Presentation on theme: "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."— Presentation 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; ,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; stamp sands on shore covered with top soil; 2004 remediated shore areas delisted from EPA Superfund list
Dissolved Cu in Torch Lake
Areal picture of lake with bathymetric contours overlain
Post-mining sediments Mining-period sediments
X-rays of Torch Lake sediment cores showing varves (layers) in stamp sands
Post-mining sediments Stamp sands Torch Lake Portage Lake Superior Note the high water content and lack of cohesion in the Torch Lake sediments.
Water with suspended clay Layer of stamp sand on top of “recovered” sediment Brown, post-mining sediments Stamp sands underneath recent sediments Sediment core from Torch Lake with mine residues overlaying “fresh” sediments.
Stamp sands Probable effects level Canadian Interim Sediment Quality Guideline Cessation of mining
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 - EPA's web page on AOC, Superfund activities - Public Advisory Counsel (PAC) web page - IJC web information on Torch Lake - an EPA web page on remediation of sites with contaminated sediments