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会迅速和广泛地迁移，这是由于离散的裂缝和裂缝相互连接所提供的路径。 输运过程包括单个裂缝内通道的弯曲度、基质孔隙度的可变性、裂缝互连的可变性、通过优先通道的侧向迁移、水力梯度的时间效应，在建议的研究中，我们将从现有的井特征现场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，以及通过裂缝孔径的可变性开发的路径的复杂性，以及由于基质扩散的影响预计将占主导地位。在完整的裂隙网络研究中，数值分析将再次用于评估主要的输运机制。在这种情况下，预计主要机制是裂缝互连的复杂性，以及由于裂缝相交而产生的分散效应。在离散断裂研究和全网络分析之间，需要两名硕士生。网络实验的分析提出了一个非常显着的挑战计算和研究的一个重要组成部分将进行比较欧拉（空间固定的参考系）和拉格朗日（参考系与流体移动）的方法，这将需要一个博士生的全职工作。为了支持数值研究，将在结晶岩场环境中对离散裂缝和裂缝交叉点进行局部尺度调查。申请人开发了一个独特的最先进的现场，在花岗岩片麻岩中约20 × 30 m的区域内钻了8个钻孔。初步水力测试结果显示，有几口威尔斯井被一条或多条裂缝连接，有些井有交叉点。将在这些威尔斯井之间进行使用溶质和溶质以及热量的示踪剂实验，以专门探索裂缝孔径非均质性和裂缝交叉点所发挥的分散效应。这项研究的组成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断裂中污染物迁移的基本过程的评估，并将由水文地质学家和工程师在废物设施的风险预测和这些环境中污染场地的管理中进行实际应用。

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.