McLaren Tailings Reclamation Project Status July 21,...
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McLaren Tailings Reclamation Project Status July 21, 2011 Tom Henderson, PhD Montana Department of Environmental Quality [email protected]
Transcript of McLaren Tailings Reclamation Project Status July 21,...
McLaren Tailings ReclamationProject Status July 21, 2011
Tom Henderson, PhD Montana Department of Environmental Quality
Tailings, Ore Rock, Alluvial SedimentsEstimated 237,000 Cubic Yards
McLaren Tailings Contribution to Total Loads in Soda Butte Creek
MDEQ Water Quality Restoration Plan for the Cooke City TMDL Planning Areahttp://www.deq.state.mt.us/wqinfo/TMDL/Cooke_City_files/FinalCCTMDL.pdf
Metal Low Flow High Flow Copper 60 - 90 % > 5 %Iron 70 - 95 % 20 - 40 %Manganese 80 - 95 % 20 - 40 %
Metal Low Flow High Flow Copper ? - 90 % ?Iron 25 -30 % 5 - 10 %Manganese 80 - 95 % < 5 %
Monitoring point SBC-2 near Cooke City
Monitoring point SBC-4 near Yellowstone National Park
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TAILINGS
GROUND SURFACE
POORLY GRADED GRAVEL & SAND WITH SILT
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PIEZOMETRIC SURFACE 10/89
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PR89
-13
PR89
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TAILINGS DAM
SILTY SAND WITH GRAVEL
SILTY SAND
SOIL CAP
SEEPS?
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Horizontal Distance in Feet
Tailings Dam StabilityCross-section View
Cross-section from Lovell Parrish, Subsurface Investigation Report, U.S. Bureau of Reclamation, 1990
Previous AssessmentMarginal static stability; material under dam highly susceptible to liquefaction.
Total flow from seeps approx. 40 gpm from 5 seeps in September 2008
Chemical Target Measured FactorIron 0.3 1490 5000Manganese 0.05 19.6 400Aluminum 0.087 13.9 160Copper 0.012 1.86 159Cadmium 0.00033 0.0060 18Zinc 0.15 1.73 12
Tailings Water Quality vs. DEQ Standards
Target and Measured total recoverable metals in mg/LTarget = DEQ-7 aquatic life / human health standardsFactor = Measured / Target
Project Timeline• May 2002: Expanded Engineering Evaluation/
Cost Analysis completed• 2002-2008: Negotiations with EPA for property
purchase• October 2007 Finding of No Significant Impacts issued
by Office of Surface Mining• 2008-2009: Site Assessment/Reclamation Design • October 2009: Invitation for Bid issued • April 2010: Project award to Knife River • June 2010: First construction season • October 2015: Project completion
Project Bid Alternatives(1) Place all wastes in onsite repository
(2) Reprocess tailings at Golden Sunlight Mine in 2011 with remaining mine wastes placed in repository
(3) Reprocess tailings at Golden Sunlight Mine in 2011 and 2012 with remaining mine wastes placed in repository
Project Scope of Work• Excavate mine wastes and contaminated media• Mix quicklime with tailings to stabilize• Operate a construction dewatering and treatment
system• Place mine wastes and contaminated media in a
repository constructed onsite• Reconstruct 2,000 feet of creek channel• Amend cover soils with compost• Grade and revegetate affected areas
Tailings Stabilization
• Mix quicklime with tailings in place below ground surface to minimize lime dust
• Dry wet tailings to promote compaction and structural stability in repository
• Reduce metal mobility
Metals Leaching From TailingsPre and Post Lime Addition
Target and Measured SPLP metals in mg/LTarget = DEQ-7 aquatic life / human health standards
Chemical Target Pre-lime 3 percent limeIron 0.3 24.5 <0.01Manganese 0.05 4.29 <0.001Aluminum 0.087 0.182 0.038Copper 0.012 0.065 0.086Cadmium 0.00033 0.091 <0.010Zinc 0.15 0.23 <0.02
Water Treatment
• Pump groundwater from site margins and beneath tailings
• Apply lime slurry as needed to increase water pH and alkalinity
• Precipitate metals in a constructed sediment basin equipped with filter curtains
Water in Tailings Excavation: July 20,2011
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2009 2010
Tailings
Aquifer
Ground Elevation
Fluid Levels Under Tailings Impoundment 2009 - 2010
Artesian Conditions Below Tailings
Groundwater Pumping Wells
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7 6 307 6 30
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SODA BUTTE CREEK
P IP ING AND ELEC TRICALC ONDU ITS
S TORM WATERRUN ONC ONTROLC HA NNEL
S HE ET P ILINGC UTOF F WA LL
S EDIM ENT DE TE NTION POND #2
S EDIM ENT DE TE NTION POND #1
DE WA TE RI NG CONTROLB UI LDING
Water Treatment System
Stream Reconstruction
• Historical Soda Butte Creek and Miller Creek channels are covered by the tailings impoundment
• Create runs, pools and transitions, and flood-prone areas to enhance streambed and floodplain habitat
• Divert flows between existing Soda Butte Creek and newly constructed Soda Butte Creek in winter 2014
Reconstructed Stream Geometry
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2010 Reclamation Work• Constructed two bridges over Soda Butte
Creek• Installed surface water and sediment control
measures • Salvaged and seeded cover soil• Began repository excavation• Began stabilizing tailings using ALLU system• Placed mine wastes in repository and covered
with temporary liner
Soil Mixing: 2010
August 17, 2010
2011 Reclamation Work• Abandoned plan for offsite hauling• Constructed 2 new piezometers in repository• Deepen western portion of repository approximately
6 feet • Complete water treatment building• Complete sediment pond• Stabilize tailings using ALLU system• Compact mine wastes in repository and cover with
temporary liner
Site Conditions: May 13, 2011
New Piezometer PZ-8
New Piezometer PZ-9
2011 Fluid Level Measurementsin Feet Below Ground Surface
Date PZ-8 PZ-9June 21, 2011 15.6 NDJune 22, 2011 15.7 NDJune 23, 2011 15.8 NDJune 28, 2011 17.7 NDJune 29, 2011 17.9 NDJuly 6, 2011 19.4 NDJuly 7, 2011 ND NDJuly 12, 2011 ND NDJuly 21, 2011 ND ND
New ALLU Mixing Head
Repository Floor: June 30, 2011
Repository Floor: June 30, 2011
Stabilized Tailings: July 20, 2011
Stabilized Tailings: July 20, 2011
Water Treatment Building: June 28, 2011
2011 Project Status• New piezometers indicate adequate separation
to groundwater under expanded repository• Significant improvements in mixing lime into
tailings have occurred in 2011• Stabilization and compaction of tailings in
repository have been successful• Project currently on schedule / ahead of
schedule
