In a Federal Register notice, the government said it would extend the public comment period until Oct. 15. The previous deadline was July 16.

The U.S. mining industry is also facing pressure in two other arenas to pay more attention to the environment.

In May, Reps. Nick Rahall, a West Virginia Democrat, and Christopher Shays, a Connecticut Republican, proposed major changes in the 1872 U.S. mining law that exempts hard-rock mining companies from paying royalties or cleaning up abandoned mines. Their bill is supported by environmental groups who contend that mining companies should have to pay a royalty of up to 12 percent for using public lands.

Mining companies often use chemicals such as cyanide, cadmium, lead and arsenic to extract minerals such as gold, silver and copper from rock. The mining waste can leach into groundwater.

Separately, a federal judge in West Virginia recently threw out the federal government's authority to issue mountaintop mining permits because it violated the Clean Water Act. In mountaintop mining, the peaks of Appalachian mountains are blasted off to unearth coal, dumping huge amounts of polluting debris into rivers.

The U.S. coal mining industry plans to appeal the court ruling, saying it could put thousands of coal miners out of work.

Some experts have estimated the cost of cleaning up U.S. mining pollution as high as $35 billion.