Mining Tailings Pond &
Heap Leach Pad Liner System
Engineered geosynthetics solutions combining HDPE geomembrane, LLDPE liner, nonwoven geotextile,
and geocomposite drainage to contain acid mine drainage and recover precious metals safely.
Mining operations generate vast quantities of tailings and process solutions that must be contained to prevent acid mine drainage, heavy metal leaching, and cyanide contamination of the surrounding environment.
The mining industry presents some of the most challenging containment scenarios in geotechnical engineering. Tailings ponds store the fine-grained waste material remaining after ore processing, which may contain elevated concentrations of heavy metals, sulfides, and process chemicals. Heap leach pads are engineered platforms on which crushed ore is stacked and irrigated with acid or alkaline solutions to dissolve target metals; the pregnant leach solution (PLS) must be collected with near-perfect efficiency to recover the dissolved metals and prevent environmental contamination.
The consequences of liner failure in mining applications can be catastrophic. Acid mine drainage (AMD) from sulfide-bearing tailings can persist for centuries, rendering groundwater and surface water bodies uninhabitable for aquatic life. Cyanide solutions used in gold heap leaching are acutely toxic to wildlife and humans. High-profile tailings dam failures — including the Brumadinho disaster in Brazil (2019) and the Mount Polley failure in Canada (2014) — have focused intense regulatory and public scrutiny on the integrity of mining containment systems.
Modern geosynthetics-based liner systems for mining applications are engineered to address these challenges through a combination of chemical resistance, mechanical robustness, leak detection capability, and long-term durability. The selection of liner materials must account for the specific chemical environment (pH, oxidizing potential, solvent content), the mechanical stresses imposed by ore stacking and equipment traffic, the thermal environment (freeze-thaw, solar heating), and the design life of the facility.
"For heap leach pad applications, the liner system must achieve a solution recovery efficiency of 99% or greater to be economically viable and environmentally acceptable. This requires a combination of an impermeable geomembrane, an efficient solution collection system, and a robust leak detection capability."
This solution covers two primary mining containment scenarios: the tailings storage facility (TSF) liner system, designed for long-term containment of tailings slurry, and the heap leach pad liner system, designed for efficient collection of PLS during active operations and closure.
Tailings Storage Facility (TSF) Liner System
The TSF liner system must contain tailings slurry and supernatant water over a design life that may extend well beyond mine closure. The following double-liner configuration is recommended for facilities storing acid-generating tailings or tailings with elevated heavy metal concentrations:
Heap Leach Pad Liner System
The heap leach pad liner system must efficiently collect PLS while withstanding the mechanical stresses of ore stacking (typically 6–15 m lifts), heavy equipment traffic, and the chemical aggressiveness of leach solutions (pH 1.5–2.5 for acid leaching; pH 10–11 for alkaline cyanide leaching). The following configuration is standard for valley-fill or on/off heap leach pads:
Slope Liner Design for Valley-Fill Pads
Valley-fill heap leach pads present particular challenges for liner system design due to the steep slopes (typically 2H:1V to 3H:1V) and the high normal stresses imposed by the ore heap. The critical design consideration is the interface friction between the geomembrane and the overlying drainage/cushion layer: insufficient friction can lead to liner sliding under the weight of the ore, with potentially catastrophic consequences.
Double-textured HDPE geomembrane is specified on slopes to maximize interface friction with both the underlying secondary liner and the overlying geotextile cushion. Interface friction testing (ASTM D5321) must be performed for each specific material combination at the design normal stress, and the liner system must achieve a minimum factor of safety of 1.5 against sliding under both static and seismic loading conditions.
HDPE Geomembrane — Chemical Resistance Champion
HDPE geomembrane is the material of choice for mining containment applications due to its exceptional resistance to a wide range of aggressive chemicals. Extensive immersion testing has demonstrated that HDPE maintains its physical properties after prolonged exposure to sulfuric acid (pH 1), sodium cyanide solutions, ferric sulfate, and a broad spectrum of organic solvents. The chemical resistance of HDPE is attributable to its highly crystalline molecular structure, which limits the diffusion of chemical species through the membrane.
For heap leach pad applications where the liner is exposed to both chemical attack and significant mechanical stress, a 2.0 mm double-textured HDPE geomembrane is the standard specification. The textured surfaces provide the interface friction necessary for slope stability, while the 2.0 mm thickness provides adequate puncture resistance against the angular ore particles in the drainage layer. In particularly aggressive chemical environments (e.g., high-temperature bioleaching operations), HDPE formulated with enhanced antioxidant packages may be specified to extend service life.
LLDPE Geomembrane — Flexibility for Irregular Subgrades
Linear low-density polyethylene (LLDPE) geomembrane offers superior flexibility and conformance compared to HDPE, making it the preferred secondary liner material in applications where the subgrade surface is irregular or where differential settlement is anticipated. LLDPE has a lower modulus of elasticity than HDPE, allowing it to conform to subgrade irregularities without bridging, which is critical for maintaining intimate contact and minimizing leakage through any defects in the primary liner. LLDPE also exhibits superior stress crack resistance, which is important in applications where the liner is subjected to sustained tensile stress at anchor trenches or penetrations.
Heavy-Duty Nonwoven Geotextile — Puncture Protection
The geotextile cushion layer between the ore drainage aggregate and the primary geomembrane is one of the most critical components of the heap leach pad liner system. Ore particles, particularly those produced by blasting and crushing, can have sharp angular edges capable of puncturing a geomembrane under the high normal stresses imposed by the ore heap. A heavy-duty nonwoven needle-punched geotextile with a mass of 600–800 g/m² and a CBR puncture resistance of 6000–8000 N provides effective protection against puncture while also filtering fine particles from the PLS to prevent clogging of the drainage layer.
The geotextile must also be chemically resistant to the specific leach solution used. For acid leach applications (pH 1.5–2.5), polypropylene (PP) geotextile is preferred over polyester (PET) due to PP's superior resistance to hydrolytic degradation in acidic environments. For alkaline cyanide applications, PET geotextile may be used, but should be tested for compatibility with the specific solution chemistry.
Geocomposite Drainage Layer — Leak Detection and PLS Collection
The geocomposite drainage layer between the primary and secondary geomembranes serves the dual function of leak detection and secondary PLS collection. Any leakage through the primary geomembrane is immediately transmitted by the geocomposite to the leak detection sump, where flow rates are monitored. An increase in flow rate above the background level triggers an investigation and repair program. The geocomposite must maintain its transmissivity under the high normal stresses imposed by the ore heap (typically 200–500 kPa at the base of a 15 m ore lift), and must be chemically compatible with the leach solution.
Exceptional Chemical Resistance
HDPE geomembrane withstands sulfuric acid (pH 1), cyanide solutions, ferric sulfate, and a broad range of mining process chemicals without significant degradation over the facility design life.
High Solution Recovery Efficiency
Properly designed and installed liner systems achieve PLS recovery efficiencies of 99%+, maximizing metal recovery and minimizing environmental impact from solution losses.
Real-Time Leak Detection
The geocomposite leak detection layer provides immediate warning of primary liner failure, enabling rapid response and repair before significant environmental impact occurs.
Slope Stability Assurance
Double-textured geomembrane and interface friction testing ensure the liner system remains stable under the high normal stresses and seismic loads associated with large ore heaps.
Reduced Closure Liability
A well-documented, high-integrity liner system with a complete CQA record reduces regulatory risk and long-term closure liability, lowering the financial assurance requirements for mine operators.
Rapid Installation
Geosynthetic liner systems can be installed significantly faster than equivalent clay-based systems, reducing pad construction time and enabling earlier commencement of leaching operations.
Subgrade Preparation for Heap Leach Pads
Subgrade preparation for heap leach pads is particularly critical because the liner system must perform under high normal stresses and potential differential settlement. The subgrade must be graded to the design slope (minimum 2% toward the collection sump), compacted to at least 95% of standard Proctor density, and proof-rolled to identify soft spots. All protrusions greater than 12 mm must be removed or covered with a sand bedding layer. Rock subgrades require special attention: all loose fragments must be removed, and a 150–300 mm sand or soil bedding layer placed to provide a smooth, cushioned surface for the liner system.
Geomembrane Installation in Chemically Aggressive Environments
In mining applications, all geomembrane installation personnel must be trained in the specific chemical hazards of the leach solutions and equipped with appropriate personal protective equipment. Geomembrane panels must be inspected for manufacturing defects before deployment, and any panels with visible defects must be rejected. Seam welding must be performed by certified welders using calibrated equipment, and all seams must be tested by air pressure testing and spark testing. The completed liner system must be inspected by an independent CQA engineer before any ore or tailings is placed.
01
Site Grading & Subgrade Prep
Grade, compact, and proof-roll subgrade; remove all protrusions; obtain CQA approval.
02
Secondary Liner Placement
Deploy LLDPE secondary geomembrane; weld seams; 100% air pressure test.
03
Leak Detection Layer
Install geocomposite drainage layer; connect to leak detection sump and monitoring system.
04
Primary Liner Placement
Deploy HDPE primary geomembrane; weld seams; 100% air pressure and spark testing.
05
Geotextile Cushion & Drainage
Place heavy-duty geotextile; install solution collection pipes and granular drainage layer.
06
CQA Documentation & Approval
Complete CQA report; obtain regulatory approval; commence ore stacking operations.
Applicable Standards
- ASTM GRI-GM13 — HDPE Geomembrane Specification
- ASTM GRI-GM17 — LLDPE Geomembrane Specification
- EPA Method 9090 — Compatibility Test for Wastes and Membrane Liners
- MAC Guidelines — Mining Association of Canada Tailings Management Guidelines
- ICMM Tailings Governance Framework — International Council on Mining & Metals
- ASTM D5321 — Determining the Coefficient of Soil and Geosynthetic Friction