Monsanto aims to stop leaks at Idaho mine dump

Monsanto Co. is installing a water management system at an Idaho phosphate mine the company depends on to make its Roundup weedkiller to stop the leakage of selenium and heavy metals into a tributary of the Blackfoot River.

The company hopes capturing runoff and underground water will remedy problems at the waste rock dump below its South Rasmussen Ridge Mine that have resulted in Clean Water Act violation notices from the federal Environmental Protection Agency.

Monsanto is seeking federal approval for a new mine nearby, called Blackfoot Bridge, to supply the phosphate for Roundup; activist groups have demanded it first remedy old problems like South Rasmussen's dump.

The St. Louis-based company says this water management system would have been built regardless of its efforts to mine elsewhere in the region near the Idaho-Wyoming border.

"Our engineers have extensively studied this issue, and believe this design will work," said Dave Farnsworth, who heads Monsanto's phosphate mining operations in Soda Springs in southeastern Idaho.

Mines owned by Monsanto, the J.R. Simplot Co., and Canadian-based Agrium Inc. in Idaho's rich phosphate belt have come under increasing scrutiny since selenium pollution began killing hundreds of livestock starting in the 1990s.

None of the reported deaths have occurred at Monsanto mines, but 18 cattle died of selenium poisoning this August after eating contaminated plants near an inactive mine whose lease is controlled by Simplot.

Monsanto's water management system at its leaking dump will include shallow collection areas above the dump to capture rain- and snowmelt before it can seep into selenium-rich waste rock.

It's also adding drains at the bottom of the dump, to capture potentially contaminated groundwater before it reaches a nearby wetland and migrates further downstream.

"Water that has not been impacted by mining operations will continue to flow into the watershed," according to an e-mail from the company, which says crews are working quickly on the system so it's in place by the spring thaw.

In 2007, the EPA ordered Monsanto to stop releasing selenium- and heavy-metal tainted water from the dump into Sheep Creek, located upstream from the Blackfoot River. In May, the Idaho Department of Environmental Quality added Sheep Creek to its list of waterways that exceed selenium contamination standards.

EPA officials toured the leaking dump in recent weeks to assess Monsanto's water management system.

The area's complicated geology makes addressing problems a difficult proposition, but the EPA is optimistic these latest efforts will help reduce illegal releases of selenium, cadmium, nickel and zinc.

"These are appropriate and necessary actions that Monsanto is now taking," said Dave Tomten, an EPA geologist in Boise. "I don't know how effective they'll be, but I fully expect they'll improve the situation."

Monsanto will continue testing after next spring, to assess whether more must be done, Tomten said.

The Greater Yellowstone Coalition has been among the most outspoken critics of phosphate mining in the region.

Marv Hoyt, who heads the group's Idaho Falls office, didn't have details of Monsanto's latest proposal to contain leaks at the dump but said he remains skeptical because previous remedies, including pumping water so it could be used as dust control on roads within the South Rasmussen Mine, have proven unsuccessful.