DENVER — An abandoned mining site blamed for leaking fish-killing contaminants into a creek in southwestern Colorado was added to the Superfund list on Wednesday, clearing the way for a cleanup at federal expense.

The Environmental Protection Agency said it won't know how long the cleanup will take or cost until initial studies are completed.

"We don't know what we'll find when we start looking into the mine workings," said Peggy Linn, a Denver-based EPA spokeswoman. The EPA oversees the Superfund program, which now includes 18 hazardous waste sites in Colorado.

The Nelson Tunnel-Commodore Waste Rock Site is a mile north of Creede and 150 miles southwest of Denver. The tunnel drains water from abandoned silver, lead and zinc mines. The waste rock is from the now-closed Commodore mine.

The EPA says cadmium, lead and zinc from the tunnel are contaminating the Willow Creek watershed and are killing fish in a two-mile stretch of the waterway.

A drainage system constructed around the waste pile failed during a 2005 flood, and the EPA says another flood could send contaminated water into Creede, population about 400, and the creek.

Tunnel cleanup options include keeping water from getting into it in the first place and building a treatment plant to remove contaminants from the water as it drains out. Linn said high costs reduce the likelihood of a treatment plant. Options for the waste pile include enlarging existing drainage channels.

A grass-roots group called the Willow Creek Reclamation Committee has been cleaning the larger area since 1999 using grants, donations and volunteer labor.

Zeke Ward of Creede, chairman of the committee, estimates the grants and cash donations have totaled about $1.6 million. Ward said his group wanted to clean up the tunnel, but Colorado doesn't have a law to protect volunteer groups from the liability that would entail.

The Nelson Tunnel was 1,700 feet long and about 12 feet wide by 10 feet tall when it was dug in 1892, Ward said. Miners used it to haul out ore besides draining water from mine shafts.