Compacted Clay Liner Research Articles

The Breakthrough Time Analyses of Lead Ions in CCL considering Different Adsorption Isotherms

As the 2 m thick compacted clay liner with permeability coefficient of 1 × 10−7 cm/s is required in the Chinese technical specifications about landfill, the performance of this compacted clay liner was analyzed considering three different adsorption isotherms (convex, straight, and concave). The effects of source concentration, adsorption mode, and waterhead on the breakthrough curve and breakthrough time of Pb2+ were discussed. The results indicate that reducing the concentration of pollution sources is beneficial to prolonging the breakthrough time. With the waterhead of 10 m, the absolute breakthrough time, respectively, increased from 2.77 to 3.7 years (concave type isotherm), from 17.63 to 26.58 years (straight type isotherm), and from 35.43 to 59.6 years (convex type isotherm), as the source concentration decreased from 1000 mg/L to 10 mg/L. The effect of adsorption isotherm type on the performance of the barrier is very obvious: with the waterhead of 10 m, the absolute breakthrough time corresponding to the convex isotherm is more than twice that of the straight adsorption isotherm, and more than 12.8 times that of the concave isotherm. The absolute breakthrough time corresponding to 0.3 m waterhead is more than 4 times that of 10 m, and reducing the waterhead can effectively increase the breakthrough time.

Hydraulic and volume change characteristics of compacted clay liner blended with exfoliated vermiculite

Clays are used for the construction of waste containment barriers, because of its low hydraulic conductivity. Due to the difficulty in obtaining the natural clay satisfying the essential requirement as a liner material; commercially available bentonites are being used for the construction of clay liners. Bentonite undergoes large volume changes upon saturation. Various physical and chemical stabilisation techniques are in practice to stabilise the bentonite. Previous studies reported that contaminants with high concentrations attack clay minerals leading to increase in their permeability. Exfoliated vermiculite, finds several applications in construction industry, also found to be good absorbent material. Hence, this study has been carried out to find the optimal percentage of vermiculite that can be added to the bentonite so that it satisfies the essential requirements of clay liners and absorb the heavy metals from contaminants. Several index properties and engineering properties tests on bentonite-vermiculite mixtures were performed. From the studies, it was found that 30% of vermiculite can be added to bentonite, so that the essential requirements of liner can be maintained.

Hydraulic and volume change characteristics of compacted clay liner blended with exfoliated vermiculite

Hydraulic and volume change characteristics of compacted clay liner blended with exfoliated vermiculite

Role of Distribution and Diffusion Coefficients of Compacted Clay Liner and Geomembrane in Landfills

Role of Distribution and Diffusion Coefficients of Compacted Clay Liner and Geomembrane in Landfills

Investigation of a decommissioned landfill barrier system containing polychlorinated biphenyl (PCB) waste after 25 years in service

The excavation and analysis of the barrier systems for four engineered containment cells, constructed from 1984 to 1987, is described. Very limited polychlorinated biphenyl (PCB) migration was observed over the 22–25 year period prior to decommissioning. PCBs were predominantly, and preferentially, retarded by the geotextiles (GTXs) and, where present, geomembranes (GMBs). The migration of PCBs in the primary compacted clay liner (CCL) during this period was limited both when used alone and with a GMB. The exhumed GMBs, from both cover and base barriers, had diffusive properties (with respect to volatile organic compounds) comparable to unaged GMBs. For cells with a CCL as the primary base barrier, the inferred PCB diffusion coefficient, De, was 1–2 × 10−10m2/s and distribution coefficient, Kd, was 10–15 mL/g. For cells where a GMB was the primary base barrier, the inferred PCB partitioning coefficient, Sgf, was 150 000 and diffusion coefficient, Dg, was 1 × 10−14m2/s. Modelling beyond the 25 years in service predicts no unacceptable PCB impact of the landfill on groundwater and indicates that the design of the barrier system was adequate for an indefinite period given the low service temperatures to which it was subjected. In this diffusion-governed system, small changes to the diffusive properties were found to have a large impact on migration.

Adaptation of an Analytical Procedure for Concurrent Determination of Np and Pu in clay samples

AbstractNp and Pu are two important actinides of concern for the safe long-term disposal of nuclear waste. Both actinides are, in addition, constituents of global nuclear fallout. Investigation of their environmental behavior requires ultra-sensitive analytical methods, but current methods for a concurrent determination in clay minerals are lacking. In the present study, a Pu isotope was investigated for use as a non-isotopic yield tracer for Np in extraction, purification, and mass spectrometric determination of Np and Pu isotopes in clay materials. Inductively coupled plasma mass spectrometry was used in this developmental study, but the method is intended for future ultra-trace analysis of global-fallout Np and Pu in clay-rich soil materials by the more sensitive accelerator mass spectrometry. Another field of application may be the investigation of diffusion patterns of actinides in compacted clay liners and potential host rocks for radioactive waste disposal. The analytical procedure includes the following steps: (1) extraction of Np and Pu from clay samples; (2) adjustment of Np and Pu to Np(IV) and Pu(III); (3) pre-concentration of Np and Pu by co-precipitation with iron hydroxide; (4) adjustment of Pu to Pu(IV); (5) extraction chromatographic separation of Pu and Np from iron and matrix elements; and (6) determination of Np and Pu by mass spectrometry. The analytical procedure was applied successfully to spiked montmorillonite and illite test portions of up to 1 g. High chemical yields near 90% were obtained for both Np and Pu. The suitability of Pu as a non-isotopic tracer for Np was indicated by Np/Pu chemical yield ratios close to unity. Accurate pH adjustment during the reductive co-precipitation and short processing times are vital to obtain high chemical yields and Np/Pu yield ratios close to unity.

Analytical model for methane migration through fractured unsaturated landfill cover soil

Migration of gas in the fractured porous media plays an important role in geoenvironmental engineering issues. Compacted clay liners (CCLs) are extensively used as engineering barriers for groundwater and soil pollution induced by landfill contaminant transport. Analytical model and semi-analytical model were developed for methane transport in fractured CCL by using Laplace transformation and Laplace inversion using Stehfest method. Methane diffusion and oxidation in the matrix of CCL and gas advection-diffusion in the fracture were considered. Dimensionless analysis shows that advection plays a more important role than diffusion for methane transport through the fracture. Diffusion and oxidation of methane in the matrix of CCL have relatively less influences on methane transport in the fracture. The steady-state methane surface flux for the case with Dm = 3.14 × 10−9 m2/s is 1.02 and 1.5 times greater than that with Dm = 3.14 × 10−8 m2/s when the fracture width 2b = 5 mm and 2b = 3 mm, respectively. Methane oxidation rate in the matrix of CCL (λ1) plays a more important role on methane transport in fracture than methane oxidation rate in the fracture (λ2). When λ1 and λ2 increase by one order of magnitude, the steady-state surface fluxes decrease by factors of 1.05 and 1.53, respectively. Transport of methane can be greatly restrained by the compost-amended CCL due to the increase of methane oxidation rate. The proposed semi-analytical and analytical model can be used in the design and assessment of cover system for landfill and mining facilities with different soil moisture contents.

Zero leakage? Landfill liner and capping systems in Germany

An approach to achieve ‘zero leakage’ is discussed with respect to experience in Germany, where strict regulations for landfill lining and capping systems have been developed and issued because of large environmental problems related to landfills that accumulated in the 1970s and 1980s. Using a thick, high-quality high-density polyethylene (HDPE) geomembrane (GM) that is installed free of residual waves and wrinkles in intimate contact with a compacted clay liner or geosynthetic clay liner of very low permeability, by a qualified, experienced, well-equipped and properly third-party-controlled installer, and which is protected by heavy protection layers designed with respect to the long-term performance of the GM may result in a liner or capping system of practically no leakage. This is demonstrated by analysing results of measurements obtained from permanently installed leak-detection systems in combination with HDPE GMs. The survey was based on 32 German landfills with 1 276 500 m2 of installed GMs.

Seepage control in sand using bioslurry

Abstract This paper presents a new method for seepage control in sand using bioslurry, a suspension of CaCO3 crystals formed using a microbial calcium carbonate precipitation process (MICP). The bioslurry can be permeated through sand or deposit on top of a sand layer. The bioslurry contains high urease active bacteria cells and allows further MICP treatment when introducing cementation solution. In this way, the permeability of the bioslurry layer or bioslurry permeated sand layer could be further reduced to the order of 10−9 m/s through another 2–3 numbers of MICP treatment using a cementation solution with an optimum concentration of 1.6 M. Such a low permeability is hardly achievable using the conventional MICP method which would require many more numbers of treatment to reduce the permeability of sand to be below 10−7 m/s. Therefore, the proposed bioslurry method is not only more effective, but also more efficient. The water barrier layer formed using the proposed method is much less affected by wet and dry or temperature change cycles than compacted clay liners. It also allow cracks in the water barrier layer to be repaired if required.

Effect on Salak Tinggi residual soil mixed Bentonite as compacted clay liner

This paper present the result from experimental studies on using bentonite mixed with residual soil. The entire testings were performed on Salak Tinggi residual soil mixed with various percentage of bentonite content (5%, 10% and 15%). A series of laboratories were performed to investigate the effectiveness of mixed samples associated to physical properties testing such as: particle size distribution, pH, plastic index (PL), liquid limit (LL), plasticity index (PI) and linear shrinkage (LS). Meanwhile the standard proctor compaction test was conducted on mixed soil-benonite samples to determine the maximum dry density (MDD) and optimum moisture content (OMC). In addition the permeability test to determine the hydraulic conductivity was conducted at MDD condition at effective stress of 100 kPa. It was found that the addition of bentonite to the Salak Tinggi residual soil changed the physical properties result. Meanwhile, compaction results show a decrement in the MDD with increment of bentonite percentage mixed. The result also showed the bentonite mixed decreases the hydraulic conductivity value (k < 1x10−9 m/s) for Salak Tinggi soil significantly. This finding shows that by using the small amount of 5% bentonite significantly can be used as compacted of soil liner materials.

Analytical solutions for organic contaminant diffusion in triple-layer composite liner system considering the effect of degradation

This paper presents analytical solutions for predicting one-dimensional diffusion of an organic contaminant through a triple-layer composite liner system comprising a geomembrane (GM), a geosynthetic clay liner (GCL), and a compacted clay liner (CCL). We consider two different bottom boundary conditions, i.e., fixed-concentration bottom boundary and semi-infinite bottom boundary, for which the methods of separation of variables and Laplace transform, respectively, are used to obtain the analytical solutions. The proposed analytical solutions are then verified against the CST3 numerical model and an analytical solution available in the literature. Using the verified analytical solutions, a series of parametric studies is conducted to investigate the effect of several relevant parameters on contaminant transport through the GM/GCL/CCL liner system. The results indicate that the CCL thickness, the CCL distribution coefficient, and the effective diffusion coefficient of CCL have significant impact on contaminant diffusion in the GM/GCL/CCL liner system, whereas the effective diffusion coefficient of the GCL, the diffusion coefficient of the GM, and the partition coefficient of the GM have negligible effect on contaminant diffusion in the GM/GCL/CCL liner system. The analytical solutions presented herein can be used to aid the design of a triple-layer composite liner system and the verification of other numerical models.

A new simplified method to calculate breakthrough time of municipal solid waste landfill liners

Compacted clay liners and geomembranes are extensively used as bottom liners in municipal solid waste landfills, to minimize groundwater contamination due to the migration of landfill leachate. Seepage of leachate, however, can still transport pollutants in leachate through the bottom liner and cause environmental contamination. Design of a landfill site, therefore, requires estimation of the breakthrough time of the bottom liner. Current methods to calculate this breakthrough time are extremely complicated, so this study investigated a simplified calculation. For one–dimensional vertical transport of a key indicator pollutant, two simplified formulas are proposed to calculate breakthrough times of single compacted clay and composite liners. The proposed method considers pollutant transport mechanisms of advection, diffusion, mechanical dispersion, and adsorption. It is easy to use and can provide a reference for design, management, and subsequent restoration of such landfill sites.

Effect of Pore-Water Salinity on the Electrical Resistivity of Partially Saturated Compacted Clay Liners

The aim of this paper is to investigate the effect of pore-water salinity on the electrical resistivity (ER) of different compacted clay liners (CCLs) in terms of its mineralogical composition. For this purpose, an experimental programme was conducted where ERs of different kaolin-dominant CCL specimens, reconstituted using water having different concentrations of NaCl (0 M, 0.5 M, and 1.0 M), were measured. The kaolin-dominant CCL specimens tested in this study include pure kaolin, three different kaolin-bentonite mixtures, and three different kaolin-sand mixtures. The experimental results show that the ERs of CCL specimens decrease as the salt concentrations in pore water, moisture content, and dry density increase. At constant density and moisture content, the test results also indicate that increasing the sand content in kaolin-dominant CCL specimens increases its ER regardless of the water salinity level. This behaviour could be attributed to the lower surface conduction of sand compared to kaolin. However, at constant density and moisture content, increasing the bentonite content in kaolin-dominant CCL specimens decreases its ER in the distilled water environment as surface conduction of bentonite is higher compared to that of kaolin. On the contrary, in saltwater environments, ER increases as the bentonite content increases. This behaviour could be explained in terms of the expected aggregated microstructure of bentonite in the saltwater environment that could reduce the number and area of interparticle contacts, and consequently, increase the ER of CCL specimens.

Stability Performance of the Mixture of Bentonite and Zeolite as Landfill Liner

In some areas, compacted clay liner is chosen as leachate barrier for solid waste landfill. Due to the typical shape of the landfill, the compacted clay liner will be rested both in flat and sloping ground. Since clay has characteristics of low shear strength, improvement of shear stability of compacted clay liner is required. One of the stability methods to increase the shear strength of clay is by adding another material which has higher shear stability. In this study, bentonite is used to represent clay liner while zeolite is utilized as stabilizer material. Four compositions of bentonite with 0%, 5%, 10%, 15% addition of zeolite were prepared to investigate the stability performance of the mixtures. The results indicate that the addition of zeolite into bentonite has increased the friction angle of the bentonite. However, the addition of zeolite seems to alter the hydraulic performance of bentonite. The highest permeability is demonstrated by the bentonite with 15% of zeolite. Whether the permeability increases, the hydraulic performance of all the mixtures are still met the maximum permeability allowed for landfill liner.

Relationship between the shrinkage crack characteristics and the water content gradient of compacted clay liner in a landfill final cover

Shrinkage cracking is the primary reason for the anti-seepage failure of compacted clay liner (CCL) in a landfill final cover. With a focus on the surface crack characteristics and the water content distribution of three CCLs with different liquid limits and their mineral compositions, experiments were conducted to investigate the cracking mechanism of a CCL during the drying process. The results showed that the total crack ratio (TCR), the sum of the surface shrinkage crack ratio (SCR) and the surface boundary shrinkage ratio (BSR), is a function of the surface water content of a CCL. The change in the TCR with surface water content is consistent with the soil shrinkage characteristic curve (SSCC). The surface SCR is a function of the surface water content gradient of a CCL. The variations in the SCR with the water content gradient can be divided into the following three stages: the crack open stage, the crack linear expansion stage and the crack linear close stage. The effect of sample size, surface boundary shrinkage and shrinkage cracking are the main deformations of CCL specimens with low and high liquid limits, respectively, during the drying process. An increase in the amount of clay minerals in CCLs enhances the soil shrinkage capacity, leading to an increase in the SCR under the same water content gradient. A unified linear relationship exists between SCR/Kj (where Kj is the slope of the SSCC) and the water content gradient in the crack linear expansion stage and the crack linear close stage for different CCL types.

Crack Characteristic and Permeability Change of Compacted Clay Liners with Different Liquid Limits under Dry-Wet Cycles

The crack characteristic and permeability change in six compacted clay liners (CCLs) under dry-wet cycles were studied. Results show that as soil liquid limit (LL) increases, the crack block (CB) number, crack ratio (CR), and crack length (CL) of the CCLs increase under the dry state. The CB sizes of all the six CCLs correspond to normal distribution. A piecewise linear relationship exists between crack parameters and soil LL, and the slope at LL &lt; 50 is larger than the slope at LL &gt; 50. The size of the representative elementary volume (REV) of cracked CCL decreases linearly with the increase in soil LL when LL &lt; 50. The linear fitting result is REV = 90.5 – 1.6 LL, whereas REV change is inconspicuous with a mean value of approximately 10 cm when LL &gt; 50. The sample size of the CCLs for the permeability test must be larger than REV. Before and after three dry-wet cycles, the permeability ratio (K3/k0) initially increases and eventually decreases as soil LL increases, and LL at the peak value of K3/k0 is 36.1%. However, linear relationships exist between permeability D-value (K3 − k0) and soil LL in a semilog coordinate system when LL &lt; 50%, whereas the change in the permeability D-value is inconspicuous with a mean value of approximately 1.67 × 10−8 cm/s when LL &gt; 50%. The volume and mean width of unclosed cracks are two main factors that determine the increase in permeability after dry-wet cycles. After three dry-wet cycles, these factors decrease as soil LL increases, thereby reducing the permeability D-value.

Design and construction of a compacted clay liner in cover system of a municipal solid waste (MSW) landfill using nonstandard procedures

Design and construction of a mineral barrier layer involve many experimental and technological aspects. A specific soil water content and laboratory compaction energy, which are required to obtain permeability values according to the national regulation in force, must be determined. It is also necessary to control water content, compaction energy, and permeability of the liner actually compacted in situ. This paper shows how a compacted mineral barrier mainly composed of silty clay soil (the excavated soil is a natural but potentially re-usable waste product) was put in place to cover a large municipal solid waste (MSW) landfill and compacted using a heavy dumper, capable of achieving an adequate compaction degree. The in situ hydraulic properties of the liner were compared with those obtained by laboratory testing and to the limits imposed by the Italian regulation. The actual compaction degree was checked by in situ tests. Hydraulic conductivity tests were carried out in situ, using Boutwell and Guelph permeameters, and in the laboratory using rigid wall and flexible wall permeameters. In situ testing provided more realistic permeability values than laboratory ones and demonstrated that the actual construction procedure used was effective to obtain the design targets.

Clays of Different Plasticity as Materials for Landfill Liners in Rural Systems of Sustainable Waste Management

This paper presents a study assessing the possible application of seven clay substrates of various particle compositions and plasticity, sampled locally in rural regions, as materials allowing affordable construction of the waste landfill liners, which meet the main principles of sustainability, utilize locally available materials and limit the environmental threats posed by landfill leachate to water, public health and arable land. The researched substrates were tested according to their long-term sealing properties by their saturated hydraulic conductivity after compaction, swelling and shrinkage characteristics and ability to sustain their sealing capability after repeated drying and rewetting. The basic characteristics of soils were determined by the standard methods. Saturated hydraulic conductivity after compaction and after repeated shrinking and swelling were tested in laboratory falling head permeameters. Shrinkage characteristics were based on dimensionless indicators of the geometry and linear extensibility. The obtained results showed that the tested clay substrates were found applicable to construction of compacted clay liner for sustainable waste landfill. The environmental sustainability of a local, rural waste landfill, isolated by compacted earthen liners utilizing local materials is, in our opinion possible, but strongly related to the compaction parameters applied during liner construction for the given clay substrate.

Determination of peak and ultimate shear strength parameters of compacted clay

Shear strength parameters of compacted clay liners (CCLs) are needed for the safety design and stability analyses of mine waste dumps. The shear strengths of soils are commonly determined through laboratory direct shear or triaxial tests. However, for the same soil sample, different testing methods may produce large sets of scattered shear strength data, leading to difficulty in selecting the appropriate design parameters. In this study, extensive laboratory tests were carried out to investigate the shear strength parameters of the compacted clay for the geotechnical stability design in the McArthur River Mine (MRM). Both single-stage and multi-stage reversal direct shear tests were carried out under dry (as-sampled) and wet (in a water bath) conditions, and under applied normal stresses of 50 kPa, 100 kPa and 200 kPa. Three shearing rates of 1 mm/min (rapid), 0.1 mm/min (intermediate) and 0.01 mm/min (slow) were attempted to study the influence of shearing rate on shear strength of the compacted clay. Furthermore, one unconfined compression (UC) test, three unconsolidated undrained (UU) triaxial tests and three consolidated undrained (CU) triaxial tests were also carried out under the equivalent effective confining pressures of 50 kPa, 100 kPa and 200 kPa. Subsequently, the peak and ultimate shear strength parameters of the compacted clay are recommended in a format that allows for a more flexible use in design in the MRM.

Analytical model for vapour-phase VOCs transport in four-layered landfill composite cover systems

An analytical model for vapour-phase volatile organic compound (VOC) diffusion through four-layered landfill cover system consisting of a soil protective layer, a drainage layer, a geomembrane, and a compacted clay liner (CCL) or geosynthetic clay liner (GCL) is presented. VOCs transport in the cover system is sensitive to the changes of Sr in the protective layer and CCL rather than that of the drainage layer. When Sr1 = Sr2 = Sr4 = 0.5, in order to meet the EPA standard on benzene concentration, the thickness of CCL should be greater than 200 cm or it should be modified with 2% biochar.