Landfill Final Cover Research Articles

Sustainability aspects of geosynthetic landfill final cover systems

Progressively, geosynthetics have been used in combination with and in lieu of natural materials to solve complex geotechnical problems while offering a drastic reduction in carbon emissions and minimizing environmental impacts. Commonly used final cover systems for landfills and containment areas include soil-only, soil-geosynthetic, engineered turf cover (ETC), and evapotranspiration (ET) cover system. This presentation provides a detailed review of various sustainability aspects of a geosynthetic ETC including comparisons with traditional covers. Sustainability aspects considered include carbon emissions; deforestation, land use change and borrow areas; land, soil and water conservation; run-off water quality and downstream impacts; reduction in fugitive landfill gas emissions; and beneficial reuse opportunities.

Life cycle analysis of common landfill final cover systems focusing on carbon neutrality

Carbon emissions from landfill construction and management have become a global concern. Life cycle analysis (LCA) has been widely used to assess the environmental impacts of engineered infrastructures over their lifetimes. LCA has also been applied to landfill leachate and gas management, but rarely to landfill final cover systems. This paper reports the results of an LCA of the following landfill final cover systems: compacted clay cover, geomembrane cover, cover with capillary effects (CCBE), dual capillary barrier cover, three-layer landfill cover system using natural soils, three-layer cover using recycled concrete aggregate (RCA) and biochar-amended three-layer landfill cover system using RCA. The LCA assessment of landfill cover considers the cost, carbon emissions and carbon sequestration during the production, construction and operation phases. The effects of landfill cover on global warming, freshwater eutrophication, terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity and fossil resource scarcity are also evaluated. In addition, the sensitivities of cost and carbon emission to the use of electric-powered machines and transportation distance are analysed. It is revealed that the three-layer cover system using RCA and biochar has the lowest unit cost and carbon emission of all of the covers, up to 88 % and 66 % lower, respectively, than those of the other six covers. In addition, this cover system has the highest carbon sequestration rate, with a value of 47.9 kg CO2/(y·m2), four times higher than that of the compacted clay cover. Finally, this sustainable cover mitigates global warming and reduces adverse environmental impacts by up to 82 %. Therefore, the biochar amended three-layer cover system using RCA without geomembrane offers the greatest economic benefits, performs effectively in terms of the pursuit of carbon neutrality and promotes sustainable development.

Inclined Plane Shear Behaviour of a Recycled Construction and Demolition Material–Geocomposite Interface

Over the years, recycled construction and demolition (RC&D) materials have become useful and valuable construction materials. The applications of these materials have been increasing, and there are cases where they may be in contact with geosynthetics. This work, which is part of a broader investigation into the feasibility of replacing soils used in landfill final cover systems by RC&D materials, analysed the inclined plane shear behaviour of the interface between a fine-grained RC&D material and a drainage geocomposite. Inclined plane shear tests were performed with different vertical stresses and different compaction conditions (degree of compaction and water content) of the RC&D material. The friction angle at the RC&D material-geocomposite interface was estimated by two approaches: the standard and the one based on the Mohr–Coulomb failure envelope. The sliding mechanism of the RC&D material over the geocomposite was examined. For comparison with the RC&D material-geocomposite interface, the behaviour of the RC&D material under inclined plane shear movement was also characterised. The main findings of the work included: the friction angle (standard approach) at the RC&D material-geocomposite interface decreased by increasing the applied vertical stress and the RC&D material water content (with meaningful changes in the slinging mechanism in the latter case), and tended to increase by increasing the degree of compaction of the RC&D material; the behaviour of the RC&D material under inclined plane shear movement did not differ significantly from that of the RC&D material-geocomposite interface; the failure envelope approach was more conservative (smaller friction angles) than the standard approach.

Hotspot Detection and Estimation of Methane Emissions from Landfill Final Cover

The main objectives of this study were to identify methane hotspots through spatial distribution tests of the surface methane concentration above a landfill final cover and to investigate the effects of rainfall, atmospheric pressure, ground temperature, and ambient methane concentration on methane emissions. A portable laser methane detector was used to measure the spatial distribution of methane concentrations. The methane concentration distribution showed a distinct spatial variability. The maximum methane concentration reached 3225 ppm, while 73.0% of the methane concentration values were below 10.0 ppm. Several meteorological factors were found to be associated with the variation in methane emissions. Rainfall limited gas transport in the cover, resulting in more significant methane hotspots. Atmospheric pressure was negatively correlated with methane emission. The ambient methane concentration and methane flux had a significant positive linear correlation. Based on a linear correlation equation, the spatial distribution of methane concentrations in the landfill could be converted into a methane emission distribution. The estimated average value for methane emissions in the test area was approximately 4.3 g m−2 d−1. This study provides an experimental basis for locating methane hotspots and assessing methane emissions in landfill final covers, and proposes supplementary means for detecting geomembrane damage in landfill covers.

Field-based assessment of the design of lysimeters for landfill final cover seepage control

ABSTRACT Lysimeters are considered the most appropriate instrument for assessing percolations rates through landfill final covers. Their design, however, must take into consideration the unsaturated nature of water seepage, otherwise they may act as a sink or cause flow avoidance. The aim of this study was to investigate whether using a simple approach to lysimeter design produces reliable seepage control data. Two different design methods were compared using a three-year field database of suction and seepage data collected from large-scale lysimeters installed at the St-Nicephore landfill in Canada. The first, or control, whose side walls were as high as the thickness of the cover material, was inspired from lysimeters installed during the Alternative Cover Assessment Program (ACAP; USA). The second lysimeter was designed based on the proposed simple design methodology, which focuses on the unsaturated flow and hydraulic properties of the materials to determine the optimal wall height. Analysis of the database did not show any indication of significant preferential flow, or alteration of the flow regime by the second lysimeter, which collected as much percolation as the control one (less than 5% difference). The linear method has not been tested for extreme climatic conditions and the wall heights calculated using this method may be very high when designed for very fine-grained soil covers.

Dehydration effect of freeze-thaw on sludge: Temperature spatio-temporal distribution and multi-scale evaluation

The freeze-thaw vacuum method for conditioning pretreated sludge has been proved that it not only has greater dewatering efficiency but also is more ecologically friendly. In this paper, the experiment is improved to address shortcomings in previous freeze-thaw vacuum approach for sludge treatment. The spatio-temporal distribution relationship of distance-time-temperature is developed and divided into two stages by numerically fitting the temperature change of freezing tubes in the sludge. It is expected to guide the time control of large-scale frozen sludge in practical engineering applications to achieve optimal dewatering treatment. Furthermore, the performance of dehydration after the model test is evaluated on multi-scale: settlement and mechanical properties (macroscopic perspective), mean particle size (mesoscopic perspective), and SEM microstructure (microscopic perspective). The results reveal that the improved sludge treatment method of alternating freeze-thaw vacuum procedures, using both prefabricated horizontal drains (PHDs) and prefabricated vertical drains (PVDs), substantially benefits the sludge dewatering and reduction. This method results in an unparalleled volume reduction of 63.51% and a water content reduction to 58.54%. Moreover, in-situ vane shearing strength of the sludge obtained from the improved test meets the strength requirement for the landfill final cover soil, demonstrating that the method is superior in improving mechanical properties.

Study of the effectiveness of landfill final cover in reducing BTEX emissions

Study of the effectiveness of landfill final cover in reducing BTEX emissions

Numerical Modeling Applied to Leachate Generation using Hydrus – Case Study: Seropédica, Rio de Janeiro, Brazil

ABSTRACT Improper design and management of the cover layer of a sanitary landfill has been proven to produce harmful environmental impacts on the environment. One alternative at hand is to develop scenarios based on simulation of physical and computational models to represent the expected field water balance of a landfill coverage layer. This paper investigates the design of a sanitary landfill final cover in the municipality of Seropédica, which is located at the state of Rio de Janeiro - Brazil. More specifically, the compact soil coverage, which is widely used for landfill final cover of municipal solid waste, is evaluated in contrast to vegetation cover by grass, vegetation cover by brachiaria and capillary barrier. To accomplish such task, hydrometeorological forcing conditions, namely daily rainfall and temperature, were retrieved from the Anchieta weather station, which is situated nearby the study area. The Hydrus 1D and 2/3 D computational codes were employed to develop a set of scenarios to follow the contamination plume evolution within the landfill along the time frame of 20 years with some degree of reliability. It should be noted that the performed evaluation indicates the possibility to control the leachate release and consequently to avoid contaminating the environment, notably to prevent soil and water resources pollution. Vegetation cover by grass and brachiaria showed important control mechanisms with respect to the movement of the contaminant plume. In addition, it should be noticed that the best results for the landfill final cover were achieved for the capillary barrier, while poor performance results were obtained for the commonly employed compact soil.

Evaluating mass of soil particles eroded into geosynthetic drainage layer in landfill final cover system

Evaluating mass of soil particles eroded into geosynthetic drainage layer in landfill final cover system

Methane eruptions from landfill final cover soil during rainfall events in laboratory experiments

Landfill sites are significant sources of greenhouse gases, particularly methane. It is believed that methane gas eruptions occur under a surface ponding condition during rainfall events. In this study, based on laboratory column experiments in which mixed gas was applied to variably compacted soil columns (10 cm in diameter and 30.5 cm in height) under different rainfall intensities, the effects of the bulk density of the landfill cover soil, the gas injection rates, and the rainfall intensities on the gas eruption phenomenon were investigated. The gas pressure and the water content were monitored during rainfall events. The main results were that (1) an episodic gas compression and eruption cycle was observed under a surface ponding condition, (2) gas eruptions occurred at a higher gas pressure in the soil with a higher dry bulk density, and (3) a higher gas injection rate resulted in continuous gas eruptions. The monitoring of the gas eruption flux and gas concentration in the soil columns, using oxygen-mixed gas as an injected gas, showed that longer gas compression led to higher gas fluxes during the gas eruptions. The concentration of gas in the soil increased over time because of the upward gas flow in accordance with the eruptions. The calculation of the oxygen mass balance indicated that the eruptions had slightly promoted the emission of gas from that which had been stored in the soil prior to the rainfall events.

Stability analysis on veneer cover system for landfill considering the effect of internal seeper

A drainage layer can easily cause clogging during rainfall, and a retained seeper may cause a strong uplifted-floating effect on the overlying soil layer, thereby inducing serious disasters. This paper proposes two failure modes (i.e., direct-slip failure and uplifted-floating failure) that may be encountered simultaneously by the cover soil layer of landfills. Corresponding analytical models and computing methods are established. Results demonstrate that both failure modes can potentially occur on the cover system but exhibit different performance levels. The immersion ratio (λ) of the drainage layer is an important factor influencing the safety factor (FS) of both failure modes. By increasing the λ-value, the Fs-values of both failure modes decrease evidently, but the decrease rates are vastly different. Moreover, the effects of other parameters such as slope length and slope angle on the FS of the two failure modes are also discussed in this study. Results indicate that these parameters exhibit different effect degrees on the occurrence of the two failure modes. Finally, the Fs-values of the direct-slip failure calculated in this study are compared with the results of others', and indicated that the reliability of this study is high. The results of this study can optimize the design parameters of the landfill final cover system and render its stability evaluation more accurate.

Effects of biochar on bacterial communities in a newly established landfill cover topsoil

Recent studies revealed the benefits of applying biochar in landfill final cover soil, such as adsorbing odorous compounds and promoting microbial methane oxidation. Most of these processes are related to the soil bacterial communities. However, the effects of biochar application on the overall bacterial community in newly established landfill cover soil are not yet understood, especially in field condition. The objective of the present field study is to investigate the effects of biochar on the diversity of soil bacterial community 3 months after incubation (short–term). Landfill final cover topsoil (0.6 m) was amended with 0 (control), 5, and 10% (w/w) of biochar derived from peanut–shell and wheat straw. Soil bacterial communities were analysed using the 16S rRNA–based T–RFLP approach. Biochar application significantly (p < 0.05) increased the diversity of soil bacterial communities. The Shannon diversity index of bacterial communities in soil amended with 5 and 10% of biochar was increased from 3.34 to 3.85 and 3.92, respectively. There were four bacterial phyla recorded found at both control and amended soils, namely Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. In addition, Gemmatimonadetes was found only in soil amended with 10% biochar. The interactions between soil bacterial communities and measured soil parameters including moisture content, electrical conductivity, total organic matter, total nitrogen and total phosphorus were found to be statistically non-significant (p > 0.05), according to the canonical correspondence analysis (CCA). This may be due to the highly heterogeneous nature of landfill soil. Results from this study revealed that short-term biochar application already altered the soil physicochemical properties and increased the diversity of soil bacterial communities.

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.

Aspects Regarding the Collection and Removal of Rainfall Water on Landfill Final Cover

This paper presents an analysis of the rainwater flow on the final cover slopes of an urban landfill so as to ensure the drainage of infiltrate water through the drainage layer applied across the geomembrane of cover layer, with a runoff coefficient as low as possible. It is presented a calculation model for the transmissivity of the drainage layer depending on the thickness and on its hydraulic characteristics and also on the topsoil layer applied to the surface, as well as depending on the coating slope length. This calculation is made for both a side with a single slope (tilt) as well as for sides with two slopes. Also it is presented a mathematical model for the hydraulic calculation of surface water drainage ditches drained through the drainage layers, but also through the surface runoff, in order to establish the optimal drainage section.

Effects of biochar on hydraulic conductivity of compacted kaolin clay.

Compacted clay is widely used as capillary barriers in landfill final cover system. Recently, biochar amended clay (BAC) has been proposed as a sustainable alternative cover material. However, the effects of biochar on saturated hydraulic conductivity (ksat) of clay with high degree of compaction is not yet understood. The present study aims to investigate the effects of biochar on ksat of compacted kaolin clay. Soil specimens were prepared by amending kaolin clay with biochar derived from peanut-shell at 0, 5 and 20% (w/w). The ksat of soil specimens was measured using a flexible water permeameter. The effects of biochar on the microstructure of the compacted clay was also investigated using MIP. Adding 5% and 20% of biochar increased the ksat of compacted kaolin clay from 1.2×10-9 to 2.1×10-9 and 1.3×10-8 ms-1, respectively. The increase in ksat of clay was due to the shift in pore size distribution of compacted biochar-amended clay (BAC). MIP results revealed that adding 20% of biochar shifted the dominant pore diameter of clay from 0.01-0.1μm (meso- and macropores) to 0.1-4μm (macropores). Results reported in this communication revealed that biochar application increased the ksat of compacted clay, and the increment was positively correlated to the biochar percentage.

GAS PERMEABILITY OF GEOSYNTHETIC CLAY LINERS

Geosynthetic clay liners (GCL) are manufactured hydraulic barriers consisting of mineral and geosynthetic components. They belong to a group of geosynthetic products whose primary purpose is to seal and they have been used in many geotechnical and hydrotechnical applications, landfi lls and liquid waste lagoons for quite a while. They are used in landfill final cover systems to prevent the infi ltration of precipitation into the landfi ll body and the penetration of gases and liquids from the landfill into the atmosphere and environment. Laboratory and fi eld research and observations on regulated landfi lls have proven the eff ectiveness of GCL as a barrier for the infi ltration of precipitation into the landfi ll body as well as the drainage of fl uid beneath the landfill. Due to the presence of high concentrations of gases in the landfill body, there is a growing interest in determining the efficiency of GCL as a gas barrier. It was not until the last twenty years that the importance of this topic was recognized. In this article, current GCL gas permeability studies, the testing methods and test results of gas permeability in laboratory conditions are described.

Stimulation of methane oxidation potential and effects on vegetation growth by bottom ash addition in a landfill final evapotranspiration cover

The landfilling of municipal solid waste is a significant source of atmospheric methane (CH4), contributing up to 20% of total anthropogenic CH4 emissions. The evapotranspiration (ET) cover system, an alternative final cover system in waste landfills, has been considered to be a promising way to mitigate CH4 emissions, as well as to prevent water infiltration using vegetation on landfill cover soils. In our previous studies, bottom ash from coal-fired power plants was selected among several industrial residues (blast furnace slag, bottom ash, construction waste, steel manufacture slag, stone powder sludge, and waste gypsum) as the best additive for ET cover systems, with the highest mechanical performance achieved for a 35% (wtwt−1) bottom ash content in soil. In this study, to evaluate the field applicability of bottom ash mixed soil as ET cover, four sets of lysimeters (height 1.2m×width 2m×length 6m) were constructed in 2007, and four different treatments were installed: (i) soil+bottom ash (35% wtwt−1) (SB); (ii) soil+compost (2% wtwt−1, approximately corresponding to 40Mgha−1 in arable field scale) (SC); (iii) soil+bottom ash+compost (SBC); and (iv) soil only as the control (S). The effects of bottom ash mixing in ET cover soil on CH4 oxidation potential and vegetation growth were evaluated in a pilot ET cover system in the 5th year after installation by pilot experiments using the treatments. Our results showed that soil properties were significantly improved by bottom ash mixing, resulting in higher plant growth. Bottom ash addition significantly increased the CH4 oxidation potential of the ET cover soil, mainly due to improved organic matter and available copper concentration, enhancing methanotrophic abundances in soil amended with bottom ash. Conclusively, bottom ash could be a good alternative as a soil additive in the ET cover system to improve vegetation growth and mitigate CH4 emission impact in the waste landfill system.

Soil-water retention behavior of compacted biochar-amended clay: a novel landfill final cover material

Biochar has long been proposed for amending agricultural soils to increase soil-water retention capacity and therefore promotes crop growth. Recent studies revealed the potential use of biochar-amended soil in landfill final covers to promote methane oxidation and odor reduction. However, the effects of biochar application ratio, compaction water content (CWC), and degree of compaction (DOC) on soil-water retention characteristics of biochar-amended clay (BAC) at high soil suction (dry condition) are not well understood. The present study aims to overcome this knowledge gap. Soil suction was induced using vapor equilibrium technique by a temperature- and humidity-controlled chamber, and the water desorption (drying) and adsorption (wetting) water retention curves (WRCs) of compacted pure kaolin clay and peanut shell BAC with different biochar application ratios (0, 5, and 20 %, w/w), DOCs (80, 90, and 100 %), and CWCs (30 and 35 %) were measured. The correlations between these factors and the gravimetric water content were analyzed by three-way ANOVA followed by the Tukey HSD test. The soil micro-structure was studied by scanning electronic microscope with energy-dispersive X-ray spectroscopy. Measured WRCs of BAC suggest that the soil-water retention capacity at high suction range (48.49–124.56 MPa) was in general increased, upon biochar application. The BAC compacted with CWC of 35 % at low (80 %) and high (100 %) DOCs for the 5 % BAC were increased by 7.30 and 9.77 %, when compared with clay, while the increases of 20 % BAC were 39.89 and 59.20 %, respectively. This is attributed to the embedded effects of clay particles in biochar pores, which reduce the total pore space of BAC. The soil-water retention capacity of BAC was also increased with CWC and decreased with DOC. The results of three-way ANOVA analysis show that the effects of DOC and biochar ratio on soil gravimetric water content was significant (p < 0.05) only at 48.49 MPa on drying path. For other induced suctions, only effects of CWC were significant (p < 0.05). Biochar application increases soil-water retention capacity of the BAC at high soil suction (48.49–124.56 MPa) (dry condition) at both low (80 %) and high DOC (100 %). The soil-water retention capacity of 20 % BAC was much higher than that of 5 % BAC. BAC is a potential alternative landfill final cover soil with a higher soil-water retention capacity to be used in dry areas or regions with a long period of evaporation event.

Feasibility of biochar application on a landfill final cover—a review on balancing ecology and shallow slope stability

Due to the increasing concerns on global warming, scarce land for agriculture, and contamination impacts on human health, biochar application is being considered as one of the possible measures for carbon sequestration, promoting higher crop yield and contamination remediation. Significant amount of researches focusing on these three aspects have been conducted during recent years. Biochar as a soil amendment is effective in promoting plant performance and sustainability, by enhancing nutrient bioavailability, contaminants immobilization, and microbial activities. The features of biochar in changing soil physical and biochemical properties are essential in affecting the sustainability of an ecosystem. Most studies showed positive results and considered biochar application as an effective and promising measure for above-mentioned interests. Bio-engineered man-made filled slope and landfill slope increasingly draw the attention of geologists and geotechnical engineers. With increasing number of filled slopes, sustainability, low maintenance, and stability are the major concerns. Biochar as a soil amendment changes the key factors and parameters in ecology (plant development, soil microbial community, nutrient/contaminant cycling, etc.) and slope engineering (soil weight, internal friction angle and cohesion, etc.). This paper reviews the studies on the production, physical and biochemical properties of biochar and suggests the potential areas requiring study in balancing ecology and man-made filled slope and landfill cover engineering. Biochar-amended soil should be considered as a new type of soil in terms of soil mechanics. Biochar performance depends on soil and biochar type which imposes challenges to generalize the research outcomes. Aging process and ecotoxicity studies of biochar are strongly required.

Gas breakthrough and emission through unsaturated compacted clay in landfill final cover

Determination of gas transport parameters in compacted clay plays a vital role for evaluating the effectiveness of soil barriers. The gas breakthrough pressure has been widely studied for saturated swelling clay buffer commonly used in high-level radioactive waste disposal facility where the generated gas pressure is very high (in the order of MPa). However, compacted clay in landfill cover is usually unsaturated and the generated landfill gas pressure is normally low (typically less than 10kPa). Furthermore, effects of clay thickness and degree of saturation on gas breakthrough and emission rate in the context of unsaturated landfill cover has not been quantitatively investigated in previous studies. The feasibility of using unsaturated compacted clay as gas barrier in landfill covers is thus worthwhile to be explored over a wide range of landfill gas pressures under various degrees of saturation and clay thicknesses. In this study, to evaluate the effectiveness of unsaturated compacted clay to minimize gas emission, one-dimensional soil column tests were carried out on unsaturated compacted clay to determine gas breakthrough pressures at ultimate limit state (high pressure range) and gas emission rates at serviceability limit state (low pressure range). Various degrees of saturation and thicknesses of unsaturated clay sample were considered. Moreover, numerical simulations were carried out using a coupled gas–water flow finite element program (CODE-BRIGHT) to better understand the experimental results by extending the clay thickness and varying the degree of saturation to a broader range that is typical at different climate conditions. The results of experimental study and numerical simulation reveal that as the degree of saturation and thickness of clay increase, the gas breakthrough pressure increases but the gas emission rate decreases significantly. Under a gas pressure of 10kPa (the upper bound limit of typical landfill gas pressure), a 0.6m or thicker compacted clay is able to prevent gas breakthrough at degree of saturation of 60% or above (in humid regions). Furthermore, to meet the limit of gas emission rate set by the Australian guideline, a 0.6m-thick clay layer may be sufficient even at low degree of saturation (i.e., 10% like in arid regions).