Diffusion and partitioning of different PFAS compounds through thermoplastic polyurethane and three different PVC-EIA liners

Perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorobutane sulfonic acid (PFBS), 6:2 fluorotelomer sulfonic acid (6:2 FTS), and GenX are tested for diffusion and sorption through thermoplastic polyurethane (TPU) and three ethylene interpolymer alloy (PVC-EIA) liners (EIA1, EIA2, and EIA3) with decreasing ketone ethylene ester (KEE) contents. The tests were conducted at room temperature (23 °C), 35 °C, and 50 °C. The tests show significant diffusion through the TPU as manifested by a decrease in the source concentration and an increase in the receptor concentrations of PFOA and PFOS over time, especially at higher temperatures. On the other hand, the PVC-EIA liners show excellent diffusive resistance to the PFAS compounds especially at 23 °C. At higher temperatures, the diffusion resistance of the PVC-EIA liner with the lowest KEE content, EIA3, was best at 50 °C followed by EIA1 (highest KEE content) and finally EIA2. Sorption tests showed no measurable partitioning of any of the compounds to the liners examined. Based on 535 days of diffusion testing, permeation coefficients are provided for all the compounds considered for the four liners at three temperatures. In addition, the P_g values for PFOA and PFOS are provided for a linear low density polyethylene (LLDPE) and a coextruded LLDPE - ethylene vinyl alcohol (EVOH) geomembrane based on 1246 to 1331 days of testing and are compared to those estimated for EIA1, EIA2, and EIA3.

Effects of perfluoroalkyl substances (PFAS) on antioxidant depletion from a high-density polyethylene geomembrane

To safely contain Per-and Polyfluoroalkyl substances (PFAS) in municipal solid waste landfills and contaminated soil monofills, it is necessary to understand how these substances interact with components of engineered systems designed to contain them. This paper examines the interaction between one of the most critical components of the system: a high-density polyethylene (HDPE) geomembrane. The same geomembrane is immersed in PFAS solution and synthetic municipal solid waste leachate containing PFAS for 2.5 years, and the effects of PFAS on antioxidant depletion time is examined. The geomembrane is incubated in ovens at 85-40 °C to obtain data for Arrhenius predictions at typical landfill temperatures. When exposed to PFAS solution alone, the antioxidant depletion times are smaller than when the same geomembrane is immersed in synthetic municipal solid waste leachate alone. The combination of the two has a synergistic effect which leads to an even greater reduction in antioxidant depletion time for this geomembrane, with results showing a 68% decrease in predicted antioxidant depletion time at a typical landfill temperature of 35 °C when PFAS is present in leachate. This study highlights the need to consider the potential impact of PFAS on the service life of geomembranes used to contain them.

PFOA and PFOS diffusion through LLDPE and LLDPE coextruded with EVOH at 22 °C, 35 °C, and 50 °C

Diffusion of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) through 0.1 mm and 0.75 mm LLDPE and 0.1 mm and 0.75 mm LLDPE coextruded with ethyl vinyl alcohol (denoted as CoEx) at room temperature (23 °C), 35 °C, and 50 °C is examined. These tests had negligible source depletion throughout the monitoring period, indicating limited contaminant partitioning and diffusion through the LLDPE. At 483 days, 23 °C receptor PFOA and PFOS concentrations, c_r, were <8 μg/L (c_r/c_o < 3.2 × 10^-4) for all tests, and at 399 days elevated temperature receptor concentrations were < 0.4 μg/L (c_r/c_o < 1.6 × 10^-5) at 35 °C and <0.5 μg/L (c_r/c_o < 2.0 × 10^-5) at 50 °C for both PFOA and PFOS. LLDPE partitioning coefficient, S_gf was 0.9-1.4 (PFOA) and 2.8-5.3 (PFOS) based on sorption tests at 23 °C. Based on the best estimates of permeation coefficient, P_gCoEx, for CoEx was consistently lower than P_gLLDPE. For PFOA, CoEx had P_gCoEx < 0.26 × 10^-16 m²/s at 23 °C, <11 × 10^-16 m²/s (35 °C), and < 10 × 10^-16 m²/s (50 °C) while LLDPE had P_gLLDPE < 3.1 × 10^-16 m²/s (23 °C), <13 × 10^-16 m²/s (35 °C), and <19 × 10^-16 m²/s (50 °C). For PFOS, CoEx and LLDPE had P_gCoEx < 0.55 × 10^-16 m²/s and P_gLLDPE < 3.2 × 10^-16 m²/s (23 °C), P_gCoEx < 8.3 × 10^-16 m²/s and P_gLLDPE < 40 × 10^-16 m²/s (35 °C), and P_gCoEx < 8.2 × 10^-16 m²/s and P_gLLDPE < 52 × 10^-16 m²/s (50 °C). These values are preliminary and may change (e.g., decrease) as more data comes available over time. The P_g values deduced for PFOA and PFOS are remarkably lower than those reported for other contaminants of concern, excepting BPA, which exhibits similar behaviour.

Representative stress crack resistance of polyolefin geomembranes used in waste management

The decrease in stress crack resistance (SCR) of geomembranes (GMBs) due to physical ageing is examined. It is shown that the SCR of a 1.5 mm high density polyethylene (HDPE) GMB immersed in municipal solid waste (MSW) leachate, deionized (DI) water, and air experienced a decrease to an equilibrium value, denoted herein as SCR_m, in a few months and then did not change for the remainder of a 116-month test. The same GMB was also immersed in basic mining pregnant leach solution (PLS) and brine and a similar decrease in SCR to SCR_m was observed in the first three months. For this GMB, SCR_m was about 50% of the initial SCR value (i.e., SCR_m ∼ 0.5·SCR_o) for all incubation fluids examined. It is then shown that this behaviour is not unique. Seven other high density polyethylene (HDPE) and one blended polyolefin (BPO) GMBs are shown to experience a decrease in SCR to 0.17·SCR_o ≤ SCR_m ≤ 0.56·SCR_o without any evidence of oxidative degradation. The magnitude of SCR_m is shown to be product specific. In contrast, the one linear low density polyethylene (LLDPE) examined exhibited no such physical ageing. The implications for designing with GMBs are discussed.

Analytical study of the performance of a geomembrane leak detection system

The electrical detection of leaks in geomembranes is a method that allows identifying leakage of contaminants in lined facilities (e.g. sanitary landfills, pollutant ponds, etc.). The procedure in the field involves placing electrodes above and below the geomembrane, to generate an electrical current, which in turn engenders an electric potential distribution in the protective layer (generally a clayey soil). The electric potential will be greater in areas with higher current density, i.e. near leaks. In this study, we combined models from the literature to carry out a parametric analysis to identify the variables that most influence the amplitude of the electrical signals produced by leaks. The basic hypothesis is that the electrical conduction phenomena in a liner system could be depicted by a direct current circuit. After determining the value of the current at the leak, we calculated the electric potential distribution according to the model of Darilek and Laine. This enabled analysing the sensitivity of the parameters, which can be useful in the design of landfills and facilitate the location of leaks. This study showed that geomembranes with low electrical resistance (owing to low thickness, low resistivity, or extensive area) can hinder the leak detection process. In contrast, low thickness and high resistivity of the protection layer magnify the leak signal.