Large-Scale Solute Transport in Fracture Networks

基岩含水层中的工业和废物场所产生的污染物通常由于离散裂缝和裂缝相互连接提供的通道而迅速和广泛地迁移。输运过程包括单个裂缝内路径的曲折性、基质孔隙度的变异性、裂缝连通性的变异性、优先路径的横向运移、水力梯度中的时间效应以及裂缝交界处发生的弥散效应。在拟议的研究中，我们将从现有的特征良好的场地和有限数量的大规模示踪剂实验中收集几个数据集，为通过数值分析研究主要的输运机制提供基础。最初的研究将集中在离散裂缝中发生的过程，以及由于裂缝孔径的可变性而形成的路径的复杂性，以及基质扩散的影响预计将占主导地位。在完整的裂缝网络研究中，将再次使用数值分析来评估主要的运移机制。在这种情况下，裂缝互连的复杂性和裂缝交汇处的色散效应将是主要的机制。在离散断裂研究和全网络分析之间，将需要两名硕士研究生。网络实验的分析在计算上提出了一个非常重要的挑战，研究的一个重要组成部分将在比较欧拉(空间固定参照系)和拉格朗日(随流体移动的参照系)方法方面进行，这将需要一名博士生的全部时间努力。对比将在局部尺度(&lt；50m)和大尺度(&gt；150m)进行。为了支持数值研究，将在非结晶岩石场环境中进行局部尺度的离散裂缝和裂缝交叉点的调查。申请者开发了一个独特的最先进的野外场地，在花岗岩片麻岩中大约20米乘30米的区域内钻了8个孔。初步水压测试结果显示，几口井通过一条或多条裂缝相连，其中一些裂缝相交。将在这些井之间进行溶质和溶质及热的示踪实验，以具体探讨裂缝孔口非均质性和裂缝交点所起的弥散效应。这项研究的这一部分将涉及两名博士生和一名硕士生。这项研究的结果将提供对控制污染物在裂缝中迁移的基本过程的评估，并将在这些环境中水文地质学家和工程师在预测废物设施的风险和管理污染场地方面具有实际应用价值。

Contaminants emanating from industrial and waste sites in bedrock aquifers typically migrate rapidly and widely due to the pathways provided by discrete fractures and fracture interconnections. Transport processes include the tortuosity of pathways within individual fractures, the variability of matrix porosity, the variability of fracture interconnections,lateral migration through preferential pathways, temporal effects in the hydraulic gradients,and the dispersive effects that occur at fracture intersections.In the proposed study we will assemble several data sets from existing well characterizedsites and the limited number of tracer experiments conductedat large scale to provide a basis to investigate through numerical analysis the dominant transport mechanisms. Initial studies willfocus on the processes which occur in discrete fractures, and the complexity of pathways developed through the variability in fracture aperture, and the effects due to matrix diffusion are expected to dominate. In the full fracture network study, numerical analysis will again be used to evaluate the principal transport mechanisms. In this case, the dominant mechanism is expected to be the complexity of the fracture interconnections, and the dispersive effects due to the fracture intersections. Between the discretefracture study and the full-network analysis, two Masters students will be required. The analysis of the network experiment poses a very significantchallenge computationally and a significant component of the research will be conducted in comparing Eulerian (spatially fixed frame of reference) and Lagrangian (frame of reference which moves with the fluid) approaches for this setting that will require the fulltimeeffort of one PhDstudent. The comparison will be conducted at both local scale (<50 m) and large scale (>150 m).In order to support the numerical studies, local-scaleinvestigations of discrete fractures and fracture intersections will be conducted in acrystalline rock field setting. The Applicant has developed a unique state-of-the art field site with eight boreholes drilled in an area ofapproximately 20 by 30 m, in a granite gneiss. Preliminary hydraulic testing results have shown several wells which are connected by oneor more fractures, some with intersections. Tracer experiments using both solute and solute and heat will be conducted between these wells to specifically explore the dispersive effects played by fracture aperture heterogeneity and fracture intersections. This component of the study will involve two PhD students and one Masters student.The outcome of this research will provide an assessment of thefundamental processes governing contaminant migration in fractures, and will have practical application by hydrogeologists and engineers in the prediction of risk from waste facilities, and the management of contaminated sites in these settings.