After a decade of planning, debates and numerous studies and reports on the Rosemont Mine, one of two key decisions on the proposed project is due early next month.

The U.S. Forest Service announced in the Federal Register on Monday that it expects the Coronado National Forest supervisor will sign the decision then on the $1.9 billion project proposed for the Santa Rita Mountains southeast of Tucson.

The other remaining decision is on a proposed federal Clean Water permit application to the U.S. Army Corps of Engineers. The Corps has said repeatedly in recent months, including last Friday in an email to the Star, that it has no timetable for a decision.

Because of that, opponents of the mine in environmental and community groups on Monday sharply criticized the Forest Service’s stated intent to move forward on its decision. Save the Scenic Santa Ritas and the Center for Biological Diversity said in news releases the decision will be premature because without a Corps decision, the Forest Service won’t know whether the mine will meet all federal laws. The service has said it must approve the project if it shows it can meet all environmental laws.

Last July, a lower-level Corps office recommended the mine permit be denied.

A decision now will confuse the public and hand Rosemont a public-relations victory, said Gayle Hartmann, president of Save the Scenic Santa Ritas. Hartmann added in a statement, “If the Forest Service proceeds to issue a Record of Decision before the Corps’ decision, it is wasting time, energy and tax dollars in what is nothing more than a PR exercise. In the absence of a Clean Water Act permit, a final Mine Plan of Operations and a bonding agreement, the Forest Service has no decision to make.”

Hudbay Minerals Inc., the Toronto-based company seeking to build the mine, on Monday issued its own release announcing the Forest Service’s Federal Register notice. Its only additional comment was, “Hudbay will provide further updates on the Rosemont permitting process as appropriate.”

The Forest Service didn’t immediately respond to the opposition groups’ statement that a decision next month will be premature. A little less than a year ago, Coronado Forest Supervisor Kerwin Dewberry told the Star he wasn’t necessarily going to wait for a Corps decision before making his own. But he said he would want to see the Corps’ analysis of the mine, adding: “I’m not saying I won’t wait. I’m saying my decision is not contingent on their decision.”

If the mine is approved, it would become the U.S.’ third-largest copper mine, employing up to about 450 people full-time and operating for 19 years, said the mining company’s latest feasibility study, released at the end of March. It has been hailed as an economic boon by many local business leaders and has strong support from Gov. Doug Ducey.

The mine would operate on 995 acres of private land, 3,670 acres of Forest Service land and 75 acres of state land.

The Forest Service had planned to make a final approval of the mine in spring 2014, after issuing a preliminary approval in December 2013. The final decision was delayed after the discovery of an endangered ocelot near the mine site in April 2014. But the U.S. Fish and Wildlife Service issued a formal biological opinion about a year ago — its second favorable opinion on the mine — saying that it doesn’t expect the mine to jeopardize the existence of any endangered species or to seriously damage critical endangered species habitat.

The Corps’ San Francisco regional office, however, wrote Hudbay officials in December 2016 that its Los Angeles District had concluded the mine would “cause or contribute to” violations of Arizona water-quality standards and trigger “significant degradation” of federally regulated washes.

Rosemont Copper’s plan to buy, preserve and environmentally restore more than 4,800 acres to offset its impacts is also inadequate, the Corps said.

Hudbay officials had previously said the company had paid $48 million to buy mitigation property to compensate for impacts to 68 acres.

That mitigation land includes more than 200 acres of federally regulated washes, more than 900 acres of riparian buffer lands and about 990 acre-feet of actual annual water supplies. That plan “as far as we know, exceeds anything the Corps’ Arizona office has previously required,” Hudbay Arizona general manager Patrick Merrin wrote the Corps last November.

Overall, nine years of review and analysis of this project has “helped us design a mine that minimizes associated impacts and meets or exceeds the regulatory standards for air, water and biological impacts,” Merrin wrote.

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