Towards prediction of saturated-zone pollutant movement in groundwaters in fractured permeable-matrix aquifers: the case of the UK Permo-Triassic sandstones
Towards prediction of saturated-zone pollutant movement in groundwaters in fractured permeable-matrix aquifers: the case of the UK Permo-Triassic sandstones
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预测裂隙渗透基质含水层地下水中饱和区污染物的移动：以英国二叠纪-三叠纪砂岩为例
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
R. Barker
中科院分区：
文献类型：
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作者：
J. Tellam;R. Barker
摘要 英国陆上二叠纪-三叠纪砂岩是河流和风成红层，呈现出从毫米到数百米尺度的嵌套循环结构。它们是世界各地许多大陆砂岩序列的典型。地下水流经基质和裂缝，自然流量一般小于 200 myear−1。在小于 30 m 的水平距离处，低于基质和裂缝网络渗透率的重要最小代表体积，突破可能是多峰的，尤其是靠近井的地方，具有相对较大的表观离散度。 “反裂缝”——渗透率远低于母岩的不连续性——可能具有主导作用。如果存在低渗透基质（例如泥岩），则会显着影响垂直流动，但很少会阻止最终突破。突破的定量预测与很大的不确定性相关。尽管已记录到非常快速的裂缝流，但在 30 米到几百米的尺度上，单一来源的多模式突破变得不那么常见。在数百米到几公里的距离上，有证据表明突破是单峰的，并且可能更容易立即进行定量预测，即使在某些情况下对于反应溶质也是如此。在这个和更大的尺度上，区域断层结构（滑移面和粒化缝）可能对次水平溶质运动产生重大影响，而泥岩和胶结单元将阻碍垂直渗透。尽管氧化物几乎无处不在，但含水层的氧化能力有限，还原能力有限，有机吸附能力有限。它具有中等的阳离子交换能力，并且经常含有碳酸盐。锰氧化物对于吸附和氧化很重要，但含量有限。水力性质和化学性质之间的关系在很大程度上是未知的。上述溶质迁移概念模型的“硬”证据相对有限。为了能够以合理估计的不确定性程度进行预测，需要了解以下知识：复杂砂岩结构的地质结构，以及水力和地球化学结构（包括这些特性之间的相关性）；开发适当的调查技术（特别是地球物理）来绘制结构图；以及开发包含基质、裂缝、“反基质”和抗裂缝元素的建模工具，每个元素都具有相关的水力和可能的地球化学特性。与大多数含水层类型的溶质运动研究一样，需要进行更多的地质表征。尽管专门针对（浅层）水文地质应用开发的新调查和建模工具取得了相当大的成功，但从其他学科（尤其是石油勘探和开发）引进技术可以发挥更大的优势。
Abstract The UK on-shore Permo-Triassic sandstones are fluvial and aeolian red beds showing a nested cyclic architecture on scales from millimetres to 100s of metres. They are typical of many continental sandstone sequences throughout the world. Groundwater flows through both matrix and fractures, with natural flow rates generally of less than 200 m year−1. At less than 30 m horizontal distances, below important minimum representative volumes for both matrix and fracture network permeability, breakthroughs are likely to be multimodal, especially close to wells, with proportionately large apparent dispersivities. ‘Antifractures’ — discontinuities with permeability much less than that of the host rock — may have a dominating effect. Where present, low-permeability matrix (e.g. mudstones) will significantly affect vertical flow, but will rarely prevent eventual breakthrough. Quantitative prediction of breakthrough is associated with large uncertainty. At scales of 30 to a few 100s of metres, multimodal breakthroughs from a single source become less common, although very rapid fracture flow has been recorded. At distances of hundreds of metres to a few kilometres, there is evidence that breakthroughs are unimodal, and may be more immediately amenable to quantitative prediction, even in some cases for reacting solutes. At this and greater scales, regional fault structures (both slip surfaces and granulation seams) can have major effects on sub-horizontal solute movement, and mudstones and cemented units will discourage vertical penetration. The aquifer has limited oxidizing capacity despite the almost ubiquitous presence of oxides, limited reductive capacity and limited organic sorption capacity. It has a moderate cation-exchange capacity, and frequently contains carbonate. Mn oxides are important for sorption and oxidation, but are present in limited quantity. Relationships between hydraulic and chemical properties are largely unknown. ‘Hard’ evidence for the solute transport conceptual model presented above is relatively limited. To be able to predict to a reasonably estimated degree of uncertainty requires knowledge of: the geological, and thence the hydraulic and geo-chemical, structure of the complex sandstone architecture (including the correlations between these properties); the development of suitable investigation techniques (especially geophysical) for mapping the structures; and the development of modelling tools incorporating matrix, fractures, ‘antimatrix’ and antifracture elements, each with associated hydraulic and possibly geochemical properties. In common with solute movement studies in most aquifer types, much more geological characterization needs to be undertaken. Although new investigation and modelling tools are being developed specifically for (shallow) hydrogeological applications with some considerable success, much greater advantage could be taken of importing techniques from other disciplines, and in particular from oil exploration and development.