Gas advection-diffusion in geosynthetic clay liners with powder and granular bentonites

Abstract

Gas diffusion and gas permeability tests were performed sequentially on powder and granular partially hydrated needle-punched geosynthetic clay liners (GCLs) over a range of gravimetric water content using a gas flow unified measurement system under 2 kPa and 20 kPa vertical stresses. Most of the changes in diffusion and advection occurred at intermediary levels of saturation or gravimetric water contents where diffusive and advective gas migration in the granular GCL tended to be higher than in the powder GCL. When the GCLs were relatively dry, their gas diffusion and gas permeability remained constant due to the large interconnected air voids present in the bentonites. For relatively wet conditions, the difference in their gas diffusion and gas permeability was minimal as the bentonites developed a relatively uniform gel structure. The results suggest that at a nominal overburden pressure of 20 kPa, GCLs such as the ones studied need to be hydrated to more than 160% gravimetric water content or >80% apparent degree of saturation before gas diffusion and permeability drop to 1.0 × 10−11 m2/s and 2 × 10−13 m/s, respectively.

Clayey Soil Amendment by Hydrophilic Nano Bentonite for Landfill Cover Barrier: A Case Study

“…The values of gas diffusion coefficients at 25 °C for CO 2 and CH 4 are 3×10 -6 m 2 /s and 4×10 -6 m 2 /s respectively. Laboratory gas diffusion coefficient of GCLs was around 1×10 -6 m 2 /s on different confining stresses and about 25% water content (Bouazza et al, 2017;Bouazza & Rahman, 2007).…”

“…The values of gas permeability coefficients at 25 °C for CO 2 and CH 4 are 5×10 -9 m/s and 2.5×10 -9 m/s respectively. Laboratory gas permeability coefficient of different types of GCLs using nitrogen gas varies approximately between 1×10 -7 and 1×10 -13 m/s, depending on applied confining stress and the water content (Vangpaisal & Bouazza, 2004;Bouazza et al, 2017) The coefficient of diffusion of methane is higher than that of carbon dioxide and both are proportionally affected by temperature ( Figure 10). The values of gas diffusion coefficients at 25 °C for CO 2 and CH 4 are 3×10 -6 m 2 /s and 4×10 -6 m 2 /s respectively.…”

Interactions of Per- and Polyfluoralkyl Substances (PFAS) with Landfill Liners

“…Volatile PFAS compounds can be expected to partition to, and migrate more readily in, the gaseous phase at lower water contents than at higher water contents. The heat generated in landfills [71] can result in elevated gaseous flux through even robust bentonite liners [72]. PFAS with increased water solubility (e.g., PFNA, PFBA, PFDA, PFBS, and some precursor FTCAs and FTCSs) will more likely partition into the pore waters of wetter clays and thus be more susceptible to hydraulic transport via advection and diffusion than less soluble PFAS (e.g., PFHxA, PFHxS, PFOA, PFHpA and PFOS).…”

“…The sodium bentonite component of the GCL must perform over a wide range of field conditions, but the hydration of sodium bentonite used in GCL in Australia has been the focus of intense local [72, 88, 89, 92-94, 96-101, 112-120] and international [65,87,90,104,106,108,109,[121][122][123][124][125] research. It is well established that pre-hydration and maintenance of a high hydration state of the sodium bentonite are necessary for optimal attenuation of both liquid and gaseous diffusion [72,112,126] and therefore the presence of an effective barrier against PFAS compounds (Figure 4). A variety of polymer-enhanced sodium bentonites are currently available on the worldwide market, including in Australia [127][128][129][130].…”