torch lake: enhanced recovery. 1868 first stamp mill opened on torch lake; 1/3 of lake filled in...
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Torch Lake: Enhanced Recovery
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• 1868 first stamp mill opened on Torch Lake;• 1/3 of lake filled in with stamp sands;• 1968 last stamp mill on Torch Lake closed;• 1972 27,000 gal of leaching liquor spilled in lake;• 1973 fish with tumors found in lake;• 1983 fish advisory posted;• 1983 IJC lists Torch Lake as Area of Concern;• 1986 Torch Lake becomes Superfund site;
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• 1992 EPA completes assessment and formulates remediation plan;• 1997 remediation performed in watershed (Scales Creek);• 1997 Public Action Committee formed;• 1998 fish spawning reef constructed;• 1999-2003 stamp sands on shore covered with top soil;• 2004 remediated shore areas delisted from EPA Superfund list
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Year
Co
nc.
(u
M C
l, n
M C
u)
Cu
Cl-
Dissolved Cu in Torch Lake
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Areal picture of lakewith bathymetric contoursoverlain
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Post-miningsediments
Mining-periodsediments
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X-rays of Torch Lake sediment coresshowing varves (layers) in stamp sands
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Post-mining sediments
Stamp sands
TorchLake
PortageLake
LakeSuperior
Note the high water contentand lack of cohesion in theTorch Lake sediments.
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Water withsuspended clay
Layer of stampsand on top of“recovered” sediment
Brown, post-miningsediments
Stamp sandsunderneath recentsediments
Sediment core from Torch Lakewith mine residues overlaying“fresh” sediments.
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Core 8, 13m
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0 500 1000 1500 2000 2500
Cu Conc. (mg/g)D
epth
(cm
)
Stamp sands
Probableeffectslevel
CanadianInterim SedimentQuality Guideline
Cessation ofmining
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Current Lake Status
• Sediments are accumulating very slowly (~2 mm/yr)
• Copper concentrations remain ~ 2 orders of magnitude above recommended concentrations and 1 order of magnitude above known toxic effects level;
• Some evidence exists of resuspension and mixing of stamp sands into “fresh” sediments.
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Useful Web Sites
http://www.epa.gov/glnpo/aoc/trchlke.html - EPA's web page on AOC, Superfund activitieshttp://www.torchlake.org/index.html - Public Advisory Counsel (PAC) web page http://www.ijc.org/rel/boards/annex2/tables/torchlak.html - IJC web information on Torch Lakehttp://www.epa.gov/glnpo/sediment/realizing2/RR2report.PDF - an
EPA web page on remediation of sites with contaminated sediments