The proposed Rosemont Mine’s open pit at this site would span 6,000 to 6,500 feet in all directions and descend up to 3,100 feet into the ground.

The U.S. Army Corps of Engineers is about to grant the final permit needed for construction of the Rosemont Mine, said U.S. Rep. Raúl Grijalva, a longtime opponent of the $2 billion project.

After meeting Thursday with a top Army Corps official in Washington, D.C., Grijalva told the Star, “It’s my understanding that they are going to grant the permit.”

Grijalva, chair of the House Natural Resources Committee, made the comment after he and fellow Tucson Democratic Rep. Ann Kirkpatrick met Thursday morning in a private briefing with Army Corps Gen. Pete Helmlinger. Kirkpatrick’s district includes the Rosemont site in the Santa Rita Mountains southeast of Tucson.

Grijalva and Kirkpatrick, also a mine opponent, said in a news release after the meeting they’re concerned the Corps will issue the permit “imminently, without full consideration of the facts.”

The permit, under the federal Clean Water Act, would give Toronto-based Hudbay Minerals Inc. the right to dredge and fill streams and washes near the mine site as part of the open-pit copper mine’s construction.

The permit would cap 12 years of conflicts over the proposed mine. The Environmental Protection Agency has opposed the mine almost from the start, but is now seen by Grijalva as unlikely to carry that opposition as far as vetoing an Army Corps permit.

This would be the last of numerous permits the mine needs to start construction. It would come more than a year and a half after the U.S. Forest Service approved a separate decision for the mine to be built on Coronado National Forest land.

It would also overturn a recommendation 2ƒ years ago to deny the Rosemont permit by the Corps’ Los Angeles District office. The final decision is being made by the Corps’ South Pacific Division in San Francisco, which Helmlinger headed until recently.

The Corps declined through a spokesman Thursday to say what its decision is, on the grounds that it can’t legally disclose a decision until it’s final. The final decision could come as soon as next week, said Mike Petersen, a Corps spokesman.

The Corps has sent the EPA’s San Francisco regional office a formal notice of its draft decision. The notice gives the EPA’s regional administrator until Friday, March 1, to decide whether it wants to have the decision kicked upstairs to Washington, D.C., Corps and EPA officials for a final review. Ultimately, the EPA can veto the Corps permit under Clean Water Act rules.

Notice to the EPA is required under federal rules because the agency has repeatedly warned in letters dating back to at least 2013 that the mine could damage important aquatic resources, including Cienega Creek and Davidson Canyon east of the mine site.

In an interview Thursday, Grijalva said he believes that notice was a clear sign of an impending permit approval. He said he doubts that the EPA’s San Francisco office will seek to elevate the Rosemont issue to D.C., given the agency’s broad shift toward a pro-business stance since President Trump took office.

But Peterson said the latest notice wasn’t necessarily of a favorable decision. The notice can also simply mean the Corps has resolved EPA’s concerns through other measures, he said.

Grijalva and Kirkpatrick’s news release said, “We both believe critical questions remain unanswered, including whether there has been adequate review under the National Environmental Policy Act. We’re going to pursue every avenue to ensure Rosemont is handled transparently, and we will be conducting additional oversight of this project.”

The Corps’ Petersen declined to respond directly to the Congress members’ comments. But he said the review process under the National Environmental Policy Act “is very important to the Corps.”

The Corps was involved in “extensive and collaborate processes” with the Forest Service, “multiple” other federal agencies, nine state agencies and three local agencies when the Forest Service prepared draft and final Rosemont environmental impact statements in 2011 and 2013, Petersen said.

Besides Helmingler, three other Corps officials will have to sign onto the Rosemont decision before it’s final, Petersen said.

Overall, Grijalva said, “I appreciate General Helmlinger attending the briefing on the eve of issuing a decision,” but added he wasn’t satisfied with Helmingler’s response.

Grijalva declined to elaborate, saying he and his staff are reviewing documents from the Corps before making detailed comments.

Many business groups in and outside of Tucson have supported the mine based on its stated plan to create more than 400 permanent jobs and its promises of tens of millions of dollars in tax revenues and other economic benefits annually.

Environmentalists have filed suit to challenge the Forest Service’s approval, and are certain to file suit to try to overturn a Corps permit as well, if it’s issued.

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter@tonydavis987