Data analysis of a high-density polyethylene geomembrane located in Waste Area Grouping 6 at Oak Ridge National Laboratory

The Environmental Restoration Program at Oak Ridge National Laboratory is monitoring the material properties of the High Density Polyethylene (HDPE) cap at Waste Area Grouping 6 for degradation due to exposure to the environment. The material properties of tear resistance, uniaxial yield and break stress, density and carbon black content were within an acceptable range of the minimum average values recommended. The latter three properties did not deteriorate over time when compared to the manufacturer's certificate of analysis. The results of the bent strip test showed failure of all specimens within 170 hours, compared to the recommended time of 1,500 hours without brittle failure recommended by NSF. The Notched Constant Tensile Load test reported transition times of 7 and 8 hours for a passive and active sample of the exposed HDPE liner. The percent crystallinity was found to be within the typical range of 40--60% for 80-mil HDPE; however, samples with high crystallinity, greater than 50%, tend to have poor stress crack performance. This was reinforced by the geomembrane's poor performance in the stress crack resistance tests. As a result of these data, the continued monitoring of the HDPE cap is recommended. Quality control measures must be enacted immediately if a definitive, scientific study is to be conducted that will be beneficial to manufacturers, installers, and users