What are the design criteria for selecting suitable geomembrane types and properties to be
used as bottom impervious liners of municipal solid waste landfills, and which lab tests are
needed to be done on geomembranes ?
Design Criteria for Selecting Suitable Geomembranes for Municipal Solid Waste (MSW) Landfill Liners
The selection of geomembranes for bottom impervious liners in municipal solid waste (MSW) landfills is critical to ensuring environmental protection and containment performance. The selection process is based on several design criteria and laboratory tests that evaluate the suitability of geomembranes under field conditions.
1. Design Criteria for Geomembrane Selection
1.1 Material Type
- High-Density Polyethylene (HDPE) – Most commonly used due to high chemical resistance and durability.
- Linear Low-Density Polyethylene (LLDPE) – Offers more flexibility and better elongation properties.
- Polyvinyl Chloride (PVC) – Used in cases requiring high flexibility and lower installation costs.
- Ethylene Propylene Diene Monomer (EPDM) – Suitable for applications needing high flexibility but is less resistant to chemicals.
1.2 Chemical Resistance
- The geomembrane must resist leachate exposure, which may contain organic contaminants, heavy metals, acids, and other hazardous chemicals.
- Compatibility tests should be performed using standard methods like EPA SW-846 9090.
1.3 Permeability and Impermeability
- A low coefficient of permeability (≤10⁻¹³ cm/s) ensures effective containment.
- HDPE is widely used due to its low permeability.
1.4 Strength and Durability
- High tensile strength is necessary to resist stress from waste loading and settlement.
- Puncture resistance is critical to prevent damage during installation and operation.
1.5 Thickness Considerations
- Standard landfill liners typically range between 1.5 mm to 2.5 mm (60–100 mils).
- The required thickness depends on factors like stress conditions, leachate exposure, and site-specific conditions.
1.6 Weatherability & UV Resistance
- If exposed to sunlight during installation or operation, UV-resistant formulations (e.g., with carbon black content of ~2.5%) are necessary.
- Oxidation resistance is also crucial to prevent degradation over time.
1.7 Thermal Properties
- The geomembrane should withstand the temperature variations of the landfill site.
- HDPE is preferred for high-temperature conditions, while LLDPE works better for colder environments.
1.8 Interface Shear Strength
- The geomembrane must exhibit sufficient frictional resistance to prevent sliding failures when placed over compacted clay or geosynthetic clay liners (GCLs).
- The interface shear strength depends on surface texture (smooth or textured).
1.9 Flexibility & Stress Cracking Resistance
- LLDPE and PVC have better flexibility than HDPE, which is beneficial for sites with significant differential settlement.
- HDPE requires testing for stress cracking resistance (ASTM D5397) to ensure long-term performance.
2. Laboratory Tests for Geomembrane Evaluation
To ensure compliance with design criteria, geomembranes must undergo rigorous laboratory testing, including:
2.1 Physical Tests
✅ Thickness Measurement – ASTM D5994
✅ Density Test – ASTM D1505 / D792 (Ensures polymer consistency)
✅ Surface Texture Analysis – For interface friction evaluation
2.2 Mechanical Strength Tests
✅ Tensile Strength & Elongation – ASTM D6693 (Ensures resistance to stress)
✅ Puncture Resistance – ASTM D4833 (Simulates damage during installation)
✅ Tear Resistance – ASTM D1004
2.3 Chemical Resistance Tests
✅ Leachate Compatibility – EPA SW-846 9090 (Determines chemical durability)
✅ Oxidation Induction Time (OIT) – ASTM D3895 (Measures resistance to oxidative degradation)
2.4 Hydraulic & Permeability Tests
✅ Water Permeability Test – ASTM D5887 (Confirms impermeability)
✅ Gas Permeability Test – ASTM D1434 (For controlling methane migration)
2.5 Weathering & Environmental Stress Tests
✅ UV Resistance (Carbon Black Content) – ASTM D4218
✅ Environmental Stress Cracking Resistance (ESCR) – ASTM D5397
2.6 Interface & Friction Tests
✅ Shear Strength Test – ASTM D5321 (For stability on slopes)
Conclusion
The selection of geomembranes for MSW landfill bottom liners must consider chemical resistance, impermeability, mechanical durability, thermal properties, and interface shear strength. HDPE remains the most widely used material due to its superior resistance to chemicals and long-term durability, but alternative materials like LLDPE and PVC may be used depending on project-specific requirements. Comprehensive laboratory testing is essential to validate the performance and ensure compliance with environmental regulations.