COMMON
QUESTIONS &
ANSWERS
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Volume 6, Number 2 (FALL 2001)
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Q: |
Is the water level in the Pit
rising according to predictions made in 1994? |
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A: |
No. Since Montana Resources suspended mining
June 30, 2000, more water has been entering the Berkeley Pit
than expected. The extra water - less than 3 million gallons
a day - is coming from the Horseshoe Bend flow, which had been
diverted (since 1996) from the Berkeley Pit under an EPA order
to reduce the rate of rise. Until a facility is built to treat
the Horseshoe Bend flow, the water level in the Berkeley will
be rising faster than was originally predicted in 1994.
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Q: |
How much faster is the water
level in the Pit rising since mining was suspended? |
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A: |
In the fifteen months prior to June 30, 2000,
the water level in the Pit climbed about 14 feet, or about one
foot per month. During the fifteen months since the mine closed
until September 30, 2001, the water level in the Pit has gone
up almost 26 feet, or about 1.5 feet per month.
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Q: |
If more water than expected
is flowing into the Berkeley Pit, will the Critical Water Level
be reached sooner? |
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A: |
Yes. Every year, ARCO and Montana Resources update
the computer model used to estimate the timeline for reaching
the Critical Water Level of 5,410' above sea level. The most
recent update now predicts the water level in the Anselmo shaft
(the highest monitoring point in the system) should reach 5,410'
in about 2018, about three years sooner than originally expected.
That means design work for a facility to treat Berkeley Pit water
will have to start as early as 2010, with construction complete
by 2014.
The new target dates are based on two important assumptions:
1) that mining does not start again before 2018, and 2) that
treatment of Horseshoe Bend water will start in July 2003. If
these two things don't happen, the timeline to reach the Critical
Water Level will be revised again.
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Q: |
If a facility is built by 2003
to treat Horseshoe Bend water, could the same plant eventually
be used to treat Berkeley Pit water? |
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A: |
Yes. If the mine doesn't re-open, the Horseshoe
Bend water treatment plant will have to be built and operating
by 2003 (see back page). In their current plans, ARCO and Montana
Resources have indicated that this same facility will have the
capacity to also treat the water from the Berkeley Pit - starting
in 2018 or whenever the water in the monitoring wells approaches
the Critical Water Level of 5,410'.
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Q: |
Is there a difference between
the water quality of the Berkeley Pit water and the Horseshoe
Bend water? |
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A: |
Yes, the chemistry of the Berkeley Pit and
the Horseshoe Bend water is different. Recent measurements showed
the Horseshoe Bend water has a pH ~3.2, has a copper content
of 70 ppm (parts per million), and has Total Dissolved Solids
~6500 ppm.
By contrast, the Berkeley Pit water is more
acidic, with a pH ~2.6, has more than twice as much copper, 170
ppm, and has twice as many dissolved minerals, with Total Dissolved
Solids ~12,000 ppm.
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