torch lake: enhanced recovery. 1868 first stamp mill opened on torch lake; 1/3 of lake filled in...
TRANSCRIPT
Torch Lake: Enhanced Recovery
• 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;
• 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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1965 1970 1975 1980 1985 1990 1995 2000 2005
Year
Co
nc.
(u
M C
l, n
M C
u)
Cu
Cl-
Dissolved Cu in Torch Lake
Areal picture of lakewith bathymetric contoursoverlain
Post-miningsediments
Mining-periodsediments
X-rays of Torch Lake sediment coresshowing varves (layers) in stamp sands
Post-mining sediments
Stamp sands
TorchLake
PortageLake
LakeSuperior
Note the high water contentand lack of cohesion in theTorch Lake sediments.
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.
Core 8, 13m
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Cu Conc. (mg/g)D
epth
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Stamp sands
Probableeffectslevel
CanadianInterim SedimentQuality Guideline
Cessation ofmining
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.
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