Milltown Dam Removal - Association of Conservation Engineers

Milltown Dam
Removal
Peter Nielsen
Missoula County
Milltown Dam
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Built in 1906-8
1908 flood filled reservoir with
contaminated sediments from upstream
mining and smelting
Timber crib construction, 21 ft hydraulic
height
Hydroelectric – 1.4 MW, unprofitable
Run of the river, no flood control
No-wake restriction, little recreation use
Milltown Dam
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1906-8 – Dam constructed
1908-9 - flood damage, reconstruction
1981 - Arsenic found in drinking water
1983 –federal Superfund site designation
1996 Ice jam/floe polluted river
1998 – Bull trout listed as threatened
2001 – Dam sold to NorthWestern Corp.
2003 – Governor, EPA, DEQ propose
sediment cleanup and dam removal
2006 – Remediation initiated
Why will the dam be
removed?
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Groundwater and
surface water pollution
Fisheries Issues
Electricity deregulation and change in
ownership
Dam safety concerns
Strong public support
Dam was unprofitable and provided little
public benefit
Mullan camp
Before there was a dam, there were two rivers. 186162 winter encampment of Lt. John Mullan at the
confluence of the Blackfoot and Clark Fork..
Dam
Construction
– 1906-8
Dam
construction
Spillway
Powerhouse
“…the dam will be as
complete and strong as it is
possible for human
ingenuity and science to
make it.” A.J. Wethey,
William A Clark
representative.
“…when the last piece of timber is
added to the dam it will be in such
condition that the highest waters ever
known in this vicinity will not affect
it in the least. No expense was spared
in making the dam one of strongest
of its kind…” Plant Superintendent
George Slack
1908 flood
1908 flood
“There is no more danger of the power dam going out
than there is of the mountains washing down the
river…the dam is as firm and solid as can be.”
Charles Marsh
1909 re construction
1908-9 re-construction. Note that the entire toe and
south 1/3 of dam were washed out by the flood. Photo
courtesy Library of Congress
1908 re-construction plans for Clark Montana
Realty Co. Note timber cribs placed on
“Loose Rock Deposit” - Alluvium
Drawdown
Tailings dump of Butte and Boston
Concentrator, along Silver Bow Creek
Colorado Smelting and Refining
Tailings dump - 1906
Colorado Smelting and Refining
Tailings dump - 1906
Opening at W. end of tailings dump,
Colorado Concentrator, Silver Bow
Creek, 1906
Silver Bow Creek Slickens
Clark Fork River - Slickens
Washoe
Smelter Anaconda
Silver Bow Creek Slickens
“Water practically surrounds Milltown, and
yet it has always been a problem here. In
early Milltown there was said to be only
one good well….There were a few other
wells which did not have very good water.
It was thought they were contaminated by
the copper mine residue-laden waters of
the Clark Fork River”
Mildred Dufresne
– from The Story
of Bonner,
Montana
1981 – Arsenic Found in
Water
Cfr superfund
1996 Ice Event
High concentrations of
sediment and copper released
 Fish populations impacted
 County requested evaluation of
surface water impacts and removal
option
 EPA – “We have decided to reexamine our thinking” – ordered
additional feasibility study
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Fisheries
Bull Trout listed as
Threatened in 1998
 Fish mitigation
 became costly for dam’s owner
 Fish Passage evaluated, but very costly and
ineffective
 Northern Pike introduced
in 1990’s
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Change in
Ownership
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1997 – Electricity deregulation
Montana Power sold utility assets
Dam sold to NorthWestern Corp.
NorthWestern brought new
perspective
– Publicly stated support for removal
Public support for
removal
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Clark Fork Coalition campaign -2000
County proposed Two Rivers Restoration
Plan - 2001
Bi-partisan support from elected officials
EPA received more than 10,000 public
comments in support of cleanup and
removal
Dam Safety
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1996 ice event caused concern
2000 – spillway leakage emerged
2001 Part 12 safety inspection found
minimum FERC guidelines not met
2002 - Void found in spillway crest
Public and agency confidence eroded
for alternatives that left sediments and
dam in place in perpetuity
Leak diagram
The health of our families and our wildlife
– these must come first. That is why
tonight, I am announcing that I am placing
the full support of my office behind
removal of the Milltown Dam at Bonner.
It’s simply the right thing to do.
Montana Governor Judy Martz, in her State of the State Address,
January 21, 2003
EPA Objectives
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Restore polluted aquifer
– 4-10 years
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Prevent ice scouring events and potential
catastrophic events that affect downstream
aquatic life
Permanent solution
Meet state and federal water quality
standards – groundwater and surface water
Allow free fish passage
restoration
Artwork courtesy of Clark Fork Coalition