The U.S. Supreme Court hears arguments today in a Clean Air Act case against North Carolina-based Duke Energy, one of the nation's largest power companies. Environmental Defense, et al. v. Duke Energy Corp. began six years ago after the U.S. government charged the company with expanding operations at eight coal-burning electric power plants in North Carolina and South Carolina and increasing harmful emissions, but failing to update pollution controls as required under the act's New Source Review provisions.

The plants at issue release about 1.6 million tons per year of sulfur dioxide, which causes respiratory problems in humans, acid rain and a haze that sometimes obscures North Carolina's prized mountain vistas. Over 20 million people across the South live in areas where the air fails to meet federal health standards, according to the Southern Environmental Law Center, which is helping to represent plaintiffs in the case.

The high court's ruling could impact the well being of millions of Americans. In a statement about the case from Environmental Defense, Senior Attorney Vickie Patton notes:

"The key question before the Supreme Court is whether our nation's clean air laws will protect Americans from industrial pollution for the next quarter century as they have over the past 25 years."

The Clean Air Act requires utilities to install pollution controls on old plants whenever modifications are made that result in an increase in emissions. At issue in the case is how those emissions are measured, the Raleigh News & Observer explains:

"An older plant that is renovated may not be more polluting hour to hour, but if the improvements allow it to run for more hours, its annual output of pollution may increase. The industry argues that a plant's compliance is based on the hourly standard, while regulators say the plant's annual level of pollution is what matters."

In December 2000, the U.S. government filed a Clean Air Act enforcement action against Duke in North Carolina's federal district court, charging the company with renovating a total of 30 coal-fired generating units without making required pollution control upgrades. Environmental Defense and two other environmental organizations from North Carolina -- the N.C. Sierra Club and N.C. Public Interest Research Group, now Environment North Carolina -- joined the suit the following year.

The federal district court ruled in favor of Duke, and a three-judge panel of the 4th U.S. Circuit Court of Appeals unanimously affirmed the lower court's ruling on June 15, 2005. But nine days later, while reviewing Duke's separate legal challenge to the new source review rules, a federal appeals court in Washington, D.C. reached a contrary ruling.

The environmental groups asked the Supreme Court to review the case. They have presented two issues to the court: whether the 4th Circuit impermissibly overturned national New Source Review rules that may be addressed only by the U.S. Court of Appeals in Washington, and whether the Clean Air Act and its New Source Review regulations apply to renovations at power plants and other industrial facilities that increase emissions.

Counsel of record for petitioners is Sean H. Donahue, law professor at Washington and Lee University in Lexington, Va. He recently told W&L Law School News that much is at stake with the court's ruling:

"There are currently ten enforcement actions like this one pending around the country, and they all involve old power plants, some that had even been moth-balled before they were 'modernized'. These old plants account for a disproportionately large amount of pollutants released each year because the plant upgrades did not include up-to-date emissions controls."

The United States is supporting Environmental Defense's position before the court, and argument time will be equally divided between the environmental petitioners and the government -- but don't take that as a sign the Bush administration wholeheartedly embraces the New Source Review program.

In fact, after government attorneys lost the Duke Energy case before the appeals court, the Bush administration took the company's side, as reported recently. But the environmental groups convinced the Supreme Court to take the case over the administration's objections. As Patton told Forbes:

"The Bush administration is treading the delicate line of enforcing the clean air laws at issue here while carefully reserving its right to radically weaken these same laws through new policies."

The case marks only the second time in 35 years that the Supreme Court has agreed to review a case exclusively at the request of environmental groups over the government's objections, according to Patton.

The court is expected to hand down its decision early next year.