COMMON
QUESTIONS &
ANSWERS
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Volume 2, Number 2 (October 1997)
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Q: |
How do the actual data collected
over the last few years compare to earlier computer model predictions? |
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A: |
The September 1994
Record of Decision that spelled out the monitoring and clean-up
requirements for the Pit also contained an estimated timeline
for when the Pit water would reach certain elevations. The timeline
was based on predictions generated by a computer model. As it
turns out, the actual data collected and the computer model predictions
do not match exactly, but they are leading to the same conclusion.
For example:
- The Horseshoe Bend
Diversion Project started two years later than scheduled, so
the current water level is higher than the model predicted it
would be.
- However, now that
the Horseshoe Bend diversion is up and running, quite a bit more
water per day (3.8 million gallons) is being diverted than was
predicted (2.6 million).
- Also, the amount of
water entering the Pit is less than what the computer model predicted
(3 million gallons per day instead of 3.4 million).
What does this mean?
It means that after balancing out the above factors, the computer
model remains pretty accurate, so the timeline for building and
operating a treatment plant stays the same. We'll continue to
compare predictions to reality and keep you posted.
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Q: |
How much water evaporates off
the surface of the Pit? |
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A: |
According to Montana Resources,
about twice as much water evaporates off the surface of the Pit
each year than enters the Pit through rain and snow. About 12
inches of precipitation fall into the Pit each year, and about
23.65 inches evaporate, for an annual net loss from evaporation
of roughly 11.65 inches. This water balance translates into an
annual average of about 20,000 gallons per day of evaporating
water.
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Q: |
Could the Pit ever overflow? |
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A: |
This is one of the most
common questions we receive, as people imagine the water rising
up and flowing out onto Continental Drive. While we can't say
that this could never happen, we can with confidence report that
as long as the water levels in the Pit and the associated underground
workings stay below the Critical Water Level of 5,410 feet, there's
no danger of the Pit overflowing.
The more realistic concern is that, if the water levels were
left unchecked, contaminated water might flow into the alluvial
aquifer under the ground, eventually showing up in nearby wells
and in Silver Bow Creek. Keeping the water levels below the critical
point will prevent this from happening as well. For an explanation
of the underground water flows in the Pit area, turn to the back
page.
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