Improving crystalline bedrock aquifer conceptual models using novel discrete fracture network methods

裂隙基岩含水层在加拿大和国际上广泛用于家庭和市政供水。了解基岩地层中的破裂作用对于评估深层地质储量和石油开采也是至关重要的。在只有薄薄(或没有)冰川沉积覆盖岩层的地方，浅层结晶基岩含水层很容易受到人类活动的污染。裂缝是污染物输送的主要通道。结晶裂隙基岩含水层位于加拿大中部和东部(如加拿大盾)和美国东部、中北部和西北部的大部分地区。这些含水层的岩石基质孔隙度较低，因此污染物扩散能力较低。水和污染物主要通过岩石裂隙以通常高的地下水速度传播，因此有可能快速传输。为了帮助保护这些含水层以供供水，需要采取强有力的方法来改进对结晶含水层的水力特性和了解。 系统离散裂隙网络(DFN)方法(Parker，2007)已被G360应用地下水研究中心的研究人员广泛用于描述沉积基岩含水层的流动和污染物运移应用。拟议研究计划的目标是应用DFN方法的几个新支柱，以便：1)首次在加拿大盾构的结晶基岩中使用这些方法，而不是沉积基岩(例如，白云岩)；以及2)将新的结果与以前使用不同方法(即跨座式封隔器段塞试验、抽水试验和井下视频测井)进行的水力特性研究以及在现场进行的污染物运移研究进行比较。研究结果将用于改进浅层裂隙结晶基岩含水层流动和污染物运移的概念模型。这项研究将具体包括：1)使用专门的柔性和不渗透钻孔衬垫(FLUTE™)对渗透率和流量进行深度离散测量；2)用于识别水力活动裂缝的高分辨率温度剖面法；3)使用压力、热和染料作为示踪剂与衬垫相结合的新型井间测试，通过数值模拟进行解释；以及4)使用现场探头和衬垫进行水力表征后水质(硝酸盐和浊度)监测。这项研究通过使用在泰河油田(Levison等人，2012年)和肯尼迪油田(Elmhirst和Novakowski，2012年)的加拿大盾牌中钻入的现有大量油井基础设施来节约成本。 约20%的陆地表面由水晶盾岩组成(Gustafson和Krásnè，1994)。在水资源工程、水文地质学和自然资源开发中的所有流动、污染物传输和修复工作中，都需要使用多条证据彻底了解裂缝参数，包括开度、渗透率、间距和连通性。G360 DFN方法的新方法将在研究环境中应用，有机会将结果与以前的表征工作和现场实验进行比较。此外，一个独特的原位硝酸盐探头和荧光仪将通过衬里的钻孔进行测试。这项研究将有助于供水和污染物迁移的重要应用，包括源头保护，并为顾问和研究人员提供有效、成本效益高的工具，以快速确定结晶含水层的特征。这项研究将由博士生、硕士和本科生进行，他们将获得适用于工业工作或继续研究的宝贵培训。

Fractured bedrock aquifers are widely used for domestic and municipal water supply in Canada and internationally. Understanding fracturing in bedrock formations is also critical to assessing deep geological repositories and petroleum exploitation. Where only thin (or no) glacial deposits cover rock formations, shallow crystalline bedrock aquifers can be vulnerable to contamination from human activities. Fractures are primary conduits for contaminant transport. Crystalline fractured bedrock aquifers underlie much of central and eastern Canada (e.g., the Canadian Shield) and eastern, north-central and northwestern United States. These aquifers have low rock matrix porosity and thus low capacity for contaminant diffusion. Water and contaminants travel predominantly through rock fractures at often high groundwater velocities and thus there is potential for rapid transport rates. In order to help protect these aquifers for water supply, robust methods are required to improve the hydraulic characterization and understanding of crystalline aquifers. The systematic Discrete Fracture Network (DFN) Approach (Parker, 2007) has been widely used by researchers in the G360 Centre for Applied Groundwater Research group to characterize sedimentary bedrock aquifers for flow and contaminant transport applications. The objective of the proposed research program is to apply several novel pillars of this DFN Approach in order to: 1) use the methods for the first time in the crystalline bedrock of the Canadian Shield as opposed to sedimentary bedrock (e.g., dolostone); and 2) compare new results to previous hydraulic characterization research conducted using different methods (i.e., straddle packer slug tests, pumping tests and down hole video-logging) and to contaminant transport studies conducted at the field sites. The results will be applied to improve conceptual models for flow and contaminant transport for shallow fractured crystalline bedrock aquifers. This research will include specifically: 1) depth-discrete measurements of permeability and flow using specialized flexible and impermeable borehole liners (FLUTe™); 2) high resolution temperature profiling for identifying hydraulically active fractures; 3) novel cross-hole tests using pressure, heat and dye as tracers coupled with the liners, interpreted via numerical modeling; and 4) post hydraulic characterization water quality (nitrate and turbidity) monitoring using in situ probes and liners. This research economizes by using existing extensive well infrastructure drilled into the Canadian Shield at the Tay River Field Site (Levison et al., 2012) and Kennedy Field Station (Elmhirst and Novakowski, 2012). About 20% of the land surface comprises crystalline shield rock (Gustafson and Krásný, 1994). A thorough understanding, using multiple lines of evidence, of fracture parameters including apertures, transmissivity, spacing, and connectivity are required for all flow, contaminant transport and remediation efforts, with applications in water resources engineering, hydrogeology and natural resource exploitation. Novel methods of the G360 DFN Approach will be applied in a research environment with the opportunity to compare results to previous characterization efforts and field experiments. Also, a unique in situ nitrate probe and fluorometer will be tested with lined boreholes. This research will contribute to important applications for water supply and contaminant migration, including source protection, and provide consultants and researchers effective, cost efficient tools for rapidly characterizing crystalline aquifers. The research will be carried out by doctoral, Master’s and undergraduate students who will gain valuable training applicable to work in industry or continued research.