The U.S. Environmental Protection Agency (EPA) says a containment dam built by Monsanto below its South Rasmussen Ridge Mine in Southeast Idaho’s Caribou County has halted millions of gallons of water in Sheep Creek from flowing into the Blackfoot River as the company attempts to trap polluted phosphate mine runoff.
EPA wants Monsanto, which operates an elemental phosphorus plant near Soda Springs and produces Roundup herbicide, to begin an expensive treatment to remove selenium and heavy metals from the water and discharge it clean downstream. The St. Louis-based company planned to capture the water in a 50-million-gallon lake behind the dam and use it for dust control on its mining roads.
Mark Ryan, a Clean Water Act attorney for EPA in Boise, said EPA supports Monsanto’s efforts to reduce selenium discharges into the creek, but it has serious concerns about Monsanto’s methods to dry up the creek.
In 2007, EPA warned Monsanto that selenium- and heavy metal-tainted water flushed from the waste rock dump into Sheep Creek violated the federal Clean Water Act. Sheep Creek runs into the Blackfoot River, both of which are on the Idaho Department of Environmental Quality’s (IDEQ) list of 15 waterways that exceed contamination standards for selenium, a byproduct of phosphate mining that can be toxic in large amounts.
Monsanto got a U.S. Army Corps of Engineers permit in early April to erect a roughly 20-foot dam below the dump. It also has rights to the water it has trapped behind the dam.
Trent Clark, a Monsanto spokesman in Soda Springs, said the company seeks ways to eventually resume the flow of snowmelt and rain from its waste rock dump into Sheep Creek. The springs below the dam continue to flow into Sheep Creek and meet federal clean water standards, he said. The new dam is confining pollution in one place. No water is leaving the containment area, Clark said.
IDEQ officials plan to visit the site in a few weeks to ensure that Monsanto’s dam does not significantly reduce water flows into the Blackfoot River. IDEQ Regional Administrator Bruce Olenick said his department hopes Monsanto’s dam is an interim measure that will be replaced by a long-term remediation plan.
Monsanto, the J.R. Simplot Co. of Boise, and Agrium Inc. of Canada own and operate phosphate mines and processing plants in the phosphate-rich region of Idaho near the Wyoming border. Selenium pollution began killing hundreds of livestock in the 1990s, including 18 cattle last August.
The phosphate companies and the federal government are faced with the daunting challenge of restricting natural contaminants unearthed after a century of open pit mining while protecting water supplies in Idaho, an agricultural state dependent on large volumes of water to grow its crops.