1. COVERS FOR MINE WASTE DISPOSAL FACILITIES By Andy Robertson and Shannon Shaw

2. Review of Cover Purpose Access Physical Isolation Erosion Protection Vegetation Establishment Oxygen (oxidation) Control Infiltration (leaching) Control

3. 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

4. Grey Eagle Tailings Cover

5. 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

6. Typical comparison of alternative covers

8. mm

9. Dry Cover Costs Oxygen Control Migration Control Simple Covers –Soil covers Complex Covers –Multiple soil –“Cefyl” –Clay layered –Geomembrane* * Perpetual replacement @ 50 year intervals ~22% of present value hence long term fund $0.40-0.60/tonne $2 - $6/m 2 or $0.03-0.10/tonne waste rock $20 - $30/m 2 Or $0.33-0.50/tonne waste rock

12. Water Cover Costs New Rock Waste –In natural water bodies Haulage costs –In man-made impoundments $0.25 - $1.50 + haulage costs Old Rock Waste –With treatment of storage products –>$2.75 - $4.00/tonne

13. Suitability of Cover Types

14. High Risk Elements of Cover Performance

15. 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

16. 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)