共查询到20条相似文献，搜索用时 15 毫秒
1.
Dirk Schaefer 《Environmental Earth Sciences》2012,67(8):2459-2467
Organic contaminants in aquifers are often present as non-aqueous phase liquids (NAPL), which are long-lasting sources for groundwater contamination. The existing NAPL mass is an important parameter for the persistence of the source, but its determination is difficult. One possible detection method is based on the ideal multicomponent dissolution theory, using aqueous concentrations downstream of a fully mixed NAPL source to calculate its mass. In this publication, the applicability of this method is tested for a source size of about 5 m, using numerical methods. In contrast to fully mixed source zones, on this scale the NAPL sources are not in contact with each other, do not mix and develop independently over time. Highly soluble NAPL components can be depleted or the NAPL phase can be completely exhausted locally, while in other portions of the source zone NAPL is still present with all its components. Hence, the interpretation of the resulting aqueous concentrations downstream using the ideal dissolution theory leads to erroneous NAPL masses of several orders of magnitude in the investigated scenarios. 相似文献
2.
T. Kuppusamy 《国际地质力学数值与分析法杂志》1993,17(7):457-469
Aquifer contamination by organic chemicals in subsurface flow through soils due to leaking underground storage tanks filled with organic fluids is an important groundwater pollution problem. The problem involves transport of a chemical pollutant through soils via flow of three immiscible fluid phases: namely air, water and an organic fluid. In this paper, assuming the air phase is under constant atmospheric pressure, the flow field is described by two coupled equations for the water and the organic fluid flow taking interphase mass transfer into account. The transport equations for the contaminant in all the three phases are derived and assuming partition equilibrium coefficients, a single convective – dispersive mass transport equation is obtained. A finite element formulation corresponding to the coupled differential equations governing flow and mass transport in the three fluid phase porous medium system with constant air phase pressure is presented. Relevant constitutive relationships for fluid conductivities and saturations as function of fluid pressures lead to non-linear material coefficients in the formulation. A general time-integration scheme and iteration by a modified Picard method to handle the non-linear properties are used to solve the resulting finite element equations. Laboratory tests were conducted on a soil column initially saturated with water and displaced by p-cymene (a benzene-derivative hydrocarbon) under constant pressure. The same experimental procedure is simulated by the finite element programme to observe the numerical model behaviour and compare the results with those obtained in the tests. The numerical data agreed well with the observed outflow data, and thus validating the formulation. A hypothetical field case involving leakage of organic fluid in a buried underground storage tank and the subsequent transport of an organic compound (benzene) is analysed and the nature of the plume spread is discussed. 相似文献
3.
4.
Modeling microbial processes in porous media 总被引：8，自引：1，他引：7
The incorporation of microbial processes into reactive transport models has generally proceeded along two separate lines
of investigation: (1) transport of bacteria as inert colloids in porous media, and (2) the biodegradation of dissolved contaminants
by a stationary phase of bacteria. Research over the last decade has indicated that these processes are closely linked. This
linkage may occur when a change in metabolic activity alters the attachment/detachment rates of bacteria to surfaces, either
promoting or retarding bacterial transport in a groundwater-contaminant plume. Changes in metabolic activity, in turn, are
controlled by the time of exposure of the microbes to electron acceptors/donor and other components affecting activity. Similarly,
metabolic activity can affect the reversibility of attachment, depending on the residence time of active microbes. Thus, improvements in quantitative analysis of active
subsurface biota necessitate direct linkages between substrate availability, metabolic activity, growth, and attachment/detachment
rates. This linkage requires both a detailed understanding of the biological processes and robust quantitative representations
of these processes that can be tested experimentally. This paper presents an overview of current approaches used to represent
physicochemical and biological processes in porous media, along with new conceptual approaches that link metabolic activity
with partitioning of the microorganism between the aqueous and solid phases.
Received, January 1999 · Revised, June 1999, July 1999 · Accepted, October 1999 相似文献
5.
Analytical closed-form solutions for assessing pumping cycles,times, and costs required for NAPL remediation 总被引：2，自引：0，他引：2
R. Chesnaux 《Environmental Geology》2008,55(7):1381-1388
An analytical solution is given to evaluate the number and duration of pumping cycles required for the remediation by pumping
of contaminants, both single component and multi-component non-aqueous phase liquids (NAPLs), when no free product is present
in the system. The method can be applied in a homogenous medium if the contamination zones have been delineated and residual
total NAPL concentrations assessed. Based on the principle of the NAPL partitioning in unsaturated or saturated porous media,
analytical closed-form solutions are provided for both cases of remediation by pumping in saturated and unsaturated conditions:
“pump-and-treat” and “soil vapor extraction”. In each case we determine the number of pumping cycles required to reach the
residual required concentration of NAPL (for example, according to health-based standards), considering one or more chemicals
simultaneously present in an aquifer. The method requires information on the aquifer saturation state and the properties of
the chemicals of interest. Calculations are based on the assumption of equilibrium partitioning of chemicals between the pore
water, the soil solids, and the soil gas (in the case of unsaturated conditions), and no presence of a NAPL phase. 相似文献
6.
7.
This paper deals with the theoretical aspects of nonaqueous phase liquid (NAPL)‐dissolution‐induced instability in two‐dimensional fluid‐saturated porous media including solute dispersion effects.After some weaknesses associated with the previous work are analyzed and overcome, a comprehensive dimensionless number, known as the Zhao number, is proposed to represent the main driving force and three controlling mechanisms of an NAPL‐dissolution system that has a finite domain. The linear stability analysis is carried out to derive the critical value of the comprehensive dimensionless number of the NAPL‐dissolution system in a limit case as the ratio of the equilibrium concentration to the density of the NAPL approaches zero. As a result, a theoretical criterion that can be used to assess the instability of planar NAPL‐dissolution fronts in two‐dimensional fluid‐saturated porous media of finite domains has been established. Not only can the present theoretical results be used for the theoretical understanding of the effect of solute dispersion on the instability of an NAPL‐dissolution front in the fluid‐saturated porous medium of either a finite domain or an infinite domain, but also they can be used as benchmark solutions for verifying numerical methods employed to simulate detailed morphological evolution processes of NAPL‐dissolution fronts in two‐dimensional fluid‐saturated porous media. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
8.
The role of geological heterogeneity and variability in water infiltration on non-aqueous phase liquid migration 总被引：2，自引：1，他引：1
Zhibing Yang Hanna Zandin Auli Niemi Fritjof Fagerlund 《Environmental Earth Sciences》2013,68(7):2085-2097
This study investigates the influence of two factors—geological heterogeneity and variability in water infiltration—on non-aqueous phase liquid (NAPL) migration in the unsaturated zone. NAPL migration under three-phase flow conditions resulting from a ground surface spill is modeled for multiple heterogeneous realizations of a porous medium with various water infiltration scenarios. Increased water infiltration before the spill has two counteracting effects: NAPL relative permeability (k rn) increases with increasing water saturation (S w) for a given NAPL saturation, while higher S w in the soil near the NAPL source zone leads to less NAPL mass infiltration. It is found that the former effect is overwhelmed by the latter effect, the net effect being that with longer infiltration durations before the spill, both the infiltrated NAPL mass and the depth of the front migration decrease. Simulation results also show strong effect of the medium heterogeneity. Results suggest that total infiltrated mass, front depth and plume spread increase with an increasing standard deviation of log-permeability. Also variability in modeling results among realizations is largely impacted by the log-permeability standard deviation. Spatial correlation in permeability also strongly influences NAPL infiltration. An increase in the isotropic correlation length from 0.75 to 1.5 m leads to a decrease in total infiltrated mass, plume migration depth as well as vertical spread. Lateral spread in this case is not shown to be affected by the correlation length. 相似文献
9.
Comprehensive GC/MS analysis was applied to both the mobile liquid phase (seepage water) and the immobile solid matter of discrete layers derived from a waste deposit landfill. The vertical distribution of organic compounds supports information on the transport, transfer and transformation processes with depth and, consequently, with time.Numerous low molecular weight organic contaminants of natural and xenobiotic origin were identified and partially quantified. Several were selected to act as molecular indicators for different processes. Interpretation of their occurrence and concentration profiles (considering possible waste sources) and their molecular properties allowed us to (i) differentiate immobile and mobile fractions, (ii) reveal restrictions in the vertical transport by transfer processes between particulate and water phase, (iii) identify dynamic accumulations of individual contaminants and (iv) estimate approximate residence times. In addition, intensive degradation processes were pointed out for the natural fraction of the organic matter by way of determination of specific transformation products. Besides the transformation of natural components, transformation of numerous xenobiotics was recognised. In particular, with respect to an important group of contaminants, the phthalate-based plasticisers, a detailed view of (i) the influence of transfer and transport phenomena on transformation processes as well as (ii) the consecutive appearance of different degradation steps in both seepage water and solid waste was pointed out. The information provides a valuable base for the prediction of the long term behaviour of organic contaminants in waste deposit landfills. 相似文献
10.
L. M. Keller C. A. Hauzenberger R. Abart 《Contributions to Mineralogy and Petrology》2007,154(2):205-216
In this study we use two dimensional chemical patterns and numerical modeling to estimate the relative rates of chemical transport
along interphase boundaries (ib) and through grain (s) interiors during retrograde Fe–Mg exchange between garnet and biotite
at a garnet–biotite–quartz triple junction. We demonstrate that systematic variations in garnet–rim compositions, which are
frequently observed along garnet–quartz interfaces, and deviations from concentric retrograde zoning patterns start to develop
when chemical transport along the interphase boundaries becomes slow during cooling. The capacities for chemical transport
along an interphase boundary depend on the product D
ib
K
ib/s
a, where D
ib is the diffusion coefficient of the exchangeable components within the interphase boundary medium, K
ib/s is the equilibrium partitioning coefficient between the cation exchange partners and the interphase boundary medium and a is the interphase boundary width. The model is applied to analyze the retrograde zoning patterns in garnets from the Mozambique
belt (SE-Kenya), which cooled from 820°C at a rate of ca. 2°C/my. It is found that non-equilibrated compositions in garnet along
garnet/quartz interphase boundaries started to develop below 700°C due to insufficient rates of chemical transport along these
boundaries. The transport capacities of garnet/quartz interphase boundaries was estimated to have been between about 1E-23 cm3/s (575°C) and 1E-20 cm3/s (700°C) from modeling the observed X
Fe pattern in garnet close to a garnet–quartz–biotite triple junction and relying on published data on the diffusivity of Fe2+ in garnet. Similar transport capacities are obtained; when the interphase boundary is assumed to be filled with a material
that has the transport properties and chemical composition of a free melt in equilibrium with garnet, biotite and quartz at
the respective conditions. In contrast, if the transport properties of the interphase boundary medium are related to the diffusivities
and solubility of Fe2+ and FeOH+ within a free aqueous solution, chemical transport along the interphase boundaries would be much more efficient, and exchange
equilibrium would have been maintained during the entire cooling history of the rocks. The observation of systematic deviations
from local equilibrium along the garnet–quartz interphase boundaries leads us to exclude the presence of an aqueous fluid
along the interphase boundary at any time during cooling. 相似文献
11.
Dynamic flow systems and transport of contaminants in karstic aquifers result from the actions of physical and chemical processes involving aqueous systems containing certain contaminants. These processes are elaborated, and pertinent mathematical and chemical equations are discussed, herein. Contaminant transport in karstic aquifers can be mathematically expressed by the basic equations evaluated primarily for the flow in porous, highly permeable aquifers. The effects of advection, hydrodynamic dispersion, and dilution are elaborated as physical processes that effect the movement of contaminants through groundwater in permeable rocks. Physical and chemical mechanisms that govem contaminant movement and groundwater flow through fractured media are proposed as the basis of an approximate scenario of contaminant transport through karstified carbonate rocks. 相似文献
12.
基于孔隙网络模型的非水溶相液体运移实验研究进展 总被引：1，自引：0，他引：1
进行多孔介质中非水溶相液体（Non Aqueous Phase Liquids，NAPLs）运移的微观机理研究，微观孔隙网络模型实验是目前应用比较广泛且行之有效的方法。通过网络模型实验，获得对NAPLs在多孔介质中运移更深入的认识。从多孔介质孔隙结构测量、孔隙网络模型制作、NAPLs运移网络模型实验和数值模拟4个方面评述了该方向的研究进展，结果显示测量孔隙结构方法、图像刻蚀技术、可视化测量实验数据方法等有力地促进了本实验研究的发展。分析了孔隙网络模型实验存在的问题以及未来的发展趋势，对开展孔隙网络模型实验研究有一定的启发作用。 相似文献
13.
Three-phase numerical model of water migration in partially frozen geological media: model formulation,validation, and applications 总被引：3，自引：0，他引：3
Scott L. Painter 《Computational Geosciences》2011,15(1):69-85
Water in the subsurface of the Earth’s cold regions—and possibly the subsurface of Mars—resides in the liquid, vapor, and
ice phases. However, relatively few simulations addressing full three-phase, nonisothermal water dynamics in below-freezing
porous media have been undertaken. This paper presents a nonisothermal, three-phase approach to modeling water migration in
partially frozen porous media. Conservation equations for water (as ice, liquid, and vapor) and a single gas species (in the
gas phase and dissolved in water) are coupled to a heat transport equation and solved by a finite-volume method with fully
implicit time stepping. Particular attention is given to the method of spatial differencing when the pore space is partially
filled with ice. The numerical model is able to reproduce freezing-induced water redistribution observed in laboratory experiments.
Simulations of Earth permafrost dynamics and of the formation and evolution of a planetary-scale cryosphere on Mars demonstrate
the new capabilities. 相似文献
14.
N. P. Laverov V. I. Velichkin V. I. Malkovsky N. N. Tarasov Yu. P. Dikov 《Geology of Ore Deposits》2010,52(1):5-13
The spread of radioactive contamination in the subsurface medium near Lake Karachai is considered. The complexity of this
process requires a comprehensive approach to its study. The source of radioactive contamination is overviewed. The map of
faults in subsurface medium is considered in order to determine the prevailing direction of contaminated groundwater flow.
Photometry in observation wells has been used for structural geological estimation of transport properties of the shallow
aquifer, where contaminated groundwater is moving. This study was carried out along with hydrochemical logging, which makes
it possible to estimate the dynamics of contamination of subsurface medium and vertical distribution of groundwater contamination.
Special attention is paid to transport of radionuclides in the form of radiocolloid particles. Groundwater samples were taken
from various depths corresponding to different contamination levels near Lake Karachai. The depth intervals of sampling were
determined from the data of hydrochemical logging. Ultrafiltration through membranes with a specific pore size in combination
with gamma spectrometry was used to characterize radionuclide transfer with colloidal particles differing in size. The local
elemental composition of the radiocolloid surface was studied by Auger spectroscopy. The chemical composition and structure
of radiocolloid particles were determined by X-ray photoelectron spectroscopy with consecutive etching of the particle surface
by argon ions for a certain depth. The data obtained indicate that radiocolloid particles are heterogeneous and an organic
shell consisting of humic and fulvic acids and technogenic organic compounds coat their surface. 相似文献
15.
This paper deals with the computational aspects of nonaqueous phase liquid (NAPL) dissolution front instability in two-dimensional
fluid-saturated porous media of finite domains. After the governing equations of an NAPL dissolution system are briefly described,
a combination of the finite element and finite difference methods is proposed to solve these equations. In the proposed numerical
procedure, the finite difference method is used to discretize time, while the finite element method is used to discretize
space. Two benchmark problems, for which either analytical results or previous solutions are available, are used to verify
the proposed numerical procedure. The related simulation results from these two benchmark problems have demonstrated that
the proposed numerical procedure is useful and applicable for simulating the morphological evolution of NAPL dissolution fronts
in two-dimensional fluid-saturated porous media of finite domains. As an application, the proposed numerical procedure has
been used to simulate morphological evolution processes for three kinds of NAPL dissolution fronts in supercritical NAPL dissolution
systems. It has been recognized that: (1) if the Zhao number of an NAPL dissolution system is in the lower range of the supercritical
Zhao numbers, the fundamental mode is predominant; (2) if the Zhao number is in the middle range of the supercritical Zhao
numbers, the (normal) fingering mode is the predominant pattern of the NAPL dissolution front; and (3) if the Zhao number
is in the higher range of the supercritical Zhao numbers, the fractal mode is predominant for the NAPL dissolution front. 相似文献
16.
地下环境中可移动的胶体能够促进强烈吸附的污染物质的运移,而胶体自身在运移过程中也会伴随发生沉淀、释放。根据高岭石胶体的土柱出流实验,对不同离子强度条件下胶体在饱和多孔介质中的沉淀和释放行为进行分析,并采用不同模型对其过程进行数值模拟。结果表明,离子强度是影响胶体沉淀和释放过程的重要因素,随着离子强度的增加,胶体的出流峰值逐渐降低,即胶体在多孔介质中的沉淀量逐渐增大,且沉淀速率系数K d 与离子强度成正相关;模型拟合的释放系数与NaCl 浓度显著相关,Grolimund 模型可以很好地模拟胶体的沉淀过程（R 2 >0.95）,但不能准确地模拟释放过程;而胶体运移方程耦合溶质运移方程能够模拟不同离子强度影响下胶体的释放过程（R 2 >0.9） 相似文献
17.
The fluid transfer of radionuclides in the geologic medium is considered under conditions when radionuclides are contained in fluids not only as solutes but also as colloids. The effect of colloidal transport of radionuclides on the rate of spreading of radioactive contamination in an underground medium is estimated, with assessment of this effect in mathematical models describing the transport of radionuclides by subsurface water. For this purpose, the exchange of radionuclides between subsurface water, colloid, and an immobile solid phase is considered, taking into account the precipitation of colloidal particles on both the immobile solid phase and other colloidal particles and their recurrent mobilization into the liquid phase. It is noted that, in real colloidal transfer, the heterogeneity of the geologic medium and colloidal particles in subsurface water is of great importance. The known models of colloidal transfer of radionuclides are evaluated on the basis of the analysis performed. 相似文献
18.
地球化学作用是影响岩土类多孔介质中流体流动、传质、传热的重要因素之一。基于Fredlund所提出的非饱和土四相理论,将地球化学作用所产生的溶解/沉淀视为一个独立相,在一定的假设基础上,利用溶质浓度对介质孔隙度、含水率进行修正,从而建立起传质过程与介质水力性质之间的关系,改进了传统模型中传质过程与流体密度、黏度之间单一的耦合关系;并以此为基础建立了考虑地球化学作用下饱和-非饱和介质中多组分、多相流体渗流场-浓度场-温度场耦合的数学模型。通过在实验室内对反应性煤矸石进行渗透实验的结果对笔者所建模型进行了验证,结果表明：综合考虑溶解作用时所测点处渗流速度与未考虑耦合作用的结果相比增大0.58倍;单独考虑溶解/沉淀相时,所测点处渗流速度与未考虑密度耦合作用时的结果相比增大0.44倍。水流的实际渗透速度与在使用考虑溶解/沉淀相计算模型时的结果吻合较好。 相似文献
19.
A three-dimensional, three-phase numerical model is presented for simulating the movement of immiscible fluids, including
nonaqueous-phase liquids (NAPLs), through porous media. The model is designed to simulate soil flume experiments and for practical
application to a wide variety of contamination scenarios involving light or dense NAPLs in heterogeneous subsurface systems.
The model is derived for the three-phase flow of water, NAPL, and air in porous media. The basic governing equations are based
upon the mass conservation of the constitutents within the phases. The descretization chosen to transform the governing equations
into the approximating equations, although logically regular, is very general. The approximating equations are a set of simultaneous
coupled nonlinear equations which are solved by the Newton-Raphson method. The linear system solutions needed for the Newton-Raphson
method are obtained using a matrix of preconditioner/accelerator iterative methods.
Because of the special way the governing equations are implemented, the model is capable of simulating many of the phenomena
considered necessary for the sucessful simulation of field problems including entry pressure phenomena, entrapment, and preferential
flow paths. The model is verified by comparing it with several exact analytic test solutions and three soil flume experiments
involving the introduction and movement of light nonaqueous-phase liquid (LNAPL) or dense nonaqueous-phase liquid (DNAPL)
in heterogeneous sand containing a watertable.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
The enhanced velocity mixed finite element method, due to Wheeler et al. (Comput Geosci 6(3–4):315–332, 2002), is analyzed and extended to the problem of modeling slightly compressible flow coupled to the transport of chemical species
through porous media, on non-matching multiblock grids. Applications include modeling bio-remediation of heavy oil spills
and many other subsurface hazardous wastes, angiogenesis in transition of tumors from dormant to malignant states, transport
of contaminants in ground water flow, and acid injection from well bores to increase permeability of surrounding rock. The
analysis and numerical examples presented here demonstrate convergence and computational efficiency of this method. 相似文献