But research now indicates an enormous amount of sediment contaminated by mining wastes is moving downstream, far more than predicted when the combined flows of the Clark Fork and Blackfoot rivers were released for the first time in a century.
“Everyone involved in this project wants to see it as a great environmental success story - and hopefully it will be in the longer term - but there are some short-term negatives that are being glossed over,” said Andrew Wilcox, a geomorphologist at the University of Montana.
The research data come
from scientists at the University of
Montana, the U.S. Geological Survey and
PPL Montana, which owns the Thompson
Falls hydroelectric dam downstream on
the Clark Fork.
For years, the Milltown project's
supporters and opponents argued over its
potential benefits and drawbacks. In the
end, the U.S. Environmental Protection
Agency approved the project, saying the
short-term impact - a potential fish
kill and muddy waters for several years
- was outweighed by the long-term
benefit of restoring the aquifer, the
fluvial ecosystem and fish passage.
But taken together, the latest data
suggest that while the Milltown project
is revitalizing one stretch of the
river, it also is spreading mining
pollution further across the riverine
landscape with uncertain consequences
and financial costs.
Below the dam, downstream metals
concentrations are now as high as those
in Deer Lodge, near where the mining and
smelting pollution originated 100 years
ago in Butte and Anaconda.
At Thompson Falls Reservoir, about 150
miles below the now-drained Milltown
Reservoir, metal concentrations in the
sediment have skyrocketed since the dam
breaching, including a 12-fold increase
in arsenic - a spike that far exceeds
the EPA's worst-case predictions.
UM's tests on toxicity levels of the
downstream metals haven't been
completed, “but I'd be cautious because
these are potentially very toxic
concentrations we're seeing,” said
Johnnie Moore, a geochemist and director
of UM's Center for Riverine Science and
Stream Renaturalization. “I certainly
don't believe anyone is trying to cover
up things, but I think people really
underestimated the complexity of this
river system.”
Russ Forba, the EPA's Milltown project
manager, said significantly more
sediment and metals have been released
than expected, which he attributed to
peak spring flows being slightly higher
and longer than average.
But Forba, Keith Large, Milltown project
officer for the Montana Department of
Environmental Quality, and Peter
Nielsen, environmental health supervisor
for the Missoula City-County Health
Department, said the downstream metals
concentrations pose no risk to human
health or the environment.
“We're not alarmed at all,” said Forba.
The project's standards are based on
concentrations of dissolved metals in
the water rather than the total amount
of metals in the water, suspended
sediment and bedload sediment. Federal
regulations allow Superfund and other
construction projects to temporarily
exceed water-quality standards for
aquatic life, but not for drinking
water.
Forba said additional test results are
expected in September and a public
meeting will be held in October.
He said Superfund officials are trying
to figure out how to limit further
releases before next spring's runoff,
and that preventive measures would be
taken if their costs are reasonable.
Across the United States, a growing
number of large dams have been removed
in the past decade, but the $120 million
Milltown project is considered one of
the most complicated breachings ever
attempted because of the large amount of
pollution bottled up at the confluence
of two rivers.
UM researchers and Superfund officials
agree the contaminated sediment isn't
coming from the Milltown Reservoir
cleanup site, which extends about one
mile upstream of the dam and is
protected by a bypass channel that
diverts water around the most
contaminated sediments in the lower
reservoir.
Instead, the tainted material is being
flushed from the upper reservoir, an
area that project officials expected to
remain stable, but where the riverbanks
have wildly eroded as the free-flowing
Clark Fork River re-establishes its
natural course.
The UM scientists said the movement of
mud and metals confirms that the largest
sediment load ever released by a dam
breaching in U.S. history is under way.
The “EPA can no longer ignore the
overwhelming evidence of uncontrolled
release of hazardous substances,” a
lawyer for PPL Montana told the EPA in a
July 31 letter. “PPLM demands that EPA
undertake immediate actions to limit the
risk of erosion of significant amounts
of impacted sediments from the Milltown
site.”
Gordon Grant, a hydrologist with the
U.S. Forest Service in Oregon and a
nationally known researcher on dam
removals, said he wasn't surprised the
Milltown project proved more complex
than many people anticipated.
“My overall impression of the removal to
date is that the well-intentioned desire
to ‘do something' outstripped some very
real cautions offered by knowledgeable
scientists,” Grant said. “Whether there
will be long-term negative consequences
from the removal and its aftermath
remain to be seen.”
The Milltown project includes removing
2.2 million cubic yards of the
reservoir's estimated 6.6 million cubic
yards of contaminated sediment. The rest
is being left in place: Some sediment in
the lower reservoir is to be contained
by earthen berms, while the upper
reservoir's
3 million cubic yards of sediment is
unprotected.
The project's numerical modeling
predicted the breaching and peak flows
last spring would release about 300,000
cubic yards of clean suspended sediment
from the lower Blackfoot River.
Forba downplayed the likelihood of
significant erosion in the contaminated
upper reservoir, saying it could take
centuries to occur and posed no hazard
to human health or the environment.
But based on USGS data and their own
samples and observations along the Clark
Fork, the UM scientists estimate that
about 600,000 tons of suspended sediment
were scoured this spring from both the
Clark Fork and Blackfoot rivers.
The suspended sediment figure doesn't
include material moving along the
riverbed, so the total sediment load
sent downstream is far higher, the UM
scientists said.
Since early May, university researchers
have taken sediment samples from dozens
of sites in the Clark Fork's main
channel and side channels for 150 miles
below the dam as far downstream as
Thompson Falls.
Results showed arsenic concentrations in
the riverbed were five to six times
higher, copper levels were three to four
times higher, and cadmium, lead and zinc
levels were three times higher in the
Clark Fork's main channel than before
the reservoir was lowered.
The project's general contractor,
Missoula-based Envirocon, and
subcontractor EMC2 in Bozeman used a
one-dimensional model to predict what
would happen when the reservoir was
drawn down and the dam breached.
One-dimensional modeling is a common
approach that looks at down-cutting of a
river's bed, but not at lateral erosion
of a river's banks. Superfund officials
said the modeling's projections were
established before the project started
and were not updated to reflect changes
in the project because it wasn't
considered necessary.
“Sediment transport modeling has a lot
of uncertainty,” Wilcox said. “A
relatively simple model was applied to a
very complex problem. But the first time
I walked that upper reservoir area, it
was obvious to me that the sediment
there was highly mobile and a lot of it
would be scoured once the dam was
breached.”
The UM researchers have focused on the
Clark Fork's main channel so far, but
test results are pending from downstream
side channels, where metals
contamination likely will be higher than
in the river itself, they said.
For several years, the EPA has
contracted with the USGS to monitor the
ground water, surface water and well
water above and below the dam for
suspended sediment and suspended metals.
Forba said arsenic levels slightly
exceeded the project's federal
water-quality standards after the
breaching, but dropped within 48 hours
and have not exceeded the standards
since.
David Schmetterling, a Montana Fish,
Wildlife and Parks fisheries biologist
who is studying the breaching's impact,
said there has been less of an impact on
tagged and caged fish this spring than
in previous years.
In part, the fish escaped harm because
the uncaged ones could move upstream
past the dam site and because the strong
spring runoff lowered water temperatures
and diluted copper contamination.
Doug Martin, an environmental scientist
for the state's Natural Resource Damage
program, said another aerial survey of
the upper reservoir will be completed in
the next few weeks.
He said bank stabilization, revegetation
and other measures starting next year
should slow erosion in the upper
reservoir, as will the state's plan to
remove more than 600,000 cubic yards of
contaminated sediment from that area.
Reporter John Cramer can be reached at
523-5259 or at
johncramer@missoulian.com.