热弥散对同井回灌地下水源热泵的影响

综述了多孔介质和含水层蓄能中常用的热弥散模型,把热弥散模型归结为两类：速度一次方模型和含水层滞止导热系数倍数模型。对同井回灌地下水源热泵（GWHPPRSW）引起的地下水的换热,针对这两类模型进行了数值求解。随着热弥散的加强,抽水温度降加大。含水层中某些地方,温度降随着热弥散的增加而减小,且变化幅值较大。含水层热影响范围随着热弥散的加强而加大。速度一次方模型的计算结果较含水层滞止导热系数倍数模型的计算结果的抽水温度降大,热影响范围小。     

地下水污染物迁移机制及弥散参数初步估计

本文从对流作用、分子扩散和机械弥散作用三方面论述了污染物在地下水中的迁移机制,通过对地下水中水动力弥散尺度效应研究成果的总结和分析,阐述了纵向弥散度与尺度的关系,为地下水污染模型研究提供了一种参数的初步估计。     

考虑对流-弥散效应的污染物溶质运移模型及解析解

基于饱和多孔介质反应溶质运移的对流-弥散方程,同时考虑了污染物中放射性核素进入地下水系统时的衰变。根据下边界质量浓度为零,得出该模型的解析解,编译了相应的计算程序进行求解。通过算例分析,得出了在污染物扩散问题上应考虑渗透速度的合理性和重要性。有效地将原先运用情况单一的对流-弥散方程拓展到了复杂的、敏感性强的有机污染物扩散条件下,为水文地质和环境工程中与污染物扩散相关的流体流动问题的求解提供了新的解答。     

径向流弥散试验及其参数的确定

环境影响评价项目多数都要对地下水做专项调查报告,野外弥散试验又是地下水专项调查报告的核心。文章以周口隆达发电有限公司扩建工程地下水专项调查项目的野外弥散试验为依据,确定了地下水含水层的弥散参数,为准确可靠的地下水污染预测模型提供依据。对地下水环境影响评价具有实际意义。     

基于对流弥散反应方程的渗透反应墙设计方法

渗透反应墙(PRB)是一种将通过墙体的污染物转化为无害物质或者将其沉淀降解的原位处理法。在考虑分子扩散、机械弥散、对流、吸附和降解等耦合情况下,建立了污染物通过PRB运移的数学模型。针对不同地下水渗流场和边界条件的组合,推导了一系列降解条件下模型的稳态解,并针对四氯乙烯给出了设计曲线。PRB两边的地下水渗流场对其厚度具有较大的影响,对流弥散同向情形所需厚度最大,纯扩散次之而对流弥散反向厚度最小;且最大的差别可达1 m。研究表明,有限域与半无限域出口得出的曲线图差别不大,尤其是对于对流-弥散同向和纯扩散情形。这两个工况得到的计算结果差别在10%以内。本文解可用于渗透反应墙的初步设计和试验数据拟合等。     

固结作用下非均质隔离墙中污染物二维运移规律研究

土-膨润土隔离墙广泛应用于污染场地管控和修复工程.在隔离墙自重和侧向土压力的作用下,墙体沿深度方向呈现非均质性.基于双向固结理论,建立了非均质隔离墙-含水层系统中污染物二维运移模型.模型采用高斯函数表征污染源局部非均匀分布,并考虑了屏障系统中污染物对流—弥散—吸附—降解耦合运移过程.结合边界条件和层间连续性条件,选用大...     

地下水中石油污染物运移的耦合模型及其应用研究

本文采用氯化钠作示踪剂测定含水层的弥散系数,并根据实测的溶解油吸附等温线来确定含水介质对石油污染物运移的阻滞系数,从而把反应性石油污染物在地下水中运移化为示踪剂的对流－弥散迁移和溶解油在水相与固相之间转移的叠加,最后作者把所得的耦合模型应用于评价大庆油田排污干渠对地下水污染问题。     

沙质滩涂中反应性与非反应性污染物阻滞效应研究

沙质滩涂受到石油污染后,滩涂-水系统中的石油污染物处在一个物理、化学、生物的相互联系和连续变化之中。为了定量地研究滩涂-水系统反应性石油污染物的动态变化规律,通过水动力弥散实验和一维对流、弥散模型确定了水分和溶质在滩涂-水系统的水-盐动力学参数和反应动力学参数。选择研究区代表性沙样S和Y进行试验,研究结果表明,对于沙质滩涂-水系统中的非反应性污染物,S沙样和Y沙样的渗透系数分别为1.95cm/min和0.76cm/min,弥散系数分别为0.156cm~2/min和0.463cm~2/min;对于沙质滩涂-水系统中的反应性污染物,S沙样和Y沙样的阻滞系数分别为2.55和2.30,分配系数分别为1.93cm~3/g和1.05cm~3/g。     

污染物运移过程的一维数值分析

考虑填埋场中固体废弃物的生物降解效应和含水层中土颗料对污染物的吸附性,在有限深度条件下基于对流、弥散和地球化学反应等污染物运移机理,提出了填埋场污染物运移过程数值模拟的一维计算模型。进而采用半解析方法进行数值求解,通过变动参数比较分析确定了控制填埋场污染物运移过程的主要参数。具体数值计算表明:污染物在含水层中运移浓度将于某一特定时间达到峰值,随后逐渐降低。粘土垫的厚度及其渗透性、压缩粘土垫层与含水层的吸附能力是填埋场污染物运移的重要近控制参数。     

水动力弥散温度效应的砂槽试验研究

通过改变温度条件下的二维砂槽水动力弥散实验,分析温度对弥散作用的影响,探讨弥散度在时间和空间上的变化规律,以及分析分子扩散作用在横向弥散和纵向弥散中的作用。     

EXPLORATION OF AQUIFER MANAGEMENT OPTIONS USING A GROUNDWATER MODEL

A methodology is described for harnessing the predictive capacity of a groundwater model to underpin aquifer management decisions for changing abstraction within a licensing regulatory framework. The use of a 'baseline predictive simulation' is advocated from both aquifer management and scientific perspectives, and an example of groundwater modelling predictive work on the Nottingham-Doncaster Sherwood Sandstone aquifer system is used to illustrate the methodology. Differences between the baseline predictive simulation and a predictive simulation are processed to extract quantitative information (spatially and temporally) on the response to changes in aquifer stresses. An explanation is given on the use of this information to aid aquifer management decisions for achieving environmental targets. The importance of the aquifer diffusivity with respect to a predictive simulation exercise is highlighted.     

Evaluation of a pressure pulse in a fractured‐rock aquifer to reduce uncertainty of hydraulic conductivity measurements,Rio Grande Rift,New Mexico,United States

Fractured‐rock aquifers are inherently difficult for determining flow dynamics because of variability in fracture orientation and extension. A confined, fractured‐rock aquifer in a semi‐arid mountainous area of the Rio Grande Rift Zone was analysed for its response to recharge events that produced a pressure pulse within its potentiometric surface. The pulse was evaluated at the well scale and subaquifer level to evaluate flowpaths, travel times and dispersion and compare the bulk‐scale aquifer response to possible velocities from slug test hydraulic conductivity measurements. Travel time and dispersion from the pulse proved comparable to probable travel times based on hydraulic conductivity measurements. Evaluation of the pressure pulse and the hydraulic conductivity measurements allowed for a holistic interpretation of the fractured‐rock aquifer through analysis of two distinct data sets that provided corroborative evidence of flow dynamics and fracture connectivity. This holistic approach reduced uncertainty regarding the individual hydraulic conductivity values.     

A GIS-based DRASTIC model for assessing aquifer vulnerability in Kakamigahara Heights, Gifu Prefecture, central Japan

Vulnerability assessment to delineate areas that are more susceptible to contamination from anthropogenic sources has become an important element for sensible resource management and land use planning. This contribution aims at estimating aquifer vulnerability by applying the DRASTIC model as well as utilizing sensitivity analyses to evaluate the relative importance of the model parameters for aquifer vulnerability in Kakamigahara Heights, Gifu Prefecture central Japan. An additional objective is to demonstrate the combined use of the DRASTIC and geographical information system (GIS) as an effective method for groundwater pollution risk assessment. The DRASTIC model uses seven environmental parameters (Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone, and hydraulic Conductivity) to characterize the hydrogeological setting and evaluate aquifer vulnerability. The western part of the Kakamigahara aquifer was dominated by "High" vulnerability classes while the eastern part was characterized by "Moderate" vulnerability classes. The elevated north-eastern part of the study area displayed "Low" aquifer vulnerability. The integrated vulnerability map shows the high risk imposed on the eastern part of the Kakamigahara aquifer due to the high pollution potential of intensive vegetable cultivation. The more vulnerable western part of the aquifer is, however, under a lower contamination risk. In Kakamigahara Heights, land use seems to be a better predictor of groundwater contamination by nitrate. Net recharge parameter inflicted the largest impact on the intrinsic vulnerability of the aquifer followed by soil media, topography, vadose zone media, and hydraulic conductivity. Sensitivity analyses indicated that the removal of net recharge, soil media and topography causes large variation in vulnerability index. Moreover, net recharge and hydraulic conductivity were found to be more effective in assessing aquifer vulnerability than assumed by the DRASTIC model. The GIS technique has provided efficient environment for analyses and high capabilities of handling large spatial data.     

Evaluating Natural Attenuation of Groundwater Pollution from a Coal-Carbonisation Plant: Developing a Local-Scale Model using MODFLOW, MODTMR and MT3D

The effluent from a former coal-carbonisation plant in Nottinghamshire has contaminated the underlying aquifer with ammonium and organic compounds. In terms of flow and contamination, the site has experienced a complex history. MODFLOW has been used to unravel the past flow directions and to provide a basis for solute transport and biodegradation modelling. The modelling has shown that a fine grid is required to represent local flows to prevent incorrect site interpretations. A telescopic mesh technique was essential for this study to enable the site features to be adequately represented while including the regional hydrogeological influences. The influence of grid size to numerical dispersion was investigated for the MT3D computer program. The 'method of characteristics'and 'hybrid method of characteristics'modules of MT3D were found to be relatively free from numerical dispersion for all the grid sizes investigated. However, the 'modified method of characteristics'suffered extensively, and a linear relationship between grid size and numerical dispersion was demonstrated for this complex model.     

A surrogate based multi-objective management model to control saltwater intrusion in multi-layered coastal aquifer systems

Linked simulation-optimisation (S–O) models need to simulate the physical processes either by using a rigorous numerical model, or a trained surrogate model approximating the physical processes. A methodology is proposed to evolve Pareto optimal management strategies for a multi-layered coastal aquifer system using a trained and tested Multivariate Adaptive Regression Spline (MARS) surrogate model linked to a multi-objective saltwater intrusion management model. Performance of the developed methodology is evaluated using an illustrative multi-layered coastal aquifer system. Solution results indicate that MARS is capable of approximately replacing the more rigorous numerical simulation model within the linked S–O model to ensure computational efficiency and feasibility in applying such linked S–O models for coastal aquifer management problems. Furthermore, the ability of MARS to recognise the most relevant input variables in predicting the responses as outputs enables the construction of an efficient and robust surrogate model. Integration of parallel processing capabilities within the optimisation model is shown to improve computational efficiency and feasibly of solving such large scale multi-objective problems. Therefore, the developed methodology utilising the MARS based surrogate model is potentially applicable for developing optimal groundwater extraction strategies for sustainable regional scale management of coastal aquifers.     

A Regional Multilayered Aquifer Model for Microcomputers

Evaluation of the performance of a multilayer aquifer system in a regional study is a problem frequently encountered in ground water studies. In this study a finite element Galerkin formulation is presented for the solution of steady state ground water seepage problem in a multilayer aquifer system for microcomputer environments. The computer code which is originally developed on CDC-CYBER-855 system is then adopted to an IBMPC system with 256 K core memory capacity using Microsoft version 3.2 FORTRAN Compiler (MS-FORTRAN Compiler) which runs under version 1.25 of the Microsoft Disk Operating System (MS-DOS). For fast numeric processing a 8087 processing environment is suggested but such a processor is not necessary for proper execution. In order to verify the validity of the numerical procedure proposed, several numerical experiments are performed and the results obtained are compared with the analytical solutions. The computer code generated is identified as MSGF1 (Multilayer-Steady-Groundwater-Flow) model and it is supported and maintained by the author.     

Soil-catalyzed polymerization of phenolics in polluted waters

Some biotic and abiotic soil components are able to catalyze phenol oxidation, producing water-insoluble polymers. In phenol-polluted water bodies, this phenomenon could be exploited to prevent phenol dispersion. The reaction kinetics of phenol polymerization catalyzed by soil samples drawn from unsaturated and aquifer layers was measured in slurry, aerated batch reactors. Catechol was used as a model phenol. The observed catalytic activity is essentially abiotic and can be attributed to inorganic soil components. The rate of phenol removal is first-order with respect to both catechol and soil concentration. Soil activity towards other phenolic compounds was tested, as well. Diphenols show the highest reactivity. Comparisons were performed with the enzymatic activity of phenol oxidases-containing mushroom tissues whose use has been envisaged in the treatment of phenol-polluted waters. The use of phenol oxidases can complement the intrinsic activity of soil for the removal of recalcitrant phenols.