Boise, Idaho - 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.

In 2007, the EPA ordered Monsanto to stop releasing selenium-tainted water from South Rasmussen's Horseshoe Dump. Though the company has tried to remedy the problem, it's still violating the federal Clean Water Act, federal officials said.

"The measures they have implemented aren't working," said Eva DeMaria, an EPA enforcement official in Seattle. Monsanto "is aware of our concerns. They are trying to address it."

Asked if EPA plans further action, DeMaria declined comment. "It's under investigation," she said.

In the 1990s, sheep and horses died from selenium poisoning related to mining elsewhere in southeastern Idaho's rich phosphate belt. At least 17 phosphate mines here are now under federal Superfund authority.

Just this May, the Idaho Department of Environmental Quality added Sheep Creek, a Blackfoot River tributary being polluted by South Rasmussen, to its list of waterways that don't meet state standards due to selenium contamination.

State scientists now say at least 15 streams in southeastern Idaho exceed selenium standards, up from six in 2002. Monsanto must satisfy the concerns of federal regulators - and eventually judges, in the event of lawsuits - that operations like Blackfoot Bridge won't exacerbate pollution.

"You're going to have to have assurances that there's not going to be an increase," said Greg Mladenka, a DEQ water quality scientist in Pocatello.

Monsanto lobbyist Trent Clark in Soda Springs, Idaho, said the company has resolved issues raised by two EPA violation notices.

In the latest, from September 2007, EPA inspectors found water containing "very high levels of selenium" flowing from the mine's Horseshoe Dump even in dry weather, "unlawful under the Clean Water Act," the agency said.

Despite Monsanto's efforts, the problems have continued, EPA officials said. Significant concentrations of selenium, cadmium, nickel and zinc continue to be measured downstream.

Monsanto is committed to resolving the issue, Clark said.

"The permit requirements were that Monsanto would leave no selenium problems when we're done mining," he said. "We have not finished our mining in that area, and our commitment is, we will be addressing these issues."

And, he said, Blackfoot Bridge's pollution-control measures will be much improved from South Rasmussen.

"It's a completely different process," Clark said.

Phosphate mined in southeastern Idaho is key to his company's stable of "Roundup Ready" seeds for everything from corn to cotton and sugar beets. The herbicide kills weeds; Monsanto's genetically altered plants survive.

This week, Monsanto reported its fiscal third-quarter profit fell 14 percent and it disclosed plans to cut 900 jobs, after competition from generic herbicides dented Roundup sales.

It's asked southeastern Idaho residents to support its Blackfoot Bridge proposal, urging them to send letters to BLM managers now preparing a draft environmental impact statement, due for release in July. Monsanto employs 700 in the region, with a payroll and benefits of nearly $30 million.

In January 2001, BLM officials who approved South Rasmussen wrote that Monsanto's mine wasn't likely to contaminate surrounding waterways.

"The South Rasmussen Mine site has no perennial streams and limited intermittent drainages that might serve as conduits to selenium transport," BLM officials wrote in their decision. "Monsanto has committed to implement operational practices and best management practices to minimize and control selenium generation."

Asked what went wrong, Bill Stout, a BLM geologist in Pocatello, said problems sometimes occur despite the best intentions of his agency and mining companies.

South Rasmussen, Stout said, was the last new Idaho phosphate mine where only a less-stringent environmental analysis was required; after the livestock were killed in the late-1990s by selenium poisoning, a more rigorous analysis is now mandatory.

"There's never any guarantee," Stout said. "But we do the appropriate analysis, to try and incorporate the newest and best mitigation measures."

The Greater Yellowstone Coalition, which is fighting phosphate mining expansion, said it's reserving judgment on Monsanto's Blackfoot Bridge project until after the BLM analysis is released. The coalition's Idaho Falls director, Marv Hoyt, said he's skeptical of Monsanto's promises.

"This is the not the first time we've been told a phosphate mining company has all the answers," he said.