Federal officials have approved an agricultural company's efforts to expand mining operations in southeast Idaho's phosphate patch after concluding that a $30 million liner and drainage system would adequately protect nearby streams and rivers.

The U.S. Bureau of Land Management's decision comes after years of environmental analysis and review of Monsanto Co.'s plans in a region still dealing with the side effects of harmful mineral pollution blamed on historic phosphate mining.

Federal land managers gave final approval last week to the Blackfoot Bridge Mine project, located on a combination of private and public land 10 miles northeast of Soda Springs near the Idaho-Wyoming border.

Two years ago, the federal officials balked at the company's application, citing concerns that selenium — a mineral lethal to animals when consumed at high levels — could leach into the groundwater and streams from the massive pile of waste rock amassed during the 17-year life expectancy of the mine.

But Monsanto reworked its design and proposed spending up to $30 million on a drainage system and state-of-the-art liner cap designed to prevent rain and snowmelt from mixing with the selenium-rich waste rock.

"We took this very, very serious because the stakes are so high given the past contamination in the region," said Jeff Cundick, minerals branch chief for the phosphate program of the Caribou National Forest and the Bureau of Land Management.

"There is always going to be risk. But we feel the risk is now manageable and low," he said. "This is not your grandfather or father's phosphate mine we're approving at this point. This is the culmination of a thorough and highly scientific study."

For Monsanto, the agency's green light means it can continue mining the region's rich deposits of phosphate ore, a critical ingredient for its Roundup weedkiller products. The company's current mining footprint, the South Rasmussen Ridge Mine, located just miles from the Blackfoot Bridge site, is expected to be depleted in the next year.

Dave Farnsworth, minerals chief for Monsanto's Soda Springs plant, said the company is pleased with the decision and opportunity to continue its presence in the region.

"The mine and the advanced technologies we will employ will preserve good jobs in southeast Idaho, as well as clean water and a healthy environment," Farnsworth said in a statement.

The BLM posted its record of decision in the Federal Register on Friday, starting the clock on a 30-day window for appeals.

The Blackfoot Bridge project is located at about 6,000 feet in the mountains and 600 feet from the Blackfoot River, a waterway that is already showing selenium levels exceeding federal clean water standards.