“They’re holding this very close,” said David Doniger of the Natural Resources Defense Council.

Jeff Holmstead, a former EPA air chief who now represents industry clients at Bracewell & Guiliani, said the tight deadline might lead the agency to release a less complete guidance.

“Because of the rush to get the proposal out the door, we may well see a number of proposed options rather than a true proposed rule,” he said in an email.

The rule is the product of months of meetings between EPA staff led by Air and Radiation Office Senior Counsel Joe Goffman and a wide range of state officials, environmentalists, industry representatives and other stakeholders.

But participants haven’t said what route EPA intends to take. Will its rule assume states will reach for system-wide emission reductions, including renewable and energy efficiency policies? Or will it seek to spur “inside the fence line” upgrades at power plants, as industry representative say it should?

If EPA takes the more expansive approach, said Holmstead, it could “it will run into serious legal problems.”

The OMB website says only that the rule will be “economically significant,” meaning EPA predicts compliance will cost at least $100 million a year. This is not an unusual designation for an important air quality rule, but it is a departure from last year’s proposal for new power plants. The agency determined that that rule wouldn’t have a significant economic impact because only coal-fired power plants would be required to invest in carbon capture and storage technology to limit emissions, and virtually no new coal units are in the pipeline anyway.

The rule makes its way to OMB as Senate Republicans plan to attach language that would block new and existing power plant rules for CO2 to unrelated legislation now before the chamber (Greenwire, April 1).