Monitoring and Modeling of Sand-Bentonite Cover for ARD Mitigation

This paper deals with field measurements and hydraulic, oxygen transport and geochemical speciation modeling undertaken to evaluate the performance of a sand-bentonite test cover overlying a 20% sloping waste rock platform. A pit run (gravelly sand) layer protected the sand-bentonite layer. The study site was the Whistle Mine near Capreol, Ontario, Canada. The purpose of the study was to evaluate a number of test covers and select a final cover for the decommissioning of 7 million tonnes of acid-generating waste rock at the site. The sand-bentonite test plot and a control plot consisting of waste rock without cover were monitored over 3 years for water content, suction, soil temperature, gaseous oxygen concentrations, and water percolation. Air temperature, rainfall, snow pack and potential evaporation were also monitored. Finite element modeling showed very good agreement between modeled and measured cumulative precipitation, daily potential evaporation and cumulative evaporation, and to a lesser extent, the cumulative water percolation through the test cover. Due to construction difficulties in the field, the back of the waste rock platform was not covered with the test cover. This resulted in oxygen ingress from the back side of the waste rock. Oxygen transport modeling showed that if the entire waste rock pile had been covered, the daily oxygen flux would have been reduced by 90% to only 0.003 g/m²/day. Such low oxygen flux would minimize sulphide oxidation and hence acid generation in the waste rock. Aqueous equilibrium speciation modeling suggested that the concentrations of sulphate $\left( {{\text{SO}}_{\text{4}}^{{\text{2 - }}} } \right)$ , iron (Fe), and aluminum (Al) in percolate water in contact with waste rock were controlled by secondary minerals such as gypsum, alunite, and ferrihydrite.     

Repeatability Evaluation of Instrumented Column Tests in Cover Efficiency Evaluation for the Prevention of Acid Mine Drainage

Instrumented column tests are often used to assess the effectiveness of methods to prevent acid mine drainage (AMD). These tests are seldom duplicated, and this lack of duplicate can cast some doubt about their repeatability and reliability. This paper provides an analysis of column test studies (with duplicates) performed with a commonly used methodology. The paper presents the analysis of two multi-layer covers with capillary barrier effects in which the water retention layer was made of a non-plastic silt and of two cover scenarios involving a single-layer low sulphide cover. The first study compared the cover performance to limit AMD when different cover materials are used, while the second study compared the thickness of covers on cover performance. Statistical comparison between duplicates was made using available geochemical data, hydro-geotechnical data, and gas concentrations. Student??s t-test statistical tools and analysis of variances were used to determine the repeatability of the data. The results indicate that a good reproducibility of the column tests can be achieved with a good set-up methodology and rigorous control of the boundary conditions.     

日光温室保温被传热的理论解析及验证

为掌握日光温室保温被的传热及其保温特性,该文运用传热学理论,建立了模拟辐射、对流以及导热等形式的传热方程,在此基础上构建了日光温室保温被这类厚型覆盖材料的传热理论模型,编制了计算机程序。该模型通过对保温被内、外表面与环境间的有效辐射、投射辐射的分析,来确定辐射换热量;根据能量平衡的原理,建立了保温被表面通过对流传热、辐射传热的传热量与内部传热量之间的关系。所建立的计算方法与程序可根据覆盖材料的红外辐射特性、导热系数、覆盖层的构造参数及工作环境等条件,定量分析保温被覆盖层的传热,计算其传热量及传热系数值。试验测试结果表明,保温被的传热量及传热系数的理论计算值与试验测定值较为一致,该文的方法为保温被一类厚型覆盖材料提供了保温性定量分析评价的理论手段。     

Accelerated methane oxidation cover system to reduce greenhouse gas emissions from MSW landfills in cold, semi-arid regions

Many regional landfills for municipal solid waste (MSW) and industrial, commercial, institutional (ICI) wastes in cold, dry regions do not produce enough gas to support conventional gas extraction, treatment, and utilization or flaring. Yet, some solution is required to reduce emissions of methane and trace constituents to the atmosphere for the protection of the public and of the global climate. Methane oxidation, as a natural biochemical process, offers an opportunity to reduce methane emissions with a simple, passive alternative cover system. The goal of this article is to develop an effective design of Methane Oxidation Covers to achieve superior methane management performance while still producing equivalent closure conditions to conventional covers in semi-arid, cold climates. specifically, the goal is to reduce methane surface emissions by 50% to 80%, with no significant increase in leachate production compared with conventional covers of clay and topsoil. A field pilot test of an alternative cover system with gas collection, methane oxidation and heat extraction was conducted on an operating MSW/ICI waste landfill in Western Canada from August 2001 to February 2005. The cool, semi-arid region experiences cold winters (down to minus 40^?C) for up to 5 months of the year, and annual precipitation rates of 150 mm to 450 mm p.a., of which one third to one half falls as snow. The need to direct gas from large surface areas to gas control zones of minimal area led to the configuration of the system of gas collection trenches connected to a central methane oxidation (MethOx) bed. The need to keep the bed above 5^?C in winter required the development of a simple, passive heat transfer system. The maintenance of suitable moisture contents and the restriction of percolation were accomplished by the choice of filter material and the layering of the bed over the gas percolation layer. The test program was conducted in three phases from August 2001 to February 2005. In the first test phase, a methane oxidation bed of yardwaste compost performed well during the summer, but froze from November to April and did not resume oxidation until May. Oxygen was always present at or above 3%(vol.) and the moisture content remained above 25%(vol.) in the lower layer of the bed. The freezing temperature caused the most serious performance reduction. In the next phases of the study, a passive heating system was installed in an accelerated methane oxidation bed. Heat exchange from inside the landfill to the filter raised the bed temperature to 14 to 18^?C during the third winter of the test. The moisture contents of 25% to 50% (v/v) in the bed were high, but the percolation rate was only 7.3 mm/a, or about 2% of total precipitation. The methane oxidation performance increased with the heating of the bed, from a 33% emission reduction in an unheated bed, up to 89% in a well heated filter bed. The achievement of high oxidation performance (over 80%), the complete reduction of surface emissions from the test area (to zero), and the low percolation rate through the filter bed (less that 2%) constitute a proof of principle for MethOx covers in cool, semi-arid climates. The possible improvement of the Alternative Cover System's performance by adding vegetation to the filter bed is currently being tested in the ongoing research project.     

A Quantitative Respirometric Method for Monitoring Compost Stability

Compost stability was quantified using dissolved oxygen (D. O.) respirometry during composting of municipal solid waste (MSW) in a pilot-scale system. Changes in stability of samples taken at various times during the composting process were verified with chemical and physical tests. Rates of change of oxygen level in air over a compost sample incubated in a flask at 37°C were converted to a rate of O₂ uptake/(g volatile solids · hour). Oxygen uptake, determined with D. O. respirometry and converted to rates of dry matter loss, was correlated with actual rates, calculated from energy balances observed in the pilot-scale system. The method can be used either as a simple quality control measure or in a more complex way to calculate rates so that efficiency within or among composting facilities can be compared.     

Evaluation of the rehabilitation procedure of a pyritic mine tailings pond in Avoca,Southeast Ireland

A 32 ha tailings pond used for the disposal of pyritic mine waste was examined after a period of eight years to determine the success of the rehabilitation plan used to revegetate the site. This was achieved by examining both the vegetation cover and the quality of the topsoil in order to determine the effect of the tailings. A number of floristic habitats were identified within the site indicating that succession had occurred since revegetation of the area with metal-tolerant grass species. Four main habitats were investigated: leguminous, grass, gorse and low canopy. The soil layer in Shelton Abbey was 25–30 cm deep and contained levels of nutrients and metals comparable to those found in unpolluted soils. It was followed by a 20–25 cm layer of mixed soil and tailings, followed by the tailings only. The tailings retained elevated concentrations of metals indicating their unsuitability for growth of unadapted plant species. Vegetation from all habitats, analysed both in the summer and winter, contained higher levels of iron only compared with vegetation grown on unpolluted soils. Metals do not appear to be significantly leached from the tailings either into the soil or into surface and ground waters, and have not been accumulated to above normal levels by plant uptake. The rehabilitation protocol used at the site appears to have been successful. However, the site needs to be managed on an on-going basis to ensure the integrity of the bund and revegetated area. © 1998 John Wiley & Sons, Ltd.     

Greenhouse gas accounting for landfill diversion of food scraps and yard waste

Diverting organics from landfills to compost piles is generally recognized as a means to reduce greenhouse gas emissions. This article provides a detailed review of the Climate Action Reserve (CAR) and the U.S. EPA Waste Reduction Model (WARM) protocols on landfill diversion and composting for food scraps and yard waste. The primary benefits associated with diversion are methane avoidance. The equations used to quantify methane avoidance include first-order decay rate constants for different feedstocks to predict how quickly organics will decay. The total methane generation potential of the different feedstocks is also included. The equations include estimates of gas collection efficiencies in landfills. The decay rate constants have been determined from laboratory incubations and may not be representative of decomposition within a landfill. Estimates of gas capture efficiency have been improved and more closely reflect actual landfill conditions. Gas capture efficiency will vary based on landfill cover material, portion of the landfill where measurements take place, and whether the gas collection system is operational. Emissions during composting are included in these calculations. Only the WARM model includes a consideration of benefits for compost use. Nevertheless, significant benefits are recognized for landfill diversion of food scraps. The WARM model suggests that landfilling yard waste is superior to composting.     

Isomeric enhancement of davanone from natural davana oil aided by supercritical carbon dioxide

The chemical nature of davanone isolated from natural davana oil via packed column preparative supercritical fluid chromatography with a carbon dioxide-based mobile phase has been defined. Analyses used to characterize davanone included nuclear magnetic resonance spectroscopy, optical rotation, mass spectrometry, headspace solid-phase microextraction, enantiomeric purity via gas chromatography (GC), and GC-coupled olfactometry. For comparison, natural davana oil was subjected to the same types of measurements. The enriched davanone sample was nearly 100% optically pure. This indicates that fractionation of the davana oil with supercritical fluids at near room temperature had little effect on the optical integrity of the sample.     

韩城市西山废弃采石矿山环境恢复治理的途径

[目的]探索废弃采石矿山生态环境恢复治理模式及治理成本,为陕西省韩城市西山一带其余废弃采石矿山和煤矿山的生态环境恢复治理提供借鉴。[方法]通过现场调查、勘探及室内试验,分析韩城市西塬废弃采石矿山的环境地质问题,即采石不稳定边坡地质结构及变形破坏特征与废弃渣石占用耕地及泥流等问题。[结果]提出采石不稳定边坡与废渣的工程治理及生态恢复治理方案。采石不稳定边坡选用削方压脚与坡面植被混凝土技术,植面的植被类型应耐旱、耐寒和耐贫瘠;废弃渣石以挖高填低与分级填筑压实,坡脚修筑挡墙,坡面覆盖土壤并栽植乔灌花草等进行环境恢复治理。[结论]研究区的采石不稳定边坡和矿区堆积废渣应采用"削高填低"的工程治理方案,坡面采用植被技术的生态环境恢复治理方案。     

Gas chromatographic determination of systemic fungicide tricyclazole in soil and water

A method is described for determination of tricyclazole residues in soil and water. Tricyclazole is extracted from soil by refluxing with ethyl acetate-acetone (80 + 20 v/v) and from water by partitioning into dichloromethane. The soil extract is purified by coagulation. The compound is detected and measured by gas chromatography using a flame photometer operated in the sulfur mode. Detection limits are 8 ppb for soil and 0.8 ppb for water. Recoveries for control samples fortified with tricyclazole at 0.1-5.0 ppm averaged 97.1% for soil and 108.1% for water.     

Effects of Topography and Surface Soil Cover on Erosion for Mining Reclamation: The Experimental Spoil Heap at El Machorro Mine (Central Spain)

Mining reclamation tries to reduce environmental impacts, including accelerated runoff, erosion and sediment load in the nearby fluvial networks and their ecosystems. This study compares the effects of topography and surface soil cover on erosion on man‐made slopes coming from surface mining reclamation in Central Spain. Two topographic profiles, linear and concave, with two surface soil covers, subsoil and topsoil, were monitored for two hydrologic years. Sediment load, rill development and plant colonization from the four profiles were measured under field conditions. The results show that, in the case of this experiment, a thick and non‐compacted topsoil cover on a linear slope yielded less sediment than carbonate colluvium or topsoil cover on a concave slope. This study also shows that vegetation establishment, which plays an important role in erosion control, depends on topography. Plant cover was more widespread and more homogeneous on linear profiles with topsoil cover. On concave slopes, plant establishment was severely limited on the steepest upper part and favoured in the bottom. This study suggests that management of topography and surface soil cover should be approached systematically, taking three outcomes into consideration: (i) topsoil can lead to a successful mining reclamation regardless of topography, (ii) created concave slopes can lead to a successful mining reclamation and (iii) topography determines the vegetation colonization pattern. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of water and gas transport in layered soil covers for coal ash deposits: 2d-calculations and impact of a weak zone

A methodology for evaluating the efficiency of a soil cover to reduce water infiltration and gas transport has been adapted for coal ash deposits and two dimensions. A cover consisting of two layers, a tight layer and a protecting layer, is studied. Studied design parameters are primarily the slope and the quality of the tight layer. Simulations show that the slope has a minor impact, while the hydraulic conductivity of the tight layer is shown to be of major importance. The calculations indicate that the hydraulic conductivity of the tight layer should be smaller than 10^?8 m s^?1. However, for longer covers a lower hydraulic conductivity gives overflow indicating that a better lateral drainage must be provided for. This may be obtained by inserting a drainage layer. A negative side-effect, however, is that gas transport may increase due to the lower saturation of the cover. The impact of a high conductivity zone in the tight layer is illustrated with 3D calculations. For example, a weak zone covering 0.5% of the area with a hydraulic conductivity of 10^?7 m s^?1 (10^?9 m s^?1 for the rest of the layer) will increase the total water flow through the bottom by about 25%. The gas transport in such a heterogeneous cover will increase totally by a factor of 1.2 and locally by a factor of 5.     

露天煤矿排土场覆土厚度对土壤水分入渗及植物水分利用的影响

表土回覆是露天煤矿排土场生态修复的关键步骤，覆土厚度直接影响植物生长和复垦成本，为研究露天煤矿排土场不同覆土厚度对土壤水分入渗及植物水分利用的影响，采用室内土柱模拟试验，设置10,20,30,40,50 cm共5个覆土厚度，分别进行垂直入渗试验和室内盆栽试验(玉米),并结合氢氧同位素稳定示踪技术，研究不同覆土厚度土壤入渗和玉米水分利用特征，筛选研究区排土场最佳覆土厚度。结果表明：覆土厚度为10～30 cm(27.05～33.02 mm/min)的初始入渗速率显著高于40～50 cm(21.59～24.89 mm/min)的初始入渗速率(p<0.05),稳定入渗速率随覆土厚度的增加而增大，当覆土厚度高于40 cm后，随着覆土厚度的增加稳定入渗速率维持在3 mm/min左右。矸石层入渗过程受覆土层的影响较大，覆土厚度高于40 cm后，矸石层入渗速率基本稳定在土层连接面的入渗速率上。不同覆土厚度下玉米木质部水氢氧同位素值与土壤水氢氧同位素随土层变化曲线交点主要集中在覆土层，因此，玉米生长水分主要来源于覆土层。覆土厚度越大，2条线交点增多、交点分布范围增大，玉米对土壤水分的利用范围越大，...     

Coastal urbanization and the integrity of estuarine waterbird communities: Threshold responses and the importance of scale

Estuarine ecosystems are becoming increasingly altered by the concentration of human populations near the coastline, however a robust indicator of this change is lacking. We developed an index of waterbird community integrity (IWCI) and tested its sensitivity to anthropogenic activities within 28 watersheds and associated subestuaries of Chesapeake Bay, USA. The IWCI was used as a tool to gain insight into how human land use affects estuarine ecosystem integrity. Based on Akaike’s information criteria (AIC), a single variable model including percent developed land in estuarine watersheds was thirteen (2002) and twenty-six (2003) times more likely than models including percent agriculture and forest cover to fit the IWCI data. Consequently, we examined how suburban, urban, and total development shaped IWCI scores at three spatial scales: (1) watershed; (2) inverse-distance-weighted (IDW) watershed (land cover near the coastline weighted proportionally greater than that farther away); (3) local (land cover within 500 m of the coastline). Suburban, urban, and total development were all significant predictors of IWCI scores. Relationships were stronger at the IDW and local scales than at the whole watershed scale. Nonparametric changepoint analysis revealed a >80% probability of a threshold in IWCI scores when as little as 3.7% (2002) and 3.5% (2003) of the IDW land cover within the watershed was urban. Our results indicate that, of the landscape stressors we examined, development near estuarine coastlines is the primary stressor to estuarine waterbird community integrity, and that estuarine ecosystem integrity may be impaired by even extremely low levels of coastal urbanization.     

Thermochemical Conversion of Biomass Storage Covers to Reduce Ammonia Emissions from Dairy Manure

Manure storages, and in particular those storing digested manure, are a source of ammonia (NH₃) emissions. Installing floating manure covers provide resistance to gas transfer from manure storage surface to air and reduces NH₃ emissions; however, performance can be limited to durability. Biochar and steam-treated wood have strong potential as manure storage covers as they are capable of repelling water, resistant to microbial degradation, and could be applied to crop acreage. An additional benefit of biochars as a cover is their capability of NH₃ sorption trapping TAN (total ammoniacal N) before it is volatilized resulting in further abatement. Installation of permeable manure storage covers is difficult and adding covers with agitators could facilitate implementation. This study measured NH₃ emissions from laboratory scale storages of digested manure with raw wood (white birch, Betula papyrifera), steam-treated wood, wood biochar, and corncob biochar covers. Additional treatments included mixing biomass treatments into manure storages to measure the reduction potential of incorporated biomass. All treatments reduced emissions of NH₃ from the control by 40 to 96%. The highest NH₃ emissions reductions of 96% were achieved with the wood biochar cover. The primary mechanism for treatment was resistance to gas transfer provided by the physical barrier of covers as NH₃ sorption did not correspond to reductions. Covering digested manure storages with any of the treatments can reduce NH₃ emissions; biochar covers are a more effective barrier to NH₃ emissions and are recommended to minimize NH₃ manure storage losses.     

A Kinetic Model of the Yard Waste Composting Process

A new kinetic concept was applied to the yard waste composting process. Yard waste mixtures with different fractions of grass clippings were composted in pilot-scale vessels. Ammonia emissions were highest with high fractions of grass clippings. Calculation of reaction rate constants was based on heat and materials balances. Although the compost mass ratios (a dimensionless number that describes how far the process has advanced) of the mixtures after composting were similar, their chemical and biological analyses reveal differences. A first order reaction model is presented that can be used for plant design. The effects of temperature and particle size on process kinetics need to be investigated further.     

Acute and genetic toxicity of municipal landfill leachate

The large number of municipal solid waste (MSW) landfills and the many hazardous materials which they contain pose a serious environmental threat to our groundwater reserves. The present study was conducted to assess the environmental hazards that four MSW landfill leachates pose to the groundwater. Genetic toxicities of the landfill leachate and groundwater samples were assessed using the Salmonella/microsome (Ames test) mutagenicity bioassay, the Bacillus subtilis DNA repair bioassay, and the diploid Aspergillus nidulans chromosome damage bioassay. Acute toxicities of the leachate samples were assessed using the Microtox test. The leachate and groundwater samples were also analyzed for organic constituents using gas chromatography and gas chromatography/mass spectrometry. The chemical data were used to calculate the estimated cumulative cancer risk for each sample. All leachate samples were acutely toxic, and three of the four leachate samples were genetically toxic. Two of the four leachate samples and the groundwater sample contained concentrations of USEPA priority pollutants in excess of promulgated standards for potable water. Two of the leachates had mean estimated cumulative cancer risks on the same order of magnitude (10^?4) as leachates from co-disposal and hazardous waste landfills. The use of a battery of acute and genetic toxicity bioassays, chemical analysis, and an estimated cancer risk calculation resulted in evidence that MSW landfill leachates are as acutely and chronically toxic as co-disposal and hazardous waste landfill leachates.     

Geomorphic estimates of the stability of a uranium mill tailings containment cover: Nabarlek,Northern Territory,Australia

The geomorphic stability of the cover (cap) over the pit of Nabarlek Uranium Mine in Arnhem Land, Northern Australia, is important because radon gas and other long-lived radio-nuclides arising from mill tailings must be contained for long periods. The primary agents of denudation in the region's seasonally wet tropical environment of low relief are rainwash, overland flow, rilling and gullying. Other agents of erosion are of less concern, although biogenic agents of erosion (e.g. termites and windthrow) may enhance fluvial activity. A combination of modelling, using the Universal Soil Loss Equation, and analogue estimates of denudation and thresholds of rilling and gullying from areas with similar geology, topography and climate are used to estimate the stability of the Nabarlek cover. Denudation rates are conservatively estimated at less than 100mm ky⁻¹. It is suggested that with some minor design modifications the cover will retain its integrity for several thousand years.     

A Comparison of Spectrophotometric and Gas Chromatographic Measurements of Heavy Petroleum Products in Soil Samples

Laboratory studies were conducted to compare the infrared spectrophotometry (TPH-IR) and gas chromatography (TPH-GC) measurements of total petroleum hydrocarbon in soil samples.Real world soil samples containing #2 to #6 fuel oils, mechanical lubricating oil, diesel fuel, kerosene, jet fuel andweathered gasoline were extracted with trichlorotrifluoroethane(Freon-113) and methylene chloride. The extractants were analyzed using gas chromatography with flame ionization detection (GC-FID) and infrared spectroscopy (TPH-IR) methods.A paired statistical t-test was applied to compare the average of paired differences in the analytical results. Statistical tests were evaluated with graphical presentation of the results. In general, a trend was observed in the measured concentrations.Total petroleum hydrocarbon (TPH) concentrations measured withTPH-IR had the highest readings. The same samples extracted withmethylene chloride and analyzed with GC-FID showed lower concentrations than the TPH-IR method while the GC-FID analysisof the same samples extracted with Freon-113 produced the lowestconcentrations. Laboratory experiments indicated that TPH concentrations measured with the TPH-IR method were higher thanthe actual quantities of petroleum hydrocarbon in the soil samples.     

Determination of oxyfluorfen herbicide and oxyfluorfen amine residues in garbanzo beans by liquid chromatography

Oxyfluorfen and oxyfluorfen amine were determined by liquid chromatography (LC) with ultraviolet (UV) and photoconductivity detection (PCD). A simple extraction procedure acceptably recovered both analytes from garbanzo beans over a wide range of fortifications (0.05 to 20 ppm) (83 +/- 4 for oxyfluorfen; 85 +/- 4 for oxyfluorfen amine). Percent recoveries decreased slightly as the fortification level decreased. Both analytes could be determined simultaneously at a concentration greater than 0.2 ppm in garbanzo beans. Detection limits were 3 ng for oxyfluorfen and 100 ng for oxyfluorfen amine using LC/UV, and 12 ng for both oxyfluorfen and oxyfluorfen amine with LC/PCD. Different knitted reaction coils and photoreactors were evaluated. Photoproduct yields and identification were determined by ion chromatography. The LC/PCD method measures oxyfluorfen and oxyfluorfen amine separately and has a shorter analysis time, while the standard method using gas chromatography measures total residues and is more sensitive.