COMMON
QUESTIONS &
ANSWERS
|
|
|
Volume 4, Number 2 (October 1999)
|
Q: |
Where is the water coming from? |
|
A: |
The water is naturally
occurring groundwater. It started flowing back into the area
in 1982 when the central pump station in the Kelley Mine was
turned off. For nearly a century before 1982, groundwater under
the Butte Hill had been constantly pumped to the surface to allow
for mining.
This pumping created a vast cone-shaped area underground that
was kept unnaturally dry. The bottom of the Berkeley Pit lay
near the bottom of this dry area. When the pumping stopped, the
Pit started working like a big sink, drawing water toward it
from all directions.
Back to top |
|
Q: |
Why is the water polluted? |
|
A: |
The water in the Berkeley
Pit is a good example of acid mine drainage, which is mainly
caused by the high sulfur content in the rock in the Butte Hill.
The sulfur reacts with air and water to become sulfuric acid.
As this acidic water flows through the underground mine workings
and rock fractures, it eats away at the metals in the rocks and
dissolves them into the water.
Back to top |
|
Q: |
When will the water be pumped
and treated? |
|
A: |
Some pumping and treating
is underway. In April 1996, water flow into the Pit was reduced
by about half when a surface stream called Horseshoe Bend started
being diverted. Horseshoe Bend water is treated with lime and
pumped up to Montana Resources' (MR's) tailings pond north of
the Pit. From there, some of the water is piped down to MR's
concentrator for reuse. To date, more than 6 billion gallons
of Horseshoe Bend water have been kept out of the Pit.
As for the water in the Pit, pumping and treating must start
before the Pit water level - OR the water level in surrounding
mine shafts and monitoring wells - approaches 5,410 feet above
sea level. If present trends continue, the water will approach
that elevation around 2021.
Back to top |
|
Q: |
What assurances are there that
a treatment plant will be ready to go when it’s needed? |
|
A: |
Design for the treatment
plant must begin eight years before the water is due to approach
5,410, and the plant must be ready to go four years before it's
needed. Based on current water flows and monitoring data, plant
design should start around 2013, with plant completion around
2017.
But each year, water level changes are reviewed and the timeline
is adjusted accordingly. Updating the timeline is part of the
official Record of Decision (ROD) that spells out the treatment
requirements. This decision was issued in September 1994 by the
U.S. Environmental Protection Agency (EPA) and the Montana Department
of Environmental Quality (MDEQ).
Back to top |
|
Q: |
How will the water be treated? |
|
A: |
That decision is not yet
final. Right now, the only proven, cost-effective treatment method
is adding lime. Lime would clean the water by reducing its acid
content and pulling out the metals. But this process would generate
500 to 1,000 tons per day of heavy metal sludge, creating a huge
waste disposal problem.
Several other water treatment technologies are under development.
It is hoped that by the time plant design must start, one or
a combination of new treatment methods will be proven effective
on a large scale.
Back to top |
|
Q: |
Why postpone additional treatment
until the water approaches 5,410-foot elevation? |
|
A: |
After years of study,
EPA and MDEQ determined that the water does not pose a threat
to human health or the environment as long as it is kept below
the 5,410-foot level. Officials are confident that the contaminated
water in the underground workings will continue to flow toward
the Pit and stay there.
Potential advantages to postponing treatment include the following:
1) It reduces project costs for operation and maintenance of
a treatment plant; 2) It allows time for new treatment technologies
to be perfected, and 3) It may lead to improved water quality.
Some scientists believe that letting the water rise to maximum
safe levels will eventually lower its acid and metals content
by reducing the amount of sulfur-bearing rock that’s exposed
to air.
Back to top |
|
Q: |
What would happen if the water
were to rise above 5,410? |
|
A: |
Above 5,410, the water
would not flood Butte by coming up over the rim of the Pit onto
Continental Drive. The rim's elevation, at its lowest point,
is about 5,510, some 100 feet higher. But above 5,410—scientists
believe at about the 5,460-foot level—the water could begin to flow
away from the Pit into the cracks and crevices of the groundwater
system below the surface, potentially harming the water quality
of local wells and Silver Bow Creek.
Back to top |
|
Q: |
Who is responsible for treating
the water? |
|
A: |
The Atlantic Richfield
Co. (ARCO), which bought out the Anaconda Co. in 1977, and Montana
Resources (MR), the company now mining in the Continental Pit
adjacent to the Berkeley, are responsible, along with four other
entities affiliated with MR–Asarco, Inc.; AR Montana Corp.;
MR Inc., and Dennis Washington. If they fail to pump and treat
the water to keep water levels below 5,410 feet, the U.S. government
(EPA) can take over the project and charge these companies up
to three times the project cost.
Back to top |
|
Q: |
What's happening in the meantime? |
|
A: |
The entire mine-flooding
system is being monitored to track water movement and water quality.
Water levels are measured every month in the Pit and in 13 mine
shafts and 58 monitoring wells. Water quality is analyzed twice
a year.
The monitoring program keeps tabs not only on the East Camp groundwater
system centered around the Pit, but also on water movement in
the West and Outer camps, generally west of the Pit. If the monitoring
data reveal that water levels are rising faster than expected,
the responsible companies will be required to take the necessary
actions sooner than planned.
Back to top |
|
|
