Detection and Implications of Hydraulic Relationships between Fractured-Rock and Deposit Aquifers

裂隙岩与沉积含水层之间水力关系的检测及其意义

• 批准号: RGPIN-2014-05353
• 负责人: Chesnaux, Romain
• 金额: $ 1.6万
• 依托单位: Université du Québec à Chicoutimi
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611585
• 关键词: Detection; Implications; Hydraulic; Relationships; between

Pumping wells are usually installed in a well-identified aquifer, either granular (composed of sand and gravel) or fractured rock. It is assumed that the groundwater extracted from the well comes from the aquifer in which the well is installed. However, there is a particular case which has not yet been well documented in the literature, nor thoroughly investigated so far: that of pumping wells which are installed either in deposit or in fractured rock, but in both instances, close to the interface between these two types of aquifers. Within a regional geological framework where granular layers usually overlay the fractured bedrock, pumping wells may happen to be installed either in the lower part of the deposit just above the bedrock, or in the upper part of the bedrock, just below the deposit. In both of these configurations, one may suspect that the water produced by the pumping well could be composed of a mix of two different groundwaters: one coming from the deposit and the other coming from the bedrock. This situation would arise if hydraulic connections exist between the two types of aquifers. Such connections may be naturally preexisting, where discontinuities of the fractured rock would naturally intersect with the deposit. Or they may be artificially induced, in the case where drilling operations through the rock have created a hydraulic connection between the aquifers (preferential pathways along the bottom part of the casing, penetrating the upper part of the fractured rock). In both configurations, the pumping wells could be qualified as “mixt wells” because they collect waters originating from both the granular aquifer and the fractured rock aquifer. The aim of this proposed research is to set up a methodology allowing on the one hand to detect mixt wells, and on the other hand to characterize the hydraulic connections and preferential flow rates of the two types of aquifers. This detection and characterization would allow us to assess the consequences of mixt wells, to quantify the groundwater exchanges between the two types of aquifers close to the wells and at local and regional scales, and to help to understand the origin of groundwater supplied by wells. These aspects are of crucial importance when appropriately managing groundwater resources and being able to better quantify the quantity of groundwater flowing not only within an aquifer but also between different aquifers. Furthermore, a better knowledge of the origin of groundwater will allow to better understand the chemical composition of groundwater and its possible contamination when pumped by a mixt well (cross-contamination between aquifers), depending on its flow paths through different aquifers. More knowledge will be gained about origins of possible contaminations. This proposed research will also lead to the establishment of new tools for assessing the vulnerability of aquifers and ensuring a better protection of the resource. The proposed approach to perform this research is holistic in nature and combines the following: establishing the theoretical bases of the investigated issue, performing in situ field tests, laboratory tests, modeling and numerical tests. Two aspects of the research will be developed more specifically in order to address methodology issues. Firstly, the strictly physical consequences (hydraulics) of the connections between fractured rock and granular aquifers on the hydraulic tests performed in mixt wells should allow us to detect these connections. Secondly, we will study the chemical signature of the water sources, establishing that groundwater supplied by mixt wells is composed of a combination of two different chemical signatures, one from a fractured rock aquifer and the other from a deposit aquifer.

抽水威尔斯井通常安装在一个明确的含水层，颗粒（由沙子和砾石组成）或破碎的岩石。假设从水井中抽取的地下水来自水井所在的含水层。然而，有一种特殊情况尚未在文献中得到很好的记载，迄今也没有得到彻底的调查：即安装在存款或破碎岩石中的抽水威尔斯井，但在这两种情况下，都靠近这两种含水层之间的界面。在区域地质框架内，颗粒层通常覆盖在断裂基岩上，抽水威尔斯井可能恰好安装在基岩上方的存款下部，或在存款下方的基岩上部。在这两种配置中，人们可能会怀疑抽水井产生的水可能由两种不同的地下水混合而成：一种来自存款，另一种来自基岩。如果两类含水层之间存在水力联系，就会出现这种情况。这种连接可能是自然预先存在的，其中断裂岩石的不连续性将自然地与存款相交。也可能是人为引起的，在钻穿岩石的作业已在含水层之间建立了水力联系的情况下（优先通道沿着套管底部，穿透断裂岩石的上部）。在这两种配置中，抽水威尔斯井可被称为“混合威尔斯井”，因为它们收集来自粒状含水层和裂隙岩石含水层的沃茨。这项拟议研究的目的是建立一种方法，一方面允许检测混合威尔斯井，另一方面，描述两种类型的含水层的水力连接和优先流速。这种检测和表征将使我们能够评估混合威尔斯井的后果，量化接近威尔斯的两种类型的含水层之间的地下水交换，并在当地和区域尺度，并帮助了解由威尔斯井供应的地下水的来源。在适当管理地下水资源和能够更好地量化含水层内部以及不同含水层之间流动的地下水数量时，这些方面至关重要。此外，更好地了解地下水的来源，将有助于更好地了解地下水的化学组成及其在通过混合井抽水时可能受到的污染（含水层之间的交叉污染），这取决于地下水流经不同含水层的路径。将获得更多关于可能污染物来源的知识。这项拟议的研究还将导致建立新的工具，以评估含水层的脆弱性，并确保更好地保护资源。所提出的方法来执行这项研究是整体性的，并结合了以下内容：建立所调查的问题的理论基础，进行现场试验，实验室试验，建模和数值试验。为了解决方法问题，将更具体地开展研究的两个方面。首先，在混合威尔斯井中进行的水力试验中，断裂岩石和粒状含水层之间的连接的严格物理后果（水力学）应该允许我们检测这些连接。其次，我们将研究水源的化学特征，确定由混合威尔斯井供应的地下水由两种不同化学特征的组合组成，一种来自裂隙岩石含水层，另一种来自存款含水层。