The lawsuit filed late Tuesday in District Court in Colorado appears likely to again delay BHP Billiton's plan to mine in Area IV North, a large and undeveloped tract that holds vast coal deposits.
Navajo Mine feeds the adjacent Four Corners Power Plant, a 2,040-megawatt coal-fired power plant west of Farmington operated by Arizona Public Service Co.
In 2010, a Colorado judge ordered the federal Office of Surface Mining, Reclamation and Enforcement to revisit its analysis of BHP Billiton's plans to mine 3,800 acres of Area IV North.
BHP Billiton responded with a more tightly focused analysis of a 714-acre area the company seeks to develop.
The environmental groups want a broader analysis under the National Environmental Policy Act.
"By focusing just on this smaller area, they're not really looking at the bigger picture," said Mike Eisenfeld, New Mexico energy coordinator for San Juan Citizens Alliance, a party to the lawsuit. "They failed to look at the impacts besides that small mining area. It's a tactic to say, hey, look, no impacts.'"
BHP Billiton representatives said the environmental assessment process went above and beyond the requirements of the law and was properly approved.
"We are committed to having a dialogue with the environmental groups to understand and address their concerns, including how we can study the cumulative impact of the mine and the power plant," said Jac Fourie, president of BHP Billiton's New Mexico Coal unit, in a prepared statement Wednesday.
"We believe that our recent success in negotiating a settlement with the Sierra Club at our San Juan Mine demonstrates that we are committed and serious about being transparent, protecting the environment and willing to listen to other points of view," Fourie added. "We look forward to having similarly productive conversations with these groups in the future."
Anna Frazier of Diné Citizens Against Ruining Our Environment said the mine has polluted the air and water.
"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," she said.
Rachel Conn, projects director for Amigos Bravos, added: "Pollution and other impacts from coal mining and coal power plants broadly impact New Mexico's rivers and streams, in particular the Chaco and San Juan rivers. These rivers must be better protected for agriculture, drinking water and fish."
Navajo Mine is a rare source of high-paying jobs on the Navajo reservation. The mine employs 462 workers, the majority of whom are Navajo.
The mine opened in 1963. It has grown south from the power plant as the nearest coal supplies were exhausted. Most mining now occurs in Area III as the two oldest areas reach their end. The mine produces several million tons of coal annually.
The plaintiffs in the case are San Juan Citizens Alliance, Diné CARE, the Center for Biological Diversity, Amigos Bravos and the Sierra Club. The groups are represented by the Western Environmental Law Center.
BHP Billiton New Mexico Coal is a division of the Melbourne, Australia-based mining company.