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1.
Xiaoqiang Dong Xiaofeng Liu Heesoo Woo Junboum Park 《Environmental Earth Sciences》2014,72(9):3715-3722
To obtain the breakthrough curves without efforts required in the sampling and chemical analysis, a new soil column test device was developed. The device can conduct time-continuous electrical conductivity (EC) measurements without disturbing the soil matrix at all stages of the test. This device is composed of soil column, channel selector, LCR meter, and data logger. The soil column employs three 4-electrode sensors installed at different positions. To verify its applicability, the electrical conductivity breakthrough curves at different distances have been obtained with the use of five different species influent solutions (KCl, NaCl, CaCl2, MgCl2, and seawater). Results showed that the EC breakthrough curves and the transport parameters (the pore-water velocity, the dispersion coefficient, and the dispersivity) are very reasonable, and understand the one-dimensional steady flow exactly. The developed soil column test device proposed in this study provides a nondestructive, convenient, and inexpensive means of obtaining EC breakthrough curves. 相似文献
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3.
William G. Harrar Lawrence C. Murdoch Bertel Nilsson Knud Erik S. Klint 《Hydrogeology Journal》2007,15(8):1473-1488
A study of the fracture distribution, hydraulic properties, groundwater levels and the transport of bromide was conducted to characterize vertical transport in the oxidized and reduced zones of a fractured glacial till. Detailed vertical profiles of groundwater levels and solute concentrations were obtained over a 4.5-year period. Vertical migration occurred at several time scales, as a low concentration front was rapidly transported at rates of 100–500 m/year ahead of a slower moving main plume, which advanced at rates of 0.2–0.8 m/year. Concentrations in the leading edge of the plume displayed a high degree of spatial variability over short vertical distances through day 1,000. Late in the test, the influence of matrix diffusion became apparent as concentration patterns developed from being irregular to more uniform distributions. Calculations show that the mass within the low concentration plume front accounts for less than 1% of the total solute mass. Simulation of the breakthrough curves using a simple one-dimensional advection-dispersion model of transport in porous media indicates that vertical transport is dominated by advection. Furthermore, the results indicate that vertical transport of solutes in oxidized and reduced zones of the till can be adequately simulated using an equivalent porous media. 相似文献
4.
1 IntroductionIncorporation of potentially toxic metals ( e.g.Cd, Cu, Cr, Pb, Hg, As, Se, Zn, Ni) into soils ei-ther through sewage-sludge irrigation or some othersources of pollution (e.g. atmospheric deposition, ap-plication of agri-chemicals) has posed… 相似文献
5.
Matrix-diffusion parameters deduced from an infiltration tracer test at Idaho National Laboratory (INL), USA, are combined with other site information in an analysis involving two dimensionless lumped parameters to assess the effects of matrix diffusion on contaminant transport at the INL over longer distance and time scales than were evaluated in the test. Matrix diffusion was interrogated in the test by comparing, in three different observation wells, the breakthrough curves of two simultaneously injected nonsorbing solutes that have different diffusion coefficients. The matrix-diffusion parameters deduced from the different breakthrough curves were in good agreement, suggesting that the parameters may be broadly applicable at the INL. With this in mind, the uncertainties in the individual parameters that make up the two lumped parameters were estimated, and the resulting ranges of parameter values were used to assess matrix diffusion over larger scales. Assessments of the effects of flow transients, spatial heterogeneity in transport parameters, and sorption on solute transport in the shallow subsurface flow system were also conducted. The methods presented here should be generally applicable to other settings for making bounding assessments of the effects of matrix diffusion while honoring the information obtained from tracer tests and other supporting data. 相似文献
6.
S. A. Junejo Qi You Zhou M. A. Talpur Dongqing Wang Jian-long Yang 《Geochemistry International》2014,52(9):794-804
Accurate prediction of solute transport processes in surface water and its underlying bed is an important task not only for proper management of the surface water but also for pollution control in these water bodies. Key issue in this task is an estimation of parameters as diffusion coefficient and velocity for solute transport both in water body and in the underlying bed. This estimation would greatly help us to understand the deposition and release mechanism of solute across the water-bed interface. In this study, a column experiment was conducted in laboratory to estimate the velocity and diffusion coefficient of sodium chloride (NaCl) in water body and underlying sand layer (bed). The column used with a diameter of 30 cm and a height of 100 cm, was filled with sand at the lower half part and water at the upper half part. Total 64 stainless steel electrodes were installed on its surface around. The sodium chloride solution was injected from the top of the column, and electrical resistance between electrodes was monitored for 71 h. Then the dimensionless resistance breakthrough curve was fitted with one dimensional analytic solution for solute transport and the related diffusion coefficient and velocity parameters were estimated. The results show that the NaCl transport velocity was high in the water body but extremely low in the underlying sand layer (bed). The diffusion coefficient estimated in sand layer coincides with those reported well. This indicates that the electrical resistance based solute transport parameter estimation method is not only effective but also has an advantage of multipoints monitoring. This is useful both in mapping solute transport parameter for solute transport process analysis and in providing parameter input for solute transport numerical modeling. 相似文献
7.
Lee Seokjae Yang Subin Lee Dongjoon Choi Hangseok Won Jongmuk 《Hydrogeology Journal》2023,31(5):1245-1257
Understanding contaminant transport in clay-containing soils is critical for accurate prediction of the travel distances of contaminants and for the design and implementation of corresponding remediation plans. This study examined the breakthrough behavior of methylene blue (MB) through sand-illite mixtures using laboratory soil-column experiments at five inlet concentrations, three flow rates, and five illite contents. Kinetic and equilibrium adsorption tests were performed to evaluate the maximum adsorption capacities of the sand and illite used in the soil-column experiments. In addition, the bed efficiency, MB saturation, and adsorption rate were calculated to quantitatively describe the observed breakthrough curves. The observed breakthrough curves, bed efficiencies, MB saturations, and adsorption rates in this study demonstrated the presence of a threshold illite content of ~10% for the adsorption efficiency of contaminants. This implies the need to evaluate the threshold clay content for accurate predictions of contaminant transport through gap-graded clay-containing soils.
相似文献8.
Lianchuan Zhou Xiaomin Chen Xiaoliang Li Xinqiang Yang Daimin Huang Wen Xia Chen Cui 《Environmental Earth Sciences》2011,63(2):273-278
The characteristics of nitrate vertical transport in soils collected from Libo and Puding in Guizhou Province were studied
by simulating soil column in laboratory. The results were as follows: (1) Vertical transport velocity of nitrate decreased,
and the breakthrough curves (BTCs) of nitrate were more dispersed, in each horizon from surface layer to bottom layer in every
soil profile. As rocky desertification progressed, the BTCs experienced a gentle up and down trend, and tailing was more obvious.
(2) An analytical solute transport model (CXTFIT 2.0) was used to estimate nitrate dispersion coefficient (D) and average pore water velocity (V) from the observed BTCs. The results showed that CXTFIT 2.0 model was suitable in fitting the nitrate transport in these
soils. The dispersion coefficient was found to be a function of average pore water velocity. (3) The transport of nitrate
was mainly affected by the soil structural coefficient. As soil structural coefficient decreased, nitrate outflow was retarded,
and the peak concentration was reduced. Soil bulk density, organic matter, and clay also affected the vertical transport of
nitrate. Low bulk density, clay content, and high organic matter content were each associated with faster nitrate transport. 相似文献
9.
溶质暂态存储是岩溶地下水溶质运移过程中的普遍现象。为揭示岩溶管道与裂隙介质间溶质暂态存储机制,本文构建室内管道-裂隙物理模型,开展集中补给条件下的定量示踪试验,运用双区对流弥散模型实现溶质运移过程模拟。研究表明:随着集中补给水动力条件的增强,裂隙暂态存储水量呈线性增加趋势,溶质穿透曲线由单峰型向双峰型转变;管道和裂隙中的平均流速呈负相关关系,溶质在管道和裂隙中的滞留时间差决定了穿透曲线的形态;溶质暂态存储引发了穿透曲线的拖尾效应和双峰现象,对岩溶地下水溶质运移过程具有重要的控制作用。 相似文献
10.
非均质介质中溶质迁移往往出现非费克现象,传统的对流弥散方程(ADE)则难以较好地描述这种现象.采用连续时间的随机游走理论(CTRW)研究1250cm长一维非均质土柱中溶质运移问题,探讨CTRW模型中参数及非费克迁移的变化特征.研究结果表明,β值的大小与介质的非均质特征有关,非均质性越强,β值越小,但β值具有相对的稳定性,然而ADE的弥散系数则具有随尺度增大而增大的现象.对于介质非均质性较强和非费克现象较明显的溶质穿透曲线,尤其是在拖尾部分,与ADE相比,CTRW具有较高的模拟精度. 相似文献
11.
Solute transport experiments were conducted in a one-dimensional saturated column using dissolved methoxy-nonafluorobutane (HFE-7100), a Novec engineered fluid developed by the 3M Corporation, as the solute. Novec engineered fluids are considered dense non-aqueous phase liquids (DNAPLs) because they are immiscible with water and have a specific gravity greater than one. The HFE-7100 fluid is safer and environmentally friendlier than common DNAPL contaminants such as tetrachloroethylene (PCE) or trichloroethylene (TCE); thus, it is an ideal substitute DNAPL for laboratory groundwater contamination research. Three sets of solute transport experiments were conducted. The first set of experiments was conducted in a glass-bead-packed column using dissolved HFE-7100 as the solute. The second set of experiments was conducted in a sand-packed column using dissolved HFE-7100 as the solute. The third set of experiments was conducted in a sand-packed column using dissolved PCE as the solute. The dissolved HFE-7100 column breakthrough concentrations were compared with dissolved PCE breakthrough concentrations. Results show that the one-dimensional solute transport equation was successful in describing the transport behavior of dissolved HFE-7100. This study demonstrates that the HFE-7100 fluid can be used as a safer substitute DNAPL for groundwater contaminant dissolution and transport research. 相似文献
12.
迄今为止,注入时间和静水压力对溶质在深层承压地热水中的运移规律影响研究少有报道。通过模拟35℃的低温地热环境,开展了注入时间1,2,3,4,5 h以及静水压力0,6,9 MPa条件下Cl-的运移柱模拟试验。采用CXTFIT 2.1软件进行数值模拟,探讨了孔隙型热储砂土中Cl-的运移规律和影响因素。结果表明：在模拟的低温孔隙型热储层中,不同注入时间和静水压力下,Cl-的运移曲线均呈正态对称分布,一维对流弥散(CDE)模型也可较好地表征其穿透曲线,因此溶质扩散过程符合菲克定律。注入时间的不同,会引起Cl-的穿透曲线、运移参数发生变化,这与不同注入时间条件下溶质注入总量、柱内溶质浓度差以及分子扩散能力不同有关。在不同静水压力条件下,弥散系数从0 MPa的25.22 cm2/h增加到9MPa的36.13 cm2/h,分子扩散系数、机械弥散系数以及弥散度也随之增大,因此溶质的弥散作用随静水压力的增大而增强。研究结果对于丰富地下水的溶质运移理论具有重要意义。 相似文献
13.
Gravely calcareous soils cover approximately most of arid lands (in percent); however, the solute transport behavior in these soils remains a current issue. This research aimed at estimating and correlating the solute transport parameters in gravely calcareous soils as being affected by different land uses through the knowledge of the soil morphological, physical, and chemical properties. Four different land use sites were selected: irrigated trees and bare, range, and alluvial sediment lands. Solute transport parameters of soil pore water velocity (V), dispersion coefficient (D), and retardation factor (R) were estimated using bromide breakthrough curve tests for surface soil columns. In addition, field Brilliant Blue FCF dye tracing experiment was conducted to determine the maximum dimensional movements. Soil morphological analysis was able to explain the heterogeneity in the solute transport parameters. Conductive solute transport mechanism with V of 17.99 m/day was favored in a high continuous pore system observed under tree lands. Presence of high gravel and CaCO3 contents under range lands increased pore system tortuosity and thus increased D magnitude up to 1,339.88 cm2/day. Existence of thin surface crusts at both bare soils and alluvial sediments had considerably restricted V down to 1.46 m/day. Dye staining technique aided the explanation of the existing variations by providing visual evidence on the preferential flow paths and patterns governing the solute transport mechanism at each site. 相似文献
14.
Macropores resulting from soil pedogenesis and biological activity play important roles in soil water and chemical transport. Numerous studies have examined individual macropores and the effects of their size on solute transport, but few have assessed the effects of macropore continuity and of neighboring macropores. This paper describes a laboratory investigation of the effects of macropores, with varying degrees and types of continuity, on the transport and distribution of solutes in a sandy soil from the northern Loess Plateau, China. Breakthrough curves were obtained from 60 cm tall, 2-D columns containing standardized artificial macropores using an input solution of 1,190 mg/L KBr and 100 mg/L FD&C Blue #1 under a constant hydraulic head of 8 cm. The types of macropore were: open at both the surface and bottom of the soil column (O–O); open at the surface, closed at the bottom (O–C); and closed at the surface, open at the bottom (C–O). Columns with no macropores served as a control. In the O–O columns the solution reached the bottom 10–50 times faster than in any other treatment, bypassing most of the soil matrix. The presence of an O–C macropore resulted in weak retardation and much deeper penetration of the bromide and FD&C Blue #1 solution than in the control columns. However, the C–O macropore had little effect on either breakthrough curves or solute distributions. In further experiments that considered neighboring macropores effects, an inclined macropore strongly affected solute concentrations in the profile around a nearby vertical macropore. It was concluded that the length, type and position of single macropores, and the presence of neighboring macropores, all affect soil water flow and solute infiltration parameters in a sandy loam soil. 相似文献
15.
A number of models have been established to simulate the behaviour of solute transport due to chemical pollution, both in croplands and groundwater systems. An approximate polynomial solution to convection–dispersion equation (CDE) based on boundary layer theory has been verified for the use to describe solute transport in semi-infinite systems such as soil column. However, previous studies have only proposed low order polynomial solutions such as parabolic and cubic polynomials. This paper presents a general polynomial boundary layer solution to CDE. Comparison with exact solution suggests the prediction accuracy of the boundary layer solution varies with the order of polynomial expression and soil transport parameters. The results show that prediction accuracy increases with increasing order up to parabolic or cubic polynomial function and with no distinct relationship between accuracy and order for higher order polynomials (\(n\geqslant 3\)). Comparison of two critical solute transport parameters (i.e., dispersion coefficient and retardation factor), estimated by the boundary layer solution and obtained by CXTFIT curve-fitting, shows a good agreement. The study shows that the general solution can determine the appropriate orders of polynomials for approximate CDE solutions that best describe solute concentration profiles and optimal solute transport parameters. Furthermore, the general polynomial solution to CDE provides a simple approach to solute transport problems, a criterion for choosing the right orders of polynomials for soils with different transport parameters. It is also a potential approach for estimating solute transport parameters of soils in the field. 相似文献
16.
在地下水的相关研究中,农药和石油等地下水污染、土地盐碱化、海水入侵等诸多实际问题主要的研究方法都涉及地下水溶质迁移模拟. 相比地下水水流模拟的相对完善,对溶质迁移的模拟比较薄弱且迁移过程本身复杂性较高,目前地下水溶质迁移的研究工作还处在全面发展的阶段. 文中阐述了反映地下水溶质迁移机理和过程的数学模型,综述了溶质迁移模拟在地下水污染物防治、土地盐碱化、海水入侵、石油和放射性废物扩散等问题的诸多应用,归类了目前溶质迁移模拟所使用的对流迁移、对流-弥散模拟等主要数值方法,并对这些方法的优缺点和应用实例做了总结. 最后,分析了目前溶质迁移模拟中存在的不足,展望了未来在参数确定、裂隙介质运移机理和多相介质条件下运移模拟可能取得的突破. 相似文献
17.
Consolidation of clayey contaminant barriers such as landfill liners has been postulated as a cause of early breakthrough of contaminants. In this paper we theoretically investigate this proposition. For this purpose a sophisticated one‐dimensional, large‐deformation model of coupled mechanical consolidation and solute transport is employed. This new model is a generalization of existing coupled consolidation and solute transport models described in the literature. It takes into account both non‐linearities in geometry as well as constitutive relations. The latter relate the compressibility, hydraulic conductivity and coefficient of effective diffusivity to the deformation of the soil. The model is applied to a case study of a clay liner and geomembrane system. Results obtained from numerical solution of the model equations are compared with those from various simplified models, including a ‘diffusion only’ (i.e. a rigid soil) model traditionally used in contaminant barrier design. For barriers incorporating low compressibility soils (as for many well compacted clays), there is little difference between contaminant transit (i.e. breakthrough) times predicted by the two models. However, for contaminant barriers incorporating more compressible soils, consolidation is shown to significantly accelerate transport. These results indicate the potential importance of accounting for the effects of soil consolidation and highlight the limitations of existing models when modelling solute transport through composite barriers utilizing soft soils. Based on these limited results, we suggest a possible way of taking into account soil consolidation using simplified models. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
18.
Sheng Peng 《Frontiers of Earth Science》2009,3(2):208-213
Heap leaching is essentially a process in which metals are extracted from mine ores with lixiant. For a better understanding
and modeling of this process, solute transport parameters are required to characterize the solute transport system of the
leach heap. For porous media like leach ores, which contain substantial gravelly particles and have a broad range of particle
size distributions, traditional small-scale laboratory experimental apparatus is not appropriate. In this paper, a 2.44 m
long, 0.3 m inner diameter column was used for tracer test with boron as the tracer. Tracer tests were conducted for 2 bulk
densities (1.92 and 1.62 g/cm3) and 2 irrigation rates (2 and 5 L/ (m2·h−1)). Inverse modeling with two-region transport model using computer code CXTFIT was conducted based on the measured breakthrough
curves to estimate the transport parameters. Fitting was focused on three parameters: dispersion coefficient D, partition coefficient β, and mass transfer coefficient ω. The results turned out to fall within reasonable ranges. Sensitivity
analysis was conducted for the three parameters and showed that the order of sensitivity is β > ω > D. In addition, scaling of these parameters was discussed and applied to a real scale heap leach to predict the tracer breakthrough. 相似文献
19.
岩溶管道溶质运移的尺度效应研究对穿透曲线的正确解译非常重要,但目前针对单一弯曲管道中溶质运移尺度效应的研究仍比较缺乏。文章将岩溶管道和溶潭分别概化为透明软管和水箱,基于前期建立的水箱-管道系统(简称“管道系统”),在水箱下游设置不同长度的弯曲管道,通过示踪试验研究管道运移尺度对穿透曲线的影响,并采用暂时存储模型模拟试验曲线。结果表明：(1)随着水箱下游管道长度的增加,峰值质量浓度逐渐缓慢降低,穿透曲线上升段斜率无明显变化,穿透曲线拖尾逐渐缩短,表明运移管道长度增加对溶质运移的影响大于下游管道弯曲;(2)穿透曲线偏度系数、后段溶质羽穿透时间和溶质羽穿透时间与管道系统长度呈良好的负线性相关关系(R2>0.96);(3)当对称和不对称水箱管道系统长度分别增加至154.5 m和164.3 m时,偏度系数接近0,穿透曲线分布接近对称;(4)弥散系数、存储区截面积和交换系数与管道系统长度呈良好的负线性相关关系,当对称和不对称水箱管道系统长度分别增加至159.9 m和178.1 m时,存储区截面积接近0,水箱导致的溶质运移滞后效应基本消失。研究结果对野外岩溶管道穿透曲线的... 相似文献
20.
溶质在土工合成衬垫（GCL）长期入渗过程中具有明显的化学-渗透特性。室内渗透试验表明：阳离子之间的置换效应对GCL衬垫渗透系数影响较大,10 mM的CaCl2溶液使渗透系数上升至2.5×10-11 m/s,而30 mM的CaCl2溶液使渗透系数上升至5.6×10-11 m/s。渗透液体浓度的增加缩短了溶质穿透GCL的时间,且预饱和处理试剂对GCL渗透系数的变化影响较大,采用蒸馏水作为预饱和试剂处理GCL衬垫对其渗透系数的影响明显小于CaCl2溶液;建立了考虑膜效应和离子交换效应条件下溶质运移耦合动力学模型,并对GCL穿透试验过程中溶质浓度的变化进行了预测,仿真计算结果表明,10 mM和30 mM两种CaCl2溶液渗透条件下,Ca2+浓度变化的试验结果和计算结果均相吻合,验证了耦合动力学模型的可靠性;从Ca2+浓度及流量穿透曲线分布可知,化学-渗透效应可有效地延缓溶质的迁移速度。随着溶质浓度的降低,阻滞作用更显著。因此,在分析GCL衬垫中溶质入渗特征时,必须考虑化学-渗透效应的影响。 相似文献