HYDRUS-1D软件在地下水污染源强定量评价中的应用

以垃圾填埋场渗滤液中的氨氮为研究对象,利用HYDRUS-1D模型模拟其在包气带中的迁移转化规律,最终预测出氨氮到达地下水位处时的浓度值。引入折减系数的概念,通过改变填埋场渗滤液中氨氮的初始浓度及土壤包气带结构,计算不同输入条件下的折减系数值,用其综合反映包气带对于某一特征污染物的衰减能力,为地下水污染源强定量评价提供数据支持。     

不同龄渗滤液及其在包气带中的迁移转化研究

通过实验室土柱模拟方法,研究了不同场龄渗滤液中有机污染物、氮以及 Fe、Mn、Zn、Cd 在包气带中的迁移转化规律.结果表明,不同场龄渗滤液理化性质差别很大,随着场龄的增加,COD 从40 194 mg/L降低到 1 778 mg/L,NH4 浓度从1 758 mg/L升高到2 166 mg/L,金属浓度则减小.经过以细砂为介质的包气带后,新渗滤液易对地下水造成高浓度有机物污染,而老渗滤液更容易造成地下水的高浓度氮污染.Fe、Mn 和 Cd 在包气带中比较稳定,而 Zn 的迁移能力很强,易对地下水构成威胁.     

渗滤液污染包气带中铁的形态变化

从渗滤液场龄和包气带岩性两方面出发,研究了新、老渗滤液对亚粘土和细砂包气带环境中Fe的含量及存在形态的影响。结果表明：新、老渗滤液分别能使细砂包气带介质中除残渣态以外Fe的含量增加16.68%或降低13.82%。亚粘土比细砂作为包气带介质更能缓冲渗滤液对介质中Fe的影响程度,其受影响范围在包气带0～20 cm深度处。当亚粘土为介质的包气带被新渗滤液污染后,其表层介质中碳酸盐结合态Fe的含量会增加15倍之多,为缓冲渗滤液Fe的污染做出了巨大贡献,但这部分Fe的存在也是潜在的二次污染源,在环境pH急剧变化的情况下,它可能会引起地下水高铁污染。     

防止地下水监测误差

在地下水监测工作中,防止人为因素产生的误差,取得有代表性的地下水样,及时、准确地反映地下水水质状况,是极为重要的. 由于地下水的存在形式而产生了一系列特点.如因包气带将地下水和大气隔开,使地下水一般处于还原状态;因包气带的自净作用,使地表污染物经包气带进入地下水之后含量一般比较低;地下水的运动特点也使进入地下水中的污染物遵循一定规律进行迁移、扩散和变化等等.这些特点在一定程度上使监测     

基于DRASTIC的包气带阻滞污染物能力研究

对包气带阻滞污染物能力的研究,对保护地下水脆弱性具有重要意义.将传统DRASTIC方法结合层次分析法,对各评价指标赋以新的权重,并依托地理信息系统(GIS)平台,对河南省土壤包气带阻滞污染物的能力进行评价,得到了河南省包气带阻滞能力分区图.结果表明,针对现状所进行的包气带阻滞污染物能力的评价对实际情况具有一定的代表性,...     

武汉金口垃圾填埋场对地下水环境的影响分析

分析了武汉金口垃圾填埋场中不同填埋时间的垃圾渗滤液特性和周边地下水水质,并结合场地条件分析垃圾渗滤液对地下水环境的影响机制。结果表明:(1)所有垃圾渗滤液(均超过7年)中COD、氨氮、Cl-均分别低于500、1 000、1 000mg/L;重金属含量较低。垃圾渗滤液中COD、氨氮和Cl-均随填埋时间延长而降低。(2)填埋场周围50m内的上层滞水均受到垃圾渗滤液水平渗透的影响,主要表现为高锰酸盐指数和氨氮均不能满足《地下水质量标准》(GB/T 14848—93)中Ⅲ类标准,其中氨氮超标严重,平均超标89.3倍,高锰酸盐指数平均超标1.0倍。相比场区地下水的下游方向,上游方向的上层滞水受污染程度较轻。(3)由于厚层黏土的阻隔,距地表约25m的上更新统承压水的水质相对较好,除武汉市上更新统承压水普遍存在的超标组分(氨氮和Mn)外,其他指标基本满足GB/T 14848—93中Ⅲ类标准,其受垃圾填埋场渗滤液垂直渗透影响较小。这为简易填埋场关闭后的场地维护和开发利用以及新建填埋场的选址提供借鉴。     

原位回灌对垃圾填埋场稳定化进程影响的实验研究

针对填埋法处理城市生活垃圾造成的土地占用和水资源污染等系列环境问题,通过在实验室搭建的模拟城市生活垃圾填埋场实验台,系统研究了淋滤介质、淋滤量和淋滤频率等条件对生活垃圾填埋场稳定化进程的影响。结果表明:采用垃圾渗滤液原液淋滤、淋滤频率为3次/d、淋滤总量为10L时,垃圾填埋场初期稳定化进程最快;在此条件下,垃圾渗滤液中污染物COD、氨氮和TP出现负增长对应的时间分别为17、29、18d。研究结果对进一步开展垃圾渗滤液深度处理和工程应用等相关研究具有重要的指导意义。     

包气带土壤对石油烃的截留作用研究

包气带土壤对地表污染物的截留作用是地下水免受污染的一道天然屏障.土壤截留污染物的能力对地下水石油烃污染的治理起着关键作用,在对实际污染场地进行调查研究的基础上,采用土柱淋滤、吸附/解吸、石油挥发等室内模拟实验,研究包气带土壤对石油烃的截留作用及其影响因素.结果表明,细砂、中砂和粗砂3种土壤对石油烃的截留率分别为81.0...     

基于文献计量的垃圾填埋场污染物研究现状与趋势分析

基于Web of Science核心合集数据库，利用VOSviewer和CiteSpace软件，对2000—2020年有关垃圾填埋场污染物的文献进行了计量分析。结果表明：(1)2000—2020年，垃圾填埋场污染物领域的发文量总体呈逐年增加态势，2015年后中国的发文量直线上升；(2)中国的机构虽然发文量多，但均篇被引频次不是很高，影响力还有待进一步提升；(3)垃圾填埋场污染物研究的热点包括城市固体废弃物及其处置过程，垃圾渗滤液或污废水中有机污染物的去除、降解，垃圾填埋场周边地表水和地下水中污染物的环境行为，无机污染物氮元素的去除，垃圾填埋场中新污染物的环境行为和去除5大类；(4)垃圾填埋场污染物主要分为重金属和有机污染物两大类，其中重金属在不同环境介质中出现的频次高于有机污染物，填埋气等气态污染物造成的环境问题也不容忽视。     

垃圾填埋场对地下水污染的模拟研究

在对长春市某垃圾填埋场进行野外调查的基础上 ,于室内进行了垃圾淋滤模拟实验。分析了垃圾渗滤液污染组分的自然衰减规律 ,建立了垃圾填埋场地下水污染的数值模型 ,采用FEFLOW软件对其进行模拟和预报 ,并取得了较好的效果 ,最后提出防止和防治垃圾填埋场污染地下水的若干措施。     

Modelling the migration of contaminants through variably saturated dual-porosity, dual-permeability chalk

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water recharge conditions prevailing during the experiments. Under intense recharge conditions, tracers migrated across the partially or fully saturated fissure network, at high velocity in accordance with the high hydraulic conductivity and low effective porosity (fracture porosity). At the same time, a portion of the tracer was temporarily retarded in the almost immobile water located in the matrix. Under natural infiltration conditions, the fissure network remained inactive. Tracers migrated downward through the matrix, at low velocity in relation with the low hydraulic conductivity and the large porosity of the matrix. Based on these observations, Brouyère et al. (2004a) [Brouyère, S., Dassargues, A., Hallet, V., 2004a. Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation, J. Contam. Hydrol., 72 (1-4), 135-164, doi: 10.1016/j.conhyd.2003.10.009] proposed a conceptual model in order to explain the migration of solutes in variably saturated, dual-porosity, dual-permeability chalk. Here, mathematical and numerical modelling of tracer and contaminant migration in variably saturated fissured chalk is presented, considering the aforementioned conceptual model. A new mathematical formulation is proposed to represent the unsaturated properties of the fissured chalk in a more dynamic and appropriate way. At the same time, the rock water content is partitioned between mobile and immobile water phases, as a function of the water saturation of the chalk rock. The groundwater flow and contaminant transport in the variably saturated chalk is solved using the control volume finite element method. Modelling the field tracer experiments performed in the variably saturated chalk shows the adequacy and usefulness of the new conceptual, mathematical and numerical model.     

Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation

This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone overlying a chalk aquifer in Belgium. Various laboratory measurements were performed on core samples collected during the drilling of boreholes in the experimental site. In the field, experiments consisted of well logging, infiltration tests in the unsaturated zone, pumping tests in the saturated zone and tracer tests in both the saturated and unsaturated zones. Results show that gravitational flows govern groundwater recharge and solute migration mechanisms in the unsaturated zone. In the variably saturated chalk, the migration and retardation of solutes is strongly influenced by recharge conditions. Under intense injection conditions, solutes migrate at high speed along the partially saturated fissures, downward to the saturated zone. At the same time, they are temporarily retarded in the almost immobile water located in the chalk matrix. Under normal recharge conditions, fissures are inactive and solutes migrate slowly through the chalk matrix. Results also show that concentration dynamics in the saturated zone are related to fluctuations of groundwater levels in the aquifer. A conceptual model is proposed to explain the hydrodispersive behaviour of the variably saturated chalk. Finally, the vulnerability of the chalk to contamination issues occurring at the land surface is discussed.     

Electrokinetic ion transport through unsaturated soil: 1. Theory, model development, and testing

An electromigration transport model for non-reactive ion transport in unsaturated soil was developed and tested against laboratory experiments. This model assumed the electric potential field was constant with respect to time, an assumption valid for highly buffered soil, or when the electrode electrolysis reactions are neutralized. The model also assumed constant moisture contents and temperature with respect to time, and that electroosmotic and hydraulic transport of water through the soil was negligible. A functional relationship between ionic mobility and the electrolyte concentration was estimated using the chemical activity coefficient. Tortuosity was calculated from a mathematical relationship fitted to the electrical conductivity of the bulk pore water and soil moisture data. The functional relationship between ionic mobility, pore-water concentration, and tortuosity as a function of moisture content allowed the model to predict ion transport in heterogeneous unsaturated soils. The model was tested against laboratory measurements assessing anionic electromigration as a function of moisture content. In the test cell, a strip of soil was spiked with red dye No 40 and monitored for a 24-h period while a 10-mA current was maintained between the electrodes. Electromigration velocities predicted by the electromigration transport model were in agreement with laboratory experimental results. Both laboratory-measured and model-predicted dye migration results indicated a maximum transport velocity at moisture contents less than saturation due to competing effects between current density and tortuosity as moisture content decreases.     

地下水中轻质有机污染物(LNAPL)透镜体研究

在二维砂槽模型中模拟了轻质油在均匀多孔介质地下水非饱和区中的运移过程。模拟结果表明,地下水毛细区是轻质油污染的重点区,除了ＬＮＡＰＬ的残留以外,进入地下水饱和的ＬＮＡＰＬ终将被地下水顶托回到毛细区中,毛细区以上的约大多民将在重力作用下进入毛细区中,试验中观察到达稳定状态时ＬＮＡＰＬ透镜体的上边缘略微高出毛细区。利用多孔介质毛细管模型,建立了利用界面张力、接触角、介质特征孔隙直径等物理量估算不同位置     

Gas production and migration in landfills and geological materials.

Landfill gas, originating from the anaerobic biodegradation of the organic content of waste, consists mainly of methane and carbon dioxide, with traces of volatile organic compounds. Pressure, concentration and temperature gradients that develop within the landfill result in gas emissions to the atmosphere and in lateral migration through the surrounding soils. Environmental and safety issues associated with the landfill gas require control of off-site gas migration. The numerical model TOUGH2-LGM (Transport of Unsaturated Groundwater and Heat-Landfill Gas Migration) has been developed to simulate landfill gas production and migration processes within and beyond landfill boundaries. The model is derived from the general non-isothermal multiphase flow simulator TOUGH2, to which a new equation of state module is added. It simulates the migration of five components in partially saturated media: four fluid components (water, atmospheric air, methane and carbon dioxide) and one energy component (heat). The four fluid components are present in both the gas and liquid phases. The model incorporates gas-liquid partitioning of all fluid components by means of dissolution and volatilization. In addition to advection in the gas and liquid phase, multi-component diffusion is simulated in the gas phase. The landfill gas production rate is proportional to the organic substrate and is modeled as an exponentially decreasing function of time. The model is applied to the Montreal's CESM landfill site, which is located in a former limestone rock quarry. Existing data were used to characterize hydraulic properties of the waste and the limestone. Gas recovery data at the site were used to define the gas production model. Simulations in one and two dimensions are presented to investigate gas production and migration in the landfill, and in the surrounding limestone. The effects of a gas recovery well and landfill cover on gas migration are also discussed.     

Effects of degree of water saturation on dispersivity and immobile water in sandy soil columns

Three natural nonaggregated soil samples, with similar grain-size distributions, have been used to determine the dispersive behavior of porous media under steady, saturated and unsaturated flow conditions. Tritium was used as a tracer and was found to have no sorption on the solid matrix. Generated breakthrough curves (BTCs) for the unsaturated experiments were symmetrical with no evidence of tailing. The unsaturated experiments for two of the soils were adequately described by considering all the water in the pore volume as mobile. However, about 10% of the pore water, independent of the degree of saturation, was found to be immobile in the case of the third soil during unsaturated flow. For this soil, there was no mass transfer between the two water regions, indicating that the immobile water is essentially isolated from the flowing water fraction. For all three soils, dispersivity under unsaturated conditions was found to be higher, independent of the degree of water saturation, than the value determined for the saturated experiments. This is inconsistent with what would be expected from the simple bundle-of-capillary-tubes model and does not agree well with a more sophisticated conceptualization of the porous medium. The data, however, clearly indicate a wider range in pore-water velocities when these soils are desaturated.     

Chemical modifications of groundwater contaminated by recharge of treated sewage effluent

Long-term monitoring of the chemical composition of recharge sewage effluent and associated contaminated groundwater from the Dan Region Sewage Reclamation Project shows, after 16 years of recharge operation, the presence of a distinct saline plume (up to 400 mg/l Cl), extending 1600 m downgradient in the Coastal Plain aquifer of Israel. The recorded electrolyte composition of groundwater in the vicinity of the recharge area reflects the variations in the compositions of the sewage effluents, as well as water-rock interactions induced by the recharge of treated sewage effluents. The original sewage composition was modified, particularly during early stages of effluent migration in the unsaturated zone, by cation-exchange and adsorption reactions. Since the soil sorption capacity is finite these reactions caused only limited modifications, and once the system reached a steady state the inorganic composition of the contaminated groundwater became similar to that of the recharge water. Decomposition of organic matter in the unsaturated zone resulted in CO₂ generation and dissolution of CaCO₃ minerals in the aquifer. It was shown that chemical and/or bio-degradation of organic matter takes place mainly in the unsaturated (vadose) zone. Hence, monitoring the efficiency of the vadose zone to retain contaminants is essential for evaluating the quality of groundwater since it was shown that organic compounds behave almost conservatively once the effluents enter and flow within the saturated zone.     

Geostatistical analysis of soil hydrologic properties in a field plot

A 91-m transect was set up in an irrigated field near Las Cruces, New Mexico to obtain soil water tension and water content data to investigate their spatial variability. A total of 455 sampling points were monitored along a grid consisting of 91 stations placed 1 m apart by 5 depths per station (at 0.3, 0.6, 0.9, 1.2 and 1.5 m below the surface). Post-irrigation tension and wetness measurements were recorded over 45 days at 11 time periods. Soil water tension was measured with tensiometers using a hand-held pressure transducer. A neutron probe was used to obtain volumetric water content. Using the observed wetness and tension data, unsaturated hydraulic conductivity values were derived (using a cubic spline function to estimate the gradient), and an exponential model was used to fit the calculated conductivity-tension curves to obtain hydraulic conductivity parameter values. The spatial and temporal variability of wetness, tension, saturated hydraulic conductivity and pore-size distribution parameters, and texture at the 0.3-m depth were examined using geostatistical techniques.The exponential model was found to inadequately describe the hydraulic conductivity/tension relationship for the full range of tension, particularly in the tension range near saturation. The derived values of the saturated hydraulic conductivity parameter were much greater than expected and do not correspond to reasonable saturated hydraulic conductivity values.All of the soil parameters studied exhibited large spatial variability horizontally and vertically in the field. Ranges of dependence determined from semivariogram analysis over the 44-day drainage period are 3–32 m for wetness, 6–34 m for soil water tension, 5–35 m for natural log of saturated hydraulic conductivity parameters, 5–11 m for pore-size distribution parameter, and 8–24 m for percent sand, silt and clay at the 0.3 m depth. An alternate hole-effect model is suggested to describe the texture semivariograms.It was determined that the variance of volumetric water content generally increased at each depth over the measured time periods, which is consistent with certain past field studies and a stochastic analysis of unsaturated flow in heterogeneous soils. Future research is recommended relating soil texture to soil hydrologic parameters with the goal of predicting soil behavior with less extensive sampling schemes.     

Movement and degradation of aldicarb residues in the saturated zone under citrus groves on the Florida ridge

A 1.7-ha section of citrus grove near Lake Hamilton was the site of a three-year field study designed to monitor the movement and degradation of the nematicide and insecticide aldicarb in the central ridge area of Florida. Soil cores were used to monitor the fate of aldicarb residues in the unsaturated zone and over 2,000 groundwater samples were collected from 174 monitoring wells to measure horizontal and vertical transport of aldicarb residues in the saturated zone. A simple saturated zone model was used to estimate the degradation rate of aldicarb residues and extrapolate findings to other ridge areas.The results of the study suggest that in the saturated zone aldicarb residues degrade at a rate corresponding to a half-life of approximately eight months. The predominantly horizontal movement of groundwater at this site limits aldicarb residues to the upper three to five meters of the saturated zone. Field data from this site together with unsaturated and saturated zone simulations suggest that in this area of Florida current restrictions on aldicarb used near potable wells are adequate to protect drinking water supplies.     

Metal ion and other key water quality constituent attenuation in soil columns

A set of soil columns was constructed to simulate discharge of disinfected tertiary treated wastewater to a river via nearby land application or indirect discharge. The system was primarily designed to observe the fate of metal ions and nutrients. The following three experiments were conducted: (1) flow through saturated soils only, which simulates indirect discharge where water is directly applied to groundwater; (2) flow through unsaturated soil followed by saturated flow, which simulates vadose then saturated zone transport; and (3) saturated flow only using ethylene diamine tetraacetic acid-metal chelates, which determined effects of metal organic complexes on metal mobility through the soil. Metal ion attenuation was substantial but not complete in experiments 1 and 2 (removal: 68% Cu2+, 43% Ni2+, 98% Pb2+, and 96% Hg2+), which was somewhat contrary to modeling results. Cyanide attenuation was also monitored (92% removal). In experiment 3, lead attenuation was somewhat reduced (92% removal) and delayed (requiring additional residence time); copper attenuation was significantly reduced (38% removal) and delayed; and nickel concentrations were higher in the 28-day sample (> 80 microg/L) than in the column feed water (58 microg/L). Near-complete denitrification and total phosphorus attenuation were observed. For the water quality constituents studied, unsaturated (vadose zone) transport did not appear to add additional benefit.