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In the fall of 1997, Newmont Mining Corporation completed a five-year
Remedial Action Plan (RAP) at its subsidiary Idarado Mining Company in
Ouray and Telluride, Colorado. The project is now in the monitoring-only
phase. The $20 million project consists of remediation of two tailing piles
above Telluride and four on Red Mountain, south of Ouray, as well as the
diversion of water from historic mine waste rock and portals. Results to
date indicate the plan is working as predicted. Under the RAP, agreed to
by Idarado and the State of Colorado in 1992, certain criteria must be
met for plant coverage of the tailing piles, the diversity of species growing
on the piles, and water quality.
The very act of growing plants on mine tailings makes Idarado unusual.
In many cases, historic waste rock and mine tailings are buried to avoid
contact with water, resulting in acid drainage and the leaching of metals.
This method often requires large amounts of soil to be brought in, which
in turn impacts the area where the soil was taken. Under the Idarado RAP,
the tailing was made into fertile ground by the addition of 40 tons per
acre of manure, 20 tons per acre of hay or straw, and limestone. The mixture
was tilled to a depth of 18 inches and planted with a scientifically selected
blend of grasses and flowers. The plants absorb moisture and prevent erosion
of the tailings. The re-vegetation covers 150 acres.
Ed Redente, a professor of rangeland ecosystem science at Colorado State
University, developed the seed mix used by Idarado. “My first reaction
when I saw the site was that it would be difficult to cover with soil.
That led to a different approach - direct re-vegetation. This is the largest
project and the highest altitude where direct re-vegetation has been tried
in Colorado. And it’s the only one that’s come this far,” he says. “We’ve
created a stable tailings environment not subject to wind or water erosion
and not contributing contaminants to air or water. It opens the door in
that it provides an alternative to reclaiming tails and waste where soil
is unavailable or expensive.”
The RAP includes a five-year establishment period, which began in 1998.
In the first two years the plants are watered and fertilized. In the final
three years they are allowed to grow naturally, unless the precipitation
level dips below normal. A ten-year “hands off’ period follows while the
results are monitored.
In addition to re-vegetation of tailing piles, ten miles of concrete
channels are used to divert water off waste rock and tailings from mines
that pre-date Idarado. Shafts and collapsed drifts dot the mountains, allowing
water to seep inside and pick up metals before discharging out of the lower
workings of the mines. The water within the workings has been diverted
to areas with little mineralization and discharged at the Treasury Tunnel
on the Red Mountain side and at the Meldrum and Mill Level tunnels on the
Telluride side. The water is then placed in ponds containing material that
acts as a natural filter for any residual metals. Once the water is filtered,
it is released and becomes groundwater.
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