Landfill Barrier Research Articles

Effect of Bentonite on Compacted Clay Landfill Barriers

Compacted clay barriers (liner and cap) are one of the most important components of municipal waste landfills. On-site soils are generally used to construct the clay barriers as long as they can be compacted to standard specifications, including hydraulic conductivity. Wherever the available on-site soils are not suitable to be used for constructing clay barriers, soils amended with bentonite are commonly used. This article presents the results of an experimental study conducted on compacted clay-bentonite mixtures to develop data on the effects of bentonite on engineering properties of compacted clay-bentonite mixtures. Clay-bentonite mixtures with bentonite contents of up to 7% were tested to determine consistency using Atterberg limits, moisture-density relationships using standard Proctor compaction tests, shear strength using unconfined compression tests, hydraulic conductivity using triaxial flexible-wall hydraulic conductivity tests, and consolidation properties using one-dimensional consolidation tests. Unconfined compression tests were also performed with 11% bentonite content.The laboratory test results indicated that liquid limit, plastic limit, and plasticity index increased linearly with increased amount of bentonite. The addition of bentonite resulted in decreased maximum dry unit weight but the optimum moisture content increased slightly. Unconfined compression strength of compacted clay-bentonite mixtures increased linearly with an increase in the amount of bentonite. Hydraulic conductivity of compacted clay-bentonite mixtures decreased nonlinearly with increased amount of bentonite, but a linear relationship was observed between logarithm of hydraulic conductivity and bentonite content. The compression index increased slightly from 0 to 3% bentonite content but increased nonlinearly beyond 3% bentonite content, whereas the swelling index of clay-bentonite mixtures has been observed to increase approximately linearly with increase in the amount of bentonite.

Pozzolanic fly ash as a hydraulic barrier in land fills

The liner plays an important role in controlling migration of contaminants present in the leachate in waste containment systems such as land fills and impoundments. Although questions have been raised about the performance of clay liners, they are increasingly used singly or as double liners in disposal sites. Though the clay liners possess many advantages such as low permeability and large attenuative capacity, they also possess high shrinkage potential and hence can crack under unsaturated conditions causing instability and increase in leakage rates. Further, the permeability of the clay linear can increase due to clay–pollutant interaction. This study examines the potential of pozzolanic fly ash as a hydraulic barrier in land fill. The behaviour of three different types of fly ashes, showing a range of physical properties and chemical composition from three different sources are reported in the study. Geotechnical properties, needed to evaluate the use of fly ashes as barriers, such as shrinkage, compaction, permeability, consolidation and strength characteristics are reported. The results show that fly ashes possess low shrinkage and hence do not crack. Compacted fly ashes undergo very little volume changes. They also show that pozzolanic fly ashes develop good strength properties with time. Pozzolanic fly ashes containing sufficient lime develop strength even without addition of lime. Non-pozzolanic fly ashes do not develop strength even on addition of lime. Fly ashes generally consist of silt size particles and consequently possess high permeability. However, pozzolanic fly ashes with lime exhibit low permeability on curing because of the formation of gelatinous compounds which block the pores. Thus, pozzolanic fly ashes appear to be promising for construction of liners to contain alkaline leachate.

Suction and volume changes of a bentonite-enriched sand

Landfill barriers are used to control or prevent both migration of leachate from the landfill waste and the ingress of the surrounding groundwater. A typical barrier system may include a combination of engineered barriers and fluid collection layers. Bentonite-enriched sand is a commonly used barrier material. The addition of relatively small amounts of bentonite (5–15%) can dramatically improve the performance of a granular material, providing both a low permeability and an enhanced mechanical stability. This paper explores the suction and volume change characteristics of a bentonite-enriched sand. In addition to determining the dry density–moisture content relationships for a range of compactive efforts, a series of oedometer tests has been performed and a comprehensive number of suction measurements made. These data have allowed the suction and volume change characteristics to be defined. The results are presented and discussed, allowing a clearer understanding of the long-term behaviour of these materials to be developed.

Mechanical behaviour of landfill barrier systems

Mechanical behaviour of landfill barrier systems

Mechanical behaviour of landfill barrier systems

Landfills may need to be surrounded by engineered liner systems to prevent dangerous leakage to the environment. Depending on the location of the liner, that is, at the bottom, surface or sides of the landfill, the system may be highly stressed in bending or shear. Full-scale tests and additional field measurements were carried out to define the ultimate state of the permeability of horizontal and vertical compacted clay liners. The results of these tests can be used in the overall design of such landfill liners. The testing equipment developed may be used to improve new system designs or to test alternative combinations of materials.

Modeling of heavy metal migration in sand/bentonite and the leachate pH effect

Numerical simulations were carried out using a multicomponent reactive solute transport model to study the migration of four heavy metals (Cd 2+, Pb 2+, Cu 2+ and Zn 2+) in a sand/bentonite mixture. The numerical model is capable of simulating simultaneous processes of water flow, advective–dispersive solute transport, and chemical reactions such as acid–base reaction, complexation, ion exchange, precipitation and dissolution. The migration of the heavy metals was simulated in a hypothetical sand/bentonite clay column which was assigned realistic physical and chemical properties and boundary conditions to model one-dimensional contaminant transport through a landfill barrier. The input leachate properties used in the model were modified from those of an actual leachate containing the heavy metals. The numerical simulations were focused on the concentration profiles of these heavy metals in the simulated barrier and the effect of the leachate pH on their mobilities. Numerical results indicate that under a nearly neutral leachate, the mobility of the four heavy metals follows the order Cu 2+>Zn 2+>Pb 2+>Cd 2+. Under a more acidic leachate, the mobility order changes to: Cd 2+>Zn 2+>Cu 2+>Pb 2+. However, the differences in mobility of the four heavy metals were relatively small. The leachate pH has a significant effect on the migration of Cd 2+ and Pb 2+, but has only limited effect on the mobility of Cu 2+ and Zn 2+.

Natural clay-shredded tire mixtures as landfill barrier materials

A natural overconsolidated fissured clay, Keuper Marl, was mixed with shredded tire, 1–4 and 4–8 mm angular size particles, in weight percentages between 6 and 15%, and examined for use as a constituent in a landfill liner in terms of compaction, unconfined compressive strength, stress-strain behavior, permeability to water and paraffin, leachability, free swell behavior and swelling pressure. The results showed that the compacted dry density reduced solely due to the lighter weight of the tire and the unconfined compressive strength of the mixture was as low a 40% of the strength of the clay alone. In stress-strain behavior the clay-tire mixtures produced a prolonged strain range at failure of roughly double that observed for the clay alone. The permeability to paraffin was reduced by more than 50 times compared to that of water. The leachability results showed different leached levels of copper and nickel from the NRA and TCLP leaching tests which will need to be assessed in relation to appropriate standards. Paraffin caused considerable swelling of the clay-tire mixtures compared to the clay alone and caused the development of swelling pressures of up to 600 kPa. Combinations of the various test results will need to be assessed in relation to the design requirement of the specific landfill liner being designed.

WASTE MINIMIZATION AND RE-USE OF PAPER SLUDGES IN LANDFILL COVERS: A CASE STUDY

This investigation attempted to find a beneficial use for waste water paper mill sludges by using paper mill sludges as the impermeable barrier in landfill covers. This study investigated the geotechnical properties of seven paper mill sludges for use as the impermeable barrier in landfill covers. Paper mill sludges have a high water content and a high degree of compressibility and behave like a highly organic soil. Consolidation tests reveal a large reduction in void ratio and high strain values that result from the high compressibility. Laboratory permeability tests were conducted onin situsamples, and these samples met the regulatory requirement for the permeability of a landfill cover. To determine the effectiveness of paper sludge as an impermeable barrier layer, test pads were constructed to simulate a typical landfill cover with paper sludge and clay as the impermeable barrier and were monitored for infiltration rates for 5 years. Long-term permeability values estimated from the leachate generation rates of the test indicate that paper sludge provides an acceptable hydraulic barrier.

Waste Minimization and Re-Use of Paper Sludges in Landfill Covers: a Case Study

This investigation attempted to find a beneficial use for waste water paper mill sludges by using paper mill sludges as the impermeable barrier in landfill covers. This study investigated the geotechnical properties of seven paper mill sludges for use as the impermeable barrier in landfill covers. Paper mill sludges have a high water content and a high degree of compressibility and behave like a highly organic soil. Consolidation tests reveal a large reduction in void ratio and high strain values that result from the high compressibility. Laboratory permeability tests were conducted on in situ samples, and these samples met the regulatory requirement for the permeability of a landfill cover To determine the effectiveness of paper sludge as an impermeable barrier layer, test pads were constructed to simulate a typical landfill cover with paper sludge and clay as the impermeable barrier and were monitored for infiltration rates for 5 years. Long-term permeability values estimated from the leachate generation rates of the test indicate that paper sludge provides an acceptable hydraulic barrier. © 1997 ISWA

A model for adsorption of organic species by clays and commercial landfill barrier materials : M. C. R. Davies, L. M. R. Railton & K. P. Williams, in; Engineering geology of waste disposal, ed S.P. Bentley, (Geological Society of London; Engineering Geology Special Publication, 11), 1996, pp 273–278

A model for adsorption of organic species by clays and commercial landfill barrier materials : M. C. R. Davies, L. M. R. Railton & K. P. Williams, in; Engineering geology of waste disposal, ed S.P. Bentley, (Geological Society of London; Engineering Geology Special Publication, 11), 1996, pp 273–278

Utilizing coal fly ash as a landfill barrier material

The chemical barrier properties of a composite of coal fly ash, lime dust and bentonite were studied as a potential barrier material for a landfill. An experimental study was performed to measure the hydraulic and chemical barrier properties of the material using both water and a synthetic municipal solid waste (MSW) leachate. The composite material was found to have a hydraulic conductivity of 4.3 ± 1.6 × 10 −8 m/s with water. More importantly, the composite material had chemical barrier properties for metal ions in the leachate liquid. Results show that the principal retarding mechanism for the heavy metal ions was precipitation. In accelerated tests, for the metal ions studied, the retardation order was Pb > Zn > Fe. The migrating front of the heavy metals (Fe, Zn and Pb) under landfill conditions is estimated to be less than 0.10 m in 15 years assuming a constant pH of 6. The coal fly ash barrier appears to be an effective chemical barrier for MSW landfill leachate.

Waste disposal, regulatory policy and potential health threats

Abstract The issues with respect to development of a safe liner-barrier system for waste containment facilities in the land disposal of wastes are examined in relation to the need for minimization of potential health and environmental threats. The influence of regulatory policies or attitudes, e.g. the ‘Compliance (Mandated) Requirement’ and the ‘Performance Requirements’ attitudes, on the requirements for barrier system design and performance is seen to be very significant. Ensuring protection of public health and the environment is central to the construction and performance requirements and criteria of the barrier system. Regulatory control and measures designed to fulfil minimization of public health threats must address the basic question of ‘what constitutes a health threat’, especially since one needs to ensure proper and secure barrier performance for 250–500 years or more. The performance of substrate material and engineered landfill barriers as competent liner systems, particularly with respect to substrate control on waste leachate containment and transport, must be well understood if proper protection of public health and the environment is to be obtained.

A model for adsorption of organic species by clays and commercial landfill barrier materials

Abstract The adsorptions of four carboxylic acids and phenol onto three substrates have been examined. It has been demonstrated that modifying montmorillonite with the diethyl ammonium ion increases the adsorption of the acids at the higher concentration. The amount of adsorption cannot be explained simply by consideration of adsorbate solubilities in water, but depends on more complex interactions between adsorbate-adsorbent and solvent. A model to predict the adsorptive lifetime of a barrier has also been developed.

Design and placement considerations for clay and composite clay/geomembrane landfill final covers

The performance of clay and clay geosynthetic combinations for landfill barrier layers has not always proved predictable and the integration of geosynthetic materials into conventional landfill designs presents some interesting problems which were previously unforeseen. This paper looks at identifying and mapping the approach to some specific considerations for clay and geomembrane/clay barriers. These considerations include: long-term performance of clay barriers, short-term and long-term stability of clay barriers, clay/geomembrane interface behavior, and the phenomena of moisture build-up beneath exposed membrane liners.