An analytical model for vapor‐phase volatile organic compound diffusion through landfill composite covers

Geosynthetics in Antarctica: Performance of a composite barrier system to contain hydrocarbon-contaminated soil after three years in the field

A review of aqueous-phase VOC transport in modern landfill liners

Geosynthetic clay liners (GCLs) are widely used as hydraulic barriers because of their low saturated hydraulic conductivity and sealing capacity. However, with increasing interest in their use as a component of cover systems for landfills as well as in mining applications, the capability of GCLs to minimise gas emissions, when under an unsaturated condition, are of some concern. This research work has been undertaken to enhance general understanding of the unsaturated behaviour of GCLs and specifically, the effectiveness of unsaturated GCLs to minimise gas migration. In this investigation, the hydration (adsorption and desorption) state of bentonite in GCLs was controlled by vapour phase contact with solutions held at various relative humidity (RH) states under stress and no stress conditions. Gas permeability tests were conducted on three GCLs while monitoring gravimetric water content and total suction under different hydration conditions. A gas flow unified measurement system (UMS-G) for sequential measurement of gas diffusion and gas permeability of geosynthetic clay liners (GCLs) was developed and validated both experimentally and numerically. A series of gas diffusion and gas permeability tests were performed sequentially on two partially hydrated GCLs using UMS-G under a range of gravimetric water contents and hydration conditions. An experimental column study was conducted to understand the hydration (due to infiltration of rainfall water), dehydration (caused by solar radiation or heat) and gas flow through a defected geomembrane (GMB)/GCL composite liner where the GMB contains a defect. Results indicated that RH, applied stress, GCL bentonite form (powdered or granular) and the mineralogy of the bentonite component of the GCL, all play key roles in the hydration/dehydration behaviour with time when GCL specimens were in equilibrium with water vapour. The gas permeability was strongly influenced by gravimetric water content, total suction and applied stress. The UMS-G measured GCL gas diffusivity and gas permeability decreased with the increase of water content and applied stress. The differences in the form of bentonite and GCL structures (scrim reinforced vs non-scrim reinforced) had significant effects on the variation of gas diffusivity and permeability. The hydration behaviour of GCL underlying a defective GMB in a model composite liner was largely influenced by the bentonite form of the GCL, applied rainfall amount and rainfall events. Gas diffusion and gas permeability of GCL part of the composite liner and gas leakage rate of defective GMB/GCL composite liner were influenced by average GCL gravimetric water content and average GCL wet surface area. Uniformly hydrated GCL tended to give lower gas diffusion and permeability than non-uniformly hydrated GCL. Gas diffusion coefficient and gas permeability of GCLs were also influenced by wetting and drying cycle due to the formation of cracks in dehydrated bentonite. The results highlighted that the adjacent layers of GCL in cover system should have sufficiently high gravimetric water content to hydrate the total surface area and thickness of GCL uniformly before coming in contact with gas. It also should be ensured that there is enough cover above the GCL to prevent it from subsequent drying. The results presented here can be useful for design engineers and regulatory agencies to improve the design of landfill and mine tailing cover system.

Presented in this paper is the out-of-plane tensile behavior of a variety of geosynthetic clay liners (GCLs). Tensile response curves indicate that GCL strength is largely dependent on the carrier material types from which the GCL is manufactured. Fiber reinforcement effects as well as orientation effects were relatively small for this type of test. The effects of hydration and seams were also assessed. The study shows that GCLs can withstand considerably greater out-of-plane deformation than compacted clay liners (CCLs). Review of the results indicates that GCLs should be considered over CCLs for use as barrier layers where differential subsidence is anticipated.

Composite liners, which typically include a geomembrane, a geosynthetic clay liner (GCL), and a compacted clay liner (CCL), are essential for preventing leachate from contaminating groundwater. The characteristics of geomembrane (GM) holes, such as their size, quantity, and position, introduce significant uncertainties that can affect leakage behaviour and, consequently, pollution risk assessments. This paper introduces a novel method for evaluating leakage through composite liners in landfills, addressing these uncertainties. The study utilises statistical analysis of geoelectric leak detection survey data from China to characterise the uncertainties in the size and quantity of GM holes. A Monte Carlo simulation framework is employed to model the leakage, accounting for the uncertainties in the size, quantity, and position of GM holes. The method’s effectiveness is demonstrated through a case study of a landfill in China, where the simulation results closely match the monitored leakage data. The findings underscore the critical need to consider uncertainties in GM holes for accurate leakage estimation, offering valuable insights for landfill management, especially under the high leachate head conditions often encountered in Chinese landfills.

Geocompostos argilosos para barreira impermeabilizante (GCL, do inglês: Geosynthetic clay liners) apresentaram-se como uma alternativa a Camadas de Argila Compactada (CCL, do inglês: Compacted Clay Liners). Um produto manufaturado apresenta benefícios em comparação àqueles que se utilizam apenas de produtos naturais. Entretanto, um manejo inadequado destes produtos pode fazer com que estes se tornem inaptos a sua utilização. Se tornando, na verdade, um inconveniente onde aplicado. Assim sendo, algumas considerações básicas devem serem levadas em conta quando de sua utilização. Com isto, aspectos como principais benefícios, resultados de pesquisas, particularidades de sua utilização que prolonguem ou afetem a vida útil e desempenho, são discutidas no presente trabalho. Ao final, é realizada uma breve comparação entre as duas técnicas correlatas, GCLs e CCLs, ambas utilizadas como barreiras impermeabilizantes.

Diffusion of volatile organic compounds (VOCs) through elastomeric bituminous geomembranes (BGMs)

The effects on the nature of bentonite, natural sodium, and calcium activated, and of the cation exchange on the diffusive properties of two geosynthetic clay liners (GCLs) were examined. Diffusion laboratory tests were conducted to estimate the diffusion coefficients of 1, 2-dichloroethane (DCA), dichloromethane (DCM), thrichloroethylene (TCE), toluene, and benzene. Both GCLs were needle-punched and came from the same manufacturer. The nature of the bentonite contained in both GCLs was different because a natural sodium bentonite and a calcium activated sodium bentonite were tested. Furthermore, one of the GCLs experienced cation exchange from contact with a synthetic leachate used to generate an increase in its hydraulic conductivity by a factor of 8.5. The objective of this process was to evaluate if an increase in the hydraulic conductivity by cation exchange in a GCL would result in a significant increase in the diffusion coefficients of volatile organic compounds (VOCs). The results obtained for both virgin GCLs were very close to one another. No effect on the nature of the bentonite was observed. An increase in the diffusion coefficient was noticed for the case in which the GCL experienced cation exchange while in contact with a synthetic leachate for DCM, DCA, and TCE at a given bulk GCL void ratio. The largest increase, a factor of 2.6, was observed for TCE. However, this increase in the diffusion coefficient could have been balanced by the decrease in the bulk GCL void ratio from 3.9 to 3. The increase in the diffusion coefficient of VOCs, thus, does not seem to be of concern for the range of GCL hydraulic conductivities generated by cation exchange in this study.

Heat and moisture migration in a geomembrane–GCL composite liner subjected to high temperatures and low vertical stresses

This review synthesises the available published research on interactions of per- and polyfluoroalkyl substances (PFAS) with landfill liners, with the view to inform on the expected behaviour of these persistent environmental pollutants in landfills. The review addresses the nature and significant types of PFAS compounds that are destined for landfills, as well as their by-product. It discusses the known and anticipated interactions with separate landfill liner components, namely geomembranes, geosynthetic clay liners and compacted clay liners. Various water-soluble PFAS are shown to advectively transport through geosynthetic clay liners (GCL) and showcase the limitations of relying on mineral liners alone to retain PFAS. Addition of activated carbon, while increasing saturated hydraulic conductivity, significantly increases PFAS retention by the GCL and reduced PFAS flux to manageable concentrations. An assessment of the relative risk for environmental exposure of different types of PFAS from landfills through interaction with those liner components is achieved with reference to published case studies of PFAS detection in and around landfills from Australia and around the World.

Numerical experiments were conducted to understand the effect of geometric and transport characteristics of a geomembrane-geosynthetic clay liner (GM/GCL) composite liner on gas leakage rate through a circular defect in the geomembrane (GM). The originality of the approach proposed in this paper rests on the use of a new conceptual two-layered system for modeling of GM/GCL composite liners where the interface zone between the GM and geosynthetic clay liner (GCL) has been merged with the GCL cover geotextile and handled as one layer; the GCL bentonite layer was considered the second layer. The role of the carrier geotextile layer was ignored since it can be considered as a no pressure loss layer. Analysis of numerical simulation results shows the existence of a constitutive leakage flow surface which enables evaluation of the leakage flow state for different geometric and transport properties of GM/GCL composite liners. Furthermore, the determined surface was also exploited to evaluate gas leakage rates under the framework of the Forchheimer's analytical solution. The gas leakage rate predictions were found to be in good agreement with experimental results obtained at different GCL moisture content.

Effect of stress on water retention of needlepunched geosynthetic clay liners

A mathematical model for the transport of heavy metal contaminants (HMCs) in a triple-layer composite liner with defective geomembrane under the non-isothermal condition is developed in this study, where the GMB/GCL/CCL (geomembrane, geosynthetic clay liner and compacted clay liner) composite liner is adopted as an example and the Langmuir adsorption model is incorporated. The proposed model is solved by the finite difference approach, and its correctness is validated by comparison with the experimental results, an existing analytical solution and another numerical method. Later, the transport behaviours of HMCs are explored with the established model. Compared with the isothermal condition, the non-isothermal condition enlarges the transport flux, but also reduces the concentration of HMCs. The relative concentration based on the Langmuir adsorption model is higher than that based on the linear adsorption model, which is related to the decrease of the retardation factor under the Langmuir adsorption model. Furthermore, the parametric study shows that when the leachate head ht is between 1.0 and 3.0 m, the defined breakthrough time tb increases by about 1.57 a with the increase of GCL thickness lg by 1 cm, and the tb increases by about 9.07 a with the increase of CCL thickness lc by 0.1 m.

Because of the current need for new landfill sites in Ankara, the suitability of Ankara Clay as a liner material for landfill sites was investigated. A mineralogical and geotechnical database was created by compiling the results of previous tests by the present authors as well as those of tests performed in the present study. The mineralogical properties of the samples were investigated by X-ray diffraction, scanning electron microscopy and methylene blue adsorption. The cation exchange capacities (CEC) of the samples vary from 12 to 35 meq/100 g soil and the dominant clay minerals are illite, smectite and kaolinite. The geotechnical properties of the Ankara Clay samples that were assessed included specific gravity, the Atterberg limits (plastic limit, liquid limit, plasticity index), particle-size distribution, compaction properties (i.e.maximum dry density and optimum water content) and hydraulic conductivity. Because the hydraulic conductivity of the samples was lower than the acceptable limit of 1 × 10−9 m/s, it follows that, from a geotechnical perspective, Ankara Clay is a suitable material for use as a compacted clay landfill liner. The relationships between the mineralogical and geotechnical parameters that were investigated by regression analysis indicated that the hydraulic conductivity of the compacted soil samples decreased with increasing plasticity index, clay content, CEC, smectite content, smectite to illite ratio and decreasing illite content. According to the specifications for field construction of compacted clay liners, Ankara Clay is suitable for compaction in the field.

Numerical analysis of earthquake-induced deformation of liner system of typical canyon landfill