The plants contribute more than 30 percent of the nation's industrial carbon dioxide emissions, a prime contributor to global warming. They're the No. 1 industrial polluters of mercury, a developmental toxin, and of sulfur dioxide, a main component of acid rain and particulate matter. They're also major contributors to smog and ozone pollution.

An American Lung Association 2004 analysis attributed 24,000 premature deaths each year to power plant pollution. It also noted research showing more than 550,000 asthma attacks, 38,000 heart attacks and 12,000 other hospitalizations annually are caused by their pollution.

The federal Environmental Protection Agency calls pollution from the coal-fired power plant industry a national enforcement priority.

But environmentalists argue that not enough is being done.

Stephanie Kodish is an attorney with Environmental Integrity in Washington, D.C., one of two nonprofit environmental groups backing local residents in a citizen suit to force compliance at the Bruce Mansfield power plant in Shippingport.

She said the government should take action as soon as violations are reported and not allow them to continue for years.

"I'd like to see them take action before communities get upset and get organized - and have to take action themselves," Kodish said.

She theorized political interference and lack of foresight, or perhaps a lack of manpower, is stopping enforcement. Kodish said Environmental Integrity works for enforcement of existing laws but doesn't specifically advocate alternate energy sources.