Managing Mine Slimes and Other Lessons Learned Todd
Managing Mine Slimes and Other Lessons Learned Todd Bragdon, CDM Smith Brandon Ball, Parametrix Bill Adams, EPA Region 10 Rod Zion, USACE Seattle Jeff Johnson, US BLM Rich Hamlin, Conti Jack Waite Mine Removal Action April 5, 2012 Introduction Project Team Parametrix / CDM Smith; Engineering Design
U.S. EPA Region 10; Lead Regulatory Agency U.S. Forest Service; Property Owner, Joint Lead Regulatory Agency U.S. Army Corps of Engineers Seattle District; Construction Procurement and Administration Conti; Removal Action Contractor Site Features and 2011-2012 Removal Actions Removal of two tailings piles (TP1 and TP2) and Mill area in alluvial valley Consolidation to two repositories: TP3 and
Borrow Area 2 (BA2) Rehabilitation of Tributary Creek Managing Mine Slimes Jack Waite Mine Removal Action Jack Waite Mine Layout N Tailings Pile TP4 Tailings Pile TP3 Borrow Area 2 Borrow Area 1 Tailings Pile TP2 Tailings Pile TP1 1500-Level Adit and Waste Rock Pile
Managing Mine Slimes Jack Waite Mine Removal Action Tailings Pile 1, Mill Area, & Tributary Creek Mill TP1 Tributary Creek TP-1 (110,000 cy); Mill Area (14,000 cy); Alluvium (2,900 cy) Managing Mine Slimes Jack Waite Mine Removal Action Tailings Pile 2 TP2
TP-2 (15,000 cy Tailings) Managing Mine Slimes Jack Waite Mine Removal Action Materials Management & Restoration (MMR) Issues 2011 MMR Issues Encountered at the Jack Waite Site Difficult material types Additional waste volumes Insufficient borrow soil gradation characterization TP3 alluvial repository configuration Remote high elevation site; limited construction season
Issue Discussion Design approach 2011 construction issue Solutions / lessons learned Managing Mine Slimes Jack Waite Mine Removal Action Difficult Material Types Design Approach Borings and cone penetrometers completed through tailings piles 2011 Construction Issue TP2 slimes encountered in July 2011 Difficult to excavate material Difficult to haul material transportation caused separation of solids / liquids & spills
Solutions / Lessons Learned Temporary stockpile material to dewater, addition of Portland Cement (5%); transportable; achieved good compaction For tailings piles, focus on potential volume of this material Managing Mine Slimes Jack Waite Mine Removal Action Additional Waste Volumes Design Approach Aerial survey / LiDAR data (2-ft. topographic contouring) Test pit and boring extent / depth of mine wastes Mine waste volumetrics developed using CAD 3D Contingency volumes included (~30 Percent)
2011 Construction Issue Additional waste rock volume at Mill Site (34,000 vs. 14,000 cy) Additional tailings volume at TP2 (23,000 vs. 15,000 cy) 2012 concerns with waste volume in Tributary Creek alluvium Solutions / Lessons Learned Flexibility in repository design to allow additional capacity Steep slopes and alluvial interface difficult to estimate Managing Mine Slimes Jack Waite Mine Removal Action Insufficient Borrow Soil Gradation Characterization Design Approach Repository cover / rehabilitation area growth media and fill primarily developed from
Borrow Area 2 Test pits used to estimate depth of borrow soils Field observations / geotechnical data used to evaluate gradation (oversize vs. granular material) Borrow soil volumetrics developed using CAD 3D and gradation 2011 Construction Issue Significantly more oversize material - 19,000 cy vs. 11,000 cy Limited stockpiling areas / double handling in steep terrain Solutions / Lessons Learned
Design approach should use grizzly / screening for oversize rock Managing Mine Slimes Jack Waite Mine Removal Action TP3 Alluvial Repository Configuration Design Approach EE/CA and Action Memorandum included TP2 repository located in Tributary Creek alluvial valley Volume and cost constraints Maximize mine waste in BA2 repository Utilize low permeability cover to reduce infiltration Utilize riprap toe armoring (100-yr event) ; HEC-RAS model 2011 Construction Issue Tailings piping observed
Solutions / Lessons Learned Revised design to include toe drain system Managing Mine Slimes Jack Waite Mine Removal Action Remote High Elevation Site Design Approach Completed design / contracting process in 2010 (utilized $1.2M ARAR funding) Allowed for snow removal in bid for early mobilization Allowed for flexibility in bid for one or two-season construction 2011 Construction Issue Snow plowed in May; heavy precipitation in June; limited site construction until July Solutions / Lessons Learned Field conditions can significantly impact schedule
Consider summer traffic on hauling Managing Mine Slimes Jack Waite Mine Removal Action Questions Managing Mine Slimes Jack Waite Mine Removal Action
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