SIOUX FALLS, S.D. - The federal government plans to pay for additional studies around Custer National Forest to determine how far contamination has spread from old uranium mines near Ludlow in northwest South Dakota.

Tests show levels of arsenic, uranium and other contaminants in concentrations higher than what occurs naturally on 13 bluffs. But only now are studies being done to log how much of that pollution made its way onto surrounding land and water.

Samples taken around the North Cave Hills found that high levels of uranium and arsenic in surface water and sediment ponds are mostly limited to the land around the property owned by the U.S. Forest Service, according to a report on the findings.

The contaminants are escaping the 1960s mine sites but dissipate as they flow downstream and diminish to natural levels roughly 4 to 6 miles away, said Jim Stone, assistant professor in the Department of Civil and Environmental Engineering at the School of Mines & Technology in Rapid City.

"It's limited to this area. That's good news," he said.

But Stone said he and other researchers from the School of Mines and Oglala Lakota College have been unable to test how far contaminants have been carried by the wind.

That can't be done until it stops raining long enough for the particles to be carried and won't be done next year, he said.

Stone plans to go over the report on the findings so far next Wednesday at a public meeting in Ludlow.

Researchers will now come up with a cleanup plan for the contamination on the land around the mines, said Laurie Walters-Clark with the U.S. Forest Service in Camp Crook.

"We have found that the sediment ponds - although they were working for what they were built for, which is to catch sediments - they're not stopping the constituents of concern. It puts a red light saying that we need to continue to work on this and stop the sediments from moving," she said.

Estimates put the total bill at more than $20 million to clean up the Cold War-era mining operations.

The government is working on an agreement to cover the cost with the company that mined in the North Cave Hills, Tronox, formerly Kerr-McGee Chemical, Walters-Clark said.

Cleanup can start when that agreement is reached, she said.

"It is now progressing. It's taken a long time," Walters-Clark said.

Meantime, the federal government has approved new studies to determine the extent of contamination in the nearby South Cave Hills and Slim Buttes areas, she said.

Some Harding County and Standing Rock Indian Reservation residents have said they suspect dust and water from the mines is causing cancer and other illnesses.