GRI GM42: The Next Step in Geomembrane Design — But Only If We Use It Right

For nearly three decades, GRI GM13 has been the benchmark specification for HDPE geomembranes. It was a strong foundation for its time, focusing on UV resistance and general durability in waste containment. But the world has changed. Containment facilities are no longer just landfills; they’re complex, chemically aggressive, and high-risk environments, from tailings to PFAS ponds and salt harvesting pads. That’s why GRI GM42 was developed.

Why GM42 Was Developed

GRI GM42 was introduced to modernise HDPE specifications and address several major limitations in GM13:

1. GM13 only requires one antioxidant test — either OIT or HPOIT — not both.

2. GM13’s Stress Crack Resistance (SCR) requirement of 500 hours is no longer representative of modern resin capabilities , or of what’s needed for high-risk, exposed, or chemically active containment.

3. Manufacturers have learned to “game” GM13. Many now meet it on paper by tweaking stabiliser packages or using partially recycled resin, achieving short-term test compliance but poor long-term performance.

GM42 attempts to fix this. It lifts the bar, introducing enhanced performance indicators that better correlate to real-world longevity.

Key Improvements in GM42

• Dual Oxidative Induction Time (OIT and HPOIT) Both must be met, ensuring the liner can resist oxidation from both thermal and UV pathways.

• Higher Stress Crack Resistance (SCR ≥ 1500 hours) Recognises that SCR controls long-term ductility, and failure here is the leading cause of premature cracking.

• Updated Property Retention Requirements Encourages longer-term performance tracking under thermal and chemical ageing.

• Expanded Testing Framework Introduces accelerated testing protocols to enable enhancing values without adding time to approval processes.

The Problem: GM42’s Accelerated Methods Are Not Yet Proven

While GM42’s intent is sound, its new accelerated ageing test methods aren’t yet fully validated across all labs.

• Correlation between these accelerated tests and traditional OIT/SCR methods is still unproven.

• Designers and asset owners can’t yet compare GM13 and GM42 results one-for-one.

This means designers can, and should, adopt the performance values in GM42, but stick with the proven GM13 test methods until validation data is widely available.

What Can Be Adopted Now

Engineers can apply the spirit of GM42 immediately, even without adopting the full standard:

1. Dual OIT + HPOIT Requirements

2. SCR ≥ 1500 Hours (Minimum)

3. Focus on Resin Quality, Not Thickness Alone

Why This Matters for Containment

For decades, the industry has treated HDPE as “chemically inert.” It’s not.

• Residual stress, oxidation, and chemical attack all converge to degrade liners over time.

• In high-salt, high or low pH, or PFAS environments, this degradation accelerates, even at moderate temperatures.

By adopting the GM42 performance principles, we can finally design containment systems that reflect how liners behave in the field, not just in the lab.

The Way Forward

Until the accelerated methods in GM42 are fully validated, the path is clear:

• Keep using GM13 test methods, but lift the performance values to GM42 levels.

• Mandate dual OIT/HPOIT and SCR ≥1500 hours as the new minimum standard for high-risk containment.

• Reward suppliers using low-stress, high-quality resins that maintain their SCR and antioxidant performance after manufacturing.

GM42 isn’t perfect, but it’s a critical evolution. It is a framework that moves the industry toward durability, traceability, and design accountability. Ignoring it, or continuing to specify GM13 as-is, will only repeat the same failures we already understand too well.