裂隙岩体中污染物运移过程的数值模拟

基于双重介质理论模型建立了污染物在地下环境中运移的耦合数学模型,给出了有限元离散的数值格式。并以核废料储存过程中核素90Sr为例,采用所建立的数值模型模拟其在裂隙岩体中运移过程,预测了污染物的浓度分布范围和发展趋势。模拟结果表明:核素90Sr在处置库中运行40年后,下游地区的抽水井的浓度可达到3 100 Bq/m3,超出了国家规定的标准,为固体废物场址的选择以及污染的控制提供了决策依据。     

土地利用/土地覆被变化对长江流域水环境的影响研究

不合理的土地利用方式／土地覆被变化已成为长江流域水环境不断恶化的重要原因之一，长江上游植被破坏和陡坡开垦造成严重的水土流失，直接威胁到三峡库区的生态安全，中流的围湖造田等损害了湖泊的生态功能，导致严重的洪涝灾害，化肥，农药的过量使用，农田污水灌溉等成为长江流域农业非点源污染的重要来源。文章提出了进一步研究构想，以山－河－湖－海互动系统为研究对象，以系统内各子系统之间的能量流和物质流的联系为纽带，揭示系统自组织、自反馈机制，利用遥感技术和地理信息系统结合数学模型，动态模拟土地利用／土地覆被变化的水文及水环境效应。     

The impact of well‐field configuration on contaminant mass removal and plume persistence for homogeneous versus layered systems

A three‐dimensional numerical model was used to simulate the impact of different well‐field configurations on pump‐and‐treat mass removal efficiency for large groundwater contaminant plumes residing in homogeneous and layered domains. Four well‐field configurations were tested, Longitudinal, Distributed, Downgradient, and natural gradient (with no extraction wells). The reductions in contaminant mass discharge (CMDR) as a function of mass removal (MR) were characterized to assess remediation efficiency. Systems whose CDMR‐MR profiles are below the 1:1 relationship curve are associated with more efficient well‐field configurations. For simulations conducted with the homogeneous domain, the CMDR‐MR curves shift leftward, from convex‐downward profiles for natural gradient and Longitudinal to first‐order behaviour for Distributed, and further leftward to a sigmoidal profile for the Downgradient well‐field configuration. These results reveal the maximum potential impacts of well‐field configuration on mass‐removal behaviour, which is attributed to mass‐transfer constraints associated with regions of low flow. In contrast, for the simulations conducted with the layered domain, the CMDR‐MR relationships for the different well‐field configurations exhibit convex‐upward profiles. The nonideal mass‐removal behaviour in this case is influenced by both well‐field configuration and back diffusion associated with low‐permeability units.     

Theoretical investigation of the effects of consolidation on contaminant transport through clay barriers

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.     

One‐dimensional contaminant transport through a deforming porous medium: theory and a solution for a quasi‐steady‐state problem

Contaminant migration through soil is usually modelled mathematically using the dispersion–advection equation. This type of model finds application when planning the remediation of contaminated land, predicting the movement of polluted groundwater and designing engineered landfills. Usually the analysis assumes that the porous media through which the contaminant migrates is stationary. However, the construction of landfills on clay soils means that the soil beneath the landfill will undergo time‐dependent deformation as the soil consolidates. To date, there are no published data on the effect a deforming porous media may have on contaminant transport beneath a landfill; indeed, there appears to be no theory of contaminant migration through a deforming soil. In this paper, a one‐dimensional theory of contaminant migration through a saturated deforming porous media is developed based on a small and large strain analysis of a consolidating soil and conservation of contaminant mass. By selection of suitable parameters, the new transport equation reduces to the familiar one‐dimensional dispersion–advection equation for a saturated soil with linear, reversible, equilibrium controlled sorption of the contaminant onto the soil skeleton. Analytic solutions to a quasi‐steady‐state contaminant transport problem for a deforming media are presented, and a preliminary assessment made of the potential importance of soil deformation on the results of a contaminant migration analysis. Copyright © 2000 John Wiley & Sons, Ltd.     

Modelling long‐term contaminant migration in a catchment at fine spatial and temporal scales using the UP system

A method has been developed to simulate the long‐term migration of radionuclides in the near‐surface of a river catchment, following their release from a deep underground repository for radioactive waste. Previous (30‐year) simulations, conducted using the SHETRAN physically based modelling system, showed that long‐term (many decades) simulations are required to allow the system to reach steady state. Physically based, distributed models, such as SHETRAN, tend to be too computationally expensive for this task. Traditional lumped catchment‐scale models, on the other hand, do not give sufficiently detailed spatially distributed results. An intermediate approach to modelling has therefore been developed which allows flow and transport processes to be simulated with the spatial resolution normally associated with distributed models, whilst being computationally efficient.The approach involves constructing a lumped model in which the catchment is represented by a number of conceptual water storage compartments. The flow rates to and from these compartments are prescribed by functions that summarize the results from physically based distributed models run for a range of characteristic flow regimes. The physically based models used were, SHETRAN for the subsurface compartments, a particle tracking model for overland flow and an analytical model for channel routing. One important advantage of the method used in constructing the lumped model is that it makes down scaling possible, in the sense that fine‐scale information on the distributed hydrological regime, as simulated by the physically based distributed models, can be inferred from the variables in the lumped model that describe the hydrology at the catchment scale. A 250‐year flow simulation has been run and the down scaling process used to infer a 250‐year time‐series of three‐dimensional velocity fields for the subsurface of the catchment. This series was then used to drive a particle tracking simulation of contaminant migration. The concentration and spatial distribution of contaminants simulated by this model for the first 30 years were in close agreement with SHETRAN results. The remaining 220 years highlighted the fact that some of the most important transport pathways to the surface carry contaminants only very slowly so both the magnitude and spatial distribution of concentration in surface soils are not apparent over the shorter SHETRAN simulations. Copyright © 1999 John Wiley & Sons, Ltd.     

长江口和杭州湾污染物稀释扩散及交汇数值模拟研究

河口水体中污染物稀释扩散是近海水环境研究的关键问题之一。针对长江口和杭州湾的污染物稀释扩散与交汇,利用有限体积法,建立了大范围二维潮流水质数学模型,结合拉格朗日法粒子追踪技术,模拟了不同径流下两河口的污染物(COD)稀释、扩散和交汇。结果表明,长江口石洞口排放的污染物口内经过10次往复运动,历时5天扩散至口门处,随后部分进入外海,另一部分经过6天扩散至杭州湾水域;杭州湾金山排放的污染物历时10天向上下游扩散约28 km,同时由北岸向南扩散约15 km。在各排污口同时排放COD浓度为100 mg/L的污水,交汇处COD达到相对稳定后,浓度增量约为1.2 mg/L,受长江口和杭州湾的影响之比约为5∶1。对不同径流量下COD稀释扩散进行模拟,得出径流量增大有助于污染物的稀释扩散。     

胶州湾跨海大桥对海湾水体交换的影响

跨海大桥的建设有利于环湾经济的发展,但桥墩入水不可避免地会对海湾内水动力和水交换造成一定的影响。本文以胶州湾为例,利用无结构网格有限体积海洋模型,建立了能够描绘胶州湾跨海大桥入海桥墩的高精度网格,构造了胶州湾及邻近海域的三维水动力模型,模拟了胶州湾建桥前后的潮(余)流结构。在此基础上,通过污染物示踪对比了胶州湾内污染物在建桥前后的对流扩散过程。模拟结果表明,大桥的建设对胶州湾南部大部分区域的影响较小,包括潮(余)流、水交换等方面;但对大桥北侧以及南侧靠近大桥一定范围内的区域有显著影响。大桥北侧潮致余流整体减小约2cm/s,靠近桥南侧的余流则由向北转为沿桥向东流动。由于大桥的影响,污染物在大桥北侧堆积,重点集中于桥北的红岛以西(Ⅰ区)沿岸区域以及红岛以东(Ⅱ区)大部分区域。其中,Ⅰ区建桥后的半交换时间增加了2.00d,Ⅱ区增加了2.04d。在减缓污染物扩散速率的同时,大桥也同样阻碍了径流输出的淡水向胶州湾南部的输运,使得桥北水体的盐度降低,有可能是造成近年来胶州湾冬季冰情加剧的原因之一。     

土壤中可挥发性污染物清除的离心试验研究

土工离心模拟试验技术是研究环境岩土工程问题的有效手段。本文研究了非水相流体污染物在非饱和土中的迁移以及随后的抽气清除过程。 当离心机运行到要求的加速度时,汽油污染物从地下油罐中释放并在非饱和土中迁移一年,之后采用土壤通气法对污染土壤进行修复。对土壤取样分析,得到污染物在土体中的迁移规律和分布特征。试验结果表明,土壤通气法可以清除非饱和土体中的挥发性有机污染物,是一种有效的原位土壤修复技术。     

昆明地热田岩溶地下热水系统中溶质运移的模拟

通过对昆明地热田深层基岩地下热水系统的地质、水文地质条件和开采现状的分析,建立了考虑温压变化和越流条件的岩溶热储层中地下热水的水流和溶质(污染物)运移的准三维非稳定流数学模型。对开采条件下地热田Ⅱ 块段地下热水系统中水位及F- 、Cl- 、NH+4 、SO2-4 浓度的模拟结果表明,所建立的模型合理、可靠,具有较高的仿真性。模型可预测不同条件下地热田地下热水的流场和溶质浓度的动态变化趋势,为防治地下热水环境的进一步恶化提供参考。