Final Cover System Research Articles

Enhancing landfill efficiency to drive greenhouse gas reduction: A comprehensive study on best practices and policy recommendations.

This article investigates the pivotal role of non-hazardous waste landfills in achieving greenhouse gas (GHG) reduction objectives within the European Union (EU).1 This study leverages the experience of key stakeholders in the European landfilling, assesses the efficacy of 'best-in-class' landfill installations, evaluates their potential impact on GHG reduction, and offers concrete recommendations for operators and policymakers. 'Best-in-class' landfills exceed the commonly accepted best practices by implementing all the following practices: (1) an anticipated capture system during the operating phase, (2) prompt installation of the final cover and capture system, with use of an impermeable cover, (3) operated as bioreactor, keeping optimal humidity, (4) adequate maintenance and reporting, (5) recovery of captured gas and (6) treatment of residual methane emissions throughout the waste decomposition process. The main finding is that switching from the actual mix of practices to 'best in class' practices would reduce by ~21 MtCO2eq (-36%) the emissions due to the degradation of waste landfilled between 2024 and 2035, compared to the 'business-as-usual scenario', while also providing a renewable energy source, bringing potential avoided emissions and energy sovereignty. The findings underscore that in addition to implementing the organics diversion and waste reduction targets of the EU, adopting 'best-in class' landfill practices has the potential to bolster energy recovery, mitigate emissions and stimulate biomethane production, thereby advancing the EU environmental goals.

A true green cover for industrial waste landfills

Greenhouse gas (GHG) emissions in the United States totaled 5,981 million metric tons of carbon dioxide equivalent (MMT CO2eq) in 2020. Of that, GHG emissions by the pulp and paper sector amounted to 35 MMT CO2eq direct emissions and those by industrial waste landfills summed to 7.4 MMT CO2eq direct emissions. Loss of GHG sinks due to change in land use further contributes to the net GHG emissions. Industrial waste landfills are typically required to comply with certain federal and state regulations, including meeting requirements for final cover systems. Conventional final cover systems have included use of soil covers and/or soil-geosynthetic composite covers. An engineered turf cover provides for an excellent “green” alternative final cover system for industrial waste landfills. This paper discusses various sustainability aspects pertaining to use of an engineered turf final cover, including: (i) significantly low carbon footprint associated with the construction of an engineered turf alternative final cover when compared to closure using a traditional or prescriptive cover system; (ii) saving valuable soil and land resources; (iii) saving water resources by reduction in its use during and after construction; (iv) reducing impacts associated with borrow areas; and (v) reducing overall carbon footprint. Further, when using an engineered turf cover, opportunities exist for beneficial reuse of land, including development of solar energy. A brief discussion on the potential for development of solar energy is included.

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.

Low permeability sealing materials based on sewage, digestate and incineration industrial by-products in the final landfill cover system

This study explores repurposing municipal solid waste from the sewage, digestate, and incineration industries as landfill-sealing materials, aligning with circular economy principles. The main materials include digested sewage sludge (DSS), pretreated digested sewage sludge (PDSS), and digestate sludge (DS), with biomass bottom ash (BBA) and Al-anodizing waste (AAW) introduced as additives, complemented by 1.5 wt% water glass to enhance the sealing performance. The research evaluates the characteristics of the various treated and sourced sludges and additives, assessing their influence on water permeability, reaction products and the environmental consequences. Results demonstrate the achievement of low permeability in the sludge-based sealing materials, with optimal performance observed in the specimens prepared with DSS and AAW (k value = 3.78 ×10−12 m/s). Thermal Pressure Hydrolysis pre-treatment in sewage plants reduces the organic content in PDSS, resulting in a slight increase in permeability. DS-based specimens exhibit higher permeability due to their relatively lower organic content in DS. Gypsum is the primary reaction product attributed to leachable sulphate in BBA and AAW. Water glass addition in BBA-modified specimens promotes silica gel formation, while AAW effectively reduces matrix permeability as an externally added gel-like substance. Additionally, heavy metals (As, Pb and Cr) derived from the by-products are effectively immobilized in the sealing materials owning to the coagulation effect of organic matter in the sludge and sulphates in the products. Overall, this novel approach to landfill sealing materials exhibits promising applications in the Netherlands, offering cost savings and reduced environmental impact by recycling industrial by-products.

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.

VOCs emission from a final landfill cover system induced by ground surface air temperature and barometric pressure fluctuation

Volatile organic compounds (VOCs) emission flux and their concentration profiles were measured at a final municipal solid waste (MSW) landfill cover in Hangzhou, China. The influencing parameters, especially ground surface air temperature and pressure were monitored concomitantly. Furthermore, a numerical model incorporating coupled thermo-hydro-chemical interaction to assess VOCs emission from this final landfill cover (LFC) system was developed and validated with the field test results. The tested total VOC emission flux from the final cover is 0.0124 μg/m2/s, which indicates that the total amount of VOCs emitted into the atmosphere is 391 mg/m2 annually. Among these, dichloromethane (DCM) dominated VOCs emission flux during May, comprising 51.8% of the total emission flux. The numerical simulation results indicated that the diffusive emission flux of VOCs varied consistently with the fluctuation of atmospheric temperature. Whereas, the advective flux varied inversely with the fluctuation of barometric pressure. The highest difference in diffusive emission flux induced by temperature variation is 183 μg/m2/day and occurred in spring. Moreover, the results demonstrated that the impact of atmospheric temperature and pressure fluctuation on the emission of VOC from final covers is non-negligible when reasonably assessing the risks of landfill and landfill gas emission budget.

Study on Utilization of Biopolymer in Liner

Abstract: Biogeotechnology is a branch of Geotechnical Engineering that deals with the application of biotransformation, biogrouting and mineral precipitation (MICP) to geotechnical engineering problems. Soil capping is a technology to curb the interaction between a waste body and the ground surface. A final cover system in landfill capping play a major role in intercepting rainwater infiltration and percolation of surface water into the subsurface waste dumped area. In order to minimize the water infiltration through different barrier layers such as single liner system, single composite liner system and double liner system in cover system are recommended. A single composite liner system comprises of two barrier (made up of different material), placed over one another to provide beneficial effect whereas the single and double liner system consists of same material to attain the effect. The present study deals with the action of sea weed in the form of powder (produced by the cell wall) in the layer of soil capping which intercept the rainwater intrusion in liner. The results obtained from the hydraulic conductivity of different treated soils indicate that the effect of single liner system is equivalent to single composite liner system. It has been observed that the addition of sea weed powder causes dissociation of hydroxyl groups attached to silicon in silica sheets with increase in optimum water content. Thus the addition of sea weed powder decreases the infiltration rate by clogging the soil layers.

Landfill Codisposal of On-Site Vegetation and Coal Combustion Residuals: Implications for Gas Management

Historically, ash from coal combustion has been disposed of in ponds that were not designed with engineered containment systems. As a result of regulatory changes, it is estimated that coal combustion residuals (CCRs) from hundreds of unlined ponds will have to be excavated and disposed of in new lined landfills or the existing CCR ponds will have to been closed in-place with an engineered final cover system. The excavated or in-place CCR may contain vegetative matter that has the potential to decompose to CH4 and CO2. The objective of this study was to demonstrate a framework to assess the need for a gas collection system to accommodate the disposal of a mixture of CCR and vegetation in a lined landfill. Methane generation rates and yields for vegetative matter mixed with CCR were measured in biochemical methane potential and specific methane activity tests at 15, 20, and 37 °C. The data were then used to parameterize a methane generation model to estimate the gas flux at the landfill surface for a series of hypothetical disposal scenarios. Results showed that the specific decay rate constant (k) ranged from 0.00037 to 0.00872 yr–1, while the methane yield (L0) ranged from 84 to 120 mL CH4/dry g. Temperature was the most important determinant of the decomposition behavior. Simulations of gas flux for several disposal scenarios showed that the modeled flux from the decomposition of vegetation was below the CH4 and CO2 transmission rates reported for a geomembrane liner final cover system, suggesting that an active gas collection will not be necessary under the modeled disposal conditions.

Heavy metal leaching behaviour and long-term environmental risk assessment of cement-solidified municipal solid waste incineration fly ash in sanitary landfill

Cement solidification is a commonly used pre-treatment method for municipal solid waste incineration fly ash (MSWIFA) prior to sanitary landfill. However, the long-term environmental risk of cement-solidified MSWIFA blocks in the exposed scenario of zoning sanitary landfill remains unclear. In this study, the leaching characteristics of different heavy metals in cement-solidified MSWIFA blocks under deionized water and acid rain scenarios were firstly investigated. The leaching control mechanisms of heavy metals were also explored and applied to established mechanical models for the estimation of long-term environmental risk. Results revealed that Pb leaching from cement-solidified MSWIFA blocks was controlled by diffusion; Cu, Cr and As leaching was mainly controlled by surface wash-off and diffusion; and Ni leaching was mainly controlled by diffusion and dissolution. Additionally, the established bulk diffusion, first-order reaction/diffusion and diffusion/dissolution models could accurately fit the abovementioned three types of heavy metals with different leaching control mechanisms (R2 > 0.95). Under acid rain scenarios， according to the prediction results of the calibrated models, the cumulative leaching amount of Pb in 718 d was higher than the limit in GB16889-2008, the cumulative leaching amount of Cu, Cr, As and Ni did not exceed the limit in GB 16889-2008 even in 50 years. Therefore, the long-term environmental risk was relatively high for Pb but was low for Cu, Cr, As and Ni in cement-solidified MSWIFA blocks. This finding could be attributed to the strong alkali environment of cement-solidified MSWIFA blocks (pH > 12) that induced Pb salts (e.g. Pb(OH)2 and PbSO4) dissolution. Therefore, the removal of partially soluble Pb salts from freshly made cement-solidified MSWIFA blocks by water or natural rainwater (e.g. without final cover system) washing in the initial landfilling stage (e.g. the leachate drainage system remains functional) is an effective countermeasure to reduce the environmental risks in zoning sanitary landfill.

Quantification of Municipal Solid Wastes Generated in Attingal Municipality and Design of Sanitary Landfill

Management of Municipal Solid Wastes is a serious environmental and health problem which is faced in major cities all over the world. Waste management studies of municipalities will help identify the lacunae and loopholes in solid waste management and thus help to minimize generation of solid wastes and pollution. In this regard, a waste management study was carried out for Attingal Municipality, Thiruvananthapuram District, through field visits and data collection from the Municipality. The study was concentrated to investigate the present status of the solid waste management, to quantity the wastes generated in the Municipality and to suggest remedial measures for improvement. Design of sanitary landfill was done based on the quantity of wastes generated and population growth of the Municipality. A sanitary landfill of length 52m and breadth 26m was designed for a period of 10 years. The design also included liner system, final cover system, leachate collection and treatment facility and environmental monitoring system.

Seepage characteristics of three-layered landfill cover system constituting fly-ash under extreme ponding condition

A multi-layered final cover system is constructed over the landfill after it reaches its full capacity to minimize water ingress into the underlying hazardous waste. Three layered landfill cover are designed for areas experiencing very humid climatic conditions. Under the effects of climate change, the occurrences of extreme rainfall events become more frequent and this has resulted in catastrophic floods and hence extreme ponding. This study investigates the seepage characteristics of three-layered capillary barrier cover systems under an extreme ponding condition of 1.5 m water head, through detailed laboratory column tests and finite-element seepage analysis. Four 1.2 m-tall columns having different configurations (C1–C4) were studied. Fly ash (FA) was used to amend the surface and barrier layers in columns C2 and C4, in line with the novel concept of “waste protect waste”. Spatiotemporal variations of volumetric water content of the four columns were monitored for three years continuously. With FA amendment in the surface layer and an inclusion of a 0.01 m thick geosynthetic clay liner between the drainage and barrier layers, the onset of basal percolation was significantly delayed until 700 days of ponding, compared to 115 days without FA amendment. Capillary flow dominated the gravitational flow and perched water table was formed as waterfront advanced from the drainage to barrier layers. Further seepage analysis considering a realistic humid climate boundary condition showed that all four configurations were successful in preventing basal percolation for 800 days.

Unexpectedly higher soil organic carbon accumulation in the evapotranspiration cover of a coal bottom ash mixed landfill

Monolayer barriers, which are usually known as evapotranspiration (ET) covers, have long been used as alternative final cover systems in waste landfills. Coal bottom ash was evaluated as a good alternative to soil in landfill ET cover systems to increase the bottom ash (BA) recycling ratio in the past. In a previous study, applying BA promoted plant growth characteristics and improved the soil physicochemical properties, particularly the soil organic carbon (SOC) content. In this study, we investigated the effect of BA on the SOC increase by examining the chemical and physical characteristics of ET cover systems, and we compared BA mixed and pure soils. We collected two types of soil from the landfill cover, namely, BA mixed soil (BA 35% + soil 65%) and soil alone (100%), for treatments during the 5th year after installation. Bottom ash mixed soil has four times more SOC than the pure soil at the surface soil layer, but the SOC contents significantly decreased with the soil depth in BA mixed soil, and no differences were found between BA mixed soil and pure soil below a 25 cm soil depth. In addition, there was no significant difference in the chemical composition of the SOC according to a13C NMR. However, the allophane contents were significantly higher in BA mixed soil than pure soil, which physically protects the material from organic matter decomposition. Conclusively, the higher allophane content originating from BA might act as the primary factor in the high accumulation of soil organic carbon in the BA mixed soil layer by retarding the organic matter decomposition.

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

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.

Landfill Final Cover Systems Design for Arid Areas Using the HELP Model: A Case Study in the Babylon Governorate, Iraq

The main purpose of selecting proper designs for landfills is to accommodate quantities of waste without having a negative effect on the surrounding environment and human health. The Babylon Governorate (province) in Iraq was taken as an example of an arid area with very shallow groundwater and where irregular waste disposal sites had developed that had not been subject to international standards when they were selected for landfill use. In the current study, the suggested design for landfills is a base liner and final cover system. In this suggested design, the final cover system allows for three scenarios. The first scenario considers an evapotranspiration soil cover (ET) (capillary barriers type), the second scenario is a modified cover design of “RCRA Subtitle D”, and the third scenario is a combination of the first and second scenarios. The HELP 3.95 D model was applied to the selected landfill sites in the governorate to check if there was any penetration of the leachate that might in future percolate from the landfill’s bottom barrier layer in arid areas. The results from the suggested landfill design showed that there was no leachate percolation from the bottom barrier layer using the second and third scenarios. For the first scenario, however, there was a small amount of leachate through the bottom barrier layer in the years 2013 and 2014.

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.

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

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

Influence of dynamic coupled hydro-bio-mechanical processes on response of municipal solid waste and liner system in bioreactor landfills

A two-dimensional (2-D) mathematical model is presented to predict the response of municipal solid waste (MSW) of conventional as well as bioreactor landfills undergoing coupled hydro-bio-mechanical processes. The newly developed and validated 2-D coupled mathematical modeling framework combines and simultaneously solves a two-phase flow model based on the unsaturated Richard’s equation, a plain-strain formulation of Mohr-Coulomb mechanical model and first-order decay kinetics biodegradation model. The performance of both conventional and bioreactor landfill was investigated holistically, by evaluating the mechanical settlement, extent of waste degradation with subsequent changes in geotechnical properties, landfill slope stability, and in-plane shear behavior (shear stress-displacement) of composite liner system and final cover system. It is concluded that for the given specific conditions considered, bioreactor landfill attained an overall stabilization after a continuous leachate injection of 16years, whereas the stabilization was observed after around 50years of post-closure in conventional landfills, with a total vertical strain of 36% and 37% for bioreactor and conventional landfills, respectively. The significant changes in landfill settlement, the extent of MSW degradation, MSW geotechnical properties, along with their influence on the in-plane shear response of composite liner and final cover system, between the conventional and bioreactor landfills, observed using the mathematical model proposed in this study, corroborates the importance of considering coupled hydro-bio-mechanical processes while designing and predicting the performance of engineered bioreactor landfills. The study underscores the importance of considering the effect of coupled processes while examining the stability and integrity of the liner and cover systems, which form the integral components of a landfill. Moreover, the spatial and temporal variations in the landfill settlement, the stability of landfill slope under pressurized leachate injection conditions and the rapid changes in the MSW properties with degradation emphasizes the complexity of the bioreactor landfill system and the need for understanding the interrelated processes to design and operate stable and effective bioreactor landfills. A detailed discussion on the results obtained from the numerical simulations along with limitations and key challenges in this study are also presented.

Seismic Analysis of Municipal Solid Waste Dumps: Site Specific Case Studies From Delhi, India

Abstract Site specific seismic analysis is necessary for reliable assessment of performance of municipal solid waste (MSW) dump sites/landfills due to the highly heterogeneous nature of waste mass. This paper presented the results of one-dimensional site specific seismic studies performed for two old and tall MSW dump sites in Delhi, India. Unit weight profile and dynamic properties of emplaced MSW at these two sites, evaluated from field and large scale laboratory tests, were utilized in seismic analysis. Synthetically generated strong ground motions using finite source model and specific barrier model, with appropriate seismological parameters for the Delhi region, were used. It is observed that the ground motion amplification potential of MSW for low intensity events in the present study compared well with that reported for Operating Industries Inc. landfill in California, which is instrumented with strong ground motion recording stations. Amplification observed in the present study can be useful for the design of a final cover system during the closure of the dump sites studied herein. In addition, results in terms of the maximum horizontal equivalent acceleration for base-sliding case were in agreement with those reported in the literature, and can be used for preliminary estimates for the design of liner system of new engineered MSW landfills in Delhi.