A year after a Forest Service report said the Mike Horse Dam near Lincoln is a "compromised structure" that should be removed from service, the federal agency released on Wednesday six alternatives for dealing with the dam and concerns that it may breach and spew toxic tailings into the nearby Blackfoot River.

The possibilities range from doing nothing to complete removal of the dam and impounded tailings. But whatever option is pursued, it's unlikely that any work will be done this summer, with the plan calling for a final decision on what to do no earlier than August 2006.

"We would like to suggest that it may be feasible to get some dirt turned this year, but that's not likely," said Jerry Meyer, public information officer for the Helena National Forest. "The engineers are telling us we need to clearly decide what route we're going to take and get this designed correctly. We run the risk of environmental problems if we don't do it right."

Matt Clifford, conservation director and staff attorney for the Clark Fork Coalition, said he's pleased with the schedule. His organization has been trying to get the dam removed for decades and was worried when a lack of funding seemed to put the project on the back burner in recent years.

"I was afraid ... that they wouldn't even have a draft out until next fall," Clifford said. "This schedule keeps us on track and keeps things moving. Our goal is to get rid of this once and for all.

"The important thing is that taking out the dam is still on the table. There's an unsafe dam threatening one of our most beloved rivers."

The Mike Horse Dam is part of the Upper Blackfoot Mining Complex, which includes more than 50 acres about 15 miles east of Lincoln. The area was mined intermittently for silver, lead and zinc from 1890 to the 1950s, with the main workings including the Mike Horse, Anaconda, Carbonate, Edith and Paymaster mines.

As part of the ore processing, mill tailings were deposited in Beartrap Creek, which flows into the Blackfoot River. The tailings eventually created the Mike Horse Dam, and discharges from mine adits, as well as the flow over nearby tailings, are significant sources of heavy metals like copper, lead and iron flowing into the headwaters of the Blackfoot.

In 1975, the dam breached, releasing a slew of toxic tailings downstream into the Blackfoot River and killing thousands of fish. The dam, which is on Forest Service land, was repaired by the Anaconda Mining Co., which was bought by Atlantic Richfield Co. in 1977. The Mike Horse Mine itself is owned by Asarco.

The dam was never meant to hold back water, according to Bob Kirkpatrick, an environmental health engineer with the Forest Service in Missoula.

"It was more of a filtering dam intended to kind of leak water out," Kirkpatrick said.

But in the spring, water is seeping out of the dam at anywhere from 400 to 500 gallons per minute, according to the Forest Service study. The report also concluded the dam had several large "voids" or holes and probably couldn't withstand an earthquake. Last year, steady spring rains washed out the road leading to the dam.

"The downside of the schedule is that we have the heaviest snowpack up there that we've seen in recent years, and we seem to be getting some heavy spring rains," Clifford said.

Asarco officials weren't able to be reached for comment Wednesday, but have disputed the Forest Service's version of the dam's stability. The company entered into an agreement with the state to begin cleanup efforts in 1993 and some work has been accomplished, but the company's recent bankruptcy filing made the future of the dam cleanup -- and Asarco's participation -- uncertain.

ARCO may become more involved at the site in the future, according to Forest Service officials.

Alternatives under consideration for the dam include installing a spillway and diversion around the reservoir, which would be a short-term response while a long-term solution is created; stabilizing the dam in place; leaving the dam in place but removing some of the surrounding tailings and diverting water around the dam; partially removing the dam and tailings, storing them in an on-site repository; or total removal of the dam and all of the tailings.

The amount of tailings that would need to be removed hovers around 500,000 cubic yards, according to the report.

The cost of the various options is unknown at this point.

"The next thing we do is an Engineering Evaluation/

Cost Analysis (EECA) that will look at the costs and analyze the alternatives. Then we'll come out with the recommended alternative," Kirkpatrick said. "There will be a comment period for the public and based on that, we'll issue a decision."

The UBMC was listed as a state Superfund site in 1991, and the federal Environmental Protection Agency has made some recent overtures about getting more involved in the cleanup effort, especially in light of Asarco's bankruptcy filing.

Max Dodson, assistant regional administrator for the EPA in Denver, was in Helena last week and encouraged Montana officials to seek federal aid if needed.

"We had a recent conversation with the Forest Service about the Mike Horse, and want to work with them," Dodson said. "We're looking for guidance, what you want from us when these things come up."

Reporter Eve Byron can be reached at 447-4076 or by

e-mail at eve.byron@helenair.com.