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: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=647483
• 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.

抽水井通常安装在已明确的含水层中，含水层可以是颗粒状（由沙子和砾石组成）或裂隙岩石。假设从井中提取的地下水来自井所在的含水层。然而，有一种特殊情况尚未在文献中得到充分记录，也尚未得到彻底研究：抽水井安装在矿床或裂隙岩石中，但在这两种情况下，都靠近这些井之间的界面两种类型的含水层。在颗粒层通常覆盖裂隙基岩的区域地质框架内，抽水井可能恰好安装在基岩正上方的矿床下部，或矿床正下方的基岩上部。在这两种配置中，人们可能怀疑抽水井产生的水可能由两种不同地下水的混合物组成：一种来自沉积物，另一种来自基岩。如果两种类型的含水层之间存在水力连接，就会出现这种情况。这种连接可能是自然存在的，其中裂隙岩石的不连续性会自然地与矿床相交。或者，如果穿过岩石的钻井作业在含水层之间建立了水力连接（沿着套管底部的优先路径，穿透裂隙岩石的上部），则它们可能是人为引起的。在这两种配置中，抽水井都可以被称为“混合井”，因为它们收集来自粒状含水层和裂隙岩石含水层的水。这项研究的目的是建立一种方法，一方面可以检测混合井，另一方面可以表征两种类型含水层的水力连接和优先流量。这种检测和表征将使我们能够评估混合井的后果，量化靠近井的两类含水层之间以及在当地和区域范围内的地下水交换，并帮助了解井供应的地下水的来源。当适当管理地下水资源并能够更好地量化含水层内以及不同含水层之间流动的地下水量时，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成分及其在混合井泵送时可能受到的污染（含水层之间的交叉污染），具体取决于地下水通过不同含水层的流动路径。我们将获得更多有关可能污染来源的知识。这项拟议的研究还将导致建立新的工具来评估含水层的脆弱性并确保更好地保护资源。所提出的进行这项研究的方法本质上是整体性的，并结合了以下内容：建立所研究问题的理论基础、进行现场测试、实验室测试、建模和数值测试。为了解决方法论问题，将更具体地开展研究的两个方面。首先，在混合井中进行的水力测试中，裂隙岩石和粒状含水层之间的连接的严格物理后果（水力）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，确定混合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，另一种来自沉积物含水层。