McLaren Tailings ReclamationProject Status July 21, 2011

Tom Henderson, PhD Montana Department of Environmental Quality

thenderson@mt.gov

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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TAILINGS DAM

SILTY SAND WITH GRAVEL

SILTY SAND

SOIL CAP

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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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207 6 20

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SODA BUTTE CREEK

P IP ING AND ELEC TRICALC ONDU ITS

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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

Contact:Tom HendersonMontana DEQthenderson@mt.gov(406) 841-5052

Questions