The U.S. Forest Service will issue a draft decision today approving the proposed Rosemont Mine in the Santa Rita Mountains southeast of Tucson.

The decision is a huge step forward for the mine and Rosemont Copper, although it still doesn’t make the mine a sure thing. The decision comes with key issues unresolved about impacts to neighboring streams, water quality and environmental mitigation, and about the mine’s ability to meet the federal Clean Water Act. But Forest Service officials say its decision will at least enable the mine to meet federal and state environmental laws.

Word of the decision came late Thursday in a news release from Augusta Resource Corp., the Canadian-based owner of Rosemont Copper, which would build the mine. The Forest Service will post the decision today on its Rosemont environmental impact statement website:

Augusta said the Forest Service has picked the Barrel Alternative for the mine site. That proposal was floated by the service two years ago. The Barrel proposal will leave untouched neighboring McCleary Canyon, which the service said is more ecologically valuable.

The release quoted Coronado National Forest Supervisor Jim Upchurch explaining the decision. Upchurch said the mining company probably got a hard copy of the decision that the service had mailed it and other parties.

“I did not take this decision lightly. ... My decision to approve the proposal is guided by federal law,” Upchurch said. “My decision allows Rosemont Copper to develop its mineral resource while requiring a wide array of mitigation and monitoring steps that will minimize or avoid impacts on (national forest) lands to the extent practicable.”

Starting Jan. 1, anyone who had commented on the 2011 draft Rosemont environmental impact statement has 45 days to file a formal objection. The Forest Service has 45 days to review and respond to objections, and can take another 30 days if necessary to make a final decision.

After that, the U.S. Army Corps of Engineers will decide on Rosemont Copper’s application for a separate Clean Water Act permit to dredge and fill materials in washes and streams in and around the mine site. The Environmental Protection Agency — which to date has been sharply critical of the project — has legal power to veto the permit.

The EPA, Pima County, the Bureau of Land Management and the Arizona Department of Environmental Quality have raised questions about the project’s impacts on Davidson Canyon and Cienega Creek, and ADEQ must decide if the mine meets state standards protecting those creeks.

Still, for Rosemont, “The draft (decision), which includes the approval of the preferred Barrel alternative, provides the road map for the operation of the Rosemont Copper Project,” said Gil Clausen, Augusta’s president and chief executive officer. “This decision is the conclusion of six years of analysis conducted by the service and the cooperating agencies. This input allowed the service to develop a sound alternative that will meet all of the required regulations while addressing public concerns and issues.”

But mine opponent

Gayle Hartmann countered that the Forest Service is saying the mine proposal meets federal law without the final sign-off on that point from other agencies. She noted that the EPA has said repeatedly that the mine proposal doesn’t meet the Clean Water Act and that mitigation plans are inadequate.

“The Forest Service was trying, probably as much as anything, to wash its hands of this project and let other agencies take over,” said Hartmann, president of Save the Scenic Santa Ritas.