New information that the U.S. Environmental Protection Agency released on Oct. 28 could signal changes it might make to a proposed major rule that aims to cut greenhouse-gas emissions from existing powerplants, EPA watchers say.

The shape of the final regulation is significant for engineering and construction firms that will help states and electric utilities to implement plans and controls to trim carbon emissions. Some construction-industry groups and labor unions have said the proposal could shutter coal plants and cost jobs in states in which coal is a major power-generation source. They also contend it could cause grid-reliability concerns.

"We all knew the final rule that comes out next June will have a lot of changes from the [proposal]," says Kyle Aarons, a senior fellow with Climate and Energy Solutions (c2es), a non-partisan nonprofit. "This kind of shows what EPA has been thinking about."

The EPA's proposal, which it released on June 18, would require states to develop plans to cut, by 2030, existing powerplants' carbon-dioxide emissions 30% from 2005 levels.

In working on the regulation, the EPA has been drawing on Clean Air Act authority that requires the agency to issue guidelines for states to develop plans for achieving target reductions of CO2 and other greenhouse gases.

EPA's Notice of Additional Data Availability (NODA) highlights concerns and remedies that state officials and others have raised about the proposal.

Janet McCabe, EPA's Office of Air and Radiation chief, told reporters on Oct. 28 that releasing the notice was a routine part of the regulatory process. "I want to emphasize that the NODA does not change the proposal that was put out in June. It simply discusses some key ideas that we've been hearing consistently from a diverse set of stakeholders," McCabe said. "It is not about making the proposal more or less stringent."

But observers say the EPA has been fairly open to hearing from an array of stakeholders. It held four hearings over eight days in four cities and is seeking additional information.

One issue the EPA raises in its notice focuses on the proposed trajectory, or "glide path," for emissions reductions from 2020 to 2029. The American Public Power Association and others have said the current schedule "front-loads" the interim emissions targets.

In its notice, EPA asks for feedback on the idea of giving states credit for early reductions or changing the timetable—that is, before 2030—for the reductions to be achieved.

Jeff Holmstead, a former EPA air office chief, says even states and firms that, typically, have been supportive of the EPA and of paring carbon emissions have said the time lines for hitting interim targets are not achievable.

Holmstead, now a partner with Bracewell & Giuliani, says, "The NODA essentially acknowledges that and sends a pretty clear signal that the agency is going to adjust at least the starting point of the rule to make it more reasonable and more realistic."

The EPA will hold another public hearing on Nov. 19 in Phoenix and will accept comments through Dec. 1.

The agency's regulation may face a protracted battle in another arena, however: Twelve states that rely on coal, including West Virginia, Nebraska and Wyoming, filed a lawsuit in a federal appeals court in early August challenging the proposal. A few weeks earlier, coal mining company Murray Energy Corp., headquartered in St. Clairsville, Ohio, filed its own lawsuit in the same court.