Geosynthetic Clay Liners Research Articles

Finite difference solution for contaminant transport through a GCL composite cutoff wall-aquifer system considering semipermeable membrane effect

Semipermeable membrane effect is an important factor affecting the contaminant transport behavior through the bentonite-based barriers for waste containment. However, this effect has been ignored in majority of the existing analytical and numerical studies on contaminant transport, although it has been widely demonstrated in laboratory and field tests. Taking into account the semipermeable membrane effect, this study presents a numerical model for one-dimensional contaminant transport through a geosynthetic clay liner (GCL) composite cutoff wall-aquifer system consisting of a bentonite-based wall, a GCL and an aquifer. The finite difference method is used to obtain the solution. The numerical solution is validated against the laboratory experimental data, the existing analytical solution and COMSOL software simulations. A series of parametric analyses are conducted using the proposed numerical solution. The results indicate that the semipermeable membrane effect has a significant impact on the contaminant transport behavior and ignoring this effect can greatly underestimate the contaminant breakthrough time and overestimate contaminant outflow. For the conditions examined in this paper, the inclusion of semipermeable membrane effect results in a 7.1%∼78.6% increase in breakthrough time and a 5.3%∼40.7% decrease in mass flux, and the semipermeable membrane effect in bentonite-based wall, relative to that in the GCL, has greater impact on contaminant transport. The concentration-dependent semipermeable membrane efficiency coefficient ω more significantly slows down the contaminant transport relative to the constant ω, particularly under the conditions of low hydraulic conductivity, low source concentration and low hydraulic gradient. Moreover, it’s important to avoid simultaneous deterioration of both the bentonite-based wall and the GCL, otherwise the breakthrough time of the GCL composite cutoff wall can decrease significantly.

Experimental evaluation on in-soil water migration reducing performance of restraining moisture geotextile (RMG)

Engineering materials such as geosynthetics clay liners (GCL) and gravel layers are effective to cut off the in-soil water migration and have been widely employed to stabilize the moisture content of subgrades. However, the moisture stabilizing performance of GCL or gravel layer is usually compromised due to the complexity of service condition. This paper introduces an engineering material named restraining moisture geotextiles (RMG), which is expected to show low permeability as GCL. With characterization of basic properties of RMG, moisture migration column test of silty soil and test cases with employments of RMG, GCL, and gravel layer are performed, respectively. The temperature and moisture fields of soil columns subjected to a freezing-thawing process are measured, and the capillarity and in-soil water migrating behavior are analyzed. Carbon footprints of GCL and RMG are compared and discussed. Test results show that RMG, GCL and gravel layer are effective to cut off the capillarity, but the gravel layer can result in higher moisture content in silty soil due to the vapor migration and capillary isolation. In conclusion, RMG can be an alternative method with low permeability on reducing the in-soil water migration, and is much lighter and more engery-efficient than GCL.

Evaluating the Performance of Modified Geo-Synthetic Clay Liners

Waste products from human activity must always be controlled. Reusing some garbage is possible. But a lot of rubbish that could be more useful needs to be disposed of to protect the environment. Landfilling is one popular form of disposal. The most frequent issues with landfills are groundwater contamination and environmental deterioration, brought on by rainfall and leachate generated during the breakdown of organic materials. A landfill's liner is crucial to stop leachate migration and groundwater contamination. Since their development in 1986, Geo-Synthetic Clay Liners (GCLs) have gained popularity as a barrier solution for municipal solid waste landfills. In this study, fly ash and Kaolinite, two waste materials, are combined with bentonite in different percentages 10–30% and 50%, respectively to evaluate their potential usage as liner materials. Bentonite, in combination, is anticipated to function as a low permeability, self-healing, hydraulic barrier due to these swelling qualities.

Analytical Solution for Contaminant Transport through a Soil–Bentonite (SB)/Geosynthetic Clay Liner (GCL)/Soil–Bentonite (SB) Composite Cutoff Wall and an Aquifer

This study develops a one-dimensional analytical solution for contaminant advection, diffusion and adsorption through a soil–bentonite (SB)/geosynthetic clay liner (GCL)/SB–aquifer composite cutoff wall (CCW) system. The solution agrees well with an existing double-layer model. Adopting toluene as a representative contaminant, using the present solution, the analysis systematically investigates the impact of hydraulic gradient (i) and the hydraulic conductivities of GCL (kgcl) and SB (ksb). The results show the following: (1) Increasing i from 0.1 to 1 reduces the concentration breakthrough time (tcb) from 20 to 11 years and mass flux breakthrough time (tfb) from infinite to 11 years, indicating lower i significantly extend both tcb and tfb, which is crucial for optimizing CCW barrier performance; (2) lowering kgcl from 5.0 × 10−11 m/s to 1 × 10−12 m/s and reducing ksb from 1.0 × 10−9 m/s to 1.0 × 10−11 m/s, would increase the tcb by 36% and 100%, respectively. It demonstrates that reducing kgcl and ksb could enhance barrier performance. (3) To achieve equivalent barrier performance, soil–bentonite cutoff wall (SBCW) requires greater thickness compared to SB/GCL/SB CCW, indicating that GCL reduces the required amount of bentonite; and (4) CCWs can use SB with lower adsorption capacity to achieve equivalent performance, further reducing bentonite requirements. The present solution can aid in the design and optimization of GCL-enhanced CCWs.

Real-time ultrasonic water level IoT sensor for in-situ soil permeability testing

Soil permeability tests require a time series of water level measurements to determine system losses, including both infiltration and evaporation. Laboratory measurements of flow are standardised by international regulations such as ASTM International, ISO or UNE, but field measurements are not as well described and in some cases may require definition and specification of test conditions. This is the case for geosynthetic clay liner (GCL) products, where permeability is assessed by a laboratory measurement using a flexible wall permeameter as defined in standard test method D 5887-04. This method is not able to evaluate the performance of such products in the field and therefore cannot guarantee their ability to be used for the repair of landfill liner overlays. For this reason, we have defined a field test in a confined steel ring and developed a real-time ultrasonic IoT device to evaluate water losses over a period of time. The test method was applied in Mallorca (Spain) and as a result the quality of a landfill cover repair solution was evaluated, the corresponding civil works were carried out and the basis for future field measurements of soil permeability tests on different materials and conditions was established.

Evaluation of hydraulic conductivity and self-healing potential of punctured geosynthetic clay liner

ABSTRACT An experimental study was conducted on the modified geosynthetic clay liner (GCL) specimen by replacing encapsulated Sodium Bentonite (Na-B) with different percentages of locally available black cotton soil (BCS). The specimens with punctured hole sizes of 4, 8, and 12 mm in diameter were tested for hydraulic conductivity and self-healing capacity assessed by improved triaxial apparatus. The flowing permeant was prepared with the heavy metals: iron, zinc, nickel, and total chromium based on the results of the chemical analysis of leachate collected from the municipal solid waste site (MSW). The experiment results were observed at 24, 48 and 72 hours. The results were analysed to identify the best specimen mix (Na-B and BCS) regarding the lowest hydraulic conductivity and highest self-healing potential. The results demonstrated that BCS can be utilized in modified GCL as an impermeable barrier for leachate percolation at the MSW dump site.

Hydraulic conductivity of bentonite-polymer geosynthetic clay liners to aggressive solid waste leachates

Hydraulic conductivity of conventional mock sodium bentonite (Na–B) and bentonite-polymer (B–P) geosynthetic clay liners (GCLs) were evaluated with three synthetic leachates that are chemically representative of aggressive leachates from coal combustion product (CCR) (I = 3179 mM), mining waste (MW) (I = 2127 mM, pH = 2.0), and municipal solid waste incineration ash landfill (MSWI) (I = 2590 mM). The mock B–P GCLs were created by dry mixing bentonite with branched, linear, or crosslinked polymer. The polymer loading of mock B–P GCLs ranged from 3 to 15%. Comparative tests were also conducted with Na–B GCLs. The mock Na–B GCLs cannot maintain low hydraulic conductivity to aggressive CCR, MW, and MSWI leachates. Mock B–P GCLs with 10% branched polymer had low hydraulic conductivity (< 1.0 × 10−10 m/s) to synthetic MW and MSWI leachates at 20 kPa effective confining stress, whereas the hydraulic conductivity of mock B–P GCLs with 10% linear or crosslinked polymer ranged from 1.5 × 10−9 to 1.4 × 10−7 m/s. As the effective stress increased, the B–P GCLs branched polymer showed a faster decreasing trend than that of Na–B and B–P GCLs with linear or crosslinked polymer.

Numerical Investigation of Confining Pressure Effects on Microscopic Structure and Hydraulic Conductivity of Geosynthetic Clay Liners

A series of COMSOL numerical models were developed to explore how confining pressure impacts the microscopic structure and hydraulic conductivity of Geosynthetic Clay Liners (GCLs), taking into account the bentonite swelling ratio, mobile porosity, pore size, and tortuosity of the main flow path. The study reveals that the mobile porosity and pore size are critical factors affecting GCL hydraulic conductivity. As confining pressure increases, the transition of mobile water to immobile water occurs, resulting in a reduction in mobile water volume, the narrowing of pore channels, decreased flow velocity, and diminished hydraulic conductivity within the GCL. Mobile porosity undergoes a slight decrease from 0.273 to 0.104, while the ratio of mobile porosity to total porosity in the swelling process decreases significantly from 0.672 to 0.256 across the confining pressure range from 50 kPa to 500 kPa, which indicates a transition of mobile water toward immobile water. The tortuosity of the main flow path shows a slight increase, fluctuating within the range of 1.30 to 1.36, and maintains a value of around 1.34 as the confining pressure rises from 50 kPa to 500 kPa. At 50 kPa confining pressure, the minimum pore width measures 5.2 × 10−5 mm, with a corresponding hydraulic conductivity of 6.2 × 10−11 m/s. With an increase in confining pressure to 300 kPa, this compression leads to a narrower minimum pore width of 1.81 × 10−5 mm and a decrease in hydraulic conductivity to 5.11 × 10−12 m/s. The six-fold increase in confining pressure reduces hydraulic conductivity by one order of magnitude. A theoretical equation was derived to compute the hydraulic conductivity of GCLs under diverse confining pressure conditions, indicating a linear correlation between the logarithm of hydraulic conductivity and confining pressure, and exhibiting favorable agreement with experimental findings.

Hydraulic conductivity of bentonite–polymer geosynthetic clay liners subject to wet–dry cycles used in landfill cover systems

This study evaluated the hydraulic conductivity of bentonite–polymer (B-P) geosynthetic clay liners (GCLs) subjected to wet-dry cycles that simulated seasonal conditions on a GCL installed in a landfill cover system. Hydraulic conductivity tests were conducted on B-P GCLs and NaB GCLs at 10 kPa in accordance with the ASTM D5084 standard. Two wet–dry methods were used to investigate the hydraulic conductivity of the GCLs under different field exposure conditions. The hydraulic conductivities of the NaB and B-P GCLs gradually increased during four wet–dry cycles. However, the hydraulic conductivity of the B-P GCL (K = 2.3 × 10-12 m/s) was lower than that of the NaB GCL (K = 6.3 × 10-11 m/s) by two orders of magnitude after four permeation–drying cycles. In addition, the hydraulic conductivity of the B-P GCL was lower (K = 5.8 × 10-12 m/s) than that of the NaB GCL (K = 7.8 × 10-10 m/s) by two orders of magnitude after four saturation–drying cycles. The results suggest that B-P GCLs can enhance the effectiveness of landfill cover systems compared to Na-B GCLs in managing conditions during wet and dry seasons.

Landfill cap models under simulated climate change precipitation: assessing long-term infiltration using the HELP model

The Hydrologic Evaluation of Landfill Performance (HELP) model (v 3.04) was used to assess the hydrological performance of two large-scale (~ 80 × 80 × 90 cm) laboratory-based landfill cap models. Desiccation cracking under simulated climate change precipitation (CCP) events was modelled to predict the performance of landfill caps over a 50-year period in Cumbria England, UK. Cumulative infiltration values under different climate conditions were highly sensitive to macro-pore development in the clay liner which is represented by the changing hydraulic conductivity in HELP simulations. Simulation results of cap design 1 (a clay barrier layer only) show that cumulative annual infiltration under normal precipitation (NP) and CCP events, with the initial hydraulic conductivity, ranged between 1 and 2% of the annual precipitation; however, cumulative annual infiltration was 10 to 68% when maximum (degraded) hydraulic conductivity values were used in simulations. A geosynthetic clay liner (GCL) included in cap design 2 significantly reduce cumulative infiltration.

Hydraulic and Geochemical Characteristics of a Geosynthetic Clay Liner Exhumed from an Exposed Composite Liner

Hydraulic and Geochemical Characteristics of a Geosynthetic Clay Liner Exhumed from an Exposed Composite Liner

Long-term hydraulic conductivity of bentonite-polymer geosynthetic clay liners

Hydraulic conductivity tests were conducted on six bentonite-polymer (B–P) geosynthetic clay liners (GCLs) to investigate the effect of the slow cation exchange process and polymer elution on the long-term hydraulic conductivity of B–P GCLs. Tests were conducted up to 1458 days and as many as 443 pore volumes of flows (PVFs). Three B–P GCLs consist of linear polymer whereas the other three have crosslinked polymer. One sodium geosynthetic clay liner (Na–B GCL) was used as a control. Hydraulic conductivities (K6766) of B–P GCLs (5.4 × 10−12 m/s to 3.7 × 10−11 m/s) per ASTM D6766 were approximately 2-3 orders of magnitude lower than that of Na–B GCL (2.3 × 10−9 m/s to 3.5 × 10−9 m/s). Tests were continued after hydraulic and chemical equilibrium to investigate the long-term hydraulic conductivity of GCLs. Hydraulic conductivities of GCLs had an increasing trend after hydraulic and chemical equilibrium. The ratio of KL/K6766 for B–P GCLs was 3.5–14.7, whereas ratio of KL/K6766 for Na–B GCLs was 1.0–1.7. Total organic carbon (TOC) tests results confirmed that polymer elution occurred during the entire permeation process. The higher ratio of KL/K6766 for B–P GCLs was attributed to the effect of polymer elution.

Effects of Temperature, Ionic Strength and Humic Acid on the Transport of Graphene Oxide Nanoparticles in Geosynthetic Clay Liner.

With the wide application of graphene oxide nanoparticles (GONPs), a great amount of GONP waste is discarded and concentrated in landfills. It has been proven that GONPs have strong toxicity and could gather toxic substances due to their high adsorption capacity. GONPs will seriously pollute the surrounding environment if they leak through the geosynthetic clay liner (GCL) in landfills. To investigate various factors (temperature, ionic strength (IS) and humic acid (HA)) on the transport and retention of GONPs in the GCL, a self-designed apparatus was created and column tests were carried out. The experimental results show that GONPs could be transported through the GCL. The mobility and sorption ratio of GONPs in GCL decreased with an increase in temperature and IS, and increased with an increase in HA. The temperature had little effect on the deposition ratio of GONPs in the GCL. The deposition ratio of GONPs in the GCL increased with IS, and decreased with an increase in HA. The transport of GONPs in GCL, glass beads and quartz sand was compared, and the results show that the retention ability of the GCL is much better than other porous materials. The experimental results could provide significant references for the pollution treatment in landfills.

Transport parameters for PFOA and PFOS migration through GCL's and composite liners used in landfills

The effect of applied stress (20, 60, and 150 kPa) on the diffusion of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) through a geosynthetic clay liner (GCL) is examined. The diffusion coefficients deduced from GCL diffusion tests for PFOA and PFOS decrease linearly with decreasing final bulk GCL void ratio (increasing applied stresses). The different components of the same GCL are also tested for PFOA and PFOS sorption. No statistically significant sorption of PFOA is observed for any of the components of the GCL. However, some sorption of PFOS onto the cover and carrier geotextiles of the GCL is observed with in an average distribution coefficient, Kd ∼2.22 ml/g for the GCL. Permeants containing different PFAS compounds are tested to assess their impact on the Geomembrane (GMB) - GCL interface transmissivity in composite liners. Results show PFAS concentrations up to 20 ppm had negligible impact on the GMB-GCL interface transmissivity. Lastly, the GCL specimens extracted from the diffusion tests are tested for hydraulic conductivity. No impact of PFAS is seen on the hydraulic conductivity of GCLs subjected to high applied loads, but a small increase is seen on the GCLs subjected to relatively low applied stresses.

Modification of bentonite with black cotton soil and carboxyl methyl cellulose for the enhancement of hydraulic performance of geosynthetic clay liners

ABSTRACT Geosynthetic clay liners (GCLs) are mostly used as flow barriers in landfills and waste containments due to their low hydraulic conductivity to prevent the leachate from reaching the environment. The self-healing and swell-shrink properties of soft clays (expansive soils) such as bentonite enable them as promising materials for the GCL core layers. However, it is important to modify their physico-chemical properties in order to overcome the functional limitations of GCL under different hydraulic conditions. In the present study, locally available black cotton soil (BCS) is introduced in the presence of an anionic polymer named carboxymethyl cellulose (CMC) as an alternative to bentonite to enhance the hydraulic properties of GCL under different compositions. The modified GCL is prepared by stitching the liner with an optimum percentage of CMC along with various percentages of BCS mixed with bentonite. Hydraulic conductivity tests were performed on the modified GCL using the flexi-wall permeameter. The results suggest that the lowest hydraulic conductivity of 4.58 × 10−10 m/s is obtained when 25% of BCS is blended with bentonite and an optimum 8% CMC and further addition of BCS results in the reduction of the hydraulic conductivity.

Moisture uptake of a nonwoven geotextile carrier-GCL from Lateritic subsoils under simulated tropical thermal conditions

Environmental conditions have become a concern when involving the use of Geosynthetics clay liners (GCLs) as leachate barriers, particularly because they can be subjected to daily thermal cycles during construction and operation of landfills, which can affect their properties. This paper investigates the hydration behavior of a nonwoven geotextile carrier-GCL in contact with lateritic subsoils under isothermal and simulated thermal conditions as commonly found in tropical regions. A thermal insulate testing box was used to shelter an instrumented liner landfill allowing the investigation of thermal and hydraulic responses during hydration. Lateritic subsoils were observed not to provide high levels of GCLs hydration under isothermal conditions, whereas thermal daily cycles led to capillary break that restricted the moisture uptake at the interface between subsoil and the nonwoven geotextile carrier. Higher values of subsoil initial moisture contents were found to be significant to reduce capillary effects and to allow some GCL hydration. The poor hydration demonstrated to be critical in terms of GCL hydraulic behavior.

Effect of wet and dry cycles on lighter bentonite-polymer geosynthetic clay liners

This study evaluated the hydraulic conductivity (K) of lighter bentonitepolymer (B-P) geosynthetic clay liners (GCLs) subjected to wet-dry cycles which simulated seasonal conditions on a GCL installed in a landfill cover system. Lighter bentonite-polymer composite (B-P) GCLs are manufactured with a lower mass per unit area of sodium bentonite (Na-B) (approximately 2.9 kg/m2) than conventional Na-B GCLs (approximately ≥ 3.6 kg/m2) which can reduce the transportation and installation costs compared to conventional Na-B GCLs. Hydraulic conductivity tests on lighter B-P GCL and Na-B GCL were conducted with a synthetic soil porewater leachate to represent wet season conditions on a landfill cover. Between hydraulic conductivity tests, GCL samples were placed in sealed chambers with a relative humidity of 75% until the water content of the specimens decreased to 55%, which represented dry season conditions of a GCL under a geomembrane in a cover system. Slight increases of the hydraulic conductivity were measured for both the Na-B and lighter B-P GCLs. After 5 wet-dry cycles K of the Na-B GCL increased from 3.1 x 10-12 m/s to 8.3 x 10-12 m/s, and K of the lighter B-P GCL increased from 1.6 x 10-12 m/s to 8.3 x 10-12 m/s.

Evaluating the impact of bentonite granule size distribution and swelling on the hydraulic conductivity of geosynthetic clay liners

The impact of granular size, distribution, total intergranular porosity, mobile intergranular porosity, and the tortuosity of the flow paths on the hydraulic conductivity of geosynthetic clay liners (GCLs) was assessed using a COMSOL hydrodynamic model. Results showed that as the intergranular pore spaces become smaller as the bentonite granules swell, the hydraulic conductivity of the GCL decreases. This effect is more significant when the density of the bentonite is lower. Outcomes from the model also illustrate that flow in GCLs with low hydraulic conductivity occurs in fine pore spaces with a width on the order of 1 um. The mobile intergranular porosity through which flow occurs is approximately 0.05 after the bentonite swells, and is small relative to the total intergranular porosity. This indicates that most water within bentonite having low hydraulic conductivity is occluded within isolated pores. As the hydraulic conductivity decreases, the tortuosity of intergranular flow paths increases, varying from 1.38 to 1.03. The findings provide insight into the complex flow behavior in GCLs and factors that affect achieving low hydraulic conductivity.

Hydraulic conductivity of two geosynthetic clay liners with different bentonite granule sizes

Experiments were conducted to evaluate the hydraulic conductivity of two commercially available geosynthetic clay liners (GCLs) with similar properties but different bentonite granule sizes (D50=1.0 mm or 0.3 mm). A synthetic municipal solid waste (MSW) leachate prepared in the laboratory and four actual coal combustion product (CCP) leachates collected from the field were used as permeant solutions to represent different permeant chemical conditions for waste containment applications. The two GCLs had comparable hydraulic conductivity to dilute or moderate ionic strength (I) leachates (&lt; 0.1 M). With more concentrated leachates (I &gt; 0.1 M), hydraulic conductivity of the GCL containing finer bentonite granules (FG) was 10 to 500 times lower than the hydraulic conductivity of the GCL containing coarser bentonite granules (CG) under the same equilibrium conditions. These results suggest that GCLs containing finer bentonite granules may be less vulnerable to permeant chemistry.

Using viscosity as an index for polymer loading of bentonite-polymer composite geosynthetic clay liners

Bentonite-polymer composite (BPC) geosynthetic clay liners (GCLs) containing a mixture of air-dry granules of bentonite and polymer have been developed for containment of wastes that generate leachates that are too aggressive for conventional sodium bentonite GCLs. Sufficient polymer loading is essential for BPC GCLs to maintain low hydraulic conductivity, and expedient methods are needed for manufacturing quality control and construction quality control to confirm that BPC GCLs contain sufficient polymer. In this study, a methodology for developed to estimate the polymer loading based on viscosity testing of slurries prepared with the BPC. A simplified version of the method can be used to determine if polymer is present in a BPC. Factors influencing the viscosity measurement were evaluated systematically, including water-to-BPC ratio, tempering time, and mixing method. The method that was developed consists of (1) adding deionized water to dry BPCs to achieve a water-to-BPC ratio of 30, (2) blending the BPC-water mixture with an overhead stirrer at 5000 rpm for 30 min to create a homogeneous slurry, (3) tempering the slurry in a zip-top bag for 24 hr, and (4) measuring the viscosity of the slurry in a viscometer at 300 and 600 rpm. Linear relationships were developed between polymer loading and viscosity for two BPC GCLs. Independent validation confirmed that the polymer loading estimated with the method is ±0.25% of the actual polymer loading.