Geomembranes, especially high-density polyethylene (HDPE) geomembranes, play a crucial role in high-risk containment applications such as mining, landfills and tailings dams. They are often considered the backbone of long-term environmental protection for these large-scale projects. However, many industry professionals mistakenly assume that all HDPE geomembranes are identical, as long as they meet standard specifications such as Oxidation Induction Time (OIT), High Pressure Oxidation Induction Time (HP-OIT) and Stress Cracking Resistance (SCR). While these standards are vital for evaluating good manufacturing practices, they are not sufficient to predict the long-term performance of a geomembrane under real-world conditions, particularly in chemically aggressive environments.

The illusion of uniformity

In theory, different geomembranes may appear identical, with similar values on technical data sheets. However, resin formulations, including additives such as antioxidants and stabilizers, vary significantly between manufacturers. Even if two geomembranes meet the same OIT, HP-OIT and SCR standards, their long-term performance under site-specific conditions could be very different. These differences are largely driven by proprietary blends of antioxidants and stabilizers used in manufacturing, which are rarely detailed in technical data sheets, but can have a profound impact on longevity.

Breaking down industry-standard tests

• OIT (Oxidation Induction Time): This test measures the resistance of a geomembrane to oxidative degradation at elevated temperatures. The OIT provides information on the stability of certain antioxidants (such as phenolic antioxidants) within the material under thermal stress. However, this is primarily an indicator of the ability of the geomembrane to resist oxidation under high temperatures and does not take into account chemical exposure over long periods under actual conditions.
• HP-OIT (High Pressure Oxidation Induction Time): HP-OIT is performed at lower temperatures, but under higher pressure than OIT, measuring different antioxidants (such as hindered amine stabilizers or HALS) that may be more volatile at the higher temperatures used in the OIT test. Although it provides essential data on UV resistance and stabilizer performance, like the OIT, it has limitations in predicting how a membrane will behave when exposed to harsh chemicals for extended periods.
• SCR (Stress Cracking Resistance): SCR measures the resin’s resistance to stress cracking, a common failure mode for HDPE membranes. It reflects the quality of the geomembrane at the time of fabrication, but does not assess how it will degrade when exposed to UV, heat or chemically aggressive environments. While SCR is valuable in indicating resin performance, it does not predict longevity when the membrane is placed in actual conditions, especially in high-risk applications.

These tests provide critical information on the initial quality of the geomembrane, but do not guarantee its long-term performance under site-specific conditions, making site-specific testing critical.

The Need for Site-Specific Immersion Testing

For high-risk applications, such as tailings dams or mining containment, standard laboratory tests such as OIT, HP-OIT and SCR only tell part of the story. In chemically aggressive environments-where geomembranes are exposed to low pH, high metal concentrations or extreme temperatures-immersion testing provides a more accurate understanding of how the geomembrane will perform over time.

Thin Film Immersion Testing: A Preliminary Evaluation Tool

Thin film immersion testing exposes geomembrane samples to aggressive chemical environments for short periods, providing a quick comparison of how different materials perform. According to the study “Rapid Test for Evaluation of Geomembrane Durability in Mining Fluids” (Koerner, G. R., et al., 2019), thin-film immersion testing can be effective in evaluating different geomembranes against the actual chemical conditions present at a site. While this test is cheaper and faster than more detailed tests, such as cuvette dipping, it serves as a preliminary step in material selection, rather than a comprehensive prediction of material life.

Bucket Immersion Testing: A More Comprehensive Approach

For long-term performance predictions, bucket immersion testing is recommended. This test involves immersing geomembrane samples in sealed buckets filled with site-specific chemicals for extended periods of time, typically up to 12 months. Samples are periodically removed for testing to evaluate changes in mechanical properties such as tensile strength, elongation and puncture resistance. This method provides a more accurate picture of how a geomembrane will perform over time in its specific application.

While bucket immersion tests are more expensive and time-consuming than thin-film immersion tests, they provide essential information for projects with long service lives (e.g., more than 100 years), such as tailings dams and containment systems in mining. These tests help engineers and asset owners predict service life, reducing the likelihood of premature failure and ensuring that the selected geomembrane can withstand the harsh chemical environment for decades.

Advanced Quality Assurance Tools: HPLC and NMR

Incorporating NMR (Nuclear Magnetic Resonance) and HPLC (High Performance Liquid Chromatography) can play a crucial role in Construction Quality Assurance (CQA) for geomembranes. These techniques are used to perform deformation testing, allowing reverse engineering of geomembrane formulations and ensuring consistency between what is tested and what is delivered to the project.

• HPLC analyzes the concentration of antioxidants and additives, ensuring that the resistance of the geomembrane to oxidation is maintained.
• NMR reveals the molecular structure of the material, which helps to identify potential degradation risks in real applications.

These methods provide a deeper understanding of the additive package and the quality of the resin used in the geomembranes. This is critical in high-risk projects, as it ensures that the material meets long-term containment requirements in aggressive environments. Incorporating NMR and HPLC into CQA ensures that manufacturers are accountable for delivering consistent, high-performance products, reducing the risk of unexpected failures.

Evaluating the Costs and Benefits of Immersion Testing

Site-specific immersion testing, whether thin film or vessel immersion, requires a greater investment in both time and cost. However, in high-risk projects, such as tailings dams or mine containment systems, the cost of premature membrane failure is far greater than the initial testing expenses. Membrane failure can result in environmental disasters, costly cleanups, legal liabilities and regulatory sanctions.
The Global Industry Standard for Tailings Management (GISTM) emphasizes the importance of best practices in membrane selection and testing. Immersion testing should be considered mandatory for any project that is expected to last more than 10 years or involves exposure to low pH, high metal concentrations or other aggressive conditions. In these situations, the long-term financial and environmental benefits of comprehensive testing far outweigh the initial cost.

Moving Forward: Innovation and Education in Geomembrane Testing

Many early geomembrane failures stem from the assumption that all HDPE membranes are equal if they meet industry standard tests. However, education is crucial to address this misconception. Asset owners, engineers and regulators must understand that site-specific testing, whether through immersion testing or advanced analytical tools such as HPLC and NMR, provides a more complete picture of a geomembrane’s actual performance in real-world conditions.
At Atarfil, we believe that promoting more comprehensive testing and adopting advanced analytical tools will reduce the risk of premature membrane failure. By integrating both traditional testing standards and site-specific testing methods, we can ensure that geomembranes not only meet, but exceed performance expectations in even the most challenging environments.