COVERS FOR MINE WASTE DISPOSAL FACILITIES By Andy Robertson and Shannon Shaw
Review of Cover Purpose Access Physical Isolation Erosion Protection Vegetation Establishment Oxygen (oxidation) Control Infiltration (leaching) Control
Soil Covers Types of Covers: Simple –Permeability depends on grain size –Compaction –Oxygen diffusion depends on moisture content Compound Complex –Variable –Multi-layered waste low density high density waste moisture
Grey Eagle Tailings Cover
Trends in Cover Design Infiltration barrier design for wet climates (water barrier) Evaporation enhancing designs for dry climates (water balance/store and release) Thick HDPE geomembrane covers to resist disruption
Typical comparison of alternative covers
mm
Dry Cover Costs Oxygen Control Migration Control Simple Covers –Soil covers Complex Covers –Multiple soil –“Cefyl” –Clay layered –Geomembrane* * Perpetual 50 year intervals ~22% of present value hence long term fund $ /tonne $2 - $6/m 2 or $ /tonne waste rock $20 - $30/m 2 Or $ /tonne waste rock
Water Cover Costs New Rock Waste –In natural water bodies Haulage costs –In man-made impoundments $ $ haulage costs Old Rock Waste –With treatment of storage products –>$ $4.00/tonne
Suitability of Cover Types
High Risk Elements of Cover Performance
Minimizing Risk of Cover Failure 1. Materials –Maximize use of natural, durable materials –Minimize use of geosynthetics which deteriorate –Rip-rap control of erosion in dry climates 2. Climate In dry climates: –consider evaporative cover designs –increase use of rip-rap for erosion protection –provide for sedimentation control In wet climates: –consider infiltration cover designs –consider water covers
Minimizing Risk of Cover Failure 3. Biota –Beaver (beaver control or wide channels) –Burrowing animals (bio-intrusion layers) –Ants & insects (bio-intrusion layers) –Anthropogenic activity (institutional control) –Roots (control vegetation species) 4. Monitoring & Maintenance –Erosion –Settlement –Sedimentation (& Glaciation) –Biotic factors (fauna, flora, man)