Ohio’s more notorious sources of air pollution, according to U.S. Environmental Protection Agency toxic release inventories.

The Sammis plant helped set the tone for many of America’s air pollution laws. FirstEnergy for several years was mired in a high-profile legal battle with the government over orders to install smokestack scrubbers and other modern-era pollution technology there, then struck a deal to put $1.8 billion of pollution controls into it. Those were completed in 2010.

More recently, FirstEnergy drew controversy for seeking guaranteed cash flow to ensure the viability of its Sammis plant and its Davis-Besse nuclear plant in Ottawa County, near Oak Harbor, Ohio.

That case, filed with the Public Utilities Commission of Ohio, is still pending. It has gained national attention as states with deregulated electricity markets try to cope with natural gas prices that have plummeted during the modern era of hydraulically fracturing, or “fracking” shale bedrock, a process oil and gas companies have described as an industry game-changer worldwide because of how it has made previously trapped reserves accessible.

FirstEnergy ceased to operate Bay Shore Units 2-4 in 2012.

Each of those three was coal-fired. The utility said at the time it could not justify the costs of getting them into sync with tougher regulations the Obama Administration had imposed on coal-fired power plants.

Since 2000, Bay Shore Unit 1’s boiler has been operating exclusively off petroleum coke produced at the nearby BP-Husky refinery.

Petroleum coke is a waste by-product, but can become a low-sulfur fuel for power plants when mixed with limestone.

FirstEnergy said the fluidized-bed combustion boiler at Bay Shore Unit 1 is “the largest of its kind in the world.”

The utility said it will shut down or sell Bay Shore Unit 1 by October, 2020, when its agreement with the BP-Husky refinery expires.

Under that arrangement, Bay Shore Unit 1 uses up the refinery’s petroleum coke, also known, as petcoke. The refinery gets the power plant’s steam, Jennifer Young, FirstEnergy spokesman, said.

“We’re looking for a buyer,” Ms. Young said. “We’re looking for reasonable offers.”

Bay Shore Unit 1 employs 78 people. Efforts will be made to retain them if a buyer emerges, she said.

Sammis employs 368 people at the four units being shuttered.

FirstEnergy said it is motivated to take action at its Bay Shore and Sammis plants “in response to challenging market conditions.”

Bay Shore Unit 1 generates 136 megawatts of electricity. The four Sammis units being retired generate another 720 megawatts.

Together, that’s about 4 percent of the electricity FirstEnergy generated in 2015, the utility said.

Every megawatt generates about enough electricity to power 1,000 homes.

The three Sammis coal-fired units that will remain in operation — each of which came online between 1967 and 1971 — produce a collective 1,490 megawatts of power.

“We have taken a number of steps in recent years to reduce operating costs of our generation fleet,” Jim Lash, FirstEnergy Generation president, said. “However, continued challenging market conditions have made it increasingly difficult for smaller units like Bay Shore and Sammis 1-4 to be competitive. It’s no longer economically viable to operate these facilities.”

Contact Tom Henry at: thenry@theblade.com, 419-724-6079, or via Twitter @ecowriterohio.

First Published July 23, 2016, 4:00 a.m.