The company proposing to build the Rosemont Mine is raising the possibility of challenging the U.S. Army Corps of Engineers’ authority to regulate washes on the site if the Corps denies a permit to build the project.

Federal jurisdiction over those washes hasn’t been questioned since Rosemont Copper first announced its plans to build the $1.5 billion project a decade ago. The company, now owned by Toronto-based Hudbay Minerals Inc., applied for a Clean Water Act permit for the project back in 2011 and announced its intention to apply in 2008.

The proposed Rosemont Mine would “cause or contribute to” violations of Arizona water quality standards and trigger “significant degradation” of federally regulated washes, said a lower-level Army Corps of Engineers office in recommending against granting it a key federal permit.

In a recent letter to the mine company’s general manager, a top Corps official for the first time revealed these and other reasons underlying that office’s recommendation last year to deny a federal Clean Water Act permit for the $1.5 billion, Tucson-area project.

A key permit decision on the proposed Rosemont Mine — which would be the country’s third-largest copper mine — won’t be made until after President-elect Donald Trump takes office.

The Army Corps of Engineers said last week it doesn’t expect to issue its decision on a Clean Water Act permit for the mine until after Jan. 20, when Trump is inaugurated. It declined in response to a question from the Star to give a timeline for the decision.