## 5 Test Results  
Table 2 shows the average values and coefficients of variation (CVs) obtained for each geomembrane test. Since the authors did not have access to the initial geomembrane data prior to exposure, the analysis was based on the values established by the GRI GM13 standard [45] at the time of the geomembrane's installation. This standard is a specification developed by the Geosynthetic Institute (GRI) for the test methods, test properties, and testing frequency for smooth and textured high-density polyethylene (HDPE) geomembranes. It sets minimum values for the physical, mechanical, and chemical properties that the geomembrane must meet or exceed [45]. For all the samples, the average values for tear resistance, puncture resistance, and carbon black content were higher than those recommended by GRI GM13 [45]. The CVs for the density, thickness, tensile strength, and strain are sufficient to account for any difference between the average values from the results and those recommended by that standard. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **SP1** & **SP2** & **SP3** & **GRI GM13** \\ \hline Density [g/cm\({}^{3}\)] & 0.948 (1.1 \(\times\) 10\({}^{-5}\)\%) [(1)] & 0.954 (1.6 \(\times\) 10\({}^{-5}\)\%) & 0.939 (9.6 \(\times\) 10\({}^{-6}\)\%) & 0.940 \\ Thickness [mm] & 2.05 (1.3\%) & 1.87 (3.4\%) & 1.88 (1.6\%) & 2.00 \\ Tensile strength—yield [kN/m] & 39.4 (3.6\%) & 41.2 (4.5\%) & 41.9 (2.4\%) & 29.0 \\ Tensile strength—break [kN/m] & 59.6 (8.0\%) & 54.5 (12.9\%) & 49.4 (27.3\%) & 53.0 \\ Tensile strain—yield [\%] & 16.0 (5.3\%) & 17.8 (4.1\%) & 16.2 (3.2\%) & 12.0 \\ Tensile strain—break [\%] & 789.8 (7.9\%) & 748.4 (10.7\%) & 686.7 (20.8\%) & 700.0 \\ Tear resistance [N] & 316.3 (7.9\%) & 323.6 (3.5\%) & 326.3 (1.5\%) & 249.0 \\ Puncture resistance [N] & 878.4 (1.4\%) & 839.1 (4.6\%) & 847.9 (3.2\%) & 640.0 \\ Carbon black content [\%] & 2.4 (14.8\%) & 2.9 (8.9\%) & 2.9 (8.2\%) & 2.0–3.0 \\ Dispersion of carbon black & Category 1 & Category 1 & Category 1 & (2) \\ SCR [h] & 500 (3) & 120 (9.1\%) & 95 (6.6\%) & 300 (4) \\ Std-OIT [min] & 24.5 (8.6\%) & 7.5 (9.5\%) & 5.5 (12.9\%) & 100 \\ HP-OIT [min] & 195.7 (7.7\%) & 162.8 (5.1\%) & 123.5 (11.5\%) & 400 \\ \hline \hline \end{tabular} \({}^{(1)}\) Coefficients of variation are indicated in parentheses. \({}^{(2)}\) The GRI GM13 standard [45] indicates that the carbon black dispersion for 10 different views should be 9 in Categories 1 or 2 and 1 in Category 3. \({}^{(3)}\) The test was stopped upon reaching 500 h for all the specimens. \({}^{(4)}\) Value indicated in GRI GM13 standard [45] at the time of installation of the geomembrane, before update to 500 h.  
\end{table} 
Table 2: Average values and coefficients of variation from the geomembrane tests. The intrinsic variability of the geomembrane, even within the same batch (SP2 and SP3), contributes to such variations represented by the CVs. All the specimens from all the samples were categorized as Category 1, according to ASTM D5596 [76]. However, for SCR (with the exception of SP1), Std-OIT, and HP-OIT, the CVs do not account for the difference between the average values of the results and those recommended by the GRI GM13 standard [45]. It is important to note that the geomembrane was installed in 2009 (SP2 and SP3) and 2013 (SP1--raising). At these times, the minimum recommended SCR value according to the standard was 300 h, and there are no records of changes in the tensile strain or OIT values. High values for the CVs (greater than 20%) were observed for tensile strength and strain at break. These elevated values are attributable to an outlier in the dataset. Excluding this outlier would reduce the respective coefficients of variation from 27.3% to 16.3% and from 20.8% to 13.7%. While still significant, such magnitudes are justifiable, as samples exposed to weathering typically exhibit greater variability in durability test results [44; 46].