By JOHN MILLER

Associated Press

BOISE, Idaho (AP) -- Federal regulators signed documents on Tuesday outlining an interim cleanup plan for a polluted southeastern Idaho Superfund site they say will cost $57 million and take up to five years to complete.

The Environmental Protection Agency said it opted to move forward with the plan for FMC Corp.'s former plant near Pocatello, but reserved the right to make changes, if necessary.

"EPA will continue to monitor the soil, air and groundwater to ensure the remedies outlined in this new cleanup plan are protective of people and the environment," the EPA said. "Adjustments will be made if needed."

Among other measures, rain barriers will be installed to prevent precipitation from seeping into contaminated areas at the site near U.S. Interstate 86. In addition, polluted groundwater that could leave the site will be treated before it reaches springs and the nearby Portneuf River.

The site is located on the reservation of the Shoshone-Bannock Tribes, which has questioned whether the plan will remedy contaminated soil to tribal standards.

Bill Bacon, an attorney for the tribes, said Indian leaders are meeting on Tuesday, to formulate an official response to the plan. But their initial assessment wasn't favorable.

"This is a cover-up, not a cleanup," said Bacon. "We've always advocated that FMC needs to clean up."

Lori Cohen, deputy director of EPA's Superfund Cleanup Office in Seattle, said the plan -- including capping pollution to prevent penetration from rain or snow -- has been employed effectively at other polluted sites, including landfills.

However, given the tribe's objections, the EPA has opted to keep open the option of making changes, she said.

For instance, the EPA has agreed to an independent review of soil cleanup technologies, to be undertaken during the next year, to see if any would be effective at the FMC site.

"Certainly we have heard a lot of concerns, we've been in many discussions and consultations with the tribe about this cleanup plan," Cohen said.

The EPA's announcement came on the heels of an initial cleanup plan dating to 1998.

During the intervening years, the site has been plagued by other problems, including "burping" ponds -- volatile waste repositories that produce phosphine gas that smells of rotten fish and can damage respiratory, nervous and gastrointestinal systems.

Tests have detected elemental phosphorus from spills and leaks 85 feet below ground. Refined elemental phosphorous is unstable and can burn uncontrollably or explode when exposed to air.

The EPA says cost of the cleanup will be borne by the company and overseen by the agency and the Shoshone -Bannock tribes. The effort could start in about a year after the completion of preliminary engineering work.

Philadelphia-based FMC, which had $3.4 billion in sales in 2011, operated an elemental phosphorous production plant from the 1940s to 2001 on the Eastern Michaud Flats area of the Shoshone-Bannock reservation. Its customers included the food industry, which uses phosphate in a number of products, including soft drinks and toothpaste.

The company blamed rising electricity costs for the shutdown.

Paul Yochum, the last plant manager who remains on contract with FMC, said the company is pleased the EPA released the cleanup plan after months of negotiations, because it will allow the company to begin work on a final remedy to address pollution concerns -- and prepare the site for eventual redevelopment.

Copyright 2012 The Associated Press.