The lawsuit asks for a court order that would, in various ways, curb the size and impact of mountaintop removal coal mining. Named as a defendant in the case, along with the Corps, is the state Division of Environmental Protection.

On Friday, lawyers for three Arch Coal Inc. subsidiaries asked that the companies be allowed to intervene in the case.

The subsidiaries are Hobet Mining Inc., Catenary Coal Co. and Mingo-Logan Coal Co. The companies operate large mountaintop removal mines in Boone, Lincoln, Logan, Kanawha and Mingo counties.

In the motion to intervene, Jackson & Kelley lawyer Roger Wolfe wrote that the suit "threatens to substantially affect the value of the companies' property interests in the relevant permits and the underlying mineral rights by impairing or destroying their ability to mine coal under those permits."

Wolfe wrote that if the lawsuit results in any changes in the mountaintop removal regulatory process, "a substantial burden of compliance or the burden of having permits denied would fall" on the companies.

According to Wolfe, the DEP and the Corps cannot adequately defend against the lawsuit to protect the companies' rights.

"As to WVDEP, it regulates the companies' activities, both with respect to the surface mining laws and the water pollution control laws," Wolfe wrote.

"In that capacity, it represents the interests of the public, not private coal companies," he wrote. "The companies' are often adverse to WVDEP on regulatory matters in these areas."

Lawyers for the U.S. Army Corps of Engineers asked U.S. District Judge Charles H. Haden III to approve the moratorium to run through at least Oct. 5.

Corps lawyers said the action is hoped to promote discussion and/or negotiations among the interested federal agencies.

The Corps filed the request as a joint motion with lawyers for environmentalists and coalfield residents who allege mountaintop removal mining permits have been issued in violation of the federal Clean Water Act.

The joint motion was filed just a day after Rep. Bob Wise, D-W.Va., urged the U.S. Office of Surface Mining to impose a temporary moratorium on new mountaintop removal permits until regulators finish a series of studies on the issue.

Unlike old-time strip mining, mountaintop removal shaves off entire hilltops to reach valuable low-sulfur coal underneath. Leftover rock and earth are dumped into stream beds, forming waste piles called valley fills.

A lawsuit filed in mid-July by the West Virginia Highlands Conservancy and 10 coalfield residents alleges, among other things, that the Corps has illegally authorized valley fills under the Clean Water Act's "dredge and fill" permits.

Court rulings have held those permits cannot be issued for dumping of waste material, such as mine spoil.

Corps officials conceded publicly several weeks ago that they had stopped issuing valley fill permits after environmental groups' lawyers showed those court rulings out to them.

The lawsuit asks for a court order that would, in various ways, curb the size and impact of mountaintop removal coal mining. Named as a defendant in the case, along with the Corps, is the state Division of Environmental Protection.

On Friday, lawyers for three Arch Coal Inc. subsidiaries asked that the companies be allowed to intervene in the case.

The subsidiaries are Hobet Mining Inc., Catenary Coal Co. and Mingo-Logan Coal Co. The companies operate large mountaintop removal mines in Boone, Lincoln, Logan, Kanawha and Mingo counties.

In the motion to intervene, Jackson & Kelley lawyer Roger Wolfe wrote that the suit "threatens to substantially affect the value of the companies' property interests in the relevant permits and the underlying mineral rights by impairing or destroying their ability to mine coal under those permits."

Wolfe wrote that if the lawsuit results in any changes in the mountaintop removal regulatory process, "a substantial burden of compliance or the burden of having permits denied would fall" on the companies.

According to Wolfe, the DEP and the Corps cannot adequately defend against the lawsuit to protect the companies' rights.

"As to WVDEP, it regulates the companies' activities, both with respect to the surface mining laws and the water pollution control laws," Wolfe wrote.

"In that capacity, it represents the interests of the public, not private coal companies," he wrote. "The companies' are often adverse to WVDEP on regulatory matters in these areas."