Federal regulators said Thursday an Idaho mine that Monsanto Co. depends on to make its Roundup weed killer has violated federal and state water quality laws almost since it opened, sending selenium and other heavy metals into the region’s waterways.

The Environmental Protection Agency said problems at the St. Louis-based company’s South Rasmussen Mine near the Idaho-Wyoming border were first documented in April 2002. That’s just 15 months after the mine won Bureau of Land Management approval, according to documents released by the EPA to The Associated Press.

More recently, the mine has been unable to stop discharges of heavy metal-laden water from a waste dump, despite BLM conclusions nearly a decade ago that precautions wouldn’t “allow selenium or other contaminants to migrate from the lease.”

Monsanto takes phosphate ore from the mine and turns it into elemental phosphorous, a key Roundup ingredient. Toxic selenium and other heavy metals are also exposed during open pit mining and dumped in waste rock piles, where they can concentrate and be carried away by runoff or natural springs.

Disclosure of South Rasmussen’s problems comes at a sensitive time for Monsanto: It’s seeking federal approval for a new mine nearby, Blackfoot Bridge, to supply the Roundup component once Rasmussen is played out in 2011. But environmentalists contend the company’s assurances that cutting-edge measures will keep naturally occurring selenium from spreading remind them of earlier promises long since broken.

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