COMMON
QUESTIONS &
ANSWERS
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Volume 1, Number 1 (April 1996)
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Q: |
What is the Critical Water
Level? |
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A: |
The official "Record
of Decision" (called a "ROD"), issued in September
1994 by the U.S. EPA and Montana Department of Environmental
Quality (MDEQ), established the critical water level at 5,410
feet.
According to the agencies, the 5,410' level includes a safety
buffer of at least 50 feet and represents the point at which
the Pit water could potentially seep into Silver Bow Creek or
into the alluvial groundwater aquifer that supplies some local
wells.
The ROD stipulates that the parties responsible for treating
the Pit water—ARCO and Montana Resources—must begin
pumping and treating the Pit water before the water reaches this
critical level. If they don't, they will be fined $25,000 per
day.
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Q: |
Does this Critical Water Level
apply only to the Pit? |
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A: |
No. Pumping and treating
of Pit water must begin when the 5,410-foot level is reached
at ANY of the water-level monitoring sites on the Hill, in what's
called the "East Camp." These sites include the Anselmo,
Granite Mountain, Kelley, Belmont, and Steward mine shafts, as
well as several other monitoring wells established to the south
and the east of the Pit.
Presently, the water level at these sites is now 20-40 feet higher
than the level in the Pit. So, the 5410-foot level should be
reached sooner at these sites than in the Pit, which means water
pumping and treating would begin that much sooner.
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Q: |
When will the Critical Water
Level be reached? |
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A: |
It's impossible to predict
exactly when the water will reach the 5,410-foot mark. Today,
we know the water level in the Pit is 284 feet below the 5,410-foot
mark, and it is expected to take about 25 years, until the year
2021, for the water to reach that critical level.
But over time, things can happen that may affect the prediction.
For example, in 1995, more water flowed into the Pit than was
expected, presumably due to higher than normal rainfall.
Over the next two decades, we have to keep a close watch on the
actual data from the monitoring sites. If the measurements prove
to be different from the predictions, the timeline to build the
treatment plant will have to be adjusted accordingly.
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Q: |
How does the Horseshoe Bend
pumping project affect the water level in the Pit? |
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A: |
Now that the Horseshoe
Bend pumping station is on line, the amount of water entering
the Pit has been cut in half. So, the rate at which the water
level will rise should slow down considerably.
Before the diversion project, 3 million gallons of water flowed
into the Pit from underground aquifers and another 3 million
gallons of surface water flowed in via the Horseshoe Bend "waterfall,"
which was visible from the Pit viewing stand. On April 15, 1996
ARCO and Montana Resources started diverting this surface water
into Montana Resources' tailings ponds.
This action is the first of many that were ordered by the EPA
and the MDEQ as part of the ROD concerning the Pit Superfund
project. The next PitWatch will discuss the Horseshoe
Bend diversion project in detail.
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Q: |
Why wait until the water reaches
the 5,410-foot level before starting the pumping and final treatment? |
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A: |
The main reasons to postpone the construction
of a treatment plant is to allow time for new treatment technologies
to be perfected and to reduce the generation of acid mine drainage
as much as possible.
Right now, the only feasible and proven water treatment method
is hydroxide precipitation, which cleans the water but also creates
a big disposal problem—about 500 to 1000 tons per day of
heavy metal sludge.
A handful of technologies that could both clean the Pit water
and recover the valuable metals are in the development stages.
The theory is that when it becomes absolutely necessary to begin
pumping and treating the water, perhaps one or a combination
of these new technologies will be ready to be applied to such
a large-scale project.
The ROD calls for a reevaluation of treatment technologies to
take place when the water level reaches 5,260 feet, which is
projected to be around 2008. PitWatch will devote
a future edition to potential treatment technologies.
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