The documentation was filed in the US District Court for the District of Colorado, and includes allegations of the federal agency’s “rubber-stamping” the San Juan County mine’s plans.

BHP plans to grow its surface mining operation into the undeveloped Area IV North.

“The Navajo mine has torn up the land, polluted the air, and contaminated waters that families depend on,” Dine Citizens Against Ruining Our Environment spokeswoman Anna Frazier said.

“Residents in the area deserve a full and thorough impact analysis that is translated into the Navajo language to provide for real public participation, not another whitewash for the coal industry.”

BHP first commenced its plans for expansion in 2010, when it sought to mine about 3800 acres of the tract but a Colorado judge ordered the OSM to revisit its evaluation of the proposal.

The producer returned with a smaller, 714-acre planned development area.

But the groups claimed the OSM’s latest analysis “exacerbates the deficiencies” of its first review.

“[Its] analysis justified a finding of no significant impact in a vacuum by focusing only on a cursory analysis of impacts within the mine expansion’s perimeter and ignoring indirect and cumulative impacts from mercury, selenium, ozone, and other air and water pollutants caused by the combustion of coal at the [minemouth facility] Four Corners Power Plant and the plant’s disposal of coal ash waste generated by the coal mined from the expansion area,” the groups said in a statement.

San Juan Citizens Alliance New Mexico energy coordinator Mike Eisenfeld said the approval was rushed, and that the agency had blinders on to the consequences of the complex.

“It hides the true magnitude of the damage going on with coal in our region and the risks of green-lighting more of the same with no change,” he said.

Western Environmental Law Care Centre attorney and group representative Erik Schlenker-Goodrich added: “Where so much is at stake for clean air, vital waterways, and the people who depend on them, that leaves no alternative but legal action to try to ensure fairness and accountability.”

Environmentalists are seeking a comprehensive analysis of the mine and plant’s impacts.

The Navajo mine and Four Corners Power Plant, built in 1962, provides electricity to California, Arizona, New Mexico and Texas.

BHP did not release public statement on the suit Wednesday, and a spokesman told local newspaper the Farmington Daily Times he had not seen the documentation.