Geomembrane Research Articles

Comparison of Volatile Organic Compound Transport in Composite Liners with HDPE and Ethylene-Vinyl Alcohol Co-Extruded Geomembranes

AbstractThis study evaluated migration of five common volatile organic compounds (VOCs) through simulated composite landfill liners that employ a co-extruded geomembrane (GM) with an interior layer...

Antioxidant Depletion and Service Life Prediction for HDPE Geomembranes Exposed to Low-Level Radioactive Waste Leachate

AbstractAntioxidant depletion was evaluated in high-density polyethylene (HDPE) geomembrane (GM) coupons immersed in radioactive synthetic leachate (RSL) representative of leachate in low-level rad...

Reliability Based Approach for the Prediction of Leachate Head in MSW Landfills

The paper presents the reliability-based approach to assess the performance of landfill considering uncertainties associated with the hydraulic properties of various components of the system. A model domain having final cover system and municipal solid waste (MSW) layer is considered as an integrated system for the analysis. Water balance is computed using the Hydrologic Evaluation of Landfill Performance (HELP) model to construct response surfaces for the reliability analysis. The probability of accumulation of leachate head \(({{h}_{ac}})\) at the bottom of the MSW layer above an allowable head \(({{h}_{al}})\) is considered as the criterion for reliability estimates in this study. The results of the analysis are discussed in terms of the reliability index, \(\beta\). The impact of variations in (a) hydraulic characteristics of the various layers (b) defects and placement conditions of geomembrane (GM) on the system performance have been studied. The results reveal that the hydraulic conductivity of compacted clay layer (CCL) of the cover component along with the porosity and saturated hydraulic conductivity of MSW layer are the significant parameters, which influence the reliability. Further, impact of model uncertainty and parametric analysis of significant variables are conducted and the results are discussed.

Provisional Equations for Determining Leachate Leakage Rate through Composite Barriers from Compromised Geomembrane

From years ago to present date the equations available for determining the rate of leachate leakage through composite barriers from geomembrane (GM) failures necessitated the use of graphs to attain the value of one of the terms of the equations for the case where the leachate head is larger than the thickness of the low-permeability soil medium of the composite barrier. This work reveals that the terms requiring graphs can be expressed analytically, which shows a new set of equations that leads to an entirely analytical approach of determining the rate of leachate leakage through composite barriers. The provisional set of equations is principally beneficial when the leachate level is large as against the thickness of the low-permeability soil medium of the composite barrier. This is usually the case when the low-permeability soil medium allied with the GM to form a composite barrier is a geosynthetic clay liner (GCL). Whether the failure in the GM is small or large or where the leachate level on top of the barrier is large as against the thickness of the low-permeability soil layer of the composite system, a provisional equation can be used to determine the leakage rate through the system. Although in such a scenario, graphs are essential in attaining the value of one of the terms of the equations. Therefore, this paper shows that the graphs can be replaced by equations, which proceeds to the generation and utilization of an entirely analytical method of determining the rate of leachate leakage through a failed composite waste containment barrier, irrespective of the leachate level overlying the system.

Optimum Tensile Strength of Geomembrane Liner for V-Shaped Anchor Trenches Using Target Reliability Approach

This paper presents the target reliability based design framework for V-shaped anchored trenches to resist the sliding action and pull-out of geosynthetic liners. V-shaped anchor trenches are subject to various uncertainties arising from inconsistency in parameter estimation, improper compaction of cover/backfilled soils, field construction practices, the assumption of relative slippage at soil-liner interface and invention of new design methods. Therefore, based on the compilation of interface friction angles between different types of geomembranes (GMB) and granular soils according to several published studies, the mean, standard deviation, and coefficient of variation are computed using statistical analysis. Moreover, a framework for reliability based design is presented by considering the unit weights of backfill and cover soil, interface friction angle and allowable GMB tensile force. The optimum allowable GMB tensile force needed to maintain the stability against pull-out failure by targeting various reliability indices is obtained for various design parameters. The obtained results highlight the potential benefits of reliability methods and encourage their implementation during the design of MSW landfills.

Effect of geomembrane colour and cover soil on solar-driven down-slope bentonite erosion from a GCL

The surface temperature of an exposed composite liner consisting of a geosynthetic clay liner (GCL) covered by a black geomembrane (GMB) can routinely exceed 60°C during summer solar exposure before falling to ambient air temperature at night. Observations at the Queen's University Environmental Liner Test Site (QUELTS) have recently shown that the evaporation and cooling of the air space at the GMB–GCL interface causes condensed water to form underneath the GMB. These water drops flow down-slope until they are released onto the top surface of the GCL at points of contact, seams, or changes in geomembrane curvature. An unforeseen consequence of this solar-driven generation and release of distilled water onto the GCL was discovered to be down-slope erosion of bentonite from the GCL. The objective of the current study was to repeat the QUELTS field exposure experiment to confirm whether the immediate covering of the GMB will supress the mechanism of down-slope bentonite erosion through the elimination of the air gap at the GMB–GCL interface and a reduction in thermal cycling. Further, this study examined whether the use of a white-coloured GMB can reduce the time to onset of erosion if immediate cover is not possible. Results confirm that no erosion occurred on the composite liner test section covered by 0.3 m of gravel after the 15 month duration of the study. In contrast, erosion was observed to occur on the exposed white GMB section, but at a slower rate than that observed on the exposed black GMB section. The timely placement of cover soil on the composite liner as per manufacturers' recommendations is therefore the most effective strategy to avoid the issue of down-slope bentonite erosion.

Interface Shear Strengths Between Geosynthetics and Clayey Soils

Interface shear behavior between geosynthetics and clayey soil was investigated by large scale direct shear tests. The interfaces investigated are geomembrane (GM) and clayey soil; GM and geotextile (GT); and GT encased geosynthetics clay liner (GCL) and clayey soil. For GM/clayey soil interfaces, a softer GM resulted in a higher apparent adhesion, and higher water content of the soil yielded lower interface strength. A GM/bentonite interface had a small friction angle of 3 –4° only. For all cases tested, the interface shear strength (τ f) was lower than the shear strength of the corresponding soil (τ fs), and the lowest τ f /τ fs ratio was about 0.55. For GM/GT interfaces, the stiffer a GM, the lower the interface shear strength. Also a GT with a woven slit film layer, which is smoother than a randomly aligned nonwoven fiber surface, had a lower interface shear strength. The moisture content of a cover silty soil layer also had a considerable effect on the interface shear strength. Higher water content of the cover soil promoted soil particles entering the openings of the GT and increased the strength. For GCL/clayey soil interfaces, increase the water content of the bentonite in the GCL, reduced the interface friction angle, but increased apparent adhesion. The ratios of τ f /τ fs was about 0.8–1.0, and it reduced with the increase of the water content of the bentonite and overburden pressure possibly due to migration of water from the GCL to the interface.

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

An overview of the design and performance of geosynthetics in composite barrier systems for biopiles used to remediate hydrocarbon-contaminated soil at Casey Station, Antarctica, is presented. Seven instrumented biopiles were constructed over three field seasons. To minimize the risk of hydrocarbon migration to groundwater, composite barrier systems were used (each using different combinations of geosynthetic clay liners (GCLs), high density polyethylene (HDPE) geomembranes (GMB), and geotextiles (GTXs)). One biopile used a co-extruded geomembrane (HDPE with an ethylene vinyl alcohol (EVOH) core). The liner system was subject to a combination of coupled phenomena that could interact and affect the GMB–GCL composite barrier performance. The exposure conditions involved potential freeze–thaw cycling, hydration–desiccation cycles, cation exchange, direct and diffusive exposure to hydrocarbons. The effect of these phenomena was investigated by monitoring GCL and GMB sacrificial coupons. GCL coupons were placed between the main GCL component and the main geomembrane component of the composite liner and GMB coupons placed between the main GMB sheet and the GTX protection layer. Coupons were exhumed from the biopiles each year. The exhumed GCL field moisture content values ranged from 162% to 22%. After three (3) years in the field, GCL coupons that had undergone at least one hydration/desiccation cycle showed no significant change in swell index values or fluid loss values. The measured hydraulic conductivity of exhumed GCL coupons from Biopiles 1 and 2 (3 × 10−11 m s−1) was within the expected range and not significantly different from the values for virgin GCL. GMB coupons exhumed after three years from Biopiles 1 and 2 showed no significant change in oxidative induction time (OIT), melt flow index or tensile properties. Diffusion tests were performed as an index test for establishing the performance of the GMBs as a diffusive barrier to hydrocarbons, with permeation parameters for BTEX contaminants ranging from Pg = 0.9–9.2 × 10−13 m2 s−1 for the exhumed GMB (with values depending on the contaminant and GMB). These values were similar to the parameters obtained for virgin GMBs and there was no significant change with field exposure, with GMBs appearing to be performing well.

Field and laboratory observations of down-slope bentonite migration in exposed composite liners

GCL manufacturers recommend that composite liners (i.e., a geomembrane (GMB) over geosynthetic clay liner (GCL)) be covered in a timely fashion. This paper highlights the importance of following this recommendation by reporting on significant down-slope bentonite migration first noted at the Queen's University Environmental Liner Test Site (QUELTS) constructed in 2006 (QUELTS I). The down-slope erosion is attributed to thermal cycles that caused evaporation of moisture from the GCL on sunny days (when the black geomembrane heated to 60–70 °C) followed by condensation of moisture on the underside of the geomembrane at night when the geomembrane cooled. The condensed moisture would drip onto the GCL and run down-the slope. Repetition of this process over an extended period of time caused the erosion of bentonite at some locations in all four GCLs examined in the 3.7 years the liner was exposed before the full inspection of the GCL which detected the mechanism. A series of laboratory experiments confirmed that dripping of evaporative water could cause down-slope erosion in relatively few cycles. These tests also identified several GCL products with a high resistance to down-slope erosion prompting the desire to construct a second field study to examine the issue. Thus, in 2012, the liner system was removed and QUELTS II was constructed with a new series of 7 composite liners. This paper highlights the key findings from these studies with particular emphasis on issues of importance to designers, regulators and installers.

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

SummaryOne‐dimensional mathematical models for vapor‐phase volatile organic compound (VOC) diffusion through composite cover barriers are presented. An analytical solution to the model was obtained by the method of separation of variables. The results obtained by the proposed solution agree well with those obtained by a numerical analysis. Based on the proposed analytical model, the VOC breakthrough curves of five different composite covers are compared. The effects of degree of saturation of geosynthetic clay liner (GCL) or compacted clay liner (CCL) on VOC migration in the composite covers are then presented. Results show that the composite cover barriers provide much better diffusion barriers for VOC than the single CCL. The top surface steady‐state flux for a composite barrier, consisting of a 1.5 mm geomembrane (GM) and a 20 cm CCL, can be 8.3 times lower than that for a 30 cm CCL. The surface steady‐state flux for the case with (1.5 mm GM + 6 mm GCL) was found to be 2.3 times lower than that for the case with (1.5 mm GM + 20 cm CCL). The degree of saturation Sr of the CCL has a great influence on VOC migration in composite covers when Sr is larger than 0.5. The steady‐state flux at the surface of GM for the case with Sr = 0.7 can be 1.8 times lower than that for the case with Sr = 0.2. The proposed analytical model is relatively simple and can be used for verification of complicated numerical models, analysis of experimental data and performance assessment of composite cover barriers. Copyright © 2016 John Wiley & Sons, Ltd.

Transient hydraulic behavior of two GMBs–GCLs composite liners

In general, interface transmissivity is obtained based on measurements of the steady-state flow in composite geomembranes (GMBs) – geosynthetic clay liners (GCLs). However, transient flow rate has not been studied prior to this study. It has been already noticed that its consideration can lead to an important increase in predicted effluent volumes penetrating the liner, the subgrade soil and the ground water. The goal of the study presented herein is to study the transient state by quantifing the reduction in flow rate with time for two different composite liners. In these composite liners, a needle-punched GCL was combined to a high-density polyethylene GMB. The first GCL contained granular sodium bentonite and the second GCL contained powdered sodium bentonite. While the GCLs hydrated their water content and deformation were quantified. To this aim, various tests were conducted over various periods of time, corresponding to different flow rate values through the composite liner. Relationships between the flow rate and water uptake of the GCL on one side and swell on the other side are given for both GCLs. The results show that the mass per unit area in addition to the granulometric distribution of bentonite in GCL specimens may affect the hydration process and the flow rate evolution through composite liners. In addition, For both GCLs, the deformation follows the same trend of evolution with water content.

Effect of high temperatures on the physical and mechanical properties of HDPE geomembranes in air

ABSTRACT: The effect of elevated temperatures, particularly between 95 and 115°C as encountered in some geoenvironmental applications, on the physical and mechanical properties of high-density polyethylene (HDPE) geomembranes (GMBs) is examined. Four commercially available HDPE GMBs were incubated in air at temperatures ≥ 85°C. Investigation of the thermograms by differential scanning calorimetry showed a significant change in the polymer morphology with an increase of the incubation temperature and duration, especially at 105 and 115°C. The morphological changes due to annealing involve thickening of the lamella crystals of the polymer and a change in the tie molecules joining the lamella crystals. The effect of annealing was most evident in the stress crack resistance of the GMB incubated at 105 and 115°C prior to polymer degradation. In particular, an increase in stress crack resistance due to annealing could mask the effects of polymer degradation at temperatures above 95°C. Changes in morphology did not affect melt index whose changes were largely attributed to polymer degradation.

Steady-state analytical models for performance assessment of landfill composite liners.

One-dimensional mathematical models were developed for organic contaminant transport through landfill composite liners consisting of a geomembrane (GM) and a geosynthetic clay liner (GCL) or a GM and a compacted clay liner (CCL). The combined effect of leakage through GM defects, diffusion in GM and the underlying soil liners, and degradation in soil liners were considered. Steady state analytical solutions were provided for the proposed mathematical models, which consider the different combinations of advection, diffusion, and degradation. The analytical solutions of the time lag for contaminant transport in the composite liners were also derived. The performance of GM/GCL and GM/CCL was analyzed. For GM/GCL, the bottom flux can be reduced by a factor of 4 when the leachate head decreases from 10 to 0.3 m. The influence of degradation can be ignored for GM/GCL. For GM/CCL, when the leachate head decreases from 10 to 0.3 m, the bottom flux decreases by a factor of 2-4. Leachate head has greater influence on bottom flux in case of larger degradation rate (e.g., half-life = 1 year) compared to the case with lower degradation rate (e.g., half-life = 10 years). As contaminant half-life in soil liner decreases from 10 to 1 year, bottom flux decreases by approximately 2.7 magnitudes of orders. It is indicated that degradation may have greater influence on time lag of composite liner than leachate head. As leachate head increases from zero to 10 m, time lag for GM/CCL can be reduced by 5-6 years. Time lag for the same composite liner can be reduced by 10-11 years as contaminant half-life decreases from 10 to 1 year. Reducing leachate head acting on composite liners and increasing the degradation capacity of the soil liner would be the effective methods to improve the performance of the composite liners. The proposed analytical solutions are relatively simple and can be used for preliminary design and performance assessment of composite liners.

Breakthrough time-based design of landfill composite liners

Breakthrough time based design methods for determining the design thickness of landfill composite liners are proposed. The composite liners consist of either 1) a geomembrane (GMB) and a compacted clay liner (CCL), 2) a geomembrane (GMB), a geosynthetic clay liner (GCL) and a soil liner (SL), or 3) a GCL and a SL. The design methods are based on analytical solutions developed for solute advection and dispersion of leachate contaminants in composite liners. Both solute concentration and solute flux are considered in the analyses. Two dimensionless parameters involving contaminant concentration and contaminant flux are introduced and the design curves are proposed for breakthrough time based design of composite liners. The results obtained by the proposed analytical solutions are in good agreement with the experimental data published in the literature. Illustrative examples are presented to demonstrate the application of the design methods for composite liners consisting of a GMB and a compacted soil liner and those consisting of a GMB, a GCL, and a SL. The effect of leachate head on the design thickness of composite liners was investigated. It is shown that the design methods presented in this paper is easy to be used to design the landfill composite liners in different leachate head cases.

Thermal exposure conditions for a composite liner with a black geomembrane exposed to solar radiation

ABSTRACT: A black 1.5 mm geomembrane (GMB) and geosynthetic clay liner (GCL) liner were placed on both a 3H: 1V (18.4°) slope and a gently sloping (3%) base (latitude 44°34′15″N) and left exposed for 4.7 years. The observed solar radiation, ambient air temperature, temperature at the interface between the GMB and GCL, and temperature at various depths (to 600 mm) in the underlying silty sand soil are reported. The interface temperature was up to 40°C higher than ambient temperature on a sunny day. The difference between interface temperature on the slope and base was minimal near summer solstice and increased significantly earlier and later in the year (except when covered in snow). There was significant variability in GMB and interface temperature depending on the contact conditions between the GMB and GCL. The interface temperatures at wrinkles could be 15°C higher than other locations where there was intimate contact between GMB and GCL. Snow-cover insulated the liner from solar radiation and extreme temperature. These insulating effects were lost on the south-facing slope before the base, subjecting the GCL on the slope to more daily freeze–thaw cycles than on the base. A correlation between the interface temperature, ambient air temperature, and the solar radiation gave good agreement with the observed temperatures. The cycling of interface temperatures is considered to be central to the mechanism of moisture evaporation from the GCL that may cause GCL panel shrinkage and moisture condensation-driven downslope bentonite erosion. Covering the composite liner with a ballast layer as quickly as possible is recommended.

Flow-rate measurements in meter-size multicomponent geosynthetic clay liners

ABSTRACT: To quantify the flow rate through multicomponent geosynthetic clay liners (GCLs), three different meter-sized specimens from different manufacturers were characterized in a dedicated experimental column. This study allows quantification of the interface transmissivity of multicomponent GCLs when the coating or attached film is damaged over an area large enough to make edge effects negligible. For all multicomponent GCLs characterized, the coating or attached film was less than 0.7 mm thick. Steady-state results indicated flow rates ranging from 4.61 × 10−12 to 3.01 × 10−11 m3/s with interface transmissivities ranging from 1.20 × 10−11 to 7.59 × 10−11 m2/s, which are broadly in line with flow rates obtained from conventional geomembrane (GM)–GCL composite liners. Consequently, when the coating or attached film is damaged, the thickness and rigidity of the coating or attached film appears not to affect the steady-state flow rate and interface transmissivity, which leads to a good contact at the interface.

Long-term performance of EPDM geomembrane in El Boquerón reservoir

ABSTRACT: El Boquerón reservoir (Canary Islands, northern hemisphere) is waterproofed with an ethylene-propylene-diene terpolymer (EPDM) geomembrane (GM). To evaluate the durability of EPDM GMs in hydraulic applications, the characteristics of the EPDM GM (resin and additives) installed in the El Boquerón reservoir were followed for over 21 years. The results of this study are presented herein and show that, based on measurements of specimens from the north and south slopes of the reservoir, the orientation of the GM influences its ageing, with the north slope in the coronation or crest area ageing the most rapidly. Over the years, the El Boquerón EPDM GM oxidised, which may be the main cause of crosslinking in the EPDM. In turn, crosslinking could be the mechanism behind some of changes observed in the EPDM GM characteristics over time. In addition, some of the mechanical characteristics of the EPDM GM were influenced by the additives in the formulation; in particular, the loss and oxidation of paraffinic oils. However, despite the age-induced evolution of the mechanical and physicochemical characteristics of the GM, the El Boquerón EPDM GM, after 21 years of exposure, still satisfies the minimum requirements established by French standards for virgin GMs.

Durability of Three HDPE Geomembranes Immersed in Different Fluids at 85°C

Abstract The long-term performance of three different high-density polyethylene (HDPE) geomembranes (GMBs) is investigated at 85°C using immersion tests. By comparing the degradation behavior of the three GMBs in different synthetic leachates, it is shown that different chemical constituents in the leachate affected different stages of the degradation, with surfactant having the greatest effect on antioxidant depletion (Stage I) and salts having the greatest effect on the degradation after antioxidant depletion (Stages II and III). The magnitude of the effect of these chemical constituents differed from one GMB to another. Thus, for the purpose of comparing the relative long-term performance of the three GMBs for municipal solid waste (MSW) landfill applications, the GMBs were immersed in a synthetic leachate (Leachate A), which contained the primary constituents (i.e., salts, volatile fatty acids, surfactant, and trace metals under reduced conditions) present in the leachate from a large MSW landfill lea...

Effect of stress on water retention of needlepunched geosynthetic clay liners

Geosynthetic clay liners (GCLs) are placed at the bottom of waste disposal facilities where they hydrate from the subsoil and eventually from a hydraulic head on geomembranes (GMs) defects. Predicting hydration behavior of GCLs requires knowledge of the water-retention properties of the GCL along wetting paths. Given that GCLs could be subjected to different ranges of vertical stresses that are induced by the weight of the supported waste, the confining stress could affect water-retention properties of GCLs and should be investigated. To do so, a laboratory methodology to establish the water-retention curves (WRCs) of needlepunched GCLs under stress was undertaken. Various constant vertical stresses corresponding to different weights of the supported waste were applied to GCL specimens placed in controlled-suction oedometers. Suction values were selected so as to mimic a wetting path from the initial dry state to zero suction. Suction was controlled by using controlled suction techniques with controlled humidity imposed by a saturated saline solutions and using the osmotic technique with polyethylene glycol (PEG) solutions. Measurements were undertaken on oedometer systems as to apply confining stresses and have been complemented by standard saturated oedometer swelling tests. The data obtained confirm that increasing the stress on to the GCL results in less, albeit faster, water uptake, which could emphasize on recommendations about rapidly covering GCLs after they are placed at the bottom of a waste disposal facilities. Finally, the potential validity of the state-surface concept, which was developed in unsaturated soil mechanics, is discussed using van Guenuchten's and Fredlund and Xing's equations for water retention curves.

An analytical model for volatile organic compound transport through a composite liner consisting of a geomembrane, a GCL, and a soil liner.

An analytical model for volatile organic compounds (VOCs) transport through a composite liner consisting of a geomembrane (GM), a geosynthetic clay liner (GCL), and a soil liner (SL) was developed for the assessment of the performance of this triple liner system. Both advection through the defects of GM and diffusion in the intact GM were considered in the model, and dimensionless analytical solution was obtained. The soil concentration profiles obtained by the proposed analytical solution have a good agreement with those obtained by the finite-layer-based software POLLUTE v7. The effects of leachate head, length of the connected wrinkles, and the interface transmissivity of GM/GCL on the breakthrough curves of the liner system were then investigated. Results show that the 30-year base flux of the liner system for the case with leachate head = 10 m and length of the connected wrinkles = 1,000 m can be over 60 times greater than that of the pure diffusion case. The length of the connected wrinkles of the GM has greater influence on the base flux of the liner system than on the base concentration. The interface transmissivity has negligible effect on the solute breakthrough curves of the liner system for relatively low values of the length of the connected wrinkles (e.g., <100 m). The groundwater protection level achieved by GM/CCL is more effective than that by GM/GCL/SL in the earlier times. However, the steady state base flux for GM/GCL/SL can be seven to eight times lower than that for GM/CCL. The analytical solution can also be used for experimental data fitting, verification of complicated numerical models, and preliminary design of composite liners.