Newmont showcases environmental success story in Colorado

At a time when the mining industry is coming under criticism for proposing to build a mine near Yellowstone National Park and for a tailings dam spill in French Guyana, it easy to overlook certain advances the industry is making in the area of environmental protection.

On a recent visit to the scenic San Juan Mountains of southwestern Colorado, The Northern Miner witnessed first-hand the success Newmont Mining (NYSE) is enjoying in its effort to remediate several old mine sites. Through its 80%-owned subsidiary, Idarado Mining, Newmont has adopted innovative techniques aimed at reducing the amount of metallic pollution discharged from these past producers into the San Miguel River and Red Mountain Creek.

The production history of the Telluride region dates back to the past century when silver was mined from high-grade veins. From 1939 to 1978, Idarado (then controlled by Newmont) mined copper, lead and zinc from these veins in the mineral-stained mountains.

The mines eventually became uneconomic and were shut down. Environmental problems then came to light, and in 1983 the state of Colorado filed suit against Idarado under the Superfund Act. The company proposed remedial action to prevent erosion of the many tailings piles. However, this proposal was not accepted by the court, which, instead, ordered Idarado to clean up the water and soil pollution caused by past mining. The price tag for this court-directed program was estimated at more than US$80 million.

The state had determined that zinc levels were too high to sustain aquatic life in the streams, although they posed no health risk to humans. But it soon became clear that past mining practices were not the sole cause of pollution problems. Hydrothermal alteration has been so pervasive around the rim of the Tertiary-aged Silverton caldera that many of the streams in the area literally ran red with iron.

Idarado appealed the court decision, and negotiating committees were then appointed by the state governor to work on a compromise for the remediation plans at Telluride and Red Mountain.

The courts eventually decided that the state had no authority to make Idarado clean up under the Superfund Act. Even so, the company pressed ahead with its own clean-up plan. By 1992, a consent decree and remediation action plan were submitted, which called for the revegetation of the tailings piles and source control of the runoff. Ironically, the court ultimately accepted the same plan Idarado had proposed in 1985.

David Baker, Newmont’s vice-president of environmental affairs, said the original plan had been denied because it was based on techniques that had not been practised before. But persistence paid off, and the consent decree laid the groundwork for these innovative techniques to be used.

For example, Idarado was able to go ahead with its proposed vegetative cap on the tailings pile. This project called for the mixture of hay and manure into the tailings pile to make the vegetative cap, rather than dig up topsoil from the surrounding area to cover the piles.

“The idea was to create the soil out of the tailings material rather than simply cover it with something else,” explained Baker.

According to the remediation plan, the tailings piles were recontoured with a shallow slope to promote water runoff, but not erosion.

The vegetative cap is made by tilling 22 tons of hay and 40 dry tons of manure per acre into the top of the piles. Limestone is added to neutralize acidity. Then 13 species of grasses and flowering plants were sprinkled over the mixture to stabilize the slope and keep the tailings from eroding.

Idarado also turned its attention to reducing zinc emssions into the streams by restricting the likelihood that water would come into contact with tailings. The company built 5-6 miles’ worth of concrete drainage lines that carry water around, and away from, mine dumps and tailings. This 5-year remediation project is already more than half finished.

Our tour of the site showed tailings piles at different stages of development. The Telluride 1-4 tailings pile, about a mile upstream from the ski town of Telluride, features thigh-high grass after only two years of growth, and no sign of erosion. The 70-acre Telluride 5-6 tailings pile, just outside of the city, is in the final stage of construction and will become a large, grassy meadow next year.

Another part of the reclamation involves closing shafts, portals and open stopes in the high country, as well as rerouting water away from waste piles. The company is also remediating several mine portals and waste piles that are not part of its property.

Newmont and Idarado are expected to spend a total of US$17 million on the project. The five years of remediation work will be followed by five years of maintenance and another 10 years of monitoring.

If the methods prove unsuccessful, Idarado is bound by the consent decree to go back and redo the work using other methods. However, water samples already reveal some immediate reductions in zinc loading.

Water samples from the San Miguel River show a 50% reduction in zinc loading, while a 60% reduction is reported from the Red Mountain side (when compared with figures from the same month over the past 20 years).

Newmont, state officials and the local community are unanimous in their acclaim for the project.

“Idarado is becoming a model for dealing with historic mine issues in the West,” said Baker. Indeed, Newmont recently began applying the same techniques of source control to its California Gulch superfund site near Leadville, Colo.