Partitioning Gas Tracer Tests for Measurement of Water in Municipal Solid Waste

Abstract

A key component in the operation of almost all bioreactor landfills is the addition of water to maintain optimal moisture conditions. To determine how much water is needed and where to add it, in situ methods are required to measure water within solid waste. Existing technologies often result in measurements of unknown accuracy, because of the variability of solid waste materials and time-dependent changes in packing density, both of which influence most measurement methods. To overcome these problems, a new technology recently developed by hydrologists for measuring water in the vadose zone—the partitioning gas tracer test—was tested. In this technology, the transport behavior of two gas tracers within solid waste is used to measure the fraction of the void space filled with water. One tracer is conservative and does not react with solids or liquids, while a second tracer partitions into the water and is separated from the conservative tracer during transport. This technology was tested in four different solid waste packings and was capable of determining the volumetric water content to within 48% of actual values, with most measurement errors less than 15%. This technology and the factors that affect its applicability to landfills are discussed in this paper.     

Effect of biogas generation on radon emissions from landfills receiving radium-bearing waste from shale gas development

Dramatic increases in the development of oil and natural gas from shale formations will result in large quantities of drill cuttings, flowback water, and produced water. These organic-rich shale gas formations often contain elevated concentrations of naturally occurring radioactive materials (NORM), such as uranium, thorium, and radium. Production of oil and gas from these formations will also lead to the development of technologically enhanced NORM (TENORM) in production equipment. Disposal of these potentially radium-bearing materials in municipal solid waste (MSW) landfills could release radon to the atmosphere. Risk analyses of disposal of radium-bearing TENORM in MSW landfills sponsored by the Department of Energy did not consider the effect of landfill gas (LFG) generation or LFG control systems on radon emissions. Simulation of radon emissions from landfills with LFG generation indicates that LFG generation can significantly increase radon emissions relative to emissions without LFG generation, where the radon emissions are largely controlled by vapor-phase diffusion. Although the operation of LFG control systems at landfills with radon source materials can result in point-source atmospheric radon plumes, the LFG control systems tend to reduce overall radon emissions by reducing advective gas flow through the landfill surface, and increasing the radon residence time in the subsurface, thus allowing more time for radon to decay. In some of the disposal scenarios considered, the radon flux from the landfill and off-site atmospheric activities exceed levels that would be allowed for radon emissions from uranium mill tailings.

Implications: Increased development of hydrocarbons from organic-rich shale formations has raised public concern that wastes from these activities containing naturally occurring radioactive materials, particularly radium, may be disposed in municipal solid waste landfills and endanger public health by releasing radon to the atmosphere. This paper analyses the processes by which radon may be emitted from a landfill to the atmosphere. The analyses indicate that landfill gas generation can significantly increase radon emissions, but that the actual level of radon emissions depend on the place of the waste, construction of the landfill cover, and nature of the landfill gas control system.     

Non-controlled biogenic emissions to the atmosphere from Lazareto landfill, Tenerife, Canary Islands

GOAL, SCOPE AND BACKGROUND: [corrected] Historically, landfills have been the simplest form of eliminating urban solid waste with the minimum cost. They have been the most usual method for discarding solid waste. However, landfills are considered authentic biochemical reactors that introduce large amounts of contaminants into the environment in the form of gas and leachates. The dynamics of generation and the movement of gas in landfills depend on the input and output parameters, as well as on the structure of the landfill and the kind of waste. The input parameters include water introduced through natural or artificial processes, the characteristics of the urban solid waste, and the input of atmospheric air. The main output parameters for these biochemical reactors include the gases and the leachates that are potentially pollutants for the environment. Control systems are designed and installed to minimize the impact on the environment. However, these systems are not perfect and a significant amount of landfill gas could be released to the atmosphere through the surface in a diffuse form, also known as Non-controlled emission. In this paper, the results of the Non-controlled biogenic gas emissions from the Lazareto landfill in Tenerife, Canary Islands, are presented. The purpose of this study was to evaluate the concentration of CH4 and CO2 in the soil gas of the landfill cover, the CH4 and CO2 efflux from the surface of the landfill and, finally, to compare these parameters with other similar landfills. In this way, a better understanding of the process that controls biogenic gas emissions in landfills is expected. METHODS: A Non-controlled biogenic gas emission survey of 281 sampling sites was carried out during February and March, 2002. The sampling sites were selected in order to obtain a well-distributed sampling grid. Surface landfill CO2 efflux measurements were carried out at each sampling site on the surface landfill together with soil gas collection and ground temperatures at a depth of 30-40 cm.The CH4 efflux was computed from CO2 efflux and from the ratio CH4/CO2 in the soil gas. Soil gas samples were collected at a depth of 30-40 cm using a metallic probe and 20 cc hypodermic syringes, and later stored in evacuated 10 cc vacutainers for laboratory analysis of bulk composition. The gas sample was introduced in a vacutainer filled with deionized water and displacing the water until the vacutainer was filled with the gas sample in order to avoid air contamination from entering. The surface landfill temperature of the landfill was measured at a depth of 40 cm using a digital thermometer type OMEGA 871A. Landfill gases, CO2 and CH4, were analyzed within 24 hours using a double channel VARIAN micro-GC QUAD CP-2002P, with a 10 meter PORAPLOT-Q column, a TCD detector, and He as a carrier gas. The analysis temperature was 40 degrees C and the injection time was 10 msec. Surface landfill CO2 efflux measurements were performed using a portable NDIR spectrophotometer Licor-800 according to the accumulation chamber method (Chiodini et al. 1996). The data treatment, aimed at drawing the flux map and computing the total gas output, was based on the application of stochastic simulation algorithms provided by the GSLIB program (Deutsch and Journel 1998). RESULTS: Diffuse CH4 and CO2 efflux values range from negligible values up to 7,148 and 30,573 g m(-2) d(-1), respectively. The spatial distribution of the concentration and efflux of CO2, CH4 and soil temperature, show three areas of maximum activity in the landfill, suggesting a non-uniform pattern of diffuse degassing. This correlation between high emissions and concentration of CO2, CH4 and soil temperatures suggests that the areas of higher microbial activity and exothermic reactions are releasing CO2 and CH4 to the atmosphere from the landfill. Taking into consideration the spatial distribution of the CO2 and CH4 efflux values as well as the extension of the landfill, the Non-controlled emission of CO2 and CH4 to the atmosphere by the Lazareto's landfill are of 167 +/- 13.3 and 16 +/- 2.5 t d(-1), respectively. DISCUSSION: The patterns of gas flow within the landfill seem to be affected by boundary materials at the sides. The basalt layers have a low permeability and the gas flow in these areas is extensive. In this area, where a basalt layer does not exist, the flow gas diffuses toward the sea and the flux emissions at the landfill surface are lower. This behavior reflects the possible dissolution of gases into water and the deflection of gases towards the surface at the basalt boundary. The proximity to the sea, the installation of a palm tree garden and, as a result, the contribution of water coming from the watering of this garden has reactivated the system. The introduction of sea water into the landfill and the type of boundary could be defining the superficial gas discharges. CONCLUSIONS: Results from this study indicate that the spatial distribution of Non-controlled emission of CO2 and CH4 at the Lazareto's landfill shows a non-uniform pattern of diffuse degassing. The northeast, central and northwest areas of the Lazareto's landfill are the three areas of high emissions and concentration of CO2 and CH4, and high temperatures. The correlation between high emissions and the concentration of CO2, CH4, and the high temperatures suggest that the areas of higher microbial activity and exothermic reactions are releasing more CO2 and CH4 to the atmosphere from the landfill. A high concentration of CO2 is probably due to the presence of methanotrophic bacteria in the soil atmosphere of the landfill. Patterns of gas flow within the landfill seem to be affected by boundary materials (basalt layers) of low permeability, and side boundaries of the flux emissions at the surface are higher. At the sides of seawater and sediment boundaries, flux emissions at the landfill surface are lower. This behavior reflects a possible dissolution of gases into the water and the deflection of gases towards the surface at the basalt boundary. With this study, we can compare the data obtained in this landfill with other landfills and observe the different levels of emission. The proximity to the sea and the installation of the palm tree garden palms and, as a result, the contribution of water coming from the watering of this garden has reactivated the system. Many landfills worldwide located in similar settings could experience similar gas production processes. RECOMMENDATIONS AND PERSPECTIVES: The need for investigating and monitoring sea water and sediment quality in these landfills is advisable. Concentrations and fluxes of contaminants and their impact in the area should be assessed. With this study we can compare the data obtained in these landfills with other landfills and observe the different levels of emission.     

Sewage sludge to landfill: some pertinent engineering properties

More stringent controls on the quality of wastewater discharges have given rise to increasing volumes of sewage sludge for disposal, principally to land, using either land-spreading or sludge-to-landfill operations. Current sludge-to-landfill methods generally involve mixing the concentrated sludge with other solid waste in municipal landfills. However, stricter waste disposal legislation and higher landfill taxes are forcing the water industry to look for more efficient disposal strategies. Landfill operators are also increasingly reluctant to accept sludge material in the slurry state because of construction difficulties and the potential for instability of the landfill slopes. The engineering and drying properties of a municipal sewage sludge are presented and applied, in particular, to the design, construction, and performance of sewage sludge monofills. Sludge handling and landfill construction are most effectively conducted within the water content range of 85% water content, the optimum water content for standard proctor compaction, and 95% water content, the sticky limit of the sludge material. Standard proctor compaction of the sludge within this water content range also achieves the maximum dry density of approximately 0.56 tonne/m3, which maximizes the storage capacity and, hence, the operational life of the landfill site. Undrained shear strength-water content data (pertinent to the stability of the landfill body during construction) and effective stress-strength parameters, which take into account the landfill age and the effects of ongoing sludge digestion, are presented. Landfill subsidence, which occurs principally because of creep and decomposition of the solid organic particles, is significant and continues indefinitely but at progressively slower rates.     

Polymers as Solid Waste in Municipal Landfills

Abstract

Synthetic polymers reach municipal landfills as components of products such as waste household paints, packaging films, storage containers, carpet fibers, and absorbent sanitary products. Some polymers in consumer products that reach landfills are designed to photodegrade or biodegrade. This article examines the significance of degradable polymers in management of solid waste in municipal landfills. Most landfills are not designed to photodegrade or biodegrade solid waste. Landfill disposal of stable polymers such as polyacrylics and polyethylenes is not associated with significant polymer degradation or mobility. Stability to photodegradation and biodegradation is an advantage when municipal landfills are used for disposal of polymer products as solid waste. Use of landfill disposal can be a responsible means to manage polymer waste and can be part of an overall waste management plan which includes source reduction, recycling, reuse, composting, and waste-to-energy incineration.     

非规范生活垃圾填埋场填埋气横向迁移规律及控制

我国城市中尚有大量非规范生活垃圾填埋场存在,对其进行污染整治消除填埋气导致的环境安全隐患刻不容缓.以重庆某垃圾填埋场为例,研究重庆市主城区的非规范生活垃圾填埋场填埋气的横向迁移问题,在垃圾场周边区域布设36个监测井,对监测井中的填埋气进行分析监测,以填埋气特征组分CH4气体的体积浓度变化研究填埋气的横向迁移规律.结果表明,监测井到填埋场边界的距离为监测井中CH4气体浓度的主要影响因素;垃圾场周边距离填埋场场界50 m以外的区域,填埋气的横向迁移已经相当微弱;但是距离填埋场边界50 m以内区域的填埋气的横向迁移明显,需要在距离填埋场边界50 m范围内采取措施与场内填埋气的导排措施配合,进行填埋气的污染控制.     

软土地基上生活垃圾卫生填埋场的岩土工程问题与对策

生活垃圾卫生填埋场是处理固体废弃物的有效方法之一.尽管国内外学者对与垃圾填埋场相关的许多问题已经做了大量的研究工作,但是对软土地基上填埋场可能引起的一些岩土工程问题研究不多.针对软土地基上的填埋场,分析了填埋场在建设与运营过程将会遇到的若干岩土工程问题.针对填埋场的沉降、稳定性等问题,提出了将垃圾荷载看作变量对地基沉降进行计算和设计.考虑垃圾体的稳定性,分析由于地基破坏而引起的整体稳定性问题和变形引起的衬里系统的内部稳定性问题,研究地基处理的可行性和适应性,并加强填埋过程中的岩土工程监测工作.     

Economic evaluation of a landfill system with gas recovery for municipal solid waste management: a case study

Economic activity uses resources, which leads to waste generation. With rapid industrialisation and urbanisation, per capita solid waste generation has increased considerably. Solid waste generation data for last two decades shows an alarming increase. Owing to its improper and untimely collection, the transport and disposal of municipal solid waste poses a severe threat to various components of the environment and also to public health. This paper describes the merits and demerits of various technological aspects of solid waste management. Landfill technology, as it is the most widely employed and is regarded as the most suitable and simple mechanism, especially for tropical countries such as India, is emphasised. All possible costs and benefits and externalities are examined. A cost-benefit analysis of a landfill system with gas recovery (LFSGR) has been carried out for Mumbai city's solid waste, accounting for certain external costs and benefits, and found that it could make a huge difference of savings of about Rs. 6.366 billion (approx. $0.l40 billion) per annum with reference to the existing system of waste disposal.     

Sewage Sludge to Landfill: Some Pertinent Engineering Properties

Abstract

More stringent controls on the quality of wastewater discharges have given rise to increasing volumes of sewage sludge for disposal, principally to land, using either land-spreading or sludge-to-landfill operations. Current sludge-to-landfill methods generally involve mixing the concentrated sludge with other solid waste in municipal landfills. However, stricter waste disposal legislation and higher landfill taxes are forcing the water industry to look for more efficient disposal strategies. Landfill operators are also increasingly reluctant to accept sludge material in the slurry state because of construction difficulties and the potential for instability of the landfill slopes. The engineering and drying properties of a municipal sewage sludge are presented and applied, in particular, to the design, construction, and performance of sewage sludge monofills. Sludge handling and landfill construction are most effectively conducted within the water content range of 85% water content, the optimum water content for standard proctor compaction, and 95% water content, the sticky limit of the sludge material. Standard proctor compaction of the sludge within this water content range also achieves the maximum dry density of ～0.56 tonne/m³, which maximizes the storage capacity and, hence, the operational life of the landfill site. Undrained shear strength-water content data (pertinent to the stability of the landfill body during construction) and effective stress-strength parameters, which take into account the landfill age and the effects of ongoing sludge digestion, are presented. Landfill subsidence, which occurs principally because of creep and decomposition of the solid organic particles, is significant and continues indefinitely but at progressively slower rates.     

Permeability test and slope stability analysis of municipal solid waste in Jiangcungou Landfill,Shaanxi, China

With the rapid increase of city waste, landfills have become a major method to deals with municipal solid waste. Thus, the safety of landfills has become a valuable research topic. In this paper, Jiangcungou Landfill, located in Shaanxi, China, was investigated and its slope stability was analyzed. Laboratory tests were used to obtain permeability coefficients of municipal solid waste. Based on the results, the distribution of leachate and stability in the landfill was computed and analyzed. These results showed: the range of permeability coefficient was from 1.0 × 10^–7 cm sec^–1 to 6.0 × 10^–3 cm sec^–1 on basis of laboratory test and some parameters of similar landfills. Owing to the existence of intermediate cover layers in the landfill, the perched water level appeared in the landfill with heavy rain. Moreover, the waste was filled with leachate in the top layer, and the range of leachate level was from 2 m to 5 m in depth under the waste surface in other layers. The closer it gets to the surface of landfill, the higher the perched water level of leachate. It is indicated that the minimum safety factors were 1.516 and 0.958 for winter and summer, respectively. Additionally, the slope failure may occur in summer.

Implications: The research of seepage and stability in landfills may provide a less costly way to reduce accidents. Landslides often occur in the Jiangcungou Landfill because of the high leachate level. Some measures should be implemented to reduce the leachate level. This paper investigated seepage and slope stability of landfills by numerical methods. These results may provide the basis for increasing stability of landfills.     

Tracer test for the measurement of gas diffusion and non-aqueous phase liquid (NAPL) saturation in soil

During soil bioremediation, the diffusion of oxygen into the soil is an important prerequisite for aerobic biodegradation, and the decrease of petroleum products is the ultimate goal. Both processes need to be monitored. The aim of this work was to develop a gas tracer test that yields information on both, gas diffusion and residual saturation with non-aqueous phase liquids (NAPLs) in unsaturated soil heaps. One conservative tracer (methane) and 4 partitioning gas tracers (diethylether, methyl tert-butyl ether, chloroform and n-heptane) were injected as vapors into laboratory columns filled with unsaturated sand with increasing NAPL saturation. Breakthrough curves of gaseous compounds were measured at two points and compared to analytical solutions of an analytical diffusive-reactive transport equation. By fitting of methane data, robust results for effective diffusivity (tortuosity) were obtained. NAPL saturation was most accurately measured by the moderately water soluble tracers (ethers and chloroform). The hydrophobic tracer n-heptane did not partition into water-immersed NAPL. An easy and accurate way to assess air-NAPL partitioning constants from gas chromatography retention times is furthermore reported. It is concluded that gas tracer tests have the potential for measuring two important properties in soil bioremediation systems easily and quickly.     

Greenhouse gas emission potential of the municipal solid waste disposal sites in Thailand

Open dumping and landfilling are the prevalent solid waste disposal practices in Thailand. Surveys on the disposal sites revealed the presence of 95 landfills and 330 open dumps. Methane emission potential at these sites was estimated by three methods. Results of the Intergovernmental Panel on Climate Change (IPCC) method, Landfill Gas Emission model (LandGEM), and closed flux chamber technique were compared. The methane emission potential of 366 Gg/yr using the IPCC method was higher than the estimations of the LandGEM and closed flux chamber method of 115 Gg/yr and 103 Gg/yr, respectively. An understanding of the methane emission potential initiated the analysis of upgrading the open dumps into landfills, adding landfills to meet the future needs and utilization of landfill gases. Upgrading the open dumps to landfills increased the methane emission rates and their utilization potential. Approximately 20 additional landfills may be required to meet future demands. Landfill gas (LFG) utilization appears to be feasible in the large-scale landfills.     

固体废物在固定床式热解炉内热解产气特性的实验研究

垃圾热解技术以其较低的污染排放和较高的能源回收率在固体废弃物处理领域里占有重要地位。利用小型外热型热解炉对城市垃圾、生物质及有害固体废弃物进行热解实验 ,分析发现 ,物料的挥发分、加热方式以及热解终温等对产气影响大 ,随温度的增加产气中H2 含量逐渐增多 ,C2 H4和C2 H6 的含量逐渐下降 ,气体热值有一个最大值。     

Geochemical characterization of acid mine drainage from a waste rock pile, Mine Doyon, Québec, Canada

Water quality in the unsaturated and saturated zones of a waste rock pile containing sulphides was investigated. The main objectives of the project were (1) the evaluation of geochemical trends including the acid mine drainage (AMD)-buffering mechanism and the role of secondary minerals, and (2) the investigation of the use of stable isotopes for the interpretation of physical and geochemical processes in waste rock. Pore water in unsaturated zone was sampled from suction lysimeters and with piezometers in underlying saturated rocks. The investigation revealed strong temporal (dry period vs. recharge period), and spatial (slope vs. central region of pile) variability in the formation of acid mine drainage. The main secondary minerals observed were gypsum and jarosite. There was a higher concentration of gypsum in solid phase at Site TBT than at Site 6, suggesting that part of the gypsum formed at Site 6 in the early stage of AMD has been already dissolved. Formation of secondary minerals contributed to the formation of AMD by opening of foliation planes in waste rock, thus increasing the access of oxidants like O2 and Fe3+ to previously encapsulated pyrite. The behavior of several dissolved species such as Mg, Al, and Fe2+ can be considered as conservative in the leachate. Stable isotopes, deuterium and 18O, indicated internal evaporation within the pile, and were used to trace recharge pulses from snowmelt. Isotope trends for 34S and 18O(SO4) indicated a lack of sulfate reduction and zones of active oxidation of pyrite, respectively. Results of numerical modeling of pyrite oxidation and gas and water transport were consistent with geochemical and isotopic trends and confirmed zones of high evaporation rate within the rock pile close to the slope. The results indicate that physical and chemical processes within the pile are strongly coupled and cannot be considered separately when oxidation rates are high and influence gas transport as a result of heat generation.     

A survey of municipal solid waste landfills in Beijing during 2009–2011

The investigation of municipal solid waste (MSW) treatment in China is rare due to its sensitivity and difficulty in terms of access. We chose Beijing, the capital of China, as an example to identify the characteristics of MSW landfill treatments using a 2-month investigation with 20 participants. MSW landfill treatments account for nearly 70% of the annual MSW disposal in Beijing; the landfill processes are equipped with many kinds of technologies and consume a large amount of energy and produce a variety of contaminants. The cover method (the most obvious difference in landfill tamping) mainly includes high-density polyethylene (HDPE) geomembranes with loess and soil alone (i.e., loess or sandy soil). We investigated the actual conditions of landfills and collected data on leachate and landfill gas (LFG) emissions and energy consumption during 2009–2011. The results indicated that the cover method employed by landfills was related to treatment quantity, operation, and especially landfill location. Early large-scale landfills located in plains were covered with HDPE geomembranes, and newly built landfills covered with soil tended to be equipped with HDPE covers. Using HDPE cover also contributed greatly to LFG production due to its impermeability but had no remarkable effect on leachate yield reduction due to the dry climate in Beijing. The potential was reinforced by the potentials of decrement and reuse. The disposal method of LFG can be optimized, and the power generated by the LFG process can meet the landfill demand. The gray water recycled from the leachate could be used in the landfill process.

     

Effects of water content on reactive transport of 85Sr in Chernobyl sand columns

It is known that under unsaturated conditions, the transport of solutes can deviate from ideal advective-dispersive behaviour even for macroscopically homogeneous porous materials. Causes may include physical non-equilibrium, sorption kinetics, non-linear sorption, and the irregular distribution of sorption sites. We have performed laboratory experiments designed to identify the processes responsible for the non-ideality of radioactive Sr transport observed under unsaturated flow conditions in an Aeolian sandy deposit from the Chernobyl exclusion zone. Miscible displacement experiments were carried out at various water contents and corresponding flow rates in a laboratory model system. Results of our experiments have shown that breakthrough curves of a conservative tracer exhibit a higher degree of asymmetry when the water content decreases than at saturated water content and same Darcy velocity. It is possible that velocity variations caused by heterogeneities at the macroscopic scale are responsible for this situation. Another explanation is that molecular diffusion drives the solute mass transfer between mobile and immobile water regions, but the surface of contact between these water regions is small. At very low concentrations, representative of a radioactive Sr contamination of the pore water, sorption and physical disequilibrium dominate the radioactive Sr transport under unsaturated flow conditions. A sorption reaction is described by a cation exchange mechanism calibrated under fully saturated conditions. The sorption capacity, as well as the exchange coefficients are not affected by desaturation. The number of accessible exchange sites was calculated on the basis that the solid remained in contact with water and that the fraction of solid phase in contact with mobile water is numerically equal to the proportion of mobile water to total water content. That means that for this type of sandy soil, the nature of mineral phases is the same in advective and non-advective domains. So sorption reaction parameters can be estimated from more easily conducted saturated experiments, but hydrodynamic behaviour must be characterized by conservative tracer experiments under unsaturated flow conditions.     

Analysis of long-term settlement of municipal solid waste landfills as determined by various settlement estimation methods

In this study, several existing municipal solid waste (MSW) settlement estimation methods are reviewed and applied to analyze the settlement data of nine MSW landfills. Because a biodegradation-related settlement contributes differently to a long-term total settlement depending on the age of landfills, the actual MSW landfill sites are classified into three groups to specifically address the validity of each method in its prediction of a long-term settlement for each age category. Results demonstrate that there are considerable decreases in predicted settlement potentials as fill age increases. Comparisons indicate that the individual estimation methods display a considerable variation in predicting settlements in the fresh MSW landfills. On the other hand, for the old refuse landfills, all of the estimation methods, except the extended soil model, predict low settlement potentials.     

Monitoring leachate composition at a municipal landfill site in New Delhi, India

Most of the landfills in developing countries do not have any liner at the base, or a drainage layer or a proper top cover, which results in the potential problem of groundwater/surface water contamination due to the leachate. Hence, to decide whether the leachate is to be collected and treated, or may be allowed to discharge into the adjoining soil or public sewer or surface waterbody, it is essential to have an estimate of the amount of leachate and, more importantly, the composition and strength of the leachate and variation of leachate contaminants with time as the landfill site develops. In this paper, the experimental work carried out at one of the landfills in New Delhi, India, to ascertain the composition of leachate, and its effect on the groundwater in the existing situation is presented. The variation in the leachate composition with the age of deposition of solid waste has been studied. The study indicates that the leachate composition varies considerably with the age of deposition of the waste. It may be worthwhile to use different methods for the treatment of leachate from different parts of the landfill, if collected separately. It has also been concluded that since leachate contains high concentrations of organic and inorganic constituents, including heavy metals, liners must be used at the landfills. The presence of bore wells at landfill sites to draw groundwater threatens to contaminate the groundwater, and immediate remediation steps should be taken at all landfill sites that have groundwater bore wells.     

Limitations of the toxicity characteristic leaching procedure for providing a conservative estimate of landfilled municipal solid waste incineration ash leaching

Limitations of the toxicity characteristic leaching procedure (TCLP) for simulating pollutant leaching from wastes disposed of in full-scale landfills are well understood in the waste management profession; the TCLP solution has a lower pH and greater organic acid content than typical landfill leachate. The TCLP serves its intended regulatory objective, however, as long as a conservative estimate of leaching is provided. Here, we examine TCLP’s ability to represent worst-case leaching conditions for monofilled municipal solid waste incineration (MSWI) ash. A critical examination of TCLP’s applicability to MSWI ash is especially relevant, as ash management at MSWI facilities often centers on passing TCLP, regardless of environmental risk posed by the ash or its recyclability. Multiple batch leaching tests were conducted on different MSWI ash streams: mixed ash, fly ash, and different size fractions of bottom ash. Batch-test results were compared with leachate simulating MSWI ash monofills. The TCLP did not consistently provide the most conservative estimate of leaching, supporting the need to consider alternative methodologies in future regulatory development.

Implications: This paper analyzes the existing hazardous waste regulatory testing requirement for municipal solid waste incinerator (MSWI) ash management to evaluate whether the TCLP serves its intended purpose in providing the most conservative estimate of landfilled MSWI ash. The results will serve as guidance and motivation for policy makers and the regulatory community to reevaluate the TCLP’s application for characterizing MSWI ash leaching in certain disposal scenarios and could promote consideration of alternative testing procedures based upon results of this study. This study serves to promote representative and accurate quantification of leaching risk from MSWI ash.     

Flow and transport in unsaturated fractured rock: effects of multiscale heterogeneity of hydrogeologic properties

The heterogeneity of hydrogeologic properties at different scales may have different effects on flow and transport processes in a subsurface system. A model for the unsaturated zone of Yucca Mountain, Nevada, is developed to represent complex heterogeneity at two different scales: (1) layer scale corresponding to geologic layering and (2) local scale. The layer-scale hydrogeologic properties are obtained using inverse modeling, based on the available measurements collected from the Yucca Mountain site. Calibration results show a significant lateral and vertical variability in matrix and fracture properties. Hydrogeologic property distributions in a two-dimensional, vertical cross-section of the site are generated by combining the average layer-scale matrix and fracture properties with local-scale perturbations generated using a stochastic simulation method. The unsaturated water flow and conservative (nonsorbing) tracer transport through the cross-section are simulated for different sets of matrix and fracture property fields. Comparison of simulation results indicates that the local-scale heterogeneity of matrix and fracture properties has a considerable effect on unsaturated flow processes, leading to fast flow paths in fractures and the matrix. These paths shorten the travel time of a conservative tracer from the source (repository) horizon in the unsaturated zone to the water table for small fractions of total released tracer mass. As a result, the local-scale heterogeneity also has a noticeable effect on global tracer transport processes, characterized by an average breakthrough curve at the water table, especially at the early arrival time of tracer mass. However, the effect is not significant at the later time after 20% tracer mass reaches the water table. The simulation results also verify that matrix diffusion plays an important role in overall solute transport processes in the unsaturated zone at Yucca Mountain.