Apr. 27--Environmentalists who sued Duke Energy Corp. over upgrades at its coal-fired plants say a proposed EPA rule undermines their U.S. Supreme Court victory and would give utilities a free hand to pollute.

At issue is how the government measures air pollution from the smokestacks of coal-fired power plants and other sources. Environmentalists say the pollution should be counted as tons per year. The utility industry and the U.S. Environmental Protection Agency say pollution output should be judged on a per-hour basis. The distinction is important because if a company improves a plant so it operates more hours per year, its annual pollution would increase even if its hourly rate stayed the same. That scenario troubles environmentalists because an upgraded plant could scape regulations that might otherwise require millions in anti-pollution devices under an EPA program called "new source review." The agency under the Bush administration first proposed using the hourly test in 2005, and on Wednesday released an updated version of the proposal.

The agency will take public comment and hopes to have a rule in place by the end of the year. Poor air quality in Charlotte and other growing areas of the Carolinas, and concerns over global warming, has focused attention on controlling emissions. About 50 percent of the nation's electricity comes from coal, a cheap and abundant fossil fuel blam d as a cause of global warming. As utilities look to improve efficiency at older coal-fired plants, the legal and regulatory question has become how best to control air pollution from those existing plants. The proposed rule would open up a floodgate of air pollution, environmentalists contend.

Under the measure, utilities might see an opportunity to upgrade older, dirtier plants so they can operate more hours per year and escape expensive regulations, the said. "EPA's action will result in more air pollution, while trampling on the law and damaging public health," John Walke, clean air program director of the Natural Resources Defense Council, said in a written statement. The government said the concerns are overstated and that its proposed rule and the U.S. Supreme Court case that went against Duke are "apples and oranges," because the new rule would only apply to new cases. The Supreme Court case hinged on two points: What is the definition of a plant upgrade? How should air pollution be counted? Environmental Defense, a collection of groups, argued Duke's plant upgrades at its eight Carolinas plants in the 1980s and 1990s were complete overhauls and should have triggered newer, stiffer regulations.

They also argued the upgrades allowed the plan s to operate for more hours each day, increasing the total output of pollution over a year. Duke contended the upgrades, which included replacing corroded pipes and boilers, constituted "routine maintenance." The company also argued that because the emissions released per hour would not increase, the plants shouldn't be subjected to the new re ulations. But the justices said pollution should be counted as tons per year but left open the question of whether Duke's upgrades should have sparked newer regulations in the first place. That will be argued in a lower federal court.

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