Southwestern Pennsylvania is home to two of the nation's "50 Dirtiest Power Plants," and another in Clearfield County has been ranked as the fifth-dirtiest in the nation.

So says the Environmental Integrity Project, a Washington, D.C., environmental organization that advocates better enforcement of environmental laws.

Reliant Energy's Shawville Generating Station -- a 572-megawatt plant on the Susquehanna River in Clearfield County -- is listed as the nation's fifth dirtiest.

Two Allegheny Energy Inc. plants also made the list of "The 50 Dirtiest Power Plants."

The Hatfield's Ferry Power Station, the 1,710-megawatt plant straddling Monongahela and Cumberland townships and sitting along the Monongahela River in Greene County, is listed 20th, while the Armstrong Power Station, a 356-megawatt plant on the Allegheny River in Washington Township, Armstrong County, ranks 26.

All three plants were among the top 10 worst sulfur-dioxide polluters. Shawville also is listed as the second and Armstrong as the fifth-worst mercury polluter in the nation. Mercury is a neurotoxin.

The EIP based its list -- posted on the Web site, www.dirtykilowatts.org -- on U.S. Environmental Protection Agency emissions data for sulfur dioxide, carbon dioxide, nitrogen oxide and mercury.

But it altered its calculations this year by listing pollutants per megawatt hour of energy produced, rather than basing it on total tonnage emitted by each plant. It explains why small plants like Armstrong and Shawville made the list.

Last year, Pennsylvania had five plants among the nation's top 10 with the highest sulfur dioxide emission rates.

EIP and other environmental groups released the list during a nationwide telephone news conference yesterday.

"It's troubling that Pennsylvania ranks among the worst in dangerous coal-fire air pollution," said Heather Sage, of Citizens of Pennsylvania's Future, or PennFuture, a news conference participant. "Chief among our worries is toxic mercury pollution. We rank among the worst in the nation."

The EIP said power plants in Texas and Pennsylvania are among the nation's worst mercury polluters.

Although carbon dioxide rates continue rising, with no federal standards in place to control them, sulfur dioxide and nitrogen oxide emissions are easing nationwide, while mercury pollution is holding steady, the EIP said.

"Old facilities that have failed to upgrade pollution controls continued to foul the air, and have had a disproportionate impact on the air-pollution picture," Ilan Levin, EIP counsel, said.

Millions of tons of pollution produced by coal-fired power plants continue to affect health, wreck the environment and contribute to global warming, the organization said.

Pollution controls are being installed on some plants so they will comply when tighter federal Clean Air regulations take effect in 2010, the EIP said.

Allegheny Energy Inc. has announced it will spend $550 million to install scrubbers at Hatfield's Ferry to reduce sulfur dioxide emissions by 145,000 tons a year and soot emissions by up to 2,000 tons a year.

"Our environmental-improvement process is ongoing and continuous," said David Neurohr, spokesman for Greensburg-based Allegheny Energy, noting that the company is focusing on its largest plants.

"When you talk about more than half a billion dollars, that's a firm commitment on our company's part," he said.

PennFuture said new pollution controls at Hatfield's Ferry will mean 200 fewer premature deaths from plant pollution, with a savings of $1.2 billion in annual health-care costs.

Reliant Energy announced plans July 5 to spend $625 million over the next five years to install pollution controls at some of its larger plants, including the Keystone Generating Station in Indiana County and the Cheswick Generating Station in Springdale.

While it has no plans to install scrubbers at Shawville, company spokeswoman Pat Hammond said Reliant Energy does have plans to reduce mercury and sulfur dioxide emissions there.

The company has teamed with the U.S. Department of Energy to test technology to cut mercury emissions. It also will begin using low-sulfur coal to reduce sulfur dioxide emissions, she said.

Scott Segal, director of the Electric Reliability Coordinating Council -- a coalition of energy companies working on clean-air issues -- said EIP is trying to make "an improving situation look bad" with its annual list.

"In many ways, EIP can't see the forest for the trees," he said in a release, noting what he described as "an unmistakable positive trend in air quality."